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231.
Molecular dynamics simulations at atomistic level have been performed on a metal-porphyrazine complex. Starting from an isotropic state, the system was cooled until transition from isotropic to columnar phase was observed; no nematic phase was encountered. Many tools were utilized to follow the system evolution: order parameter, g(r), g(||)(r(||)), g(c)(r(||)), g(perpendicular)(r(perpendicular)), g(2)(r), also density and energy changes. Very long runs were required to get reliable results, times greater than 40 ns of simulation. The structure of columnar phase was analyzed and the organization of molecules in the columns was investigated, along with the role of conformation of side chains. We found that in columnar phase the molecules are tilted versus the column axis and the conformation of side chains changes during the phase transition to allow this kind of organization; moreover the direction of columns axes is different from that of the director. 相似文献
232.
Amati M Belviso S Cristinziano PL Minichino C Lelj F Aiello I La Deda M Ghedini M 《The journal of physical chemistry. A》2007,111(51):13403-13414
The low fluorescence quantum yield of 8-hydroxyquinoline cannot be correctly interpreted without knowing the form that such a compound assumes in different environments. The commonly accepted emission-quenching excited-state proton transfer can follow different reaction paths if 8-hydroxyquinoline is dimeric or monomeric or if it exists in the form of cis and trans conformers; in this light, the knowledge of the compound form in a particular environment is basic. We have performed a spectroscopic and computational investigation aimed at the determination of the form of 8-hydroxyquinoline in different solvents. UV-vis, fluorescence, and IR spectral features have been assigned by ab initio computations based on the density functional theory and time-dependent density functional theory; the density functional theory and MP2 computations have been applied to the determination of the relative stability of the dimeric and monomeric cis and trans forms of 8-hydroxyquinoline in different solvents. Molecular dynamics computations have been used to determine the compound behavior in water solutions. According to our results, 8-hydroxyquinoline shows a clear preference for the cis conformation (as dimer or monomer), but, in water solutions, a small fraction of the trans conformation is also present. 相似文献
233.
234.
Enzymatic Chemoselective Aldehyde–Ketone Cross‐Couplings through the Polarity Reversal of Methylacetoin
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Dr. Giovanni Bernacchia Prof. Olga Bortolini Dr. Morena De Bastiani Dr. Lindomar Alberto Lerin Dr. Sabrina Loschonsky Prof. Alessandro Massi Prof. Dr. Michael Müller Dr. Pier Paolo Giovannini 《Angewandte Chemie (International ed. in English)》2015,54(24):7171-7175
The thiamine diphosphate (ThDP) dependent enzyme acetoin:dichlorophenolindophenol oxidoreductase (Ao:DCPIP OR) from Bacillus licheniformis was cloned and overexpressed in Escherichia coli. The recombinant enzyme shared close similarities with the acetylacetoin synthase (AAS) partially purified from Bacillus licheniformis suggesting that they could be the same enzyme. The product scope of the recombinant Ao:DCPIP OR was expanded to chiral tertiary α‐hydroxy ketones through the rare aldehyde–ketone cross‐carboligation reaction. Unprecedented is the use of methylacetoin as the acetyl anion donor in combination with a range of strongly to weakly activated ketones. In some cases, Ao:DCPIP OR produced the desired tertiary alcohols with stereochemistry opposite to that obtained with other ThDP‐dependent enzymes. The combination of methylacetoin as acyl anion synthon and novel ThDP‐dependent enzymes considerably expands the available range of C? C bond formations in asymmetric synthesis. 相似文献
235.
Dr. Morten T. Jarlstad Olesen Dr. Raoul Walther Pier Paolo Poier Frederik Dagnæs-Hansen Dr. Alexander N. Zelikin 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(19):7460-7466
In this work, a tumor growth intervention by localized drug synthesis within the tumor volume, using the enzymatic repertoire of the tumor itself, is presented. Towards the overall success, molecular, macromolecular, and supramolecular glucuronide prodrugs were designed for a highly potent toxin, monomethyl auristatin E (MMAE). The lead candidate exhibited a fold difference in toxicity between the prodrug and the drug of 175, had an engineered mechanism to enhance the deliverable payload to tumours, and contained a highly potent toxin such that bioconversion of only a few prodrug molecules created a concentration of MMAE sufficient enough for efficient suppression of tumor growth. Each of these points is highly significant and together afford a safe, selective anticancer measure, making tumor-targeted glucuronides attractive for translational medicine. 相似文献
236.
The essential oils obtained by hydrodistillation from leaves and fruits of Daucus sahariensis Murb. were analyzed by GC/MS. The main constituents of the essential oil from the leaves were myristicin (34.3%), alpha-pinene (5.4%), cis-chrysanthenyl acetate (5.3%) and epi-alpha-bisabolol (4.8%), and those from the fruits myristicin (43.9%), alpha-pinene (13.1%), limonene (9.4%), and cis-chrysanthenyl acetate (7.4%). Myristicin, the main constituent of both essential oils, is generally absent in the oils from other Daucus species, permitting the hypothesis that this compound is a chemical marker of this Saharan species. 相似文献
237.
The Phenomenological Universalities (PUN) approach has been recently proposed for the purpose of inferring from an experimental dataset a model of the underlying phenomenology in a completely unbiased fashion. The goal of the present contribution is to extend the formalism of the PUN family of classes UN from the real to the complex field, and, in the process, to introduce oscillations in the time-evolution curves. The properties of the Complex UN (CUN) classes are analyzed in detail in the present contribution and are characterized, in order to enable experimentalists to recognize datasets belonging to them and to extract from them a suitable model. 相似文献
238.
The four classical modes of electrophoresis of protein molecules (sodium dodecyl sulphate electrophoresis, SDS-PAGE, isoelectric focusing, IEF, and immobilized pH gradients, IPGs, two-dimensional maps, 2D, and capillary electrophoresis, CE) are here reviewed, with special emphasis on recent innovations. Thus, in the case of SDS-PAGE, a novel method, consisting in focusing SDS-protein micelles against a gradient of cationic charges grafted onto a polyacrylamide gel is presented. In the case of IEF, the recent decoding of the structure, polydispersity, molecular mass distribution and buffering properties of the soluble carrier ampholyte buffers are here discussed. In regard to two dimensional mapping, recent instrumentation for performing 2D maps in horizontal, large gel slabs (up to 30 cm × 40 cm) and in a radial format for the SDS dimension is here evaluated. Finally, in the case of CE, three major applications are presented: a thorough study of capillary IEF and of all experimental variables, a method of importance in screening of rDNA products; the possibility of running proteins and peptide separations in very acidic, amphoteric, isoelectric buffers in absence of any capillary coating; finally, the possibility of producing a facile, user friendly, covalent coating of the wall silanols via bonding of quaternarized piperazines endowed with an iodinated tail. In acidic, volatile buffers, such protein/peptide runs can be directly interfaced with mass spectrometry instrumentation. 相似文献
239.
Aldo Arrais Eliano Diana Domenica Marabello Giuliana Gervasio Pier Luigi Stanghellini 《Journal of organometallic chemistry》2011,696(11-12):2299-2305
The synthesis of organometal complexes from chromium hexacarbonyl with 1-methyl-naphthalene ligand is reported. Two arene-chromium-tricarbonyl isomers are formed at competitive yields, featured with the metal fragment coordinated to both the methylated and the benzenic aromatic ring. A single-crystal X-ray diffraction measurement has been performed on the [(η6-5,6,7,8,9,10-C11H10)Cr(CO)3] isomer, which presents the metal carbonyl moiety attached to the benzenic arene ligand. The products of reaction have been studied by UV–VIS–NIR, fluorescence and 1H NMR spectroscopies. A detailed vibrational characterisation by mean of experimental FT-IR and Raman spectroscopy and DFT calculations is reported. The electron ligand donation to the metal carbonyl system, determined by FT-IR spectroscopy, has been related to the actual decrease of resonance energy of the aromatic hydrocarbon in the complex and compared with other chromium tricarbonyl complexes of different polycyclic aromatic hydrocarbons provided with the naphthalenic moiety. 相似文献
240.
The performance of sera pre-treatment for biomarker searching via combinatorial peptide ligand libraries (CPLL) has recently been challenged (Proteomics 2010, 10, 1416-1425) and stated to allow discovery of only medium to high-abundance proteins. We have thus investigated four elution protocols, as published in recent reports: (i) in 4?M urea+1% CHAPS; (ii) in 4?M urea+1% CHAPS+5% acetic acid; (iii) in 8?M urea+2% CHAPS+5% acetic acid; (iv) in boiling 4% SDS+25?mM DTT. One milliliter of serum, in all cases, was captured with 50?μL of CPLL beads, which were then eluted with the four eluants described above. In the first three cases, after the first elution, the beads were re-eluted with cocktail (iv), known to offer maximal release of proteins adsorbed by the CPLL ligands. Eluant (i) released only ca. 20% of the species adsorbed, eluant (ii) ca. 60%, eluant (iii) ca. 80%. Thus, the poor performance of the CPLL methodology, as reported in (i) is not due to any fault of the capture technique, but simply to the adoption of a very poor elution protocol. Even those using eluants (ii) and (iii) should know that a substantial fraction of the captured species still remains bound to the beads and is thus not available to biomarker discovery. Once more, eluant (iv) is recognized as the only one able to offer optimal recovery from the CPLL baits. 相似文献