Metal-nucleotide complexes

The second major type of stereochemical information that can be obtained about phosphotransferases and nucleotidyltransferases is the coordination structure of nucleotide-metal complexes as they are bound at the active sites of enzymes. Two of the simplest coordination complexes of MgATP are shown below to exemplify the stereochemical difference. These are two stereoisomers differing in screw sense in the coordination ring. 

Dowex 1-X2 0.6 0.65 Strongly basic anion exchanger with S-DVB matrix for separation of small peptides, nucleotides, and large metal complexes. Molecular weight exclusion is <2700. 

Metal complexes of nucleic acid derivatives and nucleotides binding sites and structures. L. G. Marzilli, Adv. Inorg. Biochem., 1981, 3, 48-85 (138). 

Electrostatically-controlled pre-association interactions have an important effect on rates for [Pd(dien)Cl]+ reacting with thione-containing nucleosides, nucleotides and oligonucleotides, as is often the case for reactions between metal complexes and this type of biological ligand. Interaction between the charged complex and the polyanionic oligonucleotide surface leads to an increase in both enthalpy and entropy of activation in the DNA or model environment (252). 

In even more disadvantageous circumstances, the thermal decomposition does not yield a single defined product, but a complex mixture that results in almost useless spectra, e.g., in case of highly polar natural products such as saccharides, nucleotides, and peptides or in case of ionic compounds such as organic salts or metal complexes. 

ORD spectra of copper complexes with a variety of proteins and peptides give conformational as well as quantitative information on the metal binding (9, 10, 35). This method also has been successfully applied to study metal complexes with nucleotides (53, 70). 

This method is especially suitable for studies with polymer nucleotide-metal ion interaction. When dissolved nucleic acids are exposed with and without metal ions to an increase of temperature structural changes, some reversible, some irreversible can be observed (27, 24, 27, 30, 39, 54—56, 75, 100, 108). The two parameters Tm (or midpoint of the transition) and a (the width of the transition) allow conclusions about conformational alterations. The application of this procedure for quantitative studies of metal complexing still needs to be elucidated. 

Relaxation experiments with the temperature jump method (18) give valuable information about the kinetics of nucleotidepolyphosphate and metal ion interaction in solution (20). Differences of kinetic dissociation or association constants of such metal complexes are helping to reveal some biochemical specificities of certain metal ions in metal-nucleotide complexes. 

Phillips, R. S. J. Adenosine and the adenine nucleotides, ionization, metal complex formation and conformation in solution. Chem. Rev. 66, 501 (1966). 

In contrast to the relatively simple structures incorporating one of the first three binding motifs, the polymeric complex [Cu3(5 -GMP)3(H20)8] has three distinct coordination environments about different Cu + ions. While this complex is unusually sophisticated, the polymeric nature of the material is common for many metal complexes with GMP or IMP, in which inner-sphere binding occurs to both the N-7 atom and phosphate oxygens of a single nucleotide residue, but does not involve the same metal ion. As described in Section 5.5, there are also unusual structures ( open complexes ) of Cu + species and GMP, which involve only inner-sphere metal binding to the phosphate group. 

Metal complexes of pyrimidine nucleotides have been studied much less intensively than those involving purines, undoubtedly reflecting the weaker coordination ability of the pyrimidine N-3 atom, relative to atoms N-7 and N-1 of purines. Nonetheless, the principal structures of such complexes have been determined. " Some of these are described below. 

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. 

Metal Complexes of Purines, Purine Nucleosides, Nucleotides,... 

During 1966, a review of methods in nucleoside syntheses and a review of the ionization and metal complex formation of adenosine and adenine nucleotides were published. ... 

There has been considerable interest in recent years in the formation of condensed films of purine and pyrimidine bases at the solid-liquid interface. It is well recognised that non-covalent affinities between base pairs play a prevalent role in determining nucleic acid conformation and functionality. Likewise, there has been interest in the role of substrate and non-covalent intermolecular interactions in the configuration of ordered monolayers of purine and pyrimidine bases. There is also more general interest in the interaction of bases with metal surfaces and metal complexes. In the latter case it is noted that the biological role of nucleic acids and certain nucleotides are dependent on metal ions, particularly Mg, Ca, Zn, Mn, Cu and Ni. " Also certain metal complexes, notably of platinum, have the anti-tumour activity, which is linked to their ability to bind to bases on DNA. On a different note, the possibility that purine-pyrimidine arrays assembled on naturally occurring mineral surfaces might act as possible templates for biomolecular assembly has been discussed by Sowerby et al. 

---