Speciation in Vanadium Bioinorganic Systems. 1. A Potentiometric and 51V NMR Study of Aqueous Equilibria in the H+--Vanadate(V)--L-alpha-Alanyl-L-histidine System.

A Potentiometric and (31P,51V) NMR Study of the Aqueous Molybdovanadophosphate System

“…Table 1 shows the polyhedral structures, symmetries, and statistically predicted relative abundances for the α-isomers of Mo 9 V 3 P. We were able to track the pH dependence of the 31 P resonances of the more abundant, but not all, Mo 9 V 3 P isomers at 25°C. Figure 2 shows the 31 P chemical shifts of six Mo 9 V 3 P resonances plotted against pH over the range 0Ϫ6, along with the 31 P chemical shift vs. pH dependence for [Mo 11 VPO 40 ] 4Ϫ and the Mo 10 V 2 P isomers determined previously. [18] Equilibrium calculations were directed at identifying the Keggin compositions, [H z Mo 12Ϫx V x PO 40 ] (3ϩxϪz)Ϫ , present and for determining their formation constants, for x ϭ 1Ϫ3.…”

“…The [Mo 11 VPO 40 ] 4− anion does not protonate, [Mo 10 V 2 PO 40 ] 5− anions can be monoprotonated, and [Mo 9 V 3 PO 40 ] 6− anions can be triprotonated. The six most intense 31 P NMR resonances of [H z Mo 9 V 3 PO 40 ] (6 − z)− could be followed over the pH range studied.…”

“…In the parent α-Keggin [Mo 12 PO 40 ] 3Ϫ structure, which has T d symmetry, all Mo sites are equivalent by symmetry, so that one isomorphous substitution of V for Mo results in a single α-[Mo 11 VPO 40 ] 4Ϫ structure. By isomorphous substitution of two, three, or four V for Mo, 5, 13, or 27 positional α-Keggin isomers and an increasing number of β-isomers can be formed.…”

Fifteen Years of Dancing with Vanadium

“…The reaction of vanadate with ethanol [20] was the first of a series of organic systems that included numerous coordinating functionalities such as hydroxyl [20,21], carboxyl [35,48,49], amino [35,38,50,51], amido [52][53][54], phospho [22,55], and bi- [21,35,38,49,56] and multidentate [34,37,39,51,[53][54][55][57][58][59][60][61][62] ies mapped out what types of complexes formed, the pH dependence of complex formation, and the stoichiometry of the systems. This approach was followed in most subsequent studies.…”

“…Combined potentiometric and NMR studies were particularly powerful in detailing the properties of oxovanadates [29,30], which were critical for the studies that explored the reactions of vanadium(V) in the physiological relevant pH range. Such studies were carried out by the Tracey/Gresser group [20][21][22], the Crans group [34][35][36], the Rehder group [23,37,38], and others [39][40][41].…”