排序方式: 共有8条查询结果,搜索用时 15 毫秒
1
1.
Tomasz Gubica Jadwiga Stroka Andrzej Temeriusz Marianna Kańska 《Journal of Physical Organic Chemistry》2011,24(12):1229-1234
Ten nitrophenyl N‐glycosides have been studied electrochemically in neutral (at pH 7) water–organic solutions by cyclic voltammetry using static mercury drop electrode. For all compounds under investigation the two electrochemical processes have been observed: the four‐electron irreversible reduction of their nitro groups to the corresponding phenylhydroxylamine derivatives, as well as the two‐electron quasi‐reversible process between phenylhydroxylamine and nitroso derivatives. For three compounds the additional electrochemical processes have been also observed, which can be connected with the formation of azoxybenzene derivatives. The potentials of both redox processes: a two‐electron quasi‐reversible R? NHOH/R? NO (Ef) and four‐electron irreversible R? NO2/R? NHOH (Epc(I)) systems have been determined and discussed according to crystal structures of selected compounds. Ef and Epc(I) depended strongly on the positive mesomeric effect (caused by glycosidic nitrogen atom), as well as on the intramolecular hydrogen bond between electroactive nitro group and the hydrogen atom at the glycosidic atom observed in N‐o‐nitrophenyl‐2,3,4,6‐tetra‐O‐acetyl‐β‐D ‐glucopyranosylamine. Moreover, the chirality of selected reactants has had the pronounced effect on the Epc(I). Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
2.
Tomasz Gubica Jadwiga Stroka Andrzej Temeriusz 《Journal of Physical Organic Chemistry》2007,20(6):375-383
A series of nitrophenyl β‐cyclodextrin derivatives: mono[6‐deoxy‐6‐(4‐nitrobenzamido)]‐per‐ O‐methyl‐β‐cyclodextrin (R1? Ph? NO2), mono[6‐deoxy‐6‐(3‐nitrobenzamido)]‐per‐O‐methyl‐β‐cyclodextrin (R2? Ph? NO2) and heptakis[6‐deoxy‐6‐(4‐nitrobenzamido)‐2,3‐di‐O‐methyl]‐β‐cyclodextrin [R3? (Ph? NO2)7] were synthesized. Purity and composition of the obtained substances were checked. Electroreduction of nitro groups of the new synthesized compounds was investigated on mercury electrode using cyclic voltammetry and chronocoulometry. The parameters of the reduction processes of ? NO2 groups of the investigated compounds were found not to be comparable to the reduction of nitrobenzene under the same experimental conditions. Moreover, the electroreduction of nitro groups in these nitrophenyl derivatives was dependent on pH, the type of the studied compound, and slightly on the solvent composition. All the reactants were strongly adsorbed on mercury electrode. In the case of R3? (Ph? NO2)7, its seven nitro groups were reduced practically at the same potential, and no radical anion formation was observed. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
3.
Tomasz Gubica Andrzej Temeriusz Pawe? Paw?owski Jadwiga Stroka 《Journal of Physical Organic Chemistry》2010,23(9):853-858
The effect of the non‐electroactive groups on the redox potentials of the active centres of 26 nitrophenyl O‐glycosides possessing various substituents has been studied electrochemically using cyclic voltammetry. The potentials of both redox processes, a two‐electron quasi‐reversible R‐NHOH/R‐NO (Ef) and four‐electron irreversible R‐NO2/R‐NHOH (Epc(I)) systems, have been determined and compared for all the compounds under investigations. The nitrophenyl O‐glycosides were chosen as model compounds as they significantly vary in many aspects of their structure such as: (i) the isomeric substitution of nitro group in benzene ring to the sugar moiety (ortho, meta and para isomers); (ii) the size of sugar moieties (the derivatives of mono‐ and disaccharides); (iii) the presence and absence of additional groups in saccharidic fragments (e.g. pentose and hexose); (iv) functionalisation of hydroxyl groups (free or acetylated hydroxyl groups) and (v) absolute configurations of selected sugar carbon atoms (e.g. the pairs of anomers). Among other effects, a significant variation in the increasing order of the two‐electron quasi‐reversible (Ef, ortho > meta > para) and four‐electron irreversible (Epc(I), meta > ortho > para) redox processes has been found and explained taking into account the negative inductive effect (–I) caused by the glycosidic oxygen atom that facilitates the electroreduction of the nitro group, and the positive mesomeric effect (+M) which makes the electroreduction more difficult. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
4.
Efficient solid-state structure evaluation of β-maltose octaacetate (1), methyl β-maltoside heptaacetate (2), and ethyl 1-thio-β-maltoside heptaacetate (3) was performed. The search for the best conformers for 1–3 was conducted in three consecutive steps: grid search, genetic algorithm refinement and DFT study. The use of a genetic algorithm caused a spectacular time shortening of the calculations. The obtained theoretical conformation for 1 resembled its XRD refinement almost perfectly. Although XRD analysis was impossible to perform for 2 and 3 (they form improper crystals), their reliable conformations were obtained. It was proved by the use of 13C CP/MAS NMR spectroscopy. 相似文献
5.
Tomasz Gubica Łukasz Szeleszczuk Dariusz M. Pisklak Dorota K. Stępień Michał K. Cyrański Marianna Kańska 《Tetrahedron》2014
In this paper the comparative structural analysis of a series of compounds (methyl α-d-glucopyranoside, methyl 4,6-O-ethylidene-α-d-glucopyranoside (2), methyl 2,3-di-O-nitro-4,6-O-ethylidene-α-d-glucopyranoside and methyl 3-O-nitro-4,6-O-ethylidene-α-d-glucopyranoside) by way of synthesis leading to methyl 3-O-nitro-α-d-glucopyranoside (5) is reported. The title compound (5) is a novel d-glucosidic mononitrate having potential biological activity against cardiovascular diseases. The structural analysis was supported by single-crystal X-ray diffraction (XRD), 13C CP/MAS NMR spectroscopy and DFT calculations. In the case of 2 and 5, XRD analysis could not be performed due to the fact that 2 is highly hygroscopic and 5 forms improper crystals. However, the molecular structures of 2 and 5 were obtained on the basis of experimental (existing XRD data for similar compounds) and theoretical (DFT optimization) approaches. This showed of very good agreement with the 13C CP/MAS NMR spectral data. 相似文献
6.
Tomasz Gubica Dorota K. Stępień Andrzej Ostrowski Dariusz M. Pisklak Andrzej Temeriusz Ewa Głowacka Katarzyna Paradowska Michał K. Cyrański 《Journal of Molecular Structure》2012
Comprehensive structural analyses were performed for o-, m-, and p-nitrophenyl 2,3,4-tri-O-acetyl-β-d-xylopyranosides. Single-crystal X-ray diffraction data were collected and revealed that meta isomer undergoes temperature-dependent polymorph transition (crystal structures of two polymorphs were obtained). This transition was verified by differential scanning calorimetry. The number of molecules in the independent part of the crystal unit cells of the compounds under investigation was in agreement with the number of resonances in solid-state 13C and 15N NMR spectra. The o- and p-nitrophenyl 2,3,4-tri-O-acetyl-β-d-xylopyranosides exist as single polymorph at room temperature, as confirmed by powder X-ray diffraction measurements. 相似文献
7.
Tomasz Gubica Elżbieta Boroda Andrzej Temeriusz Marianna Kańska 《Journal of inclusion phenomena and macrocyclic chemistry》2006,54(3-4):283-288
The impact of native and permethylated α-, β-, and γ-cyclodextrins on the L-tryptophan indole lyase-catalyzed decomposition of L-tryptophan was investigated by means of spectrophotometric measurements. The inhibitory effects of cyclodextrins on the catalytic activity of the enzyme are shown. The observed inhibition is of mixed type, i.e. competitive and non-competitive. This phenomenon is supposed to be the result of host–guest complex formation involving cyclodextrins and L-tryptophan, and probably between aromatic amino acid residues on the surface of the investigated enzyme. Therefore cyclodextrins were found to have an impact on the maximal velocity and on the Michaelis constant of the described catalysis. The competitive inhibition does not only depend on the stabilities of inclusion complexes, but mainly on their structures. 相似文献
8.
Szeleszczuk Łukasz Gubica Tomasz Szmeja Sebastian Ciesielski Arkadiusz Cyrański Michał K. Pisklak Dariusz M. 《Structural chemistry》2021,32(1):297-307
Structural Chemistry - A reliable method for molecular structure determination, excluding single-crystal X-ray diffraction (SCXRD), has been applied to six methyl glycoside tetrabenzoates. The... 相似文献
1