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11.
Ko C Levine B Toniolo A Manohar L Olsen S Werner HJ Martínez TJ 《Journal of the American Chemical Society》2003,125(42):12710-12711
The photoisomerization mechanism of the neutral form of the photoactive yellow protein (PYP) chromophore is investigated using ab initio quantum chemistry and first-principles nonadiabatic molecular dynamics (ab initio multiple spawning or AIMS). We identify the nature of the two lowest-lying excited states, characterize the short-time behavior of molecules excited directly to S2, and explain the origin of the experimentally observed wavelength-dependent photoisomerization quantum yield. 相似文献
12.
In an effort to identify promising non-hydroxamate inhibitors of matrix metalloproteinases (MMPs), several new zinc-binding groups (ZBGs) based on pyrone, pyrothione, hydroxypyridinone, and hydroxypyridinethione chelators have been examined. Structural studies with tris(pyrazolyl)borate model complexes show that these ligands bind to the MMP active site zinc(II) ion in a bidentate fashion, similar to that found with hydroxamate-based inhibitors. Fluorescence- and colorimetric-based enzyme assays have been used to determine the IC50 values for these ZBGs against MMP-3; mixed O,S-donor ligands were found to be remarkably potent, with IC50 values as much as 700-fold lower than that found for acetohydroxamic acid. Inhibitory activity was found to parallel metal binding affinity as determined in titrations with model complexes. These results demonstrate that MPIs based on new ZBGs are feasible and may indeed improve the overall performance of inhibitors designed against these important medicinal targets. 相似文献
13.
A solid-phase synthetic route to quinoxaline, thiazine, and oxazine analogs is described. N-Alloc-3-amino-3-(2,4-difluoro-5-nitrophenyl)propanoic acid was tethered to Rink resin via its carboxylic acid group. The 4-arylfluorine was displaced with a primary amine, alcohol, or thiol to create, respectively, a resin bound aniline, phenol, or thiophenol derivative with one diversity element and one single atom (e.g., N, S, or O) diversity point. A fused heterocyclic system was subsequently created via a benzyne heterocyclization initiated by dehydrofluorination with strong base. Acid treatment released the desired products in high yield and moderate purity. 相似文献
14.
A heterocyclic peptide nanotube 总被引:3,自引:0,他引:3
An open-ended hollow tubular structure is designed based on hydrogen-bond-directed self-assembly of a chimeric cyclic peptide subunit comprised of alternating alpha- and epsilon-amino acids. The design features a novel 1,4-disubstituted-1,2,3-triazole epsilon-amino acid and its utility as a peptide backbone substitute. The N-Fmoc-protected epsilon-amino acid was synthesized in high yield and optical purity in three steps from readily available starting materials and was employed in solid-phase peptide synthesis to afford the desired cyclic peptide structure. The cyclic peptide self-assembly has been studied in solution by (1)H NMR and mass spectrometry and the resulting tubular ensemble characterized in the solid state by X-ray crystallography. 相似文献
15.
A procedure for calculating the magnetic circular dichroism C/D ratio from density functional theory calculations is discussed. The method is simplified considerably through the application of group theory and the irreducible-tensor method and only requires integrals of the magnetic dipole moment operator over a few orbitals and published tables of symmetry factors. The implementation of the method is tested through application to several small and medium-sized molecules. 相似文献
16.
To understand the coordination chemistry of zinc-binding groups (ZBGs) with catalytic zinc centers in matrix metalloproteinases (MMPs) and disintegrin metalloproteases (ADAMs), we have undertaken a model compound study centered around tris(3,5-methylphenypyrazolyl)hydroboratozinc(II) hydroxide and aqua complexes ([Tp(Ph,Me)ZnOH] and [Tp(Ph,Me)Zn(OH2)]+, respectively, wherein (Tp(Ph,Me))- = hydrotris(3,5-methylphenylpyrazolyl)borate) and the products of their reactions with a class of chelating Schiff's base ligands. The results show that the protic ligands, HL (HL = N-propyl-1-(5-methyl-2-imidazolyl)methanimine (5-Me-4-ImHPr), N-propyl-1-(4-imidazolyl)methanimine (4-ImHPr), and N-propyl-1-(2-imidazolyl)methanimine (2-ImHPr)), react with [Tp(Ph,Me)ZnOH] and give products with the general formula [Tp(Ph,Me)ZnL], whereas reactions with neutral aprotic ligands, L' (L' = N-propyl-1-(1-methyl-2-imidazolyl)methanimine (1-Me-2-ImPr) and N-propyl-1-(2-thiazolyl)methanimine (2-TaPr)), yield the corresponding [Tp(Ph,Me)ZnL]+ complexes. Although the phenol group of N-propyl-1-(2-hydroxyphenyl)methanimine (2-HOPhPr) is protic, this ligand forms a cationic four-coordinate complex containing an intraligand hydrogen bond. The solid-state structures of these complexes were determined by single-crystal X-ray diffraction, and the results showed that the protic ligands form five-membered chelates of the Zn2+ ion. All ligands displace the aqua ligand in [Tp(Ph,Me)Zn(OH2)]+ to yield complexes having 1H NMR spectra consistent with the formation of five membered chelates. The 1H resonance frequencies of the chelating ligands typically shift upfield upon coordination to the zinc center, due to ring current effects from the pendant phenyl groups of the (Tp(Ph,Me))- ligand. Thus, the 1H NMR spectra provide a convenient and sensitive means of tracking the solution reactions by titration. The resulting series of spectra showed that the stabilities of the chelates in solution depend on the propensity of the ligands to deprotonate upon chelation of the zinc center. The behaviors of these bidentate ZBGs provide insight into the structural and electronic factors that contribute to the stabilities of inhibited MMPs and ADAMs and suggest that the proton acidity of the coordinated ZBG may be a crucial criterion for inhibitor design. 相似文献
17.
The tetrahedral zinc complex [(Tp(Ph,Me))ZnOH] (Tp(Ph,Me) = hydrotris(3,5-phenylmethylpyrazolyl)borate) was combined with 2-thenylmercaptan, ethyl 4,4,4-trifluoroacetoacetate, salicylic acid, salicylamide, thiosalicylic acid, thiosalicylamide, methyl salicylate, methyl thiosalicyliate, and 2-hydroxyacetophenone to form the corresponding [(Tp(Ph,Me))Zn(ZBG)] complexes (ZBG = zinc-binding group). X-ray crystal structures of these complexes were obtained to determine the mode of binding for each ZBG, several of which had been previously studied with SAR by NMR (structure-activity relationship by nuclear magnetic resonance) as potential ligands for use in matrix metalloproteinase inhibitors. The [(Tp(Ph,Me))Zn(ZBG)] complexes show that hydrogen bonding and donor atom acidity have a pronounced effect on the mode of binding for this series of ligands. The results of these studies give valuable insight into how ligand protonation state and intramolecular hydrogen bonds can influence the coordination mode of metal-binding proteinase inhibitors. The findings here suggest that model-based approaches can be used to augment drug discovery methods applied to metalloproteins and can aid second-generation drug design. 相似文献
18.
Heteroleptic copper complexes containing an acetylacetonato ligand and a thioether derivatized dipyrrinato ligand are shown to form oligomers and polymers in the solid state. 相似文献
19.
Study of EPR, optical properties and electrical conductivity of vanadyl doped Bi2O3.PbO.B2O3 glasses
Gahlot PS Agarwal A Seth VP Sanghi S Gupta SK Arora M 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(6):1189-1194
Heavy metal based oxide glasses having composition xBi(2)O(3).(0.30 - x)PbO.0.70B(2)O(3) have been prepared (0.00 < or = x < or = 0.15, mol%) containing 2.0mol% of V(2)O(5) by normal melt-quenching technique. Electron paramagnetic resonance (EPR), optical spectra and dc conductivity of these glasses have been studied. Spin Hamiltonian parameters (SHP) of VO(2+) ions, dipolar hyperfine parameter, P and Fermi contact interaction parameter, K, molecular orbital coefficients (alpha(2) and gamma(2)) and optical band gap have been calculated. It is observed that in these glasses, the tetragonal nature of V(4+)O(6) complex increases with Bi(2)O(3) content. Increase in Bi(2)O(3):PbO ratio results in the contraction of 3d(xy) orbit of the unpaired electron in the vanadium ion, and the SHP are dependent on the theoretical optical basicity, Lambda(th). In present glasses, the conductivity (activation energy) first decreases (increases) with increase in mol% of Bi(2)O(3) content upto x = 0.08 and then shows a maxima (minima) at x = 0.10 and then starts decreasing (increasing) upto x < or = 0.15 with mol% of Bi(2)O(3) content. 相似文献
20.
[reaction: see text] A detailed study concerning the formation of Meisenheimer adducts in biphasic solvent systems is described. The process relies on utilizing a significantly lipophilic quaternary ammonium salt to transfer a nucleophile (e.g., hydroxide ion) between an aqueous and organic layer containing the electron-deficient aromatic substrate. Provided that the organic layer is sufficiently apolar, the resultant Meisenheimer adduct is considerably stable, likely the result of a strong ion-pairing interaction between the large polarizable anionic complex and the diffusively charged tetraalkylammonium cation. Using the diethylamide of 3,5-dinitrobenzoic acid as a model compound, the influence of ion-pairing reagents and solvents on adduct formation was investigated. Dramatically increased equilibrium formation of the Meisenheimer adduct is observed in the biphasic medium (e.g., benzene/2 M NaOH) relative to the same adduct generated in single-phase systems. Spectroscopic studies on this adduct are consistent with those conducted in single-phase polar or dipolar aprotic solvents. The methodology is extended to performing highly enantioselective biphasic kinetic resolutions of several racemic electron-deficient amides. 相似文献