Pseudo First Order Reaction Lab Report

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AIM: Is to determine the kinetics of a pseudo first order reaction. THEORY The pseudo first order reaction is the reaction that is a second order but can be approximated to be first order under a special circumstances. In the experiment the kinetics of the oxidation of GSH by Cr (VI) is studied at neutral pH, which result in formation of glutathionyl disulfide. The glutathione is a tripeptide with a gamma peptide bond between carboxyl group of the glutamate side chain and the amine group of cysteine. Due to its chemical structure, glutathione may protect against oxidation. The overall reaction mechanism for the reaction: Figure 1: structure of GSH (R.J.Silbey, etal.2004) figure 2: formation of GSSG (R.J.Silbey, …show more content…

The reversible formation of chromium (IV) thioester intermediate: CrO42- + GSH ↔ CrO42- - GSH (Thioester) Thioester + GSH → GSSG The spectrophotometer at the wavelength of 370 used to measure the absorbance of the solution. Oxidation: occur when a reactant loses electrons during the reaction. Reduction: occur when a reactant gains electrons during the reaction. Absorbance: is a measure of the quantity of light absorbed by a sample. Spectrophotometer: is an instrument that measures the amount of photons absorbed after it passes through sample …show more content…

The sample cell was removed and the data acquisition began. 200µl of the Cr (VI) solution was injected with a micropipette into the sample, inverted it several times and placed in a cell compartment fasted. The absorbance values were recorded every 20 seconds for a period of 40 minutes. DISCUSSION During the experiment the kinetic behaviour of the redox reaction between the GSH and Cr(IV) was investigated. The GSSG which is glutathionyl disulfied formed by two GSH units that coupled together through the thiol groups. The Chromium ion in the 6 oxidation reduced to Cr (III) due to the present of oxygen. The GSH and GSSG operate as redox couple, both in intracellular and plasma environments. GSH provides an important defence mechanism against certain toxic compounds that scavenges reactive species such as free radicals and peroxides, and the Cr(VI) interfered these process by causing a depletion of GSH. In the experiment the GSH and H+ behave as a first order in the presence of excess concentration, which means they are pseudo first order reaction. The concentration of chromium ions monitored throughout the

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