The syntheses and the solid state structural and s
pectrosco
pic solution characterizations of VO(Me-acac)
2 andVO(Et-acac)
2 (where Me-acac is 3-methyl-2,4-
pentanedionato and Et-acac is 3-ethyl-2,4-
pentanedionato) havebeen conducted since both VO(acac)
2 and VO(Et-acac)
2 have long-term
in vivo insulin-mimetic effects instre
ptozotocin-induced diabetic Wistar rats. X-ray structural characterizations of VO(Me-acac)
2 and VO(Et-acac)
2show that both contain five-coordinate vanadium similar to the
parent VO(acac)
2. The unit cells for VO(Et-acac)
2and VO(Me-acac)
2 are both triclinic,
P, with
a = 9.29970(10) Å,
b = 13.6117(2) Å,
c = 13.6642(2) Å,
pha.gif" BORDER=0> =94.1770(10)
,
= 106.4770(10)
,
= 106.6350(10)
for VO(Et-acac)
2 and
a = 7.72969(4) Å,
b = 8.1856(5) Å,
c = 11.9029(6) Å,
pha.gif" BORDER=0> = 79.927(2)
,
= 73.988(2)
,
= 65.1790(10)
for VO(Me-acac)
2. The total concentrationof EPR-observable vanadium(IV) s
pecies for VO(acac)
2 and derivatives in water solution at 20
C was determinedby double integration of the EPR s
pectra and a
pportioned between individual s
pecies on the basis of com
putersimulations of the s
pectra. Three s
pecies were observed, and the concentrations were found to be time,
pH,tem
perature, and salt de
pendent. The three com
plexes are assigned as the
trans-VO(acac)
2·H
2O adduct,
cis-VO(acac)
2·H
2O adduct, and a hydrolysis
product containing one vanadium atom and one R-acac
- grou
p. The reactionrate for conversion of s
pecies was slower for VO(acac)
2 than for VO(malto)
2, VO(Et-acac)
2, and VO(Me-acac)
2;however, in aqueous solution the rates for all of these s
pecies are slow com
pared to those of other vanadiums
pecies. The concentration of vanadium(V) s
pecies was determined by
51V NMR. The visible s
pectra were timede
pendent, consistent with the changes in s
pecies concentrations that were observed in the EPR and NMR s
pectra.EPR and visible s
pectrosco
pic studies of solutions
pre
pared as for administration to diabetic rats documentedboth a salt effect on s
peciation and formation of a new halogen-containing com
plex. Com
pound efficacy withres
pect to long-term lowering of
plasma glucose levels in diabetic rats traces the concentration of the hydrolysis
product in the administration solution.