Mussel adhesion to mineral surfaces is widely attributed to 3,4-dihydroxyphenylalanine (Dopa) functionalities in the mussel foot proteins (mfps). Several mfps, however, show a broad range (30%-100%) of tyrosine (Tyr) to Dopa conversion suggesting that Dopa is not the only desirable outcome for adhesion. Here, a partial recombinant construct of mussel foot protein-1 (rmfp-1) and short decapeptide dimers with and without Dopa are used and both their cohesive and adhesive properties on mica are assessed using a surface forces apparatus. Our results demonstrate that at low pH, both the unmodified and Dopa-containing rmfp-1s show similar energies for adhesion to mica and self-self-interaction. Cohesion between two Dopa-containing rmfp-1 surfaces can be doubled by Fe³⁺ chelation, but remains unchanged with unmodified rmfp-1. At the same low pH, the Dopa-modified short decapeptide dimer did not show any change in cohesive interactions even with Fe³⁺. The results suggest that the most probable intermolecular interactions are those arising from electrostatic (i.e., cation-π) and hydrophobic interactions. It is also shown that Dopa in a peptide sequence does not by itself mediate Fe³⁺ bridging interactions between peptide films: peptide length is a crucial enabling factor.