Melanocortin receptor-specific peptide combinatorial libraries for forming metallopeptides and metallopeptide combinatorial libraries are provided for use in biological, pharmaceutical and related applications. The combinatorial libraries are constructed of peptides constructed from naturally occurring amino acids, stereoisomers and modifications of such amino acids, non-protein amino acids, post-translationally modified amino acids, enzymatically modified amino acids, or constructs or structures designed to mimic amino acids, in which the peptides are conformationally fixed on complexation of a metal ion-binding portion thereof with a metal ion.