Ferrocenyl triazole amino acid (L-leucine methyl ester (2, 5), L-phenylalanine methyl ester (3, 7), L-alanine methyl ester (4), L-valine tert-butyl ester (6), L-proline methyl ester (8)) and peptide derivatives ([Leu 5 ]-enkephalin (9, 10)) were prepared by Cu(I)-catalyzed [3+2] cycloaddition of azidoferrocene and 1,1′-diazidoferrocene with the corresponding alkyne-modified amino acids and peptide. A purity of >95% for the peptide conjugates was confirmed by HPLC. All new compounds were comprehensively characterized by elemental analysis, mass spectrometry (FAB and ESI-MS, including high-resolution MS), IR, and multinuclear 1D and 2D NMR spectroscopy. Solution structures were studied by circular dichroism (CD) and NMR spectroscopy, showing that compounds 5, 6, and 7 form intramolecular hydrogen bonds (IHBs) in noncoordinating solvents. Electrochemical studies show reversible processes of the redox couple Fc 0 /Fc + (Fc ) ferrocenyl) for compounds 2-9, whereas compound 10 exhibits an irreversible oxidation. A good correlation between the diffusion coefficients as determined by electrochemical methods and the molecular weight was established.

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The potassium salt of the Schiff base derived from o-vanillin and taurine is involved in enol-imine (I) and keto-amine (II) tautomerism. Both tautomeric forms coexist in the crystal and they are stabilized by strong O–H⋯N and O⋯H–N intramolecular hydrogen bonds.

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