Chemistry 112 Final Exam, Part II February 12, 1999 NAME

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1 NAME UNIVERSITY OF CALIFORNIA School of Pharmacy Chemistry 2, Final Examination Part II: Open Book Directions: Work the following four problems; note that they are equally weighted in point value. You may use two pages of notes, front and back, for your reference purposes; you may also use the enzyme kinetics supplement handed out in class. Up to 90% partial credit will be given for solutions where your method and logic are sound, but you have made arithmetic errors; however you must show all of your work. In order to qualify for the 90% maximum, you must reach a final answer. Units must accompany answers. Circle or underline your final answers. Be sure to write your name on every page of the examination. Examinations are due at 5:00 PM; if turned in appreciably after this time, ten points will be deducted from the total score. If you put any answers or work on loose notepaper, be sure it is attached firmly to your examination. Problem Scores: CB. TOTAL COURSE AVERAGE: COURSE GRADE:

2 . (35 points) The reaction A + B + C + D + E + OH- P is known to have a rate law of the form shown below: d[p]/dt = k[a] a [B] b [C] c [D] d [E] e [OH - ] f The following initial rate data was taken: note that the units of concentration are moles/liter (M) and the unit of time is minutes. {d[p]/dt} 0 [A] 0 [B] 0 [C] 0 [D] 0 [E] 0 [OH - ] In addition, studies of the half life of the reaction were done under conditions where the concentrations of A, C, D, E and OH - were held constant; the data displayed on the left hand graph below were obtained. (Recall that the half life of a reaction of nth order in a single component X is given by the relation t /2 = (2 n- -)/{(n-)k[x] 0 n- }. Further studies of the system were carried out where [C] 0 and [OH - ] 0 were allowed to vary one at a time, while the concentrations of all other reactants in the system were held constant. The results of these studies are displayed on the right hand graph below. The squares correspond to data taken in the study of C, while the diamonds correspond to values obtained from the study on OH -. a. (30 points) Determine the values of the exponents a, b, c, d, e, and f in the above rate law. b. (5 points) Determine the value of the rate constant k in the above rate law. Be sure and include units. 0 t /2, min 00 0 {d[p]/dt} 0, M/min 0 [B] 0, M 0 00 [X] 0, M

3 2. (35 points) The data set plotted on the graph below was taken by a pharmacy student studying the destruction of the protein Writeclearin (W), which is thought to participate in maintaining the health of certain neurons in the brains of those graduating from medical school. The grant paying for the study postulated that long term destruction of this protein by the enzyme legiblase (L) is a major cause of many physicians losing the ability to write out readable prescriptions; as one objective, the grant proposed to test the effect of a Readablin, a peptide inhibitor of this enzyme, on the rate of destruction of Writeclearin by legiblase. (a) (0) Using the information provided, determine values for K m and V max for the enzymatic destruction of Writeclearin by legiblase. (b) (0)What type of inhibition is induced by Readablin in this enzymatic system? Why did you reach this conclusion? (c) (8) Determine the value of K I for the inhibition of the destruction of Writeclearin by Readablin. (d) (7) What concentration of Readablin would be needed to reduce the rate of Writeclearin destruction to five percent of its value in the absence of inhibitor when the Writeclearin concentration is 50 µm. v 00, [R] = µm; v 0, [R] =.393 µm; v 02, [R] = µm /v oj, µm - min /[W], µm - /v 00 /v 0 /v 02

4 3. (35 points) Compound A reacts to form compounds B and C via parallel unimolecular pathways as shown immediately below. A A k B () k 2 C (2) The graph, shown below, displays the temperature dependence of the ratio of the rate constant k 2 to the rate constant k. (a) (20) Calculate the values of H 2 - H and S2 - S for this pair of reactions. (b) (6) Analysis of the data shows that H 2 = 40 kj/mole and S2 = -45 J/K mole. What are the values of H and S? (c) (6) What are the values for G 2 - G and Κ2 /Κ for this pair of reactions at 27 C? (d) (3) What fraction of the total product in the reaction mixture will be B after 45 minutes at 27 C? You may assume the initial concentrations of B and C are zero. k 2 /k /T, K -

5 4. (35 points) The mechanism below describes the reaction A + B + D E. Z A Z B k k - A + B C 0 C 0 + D -2 E -2 k 2 Reaction I Reaction II The following data set was taken as a function of ionic strength: I k (M - s - ) (a) (0) What is the value of the product of the charges Z A and Z B? (b) (5) What are the possible values of Z A and Z B individually? (c) (5) What is the value of k when I = 0? (d) (5) The rate constant for reaction II at zero ionic strength is 0 4 liter/mol sec. What is the corresponding value of k 2 in M NaCl? (e) (0) Calculate the ratio of the rate of formation of E in M MgCl 2 to that in the absence of MgCl 2. You may assume that C is an unstable intermediate. You may further assume that reactants and products make negligible contributions to the ionic strength and that addition of MgCl 2 has a negligible effect on the concentrations of A, B and D.