Table of Contents
Metal-Based Drugs
Volume 3 (1996), Issue 3, Pages 131-141
http://dx.doi.org/10.1155/MBD.1996.131

Extent of the Acidification by N7-Coordinated cis-Diammine-Platinum(II) on the Acidic Sites of Guanine Derivatives

1Institute of Inorganic Chemistry, University of Basel, Spitalstrasse 51, Basel CH-4056, Switzerland
2Department of Chemistry, University of Dortmund, Otto-Hahn-Strasse 6, Dortmund D-44221, Germany

Received 23 March 1996; Accepted 25 April 1996

Copyright © 1996 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Coordination of two monoprotonated 2'-deoxyguanosine 5'-monophosphate species, H(dGMP), via N7 to cis-(NH3)2Pt2+ gives the complex cis-(NH3)2Pt(H·dGMP)2 which is a four-protonic acid. The corresponding acidity constants were measured by potentiometric pH titrations (25℃; I = 0.1 M, NaNO3). The first two protons are released from the two -P(O)2(OH) groups (PKa/1 = 5.57; PKa/2 = 6.29) and the next two protons are from the H(N1) sites of the guanine residues (PKa/3 = 8.73; PKa/4 = 9.48). The micro acidity constants of the various sites are also evaluated. Comparison of these data with those determined for the three-protonic H2(dGMP)± (PKa/1 = 2.69 for the H+(N7) site; PKa/2 = 6.29 for -P(O)2(OH) ;PKa/3 = 9.56 for H(N1)) shows that on average the N-7-coordinated Pt2+ acidifies the phosphate protons by Δ pKa = 0.36 and the H(N1) sites by Δ pKa = 0.46. These results are further compared with those obtained previously for cis-(NH3)2Pt(L)2, where L = 9-ethylguanine or monoprotonated 2'-deoxycytidine 5'-monophosphate. Conclusions regarding platinated DNA are also presented.