Nucleic acids reactions with metals

The relative rates of reaction of the nucleic acid bases with heavy transition metal ions at neutral pH are in the same order as the relative nucleophilicites of the bases, that is G > A > C > U or T. This order parallels the relative rates of reactions for cA-[(NH3)2Pt(OH2)2] (see Figure 9), while the equilibrium constants for the same reactions are very close in magnitude. In contrast, HsCHgOH, which is more labile to substitution, nndergoes more favorable binding with deprotonation at N-3 of thymine residues in nucleic acids. Thus the relative facilities of individual reactions can lead to differences in initial product formation (kinetic control). Subsequent changes in the metal-nucleic acid complexes can be nnder kinetic or thermodynamic control. 

Ligandoside A ligand inserted into oligomeric DNA or tethered to synthetic backbone, which, upon reaction with metals, forms metal complexes that mimic nucleic acid base pairing. 

Reaction of some transition metals with nucleic acids and their constituents. U. Weser, Struct. Bonding (Berlin), 1968, 5, 41-67 (108). 

Weser U (1967) Chemistry and Structure of some Borate Polyol Compounds. 2 160-180 Weser U (1968) Reaction of some Transition Metals with Nucleic Acids and Their Constituents. 5 41-67... 

Copper is an essential trace element. It is required in the diet because it is the metal cofactor for a variety of enzymes (see Table 50—5). Copper accepts and donates electrons and is involved in reactions involving dismu-tation, hydroxylation, and oxygenation. However, excess copper can cause problems because it can oxidize proteins and hpids, bind to nucleic acids, and enhance the production of free radicals. It is thus important to have mechanisms that will maintain the amount of copper in the body within normal hmits. The body of the normal adult contains about 100 mg of copper, located mostly in bone, liver, kidney, and muscle. The daily intake of copper is about 2—A mg, with about 50% being absorbed in the stomach and upper small intestine and the remainder excreted in the feces. Copper is carried to the liver bound to albumin, taken up by liver cells, and part of it is excreted in the bile. Copper also leaves the liver attached to ceruloplasmin, which is synthesized in that organ. 

Reaction of some Transition Metals with Nucleic Acids and their Constituents. Vol. 5, pp. 41-67. 

Magnesium has its role intimately intertwined with phosphate in many phosphoryl transfer reactions, as Mg-ATP in muscle contraction, in the stabilization of nucleic acid structures as well as in the catalytic activity of ribozymes (catalytic RNA molecules). It also serves as a structural component of enzymes, and is found as the metal centre in chlorophylls, which absorbs light energy in photosynthesis. 

Reactions with electrophilic reagents. Reactions of nucleic acids with the simplest electrophile, the proton, have been considered in Section A2. Somewhat similar are the reactions by which metal ions bind at many sites on both the bases and the phosphate groups of the backbone.550... 

Nucleic acids catalyze many different types of reactions. Some RNA-catalyzed transformations show stereoselectivity [10,34]. The potential scope of organic reactions is quite broad, with a commensurate variability in reaction conditions. The essential components present in successful nucleic acid-catalyzed reactions are divalent metal ions such as Mg2+, Ca2+, Cu2+, Zn2+, as well as K+ [7,10,21,35,36]. A buffer is also required but should not contain functional groups that are reactive under the reaction conditions. A commonly used buffer is HEPES (2-[4-(2-hydroxyethyl)-l-piperazine]ethanesulfonic acid). These essential components are present to maintain the RNA s tertiary structure and prevent its aggregation. Because these reactions are carried out in aqueous solution, the addition of a co-solvent (e. g., DM SO or EtOH) may be necessary, depending on the solubility of the substrates. 

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