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1.
The study of possible chiral recognition of a series of peptide models (For-Gly-NH2, For-Ala-NH2 and four of their fluoro substituted derivatives) has been carried out by means of DFT calculations. Homo (L,L) and heterochiral (L,D) dimers formed by hydrogen bond (HB) complexation have been considered. Initially, the conformational preferences of the monomers have been calculated and used to generate all the possible homo and heterochiral dimers. The energetic results show that in most cases, the β monomers are the most stable while in the dimers, the γ–γ complexes show the strongest interaction energies. In three of the four chiral cases studied, a heterochiral dimer is the most stable one. In addition, the electron density and nuclear shielding of the complexes have been studied. 相似文献
2.
Om Prakash Ajay Kumar Richa Prakash Rosa M. Claramunt Ibon Alkorta José Elguero 《Tetrahedron》2005,61(27):6642-6651
Treatment of α,β-unsaturated carbonyl compounds, obtained by the reaction of DHA and aromatic (or heteroaromatic) aldehydes, with o-aminothiophenol results in the formation of 1,5-benzothiazepines and/or 1,4-benzothiazines depending upon the reaction conditions and structure of the aldehydes. The products were characterized by the combined use of multinuclear 1D and 2D NMR and GIAO/DFT calculations of 1H, 13C and 15N chemical shifts. The tautomerism of these compounds in solution was determined, they have an exocyclic CC double bond. 相似文献
3.
Two kinds of ab initio calculations (B3LYP and HF) using the GIAO approach have been carried out for fifteen H, three Li, three B, eleven C, seven N, nine O, four F, three Si, four P, six S and five Cl containing derivatives. The calculated absolute nuclear shieldings have been compared with experimental absolute values (either measured or estimated from relative chemical shifts) when available or with relative chemical shifts (11B, 35Cl). The correlations range from good to excellent and only three compounds (PN, P2H2, SO2) deviate significantly. 相似文献
4.
Summary A model of the mechanism for recognition of the D1 receptor has been developed. Conformational analysis for 10 agonists from diverse chemical families was carried out as a first step toward the characterization of the bioactive form. First, maximum structural overlap of the features common to all ligands allowed a simple identification of the candidate bioactive form for each ligand. At a second level of characterization, steric and electronic properties were computed for all accessible structures to analyze those properties that may modulate receptor recognition. 相似文献
5.
The molecular structure of 1-formyl-3-phenyl-Δ2-pyrazoline was determined by X-ray crystallography (triclinic, P-1). The geometry thus obtained was compared with that obtained by DFT calculations. The GIAO method was used to calculate absolute shieldings, which agree conveniently with those measured by 13C and 15N NMR. The title compound appears to be an essentially planar molecule. 相似文献
6.
We computed the free energy of solvation for a series of ions and neutral molecules using two different continuum approaches. First, we used the AM1–SM1 technique, where the AM1 Fock matrix is modified to include a generalized Born contribution. Second, we applied the DelPhi approach, where the electrostatic component of the free energy of solvation is evaluated by resolving the Poisson–Boltzman equation by a finite difference method. Both methods appear equally reliable for ionic systems. For neutral compounds, AM1–SM1 performs better than DelPhi; however, the differences become less pronounced for compounds with larger free energies of solvation. In parallel, both methods were applied to study the influence of the solvation process in the overall drug receptor interaction for a series of closely related ligands for the D1 dopamine receptor. An inverse linear relationship was found between the free energy of solvation and the logarithm of the affinity of the ligands; nevertheless, electrostatic properties are likely to modulate affinity as well. © 1993 John Wiley & Sons, Inc. 相似文献
7.
Ibon Alkorta Janet E. Del Bene José Elguero Otilia Mó Manuel Yáñez 《Theoretical chemistry accounts》2009,124(3-4):187-195
Ab initio calculations were carried out to investigate the structures, binding energies, bonding, and NMR spin–spin coupling constants of complexes HLB=BLH, for L=CO, NH3, OH2, PH3, SH2, and ClH. Both B–B and B–H bonds lengthen on complex formation relative to singlet HBBH, and except for L=CO, the B–B bonds are double bonds. The order of stability of the trans isomers correlates with the ordering of ligands in the spectrochemical series of ligand field theory. The trans isomer is always more stable than the corresponding cis. Inverse correlations are found between 1 J(B–B) and 1 J(B–H) and the corresponding B–B and B–H distances. For the trans isomers, 1 J(B–B) appears to be related to the ordering of ligands in the spectrochemical series, while 1 J(B–H) is related to the protonation energy of the ligand L. 相似文献
8.
Del Bene JE Elguero J Alkorta I Yañez M Mó O 《The journal of physical chemistry. A》2006,110(32):9959-9966
Ab initio equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) calculations have been performed to investigate substituent effects on coupling constants for borazine and selected substituted borazines. For molecules in which F atoms are not bonded to adjacent atoms in the ring, F substitution increases the one-bond (11)B-(15)N coupling constants involving the atom at which substitution occurs but leaves the remaining one-bond B-N coupling constants essentially unchanged. For these molecules, the magnitudes of one-bond B-N coupling constants are only slightly dependent on the number of F atoms present. Fluorine substitution at adjacent B and N atoms in the borazine ring further increases the one-bond B-N coupling constant involving the substituted atoms and has the same effect on the other one-bond coupling constants as observed for corresponding molecules in which substitution occurs at alternate sites. In contrast to the effect of F substitution, substitution of Li at either N or B decreases one-bond B-N coupling constants relative to borazine. The effects of F and Li substitution on one-bond B-N coupling constants for borazine are similar to F and Li substitution effects on (13)C-(13)C coupling constants for benzene. 相似文献
9.
The inversion and rotation mechanisms for the isomerization of Feringa’s bithioxanthenes existing in two conformations, up/up and up/down, have been calculated at the B3LYP/6-31G(d) and B3LYP/6-311++G(d,p) levels. The inversion mechanism that maintains the double bond nature of the central bond is a classical one but the rotation mechanisms that break the double bond to form a biradical needs to explore the singlet and triplet states. To do this we have removed the four fused phenyl rings of bithioxanthene and calculated at the CASSCF and CASPT2 levels bis(4H-thiopyran) proving that B3LYP calculations yield reasonable results for the rotation barriers. 相似文献
10.
Claramunt RM López C Alkorta I Elguero J Yang R Schulman S 《Magnetic resonance in chemistry : MRC》2004,42(8):712-714
The tautomerism of 5(6)-methoxy-2-([(4-methoxy-3,5-dimethyl-2-pyridinyl)methyl] sulfinyl)-1H-benzimidazole (omeprazole) was determined in solution, K(T) = 0.59 in THF at 195 K, in favor of the 6-methoxy tautomer. The assignment of the signals was made by comparison with its two N-methyl derivatives in acetone-d6 and through theoretical calculations of the absolute shieldings (GIAO/DFT/6-311++G**). 相似文献