Out of the following, which type of interaction is responsible for the stabilisation of $$\alpha$$-helix structure of proteins?

We need to identify the type of interaction responsible for stabilising the $$\alpha$$-helix structure of proteins.

The $$\alpha$$-helix is a common secondary structure in proteins. In an $$\alpha$$-helix, the polypeptide chain coils in a right-handed helical fashion. This structure is stabilised by intramolecular hydrogen bonds.

Specifically, the hydrogen bonds form between the $$C=O$$ group of one amino acid residue and the $$N-H$$ group of the amino acid residue that is four positions ahead in the chain. Each hydrogen bond has the form $$N-H \cdots O=C$$.

Covalent bonds hold the primary structure (peptide bonds between amino acids). Ionic bonding and van der Waals forces contribute to tertiary and quaternary structures but are not the primary stabilising force for the $$\alpha$$-helix.

Hence, the correct answer is Option C.