In order to study the possible effects on permanganate oxidation reactions of a carboxyl sustituent near the reacting centre, three systems were investigated. The first of these systems consisted of the 2-and 4-benzhydrolcarboxylic acids. It was found that the 2-compound reacted more slowly than the 4-compound. The activation parameters at pH 5.45 show that the rate difference is accounted for entirely in terms of the difference in entropy of activation between the two compounds. Solubility difficulties prevented a study of the reaction below about pH 5. The kinetic results in more basic solution indicate that the pK corresponding to alcoholic OH ionization is greater for the 2-isomer than the 4-isomer. This behaviour is readily explained by examining the pK’s of several model compounds. The second system consisted of phthalaldehydic acid and terephthalaldehydic acid. The behaviour expected for aldehydes is observed except for phthalaldehydic acid at pH 1.55. The kinetic results for phthalaldehydic acid suggest rather strongly that it exists as 3-hydroxy- phthalide in acid solution (pH 1.55) and as the free aldehyde above pH 6. This result is shown to be in accord with previous work dealing with the diverse chemical behaviour of phthalaldehydic acid. The third system was the 2-carboxy cyclohexanol system. The pH-rate profiles of a number of isomeric 2-carboxy cyclohexanols were investigated as well as-that of the parent compound, cyclohexanol. It was found that cis-2-hydroxy-cyclohexanecarboxylic acid (XIV) showed a bell-shape rate maximum in its pH-rate profile around pH 6, while trans-2-hydroxycyclohexanecarboxylic acid did not. The parent compound, cyclohexanol, does not show such an effect - the pH-rate profile is almost flat in the region pH 4 to 8. The pH-rate profiles of cis-5-t-butyl-cis-2-hydroxycyclohexanecarboxylic acid (X), cis-5-t-butyl-trans-2- hydroxycyclohexanecarboxylic acid (XI), and trans-5-t-butyl-cis-2-hydroxycyclohexanecarboxylic acid (XII) were also investigated. A mechanism is proposed which involves two opposed dissociation equilibria involving hydrogen ions. A comparison of the reactivity of XIV in protium oxide with that in deuterium oxide gives evidence consistent with the mechanism. The conformational aspects of the reaction (elucidated by means of the conformationally biased compounds -X, XI and XII) were found also to be consistent with the proposed mechanism. It was possible to make a decision between the two kinetically indistinguishable forms of the proposed mechanism on the basis of the assembled data / Science, Faculty of / Chemistry, Department of / Graduate

Carboxyl groups in porcine pepsin were chemically modified "by the carbodiimide reaction using waterrsoluble l-ethyl-3-(3-dimethylaminopropyl) carbodiimide and amino acid esters as nucleophiles. The modification resulted in profound changes in the activities, specificity and some physico-chemical properties of the enzyme. These include (1) significant decrease in milk clotting activity without changes in proteolytic activity against hemoglobin; (2) decrease in peptidase activity against N-acetyl-L-phenylalanyl-diiodo-L-tyrosine; (3) increase in clotting activity against k-casein but decrease in clotting activity against K-α sl⁻casein mixture; (4) shift -in proteolytic pH profile with pH optimum increased from 2.0 to about 3.5; (5) decrease in relative electrophoretic mobility and a slight decrease in isoelectric point; (6) increase in Km without much change in kcat; and (7) increase in stability at pH above 6.0. Results suggest that the drop in milk clotting activity was due to a change in the charge distribution on the enzyme affecting enzyme-micelle interaction. The presence of dipeptide substrates interfered with the carboxyl modification suggestive of the proximity of the modified groups to the enzyme active site. The modified enzyme remained reactive to site-specific inactivators but at rates slower than the native enzyme. The modification was not specific, causing similar changes in pepsinogen and chymosin. The modified and native pepsins had similar caseinolytic properties and produced comparable rates of syneresis and curd tension development on curdled milk. The increase in pH stability suggested that the modified enzyme may be a better calf rennet substitute than native pepsin for cheese-making. / Land and Food Systems, Faculty of / Graduate

The pK values of valeric, 2,2-dimethylpropionic, 2-methylvaleric, 3-methylvaleric, 2,2-dimethylvaleric, heptanoic, and octanoic acids at 10, 25, and 40° were determined from pH titration data. All the measurements were made in an aqueous solution. It was assumed that the γ values were the same for all species of the same charge type and that the activity coefficients for neutral species were unity. A Debye-Hückel equation was used to correct the concentration quotient to the corresponding thermodynamic constant. The pK values as a function of temperature fall in two different groups as predicted by King: (1) the pK values show a minimum at room temperature; (2) the pK values show a minimum near O° and increase as the temperature rises. The length of the carbon chain of an unsubstituted aliphatic carboxylic acid has little effect on the pK values; however, the methyl group attached on the C-2 position has the effect of increasing the pK value of the carboxylic acid. This is shown by the experimental results and a suggested explanation is given. The calculation of the pK values was carried out using an IBM 360 computer.

Diss. (sammanfattning) Stockholm : Karol. inst., 2004. / Härtill 4 uppsatser.

published_or_final_version / Botany / Master / Master of Philosophy

Thesis (Ph. D.)--Michigan State University. Dept. of Chemistry, 2006. / Alpha in title represented by the lower case Greek letter. Title from PDF t.p. (viewed on Nov. 20, 2008) Includes bibliographical references (p. 235-245). Also issued in print.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1964. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 211-213).

No description available.

A calorimetric enthalpy of dilution technique was applied to the investigation of carboxylic acid self-association in organic solvents at 25°C. Data were analyzed in terms of the apparent relative molar enthalpy, Φ_L, and were found to fit adequately a monomer-dimer model. Values of the thermodynamic dimerization parameters K_2 and ΔH°_2 were obtained for several methyl-, halo-, and phenyl-substituted acetic and propionic acids in benzene. Some of the acids were also studied in toluene and carbon tetrachloride. Substituent effects on K_2 and ΔH°_2 were in general small and were explained adequately by an electrostatic model of the monomer-dimer interaction. Solvent effects were explained by considering an acid-solvent interaction. The effect on the results of small amounts of water in the solvent was found to be a function of aqueous acid strength. Acetic acid and other weak acids were unaffected by water in the solvent, but a significant affect was observed with stronger acids, such as the haloacetic acids.

No description available.