***Please answer Question 3***

1. Calculate the Coulombic (ionic) interaction energy between atoms for the C=O H-N hydrogen bond in a peptide at a distance of 1.5 in units of kJ/mol. Assume that the partial charge on O is 0.434, the partial charge on H is +0.417 and the permittivity of the protein environment is 6.
2. The dipole moment of an individual peptide group is approximately 3.46 D. Assuming that the dipoles line up linearly estimate the energy of interaction (in kJ.mol) of the hydrogen bond in Q1 using a dipole-dipole model.
3. Proteins frequently bind metals such as Zn²⁺.
   1. Compare the energy of interaction of a Zn²⁺ ion with the peptide group in Q2 through ion-dipole interactions and through ion-induced dipole at a distance of 1.5. Take the polarizability volume of the peptide to be 2.00 x10^-30 m³. Which is stronger at this distance?
4. 2. Would your answer change if the distance between the groups were doubled, and why or why not?