Editorial [Hot Topic:Polyphenols(Guest Editor: Poul Erik Hansen)]

Polyphenols are a very diverse class of compounds. In the present volume the emphasis is on Schiff bases and azo compounds containing one or more hydroxy group. Such polyphenols have many interesting properties and uses. Many Schiff bases with hydroxy groups have a hydroxy group in ortho position to the imine function resulting in intra molecular hydrogen bonding and possibly tautomerism. This can happen both in the liquid and solid state. The hydrogen bond is often of the low barrier type and Schiff bases are therefore valuable models in order to describe this phenomenon in particular because the N…O distance can conveniently be varied as a function of substituents in the vicinity. The Schiff bases and azo compounds have interesting biological properties and it is vital to understand how this is a function of the structure. Schiff bases are clearly of great importance in material science in general and in optical materials in particular. Schiff base metal complexes have become important catalysts. The contributions cover all these aspects and give a thorough overview of theoretical calculations. Spectroscopic approaches such as NMR and IR are clearly important in order to elucidate the properties not the least in order to understand the biological properties. The present contributions will shortly be followed by another volume dealing with further aspects of Schiff bases and azo compounds.