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Physico-Chemical Characteristics of Fe-Co/SiO2 Catalysts

Kwintal P., Bojarska J., Jóźwiak W. K.

Polish Journal of Chemistry

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2009

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Vol. 83, nr 10

1837-1847

EN

Bimetallic catalysts for Fischer-Tropsch synthesis containing iron-cobalt phase deposited on silica surface were prepared using three methods: co-precipitation deposition, wet impregnation and mechanical mixing. The aim of this work was to determine the mutual interaction between oxide components created in the course of subsequent stages of catalyst 34%Fe/51%Co/15%SiO2 preparation, calcinations and reduction. The physico-chemical properties of obtained catalysts were characterized by BET, XRD and TPR methods.

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Strukturalne zagadki kompleksowanych gramicydyn w ich kryształach

Główka M.L., Olczak A., Bojarska J., Szczesio M.

Wiadomości Chemiczne

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2007

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[Z] 61, 3-4

167-187

EN

Gramicidin D (gD) is a naturally occurring mixture of six linear pentadecapeptides produced by Bacillus brevis species in soil, which exhibit significant antibacterial activity against all Gram+ bacteria. The peptides are modified at both ends and the six forms differ at 1st (Val or Ile) and 11th (Trp, Phe or Tyr) positions. The most populated gramicidin A (VgA) has a sequence CH(O)-Val_1-Gly-Ala-D-Leu-Ala-D-Val-Val-D-Val-Trp-D-Leu-Trp_11-D-Leu-Trp-D-Leu-Trp-NHCH_2CH_2OH. Gramicidin was isolated in 1939 and its sequence was determined five years later. First models of its secondary structure based on helical conformation were proposed in 1971-1974 explaining channel-like properties of the peptide. Despite over 60 years of studies on gramicidin, there are still numerous unans-wered questions concerning its structure and functioning. Even fundamental issues of dimers type and handedness of helices in the gramicidin channel formed by the peptide in the bacterial cell membranes are not univocally accepted. After refining several crystal structures of gramicidin D complexes with alkali metal salts, we have at hands not only more facts concerning double-stranded antiparallel gramicidin dimers, but also new puzzled observations due to very high reso-lution data collected. These, among others, include visible asymmetry of cations' sites and occupations in the gramicidin channels, as well as specific arrangement of heterodimers in the crystals. The paper describes these interesting features of the complexed gramicidin structure and proposes some new explanations.

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Geometry of alfa-Diaryl Type CH-NH Acids of Pharmacological Interest. Crystal Structures of alfa-(4-Chlorophenyl)- and alfa-(2,4-Dichlorophenyl-alfa-2-pyrazilideneacetonitrilles

Główka M., Olczak A., Bojarska J., Szczesio M., Kozłowska K., Foks H.

Polish Journal of Chemistry

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2005

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Vol. 79 / nr 8

1275-1284

EN

alfa-Diarylacetonitriles represent a very interesting model for studying the structure-activity relationship, due to restricted freedom of conformational diversity and, on the other hand, a very wide range of biological activities, including analgesic, non-narcotic antiinflammatory and antirheumatic. The two studied representatives have in the crystal state very uniform molecular structures, which may be characterized by a dihedral angle between the two aromatic rings, being 77 graduate in 4-chlorophenyl; 74 graduate and 80 graduate in 2,4-dichlorophenyl derivative, respectively. Despite the presence of groups capable of weak C-H hydrogen bonds formation there is only one short C-H...X contact (X = N in 4 position of the pyrazinyl ring) of 2.40 ?, being significantly shorter than the sum of van der Waals radii of respective atoms. The contact found in the 2,4-dichlorophenyl derivative crystal is in accord with CH-NH proton transfer observed in these compounds.