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Charge Model (charge + model)
Selected Abstracts1H chemical shifts in NMR: Part 22,,Prediction of the 1H chemical shifts of alcohols, diols and inositols in solution, a conformational and solvation investigationMAGNETIC RESONANCE IN CHEMISTRY, Issue 8 2005Raymond J. Abraham Abstract The 1H NMR spectra of a number of alcohols, diols and inositols are reported and assigned in CDCl3, D2O and DMSO- d6 (henceforth DMSO) solutions. These data were used to investigate the effects of the OH group on the 1H chemical shifts in these molecules and also the effect of changing the solvent. Inspection of the 1H chemical shifts of those alcohols which were soluble in both CDCl3 and D2O shows that there is no difference in the chemical shifts in the two solvents, provided that the molecules exist in the same conformation in the two solvents. In contrast, DMSO gives rise to significant and specific solvation shifts. The 1H chemical shifts of these compounds in the three solvents were analysed using the CHARGE model. This model incorporates the electric field, magnetic anisotropy and steric effects of the functional group for long-range protons together with functions for the calculation of the two- and three-bond effects. The long-range effect of the OH group was quantitatively explained without the inclusion of either the CO bond anisotropy or the COH electric field. Differential , and , effects for the 1,2-diol group needed to be included to obtain accurate chemical shift predictions. For DMSO solution the differential solvent shifts were calculated in CHARGE on the basis of a similar model, incorporating two-bond, three-bond and long-range effects. The analyses of the 1H spectra of the inositols and their derivatives in D2O and DMSO solution also gave the ring 1H,1H coupling constants and for DMSO solution the CHOH couplings and OH chemical shifts. The 1H,1H coupling constants were calculated in the CHARGE program by an extension of the cos2, equation to include the orientation effects of electronegative atoms and the CHOH couplings by a simple cos2, equation. Comparison of the observed and calculated couplings confirmed the proposed conformations of myo -inositol, chiro -inositol, quebrachitol and allo -inositol. The OH chemical shifts were also calculated in the CHARGE program. Comparison of the observed and calculated OH chemical shifts and CH. OH couplings suggested the existence of intramolecular hydrogen bonding in a myo -inositol derivative. Copyright © 2005 John Wiley & Sons, Ltd. [source] 1H chemical shifts in NMR.MAGNETIC RESONANCE IN CHEMISTRY, Issue 1 2005Part 2, Prediction of the 1H chemical shifts of molecules containing the ester group: a modelling, ab initio investigation Abstract The 1H NMR spectra of 24 compounds containing the ester group are given and assigned. These data were used to investigate the effect of the ester group on the 1H chemical shifts in these molecules. These effects were analysed using the CHARGE model, which incorporates the electric field, magnetic anisotropy and steric effects of the functional group for long-range protons together with functions for the calculation of the two- and three-bond effects. The effect of the ester electric field was given by considering the partial atomic charges on the three atoms of the ester group. The anisotropy of the carbonyl group was reproduced with an asymmetric magnetic anisotropy acting at the midpoint of the carbonyl bond with values of ,,parl and ,,perp of 10.1 × 10,30 and ,17.1 × 10,30 cm3 molecule,1. An aromatic ring current (=0.3 times the benzene ring current) was found to be necessary for pyrone but none for maleic anhydride. This result was confirmed by GIAO calculations. The observed 1H chemical shifts in the above compounds were compared with those calculated by CHARGE and the ab initio GIAO method (B3LYP/6,31G**). For the 24 compounds investigated with 150 1H chemical shifts spanning a range of ca 10 ppm, the CHARGE model gave an excellent r.m.s. error (obs , calc) of <0.1 ppm. The GIAO calculations gave a very reasonable r.m.s. error of ca 0.2 ppm although larger deviations of ca 0.5 ppm were observed for protons near to the electronegative atoms. The accurate predictions of the 1H chemical shifts given by the CHARGE model were used in the conformational analysis of the vinyl esters methyl acrylate and methyl crotonate. An illustration of the use of the CHARGE model in the prediction of the 1H spectrum of a complex organic molecule (benzochromen-6-one) is also given. Copyright © 2004 John Wiley & Sons, Ltd. [source] Parameterization of charge model 3 for AM1, PM3, BLYP, and B3LYPJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 11 2003Jason D. Thompson Abstract We have recently developed a new Class IV charge model for calculating partial atomic charges in molecules. The new model, called Charge Model 3 (CM3), was parameterized for calculations on molecules containing H, Li, C, N, O, F, Si, S, P, Cl, and Br by Hartree,Fock theory and by hybrid density functional theory (DFT) based on the modified Perdew,Wang density functional with several basis sets. In the present article we extend CM3 to semiempirical molecular orbital theory, in particular Austin Model 1 (AM1) and Parameterized Model 3 (PM3), and to the popular BLYP and B3LYP DFT and hybrid DFT methods, respectively. For the BLYP extension, we consider the 6-31G(d) basis set, and for the B3LYP extension, we consider three basis sets: 6-31G(d), 6-31+G(d), and MIDI!6D. We begin with the previous CM3 strategy, which involves 34 parameters for 30 pairs of elements. We then refine the model to improve the charges in compounds that contain N and O. This modification, involving two new parameters, leads to improved dipole moments for amides, bifunctional H, C, N, O compounds, aldehydes, ketones, esters, and carboxylic acids; the improvement for compounds not containing N results from obtaining more physical parameters for carbonyl groups when the OCN conjugation of amides is addressed in the parameterization. In addition, for the PM3 method, we added an additional parameter to improve dipole moments of compounds that contain bonds between C and N. This additional parameter leads to improved accuracy in the dipole moments of aromatic nitrogen heterocycles with five-membered rings. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 1291,1304, 2003 [source] Adiabatic bond charge model for lattice dynamics of ternary chalcopyrite semiconductorsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 1 2006T. Gürel Abstract The adiabatic bond charge model of Rustagi and Weber is extended to study lattice dynamical properties of ternary chalcopyrite semiconductors AgGaS2, AgGaSe2, CuInS2, CuInSe2, CuGaS2, CuGaSe2, CuAlS2 and CuAlSe2. The new model calculations agree well with the results of Raman/IR and neutron measurements of Brillouin zone center phonon frequencies for both low and high frequency modes which was difficult for other phenomenological lattice dynamical models. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Study of peptide conformation in terms of the ABEEM/MM methodJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 1 2006Zhong-Zhi Yang Abstract The ABEEM/MM model (atom-bond electronegativity equalization method fused into molecular mechanics) is applied to study of the polypeptide conformations. The Lennard,Jones and torsional parameters were optimized to be consistent with the ABEEM/MM fluctuating charge electrostatic potential. The hydrogen bond was specially treated with an electrostatic fitting function. Molecular dipole moments, dimerization energies, and hydrogen bond lengths of complexes are reasonably achieved by our model, compared to ab initio results. The ABEEM/MM fluctuating charge model reproduces both the peptide conformational energies and structures with satisfactory accuracy with low computer cost. The transferability is tested by applying the parameters of our model to the tetrapeptide of alanine and another four dipeptides. The overall RMS deviations in conformational energies and key dihedral angles for four di- or tetrapeptide, is 0.39 kcal/mol and 7.7°. The current results agree well with those by the accurate ab initio method, and are comparable to those from the best existing force fields. The results make us believe that our fluctuating charge model can obtain more promising results in protein and macromolecular modeling with good accuracy but less computer cost. © 2005 Wiley Periodicals, Inc. J Comput Chem 27: 1,10, 2006 [source] Parameterization of charge model 3 for AM1, PM3, BLYP, and B3LYPJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 11 2003Jason D. Thompson Abstract We have recently developed a new Class IV charge model for calculating partial atomic charges in molecules. The new model, called Charge Model 3 (CM3), was parameterized for calculations on molecules containing H, Li, C, N, O, F, Si, S, P, Cl, and Br by Hartree,Fock theory and by hybrid density functional theory (DFT) based on the modified Perdew,Wang density functional with several basis sets. In the present article we extend CM3 to semiempirical molecular orbital theory, in particular Austin Model 1 (AM1) and Parameterized Model 3 (PM3), and to the popular BLYP and B3LYP DFT and hybrid DFT methods, respectively. For the BLYP extension, we consider the 6-31G(d) basis set, and for the B3LYP extension, we consider three basis sets: 6-31G(d), 6-31+G(d), and MIDI!6D. We begin with the previous CM3 strategy, which involves 34 parameters for 30 pairs of elements. We then refine the model to improve the charges in compounds that contain N and O. This modification, involving two new parameters, leads to improved dipole moments for amides, bifunctional H, C, N, O compounds, aldehydes, ketones, esters, and carboxylic acids; the improvement for compounds not containing N results from obtaining more physical parameters for carbonyl groups when the OCN conjugation of amides is addressed in the parameterization. In addition, for the PM3 method, we added an additional parameter to improve dipole moments of compounds that contain bonds between C and N. This additional parameter leads to improved accuracy in the dipole moments of aromatic nitrogen heterocycles with five-membered rings. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 1291,1304, 2003 [source] Separation of dyes using composite carbon membranesAICHE JOURNAL, Issue 7 2009Sonny Sachdeva Abstract A composite, clay supported carbon membrane has been synthesized by carbonization of a blend of polyethylene glycol and phenol formaldehyde resin and the membrane thus obtained is characterized by separation of dyes. This membrane is subjected to permeability test using pure water which is found to be considerably higher than that reported in literature. It is subsequently shown to reject Acid Orange 7 dye from water with the rejection dependent on pressure and concentration of the dye which is typical phenomenon observed for a charged membrane. The separation data has been analyzed using the Space charge model and the membrane charge is estimated by minimizing the root mean square error between the experimental results and those calculated from the model. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] THE PALEOCENE SANDY SIRI FAIRWAY: AN EFFICIENT "PIPELINE" DRAINING THE PROLIFIC CENTRAL GRABEN?JOURNAL OF PETROLEUM GEOLOGY, Issue 1 2006S.E. Ohm A new petroleum charge model is presented for the sand-dominated Paleocene channel system known as the Siri Fairway in the Central Graben of the North Sea. The Siri Fairway is located in the platform area along the Danish - Norwegian border and extends from the Norwegian palaeo shelf into the Tail-End Graben and Søgne Basin. The nearest known expelling source rocks are located in the Central Graben. The discovery of the Siri oilfield and later the Cecilie and the Nini fields proves that petroleum has migrated through these Paleocene sandstones for up to 70 km, which is a considerable distance in the North Sea. If the Siri Fairway has acted as a "pipeline" for petroleum migrating from the Graben to the platform area, the chemical composition of the hydrocarbons discovered in the Graben and within the Fairway itself should be similar in terms of maturity and organic facies signature. This study shows this not to be the case. The Graben oils have a mature signature, whereas the oils from the Siri field have an early mature signature and are mixed with biogenic gas generated in situ. The biogenic gas "signature", which was inherited from gas which accumulated in the trap before the arrival of the oil charge, should have disappeared if petroleum had continuously been introduced to the Fairway. It therefore appears that hydrocarbon charging to the Fairway ceased for some reason before the source rocks in the Graben entered the main oil window; the Siri Fairway therefore represents an aborted migration route, and limited charging of the Paleocene sandstone deposits in the platform has occurred. The chemical composition of the oils from the Siri field indicates that the Fairway was charged from two different basins with different subsidence histories. The Siri-2 trap is thus interpreted to have been filled with the same oil as that found in Siri-1 and Siri-3, but this oil was later partly displaced by oil generated in a shallower sub-basin. The sandstones in the Siri Fairway were deposited as turbidites and/or gravity slides in the Late Paleocene, and consist of stacked interfingering sandstone lobes which are encased to varying degrees in fine-grained sediments. Although long distance migration through the sandstones has been proved to occur, connectivity between individual sandlobes may be problematic. The number of dry wells drilled in the Fairway and the early-mature character of the analysed oils, together with the general absence of more mature later petroleum, indicate that migration routes in this region are limited and difficult to predict. [source] Cation Ordering and Domain Boundaries in Ca[(Mg1/3Ta2/3)1,xTix]O3 Microwave Dielectric CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2008Mao Sen Fu Cation ordering and domain boundaries in perovskite Ca[(Mg1/3Ta2/3)1,xTix]O3 (x=0.1, 0.2, 0.3) microwave dielectric ceramics were investigated by high-resolution transmission electron microscopy (HRTEM) and Rietveld analysis. The variation of ordering structure with Ti substitution was revealed together with the formation mechanism of ordering domains. When x=0.1, the ceramics were composed of 1:2 and 1:1 ordered domains and a disordered matrix. The 1:2 cation ordering could still exist until x=0.2 but the 1:1 ordering disappeared. Neither 1:2 nor 1:1 cation ordering could exist at x=0.3. The space charge model was used to explain the cation ordering change from 1:2 to 1:1 and then to disorder. A comparison between the space charge model and random layer model was also conducted. HRTEM observations showed an antiphase boundary inclined to the (111)c plane with a projected displacement vector in the ,001,c direction and ferroelastic domain boundaries parallel to the ,100,c direction. [source] 7Li and 13C solid-state NMR spectra of lithium cuprates,MAGNETIC RESONANCE IN CHEMISTRY, Issue 10 2006Steffen Jost Abstract 7Li and 13C solid-state MAS NMR spectra of three lithium cuprates with known X-ray structures,lithium([12]crown-4)2 dimethyl and diphenyl cuprate (1,2) and lithium(thf)4 -[tris(trimethylsilyl) methyl]2 cuprate (3),have been measured and analysed with respect to the quadrupolar coupling constants of lithium-7, ,(7Li), and the asymmetry parameters of the quadrupolar interactions, ,(7Li), as well as the 6, 7Li and 13C chemical shifts. The ,(7Li) values of 23, 30, and 18 kHz for 1, 2 and 3, respectively, are in line with the high symmetry around the lithium nucleus in the solvent-separated structures and may be used as reference data for this structural motif. Calculations based on charges derived from ab initio 6-31 G* HF computations using the point charge model (PCM) and the program GAMESS support the experimental findings. Copyright © 2006 John Wiley & Sons, Ltd. [source] 1H chemical shifts in NMR: Part 23,, the effect of dimethyl sulphoxide versus chloroform solvent on 1H chemical shiftsMAGNETIC RESONANCE IN CHEMISTRY, Issue 5 2006Raymond J. Abraham Abstract The 1H chemical shifts of 124 compounds containing a variety of functional groups have been recorded in CDCl3 and DMSO- d6 (henceforth DMSO) solvents. The 1H solvent shift ,, = ,(DMSO) , ,(CDCl3) varies from ,0.3 to +4.6 ppm. This solvent shift can be accurately predicted (rms error 0.05 ppm) using the charge model of ,, ,, , and long-range contributions. The labile protons of alcohols, acids, amines and amides give both, the largest solvent shifts and the largest errors. The contributions for the various groups are tabulated and it is shown that for H.C.C.X ,-effects (X = OH, NH, O, NH.CO) there is a dihedral angle dependence of the ,-effect. The group contributions are discussed in terms of the possible solvent,solute interactions. For protic hydrogens, hydrogen bonding is the dominant interaction, but for the remaining protons solvent anisotropy and electric field effects appear to be the major factors. Copyright © 2006 John Wiley & Sons, Ltd. [source] | ||||||||||