Interaction Between Nickel Research Articles

Interaction between nickel(II) and anions of short-chain dialkyl dithiphosphoric acids in aqueous surfactant solutions

Spectrophotometry was used to study the complexation of nickel(II) with anions L– of diisopropyl and dibutyl dithiophosphoric acids in water and aqueous solutions of nonionic surfactant, Triton X-100 (T). Weak bis-complexes [NiL2], whose formation are stimulated by the addition of nonionic surfactant, were found in water. Within the framework of simple model including equilibria of the formation of micelle-bound complexes {[NiL2]T} and ligand associates {LT2-}, the values of log K = 3.87 ± 0.01 and 1.3 ± 0.3 for diisopropyl dithiophosphoric acid anions and log K = 5.47 ± 0.03 and 2.8 ± 0.2 for dibutyl dithiophosphoric acid anions, respectively, were calculated. The obtained results showed that the stability of associates of hydrophobic anions of dialkyl dithiophosphates and their nickel bis-complexes with nonionic micelles increases with the length of ligand chain.

Synthesis and magnetic properties of nickel(II) complexes with the nitronyl nitroxides

Four novel complexes of nickel(II), Ni(tfac)2(NITPa)2 (1), Ni(tfac)2(NITPhNO2)2 (2), Ni(pfpr)2(NITPa)2 (3) and Ni(pfpr)2(NITPhNO2)2 (4), [tfac=trifluoro- acetato, NITPa=2-(3,4-methylenedioxyphenyl)-4,4,5, 5-tetramethylimidazoline-1-oxy-3-oxid, NITPhNO2= 2-(3-nitrophenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxid, pfpr=pentafluoropropionato], have been prepared and characterized by elemental analysis, i.r., and electronic spectra, and molar conductances. The temperature dependence of the magnetic susceptibility for complexes (1) and (3) was measured (4–300K). The observed data were successfully simulated giving the exchange integral J=−1.48cm−1 for (1) and J=−1.25cm−1 for (3). These results indicate a weak antiferromagnetic spin exchange interaction between nickel(II) ion and the radicals.

Spectroscopic studies of the interaction of nickel(II) carboxypeptidase with phosphate and pyrophosphate

The interaction between nickel(II)-substituted carboxypeptidase A and the inhibitors phosphate and pyrophosphate has been investigated at pH 7 by electronic absorption and 1H, 31P, and 13C NMR spectroscopies. Upon binding to the nickel enzyme, the longitudinal relaxation rates T1–1 of the 31P nucleus of these inhibitors are enhanced significantly compared to the diamagnetic zinc enzyme. The NiII⋯31P distances indicate that both inhibitors bind directly to the metal ion under rapid-exchange conditions. From the temperature dependence of the isotropic shifts and the molar absorbance values of the 1 : 1 adducts formed, a pseudo-octahedral co-ordination for the metal ion is suggested. Proton NMR titrations of nickel(II) carboxypeptidase with phosphate in the presence and absence of D-phenylalanine (D-Phe) indicate that the occupancy of the S′1 subsite of the enzyme does not substantially modify the affinity of the phosphate anion for the metal ion. Carbon-13 NMR T2–1 measurements on 13CO2-labelled D-Phe show that phosphate or pyrophosphate do not compete for binding to Arg-145. These results are discussed in terms of the general model of anion interaction with carboxypeptidase.