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Institute of Engineering and Technology, Sitapur Road, Lucknow-226 021, Uttar Pradesh, India E-mail : amarikasingh@rediffmail.com Manuscript received online 23 January 2013, revised 20 March 2013, accepted 12 May 2013 Cysteine is a sulphur containing α-amino acid having chemical formula HO2CCH(NH2 )CH2 SH. Its sulphur atom has been shown to inhibit the mercury catalysed substitution of cyanide in hexacyanoferrate(II) by phenanthroline [Phen]. The inhibitory effect is due to the binding capacity of catalyst with the inhibitor. The reaction was followed spectrophotometrically in aqueous medium at 528 nm by the formation of a dark coloured complex, [Fe(CN)5Phen]3– at pH = 3.0 ± 0.02, temp. = 25.0 ± 0.1 ºC, ionic strength (µ) = 0.05 M (KNO3 ). Linear calibration curves were obtained at different times (At ) and different cysteine concentrations, under the above conditions. The detection limit was 5 × 10–7 M, the Michaelis-Menten constant (Km) and equilibrium constant for the complex of catalyst and inhibitor (KCI) and for the complex of catalyst and substrate (Ks ) were calculated from the kinetic data. A general mechanistic scheme is also proposed for this reaction. |
