Decomposition Kinetics of Ni(III)−Peptide Complexes with Histidine and Histamine as the Third Residue

Abstract

The decomposition kinetics of the Ni(III) complexes of Gly(2)HisGly and Gly(2)Ha are studied from p[H(+)] 3.5 to 10, where His is l-histidine and Ha is histamine. In these redox reactions, at least two Ni(III) complexes are reduced to Ni(II) while oxidizing a single peptide ligand. The rate of Ni(III) loss is first order at low pH, mixed order from pH 7.0 to 8.5, and second order at higher pH. The transition from first- to second-order kinetics is attributed to the formation of an oxo-bridged Ni(III)-peptide dimer. The rates of decay of the Ni(III) complexes are general-base assisted with Brønsted beta values of 0.62 and 0.59 for Ni(III)Gly(2)HisGly and Ni(III)Gly(2)Ha, respectively. The coordination of Gly(2)HisGly and Gly(2)Ha to Ni(II) are examined by UV-vis and CD spectroscopy. The square planar Ni(II)(H(-2)Gly(2)HisGly)(-) and Ni(II)(H(-2)Gly(2)Ha) complexes lose an additional proton from an imidazole nitrogen at high pH with pK(a) values of 11.74 and 11.54, respectively. The corresponding Ni(III) complexes have axially coordinated water molecules with pK(a) values of 9.37 and 9.44. At higher pH an additional proton is lost from the imidazole nitrogen with a pK(a) value of 10.50 to give Ni(III)(H(-3)Gly(2)Ha)(H(2)O)(OH)(2-).

Zinc(ii) coordination polymers with pseudopeptidic ligands

“…2.165 (4) As mentioned above, there is a marked difference on the conformation of the amide 257 substituents of all the coordination polymers studied here. In 6 and 7 three ligands are were carried out and the corresponding TG curves obtained (see Figures S12-S15 showed the sample to be amorphous; this might be due to the inconsistent loss of solvent 298 molecules in these samples.…”

“…Thus, it is not surprising that many efforts have been 28 devoted to developing different catalytic systems based on the coordination of pseudopeptidic 29 ligands to different metals. [1][2][3][4] In this regard, we have recently studied the Cu 2+ and Zn 2+ …”

Nickel Ion Complexes of Amino Acids and Peptides

“…The decomposition products of [Ni III (H Ϫ2 Gly 2 HisGly)] in neutral and basic solution [207] as well as the decomposition kinetics of the Gly 2 HisGly and Gly 2 Hm complexes of Ni(III) [208] were recently studied. Self-decomposition of the Ni(III)-peptide complex of Gly 2 HisGly occurs by base-assisted oxidation of the peptide.…”

“…Ions Life Sci. 2, 63-108 (2007) Ni(III)-peptide complexes with histidine and histamine as the third residue are relatively stable in acidic solution with half-lives of more than 10 h [208]. However, in basic solution these Ni(III)-peptide complexes are unstable, and the loss of Ni(III) is complete within milliseconds to seconds.…”

Catalytic metallodrugs

“…This is consistent with formation and immediate reaction of a metal-associated ROS. While reaction via a Cu 2+/+ couple would be expected from prototypical Cu redox chemistry, the family of ATCUN motifs is known to stabilize Cu 3+ [56][57][58][59], and is electrochemically well defined. In fact, all of the Cu-ATCUN complexes that we have studied display only the Cu 3+/2+ redox couple.…”