The SIBFA procedure (Sum of Interactions Between Fragments computedAb initio, Ref [1]) is extended to the study of the conformational behavior of representative molecules containing amide nitrogens and carbonyl and carboxylate oxygens. The molecules studied are C- and N-ethylammonium formamide, C- and N-ethanol-formamide, ethylammonium formate and ethanolformate. The cases investigated include interactions of the types which occur between functional groups in proteins or ionophores. The accuracy of the procedure, assessed by comparing the results to those of correspondingab initio SCF computations, is very satisfactory. An application of the procedure to study the conformation of the glycyl and alanyl dipeptides as a function of the backbone torsional angles and is presented. 相似文献
Summary A possibility of obtaining insoluble gels with the help of freezing-thawing procedures was demonstrated on an example of aqueous solutions of a thiol-containing poly(acryl amide) derivative. The gel formation was proved to occur as a result of oxidation of free SH groups of polymer chains by water-dissolved air oxygen. 相似文献
A new kind of perfluoroalkyl-containing multifunctional groups compound was designed. Treatment of 1H,1H,2H,2H-perfluorooctyltrichlorosilane (4) with allylmagnesium bromide provided key intermediate 1H,1H,2H,2H-perfluorooctyltriallylsilane (2). Hydroboration followed by oxidation, epoxidation and dihydroxylation of 2 gave perfluoroalkyl-containing multifunctional groups compound 1a, 1b and 1c, respectively. 相似文献
A study of the spin lattice relaxation (T1) and the nuclear quadrupole resonance frequency (νQ) gives an important information about the dynamics of molecular groups in molecular solids. In the present paper, we analyze the contributions of the reorientational motion of nitro groups of 2,4-dinitrochlorobenzene to the NQR parameters of the chlorine nucleus in the molecule.
We found two contributions to T1 and νQ due to the onset of the reorientation of nitro groups in the molecule; one of these contributions is mostly due to intermolecular effects in the crystal. For the chlorine nuclei, the efficiency of the modulation mechanism is usually provided by the change of the electric field gradient due to the moving molecular group; this gives us a way of how to assign each contribution to T1 from the ortho and para positions of the NO2 groups in the molecule. It is observed that there are two different potential barriers depending on the position of the nitro groups in the molecule. The behavior in the temperature dependence of the line width shows a thermal history dependence of the molecular crystal. 相似文献
It has been proven qualitatively by a number of authors using variable temperature NMR experiments that most metal carbonyl complexes are nonrigid. A quantitative determination of the ligand exchange frequency ve is often achieved by a line shape analysis or by measurement of the transverse relaxation time T2 using the Carr-Purcell method. In the case of a “very fast” exchange, however, both methods prove unsuccessful. It is shown in this study that a simultaneous fit of IR or Raman spectra on the one hand and NMR spectra on the other can make possible the determination of ve for the “very fast” exchange and can also facilitate the determination of ve in “slow” and “medium” exchange cases considerably. The ligand exchange frequency thus found for Fe(CO)5, 1.1 × 1010s?1, is unexpectedly high; comparison with variable temperature measurements on solid Fe(CO)5, yields similar energy barriers. A mechanism of exchange closely related to the “Berry mechanism” is proposed. Finally the consequences of this surprisingly large ligand exchange rate are discussed with respect to IR band assignments for molecular “fragments” M(CO)x (where x=coordination number, and M is a transition metal, typically lanthanoid or actinoid). 相似文献
The self-consistent mean field model of Scheutjens and Fleer is used to model spherical aggregates of homopolymers and monomer—polymer particles in solution. For homopolymer aggregates we found that the chain ends are preferentially located at the exterior side of the polymer/solvent interface. The distribution of the end segments may be an important parameter in latex film formation. For monomer—polymer particles a “core-shell” structure is found with an extended core containing a monomer—polymer mixture and a thin shell a few nanometres thick strongly enriched with monomer. The monomer-enriched shell seems to function as a solvating envelope for the dangling chain ends. These results are compared with other simulations based on a single chain in a spherical-cavity model. 相似文献
The adsorption properties of silica gel with grafted aminopropyl and guanidinoethanethiol (GET) groups were studied by the
techniques of adsorption under static conditions and gas chromatography. It was shown that molecules capable of forming hydrogen
bonds are adsorbed on all modified samples more weakly than on the initial silica gel. The grafting of GET radicals on the
surface results in a noticiable increase in the dispersion interaction with adsorbed molecules. Calculation of the contributions
of molecular groups to the constant of adsorption equilibrium showed that the thermodynamic characteristics of adsorption
on aminosilochromes and aminosilicas with a polymeric layer of the modifying agent have similar values. Such adsorbents can
be used for investigation of polar compounds, including organic bases.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 452–457, March, 1997. 相似文献
We show that the homotopy groups of the group of quasi-unitaries inC*-algebras form a homology theory on the category of allC*-algebras which becomes topologicalK-theory when stabilized. We then show how this functorial setting, in particular the half-exactness of the involved functors, helps to calculate the homotopy groups of the group of unitaries in a series ofC*-algebras. The calculations include the case of all AbelianC*-algebras and allC*-algebras of the formAB, whereA is one of the Cuntz algebras On n=2, 3, ..., an infinite dimensional simpleAF-algebra, the stable multiplier or corona algebra of a-unitalC*-algebra, a properly infinite von Neumann algebra, or one of the projectionless simpleC*-algebras constructed by Blackadar. 相似文献
A rapid, sensitive, and convenient spectrophotometric assay was developed for the measurement of amino groups on solid supports.
This method is based on the reaction of amino groups of solids with an excess ofo-phthaldialdehyde (OPA) and subsequent quantitative determination of unreacted OPA by reaction with glycine. Four solids possessing
variable quantities of amino groups were examined. Results indicate that about 70% of the total surface amino concentration
(determined by the microKjeldahl method) are available for ligand attachment. Unlike the spectrophotometric 2,4,6-trinitrobenzenesulfonic
acid method, the OPA spectrophotometric assay is more rapid, sensitive, and convenient, and unlike the spectrofluorimetric
OPA, it does not require sophisticated instrumentation. 相似文献
We first determine the homotopy classes of nontrivial projections in a purely infinite simpleC*-algebraA, in the associated multiplier algebraM(A) and the corona algebraMA/A in terms ofK*(A). Then we describe the generalized Fredholm indices as the group of homotopy classes of non-trivial projections ofA; consequently, we determine theK*-groups of all hereditaryC*-subalgebras of certain corona algebras. Secondly, we consider a group structure of *-isomorphism classes of hereditaryC*-subalgebras of purely infinite simpleC*-algebras. In addition, we prove that ifA is aC*-algebra of real rank zero, then each unitary ofA, in caseA it unital, each unitary ofM(A) and ofM(A)/A, in caseA is nonunital but -unital, can be factored into a product of a unitary homotopic to the identity and a unitary matrix whose entries are all partial isometries (with respect to a decomposition of the identity).Partially supported by a grant from the National Science Foundation. 相似文献