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139 La NMR Kinetic Study of Lanthanum(III) Complexation with Acetohydroxamic Acid
Author(s) -
Biruš Mladen,
van Eldik Rudi,
Gabričević Mario,
Zahl Achim
Publication year - 2002
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/1099-0682(200203)2002:4<819::aid-ejic819>3.0.co;2-e
Subject(s) - chemistry , acetohydroxamic acid , equilibrium constant , lanthanum , reaction rate constant , kinetics , relaxation (psychology) , kinetic energy , nuclear magnetic resonance spectroscopy , analytical chemistry (journal) , inorganic chemistry , stereochemistry , organic chemistry , psychology , physics , quantum mechanics , urease , enzyme , social psychology
The application of 139 La NMR spectroscopy to kinetic and equilibrium studies of the substitution of coordinated water by acetohydroxamic acid (HA) is described. The reaction of La 3+ with HA can be represented by the following equation (with equilibrium constant K 1 ): La 3+ + HA ↔ La(A) 2+ + H + (1). The following equilibrium parameters were calculated from the 139 La NMR chemical shift of the equimolar reactants measured as a function of acidity and temperature: K 1 (298) = 2.36(8)·10 −4 , Δ r H 1 = −28(1) kJ·mol −1 , Δ r S 1 = −162(4) J·K −1 ·mol −1 . The kinetics of the reaction between La 3+ and HA can be represented by the following equations: La 3+ + HA ↔ La(A) 2+ + H + (11) and La 3+ + A − ↔ La(A) 2+ (12). The complexation rate constants were calculated from the line widths of the corresponding signals as a function of acidity and temperature: k 11 (298 K) = 1.54(4)·10 6 M −1 ·s −1 , Δ H 11 ‡ = 70(14) kJ·mol −1 and Δ S 11 ‡ = +108(47) J·K −1 ·mol −1 , k 12 (298 K) = 1.6 10 10 M −1 ·s −1 , Δ H 12 ‡ = 35(6) kJ·mol −1 and Δ S 12 ‡ = +68(20) J·K −1 ·mol −1 . The spin‐spin relaxation times of La III in the aqua ion and the hydroxamato complex are 4.36(4) ms and 54(1) μs at 298 K, respectively.