No abstract

Dipyridamole augments nitrite/NO production, leading to enhanced arteriogenesis activity and blood perfusion in ischaemic limbs. Together, these data suggest that dipyridamole can augment ischaemic vessel function and restore blood flow, which may be beneficial in peripheral artery disease.

A Li 7 K salt of [Nb 6 O 19 ] 8and a Li 13 K salt of [SiNb 12 (OH) 2 O 38 ] 14have been prepared and characterized by singlecrystal X-ray diffraction and 6 Li MAS NMR. The structure of Li 7 K[Nb 6 O 19 ]‚15H 2 O (a ) 9.859(10) Å, b ) 17.500(17) Å, c ) 17.384(17) Å, β ) 91.609(16)°, monoclinic, P2 1 /c, R1 ) 4.94% based on 5343 reflections) consists of a super-octahedron of six edge-sharing NbO 6 octahedra capped by a Li 4 O 10 adamantane-like structure. The 6 Li MAS NMR data are consistent with five tetrahedral Li + sites (δ ) 0.20 ppm) and two octahedral Li + sites (δ ) -1.38 ppm). The reaction of Li 7 K[Nb 6 O 19 ]‚15H 2 O and Si(OC 2 H 5 ) 4 yields Li 13 K[SiNb 12 (OH) 2 O 38 ]‚17H 2 O (a ) 20.341(4) Å, b ) 10.735(2) Å, c ) 21.438(4) Å, β ) 105.41(3)°, monoclinic, P2 1 /c, R1 ) 6.49% based on 6161 reflections), an R-Keggin ion ([SiNb 12 (OH) 2 O 38 ] 14-) linked by Li + cations and a single K + cation. Interpretation of structural data suggests that Li + has weaker ion pairing to [Nb 6 O 19 ] 8in the solid state than do Na + , K + , Rb + , or Cs + (i.e., ion pairing increases with an increase in the ionic radius of the alkali metal cation). Given the high charge density of [Nb 6 O 19 ] 8-, the increase in solubility of alkali salts of [Nb 6 O 19 ] 8in water from Li + to Cs + (Li + < Na + < K + < Rb + < Cs + ) suggests that similar ion pairing in solution decreases the effective charge of the polyanion and increases stability as long as charge neutralization is not achieved. In addition, Li + facilitates the formation of discrete [SiNb 12 (OH) 2 O 38 ] 14clusters from a [Nb 6 O 19 ] 8precursor; the analogous reaction with Na 7 [HNb 6 O 19 ] produces a Keggin chain material.