THE ELECTROSTATIC POTENTIAL FOR SPERMINE PHOSPHATE HEXAHYDRATE. A. E. Cohen, J. R. Ruble, and B. M. Craven, Department of Crystallography, University of Pittsburgh, Pittsburgh, PA 15260

Spermine, a water soluble, tetra-basic polyamine, is widely found in nature and may function to stabilize DNA secondary structures. The crystal structure of spermine phosphate hexahydrate ([C₁₀H₃₀N₄]⁺⁴ 2[HP0₄]^-2.6H₂0) was first determined by Iitaka and Huse (1965) from X-ray Weissenberg photographic data. Their proposed hydrogen-bonding has been confirmed by low temperature neutron diffraction (Cohen, Klooster & Craven). Now a high resolution X-ray data set has been collected at 125 K using Mo K[[alpha]] radiation and the charge density distribution has been determined. The map of the electrostatic potential of the isolated spermine cation (below) shows that the electrostatic potential is an almost uniformly electropositive cylinder. The spermine cation while attracted to the negatively charged phosphate groups would have freedom to slide along the major groove of native DNA.

The electrostatic potential of the isolated spermine cation is shown. The nitrogen atoms are labeled with black dots. Contours are at intervals of 0.05 eÅ^-1.

This work is supported by grant No. GM-39513.