Precise potential harmonic approach to directly solving Schrödinger equations of helium-like three-body systems

A complete potential harmonic scheme is presented, including the linked coupled hyperradial ordinary differential equations and the secular equation of eigenenergy. It has been used to directly solve the Schrödinger equations of helium-like three-body systems (nuclear chargeZ = 1–9). and very accurate ground state eigenenergies as well as low-lying singlet excited state ones have been obtained.     

Trial introduction of a complex potential function for perturbation that causes quantum mechanical transition in a one‐dimensional harmonic oscillator

Some results of computer simulation of the behavior of a one‐dimensional quantum mechanical oscillator are reported in this article. This harmonic oscillator comprises a particle trapped within a hyperbolic potential V(x) = x². Further, a perturbation potential function V′(x, t) was superposed upon the hyperbolic potential in order to induce a quantum mechanical transition. This perturbation function V′(x, t) is a function of both of space and time variables, and is set to represent a wave packet that is enveloped by a Gaussian bell‐shaped curve. A wave that probably has an appropriate wave number and angular frequency was inputted into the expression for the wave packet. In the initial phase, while the harmonic oscillator was allowed to oscillate almost freely, the wave packet was allowed to approach the harmonic oscillator. In the middle phase, the wave packet passes through the harmonic oscillator, affecting the shape of the quantum mechanical wave that represents the physical state of the system. In the last phase, when the wave packet left the system of the harmonic oscillator, the system settled onto an energetically stable state. The main objective of the simulation was to simulate the instance of a quantum mechanical transition from one eigenstate to another. After several trials, it was found that the perturbation function consisting of a complex function was, at least superficially, able to cause one desired transition, that is, a transition from one eigenstate to another eigenstate. By using such a complex perturbation function, a transition from the first excited state to the ground state was observed to occur. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

Understanding topological symmetry: a heuristic approach to its determination

An algorithm based on heuristic rules for topological symmetry perception of organic structures having heteroatoms, multiple bonds, and any kind of cycle, and configuration, is presented. This algorithm identifies topological symmetry planes and sets of equivalent atoms in the structure, named symmetry atom groups (SAGs). This approach avoids both the need to explore the entire graph automorphism groups, and to encompass cycle determination, resulting in a very effective computer processing. Applications to several structures, some of them highly symmetrical such as dendrimers, are presented.     

C-H bond activation of methane in aqueous solution: a hybrid quantum mechanical/effective fragment potential study

In this study, we investigated the C? H bond activation of methane catalyzed by the complex [PtCl₄]^2?, using the hybrid quantum mechanical/effective fragment potential (EFP) approach. We analyzed the structures, energetic properties, and reaction mechanism involved in the elementary steps that compose the catalytic cycle of the Shilov reaction. Our B3LYP/SBKJC/cc‐pVDZ/EFP results show that the methane activation may proceed through two pathways: (i) electrophilic addition or (ii) direct oxidative addition of the C? H bond of the alkane. The electrophilic addition pathway proceeds in two steps with formation of a σ‐methane complex, with a Gibbs free energy barrier of 24.6 kcal mol^?1, followed by the cleavage of the C? H bond, with an energy barrier of 4.3 kcal mol^?1. The activation Gibbs free energy, calculated for the methane uptake step was 24.6 kcal mol^?1, which is in good agreement with experimental value of 23.1 kcal mol^?1 obtained for a related system. The results shows that the activation of the C? H bond promoted by the [PtCl₄]^2? catalyst in aqueous solution occurs through a direct oxidative addition of the C? H bond, in a single step, with an activation free energy of 25.2 kcal mol^?1, as the electrophilic addition pathway leads to the formation of a σ‐methane intermediate that rapidly undergoes decomposition. The inclusion of long‐range solvent effects with polarizable continuum model does not change the activation energies computed at the B3LYP/SBKJC/cc‐pVDZ/EFP level of theory significantly, indicating that the large EFP water cluster used, obtained from Monte Carlo simulations and analysis of the center‐of‐mass radial pair distribution function, captures the most important solvent effects. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011     

Streaming potential measurements as a characterization method for nanofiltration membranes

The streaming potentials of two different nanofiltration membranes were studied with several electrolyte solutions to investigate the influence of salt type and concentration on the zeta potential and kinetic surface charge density of the membranes. The zeta potentials decreased with increasing salt concentration, whereas the kinetic surface charge densities increased. The kinetic surface charge densities could be described by Freundlich isotherms, except in one case, indicating that the membranes had a negligible surface charge. The kinetic surface charge density observed was caused by adsorbed anions. Salt retention measurements showed different mechanisms for salt separation for the two investigated membranes. One membrane showed a salt retention that could be explained by a Donnan exclusion type of separation mechanism, whereas for the other membrane the salt rejection seemed to be a combination of size and Donnan excluion. Comparing the results obtained by the streaming potential measurements with those of the retention measurements, it could be concluded that the membrane with the highest kinetic surface charge density showed the Donnan exclusion type of separation, whereas the membrane with the lower surface charge density showed a separation mechanism that was not totally determined by Donnan exclusion, size effects seemed to play a role as well.     

Tunneling and quantum localization in chaos‐driven symmetric triple well potential: An approach using quantum theory of motion

For a symmetric triple well potential, driven by the forces associated with the bifurcation diagram of a logistic map, the tunneling and quantum localization are studied using quantum theory of motion and time‐dependent Fourier grid Hamiltonian methods. Detailed analysis reveals that application of only asymmetric or symmetric perturbation results into either quantum localization or over‐barrier transition and no tunneling while application of mixed symmetry perturbation gives either tunneling or over‐barrier transition, depending on temporal nature and initial position of the particle. For bifurcative and chaotic symmetric‐asymmetric perturbation, with truncation of mixed symmetry perturbation, a sudden jump in energy causes a transition from the tunneling phenomenon to the over‐barrier transition. With particle located initially near to either of the minima of the unperturbed well, quantum localization, or over‐barrier transition is observed, depending on types of perturbation used.     

Light emitting diode induced chemiluminescence and its application as a detector for high performance liquid chromatography

Some categories of compounds, including quinones, coumarins, flavins, and xanthene dyes, were found to produce strong chemiluminescence (CL) signals with luminol in sample solution under the irradiation of light emitting diodes (LED) with proper wavelengths. Based on this phenomenon, a compact photochemical reactor was constructed to develop a novel LED induced CL detector for high performance liquid chromatography (HPLC). The effects of related parameters including LED wavelength, luminol concentration, flow rate, pH, and eluents of HPLC were investigated in detail. Under the optimized conditions, the limits of detections (LODs) were in the range of 0.2–80 ng mL⁻¹. The applications and accuracy of the proposed method were validated by analyzing food samples such as milk powder, beer, candy and beverage with satisfactory results.     

ForceFit: A code to fit classical force fields to quantum mechanical potential energy surfaces

The ForceFit program package has been developed for fitting classical force field parameters based upon a force matching algorithm to quantum mechanical gradients of configurations that span the potential energy surface of the system. The program, which runs under UNIX and is written in C++, is an easy‐to‐use, nonproprietary platform that enables gradient fitting of a wide variety of functional force field forms to quantum mechanical information obtained from an array of common electronic structure codes. All aspects of the fitting process are run from a graphical user interface, from the parsing of quantum mechanical data, assembling of a potential energy surface database, setting the force field, and variables to be optimized, choosing a molecular mechanics code for comparison to the reference data, and finally, the initiation of a least squares minimization algorithm. Furthermore, the code is based on a modular templated code design that enables the facile addition of new functionality to the program. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Oxidation potential of thiophene oligomers: Theoretical and experimental approach

Intrinsic properties of conducting polymers, such as oxidation potential and band gap, are very important for designing new materials with improved properties. Computational chemistry offers suitable tools capable of predicting these quantities. This work presents electrochemical information about accurate oxidation potentials of oligothiophenes and polymer band gap. These are compared to theoretical predictions based on electronic structure calculations at Density Functional Theory levels, coupled with self‐consistent reaction field. All computational protocols gave a qualitative prediction of the experimental trend. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Theoretical study of positron scattering by group 14 tetra hydrides: A quantum mechanical approach

The present work provides a comprehensive set of positron impact scattering cross sections for group 14 tetrahydrides, namely, SiH₄, GeH₄, SnH₄, and PbH₄. The well‐established spherical complex optical potential and complex scattering potential‐ionization contribution methods are modified to incorporate positron scattering in the present work to calculate various cross sections. The positronium formation channel is adequately included through an improved inelastic threshold. The energy range chosen for the direct ionization cross section is from the respective ionization potential (I) of the molecule to 5 keV. Likewise, positronium formation and total ionization cross sections are reported from the positronium formation threshold to 300 eV and 5 keV, respectively, and the total cross section is computed for an extensive energy range of 1 eV to 5 keV. The positron impact total cross section for stannane molecule is computed for the first time. A characteristic valley is observed in the total cross sections with minima close to the positronium formation threshold. Further increase of cross section signifies the opening of inelastic channels especially positronium formation. In general, a reasonable agreement is found between the present results and other comparisons, wherever available. Furthermore, this is the first report of the inelastic cross sections (direct ionization, positronium formation, and total ionization) for the present set of targets.     

Elemental composition of wood as a potential marker to evaluate heat treatment intensity

Microanalyses of pine and beech blocks treated under nitrogen at 240 °C for different times have been investigated to evaluate correlation between mass loss due to treatment and elemental composition. Oxygen content decreases with treatment intensity and is directly proportional to treatment time. In the same time, carbon content increases significantly indicating formation of carbonaceous materials within the wood structure. Acetylation has been investigated to evaluate the effect of heat treatment on the quantity of free hydroxyl groups present in the wood. The results indicate a significant decrease of reactivity of heat-treated samples compared to untreated ones. Although this decrease depends on the treatment intensity, no obvious correlation was observed between weight gain due to acetylation and mass loss due to treatment. All these results suggest that elemental composition of heat-treated wood could be a valuable marker to evaluate mass losses due to thermal degradation and consequently treatment intensity.     

Bismaleimide/carbon nanotube hybrids for potential aerospace application: I. Static and dynamic mechanical properties

Two kinds of hybrids based on diallyl bisphenol A modified bismaleimide (BMI‐BA) and carbon nanotubes (CNTs) or aminated carbon nanotubes (A‐CNTs) were prepared, their static and dynamic mechanical properties were investigated in detail by using impact and flexural measurements as well as dynamic mechanical analysis (DMA). Results show that these mechanical properties of hybrids greatly depended on the nature (or the functional groups on CNTs) and loading in BMI‐BA matrix of hybrids. For example, the BMI‐BA/A‐CNT hybrid with a desirable amount of A‐CNTs has a higher impact strength than the original BMI‐BA resin, while all BMI‐BA/CNT hybrids have lower impact strength than the original BMI‐BA resin. DMA test shows that all hybrids have somewhat lower storage modulus and glass transition temperature than a pure polymer, which maybe attributed to the fact that both CNTs and A‐CNTs shift the curing peak to a higher temperature range and thus decrease the crosslinking density of networks. Copyright © 2007 John Wiley & Sons, Ltd.     

Surveying FDA-approved drugs as new potential inhibitors of N-cadherin protein: a virtual screening approach

Since N-cadherin protein plays a remarkable role in cancer metastasis and tumor growth and progression, finding new effective inhibitors of this protein can be of high importance in cancer treatment. Nevertheless, few molecules have been introduced to inhibit N-cadherin protein to date. In this work, in order to find and present potent inhibitors, 3358 FDA-approved small molecules were docked against N-cadherin protein. All complexes with binding energy ??9 to ??8 kcal/mol were selected for protein-ligand interaction analysis. In the following, Tanimoto coefficient (T_c) was calculated for those molecules that established appropriate interactions with N-cadherin in order to compute the similarity score between them. Afterwards, molecular dynamics simulation and free energy calculations were done to estimate the stability and ability of the chosen ligands in complex with the target protein. Finally, seven small molecules among 3358 FDA-approved were suggested as potential inhibitors of N-cadherin protein.

     

Zeta potential measurement as a diagnostic tool in enzyme immobilisation

The efficiency of binding during enzyme immobilisation does not only depend on the chemical properties of the enzyme and the matrix particle, but also on their surface potential. Zeta potential quantifies the electrostatic interactions between enzyme and matrix particles, and can therefore, be used as an indicator of the binding efficiency in the enzyme immobilisation studies. In order to establish a correlation between the zeta potential and the binding efficiency, we used CALA (Candida antarctica A-type lipase) as a model protein for immobilisation on non-porous magnetic microparticles with epoxy (M-PVA E02), carboxy (M-PVA C12) and amine (M-PVA N12) terminations. We observed maximal binding of CALA onto the M-PVA N12 beads, due to the electrostatic attraction between negatively charged protein and carrier particles with slightly positive zeta potential. The binding of CALA was lower when M-PVA E02 beads were used, followed by M-PVA C12 beads. The decreasing binding efficiency was obviously the result of increasing electrostatic repulsion between the interaction partners. This could be correlated to the increasing negative zeta potential of the magnetic particles. Moreover, the medium of suspension of the particles also makes a significant difference. We found highest specific activity of the lipase immobilised on M-PVA E02 beads in a medium concentrated buffer (0.3M). The results demonstrate a clear correlation between zeta potential and binding efficiency but no correlation between the bead related specific activity and the zeta potential. These findings are advocating the possibility of using the zeta potential as a diagnostic tool in enzyme immobilisation.     

Cucurbiturils as potential free radical chemoradiosensitizers for enhanced cisplatin treatment of cancers: a quantum mechanical study

It has been shown in this study that the {CisPt@CB[7]} complex can be a source of Pt based free radicals such as (H₃N)₂PtCl· and (H₃N)₂Pt·· species in water within a radiation environment which can produce hydrated electrons. Encapsulating CisPt within the CB[7] host takes advantage of the previously described drug delivery and reduced side effect advantages of CBs. Based on quantum mechanical modelling and literature results, it is predicted that {CisPt@CB[7]} may interact with cellular macromolecules and engage in an enhanced permeation and retention mechanism in solid tumours, offering further synergistic advantages for a radiation-{CisPt@CB[7]} regimen over that of the conventional radiation-CisPt regimens in current use in anti-cancer chemoradiotherapies.     

Dynamical similarity in the highly excited vibrations of HCP and DCP: The dynamical potential approach

The fixed points in the dynamical potentials of phosphaethyne (HCP) and deuterated phosphaethyne (DCP) derived in the coset space are identified and shown to govern the various quantal environments in which the vibrational states lie. The state dynamics is interpreted and classified by the classical actions and action integrals. This is closely related to the fixed point structure. Localized modes even at high excitation are identified. Most important is that the dynamical similarity between these two systems is identified which enables us to understand the DCP dynamics simply from that of HCP without repeated elaboration.     

POSS nanoparticles as a potential compatibilizer for natural rubber/butadiene rubber blends

In this study, it was aimed to investigate octavinyl‐polyhedral oligomeric silsesquioxane (OV‐POSS) incorporation into natural rubber (NR)/butadiene rubber (BR) elastomer blends as a potential compatibilizer. The effects of OV‐POSS loading levels on the thermal, mechanical, morphological, and dynamic‐mechanical properties of elastomer blends were explored. Fourier‐Transform Infrared Spectrometer (FTIR), Temperature Scanning Stress Relaxation (TSSR), and Differential Scanning Calorimetry (DSC) results revealed the conceivable effect of OV‐POSS nanoparticles in the vulcanization through reacting with sulfur and/or elastomers. Scanning Electron Microscope (SEM), X‐Ray Diffraction (XRD), and tensile test measurements supported the improvement of mechanical properties due to homogeneous dispersion at low loading levels. On the other hand, high amount of OV‐POSS incorporation (7 and 10 phr) resulted in a decrease in mechanical properties, owing to the agglomeration of nanoparticles. According to contact angle and Dynamic mechanical analysis (DMA) results, it could be concluded that OV‐POSS nanoparticles were localized at the interface of the elastomers and enabled the compatibilization of immiscible NR/BR blends.     

Exact solution to a general quantum mechanical problem with time-dependent boundary conditions

Exact analytical solutions are found for the quantum mechanical problem of a particle subject to a time-dependent potential with time-dependent boundary conditions. The method of solution employs time-dependent invariants, rescaling of space and time variables along with an unitary transformation. Several applications are discussed. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 63: 827–833, 1997     

Light mirror reflection combined with heating/cooling curves as a method of studying phase transitions in transparent and opaque petroleum products: Apparatus and theory

A portable low weight low cost apparatus “Phasafot” and method for determining pour and cloud points of petroleum products, as well as precipitation and melting temperatures of paraffins in both transparent (diesel fuels), semi-transparent (lube oils) and opaque (crude oils) samples are described. The method consists in illuminating the surface of a sample with an oblique light beam and registering the intensity of specularly reflected light while heating/cooling the sample in the temperature range of its structural transitions. The mirror reflection of a light beam from an ideally smooth liquid surface falls in intensity when the surface becomes rough (dim) due to crystal formation. Simultaneous recording of the temperature ramp curve and the mirror reflection curve enables the determination of the beginning and end of crystallization of paraffins in both transparent and opaque petroleum products. Besides, their rheological properties can be accurately determined by rocking or tilting the instrument while monitoring the sample movement via its mirror reflection.