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Investigations of hydrogen bonding in the poly(urethane-urea)-based membrane materials by using FTIR spectroscopy

100%
Wolińska-Grabczyk A., Kaczmarczyk B., Jankowski A.
Polish Journal of Chemical Technology
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2008
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vol. 10
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issue 4
53-56
EN
FTIR analysis was used to study the hydrogen bonding in 4,4'-diaminodiphenylmethane-based segmented poly(urethane-urea)s varying in the length of the poly(tetramethylene oxide) (PTMO)-based soft segments. Experiments were designed to follow the IR absorption of both the NH and carbonyl regions as a function of temperature in order to directly investigate the extent and strength of the hydrogen bonds, and thereby to gain some information about the possible alteration of the initial phase-segregated morphology as a result of the applied thermal treatment.
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Conformational isomerism of 1-butene secondary ozonide as studied by means of matrix isolation infrared absorption spectroscopy

100%
Strazdaite S., Bariseviciute R., Ceponkus J., Sablinskas V.
Open Chemistry
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2012
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vol. 10
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issue 5
1647-1656
EN
Theoretical calculations of structures, stability and vibrational spectra of 1-butene secondary ozonide (SOZ) conformers were performed using DFT method B3LYP with a 6-311++G(3df, 3pd) basis set. The calculations predict six staggered structures of 1-butene SOZ. The FTIR spectra of 1-butene SOZ isolated in Ar, N2 and Xe matrices were recorded. It was found that nitrogen is the best suited for the matrix isolation of 1-butene SOZ. The bandwidth of the spectral bands of the ozonide isolated in nitrogen was as narrow as 2 cm−1. For the first time the existence of five conformers of 1-butene SOZ were confirmed experimentally by means of matrix isolation infrared absorption spectroscopy. The equatorial gauche (∠OCCC=−66.1°) conformer was proved theoretically and experimentally to be the most stable. It was found that due to high potential barriers of the conformational transitions annealing of the matrix is useless for the assignment of spectral bands to various conformers of 1-butene SOZ. Using the hot nozzle technique the van’t Hoff experimental plots were made for three additional conformers of 1-butene SOZ and experimental ΔH values for these additional conformers were established. The crystallization problems of 1-butene SOZ are discussed which accounts for the rich conformational diversity of the ozonide as well as high conformational barriers for axial-equatorial transitions. [...]
3
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Impurity profile analysis of drug products containing acetylsalicylic acid: a chemometric approach

88%
Ronowicz J., Kupcewicz B., Mydłowska J., Budzisz E.
Open Chemistry
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2013
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vol. 11
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issue 7
1091-1100
EN
In this work attention is focused on impurity profile analysis in combination with infrared spectroscopy and chemometric methods. This approach is considered as an alternative to generally complex and time-consuming classic analytical techniques such as liquid chromatography. Various strategies for constructing descriptive models able to identify relations among drug impurity profiles hidden in multivariate chromatographic data sets are also presented and discussed. The hierarchical (cluster analysis) and non-hierarchical segmentation algorithms (k-means method) and principal component analysis are applied to gain an overview of the similarities and dissimilarities among impurity profiles of acetylsalicylic acid formulations. A tree regression algorithm based on infrared spectra is used to predict the relative content of impurities in the drug products investigated. Satisfactory predictive abilities of the models derived indicate the possibility of implementing them in the quality control of drug products. [...]
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