28,989 results for Thesis

  • The association between childhood and adolescent television viewing and antisocial behaviour in adulthood

    Robertson, Lindsay Anne (2012)

    Masters thesis
    University of Otago

    Antisocial behaviour is a public health concern in many societies and can adversely affect not only individual perpetrators and victims, but the social and economic functioning of communities as a whole. Strategies aimed at preventing antisocial behaviour tend to take a developmental approach though many interventions have been criticised for their narrow focus on individual, rather than societal risk factors. The media is one of several potentially important contributing factors to antisocial behaviour and a large number of studies have been conducted to examine the relationship between television violence and antisocial behaviour. Experimental studies have provided good evidence that exposure to screen violence increases aggressive behaviour in the short-term. Cross-sectional studies indicate that increased exposure to media violence is associated with increased antisocial behaviour, however, the debate about whether television plays a causal role in the development of antisocial behaviour is ongoing. Few longitudinal studies have been carried out in this area, and those that have been completed have produced inconsistent results. The present study uses data from the Dunedin Multidisciplinary Health and Development Study (DMHDS), to test the hypothesis that watching larger amounts of television during childhood and adolescence is associated with increased antisocial behaviour in early adulthood. The DMHDS is an ongoing longitudinal study of 1,037 Study members born between 1972 and 1973 in Dunedin, New Zealand. Study members have been assessed at birth, then every 2 years until age 15, then again at ages 18, 21 and 26 years. The main exposure measure was the mean weekday television viewing hours between 5 and 15 years old. Primary outcome measures were 1) having any type of conviction; 2) having a violent conviction, and 3) being diagnosed with antisocial personality disorder by age 26, and 4) levels of Negative Emotionality at ages 18 and 26. More television viewing between the ages of 5 and 15 years old was significantly associated with increased odds of having a criminal conviction and a diagnosis of antisocial personality disorder by age 26, and higher Negative Emotionality scores, after a range of potential confounders was controlled for. Supplementary analyses provided some evidence that children aged 5 to 11 may be particularly susceptible to any effects of television viewing on antisocial behaviour. Given these findings, public health interventions aimed at reducing exposure to television violence would likely reduce antisocial behaviour in a population. Legislative measures concerning television broadcasting have been introduced in the United States, though these approaches have been largely ineffective. An alternative approach could include encouraging health professionals to incorporate advice about media use into child health assessments, and supporting health promoters to develop community-based programmes aimed at reducing television violence exposure. Further research is required on the effectiveness of media literacy as a way of mitigating the effects of exposure to television violence. Given the growth in new media technologies, and the fact that excessive use of media has been implicated in a range of adverse outcomes for young people, more research on the effectiveness of interventions to reduce overall media use is critical.

    View record details
  • The function of secondary metabolites in the leaves of Pseudowintera colorata

    Youard, Luke William (2012)

    Doctoral thesis
    University of Otago

    The leaves of Pseudowintera colorata (Winteraceae) are well known for their bright displays of red colour, and their strong peppery flavour. The variable patterns of red and green colour seen across the leaves of this species are caused by pigments called anthocyanins, while the peppery flavour is caused by the presence of two colourless sesquiterpene dialdehydes, polygodial and 9-deoxymuzigadial. Anthocyanins, and to a lesser extent sesquiterpene dialdehydes, are widespread in nature, occurring across a large number of plant species. Anthocyanins are known for their functionality against a wide variety of biotic and abiotic stresses, including light stress and herbivory. The rarer sesquiterpene dialdehydes have strong anti-herbivore, anti-fungal and anti-bacterial properties. In this thesis I explored the significance of these compounds in P. colorata leaves, by investigating two possible functions of anthocyanins that are previously untested on this species: aposematism and photoprotection. One of these functions, aposematism, links anthocyanin functionality to that of sesquiterpene dialdehydes. Aposematism is the phenomenon where organisms produce signals, such as bright colours, that warn potential predators of their defences, such as toxic compounds. In this study it was determined whether anthocyanins could function as the bright colours of an aposematic signal, and sesquiterpenes as the defence component. Anthocyanins could also function as a photoprotectant, protecting the leaves of P. colorata against high irradiances of natural sunlight by absorbing excess light or mitigating the effective of oxidative damage caused by such exposures. Chilling temperatures have the potential to increase photoinhibition, and therefore were also investigated because P. colorata grows in a climate where such temperatures are common in the winter. Three other properties of P. colorata leaves were also examined as they had the potential to influence the functional significance of these compounds. Firstly, the effects of leaf wounding were explored as this species is known to produce anthocyanins when wounded, but it was unknown how sesquiterpenes would respond. Secondly, sesquiterpenes are stored in specialised oil cells in Tasmannia lanceolata, another member of the Winteraceae. These structures were present in P. colorata leaves, but their chemical content was unknown. The chemical content, development and density of oil cells in P. colorata leaves had the potential to explain the chemical responses of these leaves to wounding. Thirdly, leaf age could affect the functionality of anthocyanins, and possibly sesquiterpenes, if younger leaves are redder than older leaves. During the course of investigating these attributes of P. colorata I developed novel methods for analysing leaf colour and responses to wounding, and for extracting and analysing oil cell contents. The results of this study did not support an aposematic function of anthocyanins in relation to the presence of sesquiterpene dialdehydes. Instead this study demonstrated that anthocyanin and sesquiterpene dialdehyde production are largely decoupled in P. colorata leaves. Anthocyanins were found to be positively correlated with sesquiterpene dialdehydes in naturally occurring fully expanded leaves, but this relationship was weakened by leaf wounding. Wounding decreased the concentration of polygodial and 9-deoxymuzigadial by an average of 3.3 mg/g and 1.3 mg/g respectively in new leaves, and 3.2 mg/g and 2.5 mg/g respectively in mature leaves. In contrast, wounding increased the concentration of anthocyanins by an average of 0.52 mg/g in new leaves, and 0.18 mg/g in mature leaves. The loss of sesquiterpene dialdehydes was explained by their presence in the oil cells. Oil cells were found to occur across the entire leaf surface area at densities ranging from 23 to 205 cells per mm2, and therefore some were destroyed during leaf wounding. Leaves only produced oil cells during their period of expansion, so the loss of oil cells in fully expanded leaves meant that they could not be replaced. The positive relationship between anthocyanins and sesquiterpene dialdehydes was also found to be a function of leaf age. Fully expanded new leaves had an average anthocyanin concentration of 0.88 mg/g, which was significantly higher than that of the mature leaves, 0.52 mg/g. The average concentration of polygodial for new leaves was 29.41 mg/g, and was significantly higher than that of the mature leaves, 9.99 mg/g. Average levels of 9-deoxymuzigadial in the new leaves were 19.14 mg/g dry leaf, and were not significantly different to that of the mature leaves, 17.59 mg/g. Within these age groups, there was no consistent relationship between the concentrations of these compounds. The results of this study did support a photoprotective function of anthocyanins. Anthocyanins were suitably located to intercept light before it reached the photosynthetic tissues, being located in the uppermost tissue layers. Most notably, red leaf tissue was better protected against photoinhibition than green leaf tissue. This protection was evident after the leaves were exposed to 1500 μmol m-2 s-1 white light for 4 hours, which caused a smaller decline in Fv/Fm in the red regions compared to the green regions, a difference of approximately 0.07 units. This protection was not enhanced at chilling temperatures, as commonly observed in some other plant species. Younger leaves are redder than older leaves and also likely to be more exposed to light in a natural environment because of their position on the stems, therefore anthocyanins probably function to protect these leaves from high light over long exposures. Previous studies investigating aposematism in plants have focused on anthocyanins in the autumn leaves of deciduous trees, with few focusing on young developing leaves. The findings of this thesis build upon the knowledge concerning anthocyanin function in young leaves. Furthermore, it is the first study to demonstrate the importance of the cellular distribution of toxic compounds, and the responses of leaves to wounding, when investigating foliar aposematism.

    View record details
  • Thinking about Feeling: Adults' and Children's Judgements of Emotional Expressions in Others

    Martin, Jillisa Alice (2012)

    Masters thesis
    University of Otago

    Both adults and children hold gender stereotypes related to emotion. These stereotypes are thought to be socialised in accordance with emotion display rules – social norms that govern how, when, and where males and females can express certain emotions. Happiness, sadness, and fear are generally associated with females, whereas anger and pride are more often associated with males. The present study aimed to determine whether gender stereotypes held by adults and children would influence their interpretation of emotional expressions in others. 73 adult participants, 18 years and over, and 63 child participants, between 7-10 years old, rated emotional expressions portrayed by male and female adults and children. Participants rated the expressions in terms of whether they were acceptable, sincere, dispositional, and situation caused. The emotions used in this study were anger, happiness, sadness, fear, and pride. Emotional expressions also ranged in intensity from neutral (no emotion), to mild and extreme expressions. Accompanying the emotional expression was a short story explaining the context of the emotional expression, and a statement about the target’s mental state e.g., “Sarah is feeling happy”. Emotional expressions either occurred in an interpersonal or an achievement context. It was hypothesised that acceptability ratings would conform to gender stereotypes of emotion whereby happiness, sadness, and fear would be rated as more acceptable for females to express, whereas anger and pride would be rated as more acceptable for males to express. Gender consistent emotions were also hypothesised to be rated as more dispositional. On the other hand, gender inconsistent emotions were hypothesised to be rated as more sincere and more due to the situation. It was also hypothesised that there would be context effects, whereby gender inconsistent emotions would be tolerated if expressed in a context associated with that gender (i.e., interpersonal contexts for females, achievement contexts for males). Finally, it was expected that children’s ratings would closely resemble adults’ ratings. The results showed that the acceptability ratings largely conformed to gender stereotypes of emotion. Happiness, sadness, and fear were rated as more acceptable for females to express, and the expression of anger was rated as more acceptable for males. An unexpected finding was that the expression of pride was rated as more acceptable for females compared to males. Children tended to rate the emotional expressions in the same manner as the adults. The sincerity, disposition, and situation findings obtained in the present study were inconsistent with the initial predictions. Although there was an influence of context on adults’ ratings, children’s ratings were inconsistent with the idea that interpersonal contexts are female oriented and achievement contexts are male oriented. It can be concluded that both adults and children interpret emotional expressions differently based on gender, however there is still a lot to learn in the area of gender and emotion.

    View record details
  • The Anatomy of the Oblique Popliteal Ligament

    Hedderwick, Mandy (2012)

    Masters thesis
    University of Otago

    Purpose: A major structure on the posterior aspect of the knee is the oblique popliteal ligament (OPL). Current literature on the morphology of the ligament is inconsistent and provides minimal quantitative data. The aim of this study was to reinvestigate the anatomy of the OPL, obtain quantitative data and determine its visibility on magnetic resonance imaging (MRI). Methods: The region of the posterior knee was investigated using dissection, serial E12 plastinated slices, MRI and histology. For the dissection study, 13 lower limbs from 7 embalmed cadavers aged 64-87 years were used; 5 of these were randomly selected for histology. Serial E12 slices (2mm thick) of 4 knees from 2 additional male cadavers (aged 69 and 77 years) were prepared and examined. The knees of 10 healthy, physically active males aged 21-30 years were investigated using MRI. Some measurements from the dissection, E12 and MRI studies were repeated and the intraclass correlation coefficients were calculated to determine repeatability of the measurements. Results: The OPL is a distinct expansion of the semimembranosus tendon and courses superolaterally to attach to the fabella (when present) or to the tendon of the lateral head of the gastrocnemius at the lateral femoral condyle. The OPL also inserts into the knee joint capsule at the medial border of the lateral femoral condyle. Ligamentous fibres from the medial joint form a secondary medial origin. The OPL splits into two bands where the middle genicular neurovascular bundle pierces the posterior joint capsule. The mean width of the OPL was 50.5mm (43-55.7mm) and its mean height at origin and lateral attachment was 11mm (range 6.3-16.8mm) and 9.7mm (range 6.5-12mm) respectively. Fibres from the medial and lateral knee joint capsule blended with the ligament. The OPL was composed of transverse layers of collagen; it was visible as a distinct entity in all proton density scans. Conclusion: The OPL is a distinct ligament with distinct anatomical boundaries. It is clearly visible on MRI scans. A better understanding of the ligament may help define its involvement in posterior knee joint injuries and consequences of sectioning in posterior knee surgery.

    View record details
  • Geochemical Authentication of New Zealand Honey

    McComb, Kiri Alan (2012)

    Doctoral thesis
    University of Otago

    Fraudulent practices in relation to production and distribution of foodstuffs have been prevalent throughout history. The intentional or accidental tampering of a food supply for profit is of great concern to many including regulatory bodies, producers and consumers. Extreme cases of food fraud have caused significant detriment to the health and wellbeing of sectors of the general public. As such, interest in procedures to combat the varying forms of food fraud has peaked over the last decade. Honey is a foodstuff that has wide spread use in the food industry, on its own or as a natural sweetening ingredient in many processed food products. This makes honey a high value commodity and as such it is particularly vulnerable to fraudulent practices. The properties of honey vary greatly dependent upon its origins, with some honeys exhibiting unique properties that make them more desirable than others, such as the antibacterial properties of New Zealand Manuka honey. These unique properties result in higher prices in global markets for these honeys. Higher prices also results in these honeys being greater targets for fraud and counterfeiting. This thesis is concerned with the analysis of geochemical parameters in New Zealand honeys and the utilisation of these geochemical parameters to the application of authentication for New Zealand export honeys, including Manuka honey. The extension and development of these methods for the determination of the provenance of honeys is also investigated along with the application of the measured geochemical parameters as indicators of honey adulteration. The applied methods show promise for the authentication of New Zealand export honeys and may provide a useful tool for the protection of a valuable New Zealand economic commodity. The application of these methods for provenancing of honey is feasible but this would require large comprehensive datasets that are representative of the whole honey population of concern. The development of these datasets would be labour intensive and expensive. The geochemical parameters measured in the course of this study were observed to differ between Manuka honey and a common adulterating sugar. There is a basis to utilise these differences in composition as an indicator of Manuka honey adulteration.

    View record details
  • GnRH Neuron Dendritic and Axonal Morphology

    Herde, Michel K (2012)

    Doctoral thesis
    University of Otago

    Gonadotropin-releasing hormone (GnRH) neurons are the final output neurons of a hypothalamic network controlling fertility in mammals. They release GnRH from axon terminals into the portal blood circulation of the pituitary, where GnRH triggers the secretion of luteinizing and follicle stimulating hormones. GnRH neuron anatomy, morphology and physiology have been studied extensively at the levels of the cell bodies and dendrites in the basal forebrain and axons in the median eminence. However little is known about the subcellular origin of the axon and the physiological role of the dense GnRH fiber innervation of the organum vasculosum of the lamina terminalis (OVLT). Using a cell-filling approach in acute brain slices from GnRH-green fluorescent protein mice, GnRH neuron morphology was analyzed with a confocal microscope. The vast majority (83%) of GnRH neurons were found to extend long dendrites in the direction of the median eminence. When these dendrites were analyzed in a novel brain slice preparation that keeps GnRH neuron projections to the median eminence intact, dendrites were observed to innervate the median eminence and elaborate hypophysiotropic terminals. This projection received continuous synaptic input as indicated by the presence of spines and VAMP2-positive appositions. Moreover, analysis of the position of the action potential-generating initial segment using the marker Ankyrin G, revealed that GnRH neurons exhibit initial segments in one of their dendrites in >80% of cases. This suggests that the long GnRH neuron dendrite has both dendritic and axonal functions and that this unique structure, termed the “dendron”, necessitates a considerable revision of how GnRH neurons integrate inputs and regulate GnRH release at the median eminence. Cell-filling of GnRH neurons with cell bodies located near the OVLT revealed that, unlike other GnRH neurons in the preoptic area, these neurons elaborate complex, highly branched dendritic trees which specifically target the OVLT. Dendritic identity was confirmed morphologically at the light and electron microscopic level and functionally by electrophysiological recordings of the response to glutamate. Further, these dendrites were shown to reside outside the blood-brain barrier and belong to GnRH neurons involved in the generation of the GnRH/LH surge. This suggests that GnRH neuron activity, and hence fertility, may be directly modulated by blood-borne factors. While kisspeptin puffed onto dendrites in the OVLT was found to activate GnRH neurons, luteinizing hormone did not exert feedback actions at this site and no evidence was found for a role of OVLT-GnRH neurons in the suppression of fertility during systemic infection. In summary, work in this thesis has re-defined the morphology of the GnRH neuron by showing that the dendrites of GnRH neurons target highly vascularized regions outside the blood-brain barrier. Most importantly, the work demonstrates that the long hypophysiotropic projections of GnRH neurons to the median eminence are, in fact, dendritic in nature.

    View record details
  • Brand New Zealand: Media Governmentality and Affective Biopower

    Begg, Anne Marie (2012)

    Doctoral thesis
    University of Otago

    This thesis argues that in an age of brand identity and media governmentality, Brand New Zealand capitalizes on concepts of community, patriotism and nationhood to (re)frame Aotearoa New Zealand as a business enterprise, as Aotearoa New Zealand Incorporated. I claim that the branding phenomenon in general and nation-branding in particular represent, first, the (re)inscription and dominance of market imperatives on a global scale and, second, the rising influence of media governmentality as the predominant strategy of social control. Media governmentality concerns, first and foremost, the constitution and organisation of affect, and branding is the structuring principle through which affect is appropriated and extracted. I coin the term ‘affective biopower’ to link Michel Foucault’s concepts of biopower and governmentality with affect and with the power inherent in productive sociality and in the human capacity for building a common. I characterize neoliberal government, not only in terms of particular economic policies and political rationality, but more precisely in terms of the production of subjectivity and the biopolitical regulation of the social through increasingly ubiquitous modes of media governmentality. At stake here is the problematic contradiction between direct forms of governance that address rational autonomous citizens of the neoliberal nation-state and indirect forms of governance that shape neoliberal subjectivity through the affective domains of brand identity and media culture. My specific contribution to this field of study consists in positing the concept of affective biopower as fundamental to brand logic and media governmentality and as key to governance in a neoliberal state. My study highlights the commodification of the social and the articulation of the social bond in terms of capitalist enterprise and focuses on the promotion and marketing of Aotearoa New Zealand. I situate affective biopower as the vital mode of production in contemporary capitalist relations and claim media networks and brand technologies access and harness affective biopower for global capital. What is most significant and relevant about this critical-theoretical approach is that it forefronts the crucial role of affect and affective biopower in normalizing brand society, media governmentality and neoliberal capitalism.

    View record details
  • The resected root-end: is what you see what you get? A naked-eye, optical and SEM study

    Kim, Yeon-Ju (2012)

    Doctoral thesis
    University of Otago

    Aims: To determine the influence of bur types and vision aids on the detection of cracks, root filling deficiencies and anomalies in resected root ends and on the quality of root-end cavities and fillings. To determine the influence of the resected root surface on the quality of root-end fillings, under different optical conditions. Method: In this three-part study, 48 human teeth were prepared using ProTaper™ files (Dentsply) and filled with matching gutta percha (GP) cones and AH Plus sealer (Dentsply). In Part 1, half were resected 3 mm from the apex using a low-speed tungsten carbide (TC) surgical bur (H33L, Komet, Brasseler, Germany) and the rest with a high-speed bur (H162, Komet). Twelve specimens from each group were then polished (H135UF, Komet). In Part 2, root-end cavities were prepared in all teeth using ProUltra® surgical tip, SURG 2 (Dentsply), powered by Satelec P5 Newtron® ultrasonic unit (Acteon, Merignac, France). In Part 3, the teeth were filled with either Super-EBA or Mineral Trioxide Aggregate. On completion of each stage, the root ends were examined by three endodontists, with the naked eye, loupes (x3.25) and a dental operating microscope (DOM, x31). Silicone impressions were made at each stage to produce epoxy resin replicas for scanning electron microscopy (SEM), x25. In each part, three examiners used a designated scoring sheet and examined the teeth together to reach a consensus. Regression analyses were performed on the data. Results: In Part 1, there was an odds ratio of one between DOM and SEM in scoring surface roughness; however, these were not all in the same teeth. No cracks were observed with naked eye or loupes, but five were seen with DOM. Two cracks identified with DOM were not seen on SEM. A total of thirteen cracks were detected in seven teeth by SEM. Under SEM, fourteen root canal filling deficiencies were found and under DOM eight deficiencies noted, but only two were in the same teeth. Under loupes and naked eye, six deficiencies were found and under DOM, one anomaly was seen by DOM but not identified by SEM. In Part 2, false positives and negatives were found with all three optical methods when assessing cracks and the presence of GP at the cavity margin. All optical systems allowed detection of fewer cracks than SEM. In Part 3, there was no significant difference in crack identification between DOM and loupes and both were marginally better than the naked eye. None of the optical methods, when compared to SEM, reliably reported the surface roughness of the root-end filling, the presence of marginal discrepancy or the level of filling compared to the SEM. There was no influence of resection bur combination on the ability to describe the quality of root-end fillings under different optical parameters. Conclusions: Loupes or the DOM may result in the false identification of cracks, anomalies, root filling deficiencies and detection of GP at the cavity margin. The usefulness of the DOM and loupes when describing the quality of root-end cavities and fillings appears to be somewhat limited. Factors other than magnification require further evaluation.

    View record details
  • Volatile organic compound release from β-lactoglobulin stabilized emulsion systems under oral conditions

    Benjamin, Ofir (2012)

    Doctoral thesis
    University of Otago

    The release of volatile organic compounds (VOCs) from liquid food strongly contributes to the perception of flavour and aroma during food consumption. The VOCs that are odour active can be referred as aroma compounds. Oil-in-water (O/W) emulsions, in particular are known for their capability to carry non-polar compounds through the oil phase. Previously, many studies have been performed on emulsion systems, emphasizing the effects of emulsion structure and composition (e.g. droplet size, oil content, emulsifier type and content) on VOC release. However, there is little knowledge on the relationship between the emulsion systems structure and VOC release under environmental and dynamic oral processing conditions. Earlier studies showed how oral conditions such as saliva, pH and ionic strength can cause the emulsions to flocculate while changing their properties and attributes. In addition, the functionality of β-lactoglobulin (β-lg) as an emulsifier and potential VOC binding protein is not fully known and needs further investigation. The objectives of this research were to investigate the release patterns of different types of VOCs (e.g. family class, polarity, volatility) from primary and multilayer emulsion systems (P-O/W and M-O/W) stabilized with β-lg using static and dynamic headspace analysis, and at the same time to characterize the structural changes occurring in emulsions under oral and processing conditions. The role of the tongue in pre-swallowing mastication with emulsions and other liquid systems was also investigated. Under equilibrium conditions, the release of volatile organic compounds (VOCs) from oil-in-water emulsions stabilized by β-lg was studied. Gas-matrix partition coefficients (K) for different volatile compounds were determined by static headspace gas chromatography (GC). Two indirect methods to measure K were used: phase ratio variation (PRV) and phase ratio calibration (PRC). These two methods were found to be simple and accurate alternatives to measuring K without using external calibration. The VOC release depended mainly on the physicochemical properties and affinity of the compounds to the matrix. The role of β-lg on VOC release was compared with Tween 20, both as emulsifiers. In emulsion systems, the presence of the emulsifier conformation at the interface had an effect on the affinity with intermediate hydrophobic VOCs. This may be attributed to the hydrophobic cavity site of the protein and covalent bonds with the aldehydes. The binding affinity of β-lg to VOCs increased at high pH as the protein had a more flexible and open conformation (with an increase in the surface hydrophobicity (S0) and retinol binding). To investigate the dynamic release of VOCs under oral conditions, a model mouth with an artificial tongue was developed. The role of the tongue in transporting the bolus through the mouth by pressing it against the palate has been widely studied, however, the relationship between tongue pressures generated and VOC release is not clear. Pressure patterns during swallowing were found to vary across subjects which may explain some of the differences in individual flavour perception. The model mouth described here is capable of reproducing actual human tongue pressure patterns by a computer controlled artificial tongue driven by an actuator. The tongue functionality is monitored by pressure and force sensors. The model was designed to incorporate oral features and conditions (e.g. temperature, saliva flow, air flow and appropriate oral cavity volumes) combined with on-line VOC measurement using proton transfer reaction-mass spectrometry (PTR-MS). Three liquid model systems (e.g. aqueous solution, oil, and O/W emulsions) were used to evaluate the model mouth operation. Different tongue pressure patterns were applied to the liquid systems, and the release of VOCs was monitored in real time. The release was significantly more intense for longer tongue pressure duration and was affected by the initial tongue position above the sample surface. The role of saliva (artificial vs. human) and the sample temperature on VOC release was also investigated. The release was enhanced by the addition of saliva containing mucin, and at a higher temperature. A multilayer oil-in-water (M-O/W) emulsion system was compared to a primary oil-in-water (P-O/W) emulsion as a carrier for VOCs under various environmental conditions (pH and salt). The M-O/W emulsion consisted of soy oil coated with β-lg and pectin layers that have opposite charges. The release of VOCs was measured using static and dynamic headspace methods (including the use of the model mouth). The partition coefficients (K) calculated by the PRV method, showed different volatile release profiles between the emulsion types. An increase in VOC release was found for the unstable P-O/W emulsion at pH 5, whereas M-O/W emulsions were stable at the same pH and retained the hydrophobic VOCs. Hydrophobic interactions and hydrogen bonds, with the secondary dense layer of pectin, may be responsible for the improved retention. Increasing pH and ionic strength acts as a VOC release trigger to detach the pectin from the interface. Pectin attachment to β-lg at pH 4 had a significant impact on S0 due to the protein unfolding. The VOC release from the emulsion systems using the model mouth support the results under equilibrium conditions. Addition of artificial saliva (containing 1% wt mucin) caused the emulsion sample to become unstable through bridging and depletion flocculation, mostly observed for P-O/W emulsion. The VOC release was found to increase with the changes in the oil volume phase distribution due to emulsion flocculation. The results of this study contribute to the knowledge on VOC release from emulsions by providing a novel platform to better understand the impact of emulsion structure on aroma release in the mouth. Applying new systems, such as the M-O/W emulsion, could provide useful tools to design a desired delivery system of aroma and other bioactive compounds into the mouth.

    View record details
  • What makes a good neighbour? Drivers of facilitation in alpine cushion plant communities

    Cranston, Brittany Hope (2012)

    Doctoral thesis
    University of Otago

    Species interactions, whether facilitative or competitive, play key roles in structuring plant communities. Research into these associations has focused on competitive interactions, however recently, facilitation research has increased in popularity. Using cushion plants as a model, the objective of this thesis is to determine the effect of abiotic drivers on species interactions as well as on the morphology and reproduction of a potential facilitator. Results from a New Zealand cushion species, Donatia novae-zelandiae found in mosaic alpine environments and oceanic sea-level sites were compared to those from a widespread Northern Hemisphere cushion species, Silene acaulis. Alpine (~1000m) D. novae-zelandiae cushions produced three times as many flowers and seven times as many seeds per capsule than at sea-level, but leaves were larger at sea-level. Cushion compactness was greatest at alpine sites. After two seasons of artificially warming 1.8°C, significant decreases in seed production (35%), leaf length (5%), and width (13%) were observed in the cushions. Donatia novae-zelandiae modestly increased species richness at the sea-level sites (1.4 ± 0.5 more species), but no species was specifically limited to growing within the cushions. Most species showed no significant association, although Dracophyllum longifolium, D. prostratum, Phyllachne colensoi, Rhacomitrium pruinosum, and Coprosma cheesemanii showed significant negative associations with Donatia novae-zelandiae at the alpine sites. Donatia novae-zelandiae may marginally increase species diversity locally, but diversity is not affected at the community level. At alpine sites, D. novae-zelandiae decreased species richness (2.5 ± 0.8 fewer species) compared to open areas. Removing neighbours growing within the D. novae-zelandiae resulted in significant heat stress to the cushions, reducing seed production, compactness, and leaf size. Donatia novae-zelandiae, unlike other cushion species, does not appear to be acting as key a facilitator regardless of whether they grow in an alpine community, or in a more mesic, low altitude habitat. D. novae-zelandiae may in fact benefit from their association with neighbouring plants. Unlike D. novae-zelandiae, Silene acaulis fitness at a high elevation site (2560 m) was reduced compared to the lower site (2317 m); female flower production decreased by 40%, seeds per fruit by 11.6%, and leaf size by 24% at the high site. Strong facilitators, hermaphroditic Silene acaulis individuals supported a greater number of plant species than females (hermaphrodites: 4.2 ± 0.3, females: 3.5 ± 0.2). Facilitative effects also significantly increased with elevation (2560 m: 2.1 ± 1.6, 2317 m: 3.2 ± 1.8). The typical ‘cushion model’ so often reported in the facilitation literature does not accurately represent the cushion plant functional type as a whole. D. novae-zelandiae is not a facilitator, but may rather be acting as a competitor, particularly in alpine cushion mosaic communities. This is likely driven by the peat substrate, typical of cushion mosaic communities. In comparison, cushions growing on more skeletal substrates, such as Silene acaulis are important facilitators. Results of this thesis stress the importance of studying cushion facilitation over a broader spectrum of cushion life forms and habitats.

    View record details
  • Smoking, genes and inflammation

    Kazantseva, Marina Grigorievna (2012)

    Doctoral thesis
    University of Otago

    Rheumatoid arthritis (RA) is an, autoimmune disease where genetic predisposition and environmental factors increase the risk of developing RA and the severity of the disease. Cigarette smoking is the major recognised environmental risk factor, and there is a combined effect from smoking and the human leukocyte antigen (HLA)-DRB1 shared epitope (SE) genotype on the risk of developing RA. This study sought to establish any direct effect of smoking and/or the genetic predisposition on the inflammation driving RA and to identify biological mechanism(s) that might explain epidemiological data linking smoking, genetics and RA. The aim of initial work was to establish any involvement of aryl hydrocarbon receptor (AHR)-mediated mechanisms within inflamed rheumatoid tissues. The expression of AHR, CYP1A1 and AHRR genes were quantified by real-time PCR in twenty synovial and eighteen subcutaneous nodule tissues. Patient’s smoking status was established at the time tissue was obtained. The results show smoking causes significant AHR activation in joint synovial tissue, but not in rheumatoid nodule tissues. A subset of synovial DCs show activated AHR in smokers, consistent with the sensitivity of human mo-DCs stimulated with the AHR agonist, benzo(a)pyrene (BaP) in vitro. It is concluded that DCs within the joint synovium are the principal immune cells that respond to cigarette smoke exposure. Microarray analysis revealed that the expression of 547 synovial genes was up-regulated by smoking, including folate receptor 1 (FOLR1), matrix metalloproteinases (MMP)9, MMP11 and MMP14, TNF-superfamily members, TNFSF10/TRAIL and TNFRSF10B/TRAILR2 and transcription factors, RUNX1 and RUNX2. Cell motility and adhesion were the biological processes in synovium most affected by smoking. The expression of 307 synovial genes was down-regulated by smoking, including the vascular “protective” genes, KLF2 and eNOS, suggesting that endothelial function is affected by smoking with implications for vasculitis and the development of rheumatoid nodules associated with severe RA. Any effect of smoking and SE copy number on genes associated with AHR signalling and other immune-inflammatory genes was established. Results suggest there are solitary, reciprocal or synergistic effects from smoking and the SE in rheumatoid inflammation, which are gene dependent. Thus, smoking increases AHR activation in synovium; the SE has no effect. Furthermore, while smoking reduces IL17A expression in synovial tissue, indications are that SE copy number increases IL17A expression. In combination, smoking and the SE increase synovial MMP9 gene expression. Human promonocytic U937 cells were used to model the effect of BaP exposure on MMP9 expression. PMA-activated U937 cells acquire an ability to respond to BaP, including with increased MMP9 gene expression. AHR-specific siRNA, confirmed that AHR regulates MMP9 gene expression. Further data implicate different MMPs in rheumatoid tissue destruction. High MMP7 expression by macrophages occurs in a subset of nodule tissues. This high MMP7 expression is associated with a -181G/G polymorphism within the MMP7 gene promoter but is reliant on the nodule environment for effect. Overall, the data presented in this thesis shows that smoking has a direct effect on rheumatoid synovial tissue. Gene-environment interactions are likely to determine the overall outcome for the inflammatory process in patients with RA.

    View record details
  • Psychosocial and malocclusion characteristics of adolescents

    Ukra, Ali (2012)

    Doctoral thesis
    University of Otago

    Introduction: The association between malocclusion, psychosocial characteristics and oral health-related quality of life (OHRQoL) remains complex and controversial. A large number of recent studies using standardised instruments have shown an association between malocclusion and OHRQoL, but the nature of that association has recently been questioned, with the notion that psychosocial characteristics may, in fact, play a confounding role in the relationship. Furthermore, there has been considerable interest in the association between malocclusions and temporomandibular disorders (TMDs). Reviews during the last century concluded that dental occlusion is only weakly related to TMDs and that no causal relationship could be determined. Moreover, the bulk of the literature also reinforces the notion that TMD shares common behavioural and psychological characteristics with other chronic pain conditions. In light of the reported associations, the objective of the current study was to explore the possible confounding roles that various psychosocial characteristics (such as self-esteem, somatisation and self-perception of body image play in relation to both malocclusion and OHRQoL, and malocclusion and TMD. Method: The study protocol was approved by the Regional Ethics Committee. The sample for this cross-sectional study comprised 353 young adolescents (48.4% female). This included 272 12-to-13-year-old participants enrolled with the Otago District Health Board school dental service, who were selected from the five largest intermediate schools in Dunedin, New Zealand, and a consecutive clinic sample of 81 similarly aged patients attending the orthodontic clinic at the University of Otago Faculty of Dentistry (Dunedin). Each participant completed a self-administered questionnaire and underwent a clinical examination. Information collected included socio-demographic characteristics (sex, ethnicity and household deprivation), psychosocial characteristics (self-esteem, general wellbeing, somatisation and self-perception scores for body image) and malocclusion (Dental Aesthetic Index). OHRQoL was measured using the 16-item impact short-form CPQ11-14 questionnaire; and self-reported TMD was assessed using three items from the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD). Results: The CPQ11-14 score was strongly associated with psychosocial characteristics. Linear regression modelling of the CPQ11-14 score showed that socio-demographic characteristics were predictors, but the model’s overall explanatory power was low (R2 =0.05). This increased slightly with inclusion of the clinical variables. When the psychosocial variables were added, however, the R2 increased to 0.50; all psychosocial variables (except self-esteem) were strongly associated with the CPQ11-14 score. General wellbeing was the strongest predictor. Self-reported TMD was associated with higher somatisation scores and with body image concerns (p<0.001), and tended to report TMD clicking more often (26.3% and 7.7% respectively; p=0.41). . Conclusions: Psychosocial characteristics are important contributors to OHRQoL in adolescents and appear to be more important than socio-demographic characteristics or malocclusion. With regards to TMD, self-reports of TMD in adolescents are associated with propensity to somatisation and concerns with body image. Self-reports of TMD were more common in adolescents with no or minor malocclusion than in those with severe or handicapping malocclusions. Care-seeking adolescents have increased somatisation, body image concerns, and tended to report TMD more often.

    View record details
  • An Examination of the Effectiveness of Non-Executive Directors, Independent Directors, and New Zealand Firm Performance Before and After the Adoption of the NZX Corporate Governance Best Practice Code

    Struthers, Samuel (2012)

    Masters thesis
    University of Otago

    Board of director composition has become an important mechanism in the mitigation of agency costs through alignment of manager-shareholder interests. The board can be seen as a market solution to the monitoring and contracting problems prevalent in most organizations. However, the effectiveness of board composition in enhancing firm performance in practice is not clear. Using the method of three stage least squares, I estimate the endogenous relationship between firm performance measures and outside/independent board representation using a sample of New Zealand listed companies over the period 1997-2008. I find empirical evidence that board composition and firm performance impact each other. Consistent with agency theory, I find that firms with a higher proportion of outside directors have a greater Tobin’s Q. Simultaneously; Tobin’s Q is inversely related to the proportion of outside directors. Outside board representation has an insignificant effect on a firm’s return on assets. Changes in the listing requirements imposed by the New Zealand Stock Exchange (NZX) in August 2003 has fundamentally altered corporate governance within New Zealand and impacted the outside/independent board–firm performance relationship. I find that the code improved New Zealand firm performance measured by Tobin’s Q. Firms responded to the code by increasing the proportion of outside directors. However, the code reduced the sensitivity of outside directors to firm performance which casts doubt on the effectiveness of outside board representation. Furthermore, over the sub-sample period 2004–2008, the proportion of both outside and independent directors is inversely related to Tobin’s Q, consistent with the stewardship argument. A possible interpretation is that New Zealand firms over-invested in outside/independent directors after implementation of the NZX code, leading to poor board function. This conflicting result indicates the firm performance board representation relationship is dynamic and evolves over time. The implication from a regulatory point of view is that it is preferable for governance-related regulation to have an element of flexibility that caters for changes in the economic environment, rather than a strict “one size fits all” rules-based approach that is likely to be counter-productive. I include measures of firm-level risk and directorial remuneration to test the effectiveness of outside and independent directors in enhancing firm performance. Both total fees paid to outside directors and firm-level risk does not enhance the efficacy of outside directors to firm performance. However, these measures do enhance the efficacy of independent directors to Tobin’s Q. Overall, results indicate that board composition is an important mechanism in the mitigation of agency within the firm and has implications for firm performance. However, firms that focus solely on agency reduction and adopt a high proportion of outside/independent directors must be wary that this could compromise the effectiveness of the board and may not be optimal over different time frames.

    View record details
  • TIRF detection of conformational change in DnaK by single-molecule FRET

    Walsh, Samuel McEwen (2012)

    Masters thesis
    University of Otago

    Experiments pursuing the dynamics of single protein molecules present unique insights into structural mechanics and behaviour at the molecular level. Circumventing the ensemble requirement of molecule synchronisation, single-molecule studies are able to track the stochastic and heterogeneous kinetics of individual molecular machines. Here we establish a single-molecule assay to measure conformational change in the E. coli Hsp70 molecular chaperone DnaK. Re-arrangement of the nucleotide and substrate binding domains of DnaK present a useful system to follow large and dynamic changes in physical structure. Therapeutic agents targeted at eukaryotic Hsp70s to modulate activities in oncogenesis and neurodegenerative disorders, give real-world interest to understanding the basic mechanisms of DnaK. Using total internal reflection fluorescence (TIRF) microscopy we measure conformational cha nge in single DnaK molecules through Förster resonance energy transfer (FRET). Suitable constructs for the single-molecule FRET assay were selected from eight engineered DnaK cysteine variants. Biochemical activity assays showed variants retained wild type ability to undergo ATP-stimulated conformational change, hydrolysed ATP in the presence of co-chaperones grpE and DnaJ at 75-200% of wild type levels, and refolded denatured protein substrate at 20-35% the wild type level. Conjugation of these variants with thiol-reactive fluorophores gave proteins suitable for FRET assays, i.e. bearing both acceptor and donor fluorophores. Three DnaK variants, C15S/N254C/E430C, C15S/K321C/E430C, and C15S/N254C/R517C, showed nucleotide dependent changes to ensemble FRET indicative of conformational change. These three variants were used to establish a single-molecule FRET assay to observe transitions between discrete conformational states in immobilised and fluorescently labelled single DnaK proteins in real time. We show that DnaK visits multiple conformations and that nucleotide influences the distribution occupancies of these conformations. Rates of transitions between discrete conformations occur ≈ 100-2000 fold faster than ATP hydrolysis (0.7 x 10-3 s-1) in conditions without nucleotide. We survey a landscape of DnaK conformation transitions where structural states are visited dynamically, and used the calculated rates of transition to accurately predict occupancies observed in our data.

    View record details
  • Water Politics and Political Culture: Turkey's Compatibility with the European Union

    Oktem, Onur (2012)

    Doctoral thesis
    University of Otago

    Turkey’s willingness to enter the EU brought forward a set of issues regarding harmonisation that needed urgent solutions before such joining could take place. Harmonisation work requires rigorous agreement between Turkey and the EU around how Turkish law and institutions are going to function in harmony with the European statutory and institutional setting. One of the most important areas of work is fresh water management. If Turkey wants to join the EU they are required to apply the European Water Framework Directive (EU WFD), the community’s water policy for member countries. This means that Turkey is required to adopt the fundamental principles of the Directive and also has to undertake a series of actions to change its water governance system into an Integrated Water Resources Management (IWRM) framework. IWRM is promoted, as the core principle of how freshwater should be managed under the WFD. IWRM offers a systemic approach to water management where citizen participation and conciliation of vested interests among the users of the river basin should ideally produce optimum results for ecosystems and socio-economic values. In this sense, IWRM supports ‘processes’ that lead to democratic water decision-making. However, there is a practical difficulty with the implementation of IWRM. This thesis explores how the concept becomes abstract and theoretical where political cultures of water bureaucracies impede vigorous discussion around the issues of water management. This study looks into this phenomenon in the Turkish case and argues that Turkey is a good example of where IWRM is difficult to implement due to the social constructions embedded within how Turkish water bureaucracy functions. Turkish water institutions are set around a paternalistic system. Water policy is being formulated within a technical-economic engineering dominated setting where other points of view can be pushed out of the way in pursuit of political agendas. The closed knowledge system of orthodox engineering is useful politically and a monopoly on this knowledge by particular groups affords them a lot of power; paternalistic transactions over issues of water management is a case where particular engineering mind-set silence potentially dissenting views of how to go about democratic water management. A comparison with Spain shows that similar political culture exists despite the Spanish government’s attempt to implement the EU’s Water Framework Directive.

    View record details
  • A novel set of condition-specific quality of life questionnaires in elective general surgical patient prioritization and outcome assessment

    Chen, Tina Yen-Ting (2012)

    Doctoral thesis
    University of Otago

    Health-related quality of life (QOL) has become an indispensible measure of health. It is an important patient-reported outcome (PRO) endpoint for elective surgery, and is one of the key factors in determining patient priority for elective surgery. In general surgery, there has been a lack of suitable condition-specific QOL instruments to effectively evaluate PRO of elective treatment, examine the current patient prioritization system for elective treatment, and investigate the role of QOL in relation to clinical and other more objective measures of health. In response to the above, this thesis documents the development, validation, and application of the “Otago Condition-Specific Questionnaire” (OCSQ). The OCSQ is a novel, standardized set of condition-specific QOL instruments tailored for general surgery, and specific for some common elective general surgical conditions, including anorectal conditions, gallstone disease, abdominal wall hernias, varicose veins, and colorectal conditions. The OCSQ was developed based on an extensive conceptual model of condition-specific QOL, thorough literature review, as well as clinician and patient input. It was validated with rigorous psychometric tests, and was shown to be practical, valid, reliable and responsive. The QOL information obtained with the OCSQ was correlated against clinical, physiological, and sonographic measures of disease severity in the setting of varicose veins. It was found that QOL related poorly to the objective measures, indicating that QOL is independent of these measures, and can broaden the scope of patient assessment by complementing these measures with a unique facet of information rooted in the patient’s subjective perception. The OCSQ was used to assess the PRO in a large cohort of patients over a three-year period following elective general surgery. In addition to QOL, the OCSQ was also designed to obtain other PRO information, including patient satisfaction with treatment, patient-perceived treatment-related problems, and duration until return to usual activities after treatment. Overall, PRO was found to be satisfactory. The OCSQ was shown to be valuable in monitoring treatment efficacy, in identifying patients with suboptimal QOL outcome, and in facilitating the comparison of PRO between different conditions and treatments. The OCSQ was also used to explore how well QOL was represented in the patient’s priority to accessing elective general surgery. It was found that QOL had no bearing on the patient’s priority status. Patients with different levels of QOL had similar priority. The surgeon’s assessment of QOL was not in keeping with the patient’s own view of QOL, and the surgeon did not incorporate his or her assessment of QOL into the final judgement of priority. The OCSQ could help in improving the integrity of patient prioritization by being an integral part of the priority scoring tool, as well as the cognitive feedback package presented to surgeons to enhance their priority scoring performance.

    View record details
  • Nutrition Forced Extension of Lifespan in Drosophila: A Whole-Genome Investigation

    Morgan, Sarah Margaret (2012)

    Doctoral thesis
    University of Otago

    The life history trade off between longevity and reproduction is seen in a variety of animals. In the model organism Drosophila melanogaster, regulation of lifespan and reproductive rate are linked to various ratios of protein to carbohydrate diet ingested by the flies throughout their lifetime. Dietary Restriction and its effects on lifespan has been studied for many years, with consistent results seen between different organisms. Restriction of caloric intake is known to extend lifespan in different organisms. In Drosophila isocaloric diets of yeast (as a protein source) and sugar (as carbohydrate), in varying ratios, results in organisms trading-off lifespan and reproduction, implying macronutrient status rather than caloric restriction extends lifespan. The aim of the current study is to determine the patterns of gene expression associated with longevity in fruit fly. Drosophila were fed varying ratios of a protein/carbohydrate diet, and whole fly RNA was microarray assayed to identify genes differentially expressed between flies fed high carbohydrates and those fed high protein diets. Differentially expressed genes were verified with Q RT-PCR and a selection of candidate genes were analysed using P element interrupted mutant lines. Immune system stress assays were used to further investigate the response of flies raised on the specified diets. We show genes annotated as being involved in the immune system and stress response pathways to be significantly differentially expressed in array studies and overrepresented in gene ontology analysis; implying a role in the establishment and control of the lifespan extension phenomenon. We show an absence of significant differential expression in genes previously recorded as being involved in the control of the lifespan extension phenotype, and establish survivorship and lifespan data for a cohort of mutant and control lines. The current experiment provides direction for new functional assays, and adds to the growing body of knowledge as to what drives the extension of lifespan following dietary restriction.

    View record details
  • Exploring the provocation of postconcussion-like symptoms in response to a standardised exercise protocol incorporating a cognitive task

    Lee, Hopin (2012)

    Masters thesis
    University of Otago

    Safely returning an athlete back to sport following a concussion is a challenging task for sports medicine practitioners. To facilitate safe management practices, best practice guidelines published from the most recent Concussion in Sport group’s consensus and agreement meetings included a progressive stepwise return to play (RTP) exercise protocol to assist the clinician. Although this stepwise progressive RTP protocol imitates fundamental aspects of sporting performance by including a basic progressive exercise regimen, the exact parameters of these exercise protocols are only loosely defined. The evaluation of baseline symptoms and the monitoring of their response to exercise and cognitive demands are integral to the understanding and development of RTP guidelines for concussion. This thesis explored the role of exercise alone, and in combination with two separate cognitive tasks (Paced Auditory Serial Addition Task and the electronic game Tetris), related to the cognitive function of working memory in provoking postconcussion-like symptoms in non-concussed individuals. A single cohort repeated measures cross-over randomised design was employed where 36 participants (aged 21.9 ± 2.8 years) without a history of a recent concussion were assessed with three submaximal exercise based protocols, namely: exercise alone (SMEP), exercise with the Paced Auditory Serial Addition Task (SMEP+P) and exercise with Tetris (SMEP+T). Each exercise protocol involved three (five-minute) progressive stages of stationary cycling in predefined target heart rate (THR) zones at submaximal levels. During the SMEP+P and SMEP+T sessions, the cognitive tasks were administered before the exercise protocol and during the last two-minutes of each incremental stage. For the SMEP condition, no cognitive tasks were administered. At each session, the primary outcome measure (self-reported symptoms) was administered before (PRE), one-minute (POST-1) and 15-minutes (POST-2) after the exercise intervention. Exercise related variables such as heart rate, rate of perceived exertion, and cycling cadence were monitored throughout the protocol and the participants’ performance on the cognitive tasks were also documented. A repeated measures analysis of variance of the total number of symptoms (TNS) reported on the Sport Concussion Assessment Tool 2 post-concussion symptom scale indicated a significant main effect over time (p < .001), no main effect between conditions (p = .371) and a non-significant time x condition interaction (p = .444). Post-hoc pairwise comparisons confirmed a significant increase in symptom scores in response to all three exercise protocols (p < .001) and symptom resolution over a 15-minute rest period (p < .001). No significant differences were detected between PRE and POST-2 (p = 1.000). A similar trend was observed for the other symptom variables analysed. The three variations of the submaximal exercise protocol studied here provoked postconcussion-like symptoms in non-concussed individuals. The administration of a cognitive task together with a standardised exercise protocol did not have an additional impact on the provocation of postconcussion-like symptoms. These findings have implications for modelling future RTP protocols and the standardisation of rehabilitation strategies for sports-related concussions.

    View record details
  • A Photophysical Investigation of d6 Metal Polypyridyl Complexes

    Horvath, Raphael (2012)

    Doctoral thesis
    University of Otago

    A number of polypyridyl complexes based on d6 metals have been investigated using a range of spectroscopic and computational techniques. Interest in these systems stems from potential applications in molecule based devices, such as dye sensitised solar cells, as well as the potential to gain insight into fundamental photophysical properties of metal complexes and the development of techniques to probe these. Several techniques have been used and are described. The ground states of complexes have been characterised using FT-IR and FT-Raman spectroscopic techniques, which allow for verification of observable quantities obtained from density functional theory calculations. Electronic absorption and resonance Raman allow the initially excited state to be investigated, while transient absorption and transient and time resolved resonance Raman are sensitive toward excited states with the longest lifetimes. Picosecond time resolved infrared is used to bridge this gap, to provide a comprehensive description of processes post initial photoexcitation. Chapter 3 involves discussion of N3, a commonly used dye for dye sensitised solar cells, and derivatives thereof. Derivatisation was carried out to enhance the solar absorption properties of the dyes; however, it was found that the acceptor molecular orbitals do not extend over the attached units in the absorbing state. Time resolved infrared spectroscopy was carried out to probe the excited state, which showed, for an anthrylethenyl-substituted complex, an unusual charge-separated excited state based on a single ligand. In Chapters 4 and 7, investigations on complexes based on the ligand 2,2’;6’,2”-terpyridine, including multimetallic assemblies, are described. The terpyridine allows for the constructions of linear structures; however, corresponding metal complexes possess short lifetimes. Replacing two carbon of this ligand with nitrogen gives 2,6-di-2-pyridyl-1,3,5-triazine, which imbues the corresponding ruthenium complexes with extended lifetimes. Resonance Raman spectroscopy was able to show predominant population of the triazine-containing ligand when the complex is excited in the visible region. The ability of multimetallic assemblies comprised of similar ligands to quench excited state populations was probed. To that end, transient absorption and time resolved resonance Raman spectroscopic techniques have been used to show that initially populated excited state electrons return to the ground state by interacting with attached secondary metal subunits. In Chapters 5 and 6, the effects of substitution of electron donating units on well studied complexes of the ligands 2,2’-bipyridine and dipyrido[3,2-a:2’,3’-c]phenazine are investigated. Rhenium complexes of these ligands show unusual excited states that are thought to originate from the electron donating properties of the substituents. The bipyridine complexes, substituted with ethenyl-linked diphenylaniline, possess an intraligand charge transfer reaction that exists without contribution from the metal; these are well described using resonance Raman and computational methods. Complexes of the substituted dipyridophenazine ligand possess a complex system of excited states that are shown to interconvert on the picosecond and nanosecond timescales. Time resolved infrared spectroscopy was used to assign these states.

    View record details
  • Analysis of the Aspergillus nidulans PRP8 intein

    Islam, Sumana (2012)

    Doctoral thesis
    University of Otago

    Inteins are naturally-occurring intervening sequences that are translated along with their host protein. The intein insertion is excised from its host protein post-translationally in an autocatalytic process known as intein splicing. Full-length inteins encode a second homing endonuclease (HEase) function which allows their genetic mobility. In higher organisms, intein homing occurs during meiosis. In a cell that is heterozygous for the intein+/intein- allele of the host gene, the HEase causes a double-stranded break (DSB) in the intein- allele. The resulting homologous repair by host organism cellular machinery results in the duplication of the intein+ allele. In meiosis, homing results in the super-Mendelian inheritance of the intein sequence with all meiotic progeny carrying the intein+ allele. This should lead to the spread of the intein through the population. The nuclear intein found in the essential PRP8 gene is the most widespread among fungi. This study describes the analysis of the full-length PRP8 intein – AniPRP8 – found in the genome of the filamentous fungus Aspergillus nidulans. AniPRP8 was characterized with regard to its evolutionary history, HEase and splicing activities. It was found that the PRP8 gene in A. nidulans is saturated with the intein+ allele. Three distinct intein types are present corresponding to three varieties of this fungus. Sequence analysis indicates that the HEases of all three intein types are active. The distribution of AniPRP8 within A. nidulans suggests that the evolution of this sequence cannot be easily explained by the currently accepted model of intein evolution. An alternative evolutionary scenario is offered. Two independent experimental avenues were utilized to demonstrate that the HEase encoded by AniPRP8 – PI-AniI – is active. The first of these employed an A. nidulans-based fungal system, which was constructed and characterized to enable the examination of PI-AniI activity. The endonuclease activity of this HEase was demonstrated in vivo in its native A. nidulans context. In a second avenue confirming PI-AniI endonuclease activity, it was established that the purified enzyme mediates DSBs of its substrate DNA in vitro. HEase activity in vitro requires the presence of the divalent cation Mn2+ as a co-factor. The design of an in vivo assay in E. coli for the gene conversion events mediated by the HEase PI-AniI was investigated. The splicing reaction mediated by inteins is required to produce the mature, functional form of the host protein. Inhibition of intein splicing in the essential genes of pathogenic organisms presents an attractive drug target. AniPRP8 splicing was demonstrated in a foreign extein context in an in vivo LacZ-based E. coli system. The assay can distinguish splicing and non-splicing variants of the intein.

    View record details