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21.
Asim K. Bera Asok Banerjee Bishnu P. Mukhopadhyay 《Journal of chemical crystallography》2002,32(12):531-536
The direct and indirect roles of the C2- and C8-bonded water molecules (C–H OW) in the stabilization of unusual inosine monophosphate containing nucleotides have been observed in their highly hydrated and amino acid cocrystals, which have been discussed in this work for the first time. The intermolecular H-bonding of WR (the oxygen of ribose 2- and 3-hydroxyls bonded water molecule, O2 WR O3) with the C2–H bonded OW's (OW WR 2.43–2.78 Å) can influence the ribose and thus the nucleotide stability, whereas the water molecule (OW) of C8–H OW can participate in the base stability by sandwiching the stacked purines through N7 OW N7 intermolecular interactions, with N7 OW 2.63–2.75 Å. However, in some cases the water oxygen (OW) of C8–H can get intermolecularly H-bonded to water molecular oxygen WN (with OW WN 2.57–2.85 Å), which has previously stabilized the nucleotide single-strand through intermolecular stacking N7 WN N7 interaction (N7 WN 2.56–2.63 Å). The conjugal survival of the H-bonded nucleotide single-strand with the water-helix thus forming the duplex and its stabilization through the C–H OW mediated water molecular (OW) cooperative H-bonding network, specially with the ribose and the base units, in the crystals could favor the support of single-stranding potentiality and thus the stability of the purine-rich RNAs or the small unusual nucleotides in the aquated environment besides the other interactive factors. 相似文献
22.
Atiyah and Bott used equivariant Morse theory applied to theYang–Mills functional to calculate the Betti numbers ofmoduli spaces of vector bundles over a Riemann surface, rederivinginductive formulae obtained from an arithmetic approach whichinvolved the Tamagawa number of SLn. This article attempts tosurvey and extend our understanding of this link between Yang–Millstheory and Tamagawa numbers, and to explain how methods usedover the last three decades to study the singular cohomologyof moduli spaces of bundles on a smooth projective curve over can be adapted to the setting of 1-homotopy theory to studythe motivic cohomology of these moduli spaces over an algebraicallyclosed field. 相似文献
23.
Samples of poly(vinylidene fluoride) (PVF2) and (vinylidene fluoride‐tetra fluoroethylene) (VF2‐VF4) copolymer were etched with a chromium‐based etching reagent. The etching rate was lower for the VF2‐VF4 copolymer samples than for the PVF2 samples. The melting point and enthalpy of fusion increased with increased etching time of the etched specimen. This was also true for the melt‐quenched (etched) samples, whose values were always lower than those obtained from the direct run of the etched samples. The scanning electron micrographs of specimens etched for 24 h indicated that only the amorphous portion was etched without affecting the crystalline lamella. The sequence distribution of the PVF2 and VF2‐VF4 copolymer crystals were determined by 19F NMR measurements of the samples and their etched species. The observed probabilities (Pobs), calculated from the integrated area of the NMR peaks, indicated that the crystalline lamella had a more oriented chain structure than that of the amorphous overlayer portion. The head‐to‐head defects calculated from the aforementioned sequence analysis indicated a greater propensity in the amorphous portion than in the crystalline lamella. The equilibrium constant (K) for the distribution of defects between the lamella and amorphous portion of the crystal varied from 0.7 to 0.9. It was higher at a higher quenching rate of the crystallization, and in the isothermal crystallization, it also had a substantially high value, indicating the equilibrium inclusion of defects in the crystal. The distribution constant increased with an increase in the defect content in the chain and decreased with an increase in the defect size. The sequence distribution data, analyzed through a suitable melting‐point depression equation, indicated a defect energy of 2.25 kcal/mol for the α‐phase PVF2 crystals and 0.68 kcal/mol for the β‐phase VF2‐VF4 copolymer. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 297–308, 2000 相似文献
24.
[70]fullerene solutions in carbon tetrachloride and o-xylene exhibit a noteworthy spectral variation with time when acetonitrile is added. This has been ascribed to self-aggregation of [70]fullerene caused by the repulsion between polar acetonitrile and hydrophobic [70]fullerene, and the aggregation numbers have been determined from a kinetic scheme and also from a scanning electron microscopic study. The numbers thus obtained follow a cuboctahedral stacking pattern proposed recently and also agree with the magic formula n=55+3m (m=1 to 14) proposed by Branz et al. for [60]fullerene clusters [Phys. Rev. B. 66, 094107 (2002)]. 相似文献
25.
Pal P Saha A Mukherjee AK Mukherjee DC 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(1-2):167-171
Menadione (vitamin K(3)) has been shown to form charge transfer complexes with N,N-dimethyl aniline, N,N-dimethyl p-toluidine and N,N-dimethyl m-toluidine in CCl(4) medium. The CT transition energies are well correlated with the ionisation potentials of the anilines. The formation constants of the complexes have been determined at a number of temperatures from which the enthalpies and entropies of formation have been obtained. The formation constants exhibit a very good linear free energy relationship (Hammett) at all the temperatures studied. 相似文献
26.
Sumanta Bhattacharya Sandip K Nayak Subrata Chattopadhyay Manas Banerjee Asok K Mukherjee 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2002,58(2):289-298
[70]fullerene has been shown to form 1:1 EDA complex with anthracene, naphthalene, phenanthrene, pyrene and acenaphthene in CCl4 medium. Charge transfer (CT) bands have been detected in all the cases. Isosbestic points have been observed in the cases of phenanthrene and acenaphthene complexes. Ionisation potentials of the donors and CT transition energies have been found to correlate in accordance with Mulliken equation and from this correlation the electron affinity of C70 has been found to be 2.59 eV. Enthalpies and entropies of formation of the complexes have been estimated from the formation constants of the complexes determined spectrophotometrically at three different temperatures. 相似文献
27.
The aim of this study is to investigate the antitumour and antioxidant activities of the ethanol extract of Scutia myrtina (EESM) against Ehrlich's ascites carcinoma (EAC) in mice. Twenty-four hours after tumour inoculation, EESM was administered at doses 100, 200 and 300?mg?kg?1 bodyweight/mice/day for 21 days. EESM caused a significant (p?0.01) decrease in ascites volume, packed cell volume and viable cell count, and also prolonged the life span of EAC tumour-bearing mice. Haematological profiles reverted to near-normal levels in extract-treated mice (p?0.01). EESM also produced protective effects by significantly decreasing the activity of serum enzymes and bilirubin and increasing the protein and uric acid levels (p?0.05). EESM significantly (p?0.05) decreased the levels of lipid peroxidation, while it significantly (p?0.05) increased the levels of enzymatic and non-enzymatic antioxidants. The results indicate that EESM exhibited significant antitumour and antioxidant activities in EAC-bearing mice. 相似文献
28.
Hybrid density functional theory is used to study the stability and behavior of rare gases in uranium dioxide. Three insertion sites are considered: the octahedral interstitial position and the oxygen and uranium substitution sites. The optimized lattice constant, the volume variation induced by gaseous atom incorporation, and the defect formation energy are studied for each rare gas. Both lattice constants and formation energies increase with increase in radii of the rare gases. The octahedral interstitial position is the most favorable occupation site. The formation energy is found to be negative only for He at an interstitial site. 相似文献
29.
The Hazard Rate and the Reversed Hazard Rate Orders, with Applications to Order Statistics 总被引:1,自引:0,他引:1
In this paper we first point out a simple observation that can be used successfully in order to translate results about the hazard rate order into results about the reversed hazard rate order. Using it, we derive some interesting new results which compare order statistics in the hazard and in the reversed hazard rate orders; as well as in the usual stochastic order. We also simplify proofs of some known results involving the reversed hazard rate order. Finally, a few further applications of the observation are given. 相似文献
30.
The crystal structure of a dodecahydrated co-complex between two Inosine 5-monophosphate (IMP) and one L-serine, the first of its kind reported, has been determined at atomic resolution by X-ray crystallographic methods. The crystal belongs to a monoclinic space group, P21, with the cell dimensionsa=8.695(7),b=21.898(6),c=12.374(3)Å, =110.59(3)°. This structure reveals the recognition mechanism of serine to the nucleotides through direct and water-mediated hydrogen bonds. The phosphate oxygen (O22) seems to prefer the nonspecific interaction with the functional sites of serine (N...O22=2.735, OG...O22=2.970, O1...O22 =3.121 Å), whereas the bases prefer specific (N17...N=3.199, N23...O2=2.784 Å) bondings. The solvent-mediated hydrogen bonds N17...W3...N27 endow extra stabilization to the stacked bases. The presence of hydrogen-bonded water spines and their interplay in the specific and nonspecific bindings with potential ligands indicate the functional involvement of solvent molecules through cooperative donor-acceptor network and could act as viable centers of intricate interactions in protein-DNA complexation processes. 相似文献