The Kozlowski group is mainly focused on the application of electronic structure theory (DFT, CASSCF, MP2) and hybrid quantum mechanics/molecular mechanics (QM/MM) methods to understand the catalytic and photolytic mechanisms of vitamin B12-dependent enzymes. Vitamin B12 which is also known as cyanocobalamin (CNCbl) is biologically inactive. It has two biologically active derivatives, adenosylcobalamin (AdoCbl) and methylcobalamin (MeCbl). These two molecules act as a cofactor to catalyze numerous enzymatic reactions and also undergo photolysis upon the excitation with light. A primary motivation of our work is to understand the mechanism of photolysis and the native catalytic mechanisms for AdoCbl and MeCbl-dependent metalloenzymes. The three focal points of our current studies are the photolysis of the Co-C bond in the enzymatic environment, coenzyme B12-dependent enzymatic catalysis, and cobalamin mediated methyl transfer reactions. AdoCbl-dependent eliminases and mutases, MeCbl-dependent methyltransferases, and the AdoCbl based photoreceptor CarH are preferred systems for study. There are many applications of B12 chemistry and photochemistry including light-activated drug design, DNA photo regulation and OH radical generation. In addition, we actively collaborate with different experimental groups inside and outside of the USA.