COLLEGE OF SAINT MARY FALL 2008 PHYSICAL CHEMISTRY

INSTRUCTOR: DR. PETER ILICH YOUR NAME: _____________________________

EXAM # 2B

I love lysine:

1. (60 pts) Lysine, Lys, K, is a basic amino acid which in free form contains three groups that exchange proton in the pH 0 to 14 domain, figure at right. (a) Look at the formula at right and the corresponding pKa values and draw the structural formula of the dominant form of free lysine in aqueous solution at pH 7. (b) Toward which electrode, anode or cathode, would this lysine ion travel in a DC (Direct Current) electric field? (c) From the pKa data given at right and the Henderson-Hasselbalch equation calculate the approximate concentration of the dominant species in the lysine solution of total concentration of c = 1.37*10^-3 M.

Don't drink and drive:

2. (30 pts) The redox reaction given below,

where the reduction of C4 in the pyrimidine ring of the nicotineamideadenine dinucleotide corresponds to the oxidation of one ethanol molecule to ethanal (acetaldehyde) provides the electrochemical basis for the metabolism of ethanol with the catalytic help of LADH (liver alcohol dehydrogenase) enzyme in our liver. Given that E^ө (NAD/NADH) at pH = 7 is -0.320 V, and E^ө (CH₃CHO/CH₃CH₂OH) is -0.197 V, calculate the standard Gibbs energy for this reaction and determine whether the reaction is thermodynamically spontaneous or driven.

The little N-bomb in your heart:

3. (30 pts) The less well known plutonium isotope, ²³⁸Pu₉₄ undergoes the following radioactive decay reaction:

²³⁸Pu₉₄ → ²³⁴U₉₂ + [He]⁺²

This is a highly exothermic nuclear reaction producing 0.54 kW/kg plutonium and is used in the so-called RTG (Radioisotope Thermoelectric Generator) power units in interplanetary space probes (e.g. Cassini) as well as in some experimental-type pacemakers. A newly manufactured ²³⁸Pu₉₄-powered pacemaker is surgically implanted into a patient. Keeping in mind that the Pu-238 half life is 87.74 yr calculate how much Pu-238 fuel, in grams, is needed in order to maintain a minimum of 100 mW output for 25 years?

Not published yet:

4. (30 pts) Xanthine dehydrogenase, XDH [E.C. 1.1.1.204], is a molybdo-pterin oxidoreductive enzyme involved in the processing of nucleic acid metabolites in human body. The reductive rate constant of XDH, k_red, is 67 [s^-1] for xanthine substrate [Leimkühler et al., J. Biol. Chem. 2004, 279, 40437, Table 2]. Electronic structure calculations suggest a drop in the activation Gibbs energy from 76 kcal mol^-1 to 66 kcal mol^-1. with the transition-state-coupled proton release [Ilich & Hille, J. Inorg. Biochem. 2008, submitted]. Assuming the same, pseudo-first order kinetics, use the Arrhenius activation energy formalism to calculate the change in the reaction rate induced by this activation energy decrease.

COLLEGE OF SAINT MARY FALL 2008 PHYSICAL CHEMISTRY EXAM # 2

YOUR NAME: _____________________________