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The structure of enterosgel before and after freezing (samples I and II, respectively) was comparatively analyzed by gravimetric analysis and NMR methods [PMR, 13C NMR, diffusion-ordered NMR spectroscopy (DOSY)] to understand the reason for the negative effect of freezing on the adsorption capacity of enterosgel. The methylsiloxane moieties in samples I and II were shown to be magnetically equivalent by PMR and 13C NMR methods. The molecular masses of samples I and II were estimated by the DOSY method and corresponded to the cyclic dimer of methylsilicic acid (MM 152 Da) for sample I and the linear dimer of methylsilicic acid (MM 170 Da) for sample II. It was hypothesized that the conformationally rigid cyclic dimer structure was destroyed upon freezing of enterosgel due to rupture of a siloxane bond. The adsorption capacity of enterosgel deteriorated because of the structure disruption and hydrophobicity change. Thermogravimetric analysis revealed that water did not participate in hydrogen bonding with enterosgel. [ABSTRACT FROM AUTHOR]

The structure of nitisinone (β, β′-triketone reversible inhibitor of the enzyme 4-hydroxyphenylpyruvate dioxygenase) in various protic and aprotic solvents was studied using PMR and 13C NMR spectroscopy. Nitisinone was shown to exist in solutions at room temperature as the endo-enol tautomer while the exo-enol tautomer was not found. Prototropic ring tautomerism (migration of a proton between the 1- and 3-positions), the rate of which increases with increasing solvent polarity, occurs in the endo-enol tautomer. The mineral composition of the biological fluid does not affect the tautomeric equilibrium. The conformational rigidity of the nitisinone molecule accounts for the nonequivalence of the 1- and 3-positions in the cyclohexene fragment from the standpoint of binding of nitisinone to the Fe(II)*4-hydroxyphenylpyruvate dioxygenase complex. [ABSTRACT FROM AUTHOR]

Clinically applicable lipopolysaccharides (LPSs) from Shigella flexneri, lipid A of which contains at most three higher fatty-acid residues, are promising candidates for creating vaccines against it. NMR studies of modified LPS are practically unreported. Most publications in this field are devoted to studying the polysaccharide structure of native LPS, i.e., O-specific polysaccharide (OPS) that can be isolated after mild hydrolysis of LPS and separation of lipid A. The present article describes the development of an NMR procedure for authenticity verification of modified LPS, i.e., vaccine polysaccharide components. Characteristic 13C resonances in the region of anomeric C atoms are identified. The confidence intervals of their chemical shifts are determined. The procedure is demonstrated to be specific for modified LPS subtypes 1b, 2a, 3a, Y, and 6 from S. flexneri. [ABSTRACT FROM AUTHOR]

A procedure for validation of an assay method for fluorine in residual trifluoroacetates in the pharmaceutical substance glatiramer acetate by 19F NMR spectroscopy is described. The method provides for assay of the content of trifluoroacetates without destruction of the substance under analysis. The validation process established the detection limit and assessed the linearity, accuracy, convergence, intralaboratory precision, and specificity of the method under validation. Measurement of "found:added" coefficients were used to calculate standard deviations, coefficients of variation, significance intervals, and systematic errors, using Fisher's F test and Student's t test to assess the assay results. The statistical characteristics were found to satisfy the criteria for acceptability of the validation parameters given in Russian and foreign normative documentation. [ABSTRACT FROM AUTHOR]

The acid hydrolysis procedure for glatiramer acetate was modified and the characteristic signals in the H and C spectra were identified, allowing its amino acid composition to be determined. The relative molar contents of amino acids in glatiramer acetate measured by HPLC-MS and by C and H NMR had close values. C NMR was found to be a more precise method for assaying the amino acid composition of glatiramer acetate than H NMR. [ABSTRACT FROM AUTHOR]

Amethod for determining molar substitution of hydroxyethylstarches by H NMR spectroscopy was validated in terms of specificity, linearity, correctness, precision, and range of application. The method can be used to evaluate the parameter 'molar substitution' in the framework of pharmacological expert assessment of hydroxyethylstarches as components of medicines. [ABSTRACT FROM AUTHOR]

The PMR spectroscopy technique for determining the molar substitution (MS) in hydroxyethyl starch (HES) was modified. It was shown that allowance for integrated intensities of resonances for anomeric H(1) protons of terminal and branching substituted and unsubstituted α-D-glucopyranose residues in HES decreased the calculated MS values and eliminated differences in the MS values obtained by PMR spectroscopy and gas chromatography. [ABSTRACT FROM AUTHOR]