Cd2+and Pb2+complexation by glutathione and the phytochelatins.
Phytochelatins or PCn, (γGlu-Cys)n-Gly, and their glutathione (GSH) precursor are thiol-rich peptides that play an important role in heavy metal detoxification in plants and microorganisms. Complex formation between Cd2+and Pb2+and GSH or PCn (n = 2, 4 and 6) are investigated by microcalorimetry, absorption spectrophotometry and T-jump kinetics. Complex formation with Pb2+or Cd2+is exothermic, and induces ligand metal charge transfer bands in UV absorption spectral range, which implies the formation of a coordination bond between the metal and the thiol groups of the phytochelatins. Absorption spectra and microcalorimetry experiments allow the determination of the affinity constants and the stoichiometry of the complexes. We show that the three PCn interact with Pb2+to form the 1:1 and 2:1 M:L complexes, with similar affinity constants (log K11Pb∼4.6, log K21Pb∼11.4). These affinities are independent of the number of thiols and are, moreover, lower than those determined for complex formation with Cd2+. On the other hand, with Cd2+, PC2-Cd, PC2-Cd2, (PC2)3-Cd2, PC4-Cd, PC4-Cd2, PC6-Cd, (PC6)2-Cd3and PC6-Cd3complexes are detected. Furthermore, for PC4-Cd, the 1:1 complex is the most stable: affinity constant (log K11Cd∼7.5). Kinetic studies indicate that complex formation between Cd2+and GSH occurs in the ms range; direct rate constant kobs= (6.8 ± 0.3) 106M-1s-1and reverse rate constant k-obs= 340 ± 210 s-1. Thus, when encapsulated in a silica matrix, PCn can be good candidates for heavy metal detection.
Univ Paris Diderot, Sorbonne Paris Cité, Interfaces, Traitements, Organisation et Dynamique des Systèmes (ITODYS), UMR 7086, CNRS, 15 rue Jean Antoine de Baïf, F-75205 Paris Cedex 13, France.
Aurélie
A
Jacquart
Univ Paris Diderot, Sorbonne Paris Cité, Interfaces, Traitements, Organisation et Dynamique des Systèmes (ITODYS), UMR 7086, CNRS, 15 rue Jean Antoine de Baïf, F-75205 Paris Cedex 13, France.
Roberta
R
Brayner
Univ Paris Diderot, Sorbonne Paris Cité, Interfaces, Traitements, Organisation et Dynamique des Systèmes (ITODYS), UMR 7086, CNRS, 15 rue Jean Antoine de Baïf, F-75205 Paris Cedex 13, France.
Jean-Michel
JM
El Hage Chahine
Univ Paris Diderot, Sorbonne Paris Cité, Interfaces, Traitements, Organisation et Dynamique des Systèmes (ITODYS), UMR 7086, CNRS, 15 rue Jean Antoine de Baïf, F-75205 Paris Cedex 13, France. Electronic address: thanh.haduong@univ-paris-diderot.fr.
Nguyet-Thanh
NT
Ha-Duong
D002104:Cadmium / Q000737:chemistry*; D002151:Calorimetry; D056831:Coordination Complexes / Q000737:chemistry* / Q000378:metabolism; D005978:Glutathione / Q000737:chemistry*; D007700:Kinetics; D007854:Lead / Q000737:chemistry*; D054811:Phytochelatins / Q000737:chemistry*; D010944:Plants / Q000378:metabolism; D013053:Spectrophotometry; D013816:Thermodynamics
D056831:Coordination Complexes; D002104:Cadmium; D007854:Lead; D054811:Phytochelatins; D005978:Glutathione
Fast kinetics; Metal interactions; Microcalorimetry; Phytoremediation; Spectroscopy