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Volumn 12, Issue 2, 2005, Pages 477-488

Simulation of59Co NMR chemical shifts in aqueous solution

Author keywords

Density functional calculations; Molecular dynamics; NMR spectroscopy; Solvation effects; Transition metals

Indexed keywords

MATHEMATICAL MODELS; MOLECULAR DYNAMICS; NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY; OPTIMIZATION; PERTURBATION TECHNIQUES; QUANTUM THEORY; SOLUTIONS; TRANSITION METALS; WATER;

EID: 29544437682     PISSN: 09476539     EISSN: None     Source Type: Journal    
DOI: 10.1002/chem.200500285     Document Type: Article
Times cited : (62)

References (114)
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    • Computing highly charged anions such as 1 in the gas phase is unrealistic in the sense that the expected spontaneous electron detachment is only prevented by the finite basis set (or, in the periodic plane-wave calculations, by a compensating, smeared-out background charge).
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    • copyright by IBM Corp. and Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany
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    • Molecular Simulations, Inc., 9685 Scranton Rd. San Diegom CA 92121. The published results were generated using the program CKARMm. This program is distributed by Molecular Simulations Inc.
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    • A hydrogen bond is assigned if the O⋯X distance is 'smaller thap 3.5 Å and the O-H bond is directed towards the heteroatom such that the O-H⋯X angle is larger than 140°; cf. the corresponding criteria in bulk water: E. Schwegler, G. Galli, F. Gygi, Phys. Rev. Lett. 2000, 84, 2429-2432.
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    • The most promising route would probably be a supermolecular approach involving PCM calculations for an explicitly hydrated cluster; however, any single, static equilibrium structure of such a model would be highly arbitrary, and ultimately, one would have to form ensemble averages, as for instance in a recent combined CPMD and PCM study of acetone in water: O. Crescenzi, M. Pavone, P. De Angelis, V. Barone, J. Phys. Chem. B 2005, 109, 445-453.
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    • It should be kept in mind that both approaches - quantum-mechanical zero-point corrections and MD-based thermal averaging - describe very different things and that it is not possible to simply use the computed changes in r or δ as increments and add them up. However, since both effects have the same physical origin, namely, the anharmonicity of the PES and the curvature of the magnetic shielding hypersurface, it is sensible to discuss them together.
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    • An even more deshielded complex containing two tripod ligands with O donors is known, which at ambient temperature shows evidence for significant spin crossover (i.e., thermal population of a paramagnetic high-spin state): G. Navon, W. Kläui, Inorg. Chem. 1984, 23, 2722-2725.
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    • note
    • We have not included counterions in our simulations, because those present in the experiments (alkali metal cations for 1 and 4, and halide anions for 2 and 3) are usually well hydrated, forming solvent-separated, rather than contact ion pairs. Realistic computational modeling of the real solutions would require much larger boxes (or QM parts) and, in particular, much larger simulation times, as the relative diffusion of hydrated ions happens on a longer time-scale. It is possible that even such distant counterions could exert noticeable effects on the properties under scrutiny, but most likely this would just fine-tune the latter, not radically alter them.
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    • -1.
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    • At no point is proton transfer from an ammine ligand to the solvent observed.
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    • A referee suggested that the apparent discrepancy between the two approaches could originate from the inherent differences in the QM methods (Gaussian all-electron basis versus plane waves with pseudopotentials). Given the good mutual accord between the CPMD and BOMD results for the pristine complexes, this suggestion appears quite unlikely.
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    • The apparent shallow maximum in the g(r) curve in Figure 5 around r ≈ 3.5 Å arises because for distances beyond that value a considerable fraction of the corresponding sphere around the carbonyl O atom is taken up by the complex and cannot be occupied by water molecules from the solvent. As r approaches half the box length, g(r) attains the value of 1 for the ideal random distribution.
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    • For recent analyses of transition metal NMR parameters in terms of individual MO pair contributions see, for example: a) L. Orian, A. Bisello, S. Santi, A. Ceccon, G. Saielli, Chem. Eur. J. 2004, 10, 4029-4040;
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    • Orian, L.1    Bisello, A.2    Santi, S.3    Ceccon, A.4    Saielli, G.5


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.