Annual Reports Section "C" (Physical Chemistry) (v.107, #00)

Front cover (1-2).

Contents (3-12).

Introduction by G. A. Webb (13-13).

Disordered porous materials filled with liquid or solution may be considered as partly-quenched, i.e., as systems in which some of the degrees of freedom are quenched and others annealed. In such cases, the statistical-mechanical averages used to calculate the system's thermodynamical properties become double ensemble averages: first over the annealed degrees of freedom and then over all possible values of the quenched variables. In this respect, the quenched-annealed systems differ from regular mixtures. The multi-faceted applications of the partly-quenched systems to a kaleidoscope of technological and biological processes make the understanding of these systems important and of interest. Present contribution reviews recent developments in theory and simulation of partly-quenched systems containing charges. Specifically, two different models of such systems are discussed: (a) the model in which the nanoporous system (matrix subsystem) formed by charged obstacles is electroneutral, and (b) the model, where the subsystem of obstacles has some net charge. The latter model resembles, for example, the situation in ion exchange resins etc. Various theoretical methods are applied to investigate structural and dynamical peculiarities of such systems. One is the replica Ornstein-Zernike theory, especially adapted for charged systems, and the other is the Monte Carlo computer simulation method. These two approaches are well suited to study thermodynamical parameters, such as the mean activity coefficient of the annealed electrolyte or Donnan's exclusion parameter. Highly relevant issue of dynamics of ions in partly-quenched systems is also addressed. For this purpose, the Brownian dynamic method is used: the self-diffusion coefficients of ions are calculated for various model parameters and discussed in light of the experimental data. These results, together with the thermodynamical data mentioned above, provide additional evidence that properties of the adsorbed fluid substantially differ from those of its bulk counterpart.

Electron spin resonance by Christopher J. Rhodes (47-87).
The technique variously known as Electron Spin Resonance (ESR) or Electron Paramagnetic Resonance (EPR) continues to find important applications mainly in the Biomedical, Materials and Environmental Sciences. Among the advances which feature information gleaned through its agency, are studies of enzymes and membranes, conductive polymers and novel materials, fuel cells, antioxidants, environmental samples, catalysts and photocatalysts, spin-trapping agents, spin-probes and spin-labels. High-field methods are particularly useful in obtaining improved resolution of overlapping signals and the interpretation of many systems had benefited from the use of Density Functional Theory (DFT) calculations.

Studies of the local structures of molten metal halides by Anne-Laure Rollet; Mathieu Salanne (88-123).
This review covers the local structure of molten metal halide, where a somewhat wide definition of “local structure” is employed, i.e. from the first shell of interacting neighbours up to correlations arising at the nanometer length scale. These particular liquids are indeed strongly organized at unusually long distances due to the predominance of coulombic interactions. Many of them are also characterized by the formation of intermediate range ordering. It is therefore impossible to describe the local structure of these liquids omitting this longer-ranged correlation. Finally, a deeper attention is given to the systems on which recent progresses have been made in the last decade, as for instance molten fluorides and rare earth halides.

Recent advances in aromaticity and antiaromaticity in transition-metal systems by Timur R. Galeev; Alexander I. Boldyrev (124-147).
The concept of aromaticity/antiaromaticity was recently extended to polynuclear transition metal compounds. In the current report we review recent advances made in the field of aromaticity and antiaromaticity in bare transition-metal clusters, clusters of transition metal suboxides and transition-metal clusters embedded in metalloorganic and inorganic compounds. We analyzed aromaticity in reported aromatic/antiaromatic species through the recently developed Adaptive Natural Density Partitioning method. We confirmed aromaticity in most cases though there are a few cases where no aromaticity or a different type of aromaticty was revealed by the AdNDP method. The peculiarity of aromaticity in polynuclear transition metal compounds is frequently its multifold (σ-, π-, and δ-) nature. Moreover, the presence of simultaneous multifold aromaticity/antiaromaticity leads to conflicting aromaticity which complicates assignment of aromaticity/antiaromaticity in such compounds.

All life on our earth can be viewed as an application of supramolecular chemistry, with noncovalent interactions playing a central role. The knowledge of total interaction energies as well as their components is topical for understanding the nature of these interactions and, in a broader sense, also for understanding the nature of stabilization of noncovalent systems like biomacromolecules. Accurate data on interaction energies can only be obtained from coupled-cluster with single and double and perturbative triple excitations (CCSD(T)) calculations performed with extended basis sets. The CCSDD(T) calculations thus provide benchmark data which can be used for testing and/or parameterizing other, computationally economical techniques. In the present review the applicability and performance of various recently introduced wavefunction and density functional methods are examined in detail.

State-specific multireference coupled-cluster theory of molecular electronic excited states by Vladimir V. Ivanov; Dmitry I. Lyakh; Ludwik Adamowicz (169-198).
A state-specific coupled cluster (CC) theory with the CAS (complete active space) reference (CASCC) and based on an approach that employs single reference determinant (so-called “formal reference” determinant) in the expression for the wave function has been developed to study electronic excited states with different spatial and spin symmetries. The formal reference determinant is used to generate the reference wave function in the form of a linear combination of the CAS determinants contracted to configurations with the spin and spatial symmetries of the target state. Such properly symmetrized multideterminantal reference provides the zero-order description of the state under consideration. To that reference an exponential CC operator is applied to describe the dynamic electron correlation effects in the CASCC wave function of the considered state. All necessary equations for the CASCC energy and configurational amplitudes are generated using an automated computer-based method which constructs all necessary coupled cluster diagrams for any arbitrary level of the electronic excitation.

Mass spectrometric studies of dissociation constants of noncovalent complexes by Elisabetta Boeri Erba; Renato Zenobi (199-228).
Specific interactions among biomolecules to form noncovalently bound complexes play a pivotal role in key cellular processes such as cell division, cell signalling, gene transcription and translation. The propensity of noncovalently bound complexes to dissociate into their components can be quantified and constants of dissociation (Kd) can be obtained by various methods. Mass spectrometry has become an important method to measure Kd. The advent of soft ionisation techniques, in particular electrospray ionisation (ESI) and matrix-assisted laser desorption/ionisation (MALDI) has established mass spectrometry as a viable technique for investigating noncovalent interactions and for quantifying their binding strengths. Under carefully chosen experimental and instrumental conditions, it is possible to observe intact noncovalent complexes in the gas phase using ESI and MALDI, and to use the mass spectra as a read-out for determining solution-phase Kd. Compared to other biophysical methods, mass spectrometry is highly sensitive and fast, and gives additional information about the stoichiometry and specificity of noncovalent interactions. This review focuses on recent MS-based methodologies for quantification of binding strengths, in particular those that promise to complement conventional biophysical methods.

Intracule functional models by Peter M. W. Gill (229-241).
After introducing the electron correlation problem, we discuss a variety of two-electron probability distributions (intracules), showing how these are interrelated and how they can be constructed from the results of standard molecular orbital calculations. We then consider how these intracules may be used to estimate molecular correlation energies.

This contribution is aimed at assessing the current knowledge of stacking interactions in proteins focusing on the thermodynamic origin of their strength. First, the energetic nature of π–π interactions is critically discussed by using recent accurate quantum chemical calculations. Then, the intimate relation between energetics and thermodynamics is analyzed via a survey on the last decade computer simulations and experimental data involving interactions of aromatic side chains in solution. The thermodynamics of stacking in protein is further assessed by reviewing studies based on a knowledge-based approach on updated databases of experimental protein structures. Finally the contribution selectively includes some recent authoritative progresses that highlights the paramount importance of stacking in the stabilization and destabilization of protein tertiary structures.

Shape dependent electrocatalysis by J. Solla-Gullón; F. J. Vidal-Iglesias; J. M. Feliu (263-297).
In this paper we will review the state-of-the-art in the application of shape-controlled metal nanoparticles in Electrocatalysis, especially in reactions of interest in PEMFCs such as O2 reduction and CO, methanol, ethanol and formic acid electrooxidations. In particular, we will focus our attention on shape-controlled platinum (Pt), gold (Au) and palladium (Pd) nanoparticles. In addition, electrocatalytic applications of shape-controlled Pt-based alloy nanoparticles will be also reviewed. The results reported will highlight how important can be controlling the shape of the nanocatalyst and how effective this parameter may be to improve the activity and thus, develop highly active electrocatalysts.

Conjugated polymers for radiation detection by Qi Chen; Tibor Hajagos; Qibing Pei (298-318).
There is a revived interest in the discovery and development of new materials and devices for radiation detection for nuclear non-proliferation and medical imaging. Conjugated polymers emerge as a potential candidate for dosimetry and scintillation. This report provides an overview of the fundamental detection physics and existing materials. The unique semiconductivity and photonic properties of conjugated polymers are discussed in the context of detecting high energy photons such as gamma rays. Approaches to enhance the sensitivity, particularly via the addition of compounds with high atomic numbers, are described.

Back cover (319-320).