Determination of sulfur-containing amino acid residues in proteins by pyrolysis-gas chromatography with flame photometric detection

Summary A new method for the determination of sulfur-containing amino acid residues, cysteine (Cys) and methionine (Met) in proteins has been developed with pyrolysis-gas chromatography. Characteristic sulfur compounds among the complicated pyrolysis products formed from protein samples were separated by using a high resolution fused silica capillary column and selectively detected by flame photometric detector (FPD). In order to improve the reproducibility, an internal standard substance, benzothiophene, was pyrolyzed at 600 °C together with the protein samples. Thus the observed pyrograms were interpreted in terms of the compositional analysis. On the basis of the relative peak intensities of CH₃SH and H₂S, the simultaneous determinations of Cys and Met residues in various enzyme proteins were successfully carried out with 10–12% and 5–6% of relative standard deviations, respectively.

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Bestimmung von schwefelhaltigen Aminosäureresten in Proteinen durch Pyrolyse-GC mit flammenphotometrischer Detektion

     

Dissolving metal reduction by crown ether —hydrogenolysis of alkyl fluorides

A black-blue solution of potassium and dicyclohexyl-18-crown-6 in toluene or diglyme has been proved to be effective in the reductive cleavage of the unactivated carbon—fluorine bond.     

Equilibrium anionic polymerization of β-methoxypropionaldehyde

Anionic polymerization of β-methoxypropionaldehyde (MPA) was carried out in tetrahydrofuran (THF) by using benzophenone–monolithium complex as an initiator. An equilibrium between polymerization and depolymerization was observed at a temperature range of ?90 to ?70°C. From the temperature dependence of the equilibrium monomer concentration, thermodynamic parameters for the polymerization of MPA in THF were evaluated as follows: ΔH_ss = ?4.8 ± 0.2 kcal/mole, ΔH_SS = ?22.4 ± 1.3 cal/mole-deg, and (T_c)_ss = ?59°C. The thermodynamic change upon the conversion of liquid monomer to condensed polymer was computed from both the partial mixing energy of MPA with THF and the linear relationship between the equilibrium volume fraction of MPA monomer and that of the resulting polymer: ΔH_1c = ?4.7 ± 0.2 kcal/mole, ΔS_1c = ?19.5 ± 1.3 cal/mole-deg, and (T_c)_1c = ?35°C.     

Laser diffraction estimation of particle size distribution of slightly water-soluble drugs coexisting with additives: application to solid dosage forms.

A simple and quantitative evaluation method for particle size distribution (fx(r)) of slightly water-soluble drugs dispersed in an aqueous medium together with other water-insoluble additives was developed using a laser diffraction method. The particle size distribution function of the powder mixture, (f(r)), was assumed as f(r) = phi x.fx(r) + phi a.fa(r), where phi is the volume fraction of each component dispersed in a measurement medium and fa(r) is the distribution function of another water-insoluble additive "a". In order to calculate fx(r) from f(r), it is necessary to know the density of drug and additive in the measurement medium, d(x) and d(a), but this is difficult to determine since particles usually swell in the medium. Thus, a method was developed to use their relative value, delta a (= da/dx). As a practical application, oxolinic acids (OA) of three sizes (OA-S (about 2 microns), OA-M (about 7 microns) and OA-L (about 24 microns)) were used as model drugs. delta a values were determined for various additives using the mixture of OA-S and each additive. Then, using delta as, fx(r) of OA-M or OA-L in the mixture containing OA-M or OA-L and additives was calculated from the f(r) experimentally determined for the mixture. They agreed well with their original distributions. The method was applied to some dosage forms, and the results obtained had good correlation with those from turbidity, wet sieving or dissolution test.