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11.
Semiempirical iterative extended Hückel calculations are performed for the dipolar ions of cystine, cysteine, methionine and their selenium analogues. An attempt has been made to interprete the wave function of cysteine in terms of localized molecular orbitals.
Work performed with the financial support of the Consiglio Nazionale delle Ricerche. 相似文献
Zusammenfassung Semiempirische iterative Rechnungen wurden nach der erweiterten Hückeltheorie für die dipolaren Ionen Cystin, Cystein, Methionin und ihre Selen-Homologen durchgeführt. Für den Fall des Cysteins wurde die Wellenfunktion auf lokalisierte Orbitale transformiert.
Résumé On a analisé les ions dipolaires de la cystine, cystéine, methionine et leurs analogues séléniates avec la méthode semiempirique de Hückel étendue itérative. On a cherché à intérpreter la fonction d'onde pour la cystéine dans le schème des orbitales moleculaires localisées.
Work performed with the financial support of the Consiglio Nazionale delle Ricerche. 相似文献
12.
In this work, an analytical procedure was developed to monitor the ethanolysis of degummed soybean oil (DSO) using Fourier-transformed mid-infrared spectroscopy (FTIR) and methods of multivariate analysis such as principal component analysis (PCA) and partial least squares regression (PLS). The triglycerides (reagents) and ethyl esters (products) involved in ethanolysis were shown to have similar FTIR spectra. However, when the FTIR spectra derived from seven standard mixtures of triolein and ethyl oleate were treated by PCA at the region that represents the CO stretching vibration of ester groups (1700-1800 cm−1), only two principal components (PC) were shown to capture 99.95% of the total spectral variance (92.37% for the former and 7.58% for the latter PC). This observation supported the development of a multivariate calibration model that was based on the PLS regression of the FTIR data. The prevision capability of this model was measured against 40 reaction aliquots whose ester content was previously determined by size exclusion chromatography. Only small discrepancies were observed when the two experimental data sets were treated by linear regression (R2=0.9837) and these deviations were attributed to the occurrence of non-modeled transient species in the reaction mixture (reaction intermediates), particularly at short reaction times. Therefore, the FTIR/PLS model was shown to be a fast and accurate method to predict reaction yields and to follow the in situ kinetics of soybean oil ethanolysis. 相似文献
13.
Corrado Barghigiani Giuliano Colombetti Barbara Franchini Francesco Lenci 《Photochemistry and photobiology》1979,29(5):1015-1019
Abstract—Light-induced behavioral responses of Euglena gracilis have been investigated in single cells by means of a video system coupled to an optical microscope. Light intensity-effect curves at different wavelengths in the near UV and visible range have been determined. From these curves the action spectrum for the step-down photophobic response of Euglena has been calculated. From a comparison with the results obtained using a population method by means of a phototaxigraph, it is concluded that a single photomotile reaction is responsible for cell accumulation, brought about by trapping in the light spot and possibly by phototaxis towards scattered light from organisms already in the light field. 相似文献
14.
Francesco Demartin Fabrizia Fabrizi de Biani Cristina Femoni Maria Carmela Iapalucci Giuliano Longoni Piero Macchi Piero Zanello 《Journal of Cluster Science》2001,12(1):61-74
The [Ni36Pt4(CO)45]6- and [Ni37Pt4(CO)46]6- clusters have been obtained in mixture upon reaction in acetonitrile of [Ni6(CO)12]2- salts with K2PtCl4 in a 2.5:1 molar ratio. The two hexaanions were indistinguishable by spectroscopic techniques. Crystallization of their trimethylbenzylammonium salts led to crystals of composition 0.5[NMe3CH2Ph]6[Ni36Pt4(CO)45]-0.5[NMe3CH2Ph]6[Ni37Pt4(CO)46]·C3H8O, hexagonal,space group P63 (No. 173), a=17.853(9), c=27.127(13) Å, Z=2; final R=0.057. The metal core of the [Ni36Pt4(CO)45]6- anion consists of a Pt4 tetrahedron fully encapsulated in a shell of 36 Ni atoms belonging to a very distorted and incomplete 5 tetrahedron. The [Ni37Pt4(CO)46]6- hexaanion derives from the former by capping the unique triangular face of the metal polyhedron with an additional Ni(CO) fragment. The [Ni36Pt4(CO)45]6--[Ni37Pt4(CO)46]6- mixture is rapidly degraded to the known [Ni9Pt3(CO)21]4- cluster by exposure to carbon monoxide. Its reaction with protic acids initially affords the corresponding [H6-nNi36Pt4(CO)45]n--[H6-nNi37Pt4(CO)46]n- (n=5, 4) derivatives, and eventually leads to rearrangement to the known [H6-n Ni38Pt6(CO)48]n- species. Both [Ni36Pt4(CO)45]6--[Ni37Pt4(CO)46]6- and [HNi36Pt4(CO)45]5--[HNi37Pt4(CO)46]5- mixtures have been chemically and electrochemically reduced to their corresponding [Ni36Pt4(CO)45]n--[Ni37Pt4(CO)46]n- (n=7–9) and [HNi36Pt4(CO)45]n--[HNi37Pt4(CO)46]n- (n=6–8) mixtures. 相似文献
15.
The reactivity of free radical cations, produced by anodic oxidation of 9, 10-diphenylanthracene (and perylene), with polymerizable organic monomers has been investigated by amperometry.It results that the radical cations, which are relatively stable in acetonitrile and nitrobenzene, decay with the monomer substrate by either an addition reaction or an electron transfer process. The cationic species of the monomer thus produced by catalyze the cationic polymerization of the substrate.The cationic polymerization initiated in this way has been investigated in the case of styrene: this reaction shows some similarity with the process initiated by perchloric acid, but carbonium ion carriers seem to give the main contribution to the propagation stage. 相似文献
16.
Licia Guzzella Fiorenzo Pozzoni Giuseppe Giuliano 《International journal of environmental analytical chemistry》2013,93(1):87-106
Abstract A field site equipped with suction cup lysimeters was installed at Treviglio (BG) to assess the migration capacity of the herbicides linuron and monolinuron from topsoil to groundwater and to verify the appearance of their relevant transformation products in soil and water samples. A constant hydraulic head was applied in order to develop water saturation conditions in the upper layers. KCl was used as a tracer to evaluate water infiltration velocity through the vertical soil profile. The constant hydraulic head accelerated infiltration rates, while herbicide concentrations reached maximum contamination because soil adsorption capacity was underdeveloped. The results indicated two main processes of pesticide transport: firstly transport due mainly to water infiltration through macropores; secondly the transport driven by matrix flow. Linuron was found to be the most mobile herbicide, while chloroanilines were found to be the major transformation products of the herbicides considered. 相似文献
17.
Giuliano Bandoli Sandro Calogero Domenico Idá Giuseppe C. Pappalardo Giuseppe Scarlata 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3):265-270
Abstract Crystals of 2-pyridyl-phenyl sulphone are monoclinic, space group P21/c, with eight molecules in the unit cell of dimensions a = 11.781, b = 5.903, c = 29.748 Å and B = 94.13°. The dihedral angles between the best planes of the two aromatic rings are significantly different in two crystallographically independent molecules (88.4° and 71.9° for molecule A and molecule B, respectively), as well as those between the CSC plane and the pyridine ring (59.4° and 67.4°) and between the CSC plane and the phenyl ring (51.7° and 81.8°). The average bond distances of interest include C?S 1.77(1) and S?O 1.44(1) Å; among the bond angles there are CSO = 108.1(7), CSC = 105.0(6) and OSO = 118.7(6)°. The packing of the molecule in the crystal is determined by the van der Waals interactions and by two intermolecular H?O contacts of 2.43 and 2.49 Å. The observed conformation in the solid state agrees well with results of previous investigations, in the solution state, by means of dipole moment method and theoretical M.O. calculations, for the analogous di-2-pyridyl sulphone. 相似文献
18.
Abstract In 1981, Mallams and coworkers reported1 the discovery of - D-kijanose 1, a branched-chain nitro sugar, isolated from the antitumor antibiotic kijanimicin by acid hydrolysis. The structure of this unusual carbohydrate was established 1,2 as 2,3,4,6-tetadeo xy-4 - (methoxy carbony1 amino 1-3-c-methyl - 3 -nitro - D-xylo-hexopyranose by spectroscopic and crystallographic analysis, and comparison with D-rubranitrose 2, a carbohydrate found in the antibiotic rubradirin .3Two other nitro sugars, L-evernitrose 3 and - L-decilonitrose 45, have been discoveredas components of antibiotics. 相似文献
19.
Iacopo Ciabatti Cristina Femoni Maria Carmela Iapalucci Giuliano Longoni Stefano Zacchini 《Journal of Cluster Science》2014,25(1):115-146
The state of art of the chemical, spectroscopic and structural characterization of platinum carbonyl clusters is reviewed. We begin by enlightening the fundamental contribution given to this chemistry of two great scientists: Paolo Chini and Larry Dahl, two without equal maestros of science and life. We then focus the main body of this review on the challenge represented by studying molecular ions already belonging to the nano regime by size almost 50 years ago, and the challenges their chemistry continues to present also nowadays. In detail, the possible reasons which enable the [Pt3n (CO)6n ]2? oligomers to grow up to n = 10, and why the oligomers with n > 5 may self-assemble in infinite molecular conductor wires are suggested. The interplay between the CO/Ptsurface ratios and electronic effects in driving the platinum cluster from pseudo one- to tri-dimensional globular structures, often representing chunks of the fcc metal lattice or interpenetrated pentagonal prisms and icosahedra, is examined by means of two significant examples. The nanocapacitor behavior of most high-nuclearity carbonyl clusters is briefly recalled and is confirmed by most recent results. The size-induced transition of their metal kernels from insulator to semiconductor and the expected consequences of their eventual transition to a metallic state are also discussed. Finally, we conclude by commenting the present lack of Pt cluster interstitially lodging a main group element and not yet quantitatively-assessed aggregation phenomena in solution, perhaps peculiar of ionic salts of carbonyl clusters, which could make undetectable the NMR signal of any spin-active nuclei beyond a cluster nuclearity of ca. 20–25. 相似文献
20.
Using the quantum trajectories approach, we study the quantum dynamics of a dissipative chaotic system described by the Zaslavsky map. For strong dissipation the quantum wave function in the phase space collapses onto a compact packet which follows classical chaotic dynamics and whose area is proportional to the Planck constant. At weak dissipation the exponential instability of quantum dynamics on the Ehrenfest time scale dominates and leads to wave packet explosion. The transition from collapse to explosion takes place when the dissipation time scale exceeds the Ehrenfest time. For integrable nonlinear dynamics the explosion practically disappears leaving place to collapse. 相似文献