Polarised Raman spectroscopy as a quantitative probe of interfacial molecular orientation

Raman scattering is a ubiquitous phenomenon that can be used to great effect to study molecules near interfaces. It has traditionally been used as an analytical tool to identify materials, but by using polarised light, the degree of order within that material can be assessed simultaneously. This thesis seeks to enhance this technique by accurately quantifying interfacial molecular orientation from peak intensities in polarised Raman spectra. This requires a joint modelling and experimental approach. The experimental system, previously developed in our group, obtains surface selectivity through total internal reflection (TIR) of an incident laser beam at the interface under investigation. The evanescent wave generated by TIR causes Raman scattering by the molecules of interest. This system enables investigation of molecular layers at solid-air, solid-liquid and solid-solid interfaces. A numerical model is constructed to predict Raman scattering intensities based on a generalised experimental geometry, the Raman tensor of the vibrational mode under investigation and the orientation of the scattering molecule. A local field correction is implemented for incident as well as emitted radiation. The scattered intensity is calculated with Lorentz reciprocity and integration over the microscope objective that collects the Raman signal. The modelling outcomes are fitted to experimental Raman scattering intensities to deduce molecular orientation. The electrodynamic model of the scattering process is complemented with Raman tensors, polarisabilities and molecular radii obtained by ab initio computation. The novel methodology is validated with isotropic scatterers and a supported monolayer of zinc arachidate. Analysis of Raman spectra of zinc arachidate in a contact under static load reveals a variation in alkyl chain tilt of (4.8±0.5)° per 100 MPa around (27±4)° at 500 MPa. The exact tilt angle depends on the intensity and fitting metrics used. The model further allows quantitative interpretation of Raman spectra as well as optimisation of experimental design. Limitations as well as future applications of this approach are discussed

Application of optical single-sideband laser in Raman atom interferometry

A frequency doubled I/Q modulator based optical single-sideband (OSSB) laser system is demonstrated for atomic physics research, specifically for atom interferometry where the presence of additional sidebands causes parasitic transitions. The performance of the OSSB technique and the spectrum after second harmonic generation are measured and analyzed. The additional sidebands are removed with better than 20 dB suppression, and the influence of parasitic transitions upon stimulated Raman transitions at varying spatial positions is shown to be removed beneath experimental noise. This technique will facilitate the development of compact atom interferometry based sensors with improved accuracy and reduced complexity

Indices Seminum:

This manuscript investigates whether indices seminum are currently aiding conservation or whether they require modernisation. It is widely assumed that the proportion of wild-collected seeds has increased within botanical seed lists. Through a number of studies we found the reverse to be true. Our paper also found that very widespread taxa were needlessly offered from garden origin. More worrying is that taxa well known for their invasiveness were also freely available for distribution. Another concern was the failure to supply or request associated data for wild-collected seeds despite its availability, a neglect counter-intuitive to botanic gardens. We highlight that in their present form indices seminum are a waste of resources and offer little to legitimate conservation. A range of recommendations is provided for modernising this activity in order to prioritise conservation, one of our biggest challenges of the 21st century

Examination of the effect of the natural plant extract, withaferin A, on heat shock protein gene expression in Xenopus laevis A6 cells

In eukaryotes, the ubiquitin-proteasome system (UPS) degrades most cellular protein. Inhibition of the UPS has been associated with different disease states and can affect various intracellular processes including the activation of heat shock protein (hsp) gene expression. During cellular stress, HSPs act as molecular chaperones by inhibiting protein aggregation and assisting in their refolding once normal conditions are re-established. In the present study, Withaferin A (WA), a steroidal lactone with possible anti-inflammatory and antitumor properties, was found to inhibit proteasome activity and induce the expression of hsp genes in the amphibian model system, Xenopus laevis. Treatment of Xenopus kidney epithelial A6 cells with WA produced an increase in the accumulation of ubiquitinated protein and a significant decrease in chymotrypsin-like activity. Furthermore, immunoblot analysis revealed that WA induced HSP30 and HSP70 accumulation. For example, cells treated with 5 μM WA for 18 h resulted in the optimal accumulation of HSP30 and HSP70. Northern blot analysis revealed that exposure of cells to 5 μM WA induced hsp30 and hsp70 mRNA accumulation in a time-dependent manner up to 12 h. The activation of heat shock factor 1 (HSF1) DNA-binding may be involved in WA-induced hsp gene expression in A6 cells, since pretreatment with the HSF1 inhibitor, KNK437, reduced the accumulation of HSP30 and HSP70. Also, WA acted synergistically with mild heat shock to enhance HSP accumulation to a greater extent than the sum of both stressors individually. In cells recovering from WA, the relative levels of HSP30 and HSP70 accumulation remained elevated from 6 to 12 h after removal of WA. Immuocytochemical analysis and laser scanning confocal microscopy revealed that WA-induced HSP30 accumulation occurred primarily in the cytoplasm with some staining in the nucleus in a granular or punctate pattern. Prolonged exposure to WA resulted in some disorganization of the actin cytoskeleton as well as large cytoplasmic HSP30 staining structures in some cells. Prior exposure of cells to WA treatment conferred thermotolerance since it protected them against a subsequent thermal challenge at 37 °C. In conclusion, this study has shown that WA can induce an inhibition of proteasome activity and an increase hsp gene expression. Activating the heat shock response is a potential avenue for novel drug therapies, which can confer cytoprotection in disease states involving cytotoxic protein aggregation