Elucidation of the CO-Release Kinetics of CORM-A1 by Means of Vibrational Spectroscopy.

CO-releasing molecules (CORMs) are developed for investigations of the interaction between the signaling molecule carbon monoxide (CO) and cells or tissue. Prior to their application these molecules must be fully characterized with respect to their CO-release mechanism. One widely used CORM for biological application is sodium boranocarbonate (CORM-A1), which shows pH-dependent CO liberation. The complete reaction mechanism of CORM-A1 is not fully understood yet. Therefore, in this contribution time-resolved gas-phase IR spectroscopy is used to monitor the headspace above decaying CORM-A1 solutions at four different pH values (5.8 to 7.4). Borane carbonyl is found as an intermediate in the gas phase, which is formed during CORM degradation and further decays to CO. Concentration profiles of a pseudoconsecutive first-order reaction are successfully fitted to specific band areas of the measured gas-phase spectra, and the rate constants are obtained. The production of borane carbonyl is strongly pH dependent (half-lives between 5 and 106 min), whereas the decay of borane carbonyl in the gas phase is nearly constant with a half-life of about 33 min. The ratio of liberated CO molecules per CORM-A1 is determined to be 0.91±0.09, and boric acid is identified as further end product.