201
|
Zhao Z, Rogers DM, Beck TL. Polarization and charge transfer in the hydration of chloride ions. J Chem Phys 2010; 132:014502. [DOI: 10.1063/1.3283900] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|
202
|
Electrostatic origin towards the reversal of π-facial selectivity of 5,6-cis,exo-disubstituted bicyclic[2.2.2]oct-2-enes with m-chloroperbenzoic acid and diazomethane: a computational study. Tetrahedron Lett 2010. [DOI: 10.1016/j.tetlet.2009.10.100] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
203
|
Xu Q, Liu D, Yang Q, Zhong C, Mi J. Li-modified metal–organic frameworks for CO2/CH4separation: a route to achieving high adsorption selectivity. ACTA ACUST UNITED AC 2010. [DOI: 10.1039/b912407a] [Citation(s) in RCA: 108] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
|
204
|
Milani A, Castiglioni C. Modeling of Molecular Charge Distribution on the Basis of Experimental Infrared Intensities and First-Principles Calculations: The Case of CH Bonds. J Phys Chem A 2009; 114:624-32. [DOI: 10.1021/jp908146d] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Alberto Milani
- Politecnico di Milano - Dip. Chimica, Materiali e Ing. Chimica “G. Natta”, P.zza Leonardo da Vinci 32, I-20133 Milano, Italy
| | - Chiara Castiglioni
- Politecnico di Milano - Dip. Chimica, Materiali e Ing. Chimica “G. Natta”, P.zza Leonardo da Vinci 32, I-20133 Milano, Italy
| |
Collapse
|
205
|
Beran GJO. Approximating quantum many-body intermolecular interactions in molecular clusters using classical polarizable force fields. J Chem Phys 2009; 130:164115. [PMID: 19405569 DOI: 10.1063/1.3121323] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Many-body intermolecular interaction expansions provide a promising avenue for the efficient quantum mechanical treatment of molecular clusters and condensed-phase systems, but the computationally expensive three-body and higher terms are often nontrivial. When polar molecules are involved, these many-body terms are typically dominated by electrostatic induction effects, which can be approximated relatively easily. We demonstrate an accurate and inexpensive hybrid quantum/classical model in which one- and two-body interactions are computed quantum mechanically, while the many-body induction effects are approximated with a simple classical polarizable force field. Whereas typical hybrid quantum/classical models partition a system spatially into distinct quantum and classical regions, the model demonstrated here partitions based on the order in the many-body interaction series. This enables a spatially homogeneous treatment of the entire system, which could prove advantageous in studying a wide range of condensed-phase molecular systems.
Collapse
Affiliation(s)
- Gregory J O Beran
- Department of Chemistry, University of California, Riverside, California 92521, USA.
| |
Collapse
|
206
|
Swanson JMJ, Simons J. Role of charge transfer in the structure and dynamics of the hydrated proton. J Phys Chem B 2009; 113:5149-61. [PMID: 19309128 PMCID: PMC2680231 DOI: 10.1021/jp810652v] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Although it has long been recognized that multiple water molecules strongly associate with an extra proton in bulk water, some models and conceptual frameworks continue to utilize the classical hydronium ion (H(3)O(+)) as a fundamental building block. In this work, the nature of the hydronium ion in aqueous systems is examined using an ab initio energy decomposition analysis (EDA) that evaluates both the magnitude of and energetic stabilization due to charge transfer among H(3)O(+) and the surrounding water molecules. The EDA is performed on structures extracted from dynamical bulk-phase simulations and used to determine how frequently the pure hydronium ion, where the excess charge is primarily localized on H(3)O(+), occurs under dynamic conditions. The answer is essentially never. The energetic stabilization of H(3)O(+) due to charge delocalization to neighboring water molecules is found to be much larger (16-49 kcal/mol) than for other ions (even Li(+)) and to constitute a substantial portion (20-52%) of the complex's binding energy. The charge defect is also shown to have intrinsic dynamical asymmetry and to display dynamical signatures that can be related to features appearing in IR spectra.
Collapse
Affiliation(s)
- Jessica M J Swanson
- Henry Eyring Center for Theoretical Chemistry, University of Utah, Department of Chemistry, 315 South 1400 East Room 2020, Salt Lake City, Utah 84112-0850, USA.
| | | |
Collapse
|
207
|
Schwöbel J, Ebert RU, Kühne R, Schüürmann G. Prediction of the Intrinsic Hydrogen Bond Acceptor Strength of Organic Compounds by Local Molecular Parameters. J Chem Inf Model 2009; 49:956-62. [DOI: 10.1021/ci900040z] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Johannes Schwöbel
- UFZ Department of Ecological Chemistry, Helmholtz Centre for Environmental Research, Permoserstrasse 15, 04318 Leipzig, Germany, and Institute for Organic Chemistry, Technical University Bergakademie Freiberg, Leipziger Strasse 29, 09596 Freiberg, Germany
| | - Ralf-Uwe Ebert
- UFZ Department of Ecological Chemistry, Helmholtz Centre for Environmental Research, Permoserstrasse 15, 04318 Leipzig, Germany, and Institute for Organic Chemistry, Technical University Bergakademie Freiberg, Leipziger Strasse 29, 09596 Freiberg, Germany
| | - Ralph Kühne
- UFZ Department of Ecological Chemistry, Helmholtz Centre for Environmental Research, Permoserstrasse 15, 04318 Leipzig, Germany, and Institute for Organic Chemistry, Technical University Bergakademie Freiberg, Leipziger Strasse 29, 09596 Freiberg, Germany
| | - Gerrit Schüürmann
- UFZ Department of Ecological Chemistry, Helmholtz Centre for Environmental Research, Permoserstrasse 15, 04318 Leipzig, Germany, and Institute for Organic Chemistry, Technical University Bergakademie Freiberg, Leipziger Strasse 29, 09596 Freiberg, Germany
| |
Collapse
|
208
|
Choi Y, Kim H, Cho KW, Paik SR, Kim HW, Jeong K, Jung S. Systematic probing of an atomic charge set of sialic acid disaccharides for the rational molecular modeling of avian influenza virus based on molecular dynamics simulations. Carbohydr Res 2009; 344:541-4. [DOI: 10.1016/j.carres.2008.12.018] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2008] [Revised: 12/19/2008] [Accepted: 12/23/2008] [Indexed: 11/26/2022]
|
209
|
Hulkko E, Kiljunen T, Kiviniemi T, Pettersson M. From monomer to bulk: appearance of the structural motif of solid iodine in small clusters. J Am Chem Soc 2009; 131:1050-6. [PMID: 19123809 DOI: 10.1021/ja806537u] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Formation of iodine clusters in a solid krypton matrix was studied using resonance Raman spectroscopy with a 1 cm(-1) resolution. The clusters were produced by annealing of the solid and recognized by appearance of additional spectral transitions. Two distinct regions, red-shifted from the fundamental vibrational wavenumber of the isolated I(2) at 211 cm(-1), were observed in the signal. The intermediate region spans the range 196-208 cm(-1), and the ultimate region consists of two peaks at 181 and 190 cm(-1) nearly identical to crystalline I(2). The experimental results were compared to DFT-D level electronic structure calculations of planar (I(2))(n) clusters (n = 1-7). The dimer, trimer, and tetramer structures, where the I(2) molecule is complexed from one end, were found to exhibit vibrational shifts corresponding to the intermediate size clusters. The larger, bulklike shift appears when the iodine molecule is coordinated from two opposite directions as in the case of a pentamer and higher clusters. Starting from the pentamer, the structural motif of crystalline iodine is clearly recognized in the clusters.
Collapse
Affiliation(s)
- Eero Hulkko
- Nanoscience Center, Department of Chemistry, P.O. Box 35, FI-40014 University of Jyvaskyla, Finland
| | | | | | | |
Collapse
|
210
|
Chou HH, Lin YC, Huang SL, Liu YH, Wang Y. Reactions of Ruthenium Acetylide and Vinylidene Complexes Containing a 2-Pyridyl Group. Organometallics 2008. [DOI: 10.1021/om800253e] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Hsien-Hsin Chou
- Department of Chemistry, National Taiwan University, Taipei, Taiwan 106, Republic of China
| | - Ying-Chih Lin
- Department of Chemistry, National Taiwan University, Taipei, Taiwan 106, Republic of China
| | - Shou-Ling Huang
- Department of Chemistry, National Taiwan University, Taipei, Taiwan 106, Republic of China
| | - Yi-Hong Liu
- Department of Chemistry, National Taiwan University, Taipei, Taiwan 106, Republic of China
| | - Yu Wang
- Department of Chemistry, National Taiwan University, Taipei, Taiwan 106, Republic of China
| |
Collapse
|
211
|
|
212
|
Puibasset J, Pellenq RJM. Grand Canonical Monte Carlo Simulation Study of Water Adsorption in Silicalite at 300 K. J Phys Chem B 2008; 112:6390-7. [DOI: 10.1021/jp7097153] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- Joël Puibasset
- Centre de Recherche sur la Matière Divisée, CNRS-Université d’Orléans, 1b, rue de la Ferollerie, 45071 Orléans cedex 02, France, and Centre de Recherche en Matière Condensée et Nanosciences, CNRS, Campus de Luminy, case 913, 13288 Marseille cedex 09, France
| | - Roland J.-M. Pellenq
- Centre de Recherche sur la Matière Divisée, CNRS-Université d’Orléans, 1b, rue de la Ferollerie, 45071 Orléans cedex 02, France, and Centre de Recherche en Matière Condensée et Nanosciences, CNRS, Campus de Luminy, case 913, 13288 Marseille cedex 09, France
| |
Collapse
|
213
|
Chai L, Goldberg R, Kampf N, Klein J. Selective adsorption of poly(ethylene oxide) onto a charged surface mediated by alkali metal ions. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2008; 24:1570-1576. [PMID: 18062712 DOI: 10.1021/la702514j] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Using a surface force balance, we have measured normal and shear interactions between mica surfaces across pure water and across 0.1 M aqueous solutions of LiNO3, NaNO3, KNO3, and CsNO3, both prior to adding polymer and following addition of 1.5 x 10(-4) w/w poly(ethylene oxide) (PEO, Mw = 170 kD) and overnight incubation. Our results reveal that while the PEO adsorbs strongly from the KNO3 and CsNO3 solutions, unexpectedly it does not adsorb at all from the LiNO3 and NaNO3 salt solutions. We attribute this to the different nature of the hydration layers about the alkali metal ions: these favor liganding to the negatively charged mica surface of the etheric -O- group on the ethylene oxide monomer for the case of the more weakly hydrated K+ and Cs+, but not for the case of Na+ or Li+ with their more strongly bound water. A simple model relating the electrostatic energy changes occurring upon such liganding to the experimentally measured hydration energies of the different alkali metal ions supports this attribution.
Collapse
Affiliation(s)
- Liraz Chai
- Materials and Interfaces Department, Weizmann Institute of Science, Rehovot, Israel
| | | | | | | |
Collapse
|
214
|
Chiş V, Pîrnău A, Vasilescu M, Varga RA, Oniga O. X-ray, 1H NMR and DFT study on 5-para-X-benzylidene-thiazolidine derivatives with X=Br, F. ACTA ACUST UNITED AC 2008. [DOI: 10.1016/j.theochem.2007.10.041] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
|
215
|
Favre S, Vogel P, Gerber-Lemaire S. Recent synthetic approaches toward non-anomeric spiroketals in natural products. Molecules 2008; 13:2570-600. [PMID: 18927519 PMCID: PMC6245442 DOI: 10.3390/molecules13102570] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2008] [Revised: 09/29/2008] [Accepted: 10/15/2008] [Indexed: 11/16/2022] Open
Abstract
Many natural products of biological interest contain [6,5]- and [6,6]-spiroketal moieties that can adopt various configurations, benefiting or not from anomeric conformation stabilizing effects. The spiroketal fragments are often important for the biological activity of the compounds containing them. Most stable spiroketal stereoisomers, including those benefiting from conformational anomeric effects (gauche conformers can be more stable than anti conformers because of a contra-steric stabilizing effect), are obtained easily under acidic conditions that permit acetal heterolysis (formation of tertiary oxycarbenium ion intermediates). The synthesis of less stable stereoisomers requires stereoselective acetal forming reactions that do not permit their equilibration with their most stable stereoisomers or, in the case of suitably substituted derivatives, concomitant reactions generating tricyclic products that quench the less stable spiroketal conformers. Ingenuous approaches have been recently developed for the synthesis of naturally occurring [6,6]- and [5,6]-nonanomeric spiroketals and analogues. The identification of several parameters that can influence the stereochemical outcome of spirocyclization processes has led to seminal improvements in the selective preparation of the non-anomeric isomers that are discussed herein. This review also gives an up-dated view of conformational anomeric effect which represents a small fraction of the enthalpic anomeric effect that makes gem-dioxy substituted compounds much more stable that their 1,n-dioxy substituted isomers (n > 1). Although models assuming sp3-hybridized oxygen atoms have been very popular (rabbit ears for the two non-bonding electron pairs of oxygen atom), sp2-hybridized oxygen atoms are used to describe the conformational anomeric effect.
Collapse
Affiliation(s)
| | | | - Sandrine Gerber-Lemaire
- Laboratory of Glycochemistry and Asymmetric Synthesis, Ecole Polytechnique Fédérale de Lausanne, Batochime, CH-1015 Lausanne, Switzerland
| |
Collapse
|
216
|
Abstract
The block-localized wave function (BLW) method is a variant of ab initio valence bond method but retains the efficiency of molecular orbital methods. It can derive the wave function for a diabatic (resonance) state self-consistently and is available at the Hartree-Fock (HF) and density functional theory (DFT) levels. In this work we present a two-state model based on the BLW method. Although numerous empirical and semiempirical two-state models, such as the Marcus-Hush two-state model, have been proposed to describe a chemical reaction process, the advantage of this BLW-based two-state model is that no empirical parameter is required. Important quantities such as the electronic coupling energy, structural weights of two diabatic states, and excitation energy can be uniquely derived from the energies of two diabatic states and the adiabatic state at the same HF or DFT level. Two simple examples of formamide and thioformamide in the gas phase and aqueous solution were presented and discussed. The solvation of formamide and thioformamide was studied with the combined ab initio quantum mechanical and molecular mechanical Monte Carlo simulations, together with the BLW-DFT calculations and analyses. Due to the favorable solute-solvent electrostatic interaction, the contribution of the ionic resonance structure to the ground state of formamide and thioformamide significantly increases, and for thioformamide the ionic form is even more stable than the covalent form. Thus, thioformamide in aqueous solution is essentially ionic rather than covalent. Although our two-state model in general underestimates the electronic excitation energies, it can predict relative solvatochromic shifts well. For instance, the intense pi-->pi* transition for formamide upon solvation undergoes a redshift of 0.3 eV, compared with the experimental data (0.40-0.5 eV).
Collapse
Affiliation(s)
- Yirong Mo
- Department of Chemistry, Western Michigan University, Kalamazoo, Michigan 49008, USA.
| |
Collapse
|
217
|
Aparicio S. Computational Study on the Properties and Structure of Methyl Lactate. J Phys Chem A 2007; 111:4671-83. [PMID: 17489567 DOI: 10.1021/jp070841t] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
A theoretical study on the properties and molecular level structure of the very important green solvent methyl lactate is carried out in the gas phase and methanol and water solutions, with the solvent treated both explicitly and as a continuum. Torsional barriers giving rise to different conformers by rotation of the hydroxyl and methyl groups were analyzed using density functional theory (DFT) to establish the most stable conformer both in gas phase and solution. DFT computations on lactate dimers were also done to study short-range features, and the effect of the surrounding solvent on intra- and intermolecular hydrogen bonding was analyzed according to the polarizable continuum model approach. We have also studied lactate/water and lactate/methanol small clusters together with the corresponding binding energies. Moreover, classical molecular dynamics simulations (MD) were carried out to study medium- and large-range effects at lower computational cost. MD simulations at different pressure and temperature conditions on pure lactate were carried out, and mixtures with water and methanol of different compositions were also studied. Structural information, analyzed through the radial distribution functions, together with dynamic aspects of pure and mixed fluids were considered. The intramolecular hydrogen bonding ability of methyl lactate together with the possibility of homo- and hetero-intermolecular association determines the behavior of this molecule in pure fluids or in mixed.
Collapse
Affiliation(s)
- Santiago Aparicio
- Departamento de Química, Universidad de Burgos, 09001 Burgos, Spain.
| |
Collapse
|
218
|
Hu H, Lu Z, Yang W. Fitting Molecular Electrostatic Potentials from Quantum Mechanical Calculations. J Chem Theory Comput 2007; 3:1004-13. [DOI: 10.1021/ct600295n] [Citation(s) in RCA: 106] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Hao Hu
- Department of Chemistry, Duke University, Durham, North Carolina 27709
| | - Zhenyu Lu
- Department of Chemistry, Duke University, Durham, North Carolina 27709
| | - Weitao Yang
- Department of Chemistry, Duke University, Durham, North Carolina 27709
| |
Collapse
|
219
|
Kemnitz CR, Loewen MJ. “Amide Resonance” Correlates with a Breadth of C−N Rotation Barriers. J Am Chem Soc 2007; 129:2521-8. [PMID: 17295481 DOI: 10.1021/ja0663024] [Citation(s) in RCA: 202] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Complete basis set calculations (CBS-QB3) were used to compute the CN rotation barriers for acetamide and eight related compounds, including acetamide enolate and O-protonated acetamide. Natural resonance theory analysis was employed to quantify the "amide resonance" contribution to ground-state electronic structures. A range of rotation barriers, spanning nearly 50 kcal/mol, correlates well to the ground-state resonance weights without the need to account for transition-state effects. Use of appropriate model compounds is crucial to gain an understanding of the structural and electronic changes taking place during rotation of the CN bond in acetamide. The disparate changes in bond length (DeltarCO << DeltarCN) are found to be consonant with the resonance model. Similarly, charge differences are consistent with donation from the nitrogen lone pair electrons into the carbonyl pi* orbital. Despite recent attacks on the resonance model, these findings demonstrate it to be a sophisticated and highly predictive tool in the chemist's arsenal.
Collapse
Affiliation(s)
- Carl R Kemnitz
- Department of Chemistry, California State University-Bakersfield, 9001 Stockdale Highway, Bakersfield, CA 93311, USA.
| | | |
Collapse
|
220
|
Komeiji Y, Ishida T, Fedorov DG, Kitaura K. Change in a protein's electronic structure induced by an explicit solvent: Anab initio fragment molecular orbital study of ubiquitin. J Comput Chem 2007; 28:1750-62. [PMID: 17340606 DOI: 10.1002/jcc.20686] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The effect of solvation on the electronic structure of the ubiquitin protein was analyzed using the ab initio fragment molecular orbital (FMO) method. FMO calculations were performed for the protein in vacuo, and the protein was immersed in an explicit solvent shell as thick as 12 A at the HF or MP2 level by using the 6-31G* basis set. The protein's physical properties examined were the net charge, the dipole moment, the internal energy, and the solvent interaction energy. Comparison of the computational results revealed the following changes in the protein upon solvation. First, the positively charged amino acid residues on the protein surface drew electrons from the solvent, while the negatively charged ones transfer electrons to the solvent. Second, the dipole moment of the protein was enhanced as a result of the polarization. Third, the internal energy of the protein was destabilized, but the destabilization was more than compensated for by the generation of a favorable protein-solvent interaction. Finally, the energetic changes were elicited both by the electron correlation effect of the first solvent shell and by the electrostatic effect of more distant solvent molecules. These findings were consistent with the picture of the solvated protein being a polarizable molecule dissolved in a dielectric media.
Collapse
Affiliation(s)
- Yuto Komeiji
- Research Institute for Computational Sciences, AIST Tsukuba Central 2, Tsukuba 305-8568, Japan.
| | | | | | | |
Collapse
|
221
|
Mrázek J, Burda JV. Can the pH value of water solutions be estimated by quantum chemical calculations of small water clusters? J Chem Phys 2006; 125:194518. [PMID: 17129134 DOI: 10.1063/1.2363383] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
In the study, various water clusters were explored from the point of view of the proton transfer between H-bonded neighbors. A relatively modest approach--the MP26-31++G(d,p) level--was chosen as acceptable considering the fact that also larger systems have to be included. The tight ion-pair model (with usually three fixed O-O distances) was adopted for the autodissociation process. First, cluster-estimated pH values rapidly decrease as cluster size increases from 2 to 6. For larger clusters in gas phase, the topology of H bonds plays an important role, varying pH from 7 to 13 in hexamers and from 5 to 15 in octamer clusters. The relationship energy/distance was quantified, too. Enhancing our model with the conductorlike screening model (COSMO) approach brought significant improvement in description of the autodissociation reaction with a stable zwitterionic structure. However, when the O-O restrictions were released, the small barrier for backward reaction disappeared, reforming neutral cluster spontaneously. Also Boltzmann weighting procedure was applied, and for the explored clusters in vacuo, the series of pH 25-18-14-13-10 was obtained for cluster sizes n=2, 3, 4, 6, 8. Using the COSMO approach, the analogous series is 15-14-12-10-9. The limit of the series is still about two to three units above the experimentally known pH. In order to reach the size-independent (bulk) value, larger clusters are needed. However, the situation is far from hopeless since (as it was proven in the study) four-coordinated molecules are not involved in the proton transfer process directly; they can only be a part of the surrounding environment.
Collapse
Affiliation(s)
- Jirí Mrázek
- Department of Chemical Physics and Optics, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, 121 16 Prague 2, Czech Republic
| | | |
Collapse
|
222
|
Palusiak M, Rudolf B, Zakrzewski J, Pfitzner A, Zabel M, Grabowski SJ. Intramolecular carbonyl⋯carbonyl interactions in W, Mo and Fe complexes containing the η1-N-maleimidato ligand: X-ray, DFT and AIM studies. J Organomet Chem 2006. [DOI: 10.1016/j.jorganchem.2006.03.035] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
|
223
|
Van Speybroeck V, Moonen K, Hemelsoet K, Stevens CV, Waroquier M. Unexpected Four-Membered over Six-Membered Ring Formation during the Synthesis of Azaheterocyclic Phosphonates: Experimental and Theoretical Evaluation. J Am Chem Soc 2006; 128:8468-78. [PMID: 16802812 DOI: 10.1021/ja0584119] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The cyclization of functionalized aminophosphonates is studied on both experimental and theoretical grounds. In a recently described route to phosphono-beta-lactams [Stevens C. V.; Vekemans, W.; Moonen, K.; Rammeloo, T. Tetrahedron Lett. 2003, 44, 1619], it was found that starting from an ambident allylic anion only four-membered rings were formed without any trace of six-membered lactams. New anion trapping experiments revealed that the gamma-anion is highly reactive in intermolecular reactions. Ab initio calculations predict higher reaction barriers for the gamma-anion due to restricted rotation about the C-N bond and due to highly strained transition states during ring closure. The sodium or lithium counterion, explicit dimethyl ether solvent molecules, and bulk solvent effects were properly taken into account at various levels of theory.
Collapse
|
224
|
Charges derived from electrostatic potentials: Exploring dependence on theory and geometry optimization levels for dipole moments. Chem Phys Lett 2005. [DOI: 10.1016/j.cplett.2005.04.075] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|