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H N Borazan

Publications and source records attributed to H N Borazan.

17 recordsLinked to original sources
PubMed1988

Charge transfer complexes of indole:catechol type II.

Charge transfer complexes between tryptamine:epinephrine, tryptamine:isoproterenol, tryptamine:catechol, and indole:catechol were demonstrated spectrophotometrically in aqueous solutions containing 0.1 M HCl. It was possible to make precise measurements and to calculate thermodynamic parameters and molar absorptivities. In general, the equilibrium constant was found to be quite low and ranged from 4.00 +/- 0.04 to 0.30 +/- 0.02 M-1. These interactions are exothermic and have relatively large standard enthalpy and entropy changes (delta Ho values ranged from -7.4 +/- 0.3 to -5.2 +/- 0.4 kcal mol-1; delta So ranged from -25 +/- 5.0 to -16 +/- 1.3 cal K-1 mol-1). The similarity in delta Ho and delta So values for all the combinations indicates a similar interacting system. This result has led us to propose the involvement of the charge transfer effect, induced in the indole:catechol system, in the mechanism occurring in nerve conductions.

Catechols↗
PubMed1984

Binding parameters of interactions of monomer-polymer systems based on quenching of their completely overlapped fluorescence: a theory.

A theory is presented which describes the interactions between completely overlapping fluorescing monomer-polymer systems and affords a method to calculate binding parameters. The theory is based on the assumptions that the complex formed from the fluorescing binding site and the monomer molecule does not fluoresce and that the fluorescence intensity is linearly related to concentration. The relationships derived from this theory have provided a sensitive and easy method for calculating the number of binding sites on a polymer molecule from only three emission-intensity values. The theory has been tested on systems containing trimethoprim-serum albumins and found to yield results which are consistent with a curve-fitting approach to the experimental data. This reflects the validity of the theoretical model presented and the various assumptions and approximations made.

Animals↗
PubMed1983

Coil leads to helix transition in polyadenylic acid induced by the binding of epinephrine, norepinephrine, and isoproterenol: circular dichroism study.

A circular dichroism spectropolarimetric study on the conformation of polyadenylic acid (poly A) in neutral solutions demonstrated a coil leads to helix transition induced by intercalative binding of critical amounts of epinephrine, norepinephrine, and isoproterenol relative to poly A. Theoretical treatment of the experimental data indicated a first-order kinetic transition in poly A. It was possible to measure transition rate constants of the epinephrine-poly A and norepinephrine-poly A systems and to calculate the activation energies. The results indicate a high level of temperature dependence of the rate constants. The effects can be reversed by increasing ionic strength, indicating the significance of the electrostatic interactions. The importance of the results is discussed in terms of the possible role of the catecholamines as control mechanisms for the poly A-regulated translation of the genetic code on mRNA.

Circular Dichroism↗
PubMed1979

UV studies of nucleic acid vase complexation with isoproterenol in different solvents.

Charge transfer complex formation between nucleic acid bases and isoproterenol was demonstrated from UV absorption measurements. The solvent polarity effects on equilibrium constants were investigated. The solvent systems containing 0.1 N HCl were 20% aqueous ethanol, water, and water containing sodium chloride. The equilibrium constants, calculated from UV absorption data by the application of the Benesi-Hildebrand equation, were small and increased with increasing ionic strength. Equilibrium constant wavelength dependence was demonstrated in some cases.

Isoproterenol↗
PubMed1978

Interactions of caffeine and theophylline with p-cresol: UV studies.

UV absorption studies demonstrated the formation of weakly bonded charge transfer complexes between caffeine and theophylline with p-cresol in chloroform. The transitions involved were detected at wavelengths longer than those of the single pure substances. Equilibrium constants from the Benesi-Hildebrand equation could be measured together with other thermodynamic constants and molar extinction coefficients. In general, the equilibrium constants were very small while the entropies of formation were quite high. Even though the equilibrium constants of caffeine--p-cresol were independent of wavelength over a narrow range, the apparent enthalpies of formation of both complexes indicated wavelength dependence.

Caffeine↗
PubMed1976

Interactions of nucleic acid bases with catechol: UV studies.

UV absorption studies on weak interactions of adenine, cytosine, thymine, and uracil with cathechol in aqueous solutions containing 0.1 N HCl gave evidence for the formation of charge transfer complexes. The absorptions of these complexes were found in the UV region at longer wavelengths than those of the pure components. It was possible to calculate various thermodynamic parameters and molar extinction coefficients at different wavelengths. The biological significance of the results is discussed.

Adenine↗
PubMed1976

Interactions of adenine, thymine, and uracil with epinephrine: UV studies.

Based upon UV absorption studies, charge transfer complex formations by the nucleic acid bases adenine, thymine, and uracil with epinephrine were demonstrated. The pertient equilibrium constants were calculated by assuming 1:1 complexes using the Benesi-Hildebrand equation and were found to decrease in the following order: uracil-epinephrine greater than thymine-epinephrine greater than adenine-epinephrine. The values of delta G degrees, delta H degrees, and delta S degrees were calculated for the various interactions. Theoretical arguments are presented as to the possible stoichiometries of the various complexes existing in aqueous solutions. The electron-donating or electron-accepting abilities of the interacting molecular species are discussed.

Adenine↗
PubMed1976

Nucleic acids-protein interactions. Conformational changes induced by the binding of aromatic amines to polyadenylic acid.

The binding of Tryptamine, Serotonine, Phenylethylamine and Histamine to poly(A) in its single stranded form at pH 7 leads to a decrease of its circular dichroism (C.D) amplitude without any appreciable alteration of the shape of the C.D. spectrum. The magnitude of the effect depends on the size of the aromatic ring and decreases in the order : tryptamine greater than tyramine greater than phenylethylamine greather than histamine. A method is described which allows the calculation of association constants from C.D. data. The C.D. amplitude decreases linearly with concentration of bound molecules. Binding of aromatic amines to poly(A) leads to a change in the proton chemical shifts of both the amine and the poly(A) protons. Quantitative analysis of P.M.R. data demonstrates that the shifts of poly(A) protons are linearly related to the concentration of bound molecules.

Amines↗
PubMed1975

Interaction of aromatic residues of proteins with nucleic acids. Circular dichroism studies of the binding of oligopeptides to poly(adenylic acid).

The binding of peptides containing lysyl and aromatic residues to poly(A) in its single-stranded form at pH 7 leads to a change of its circular dichroism (CD) spectrum, which is mainly due to the stacking of the aromatic amino acid with the bases of poly(A). Comparison is made between the binding of peptides having different primary structures which gives indications on the way the peptides bind to poly(A). A method is described which allows the calculation of the binding parameters from CD data. The magnitude of the association constant depends on the size of the aromatic ring and decreases in the order tryptophan greater than tyrosine greater than phenylalanine. The CD amplitude decreases linearly with the concentration of bound molecules. These results are discussed with respect to the role played by aromatic amino acids in complex formation between nucleic acids and proteins.

Adenine Nucleotides↗
PubMed1975

Theoretical considerations on mononuclear aggregations of mixed nucleosides in dilute aqueous solutions based upon osmometric measurements.

A theory is presented based on experimental work reporting shifts in the critical micelle-like concentrations of nucleosides and caffeine. An increase in these concentrations by multiple integers (called complexing capacity numbers) of the concentration of the vehicle compound, whose concentration was fixed, was observed for substances that tend to form complexes with each other and with some other compounds and to self-associate as well when their concentrations are varied. The physical model presented assumes the significance of the potential hydrogen bonding sites in determining the mode of aggregation as well as the magnitude of these complexing capacity numbers. This assumption was verified experimentally when reducing the hydrogen bonding by using 1,3-dimethyluracil. The mathematical model hypothesized has provided a means for calculating equilibrium constants for various consecutive processes as well as other quantities of theoretical interest.

Caffeine↗