Purine complexes

Tphe complexing of virtually all purines with aromatic molecules seems - to have far-reaching biological significance. For example, it is known that caffeine affects the rates of many enzymatic reactions (e.g., 0.01, 0.05, and 0.10M caffeine will inhibit salivary amylase 29, 54, and 72% respectively) (12), and purine can decrease the helix-coil transition temperature of the proteins bovine serum albumin and lysozyme (2). It is not unreasonable to expect the involvement of caffeine-aromatic and purine-aromatic complexes because caffeine derivatives and purine complex with the aromatic amino acids tyrosine, phenylalanine, and tryptophan (2). (In fact tryptophan forms a stable 1 to 1 crystalline complex in 0.5M theophylline glycol.)... 

Kelman AD, Clarke MJ, Edmonds SD, Peresie FIJ (1977) Biological activity of ruthenium purine complexes. J Clin Hematol Oncol 7 274—288... 

The extent of intramolecular stacking interactions depends strongly on both the nature of the bases involved (i.e. purines stack better than pyrimidines) and the steric features of the nucleotides. For example, the stability of Cu + complexes of the type [Cu(phen)(AMP)] decreases in the order 2 -AMP > 5 -AMP > 3 -AMP. [Cu(5 -AMPH)(bipy)(H20)]2 and [Cu(3 -GMP)(phen)(H20)]2 are the only known Cu-purine complexes in which N-7 is not involved in coordination to Cu +. ... 

Finally, we should point out that the existence of N(7)-S(6) chelates to platinum does not mean that N(7)-0(6) chelates to platinum are also present in the corresponding platinum-purine complexes. In fact, Heitner and Lippard have pointed out that the steric requirements for a [N—C—C—S—M] five-membered ring are significantly different from those for a [N-C-C-O-M] five-member ring, so that the existence of the former does not necessarily imply the existence of the latter. 

BRUCKET AL. EXAFS Analysis of Purine Complexes TABLE III Least-Squares Regression Coefficients... 

Ruthenium Anticancer Agents and Relevant Reactions of Ruthenium—Purine Complexes... 

In the case of ODN, the formation of the corresponding Cu(l)-purine complex is suppressed and its determination is possible after the release of nucleobases from its chain by acid hydrolysis. Purine nucleobases from an oligonucleotide chain can be released under acid hydrolysis, for example, 0.5 M perchloric acid, at a temperature of 75°C for 30 min. Under these conditions, only purine bases are released from the oligonucleotide chain. Then the sample is cooled and neutralized, and aliquots are mixed with the background electrol5d e for voltammetric measurements. 

Voltammetric measurements confirm that Hg-modified carbon electrodes are suitable for sensitive electrochemical detection of ODN compared to mercury electrodes. In the presence of the copper ions, these electrodes modified by a mercury layer were used for the detection of a picomolar quantity of ODN. The electrochemical step includes a potential-controlled reduction of the copper ions Cu(II) and accumulation of the Cu(I)-purine base residue complex on the Hg-modified carbon surface. The proposed electrochemical method can be used for the determination of different ODN lengths because the stripping current peak of the electrochemically accumulated Cu(I]-purine complex increased linearly with the length of ODN. The optical microscope images were used for the visualization of the surface morphology of the bare and Hg-modified carbon electrodes [64]. 

M. J. Clarke Ruthenium Anticancer Agents and Relevant Reactions of Ruthenium-Purine Complexes (Platinum, Gold and Other Metal Chemotherapeutic Agents v. 209, Ed. S. J. Lippard), p. 335. ACS, Washington (1983). 

The different coordination sites of the adenine nucleobase generate a markedly different topology of the polymerie ehains, relative to the purine complexes. The coordinated adenine molecules are almost perpendicular to the metal-oxalato framework instead of being arranged along the growing axis of the polymeric chain like in the purine complexes. This feature results in the presence of bulkier chains, which leads to a less effective packing with crystallization water molecules and noncoordinated adenine molecules inserted between the chains. 

---