Shaillee Kaushal is teaching live on Unacademy Plus
XII - 05 SURFACE CHEMISTRY -VI
Mechanism of Acid-Base catalyst- In acid catalysis, the proton given by bronsted acids forms an intermediate complex with the reactant which that reacts to give back the proton (H+). For example, the hydrolysis of ester occurs in the following manner. O-H O-H CH3 CO-CH2CH3 O-CH2CH3
In base catalyzed hydrolysis, the oH-ions or any Bronsted base accepts a proton form the reactant to form an intermediate complex. Which then decomposes to regenerate OH ions NH2NO2 + OH- NHNo5 + H2O N20+ OH NH2 NO2 + CH3COO- NHNO + CH3COOH N20 + OH-
Enzyme catalysis: Enzymes are complex nitrogenous organic compounds which are produced by living plants and animals Enzymes are high molecular mass protein molecules. They catalyze numerous reactions, especially those connected with natural processes. Numerous reactions occur in the bodies of animals and plants to maintain the life process. The enzymes are thus called biochemical catalysts.
Inversion of cane sugar: C12H22011 H20 Invertase cane sugar Gluscose Fructose Decomposition of urea into ammonia and carbon dioxide NH2 CONH2 + H202NH3 + CO2 Conversion of milk into curd: It is an enzymatic reaction brought about by lactic bacilli enzyme present in cured. Lysozyme is found in the tear of our eyes. It protects our eyes from bacteria. Urease > Nitrogenase enzyme is found in the bacteria of the root nodules of leguminous plants such as peas and beans.
Characterstics of Enzyme catalysis Enzyme catalysis is intermediate between homgenous and heterogenous catalysis It is called microheterogenous catalysis. i) Most efficient catalysts The enzyme reaction is very fast as compound to reactions catalysed by inorganic catalysts. One molecules of an enzyme may transfer one million molecules of the reaction per minute. li) High specific nature Each enzyme is specific for a reaction One catalyst cannot catalyse more than one reaction.
liii)Temperature dependence: The rate of reaction depends upon temperature The enzyme activity rises with temperature and becomes definite at a given temperature called optimum temperature The optimum temperature of enzymes reactions. Occurring in the human body in 37 C Civ) pH dependence The rate of the reaction varies with pH of the system The enzyme activity is maximum at an optimum pH of 7.4 The favorable range of pH for enzyme activity is 5-1 [v) The enzyme catalysis has not effect on the equilibrium of the reaction
(ii) Activators or co-enzyme The enzymatic activity is increased in the presence of certain substances known as cO- enzymes Activators are generally metal ions such as Nat, Mn2+, Co2+, Cu2+ etc. These metal ions when weakly bonded to enzyme molecules increases their catalytic activity tviii) Inhibitors and poisons: Certain substances inhibit the activity of the catalyst. The inhibitors or poisons interact with the active functional groups on the enzyme surface and often reduce or completely destroy the catalytic activity of the enzymes.
Mechanisms of enzyme catalysis: There are a number of cavities present on the surface of colloidal particles of enzymes These cavities are of characteristic shape and possess active groups such as NH2,-COOH SH,-0H etc. These are actually the active centers on the surface of enzyme particles The molecules of the reactant [substrate), which have complementary shape, fit into these cavities just like key fits into a lock on account of the presence of active groups, an activated complex is formed which the decomposes to yield the products E + S -E-S complex E + P
Step 1: Binding of enzyme to substrate to form an activated complex: R 1 Step 2 Product formation in the activated complex ES-EP
Casel:When, [S] >km, then km can be neglected at-max = k2[E] Dividing equation i) by equation lii r max [S]+km When, Km = [S], r = 2 max Case ll: When ISl <<<km the reactions will be of second order Rate = k2[EIS] Km