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Theoretical Investigation (theoretical + investigation)
Selected AbstractsA THEORETICAL INVESTIGATION OF SYMPATRIC EVOLUTION OF TEMPORAL REPRODUCTIVE ISOLATION AS ILLUSTRATED BY MARINE BROADCAST SPAWNERSEVOLUTION, Issue 11 2007Maurizio Tomaiuolo Recent theory suggests that frequency-dependent disruptive selection in combination with assortative mating can lead to the establishment of reproductive isolation in sympatry. Here we explore how temporal variation in reproduction might simultaneously generate both disruptive selection and assortative mating, and result in sympatric speciation. The conceptual framework of the model may be applicable to biological systems with negative frequency-dependent selection, such as marine broadcast spawners or systems with pollinator limitation. We present a model that is motivated by recent findings in marine broadcast spawners and is parameterized with data from the Montastraea annularis species complex. Broadcast spawners reproduce via external fertilization and synchronous spawning is required to increase the probability of successful fertilization, but empirical evidence shows that as density increases, so does the risk of polyspermy. Polyspermy is the fusion of multiple sperm with an egg at fertilization, a process that makes the embryo unviable. Synchrony can therefore also act as a source of negative density-dependent disruptive selection. Model analysis shows that the interaction between polyspermy and spawning synchrony can lead to temporal reproductive isolation in sympatry and that, more generally, increased density promotes maintenance of genetic variation. [source] A Theoretical Investigation of Substituent Effects on the Absorption and Emission Properties of a Series of Terpyridylplatinum(II) Acetylide ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 10 2005Xiao-Juan Liu Abstract A comprehensive calculational investigation has been carried out on a series of complexes of the type [(terpyridyl-R1)Pt(C,C-R2)], where terpyridyl-R1 is a series of substituted 2,2':6',2"-terpyridyl ligands and C,C-R2 is a series of substituted acetylide ligands. In one series of complexes (I), the energy of the electronic excited state is varied by changing the substituents on the terpyridyl ligand (R1). In a second series of complexes (II), this electronic structure variation is obtained by changing the para substituents (R2) of the acetylide ligand. The effect of varying the substituents on the lowest-energy excited states of the complexes has been assessed by calculating their electronic structures and excitation energies. We anticipated that introduction of electron-withdrawing substituents on the terpyridyl ligand will benefit the LLCT (or MLCT) and prohibit the nonradiative pathways via d-d transitions in these complexes; introduction of electron-donating substituents on the acetylide ligand can also prohibit the nonradiative pathways by increasing the energy gaps between the HOMO,LUMO and d-d transitions. The results also reveal that the lowest-energy excitations of all complexes of series I and IIa,b complexes are dominated by a ,(C,C),,,,*(terp) (LLCT) transition mixed with some energetically d,(Pt),,,terpyridyl (MLCT) transition. However, for the complexes IIc,IId, in which phenyl rings are introduced on the acetylide ligand, the lowest-lying absorptions of IIc and IId are predominately LLCT in character, with less MLCT mixture, due to a lower contribution of the Pt(d) orbital to the HOMO, while for IIe, with a stronger donor on the acetylide, the lowest-lying absorption is completely LLCT in character. The absorption and emission calculations using the TDDFT method are based on the optimized geometries obtained at the B3LYP/LanL2DZ and CIS/LanL2DZ levels, respectively. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Computational NMR Spectroscopy of Transition-Metal/Nitroimidazole Complexes: Theoretical Investigation of Potential RadiosensitizersHELVETICA CHIMICA ACTA, Issue 10 2005Teodorico The computed chemical shifts of transition-metal complexes with dimetridazole (=,1,2-dimethyl-5-nitro-1H -imidazole; 1), a prototypical nitro-imidazole-based radiosensitizer, are reported at the GIAO-BP86 and -B3LYP levels for BP86/ECP1-optimized geometries. These complexes comprise [MCl2(1)2] (M,=,Zn, Pd, Pt), [RuCl2(DMSO)2(1)2], and [Rh2(O2CMe)4(1)2]. Available ,(1H) and ,(15N) values, and ,,(1H) and ,,(15N) coordination shifts are well-reproduced theoretically, provided solvation and relativistic effects are taken into account by means of a polarizable continuum model and suitable methods including spin,orbit (SO) coupling, respectively. These effects are particularly important for the metal-coordinated N-atom, where the contributions from solvation and relativity can affect ,(15N) and ,,(15N) values up to 10,20,ppm. The 195Pt chemical shifts of cis - and trans -[PtCl2(1)2] are well-reproduced using the zero-order regular approximation including SO coupling (ZORA-SO). Predictions are reported for 99Ru and 103Rh chemical shifts, which suggest that these metal centers could be used as additional, sensitive NMR probes in their complexes with nitro-imidazoles. [source] Theoretical Investigation of Heat Transfer in Glass FormingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2001Raymond Viskanta A theoretical study to investigate internal heat transfer in glass undergoing cooling between glass and mold, as well as plunger, during and after pressing, is described. A thermal model has been formulated to simulate the cooling. The heat-transfer analysis accounts for the spectral nature of radiation in glass, the dependence of the thermophysical properties of glass on temperature, and the contact heat transfer between and after pressing, as well as subsequent cooling. Heat exchange between glass and mold by contact conduction across a very small gap and that by thermal radiation are considered separately. Numerical solutions have been obtained for typical conditions simulating symmetric and nonsymmetric cooling, and the results obtained are presented and discussed. During the dwell time, thermal-contact conduction between glass and mold is the dominant mechanism for heat extraction from glass. Results show that radiation from the surface of the glass plays a relatively small role in the heat extraction from the glass, but that radiation from the interior of the glass is much more significant. [source] ChemInform Abstract: Theoretical Investigation of Clusters of Phosphorus and Arsenic: Fascination and Temptation of High Symmetries.CHEMINFORM, Issue 30 2008Paola Nava Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Theoretical Investigation on the Electronic and Geometric Structure of GaN2+ and GaN4+CHEMINFORM, Issue 49 2007Demeter Tzeli Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Theoretical Investigation of the Electronically Excited States of Chlorine HydrateCHEMINFORM, Issue 43 2007Daniel P. Schofield Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Theoretical Investigation of the Stepwise Hydrolysis of the [Re3(,-Cl)3Cl9]3- AnionCHEMINFORM, Issue 22 2007Dimitrios G. Liakos Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Integrated Experimental,Theoretical Investigation of the Na,Li,Al,H System.CHEMINFORM, Issue 21 2007Susanne M. Opalka Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Theoretical Investigation of Uranyl Dihydroxide: Oxo Ligand Exchange, Water Catalysis, and Vibrational SpectraCHEMINFORM, Issue 48 2005Hrant P. Hratchian Abstract For Abstract see ChemInform Abstract in Full Text. [source] Theoretical Investigation of the Influence of Ligands on Structural and Electronic Properties of Indium Phosphide Clusters.CHEMINFORM, Issue 18 2005Sudip Roy No abstract is available for this article. [source] Experimental and Theoretical Investigation of the Coarctate Cyclization of (2-Ethynylphenyl)phenyldiazenes.CHEMINFORM, Issue 8 2005Laura D. Shirtcliff Abstract For Abstract see ChemInform Abstract in Full Text. [source] Metallo-Antiaromatic Al4Na4 and Al4Na - 3 Compounds: A Theoretical Investigation.CHEMINFORM, Issue 16 2004Sharan Shetty No abstract is available for this article. [source] Theoretical Investigation of the Solid State Reaction of Silicon Nitride and Silicon Dioxide Forming Silicon Oxynitride (Si2N2O) under PressureCHEMINFORM, Issue 49 2003Peter Kroll Abstract For Abstract see ChemInform Abstract in Full Text. [source] Bis(oxazoline)titanium Complexes as Chiral Catalysts for Enantioselective Hydrosilylation of Ketones , A Combined Experimental and Theoretical Investigation.CHEMINFORM, Issue 47 2003Marco Bandini Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: A Comparative Theoretical Investigation of Three Sodalite Systems: Cd4S(AlO2)6, Zn4O(BO2)6, and Zn4S(BO2)6.CHEMINFORM, Issue 19 2002Maurizio Casarin Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] An Experimental and Theoretical Investigation of Gas-Phase Reactions of Ca2+ with GlycineCHEMISTRY - A EUROPEAN JOURNAL, Issue 26 2006Inés Corral Dr. Abstract The gas-phase reactions between Ca2+ and glycine ([Ca(gly)]2+) have been investigated through the use of mass spectrometry techniques and B3-LYP/cc-pWCVTZ density functional theory computations. The major peaks observed in the electrospray MS/MS spectrum of [Ca(gly)]2+ correspond to the formation of the [Ca,C,O2,H]+, NH2CH2+, CaOH+, and NH2CH2CO+ fragment ions, which are produced in Coulomb explosion processes. The computed potential energy surface (PES) shows that not only are these species the most stable product ions from a thermodynamic point of view, but they may be produced with barriers lower than for competing processes. Carbon monoxide is a secondary product, derived from the unimolecular decomposition of some of the primary ions formed in the Coulomb explosions. In contrast to what is found for the reactions of Ca2+ with urea ([Ca(urea)]2+), minimal unimolecular losses of neutral fragments are observed for the gas-phase fragmentation processes of [Ca(gly)]2+, which is readily explained in terms of the topological differences between their respective PESs. [source] The Origin of the Improved Efficiency and Stability of Triphenylamine-Substituted Anthracene Derivatives for OLEDs: A Theoretical Investigation,CHEMPHYSCHEM, Issue 17 2008Bing Yang Dr. Abstract Herein, we describe the molecular electronic structure, optical, and charge-transport properties of anthracene derivatives computationally using density functional theory to understand the factors responsible for the improved efficiency and stability of organic light-emitting diodes (OLEDs) with triphenylamine (TPA)-substituted anthracene derivatives. The high performance of OLEDs with TPA-substituted anthracene is revealed to derive from three original features in comparison with aryl-substituted anthracene derivatives: 1) the HOMO and LUMO are localized separately on TPA and anthracene moieties, respectively, which leads to better stability of the OLEDs due to the more stable cation of TPA under a hole majority-carrier environment; 2) the more balanceable hole and electron transport together with the easier hole injection leads to a larger rate of hole,electron recombination, which corresponds to the higher electroluminescence efficiency; and 3) the increasing reorganization energy for both hole and electron transport and the higher HOMO energy level provide a stable potential well for hole trapping, and then trapped holes induce a built-in electric field to prompt the balance of charge-carrier injection. [source] CO Adsorption on a LaNi5 Hydrogen Storage Alloy Surface: A Theoretical InvestigationCHEMPHYSCHEM, Issue 11 2008Song Han Dr. Abstract Density functional theory calculations are carried out to study CO adsorption on the (001) surface of a LaNi5 hydrogen storage alloy. At low coverages, CO favors adsorption on NiNi bridge sites. With an increase in CO coverage, the decrease in the adsorption energy is much larger for NiNiCO bridge adsorption than that for NiCO on-top adsorption. Thus, the latter sites in the relatively stable adsorption structure are preferentially utilized at high CO coverages. The nature of the bonding between CO and the LaNi5 (001) surface is analyzed in detail. [source] Experimental and Theoretical Investigation of the Room-Temperature Photoluminescence of Amorphized Pb(Zr,Ti)O3CHEMPHYSCHEM, Issue 8 2005Emmanuelle Orhan Dr. Abstract Ultrafine PbZr0.20Ti0.80O3 was amorphized through high-energy mechanical milling. The structural evolution through the amorphization process was accompanied by various characterization techniques, such as X-ray diffraction, Fourier-transformed IR spectroscopy (FTIR), high-resolution transmission electron microscopy (HR-TEM), and Raman spectroscopy. A strong photoluminescence was measured at room temperature for amorphized PbZr0.20Ti0.80O3, and interpreted by means of high-level quantum mechanical calculations in the density functional theory framework. Three periodic models were used to represent the crystalline and amorphized PbZr0.20Ti0.80O3, and they allowed the calculation of electronic properties that are consistent with the experimental data and that explain the appearance of photoluminescence. [source] Theoretical Investigation on the Mechanism and Design of Catalysts for Nitrolysis of Hexamine,CHINESE JOURNAL OF CHEMISTRY, Issue 9 2010Liangwei Shi Abstract The mechanism of nitrolysis of hexamine (HA) by DFT method has been explored to understand the classical organic reaction and assist the design of new catalyst. The potential energy surface of NO+2 was firstly investigated. A reasonable configuration evolution of NO+2 during the process of its reaction with HA was figured out. The role of H+ and NH+4 for the nitrolysis of HA was analyzed and discussed. The route of nitrolysis reaction from HA to 1-acetoxylmethene-3-nitro-tetrazabicyclo[3,3,1]nonane intermediate is similar to that of acetylation of HA. The relative free energy calculation proves the priority of nitrolysis relative to acetylation. Two types of Lewis salts, M(OSO2CF3)3 and M[N(SO2CF3)2]3 (M: Yb, Sm, Y, and Eu), are designed on the basis of discussed mechanism. The calculation for the key bond order in IM2[CH2R] model intermediates gives an indicator as the preferable catalyst. The experimental results support the theoretical conclusion. [source] Excited State Intramolecular Proton Transfer of New Diphenyl- ethylene Derivatives Bearing Imino Group: A Combination of Experimental and Theoretical InvestigationCHINESE JOURNAL OF CHEMISTRY, Issue 7 2010Fang Gao Abstract In this paper, we described the synthesis and characterization of new diphenylethylene bearing imino group. We concentrated particularly on the investigation of the possibility of the excited state intramolecular charge transfer (ESIPT) of the new dyes experimentally and theoretically. The absorption and fluorescence spectroscopy of the dyes were determined in various solvents. The results showed that the maximal absorption wavelength of 2-[(4,- N,N -dimethylamino-diphenylethylene-4-ylimino)methyl]phenol (C1) and 4-[(4,- N,N -dimethylamino-diphenylethylene-4-ylimino)methyl]phenol (C2) exhibited almost independence on the solvent polarity. While as contrast, the maximal fluorescence wavelength of the dyes showed somewhat dependence on the solvent polarity. In particular, C1 displayed well-separated dual fluorescence spectroscopy. The second fluorescence peak was characterized with an "abnormal" fluorescence emission wavelength in aprotic solvents with large Stokes shift (ca. 140 nm in THF), which was much more than normal Stokes shift (ca. 30 nm in THF). This emission spectroscopy could be assigned to ESIPT emission. On the other hand, the ESIPT fluorescence of C1 was much reduced or lost in the protic solvents. While, only normal fluorescence emission was detected in various solvents. Although the absorption maxima of C1 exhibited about 10 nm red-shift with respect to those of C2, the normal fluorescence maxima of C1 and C2 were almost identical in various solvents. These results suggested that C1 could undergo ESIPT, but C2 was not able to proceed ESIPT. The molecular geometry optimization of phototautomers in the ground electronic state (S0) was carried out with HF method (Hartree-Fock) and at DFT level (Density Functional Theory) using B3LYP both, while the CIS was employed to optimize the geometries of the first singlet excited state (S1) of the phototautomers of C1 and C2 respectively. The properties of the ground state and the excited state of the phototautomers of C1 and C2, including the geometrical parameter, the energy, the frontier orbits, the Mulliken charge and the dipole moment change were performed and compared completely. The data were analyzed further based on our experimental results. Furthermore, the absorption and fluorescence spectra were calculated in theory and compared with the measured ones. The rate constant of internal proton transfer (9.831×1011 s,1) of C1 was much lower than that of salicylidene methylamine (C3, 2.045×1015 s,1), which was a typical Schiff base compound and was well demonstrated to undergo ESIPT easily under photoexcitation. [source] Theoretical Investigation on the Absorption and Emission Properties of the Three Isomers of Bis(thiocyanato)(2,2,-bipyridyl)platinum(II)CHINESE JOURNAL OF CHEMISTRY, Issue 9 2007Xiao-Ying Hu Abstract This paper presents a Density Functional or Time Dependent Density Functional (DFT/TDDFT) study of the molecular and electronic structures, optical absorption and emission spectra of three linkage isomers:bis(isothiocyanato-S)(2,2,-bipyridyl) platinum(II) ([Pt(SCN)2(bpy)]), (isothiocyanato-S)(thiocyanato-N)-(2,2,-bipy- ridyl) platinum(II) ([Pt(SCN)(NCS)(bpy)]), and bis(thiocyanato-N)(2,2,)-bipyridyl)platinum(II) ([Pt(NCS)2(bpy)]), in which different coordination ligands based on the N- and S-coordination of the thiocyanato ligands control the luminescent color. The electronic structures were studied using the B3LYP functional. Optimized geometries were compared to the experimentally observed structures. TDDFT calculation was carried out to investigate the excited singlet and triplet states. Calculations have been performed both in vacuo and in solvents, using a polarized continuum model (PCM) to account for solute-solvent interactions. Inclusion of the solvent led to a significant energy change, and as a consequence, the computed spectrum calculated in the presence of the solvent was in good agreement with the experimental determinations. The first two absorptions were found to originate from mixed platinum-SCN (or NSC) to bipyridyl-,* transitions rather than pure metal-to-ligand-charge-transfer (MLCT) transitions, whereas the higher-energy bands arose from intraligand ,,,* transitions. The stretching frequencies of C,N have been calculated both in the ground and excited states, which are relative to the charge transition during the excitation. In addition, different sizes of basis sets were also discussed in this paper. [source] Syntheses, Structures and Theoretical Investigations of [Li(thf)4]2[Ti2Cu8S4(SPh)10] and [Ti2Ag6S6Cl2(PPhiPr2)6]EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 28 2009Heino Sommer Abstract The reaction of CuOAc (OAc = acetate) with TiCl4·2thf and LiSPh in thf leads to the formation of tiny deep-red crystals of [Li(thf)4]2[Ti2Cu8S4(SPh)10]. The silver/titanium cluster complex [Ti2Ag6S6Cl2(PPhiPr2)6] was synthesized by the reaction of TiCl4·2thf with AgPhCO2 and S(SiMe3)2 in the presence of PPhiPr2. The crystal structures of the compounds were determined by X-ray analysis of single crystals. Additionally, theoretical investigations were performed to assign the proper chlorine/sulfur atomic positions and to rationalize the bonding situation in 1 and 2. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Syntheses, Structures and Theoretical Investigations of 1,4,3,4,5,4 -Trithia-2,4,6,8,9-pentaazabicyclo[3.3.1]nona-1(9),2,3,5,7-pentaenesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2003Carsten Knapp Abstract The syntheses of the title compounds RCN5S3 with electron-withdrawing aryl substituents [R = 2-FC6H4 (1m), 4-FC6H4 (1n), 2,6-F2C6H3 (1o), C6F5 (1p), 4-NCC6H4 (1q) and Cl3C (1r)] are described. The X-ray structures of 1n, 1o, 1q and 1r, together with those of Me2NCN5S3 (1b) and 4-CH3C6H4CN5S3 (1f), are reported. The experimentally determined dependence of the bond lengths on the substituents R within the bicyclic system RCN5S3 is well-reflected in the results of the theoretical calculations (RHF, MP2, B3LYP). The bonding model developed shows that acceptor substituents do not influence bonding within the bicycle. In the solid state, two fundamentally different primary interactions of the RCN5S3 molecules are observed; "stacking" and "dimerisation", which can be rationalised by electrostatic interactions between the CN5S3 units. However, secondary effects , the interactions between the R substituents , may be even more dominant. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Learning from Directed Evolution: Theoretical Investigations into Cooperative Mutations in Lipase EnantioselectivityCHEMBIOCHEM, Issue 2 2004Marco Bocola Dr. Abstract Molecular modeling with classical force-fields has been used to study the reactant complex and the tetrahedral intermediate in lipase-catalyzed ester hydrolysis in 20 enzyme/substrate combinations. The R and S enantiomers of,-methyldecanoic acid ester served as substrates for the wild-type lipase from Pseudomonas aeruginosa and nine selected mutants. After suitable preparation of initial structures from an available wild-type crystal structure, each system was subjected to 1 ns CHARMM force-field molecular dynamics simulations. The resulting geometric and energetic changes allow interpretation of some experimentally observed effects of mutations, particularly with regard to the "hot spots" at residues 155 and 162. The replacement S155F enhances S enantiopreference through a steric relay involving Leu162. The double mutation S53P + L162G improves S enantioselectivity by creating a new binding pocket for the S enantiomer with an additional stabilizing hydrogen bond to His83. The simulations provide insight into remote and cooperative effects of mutations. [source] ChemInform Abstract: Carboazidation of Chiral Allylsilanes: Experimental and Theoretical Investigations.CHEMINFORM, Issue 29 2008Laurent Chabaud Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Theoretical Investigations of Uranyl,Ligand Bonding: Four- and Five-Coordinate Uranyl Cyanide, Isocyanide, Carbonyl, and Hydroxide ComplexesCHEMINFORM, Issue 24 2005Jason L. Sonnenberg Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Experimental and Theoretical Investigations of the Stability, Energetics, and Structures of H2PO4 - , H2P2O72- , and H3P3O102- in the Gas Phase.CHEMINFORM, Issue 1 2002Xue-Bin Wang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Carboazidation of Chiral Allylsilanes: Experimental and Theoretical InvestigationsCHEMISTRY - A EUROPEAN JOURNAL, Issue 9 2008Laurent Chabaud Dr. Abstract The carboazidation of chiral allylsilanes has been investigated by varying the nature of the substituents at the silicon center and on the carbon framework. The influence of temperature and the nature of the sulfonyl azide, as well as the stereochemistry of the remote stereogenic center, on the 1,2-diastereocontrol of the process were considered. Good to excellent levels of diastereocontrol were generally observed, with the syn -,-azidosilane always being formed as the major isomer. An illustration of the value of this methodology has been provided with a short and efficient synthesis of an analogue of castanospermine. EPR spectroscopy was carried out on various ,-silyl radicals providing useful information about their conformations in the ground state. Based on this experimental evidence and DFT calculations, reactant-like transition state models were finally proposed that rationalize the observed 1,2-stereoinduction. [source] | |||||||||||||||||||||||||||||||||||||||||||