Condensation reactions between vanadate and small functionalized peptides in aqueous solution

Abstract

Abstract:The role that histidyl, seryl, tyrosyl, and other side chains of small peptides play in the formation of vanadate complexes has been investigated using 'H, I3c, and "V nuclear magnetic resonance spectroscopy. Formation constants of product complexes in aqueous solution have been determined and the influence of pH on the equilibria established. The results revealed that, in histidine-containing compounds, the protonation state of the imidazole ring of the free ligand strongly influences product formation. The results unequivocally showed that no vanadium-to-imidazole bond was formed for any of the histidine-containing complexes studied. However, imidazole and other aromatic side-chain residues have an effect on product stability via their influence on the protonation state (pK,) of the products. Aliphatic side-chains, such as those in asparagine or glutamate, do not appear to play a significant role in the formation of products. This is not true, however, of serine or threonine where the side-chains readily generate vanadium-oxygen bonds.

Interaction of Vanadyl (VO2+) with Ligands Containing Serine, Tyrosine, and Threonine

“…Tyrosine itself interacts rather ineffectively with vanadate; the formation constants K f for the formation of HVO 3 (OTyr) - amounts to 1.8 M -1 . Dipeptides containing tyrosine are more effective binders ( K f = 128 M -1 for Gly-Tyr 17 ), although the main complexes formed with VO 3+ and VO 2+ exclude tyrosine from direct binding. − In this respect, i.e., leaving the OH function uncoordinated, dipeptides containing serine behave accordingly. , In the structurally characterized complexes [VO(NH 2 O)Ser] and [VO(His-en-Tyr)] (en = ethylenediamine), the OH again remains uncoordinated. An additional implication is the redox lability of vanadate in the presence of peptides with tyrosine residues …”

“…16 Dipeptides containing tyrosine are more effective binders (K f ) 128 M -1 for Gly-Tyr 17 ), although the main complexes formed with VO 3+ and VO 2+ exclude tyrosine from direct binding. [18][19][20] In this respect, i.e., leaving the OH function uncoordinated, dipeptides containing serine behave accordingly. 21,22 In the structurally characterized complexes [VO(NH 2 O)Ser] 23 and [VO-(His-en-Tyr)] (en ) ethylenediamine), 24 the OH again remains uncoordinated.…”

Oxovanadium(iv and v) and copper(ii) complexes of N-salicyl-glycylglycine and N-salicyl-glycylglycylglycine

“…N amide binding has been documented for several vanadium()-dipeptide systems, e.g. GlyTyr, 14 AlaHis, 15 GlyGly, 16 and a set of dipeptides, 17 and for several vanadium() systems. 18 It has also been found for many metal ions that the presence of a suitable anchoring donor in the molecule, which can bind metal ions strongly enough to be able to promote co-ordination of the amide, plays a crucial role in the metal binding.…”

Vanadium(V) Hydroxylamido Complexes: Solid State and Solution Properties1

“…Spectroscopic and X-ray crystallographic studies of the vanadium-containing halogenase has been accompanied by rich model chemistry probing both the structure and catalytic properties of the vanadium(V) protein adduct. − Particular attention has been paid to vanadium−imidazole complexes due to the presumed axial coordination of histidine to the vanadium center in haloperoxidase. ,− Despite much effort, little progress has been made in structurally characterizing the vanadium−amino acid complexes in the absence of other organic ligands. Most of the efforts in this area have focused on either stabilizing the amino acid complex with another organic ligand ,,,, or solution studies in which spectroscopic studies have been employed to characterize the vanadium−amino acid adduct. − The former approach has led to several reports on a variety of new families of compounds using various supporting ligand groups such as thiocyanate or Shiff-bases of the amino acid with salicylaldehyde to stabilize the vanadium−amino acid complex. ,,, Although, there are several reports on other oxidation states of vanadium, including the vanadium(IV)−1-vinylimidazole complex, the corresponding vanadium(V) complexes have remained elusive.…”

“…Most of the efforts in this area have focused on either stabilizing the amino acid complex with another organic ligand 9,10,14,15,17 or solution studies in which spectroscopic studies have been employed to characterize the vanadiumamino acid adduct. [18][19][20][21][22] The former approach has led to several reports on a variety of new families of compounds using various supporting ligand groups such as thiocyanate 23 or Shiff-bases of the amino acid with salicylaldehyde to stabilize the vanadiumamino acid complex. 10,15,17,24 Although, there are several reports on other oxidation states of vanadium, including the vanadium(IV)-1-vinylimidazole complex, 25 the corresponding vanadium(V) complexes have remained elusive.…”