Environmental Effects in Computational Spectroscopy: Accuracy and Interpretation

Spectroscopic techniques are valuable tools for understanding the structure and dynamics of complex systems, such as biomolecules or nanomaterials. Most of the current research is devoted to the development of new experimental techniques for improving the intrinsic resolution of different spectra. However, the subtle interplay of several different effects acting at different length and time scales still makes the interpretation and analysis of such spectra a very difficult task. In this respect, computational spectroscopy is becoming a needful and versatile tool for the assignment and interpretation of experimental spectra. It is in fact possible nowadays to model with relatively high accuracy the physical–chemical properties of complex molecules in different environments, and to link spectroscopic evidence directly to the structural and dynamical properties of optically or magnetically active solvated probes. In this Review, significant steps toward the simulation of entire spectra in condensed phases are presented together with some basic aspects of computational spectroscopy, which highlight how intramolecular and intermolecular degrees of freedom influence several spectroscopic parameters.     

Constructive role of noise: Fast fluctuation asymptotics of transport in stochastic ratchets

The constructive role of random fluctuations is studied in the context of transport in stochastic ratchets. We discuss the interplay of independent white (thermal) and discrete (external) noises and their generation of transport in anisotropic potentials. The constructive cooperation of such fluctuations is most apparent in the asymptotic limit of fast discrete-valued noise, a limit which presents some interesting mathematical features. We describe the asymptotic analysis of the current in the limit of fast external noise, pointing out the strong qualitative dependence of the current on the interplay of the independent noise sources and its surprising sensitivity to the regularity of the underlying anisotropic ratchet potential. (c) 1998 American Institute of Physics.     

A note on Davis type error bounds

Bounds for the error of the approximation of the value of a bounded linear functionalUf by the weighted sumU _n f= _k ^=0/n–1 a _k f (x _k ) in Hilbert function spacesH(B) based upon the Davis method are considered. Taking into account that functionsf H (B) withUf=U _n f are known, improved error bounds are computed. Applying the explicit formulas numerical examples are treated and comparisons are made.     

The pseudopotential-CI study of the interaction between ethylene and metal atoms,metal Oxides,and their cations (Me = Be,Mg, and Zn)

Potential energy curves for the lowest singlet and triplet states of Me + C₂H₄, Me⁺ + C₂H₄, MeO, MeO + C₂H₄, and (MeO + C₂H₄)⁺ systems for Me = Be, Mg, and Zn have been determined employing PP-MRD-CI or an all electron MRD-CI procedure. A binding interaction in the ground state has been found for oxides, all cation systems, and the BeO + C₂H₄ system. In the cases of MgO + C₂H₄ and ZnO + C₂H₄, only low lying excited states exhibit attractive interactions. Among three oxides considered, BeO is less pronounced biradically than MgO and ZnO. In order to obtain a binding interaction between an oxide and the olefin in the ground state, the p orbital of the metal must be sufficiently involved in binding.     

DSC study of linolenic acid autoxidation inhibited by BHT,dehydrozingerone and olivetol

Non-isothermal oxidation of linolenic acid (LNA) in bulk phase was monitored by differential scanning calorimetry. The kinetic parameters E _a, Z and k (activation energies, pre-exponential factors, and rate constants, respectively) were calculated by Ozawa-Flynn-Wall method for the first detectable exothermic effect of uninhibited LNA oxidation. The kinetic parameters were also calculated for LNA oxidation inhibited by 2,6-di-tert-butyl-4-methylphenol (BHT), and two natural compounds, 1,3-dihydroxy-5-pentylbenzene (olivetol), and 4-(4’-hydroxy-3’-methoxyphenyl)-3-buten-2-one (DHZ, dehydrozingerone) at various concentrations. For oxidation processes at 25, 90 and 180°C the plots of logk values vs. concentration of phenolic compounds indicated that optimal concentration of inhibitor determined for one particular temperature cannot be extrapolated to other temperatures.     

Characteristics of glucose electrode with enzyme immobilised on nylon net

Glucose oxidase was immobilised on nylon net by the method of O-alkylation using dimethyl sulfate and lysine as a spacer. The influence of alkylation conditions on the characteristics of the resulting glucose electrode was evaluated. The best electrode was then tested under batch and flow conditions, respectively. The influence of pH and temperature on electrode response were examined. The glucose oxidase immobilised on nylon net seemed to be inhibited by glucose in alkaline pH and at higher temperatures. Moreover, the shape of the electrode signal after addition of glucose was unusual. Glucose oxidase immobilised on nylon net was unstable and lost its activity rather quickly, especially when stored dry in the refrigerator. Also the operational stability of the electrode in the flow system was rather poor. Received: 26 February 1998 / Revised: 22 May 1998 / Accepted: 29 June 1998     

Characteristics of glucose electrode with enzyme immobilised on nylon net

Glucose oxidase was immobilised on nylon net by the method of O-alkylation using dimethyl sulfate and lysine as a spacer. The influence of alkylation conditions on the characteristics of the resulting glucose electrode was evaluated. The best electrode was then tested under batch and flow conditions, respectively. The influence of pH and temperature on electrode response were examined. The glucose oxidase immobilised on nylon net seemed to be inhibited by glucose in alkaline pH and at higher temperatures. Moreover, the shape of the electrode signal after addition of glucose was unusual. Glucose oxidase immobilised on nylon net was unstable and lost its activity rather quickly, especially when stored dry in the refrigerator. Also the operational stability of the electrode in the flow system was rather poor.     

Structural Balance of Opinions

The concept of Heider balance, usually applied to interpersonal relations, is generalized here to opinions gathered in surveys. At first, we compare four algorithms, which drive a matrix dataset to a balanced state. The criterion is that the final state obtained with an algorithm should be as close as possible to the initial state. The result is that deterministic differential equations work better than their Monte Carlo counterparts. Next, we apply the winning algorithms to the matrix of correlations between opinions gathered in American states between 1974 and 1998. The results are interpreted in terms of the classic comfort hypothesis (E. Babbie, 2007).     

Extraction and determination of hexavalent chromium in soil samples

A procedure for the extraction of Cr(VI) from solid soil-like samples was presented in which the complexing properties of diethylenetriaminepentaacetic acid (DTPA) were exploited to extract insoluble compounds of Cr(VI). A concentration of DTPA in an ammonium sulphate/ammonium hydroxide buffer equal to 0.02 mol l⁻¹ was chosen. The conditions of extraction of insoluble Cr(VI) from solid samples were optimised using soil certified reference material spiked with known concentration of insoluble Cr(VI) added as PbCrO₄. The extracts were analysed by adsorptive stripping voltammetry. Validation of the proposed procedure of extraction was carried out by analysis of certified reference material (CRM) 545 and comparison of the results obtained using the proposed and other methods of extraction in the course of analysis of natural soil samples.