Turnover number the average number of reactants that a catalystacts o - PDF document

Turnover number: the average number of reactants that a catalystacts on before the The thermodynamics of a catalyzed reaction are unaffected by thecatalyst.All calaystsoperate by the same general princi

ple –that is, the activation energy of the rdsmust be lowered in order for a rate enhancement to occur. for the uncatalyzedone.To achieve catalysis, the catalyst must stabilize the transitionstate more

than it stabilizes the ground state. That is, the transition state must be boundbetter than the ground state. 9.1.3 A spatial temporal approach To achieve catalysis, the catalyst must stabilize the tra

nsitionstate more than it stabilizes the ground state. That is, the transition state must be boundbetter than the ground state.Another explanation for catalysis: spatial temporal postulate, many intramo

lecularreactions 9.2.2 Proximity as binding phenomenon Intermolecular aminolysis(Intramolecularcyclization(Effective molarity(E.M.) or intramolecularity; ratio of the first order in the intramolecularr

eaction 1.3 x 10�- a rate enhancement of 1200 Entropies of translation and rotation Gem-dimethyleffect: stericallycompress two groups together and preorganize RRdecrease of angleclose �- i

nfinitely stable�- very reactive 9.2.3 ElectrophiliccatalysisElectrophiliccatalysis includes simple electrostatics, hydrogen bonding, acid catalysis,and electrophilicmetal coordination.Electrosta

tic interactions Oxyanionhole 150-fold rate enhancement Cation- 16-fold rate enhancement pKaof metal-bound water = 7.2 (10 9.2.4 Acid-base catalysis; 9.3에서설명9.2.5 NucleophiliccatalysisNucleophil

iccatalysis arise when a nucleophilebinds to a reactant and enhances its rate NMe NH NMe DMAP; N,N'-dimethylaminopyridine better electrophileand more reactive 9.2.6 Covalent catalysis Iminiumion chara

ceristicsto the transition state, the substrate may distort in order to optimize binding 9.3 Brønstedacid-base catalysis is defined as the protonatedform of the solvent in which the reaction is is def

ined as the conjugate base of the solvent.eg) HO-, -CN, CH3-The specific acid catalysis refers to a process in which the reaction rate depends uponthe specific acid, not upon other acids in the solution

.The specific base catalysis refers to a process in which the reaction rate depends uponthe specific base, not upon other bases in the solution.kO+ added acid (AcOHin HIf the acid catalysis is involved

in an equilibrium prior to therds, and it is not involved 앞과동일 는반응에관여하지않음에포함되지않음 -][H3O+]/[HA]KaRH+= [R][H3O+]/[RH+][HA] 항없음 O+] -][H3O+]/[RH]BH+는반ì

‘에관여하지않음에포함되지않음 [B] 항없음에서다시설명 Kinetic plots ecific base catalysis is thatthe rate depends on the pH and not on the concentration of various acids or bases.

Thisacid or base occur prior to rds, and the acid or base is not involved in rdsitself.specific acid catalysisspecific base catalysispecific base catalysis3O+]/KaRH+kobs= kKaRH/[H3O+]logkobs= logk–pH-lo

gKaRH+logkobs= logk+pH+logKaRH+added acidadded base The term ‘general’refers to the fact that any acid or base we added to the solution The term ‘specific’refers to the fact that just one acid or base,

that from the solvent, 는반응에관여함에포함 a= [A-O+[HA] or kO+a-Since the acid is always regenerated after the reaction, �its concentration never changes over the course of the reactio

n - pseudo-first order-the concentration of either HA or A-is in the rate expression. General acid catalyzed reactions 는반응에관여함에포함 [B] or kb-Since the base is always regenerated afte

r the reaction, �its concentration never changes over the course of the reaction - pseudo-first order-the concentration of either B or BH+is in the rate expression. Note: ‘specific’is used to de

signate the protonatedor deprotonatedform of the solvent However, sometimes hydroniumor hydroxide can be involved in rds. 19 page 실제로는첫번째단계가로작용 Kinetic plots ecific base catal

ysis is thatthe rate depends on the pH and not on the concentration of various acids or bases. Thisacid or base occur prior to rds, and the acid or base is not involved in rdsitself. general acid cataly

sisgeneral base catalysiseneral base catalysisk[H3O+][A-]/Kakobs= k[B] or k[HO-][HB+]/Kb페이지20과비교로주로존재의변화없음이것은반응에관여하지않음이공존가점차적으로ë

¡œë°”뀌어가지㏣적으로감㏢general acid catalysisgeneral base catalysis eral-acid-general-base catalysisBoth a general acid and a general base catalyst are required fora reaction. acidbase the p

roduct of the concentrations of 9.4.1 Michaelis-Mentenkinetics←→k1→k-1kcatE·S: Michaeliscomplex S rate = d[P]/dt= d[ES]/dt= 0-[ES] Km+ [S]rate = d[P]/dt= Michaelis-MentenequationKinetic parame

ters to be determ physical processchemical process turnover number: the maximum number of substrate moleculesconverted to productsper active site per unit time product within the active site�- pr

oximity, acid-base catalysis, electrostatic consideration, covalent catalysis,and the cat: apparent dissociation constant that may be tof all enzyme-bound species.the dissociation constant for ES comple

x.Under these circumstances, the catalyst is. The smaller mean�s a better receptor. - physical process (binding) rather than a chemical transformation.(a very good catalyst) does not resemble the

dissociation constant for ES complex ; apparent second order rate constantnds the substrate and how well the catalyst turnsover the substrate to pr�oduct. - Information on both binding and catal

ysis 9.4.3 Enzyme active sites Proposed mechanismRicinA is a potent cytotoxinfrom attacks ribosomes, hydrolyzing the of specific adenosine nucleot�- enhances nucleophilicityof water Rate enhancem