Diffusion ordered NMR (DOSY) was applied to the determination of the average molecular weights of polymers based on the dependence of the measured self diffusion coefficient D on the correspond ing weights of a number of polymers of the same type. As a rule, a calibration function is plotted by varying DOSY experimental parameters for each particular test sample; however, this approach is inapplicable to the development of a standard procedure for the quantitative assessment of the molecular weights of dextrans. In this article, an optimization method is considered to ensure high resolution in terms of the values of D for dex trans without varying experimental conditions; this method makes it possible to evaluate the average molec ular weights of dextrans with a high accuracy over a wide range of their values.

Reactions of N pyrrolylpotassium with fluorinated electrophiles yielded N substituted pyr roles containing polyfluoroalkyl, polyfluoroalkenyl, polyfluoroalkylsulfonyl, and polyfluoroaryl substituents. N Polyfluoro substituted pyrroles did not isomerize at >100 °C; they were found to be reactive in [4+2] cycloaddition reactions with perfluorobut 2 yne. hexafluoropropylpyrroles) were obtained rather long ago 1,2 by addition of pyrrole to polyfluorinated alkenes at 100 °C in the presence of metallic potassium. In the same studies, 1,2 two examples of the synthesis of N (polyfluoroalkenyl)pyrroles, namely, N (2 chloro difluorovinyl)pyrrole and 2 fluoro 2 phenyl 1,1 dipyr rolylethylene, were reported, although the researchers themselves were doubtful about their structures. 3,4 Di methyl 1 pentafluorophenylpyrrole was obtained by de sulfooxidation of the corresponding thiazine oxide with a solution of alkali in aqueous alcohol and this was the only example of the synthesis of fluorinated arylpyrrole. 3 The goal of the present study was to investigate the preparative possibility of using N pyrrolylpotassium to obtain pyrroles containing polyfluorinated substituents at the N atom. Earlier, 4 N pyrrolylpotassium was prepared by a reaction of pyrrole with solid KOH followed by dry ing. Our attempted synthesis of N substituted pyrroles by reactions of the reagent thus prepared with polyfluoro olefins failed. The major process was mineralization of fluoroolefins by the action of KOH.We found that reactions of chlorotrifluoroethylene and perfluoropropylene with N pyrrolylpotassium (in situ pre pared by dissolution of metallic potassium in an excess of pyrrole (1 : 1.2) in ether) occur even at -60 °C and proceed exothermically to give 2 : 7 and 2 : 5 mixtures of N polyfluoroalkyl and N polyfluoroalkenylpyrroles 1, 2 and 3, 4, respectively. Repeated fractionation of these mixtures allowed individual compounds 1, 3 and 2, 4 to be isolated in low (≤5%) yields (Scheme 1).It should be noted that pyrrole does not react with fluoroolefins in the absence of potassium.N Polyfluoroalkenylpyrroles were selectively obtained with N pyrrolylpotassium dried in vacuo. Reactions of the dispersed N pyrrolylpotassium thus prepared with chloro trifluoroethylene, perfluoropropylene, and perfluoroiso butylene in ether proceed exothermically at -60 °C to give polyfluoroalkenylpyrroles 2, 4, and 5 in satisfactory yields (Scheme 2). The reaction with the most reactive polyfluoroalkene (perfluoroisobutylene) also yielded di substituted olefin 6. Pyrroles 2 and 4 were obtained as mixtures of the geometrical Z,E isomers in the 7 : 5 ratio for compound 2 and of the E,Z isomers in the 8 : 1 ratio for compound 4. Pyrroles 2 and 4 were distilled over dry KOH to remove minor amounts of polyfluoroalkylpyrro les 1 and 3, which can form in the presence of water or pyrrole traces. The Z isomer of compound 2 and the E isomer of compound 4 were dominant (>95%). This follows from the constants of F-F spin spin coupling in the 19 F NMR spectra (J trans = 126.2 and 1...

The possibility of the application of diffusion ordered NMR spectroscopy to the study of the molecular weight distribution of hydroxyethyl starch is investigated. The use of regression equations relating these parameters to the coefficients of the self diffusion of polymer macromolecules as a whole, namely, the average coefficient of self diffusion D s and the coefficient of self diffusion at the peak maximum D p , is pro posed for the quantitative assessment of weight average (M w ) and number averaged (M n ) molecular weights and molecular weight at the peak maximum (M p ). It is shown that the determination of M w , M n , M p based on the data on D s gives the best results. It was found that the values of polydispersity indexes found using diffu sion ordered NMR spectroscopy are independent of the choice of diffusion parameter D s or D p .Keywords: diffusion ordered NMR spectroscopy, parameters of the molecular weight distribution of poly mers, average coefficient of self diffusion, self diffusion coefficient at the peak maximum, hydroxyethyl starch

Оценена специфичность различных вариантов методики подтверждения подлинности фармацевтической субстанции «бусерелина ацетат» методом ЯМР спектроскопии путем сравнительного анализа спектров 1H и 13C бусерелина ацетата и [5-D-тирозин]бусерелина ацетата в различных растворителях. Найдено, что максимальное различие в спектральных данных диастереомеров наблюдается при использовании дейтерированной воды в качестве растворителя. Показано влияние растворителя и внутримолекулярных невалентных взаимодействий на обменные прототропные превращения в L-гистидиновом фрагменте анализируемых олигомеров. От скорости прототропной таутомерии зависит ширина сигналов данной аминокислоты в спектрах 13C. Рекомендовано использовать в фармакопейном анализе вариант методики, основанный на 13C ЯМР спектроскопии (растворитель — D2O).

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