Reduction potential (E(red)) values have been calculated and compared with available cyclic voltammetry (CV) data for 10 metallofullerene complexes with the mu(3)-eta(2):eta(2):eta(2)-C(60) (M(3)-C(6)[C(60)]) bonding mode. Consideration of bulk solvent effects is essential for the calculation of the E(red) values. Scaling factors for the electrostatic terms of the solvation energies have been introduced to fully describe the experimental cyclic voltammograms with a small mean deviation of 0.07 V. Multiple electron reductions induce movement of the metal cluster moieties on the C(60) surface, which is accompanied with the changes in some M-C[C(60)] bonds from pi-type to sigma-type mode. However, the changes in M(3)-C(60) distances, as well as the geometric changes of M(3) and C(60), are small for the reductions, which is in harmony with the high chemical and electrochemical stability of the metallofullerenes. Our population analyses reveal that the added electrons are not localized at the C(60) moieties, and electron population in the metal clusters is significant, more than 20% (av. 37%), for all the reductions. Furthermore, we demonstrated that the two close one-electron redox waves in CV diagrams are strongly correlated with significant electron delocalization, about 40-80%, to the metal-cluster moieties in these metallofullerene complexes.
[Show abstract][Hide abstract] ABSTRACT: We performed extensive density functional calculations on various metallofullerene complexes and their polyanions to gain insight into novel η1 and η2[6:5] metal (M)–C60 bonding modes. For LnMC60 (L = ligand), the η1 mode is calculated to be the most stable, followed by η2[6:5] and η2[6:6] for –3 anions, in contrast to η2[6:6] >> η2[6:5] ≈ η1 for neutral cases. This observation is responsible for the transformation from η2[6:6] to η1 for LnM3C60, such as [Os3(CO)9C60], upon successive electron reductions. Our energy partitioning analysis (EPA) indicates that the π-type character of η2[6:6] is much larger than that of η2[6:5]. An electron addition decreases the π-type interaction of both the η2[6:6] and η2[6:5] modes by about 35 %, whereas it has little effect on σ-type interactions. Because of the large proportion of π-character in η2[6:6] coordination, the stability of η2[6:6] coordination decreases steeply as electron reductions continue. On the basis of the EPA results, we could explain why the reaction of [Os3(CO)8(CNR)(μ3-η2[6:6],η2[6:6],η2[6:6]-C60)] (R = CH2Ph) with CNR (4e donor) produces [Os3(CO)8(CNR)(μ3-CNR)(μ3-η1,η2[6:5],η1-C60)]. The η1 and η2[6:5] bonding modes of M–C60 are crucial to fully understand the bonding nature of M–C60 bonds in exohedral metallofullerene complexes.
Berichte der deutschen chemischen Gesellschaft 04/2010; 2010(10):1530 - 1535. DOI:10.1002/ejic.200901188 · 2.94 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In a joint study involving electrochemical experiments and density functional calculations, we determined the oxidized and reduced structures of ethylene carbonate (EC), vinylene carbonate (VC), N-methyl-ε-caprolactam (Me-CL), and N-acetyl-ε-caprolactam (Ac-CL). This study reveals that the four molecules maintain their ring structures under the one-electron oxidation condition. Me-CL and Ac-CL have linear chain forms, whereas EC and VC still have ring-structures under the one-electron reduction condition. We suggest that such a collabora-tive study, including both experimentation and theory, is a simple and practical method for determining the structures of oxidized and reduced molecules.
[Show abstract][Hide abstract] ABSTRACT: Current practice of validating predicted protein structural model is knowledge-based where scoring parameters are derived from
already known structures to obtain decision on validation out of this structure information. For example, the scoring parameter,
Ramachandran Score gives percentage conformity with steric-property higher value of which implies higher acceptability. On the
other hand, Force-Field Energy Score gives conformity with energy-wise stability higher value of which implies lower
acceptability. Naturally, setting these two scoring parameters as target objectives sometimes yields a set of multiple models for the
same protein for which acceptance based on a particular parameter, say, Ramachandran score, may not satisfy well with the
acceptance of the same model based on other parameter, say, energy score. The confusion set of such models can further be
resolved by introducing some parameters value of which are easily obtainable through experiment on the same protein. In this
piece of work it was found that the confusion regarding final acceptance of a model out of multiple models of the same protein can
be removed using a parameter Surface Rough Index which can be obtained through semi-empirical method from the ordinary
microscopic image of heat denatured protein.
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