What do you think are the possible interactions between glycine molecules?

There are three types of bonding among covalent molecules, namely:
Induced dipole moments (due to momentary fluctuations of electrons in the molecule)
Permanent dipole moments (due to electronegative atoms attached to less electronegative atoms)
Hydrogen bonding (due to the moments induced to a hydrogen atom when the latter is attached to one of the three most electronegative atoms, that is N, O and Cl)

What do you think are the possible forces of attraction?

Unknown008 has answered your question. All the bonds in a glycine molecule are covalent bonds.