Browsing by Author "Hsiao, Chih-Hsiang"

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Effects of Concentration of Some Lanthanide(III) Complexes of 1,7-Bis(carboxymethyl)-1,4,7,10-tetraazacyclododecane on Bis(p-nitrophenyl)-phosphate Hydrolysis
(2009-04-01)
Chang, C. Allen
;
Wu, Bo Hong
;
Hsiao, Chih-Hsiang
;
生物科技學系
;
Department of Biological Science and Technology
A detailed study of the effects of the concentration of some lanthanide(III) complexes [LnDO2A(+); DO2A = 1,7-bis(carboxymethyl)-1,4,7,10-tetraazacyclododecane] on the hydrolysis of the phosphodiester bond of the compound BNPP [sodium bis(4-nitrophenyl)phosphate] is reported at 25 degrees C and pH 7.90 (Ln = Eu), 9.35 (Ln = Eu), and 9.90 (Ln = Eu, Er and Yb). The reaction is found to be first order with respect to BNPP concentration at pH 7.90 and 9.35 and to increase to 1.78 +/- 0.09, 1.64 +/- 0.07, and 1.63 +/- 0.09 with respect to [EuDO2A(+)] concentration at pH 7.90, 9.35, and 9.90, respectively, thereby indicating that dinuclear species are involved in the reactions. Similar observations were found for the other two LnDO2A(+) complexes at pH 9.90 [1.63 +/- 0.11 (Er) and 1.49 +/- 0.09 (Yb)]. The k(obs) data obtained by the initial rate method could be fitted to a monomer-dimer reaction model for all LnDO2A(+) complexes at pH 7.90, 9.35, and 9.90 in the [LnDO2A(+)] concentration range 1.0-20.0 mM. The dinuclear species, namely the mono-hydroxo-bridged complexes [Ln(2)(DO2A)(2)(mu-OH)(OH)(H(2)O)(n=1-3)] and the di-hydroxo-bridged complexes [Ln(2)(DO2A)(2)(mu-OH)(OH)(H(2)O)(n=0.2)] are found to be more reactive, with reactivities in the order Eu > Yb > Er. The overall formation constants for [Ln(2)(DO2A)(2)(mu-OH)(OH)(H(2)O)(n)]-BNPP are around 10(4)M(-1). The EuDO2A(+)-promoted BNPP hydrolysis rates are similar to, or up to two orders of magnitude faster than, most of those reported for other lanthanide and transition-metal complexes. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
Kinetics of Bis(p-nitrophenyl)phosphate (BNPP) Hydrolysis Reactions with Trivalent Lanthanide Complexes of N-Hydroxyethyl(ethylenediamine)-N,N ', N '-triacetate (HEDTA)
(2009-03-01)
Chang, C. Allen
;
Chen, Yu-Ping
;
Hsiao, Chih-Hsiang
;
生物科技學系
;
Department of Biological Science and Technology
Kinetic studies of hydrolysis reactions of BNPP [sodium bis(p-nitrophenyl) phosphate] with trivalent lanthanide (Ln(3+)) complexes of HEDTA [HEDTA = N-hydroxyethyl(ethylenediamine)-N,N',N'-triacetate] were performed at pH 6.96-11.34 and 25 degrees C by a spectrophotometric method and by HPLC analysis. The reaction rates increase with increasing atomic number of lanthanide and solution pH from PrHEDTA to EuHEDTA and then decrease for heavier LnHEDTA complexes. Plots of pseudo-first-order rate constants (k(obs)) vs. pH could be fitted to the equation k(obs) = k(LnL(OH))[LnL](T)/{1+exp-[-2.303(pH-pK(h))]} where K(LnL(OH)) is the rate constant for the reaction of LnHEDTA(OH)(-) with BNPP, K(h) is the hydrolysis constant of LnHEDTA, and [LnL](T) is the total concentration of LnHEDTA. The pK(h) values obtained by the kinetic method are in the range 8.2-10.3 and are similar to those measured by potentiometric methods. At [LnL](T) = 10-70 mM and pH 10.5, most of the observed pseudo-first-order rate constants could be fitted to a simple saturation kinetic model, k(obs) = K(1)K[LnHEDTA(OH)(-)]/[1 + K[LnHEDTA(OH)(-)]}, where K is the equilibrium constant for the formation for LnHEDTA(OH)(-)BNPP and is in the range 2-147 M(-1). The k(1) values are in the range 1.12X10(-5)-2.71 X 10(-3) s(-1). The k(obs) data for TbHEDTA and HoHEDTA were fitted to a quadratic equation. It was observed that the dinuclear species are more reactive. ESI mass spectrometry confirmed that the reaction between BNPP and EuHEDTA is a simple hydrolysis but not a transesterification, presumably because the three inner-sphere coordinated water molecules are far away from the coordinated hydroxyethyl group. Hydrolysis is likely to occur by proton transfer from one inner-sphere coordinated water molecule to the deprotonated ethyl oxide group followed by nucleophilic attack of the resulting hydroxide ion on the bonded BNPP anion, ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)