Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

M.Sc. / The main objective of the work presented in this dissertation was to investigate the application of the phosphorus atom as a probe to evaluate stereo-electronic effects in arylphosphines. Traditionally, electronic effects are described as having inductive or resonance origins. In addition to the aforementioned mechanisms, the possibility of an additional field effect pathway was also investigated. For this purpose, a series of ortho, meta and para mono-substituted triaryl phosphines, i.e. Ph2(C6H4-X), were synthesised using a lithium-halogen exchange pathway. This series included a selection of electron-withdrawing and electron-donating substituents (X = F, CN, COOtBu, Me, OMe, NMe2) as well as combinations of these. Most of these ligands are crystalline which allowed analysis of their electronic nature by means of X-ray crystallography. From these ligands a representative range of electron-donating and electron-withdrawing aryl substituted phosphines was chosen to collect high-resolution (d=0.5 Å) data. An aspherical multipole refinement was carried out on each of the high-resolution data sets by employing the Hansen Coppens multipole formalism. This was followed by an experimental charge density analysis of each phosphine by employing the principles of QTAIM employed in WinXD. From topological analysis of the Laplacian of the electron density, properties at the (3,-3) lone pair critical points were evaluated. Similarly, the density properties at the (3,-1) bond critical points of the P-Cipso bond were evaluated by analysis of the topology of the electron density. In addition, several integrated properties including the volume, charge and electron population of the phosphorus atom were evaluated. All of the above properties showed very good linear correlations with the infrared CO stretching frequencies of the Rh-Vaska-type complexes corresponding to these phosphines. Furthermore, computational chemistry was employed as a complementary investigation tool to the X-ray crystallographic study. A theoretical charge density study was conducted for the complete range of phosphines described above in paragraph 1 of this Synopsis by employing the principles of QTAIM employed in AIMAll. All of the properties mentioned in the above paragraph were also calculated. In addition, the calculated molecular electrostatic potential properties of the phosphorus lone pair (Vmin and dcp), the integrated substituent bond dipole and NBO (Natural bond orbital) analysis was used to evaluate substituent electronic effects. All of the calculated properties (with the exception of the charge and electron population of the phosphorus atom calculated from NBO analysis) showed good linear correlations with the infrared CO stretching frequencies of the Vaska-type complexes corresponding to these phosphines within a particular electron-withdrawing/electron-donating or ortho/meta and para series. In addition, very ii good linear correlations were obtained between the experimental and theoretical properties within a particular electron-withdrawing/electron-donating or ortho/meta and para series. As additional investigation tools, the ligands were characterised by several techniques including infrared CO stretching frequency measurements performed on Rh Vaska-type compounds derived from the synthesised ligands, 31P NMR chemical shift measurements as well as 103Rh-31P coupling constant measurements to evaluate the effect of various substituents on the electron density at the phosphorus lone pair. In conclusion, it was found that the phosphorus atom is a sensitive probe of substituent electronic effects. Furthermore, it was found that high-resolution X-ray crystallography, computational chemistry, 31P NMR and infrared spectroscopy are all excellent techniques that can be employed to obtain a better understanding of the nature and transmission of substituent effects. From this study, it appeared that the electronic effects in phosphine ligands could not be rationalised by an inductive mechanism alone, but seemingly more correctly by an additional field effect mechanism.

The principle calcium regulator in the muscle cell is the calcium ion release channel (RyR). Improper calcium homeostasis in the muscle cell is the foundation of many pathological states and has been targeted as a contributing factor to ventricular tachycardia, which is known to precede sudden cardiac arrest. Numerous endogenous and exogenous compounds can affect the way RyR regulates calcium. In this study the anthocyanidin Pelargonidin (Pg), an important natural colorant and dietary antioxidant, is evaluated for its effect on regulating the transport of calcium through the RyR1 of skeletal muscle sarcoplasmic reticulum. Pelargonidin undergoes time dependent structural changes in aqueous solutions at physiological pH and a mixture of up to seven forms of Pelargonidin are present in solution simultaneously. Pelargonidin is a unique RyR1 modulator. It can both stimulate and inhibit the RyR1 depending on the experimental conditions. In addition, when Pelargonidin is irradiated with white light, its inhibition properties on the RyR1 are essentially nullified. Proposed mechanisms include excited state charge shift within RyR1-Pg complexes.

Electron transfer to and between the redox centers of milk xanthine oxidase was investigated by laser flash-photolysis. Evidence is presented for slow equilibration of electrons (k < 38 s⁻¹) between the various redox centers of the enzyme. The enzyme-bound flavin and the heme moieties of the flavoprotein and cytochrome subunits of p-cresol methyl hydroxylase from Pseudomonas putida are both reduced rapidly in a second order manner by 5-dRF generated by the laser flash, followed by slower first order intramolecular electron transfer (k = 220 s⁻¹) from the protein-bound neutral flavin radical to the oxidized cytochrome. Complex formation between spinach ferredoxin:NADP⁺-reductase (FNRₒᵪ), spinach ferredoxin (Fdₒᵪ), rubredoxin (Rdₒᵪ) from Clostridium pasteurianum, two homologous HIPIP's from Ectothiorhodospira halophila (iso-1 and iso-2) and two homologous cytochromes (cytochromes-c₂ from Paracoccus denitrificans and Rhodospirrilum rubrum) have been investigated. Evidence is presented supporting the formation of 1:1 complexes that are stabilized by attractive electrostatic interactions at low ionic strength. Kinetic studies of the above-mentioned complexes provide evidence for extremely rapid to relatively slower intracomplex electron transfer rates (k 7000 s⁻¹ to 4 s⁻¹). In addition the effect of complexation on the degree of accessibility of the various redox centers of the respective complexes to reduction by small reductants such as 5-dRF· and LfH· generated by the laser flash has been evaluated. The effect of both pH and ionic strength on the second order rate of reduction and the intracomplex rates in the respective complexes have also been investigated. The results have been interpreted in terms of redox potential differences, electrostatic and structural features that influence the electron transfer rates in these systems.

No description available.

Charge transfer (CT) complexes have been used in a number of radiation polymerisation processes including grafting and curing. The complexes studied include donor (D) monomers like vinyl ethers and vinyl acetate (VA) with acceptor (A) monomers such as maleic anhydride (MA). Both UV and EB have been utilised as radiation sources. The complexes are directly grafted to these substrates in the presence of radiation. The complexes yield novel copolymers when radiation cured with concurrent grafting improving the properties of the finished product. The term cure grafting has been proposed for this concurrent grafting process. Studies in basic photografting work to complement the cure grafting have been proposed. The role of solvent in grafting is discussed, particularly the effect of aromatics in photografting to naturally occurring trunk polymers like wool and cellulose. The effect of the double bond molar ratio (DBMR) of the DA components in grafting is examined. The ultraviolet (UV) conditions for gel formation during photografting, hence the importance of homopolymer yields in these processes is reported. A plausible mechanism to explain the results from this photografting work is proposed. The significance of these photografting studies in the related field of curing, especially in UV and ionising radiation (EB) systems, is discussed. EB curing and cure grafting of charge transfer (CT) monomer complexes is investigated. The EB results are compared with UV curing and cure grafting of the same complexes. The work has been extended to include EB/UV curing and cure grafting of thiolene systems. The significance of these results in the potential commercial application of these complexes is discussed. Variables affecting the UV/EB curing and cure grafting of thiolenes on cellulose have been studied. These include effect of varying the type of olefin, increasing the functionality of the thiol, use of acrylate monomers and oligomers in hybrid systems, altering the surface structure of the cellulose and finally the role of air in these processes particularly with EB. Photopolymerisation of the thiol-enes in bulk has also been investigated. The thesis content is based on the published work of 14 research papers over the course of the project. / Doctor of Philosophy (PhD)

Multi-step photoinduced electron transfer takes place over a large distance in the photosynthetic reaction centres (PRCs). Electron donor in this life-spending event is the photo-excited 'special pair', a unit of two electronically coupled porphyrinoid chromophores. Bacteriopheophytin and two quinone molecules function as electron acceptors and contribute to the charge separation with almost unit quantum efficiency. The natural photosynthetic reaction centre is the most sophisticated molecular electronic device to date and interest is high in increasing our understanding of the basic quantum mechanical principles behind efficient electron transfer and ultimately copying Nature and construct similar efficient devices. Two main approaches towards a better understanding of the mechanisms involved have been taken. The more biological disciplines isolate, cultivate and alternate reaction centres whereas synthetic chemists prefer to construct well-defined models that mimic certain aspects of the reaction centres. Such a synthetic approach is described in the 'Synthesis of Advanced 'Special Pair' Models for the Photosynthetic Reaction Centre'. The aspect to be mimicked is the 'special pair'. One or two porphyrins in a well-defined spatial disposition (kinked or non-kinked in respect to each other) were to act as electron donor in rigid bichromophoric and trichromophoric systems. A tetracyanonaphthoquinodimethane (TCNQ) unit was employed as the electron acceptor in the series of dyads synthesised. The TCNQ acceptor was replaced by a naphthoquinone (NQ) primary acceptor covalently linked to a TCNQ secondary electron acceptor in the series of triads. Rigid norbornylogous bridges held the chromophores in place and Diels-Alder methodology as well as condensation reactions were applied to link donor, bridge and acceptor components. Despite larger interchromophoric separation than in the natural 'special pair', the two porphyrin chromophores of the series of 'special pair' dyads show some interaction and thereby prove the success of our approach towards 'special pair' mimics. Strong fluorescence quenching in the porphyrin-TCNQ dyads indicates the sought after electron transfer process. A number of synthetic problems experienced and overcome in the synthesis of the series of triads led to discovery of a one-step 'bis-ketonisation' from an olefin under Sharpless bis-hydroxylation conditions with N-methylmorpholine-N-oxide. High pressure was applied to circumvent a lack of reactivity in the condensation reaction used to attach the porphyrin moieties (one or two) to the donor backbone. For the linkage of donor, bridge and acceptor component, a procedure was developed and successfully applied to give the giant mono-porphyrin-NQ-TCNQ trichromophore. In a similar manner 'special pair' trichromophoric systems should be available as part of future work.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of New South Wales, 2000. / Includes bibliographic references. Also available online.