A Stability-Indicating HPLC Method for the Determination of Nitrosylcobalamin (NO-Cbl), a Novel Vitamin B12 Analog

Nitrosylcobalamin (NO-Cbl), a novel vitamin B₁₂ analog and anti-tumor agent, functions as a biologic ‘Trojan horse’, utilizing the vitamin B₁₂ transcobalamin II transport protein and cell surface receptor to specifically target cancer cells. A stability-indicating HPLC method was developed for the detection of NO-Cbl during forced degradation studies. This method utilized an Ascentis^® RP-Amide (150 mm × 4.6 mm, 5 μm) column at 35 °C with a mobile phase (1.0 mL min^?1) combining a gradient of methanol and an acetate buffer at pH 6.0. Detection wavelengths of 450 and 254 nm were used to detect corrin and non-corrin-based products, respectively. NO-Cbl, synthesized from hydroxocobalamin and pure nitric oxide gas, was subjected to degradative stress conditions including oxidation, hydrolysis and thermal and radiant energy challenge. The method was validated by assessing linearity, accuracy, precision, detection and quantitation limits and robustness. The method was applied successfully for purity assessment of synthesized NO-Cbl and for the determination of NO-Cbl during kinetic studies in aqueous solution and in solid-state degradation assessments. This HPLC method is suitable for the separation of cobalamins in aqueous and methanolic solutions, for routine detection of NO-Cbl and for purity assessment of synthesized NO-Cbl. Additionally, this method has potential application in identification and monitoring of diseases involving altered nitric oxide homeostasis where vitamin B₁₂ therapy is utilized to scavenge excess nitric oxide, subsequently resulting in the in vivo production of NO-Cbl.     

Tris‐Functionalized Hybrid Anderson Polyoxometalates: Synthesis,Characterization, Hydrolytic Stability and Inversion of Protein Surface Charge

Single‐ and double‐sided functionalized hybrid organic–inorganic Anderson polyoxomolybdates with Ga^III and Fe^III positioned as central heteroatoms have been synthesized in a mild, two‐step synthesis in an aqueous medium. Compounds 1 – 4 were isolated as hydrated salts, [TBA]₃[GaMo₆O₁₈(OH)₃{(OCH₂)₃CCH₂OH}]×12 H₂O ( 1 ) (TBA=tetrabutylammonium), Na₃[FeMo₆O₁₈{(OCH₂)₃CCH₂OH}₂]×11 H₂O ( 2 ), [TMA]₂[GaMo₆O₁₈(OH)₃{(OCH₂)₃CNH₃}]×7 H₂O ( 3 ) (TMA=tetramethylammonium), and Na[TMA]₂[FeMo₆O₁₈(OH)₃{(OCH₂)₃CNH₃}](OH)×6 H₂O ( 4 ). All the compounds were characterized based on single‐crystal X‐ray diffraction (SXRD), FTIR, UV/Vis, thermogravimetric, ESI‐MS, NMR, and elemental analyses. Compound 1 was also crystallized with two smaller organic cations, giving [TMA]₃[GaMo₆O₁₈(OH)₃{(OCH₂)₃CCH₂OH}]×n H₂O ( 5 ) and [GDM]₃[GaMo₆O₁₈(OH)₃{(OCH₂)₃CCH₂OH}]×n H₂O ( 6 ) (GDM=guanidinium) and were characterized based on UV/Vis, NMR, FTIR, and elemental analyses. The use of these compounds as additives in macromolecular crystallography was investigated by examining their hydrolytic stability by using ESI‐MS in a pH range of 4 to 9. Sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE) analysis showed that BSA remains intact in a solution containing up to 100 equivalents of 1 or 4 over more than four days at 20 °C. Zeta potential measurements demonstrate that 1 – 4 induce charge inversions on the positively charged surface of BSA (1 mg mL^?1) with concentrations starting as low as 1.29 mM for compounds 1 and 2 , which have the highest negative surface charge.     

Cobalt Single‐Atom Catalysts with High Stability for Selective Dehydrogenation of Formic Acid

Metal–organic framework (MOF)‐derived Co‐N‐C catalysts with isolated single cobalt atoms have been synthesized and compared with cobalt nanoparticles for formic acid dehydrogenation. The atomically dispersed Co‐N‐C catalyst achieves superior activity, better acid resistance, and improved long‐term stability compared with nanoparticles synthesized by a similar route. High‐angle annular dark‐field–scanning transmission electron microscopy, X‐ray photoelectron spectroscopy, electron paramagnetic resonance, and X‐ray absorption fine structure characterizations reveal the formation of Co^IIN_x centers as active sites. The optimal low‐cost catalyst is a promising candidate for liquid H₂ generation.     

Formal C−H Carboxylation of Unactivated Arenes

A formal C−H carboxylation of unactivated arenes using CO₂ in green solvents is described. The present strategy combines a sterically controlled Ir-catalyzed C−H borylation followed by a Cu-catalyzed carboxylation of the in situ generated organoboronates. The reaction is highly regioselective for the C−H carboxylation of 1,3-disubstituted and 1,2,3-trisubstituted benzenes, 1,2- or 1,4-symmetrically substituted benzenes, fluorinated benzenes and different heterocycles. The developed methodology was applied to the late-stage C−H carboxylation of commercial drugs and ligands.     

Hexavalent chromium quantification in solution: Comparing direct UV–visible spectrometry with 1,5-diphenylcarbazide colorimetry

Quantification of Cr(VI) in an aqueous solution is conducted by direct UV–visible spectrophotometry based on the yellow coloring of the chromate ion. Measurements show that absorption follows the Beer–Lambert law over a wide range of concentrations. At pH below the pK_a of 6.4 (HCrO₄^?/CrO₄^?2), the absorption maximum lies at 350 nm wavelength and the linear range spans from 0.5 to 100 mg Cr(VI)/L; above the pK_a (pH 6.4), the absorption maximum is 373 nm and linearity occurs in the range of 0.5–25 mg/L. The wide range of validity of the Beer–Lambert law is advantageous for the measurement of concentrated samples. The standard method of analysis of aqueous Cr(VI) is by colorimetry with the 1,5-diphenylcarbazide (DPC)–Cr(VI) complex. This method, although very sensitive, bears a narrow range of linearity from 0 to 0.8 mg Cr(VI)/L. It is shown that when analyzing Cr(VI) solutions with concentrations in the range of 30–500 mg/L, the DPC method gives inaccurate results and relative standard deviations of 20–50%. This is due to high dilution factors. On the contrary, the direct method performs with high accuracy. Relative standard deviation is only 0.5% at 500 mg Cr(VI)/L. The direct method is fast, reliable, and nondestructive for the sample. The direct method is recommended for the quantification of Cr(VI) at concentrations greater than 1 mg/L.