# Enzyme Technology Questions and Answers – Recent Advances – Equilibria in Biphasic Aqueous-Organic Systems

This set of Enzyme Technology Multiple Choice Questions & Answers (MCQs) focuses on “Recent Advances – Equilibria in Biphasic Aqueous-Organic Systems”.

1. In the below reaction, Kw is represented by ___________ a) $$\frac{[B_w]}{[A_w]}$$
b) $$\frac{[B_{org}]}{[A_{org}]}$$
c) $$\frac{[A_{org}]}{[A_w]}$$
d) $$\frac{[B_{org}]}{[B_w]}$$

Explanation: The reaction below represents a biphasic system consisting of a mixture of an aqueous and an organic solvent. Kw and Korg represents equilibrium constants for water and organic phase respectively. PA and PB are partition co-efficients of A and B respectively.
Korg = $$\frac{[B_{org}]}{[A_{org}]}$$
PA = $$\frac{[A_{org}]}{[A_w]}$$
PB = $$\frac{[B_{org}]}{[B_w]}$$
Equilibrium constant for water Kw is given by $$\frac{[B_w]}{[A_w]}$$,
Where Aw and Bw are concentrations of A and B.

2. What does PA represent in the following reaction? a) $$\frac{[B_w]}{[A_w]}$$
b) $$\frac{[B_{org}]}{[A_{org}]}$$
c) $$\frac{[A_{org}]}{[A_w]}$$
d) $$\frac{[B_{org}]}{[B_w]}$$

Explanation: The above reaction represents a biphasic system consisting of a mixture of an aqueous and an organic solvent. Kw and Korg represents equilibrium constants for water and organic phase respectively. PA and PB are partition co-efficients of A and B respectively.
Korg = $$\frac{[B_{org}]}{[A_{org}]}$$
PB = $$\frac{[B_{org}]}{[B_w]}$$
Kw = $$\frac{[B_w]}{[A_w]}$$
Partition coefficient for A is represented by PA = $$\frac{[A_{org}]}{[A_w]}$$,
Where Aorg and Aw are the concentration of A in organic solvent and water respectively.

3. The apparent equilibrium constant (Kbiphasic) of this system may be defined as _____________
a) $$\frac{[B_{org}]}{[A_{org}]}$$
b) $$\frac{[B_w]}{[A_w]}$$
c) $$\frac{[B_t]}{[A_t]}$$
d) $$\frac{[B_{org}]}{[B_w]}$$

Explanation: The biphasic system is represented by the following reaction Kw and Korg represents equilibrium constants for water and organic phase respectively. PA and PB are partition co-efficients of A and B respectively.
Kbiphasic represents the apparent equilibrium constant and is given by, $$\frac{[B_t]}{[A_t]}$$,
Where At = Concentration of A in total solution and Bt = Concentration of B in total solution.

4. Which of the following does not represent Kbiphasic?
a) $$\frac{[B_{org}]}{[A_{org}]}$$
b) $$\frac{[B_t]}{[A_t]}$$
c) $$K_w (\frac{1+αP_B}{1+αP_A})$$
d) $$K_w \frac{P_B}{P_A}$$

Explanation: Kbiphasic is the apparent equilibrium constant and is represented in the following ways:
$$K_{biphasic} = \frac{[B_t]}{[A_t]}$$
$$K_{biphasic} = K_w (\frac{1+αP_B}{1+αP_A})$$
$$K_{biphasic} = K_w \frac{P_B}{P_A}$$
Equilibrium constant for organic solvent reaction is given by Korg = $$\frac{[B_{org}]}{[A_{org}]}$$,
Where Aorg and Borg gives the concentration of A and B in organic solvents respectively.

5. What does α represent in the below equation?
$$K_{biphasic} = K_w (\frac{1+αP_B}{1+αP_A})$$
a) $$\frac{[B_w]}{[A_w]}$$
b) $$\frac{V_{org}}{V_w}$$
c) $$\frac{[B_t]}{[A_t]}$$
d) $$\frac{[B_{org}]}{[B_w]}$$

Explanation: Kbiphasic in terms of volumes is represented by
$$K_{biphasic} = K_w (\frac{1+αP_B}{1+αP_A})$$,
Where Kw = equilibrium constant of water, PA and PB are partition coefficients of A and B respectively.
α is the ratio of the volumes of the organic (Vorg) and water (Vw) phases and is given by $$\frac{V_{org}}{V_w}$$.
Kw = $$\frac{[B_w]}{[A_w]}$$ ; $$K_{biphasic}=\frac{[B_t]}{[A_t]}$$ ; and PB = $$\frac{[B_{org}]}{[B_w]}$$.

6. What does the following graph represents? a) Effect of the polarity of A and B
b) Variation in the apparent equilibrium constants
c) Effect of the ratio of the partition coefficients
d) Variation in the apparent equilibrium constant and percentage yield

Explanation: The graph represents the effect of the ratio of the partition coefficients (PB/PA). The curves are generated by using the equation $$K_{biphasic} = K_w (\frac{1+αP_B}{1+αP_A})$$. In the plot, the variation in the apparent equilibrium constants of a one-substrate one-product reaction with the relative component composition of a biphasic aqueous-organic system is shown.

7. What is represented in the following plot? a) Effect of the polarity of A and B
b) Variation in the apparent equilibrium constants
c) Effect of the ratio of the partition coefficients
d) pH dependence on the apparent equilibrium constant

Explanation: The plot represents the effect of polarity he polarity of A and B, keeping the ratio of the partition coefficients constant (PB/PA = 100). This plot is drawn considering the variation in the apparent equilibrium constants of a one-substrate one-product reaction with the relative component composition of a biphasic aqueous-organic system. The following values for the partition coefficients have been used, from the top downwards; PB = 100, PB = 10, PB = 1, PB = 0.1, PB = 0.01, PB = 0.001, PB = 0.0001.

8. What does the diagram depict? a) Variation in the apparent equilibrium constants of a one-substrate one-product reaction
b) Variation in the apparent equilibrium constants of a two-substrate two-product reaction
c) pH dependence on apparent equilibrium constant
d) Effect of the polarity of A and B

Explanation: The diagram depicts a plot which shows the variation in the apparent equilibrium constants of a two-substrate two-product reaction with the relative component composition of a biphasic aqueous-organic system. The 2 substrate 2 product reaction may be given as,
A+B ⇋C+D
In all cases the partition coefficients are PA = 1, PB = 1 and PC = 100. The following values for the partition coefficient have been used, from the top downwards; 1, 0.1, 0.01, 0.001 and 0.0001.

9. What is represented in the plot? a) Variation in the apparent equilibrium constants of a one-substrate one-product reaction
b) Variation in the apparent equilibrium constants of a two-substrate two-product reaction
c) Variation in the apparent equilibrium constant and percentage yield
d) pH dependence on apparent equilibrium constant

Explanation: In the plot, variation in the apparent equilibrium constant and percentage yield is represented which is semi-logarithmic plot. This plot is portrayed for a reaction of synthesizing N-Benzoyl-L-phenylalanine ethyl ester by the action of chymotrypsin on N-Benzoyl-L-phenylalanine and ethyl alcohol in a biphasic chloroform-water system (pH 7). Straight red line represents apparent equilibrium constant, whereas red dotted line represents % yield.

10. What does the plot in the diagram depict? a) Variation in the apparent equilibrium constants of a one-substrate one-product reaction
b) Variation in the apparent equilibrium constants of a two-substrate two-product reaction
c) Variation in the apparent equilibrium constant and percentage yield
d) pH dependence on apparent equilibrium constant 