Hydrogen bond
Hydrogen bonds can vary in strength from weak (1–2 kJ mol) to strong (161.5 kJ mol in the ion ). Typical enthalpies in vapor include:
Protein secondary structure
Secondary structure is defined by hydrogen bonding, so the exact definition of a hydrogen bond is critical. The standard hydrogen-bond definition for secondary structure is that of DSSP, which is a purely electrostatic model. It assigns charges of ±"q" ≈ 0.42"e" to the carbonyl carbon and oxygen, respectively, and charges of ±"q" ≈ 0.20"e" to the amide hydrogen and nitrogen, respectively. The electrostatic energy is