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Kinetics of the Interaction of Indium( III ) with 8‐Quinolinol‐5‐sulfonic Acid and with Sulfate
Author(s) -
Ricciu Alessio,
Secco Fernando,
Venturini Marcella,
García Begoña,
Leal José María
Publication year - 2001
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20011105)7:21<4613::aid-chem4613>3.0.co;2-2
Subject(s) - chemistry , reaction rate constant , ionic strength , zwitterion , sulfonic acid , acid dissociation constant , aqueous solution , kinetics , ligand (biochemistry) , chelation , dissociation (chemistry) , stability constants of complexes , inorganic chemistry , analytical chemistry (journal) , molecule , chromatography , organic chemistry , biochemistry , physics , receptor , quantum mechanics
The kinetics and equilibria of indium( III ) binding to 8‐quinolinol‐5‐sulfonic acid (HQSA) have been investigated in acidic aqueous solution at 0.2 M ionic strength and 25 °C by stopped‐flow, absorption and fluorescence spectrometric methods. Absorption and fluorescence spectrometry revealed that a monoprotonated MHL 3+ complex is formed in addition to the ML 2+ chelate. The stability constants of the chelate (log K ML =6.53), of the monoprotonated complex (log K MHL =3.51) and its acid dissociation constant (p K C2 =1.4) have been determined. Stopped‐flow measurements indicate three reaction paths that involve the interaction of M 3+ with H 2 L + ( k 1 =(3.21±0.04)×10 2 M −1 s −1 ), M 3+ with HL ( k 2 =(6.52±0.04)×10 4 M −1 s −1 ) and MOH 2+ with HL ( k 3 =(1.60±0.08)×10 6 M −1 s −1 ), respectively. The reactivity of In 3+ toward the uncharged form of HQSA has been found to be approximately two orders of magnitude less than expected based upon water exchange experiments. This behaviour has been explained with the assumption that the ligand is distributed between two forms (neutral and zwitterion) of which only the neutral form is reactive. The rate of complex formation between In 3+ and SO 4 2− ion has been measured by the temperature‐jump method with Tropaeolin 00 as the indicator. The second‐order rate constant of the binding process is 5.1×10 4 M −1 s −1 . This quantity yields a value for the first‐order rate constant of 570 s −1 for ligand penetration into the In 3+ coordination shell, approximately two orders of magnitude less than normal. This finding is interpreted by the hypothesis that SO 4 2− forms a chelate with In 3+ for which ring closure is the rate‐determining step.