Geometric Parameters in Nucleic Acids:  Nitrogenous Bases

We present estimates of the bond-length and bond-angle parameters for the nitrogenous base side groups of nucleic acids. These values are the result of a statistical survey of small molecules in the Cambridge Structural Database for which high-resolution X-ray and neutron crystal structures are available. The statistics include arithmetic means and standard deviations for the different samples, as well as comparisons of the population distributions for sugar- and non-sugar-derivatized bases. These accumulated data provide appropriate target values for refinements of oligonucleotide structures, as well as sets of standard atomic coordinates for the five common bases.