Foreword

ioinorganic chemistry is a highly interdisciplinary research field aiming at a detailed understanding of the evolutionarily optimized principles that nature developed for making efficient use of the specific properties of metal ions in biochemical transformations underlying life processes. This subject provides great intellectual and technical challenges, and enormous efforts have been made to design small metal complexes that mimic the chemical and/or spectroscopic properties of metalloprotein active sites. These model systems can be analyzed in much greater detail than the highly complex metalloprotein structures themselves. Furthermore, by ligand design, metal substitution, or variation of the environmental parameters selected structural and functional aspects, can be studied individually, whereas enzyme functions can only be observed in their cooperative effect. As an integral part of contemporary bioinorganic research, Computational Chemistry today has matured to a point were well-established methods can provide indispensable insights into the geometric and electronic structures of even more complex species. Yet, it was not so long ago that reliable quantum chemical studies on structures and thermochemical properties of transition metal complexes were considered an elusive goal. The origin of the many vexing problems for quantum chemists is, at the same time, the starting point for the multifaceted chemistry of transition metal ions: both are a direct consequence of the presence of various low-lying and often energetically nearly degenerate states, each with a different chemical behavior. The primary problem of quantum chemical computations then is to provide a balanced, sufficiently accurate description of the subtle electronic effects present in transition metal species. On the one hand, this inevitably requires use of high-level quantum chemical methods, which, on the other hand, can be B applied to the smallest systems only. Without doubt, a critical ingredient to the success of computational chemistry in the bioinorganic context has been the development of the density functional theory (DFT). Notwithstanding the many fundamental problems of modern functionals documented in the literature, DFT in the form of hybrid functionals represents the most efficient way to study transition metal reactivity in medium-sized systems in the foreseeable future. The extraordinary progress made in the recent past is not only a result of the development of improved computational methods; it has, to a large extent, been a result of systematic benchmarking of computed results against available experimental data. Bioinorganic chemistry in particular is a field in which experimentalists have gathered a wealth of accurate kinetic, thermodynamic, and spectroscopic data for a broad variety of comparably small molecular systems to carefully calibrate a chosen theoretical approach to a relevant set of benchmark data, before it is applied to solve new chemical problems. All this renders bioinorganic chemistry a most promising field to use experiment and theory in a complementary way to obtain insights that would not be accessible for either side alone. The scope of this kind of research is enormous, and the aim is highly rewarding: the extraordinarily high efficiency of chemical transformations that take place in biological systems remains unmatched in modern industrial processes. The detailed understanding of the function of representative biomimetic models is thus not only an objective for basic biochemical research as such, it is also a prerequisite for the transfer of the highly optimized bio-