Synthetic analogues for oxovanadium(IV)-glutathione interaction: An EPR, synthetic and structural study of oxovanadium(IV) compounds with sulfhydryl-containing pseudopeptides and dipeptides
Aj. Tasiopoulos et al., Synthetic analogues for oxovanadium(IV)-glutathione interaction: An EPR, synthetic and structural study of oxovanadium(IV) compounds with sulfhydryl-containing pseudopeptides and dipeptides, CHEM-EUR J, 5(3), 1999, pp. 910-921
Valuable analogues of the (VO2+)-O-IV - glutathione complex have been synth
esized and characterized. The reaction of [(VO)-O-IV(CH3COO)(2)(phen)] (phe
n = 1,10-phenanthroline) with the sulfhydryl-containing pseudopeptides (scp
) N-(2-mercaptopropionyl)cysteine (H(4)m(2)pc), and N-(3-mercaptopropionyl)
cysteine (H(4)m(3)pc) in the presence of triethylamine gives the oxovanadi
um(rv) compounds [(Et3NH)(2)][VO(m(2)pc)] (1) and [(Et3NH)(2)][VO(m(3)pc)]
(2), while reaction of [VOCl2(phen)] with the sep N-(2-mercaptopropionyl)gl
ycine (H(3)mpg) and the dipeptides glycylglycine (H(3)glygly) and glycyl-(L
)-alanine (H(2)glyala) in the presence of triethylamine results in the form
ation of the compounds [Et3NH][VO (mpg) (phen)] (3), [VO(glygly)(phen)] -2C
H(3)OH (4 2CH(3)OH), and [VO(glyala)(phen)] CH,OH (5 CH,OH). Complex [VOCl2
(phen)(CH3OH)] (7) was prepared by the reaction of [VOCl2(thf)(2)] with phe
n in a methanolic solution. The X-ray structure of 3 shows that the vanadiu
m(rv) atom is ligated to a tridentate mpg(3-) Ligand at the S-thiolato, N-p
eptide and O-carboxylato atoms. The X-ray structure of 7 is also reported.
The optical, infrared, magnetic, electron paramagnetic resonance, and elect
rochemical properties of compounds 1-5 CH,OH and 7 were studied. Combinatio
n of the correlation plots of the EPR parameters g(z) versus A(z), or the g
round state orbital population (beta*)(2) versus A(z), together with the ad
ditivity relationship, A(z,calcd) = Sigma n(i)A(zi)/4, were shown to provid
e a powerful tool for probing the equatorial donor atoms in an oxovanadium(
Iv) compound and consequently in biomolecules. Thus, these methods provide
valuable evidence for the assignment of the equatorial donor atoms for the
(VO2+)-O-IV center of the (VO2+)-O-IV-glutathione system at various pH valu
es. Model NMR studies (interaction of vanadium(v) with H(3)mpg) showed that
there is a possibility of vanadium(v) ligation to glutathione. The contrib
ution of a deprotonated peptide(amide) nitrogen to A, is not a fixed quanti
ty tit varies from 29 to 43 x 10(-4) cm(-1)), but is influenced by the pres
ence df the three other donor atoms in the equatorial plane and, in particu
lar, their charge.