Cobinamide chemistries for photometric cyanide determination. A merging zone liquid core waveguide cyanide analyzer using cyanoaquacobinamide

Abstract

Diaquacobinamide (H2O)2Cbi2+ or its conjugate base hydroxyaquacobinamide (OH(H2O)Cbi+)) can bind up to two cyanide ions, making dicyanocobinamide. This transition is accompanied by a significant change in color, previously exploited for cyanide determination. The reagent OH(H2O)Cbi+ is used in excess; when trace amounts of cyanide are added, CN(H2O)Cbi+ should be formed. But the spectral absorption of CN(H2O)Cbi+ is virtually the same as that of OH(H2O)Cbi+. It has been inexplicable how trace amounts of cyanide are sensitively measured by this reaction. It is shown here that even with excess OH(H2O)Cbi+, (CN)2Cbi is formed first due to kinetic reasons; this only slowly forms CN(H2O)Cbi+. This understanding implies that CN(H2O)Cbi+ will itself be a better reagent. We describe a single valve merging zone flow analyzer that allows both sample and reagent economy. With a 50 cm liquid core waveguide (LCW) flow cell and an inexpensive fiber optic - charge coupled device array spectrometer, a S/N=3 limit of detection of 8 nM, a linear dynamic range to 6 μM, and excellent precision (RSD 0.49% and 1.07% at 50 and 100 nM, respectively, n=5 each) are formed. At 1% carryover, sample throughput is 40 h−1. The setup is readily used to measure thiocyanate with different reagents. We demonstrate applicability to real samples by analyzing human saliva samples and hydrolyzed extracts of apple seeds, peach pits, and almonds.

Kinetic Studies on the Reaction between Dicyanocobinamide and Hypochlorous Acid

“…Similar products have been obtained when the reaction was carried out in plasma, indicating the biological relevance of our finding [40]. A biphasic reaction has also been reported for CN - with (OH)(H 2 O)-Cbi to form (CN) 2 -Cbi [2], [45]. In this reaction, the replacement of the H 2 O molecule by CN - has been suggested as an initial step due to favorable thermodynamic and kinetic reasons, subsequently (OH)(CN)-Cbi was attacked by the second CN - molecule to form (CN) 2 -Cbi.…”

Kinetics and Mechanism of the Reaction of Hydrogen Sulfide with Diaquacobinamide in Aqueous Solution

“…The same behavior was observed during formation of a cobinamide complex with one and two molecules of thiocyanate [4] or cyanide. [22] We, therefore, suggest that Cbi reacts with one (at low concentration, reaction 1) and two molecules of H 2 S (at high concentration, reaction 2) This is confirmed by the shape of the kinetic traces and the linear (k obs(1) ) and square (k obs(2) ) dependencies on the initial hydrogen sulfide concentration in alkaline medium. Thus, our data confirm that Cbi can bind two times more sulfide than Cbl.…”

“…[16] Comparison of k` 1 , k` 2 , k` 3 and k` 4 clearly shows that HS − is more active in reaction with cobinamide(III) than H 2 S. At the same time, (H 2 O) 2 Cbi(III) reacts faster with hydrogen sulfide than (H 2 O)(OH)Cbi(III). This is expected because (H 2 O) 2 Cbl(III) (total charge +2) [22] and (H 2 O)(OH)Cbi(III) (total charge +1) are positively charged and coordination of the negatively charged HS − must support the complex-formation reaction with cobinamide.…”

Reactions of Cobinamide with Glucose and Fructose

“…Recently this compound has attracted researchers' interests due to the high efficacy of its derivatives as cyanide antidotes (sulfitocobinamide) [15][16][17] and cyanide chemosensors (monocyanocobinamide). [18][19][20] Cbi application is also of interest in the study of both Co 3+ → Co 2+ and Co…”