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41.
Millet O Muhandiram DR Skrynnikov NR Kay LE 《Journal of the American Chemical Society》2002,124(22):6439-6448
New pulse sequences are presented for the measurement of the relaxation of deuterium double quantum, quadrupolar order, and transverse antiphase magnetization in (13)CH(2)D methyl groups of (15)N-, (13)C-labeled, fractionally deuterated proteins. Together with previously developed experiments for measuring deuterium longitudinal and transverse decay rates [Muhandiram, D. R.; Yamazaki, T.; Sykes, B. D.; Kay, L. E. J. Am. Chem. Soc. 1995, 117, 11536], these schemes allow measurement of the five unique decay constants of a single deuteron, providing an unprecedented opportunity to investigate side-chain dynamics in proteins. All five deuterium relaxation rates have been measured for deuterons in the methyl groups of the B1 immunoglobulin binding domain of peptostreptococcal protein L and the N-terminal SH3 domain from the protein drk. Since values of the spectral density function at only three different frequencies contribute to the five relaxation rates, the self-consistency of the relaxation data is readily established. Very good agreement is obtained between calculated parameters describing the amplitudes and time scales of motion when different subsets of the relaxation data are employed. 相似文献
42.
Peter M. Tolstoy Sergei N. Smirnov Ilya G. Shenderovich Nikolai S. Golubev Gleb S. Denisov Hans-Heinrich Limbach 《Journal of Molecular Structure》2004,700(1-3):19-27
1H and 15N NMR spectra of 10 complexes exhibiting strong OHN hydrogen bonds formed by 15N-labeled collidine and different proton donors, partially deuterated in mobile proton sites, have been observed by low-temperature NMR spectroscopy using a low-freezing CDF3/CDF2Cl mixture as polar aprotic solvent. The following proton donors have been used: HCl, formic acid, acetic acid, various substituted benzoic acids and HBF4. The slow hydrogen bond exchange regime could be reached below 140 K, which allowed us to resolve 15N signal splittings due to H/D isotopic substitution. The valence bond order model is used to link the observed NMR parameters to hydrogen bond geometries. The results are compared to those obtained previously [Magn. Reson. Chem. 39 (2001) S18] for the same complexes in the organic solids. The increase of the dielectric constant from the organic solids to the solution (30 at 130 K) leads to a change of the hydrogen bond geometries along the geometric correlation line towards the zwitterionic structures, where the proton is partially transferred from oxygen to nitrogen. Whereas the changes of spectroscopic and, hence, geometric parameters are small for the systems which are already zwitterionic in the solid state, large changes are observed for molecular complexes which exhibit almost a full proton transfer from oxygen to nitrogen in the polar liquid solvent. 相似文献
43.
Leonid M. Goldenberg Nikolai N Denisov Jan F. Biernat 《Journal of inclusion phenomena and macrocyclic chemistry》2000,38(1-4):171-186
The complexation of 13- and 16-memberedazo- and azoxycrowns with metal cations of similarionic diameter (Na+ and Ca2+; and K+,Ba2+, Ag+ and Pb2+) was studied byuv/visible spectroscopic titration in acetonitrile andMeOH. In MeOH the 13-membered azo- and azoxycrowns 1 and 2 are weakly and non-selectively bound tohard cations of similar ionic diameter, but differentcharge (Na+ and Ca2+). At the same time thebinding to the soft cation Ag+ of larger sizethan the macrocycle cavity is considerably stronger.In contrast to solutions in acetonitrile no bindingwith the small Li+ cation was found.The 16-membered azocrowns 3 and 4 alsodiscriminate silver cation in MeOH withlog K = 3.65 ± 0.1 for both compounds.Unexpectedly low bindingwith the hard barium divalent cation of similar size(log K = 1.55 ± 0.4 and 1.95 ± 0.2, respectively)was found for these compounds. Similarly to13-membered compounds no binding with the smallLi+ cation was detected. A reverse order ofselectivity was observed for these crowns inacetonitrile with binding constant for association of3 with Ba2+ (log K 5.3) considerablyhigher than for other cations. The previously observedstrong binding with the smaller Li+ and Na+cations is confirmed. 相似文献
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Nina I. Simirskaya Nikolai V. Ignat’ev Michael Schulte Sergei G. Zlotin 《Mendeleev Communications》2012,22(6):317-319
Terminal alkynols react with formaldehyde and secondary amines in aqueous ionic liquid [emim]HSO–4 in the presence of Cu(OAc) to afford the corresponding 1-(a-hydroxyalkyl)- or 1-(b-hydroxyalkyl)-2-(aminomethyl)acetylenes in better yields in comparison with the reaction in conventional organic solvents. The catalytic system can be easily recovered and recycled. 相似文献
49.
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50.
Nikolai G. Faleev Marina A. Tsvetikova Mikhail M. Ilyin Vyacheslav S. Yufryakov Natal’ya G. Kolotyrkina Viktoria V. Kulikova Tatiana V. Demidkina Konstantin A. Kochetkov 《Mendeleev Communications》2021,31(2):236-238
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