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Biomedical subjects

T Higuchi

Publications and source records attributed to T Higuchi.

At least 721 records · Page 40Linked to original sources
PubMed1975

Acylation of ascorbic acid in water.

The acylation of ascorbic acid by acetic anhydride was studied in water at 25 degrees. The results indicate that the initial products of reactions between these two compounds were acetic acid and 3-o-acetylascorbic acid. The latter product then underwent two parallel reactions: hydrolysis to ascorbic and acetic acids and an intramolecular O leads to O acyl migration to yield-O-acetylascorbic acid. The former reaction was predominant at pH values below 4, whereas the latter reaction predominated at pH values between 4 and 7. These results are used as a basis for questioning the structural assignments previously made to some ascorbic acid esters.

Acetylation↗
PubMed1975

Solvolytic reactions of cyclic anhydrides in anhydrous acetic acid.

The reversible reactions of several cyclic anhydrides with acetic acid to form acetic anhydride and the corresponding dicarboxylic acid, catalyzed by perchloric acid at 25degree, were studied. The equilibrium constants, calculated from spectral data, were 4.85 X 10-4, 1.08 X 10-1, and 4.6 X 10-1 M for succinic, trans-1,2-cyclohexanedicarboxylic, and glutaric anhydrides, respectively. Maleic, phthalic, and cis-1,2-cyclohexanedicarboxylic anhydrides did not undergo any detectable reaction with acetic acid under these conditions, suggesting still higher stability. The reverse rate constants were found to be relatively independent of the structure of the attacking diacid, while the forward rate constants were found to parrallel the equilibrium constants. The rate-determining step for the forward reaction appears to be the breakdown of the tetrahedral intermediate formed by the attack of an acetic acid molecule on the protonated cyclic anhydride.

Acetates↗
PubMed1975

Acylation of phenol by cyclic and acyclic anhydrides in anhydrous acetic acid.

Acylation of phenol with succinic, glutaric, trans-1,2-cyclohexanedicarboxylic, maleic, phthalic, and cis-1,2-cyclohexanedicarboxylic anhydrides in anhydrous acetic acid generally resulted in phenyl acetate as the major product. The formation of phenyl acetate as the major reaction product could be rationalized as being due to the reactivity of the cyclic anhydrides with acetic acid to form acetic anhydride as well as the greater reactivity of phenol with formed acetic anhydride than with the cyclic anhydride.

Acetates↗
PubMed1975

Solubilization and stabilization of the cytotoxic agent coralyne.

Kinetic studies were carried out on the ring opening of the quaternary nitrogen cation, coralynium ion (I), to yield 6'-acetylpapaverine (III), on the cyclization of III to yield I, and on a photochemical reaction undergone by I in aqueous solutions exposed to visible light. From the results, it was concluded that: (a) I and III are in facile equilibrium in aqueous solution but appreciable amounts of III do not exist in dilute solutions with pH values below 10: (b) the photochemical reaction of I in water (presumably a photohydration) can be reversed by lyophilization, by heatiing, and by increasing the pH of solutions to values greater than 12; (c) the photochemical reaction of I can be inhibited by protecting the aqueous solutions from visible light, and the rate in the presence of light can be reduced by increasing the concentration of I in the solution; and (d) although the chloride and sulfoacetate salts of I react identically and have similar solubilities in water, it is possible to prepare more concentrated and, hence, more stable solutions of the sulfoacetate salt by including sodium hydroxide in the solvent. The solubility of coralyne chloride remains about the same in dilute sodium hydroxide as in water.

Antineoplastic Agents↗
PubMed1975

Complexation in formulation of parenteral solutions: solubilization of the cytotoxic agent hexamethylmelamine by complexation with gentisic acid species.

The apparent solubility of hexamethylmelamine in aqueous solutions suitable for intravenous use was increased by complexation with gentisic acid. Studies were carried out in the pH 0-8 range. Unprotonated hexamethylmelamine did not form complexes with the gentisate ion, while the hexamethylmelammonium ion appeared to form several different complexes with both the gentidate ion and gentisic acid. Two different solid complexes were isolated and characterized. The solubility increases observed at pH 3.5-5.0 are described by mathematical relationships involving the stability constants of some postulated complex species. From these results, sultable formulations for use as parenteral solutions are proposed. The increase in the apparent aqueous solubility of hexamethylmelamine in such formulations may range from five- to 90-fold, depending upon the pH and total gentisateion concentrations.

Altretamine↗
PubMed1975

Binding of bile acids to cholestyramine at gastric pH conditions.

The binding of bile salts to cholestyramine was studied under varying conditions of pH and added electrolyte. The taurine-conjugated bile salts were strongly absorbed by the anion-exchange resin at low pH and in the presence of chloride anions. Glycocholic acid binding was very weak at low pH but increased strongly with increasing pH. The presence of chloride ions strongly decreased the amount of glycocholate bound by the anion-exchange resin.

Adsorption↗
PubMed1975

Neural control of LH release in anterior periventriculo-median eminence-pituitary system.

Separate regions of the anterior periventricular area (PVA), median eminence (ME) and frontal cortex from brains of hypophysectomized female and intact male rats were extracted and homogenized. The LH-RH content of these homogenates was determined by a specific double antibody radioimmunoassay. LH-RH was found in the PVA as well as in the ME of both hypophysectomized female and intact male rats; it was not detected in the frontal cortex. Extracellular recordings were made from neurons in the PVA and 55 neurons were activated antidromically by stimulating the ME. This suggests that PVA neurons exist with axons terminating in the ME. It is assumed that these axons are unmyelinated since their conduction velocity was approximately 0.3-0.8 m/sec. In addition to the antidromically-activated neurons, 26 neurons with characteristics of transsynaptic activation were recorded in the PVA following stimulation of the ME. Some of the units recorded from the ME-arcuate (ARC) region were also activated either antidromically or transsynaptically by stimulating the PVA. The effect of PVA stimulation on LH release was tested in ovariectomized, estrogen-treated rats with or without anterior deafferentation of the hypothalamus. Increased LH concentration in serum was elicited by PVA stimulation of rats in which deafferentation was either not performed or not completed; no increase in serum LH level was observed following PVA stimulation in rats with complete deafferentation. These data suggest that PVA neurons synthesize LH-RH, which is released at the ME.

Afferent Pathways↗