Coupling Constant Increases Research Articles

Interactive binding to the two principal ligand binding sites of human serum albumin: effect of the neutral-to-base transition

The relationship between the two principal ligand binding sites, sites I and II, on human serum albumin (HSA) was quantitatively and qualitatively examined by equilibrium dialysis and fluorescence spectroscopy. Among the three subsite markers to site I, only the binding of dansyl- l-asparagine (DNSA), which is a subsite Ib marker (K. Yamasaki et al., Biochim. Biophys. Acta 1295 (1996) 147), was inhibited by the simultaneous binding of a site II ligand, such as ibuprofen and diazepam. This indicates that, in contrast to subsite Ib, subsites Ia and Ic do not strongly interact with site II. The thermodynamic characteristics for the coupling reaction between DNSA and ibuprofen and between DNSA and diazepam, which gave positive coupling free energies and negative values for both coupling enthalpy and entropy, indicated that the reaction process was entropically driven. Increase of pH from 6.5 to 8.2 caused an increase in coupling constant and entropy for the mutual antagonism between DNSA and the site II ligands on binding to HSA. The site II ligand-induced red-shift of λ max and solvent accessibility of DNSA in subsite Ib were decreased when the albumin molecule was isomerized from the neutral (N) to the base (B) conformation in the physiological pH region. Based on these findings, we conclude that a ‘competitive’ like strong allosteric regulation exists for the binding of these two ligands to the N conformer, whereas for the B conformer this interaction can be classified as nearly ‘independent’. Since the distance between Trp-214, which resides within the site I subdomain, and Tyr-411, which is involved in site II, is increased by 6 Å during the N–B transition (N.G. Hagag et al., Fed. Proc. 41 (1982) 1189), we propose a mechanism for the pH-dependent antagonistic binding between subsite Ib and site II, which involves the transmission of ligand-induced allosteric effects from one site to another site, modified by changes in the spatial relationship of sites I and II caused by the N–B transition.

Frenkel-Kontorova Model: Crossover from the Classical to the Quantum Mechanical

The Frenkel-Kontorova (FK) model describes a chain of atoms connected by springs subject to an external potential. This simple classical model exhibits a wealth of complex behavior. It has also found applications in many condensed matter systems such as charge density waves, magnetic spirals, modulated phases and tribology. However, an in-depth understanding of some of these problems, for example, tribology in the nano-regime, demands an understanding of its quantum mechanical behavior. To achieve this goal, we use a squeezed-state approach rst used in quantum optics. We found that quantum uctuations renormalize the standard map, which governs the classical behavior of the FK model, to a sawtooth map. This result is borne out by Monte-Carlo simulations. We also found that the ground state wave function changes from an extended state to a localized state when the coupling constant increases. Although quantum uctuations largely smear the transition by breaking of analyticity observed in the classical case, the remnant of this transition is still discernible.

Mode-competition effects of a two-mode laser with multiplicative colored noise with saturation effects

The effect of multiplicative colored noise on mode-competition of the two-mode laser with saturation effects is studied. By means of linear stability analysis, and by considering τ as a small parameter, some significant conclusions have been obtained. In strong coupling, the effect of multiplicative colored noise on mode-competition is stronger than that of multiplicative white noise, and it is enhanced with the increase of noise strength. In weak coupling, the effect of multiplicative colored noise on mode-competition is weaker than that of multiplicative white noise, and it is decreased with the increase of coupling constants.

Two- and three-dimensional polarons in a symmetric quantum dot with arbitrary electron-phonon coupling strength

Abstract A variational approach is presented for calculating the ground-state energy of two- and three-dimensional polarons in symmetric quantum dots with arbitrary electron-phonon coupling constants. It is found that the polaronic energy correction increases with the decrease in size of the quantum dot and is much more pronounced with decreasing dimensionality. Furthermore, the relative polaronic enhancement is found to be insensitive to the variation of the dimensionality and the coupling constant at weak coupling, however, as the coupling constant increases, it comes to depend on not only the dimensionality, but the coupling constant as well.

Plasma waves in a nonideal plasma

This paper shows how the concepts commonly used for a Debye plasma—Landau damping, collisional damping, short-range and long-range collisions, and plasma waves—must be revised to describe a nonideal electron-ion plasma. The degrees of freedom of a nonideal plasma are divided into collective and individual. The increase and saturation of the fraction of collective degrees of freedom as the coupling constant increases is discussed. The Tatarskii approach for a system of coupled oscillators makes it possible to model the collective degrees of freedom of a nonideal plasma by a set of Langevin oscillators in a thermostat. The correlation energy and the energy of the plasma waves are found. The concepts developed here made it possible to determine the dispersion of the plasma waves and their damping. The effect of damping on the discrepancy between the position of the maximum of the dynamic structure factor and the real part of the solution of the dispersion equation is considered. The effective collision frequency of the individual degrees of freedom (the electrons) is estimated, taking into account both short-range pairwise scattering and scattering at plasma waves.

Chiral symmetry breaking in the Nambu–Jona-Lasinio model in external constant electromagnetic field

Dynamical chiral symmetry breaking (D$\chi$SB) is studied in the Nambu-Jona-Lasinio model for an arbitrary combination of external constant electric and magnetic fields. In 3+1 dimensions it is shown that the critical coupling constant increases with increasing of the value of the second invariant of electromagentic field $\vec{E}\cdot\vec{B}$, i.e. the second invariant inhibits $D\chi SB$. The case of 2+1 dimensions is simpler because there is only one Lorentz invariant of electromagnetic field and any combination of constant fields can be reduced to cases either purely magnetic or purely electric field.

NMR and EPR Study of the Nitroxide Radical Tempo Interaction with Phenols

The 2,2,6,6-tetramethyl-I-piperidinyloxy free radical (TEMPO) was used as a probe to study the changes in hydrogen bonding between the phenolic OH group and the ON group of the radical by means of NMR and EPR. 13C NMR contact shifts induced by TEMPO were measured for five phenols. Formation of intermolecular hydrogen bond between a phenol and TEMPO molecule causes noticeable increase of 14N hyperfme coupling constant in the radical and appearance of negative spin density on carbon nuclei of C-OH fragment in the phenol.

One-dimensional electron-phonon system at arbitrary coupling constant

The ground state of a quasi-particle (exciton, electron or hole) interacting with optical and acoustic phonons in a one-dimensional chain, is investigated using a variational method. The phase diagrams are obtained which show the regions of the electron-phonon coupling constant and nonadiabaticity parameter where the ground state of a quasiparticle is described as almost free electron state, small polaron, or spontaneously localized state. It is shown that the formation of a soliton-like state has a threshold with respect to the value of electron-phonon interaction. The corresponding critical value of the coupling constant increases with the nonadiabaticity parameter increasing.

Brillouin Scattering from the Soft Optical Phonon in the Orthorhombic Form of a K 3Co 1-xFex(CN) 6 (x≤ 0.03) Crystal

The soft optical phonon in the two-layer orthorhombic form of a K3Co1-xFex(CN)6 (x≤0.03) single crystal has been reinvestigated using a (3+3)-pass tandem Fabry-Pérot interferometer around the structural phase transition temperature. The soft phonon response can be well described using the phonon-relaxator coupled model. The soft phonon frequency ω∞/2π obeys the |T-T c±|1/2 law except in the vicinity of T c=82.5 ±0.1 K; (ω∞/2π)2=1.20×103(T-82.1) (GHz2) for T>T c and 4.55×103(83.0-T) (GHz2) for T<T c. The soft phonon-relaxator coupling constant increases linearly above the T c as the temperature decreases and the slope becomes steeper below T c. The relaxation time is longer than 40 ps and independent of temperature above T c, but becomes one order of magnitude shorter below T c. The Fe3+ defects seem to be responsible for these unusual temperature dependences.

Intrinsic localized spin wave modes in easy-axis antiferromagnetic chains

Two types of intrinsic localized spin wave modes are found in perfect antiferromagnetic chains of classical spins with on-site easy-axis anisotropy: the amplitude is either double or single peaked. In the small spin deviation limit, both types become identical envelope solitons. The degree of localization increases as either the maximum spin deviation or the ratio of the anisotropy constant to the exchange coupling constant increase. However, only the single peaked intrinsic localized mode is stable with regard to a noise perturbation.

Quantum phase transition and long-range order in the ground state of a lattice of pseudospins coupled with optic phonons.

We study a pseudospin-phonon coupling system in its ground state and show that, as a result of the competition between the intrasite pseudospin tunneling and the phonon-induced intersite pseudospin correlation, a quantum phase transition to the pseudospin long-range ordering phase may occur at some critical coupling constant. In the disordered phase the short-range ferroelectric or antiferroelectric correlation gets stronger as the coupling constant increases. The calculated renormalized tunneling matrix element, which is reduced by the pseudospin-phonon interaction, is not as small as the theory of previous authors predicts, that is, the reduction is alleviated by taking into account the retardation effect of the coupling. \textcopyright{} 1996 The American Physical Society.

On Bogoliubov's method in superconductivity

The Frolich Hamiltonian, with the addition of the electron-boson interaction of the fourth degree in fermion operators, is studied. The Hamiltonian takes into account the exchange interactions of the magnetic moments of the conduction electrons. The boson spectrum consists of the normal modes of coupled phonon-magnon oscillations. Using the Bogobliubov method in the theory of superconductivity and a generalized canonic transformation, a system of equations describing the mutual compensation of “dangerous” (i.e., leading to divergences) dingrams corresponding to the creation of two (bivertexes) and of four (tetravertexes) electron excitations from vacuum is obtained. The bivertex compensation equation, modified by a four-fermion interaction, indicates the possibility of an effective increase in the electron-boson coupling constant and an increase in the superconductive energy gap. Numerical investigation of the obtained system of equations was carried out. The considerable increase in the energy gap was revealed in comparison with the Frolich model.

Phonon assisted electronic transition in telluric acid ammonium phosphate single crystals

Abstract The effect of gamma-irradiation on the absorption optical spectra of telluric acid ammonium phosphate single crystals (TAAP) has been studied, in the wave length of 200–600 nm, for samples irradiated by various doses up to 10 Mrad. The results show that the electron phonon coupling constant increases with the irradiation dose.

Multi‐Nuclear Solid‐State NMR Study of the Local Structure of SiOHAl Groups and their Interaction with Probe‐Molecules in Dehydrated Faujasite, Mordenite and Zeolite ZSM‐5

AbstractStructural variations of Si–O–Al bridges in dehydrated zeolites have been studied by 29Si CP/MAS NMR and 27Al NMR spectroscopy. After deammoniation of zeolites Y (nSi/nAl = 2.6 and 8.0), mordenite (nSi/nAl = 8.0) and ZSM‐5 (nSi/nAl = 22.0) 29Si NMR high‐field shifts of Si(1 Al) signals of maximum 0.8 ppm and of about 2.7 ppm and 4.0 ppm, respectively, were observed. This is explained by a protonation‐induced increase in the mean Si–O–T bond angles of SiOHAl groups. Simultaneously, an increase in the aluminium quadrupole coupling constant from about 5.0 MHz to about 16.0 MHz was determined indicating a strong protonation‐induced shear strain of framework AlO4 tetrahedra. On the other hand, the proton transfer from Si–O–Al bridges to basic probe‐molecules causes a decrease in the aluminium quadrupole coupling constant which corresponds to a higher AlO4 symmetry. The high symmetry of AlO4 tetrahedra in zeolite HZSM‐5 loaded with one methanol molecule per SiOHAl group, the mobility of the hydroxyl protons existing in this sample and their chemical shift value observed at the temperature of T = 295 K by 27Al, 2H and 1H NMR, respectively, indicate a rapid exchange of hydroxyl protons between bridging OH groups, hydrogen‐bonded methanol molecules and methoxonium ions. At the temperature of T = 85 K methanol molecules are fixed at the zeolite framework by hydrogen bonds.

Formation Mechanism of Self-Pumped Phase-Conjugate Mirror Using a Cu-Doped (K0.5Na0.5)0.2(Sr0.61Ba0.39)0.9Nb2O6 Crystal

In this work, we study the formation mechanism of the self-pumped phase-conjugate mirror (SPPCM) in a Cu-doped (K0.5Na0.5)0.2(Sr0.61Ba0.39)0.9Nb2O6 (KNSBN:Cu) crystal using an Ar+ laser ( λ=514 nm). The gain of self-pumped four-wave mixing is greater than that of self-generated fanning, which leads the self-formation of the SPPCM. The beam-fanning profiles vary with the laser beam incident angle. We observed that multiple fanning loops are formed and change with the change in incident angle in the SPPCM. Experimental results and discussion show that the transmission grating is responsible for the generation of the SPPCM. The phase-conjugate reflectivity increases with the increase in coupling constant.

A study of tunneling in Hamiltonian systems via Monte Carlo simulation and Rayleigh-Ritz variation

Energy spectra of Hamiltonian systems which contain potential barriers are studied in the Monte Carlo simulation and the Rayleigh-Ritz variation. The onset of tunneling and splitting of the eigenergies are observed as the coupling constant increases. Consistency of the results of the Monte Carlo simulation is checked by two independent data fittings.

121-Sb Mössbauer study of insulating and ion-conducting antimony chalcogenide-based glasses

The local environment of antimony in As 2S 3Sb 2S 3, AgISb 2S 3, AsSbSe and A AgAsSbSe glasses, glassy/crystalline alloys and crystals is investigated using 121-Sb Mössbauer spectroscopy. The isomer shift both for sulfide and selenide vitreous alloys is 1.2–2.0 mm/s more positive than that for corresponding crystalline parents. The smaller s-electron density at the 121Sb nucleus for glasses indicates a decrease of the antimony-chalcogen interatomic distances in comparison with those for crystalline materials. The isomer shift systematics and composition dependencies of the electric-quadrupole coupling constant, eQV zz , and the asymmetry parameter, ν, shows that in As 2S 3Sb 2S 3 and AsSbSe insulating glasses an isomorphous substitution of arsenic by antimony occurs accompanied by an increase of interatomic distances. In the case of Ag + ion-conducting vitreous alloys, however, the antimony-chalcogen distances are governed by the silver content and do not depend on the Sb fraction of the glass. Geometric and topological disorder in the glass network is correlated with an increase of the electric-quadrupole coupling constants and values of the asymmetry parameter ν between 0.4 and 1.0.

Transformation of the vibrational spectrum and structure of glasses after quenching

Raman scattering and neutron diffraction and inelastic scattering spectra of well annealed and quenched As 2S 3 glasses are analyzed. It is found out that the quenching of the sample leads to negligible variation of structure on a short range scale, but significantly influence structural order on a medium range scale. These structure modifications lead to significant changes in the low-energy (2–12 meV) vibrational spectrum: the density of vibrational states and light to vibration coupling constant increase uniformly along the spectrum. The results obtained confirm the connection of low-energy anomalies of the vibrational spectrum of amorphous materials with the peculiarities of their structure on the medium range scale.

Electric-field gradients in Sm2O3, Gd2O3, and Ho2O3 measured with perturbed-angular-correlation spectroscopy.

The time-differential perturbed-angular-correlation (PAC) method with ion-implanted $^{111}\mathrm{In}$ tracers was employed to study the hyperfine interactions of $^{111}\mathrm{Cd}$ nuclei in the rare-earth sesquioxides ${\mathrm{Sm}}_{2}$${\mathrm{O}}_{3}$, ${\mathrm{Gd}}_{2}$${\mathrm{O}}_{3}$, and ${\mathrm{Ho}}_{2}$${\mathrm{O}}_{3}$. Up to five electrical quadrupole interactions appeared in each oxide, two of which we attribute to the electric-field gradients (efg) acting on $^{111}\mathrm{Cd}$ on the substitutional lattice sites in the cubic bixbyite phase; in ${\mathrm{Gd}}_{2}$${\mathrm{O}}_{3}$ and ${\mathrm{Sm}}_{2}$${\mathrm{O}}_{3}$ small fractions can also be related to the B phase. The scaling of the efg in the C phase is discussed in connection with previous findings in other ${\mathrm{M}}_{2}$${\mathrm{O}}_{3}$ sesquioxides. A slight linear increase of the quadrupole coupling constants ${\ensuremath{\nu}}_{\mathit{Q}}$ for increasing temperature was found.

The synthesis and properties of Pt 2→M (M=Ag(I), Hg(II)) adducts of Pt 2{ o-C 6H 4P(Ph)(CH 2) 3PPh 2} 2 with Ag(O 2CCF 3), HgCl 2 and Hg(O 2CCF 3) 2. X-ray crystal structure of [Pt 2{ o-C 6H 4P(Ph) (CH 2) 3PPh 2} 2Hg(O 2CCF 3) 2

During the attempted synthesis of (dppp)Pt(C 2H 4) (dppp =1,3-bis(diphenylphosphino)propane) a Pt(I)Pt(I) dimer, Pt 2{ o-C 6H 4P(Ph)(CH 2) 3PPh 2} 2, was formed in approximately 5–10% yield. In this dimer the dppp ligand coordinates with two phosphorus atoms to one Pt centre, while one of the phenyl groups of the ligand is ortho-metallated to the second Pt centre. The reaction of this Pt(I)Pt(I) dimer with Ag(O 2CCF 3), HgCl 2 and Hg(O 2CCF 3) 2 resulted in the formation of Pt 2-to-M donor adducts [Pt 2{ o-C 6H 4P(Ph)(CH 2) 3PPh 2} 2Z] (Z=Ag(O 2CCF 3), HgCl 2 and Hg(O 2CCF 3) 2) in which the PtPt bond, although weakened, remained intact. The 31p{ 1H} NMR spectra showed, with increasing electronegativity of Z, an increase in coupling constant 1 J(PtP1) and a decrease in coupling constant 1 J(Pt′P1) for the approximately linear P1PtPt′P1′ unit, indicating a weaker PtPt bond and a stronger Pt 2→M bond in the order M=Hg(II)>;Ag(I). An X-ray structure of the red-brown crystals of [Pt 2{ o-C 6H 4P(Ph)(CH 2) 3PPh 2} 2Hg(O 2CCF 3) 2] has been determined (space group Cc2a, a=14.392(2), b=19.950(1), c=19.427(1) Å, V=5577.9(9) Å 3, Z=4, R=0.038, R w=0.061). The structure shows a PtHgPt triangle with bond lengths PtPt=2.7608(7) and PtHg=2.6690(10) Å.