| A functional, catalytic model of organic nitrate reduction by oxygen-transfer molybdenum enzymes was developed. The molybdenum enzyme model, {HB(Me2-pz)3}MoO2Cl, where HB(Me 2pz)2- is hydrotris(3,5-dimethyl-1-pyrazole)borate, referred to as Mo-TPB, was shown to be capable of reducing nitroglycerin (GTN) to nitric oxide (NO) using Ph3P as a reducing cofactor. Organic nitrites and NO2- are also reduced to NO by Mo-TPB using Ph3P as a reducing cofactor although Mo-TPB is not required. NO2- reduction to NO is observed in CH2Cl2 but not in aqueous solution.;Mo-TPB was shown to catalyse the oxidation of Ph3P by GTN generating good pseudo-first order rates. Oxidation of Ph3P by GTN and Mo-TPB produced Ph3PO and a trace amount of Ph3P +N=PPh3. Oxidation of Ph3P by organic nitrite and Mo-TPB also produced Ph3PO and Ph3P+N=PPh 3, while oxidation of Ph3P by NO2- and Mo-TPB produced only Ph3PO, implicating the organic nitrite as a reaction intermediate. Oxidation of Ph3P by GTN occurs without Mo-TPB at a much slower rate.;Ph3PO, 1,2- and 1,3-glycerol dinitrate, NO2 - and NO have been observed as products of the reaction of GTN, Mo-TPB and Ph3P. The simplest mechanism for GTN reduction by the model system involves a two-electron reduction of GTN to an organic nitrite, followed by a one-electron reduction of organic nitrite to NO although NO 2- is also a potential intermediate. The observed stoichiometry for the reaction of GTN (100 mM), Ph3P (20 mM) and Mo-TPB (1 mM) in aerobic CH2Cl2 after 1 hour is such that for every 1 mol of Ph3P oxidized, 2 mol of GTN are reduced, and for every 1 mol of GTN reduced, 0.14 mol of NO2- and 0.003 mol of NO are produced. Possible mechanisms are discussed.;It is concluded that molybdenum enzymes possess the catalytic apparatus for mechanism-based biotransformation of GTN to NO. |
