Are metal alkoxides linear owing to electrostatic repulsion?

Density functional theory calculations on [LnCp2APh] (Ln = La, Lu; Cp = eta 5-C5H5; A = O, S; Ph = C6H5) suggest that the linearity of the Ln-O-C vectors arises largely as a result of electrostatic repulsion between the alpha carbon and the trivalent metal centre.     

Calculations of heat of solvation by a simple electrostatic approach to molecular interactions

An extremely simple formula to estimate the heat of formation of complexes between anion and a polar molecule or between highly polar systems is presented.The formula is entirelyelectrostatic and the expression used is verified by means of perturbation theory.This formula is test-ed for several ion-molecule and molecule-molecule pairs.It is also applied to estimate the heat ofhydration of simple salts.     

In silico prediction of drug solubility: 4. Will simple potentials suffice?

In view of the extreme importance of reliable computational prediction of aqueous drug solubility, we have established a Monte Carlo simulation procedure which appears, in principle, to yield reliable solubilities even for complex drug molecules. A theory based on judicious application of linear response and mean field approximations has been found to reproduce the computationally demanding free energy determinations by simulation while at the same time offering mechanistic insight. The focus here is on the suitability of the model of both drug and solvent, i.e., the force fields. The optimized potentials for liquid simulations all atom (OPLS‐AA) force field, either intact or combined with partial charges determined either by semiempirical AM1/CM1A calculations or taken from the condensed‐phase optimized molecular potentials for atomistic simulation studies (COMPASS) force field has been used. The results illustrate the crucial role of the force field in determining drug solubilities. The errors in interaction energies obtained by the simple force fields tested here are still found to be too large for our purpose but if a component of this error is systematic and readily removed by empirical adjustment the results are significantly improved. In fact, consistent use of the OPLS‐AA Lennard‐Jones force field parameters with partial charges from the COMPASS force field will in this way produce good predictions of amorphous drug solubility within 1 day on a standard desktop PC. This is shown here by the results of extensive new simulations for a total of 47 drug molecules which were also improved by increasing the water box in the hydration simulations from 500 to 2000 water molecules. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009     

SUBJECT INDEX to Vol.16,2005

Analytical Chemistry A model-based phenomenological investigation of char combustion kinetics through thermogravimetry.….....Q. CHEN, R. HE, Z. G. LIANG, X. C. XU, C. H. CHEN 393 A Multiwall carbon nanotube-chitosan modified electrode for selective detection of dopamine in the presence of ascorbic acid……….……………….................………. …………………………………………..L. Y. JIANG, C. Y. LIU, L. P. JIANG, G. H. LU 229 A new approach for removal of nitrogen oxides …     

AUTHOR INDEX to Vol.16,2005

AI X. P. 947 AN B. L. 1405 AN D. G. 212 AN L. K. 7 AN L. K. 49 AN L. K. 1451 AN L. K. 1581 AN Y. 681 ANDO M. 736 AO L. 1189 BAI H. 11 BAI H. 457 BAI H. 997 BAI H. 1189 BAI S. Y. 1158 BAI X. L. 975 BAI X. Z. 846 BAI Y. F. 651 BAO Y. D. 49 BAO Z. Y. 1297 BAUDOIN O. 1279 BERG D. J. 4 BIAN Z. P. 1625 BU X. Z. 7 BU X. Z. 1451 BU X. Z. 1581 CAI B. 215 CAI B. 471 CAI C. 812 CAI C. 1313 CAI G. P. 405 CAI J. B. 1503 CAI J. C. 465 CAI J. C. 127…     

Significant electrostatic effects in π-facial stereoselection of nucleophilic addition reactions to β,γ-unsaturated carbonyl compounds

The Significance of electrostatic effects on the origin of π-facial stereoselectivity in nucleophilic additions to β,γ-unsaturated carbonyl systems was shown through theoretical studies (ab initio MO calculations of transition structures for NaH + HCOCH₂CCH) and experimental results (M(BH₄)_n reduction of PhCOCH(CH₃)R (M  Na, Zn, Cd; R  C₂H₅, CHCH₂, CCH)).     

Reduction potentials of reagents: II - a tool to anticipate yields of organometallic reactions?

Reduction potentials of four cage-structure halogenated derivatives and five alicyclic and aromatic ketones have been determined by cyclic voltammetry. For the Barbier reaction these parameters are used to anticipate the behaviour of intermediates formed at the metal surface and on which the distribution product depends. Semiquantitative relationships are obtained between these potentials and yields of condensation products.     

Use of electrostatic interaction for chiral recognition. Enantioselective complexation of anionic binaphthyls with protonated amino-β-cyclodextrin

The studies using NMR and capillary zone electrophoresis clearly reveal that protonated 6^A-amino- 6^A-deoxy--cyclodextrin recognizes the chirality of anionic binaphthyl derivatives such as 1,1-binaphthyl-2,2-diyl phosphate and 1,1-binaphthyl-2,2-dicarboxylate through electrostatic interaction between the host and the guest and simultaneous inclusion.     

N. S. Kurnakov’s contribution to coordination chemistry

N.S. Kurnakov’s most important works in coordination chemistry are overviewed. Special attention is given to Kurnakov’s dissertation “On Complex Metal Bases,” to his understanding of the structure of coordination compounds, to the mutual effects of ligands, and to the key ideas in coordination chemistry developed by Chugaev and Chernyaev’s school. Kurnakov’s role in the foundation of the Soviet platinum industry is pointed out.     

Comparison of the Hartree-Fock,Møller-Plesset,and Hartree-Fock-Slater method with respect to electrostatic properties of small molecules

Summary The results of various quantum chemical calculations, the Hartree-Fock (HF) method, the Møller-Plesset perturbation theory (MP2), and the Hartree-Fock-Slater (HFS) method are compared. Atomic charges, dipole moments, topological properties of the electron density distribution and polarizabilities, and first hyperpolarizabilities are calculated. Atomic charges obtained with the HFS method are found to be very close to those calculated with the MP2 method, from which we conclude that the HFS method describes to some extent electron correlation effects. Performing an MP2 calculation after an HF calculation improves the molecular dipole moments considerably, yielding values close to the experimental ones. HFS calculations are computationally less demanding than MP2 and yield comparable results for the electron density distributions, dipole moments and polarizabilities.     

A new approach to δ-lactones,related to the Prelog-Djerassi lactone.

The reductive rearrangement of 2-ethoxy-5-(2-alkenyl)-2H-tetrahydropyrane systems, in the presence of AlBu¹₃, was used as the key-step in the synthesis of Prelog-Djerassi related lactones.     

Is DNA's rigidity dominated by electrostatic or nonelectrostatic interactions?

Double-stranded DNA is among the stiffest biopolymers, whose bending propensity crucially influences many vital biological processes. It is not fully understood which among the two most likely forces, electrostatic self-repulsion or the compressive base pair stacking, plays a dominant role in determining the DNA's unique rigidity. Different theoretical and experimental studies led so far to contradictory results on this issue. In this Communication, we address this important question by means of Molecular Dynamics (MD) simulations using both atomistic and coarse-grained force fields. Using two independent sets of calculations, we found that electrostatic and nonelectrostatic effects play a comparable role in maintaining DNA's stiffness. Our findings substantially differ from predictions of existing theories for DNA rigidity and may indicate that a new conceptual understanding needs to be developed.     

Electrochemical oxidation of organosilicon compounds: V. Electrochemical oxidation of α-silyethers. remarkable effect of silicon on oxidation potentials and reaction pathways

Substitution of a silyl group for hydrogen at the α-position of ethers caused a significant decrease in their oxidation potentials. This effect is attributed to an interaction of the carbonsilicon σ-bond with the lone pair of the oxygen atom. The preparative anodic oxidation of α-silylethers proceeded smoothly in methanol and the carbonsilicon bond was selectively cleaved to give the corresponding acetals.     

Routes to trans-Chrysanthemic Acid. III. Syntheses from (+)-Limonene and α-Terpineol

Conversion of limonene to cis-homocaronic acid and α-terpineol to Julia's bicyclic ketoxime has been achieved, the acid and the oxime are known precursors of trans-chrysanthemic acid.     

Laser pump-probe experiments on microsecond to millisecond timescales at an electrostatic ion storage ring: Triplet—Triplet absorption by protoporphyrin-IX anions

Here we demonstrate that pump-probe experiments can be carried out on microsecond to millisecond timescales using an electrostatic ion storage ring. As a test case, we have chosen protoporhyrin IX anions that have lifetimes with respect to dissociation after photoexcitation on this time scale. Ions were photoexcited on one side of the ring with either 430- or 535-nm light (pump) and then allowed to take a certain number of revolutions before they were photoexcited by a second laser pulse (probe) with wavelengths between 650 and 950 ran. If ions were first excited by the pump, an increased yield of neutral products caused by the absorption of red light was measured in a microchannel plate detector located on the other side of the ring. This implies that it is possible to pick out ions that were photoexcited by the pump pulse and to spectroscopically characterize these ions. We report absorption spectra of 535 ran photoexcited porphyrin anions, with time delays of 0.19 and 0.57 ms between the pump and probe pulses, and find that absorption occurs over a broad region in the red.