Low-molecular-weight organic chromium complexes such as chromium picolinate are often used as dietary supplements to improve insulin sensitivity and to correct dyslipidemia. However, toxicity associated with such chromium compounds has compromised their therapeutic value. The aim of this study was to evaluate the impact of a newly synthesized complex of chromium with phenylalanine, Cr(pa) 3 on insulin-signaling and glucose tolerance. Cr(pa) 3 was synthesized by chelating chromium(III) with D D-phenylalanine ligand in aqueous solution. In mouse 3T3-adipocytes, Cr(pa) 3 augmented insulin-stimulated glucose-uptake as assessed by a radioactive-glucose uptake assay. At the molecular level, Cr(pa) 3 enhanced insulin-stimulated phosphorylation of Akt in a time-and concentration-dependent manner without altering the phosphorylation of insulin receptor. Oral treatment with Cr(pa) 3 (150 lg/kg/d, for six weeks) in ob/ ob(+/+) obese mice significantly alleviated glucose tolerance compared with untreated obese mice. Unlike chromium picolinate, Cr(pa) 3 does not cleave DNA under physiological reducing conditions. Collectively, these data suggest that Cr(pa) 3 may represent a novel, less-toxic chromium supplement with potential therapeutic value to improve insulin sensitivity and glycemic control in type II diabetes.

Glassy carbon electrodes modified by reductive electropolymerization of a thin film of poly[Ru(vbpy)(3)(2+)] or poly[Ru(vbpy)(3)(2+)/vba] (vbpy = 4-vinyl-4'-methyl-2,2'-bipyridine and vba = p-vinylbenzoic acid) were prepared. The Ru(III/II) couples for the polymer films were reversible in nonaqueous solution but were irreversible in aqueous media. The films modified with poly[Ru(vbpy)(3)(2+)] catalyzed the oxidation of aqueous guanosine 5'-monophosphate (GMP) and poly[G], producing a current enhancement in the Ru(III/II) couple for the polymer film. The catalysis was due both to electrostatic condensation of GMP and poly[G] to the Ru-modified surface and to more facile electron transfer to the Ru(III) centers in the polymer compared to the bare electrode. The presence of GMP in solution decreased the extent of decomposition of Ru(III). When single-stranded DNA containing multiple guanines was attached to the electrode modified with the poly[Ru(vbpy)(3)(2+)/vba] copolymer, enhancement of 8-13 &mgr;A for the Ru(III/II) couple was observed with 8 pmol of attached DNA. This degree of enhancement corresponds to a current efficiency of 65% based on a one-electron oxidation of guanine.

The chemisorption of the alkyl isocyanides n-butyl (C4H9NC), n-hexyl (C6H13NC), n-octyl (C8H17NC), n-dodecyl (C12H25NC), and n-octadecyl isocyanide (C18H37NC) on Au powder from 1,2-dichloroethane (DCE) was examined using both solution (FTIR) and surface (diffuse reflectance infrared fourier transform or DRIFT) spectroscopic techniques. For the isocyanides with fewer than 12 carbon units in their alkyl tails, equilibrium binding constants (K 1), surface coverages (n 1s and n a mol/gAu), and qualitative rates of solution−surface equilibria in DCE solvent are the same. Competition studies between 13C-labeled C18H37NC and nonlabeled C4H9NC show that the ratio of adsorbed isocyanides at equilibrium, C18H37N13C/C4H9NC, is 4.1. Adsorption studies show that isocyanides are bound strongly to the surface at low coverages (less than 70% of saturation coverage), but binding affinity is significantly lower at higher coverages. Studies of C18H37NC and C4H9NC in n-decane, DCE, and nitromethane (MeNO2) solvents show that solvent polarity affects the rate of monolayer formation, surface coverage, and equilibrium binding constants.

Addition of excess HOSO2CF3 (HOTf) to CpRu(L)H (1) (L = dfepe = PR2CH2CH2PR2, R = C2F5) in CD2Cl2 under N2 produces a mixture of [CpRu(L)(H)2]+ (2a), [CpRu(L)(H2)]+ (2b), and CpRu(L)(OTf) (3) in a ratio of 1:5:2. Salts of the acid [HOEt2]+ are not strong enough to protonate 1. Complexes 2 slowly eliminate H2 to give 3; this reaction is slowed by adding excess HOTf. Of all such complexes [CpRu(PR2CH2CH2PR2)(H2)]+, R = alkyl and aryl, the dihydrogen complex 2b has the greatest acidity (similar to that of HOTf) and the related HD complex has the greatest J HD (29.1 Hz) because of the electron-withdrawing substituents R = C2F5. The reaction of 3 with 1 atm H2(g) proceeds much faster in the presence than in the absence of 1 equiv of HOTf to produce 1 and HOTf. This is a rare example of the production of a strong acid from H2(g) where the intermediate dihydrogen complex has been characterized. Reaction of Cp*Ru(L)Cl (4), Cp* = C5Me5, in dry CH2Cl2 at −78 °C with AgX salts under H2(g) (1 atm) gives mixtures of Cp*Ru(L)H (5) and [Cp*Ru(L)(H)2]+ (6), which have been identified by 1H NMR. 6 is deprotonated by traces of water or by PPh3 to give Cp*Ru(L)H (5). The addition of excess HOTf to mixtures of 5 and 6 under H2(g) produces 6. Complexes 3, 4, and 5 have been characterized by single-crystal X-ray diffraction. Complexes CpRu(L)Cl, 1, 4, and 5 have very positive redox potentials that indicate that the dfepe ligand has the electron-withdrawing power close to that of two carbonyl ligands.