Cytosine metal complexes

As to the way of formation of cytosine-N4 metal complexes, initial binding to N3 and subsequent migration to N4 with displacement of an amine proton is a common way. The process can be facilitated by OH (169 a,b) or through redox chemistry (44b, 168). 

Cytosine, protonated at N3 Proton nuclear magnetic resonance Metal complex of rare cytosine tautomer 9 -Methy ladenine... 

The stability constants of zinc(n) complexes of uracil, thymine, and cytosine have been reported.249 At 45 °C in 0.1M-KNO3, 1 1 complexes are formed. The 2 1 ligand metal complexes formed between thiosalicylic acid and zinc(n), mercury(n), cadmium-(n) and lead(n) have been isolated, and formation of the 1 1 complexes in solution has been characterized by pH-titration.250 With mercury, the 2 1 complex has been assigned the structure (7), while the other metals form complexes of general structure (8). This is thought to be a consequence of the order S—M11 bond strength being Hg > Zn > Cd > Pb. 

In general the pyrimidines show a much lower reactivity towards the metal ions. Apparently no reaction was observed with uracil while the stability constants of Cu-cytosine are even lower than the lgJCi and gK% values of Cu(NH3)62+ (79). The high stability of the purine metal complexes can be attributed to the binding site at the imidazole residue. There the imino proton competes with the metal ion. Fig. 1 presents a model of the 2 1 complex of Cu-(adenine)%. 

Besides hydrophobic and coordinative interactions, hydrogen bonds and electrostatic interactions have been used to assemble luminescent metal complexes. In this context, Barigelletti and coworkers (45-47) reported on the luminescent properties of Ru(II) and Os(II) complexes containing bipyridines peripherally functionalized with nucleotide bases, cytosine, and guanine. 

Fast atom bombardment (FAB) m.s. of glucose and sucrose in the presence of various metal complexes have been studied. Potassium hexacyano ferrate(II) gave useful [M+K] lons. Components of the polyoxins, a fermentation-produced complex of nucleoside peptide antibiotics, have been identified by FAB m.s. following separation by h.p.l.c, The FAB m.s. of the natural ribo- and deoxyrlbo-nucleosldes and -nucleotides and some cytosine analogues have been Investigated. The use of the negative ion mode reduced interference from positive counter-ions (e.g., Na ) and permitted rapid... 

Table XIX contains stability constants for complexes of Ca2+ and of several other M2+ ions with a selection of phosphonate and nucleotide ligands (681,687-695). There is considerably more published information, especially on ATP (and, to a lesser extent, ADP and AMP) complexes at various pHs, ionic strengths, and temperatures (229,696,697), and on phosphonates (688) and bisphosphonates (688,698). The metal-ion binding properties of cytidine have been considered in detail in relation to stability constant determinations for its Ca2+ complex and complexes of seven other M2+ cations (232), and for ternary M21 -cytidine-amino acid and -oxalate complexes (699). Stability constant data for Ca2+ complexes of the nucleosides cytidine and uridine, the nucleoside bases adenine, cytosine, uracil, and thymine, and the 5 -monophosphates of adenosine, cytidine, thymidine, and uridine, have been listed along with values for analogous complexes of a wide range of other metal ions (700). Unfortunately comparisons are sometimes precluded by significant differences in experimental conditions.

As well as NONOates, other NO donors also showed anticancer activity independently. Sodium nitroprusside (SNP), a metal-NO complex, showed cytotoxic effects on the cells of some patients with malignant lymphoma (ML), acute myelocytic leukemia (AML) or chronic myelomonocytic leukemia (CMMoL), but not with multiple myeloma [109]. SNP and cytosine arabinoside (Ara-C) did not share the drug resistance. Interestingly, SNP had no effect on lymphocytes of healthy volunteers. These results suggest that SNP has an anti-tumor effect on human hematological malignant cells. 

The Mg+ complexes of cytosine, thymine and uracil are the most complex system studied via photodissociation spectroscopy to date . A complication for these systems is that these nucleobases can exist in various tautomeric forms and that complexation of a metal can change the stability order of the tautomers. DFT calculations located four tautomeric Mg(cytosine)+ complexes, and three of these (29, 30, and 31) were suggested to be responsible for the four reactive photofragment ions 32-35 observed at a wavelength of 360 nm (Scheme 4) . Related photofragmentation reactions were observed for the Mg(thymine)+" and Mg(uracil)+" complexes . ... 

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