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We investigated the effect of several computational variables, including the choice of the basis set, application of symmetry constraints, and zero-point energy (ZPE) corrections, on the structural parameters and predicted ground electronic state of model 5-coordinate hemes (iron(II) porphines axially coordinated by a single imidazole or 2-methylimidazole). We studied the performance of B3LYP and B3PW91 with eight Pople-style basis sets (up to 6-311+G*) and B97-1, OLYP, and TPSS functionals with 6-31G and 6-31G* basis sets. Only hybrid functionals B3LYP, B3PW91, and B97-1 reproduced the quintet ground state of the model hemes. With a given functional, the choice of the basis set caused up to 2.7 kcal/mol variation of the quintet-triplet electronic energy gap (DeltaEel), in several cases, resulting in the inversion of the sign of DeltaEel. Single-point energy calculations with triple-zeta basis sets of the Pople (up to 6-311G++(2d,2p)), Ahlrichs (TZVP and TZVPP), and Dunning (cc-pVTZ) families showed the same trend. The zero-point energy of the quintet state was approximately 1 kcal/mol lower than that of the triplet, and accounting for ZPE corrections was crucial for establishing the ground state if the electronic energy of the triplet state was approximately 1 kcal/mol less than that of the quintet. Within a given model chemistry, effects of symmetry constraints and of a "tense" structure of the iron porphine fragment coordinated to 2-methylimidazole on DeltaEel were limited to 0.3 kcal/mol. For both model hemes the best agreement with crystallographic structural data was achieved with small 6-31G and 6-31G* basis sets. Deviation of the computed frequency of the Fe-Im stretching mode from the experimental value with the basis set decreased in the order: nonaugmented basis sets, basis sets with polarization functions, and basis sets with polarization and diffuse functions. Contraction of Pople-style basis sets (double-zeta or triple-zeta) affected the results insignificantly for iron(II) porphyrin coordinated with imidazole. Poor performance of a "locally dense" basis set with a large number of basis functions on the Fe center was observed in calculation of quintet-triplet gaps. Our results lead to a series of suggestions for density functional theory calculations of quintet-triplet energy gaps in ferrohemes with a single axial imidazole; these suggestions are potentially applicable for other transition-metal complexes. 相似文献
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Yang QZ Khvostichenko D Atkinson JD Boulatov R 《Chemical communications (Cambridge, England)》2008,(8):963-965
In weakly coordinating solvents FeII meso-(N-methylimidazol-2-yl)porphine Fe exists as a stable dimer (Kd=50+/-30 nM) that binds ligands without undergoing dissociation and is presently the simplest complex in which the mono-imidazole ligation of a ferroheme is enforced without excess imidazole in solution. 相似文献
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Zhen Huang Qing‐Zheng Yang Dr. Timothy J. Kucharski Daria Khvostichenko Dr. Steven M. Wakeman Roman Boulatov Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(21):5212-5214
Sensitized photolysis : We describe a series of macrocyclic disulfides containing stiff stilbene (see scheme) as the intramolecular photosensitizer designed for fundamental mechanistic studies of sensitized photolysis of the S? S bond. Preliminary studies revealed weak temperature dependence of the quantum yields, which decreased exponentially with Boltzmann‐weighted average separation between the S? S bond and stiff stilbene.
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Khvostichenko D. S. Andersen S. I. Viktorov A. I. 《Russian Journal of Applied Chemistry》2004,77(6):1013-1018
The solubility of water in toluene solutions of asphaltenes is determined, and the state of water molecules in these solutions is studied spectroscopically. A number of water molecules bound to an asphaltene molecule is estimated from the experimental data. Aggregation in the system asphaltene-water-toluene is simulated using the pseudophase approximation, and the Flory-Huggins parameters are estimated for the pair asphaltene-water. The potentiality of this model for simulation of mixed aggregates in the asphaltene-water-toluene systems is discussed. 相似文献
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