Assessment of the chromatographic lipophilicity of eight cephalosporins on different stationary phases.

The retention behaviors were investigated for a series of eight cephalosporins in thin-layer chromatography (TLC) using stationary phases of RP-2, RP-8, RP-18, NH, DIOL, and CN chemically bonded silica gel. Additionally, various binary mobile phases (water/methanol and water/acetone) were used in different volume proportions. The retention behavior of the analyzed molecules was defined by R constant.

Hydrolysis of 2,4-dithiophenobarbital.

Hydrolysis of 2,4-dithiophenobarbital in aqueous solutions of pH 2-12 was investigated at 40 and 60 degrees C using UV spectrophotometry. The values of reaction order, rate constants, pKa1 and pKa2 and activation energy were determined. The preliminary estimation of degradation products was accomplished using thin layer chromatography.

The influence of sulfur substituents on the molecular geometry and packing of thio derivatives of N-methylphenobarbital.

The room-temperature crystal structures of four new thio derivatives of N-methylphenobarbital [systematic name: 5-ethyl-1-methyl-5-phenylpyrimidine-2,4,6(1H,3H,5H)-trione], C(13)H(14)N(2)O(3), are compared with the structure of the parent compound. The sulfur substituents in N-methyl-2-thiophenobarbital [5-ethyl-1-methyl-5-phenyl-2-thioxo-1,2-dihydropyrimidine-4,6(3H,5H)-dione], C(13)H(14)N(2)O(2)S, N-methyl-4-thiophenobarbital [5-ethyl-1-methyl-5-phenyl-4-thioxo-3,4-dihydropyrimidine-2,6(1H,5H)-dione], C(13)H(14)N(2)O(2)S, and N-methyl-2,4,6-trithiophenobarbital [5-ethyl-1-methyl-5-phenylpyrimidine-2,4,6(1H,3H,5H)-trithione], C(13)H(14)N(2)S(3), preserve the heterocyclic ring puckering observed for N-methylphenobarbital (a half-chair conformation), whereas in N-methyl-2,4-dithiophenobarbital [5-ethyl-1-methyl-5-phenyl-2,4-dithioxo-1,2,3,4-tetrahydropyrimidine-6(5H)-one], C(13)H(14)N(2)OS(2), significant flattening of the ring was detected. The number and positions of the sulfur substituents influence the packing and hydrogen-bonding patterns of the derivatives.

Lipophilicity of thiobarbiturates determined by TLC.

Lipophilicty of 29 thiobarbituric acid derivatives were assessed by reversed-phase thin-layer chromatography using methanol: water mixtures as a mobile phase. A linear relationship was found between RM values and methanol concentrations in the mobile phase. The retention parameter, RM0, was related to theoretical partition coefficients calculated by means of different theoretical procedures (AlogPs, IAlogP, miLogP, logPKowwin, xlogP).

Stability of 2-thiophenobarbital and its N-methyl derivatives in the presence of beta-cyclodextrin.

The rates of hydrolysis of thiophenobarbital and its N-mono- and N,N'-dimethyl-derivatives were determined under different conditions of pH and temperature using UV spectroscopy. They were compared with those obtained in the presence of different concentrations of beta-cyclodextrin. It was found that the compounds degrade with different rates and beta-cyclodextrin retards the hydrolysis.