Neglect Of Differential Overlap Research Articles

Molecular Ordering and Nematic Character of Nonyloxy Benzoic Acid: Solvent and Thermodynamic Potentials Effect

Abstract: Benzoic acid derivative p-n-Nonyloxy Benzoic Acid (NOBA) has been chosen for the present investigation to analyze its properties under the effect of a polar aprotic solvent. Indication of stable phase has been examined by interaction-energy values both in pure form and in a polar aprotic solvent dimethylformamide (DMF, ε=38) for different modes of interaction. Complete neglect differential overlap (CNDO/2) method has been applied for net atomic charges and dipole moments at the atomic center. Modified version of Rayleigh–Schrödinger perturbation theory and multicentered-multipole expansion method have been used to regulate long-range intermolecular interactions, where short-range interactions have been studied by 6-exponential potential function. Details on phase behavior and phase stability of NOBA have been reported using statistical thermodynamic calculations of Helmholtz free energies and entropies in several modes of interaction. Keywords: NOBA, Interaction energy, Helmholtz free energy, Entropy, Stability.

Structure and phase behavior of alkoxy benzoic acids in DMSO for thermodynamic applications: Theoretical investigation

This manuscript emphasizes the phase behavior of p-n-Octyloxy Benzoic acid (OOBA) and p-n-Nonyloxy Benzoic acid (NOBA) which are homologues of alkoxy benzoic acid. Fluctuation of the intermolecular interaction energies have been noticed according to rotational and translational co-ordinates for both the compounds in vacuum and under the influence of polar aprotic solvent Dimethyl sulfoxide (DMSO, ε=47). Structures of the molecules have been framed for both the compounds using published crystallographic data. All the charges of atoms and dipole moments of each atom have been estimated on the basis of complete neglect differential overlap (CNDO/2) method. Long-range intermolecular interactions have been considered by modified Rayleigh–Schrodinger perturbation theory and multicentered-multipole expansion method. Short-range interactions have been described by 6-exponential potential function. Theoretical thermodynamic formulations are chosen for the determination of Helmholtz free energies, entropies and internal energies. Existence of liquid crystal phase and its behavior have been discussed by the combined results achieved from relative free energy (ΔA) and relative entropy (ΔS) data. The possibility of addressing the multi-phase phenomenon is discussed from these relative values. The present data is expected to provide a route to analyze behavior of molecules in various solvents, and property prediction for thermodynamic applications.

Electronic Spectra and Photolysis of Bisphenol A in Water

A quantum chemical study of the spectral and luminescent properties of the BPA + 2H2O complex was carried out. Calculations were performed by the semi-empirical method of intermediate neglect of differential overlap using a program complex and a special parameterization. The spectral behavior of BPA in water was modeled by a complex with water molecules in the ratio 1: 2 forming the hydrogen bond. The calculated data were compared with the results of investigation of the isolated BPA molecule. The nonplanar BPA structure leads to the strong mixing of the π- and σ-type atomic wave functions. The main reason for the low quantum yield of the BPA fluorescence is the efficient process of singlet-triplet conversion in the S1(ππ*) ≳ Tn(πσ*) channel of the BPA molecule and its complex with water. A study of the photolysis of the isolated BPA molecule upon exposure to solar radiation, the short-wavelength boundary of which on the Earth’s surface is located at ~290 nm (~34480 cm–1), showed that the energy of the photodissociative state localized on the O–H bond is much higher than this value for BPA. The binding curve is characteristic of the S1(ππ*) state, while the singlet and triplet states of the πσ* type, localized on the single C–C bonds of the central fragment of the molecule, are repulsion curves with a barrier. From our point of view, the low efficiency of the BPA degradation under the influence of solar radiation is due to the presence of a significant potential barrier to the photolysis in the singlet or triplet state. The mechanisms of bond breaking in the BPA + 2H2O complex are different for the singlet and triplet states, namely, for the S3(πσ*) state, the break occurs by the predissociation mechanism, and for the Tn(πσ*) state, due to its population through the singlet-triplet conversion in the S1(ππ*) → Тn(πσ*) channel.

Single-Capture Cross Sections from Biological Molecules and Noble Gases by Bare Ion Impact

In this work, we report theoretical electron capture cross sections for single-electron removal from molecules of biological interest and noble gases by bare ion (H+ and He2+) impact at energies ranging from 25 to 10,000 keV/amu. We use a distorted wave (DW) method where the intermediate continuum state of the active electron with the target ion has been taken into account. This method is developed within the framework of the independent electron model taking particular care of the representation of the bound continuum target states. Two different approximations have been considered for molecular targets: molecular representation of the bound-state target wavefunction and Bragg’s additivity rule. The molecular orbital for targets are described within the framework of the complete neglect of differential overlap (CNDO) method based on the linear combination of atomic orbital (LCAO) approximation. Using the DW method, we have also calculated the K-, L- and M- shell electron capture in collisions of bare ions with three noble gases He, Ne, and Ar respectively. Contributions from different molecular orbitals and different shells to the total cross sections (TCS) are studied. The preference of electron capture occurs in accordance as the binding energy of the active electron in molecular orbital and atomic shell. The maximum contributions to TCS for SC comes from the less bound electrons in repetitive orbitals, whereas the tightly bound electrons dominate the TCS at higher projectile energy regime. Variation of TCS with impact energy are compared with the available experimental observation and other theoretical findings. We find that the present theoretical method is satisfactory in both intermediate and high-energy region for molecules as well as noble gas targets to give reliable outcomes compared to other theoretical methods.

Comparative Computational Study of Electronic Excitations of Neutral and Charged Small Oligothiophenes and Their Extrapolations Based on Simple Models.

This work reports electronic excitation energies of neutral and charged oligothiophenes (OTn) with repeat unit n = 2–6 computed by routinely used semiempirical and time-dependent density functional theory (TD-DFT) methods. More specifically, for OTn, OTn+, and OTn–, we calculated vertical transition energies for electronic absorption spectroscopy employing the Zerner’s version of intermediate neglect differential overlap method for structures optimized by the PM6 semiempirical method and the TD-DFT method with three different functionals, B3LYP, BVP86, and M06-2X, for structures optimized by the ground-state DFT method employing the same functionals. We also calculated vertical transition energies for the emission spectroscopy from the lowest singlet excited states by employing the TD-DFT method for the structures optimized for the lowest singlet excited states. In addition to computational results in vacuum, solution phase data calculated at the level of polarizable continuum model are reported and compared with available experimental data. Most of the data are fitted reasonably well by two simple model functions, one based on a Frenkel exciton theory and the other based on the model of independent electrons in a box with sinusoidal modulation of potential. Despite similar levels of fitting performance, the two models produce distinctively different asymptotic values of excitation energies. Comparison of these with available experimental and computational data suggests that the values based on the exciton model, while seemingly overestimating, are closer to true values than those based on the other model. This assessment is confirmed by additional calculations for a larger oligomer. The fitting parameters offer new means to understand the relationship between electronic excitations of OTs and their sizes and suggest the feasibility of constructing simple coarse-grained exciton-bath models applicable for aggregates of OTs.

Nature of Electronically Excited States of Furocoumarins

A comprehensive study of spectral-luminescent and photophysical properties of coumarin sensitizers is performed using the methods of quantum chemistry, electron spectroscopy, and fluorescence. A comparative study of photophysical processes occurring in 8-methoxypsoralen (8-MOP) and 4,9-dimethoxy-7-methylfuro [3,2-g][1] benzofuran-5-1 (khellin) is performed using the quantum-chemical software package based on the semi-empirical method of intermediate neglect of differential overlap with original spectroscopic parameterization. The dependences of the fluorescent properties and reactivity of the compounds on the geometry and composition of the solvation shell of molecules are established. It is shown that incorporation of additional methoxy groups in the structure of molecules has the strongest effect on the spectral-luminescent characteristics of khellin compared with 8-MOP.

Quantum and Thermodynamic Estimation of Mesostate Behaviour of Alkyl Benzoic Acids in Dielectric Medium: Comparative Study

Quantum and thermodynamic estimation of mesostate behaviour of p-n-alkyl benzoic acid with pentyl (PBA), hexyl (HBA) groups has been studied in dielectric medium (benzene). The complete neglect differential overlap (CNDO/2) method has been implemented for the charges, dipole moment and its components analysis. The long-range intermolecular interactions have been examined using the modified Rayleigh–Schrodinger perturbation method coupled with multicentred multipole expansion method. For understanding the short-range interactions, a ‘6-exp’ potential function has been used. The interaction energy values have been used to estimate the probability of each configuration in a dielectric medium (benzene) using the Maxwell–Boltzmann formula at room temperature (300 K) and at nematic–isotropic transition temperatures. Thermodynamic view has been presented based on Helmholtz free energy and entropy. A correlation has been made between quantum statistical and thermodynamic data to estimate the mesostate behaviour of the title molecules.

7-Hexyloxy-3-[4’-(3-methylbutyloxy) phenyl]-4H-1-benzopyran-4-one: Study of Smectic behaviour and UV absorption profile

abstractThe intermolecular interaction energies between a pair of 7-Hexyloxy-3-[4’-(3-methylbutyloxy) phenyl]-4H-1-benzopyran-4-one (HMBPB) molecules have been estimated with respect to translational and orientational motions. The complete neglect differential overlap (CNDO/S) method has been employed to calculate the net atomic charge and atomic dipole moment components at each atomic center. The modified Rayleigh-Schrodinger perturbation theory along with multicentered-multipole expansion method has been employed to evaluate the long-range intermolecular interactions, while a ‘6-exp’ potential function has been assumed for short-range interactions. The total interaction energy values obtained through these computations have been used to calculate the probability of each configuration at room temperature (300K), and isotropic-smectic transition temperature (412.6K). Molecular arrangements inside a bulk of materials and smectic behavior of the compound in terms of their relative order have been discussed. Translational and rotational rigidity of the molecule has been analyzed to understand the smectic behaviour. The UV absorption profile has been estimated using CNDO/S, and INDO/S methods.

Structural, electrochemical and optical properties of 4′-n-alkyl-4-cyanobiphenyl (nCB) – A computational approach

ABSTRACTThe structures of nCB (n = 6 & 7 where n is the number of carbon atoms in the alkyl chain) have been optimized using the Becke3-Lee-Yang-Parr (B3LYP) hybrid functional with 6–31G+(d) basis set using the crystallographic geometry as input. The electronic structures of the dimer molecules have been computed using the optimized geometries. The spectra of the dimer molecules have been calculated by employing the DFT method. The features of electronic transitions and excited states have been calculated via configuration interaction singles (CIS) with the semiempirical Hamiltonian Zerner intermediate neglect of differential overlap (ZINDO). The photo sensitivity of liquid crystalline alkyl cyanobiphenyl has been presented on ultraviolet (UV) absorption based approach through Density functional theory (DFT) calculations. The structural and electrochemical properties such as HOMO (H), LUMO (L), and energy gap (Eg = EL – EH) have been investigated. A comparison of dimers during the different modes of interactions suggests an absorption maxima at longer wavelength for 7CB, indicating the high photo sensitivity. Further, the 6CB dimers exhibit a lower band gap; hence its conductivity is high in comparison with the 7CB dimers.

Probabilistic and thermodynamic approach on phase behavior of nematic liquid crystals: A comparative study

ABSTRACTThe systems chosen for the present investigation, p-n-alkylbenzoic acid (nBAC; n = 6, 7) exhibits nematic-isotropic transition. A comparative study based on quantum probabilistic and statistical thermodynamics has been carried out with respect to translational and orientational motions. The evaluation of net atomic charges and dipole moment at each atomic centre has been carried out through the complete neglect differential overlap (CNDO/2) method. The modified Rayleigh-Schrodinger perturbation theory along with multicentered-multipole expansion method has been employed to evaluate the long-range intermolecular interactions, while the ‘6-exp’ potential function has been assumed for short-range interactions. The total interaction energy values obtained through these computations have been used as input to calculate the probability of occurrence of a particular configuration using the Maxwell-Boltzmann formula. Further, thermodynamic parameters such as Helmholtz free energy, and entropy at room temperature (300 K), and nematic-isotropic transition temperatures have been computed. An attempt has been made to understand the structure-phase behaviour relationship at molecular level.

A quantum-chemical study of conformational and electronic properties of ter-anthrylene-ethynylene derivatives in neutral and ionized states

ABSTRACTThe density functional theory (DFT) calculations are applied to the series of 9,10-ter-anthrylene-ethynylene derivatives being in neutral, cationic and anionic charge states to gain insight into their conformational properties, frontier orbitals, ionization potentials (IP), electron affinity (EA) and reorganizations energies. The evolution of intramolecular transfer integrals are investigated within the energy-splitting in dimer (ESD) model using the intermediate neglect of differential overlap (INDO) semi-empirical method, the oscillating behavior is observed both for electrons and holes charge carriers. The computed results are reasonably consistent with data of available experimental and theoretical studies.

Molecular catchers for pharmacologically active substances in wastewaters, a theoretical study

A basic and pressing need in the treatment of residual waste waters for urban and rural centers is the removal of pharmacological active residues from them, these resides are originated in a wide array of domestic, agricultural and industrial sources and can't be removed in the residual waters treatment plants by conventional methods, the result is the incorporation of them into the ecosystem altering the physiology and behavior of living organisms. Among the most active pharmacological substances found in very high concentration in residual waters is paracetamol, an analgesic of very wide excessive use due to its ease of access and low cost [1]. No pharmacological substance is entirely absorbed by the human organism and therefore a wide family of molecular residues is excreted by the urinary tract. In this work we have used the AM1 (Austin Model 1), PM3 (Parametric Method 3) and ZINDO/CI semiempirical methods, from the NDO (Neglect Differential Overlap) family [2] to study and observe the structural, electronic and optical characteristics of paracetamol while immersed in different basic and acidic aqueous environments, either alone or interacting with lignosulphonates. We have previously found that lignosulphonates, a lignin derivatives of wide industrial applications, can be engineered as a binding and flocculant agent and acts as molecular catchers therefore showing the potential to be used as a mean to filter and eliminate molecular residues from the residual waters [3].

Specific features of photoprocesses in the dye merocyanine 540 and its complexes with water

The electronic structure and spectral-luminescence properties of the dye merocyanine 540 have been calculated within the framework of the semiempirical quantum-chemical method of partial neglect of differential overlap (PNDO) with spectroscopic parameterization. The trans and cis conformations of the molecule, as well as the trans–cis photoisomerization process, have been considered. The calculation has been performed for an isolated molecule of the merocyanine 540 and its complex with water. The results of the calculation have been compared with the experimental spectral-luminescence characteristics of the molecule in different solvents. It has been shown that there is a good agreement between the calculated and experimental spectra, the nature of the excited states, and photoprocesses.

Structural and optical properties of novel nematogens based on DFT and semiempirical method—A comparative picture

ABSTRACTA comparative picture of structural, and optical properties of nematogens, viz., bis(4-propyloxyphenyl) 1,12-dicarba-closo-dodecaborane-1,12-dicarboxylate (Nematic1), and bis(4-butoxyphenyl) 1,10-dicarba-closo-decaborane-1,10-dicarboxylate (Nematic2) have been studied in ultraviolet (UV) and visible (Vis) regions. The structure of nematogens have been optimized using the Density functional B3LYP with 6–31+G (d) basis set using crystallographic geometry as input. The electronic structure of the molecules has been evaluated using the DFT, and semiempirical methods, namely; CNDO/S (complete neglect of differential overlap/ spectroscopy) and INDO/S (intermediate neglect of differential overlap/ spectroscopy). The HOMO (Highest Occupied Molecular Orbital)/LUMO (Lowest Unoccupied Molecular Orbital) energies, and oscillator strength (f) have also been reported using these methods. The electronic absorption spectra of the molecules have been simulated by employing the DFT method, semiempirical parameterizations. Molecular charge distribution and phase stability of these nematogens have been analyzed based on Mulliken and Loewdin population analysis. It has been observed that Nematic2 molecule shows the much flexibility for electronic transitions over a long wavelength region that leads to high photosensitivity.

Theoretical study of closo-decaborate novel nematogen: Thermodynamic behavior and phase stability

ABSTRACTThe present article deals with the thermodynamic behavior and phase stability of closo-decaborate nematogen viz. dinitrogen-10-(4-pentyl-1-thiacyclohexyl)-closo-decaborate (DPTD) at a molecular level. The atomic net charge and dipole moment at each atomic center have been evaluated using the complete neglect differential overlap (CNDO) method. The modified Rayleigh–Schrodinger perturbation method along with multicentered–multipole expansion method has been employed to evaluate the long-range intermolecular interactions, while a ‘6-exp’ potential function has been assumed for the short-range interactions. The total interaction energy values obtained through these computations have been used to calculate the probability of each configuration at room temperature (300 K), nematic–isotropic transition temperature (435 K), and above transition temperature (500 K) using the Maxwell–Boltazman formula. Further, the entropy of each configuration has been computed during the different modes of interactions. The adopted framework provides valuable information on thermodynamic behavior, and phase stability of novel nematogen based on parameters, i.e., molecular and thermodynamic, introduced in this article.

Ordering and Nematic Phase Behavior of a Naphthyl Ester: A Computational Model Based on Semiempirical Approach

The present article deals with the ordering and nematic phase behavior of naphthyl-ester, viz., 4-octylphenyl-6-octyloxy-2-naphthoate based on semiempirical approach at a molecular level. The atomic net charge and dipole moment at each atomic centre has been evaluated using the complete neglect differential overlap method. The modified Rayleigh–Schrodinger perturbation method along with multicentered-multipole expansion method has been employed to evaluate the long-range intermolecular interactions, while a “6-exp” potential function has been assumed for the short-range interactions. The total interaction energy values obtained through these computations have been used to calculate the probability of each configuration at room temperature, nematic-isotropic transition temperature, and above transition temperature using the Maxwell–Boltzmann formula. Further, the entropy of each configuration has been computed during the different modes of interactions. An effort has been made to develop a computational model at molecular level based on thermodynamic parameter introduced in this article.

Erratum to: Molecular Modeling of Ammonium, Calcium, Sulfur, and Sodium Lignosulphonates in Acid and Basic Aqueous Environments

Lignosulphonates (LS), also known as lignin sul- fonates or lignin, are lignins in sulfonated forms, obtained from the sulfite liquors, a residue of the wood pulp extraction process. Their main utility lies in its wide range of properties, they can be used as additives, disper- sants, binders, fluxing, binder agents, etc. in fields ranging from food to fertilizer manufacture and even as agents in the preparation of ion exchange membranes. Since they can be manufactured relatively easy and quickly, and that its molecular size can be manipulated to obtain fragments of very low molecular weight, they are used as transport agents in the food industry, cosmetics, pharmaceutical and drug development, and as molecular elements for the treatment of health problems. In this paper, we study the electronic structural and optical characteristics of LS incorporating ammonium, sulfur, calcium, and sodium ions in acidic and basic aqueous media in order to gain a better understanding of their behavior and the very interesting properties exhibit. The studies were performed using the molecular model- ing program HyperChem 5 using the semiempirical method PM3 of the NDO Family (neglect of differential overlap), to calculate the structural properties. We calculated the electronic and optical properties using the semiempirical method ZINDO / CI.

Properties of the Triplet State of Coumarin Substituted Compounds

The absorption spectra of the triplet excited state of coumarin sensitizers are investigated both theoretically and experimentally. The most intense triplet-triplet (TT) absorption bands are determined. The experimental spectra of the T-T absorption are compared with the theoretical T-T transitions. The phosphorescence spectra of five compounds are measured at a temperature of 77 K. The quantum phosphorescence yield is determined by the method of comparison with an etalon (8-methoxypsoralen). The phosphorescence lifetime is determined for the examined molecules at a temperature of 77 K. For 3,4-phenyl-4',5'-cyclohexylpsoralen, 4'-methyl-3,4-cycloheptylpsoralen, and 4'5'-dimethyl-3,4-cyclohexylpsoralen compounds, this time is equal to 1.1, 1.25, and 2.5 s, respectively. The main energy deactivation channel for all examined compounds is the phosphorescence. The positions of the lower excited triplet states, calculated by the quantum-chemical method of intermediate neglect of differential overlap with spectroscopic parameterization (INDO/S), are confirmed by the available experimental data.

The Influence of Alkyl Chain Length and Solvents on Configurational Probability of Liquid Crystalline Materials: A Computational Approach

The influence of alkyl chain length and solvents on two liquid crystalline materials, p-n-butylbenzoic acid (4BAC), and p-n-pentylbenzoic acid (5BAC) has been carried out with respect to the translational and orientational motions. The atomic net charge and dipole moment components at each atomic center have been evaluated using the complete neglect differential overlap (CNDO/2) method. The modified Rayleigh–Schrodinger Perturbation theory with the multicentered-multipole expansion method has been employed to evaluate the long-range interactions, and a “6-exp.” potential function has been assumed for the short-range interactions. The minimum energy configurations obtained during the different modes of interactions have been taken as input to calculate the configurational probability using the Maxwell–Boltzmann formula in nonpolar organic solvents, i.e., carbon tetrachloride (CCl4), and chloroform (CHCl3) at room temperature 300 K. It has been observed that the increase of alkyl chain length causes a minimization in the binding energy, and increases the total energy of 5BAC molecule. Further, the molecules produce remarkable property in the solvents.

Effect of Molecular Interactions and Homologue Number on UV Absorption Spectra of Liquid Crystalline Alkyl Cyanobiphenyl Dimers: DFT Calculations

The ultraviolet (UV) absorption spectra of the liquid crystalline dimer complexes of 4′-n-alkyl-4-cyanobiphenyls (nCB: n = 3, 4, 5 where n is the number of carbon atoms in the alkyl chain) have been presented. The nCB structures have been optimized using the density functional Becke3-Lee-Yang-Parr (B3LYP) hybrid functional with 6-31+G (d) basis set using the crystallographic geometry as input. The electronic structures of the dimer molecules have been computed using the optimized geometries. The spectra of the dimer molecules have been calculated by employing the density functional theory (DFT). The features of electronic transitions and excited states have been calculated via configuration interaction singles (CIS) with the semiempirical Hamiltonian Zerner intermediate neglect of differential overlap (ZINDO). The various modes of molecular interactions and the homologue number are found to be structural parameters affecting the formation of mesophases, UV absorption spectral characteristics, and photo stability of the compounds. These results offer a hint for the calculations involving the different modes of molecular interactions, and separations between dimers, to model photo stability or in tuning the absorbing chromophore to match the wavelength of desired application.