Changes in the hydrogen bonding pattern in ferrocene peptides

Disubstituted peptide ferrocenes conjugates were prepared from ferrocenedicarboxylic acid (Fc(OH)2) and glycineethylester. After conversion of the resulting ester Fc(Gly-OEt)21 into the corresponding acid Fc(Gly-OH)22 by ester hydrolysis, significant structural changes take place in the way the molecules interact with each other. Complex 1 adopts a 1,3′-conformation showing extensive intermolecular H-bonding forming 1-D chains, whereas complex 2 displays a compact 1,2′-conformation in which the NH on one strand engage in strong intramolecular cross-strand H-bonding involving the amide CO on the opposite strand. Additional intermolecular H-bonding in 2 allows the formation of a 2-D net. In essence, ester-deprotection allows us to switch the ferrocene conformation and the H-bonding pattern.