KINETIC AND EQUILIBRIUM STUDIES OF THE REACTIONS OF CYSTEINE AND PENICILLAMINE WITH AQUEOUS IRON(III)

被引:38
作者
SISLEY, MJ [1 ]
JORDAN, RB [1 ]
机构
[1] UNIV ALBERTA,DEPT CHEM,EDMONTON,AB T6G 2G2,CANADA
关键词
D O I
10.1021/ic00128a012
中图分类号
O61 [无机化学];
学科分类号
070301 ; 081704 ;
摘要
The reactions of cysteine (cys) and penicillamine (H(3)L(+), pen) with aqueous iron(III) have been studied in dilute acid solutions (0.01-0.2 M H+) with iron(III) concentrations (0.01-0.1 M) in excess over the amino acid ((similar to 1.5-8.5) x 10(-4) M) at 25 degrees C in 1.0 M LiClO4/HClO4. Stopped-flow and standard spectrophotometry were used to measure the kinetics of the complexation and oxidation-reduction reactions, respectively. Complexation equilibrium constants (K-f = [MLH][H+](2)/[M][LH(3)]) have been determined from the absorbance immediately after the complexation reaction. Both monomeric (Fe(OH2)(6)(3+)) and dimeric (Fe-2(OH2)(8)(mu-OH)(2)(4+)) iron(III) species form complexes with K-f values of 0.063 and 0.38 M with penicillamine and of 0.025 and 0.07 M with cysteine, respectively. The dependence of the complexation rate on iron(III) and H+ concentrations indicates that the dominant reaction pathways and their rate constants (M(-1) s(-1)) are as follows: (H2O)(5)Fe(OH)(2+) + H(3)L(+), k = 1.4 x 10(3) (cys), 1.2 x 10(3) (pen); (H2O)(5)Fe(OH)(2+) + H(2)L, k = 7.4 x 10(3) (cys), 7.4 x 10(3) (pen); Fe-2(OH2)(8)(mu-OH)(2)(4+) + H(2)L, k = 4.3 x 10(3) (cys), 8.1 x 10(3) (pen). The oxidation of cysteine is second order in cysteine with terms in the rate law first, second, and third order in Fe(OH2)(6)(3+). From the [H+] dependence, these are assigned to reactions of (H2O)(4)FeLH(2+) + H(2)L, (H2O)(4)FeLH(2+) + (H2O)(4)FeLH(2+) or Fe-2(OH2)(6)(mu-OH)(2)(LH)(3+) + H(2)L, and Fe-2(OH2)(6)(mu-OH)(2)(LH)(3+) + (H2O)(4)FeLH(2+). Penicillamine reacts similarly but more slowly, and the first pathway is not observed, but one fourth order in iron(III) is found. Limited studies with excess penicillamine show that the reaction is second order in penicillamine and is inhibited by H+ and iron(II), and the reactive species is suggested to be Fe(LH)(2)(+). Spectrophotometric results under these conditions yield K-f12=[M(LH)(2)][H+](2)/[MLH]-[H-3] = 1.6 x 10(-2) M.
引用
收藏
页码:6015 / 6023
页数:9
相关论文
共 18 条
[1]   KINETICS AND MECHANISMS OF COMPLEX-FORMATION AND REDOX REACTIONS OF IRON(III) WITH MERCAPTOCARBOXYLIC LIGANDS IN ACID PERCHLORATE-MEDIA [J].
BAIOCCHI, C ;
MENTASTI, E ;
ARSELLI, P .
TRANSITION METAL CHEMISTRY, 1983, 8 (01) :40-45
[2]   METAL-ION OXIDATIONS IN SOLUTION .15. RATE-DETERMINING DIMERIZATIONS IN REDOX REACTIONS OF IRON(III) WITH SOME ALPHA-MERCAPTOCARBOXYLIC ACIDS [J].
ELLIS, KJ ;
LAPPIN, AG ;
MCAULEY, A .
JOURNAL OF THE CHEMICAL SOCIETY-DALTON TRANSACTIONS, 1975, (19) :1930-1934
[3]   METAL-ION OXIDATIONS IN SOLUTION .9. CHARACTERIZATION OF INTERMEDIATE FORMED IN OXIDATION OF THIOMALIC ACID BY IRON(III) IONS [J].
ELLIS, KJ ;
MCAULEY, A .
JOURNAL OF THE CHEMICAL SOCIETY-DALTON TRANSACTIONS, 1973, (15) :1533-1537
[4]  
GHOSH SK, 1989, INORG CHEM, V28, P3561
[5]   ANAEROBIC OXIDATION OF CYSTEINE TO CYSTINE BY IRON(III) .1. THE REACTION IN ACIDIC SOLUTION [J].
JAMESON, RF ;
LINERT, W ;
TSCHINKOWITZ, A ;
GUTMANN, V .
JOURNAL OF THE CHEMICAL SOCIETY-DALTON TRANSACTIONS, 1988, (04) :943-946
[6]   ANAEROBIC OXIDATION OF CYSTEINE TO CYSTINE BY IRON(III) .2. THE REACTION IN BASIC SOLUTION [J].
JAMESON, RF ;
LINERT, W ;
TSCHINKOWITZ, A .
JOURNAL OF THE CHEMICAL SOCIETY-DALTON TRANSACTIONS, 1988, (08) :2109-2112
[7]   METAL-ION OXIDATIONS IN SOLUTION .14. FORMATION OF INTERMEDIATES IN REACTION OF IRON (2) WITH 2-MERCAPTOCARBOXYLIC ACIDS [J].
LAPPIN, AG ;
MCAULEY, A .
JOURNAL OF THE CHEMICAL SOCIETY-DALTON TRANSACTIONS, 1975, (15) :1560-1564
[8]  
LEE WJ, 1993, J ORG CHEM, V58, P642
[9]  
Mesmer R., 1976, HYDROLYSIS CATIONS
[10]   RADICAL REDUCTIONS OF CU(II)-PENICILLAMINE COMPLEXES - EVIDENCE FOR A CU(II)-DISULFIDE ANION INTERMEDIATE [J].
MEZYK, SP ;
ARMSTRONG, DA .
CANADIAN JOURNAL OF CHEMISTRY-REVUE CANADIENNE DE CHIMIE, 1991, 69 (03) :533-539