The evolution of the coronavirus from SARS-COV to nCOV-2019 has reshaped the interfacial hydrogen bonds with ACE2. G502 in nCOV-2019 has a persistent H-bond with residue K353 on ACE2. This residue was G488 in SARS-COV, which also makes the H-bond with K353 on ACE2. Q493 in nCOV-2019 makes H-bond with E35 and another H-bond with K31 on ACE2. This residue was an N479 in SARS-COV, which only makes one H-bond with K31 on ACE2. An important mutation from SARS-COV to nCOV-2019 is residue Q498, which was Y484 in SARS-COV. Q498 makes two H-bonds with residues D38 and K353 on ACE2, whereas Y484 in SARS-COV does not make any H-bonds. Importantly, a salt bridge between K417 and D30 in the nCOV-2019/ACE2 complex contributes to the total binding energy by −12.34 ± 0.23 kcal/mol. This residue is V404 in SARS-COV which is not able to make any salt-bridge and does not make H-bond with ACE2. Gao et al.27 used a FEP approach and showed that mutation V404 to K417 lowers the binding energy of nCOV-2019 RBD to ACE2 by −2.2 ± 0.9 kcal/mol. A salt bridge between R426 on RBD and E329 on ACE2 stabilizes the complex in SARS-COV/ACE2. This residue is N439 in nCOV-2019 which is unable to make salt-bridge with ACE2 residue E329. One of the most observed mutations in nCOV-2019 according to the GISAID database is N439K which recovers some of the electrostatic interactions with ACE2 at this position. Y436 in SARS-COV and Y449 in nCOV-2019 both make H-bonds with D38 on ACE2. The unchanged T486 in SARS-COV corresponds to T500 in nCOV-2019, both of which make consistent H-bonds with ACE2 residue D355.