Research Interests

The central themes of my research are the structure and function of Fe cofactors in proteins.  Since my college years I had curiosity and interest for coordination chemistry.  My first project as an undergraduate in Bucharest was the synthesis of some platinum coordination compounds with potential anti-cancer activity.  Later, my choice for iron was facilitated, more or less independent of my will, by the technique I studied and used in graduate school: ⁵⁷Fe-Mössbauer spectroscopy.  This is a specialized spectroscopic technique for the ⁵⁷Fe isotope.  To study one isotope may appear restrictive.  Fortunately, iron is the most abundant transition metal in biology and it is present in most important biological processes.  Therefore biological ⁵⁷Fe-Mössbauer spectroscopy (MB) has never been in danger of running out of systems to study.  Not only that we are not close to finishing the Fe-proteins in even one bacterium (take P. aeruginosa or E. coli for ex.), but we have not yet understood the structures of some proteins whose study began many years ago (e.g. hydrogenase, nitrogenase etc). 

Apart from directly studying protein samples, it is immensely instructive to study model compounds.  Model complexes are molecular compounds synthesized by chemists in an attempt to match structural features or functions of enzymatic sites.  Typically spectroscopists studying a protein would find a spectroscopic parameter or feature that they cannot explain with any theory that they cook up from books and their experience.  That is generally considered a "strange" thing (label applied not before thorough checks).  When a synthetic compound is found to match some strange spectroscopic signature of a protein, it is considered a good model.  The advantage of studying the model is that often it can be structurally and spectroscopically characterized (X-ray, FTIR, EXAFS, ESR etc).  The idea seems to be that even if you found a good model serendipitously, if you understand the model compound conceptually, i.e. you find a theory that explains the spectra, then maybe you can do what Nature does with it (say, produce hydrogen from protons).  Moreover, very often, the feature of interest in a protein, may be buried in complex spectra resulting from multiple iron sites, so it is not well resolved.  Having a compound exhibiting a well resolved spectrum, can sometimes can enable one to probe the strange feature from many points of view until it is understood.  Currently, the people who have seen and often explained the strangest things in bio-inorganic Mössbauer spectroscopy reside in Pittsburgh (Dr. Münck's lab, at Carnegie Mellon University).

MB spectroscopy has many useful features, but two are distinctive: (1) a MB spectrum is observed regardless of oxidation or spin state of the iron atoms (unlike EPR, where you don't see diamagnetic compounds); and (2) the spectral patterns of paramagnetic and diamagnetic compounds are easily distinguishable.  (Münck, E., Methods in Enzymology, Vol. LIV, pages 346-379) Thus, one analyzes spectra to determine the number of distinct Fe sites in the sample, their oxidation and spin state, and magnetic behavior.  These parameters are interpreted in terms of electronic models, allowing  predictions of molecular structure and function.  Usually it is necessary to record the spectra at cryogenic temperatures (using liquid helium, with a boiling point of 4.2 K, approx. -269 C) in order to resolve paramagnetic spectra.

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