Question

The unfolded random-coil peptide SESYINPDGTWTVH can fold into either an -helix structure with a value of∆?° of -175 kJ/mol or into a -hairpin structure with a ∆?° of -199 kJ/mol. What is the value of

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H 0 for the helix-to-hairpin conformational transition? Drawing pictures like the one I drew on the first day ofRXN

class may help.

Answer 1

The enthalpy change of the process from random coil to helix is -175 kJ/mole

So; random coil = helix ; delH⁰ = - 175 kJ/ mol

The reverse process is:

Helix = random coil; delH⁰ = + 175 kJ/ mole..... Equation 1

From random coil to hairpin conformational change; tge enthalpy change of the process is - 199 kJ/ mole

Random coil = hairpin ; delH⁰ = - 199 kJ/ mole ...... Equation 2

Adding equation 1 and 2 we get:

Helix = hairpin; delH⁰ = (- 199 +175) kJ/ mole = - 24 kJ/ mole

So; the corresponding enthalpy change from helix to hairpin is - 24 kJ/ mole