Annual Reports Section "C" (Physical Chemistry) (v.109, #00)

Front cover (1-2).

Contents list (3-8).

Introduction by G. A. Webb (9-9).

Biomedical applications of carbon nanotubes by Marta Roldo; Dimitrios G. Fatouros (10-35).
The last two decades have witnessed a wealth of research addressing the possible biomedical applications of carbon nanotubes. These new nanomaterials possess unique properties but, at the same time, present several challenges including poor solubility, potential toxicity and biopersistance. The present work reviews recent research advances in how to overcome these challenges and how new avenues are opening for applications such as drug delivery, tissue engineering and biosensing thanks to the use of carbon nanotubes.

Observed optical properties of conjugated polymers pose interesting and challenging problems that are yet to be understood quantitatively. The problem is complicated due to the competition between energy migration among chromophores influenced by defects, conformations dictated by attractions among monomers and differing fluorescence rates of the chromophores of different conjugation lengths. In a conjugated polymer in the presence of defects, these chromophores are, to a good approximation, nearly straight planar chain segments with unbroken conjugation. Defects limit the length of a conjugated segment. Single molecules spectroscopic studies have shown that conformation of PPV-derivative polymers is not spherically symmetric as was commonly described using Flory theory; instead they are better represented as defect cylinders. As the defects are randomly distributed along the segments, they render the lengths of the segments random, thus introducing a disorder that does not allow easy formation of ordered structures like rods and toroids. Interactions among side chains of monomers in a conjugated polymer (as in MEH–PPV) can also determine the shape and the arrangement. The said non-spherical shape or conformation can have tremendous implication in optical properties of these polymers. While energy migration among the chromophores may be modelled as a random walk problem, the transfer rates and fluorescence properties of each chromophores need to be obtained quantum mechanically. The rate of hopping between different chromophores can be treated as a resonance energy transfer (RET) process, although Forster's well-known expression might not be reliable because in many cases the chromophores are spatially quite close to each other. Another issue revolves around the coherent or incoherent nature of transport. We discuss a recent theoretical approach that includes some of the features of energy transport discussed above. We discuss how a photochemical funnel can develop in such a system where the longest conjugated segment can form the funnel.

The positive muon (μ+) can be incorporated into free radicals where it acts as a probe of the structure and dynamics. The muoniated radicals are characterized by a series of magnetic resonance techniques known as μSR for muon spin rotation, resonance and relaxation spectroscopy. In this review it is shown how μSR can be used to obtain information about the structure, dynamics, and local environments of transient radicals in solids like zeolites, in solution or even in exotic solvents like supercritical water. It will also be demonstrated that muoniated radicals can be used as probes in complex systems, such as rod-like and discotic liquid crystals, bilayers and polymers, where they have advantages over traditional spin labelling.

Optimal control by computer by Graham A. Worth; Gareth W. Richings (113-139).
The use of computer simulations studying how laser light can control the behaviour of atoms and molecules is reviewed. A variety of control schemes have been developed and we focus on three commonly used approaches: optimal control, local control and strong-field control. An overview is given of the types of control that can be achieved of interest to chemists, namely molecular alignment and orientation, isomerisation and bond breaking and forming. The calculations are very computer intensive and results from both exact solutions to the time-dependent Schrödinger equation and approximate solutions using the commonly employed trajectory surface hopping approach are covered. Of particular interest is the recent work using strong-field control, which promises to be more general and powerful than approaches based on weak-fields that do not perturb the molecular potential energy surfaces.

Advances in low temperature gas-phase kinetics by Ian W. M. Smith; Peter W. Barnes (140-166).
Rate constants for elementary gas-phase reactions were first measured reliably following the development of pulsed photolysis and flow methods in the 1960's. These techniques have continued to be employed as kinetics experiments have been performed at lower and lower temperatures. Sub-ambient temperatures are reached either by cryogenic methods or by using expansion techniques. In this article, we review the possibilities and limitations of these cooling techniques and the results that have been obtained. These efforts have been driven both by the desire to understand the fundamental factors that control the rates of chemical reactions and also by the wish to provide rate constants that can be used in models of complex environments, such as planetary atmospheres and the interstellar medium. In this review, some emphasis is given to the CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme) method which has now been used to determine rate constants for many elementary reactions, including those between neutral species, as well as ion–molecule reactions. This method has provided rate constants for a limited number of reactions to below 10 K. Major efforts are now being made to go to still lower temperatures and we describe some of the results obtained at these very low temperatures in the last section of this article.

Voltammetry of proteins at liquid–liquid interfaces by Damien W. M. Arrigan (167-188).
The voltammetric behaviour of proteins at interfaces between two immiscible electrolyte solutions (ITIES) is reviewed. This behaviour is of interest for a number of reasons, including the basis of label-free detection methods and the understanding of the stability of biopharmaceutical and food formulations. The review discusses electrochemical strategies for protein and polypeptide detection, and the mechanisms involved in protein detection at the ITIES. Results obtained by DC and AC voltammetry are included together with data from other complementary techniques.

Studies of reactions relevant to astrochemistry by Michel Costes; Christian Naulin (189-210).
We review experimental studies of bimolecular exchange reactions between neutral species that can occur in dense molecular clouds: kinetics experiments performed with the so-called CRESU technique which measure global reaction rates and dynamics measurements performed with crossed molecular beam apparatuses which bring information on the products and branching ratios. Special attention is devoted to reactions of the carbon atom which may contribute to the synthesis of long polyyne or polyene chains. Results on the reactions of C(3PJ) atoms with methylacetylene, allene, ethylene and acetylene, with CRESU (in terms of rate coefficients) and crossed-beam experiments (in terms of integral and differential reaction cross sections) are discussed. Emphasis is placed on the interest to use these complementary methods in conjunction to obtain detailed rate coefficients. It is also shown that crossed-beam experiments can furnish sensitive tests to the state-to-state cross sections and rates for rotational energy transfer by inelastic collisions obtained by theoretical methods, as exemplified with CO + H2 collisions.

Synthesis and applications of organic nanorods, nanowires and nanotubes by Chuang Zhang; Yongli Yan; Yong Sheng Zhao; Jiannian Yao (211-239).
One-dimensional (1D) nanostructures, including nanorods, nanowires, nanotubes, etc., exhibit the quantum confinement effects in the other two dimensions. Nanomaterials with 1D coherence are more suitable for the construction of active nanodevices and interconnects rather than zero-dimensional (0D) amorphous nanoparticles. Inorganic 1D nanomaterials have been widely investigated and widely used as building blocks in many kinds of optoelectronic integrations, and it is very reasonable to assume that their organic counterparts can also play an important role in this field. During the past ten years, organic 1D nanomaterials constructed from small functional molecules have obtained more and more attention due to their unique optical and electronic properties as well as their potential applications in nanoscale devices. Their high structural tunability, reaction activity and processability provide great opportunities to miniaturized optoelectronic chips based on organic 1D nanostructures, since they are usually assembled from molecular units with weak intermolecular interactions, such as hydrogen bonds, π–π stacking and van der Waals force. These weak interactions allow for more facile and mild conditions in the fabrication of high quality organic 1D nanostructures rather than those in the construction of their inorganic counterparts. More importantly, very recent studies reveal that the diversity of energy/electron transfer processes in organic semiconductors brings new hopes to break the performance limitations of traditional photonic and electronic devices, thus allowing higher luminescence intensity, more efficient photon confinement, stronger exciton–photon coupling, and so on. Indeed, organic 1D nanomaterials have already emerged to play increasingly an important role in many optoelectronic applications, such as nanolasers, optical waveguides, light-emitting devices, solar cells and sensors. In the past two decades, people have not only witnessed but also taken for granted the rapid development of nanomaterial science, and here we would like to promote awareness of the significance of organic 1D nanomaterials in the field of nanotechnology and optoelectronic nanodevices. This report presents a comprehensive review about recent research in the preparation and applications of 1D nanomaterials from functional low-molecular-weight organic compounds, whose optical and electronic properties are fundamentally different from those of their inorganic counterparts. Here we try to summarize the important breakthroughs from the fabrication of organic nanorods, nanowires and nanotubes, to the application of these nanostructures in integrated photonic elements and optoelectronic nanodevices. We begin with a general summary of the construction strategies (liquid-phase assembly, vapor deposition and template methods) for achieving 1D nanostructures from small organic functional molecules, then provide an overview of the unique optoelectronic properties induced by molecular aggregation in the nanostructures. Special emphasis is put on the luminescent properties of low dimensional sizes that are different from those of the corresponding bulk materials. This offers the materials better photon confinement ability or charge carrier transport property, and hence better optoelectronic performances such as optical waveguiding, multicolor emission, low-threshold nanolasers, light-emitting devices, photon-detecting devices, etc., which are presented one by one in the following section. In the last part of this report, we conclude with our personal viewpoints of the future development of organic 1D nanomaterials and also their great potentials in highly integrated photonic and electronic devices and chips.

Molecular structure by X-ray diffraction by Harold R. Powell (240-265).
X-ray crystallography has matured over the course of the last century to be the method of choice for the determination of solid-state structure. This is reflected in the lack of new developments in methods for solving and refining structures by single crystal techniques, although some advances have been made in understanding the underlying methods and extending applications to address more difficult problems; most of these are in macromolecular crystallography rather than in the small molecule field. The main areas of progress have been in sample preparation, in X-ray source and detector technology, in the software required to process the data obtained, and in applying sophisticated statistical methods to the analysis. A major visible consequence of the continued importance of the science is that the main crystallographic databases continue to grow rapidly, each with similar doubling rates to those found for the last several decades.

Case study of Rb+(aq), quasi-chemical theory of ion hydration, and the no split occupancies rule by D. Sabo; D. Jiao; S. Varma; L. R. Pratt; S. B. Rempe (266-278).
Quasi-chemical theory applied to ion hydration combines statistical mechanical theory, electronic structure calculations, and molecular simulation, disciplines which are individually subjects for specialized professional attention. Because it combines activities which are themselves non-trivial, quasi-chemical theory is typically viewed with surprise. Nevertheless, it provides a fully-considered framework for analysis of ion hydration. Furthermore, the initial calculations are indeed simple, successful, and provide new information to long-standing experimental activities such as neutron diffraction by hydrated ions. Here we review quasi-chemical theory in the context of a challenging application, Rb+(aq).

Back cover (279-280).