... Karel Doclo and Ursula Rothlisberger* . Laboratory of Inorganic Chemistry, ETH Zentrum, CH-8... more ... Karel Doclo and Ursula Rothlisberger* . Laboratory of Inorganic Chemistry, ETH Zentrum, CH-8092 Zurich, Switzerland. J. Phys. Chem. A , 2000, 104 (27), pp 64646469. DOI: 10.1021/jp0012193. Publication Date (Web): June ...
A parallel study of the radical copper enzyme galactose oxidase (GOase) and a low molecular weigh... more A parallel study of the radical copper enzyme galactose oxidase (GOase) and a low molecular weight analog of the active site was performed with dynamical density functional and mixed quantum-classical calculations. This combined approach enables a direct comparison of the properties of the biomimetic and the natural systems throughout the course of the catalytic reaction. In both cases, five essential forms of the catalytic cycle have been investigated: the resting state in its semi-reduced (catalytically inactive) and its oxidized (catalytically active) form, A semi and A ox, respectively; a protonated intermediate B; the transition state for the rate-determining hydrogen abstraction step C, and its product D. For A and B the electronic properties of the biomimetic compound are qualitatively very similar to the ones of the natural target. However, in agreement with the experimentally observed difference in catalytic activity, the calculated activation energy for the hydrogen abstraction step is distinctly lower for GOase (16 kcal/mol) than for the mimetic compound (21 kcal/mol). The enzymatic transition state is stabilized by a delocalization of the unpaired spin density over the sulfur-modified equatorial tyrosine Tyr272, an effect that for geometric reasons is essentially absent in the biomimetic compound. Further differences between the mimic and its natural target concern the structure of the product of the abstraction step, which is characterized by a weakly coordinated aldehyde complex for the latter and a tightly bound linear complex for the former.
The electronic structure of the ground and lowest excited states of the hexaamminechromium(III) i... more The electronic structure of the ground and lowest excited states of the hexaamminechromium(III) ion [Cr(NH(3))(6)](3+) has been investigated through density functional theory. The geometry of the (4)A(2g) ground state and of the (4)T(2g) excited state are optimized. The latter is relaxed along an e(g) Jahn-Teller coordinate. The experimentally known geometry distortion, i.e., an axial compression and an equatorial elongation, together with the corresponding energy gain is well reproduced by our calculations. The results for the d-d excitation energies are in reasonable agreement with experiment. The relative performance of local and gradient-corrected functionals is discussed.
... and Kanamori to develop the qualitative rules 7 that aided experimentalists for many years an... more ... and Kanamori to develop the qualitative rules 7 that aided experimentalists for many years and were recovered by the orbital model of the exchange ... et al., 8 a series of papers appeared dealing with the calculation of the singlet−triplet splitting in binuclear copper(II) complexes. ...
The electronic structures of Ti(CatNSQ) 2 and Sn(CatNSQ) 2 , where CatNSQ 2is the tridentate radi... more The electronic structures of Ti(CatNSQ) 2 and Sn(CatNSQ) 2 , where CatNSQ 2is the tridentate radical ligand (3,5-di-tert-butyl-1,2-semiquinonato 1(2-hydroxy-3,5-di-tert-butyl-phenyl)immine), were investigated with density functional (DF) calculations, using the local approximation for the exchange-correlation functional. The crystal structure of Sn(CatNSQ) 2 was solved. The complex crystallizes in the orthorhombic space group, C222 1 , with Z ) 8 in a unit cell of the following dimensions: a ) 19.580(5) Å, b ) 24.310(5) Å, c ) 23.690(5) Å. The crystals are not isomorphous with similar M(CatNSQ) 2 (M ) Ti, V) complexes previously reported. DF calculations showed that the triplet (S ) 1) spin state is stabilized with respect to the first excited singlet (S ) 0) state and the computed exchange coupling constant J is in semiquantitative agreement with the values obtained from magnetic susceptibility measurements. Using a symmetry-based multiplet structure decomposition in terms of states defined by a single determinant (single determinant method, SD) the energies of the excited singlet states were also computed in agreement with the experimental data. The calculations have shown that the main exchange mechanism between the organic radicals, responsible for the ferromagnetism of these complexes, is a superexchange pathway mediated by the 3d orbitals of Ti and the 4p empty orbitals of Sn. Magnetostructural correlations between the exchange coupling constant and the M-O and M-N bond distances have been established. S0020-1669(97)00906-3 CCC: $15.00
... Karel Doclo and Ursula Rothlisberger* . Laboratory of Inorganic Chemistry, ETH Zentrum, CH-8... more ... Karel Doclo and Ursula Rothlisberger* . Laboratory of Inorganic Chemistry, ETH Zentrum, CH-8092 Zurich, Switzerland. J. Phys. Chem. A , 2000, 104 (27), pp 64646469. DOI: 10.1021/jp0012193. Publication Date (Web): June ...
A parallel study of the radical copper enzyme galactose oxidase (GOase) and a low molecular weigh... more A parallel study of the radical copper enzyme galactose oxidase (GOase) and a low molecular weight analog of the active site was performed with dynamical density functional and mixed quantum-classical calculations. This combined approach enables a direct comparison of the properties of the biomimetic and the natural systems throughout the course of the catalytic reaction. In both cases, five essential forms of the catalytic cycle have been investigated: the resting state in its semi-reduced (catalytically inactive) and its oxidized (catalytically active) form, A semi and A ox, respectively; a protonated intermediate B; the transition state for the rate-determining hydrogen abstraction step C, and its product D. For A and B the electronic properties of the biomimetic compound are qualitatively very similar to the ones of the natural target. However, in agreement with the experimentally observed difference in catalytic activity, the calculated activation energy for the hydrogen abstraction step is distinctly lower for GOase (16 kcal/mol) than for the mimetic compound (21 kcal/mol). The enzymatic transition state is stabilized by a delocalization of the unpaired spin density over the sulfur-modified equatorial tyrosine Tyr272, an effect that for geometric reasons is essentially absent in the biomimetic compound. Further differences between the mimic and its natural target concern the structure of the product of the abstraction step, which is characterized by a weakly coordinated aldehyde complex for the latter and a tightly bound linear complex for the former.
The electronic structure of the ground and lowest excited states of the hexaamminechromium(III) i... more The electronic structure of the ground and lowest excited states of the hexaamminechromium(III) ion [Cr(NH(3))(6)](3+) has been investigated through density functional theory. The geometry of the (4)A(2g) ground state and of the (4)T(2g) excited state are optimized. The latter is relaxed along an e(g) Jahn-Teller coordinate. The experimentally known geometry distortion, i.e., an axial compression and an equatorial elongation, together with the corresponding energy gain is well reproduced by our calculations. The results for the d-d excitation energies are in reasonable agreement with experiment. The relative performance of local and gradient-corrected functionals is discussed.
... and Kanamori to develop the qualitative rules 7 that aided experimentalists for many years an... more ... and Kanamori to develop the qualitative rules 7 that aided experimentalists for many years and were recovered by the orbital model of the exchange ... et al., 8 a series of papers appeared dealing with the calculation of the singlet−triplet splitting in binuclear copper(II) complexes. ...
The electronic structures of Ti(CatNSQ) 2 and Sn(CatNSQ) 2 , where CatNSQ 2is the tridentate radi... more The electronic structures of Ti(CatNSQ) 2 and Sn(CatNSQ) 2 , where CatNSQ 2is the tridentate radical ligand (3,5-di-tert-butyl-1,2-semiquinonato 1(2-hydroxy-3,5-di-tert-butyl-phenyl)immine), were investigated with density functional (DF) calculations, using the local approximation for the exchange-correlation functional. The crystal structure of Sn(CatNSQ) 2 was solved. The complex crystallizes in the orthorhombic space group, C222 1 , with Z ) 8 in a unit cell of the following dimensions: a ) 19.580(5) Å, b ) 24.310(5) Å, c ) 23.690(5) Å. The crystals are not isomorphous with similar M(CatNSQ) 2 (M ) Ti, V) complexes previously reported. DF calculations showed that the triplet (S ) 1) spin state is stabilized with respect to the first excited singlet (S ) 0) state and the computed exchange coupling constant J is in semiquantitative agreement with the values obtained from magnetic susceptibility measurements. Using a symmetry-based multiplet structure decomposition in terms of states defined by a single determinant (single determinant method, SD) the energies of the excited singlet states were also computed in agreement with the experimental data. The calculations have shown that the main exchange mechanism between the organic radicals, responsible for the ferromagnetism of these complexes, is a superexchange pathway mediated by the 3d orbitals of Ti and the 4p empty orbitals of Sn. Magnetostructural correlations between the exchange coupling constant and the M-O and M-N bond distances have been established. S0020-1669(97)00906-3 CCC: $15.00
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