Annual Reports Section "C" (Physical Chemistry) (v.106, #00)

Front cover (1-2).

Contents (3-12).

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

Mixed surfactants at the air–water interface by Jeffrey Penfold; Robert K. Thomas (14-35).
The extensive use of surfactants in a wide range of household, technological and commercial applications usually involves mixtures of surfactants. In such formulations different types of surfactants are blended to optimise different aspects of performance, and to produce greater flexibility in processing and formulation. Hence understanding the nature of surfactant mixing in solution and at interfaces is of paramount importance. Until recently our understanding of surfactant mixing has been relatively limited. It has been based predominantly on theoretical thermodynamic treatments such as the pseudo-phase approximation and experimental data from techniques such as surface tension. In recent years new experimental approaches, such as neutron scattering, have transformed our understanding of surfactant mixing and have challenged many aspects of the current theoretical treatments. In this article we will focus on surfactant mixing at the air–water interface. The thermodynamic treatments, based on the pseudo-phase approximation, will be introduced and reviewed. The use of neutron reflectivity, in combination with isotopic substitution, to directly determine the surface composition and surface structure in mixed surfactants adsorbed at the air–water interface will be described. Recent data for different binary, ternary and multi-component mixtures will be presented, and discussed in the context of how they have contributed to an improved understanding of surfactant mixing, and how they confirm or challenge different aspects of the current theoretical treatments.

The present review focuses mainly on the interaction between molecules and the surfaces of zeolites and opens with Electron Spin Resonance (ESR) spectroscopy in view of the desire to study radical intermediates in catalytic systems. In this aim too, the family of spectroscopic techniques known collectively as μSR (Muon Spin Rotation, Relaxation or Resonance) which employ spin-polarised positive muons, and can probe radicals in porous media, including zeolites, with a unique and remarkable sensitivity are paid due attention. All such methods have undergone appreciable developments in recent years, especially in regard to pulsed-techniques and theoretical methods for data acquisition and analysis. DFT calculations continue to prove their worth in the prediction and interpretation of hyperfine coupling constants in (paramagnetic) radical species. The broader characterization of less fleeting (diamagnetic) molecules hosted in zeolites, either as deliberately introduced probes or as formed during catalytic activity, has been greatly aided by developments in infra-red (IR) spectroscopy, UV/Resonance Raman methods, inelastic neutron scattering techniques and NMR, as are surveyed in their recent applications to this topic.

Studies on hydrate film growth by C. Y. Sun; B. Z. Peng; A. Dandekar; Q. L. Ma; G. J. Chen (77-100).
The hydrate film properties and growth law at the interface between water phase and hydrate former (guest) phase are of significance to the overall study of hydrate formation kinetics and for developing methods to promote or inhibit the hydrate formation with respect to different industrial applications. In recent years, the experimental tools have become available to qualitatively observe the morphological nature of the film and quantitatively measure the growth of hydrate film. In this review, we provide an overview of the current state-of-the-art in the observation of hydrate film morphology, measurement and modeling of hydrate film growth rate. First, we review the morphological observations of hydrate formation at hydrate former/water interfaces occurring in different cases, such as bulk hydrate former phase contacting bulk water phase, small hydrate former droplets being exposed to bulk water phase, small water droplets being exposed to bulk hydrate former phase, and gas bubbles being suspended in bulk water phase. In the second section, the experimental determination of the lateral growth rate along the guest/water interface, the vertical growth rate normal to the guest/water interface and thickness of hydrate film are summarized. The mechanism and modeling of lateral growth and vertical growth of hydrate film are reviewed in the third section.

Gas hydrates by Judith Maria Schicks (101-117).
After a short introduction giving the definition of gas hydrates, their structures and their formation conditions and occurrences in nature, this article will focus on the thermodynamic properties and kinetics of gas hydrate formation. The article will inform about the state of knowledge regarding the influence of the guest molecule properties on the stability and dissociation enthalpies of hydrate phases, the occurrences of coexisting phases and structural transformations. It will present the main hypothesis on the hydrate nucleation process and recent results on hydrate formation kinetics. In addition to the fundamental knowledge more applied topics, such as the recent development of methods for the production of methane from hydrate bearing sediments will be presented.

This report describes the recent works on Conceptual Density Functional Theory (DFT) based reactivity descriptors used to predict the regioselectivity of large systems, biomolecular systems, in particular. The challenges of bio-systems, the large number of atoms and high structural flexibility, made the way to a routine application of DFT more laborious. To cope with extended systems, fragmentation based method is developed recently (given the name ‘One-into-Many’ model) for a reliable determination of the regioselectivity of biomolecular systems. Thus, our main motivation to embark on the endeavor of this report is to provide a brief introduction of Conceptual DFT and fragmentation approaches based on these reactivity descriptors for predicting the regioselectivity of large biomolecular systems.

The experimental evidence of the inhomogeneity of conducting and semiconducting organic π-conjugated polymers is reviewed. A special attention is paid to the mesoscopic inhomogeneity, which originates from variability in the interactions between the molecules that constitute these materials. First, the effects of inhomogeneity on selected macroscopic parameters of the organic materials such as conductivity, charge mobility and electrochemical responses are analysed. Next, the microscopic evidence of inhomogeneity obtained with the help of various microscopic and scanning probe techniques is reviewed. In conclusion, possible mechanisms of the emergence of the energetic and structural inhomogeneity and the domain structure of conducting and semiconducting polymers and related materials are discussed.

Molecular structure from X-ray diffraction by Harold R. Powell (192-210).
The main crystallographic databases have increased in size substantially in the last few years and been joined by a free to use alternative. Results from the most recent crystal structure prediction exercise show that there has been a significant advance in the methods used. The principal improvements in structure solution methods include the extension of techniques originally developed for protein structure determination to powder crystallography, and the application of low resolution phasing information from solution scattering to solid-state structure analysis. Methods for validating structures have highlighted some examples of problems arising from careless work and obvious fraud.

Predicting solvation energies for kinetic modeling by Amrit Jalan; Robert W. Ashcraft; Richard H. West; William H. Green (211-258).
Ab initio and empirical methods for predicting solvation energies are reviewed, focusing on the challenge of predicting the solvation energies of reactive low-concentration species (and transition states) needed for kinetic models. Several rather different approaches are being pursued with success, but none of the purely a priori methods have yet achieved the accuracy needed to quantitatively predict solution-phase kinetics. Empirical methods are quite accurate at predicting the variation of a molecule’s solvation energy with changes in solvent. Some a priori approaches based on these empirical methods are discussed. Several effects which are poorly-predicted by existing a priori methods and need further work are highlighted.

Studies of protein folding pathways by Diannan Lu; Zheng Liu (259-273).
Protein folding is a problem of great importance in both the life sciences and biotechnology industries. This review begins with a brief summary of the physics of protein folding in vivo, which we believe would provide a theoretical basis for the kinetic control of protein folding. This is followed by a summary of the established refolding methods, which are categorized according to their process kinetics. Molecular simulations are used to present the concept of establishing dynamic solution environments that mimic the molecular machinery employed for high efficiency protein folding in vivo to enhance the kinetic partitioning of the native conformation. In practice, the use of “SMART” polymers for protein folding in a decreasing temperature gradient mimics the capture-release mechanism of GroEL/GroES/ATP and promotes protein folding and inhibits protein aggregation. Oscillation of the oxidative/reductive potential of the solution by periodic loading of redox chemicals promotes the reshuffling of disulfide bridges, mimicking the action of protein disulfide isomerase (PDI), and results in increased refolding yields. Realization of the simulated “oscillatory hydrophobic driving force” that mimics the quality control system in the endoplasmic reticulum (ER) may be of enormous practical value for protein folding at high concentrations.

Some remarks on the photodynamics of NO2 by Iain Wilkinson; Benjamin J. Whitaker (274-304).
We review the literature concerning the electronic structure and spectroscopy of nitrogen dioxide for excitation energies up to 20 eV. Our aim is not to be exhaustive but rather to summarize important results and observations which we have found useful in the interpretation of recent experiments in both the frequency and time domain in which competing and often multiphoton excitation paths access high lying Rydberg and valence states. The photodynamics in NO2 are particularly fascinating and complicated by numerous non-adiabatic couplings between the various electronic states which, despite the molecule’s apparent simplicity as a triatomic species, leads to a very rich photochemistry that exemplifies many features occurring in the photochemistry of much larger molecules.

Molecular biophysics underlying gene delivery by XiuBo Zhao; Fang Pan; Mohammed Yaseen; Jian R. Lu (305-323).
The increasing knowledge about the roles of different genes involved in both acquired and hereditary diseases has made gene delivery an ever promising weapon in disease treatments. Different gene delivery strategies have been investigated in the past three decades among which non-viral gene delivery has received increasing attention due to a number of evident benefits. Delivery of a therapeutic gene to the targeted site in non-viral gene delivery is often aided by vectors such as polymers, lipids, peptides and nanoparticles, but their efficiencies and side effects such as cytotoxicity have stimulated extensive studies to explore how these effects can be balanced at the molecular-cell levels. Successful treatment strategies will ideally work on the basis of high transfection efficiency, low cell toxicity and the minimisation of other possible side effects. The vectors must overcome a number of physical and biological barriers after systemic or local administration. This review focuses on the molecular biophysics underlying non-viral gene delivery using different molecular vectors. A number of representative scientific studies will be introduced to demonstrate the relationships between the physicochemical properties of the DNA/vector complexes and their transfection efficiencies.

Back cover (324-324).