Science Progress (2002), 85 (3)

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Science Progress (2002), 85 (3), 199–217

The design and applications of

multifunctional ligands

ANDREW D. BURROWS

The properties of a metal coordination complex are determined as much by

the ligand set – the molecules and ions coordinated to the metal centre – as

by the nature of the metal itself. The design and use of new ligands is consequently

a major part of chemical research. This review considers the role

of multifunctional ligands in three separate and distinct areas of chemistry.

In homogeneous catalysis, the role of hybrid and hemilabile ligands is considered,

and the introduction of functionalities designed to overcome problems

of separation, either by tethering or solubilising, is discussed. In

supramolecular chemistry, functionalities enabling the recognition and

sensing of cations and anions are examined. In addition, ligands containing

two or more faces are discussed for their role in metallodendrimer formation

and self-assembly reactions, and the use of bifunctional ligands in

crystal engineering is addressed. The application of metal complexes in

medicine is examined by consideration of cis-platin and its derivatives as

anti-tumour agents. Imaging agents are also discussed with the uses of

gadolinium MRI contrast agents and _-emitting technetium complexes

highlighted.

Science Progress (2002), 85 (3), 219–241

Artificial transmembrane

channels for sodium and

potassium

PETER J. CRAGG

Transport of alkali metals, particularly sodium and potassium, across cell

membranes is an essential function performed by special proteins that

enable cells to regulate inter- and extracellular ion concentrations with

exceptional selectivity. The importance of these channel-forming proteins

has led to researchers emulating of their structural features: an ion-specific

filter and conduction at rates up to 108 ions per second. Synthetic helical

and cyclic polypeptides form channels, however, the specificity of ion transport

is often low. Ion-specific macrocycles have been used as filters from

which membrane-spanning derivatives have been prepared. Success has

been limited as many compounds act as ion carriers rather than forming

transmembrane channels. Surfactant compounds also allow ions to cross

membranes but any specificity is serendipitous. Overall it seems possible to

mimic either ion specificity or efficient transmembrane ion transport. The

goal for the future will be to combine both characteristics in one artificial

system.

Science Progress (2002), 85 (3), 243–262

New electrochromic materials

NATALIE M. ROWLEY AND ROGER J. MORTIMER

A number of inorganic and organic materials exhibit redox states (reduced

and/or oxidised forms) with distinct UV-Visible (electronic) absorption

bands. When electrochemical switching of these redox states gives rise to

different colours (i.e. new or different visible region bands), the material is

described as being electrochromic. By virtue of their numerous applications,

both of academic and commercial interest, electrochromic materials are

currently attracting a great deal of interest. This review provides an introduction

to the major classes of electrochromic materials, namely transition

metal oxides, Prussian blue systems, viologens, conducting polymers, transition

metal and lanthanide coordination complexes and metallopolymers,

and metal phthalocyanines. Examples of some new materials and of prototype

and commercial electrochromic devices are cited.

Science Progress (2002), 85 (3), 263–296

Chemistry in the clouds:the role

of aerosols in atmospheric

chemistry

JONATHAN P. REID* AND ROBERT M. SAYER

Ever since the discovery of the ozone hole over the Antarctic and the

recognition of the damaging effects of acid rain, the role of atmospheric

aerosol particles in determining the chemical balance of the atmosphere

has received much attention. Aerosol particles produced in combustion

can also have a deleterious effect on human health. In this article we

review the chemistry that can occur on aerosol particles, particularly on

aqueous based aerosols in the troposphere. The sources, transformation

and loss mechanisms of atmospheric aerosol will be discussed. In

particular, we will focus on the role of chemical transformation on

aerosol particles in promoting reactions that would otherwise be too slow

in the homogeneous atmospheric gas phase. Heterogeneous reaction

mechanisms of some key chemical reactions will be described. Recent

observations of a high organic content of tropospheric aerosol particles

will be described and a model of organic coated aerosols will be

reviewed.