Oligomers of Ferrocene Amino Acid

The dimeric complex 39 exhibits individual Fe(III)/ Fe(II) redox couples at +0.47 and +0.60 V v. SCE in CH2CI2. The averaged value (+0.54 V) is close to that of the corresponding monomeric complex 38 (+0.51 V). These results are explained by the electronic effect as reported in the literature. The trimer 40 exhibits two redox couples at +0.51 and +0.67 V in a similar condition. The positive peak suggests the presence of significant electronic interaction between two ferrocene units (center and C-terminus). This result indicates the possibility of constructing an expanded conjugation system of polymeric ferrocene amino acid and the development of the conductive devices by partial oxidation. 

Unfortunately, 39 and 40 show poor solubility in less polar solvents. Thus we could not determine their solution structure by NMR. In a polar solvent that is (CD3)2S0, the hydrogen bonds are broken or competing with solvation. The conformation was found to be a tum-like structure. 

The unique and appealing conformations led us to propose a unique structure for a novel organometallic non-natural polypeptide with skeletal ferrocenes as shown in Fig. 3.35(a). When the polymer is dissolved in polar solvent, the secondary structure is probably changed to a turn or random structure (Fig. 3.35(b)). The folding structure reminds us of secondary structures such as the a-helix and P-sheet of polypeptides, and the conformational change calls to mind the helix-coil transition of natural peptides. 

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