Adsorption energies of single amino acids and common capping agents on Au {111} surfaces have been computed in aqueous solution using all-atom simulations with two different force fields which include accurate Lennard-Jones parameters for fcc metals (pH=7). Highest adsorption energies are found for aromatic amino acids (Trp, Tyr, Phe, His) in the 30 kcal/mol to 10 kcal/mol range. They are followed by several polar amino acids (such as Gln, Glu, Asp, Asn, Arg) with ~10 kcal/mol adsorption energy, and the least affinity is seen for aliphatic hydrophobic amino acids. For cysteine, it is difficult to estimate the total binding energy due to reaction with the surface (the non-covalent binding contribution amounts to ~5 kcal/mol, before reaction with the Au surface). Our results are consistent with experimental findings for small peptides and ab-initio calculations, although comparison to experiment has not yet been possible. Adsorption energies of capping agents on the Au {111} surface will also be presented for comparison relative to amino acids/peptides. The adsorption energies for single molecules can be regarded as upper limits since the availability of the amino acids for binding to the metal surface is typically decreased within a larger peptide.