CHARACTERIZATION AND STRUCTURE BY NMR AND FTIR SPECTROSCOPY AND MOLECULAR MODELING OF CHROMIUM(III) PICOLINATE AND NICOTINATE COMPLEXES UTILIZED FOR NUTRITIONAL SUPPLEMENTATION

Chromium picolinate (CrPic) and chromium nicotinate preparations (CrNi c1, CrNic2, CrNic3) were investigated with H-1 and C-13 NMR, FTIR, and molecular modeling. CrPic is crystalline and bidentately coordinated. Cr-PicA bonding broadens the NMR signal or shifts it so far downfield that is not detectable. All CrNic preparations are noncrystalline, an d results provide no evidence that nicotinic acid (NicA) is O-coordina ted to Cr. The complex colors may be due to O-coordination with H2O an d/or OH, not NicA. H-1 NMR spectra of CrNic1 have two sets of peaks. O ne set has a significant delta with respect to NicA, indicating that N icA is more strongly associated with Cr. CrNic1 C-13 data show small, uniform delta with respect to NicA, indicating that strong localized C r-COOH bonding is unlikely. The magnitude of delta, C-13, and H-1 exch ange data suggests that limited Cr-N bonding may occur in CrNic1. CrNi c2 and CrNic3 show little difference from NicA spectra. FTIR spectra o f all CrNic complexes, but not CrPic, PicA, or NicA, show bound OH and /or H2O. CrNic complexes are probably elates, with Cr and NicA OH-poly merized. CrPic exchanges with CrNic1 in DMSO. This exchange may provid e a mechanism for the absorption and active transport of Cr in biologi cal systems. (C) 1997 Elsevier Science Inc.