Dissipation of classical energy in nonlinear quantum systems

We show using two simple nonlinear quantum systems that the infinite set of quantum dynamical variables, as introduced in quantized Hamilton dynamics [O. V. Prezhdo and Y. V. Pereverzev, J. Chem. Phys. 113, 6557 (2000)], behave as a thermostat with respect to the finite number of classical variables. The coherent classical component of the evolution decays by coupling to the chaotic quantum reservoir. The classical energy, understood as the part of system energy expressible through the average values of coordinates and momenta, is transferred to the quantum energy expressible through the higher moments of coordinates and momenta and other quantum variables. At long times, the classical variables reach equilibrium, and the classical energy fluctuates around the equilibrium value. These phenomena are illustrated with the exactly solvable Jaynes-Cummings model and a nonlinear oscillator.     

Interaction between a disclination and a uniaxial-isotropic phase interface in a nematic liquid crystal

We consider the interaction between a disclination line of strength +/-1/2 and an interface between the uniaxial and isotropic phases of a nematic liquid crystal. We apply a recently developed set of interface conditions including a configurational force balance which generalizes the Gibbs-Thomson equation to account for the curvature elasticity of the uniaxial phase and the orientation dependence of the interfacial free-energy density. We consider a rectangular vessel containing both phases and a disclination. We formulate a relevant free-boundary problem and use numerical methods to determine equilibrium shapes of the interface. When the interfacial free-energy is constant, the shape of the interface is insensitive to whether the strength of the defect is +1/2 or -1/2 and to rotations of the director field consistent with the boundary conditions. Accounting for the dependence of the interfacial free-energy density on the angle between the interfacial unit normal field and the director field eliminates these degeneracies. In particular, when such dependence is taken into account, different solution branches are found, indicating the presence of a bifurcation. We find also that, depending on the magnitude of the anisotropic contribution to the interfacial free-energy density, the interaction between the disclination and the interface may be repulsive or attractive. When the interaction is repulsive, the disclination line positions itself at an energetically optimal distance adjacent to the interface. Otherwise, the uniaxial phase expels the disclination to the interface where a cusp forms.     

Nonlinear Dynamics of Exciton-Polariton Condensates in a One-Dimensional Lattice

We consider the problem of exciton-polariton-condensate formation in a semiconductor microcavity in the strong coupling regime. The condensate is confined in a one-dimensional periodic potential and coupled to an exciton reservoir that is formed by the external cw pumping. The condensate dynamics is studied in the center and in the edges of the Brillouin zone (BZ). Modeling the formation of the condensate from weak initial noise shows that besides steady states the macroscopic oscillations of polariton density can also occur. Within the framework of the mean field approach, we obtain important analytic relations for the condensate eigenstates using the developed simplified model for three coupled spatial harmonics. A numerical analysis verifies the correctness of the analytic results.     

Aromaticity and conformational flexibility of five-membered monoheterocycles: pyrrole-like and thiophene-like structures

Aromaticity and conformational flexibility of the series of five-membered monoheterocycles with group 14–16 heteroatoms, having one or two lone pairs, were studied with ab initio methods using NICS, ASE and I ₅ indices. For non-planar molecules like phosphole, aromaticity of their planar transition states was also studied, and a special modification of ASE index was proposed to that end. It was found that the presence of two lone pairs is generally preferable for aromaticity of all heterocycles except CPD and silolyl dianions. Heterocycles with group 16 heteroatoms have consistently lower aromaticity compared to other groups. A lot of structures should be classified as moderate aromatic and non-aromatic. Energies of out-of-plane deformation do not correlate with other indices studied, but reveal the same qualitative trends. Generally, aromaticity of five-membered monoheterocycles depends strongly on both heteroatom type and number of lone pairs on it.     

New carbacylamidophosphates (CAPh) and CAPh-containing coordination compounds: structural peculiarities

Structural Chemistry - The new carbacylamidophosphate derivative HL1 (1) with general formula Cl3CC(O)N(H)P(O)(CH2C5H4N)2 named...     

Synthesis and structural investigation of new isothiochromen-4-one 2,2-dioxide derivatives

This article presents a combined experimental and computational study of novel isothiochromene 2,2-dioxide derivatives, which were synthesized by the electrophilic substitution reactions. The compounds have been studied by NMR, IR spectroscopy and single-crystal X-ray analysis. According to X-ray diffraction data, the six-membered ring of 6 adopts a distorted half-chair conformation, but in case of compounds 7 and 8, we have a twist-boat conformation of the six-membered ring with deviation of the S1 and C8 atoms from the mean plane of the remaining atoms of the ring, respectively. Results of quantum-chemical calculations of possible isomers and tautomers of the isolated oxime 8 and azo compounds 10 at the B3LYP/aug-cc-pVDZ level indicate that the oxime-oxo tautomer (8a) is more stable than the nitroso-hydroxy tautomer (8b) in agreement with the crystal data and that the keto tautomer (II) is more stable than the hydroxyl tautomer (I) and zwitterion tautomer (III), because of a strong intramolecular hydrogen bond N–H···O.

     

Prediction of cyclohexane-water distribution coefficient for SAMPL5 drug-like compounds with the QMPFF3 and ARROW polarizable force fields

We present the performance of blind predictions of water—cyclohexane distribution coefficients for 53 drug-like compounds in the SAMPL5 challenge by three methods currently in use within our group. Two of them utilize QMPFF3 and ARROW, polarizable force-fields of varying complexity, and the third uses the General Amber Force-Field (GAFF). The polarizable FF’s are implemented in an in-house MD package, Arbalest. We find that when we had time to parametrize the functional groups with care (batch 0), the polarizable force-fields outperformed the non-polarizable one. Conversely, on the full set of 53 compounds, GAFF performed better than both QMPFF3 and ARROW. We also describe the torsion-restrain method we used to improve sampling of molecular conformational space and thus the overall accuracy of prediction. The SAMPL5 challenge highlighted several drawbacks of our force-fields, such as our significant systematic over-estimation of hydrophobic interactions, specifically for alkanes and aromatic rings.     

A validated LC–MS/MS method for fast detection of thiodiglycolic acid in aqueous samples

A novel sensitive screening method based on liquid chromatography–tandem mass spectrometry (LC–MS/MS) has shown the feasibility of separation and detection of thiodiglycolic acid in aqueous samples. The analysis of this compound is of interest since it is specific microbiological metabolite of thiodiglycol, which is precursor and degradation product of chemical warfare agent sulfur mustard. The LC–electrospray ionisation (ESI)–MS method provides a sensitive and direct approach for thiodiglycolic acid identification and quantification using non-extracted non-derivitised samples from aqueous solutions. Chromatographic separation of the thiodiglycolic acid was produced using a reverse phase LC column with gradient mobile phases consisting of 0.1% formic acid in water and acetonitrile. Identification and quantification of species were achieved using ESI–tandem MS monitoring two precursor-to-product ion transitions for thiodiglycolic acid. The method demonstrates linearity over at least two orders of magnitude and detection limit of 10 ng...mL^–1 in environmental water samples.