Tetraglycine

Triglycyl glycine (tetraglycine) [637-84-3] M 246.2, m 270-275°(dec). Crystd from distilled water (optionally, by the addition of EtOH). 

Datta, A.K., S.L. North, K.S. Kasprzak. 1994. Effect of nickel (II) and tetraglycine on hydroxylation of the guanine moiety in 2 -deoxyguanosine, DNA, and nucleohistone by hydrogen peroxide. Sci. Total Environ. 148 207-216. 

Figure 1 shows the reactions of the triply-deprotonated tetraglycine (H G ) complex of copper(III) with acid (16). 

Figure 1. Mechanism for the acid decomposition of Cu(III) tetraglycine. The substitution reaction 111 to IV has a rate constant ks = 0.3 s 1. Other substitution steps have rate constants less...

Figure 11. Brpnsted plots for the proton transfer reactions of Cu-triglycine and yu-tetraglycine complexes. Key , Cu(H, Gtf O, Cu(H.,G,) and , Cu- - G,) (numbers refer to the acids 1, CH COOH 2, HCOOH 3, ClCH,COOH 4, CUCHCOOH and 5, H,0 ).

An opposite case is found, for example, in the reduction of Cu(III) complexes with some deprotonated peptides. For example, Figure 9 illustrates the molecular structure of the trideprotonated Cu(II) tetraglycine [Cun(H 3G4)].2 15... 

Acid treatment 125) of [NiniH 3G4(H20)2] results in cleavage of the terminal Ni-N deprotonated peptide bond with a rate constant of 0.2 sec-1 at 25°C, faster than the corresponding rate for [Ni"H 3G4]2 Further dissociation of the tridentate tetraglycine ligand is much slower and the intermediate can be trapped by the addition of terpy to give a stable, six-coordinate nickel(III) mixed-ligand complex 126). It is notable that the calculated reduction potential for the mixed complex is lower than for either [NiIMH 3G4]- or for [NiMI(terpy)2]3 +. ... 

Tetraazaporphyrin, octaphenyl-metallation, 858 Tetraazaporphyrins synthesis, 857 Tetraethylenepentamine metal complexes, 56 Tetraglycine metal complexes, 764 Tetraketones metal complexes, 399 1,3,5,7-Tetraketones metal complexes, 400 Tetramines cyclic... 

Shalaev EY, Shalaeva M, Byrn SR, Zografi G. Effects of processing on the solid state methyl transfer of tetraglycine methyl ester. Int J Pharm 1997 152 75-88. 

Burce, Paniago, and Margerum (8) first observed the formation of Cu(III)-peptide complexes in the reactions of oxygen with Cu(II)-tetraglycine(G4) in neutral solutions. Previously, Ni(II)-tetraglycine catalyzed oxygen uptake (25). The Cu(II)-tetraglycine reaction with... 

Copper (III)-Peptide Complexes. Molecular oxygen reacts with Cu(II)tetraglycine (G4) in neutral solution to produce a yellow species with an intense absorption band at 362 nm. As the oxygen in the solution is consumed, the amount of the yellow species decays (Figure 6). The uv-visible spectrum, molar absorptivity, dissociation kinetics in acid and in base, and the redox behavior of this yellow species are similar to those of Cunl(H.3G4)", which is generated by IrCl62 or by electrolytic oxidation of the corresponding Cu(II) complex. The peptide products after... 

The Cu(II)-tetraglycine complex is oxidized to Cu(III) by IrCl62" (Figure 7). The redox equilibrium is reversible with pH change. The pH dependence is a result of the variable degree of protonation of the Cu(II)-tetraglycine complexes, whereas the Cu(III) complex is present only as the triply deprotonated peptide complex. The curves in Figure 7 correspond to the redox equilibrium in Reaction 4 offset by the acid-... 

A variety of deprotonated peptide complexes of Cu111 are reasonably stable in alkaline solution. The Cu111—Cu11 potentials are very sensitive to the nature of the ligand and vary from 0.45 to 1.02 V for example, for the tetraglycine (GH4) complex (17-H-XV). 

The reaction is stoichiometric rather than catalytic and goes to completion within a few minutes at pH 7-8 at 60°-65°C. When four equivalents of chelate react with tetraglycine, four equivalents of the glycine-metal complex are formed. In view of the specificity as well as the rapidity of the reaction under rather mild conditions, it is evident that metal chelates of this type may prove useful for stepwise degradation of peptides. 

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