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71.
Julien Preat Denis Jacquemin Daniel P. Vercauteren Eric A. Perpète 《Theoretical chemistry accounts》2008,119(5-6):463-468
In this contribution, we set up a SAC-CI methodology to evaluate the n → π* and π → π* vertical transition energies of a series of thiocarbonyl derivatives. We show that Frozen-Core SAC-CI provides accurate
vertical excitations energies. Nevertheless, in order to obtain converged results, the R2S2 unliked integrals have to be taken
into account in L3-SAC-CI calculations. In addition, we present the comparative performances of three computational procedures,
INDO/S, TD-DFT, and SAC-CI, for the calculation of valence excited states energies and it turns out that: (1) no tuning of
the exact exchange (α) included in TD-DFT allows to consistently reproduce the SAC-CI results; (2) SAC-CI and TD-B3LYP both evaluate the n → π*, as well as the π → π* transition energies, with a similar accuracy.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
72.
Zampella A Sepe V Luciano P Bellotta F Monti MC D'Auria MV Jepsen T Petek S Adeline MT Laprévôte O Aubertin AM Debitus C Poupat C Ahond A 《The Journal of organic chemistry》2008,73(14):5319-5327
A new anti-HIV cyclodepsipeptide, homophymine A, was isolated from a New Caledonian collection of the marine sponge Homophymia sp. The structure of homophymine A was determined by interpretation of spectroscopic data, acid hydrolysis, and LC-MS analysis. Homophymine A contains 11 amino acid residues and an amide-linked 3-hydroxy-2,4,6-trimethyloctanoic acid moiety. Along with four D-, two L-, and one N-methyl amino acids, it also contains four unusual amino acid residues: (2S,3S,4R)-3,4-diMe-Gln, (2R,3R,4S)-4-amino-2,3-dihydroxy-1,7-heptandioic acid, L-ThrOMe, and (2R,3R,4R)-2-amino-3-hydroxy-4,5-dimethylhexanoic acid. In a cell-based XTT assay, homophymine A exhibited cytoprotective activity against HIV-1 infection with a IC50 of 75 nM. 相似文献
73.
In this Letter a fast and reliable computational protocol for the calculation of pKa* of photoacids is presented. The results obtained for several coumarins indicate that, beyond the obtained numerical accuracy, it is indeed possible to develop a reliable computational procedure for pKa* calculation by combining, in a judicious way, a reliable model for the excited states (TD-DFT) with a fast solvent model (PCM). The characteristics of the different components of the model will allow for routine applications to medium and large chemical systems, so that the proposed protocol could nicely integrate experimental analyses. 相似文献
74.
Gulbinas V Mineviciūte I Hertel D Wellander R Yartsev A Sundström V 《The Journal of chemical physics》2007,127(14):144907
Exciton diffusion in ladder-type methyl-substituted polyparaphenylene film and solution was investigated by means of femtosecond pump-probe spectroscopy using a combined approach, analyzing exciton-exciton annihilation, and transient absorption depolarization properties. We show that the different views on the exciton dynamics offered by anisotropy decay and annihilation are required in order to obtain a correct picture of the energy transfer dynamics. Comparison of the exciton diffusion coefficient and exciton diffusion radius obtained for polymer film with the two techniques reveals that there is substantial short-range order in the film. Also in isolated chains there is considerable amount of order, as revealed from only partial anisotropy decay, which shows that only a small fraction of the excitons move to differently oriented polymer segments. It is further concluded that interchain energy transfer is faster than intrachain transfer, mainly as a result of shorter interchain distances between chromophoric units. 相似文献
75.
Emmanuel Lacte Philippe Renaud 《Angewandte Chemie (International ed. in English)》1998,37(16):2259-2262
New prospects for synthetic applications are offered by the 1,2-acyloxy shift of β-(acyloxy)alkyl radicals, which proceeds with high yields under Lewis acidic conditions [Eq. (1)]. With the exception of cyclizations, this is the first Lewis acid mediated acceleration of a radical rearrangement. 相似文献
76.
77.
Julien Coulomb Victor Certal Dr. Marie‐Hélène Larraufie Cyril Ollivier Dr. Jean‐Pierre Corbet Dr. Gérard Mignani Dr. Louis Fensterbank Prof. Emmanuel Lacôte Dr. Max Malacria Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(39):10225-10232
A general and efficient method for the synthesis of cyclic sulfinates and sulfinamides based on intramolecular homolytic substitution (SHi) at the sulfur atom by aryl or alkyl radicals is described. Both alkyl and benzofused compounds can be accessed directly from easily prepared acyclic precursors. Enantiomerically enriched sulfur‐based heterocycles were formed through an SHi process with inversion of configuration at the sulfur atom. Cyclization of prochiral radicals proceeded with varying stereochemical outcomes, depending on the size of the incoming radical. 2‐Pyridyl and 2‐quinolyl radicals led to biaryl compounds, which result from attack onto the ortho position of the arylsulfinate rather than a thiophilic substitution. 相似文献
78.
Numerous mercaptopropyl-functionalized silica spheres have been prepared by either post-synthesis grafting of MCM-41 and MCM-48 or self-assembly co-condensation of mercaptopropyltrimethoxysilane (MPTMS) or mercaptopropyltriethoxysilane (MPTES) and tetraethoxysilane (TEOS) precursors in hydroalcoholic medium in the presence of a cationic surfactant as templating agent and ammonia as catalyst. These materials of approximately the same particle size and morphology featured different functionalization levels, various degrees of structural order, and variable distribution of thiol groups in the mesopores. Their reactivity in solution has been studied using Hg(II) as model analyte. Total accessibility (on a 1:1 S:Hg stoichiometry basis) was demonstrated and quantified for well-ordered materials whereas less open and less organized structures with high degrees of functionalization were subject to less-than-complete loadings. Capacities measured at pH 2 were lower than at pH 4 because of distinct mercury-binding mechanisms. Kinetics associated to the uptake process were studied by in situ electrochemical monitoring of Hg(II) consumption from aqueous suspensions containing the various adsorbents. They indicate only little difference between materials of the MCM-41 and MCM-48 series at similar functionalization levels, fast mass transport in well-ordered mesostructures in comparison to the poorly or non-ordered ones (except at pH 2 where charge formation induced some restriction in materials characterized by long-range structural order), and even faster processes in the wormlike frameworks (characterized by shorter range structural order). Hg(II) binding to thiol-functionalized materials obtained by post-synthesis grafting was found to occur more rapidly in the early beginning of the uptake process as a result of a higher concentration of binding sites at the pore entrance in comparison to the more homogeneous distribution of these groups in the mesochannels of materials obtained by co-condensation. 相似文献
79.
Catherine Michaux Johan Wouters Eric A. Perpète Denis Jacquemin 《Journal of the American Society for Mass Spectrometry》2009,20(4):632-638
The complexation of five deprotonated anionic amino acids (glycine, L-alanine, L-valine, L-Aspartic acid, and L-glutamine)
with one water molecule, has been investigated using a MP2/63-11++G(d,p) approach fully accounting for the basis set superposition
errors. For each amino acid, several energetic minima have been identified, and we provide spectroscopic information allowing
to discriminate them. Our results strongly suggest that two complexes should coexist under the experimental conditions for
[Ala − H]−, [Val − H]−, and [Asp − H]−. Comparisons with the experimental enthalpies, entropies, and Gibbs free energies recently obtained by Wincel [J. Am. Soc.
Mass Spectrom. 2008, 19, 1091–1097] show that our simulation reproduces the most significant structure/energy experimental trends, though the entropic
changes induced by hydration are slightly overestimated. 相似文献
80.
Urbonaviciūte A Jakstas V Kornysova O Janulis V Maruska A 《Journal of chromatography. A》2006,1112(1-2):339-344
Flavonoids are an important group of natural compounds, which can prevent coronary heart disease and have antioxidant properties. Hawthorn is a well known and widely used medicinal plant due to its cardiotonic activity. Previous studies refer mostly to the HPLC analysis of the flavonoids: vitexin, quercetin, hyperoside, oligomeric procyanidins, which appear to be primarily responsible for the cardiac action of the plant. Aqueous ethanolic extracts of single-styled hawthorn (Crataegus monogyna Jacq., f.: Rosaceae Juss.) leaves and sprouts were analyzed by means of capillary zone electrophoresis (CZE). Influence of vegetation period on the extract qualitative composition and flavonoids quantities was evaluated. Sample preparation by extraction using different concentration of aqueous ethanol (40-96%, v/v) and the influence of extractant composition on the recovery of flavonoids are discussed in detail. The results obtained using CZE are compared to the results of spectrophotometric and HPLC analysis of the extracts. The effect of storage conditions of extracts (solar irradiation, temperature and duration) on degradation of flavonoids was investigated. 相似文献