Cryo-bioorganic chemistry: molecular interactions at low temperature

Freezing of aqueous or organic solutions plays a pivotal role in enhancemen t of rate and/or yield of biomolecular reactions. The smooth conditions of the frozen state at low temperature can also suppress racemization and side -product formation of the reactions. Molecular interactions in liquid under cooled solutions, on the other hand, offer the possibility to study enzyme activity mechanisms in vitro and a chance for survival of organisms in vivo . This review illustrates the differences between frozen and liquid conditi ons on several small and large biomolecules, together with the synthetic us e of freezing. In relation to the freezing effect on enzyme activity, a pec uliar phenomenon is discussed: 'cryo-oscillations' are temporal motions of trypsin activity in frozen solution in the presence of Mn2+ ion. The molecu lar basis of cold adaptation is also discussed, which points to mechanisms evolved by organisms living at subzero temperatures. The factors involved i n the freezing effect are shown; i.e. the role of freeze-concentration and frozen solvent surface is demonstrated and elucidated using several example s.