The ordered water cluster in vitamin B12 coenzyme at 15 K is stabilized by C-H...O hydrogen bonds.

The hydrogen-bonding interactions of the ordered water cluster in the pocket region of vitamin B(12) coenzyme at 15 K are analyzed from published atomic coordinates. Several of these water molecules accept C-H.O hydrogen bonds from the pocket wall, most of which have the function to complete tetrahedral hydrogen-bond coordination. This is the largest water assembly for which the stabilizing function of C-H.O interactions has been described.