Nitric oxide gas

Glacial acetic acid (BDH aristar^® Plus) was purchased from VWR (Radnor, PA, USA). Sodium hydroxide (Emsure^®), HPLC-grade water, methanol, acetonitrile and biosynthesis-grade dichloromethane (OmniSolv^®) were obtained from EMD Millipore Chemicals (Billerica, MA, USA). Hydroxocobalamin acetate (vitamin B_12a, OH-Cbl) was purchased from Hebei Huarong Pharmaceutical Co. (Hebei Province, China). Cyanocobalamin (CN-Cbl), dicyanocobinamide (DCC) and 5,6-dimethylbenzimidazole (DMBI) reference standards were purchased from Sigma-Aldrich Co. (St. louis, MO, USA). nitrocobalamin (NO₂-Cbl) was synthesized as described previously in the literature [13 ]. nitric oxide gas (99.5 %) was purchased from Praxair (Bethlehem, PA, USA).

Anhydrous THF, pentane, and ether were obtained using a solvent purification system (Innovative Technologies, Inc.). [Fe(T1Et4iPrIP)(OTf)₂] was prepared according to a published method.^{[10 ]} Nitric oxide gas (99.5%, Praxair) fitted with a stainless steel regulator was first passed through an ascarite/P₂O₅ column and then through a −130 °C trap (pentane/liquid nitrogen slush bath) followed by activated 4A molecular sieves.

(Heptadecafluoro-1,1,2,2-tetrahydrodecyl)trimethoxysilane (17FTMS) was purchased from Gelest (Morrisville, PA). Methyltrimethoxysilane (MTMOS), (3-aminopropyl)triethoxysilane (APTES), reduced L-glutathione (GSH), bovine serum albumin (BSA), L-cysteine-hydrochloride (Cys), diethylene triamine pentaacetic acid (DTPA), water soluble cholesterol, and ferrous stabilized human hemoglobin A₀ were purchased from Sigma (St. Louis, MO). Nitric oxide gas (99.5% pure) was purchased from Praxair (Danbury, CT). Amicon^™ Ultra-4 centrifugal filters (30 kDA cutoff) were obtained for EMD Milliore (Billerica, MA). Nitrogen and argon gases were purchased from National Welders Supply (Raleigh, NC). A Millipore Milli-Q UV Gradient A10 System (Billerica, MA) was used to purify distilled water to a final resistivity of 18.2 MΩ·cm and a total organic content of <6 ppb. A high-power mounted 530 nm light-emitting diode (LED; model M530L2) and driver were purchased from Thorlabs Inc. (Newton, NJ). Other solvents and chemicals were analytical-reagent grade and used as received.