Journal of Theoretical Chemistry The latest articles from Hindawi © 2017 , Hindawi Limited . All rights reserved. Concomitant Effects of Transition Metal Chelation and Solvent Polarity on the First Molecular Hyperpolarizability of 4-Methoxyacetophenone Thiosemicarbazone: A DFT Study Wed, 02 Nov 2016 13:30:22 +0000 Nonlinear optical (NLO) properties of organic and metal-organic materials are of considerable interest to emerging optoelectronic and photonic technologies. Much work has been carried out on the former materials but the latter ones have received less attention till date. Herein, a density functional theory (DFT) study on the combined effects of transition metal chelation and solvent polarity on the first hyperpolarizability () of 4-methoxyacetophenone thiosemicarbazone (MAPTSC) is reported. MAPTSC exhibits a tautomeric form with higher optical nonlinearity rendering its NLO response in polar solvents potentially switchable. Our results have revealed significant modifications of the first hyperpolarizability of MAPTSC upon complexation with different transition metal chlorides in the presence of solvents with varying dielectric constants. Therefore, its second-order NLO response is highly tunable by the synergy of transition metal chelation and solvent polarity. MAPTSC and its Zn(II) and Pt(II) chloride complexes are promising NLO materials because their gas-phase values are larger than those of the prototype push-pull molecules, para-nitroaniline (PNA) and urea, by factors of about 1.40–1.76 and 19.57–37.24, respectively; these factors greatly increase in polar solvent medium. Moreover, they possess high optical transparencies in the visible region of the electromagnetic spectrum which mitigate transparency/nonlinearity trade-offs, thereby increasing the likelihood of broad band NLO response. Nyiang Kennet Nkungli and Julius Numbonui Ghogomu Copyright © 2016 Nyiang Kennet Nkungli and Julius Numbonui Ghogomu. All rights reserved. Fukui Function Analysis and Optical, Electronic, and Vibrational Properties of Tetrahydrofuran and Its Derivatives: A Complete Quantum Chemical Study Mon, 05 Jan 2015 11:38:12 +0000 The spectroscopic, optical, and electronic properties of tetrahydrofuran and its derivatives were investigated by FTIR techniques. We have done a comparative study of tetrahydrofuran and its derivatives with B3LYP with 6-311 G (d, p) as the basis set. Here we have done a relative study of their structures, vibrational assignments, and thermal, electronic, and optical properties of ttetrahydrofuran and its derivatives. We have plotted frontier orbital HOMO-LUMO surfaces and molecular electrostatic potential surfaces to explain the reactive nature of tetrahydrofuran and its derivatives. Apoorva Dwivedi, Vikas Baboo, and Abhishek Bajpai Copyright © 2015 Apoorva Dwivedi et al. All rights reserved. Ab Initio Studies on Hematite Surface and the Adsorption of Phosphate Sun, 28 Sep 2014 09:05:16 +0000 This investigation explores the ab initio DFT method for understanding surface structure of hematite and the nature and energetics of phosphate adsorption. Using the full potential linearized plane wave method (FP-LAPW), we derived the structure and energies of various magnetic forms of hematite. The antiferromagnetic (AFM) form was observed to be the most stable. Hematite surfaces with Fe-termination, O-termination, or OH-termination were studied. The OH-terminated surface was the most stable. Stability of hematite surfaces follows the order OH-termination > Fe-termination > O-termination. Thus, surface reaction with hematite would occur with the OH at the surface and not with Fe atoms. The structure of phosphate adsorbed on hematite was derived. Bonding is through the H atom of the OH at the surface. An alternative mechanism of phosphate adsorption on hematite has been derived. Adsorption energy is high and suggests chemisorption rather than physisorption of phosphate on hematite. Swati Chaudhury, Chandrika Varadachari, and Kunal Ghosh Copyright © 2014 Swati Chaudhury et al. All rights reserved. On the Importance of Water Molecules in the Theoretical Study of Polyphenols Reactivity toward Superoxide Anion Sun, 14 Sep 2014 00:00:00 +0000 Numerous studies have shown the benefits of a diet rich in fruits and vegetables. These benefits are partly due to the radical scavenging properties of polyphenols contained in fruits and vegetables since polyphenols can fight against an excess of radicals which goes along inflammation in a certain number of diseases. This pathological state, called oxidative stress, results from the aerobic condition of human organism when OH radical, hydrogen peroxide, superoxide anion, or peroxynitrite is produced in excess. If hydrogen peroxide is easily handled by human defense against radicals, the other radicals can cause damage to biological constituents like lipids, cell membranes, and other biomolecules. This paper is devoted to the theoretical study of the interaction of superoxide anion () with a very potent radical scavenger, 1,2,4,6,8-pentahydroxynaphthalene. The importance of hydration of superoxide radical for the reactivity is analyzed. Potential energy surfaces (PES) are calculated for different number of water molecules around the radical and it is shown that the transition barrier vanishes when complete hydration with six water molecules is explicitly handled. The nature of the reactivity is determined by using the natural bond orbital (NBO) analysis. Laure Lespade Copyright © 2014 Laure Lespade. All rights reserved. QSPR Models for Octane Number Prediction Tue, 19 Aug 2014 00:00:00 +0000 Quantitative structure-property relationship (QSPR) is performed as a means to predict octane number of hydrocarbons via correlating properties to parameters calculated from molecular structure; such parameters are molecular mass , hydration energy , boiling point , octanol/water distribution coefficient , molar refractivity , critical pressure , critical volume , and critical temperature . Principal component analysis (PCA) and multiple linear regression technique (MLR) were performed to examine the relationship between multiple variables of the above parameters and the octane number of hydrocarbons. The results of PCA explain the interrelationships between octane number and different variables. Correlation coefficients were calculated using M.S. Excel to examine the relationship between multiple variables of the above parameters and the octane number of hydrocarbons. The data set was split into training of 40 hydrocarbons and validation set of 25 hydrocarbons. The linear relationship between the selected descriptors and the octane number has coefficient of determination , statistical significance , and standard errors . The obtained QSPR model was applied on the validation set of octane number for hydrocarbons giving and . Jabir H. Al-Fahemi, Nahla A. Albis, and Elshafie A. M. Gad Copyright © 2014 Jabir H. Al-Fahemi et al. All rights reserved. An Assessment of Alternative Low Level Calculation Methods for the Initial Selection of Conformers of Diastereomeric Esters Mon, 23 Jun 2014 10:49:24 +0000 Critical assessment of performance of alternative molecular modeling methods depending on a specific object and goal of the investigation is a question of continuous interest. This prompted us to demonstrate the origin of the guidelines we have used for a rational choice and use of a proper low level calculation method (LLM) for an initial geometry optimization of generated conformers, with the aim of selecting a set for further optimization. What was performed herein was a comparison of LLMs: MM3, MM+, UFF, Dreiding, AM1, PM3, and PM6 on the optimization of conformers’ geometry of α-methoxyphenylacetic acid (MPA) 2-butyl esters as a set of typical diastereomeric esters of a chiral derivatizing agent. This set of esters calculated represents only compounds of this certain type in the current work. The LLM conformer energies were correlated with benchmark energies found by using higher level reference method B3LYP/6-311++G** on the geometries gained previously by optimization with LLMs. In an alternative treatment, the energy range to be covered and corresponding number of LLM optimized conformers obligatory for submitting to further optimization using a high level optimization cascade were considered on the basis of determination of the cut-off conformer (COFC). Andrus Metsala, Sven Tamp, Kady Danilas, Ülo Lille, Ly Villo, Sirje Vija, Tõnis Pehk, and Omar Parve Copyright © 2014 Andrus Metsala et al. All rights reserved. Isolation, Identification, Molecular and Electronic Structure, Vibrational Spectroscopic Investigation, and Anti-HIV-1 Activity of Karanjin Using Density Functional Theory Wed, 07 May 2014 07:48:59 +0000 “Karanjin” (3-methoxy furano-2,3,7,8-flavone) is an anti-HIV drug, and it is particularly effective in the treatment of gastric problems. The method of isolation of “Karanjin” followed the Principles of Green Chemistry (eco-friendly and effortless method). The optimized geometry of the “Karanjin” molecule has been determined by the method of density functional theory (DFT). Using this optimized structure, we have calculated the infrared wavenumbers and compared them with the experimental data. The calculated wavenumbers are in an excellent agreement with the experimental values. On the basis of fully optimized ground-state structure, TDDFT//B3LYP/LANL2DZ calculations have been used to determine the low-lying excited states of Karanjin. Based on these results, we have discussed the correlation between the vibrational modes and the crystalline structure of “Karanjin.” A complete assignment is provided for the observed FTIR spectra. This is the first report of the isolation, molecular and electronic structure using vibrational spectroscopic investigation, density functional theory, and anti-HIV-1 activity of “Karanjin.” Anoop kumar Pandey, Abhishek Kumar Bajpai, Ashok Kumar, Mahesh Pal, Vikas Baboo, and Apoorva Dwivedi Copyright © 2014 Anoop kumar Pandey et al. All rights reserved. Formation of 2s-State Hydrogen Atom in Proton-Lithium Inelastic Scattering Tue, 06 May 2014 12:16:15 +0000 Elaborate coupled static formalism is employed for treatment of proton-lithium collisions at wide range of incident energies between 10 and 1000 Kev. Coupled static and frozen core approximations are employed for calculating partial and total cross sections. Only elastic and formation of excited hydrogen, H(2s), channels are considered. Total cross sections are calculated using seven partial waves Green’s function expansion technique of total angular momentum . Proposed iterative approach allows for reliable representation of the core potentials using elaborate variational calculation of target orbitals. Polarization potential of lithium atom is taken into consideration in calculating corresponding total cross sections. Quite interesting reliable results were obtained in comparison with other theoretical approaches. S. A. Elkilany Copyright © 2014 S. A. Elkilany. All rights reserved. Calculation of the Quantum-Mechanical Tunneling in Bound Potentials Thu, 24 Apr 2014 12:21:51 +0000 The quantum-mechanical tunneling is often important in low-energy reactions, which involve motion of light nuclei, occurring in condensed phase. The potential energy profile for such processes is typically represented as a double-well potential along the reaction coordinate. In a potential of this type defining reaction probabilities, rigorously formulated only for unbound potentials in terms of the scattering states with incoming/outgoing scattering boundary conditions, becomes ambiguous. Based on the analysis of a rectangular double-well potential, a modified expression for the reaction probabilities and rate constants suitable for arbitrary double- (or multiple-) well potentials is developed with the goal of quantifying tunneling. The proposed definition involves energy eigenstates of the bound potential and exact quantum-mechanical transmission probability through the barrier region of the corresponding scattering potential. Applications are given for several model systems, including proton transfer in a HO–H–CH3 model, and the differences between the quantum-mechanical and quasiclassical tunneling probabilities are examined. Sophya Garashchuk, Bing Gu, and James Mazzuca Copyright © 2014 Sophya Garashchuk et al. All rights reserved. Mathematical Analysis of a Series of 4-Acetylamino-2-(3,5-dimethylpyrazol-1-yl)-6-pyridylpyrimidines: A Simple Way to Relate Quantum Similarity to Local Chemical Reactivity Using the Gaussian Orbitals Localized Theory Wed, 16 Apr 2014 10:04:55 +0000 Molecular Quantum Similarity (MQS) descriptors and Density Functional Theory (DFT) based reactivity descriptors were studied for a series of 4-Acetylamino-2-(3,5-dimethylpyrazol-1-yl)-6-pyridylpyrimidines compounds used for Parkinson’s disease (PD) treatment. The quantification of the steric and electronic effects was shown through scales of quantitative convergence; such scales allow us to establish a methodology to quantify the similarity from the local chemical reactivity (Fukui Functions) point of view. This procedure provides new considerations in the local reactivity of the Adenosine receptor antagonists in a disease of difficult control as PD. In addition, we present new considerations to the localized bonding theory and show a new methodology for quantum similarity on the Fukui Functions. Considering that the Fukui functions under a condensation scheme may have ambiguities in the (DFT) context. Alejandro Morales-Bayuelo, Verónica Valdiris, and Ricardo Vivas-Reyes Copyright © 2014 Alejandro Morales-Bayuelo et al. All rights reserved. Structural, Electronic, and Vibrational Properties of Isoniazid and Its Derivative N-Cyclopentylidenepyridine-4-carbohydrazide: A Quantum Chemical Study Mon, 24 Feb 2014 09:16:51 +0000 Isoniazid (Laniazid, Nydrazid), also known as isonicotinylhydrazine (INH), is an organic compound that is the first-line medication in prevention and treatment of tuberculosis. The optimized geometry of the isoniazid and its derivative N-cyclopentylidenepyridine-4-carbohydrazide molecule has been determined by the method of density functional theory (DFT). For both geometry and total energy, it has been combined with B3LYP functionals having LANL2DZ and 6-311 G (d, p) as the basis sets. Using this optimized structure, we have calculated the infrared wavenumbers and compared them with the experimental data. The calculated wavenumbers by LANL2DZ are in an excellent agreement with the experimental values. On the basis of fully optimized ground-state structure, TDDFT//B3LYP/LANL2DZ calculations have been used to determine the low-lying excited states of isoniazid and its derivative. Based on these results, we have discussed the correlation between the vibrational modes and the crystalline structure of isoniazid and its derivative. A complete assignment is provided for the observed FTIR spectra. The molecular HOMO, LUMO composition, their respective energy gaps, and MESP contours/surfaces have also been drawn to explain the activity of isoniazid and its derivative. Anoop kumar Pandey, Abhishek Bajpai, Vikas Baboo, and Apoorva Dwivedi Copyright © 2014 Anoop kumar Pandey et al. All rights reserved. Normal Modes, Molecular Orbitals and Thermochemical Analyses of 2,4 and 3,4 Dichloro Substituted Phenyl-N-(1,3-thiazol-2-yl)acetamides: DFT Study and FTIR Spectra Wed, 29 Jan 2014 00:00:00 +0000 A detailed spectroscopic analysis of two dichloro substituted phenyl-N-(1,3-thiazol-2-yl)acetamides at 2,4 and 3,4 positions of the phenyl ring has been carried out by using B3LYP method with 6-31+G(d, p) basis set within density functional scheme. The scaled theoretical wave numbers are in perfect agreement with the experimental values and the vibrational modes are interpreted in terms of potential energy distribution (PED). The internal coordinates are optimized repeatedly to maximize the PED contributions. The molecular HOMO-LUMO surfaces, their respective energy gaps, and MESP surfaces have also been drawn to explain the chemical activity of both molecules. Various thermodynamic parameters are presented at the same level of theory. Ambrish K. Srivastava, Anoop K. Pandey, B. Narayana, B. K. Sarojini, Prakash S. Nayak, and Neeraj Misra Copyright © 2014 Ambrish K. Srivastava et al. All rights reserved. Studying the Polypeptide Sequence (α-Code) of Escherichia coli Sun, 29 Dec 2013 18:30:27 +0000 This paper is devoted to algebraically simulating the α-code of bacterium Escherichia coli and studying contrast factors (words) in its polypeptide sequence. We utilize the methods of spectral theory of graphs which were previously employed by us for enumerating De Bruijn and Kautz sequences. The empirical material is borrowed from the computer investigation of contrast factors in the polypeptide sequences of prokaryotes. Vladimir R. Rosenfeld Copyright © 2013 Vladimir R. Rosenfeld. All rights reserved. Quantum Mechanics of In Situ Synthesis of Metal Nanoparticles within Anionic Microgels Wed, 25 Dec 2013 08:03:23 +0000 We discuss the quantum mechanics of many-body systems, that is, hybrid microgel consisting of negatively charged anionic microgels possessing thick sheath of water molecules solvating protruding anionic moieties and nanoparticle captivated within the microgel. Thermodynamic feasibility of synthesis of particular nanoparticle within the microgel is dependent upon the magnitude of interaction between nanoparticle, water molecules, and microgel relative to sum of magnitude of self-interaction between counterions and interaction between counterions and microgel. Nanoparticles synthesized with in the microgels have thick electronic cloud that oscillates under the influence of net interaction potential of charged anionic moieties and solvent water molecules which constitutes the chemical environment of hybrid microgel. Hamiltonian describing energy of oscillating electronic cloud of wrapped around nanoparticle is mathematically derived to be equal to product of integral electron density and product of its position vector overall space and net force acting on the oscillating electronic cloud of nanoparticle is mathematically defined as; . Mirza Wasif Baig and Muhammad Siddiq Copyright © 2013 Mirza Wasif Baig and Muhammad Siddiq. All rights reserved. Mathematical Modeling and Analysis of Nonlinear Enzyme Catalyzed Reaction Processes Tue, 24 Dec 2013 11:25:16 +0000 A mathematical model for the nonlinear enzymatic reaction process is discussed. An approximate analytical expression of concentrations of substrate, enzyme, and free enzyme-product is obtained using homotopy perturbation method (HPM). The main objective is to propose an analytical solution, which does not require small parameters and avoid linearization and physically unrealistic assumptions. Theoretical results obtained can be used to analyze the effect of different parameters. Satisfactory agreement is obtained in the comparison of approximate analytical solution and numerical simulation. D. Mary Celin Sharmila, T. Praveen, and L. Rajendran Copyright © 2013 D. Mary Celin Sharmila et al. All rights reserved. Theoretical Investigation of the D83V Mutation within the Myocyte-Specific Enhancer Factor-2 Beta and Its Role in Cancer Tue, 24 Dec 2013 08:49:28 +0000 The D83V mutation in the myocyte-specific enhancer factor-2 beta (MEF2B) gene is frequently observed in lymphomas. Surprisingly, this apparent gain-of-function mutation is within a protein that is involved in the promotion of apoptosis in B cells. To investigate the oncogenic effects of this alteration and explain its predominance over other known loss-of-function mutations of MEF2B, we propose a hypothesis that this mutation influences the dynamic folding of the C-terminal loop of the N-terminal domain of MEF2B. According to our hypothesis, the mutation allows MEF2B to bind promiscuously to a wider variety of gene promoters. A large set of molecular dynamic simulations (MD) was conducted to investigate the effects of D83V mutation in silico and support the hypothesis. Oleksandr Yakovenko, Ryan Morin, Ganna Vashchenko, and Steven J. M. Jones Copyright © 2013 Oleksandr Yakovenko et al. All rights reserved. Scale Alpha and Beta of Quantitative Convergence and Chemical Reactivity Analysis in Dual Cholinesterase/Monoamine Oxidase Inhibitors for the Alzheimer Disease Treatment Using Density Functional Theory (DFT) Mon, 23 Dec 2013 09:45:25 +0000 Molecular quantum similarity descriptors and Density Functional Theory (DFT) based reactivity descriptors were studied for a series of cholinesterase/monoamine oxidase inhibitors used for the Alzheimer's disease treatment (AD). This theoretical study is expected to shed some light onto some molecular aspects that could contribute to the knowledge of the molecular mechanics behind interactions of these molecules with acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE), as well as with monoamine oxidase (MAO) A and B. The Topogeometrical Superposition Algorithm to handle flexible molecules (TGSA-Flex) alignment method was used to solve the problem of the relative orientation in the quantum similarity (QS) field. Using the molecular quantum similarity (MQS) field and reactivity descriptors supported in the DFT was possible the quantification of the steric and electrostatic effects through of the Coulomb and Overlap quantitative convergence scales (alpha and beta). In addition, an analysis of reactivity indexes is development, using global and local descriptors, identifying the binding sites and selectivity in the (cholinesterase/monoamine oxidase) inhibitors, understanding the retrodonor process, and showing new insight for drugs design in a disease of difficult control as Alzheimer. Alejandro Morales-Bayuelo, Rosa Baldiris, and Ricardo Vivas-Reyes Copyright © 2013 Alejandro Morales-Bayuelo et al. All rights reserved. Free Will with Afterthoughts: A Quasichemical Model Tue, 17 Dec 2013 14:49:00 +0000 A model of free will is proposed, appealing to the similarity with simple, two-body chemical reactions where the energy curves for the reagents and for the products cross. The system at the crossing point has a freedom of choice to perform the reaction or not. The Landau-Zener formula, corresponding to the opportunity of meeting twice the crossing point, is interpreted as free will with an afterthought and generalized to the cases when a subject thinks about a choice times. If the probability distribution of afterthoughts is known, the probability of a final yes decision is given. The results are generalized to situations where a preference for or against a change exists or where the freedom is only partial, has to fight with conditioning factors, and possibly decreases with increasing instances of free choice. Andrea C. Levi Copyright © 2013 Andrea C. Levi. All rights reserved. Molecular Dynamics Simulation of VEGFR2 with Sorafenib and Other Urea-Substituted Aryloxy Compounds Wed, 04 Dec 2013 17:48:30 +0000 The binding mode of sorafenib with VEGFR2 was studied using molecular docking and molecular dynamics method. The docking results show that sorafenib forms hydrogen bonds with Asp1046, Cys919, and Glu885 of VEGFR2 receptor. Molecular dynamics simulation suggests that the hydrogen bond involving Asp1046 is the most stable one, and it is almost preserved during all the MD simulation time. The hydrogen bond formed with Cys919 occurs frequently after 6 ns, while the bifurcated hydrogen bonds involving Glu885 occurs occasionally. Meantime, molecular dynamics simulations of VEGFR2 with 11 other urea-substituted aryloxy compounds have also been performed, and the results indicate that a potent VEGFR2 inhibitor should have lower interaction energy with VEGFR2 and create at least 2 hydrogen bonds with VEGFR2. Fancui Meng Copyright © 2013 Fancui Meng. All rights reserved. Structures and Stabilities of Alkaline Earth Metal Oxide Nanoclusters: A DFT Study Thu, 24 Oct 2013 18:34:43 +0000 The stability orders of a number of alkaline earth oxide cluster isomers , M = Mg, Ca, Sr, Ba and have been determined by means of density functional theory studies using the LDA-PWC functional. Among the candidate structures, the hexagonal-ring-based isomers and the slab shapes are found to display similar stabilities. Stacks of hexagonal (MO)3 rings are found to be the slightly preferred growth strategy among the (MgO)6, isomers. In contrast, the slab structures are slightly preferred for the other alkaline metal oxide (MO)6 clusters. An explanation based on packing and aromaticity arguments has been proposed. This study may have important implications for modeling and understanding the initial growth patterns of small nanostructures of alkaline earth metals. Prinka Batra, Ritu Gaba, Upasana Issar, and Rita Kakkar Copyright © 2013 Prinka Batra et al. All rights reserved. Density Functional Theory with Modified Dispersion Correction for Metals Applied to Self-Assembled Monolayers of Thiols on Au(111) Mon, 23 Sep 2013 12:01:22 +0000 Using sound physical principles we modify the DFT-D2 atom pairwise semiempirical dispersion correction to density functional theory to work for metallic systems and in particular self-assembled monolayers of thiols on gold surfaces. We test our approximation for two functionals PBE-D and revPBE-D for lattice parameters and cohesive energies for Ni, Pd, Pt, Cu, Ag, and Au, adsorption energies of CO on (111) surfaces of Pd, Pt, Cu, Ag, and Au, and adsorption energy of benzene on Ag(111) and Au(111). Agreement with experimental data is substantially improved. We apply the method to self-assembled monolayers of alkanethiols on Au(111) and find reasonable agreement for PBE-D and revPBE-D for both physisorption of n-alkanethiols as well as dissociative chemisorption of dimethyl disulfide as an Au-adatom-dithiolate complex. By modifying the coefficient for Au, we obtain quantitative agreement for physisorption and chemisorption for both PBE-D and revPBE-D using the same set of parameters. Our results confirm that inclusion of dispersion forces is crucial for any quantitative analysis of the thiol and thiolate bonds to the gold surface using quantum chemical calculations. M. P. Andersson Copyright © 2013 M. P. Andersson. All rights reserved. Vibrational Spectroscopic Investigation and Conformational Analysis of Methacrylamidoantipyrine: A Comparative Density Functional Study Thu, 12 Sep 2013 11:27:09 +0000 FT-IR and Raman spectra of methacrylamidoantipyrine (MAAP) have been reported in the region of 4000–10 cm−1 and 4000–100 cm−1, respectively. The optimized geometric parameters, conformational analysis, normal mode frequencies, and corresponding vibrational assignments of MAAP (C15H17N3O2) have been examined by means of density functional theory (DFT) method using the Becke-3-Lee-Yang-Parr (B3LYP) exchange-correlation functional and the 6-31G++(d,p) basis sets. Vibrational assignments have been made on the basis of potential energy distribution (PED) and the thermodynamics functions, and the highest occupied and the lowest unoccupied molecular orbitals (HOMO and LUMO) of MAAP have been predicted. Calculations are carried out with the possible seven (amide-1–5 and imide-1-2) conformational isomers of MAAP. Comparison between the experimental and theoretical results indicates that the B3LYP method provides satisfactory evidence for the prediction of vibrational wavenumbers, and the amide-1 conformational isomer is supposed to be the most stable form of MAAP. Özgür Alver, Mehmet Fatih Kaya, Metin Bilge, and Cemal Parlak Copyright © 2013 Özgür Alver et al. All rights reserved. A Computational Determination of the Lowest Energy Electronic and Geometric States of First Row Transition Metal Dioxygen Dications Thu, 12 Sep 2013 11:00:00 +0000 The lowest energy geometric structures and electronic spin states of first row transition metal (TM) dioxygen dication molecules ([TM–O2]2+; TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) have been determined at the B3LYP/LANL2DZ level of theory (along with an extra -type polarization function added to the O atoms). In order to further verify the spin states, CASSCF(6 + , 9) energy points were determined ( = number of TM electrons). It has been found that with the exception of [Sc–O2]2+, [V–O2]2+, [Co–O2]2+, and [Ni–O2]2+, all [TM–O2]2+ molecules take on a high-spin state. [Sc–O2]2+ adopts a trigonal structure, while [Ti–O2]2+-[Mn–O2]2+ are essentially linear and [Fe–O2]2+-[Zn–O2]2+ are bent. It is further noted that the O–O bond decreases from 130.0 pm to 118.1 pm as the TM changes from Sc to Zn. However, the TM–O2 bond lengths fluctuate between values of 182.2 pm for [Ni–O2]2+ and 232.2 pm for [Zn–O2]2+. Jillian Lennartz, Eric Dumas, Lennie Ramirez, and John Morrison Galbraith Copyright © 2013 Jillian Lennartz et al. All rights reserved. DFT Description of Intermolecular Forces between 9-Aminoacridines and DNA Base Pairs Tue, 03 Sep 2013 09:55:29 +0000 The B3LYP method with 6-31G* basis set was used to predict the geometries of five 9-aminoacridines (9-AA 1(a–e)), DNA base pairs, and respective complexes. Polarizabilities, charge distribution, frontier molecular orbital (FMO), and dipole moments were used to analyze the nature of interactions that allow reasonable drug diffusion levels. The results showed that charge delocalization, high polarizabilities, and high dipole moments play an important role in intermolecular interactions with DNA. The interactions of 9-AA 1(a–e) with GC are the strongest. 9-AA 1(d) displayed the strongest interaction and 9-AA 1(b) the weakest. Sandra Cotes Oyaga, José Cotuá Valdés, Sigrid Borja Paez, and Keylin Hurtado Marquez Copyright © 2013 Sandra Cotes Oyaga et al. All rights reserved. Metal Ion Selectivity of Kojate Complexes: A Theoretical Study Sun, 07 Jul 2013 10:56:12 +0000 Density functional calculations have been performed on four-coordinate kojate complexes of selected divalent metal ions in order to determine the affinity of the metal ions for the kojate ion. The complexation reactions are characterized by high energies, showing that they are highly exothermic. It is found that Ni(II) exhibits the highest affinity for the kojate ion, and this is attributed to the largest amount of charge transfer from the ligand to the metal ion. The Ni(II) complex has distorted square planar structure. The HOMOs and LUMOs of the complexes are also discussed. All complexes display a strong band at ~1500 cm−1 corresponding to the stretching frequency of the weakened carbonyl bond. Comparison of the complexation energies for the two steps shows that most of the complexation energy is realized in the first step. The energy released in the second step is about one-third that of the first step. Sarita Singh, Jyoti Singh, Sunita Gulia, and Rita Kakkar Copyright © 2013 Sarita Singh et al. All rights reserved. Electron Momentum Density and Phase Transition in ZnS Thu, 20 Jun 2013 14:00:43 +0000 The electron momentum density distribution and phase transition in ZnS are reported in this paper. The calculations are performed on the basis of density functional theory (DFT) based on the linear combination of atomic orbitals (LCAO) method. To compare the theoretical Compton profile, the measurement on polycrystalline ZnS has been made using a Compton spectrometer employing 59.54 keV gamma rays. The spherically averaged theoretical Compton profile is in agreement with the measurement. On the basis of equal valence-electron-density Compton profiles, it is found that ZnS is less covalent as compared to ZnSe. The present study suggests zincblende (ZB) to rocksalt (RS) phase transition at 13.7 GPa. The calculated transition pressure is found in good agreement with the previous investigations. N. Munjal, M. C. Mishra, G. Sharma, and B. K. Sharma Copyright © 2013 N. Munjal et al. All rights reserved.