Bond energy

Interactions that hold molecules together:

1. Covalent bonds (共價鍵)
   (Sharing electrons withina molecule): ~ 100 kcal/mol (Hard to break)

2.Noncovalent bonds
  (Weak interactions between molecules): < 5 kcal/mol (Easily broken)
     a) Ionic bonds (Salt bridge):
          Weak in water (< 3 kcal/mol) but can be very strong within the core of macromolecule
          such as proteins.
     b)  Hydrogen bonds: (0.5 – 3 kcal/mol)
               C-O- ::: +H-N        C-O- ::: +H-O       N- ::: +H-N
     c)  Hydrophobic interaction:
               Nonpolar molecules tends to aggregate to minimize their exposure to water
              (van der Waals forces)
              ( - CH2 -, -CH3, Aliphatic group )
     d)  Hydrophilic molecules:
              Polar molecules like to interactioin with water.
              (-CO, -SH, -NH, PO, N etc)















ref :

Methyl       :  - CH3
Ethyl          :  - CH2 -
Hydroxyl    :  - OH
Carboxyl    : - CO2 –
Amino        : - NH2
Carbony    :  - CO -
Sulfhydryl  :  - SH
Phosphate : - PO4 (3-)
Amide        :  - NH -
Carboxy     : - COOH

Peptide bond: - NH – CO-


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