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排序方式: 共有498条查询结果,搜索用时 15 毫秒
151.
Renato Colle Raffaele Montagnani Pierluigi Riani Oriano Salvetti 《Theoretical chemistry accounts》1978,49(1):37-44
The optimized MO's of several excited states of formaldehyde have been calculated by means of a large basis set of modified Gaussian functions; particular attention has been paid to the * transition. The total energy of the various states has been obtained as the sum of the SCF and correlation energies; the last one has been calculated as a functional of the electronic density. The calculated values for the transition energies are in good agreement with the experiment. A strong interaction of the * state with the continuum is evidentiated; this fact can justify the absence of the * band in the absorption spectrum. 相似文献
152.
Ermanno Barni Claudia Barolo Pierluigi Quagliotto Piero Savarino Guido Viscardi Domenica Marabello 《Journal of heterocyclic chemistry》2003,40(4):649-654
A selected series of 2‐(4‐methylpyridin‐2‐yl)‐1H‐benzimidazole derivatives, bases and cyclic mono‐ and bis‐salts, were synthesized. Complete '1H nmr characterization is reported. Ambiguous assignments were solved using 1H‐1H NOESY analysis. Significant ir and 1H nmr data are presented concerning: i) tautomeric equilibrium of imidazole hydrogen; ii) hydrogen bonds; iii) conformational inversion of partially saturated rings. 相似文献
153.
Marvelli L Mantovani N Marchi A Rossi R Brugnati M Peruzzini M Barbaro P de los Rios I Bertolasi V 《Dalton transactions (Cambridge, England : 2003)》2004,(5):713-722
A family of new Fischer-type rhenium(III) benzoyldiazenido-2-oxacyclocarbenes of formula [(ReCl2[eta1-N2C(O)Ph][=C(CH2)nCH(R)O](PPh3)2][n = 2, R = H (2), R = Me (3); n = 3, R = H (4), R = Me (5)] have been prepared by reaction of [ReCl2[eta2-N2C(Ph)O](PPh3)2] (1) with omega-alkynols, such as 3-butyn-1-ol, 4-pentyn-1-ol, 4-pentyn-2-ol, 5-hexyn-2-ol in refluxing THF. The correct formulation of the carbene derivatives 2-5 has been unambiguously determined in solution by NMR analysis and confirmed for compounds 2-4 by X-ray diffraction methods in the solid state. All complexes are octahedral with the benzoyldiazenido ligand, Re[N2C(O)Ph], adopting a "single bent" conformation. The coordination basal plane is completed by an oxacyclocarbene ligand and two chlorine atoms. Two triphenylphosphines in trans positions with respect to each other complete the octahedral geometry around rhenium. The reactivity of 1 towards different alkynes and alkenes including propargyl- and allylamine has been also studied. With propargyl amine, monosubstituted or bisubstituted complexes, [(ReCl2[eta1-N2C(O)Ph][eta1-NH2CH2C triple bond CH]n(PPh3)(3-n)][n= 1 (6); n = 2 (7)], have been isolated depending on the reaction conditions. In contrast, the reaction with allylamine gave only the disubstituted complex [(ReCl2[eta1-N2C(O)Ph][eta1-NH2CH2CH=CH2]2(PPh3)] (8). The molecular structure of the monosubstituted adduct has been confirmed by X-ray analysis in the solid state. 相似文献
154.
Piergiorgio Pletta Pierluigi Mauri Valentina Appierto Marina Mostardini Ida Biunno 《Applied biochemistry and biotechnology》1994,44(2):119-124
A rapid and integrated procedure was developed for the preparation of small DNA restriction fragments ( ≤ 1000 bp) starting from a large cosmid (35,000 bp) containing exogenous DNA. The process is based on restriction enzymatic digestion followed by HPLC separation and fractions collection. All DNA fragments are separated in a single run, detected “on-line” by UV absorption, and straightforward collected with very high recovery. Small fragments can be directly subjected to the sequence procedure, whereas those larger than 1000 bp are redigested with a second enzyme, the fractionated subfragments are separated, ligated to plas-mid vector, and sequenced. A human genomic cosmid of 35,000 bp (26H7) has been chosen as a model. 相似文献
155.
The title homoazasugar, also referred as (2R,5S)-bis(hydroxymethyl)-(3R,4R)-dihydroxypyrrolidine, has been synthesized by addition of 2-lithiothiazole to the 2,3,5-tri-O-benzyl-d-arabinofuranose-derived nitrone---hydroxylamine mixture followed by reductive N-dehydroxylation and conversion of the thiazole ring into the hydroxymethyl group. 相似文献
156.
We study ball-homogeneity, curvature homogeneity, natural reductivity, conformal flatness and ϕ-symmetry for three-dimensional
contact metric manifolds. Several classification results are given.
Member of G.N.S.A.G.A.
Supported by funds of the M.U.R.S.T. 相似文献
157.
Beam width measurements of multi-mode asymmetric laser beams delivered by a XeCl laser, have been carried out in the focal plane of a lens, by the knife-edge and the variable rectangular aperture technique, respectively to determine beam divergence. It is shown that both methods provide beam width measurements in satisfactory agreement within experimental errors by properly choosing the clip levels. The analytical treatment for the clip level selection is also reported. 相似文献
158.
Andrea Zattoni Diana Cristina Rambaldi Pierluigi Reschiglian Manuela Melucci Silke Krol Ana Maria Coto Garcia Alfredo Sanz-Medel Dierk Roessner Christoph Johann 《Journal of chromatography. A》2009,1216(52):9106-9112
Synthesis and applications of new functional nanoparticles are topics of increasing interest in many fields of nanotechnology. Chemical modifications of inorganic nanoparticles are often necessary to improve their features as spectroscopic tracers or chemical sensors, and to increase water solubility and biocompatibility for applications in nano-biotechnology. Analysis and characterization of structured nanoparticles are then key steps for their synthesis optimization and final quality control. Many properties of structured nanoparticles are size-dependent. Particle size distribution analysis then provides fundamental analytical information. Asymmetrical flow field-flow fractionation (AF4) with multi-angle light scattering (MALS) detection is able to size-separate and to characterize nanosized analytes in dispersion. In this work we focus on the central role of AF4-MALS to analyze and characterize different types of structured nanoparticles that are finding increasing applications in nano-biotechnology and nanomedicine: polymer-coated gold nanoparticles, fluorescent silica nanoparticles, and quantum dots. AF4 not only size-fractionated these nanoparticles and measured their hydrodynamic radius (rh) distribution but it also separated them from the unbound, relatively low-Mr components of the nanoparticle structures which were still present in the sample solution. On-line MALS detection on real-time gave the gyration radius (rg) distribution of the fractionated nanoparticles. Additional information on nanoparticle morphology was then obtained from the rh/rg index. Stability of the nanoparticle dispersions was finally investigated. Aggregation of the fluorescent silica nanoparticles was found to depend on the concentration at which they were dispersed. Partial release of the polymeric coating from water-soluble QDs was found when shear stress was induced by increasing flowrates during fractionation. 相似文献
159.
Elena Bonetti Pierluigi Colli Mauro Fabrizio Gianni Gilardi 《Nonlinear Analysis: Theory, Methods & Applications》2007
This paper is devoted to the mathematical analysis of a thermodynamic model describing phase transitions with thermal memory in terms of an entropy equation and a momentum balance for the microforces. The initial and boundary value problem is addressed for the related integro-differential system of partial differential equations (PDEs). Existence and uniqueness, continuous dependence on the data, and regularity results are proved for the global solution, in a finite time interval. 相似文献
160.
We study the natural almost CR structure on the total space of a subbundle of hyperquadrics of the tangent bundle T(M) over a semi-Riemannian manifold (M, g) and show that if the Reeb vector ξ of an almost contact Riemannian manifold is a CR map then the natural almost CR structure on M is strictly pseudoconvex and a posteriori ξ is pseudohermitian. If in addition ξ is geodesic then it is a harmonic vector field. As an other application, we study pseudoharmonic vector fields on a compact strictly pseudoconvex CR manifold M, i.e. unit (with respect to the Webster metric associated with a fixed contact form on M) vector fields X ε H(M) whose horizontal lift X↑ to the canonical circle bundle S1 → C(M) → M is a critical point of the Dirichlet energy functional associated to the Fefferman metric (a Lorentz metric on C(M)). We show that the Euler–Lagrange equations satisfied by X↑ project on a nonlinear system of subelliptic PDEs on M.
Mathematics Subject Classifications (2000): 53C50, 53C25, 32V20 相似文献