There is a growing need for synthetic bone graft materials, which is particularly apparent for procedures requiring impaction bone grafting (IBG), such as revision hip arthroplasty. Currently allograft bone is used that has limited supply and associated risks of transmission of infectious agents. Porous bioresorbable polymeric scaffolds can be created using supercritical carbon dioxide (scCO2). This thesis investigated the use of these scaffolds for impaction bone grafting procedures. Building on previous research within the literature poly(D,L-lactide) (PDLLA) and poly(D,L-lactide-co-glycolide) (PDLLGA) scaffolds of high molecular weight (100 kDa) were investigated for this use. Scaffolds were milled using a standard bone mill and impacted to create porous milled chips of bioresorbable scaffolds and impacted for mechanical shear testing and biocompatibilities. The impaction process used forces equivalent to those experienced during IBG. In vitro cell experiments were used to assess the proliferation and osteoblastic differentiation of mesenchymal stem cells (MSCs) on impacted scaffolds to identify the most promising scaffold compositions. These compositions included pure polymer and polymer:HA microparticle composites. Further experiments using animals (murine and ovine) were then used to investigate the in vivo performance of the scaffolds. A critical sized ovine femoral condyle defect established the osteoinductive and osteoconductive potentials of milled scCO2 foamed PDLLA + 10 wt.% hydroxyapatite (HA) microparticle scaffolds in vivo. The scale-up potential of scCO2 foaming of bioresorbable scaffolds was established using a 1 L vessel. Scaffolds scCO2 foamed using either a 60 ml autoclave or a 1 L vessel were characterised using scanning electron microscopy and micro computed tomography. Scaffolds from different batches were characterised and compared to ensure process repeatability was accounted for. The final chapter investigated differences in the osteoblastic differentiation of MSCs on PDLLA and PDLLGA scaffolds observed in experiments at the start of the study. Spincoated and dipcoated flat films of PDLLA, PDLLGA, and PDLLA:PDLLGA (50:50) were used for in vitro cell culture to remove the effect of morphological differences that affected scCO2 foamed scaffold experiments. Additionally, this chapter investigated the effect of the form of HA using HA nanoparticles andHA microparticles in scCO2 foamed PDLLA:HA composites for in vitro studies.

The aims of this project were to investigate the surface chemistry and morphology of processed tea leaves the techniques of atomic force microscopy (AFM), scanning electron microscopy (SEM) and time of flight secondary ion mass spectrometry (ToF-SIMS). Data from the spectra obtained by ToF-SIMS was also analysed using principal component analysis (PCA). Further experimentation was performed on tea leaves by the addition of diluted samples of aromas, methyl salicylate, trans-2-hexenal and linalool and examining these leaves using depth profiling to discover how far into the leaf the aroma had penetrated and if there was any connection between the chemistry and size of the aromas and how far they penetrated. A general characterisation of the tea leaves was performed in Chapter 3 where layers of waxes of a comparable size were observed on both green and black tea leaves with AFM, as were micro-crystals on black tea and areas showing two distinct types of interaction between the cantilever tip and the surface of a green tea leaf indicating different surface properties. SEM images revealed a visual difference between green and black tea leaves, where the black tea leaves had more debris on the surface and greater changes in topography due to the different processing methods. The presence of lipids and epicuticular waxes were observed on the surface of the tea leaves using the ToF-SIMS. In Chapter 4 the effects of infusion in hot water on the morphology and surface chemistry of the tea leaves are examined. SEM revealed structural damage to the leaves from 30 seconds of infusion and this increased with infusion time, resulting in the formation of holes in the cutin on the adaxial surface of the tea leaf. By examining positive and negative ToF-SIMS spectra and using PCA, a change in surface chemistry could be detected from 15 seconds of infusion. The intensity of C3H5O2+ peaks in the spectra increased as infusion time increased, indicating that the waxy cuticle of the leaf surface had been removed revealing the underlying epidermal cell layer. Peaks associated with octadecenoic and octadecanoic acids were shown to have a reproducible effect on the positioning of the different infusion times within the PCA plots. Though chemical changes can be detected at 15 seconds, the first 30 seconds of infusion were found to be responsible for the majority of the chemical changes on the surface. Taken together these data indicate that the melting of the cutin layer, primarily within the first 30 seconds of infusion may be related to the release of flavour, aroma and constituents such as polyphenols. The penetration into the leaf of aroma molecules was examined in Chapter 5. Diluted solutions of methyl salicylate, linalool and trans-2-hexenal were added to tea leaves and then examined using depth profiling with ToF-SIMS. For the first time a leaf was depth profiled using a C60. The presence of trans-2-hexenal was detected in the palisade mesophyll layer of the leaf as was methyl salicylate, but to a smaller intensity. Methyl salicylate showed partitioning in diffusion across the cuticle with a large intensity in the cuticle and also in the interface between the epidermis and palisade mesophyll layers. Linalool was present on the surface of the leaf and showed partitioning in the cuticle of the tea leaves. As trans-2-hexenal was the smallest and least lipophilic of the three aromas examined it is theorized that the smaller the size of the aroma molecule plays a key role in the penetration of the dehydrated leaves.

published_or_final_version / Chemistry / Master / Master of Science

This thesis details the synthesis and study of molecular species designed to form supramolecular assemblies, in particular for surface deposition purposes. The first chapter gives a brief introduction to supramolecular chemistry concepts and the basis on which this project is built. The importance of non-covalent bonding interactions to form complex architectures capable of self-assembly is discussed, in particular hydrogen bonds and pi-pi interactions with a series of examples from the literature to illustrate the work that has been accomplished over the past few years in various fields of supramolecular chemistry and nanotechnology in particular. The present project aims at the design, the synthesis and the characterisation of two different groups of compounds, namely p-terphenyl tetracarboxylic acid derivatives and manganese based single molecule magnets. The former are dealt with in the second chapter of the present thesis. The scientific background and the recent results obtained following the surface deposition of p-terphenyl-3,5,3',5'-tetracarboxylic acid are explained and discussed in the introduction. The focus of the research is to design and synthesise similar derivatives, i.e capable of self-assembling to produce similar ordered arrays on surfaces as observed for the parent molecule, but bearing some specific functional groups that are anticipated to either induce a change in the observed assembly process or even impart the molecular functionality upon the assembly. The third chapter of the thesis describes the synthesis and functionalisation of manganese-based single molecule magnets, which are believed to be promising candidates for future applications such as high-density data storage. The crystal structures of some derivatives are discussed and a crystallographic comparative study between the as-synthesised derivatives and literature examples is detailed. In addition, the magnetic properties of selected complexes are discussed and compared. Finally, the results resulting from surface deposition studies that have been carried out in collaboration with the School of Physics and Astronomy at the University of Nottingham are presented in the last section of this chapter.

Polymers have been used as biomaterials for nearly a century and have recently become the material of choice for use in tissue engineering. However, the classes of biodegradable and biocompatible polymers available for use in biomedical devices and as tissue engineering scaffolds are limited. This lack of available polymers with suitable properties could inhibit the development of biomedical devices with improved biocompatibility and hinder the growth of the fledgling tissue engineering field. Researchers in the polymer and biomaterials fields have tried to remedy this problem by applying combinatorial and high throughput methods developed in drug discovery to the search for new polymers. A recent advance has been the development of combinatorial polymer libraries printed as microarrays. This format allows the polymers to be readily screened for their cell adhesion and differentiation properties, allowing ‘hit’ materials with ideal properties to be identified. However, without knowledge of the surface properties of these novel polymers it is impossible to rationalise their biological properties. The surface characterisation of such microarrays presents numerous practical problems included small sample size, sample number and even analysis of such large amounts of data. It is the aim of this thesis to develop methods for the characterisation of the surface chemistry, wettability and protein adsorption properties of polymers in situ in microarray format and within realistic timeframes. The thesis will explore multivariate statistics in the form of PCA and PLS as methods of analysing the large amount of data acquired. The first part of this thesis describes the surface chemical analysis of a polymer microarray using ToF-SIMS and XPS. A comparison of the polymers’ surface to bulk chemistries by XPS indicated that 64 % of the polymers had a surface chemistry which differed from the bulk. This reinforces the need for characterisation of the polymers’ surface chemistries, as it is obvious that this can not be inferred from their bulk chemistries. ToF-SIMS imaging was shown to be an ideal method of studying the distribution of specific ion species across the array and to confirm that the microarray was printed in the intended layout. Principal component analysis is shown to be an ideal technique to analyse both ToF-SIMS and XPS spectral data from the arrays, allowing similarities and differences in the surface chemistry of the polymers to be easily visualised. To estimate the surface energies of the arrayed polymers it is necessary to use picolitre volume droplets to make contact angle measurements. In Chapter 4 it is shown that contact angle measurements taken from picolitre volume water droplets are equivalent to those measured from more conventional microlitre droplets. In Chapter 5 picolitre contact angle measurements are used to estimate the polar and dispersive surface energies of a polymer microarray, which has been specifically designed to exhibit a maximum range of surface energy values. The analysis shows that there is indeed great variation in the WCA and polar surface energies of the polymers, demonstrating the power of intelligently designed combinatorial libraries. To understand the chemical basis of this large range of surface energies the results are compared to surface chemical data from ToF-SIMS and XPS. Surface atomic and functional data from XPS is unable to provide any definitive explanations for the range of surface energies observed. However, information about the molecular structure of the surface from ToF-SIMS gives an insight into what surface functionalities are responsible for high and low surface energies. In Chapter 6 PLS regression is investigated further as a method for investigating surface structure-property relationships in large polymer libraries. Specifically two issues are investigated: the influence of sample number on the results obtained and the ability of PLS to make quantitative predictions. The ToF-SIMS and surface energy dataset discussed in Chapter 5 is used for this task. It is demonstrated that the results obtained from PLS models of large polymer libraries are equivalent to those obtained from much smaller datasets, in terms of the ions identified in the regression vector. Using various test sets of polymers it is shown that there is a limit to the predictive ability of PLS: specifically, as the difference between the training and test sets increases, the quality of the predictions decreases. Potential problems with data pre-processing and re-scaling are also identified. In the final experimental chapter two methods are described for investigating protein adhesion and adsorption to micro-arrayed polymers using AFM and fluorescently labelled proteins. Both methods indicate a wide range of protein adsorption properties within the group of polymers analysed. A good correlation between the two sets of data was observed which appears to validate both methods. In summary the work described in this thesis has demonstrated the feasibility of the characterisation of the surface chemistry, energetics and protein adsorption properties of a micro-arrayed polymer library within realistic time-frames. PCA and PLS have been shown to be useful tools for analysing the data obtained. It is hoped that the methods described in this thesis will allow the biological data from polymer microarrays to be rationalised using the surface properties of the polymers, allowing the design of new biomaterials.

The aim of this dissertation has been to investigate the third order nonlinear susceptibility dispersion of molecules and polymers in order to estimate their purely electronic nonlinear response and in particular their optical Kerr nonlinear susceptibility in the 1 to 2 μm infrared spectral region. We have been successful in modeling with a four level system the near resonant cubic susceptibility of the polydiacetylene, poly(4-BCMU). In that case tunable Third-Harmonic-Generation and Two-Photon-Absorption measurements both agreed with the result of a Near-Infrared-Three-Wave-Mixing measurement. In the case of β-carotene and polythiophenes the four level model also fits the Third-Harmonic-Generation data well. In the previously mentioned cases the spectral behavior of the Two-Photon figure of merit derived by Mizrahi et al. is calculated. The four level model, when extrapolated far off resonance predicts that an all-optical switching device constructed with these materials will be dominated by Two-Photon-Absorption. A promising new class of side-chain substituted polymers with large microscopic second order nonlinearities was also investigated. Third-Harmonic-Generation measurements indicate that no forbidden two-photon transition is present in this case and that the magnitude of the nonlinear third order susceptibility is dominated by the charge-transfer nature of the nonlinear moieties combined with cascading of second order effects at a microscopic level. In the case of Sol-Gel thin films of varying TiO₂ concentration in SiO₂, the formula derived by Boling et al., based also on a three level model, predicts successfully the magnitude of the third order susceptibility. THG is in that case an invaluable technique used for the first time to measure relatively small nonlinear susceptibilities of glass-like thin films.

This dissertation presents results on the study of the temperature and internal state dependence of ion-neutral reactions. The free jet flow technique is used to measure rate coefficients for several reactions at ultralow collision energies near 1 K. The technique, and the unique considerations of free jet flow are considered. The method of analysis of the data obtained from the free jet reactor is also presented. The measurement of reaction rate coefficients for several fast reactions is reported. These studies demonstrate the utility of the technique as various types of reactions which occur at the collision rate are studied. Reactions which do not occur at the collision rate have also been studied. Several slow reaction rate coefficients of the atomic ion AR⁺ are measured, and the data acquired from the free jet flow reactor aids in the elucidation of the reaction mechanisms for these systems. The slow reaction between C₂H₂⁺ and H₂ is also considered, and a theory to account for its unusual temperature dependence is presented which depends heavily on the formation of a long lived collision complex. The experimental rate coefficients for three body association reactions of the rare gas atomic ions Ar⁺, Kr⁺ and Xe⁺ are presented. The experimental results in this case show very large rate coefficients which cannot be explained satisfactorily by any current theories. Using resonantly enhanced multiphoton ionization to create quantum state specific ions, the measurement of rate coefficients for selected vibrational states of molecular ions and spin orbit states of atomic ions are reported. Observed effects for vibrational excitation of molecular ions and spin-orbit excitation of atomic ions are discussed. Finally, the production and subsequent dynamics of negative ions by electron attachment are examined. The electrons are produced from a high resolution source by using two color resonantly enhanced multiphoton ionization spectroscopy on a suitable precursor.

The coupled-cluster (CC) equations including single, double, triple and quadruple excitations (CCSDTQ) are qraphically derived using Feynman diagrams. These equations are programmed and an iterative reduced linear equation method is used to solve these equations. A few points on the potential curves for the dissociation of some model systems with a single bond (LiH and Li₂) are calculated using CC doubles (CCD), singles and doubles (CCSD), singles, doubles and triples (CCSDT) and CCSDTQ. These calculations demonstrate the magnitude of the CC contributions arising from triple and quadruple excitation amplitudes to the stretching of a chemical bond. A multi-reference coupled-cluster singles and doubles (MRCCSD) method utilizing two reference determinants, which differ by a two electron excitation, is then proposed. One of these determinants is selected as the formal reference determinant. The proposed method is based on the single-reference coupled-cluster equations truncated after quadruples with appropriate restrictions placed on the triple and quadruple amplitudes to allow only those amplitudes which correspond to single and double excitations from the second reference determinant. The computational expense of this method is no more than twice that of singles and doubles from a single reference (CCSD). These equations are programmed and the potential curves for the dissociation of a few model systems with single bonds (LiH, BH, and H₂O) are calculated to demonstrate the correct bond dissociation properties of this method. These calculations also demonstrate how much of the CC energy contribution arising from the triple and quadruple excitation amplitudes can be attributed to single and double excitations from the second reference determinant.

General formalism for the application of explicitly correlated Gaussian-type basis functions for nonadiabatic calculations on many-body systems is presented. In this approach the motions of all particles (electrons and nuclei) are correlated at the same time. The energy associated with the external degrees of freedom, i.e., the motion of the center-of-mass, is eliminated in an effective way from the total energy of the system. Methodology for construction of the many-body nonadiabatic wave function and algorithms for evaluation of the multicenter and multiparticle integrals involving explicity correlated Gaussian cluster functions are derived and computationally implemented. Then analytical derivation of multi-center and multi-particle integrals for explicitly correlated Cartesian Gaussian-type cluster functions is demonstrated. The evaluation method is based on application of raising operators which transform spherical cluster Gaussian functions into Cartesian Gaussian functions. Next, the Newton-Raphson procedure for optimization of the non-linear parameters (Gaussian exponents) appearing in the Gaussian-type cluster functions is developed. The procedure employs the first and second analytical derivatives of the variational functional with respect to the Gaussian exponents. The computational implementation of Newton-Raphson optimization procedure is described and some numerical calculations are presented. Finally, the methodology for generating higher nonadiabatic rotational states is presented.

High resolution microwave spectra for the transition metal compounds cobalt tri-carbonyl nitrosyl (Co(CO)₃NO), cyclopentadienyl cobalt di-carbonyl (CpCo(CO)₂), and cyclopentadienyl manganese tri-carbonyl (CpMn(CO)₃) were obtained for the first time using pulsed beam Fourier transform spectroscopy. An oblate symmetric top spectrum was measured for Co(CO)₃NO and the first gas phase value of the cobalt nuclear quadrupole coupling parameter was obtained. The asymmetric top hindered rotor spectrum for CpCo(CO)₂ was measured and a barrier to internal rotation was estimated from the spectrum. Analysis of the prolate symmetric top hyperfine spectrum of CpMn(CO)₃ yielded the first gas phase measurement of the rotational constant and the Mn nuclear quadrupole coupling. High resolution microwave spectra for the iron containing transition metal complexes cyclobutadiene iron tri-carbonyl (CbFe(CO)₃), cyclohexadiene iron tri-carbonyl (C-hexFe(CO)₃) were obtained and a Kraitchman analysis of the isotopic substitution data for the butadiene iron tri-carbonyl (BuFe(CO)₃) is also discussed. Structural parameters for the HCCH-CO were obtained from the various isotopomers for this complex. An analysis of the distortion parameter D(J) yielded an estimation of the binding energy for this weakly bound complex. Analysis of spectra for nitrosyl chloride (NOCl) and chlorine tri-fluoride (ClF₃) yielded the first high resolution low J data sets for these molecules. The quadrupole coupling data are interpreted using the Townes-Dailey model for quadrupole coupling and an improved ground state structure for ClF₃ was obtained. Microwave spectra reported here were obtained using a pulsed beam Fourier transform microwave spectrometer constructed at the University of Arizona. The design is similar to original Flygare-Balle apparatus with many modifications for improving signal sensitivity and data acquisition.