Studies in a model system on the effect of hydrogen bonding at hetero atoms of oxidized flavin on its electron...

The effect of hydrogen bonding at hetero atoms of oxidized flavin on its electron acceptability was studied by the ab initio molecular orbital method. The calculations were carried out for all possible lumiflavin-H2O complexes and for some lumiflavin-formamide complexes. Calculated data showed that the magnitudes of hydrogen bonding energy at the hetero atoms are in the order of N(3)H greater than N(5) greater than O(12) greater than N(1) greater than O(14). It was found that the atomic orbital coefficient of the lowest unoccupied molecular orbital is the largest at N(5) and that hydrogen bonding at N(1), N(5), O(12), and O(14) increases the electron acceptability of the oxidized flavin at N(5), while hydrogen bonding at N(3)H decreases it.