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61.
Reipa V Mayhew MP Holden MJ Vilker VL 《Chemical communications (Cambridge, England)》2002,(4):318-319
Spectroelectrochemistry measurements are used to demonstrate that active site mutation and binding of an non-natural substrate to P450cam (CYP101) reduces the shift in the redox potential caused by substrate-binding, and thereby results in slower catalytic turnover rate relative to wild-type enzyme with the natural camphor substrate. 相似文献
62.
Anicich VG Wilson P McEwan MJ 《Journal of the American Society for Mass Spectrometry》2004,15(8):1148-1155
The results of a study of the ion-molecule reactions of N(+), N(2)(+), and HCN(+) with methane, acetylene, and ethylene are reported. These studies were performed using the FA-SIFT at the University of Canterbury. The reactions studied here are important to understanding the ion chemistry in Titan's atmosphere. N(+) and N(2)(+) are the primary ions formed by photo-ionization and electron impact in Titan's ionosphere and drive Titan's ion chemistry. It is therefore very important to know how these ions react with the principal trace neutral species in Titan's atmosphere: Methane, acetylene, and ethylene. While these reactions have been studied before the product channels have been difficult to define as several potential isobaric products make a definitive answer difficult. Mass overlap causes difficulties in making unambiguous species assignments in these systems. Two discriminators have been used in this study to resolve the mass overlap problem. They are deuterium labeling and also the differences in reactivities of each isobar with various neutral reactants. Several differences have been found from the products in previous work. The HCN(+) ion is important in both Titan's atmosphere and in the laboratory. 相似文献
63.
Drechsler U Erdogan B Rotello VM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(22):5570-5579
Monolayer and mixed-monolayer protected clusters (MPCs and MMPCs) have great potential to combine molecular functionality with the intrinsic properties of nanometer-sized scaffolds. This synergy can be used to create complex functional devices, including redox-active, electronic, or magnetic storage devices, solution-based sensors, and highly efficient catalysts. This review outlines some of the recent developments in nanoscale receptors based on synthetic and nonbiological recognition elements. In these nanoparticle systems, molecular recognition is achieved by covalent attachment of receptors on the nanoparticles coupled with noncovalent interactions to target substrates. Synthetic host-guest systems, hydrogen bonding, change in redox states, pi-pi stacking, rotaxane formation, and ion recognition are the main topics covered in this review. 相似文献
64.
Nicolas PhilippeFrançois Denivet Jean-Luc VasseJana Sopkova-de Olivera Santos Vincent Levacher Georges Dupas 《Tetrahedron》2003,59(40):8049-8056
The present report describes a stereoselective synthesis of 1,4-dihydro-4-phenyl isoquinolinones 5 based on a stereoselective Friedel-Crafts type cyclization. Cyclization precursors 1 were prepared in two steps, from the readily available (S)-mandelic acid, in 60-80% overall yield. The stereoselective electrophilic cyclization was accomplished in 20-86% yield and with 20-97% ee. In the course of this work, the presence of the amide carbonyl was found to be particularly important to guarantee a stereospecific process during the electrophilic aromatic substitution. 相似文献
65.
Boyd AS Carroll JB Cooke G Garety JF Jordan BJ Mabruk S Rosair G Rotello VM 《Chemical communications (Cambridge, England)》2005,(19):2468-2470
We report the electrochemically tuneable intramolecular hydrogen bonding interactions between a covalently linked flavin-diamidopyridine unit. 相似文献
66.
Use of molecular dynamics in the design and structure determination of a photoinducible beta-hairpin
Kräutler V Aemissegger A Hünenberger PH Hilvert D Hansson T van Gunsteren WF 《Journal of the American Chemical Society》2005,127(13):4935-4942
The study presented here consists of three parts. In the first, the ability of a set of differently substituted diazobenzene-based linkers to act as photoswitchable beta-turn building blocks was assessed. A 12-residue peptide known to form beta-hairpins was taken as the basis for the modeling process. The central (beta-turn) residue pair was successively replaced by six symmetrically ((o,o), (m,m), or (p,p)) substituted (aminomethyl/carboxymethyl or aminoethyl/carboxyethyl) diazobenzene derivatives leading to a set of peptides with a photoswitchable backbone conformation. The folding behavior of each peptide was then investigated by performing molecular dynamics simulations in water (4 ns) and in methanol (10 ns) at room temperature. The simulations suggest that (o,o)- and (m,m)-substituted linkers with a single methylene spacer are significantly better suited to act as photoswitchable beta-turn building blocks than the other linkers examined in this study. The peptide containing the (m,m)-substituted linker was synthesized and characterized by NMR in its cis configuration. In the second part of this study, the structure of this peptide was refined using explicit-solvent simulations and NOE distance restraints, employing a variety of refinement protocols (instantaneous and time-averaged restraining as well as unrestrained simulations). We show that for this type of systems, even short simulations provide a significant improvement in our understanding of their structure if physically meaningful force fields are employed. In the third part, unrestrained explicit-solvent simulations starting from either the NMR model structure (75 ns) or a fully extended structure (25 ns) are shown to converge to a stable beta-hairpin. The resulting ensemble is in good agreement with experimental data, indicating successful structure prediction of the investigated hairpin by classical explicit-solvent molecular dynamics simulations. 相似文献
67.
Claverie JM Monchois V Audic S Poirot O Abergel C 《Combinatorial chemistry & high throughput screening》2002,5(7):511-522
We outline a joint academic/industrial (CNRS/AVENTIS) functional genomics project aiming at the discovery of new anti-bacterial gene targets. Starting from all publicly available bacterial genomes, a subset of the most evolutionary conserved protein-coding genes has been identified. We retained genes with clear homolog in E. coli and at least one gram-positive bacterium among B.subtilis, M. tuberculosis, L. lactis or S. pyogenes. This subset was further reduced to genes encoding non-membrane proteins of unknown or hypothetical functions. The 221 E. coli Open Reading Frames (ORFs) identified through this comprehensive bioinformatic analysis are now submitted to a systematic 3-D structure determination protocol including cloning, protein expression and purification, crystallisation and X-ray diffraction. Our strategy was designed to focus on promising wide-spectrum targets as well as original biochemical pathways. Bioinformatics is used throughout all phases of project, including the initial large-scale comparative genomics analyses, the purification/expression and crystallisation stages for the detection of helpful sequence-specific features (e.g. cofactor binding motifs, non-structured N- or C- term extremities, etc ), and finally for the interpretation of the structures in conjunction with multiple sequence alignments for the identification of key residues, interaction areas on molecular surfaces, and overall function predictions. 相似文献
68.
Ronald G. Sutherland Adam Pirko Choi Chuck Lee Stanley H. Simonsen Vincent M. Lynch 《Journal of heterocyclic chemistry》1988,25(6):1911-1916
Synthesis of the heterocyclic skeletons of some biologically active compounds from (η6-o-dichlorobenzene)(η5-cyclopentadienyrl)iron hexafluorophosphate in a two step procedure is described. Cyclopentadienyliron hexafluorophosphate complexes of 1,4-benzodioxino[2,3-b]pyridine, 1,4-benzoxathiino[3,2-b]pyridine, 10H-pyrido[3,2-b]benzoxazine, benzo[b]naphtho[2,3-e][1,4]dioxin, 4-methylbenzo[b]benzopyran-2-one[7,6-e][1,4]dioxin and benzo[b]anthracen-9,10-diono[1,2-e][1,4]dioxin were isolated and characterized. Upon pyrolytic sublimation of these complexes the free heterocycles were obtained and characterized. (η6-1,4-Benzoxathiino[3,2-b]pyridine)(η5-cyclopentadienyl)iron hexafluorophosphate crystalizes in the orthothombic system, space group Pbca; the dihedral angle between the planes of outer rings was found to be 176.8 (1). 相似文献
69.
The nucleophilic attack of hydroxylamine at the 5 position of 2-aryl-4-trifluoroacetyl-5-amino-oxazoles leads to a mixture of stereoisomeric isoxazolines. Dehydration of these isomeric isoxazolines in the presence of trifluoroacetic anhydride gives 3-amino-4-acylamino-5-trifluoromethylisoxazoles. The structures and spectroscopic data of these compounds are discussed. 相似文献