Complexes of hydroxamates. V: Equilibrium and kinetics of the formation of the binary and ternary complexes involved in the nickel(II)-histidinehydroxamic acid-pyridoxal system.
Equilibrium-based computer models utilizing SUPERQUAD program were made to determine the formation constants of the binary complexes of Ni(II) with histidine-hydroxamic acid (HX) from pH-metric titration data at 25 degrees C and I = 0.15 M NaCl. The species were monomeric in the pH range 3.0-8.0. The mechanism of their complex formation was determined using the stopped flow technique under the same experimental conditions of the equilibrium study. It has been concluded that Ni2+ and NiOH- were the active species in the complex formation reactions. Moreover, the reaction of HX with pyridoxal (PL) was studied in the absence of metal-ions by polarographic and spectrophotometric techniques at pH greater than or equal to 5.0. No rates were observed by using the stopped-flow methods. The formation constants for the binary system (HX-PL) and the ternary system (Ni(II)-HX-PL) were also determined by the same program applied on data obtained from pH metric titration at 25 degrees C and I = 0.15 M NaCl. Ternary complex formation involving PL and the species of the Ni(II)-HX system was also investigated kinetically in the pH range of 6.5-10.5. Several rate steps have been observed which have been interpreted qualitatively in terms of sequence of processes involving the condensation of aldehydic form of PL with amino moiety of HX. A comparison with other pertinent systems is also discussed.
el-Ezaby
M S
MS
Department of Chemistry, Faculty of Science, University of Kuwait, Safat.
Shuaib
N M
NM
Marafie
H M
HM
Hassan
M M
MM
D003198:Computer Simulation; D006639:Histidine / Q000031:analogs & derivatives*; D006863:Hydrogen-Ion Concentration; D006877:Hydroxamic Acids; D007700:Kinetics; D008962:Models, Theoretical; D009532:Nickel; D011048:Polarography; D011730:Pyridoxal; D013053:Spectrophotometry
D006877:Hydroxamic Acids; C057175:histidinehydroxamic acid; D011730:Pyridoxal; D006639:Histidine; D009532:Nickel