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171.
Tüdos E Fiser A Simon A Dosztányi Z Fuxreiter M Magyar C Simon I 《Journal of chemical information and computer sciences》2004,44(2):347-351
Proteins are heteropolymers with evolutionary selected native sequences of residues. These native sequences code for unique and stable 3D structures indispensable for biochemical activity and for proteolysis resistance, the latter which guarantees an appropriate lifetime for the protein in the protease rich cellular environment. Cross-links between residues close in space but far in the primary structure are required to maintain the folded structure of proteins. Some of these cross-links are covalent, most frequently disulfide bonds, but the majority of the cross-links are sets of cooperative noncovalent long-range interactions. In this paper we focus on special clusters of noncovalent long-range interactions: the Stabilization Centers (SCs). The relation between the SCs and secondary structural elements as well as the relation between SCs and functionally important regions of proteins are presented to show a detailed picture of these clusters, which are believed to be primarily responsible for major aspects of protein stability. 相似文献
172.
Andrikopoulos PC Armstrong DR Clegg W Gilfillan CJ Hevia E Kennedy AR Mulvey RE O'Hara CT Parkinson JA Tooke DM 《Journal of the American Chemical Society》2004,126(37):11612-11620
Subjecting ferrocene, ruthenocene, or osmocene to the synergic amide base sodium-magnesium tris(diisopropylamido) affords a unique homologous series of metallocene derivatives of general formula [(M(C(5)H(3))(2))Na(4)Mg(4)(i-Pr(2)N)(8)] (where M = Fe (1), Ru (2), or Os (3)). X-ray crystallographic studies of 1-3 reveal a common molecular "inverse crown" structure comprising a 16-membered [(NaNMgN)(4)](4+) "host" ring and a metallocenetetraide [M(C(5)H(3))(2)](4-) "guest" core, the cleaved protons of which are lost selectively from the 1, 1', 3, and 3'-positions. Variable-temperature NMR spectroscopic studies indicate that 1, 2, and 3 each exist as two distinct interconverting conformers in arene solution, the rates of exchange of which have been calculated using coalescence and EXSY NMR measurements. 相似文献
173.
Szöke E Máday E Gershenzon J Allen JL Lemberkovics E 《Journal of chromatographic science》2004,42(5):229-233
Gas chromatography (GC) and GC-mass spectrometry are used to identify a new sesqiterpene, beta-eudesmol, which seems to be a characteristic essential oil component of the intact and in vitro organized root of chamomile [Chamomilla recutita (L.) Rauschert]. It is identified on three types of stationary phases by GC. The confirmation of identity is carried out by comparison of mass spectra with those reported in the literature and measured from a reference compound. The percentage evaluation of the oil component is made by area normalization, on the basis of three parallel measurements. Among the cultivated and wild chamomile species examined, the wild species from the areas of Szeghalom contain the highest quantity of beta-eudesmol (9.25% in the total essential oil). 相似文献
174.
175.
Eva?A.?Gallardo-GutiérrezEmail author Alfonso?Montes-Rodríguez 《Integral Equations and Operator Theory》2004,50(2):211-216
It is shown that the classical Volterra operator, which is cyclic, is not supercyclic on any of the spaces Lp[0, 1], 1 p < . This solves a question posed by Héctor Salas. This contrasts with the fact that the derivative operator, the left inverse of the Volterra operator, although unbounded, is hypercyclic on Lp[0, 1]. 相似文献
176.
Hevia E Gallagher DJ Kennedy AR Mulvey RE O'Hara CT Talmard C 《Chemical communications (Cambridge, England)》2004,(21):2422-2423
Only two-fold amination occurs when 3 molar equivalents of TMPH are offered to a 1:1 BuNa-Bu2Mg mixture; adding TMEDA gives the mixed alkyl amide [(TMEDA)Na(mu-Bu)(mu-TMP)Mg(TMP)], which itself affords the phenyl-bridged analogue when reacted with benzene. 相似文献
177.
A prototype calix[4]arene-based receptor for carbohydrate recognition containing peptide and phosphate binding groups 总被引:2,自引:0,他引:2
Segura M Bricoli B Casnati A Muñoz EM Sansone F Ungaro R Vicent C 《The Journal of organic chemistry》2003,68(16):6296-6303
A novel class of macrobicyclic receptors for carbohydrate recognition based on upper rim, peptide-bridged calix[4]arenes has been designed and synthesized. Receptor 12, in which a charged phosphate group cooperates with peptide hydrogen-bonding donor and acceptor groups in the binding process, is the most efficient and selective in the complexation of simple carbohydrate derivatives. The selectivity observed is toward beta-glucoside 13a, which is better bound (DeltaG degrees = 19.6 kJ mol(-)(1)) compared to the corresponding alpha anomer 13b (DeltaG degrees = 17.0 kJ mol(-)(1)) and to the beta-galactoside 13c (DeltaG degrees = 17.7 kJ mol(-)(1)) in CDCl(3). A substantial drop in the stability constant is observed by esterification of the phosphate group in the host 12 or by alkylation of the OH groups in the 2 and 3 positions in the beta-glucoside and beta-galactoside derivatives. On the basis of a careful analysis of the (1)H NMR data available, a binding mode of the beta-octylglucoside 13a to receptor 12 is proposed. 相似文献
178.
The diastereomers of two Ln(III)-EPTPA derivatives have been separated by reversed-phase HPLC, and the water exchange rate on their Gd(III) complexes has been directly determined by 17O NMR (H5EPTPA = ethylenepropylene-triamine-pentaacetic acid). 相似文献
179.
Mukherjee S Rentschler E Weyhermüller T Wieghardt K Chaudhuri P 《Chemical communications (Cambridge, England)》2003,(15):1828-1829
A series of dinuclear transition metal complexes with either six or four iminosemiquinone radicals, in which the metal centres are separated by a distance of approximately 6.8 A, together with their catalytic reactivity is reported. 相似文献
180.
Esteruelas MA Modrego FJ Oñate E Royo E 《Journal of the American Chemical Society》2003,125(44):13344-13345
Exposure of OsH2Cl2(PiPr3)2 to air or bubbling with pure O2 affords the dioxo-Os(VI) compound OsO2Cl2(PiPr3)2 as result of a direct O=O double bond activation reaction. This Os(VI) species is reduced in the presence of n-BuLi to the novel dioxo-Os(IV) derivative OsO2(PiPr3)2, a rare example of a d4 square-planar compound. 相似文献