Synthetic Analogues for Oxovanadium(IV)–Glutathione Interaction: An EPR, Synthetic and Structural Study of Oxovanadium(IV) Compounds with Sulfhydryl-Containing Pseudopeptides and Dipeptides
✍ Scribed by Anastasios J. Tasiopoulos; Anastasios N. Troganis; Angelos Evangelou; Catherine P. Raptopoulou; Aris Terzis; Yiannis Deligiannakis; Themistoklis A. Kabanos
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 294 KB
- Volume
- 5
- Category
- Article
- ISSN
- 0947-6539
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✦ Synopsis
Valuable analogues of the V IV O 2 ± glutathione complex have been synthesized and characterized. The reaction of [V IV O(CH 3 COO) 2 (phen)] (phen 1,10-phenanthroline) with the sulfhydryl-containing pseudopeptides (scp) N-(2mercaptopropionyl)cysteine (H 4 m 2 pc), and N-(3-mercaptopropionyl)cysteine (H 4 m 3 pc) in the presence of triethylamine gives the oxovanadium(iv) compounds [(Et 3 NH) 2 ][VO(m 2 pc)] (1) and [(Et 3 NH) 2 ][VO(m 3 pc)] (2), while reaction of [VOCl 2 (phen)] with the scp N-(2mercaptopropionyl)glycine (H 3 mpg) and the dipeptides glycylglycine (H 2 glygly) and glycyl-l-alanine (H 2 glyala) in the presence of triethylamine results in the formation of the compounds [Et 3 NH]-[VO(mpg)(phen)] (3), [VO(glygly)-(phen)] ´2 CH 3 OH (4 ´2 CH 3 OH), and [VO(glyala)(phen)] ´CH 3 OH (5 ´CH 3 -OH). Complex [VOCl 2 (phen)(CH 3 OH)] ( ) was prepared by the reaction of [VOCl 2 (thf) 2 ] with phen in a methanolic solution. The X-ray structure of 3 shows that the vanadium(iv) atom is ligated to a tridentate mpg 3À ligand at the S thiolato , N peptide and O carboxylato atoms. The X-ray structure of 7 is also reported. The optical, infrared, magnetic, electron paramagnetic resonance, and electrochemical properties of compounds 1 ± 5 ĆH 3 OH and 7 were studied. Combination of the correlation plots of the EPR parameters g z versus A z , or the groundstate orbital population (b*) 2 versus A z , together with the additivity relationship, A z,calcd Sn i A zi /4, were shown to provide 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 V IV O 2 center of the V IV O 2 ± glutathione system at various pH values. Model NMR studies (interaction of vanadium(v) with H 3 mpg) showed that there is a possibility of vanadium(v) ligation to glutathione. The contribution of a deprotonated peptide(amide) nitrogen to A z is not a fixed quantity (it varies from 29 to 43 Â 10 À4 cm À1 ), but is influenced by the presence of the three other donor atoms in the equatorial plane and, in particular, their charge.