Prebiotic reactions are reactions that might have occurred under the conditions prevalent on the Earth before the first living creatures emerged and that can lead to analogues of molecules necessary for life as we now know it. To qualify, a reaction must proceed with a favourable rate and have areasonable value for the equilibrium constant. An example of a prebiotic reaction is the formation of 5-hydroxymethyluracil (HMU) from uracil and formaldehyde (HCHO). Amino acid analogues can be formed from HMU under prebiotic conditions by reaction with various nucleophiles, such as H2S, HCN, indole, imidazole, etc. For the synthesis of HMU at pH = 7. the temperature dependence of the rate constant is given bylog k,/(dm3 mol-1 s-1) = 11.75- 5488/(T/K)and the temperature dependence of the equilibrium constant is given bylog K = -1.36 + 1794/(T/K)(a) Calculate the rate constants and equilibrium constants over a range of temperatures corresponding to possible prebiotic conditions, such as 0-50 oC. and plot them against temperature.(b) Calculate the activation energy and the standard reaction Gibbs energy and enthalpy at 25 oC. (c) Prebiotic conditions are not likely to be standard conditions. Speculate about how the actual values of the reaction Gibbs energy and enthalpy might differ from the standard values. Do you expectthat the reaction would still be favourable?
Prebiotic reactions are reactions that might have occurred under the conditions prevalent on the Earth before the first living creatures emerged and that can lead to analogues of molecules necessary for life as we now know it. To qualify, a reaction must proceed with a favourable rate and have areasonable value for the equilibrium constant. An example of a prebiotic reaction is the formation of 5-hydroxymethyluracil (HMU) from uracil and formaldehyde (HCHO). Amino acid analogues can be formed from HMU under prebiotic conditions by reaction with various nucleophiles, such as H2S, HCN, indole, imidazole, etc. For the synthesis of HMU at pH = 7. the temperature dependence of the rate constant is given by
log k,/(dm3 mol-1 s-1) = 11.75- 5488/(T/K)
and the temperature dependence of the equilibrium constant is given by
log K = -1.36 + 1794/(T/K)
(a) Calculate the rate constants and equilibrium constants over a range of temperatures corresponding to possible prebiotic conditions, such as 0-50 oC. and plot them against temperature.
(b) Calculate the activation energy and the standard reaction Gibbs energy and enthalpy at 25 oC. (c) Prebiotic conditions are not likely to be standard conditions. Speculate about how the actual values of the reaction Gibbs energy and enthalpy might differ from the standard values. Do you expect
that the reaction would still be favourable?
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