A new solvent suppression method via radiation damping effect

Radiation damping effects induced by the dominated solvent in a solution sample can be applied to suppress the solvent signal. The precession pathway and rate back to equilibrium state between solute and solvent spins are different under radiation damping. In this paper, a series of pulse sequences using radiation damping were designed for the solvent suppression in nuclear magnetic resonance (NMR) spectroscopy. Compared to the WATERGATE method, the solute signals adjacent to the solvent would not be influenced by using the radiation damping method. The one-dimensional (1D) ¹H NMR, two-dimensional (2D) gCOSY, and J-resolved experimental results show the practicability of solvent suppression via radiation damping effects in 1D and 2D NMR spectroscopy.     

Simulation study of solvent shifts of vibrational overtone spectra

Buckingham's theory of the solvent shift of vibrational spectral frequencies predicts that the shift of the v = 0 → n overtone transition is n times the shift of the fundamental v = 0 → 1. We test this prediction by molecular dynamics simulations using existing intermolecular potential models for liquid N₂ and dilute N₂ in liquid Ar, at standard state conditions. We extend Buckingham's theory by including additional intramolecular potential and perturbation terms which lead to solvent-induced anharmonicity, i.e. O(n ²) terms in the solvent shift. The simulations show that Buckingham's prediction is not accurate for N₂ at standard liquid state conditions. We find that at these conditions there is a significant positive O(n ²) contribution to the solvent shifts and that for n ～ 20 the shifts change sign from red to blue. Simulation results and indirect evidence from shock wave experiments with liquid N₂ show that Buckingham's prediction is more accurate for high-pressure high-temperature conditions, where the shifts are blue and only slightly nonlinear in n.     

Interaction between solute molecules in medium density solvents

Solvation properties of solutes in supercritical, medium density solvents have been analysed using hypernetted-chain theory with the emphasis on the solvent-mediated interaction between solute molecules. The solvent and solute molecules are Lennard-Jones particles, and the solute is present at infinite dilution. Also a pair of solute molecules separated by different distances has been considered using reference interaction site model theory. Mainly, solvents at two typical densities (1.09_pc and 2.91_pc; pc is the critical density) that are in medium and high density regions, respectively, are treated. The temperature is set at 1.04T_C (T_c is the critical temperature). When the solute size is larger than the solvent size and the strength of the solute-solvent attractive interaction is greater than that of the solvent-solvent in the medium density region, the solvent structure confined between a pair of solute molecules is largely different from that near a single solute molecule. The confined solvent becomes denser and more stabilized as the distance between the solute molecules decreases, and an attractive interaction is induced between them. The interaction becomes even more attractive as the strength of the solute-solvent attractive interaction increases. The observations are qualitatively different from those in the high density region. Another high density region, which is well below the critical temperature, has been considered, but the behaviour observed is similar to that in the high density region above the critical temperature.     

Importance of solute–solute interactions on glass formability

Microalloying experiments on amorphous Al₈₄La₄Er₂Ni₈TM₂ alloys were performed with the substitution of all 3d TM (transition metal) elements and one 4d TM element. The critical thickness of the amorphous alloys was used as a criterion for glass formability in this system. The results show that, other than atomic size differences and the negative heats of mixing among the solvent and solute atoms, the atomic interactions among the solute atoms play an important role on glass formation. When the solute–solute interaction becomes repulsive (positive heat of mixing), glass formability suffers. Similarly, when the solute–solute interaction becomes highly attractive, exceeding that between the solvent and solute atoms, glass formability is also degraded. Evaluation of a large number of known multicomponent bulk metallic glasses provides additional support to these conjectures. This study shows that the solute–solute interaction plays an important role in glass formation, which has not been recognized previously.     

Solvent dependent study of carbonyl vibrations of 3‐phenoxybenzaldehyde and 4‐ethoxybenzaldehyde by Raman spectroscopy and ab initio calculations

A Raman spectroscopy investigation of the carbonyl stretching vibrations of 3‐phenoxybenzaldehye (3Phbz) and 4‐ethoxybenzaldeheyde (4Etob) was carried out in binary mixtures with different polar and nonpolar solvents. The purpose of this study was twofold: firstly, to describe the interaction of the carbonyl groups of two solute molecules in terms of a splitting in the isotropic and anisotropic components and secondly, to analyze their spectroscopic signatures in a binary mixture. Changes in wavenumber position, variation in the anisotropic shift and full width half maximum were investigated for binary mixtures with different mole fractions of the reference systems. In binary mixtures, the observed increase in wavenumber with solvent concentration does not show linearity, indicating the significant role of molecular interactions on the occurrence of breaking of the self‐association of the solute. In all the solvents, a gradual decrease in the anisotropic shift reflects the progressive separation of the coupled oscillators with dilution. Γ_i(η_c), 3Phbz—solvent mixtures, exhibit a gradual decrease with decrease in the concentration of the solute which is an evidence on the influence of micro viscosity on linewidth. For 4Etob, the carbonyl stretching vibration shows two well‐resolved components in the Raman spectra, attributed to the presence of two distinct carbonyl groups: hydrogen‐bonded and free carbonyl groups. The intensity ratio of the carbonyl stretching vibration of these two types of carbonyl groups is studied to understand the dynamics of solute/solvent molecules owing to hydrogen bond interactions. Ab initio calculations were employed for predicting relevant molecular structures in the binary mixtures arising from intermolecular interactions, and are related to the experimental results. Copyright © 2009 John Wiley & Sons, Ltd.     

Large-scale shell-model calculations for even-odd <Superscript>61−65</Superscript>Fe isotopes

Large-scale shell-model calculations have been performed to calculate the negative-parity states of even-odd ⁶¹⁻⁶⁵Fe isotopes. The results are compared with the recent experimental data reported at Legnaro National Laboratories and also with earlier calculations with fpg interaction in a truncated configuration space. It is observed that negative parity states of ⁶¹Fe can be well reproduced with GXPF1A interaction in full fp space without truncation. For ⁶³Fe the correct ordering of levels is not reproduced. The structure of the wave function for the ground state and first excited state suggests that the ordering of the single-particle energy levels gets modified due to monopole correction.     

Two-scale generalized model of polypeptide chain in combined solvent

The Hamiltonian of the two-scale generalized model of the polypeptide chain is constructed for the case of combined solvent. It is shown that the partition function for the model with solvent equals to within unessential factor the partition function without solvent with redefinition of the reduced energy of interaction, for competitive interaction between solvents and biopolymer, and of the number of conformations, for non-competitive interactions. Behavior of the correlation length at changes in contributions from different types of interaction is considered.     

Comparison of variational approaches for the exactly solvable 1/r-Hubbard chain

We study Hartree-Fock, Gutzwiller, Baeriswyl, and combined Gutzwiller-Baeriswyl wave functions for the exactly solvable one-dimensional 1/r-Hubbard model. We find that none of these variational wave functions is able to correctly reproduce the physics of the metal-to-insulator transition which occurs in the model for halffilled bands when the interaction strength equals the bandwidth. The many-particle problem to calculate the variational ground state energy for the Baeriswyl and combined Gutzwiller-Baeriswyl wave function is exactly solved for the 1/r-Hubbard model. The latter wave function becomes exact both for small and large interaction strength, but it incorrectly predicts the metal-to-insulator transition to happen at infinitely strong interactions. It is thus seen that neither Hartree-Fock nor an energetically excellent Jastrow-type wave function yield a reliable prediction on the zero temperature phase transition in the one-dimensional 1/r-Hubbard chain.     

Polymer thermophoresis in solvents and solvent mixtures

The thermophoresis of homopolymer chains dissolved in a pure non-electrolyte solvent or solvent mixture is theoretically examined. Thermophoresis is related to the temperature-dependent pressure gradient in the solvent layer surrounding the monomer units (mers). The gradient is produced by small changes in the solvent or solvent mixture density due to the mer-solvent interaction. The London-van der Waals interaction was considered as the main reason of the excess pressure around mers. The resulting expression for the thermophoretic mobility (TM) contains the Hamaker constant for mer-solvent interaction, as well as solvent thermodynamic parameters, including the cubic thermal expansion coefficients of the solvents and the temperature coefficient of the solvent partition factor (for the solvent mixture). This expression is used to calculate the interaction constants for polystyrene and poly(methyl methacrylate) in several organic solvents and binary solvent mixtures using thermophoretic data obtained from thermal field-flow fractionation. The calculated constants are compared with values in the literature and found to follow the same order among the different solvents and to be of the same order of value although several times larger. Furthermore, the model explains weak polymer thermophoresis in water compared with less polar solvents, which correlates also with monomer size. The concentration dependence of polystyrene TM in solvent mixtures also provides a satisfactory explanation by the proposed theory using a concept of secondary diffusiophoresis due to secondary temperature-induced solvent concentration gradient. The method for the evaluation of the diffusiophoresis contribution is proposed.     

Effect of solvent nature on spin exchange in rigid nitroxide biradicals

Intramolecular electron spin exchange as a function of temperature and solvent viscosity and polarity has been studied by X-band electron paramagnetic resonance (EPR) spectroscopy in two rigid nitroxide biradicals existing in one spatial conformation only. Temperature variations of the isotropic hyperfine splitting constanta and exchange integral value |J/a| were measured from EPR spectra and subsequently analyzed. The interaction of polar solvent molecules with >N-O fragments of nitroxide groups led to a slight decrease of the |J/a| value with the increase of temperatureT. In contrast, the interaction of polar solvent molecules with functional groups inside the bridge resulted in a noticeable increase of |J/a| vs.T. In the last case, a coverse relationship between the values of |J/a| and the hyperfine splitting constanta has been observed for solvents with different polarity.     

Horizontal rolls in convective flow above a partially heated surface

Considering the nonlinearity arising from the interaction between electrons and lattice vibrations, an effective electronic model with a self-interaction cubic term is employed to study the interplay between electron-electron and electron-phonon interactions. Based on numerical solutions of the time-dependent nonlinear Schroedinger equation for an initially localized two-electron singlet state, we show that the magnitude of the electron-phonon coupling χ necessary to promote the self-trapping of the electronic wave packet decreases as a function of the electron-electron interaction U. We show that such dependence is directly linked to the narrowing of the band of bounded two-electron states as U increases. We obtain the transition line in the χ × U parameter space separating the phases of self-trapped and delocalized electronic wave packets. The present results indicates that nonlinear contributions plays a relevant role in the electronic wave packet dynamics, particularly in the regime of strongly correlated electrons.     

The characteristics of the <Superscript>8</Superscript>Be ground state in the effective-range approximation

We find the vertex constant for the synthesis α + α → ⁸Be and the corresponding asymptotic normalization coefficient of the Gamov wave function for ⁸Be in the ground state. We use modern data on the position and width of the narrow resonance of this state as well as the energy dependence of the αα scattering phase shift in the s-wave known from the literature. The effective-range theory was applied with the Coulomb interaction taken into account. The parameters of the standard effective-range function expansion up to the member with k ⁴ (k being the relative momentum) were found.     

Test of a method for sampling the internal degrees of freedom of a flexible solute molecule based on adiabatic decoupling and temperature or force scaling

Simulation of the folding equilibrium of a polypeptide in solution is a computational challenge. Standard molecular dynamics (MD) simulations of such systems cover hundreds of nanoseconds, which is barely sufficient to obtain converged ensemble averages for properties that depend both on folded and unfolded peptide conformations. If one is not interested in dynamical properties of the solute, techniques to enhance the conformational sampling can be used to obtain the equilibrium properties more efficiently. Here the effect on particular equilibrium properties at 298?K of adiabatically decoupling the motion a β-hepta-peptide from the motion of the solvent and subsequently up-scaling its temperature or down-scaling the forces acting on it is investigated. The ensemble averages and rate of convergence are compared to those for standard MD simulations at two different temperatures and a simulation in which the temperature of the solute is increased to 340?K while keeping the solvent at 298?K. Adiabatic decoupling with a solute mass scaling factor s _m ?=?100 and a temperature scaling factor of s _T ?=?1.1 seems to slightly increase the convergence of several properties such as enthalpy of folding, NMR NOE atom–atom distances and ³J-couplings compared to a standard MD simulation at 298?K. Convergence is still slower than that observed at 340?K. The system with a temperature of 340?K for the solute and 298?K for the solvent without scaling of the mass converges fastest. Using a force scaling factor s _V ?=?0.909 perturbs the system too much and leads to a destabilization of the folded structure. The sampling efficiency and possible distortive effects on the configurational distribution of the solute degrees of freedom due to adiabatic decoupling and temperature or force scaling are also analysed for a simpler model, a dichloroethane molecule in water. It appears that an up-scaling of the mass of the solute reduces the sampling more than the subsequent up-scaling of the temperature or down-scaling of the force enhances it. This means that adiabatic decoupling the solute degrees of freedom from the solvent ones followed by an up-scaling of temperature of down-scaling of the forces does not lead to significantly enhanced sampling of the folding equilibrium.     

Bound state solutions of the two-electron Dirac-Coulomb equation

We present a variational method for solving the two-electron Dirac-Coulomb equation. When the expectation value of the Dirac-Coulomb Hamiltonian is made stationary for all possible variations of the different components of a well-behaved trial function one obtains solutions representative of the physical bound state wave functions. The ground state wave function is derived from the application of a minimax principle. Since the trial function remains well-behaved, the method remains safe from the twin demons of variational collapse and continuum dissolution. The ground state wave function thus derived can be interpreted as a linear combination of different configurations. In particular, the admixing of intermediate states having one (two) electron(s) deexcited to a negative-energy orbital (orbitals) contributes a second-order level shiftE ₀₋ ⁽²⁾ which can be identified with the second-order shift due to the Pauli blocking of the production of one (or two) virtual electron-positron pair(s). Thus the minimax solution corresponds to the renormalized ground state in quantum electrodynamics, with deexcitations to negative-energy orbitals taking the place of the avoidance of virtual pairs. If one extends the relativistic configuration interaction (RCI) treatment by additionally including negative-energy and mixed-energyeigenvectors of the Dirac-Hartree-Fock hamiltonian matrix in the two-electron basis, the calculated energy will be shifted from the conventional RCI value by an amount that is much smaller thanE ₀₋ ⁽²⁾ . For two-electron atoms, we have derived expressions for the all-spinor limit (δE) and thes-spinor limit (δE _s) of this shift in leading orders. The all-spinor limit (δE) is of orderα ⁴ Z ^{4 1/3} whereas thes-spinor limit (δE _s) is of orderα ⁴ Z ^{3 2/3}. leading components are related to the 1-pair component ofE ₀₋ ⁽²⁾ in a simple way, and the relationships offer the possibility of computing energy due to virtual pairs. Numerical results are discussed.     

Force between unlike star-polymers versus the solvent quality

We re-examine here the computation of the effective force between two star-polymers A and B of different chemical nature, which are immersed in a common solvent. This force originates from the excluded-volume interactions and chemical segregation. We assume that the solvent quality may be different for the two unlike star-polymers, that is the solvent can be 1) a good solvent for A and B, 2) a good solvent for A and a -solvent for B, or 3) a -solvent for the two polymers. The purpose is a quantitative study of the effect of the solvent quality on the effective force, which is a function of the center-to-center distance. Calculations are achieved using the renormalization theory applied to the Edwards continuous model. We first show that, when the mutual interactions are present, the effective force decays as the inverse of distance, but with a universal amplitude depending on the solvent quality. Second, we demonstrate the existence of three kinds of forces related to situations 1), 2) and 3) described above, and give the third-order -expansions ( , 4 is the critical dimension) of the corresponding amplitudes. These series can be resummed using the Borel-Leroy techniques to obtain the best three-dimensional values for the expected force amplitudes. Finally, this work must be regarded as a natural extension of a published one which dealt with the same problem, but where the solvent was assumed to be good for the two unlike star-polymers.Received: 3 February 2004, Published online: 24 May 2004PACS: 61.25.Hq Macromolecular and polymer solutions; polymer melts; swelling - 64.75. + g Solubility, segregation, and mixing; phase separation     

Variational study of the ground state energy of theE−b 1,b 2 Jahn-Teller system

In this paper a variational method for the ground state energy approximation of theE−b ₁,b ₂ Jahn-Teller system is presented. This method is based on the choice of a suitable variational ground state wave function. This trial wave function — a correlated squeezed state — is used to account for the correlation and anharmonicity of the interaction between the two vibrational modes; the anharmonicity of both modes is taken into account by the squeeze effects of these modes. The ground state of mode 1 in this trial wave function is considered as a linear combination of the two displaced harmonic oscillators. The ground state energies for the linearE - e Jahn-Teller system calculated by this method are not only in good agreement with the exact diagonalization results, but they are also better than those from the previous analytical studies. Another conclusion which results from the presented model is the following one: the squeezing effect of mode 1 for the linearE - e Jahn-Teller system is substantially smaller, in contrast with the results which are presented in the previous analytical studies.     

Spatially resolved solvent interaction with glassy HPMC polymers studied by magnetic resonance microscopy

Magnetic resonance microscopy was used to study the interaction of an alkaline water solvent (pH=12) with hydroxypropylmethyl cellulose (HPMC) matrices with different molecular masses Mw=12,000, 86,000, and 120,000. The polymers in the form of cylinders were hydrated at 37 degrees C and monitored at equal time intervals with a 300MHz Bruker AVANCE. The spatially resolved spin-spin relaxations times T2 and diffusion coefficients D of the solvent molecules within the gel layer of HPMC samples, along with changes in the dimension of the glass core of the polymers were determined as a function of hydration times. The experimental data allows us to characterize the diffusion mechanism as being Fickian and to determine the mean diffusivity values D of the solvent molecules for each voxel within the gel of the studied polymers. The influence of the molecular mass of the HPMC polymers on swelling properties has been shown.     

The influence of energy levels fluctuation on the electron transport in a weakly polar solvent

We treat how the fluctuation of the potential surfaces of the final and initial states of the solute molecules (here, the donor-acceptor pair) affects the electron transport. The fluctuation is caused by the electron-solvent interaction. A Debye model of the solvent was used.     

The electronic structure of some transition metal alloys

Thermal neutron scattering experiments have provided detailed information on the distributions of magnetic moment in a number of disordered ferromagnet binary alloys. The general features of these distributions together with saturation magnetization data are discussed and compared with various simple theories. Attention is focused on dilute alloy systems. After an introduction the paper is divided into four sections, the first of which deals with alloys which tend to follow the Slater-Pauling curve. Here a simple Thomas-Fermi treatment due to Friedel suggests that magnetic moment changes, largely confined to the minor constituent (solute) sites, should occur with a sign dependent on the nature of the density of states at the Fermi level in the pure major constituent (solvent). Comparison with experiment shows qualitative agreement except in the case of Fe-based alloys containing transition element solutes from the right of Fe in the periodic table. This discrepancy is examined and an explanation put forward. The next section outlines a discussion of the electronic structure of alloys of transition elements with non-transition metal solutes. The view is taken that the electronic configuration of a solute atom is roughly similar to the configuration found in the pure non-transition metal: it follows that no partially filled d orbitals are expected at solute sites. Use of a simple Thomas-Fermi model based on this assumption indicates that some of the electric screening associated with a non-transition metal solute takes place in the surrounding transition metal slovent. Additional electrons introduced in this way into the solvent occupy mainly d states and cause a reduction in magnetic properties. This reduction together with the total loss of d-state effects from the solute sites themselves can account qualitatively for the changes observed in Ni, Pd and Fe-based alloys with non-transition elements. The fourth section deals with the transition metal alloys which show marked departures from Slater-Pauling behaviour, e.g. NiCr. An explanation for these alloys has been provided by Friedel's bound impurity state model and the mechanism suggested by Comly, Holden and Low to account for the similarity in shape of the magnetic disturbances observed in different systems. The final section discusses ferromagnetic alloys of PdFe and PdCo. The giant moments associated with the Fe and Co solutes result from a widespread polarization of the Pd solvent contiguous to the solute atoms. This polarization can be interpreted with the use of a non-local exchange-enhanced susceptibility function for the Pd host. With increasing solute content this function becomes modified to an extent dependent on the shift of d holes from one spin direction to the other, i.e. on the mean polarization of the Pd.