Impact of histidine residue on chelating ability of 2′-deoxyriboadenosine

Copper(II) complexes with a new chelator-type nucleoside–histidine modified 2′-deoxyriboadenosine (N-[(9-β-D-2′-deoxyribofuranosylpurin-6-yl)-carbamoyl]histidine) were studied by potentiometric and spectroscopic (UV–visible, CD, EPR) techniques, in conjunction with computer modeling optimization. The ligand can act as bidentate or tridentate depending on pH range. In acidic pH a very stable dimeric complex Cu2L2 predominates with coordination spheres of both metal ions composed of oxygen atoms from carboxylic groups, one oxygen atom from ureido group and two nitrogen atoms derived from purine base and histidine ring. Above pH 5, deprotonation of carbamoyl nitrogens leads to the formation of CuL2, Cu2L2H− 1 and Cu2L2H− 2 species. The CuL2H− 1 and CuL2H− 2 complexes with three or four nitrogens in Cu(II) coordination sphere have been detected in alkaline medium.Our findings suggest that N-[(9-beta-D-2′-deoxyribofuranosylpurin-6-yl)-carbamoyl]histidine chelates copper(II) ions very efficiently. The resulting complex might be used as an alternative base-pairing mode in which hydrogen-bonded base pairs present in natural DNA are replaced by metal-mediated ones.

The histidine residue has critical impact on chelating ability of 2′-deoxyriboadenosine towards copper(II) ions. In acidic pH a very stable dimeric complex Cu2L2 predominates and around neutral pH the complexes with Cu(II) bonded to carboxylic oxygen and three nitrogen donor atoms derived from histidine residues and purine base are formed.Figure optionsDownload as PowerPoint slide