The kinetics of the oxidation of hydrazobenzene by iodine in buffered ethanol-water solutions were studied between 0°C. and 25°C. A measurable rate was obtained by depressing the iodine concentration by the addition of excess iodide, so that most of the iodine was transformed to triiodide. The effects of initial concentrations, acidity, solvent composition and buffer ionic strength were determined, as well as that of adding quinone and several metal salts. Both iodine and triiodide were found to oxidize hydrazobenzene, but iodine Is about 100,000 times more reactive than triiodide. [formula omitted] The kinetics suggest that both reactions have a simple bimolecular mechanism, expressed by the rate law [formula omitted] The constants k₁ and k₂ were evaluated in 60 volume per cent ethanol and buffer ionic strength 0.31 as [formula omitted] In connection with this work it was found necessary to evaluate the equilibrium constant of formation of triiodide in the solvents used. The heat and entropy of formation from iodine and iodide in 60 volume per cent ethanol were found to be -9.5 ± 0.5 kcal.mol.⁻¹ and -13.2 e.u. respectively. / Science, Faculty of / Chemistry, Department of / Graduate

The primal aim of this thesis was to establish whether kinetic aspects of vitamin B6 metabolism predispose to earlier observed racial differences found in plasma pyridoxal-5'-phosphate (PLP). The active forms of vitamin B6 namely plasma PLP and pyridoxal (PL) as well as the three enzymes expressed in the erythrocyte involved in B6 metabolism, PL kinase, PLP phosphatase and pyridoxamine -5'- phosphate (pyridoxine -5'- phosphate) [PMP(PNP) ] oxidase were measured by high performance liquid chromatography. Phase one supported earlier experimental evidence and lower plasma PLP concentrations were found in blacks in a group of200 male volunteers recruited from the South African National Defence Force (SANDF). The respective enzyme activities involved in vitamin B6 metabolism, from the same test subjects, suggested similar PLP production from PMP and PL as well as PLP dephosphorylation which result in the release of PL into the circulating fluid. Since applied exclusion criteria eliminated the majority of biochemical, physiological, genetical - and disease related factors that influence vit B6 status, dietary factors and individual preferences regarding food intake, were most likely to be responsible for the significantly lower circulating plasma PLP encountered in blacks. Phase two compared pharmacokinetic parameters between 7 black - and 9 white test subjects recruited from the South African Police Services after a single 10 mg oral supplement ofpyridoxine hydrochloride. Statistical analysis of the parameters elimination half-life, elimination rate constant, clearance, volume of distribution, mean residence time, maximum peak concentration and time to maximum peak concentration failed to demonstrate any significant differences between the two groups. These results suggest consistent appearance rate, distribution and metabolism for the metabolites PLP and PL in the study population. A tendency in slower appearance rate, for both the metabolites PLP and PL, were observed in blacks and needs to be investigated further. The end product of vitamin B6 metabolism, 4-pyridoxic acid, which was expressed in terms of 24 hour urine volume, again failed to illustrate any significant differences between blacks and whites. These results suggested similar excretion properties in my population study. Furthermore, the pharmacokinetic parameters calculated for plasma PLP and PL respectively, were found to display one-compartment - and two-compartment pharmacokinetic model characteristics. This mono- and bi exponential elimination characteristics displayed by PLP and PL respectively could be of value in future research efforts in terms of sampling time. The distribution half-life can be determined by the calculation of two-compartment macro-rate constants. Fasting blood-samples should be collected when true baseline values are needed in the case of PL. Following vit B6 supplementation, one should allow at least 5 times the distribution half-life (5-6 hr in the case of PL) before blood-sampling in order to achieve true pharmacological response. Phase three of this study was conducted to illustrate the metabolic interplay ofthe enzymes PL kinase and PMP (PNP) oxidase involved in PLP production. The kinetic parameters, Michaelis- Menten constant and maximum velocity rate, at varying substrate concentrations, for the enzymes PL kinase and PMP (PNP) oxidase, were compared in 14 white - and 14 black male test subjects recruited from the SANDF. Both the average Michaelis-Menten constant and maximum velocity rate were higher in whites, but these differences were not statistically significant. The high individual variability for both parameters calculated, can possibly be ruled out if a crystalline enzyme form is used and should be investigated further. / Dissertation (MSc (Chemical Pathology))--University of Pretoria, 2001. / Chemical Pathology / unrestricted

Laser Induced Fluorescence (LIF) is one of the chief methods for detecting ambient hydroxyl radicals. To measure the absolute concentration of this important atmospheric chemical species, accurately known quenching rate constants due to the dominant gases in the air are of paramount importance. Unfortunately, these rate constants have only been measured under conditions remote from those of ambient air. This dissertation reports the measurement of the rate constants of water, argon, nitrogen and oxygen under ambient conditions. As the LIF is carried out at atmospheric pressure, the OH fluorescence life-time becomes extremely short (about 1 ns). Time Correlated Photon Counting was used to study this short fluorescence phenomenon. The unique feature this study was that the deactivation processes of the excited OH could be described completely by a kinetic model. Detailed theoretical treatments of the LIF processes are presented. The data obtained are consistent with the accepted model, thereby demonstrating the usefulness and validity of the experimental approach. The rate constants (cc molecule('-1) sec('-1)) for quenching by water and argon were accurately measured. The vibrational relaxation rate constant by water (3.4 (+OR-) 0.6 x 10('-10)) is the first value ever reported, while the electronic quenching rate constants for water (k(,Q0) = 7.9 (+OR-) 0.47 x 10('-10), k(,Q1) = 1.48 (+OR-) 0.74 x 10('-10)) are the first measured at atmospheric pressure. The electronic quenching rate constants of the ('2)(SIGMA)(v' = 1) state (k(,Q1)) and the ('2)(SIGMA)(v' = 0) state (k(,Q0)) by argon are k(,Q0) = 0.48 (+OR-) 0.14 x 10('-12) and k(,Q1) = 0.24 (+OR-) 0.06 x 10('-11). The vibrational relaxation rate constant by argon is k(,10) = 0.34 (+OR-) 0.06 x 10('-11). The rate constants for oxygen (k(,Q1) (+OR-) k(,10) = 1.83 (+OR-) 0.43 x 10('-9) and k(,Q0) = 2.6 (+OR-) 0.6 x 10('-10)) are significantly higher than the limited measurements available at low pressure. The rate constants for nitrogen are k(,Q0) = 0.71 (+OR-) 0.08 x 10('-11) and k(,10) = 8.07 (+OR-) 0.65 x 10('-11). All these values are the first obtained at atmospheric pressure and although shown to be consistent with the widely scattered low pressure values, they allow more reliable analysis of ambient OH measurements, and result in a 31.2% increase in the published values.

No description available.

No description available.

No description available.

No description available.

Certain ligand substitution reactions proceed to a complete displacement of the chelate ligand. Certain reactions proceed through a mechanism involving an initial fission of the tungsten-sulfur bond to afford a coordinatively-unsaturated intermediate which is rapidly attacked by chlorobenzene. The resulting solvated intermediate establishes an equilibrium which involves desolvation-solvation. Although main group organometallic chemistry has received a great deal of attention, this discussion will be centered in organotransition metal chemistry, in particular, metal carbonyls.

The rate constant for the reactions of oxygen atoms with nitric oxide and silane were determined using a discharge flow apparatus. A microwave discharge through O2N2 and Ar was used to produce oxygen atoms. The rate constant for the reaction O + NO + Ar was determined to be (7.0+0.4) x 10^32 cm^6 s^-1 and is in good agreement with previous measurements. Modeling of the O +SiH₄ reaction was performed to determine the correction to the rate constant due to secondary reactions. The rate constant for the reaction O + SiH₄ was determined to be (3.3 +/- 0.3) x 10⁻¹³ cm³ s⁻¹ and is in good agreement with previous measurements. Previous literature, thermochemistry, and spin conservation were used to determine a probable mechanism for the O + SiH₄ reaction.

The acid-catalyzed inversion of sucrose is often taken as an example of a first order reaction. It is, however, influenced by many factors such as temperature, type of acid used, concentration of sucrose, and the concentration of acid. What has received little attention so far is the influence of addition, in particular, other salts to the reacting solution. In this study, the influence of different salt solutions on the kinetics of sucrose inversion rate was studied at 29 °C by use of optical rotation measurements. The salts chosen for this study are readily soluble in sucrose solution and they provide an opportunity to study the interaction of electrolytes in aqueous solution of sucrose as well as their effects on the inversion of sucrose kinetics. The rates are found to be influenced by the concentration of the salts. No significant differences was measured when the salt were dissolved either in the sucrose or in the acid solutions. The influence of added salts to saccharide solutions was determined by evaluating the difference between the rotation of pure saccharides solutions and the rotation of pure saccharide solutions with salts. The changes in optical rotation were compared to the Hofmeister series. The saccharide-salt systems containing acidic salts (Na2HPO4 or NaH2PO4) were found to be dependent on the pH. Changing the molar ratio of sucrose and salt added also had an influence of the change in optical rotation. / Chemistry / M. Sc. (Chemistry)