MO Method Research Articles

H/D isotope effect in methyl torsional interaction of acetone as calculated by a multicomponent molecular orbital method

We analyzed the H/D isotope effect in the methyl torsional interactions accompanying two methyl internal rotations for acetone (CH(3)COCH(3)) and deuterated acetone (CD(3)COCD(3) and CH(3)COCD(3)) in the ground state by means of the multicomponent molecular orbital (MC_MO) method, which directly accounts for the quantum effects of protons and deuterons. Our estimated rotational constants and moments of inertia for CH(3)COCH(3) and CD(3)COCD(3) agreed well with the experimental results because of the adequate treatment of protonic and deuteronic quantum effects afforded by the MC_MO method. Because the C-D bond distance in the CD(3) group was shorter than the C-H distance in CH(3) owing to the anharmonicity of the potential, the difference in potential energy surfaces of CH(3)COCH(3), CD(3)COCD(3), and CH(3)COCD(3) was strongly related to the differences induced in geometrical parameters by the H/D isotope effect. The potential energy obtained by the MC_MO method was estimated as 290.88 cm(-1) for CH(3)COCH(3), which is in excellent agreement with the experimental results. For CH(3)COCD(3), two potential energies were obtained for CH(3) and CD(3) internal rotations. The MC_MO method successfully elucidated the H/D isotope effect for methyl-methyl repulsive interactions by allowing the adequate treatment of protonic and deuteronic wave functions. The potential energies and bond distances associated with methyl internal rotation induced by the H/D isotope effect were also controlled by the distribution of wave functions of protons and deuterons.

The Energetics of Large Deformations of a Single Polyimide Molecular Chain: DFT and MO Calculations

AbstractThe large‐deformation energetics of a single molecular chain of the rod‐like polyimide PMDA‐PDA was investigated using DFT, ab initio MO and semi‐empirical MO methods. The force/displacement curves were calculated from tensile testing simulations along the axis of the molecular chain, allowing a discussion of the distribution and change of local strain of the molecular chain. The deformation behavior of a single PMDA‐PDA molecular chain under finite deformations as functions of bending angle and dihedral angle between PMDA and PDA groups are compared. It is found that the semi‐empirical MO calculations provide sufficient accuracy to express the energetics of large deformations except for compressive deformation.magnified image

Low-temperature sintered PMnN-PZT based ceramics using the B-site oxide precursor method for therapeutic transducers

The modified PMnN-PZT based piezoelectric ceramics of composition Pb 0.99Ca 0.01 [(Mn 1/3Nb 2/3) x − (1 − x)(Zr y Ti 1− y )]O 3 (0.02 ≦ x ≦ 0.07, 0.47 ≦ y ≦ 0.54) were synthesized by B-site oxide precursor method (BO method) and conventional mixed oxide method (MO method). The morphotropic phase boundary (MPB) was adjusted by varying the Zr ratio to compromise the balance between the piezoelectric properties and the temperature stability of static capacitance. The influence of PMnN content on the microstructure, electrical, temperature stability and mechanical properties of the samples synthesized using these two methods were investigated and compared. Results showed that the samples synthesized using the BO method not only lowered the sintering temperature (from 1260 °C to 1150 °C) without adding any sintering aids but also exhibited piezoelectric properties, temperature stability of resonance frequency (TCF) and elastic stiffness coefficient superior to those of MO-type piezoelectric ceramics. Experimental results showed that the bulk density (g/cm 3), dielectric loss, K t , K p , d 33, Q m , c 33 D (×10 10 N/m 2), and TCF (ppm/°C) of BO-type ceramics were 7.78, 0.0022, 0.5, 0.63, 345, 1450, 14.65, and 85 compared to those of MO-type ceramics (i.e., corresponding values of 7.65, 0.0025, 0.48, 0.58, 280, 1400, 14.54, and 105) with optimum composition of x = 0.04. The obvious improvement is due to the fine-grain microstructure and chemical homogeneity. In addition, two types of narrow-band therapeutic transducers were fabricated and compared. According to the experimental results, the PMnN-PZT based piezoelectric ceramics using the BO method are found to be suitable for in ultrasonic therapeutic transducer applications.

Quantum Mechanical Study of Photoinduced Charge Transfer in FMN Binding Protein

CT interactions between Iso* and nearby aromatic amino acids in FBP were investigated by a semiempirical MO method. Atomic coordinates of lumiflavin as Iso, 3-methylindole as Trp, and 4-methylphenol as Tyr, used for MO calculations, were obtained from crystal, 20 NMR structures and 40 MD structures (20 ps time intervals). Geometries of Iso-Trp32, Iso-Trp106 and Iso-Tyr35 systems were optimized by the PM3 method. The interaction energies (kcal/mol) of crystal structure were -16.9 in the Iso-Trp32 system, -7.4 in the Iso-Trp106 system and 1.4 in the Iso-Tyr35 system. The interaction energies (kcal/mol) of NMR structures were -16.5 +/- 0.28 in the Iso-Trp32 system, -10.6 +/- 0.14 in the Iso-Trp106 system, and 0.97 +/- 0.09 in the Iso-Tyr35 system. The interaction energies (kcal/mol) of MD structures were -24.3 +/- 0.19 in the Iso-Trp32 system, -10.2 +/- 0.49 in the Iso-Trp106 system, and 0.285 +/- 0.037 in the Iso-Tyr35 system. CT interaction from the aromatic amino acids to Iso* was judged from negative charge at Iso*. The charge in the Iso-Trp32 system was -0.490 in crystals, -0.439 +/- -0.099 in NMR structures, -0.454 +/- 0.048 in MD structures. The charge in the Iso and Trp106 system was -0.011 +/- 0.004 in MD structures, but negligible in other structures. CT interactions in Iso-Tyr35 system were also negligible. The ET rate obtained with Kakitani and Mataga theory and MD decreased as the magnitude of the interaction energy decreased. Correlation between the ET rate and CT interaction in FBP was examined. The interaction energy (Y) was approximated with ln(ET rate) (X) by a function, Y = 0.0036X(3) + 0.0306X(2) - 1.7822X - 21.177.

MSINDO quantum chemical modeling study of water molecule adsorption at nano-sized anatase TiO 2 surfaces

In this work, we studied the adsorption of water molecule onto the (1 0 0), (0 1 0) and (0 0 1) surfaces of nano-sized anatase TiO 2 with semiempirical SCF MO method, MSINDO. The anatase TiO 2 particles are modeled with free clusters (TiO 2) n , where n = 20–80. Whereas, the surfaces have been modeled with two saturated clusters, Ti 21O 58H 32 and Ti 36O 90H 36. The surface lattice fivefold coordinated titanium atoms (Ti 5C), which represent the Lewis acid sites, are selected as adsorption centers. We also investigated the effect of TiO 2 cluster size on the computed band gap energy. Results reveal that the electronic properties of a cluster in the lowest excited state differ from that of the ground state. Furthermore, the MSINDO band gap energies of 3.68–3.77 eV for the anatase TiO 2 are in a fair accordance with other literature data. In agreement with other computational and experimental studies, the dissociated form of water molecule adsorption on anatase TiO 2 surfaces is always more stabilized than the molecular form.

Computational investigation of water and oxygen adsorption on the anatase TiO 2 (1 0 0) surface

In this work, a computational technique based on semiempirical SCF MO method MSINDO, has been adopted for adsorption of water and oxygen molecules on the anatase TiO 2 (1 0 0) surface. We employed free and saturated cluster models for simulation of TiO 2 (1 0 0) surface. In accordance with other experimental and theoretical methods, the adsorption of dissociated form of water molecule is energetically more favoured than that of molecular form. Furthermore, the hydrogen bonding of water molecule with surface titanium ion plays a significant role in stabilization of water molecule adsorption. We have also investigated the adsorption of atomic and molecular, singlet and superoxide, oxygen. The results reveal that, the adsorption of atomic and molecular oxygen on TiO 2 (1 0 0) surface is energetically possible. Further, the peroxo type adsorption of molecular oxygen at four-fold coordinated titanium (Ti 4C) atom, being predominant.

Computational investigation of the adsorption and photocleavage of chlorobenzene on anatase TiO 2 surfaces

The adsorption and photocleavage of chlorobenzene (CB) molecule on the anatase TiO 2 (0 0 1), (1 0 0) and (0 1 0) surfaces are studied with semiempirical SCF MO method, MSINDO. The surfaces have been modeled with two saturated clusters Ti 21O 58H 32 and Ti 36O 90H 36. The dissociative perpendicular adsorption of CB on TiO 2 (0 1 0) and (1 0 0) surfaces revealed comparable stabilities and much higher than on the (0 0 1) surface. The aromatic ring cleavage by atomic oxygen, singlet oxygen and superoxide anion molecules has been investigated computationally and relevant mechanisms are proposed. Molecular dynamics (MD) simulations have been implemented for the adsorption models and the early stages of photocleavage mechanisms. The oxygen-type chemistry is involved actively in the water mediated photocleavage step upon excitation. The O 2 - radical anion dependant ring opening mechanism, through the dioxetane intermediate, is thermodynamically the most favourable.

Geometrical and Kinetic Isotope Effects on R–H(D)···R Type Intramolecular Hydrogen Bonds (R = CH2, NH, and O) Using a Multi-Component Molecular Orbital Method

Abstract We theoretically analyzed the geometrical isotope effect and kinetic isotope effect for R–H(D)···R type proton (deuteron) transfer on the intramolecular hydrogen bond of (Z)-1,3-pentadiene (R=CH2), 3-imino-1-propen-1-amine (R=NH), and malonaldehyde (R=O) by using Hartree–Fock (HF) and second-order Møller–Plesset (MP2) levels of a multi-component molecular orbital (MC_MO) method to treat the quantum effects of nuclei. As the protonic and deuteronic basis functions, our proposed exponent values of 24.1725 and 35.6214 for the single protonic and deuteronic Gaussian-type functions were employed, respectively. In the case of R=NH and O, the calculated R5–D6 and R1···D6 bond lengths are shorter and longer than those of the R5–H6 and R1···H6 bonds due to the anharmonicity of the potential. The charge densities around the deuteron for all R=CH2, NH, and O cases are larger than those around the proton because the deuteron is more localized than the proton. The ratio of rate constant (kaH⁄kaD) obtained by MP2 level theory of the MC_MO method is estimated as 10.16, which is in reasonable agreement with the experimental result (12.2). For the systematic analysis of the intramolecular proton (deuteron)-transfer reaction, we also estimated the kaH⁄kaD of R=NH and O.

Computational modeling of the adsorption and photodegradation of 4-chlorophenol on anatase TiO 2 particles

In the present work, the adsorption and photodegradation of 4-chlorophenol (4-CP) on the (100) surface of TiO 2 anatase with semiempirical SCF MO method MSINDO has been investigated. The (100) surface is modeled with free clusters (TiO 2) n , where n = 20–80. The surface lattice titanium atoms, which are Lewis acid sites, are considered as adsorption sites. Molecular dynamics (MD) simulations have been used for the investigation of 4-CP adsorption conformations and the surface reaction mechanism studies. The 4-CP molecule has revealed parallel adsorption upon optimization, whereas under excitation conditions the perpendicular configuration is dominant. The aromatic ring cleavage by atomic oxygen has been studied computationally and accordingly, the relevant mechanism was suggested. By comparison with experimental and other theoretical calculations, it is shown that MSINDO can reproduce literature data with acceptable accuracy.

H ∕ D isotope effect of methyl internal rotation for acetaldehyde in ground state as calculated from a multicomponent molecular orbital method

We have analyzed the differences in the methyl internal rotation induced by the HD isotope effect for acetaldehyde (CH(3)CHO) and deuterated acetaldehyde (CD(3)CDO) in ground state by means of the multicomponent molecular orbital (MC_MO) method, which directly accounts for the quantum effects of protons and deuterons. The rotational constant of CH(3)CHO was in reasonable agreement with experimental one due to the adequate treatment of the protonic quantum effect by the MC_MO method. The C-D bond distances were about 0.007 A shorter than the C-H distances because of the effect of anharmonicity of the potential. The Mulliken population for CD(3) in CD(3)CDO is larger than that for CH(3) in CH(3)CHO because the distribution of wavefunctions for the deuterons was more localized than that for the protons. The barrier height obtained by the MC_MO method for CH(3)CHO was estimated as 401.4 cm(-1), which was in excellent agreement with the experimentally determined barrier height. We predicted the barrier height of CD(3)CDO as 392.5 cm(-1). We suggest that the internal rotation of the CD(3) group was more facile than that of the CH(3) group because the C-D bond distance was observed to be shorter than the C-H distance. Additionally the localized electrons surrounding the CD(3) group in CD(3)CDO caused the extent of hyperconjugation between the CD(3) and CDO groups to be smaller than that in the case of CH(3)CHO, which may have also contributed to the observed differences in methyl internal rotation. The differences in bond distances and electronic populations induced by the H/D isotope effect were controlled by the difference in the distribution of wavefunctions between the protons and deuterons.

Influence of intrinsic defects on the properties of zinc oxide

The effects of oxygen vacancies and zinc interstitials on the structure and energy of zinc oxide were studied with the semiempirical MO method MSINDO. Cyclic clusters were chosen as model systems. Single and multiple removal of oxygen atoms and zinc interstitials in zinc oxide served to determine the defect formation energy and the band gap. The interaction between two and three oxygen vacancies was investigated. The vacancies cause a decrease of the band gap, which originates from an occupied defect level. This is also found for zinc interstitials under zinc rich conditions. The defect formation energy of such zinc interstitials is found to be lower than that of oxygen vacancies at 0 K but decreases for oxygen vacancies and increases for zinc interstitials with increasing temperature.

Fragment distribution of thermal decomposition for PS and PET with QMD calculations by considering the excited and charged model molecules

Simulations by a quantum molecular dynamics (QMD) (MD with MO) method were demonstrated on the thermal decomposition of PS and PET polymers using the model molecules at the ground state including excited and positive charged states. For the excited and positive charged model molecules, we adopted CH 3CHC 6H 5CH 3 and CH 3OCOC 6H 4COOCH 3 of PS and PET monomers, respectively at the singlet and triplet states in single excitation, and at (+2) positive charged state by semiempirical AM1 MO method. Geometry and energy optimized results of the excited and positive charged models by MO calculations were used as the initial MD step of QMD calculations. In the QMD calculations, we controlled the total energy of the system using Nosé–Hoover thermostats in the total energy range of 0.69–0.95 eV, and the sampling position data with a time step of 0.5 fs were carried out up to 5000 steps at 60 different initial conditions. The calculated neutral, positive and negative charged fragment distributions of PS and PET models with 0.82 eV energy control were obtained as (93.5, 2.3, and 4.3%), and (87.8, 5.3, and 6.9%) to the total fragments, respectively. The ratios seem to correspond well to the values observed experimentally in SIMS.

Simulation of SIMS for monomer and dimer of lignin under the assumption of thermal decomposition using QMD method

The thermal decomposition of the monomer and dimer of lignin has been simulated by a quantum molecular dynamics (DMD) method. In the calculation, we controlled the total energy of the system using Nóse-Hoover thermostats in the total energy range of 0.69–0.95 eV, and the sampling position data with a time step of 0.5 fs were carried out up to 3000 (1.5 ps) or 5000 (2.5 ps) steps in ab initio and semiempirical MO methods, respectively. We obtained the thermally decomposed fragments with positive, neutral and negative charges from SCF MO calculation at each data of the last MD step, and simulated the fragment distribution of the monomer and dimer lignins from the last step in 30–40 runs. Simulated mass numbers of positively and negatively charged fragments for lignin monomer and dimer showed considerably good accordance with the experimental results in TOF-SIMS observed by Saito and co-workers.

Heterocycle-Based Isomeric Chromophores with Substantially Varying NLO Properties: A New Structure−Property Correlation Study

A number of heterocycle-based aromatic and quinonoid molecular systems have been considered for the theoretical study of their electric response properties. The nonlinear optical (NLO) parameters have been calculated by using the ab initio MO and DFT methods. An approximate scheme for calculating the first hyperpolarizability (beta) and second hyperpolarizability (gamma) in the framework of the sum-over-state (SOS) method have been proposed by exploiting the generalized Thomas-Kuhn sum rule (TK-SR). The NLO properties in the present scheme can be evaluated solely from the ground-state dipole moment (mu) and linear polarizability (alpha) and have been found to correlate fairly with the ab initio calculated values. The approximate scheme can be reasonably used to explain the wider range of variation of higher-order polarizabilities in terms of the above quantities. The position of the N atom in the thiazole ring at the ortho position (versus meta position) to the acceptor increases beta and decreases gamma for aromatic compounds, while the reverse trend is found with quinonoid compounds. In the case of the pyridine ring, the shifting of the N atom toward the acceptor enhances gamma, with insignificant variation of beta predicted for both the aromatic and quinonoid molecules. The negative contribution of the cubic polarizability of the quinonoid species increases linearly with alpha(2)/mean transition energy (Delta E).

Effect of Nanoparticle Surface Treatment on Nonisothermal Crystallization Behavior of Polypropylene/Calcium Carbonate Nanocomposites

Polypropylene (PP)/CaCO3 nanocomposites were prepared by melt-blending method using a Haake-90 mixer. The CaCO3 nanoparticles were surface modified with a coupling agent before compounding. A fine dispersion of the modified nanoparticles in the nanocomposites was observed by transmission electron microscopy (TEM). Effects of surface treatment of CaCO3 nanoparticles on the nonisothermal crystallization behavior and kinetics of PP/CaCO3 nanocomposites were investigated by differential scanning calorimetry (DSC). Jeziorny and Mo methods were used to describe the nonisothermal crystallization process. It was shown that the crystallization temperature of the nanocomposites increased due to the heterogeneous nucleation of the surface-treated nanoparticles. It was found that the nanoparticles modified with a proper content range of coupling agent could facilitate the nonisothermal crystallization of the nanocomposites under certain conditions (the cooling rate and the relative degree of crystallinity). This may be a potential application for the crystallization controlling of composites in manufacturing. In addition, the activation energy of crystallization for the nanocomposites and the nucleation activity of the nanoparticle were estimated by using Kissinger and Dobreva's methods, respectively. It could be concluded that the surface-treated nanoparticles had a strong nucleating activity, which caused the decrease of the activation energy of the nanocomposites.

One-pot synthesis of macrocyclic compounds possessing two cyclobutane rings by sequential inter- and intramolecular [2+2] photocycloaddition reactions

Sensitized photocycloaddition reactions of 6,6′-dimethyl-4,4′-[1,3-bis(methylenoxy)phenylene]-di-2-pyrone ( 1) with electron-poor α,ω-diolefins such as ethylene diacrylate ( 2a) and polyoxyethylene dimethacrylates ( 2b– d) afforded site- and stereoselective macrocyclic dioxatetralactones ( 3a– d) and ( 4b) having 18- to 25-membered rings across the C5–C6 and C5′–C6′ double bonds, or C5–C6 and C3′–C4′ double bonds in 1, respectively. Similar photoreactions of 1 with electron-rich α,ω-diolefins such as poly(ethylene glycol)divinyl ether ( 2e and 2f) afforded crown ether-type macrocyclic compounds ( 5e and 5f) having 18- and 21-membered rings across the C3–C4 and C3′–C4′ double bonds in 1, respectively. The stereochemical features of 3b, 5e- xx , and 5e- nn were determined by the X-ray crystal analysis. The reaction mechanism was inferred by MO methods.

Influence of Adjustable Grafted Side Chains on the Non-Isothermal Crystallisation of a Ternary-Monomer Solid Phase Graft Copolymer of Polypropylene

A solid phase graft copolymer with an adjustable structure was prepared by grafting maleic anhydride, methyl methacrylate and butyl acrylate onto polypropylene (PP). How the grafted side chains affected the crystallisation of the graft copolymer was studied by differential scanning calorimetry and polarised optical micrographs. Results show that the grafted side chains not only promoted heterogeneous nucleation but also hindered the whole crystal growth of the copolymers. The Jeziorny method and Mo method were successful in describing the non-isothermal crystallisation kinetics. The Jeziorny method showed that the Avrami exponent ranged from 2 to 3, indicating that the crystal tended to grow in a three-dimensional mode. The Mo method showed that the graft copolymer (known here as PPTM) needed a lower crystallisation rate than PP to attain the same crystallinity at unit time, due to the hetero-nucleation of the grafted side chains. Meanwhile, the hetero-nucleation of the grafted side chains caused a decrease in the crystallisation half-time and in the spherulite size of PPTM. Hindrance of the grafted side chains was shown by the incomplete crystallisation images and by the increase in the non-isothermal crystallisation activation energy of PPTM.

Lab‐on‐valve for the automatic determination of the total content and individual profiles of linear alkylbenzene sulfonates in water samples

Methods for the total content and individual determination of linear alkylbenzene sulfonates (LAS) in water samples based on the use of a lab-on-valve (LOV) module alone or coupled to CE equipment, respectively, have been developed. The total content of LAS has been determined by intrinsic absorption measurements (DA method) and after reaction with a methyl orange-cetylpyridine chloride mixture (MO method) with detection limits (LODs) of 21 ng/L and 15 microg/L, respectively, quantification limits (LOQs) of 70 ng/L, 50 microg/L, and development times of 100 and 124 s, respectively. The method for individual separation-quantification of LAS at very low concentration is based on automatic SPE preconcentration in the LOV module coupled on-line with the CE equipment. The LODs and LOQs thus obtained range between 1-21 and 4-70 ng/L, respectively, with linear dynamic ranges from the LOQ to 10 microg/L. Preconcentration factors of 10,000 and high efficiency to eliminate interferents by SPE enable application of the method to treated effluent, waste, surface and sea waters.

Ab Initio MO-MD Simulation Based on the Fragment MO Method. A Case of (−)-Epicatechin Gallate with STO-3G Basis Set

Abstract We performed ab initio MO-MD simulation based on the fragment MO (FMO) method using the (−)-epicatechin gallate in order to examine the efficiency of fragmentation pattern in comparison with conventional MO-MD. We clearly demonstrated that the FMO-MD simulation gave sufficient results concerning the trajectory of the total energy and the geometry difference.

Nonisothermal crystallization behavior of LLDPE/glass fiber composite

The nonisothermal crystallization behavior of linear low-density polyethylene (LLDPE)/glass fiber (GF) composite was investigated by differential scanning calorimetry (DSC). It was observed that the crystallization temperature peak (Tp) of LLDPE composite containing 5.0 wt % GF (LLDPE/GF5) was higher than that of the pure LLDPE at various cooling rates. The half-time of crystallization (t1/2) of LLDPE/GF5 composite was shortened under the effect of GF. The nonisothermal crystallization kinetics of LLDPE and LLDPE/GF5 composite were analyzed through the Avrami, Ozawa, and Mo equations. The results indicated that the data of the nonisothermal crystallization for LLDPE and LLDPE/GF5 composite calculated based on the Ozawa equation did not have the good linear relationship, but the nonisothermal crystallization behaviors of LLDPE and LLDPE/GF5 composite could be successfully described by the modified Avrami and Mo methods. The crystallization rate Zc of the modified Avrami parameter of LLDPE/GF5 composite was higher than that of pure LLDPE at the same cooling rate. The Mo parameter F(T) of LLDPE/GF5 composite was lower than that of LLDPE at the same degree of crystallinity. Through the Kissinger equation, the activation energies Ed of LLDPE and LLDPE/GF5 composite were evaluated, and their values were 312.3 and 251.2 kJ/mol, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008