Kinetic and thermodynamic study of the interaction of vitamine B₁₂a with ligands in aqueous and micellar environments

Vita.Rate constants for the formation, k₁(superscript app) and decomposition, k₋ ₁(superscript app), of glycine, imidazole, sodium azide, cysteine, N-butanoyl-D,L-cysteine, N-octanoyl-D,L-cysteine, and N-decanoyl-D,L-cysteine adducts of vitamin B₁₂(subscript a) have been determined in water, in aqueous micellar sodium dodecyl sulfate and hexadecyltrimethylammonium bromide as well as in dodecylammonium propionate solubilized water in benzene. Effects in aqueous micellar systems are relatively small, with the exception of the N-alkanoyl-D,L-cysteine derivatives, and are explicable in terms of electrostatic and hydrophobic considerations. Using the obtained linear correlations between the glycine solubilities versus solvent polarity parameter E (subscript T)(30) , the effective environment was determined to depend on both the concentrations of water and of surfactant. Vitamin B₁₂(subscript a) effectively shielded from the apolar solvent by some 300 surfactant molecules. Values for k₁ (superscript app) and k₋₁(superscript app) for the interaction of vitamin B ₁₂(subscript a) a with ligands in the polar cavities of surfactants in benzene are significantly greater than those in bulk water and also depend on both the water and surfactant concentrations. Not unexpectedly, the largest rate enhancements were found with the smallest water pools. For the reaction of glycine with vitamin B₁₂(subscript a) at constant concentration of solubilized water for k₁ (superscript app) and k₋₁ (superscript app) increase with increasing dodecylammonium propionate concentration up to a maximum after which they decrease logarithmically. The significance of these results is discussed

Kinetic and thermodynamic study of the interaction of vitamine B₁₂a with ligands in aqueous and micellar environments

Vita.Rate constants for the formation, k₁(superscript app) and decomposition, k₋ ₁(superscript app), of glycine, imidazole, sodium azide, cysteine, N-butanoyl-D,L-cysteine, N-octanoyl-D,L-cysteine, and N-decanoyl-D,L-cysteine adducts of vitamin B₁₂(subscript a) have been determined in water, in aqueous micellar sodium dodecyl sulfate and hexadecyltrimethylammonium bromide as well as in dodecylammonium propionate solubilized water in benzene. Effects in aqueous micellar systems are relatively small, with the exception of the N-alkanoyl-D,L-cysteine derivatives, and are explicable in terms of electrostatic and hydrophobic considerations. Using the obtained linear correlations between the glycine solubilities versus solvent polarity parameter E (subscript T)(30) , the effective environment was determined to depend on both the concentrations of water and of surfactant. Vitamin B₁₂(subscript a) effectively shielded from the apolar solvent by some 300 surfactant molecules. Values for k₁ (superscript app) and k₋₁(superscript app) for the interaction of vitamin B ₁₂(subscript a) a with ligands in the polar cavities of surfactants in benzene are significantly greater than those in bulk water and also depend on both the water and surfactant concentrations. Not unexpectedly, the largest rate enhancements were found with the smallest water pools. For the reaction of glycine with vitamin B₁₂(subscript a) at constant concentration of solubilized water for k₁ (superscript app) and k₋₁ (superscript app) increase with increasing dodecylammonium propionate concentration up to a maximum after which they decrease logarithmically. The significance of these results is discussed

Mobilidade conformacional de complexos entre calix[4]arenos e aminas : evidências para estruturas exo-calix

Os espectros de RMN de sais de calix[4]areno e aminas alifáticas , em acetonitrila, mostraram valores de deslocamento químico dos hidrogênios do calix[4]areno próximos entre si para as diversas aminas. Foram obtidas as temperaturas de coalescência ( tc), acompanhando os hidrogênios metilênicos entre 32 e 38 oC para os sais de calixareno com as aminas e o aumento de tc deve-se ao aumento da basicidade da amina e não a fatores relacionados com o volume. Os dados estão de acordo com uma proposta exo-cálix, em que os cátions amônio situam-se fora da cavidade do calixareno

Mobilidade conformacional de complexos entre calix[4]arenos e aminas : evidências para estruturas exo-calix

Os espectros de RMN de sais de calix[4]areno e aminas alifáticas , em acetonitrila, mostraram valores de deslocamento químico dos hidrogênios do calix[4]areno próximos entre si para as diversas aminas. Foram obtidas as temperaturas de coalescência ( tc), acompanhando os hidrogênios metilênicos entre 32 e 38 oC para os sais de calixareno com as aminas e o aumento de tc deve-se ao aumento da basicidade da amina e não a fatores relacionados com o volume. Os dados estão de acordo com uma proposta exo-cálix, em que os cátions amônio situam-se fora da cavidade do calixareno

Reações intramoleculares como modelos não miméticos de catálise enzimática

This review gives a critical idea on the importance of intramolecular reactions as models for enzymatic catalysis. Intramolecular lactonizations, ester and amide hydrolysis studies result in theories which try to explain the difference between intermolecular, intramolecular and enzyme reactions and rationalize the enhancement promoted by these biological catalyst

Intramolecular reactions as non mimetic models of enzyme catalysis

Submitted by Vitor de Carvalho ([email protected]) on 2014-09-12T17:51:14Z No. of bitstreams: 1 Reações intramoleculares como modelos não miméticos de catálise enzimática.pdf: 65624 bytes, checksum: d2fa7b6eb6c668b13d456fb0c96a8409 (MD5)Rejected by Paula Gautério ([email protected]), reason: Nome de autor incompleto; Falta título em inglês on 2014-09-18T21:34:26Z (GMT)Submitted by Vitor de Carvalho ([email protected]) on 2014-09-18T23:34:15Z No. of bitstreams: 1 Reações intramoleculares como modelos não miméticos de catálise enzimática.pdf: 65624 bytes, checksum: d2fa7b6eb6c668b13d456fb0c96a8409 (MD5)Approved for entry into archive by Paula Gautério ([email protected]) on 2014-09-23T22:09:16Z (GMT) No. of bitstreams: 1 Reações intramoleculares como modelos não miméticos de catálise enzimática.pdf: 65624 bytes, checksum: d2fa7b6eb6c668b13d456fb0c96a8409 (MD5)Made available in DSpace on 2014-09-23T22:09:16Z (GMT). No. of bitstreams: 1 Reações intramoleculares como modelos não miméticos de catálise enzimática.pdf: 65624 bytes, checksum: d2fa7b6eb6c668b13d456fb0c96a8409 (MD5) Previous issue date: 1997This review gives a critical idea on the importance of intramolecular reactions as models for enzymatic catalysis. Intramolecular lactonizations, ester and amide hydrolysis studies result in theories which try to explain the difference between intermolecular, intramolecular and enzyme reactions and rationalize the enhancement promoted by these biological catalyst