Nitric oxide insertion reactivity with the bismuth-carbon bond: formation of the oximate anion, [ON=(C6H2tBu2O)]-, from the oxyaryl dianion, (C6H2tBu2O)2-.

The first example of NO insertion into a Bi-C bond has been found in the direct reaction of NO with a Bi(3+) complex of the unusual (C6H2tBu2-3,5-O-4)(2-) oxyaryl dianionic ligand, namely, Ar'Bi(C6H2tBu2-3,5-O-4) [Ar' = 2,6-(Me2NCH2)2C6H3] (1). The oximate complexes [Ar'Bi(ONC6H2-3,5-tBu2-4-O)]2(µ-O) (3) and Ar'Bi(ONC6H2-3,5-tBu2-4-O)2 (4) were formed as a mixture, but can be isolated in pure form by reaction of NO with a Bi(3+) complex of the [O2C(C6H2tBu2-3-5-O-4](2-) oxyarylcarboxy dianion, namely, Ar'Bi[O2C(C6H2tBu2-3-5-O-4)-κ(2)O,O']. Reaction of 1 with Ph3CSNO gave an oximate product with (Ph3CS)(1-) as an ancillary ligand, (Ph3CS)(Ar')Bi(ONC6H2-3,5-tBu2-4-O) (5).

Bismuth-based cyclic synthesis of 3,5-di-tert-butyl-4-hydroxybenzoic acid via the oxyarylcarboxy dianion, (O2CC6H2(t)Bu2O)2-.

3,5-Di-tert-butyl-4-hydroxybenzoic acid can be made under mild conditions in a cyclic process from carbon dioxide and 3,5-di-tert-butyl-4-phenol using bismuth-based C-H bond activation and CO2 insertion chemistry starting with the Bi(3+) complex, Ar'BiCl2, of the NCN pincer ligand, Ar' = 2,6-(Me2NCH2)2C6H3. Complexes of the recently discovered oxyaryl dianion, (C6H2(t)Bu2-3,5-O-4)(2-), and the oxyarylcarboxy dianion, [O2C(C6H2(t)Bu2-3,5-O-4)](2-), are intermediates in the process. Further studies of the oxyarylcarboxy dianion in Ar'Bi[O2C(C6H2(t)Bu2-3,5-O-4)-κ(2)O,O'], show that it undergoes decarboxylation upon reaction with I2 and it reacts with trimethylsilyl chloride to produce the trimethylsilyl ether of the trimethylsilyl ester of 3,5-di-tert-butyl-4-hydroxybenzoic acid and the Ar'BiCl2 starting material.

Insertion of CO2 and COS into Bi-C bonds: reactivity of a bismuth NCN pincer complex of an oxyaryl dianionic ligand, [2,6-(Me2NCH2)2C6H3]Bi(C6H2(t)Bu2O).

The reactivity of the unusual oxyaryl dianionic ligand, (C6H2(t)Bu2-3,5-O-4)(2-), in the Bi(3+) NCN pincer complex Ar'Bi(C6H2(t)Bu2-3,5-O-4), 1, [Ar' = 2,6-(Me2NCH2)2C6H3] has been explored with small molecule substrates and electrophiles. The first insertion reactions of CO2 and COS into Bi-C bonds are observed with this oxyaryl dianionic ligand complex. These reactions generate new dianions that have quinoidal character similar to the oxyaryl dianionic ligand in 1. The oxyarylcarboxy and oxyarylthiocarboxy dianionic ligands were identified by X-ray crystallography in Ar'Bi[O2C(C6H2(t)Bu2-3-5-O-4)-κ(2)O,O'], 2, and Ar'Bi[OSC(C6H2(t)Bu2-3-5-O-4)-κ(2)O,S], 3, respectively. Silyl halides and pseudohalides, R3SiX (X = Cl, CN, N3; R = Me, Ph), react with 1 by attaching X to bismuth and R3Si to the oxyaryl oxygen to form Ar'Bi(X)(C6H2(t)Bu2-3,5-OSiR3-4) complexes, a formal addition across five bonds. These react with additional R3SiX to generate Ar'BiX2 complexes and R3SiOC6H3(t)Bu2-2,6. The reaction of 1 with I2 forms Ar'BiI2 and the coupled quinone, 3,3',5,5'-tetra-tert-butyl-4,4'-diphenoquinone, by oxidative coupling.

Comparative analysis of membrane-associated fusion peptide secondary structure and lipid mixing function of HIV gp41 constructs that model the early pre-hairpin intermediate and final hairpin conformations.

Fusion between viral and host cell membranes is the initial step of human immunodeficiency virus infection and is mediated by the gp41 protein, which is embedded in the viral membrane. The approximately 20-residue N-terminal fusion peptide (FP) region of gp41 binds to the host cell membrane and plays a critical role in fusion catalysis. Key gp41 fusion conformations include an early pre-hairpin intermediate (PHI) characterized by extended coiled-coil structure in the region C-terminal of the FP and a final hairpin state with compact six-helix bundle structure. The large "N70" (gp41 1-70) and "FP-Hairpin" constructs of the present study contained the FP and respectively modeled the PHI and hairpin conformations. Comparison was also made to the shorter "FP34" (gp41 1-34) fragment. Studies were done in membranes with physiologically relevant cholesterol content and in membranes without cholesterol. In either membrane type, there were large differences in fusion function among the constructs with little fusion induced by FP-Hairpin, moderate fusion for FP34, and very rapid fusion for N70. Overall, our findings support acceleration of gp41-induced membrane fusion by early PHI conformation and fusion arrest after folding to the final six-helix bundle structure. FP secondary structure at Leu7 of the membrane-associated constructs was probed by solid-state nuclear magnetic resonance and showed populations of molecules with either beta-sheet or helical structure with greater beta-sheet population observed for FP34 than for N70 or FP-Hairpin. The large differences in fusion function among the constructs were not obviously correlated with FP secondary structure. Observation of cholesterol-dependent FP structure for fusogenic FP34 and N70 and cholesterol-independent structure for non-fusogenic FP-Hairpin was consistent with membrane insertion of the FP for FP34 and N70 and with lack of insertion for FP-Hairpin. Membrane insertion of the FP may therefore be associated with the early PHI conformation and FP withdrawal with the final hairpin conformation.