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We report the synthesis of the lanthanide-(bis)boryloxide complex [Dy{OB(NArCH)2}2(THF)4][BPh4] (2Dy, Ar = 2,6-Pri2C6H3), with idealised D4h@Dy(III) point-group symmetry. Complex 2Dy exhibits single-molecule magnetism (SMM), with one of the highest energy barriers (Ueff = 1565(298) K) of any six-coordinate lanthanide-SMM. Complex 2Dy validates electrostatic model predictions, informing the future design of lanthanide-SMMs.

A study of the strong N-X⋅⋅⋅- O-N+ (X=I, Br) halogen bonding interactions reports 2×27 donor×acceptor complexes of N-halosaccharins and pyridine N-oxides (PyNO). DFT calculations were used to investigate the X⋅⋅⋅O halogen bond (XB) interaction energies in 54 complexes. A simplified computationally fast electrostatic model was developed for predicting the X⋅⋅⋅O XBs. The XB interaction energies vary from -47.5 to -120.3 kJ mol-1 ; the strongest N-I⋅⋅⋅- O-N+ XBs approaching those of 3-center-4-electron [N-I-N]+ halogen-bonded systems (ca. 160 kJ mol-1 ). 1 H NMR association constants (KXB ) determined in CDCl3 and [D6 ]acetone vary from 2.0×100 to >108 m-1 and correlate well with the calculated donor×acceptor complexation enthalpies found between -38.4 and -77.5 kJ mol-1 . In X-ray crystal structures, the N-iodosaccharin-PyNO complexes manifest short interaction ratios (RXB ) between 0.65-0.67 for the N-I⋅⋅⋅- O-N+ halogen bond.

This chapter deals with the facial selectivity of nucleophilic additions to carbonyl compounds. This is explained using models such as the Cram’s model, Anh–Felkin modification of Cram’s model, Houk’s transition structure model, Houk’s electrostatic model, Cieplak’s σ → σ*# model, and cation coordination model. The intricacies, variations, and predicted selectivities of these models are elaborated with examples. It has been argued that the Cieplak’s σ → σ*# model is applicable to only those reactions that proceed through product-like transition structures. Using the cation coordination model, the facial selectivities of a number of substrates, including the better anti-selectivity of endo,endo-2,3-diethyl-7-norbornanone in comparison to that of endo,endo-2,3-dimethyl-7-norbornanone, have been convincingly explained.

The structural and electronic properties of ${\mathrm{KTaO}}_{3}$/${\mathrm{KZnF}}_{3}$ and ${\mathrm{KTaO}}_{3}$/${\mathrm{KNiF}}_{3}$ oxyfluoride superlattices are studied from first-principles density functional theory calculations. We highlight, that beyond a critical layer thickness, these systems exhibit an insulator to metal transition that gives rise to the appearance of two-dimensional electron and hole gas, confined both, due the band alignment, within the oxide layer. The origin of the insulator to metal transition is related to the polar discontinuity at the interfaces. The behavior is discussed in terms of a simple electrostatic model and compared to that of the prototypical ${\mathrm{LaAlO}}_{3}$/${\mathrm{SrTiO}}_{3}$ oxide system. The magnetic properties ${\mathrm{KTaO}}_{3}$/${\mathrm{KNiF}}_{3}$ superlattices are further discussed, revealing a sizable Rashba-type spin splitting at these interfaces, much larger than in similar oxide/oxide systems.

International audience; Noncovalent interactions play a key role in functional materials. Metal–organofluorine interactions are of special interest because they directly affect the structure and reactivity of hybrid fluorinated materials. In-depth understanding and modulating of these interactions would enable the rational design of functional materials from fundamental chemical principles. In this work, we propose a computational approach that enables a comprehensive and quantitative characterization of noncovalent interactions (NCIs) in hybrid fluorinated crystals. Our approach couples dispersion-corrected density functional theory to NCI analysis. Additionally, we determine electron densities at bond critical points and identify electrostatic interactions using a simple electrostatic model. The versatility of this approach to probe a wide range of NCIs is demonstrated for a series of four bimetallic fluorinated crystals incorporating alkali–manganese(II) pairs and trifluoroacetato ligands. Noncovalent interactions in these hybrid crystals include metal–oxygen, metal–fluorine, hydrogen bonds, and van der Waals forces. Using K2Mn2(tfa)6(tfaH)2·H2O as an example, we demonstrate that its two-dimensional layered structure stems from a unique balance between these four NCIs. The computational approach presented herein should have general applicability to the quantitative study of NCIs in hybrid crystals, thereby serving as a guide for crystal engineering of novel hybrid materials.

We extend the linearized Poisson-Boltzmann (LPB) continuum electrostatic model for molecular solvation to address charge-hydration asymmetry. Our new solvation-layer interface condition (SLIC)/LPB corrects for first-shell response by perturbing the traditional continuum-theory interface conditions at the protein-solvent and the Stern-layer interfaces. We also present a GPU-accelerated treecode implementation capable of simulating large proteins, and our results demonstrate that the new model exhibits significant accuracy improvements over traditional LPB models, while reducing the number of fitting parameters from dozens (atomic radii) to just five parameters, which have physical meanings related to first-shell water behavior at an uncharged interface. In particular, atom radii in the SLIC model are not optimized but uniformly scaled from their Lennard-Jones radii. Compared to explicit-solvent free-energy calculations of individual atoms in small molecules, SLIC/LPB is significantly more accurate than standard parametrizations (RMS error 0.55 kcal/mol for SLIC, compared to RMS error of 3.05 kcal/mol for standard LPB). On parametrizing the electrostatic model with a simple nonpolar component for total molecular solvation free energies, our model predicts octanol/water transfer free energies with an RMS error 1.07 kcal/mol. A more detailed assessment illustrates that standard continuum electrostatic models reproduce total charging free energies via a compensation of significant errors in atomic self-energies; this finding offers a window into improving the accuracy of Generalized-Born theories and other coarse-grained models. Most remarkably, the SLIC model also reproduces positive charging free energies for atoms in hydrophobic groups, whereas standard PB models are unable to generate positive charging free energies regardless of the parametrized radii. The GPU-accelerated solver is freely available online, as is a MATLAB implementation.

Lone pair-π interactions are now recognized as a supramolecular bond whose existence in biological systems is documented by a growing number of examples. They are commonly attributed to electrostatic forces. This review attempts to highlight some recent discoveries evidencing the important role which lone pair-π interactions, and anion-π interactions in particular, play in stabilizing the structure and affecting the function of biomolecules. Special attention is paid to studies exploring the physical origin of these at first glance counterintuitive interactions between a lone pair of electrons of one residue and the π-cloud of another. Recent theoretical work went beyond the popular electrostatic model and inquired the extent to which orbital interactions have to be taken into account. In at least one biologically relevant case-that of anion-flavin interactions-a substantial charge-transfer component has been shown to operate.

The dynamics of the electrochemical double layer in ionic liquids can be experimentally probed by a number of experimental techniques. Earlier, we reported on the results of an X-ray photoelectron spectroscopic investigation under applied square-wave bias of two distinct frequencies. Our studies had revealed counterintuitive properties involving the physical and temporal progression of the effect of the electrochemical double layer that could not be modeled with conventional equivalent-circuit approaches. Herein, we present a new coarse-grained modeling methodology that accounts for particle diffusion, migration, and ion-association equilibrium. Our model is computationally efficient enough to be used to predict and match the results at extended time scales and distances of the experiment. Modeling efforts predict that a crucial component of the behavior is controlled by the ion-pairing equilibrium, an often overlooked aspect of ionic liquids.

© 2017, Indian Academy of Sciences. The environment of a solute molecule in an ionic liquid is likely to have large fluctuating electrostatic fields, and so the electrostatic properties of such a solute including its charge distribution and its polarizability may make a difference to both its static and dynamic properties. We have developed a new model for the static electrostatic distribution in the CS 2 molecule with 7 charged sites and anisotropic polarizability on the carbon site and isotropic polarizability on the sulfurs. We have investigated static and dynamic properties of the neat liquid and solutions of CS 2 in an ionic liquid, [dmim][NTf 2 ]. [Figure not available: see fulltext.] .

Single-molecule transistor experiments offer the ultimate probe of a molecule’s redox chemistry. With a combined quantum mechanics/molecular mechanics computational method and an electrostatic model of the junction, the Coulomb blockade diamonds can be reconstructed. We present computations on 1,4-diamino-benzene (OPVN) in a molecular transport junction, and focus on the chemical features such as electrostatic stabilization, importance of binding group, and binding distance. Thus the explicit construction of the Coulomb blockade diamonds offers a method for direct comparison between different molecular junctions and thus also with experiments.

This paper describes four programs for Windows, designed to obtain the thermodynamic properties of aqueous species from experimental data and reporting them in the Unitherm database format (HCh software package). Programs OptimA and OptimS allow users to derive the standard Gibbs free energies of aqueous species from the results of chemical experiments (e.g., potentiometry or solubility) and from ultraviolet–visible (UV–Vis) absorption spectra, respectively; programs OptimB and OptimC enable optimization of the parameters of the revised Helgeson–Kirkham–Flowers equation of state and the modified Ryzhenko–Bryzgalin electrostatic model, respectively, for an aqueous species from its standard Gibbs free energy or stability constant as a function of temperature and pressure.

Spectroscopic data on the 3d 1 transition metal activators Ti 3+ , V 4+ and Cr 5+ in compounds were collected and analysed in order to obtain an overview on the size of the 3d 1 level crystal field splitting. Results are compared with data on the 5d 1 activators Ce 3+ and Eu 2+ . Trends earlier observed for the 5d 1 lanthanides also apply to the 3d 1 transition metals. They will be interpreted with the point charge electrostatic model and a modified version thereof.

Recent experimental data on the hydrolysis of U(VI), Pu(VI), Np(V), and Th(IV) at variable temperatures are summarized in this review. Data indicate that the hydrolysis reactions of U(VI), Pu(VI), Np(V), and Th(IV) are all enhanced when temperature is increased from 283 to 358 K. In general, the tendency of actinide elements in different oxidation states toward hydrolysis follows the order: An(IV) > An(VI) > An(V), which can be well described by the electrostatic model. The enhancement of hydrolysis at higher temperatures can be attributed to the increase of ionization of water with the increase of temperature. A few theoretical thermodynamic approaches for predicting the effect of temperature, including the constant enthalpy approach, the constant heat capacity approach, the DQUANT equation, and the Ryzhenko-Bryzgalin model, are tested with the experimental data.

Background. The selectivity of biological cation channels is defined by a short, narrow selectivity filter, having a negative net fixed charge Qf . Voltage gated bacterial channels (NaChBac and some others) are frequently used in biophysics as simplified models of mammalian calcium and sodium channels. We report an experimental, analytic and numerical study of the effects of Qf and bulk ionic concentrations of Ca2+ and Na+ on conduction and selectivity of NaChBac channels, wild type and Qf -varied mutants. Methods. Site-directed mutagenesis and voltage clamp recordings were used to investigate the Na+ /Ca2+ selectivity, divalent blockade and anomalous mole fraction effect (AMFE) for different NaChBac wild type/mutants channels and the properties dependence on Qf . Experimental results were compared with Brownian dynamics simulations and with analytic predictions of the ionic Coulomb blockade (ICB) model, which was extended to encompass bulk concentration effects. Results. It was shown that changing of Qf from –4e (for LESWAS wild type) to –8e (for LEDWAS mutant) leads to strong divalent blockade of the Na+ current by micromolar amounts of Ca2+ ions, similar to the effects seen in mammalian calcium channels. The BD simulations revealed a concentration-related logarithmic shift of the conduction bands. These results were shown to be consistent with ICB model predictions. Conclusions. The extended ICB model explains the experimental (divalent blockade and AMFE) and simulated (multi-ion bands and their concentration-related shifts) selectivity phenomena of NaChBac channel and its charge-varied mutants. These results extend the understanding of ion channel selectivity and may also be applicable to biomimetic nanopores with charged walls.

We performed the first principle calculation to investigate the polarization behavior of BaTiO3(BTO)/PbTiO3(PTO) superlattices with a period-5 superlattice model. The results show that when BTO proportion increases, values of c/a increase and polarizations decrease. In BPT superlattices, polarization in each local layer keeps a constant value, indicating that short-period BPT superlattices can be approximately considered as a single ferroelectric material. Moreover, from analysis of the electrostatic model, we know the directions of internal electric fields in BTO and PTO layers are opposite. Internal electric field in PTO layer leads to polarization loss in this layer, but polarization in BTO layer is enhanced by internal electric field.

International audience; In the present work, we investigate different possibilities for the nonempirical localization of nonatomic centers within the context of the design of new generation polarizable force fields. To do so, the positions of electron localization function (ELF) and electron pair localization function (EPLF) attractors and of Boys orbital centroids are determined for a set of thirteen saturated and conjugated biologically relevant molecules. We consider the similarities and differences in the representations of localized lone pairs and π delocalized systems by these approaches, as well as the effects of the basis sets and of the level of quantum chemistry (QC). All three methods give consistent results upon dealing with the localized lone pairs. Concerning aromatic systems, whereas ELF and EPLF methods give mutually consistent results, the Boys scheme breaks the symmetry by alternating the electron distributions along the C-C bonds providing a different distribution of off-centered points. We then investigate the influence of lone pair localization in the water model of the Gaussian electrostatic model/sum of interactions between fragments ab initio computed (GEM/SIBFA) polarizable force field, which embodies an explicit representation of the lone pairs. This is done, in a series of mono- and poly-hydrated Zn(II) complexes, by comparing the overlap-dependent repulsion (Erep) and charge-transfer (Ect) contributions to their QC counterparts. We resort to either the current GEM/SIBFA water lone pair internal coordinates or to the ones derived from the previously mentioned localization procedures. The latter enables closer reproductions by Erep and Ect (GEM/SIBFA) of their exchange repulsion (Eexch) and Ect QC counterparts. The present preliminary results show that QC localization procedures can be used to derive accurate, nonempirical positions for off-centered points intervening in the formulation of the overlap-dependent contributions of next-generation polarizable force fields.; Dans la présente étude, nous examinons les différentes localisations non empiriques possibles des centres non atomiques dans le contexte de la conception de champs de forces polarisables de nouvelle génération. À cette fin, nous déterminons les positions des attracteurs ELF (Electron Localization Function, ou fonction de localisation électronique) et des attracteurs EPLF (Electron Pair Localization Function, ou fonction de localisation de paire d'électrons), ainsi que des centroïdes des orbitales de Boys pour un jeu de treize molécules saturées et conjuguées ayant une importance biologique. Nous considérons les similarités et les différences entre les représentations des paires libres et des systèmes délocalisés obtenues par ces approches, ainsi que les effets des bases et du niveau de chimie quantique (QC). Les trois méthodes donnent des résultats cohérents lorsque l'on s'intéresse aux paires libres localisées. En ce qui concerne les systèmes aromatiques, alors que les méthodes ELF et EPLF donnent des résultats mutuellement cohérents, la méthode de Boys rompt la symétrie en alternant la répartition des électrons le long des liaisons CC , ce qui donne une distribution différente des points excentrés. Nous étudions ensuite l'influence de la localisation des paires libres dans le modèle de l'eau dans le champ de forces polarisable GEM/SIBFA, qui figure une représentation explicite des paires libres. Sur une série de complexes de Zn(II) mono et polyhydratés, nous comparons les contributions des énergies de répulsion (E rép) et de transfert de charge (E tc) dépendantes de la superposition à leurs équiva-lents dans les calculs de chimie quantique (QC). Nous utilisons les coordonnées internes des paires libres de l'eau de la méthode GEM/SIBFA courante ou celles dérivées des procédures de localisation susmentionnées. Les secondes permettent que E rép and E tc (GEM/SIBFA) donnent des reproductions plus proches de leurs équivalents QC E éch et E tc. Les résultats préliminaires présentés ici montrent que des procédures de localisation basées sur la chimie quantique peuvent être utilisées pour calculer les positions exactes, non empiriques, pour les points excentrés intervenant dans la formulation des contributions dépendantes du recou-vrement des champs de forces polarisables de nouvelle génération. [Traduit par la Rédaction]

A simple electrostatic model explains the enhanced stereoselectivity of N-oxide catalyzed allylations compared to propargylations, which in turn explicates the dearth of stereoselective N-oxide propargylation catalysts. These results suggest that N-oxide catalysts that are effective for both allylations and propargylations can be designed by targeting inherently stereoselective ligand configurations and through the manipulation of distortion effects in the operative transition states.

One of the most popular and simple models for the calculation of pK(a) s from a protein structure is the semi-macroscopic electrostatic model MEAD. This model requires empirical parameters for each residue to calculate pK(a) s. Analysis of current, widely used empirical parameters for cysteine residues showed that they did not reproduce expected cysteine pK(a) s; thus, we set out to identify parameters consistent with the CHARMM27 force field that capture both the behavior of typical cysteines in proteins and the behavior of cysteines which have perturbed pK(a) s. The new parameters were validated in three ways: (1) calculation across a large set of typical cysteines in proteins (where the calculations are expected to reproduce expected ensemble behavior); (2) calculation across a set of perturbed cysteines in proteins (where the calculations are expected to reproduce the shifted ensemble behavior); and (3) comparison to experimentally determined pK(a) values (where the calculation should reproduce the pK(a) within experimental error). Both the general behavior of cysteines in proteins and the perturbed pK(a) in some proteins can be predicted reasonably well using the newly determined empirical parameters within the MEAD model for protein electrostatics. This study provides the first general analysis of the electrostatics of cysteines in proteins, with specific attention paid to capturing both the behavior of typical cysteines in a protein and the behavior of cysteines whose pK(a) should be shifted, and validation of force field parameters for cysteine residues.

We present the inclusion of distributed multipoles obtained from the Gaussian Electrostatic Model (GEM) into the AMOEBA force field. As a proof of principle, we have reparametrized water and alanine di-peptide. The GEM distributed multipoles (GEM-DM) have been obtained at the same levels of theory as those used for the original AMOEBA parametrization. The use of GEM allows the derivation of the distributed multipoles from the analytical fit to the molecular density or the numerical fit to the molecular electrostatic potential (mESP). In addition, GEM-DM are intrinsically finite of the highest order of the auxiliary basis used for the GEM fit. We also present the fitting of multipoles for the di-methyl imidazolium/chloride (DMIM(+)-Cl(-)) ionic liquid pair. Results for intermolecular Coulomb for all test systems show very good agreement. MD simulations for a reparametrized AMOEBA water model with GEM-DM provide results on par with the original AMOEBA force field for a series of bulk properties including liquid density and enthalpy of vaporization. A package for the calculation of GEM Hermite coefficients and derived distributed multipoles using the numerical procedure is also presented and released under the GNU public license.

In many cases the stability of a protein has to be increased to permit its biotechnological use. Rational methods of protein stabilization based on optimizing electrostatic interactions have provided some fine successful predictions. However, the precise calculation of stabilization energies remains challenging, one reason being that the electrostatic effects on the unfolded state are often neglected. We have explored here the feasibility of incorporating Poisson-Boltzmann model electrostatic calculations performed on representations of the unfolded state as large ensembles of geometrically optimized conformations calculated using the ProtSA server. Using a data set of 80 electrostatic mutations experimentally tested in two-state proteins, the predictive performance of several such models has been compared to that of a simple one that considers an unfolded structure of non-interacting residues. The unfolded ensemble models, while showing correlation between the predicted stabilization values and the experimental ones, are worse than the simple model, suggesting that the ensembles do not capture well the energetics of the unfolded state. A more attainable goal is classifying potential mutations as either stabilizing or non-stabilizing, rather than accurately calculating their stabilization energies. To implement a fast classification method that can assist in selecting stabilizing mutations, we have used a much simpler electrostatic model based only on the native structure and have determined its precision using different stabilizing energy thresholds. The binary classifier developed finds 7 true stabilizing mutants out of every 10 proposed candidates and can be used as a robust tool to propose stabilizing mutations., We acknowledge financial support from grants BFU2013-47064-P from MINECO (Spain) and Protein Targets group from Diputación General de Aragón, (Spain). We thank J. L. Alonso and N. Cremades for many clarifying discussions.

This work builds on our recently published anisotropic potential for polycyclic aromatic hydrocarbons (PAH) [T.S. Totton, A.J. Misquitta, M. Kraft, J. Chem. Theory Comput. 6 (2010) 683] by developing a new transferable electrostatic model for PAH molecules. Using this model, the atomic charge parameters used in the PAH anisotropic potential may be rapidly calculated from a set of predefined parameters rather than from molecule-specific ab initio calculations. The importance of the out-of-the-plane quadrupolar moments is highlighted and they are used as the basis for an accurate and transferable electrostatic model for PAHs. This model exhibits an r.m.s. deviation of 1.7 kJ mol - 1 - an order of magnitude less than previous models.

Three-dimensional quantitative structure activity relationship (3D-QSAR) studies were performed on Frusectose-1, 6-bisphosphatase (FBPase) inhibitors, based on molecular docking obtained by using GOLD and comparative molecular field analysis (CoMFA). Three random splits into training and test sets had been performed and the high leave-one-out (LOO) cross-validated correlation coefficients q(2) of 0.781, 0.725 and 0.801, respectively, revealed that the models are useful tools for the prediction of test sets as well as newly designed structures against FBPase activity. The superimposed CoMFA models on the receptor site of FBPase are guiding the design of potential inhibitory structures directed against FBPase activity. (C) 2011 Elsevier Masson SAS. All rights reserved.

To study bubble interaction with non-hydrophobic particles an imaging technique has been developed to quantify particle pick up at a pendant bubble by measuring the bubble–particle attachment angle (BPA) made by the particle bed on the bubble. The technique was verified by correlating pick up mass against BPA. Pick up of alumina was shown to correlate with difference in alumina and bubble zeta potential supporting an electrostatic model of interaction with non-hydrophobic particles. Pick up also correlated with contact angle (Washburn method) indicating the electrostatic force is sufficient to establish a solid–air interface.

The temperature dependence of spontaneous polarization and the primary pyroelectric coefficient of stoichiometric lithium niobate crystals are calculated and the specific features of structural ordering of lithium niobate in the ferroelectric phase are analyzed using a modified electrostatic model. The reasons that experimentally observed anomalies of the primary pyroelectric coefficient occur are discussed.

Au/octadecanethiol/GaAs devices were prepared using different metallization conditions: direct deposition at 77 K and 300 K samples, and indirect deposition (Ar backfilling). Time-of-flight secondary ion mass spectrometry data indicate that similar to 4x and similar to 2x more gold penetrates through the SAM after direct deposition at 300 K and 77 K, respectively, than under Ar backfill conditions. However, these devices have significantly different conductances: Ar-backfill and 77 K samples have similar to 200x and similar to 70x, respectively, larger conductances than 300 K devices. An electrostatic model has been developed to explain the very large conductance changes due to small differences in device structure.

Based on an electrostatic model, the energies interaction between substances with different electron structures on one hand, and the LiX, NaX, and KX zeolites, on the other hand, as well as the similarity factors of characteristic adsorption curves of substances, are calculated.

The similarity coefficients of the characteristic adsorption curves were calculated using the electrostatic model for substances with different electronic structures on NaX, CaA, and CaX zeolites and H-chabazite. The initial heats of adsorption on NaX, NaY, CaA, CaX, and CaY zeolites and H-chabazite were calculated for low occupancies.

In the present study a quantitative structure activity relationship (QSAR) analysis was applied to a series of 100 of 7- and 3-substituted 1,4dihydro-4-oxo-1-(2-thiazolyl)-1,8-naphthyridine derivatives. The Chem-X (version 2000) software was used to develop 3D QSAR models. The steric and electrostatic interactions between a probe atom (H þ ) and a set of aligned molecules were assessed using the comparative molecular field analysis method. Statistically relevant models were derived for both electrostatic and steric fields. A 2D model over a restricted series of close structural analogs was derived as well. A number of conclusions on the relationship between the type and size of different substituents and the antitumor activity of the compounds were derived. 2007 Elsevier Masson SAS. All rights reserved.

Various methods to parameterize an exciton model of amide I vibrations are suggested and analyzed. In the spirit of a systematic fragmentation scheme, small model peptides are employed as building-blocks to construct the vibrations of a polypeptide. As an example, extensive density functional theory (DFT) calculations at the B3LYP/6-31+G(d) theoretical level of glycine tripeptide are presented, which serve as reference data for testing various approximate schemes. The combination of a DFT description of next-neighbor interactions via dipeptide building blocks combined with an electrostatic model to account for the long-range interactions appears as a promising approach to achieve spectroscopic accuracy at low computational cost.

Pi-facial diastereoselectivity on a carbonyl group in carbonyl ene reaction has been determined using DFT calculation. The effect produced by the electropositive and electronegative group or atom present at the adjacent center reveals that, the face selectivity on the carbonyl group is guided by Cieplak or electrostatic model. The general acyclic model evolved from this observation can be used for determining the preferred orientation of the substituent on the transition structure of type-II ene cyclization.

A three-dimensional quantitative structure-activity relationship method, the comparative molecular field analysis (CoMFA), was applied to design new anticonvulsant symmetric sulfamides. The training set (27 structures) was comprised by traditional and new-generation anticonvulsant (AC) ligands that exhibit a potent activity in MES test. Physicochemical determinants of binding, such as steric and electrostatic properties, were mapped onto the molecular structures of the set, in order to interpret graphically the CoMFA results in terms of field contribution maps. The 3D-QSAR models demonstrate a good ability to predict the activity of the designed compounds (r(2)=0.967, q(2)=0.756).

A tetravalent uranium compound with a radical azobenzene ligand, namely, [{(SiMe2NPh)3‐tacn}UIV(η2‐N2Ph2.)] (2), was obtained by one‐electron reduction of azobenzene by the trivalent uranium compound [UIII{(SiMe2NPh)3‐tacn}] (1). Compound 2 was characterized by single‐crystal X‐ray diffraction and 1H NMR, IR, and UV/Vis/NIR spectroscopy. The magnetic properties of 2 and precursor 1 were studied by static magnetization and ac susceptibility measurements, which for the former revealed single‐molecule magnet behaviour for the first time in a mononuclear UIV compound, whereas trivalent uranium compound 1 does not exhibit slow relaxation of the magnetization at low temperatures. A first approximation to the magnetic behaviour of these compounds was attempted by combining an effective electrostatic model with a phenomenological approach using the full single‐ion Hamiltonian. FCT. Grant Number: UID/Multi/04349/2013 FCT (Portugal). Grant Numbers: SFRH/BD/84628/2012, SFRH/BPD/74194/2010 FCT (Portugal). Grant Number: PTDC/QEQ‐SUP/1413/2012 FCT (Portugal). Grant Number: RECI/QEQ‐QIN/0189/2012 SPINMOL FP7-ERC-247384 ERC-2014-CoG-647301 DECRESIM MAT2011‐22785 A tetravalent uranium compound with a radical azobenzene ligand, namely, [{(SiMe2NPh)3‐tacn}UIV(η2‐N2Ph2.)] (2), was obtained by one‐electron reduction of azobenzene by the trivalent uranium compound [UIII{(SiMe2NPh)3‐tacn}] (1). Compound 2 was characterized by single‐crystal X‐ray diffraction and 1H NMR, IR, and UV/Vis/NIR spectroscopy. The magnetic properties of 2 and precursor 1 were studied by static magnetization and ac susceptibility measurements, which for the former revealed single‐molecule magnet behaviour for the first time in a mononuclear UIV compound, whereas trivalent uranium compound 1 does not exhibit slow relaxation of the magnetization at low temperatures. A first approximation to the magnetic behaviour of these compounds was attempted by combining an effective electrostatic model with a phenomenological approach using the full single‐ion Hamiltonian.

The origin of local states capable of localizing charge carriers in molecular materials is discussed. The classical electrostatic model is employed to estimate the energies of chemical and structural traps in molecular materials, with particular attention being paid to polycrystalline and amorphous low-molecular weight and polymeric materials

3D-QSAR analysis has been performed on a series of previously synthesized benzonitrile derivatives, which were screened as farnesyltransferase inhibitors, using comparative molecular field analysis (CoMFA) with partial least-square fit to predict the steric and electrostatic molecular field interactions for the activity. The CoMFA study was carried out using a training set of 34 compounds. The predictive ability of the model developed was assessed using a test set of eight compounds (r(pred)(2) as high as 0.770). The analyzed 3D-QSAR CoMFA model has demonstrated a good fit, having r(2) value of 0.991 and cross-validated coefficient q(2) value as 0.619. The analysis of CoMFA contour maps provided insight into the possible modification of the molecules for better activity.

Homolytic bond dissociation energy (BDE) for CH and CX (X = F, Cl, or Br) bonds in polyhalogen methanes was successfully correlated with a two-parameter model describing the repulsion energy of the bonding electron pair with other electrons and its attraction with nuclei, respectively. BDE values for seven molecules were predicted and compared with those calculated by a DFT method. Copyright © 2006 John Wiley & Sons, Ltd.

The range of possible combinations of the components of the electronic-polarizability tensors of oxygen and iodine ions and the effective charges of these ions is established on the basis of the experimental study of the parameters of the electric-field gradient tensor at 7Li nuclei in an α-LiIO3 crystal and the calculation of the electric-field gradient from the classical electrostatic model. The I-O bonds in α-LiIO3 are shown to be mixed ionic-covalent bonds with low ionicity. Spontaneous polarization of the crystal is estimated.

In this paper, a three-center electrostatic model of diatomic bonds was put forward, as well as four physical parameter expressions of effective bonding charges, which support this model. Thus, a semi-empirical method, used to quantitatively study some physical chemistry phenomena, was raised. With the upper method in the article, many theoretical formulas were deduced for such important physical parameters as bond moment, force constant, field gradient and nonlinear optical coefficient of crystals. The available calculated values of every physical parameter basically conformed to its measured magnitude on the condition that parameters were nonadjustable.

The modified electrostatic model is applied to diffusion of 3d to 5d transition metals in nickel and γ-iron. The comparison of experimental and calculated temperature dependence of the diffusion coefficients D permits conclusions with respect to effective charges of the solute atoms. The comparison with the results of diffusion in copper permits the estimation of D(T) for systems where no reliable data are available.

The 3D QSAR analyses of antimalarial alkoxylated and hydroxylated chalcones were first conducted by Comparative molecular field analysis (CoMFA) and Comparative similarity indices analysis (CoMSIA) to determine the factors required for the activity of these compounds. Satisfactory results were obtained after performing a leave-one-out (LOO) cross-validation study with cross-validation q 2 and conventional r 2 values of 0.740 and 0.972 by the CoMFA model, 0.714 and 0.976 by the CoMSIA model, respectively. The results provided the tools for predicting the affinity of related compounds, and for guiding the design and synthesis of novel and more potent antimalarial agents.

A comparative study of effects of Mg2+ ions on specific and competitive binding of the bovine somatotropic hormone (STH) and bovine prolactin (PL) with cells of cow granulosum is carried out. It is found that Mg2+ increases the level of specific binding of 125I-PL with the cells at concentrations from 1 to 70 mM and decreases the level of specific binding of 125I-STH at a concentration of 70 mM. Analysis of the data by Scatchard's method has shown that the decrease of the level of specific binding of 125I-PL in the absence of MgCl2 and 125I-STH at a MgCl2 concentration of 70 mM is caused mainly by a decrease of the number of active binding sites on the cells. Oppositely directed effects of the studied divalent cations on the capability of unlabelled STH (25 µg/ml) and PL (25 µg/ml) for cross-suppression of specific binding of 125I-PL and 125I-STH, respectively, with the granulosum cells have been revealed. At the same time, with increase of Mg2+ ion concentration, the degree of replacement of 125I-STH and 125I-PL with unlabelled STH and PL, respectively, did not change. The obtained results are considered in connection with electrostatic model of participation of the divalent cations in interaction of PL and STH with receptors on cells.

The first hydrolysis constant (pK1h = 9.4) of Ac3+ cations has been determined using 228Ac radiotracer. The pK1h value of Ac3+is compared to the pK1h values of other Group 3 cations. It is shown that, in contrast to the Group 2, 11, 12 and 13, the heaviest member of the Group 3 Ac3+ hydrolyses at less extent than its lighter homologs. The linearity of the log K1h-1/ri (where ri is the ionic radius) function indicates that the electrostatic model of hydrolysis describes well the hydrolysis of Group 3 cations.

The procedure of calculating the effective charges of ions in ABO 3-type ferroelectrics is considered, which is based on the comparison of two experimentally determined quantities: spontaneous polarization in a crystal and the parameters of the tensor of an electric-field gradient at the quadrupolar nuclei of A ions calculated based on the classical electrostatic model. The determined effective charges of ions in an LiNbO3 crystal are considered.

The three-dimensional structures of active derivatives of N-(substitutedphenylcarbonylamino)-4-(1-hydroxymethylphenyl)-1,2,3,6-tetrahydropyri-dines, which have previously been shown to possess anti-inflammatory activities, were built using BIOMEDCAche 5.0 software program. In addition, the three dimensional structures of some of the inactive ones were similarly generated. The conformational analysis, molecular and electronic structures were examined by molecular mechanics and quantum mechanics calculations. The primary objective was to clarify the effects of physicochemical properties of substituents on activity, since the exact role of the substitution pattern on the phenyl ring is uncertain. In addition, the experimental log P values did not appear to have any influence on the anti-inflammatory potencies of these compounds, since compounds having differing lipid solubilities are equiactive. We found that strongly electron-donating group, such as the para-substituted methoxy group, detracts from activity. The conformational analysis indicated that the 4-ethyl derivative had the lowest energy conformation. Except for compound 1, which showed the lowest surface volume, compounds 2-9 had nearly similar surface volumes.

An interesting observation reported that the critical micelle concentrations of an ionic amphiphilic block copolymer increased with the salt concentration. Numerical solutions of the Poisson–Boltzm...

The complexation between uranium(VI) and acetate in 1.05 mol kg−1 NaClO4 was studied at variable temperatures (25, 35, 45, 55 and 70 °C). The formation constants of three successive complexes, UO2(OOCCH3)+, UO2(OOCCH3)2 and UO2(OOCCH3)3−, and the molar enthalpies of complexation were determined by potentiometry and calorimetry. Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS) provided structural information to identify the coordination modes of the acetate in the complexes in solution, which helped to interpret the trends in the enthalpy and entropy of the complexation. The effect of temperature on the stability of the complexes is discussed in terms of the electrostatic model.

A consistent set of atomic electronegativities of main block and d-block transition elements has been obtained from the position and value of the molecular electrostatic potential bond critical point of the C-E bond of a methyl-element-hydride system, H(3)C-EH(n) (E is an element and n = 0, 1, 2, 3, 4, and 5 depending on the position of E in the periodic table). The new scale shows very good agreement with the popular electronegativity scales such as Pauling, Allen, Allred-Rochow, Mulliken, and Sanderson scales of electronegativity, especially for the main block elements. The present scale of electronegativity for transition elements is expected to be more accurate than the previously derived values because of a more consistent approach. Further, the same approach has led to the evaluation of group electronegativities when the hydrogens of E are replaced by other substituent groups. These group electronegativity values are found to correlate well with Inamoto and Mullay scales.

A series of nonempirical intermolecular potentials has been developed for the cyanuric chloride dimer, using the overlap model to determine the anisotropy of the repulsive wall around each atom. Calibration against intermolecular perturbation theory calculations enables the penetration and charge-transfer energy to be explicitly included with the exchange-repulsion to give a simple repulsion model in an anisotropic atom−atom form. These model repulsion potentials are used in conjunction with an atomic multipole electrostatic model and an atom−atom dispersion model to give nonempirical potential models, which are tested for their ability to reproduce the crystal structure of cyanuric chloride. The best nonempirical potential is successfully used to construct a simpler transferable model for closely related azaaromatic chlorides. The nonempirical potential reproduces the experimental space group of cyanuric chloride, unlike some empirically fitted repulsion−dispersion potentials. This first nonempirical rep...

The modified electrostatic model (Neumann and Tolle 1995) is applied to the impurity diffusion in nickel.Z0 = 0.4 is used for the effective charge of the nickel ion.