Mechanistic aspects of phosphorylation, dephosphorylation, pyrophosphorylation and depyrophosphorylation reactions that mimic phosphorylases, dephosphorylases, pyrophosphorylases and depyrophosphorylases have been studied in the biologically important middle pH region. The different systems monitored are; (a) the reactions between [{CoN4(OH)(OH2)}]2+ and [HPO4]- for 1:1, 2:1 and 3:1 [{CoN4(OH)(OH2)}]2+ to [HPO4]2- ratios. (b) the reactions between [{CoN4PO4] and [O2NC6H4O]- (abbreviated as NP-) for 1:1, 2:1 and 3:1 [{CoN4PO4] to [O2NC6H4O]- ratios. (c) the reactions between [{CoN4(OH)(OH2)}]2+ and [O2NC6H4PO4]2- (abbreviated as NPP2-) for 1:1, 2:1 and 3:1 [{CoN4(OH)(OH2)}]2+ to [O2NC6H4PO4]2- ratios. (d) the reactions between [{CoN4(OH)(OH2)}]2+ and [H2P2O7]2- for 1:1, 2:1 and 3:1 [{CoN4(OH)(OH2)}]2+ to [H2P2O7]2- ratios. (e) the reactions between [{CoN4P2O7}]- and [O2NC6H4O]- for 1:1, 2:1 and 3:1 [{CoN4P2O7}]- to [O2NC6H4O]- ratios. Significant phosphorylation was noted for systems containing 1:1 molar ratio [{CoN4PO4] and [O2NC6H4O]-. Enhanced phosphorylation was depicted for system containing 1:1 molar ratio of [{CoN4(OH)}2PO4]+ and [O2NC6H4O]-. Pyrophosphorylation was noted for reactions of 1:1 molar ratio of [{CoN4P2O7}]- and [O2NC6H4O]-. The rate of pyrophosphorylation was substantially reduced for systems that were 2:1 in molar ratio of [{CoN4P2O7}]- and [O2NC6H4O]-. No appreciable pyrophosphorylation was noted for systems, which has a 3:1 molar ratio of [{CoN4P2O7}]- and [O2NC6H4O]-. Specific mechanistic features and the possible roles metal ions play in phosphorylase, dephosphorylase and pyrophosphorylase are highlighted from results of UV-Visible spectroscopy, 31P {1H} NMR spectroscopy and Surface Enhanced Raman Scattering (SERS) studies / Chemistry / D.Phil. (Chemistry)

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Triaryl phosphates were synthesized from white phosphorus and phenols in aerobic conditions and in the presence of iron catalysts and iodine. Full conversion to phosphates was achieved without the use of chlorine or chlorinated solvents, and the reactions do not produce acid waste. Triphenyl phosphate, tritolyl phosphate and tris(2,4-di-tert-butyl)phenyl phosphate were synthesized by this method with 100% conversion from P₄. Various iron(III) diketonates were used to catalyse the conversion. Mechanistic studies showed the reaction to proceed via the formation of phosphorus triiodide (PI₃), then diphenyl phosphoroiodidate (O=PI(OPh)₂) before the final formation of triphenyl phosphate (O=P(OPh)₃). The nucleophilic substitution of O=PI(OPh)₂ with phenol to form O=P(OPh)₃ was found to be the rate determining step. It was found that by modifying the reaction conditions the same catalytic systems could be used to synthesize triphenyl phosphite directly from P₄. Triphenyl phosphite was synthesized in selectivities of up to 60 %. The mechanism of these transformations was also elucidated. Independent syntheses of the intermediate in the reaction mechanism, O=P(OPh)₂I and its hydrolysis products diphenyl phosphate (O=P(OPh)₂OH) and tetraphenyl pyrophosphate ((O)P(OPh)₂-O-P(O)(OPh)₂) were developed from PI₃. The 2,4-di-tert-butyl phenol analogues of these compounds were also prepared. Bis-(2,4-di-tert-butylphenyl) phosphoroiodidate was then reacted with various alcohols to produce a series of mixed triorgano phosphates.

The research on phosphorus-chalcogen compounds enjoys a long tradition in the field of inorganic chemistry, which has led to applications such as strike-anywhere matches, precursors for metal chalcogenide thin films and versatile reagents in organic synthesis. Whereas a wide range of phosphorus-sulfur and -selenium systems is known, the literature lacks information about compounds incorporating phosphorus-tellurium bonds. This thesis describes fundamental studies that develop the basic understanding of the synthesis of phosphorus-tellurium systems and the structural characteristics of these species. The focus will be on cyclic structural motifs as these offer novel bonding modes and often an interesting reactivity. In addition, the novel compounds are compared with the properties of the sulfur and selenium analogues. Three different approaches were developed to stabilise and study compounds incorporating phosphorus-tellurium bonds: a) Stabilisation of binary organophosphorus-tellurium heterocycles by bulky substituents, b) the utilisation of P₂N₂ rings based on the dianions [{EP(NtBu)(μ-NtBu)}₂]²⁻ (E = S, Se, Te) and c) the peri-substitution of phosphorus and tellurium atoms on an acenaphthene backbone. The use of sterically demanding substituents led to the isolation of the first series of structurally characterised organophosphorus(III)-tellurium heterocycles of the type (RP)[sub]nTe[sub]m including three- to six-membered ring systems. The mild oxidation of [{EP(NtBu)(μ-NtBu)}₂]²⁻ (E = S, Se, Te) with iodine yielded macrocyclic (S, Se) or oligomeric systems (Te). Furthermore, a collection of novel P₂N₂-supported phosphorus-chalcogen heterocycles incorporating main group elements was synthesised employing [{EP(NtBu)(μ-NtBu)}₂]²⁻ (E = S, Se, Te) in metathetical reactions with main group element halides. Extension of this approach to transition metal halides generated some unusual metallocycles, as well as macrocycles and ladders incorporating coinage metals. The first peri-substituted phosphorus-tellurium species were studied regarding their interatomic and intermolecular forces. Systems of the general formula RTe–Acenap–P(iPr)₂ were shown to exhibit extensive through-space spin-spin coupling. In addition, the influence of oxidation and complexation on these interactions was investigated and the formation of peri-substituted phosphorus-tellurium cations exhibiting P–Te bonds was observed.

The Quotient Method (QM), a laboratory-based risk assessment methodology used by the Environmental Protection Agency to evaluate pesticides for registration and use, has not been thoroughly field-tested and its performance has not always been reliable. My objective was to determine if variation in vegetation structure or diet of exposed animals could result in adverse ecological effects that were not predicted by the QM. In April and early May 1993, I established populations of herbivorous gray-tailed voles (Microtus canicaudus) and omnivorous deer mice (Peromyscus maniculatus) in 24 0.2-ha enclosures planted with alfalfa (Medicago sativa). Alfalfa in 12 enclosures was mowed on 22 June to reduce vegetation height. Small mammal populations were monitored by live trapping from May through August 1993. On 14 July, an organophosphorus insecticide, azinphos-methyl, was applied at 0, 0.88, and 3.61 kg/ha. Insecticide residues were measured on canopy-level spray cards, soil samples, and alfalfa. I compared the observed residue concentrations with predictions based on the nomogram used to estimate exposure for QM risk assessments. I also compared QM predictions of risk with observed effects on population size and growth, survival, reproductive activity, recruitment, body growth, movements, and diet of the small mammals. Much of the insecticide reached ground level in mowed enclosures, but dense alfalfa intercepted most of the spray in unmowed enclosures. The mean half-life of azinphos-methyl on alfalfa was 3.4 days and was not affected by mowing. Mean residue concentrations on mowed alfalfa and the top 15 cm of unmowed alfalfa were underestimated by the QM exposure nomogram. Therefore, pesticides may pose greater risk to organisms inhabiting sparse vegetation or the tops of plants than predicted by the QM. Treatment with azinphos-methyl at 3.61 kg/ha caused severe effects in both mowed and unmowed enclosures on population size and growth, survival, recruitment, and body growth of voles. Effects of azinphos-methyl on vole recruitment and body growth and on survival of female voles were greater in mowed than in unmowed enclosures. However, I did not find that population-level responses of voles to the chemical differed between mowing treatments. Most effects on voles were of short duration (<27 days) but vole densities in 3.61 kg/ha enclosures remained depressed >6 weeks after spraying. The 3.61 kg/ha application rate resulted in a 42% decrease in deer mouse densities in mowed enclosures during the week of spraying, but the insecticide had no adverse effects on deer mice in unmowed enclosures. In addition, the insecticide may have reduced recruitment of deer mice in mowed enclosures. Analysis of deer mouse feces indicated that consumption of arthropods increased in insecticide-treated enclosures just after spraying occurred. Survival, reproductive activity, body growth, and movements of deer mice were highly variable and not significantly affected by azinphos-methyl. Mowing resulted in greater residue concentrations than predicted and, consequently, the insecticide adversely affected voles and deer mice in mowed enclosures at application rates characterized as low risk by the QM. However, food aversion or selective feeding on alfalfa tops may have resulted in similar exposure of voles to the 3.61 kg/ha treatment in mowed and unmowed enclosures. I did not find that insectivorous feeding behavior of deer mice made them more susceptible than predicted. Although residue concentrations on alfalfa did not follow predictions, the gross pattern of effects on small mammals was consistent with QM risk characterization. However, the QM may underestimate exposure and risk when pesticides are sprayed on sparse vegetation. / Graduation date: 1995

Physicians are familiar with organophosphates (OPs) as a classic, though obscure, cause of cholinergic poisoning. Many opportunities for human exposure existsixty million pounds of OPs are applied as insecticides to sixty million acres of U.S. land each year, and, until recently, over one-fifth of Americans used these chemicals in their homes. Most physicians, however, still know little about the dangers that these pesticides pose to the developing nervous system. By the late 1980s, toxicologists increasingly recognized that toxicants such as lead and mercury, even at doses well-below the level required to cause symptomatic poisoning, could induce subtle, yet permanent, neurological deficits if the exposure occurred during critical periods of brain development. In the early 1990s, scientists and regulators began to realize that developmental neurotoxicity (DNT), as this phenomenon was called, could also result from OPs. In 1996 Congress passed the Food Quality Protection Act (FQPA), marking a major turning point in the regulation of hazardous chemicals. Prior to the FQPA, the Environmental Protection Agency (EPA) based its calculations of pesticide risk on adults and largely neglected the increased susceptibility of infants and children. The new law took a precautionary stance, protecting the vulnerable neural and physical development of the fetus and child with the inclusion of a 10-X safety factor, and shifting the burden of proof from health advocates to the pesticide manufacturers. The ensuing ten-year battle between health groups, pesticide manufacturers, and the EPA over the laws enforcement now provides an instructive lesson into the complex scientific, political, and economic world of environmental health, and serves as a relatively successful example of effective policy improving public health.

Thesis (Ph.D)--Mississippi State University. College of Veterinary Medicine. / Title from title screen. Includes bibliographical references.

Thesis (Ph. D.)--Oregon State University, 2010. / Printout. Includes bibliographical references. Also available on the World Wide Web.

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Thesis (Ph.D.)--McMaster University (Canada), 1994. / Source: Dissertation Abstracts International, Volume: 56-01, Section: B, page: 0252. Adviser: C. J. L. Lock.