Ferrocene-Peptide Complexes

Ferrocene has a suitable distance between Cp (cyclopentadienyl) ligands for the spacer of anti-parallel 3-sheet (Fig. 3.36(a)). The freely rotatable bond is appropriate for adjusting the distance between two peptide chains In this section, the combination of non-natural amino acid with natural peptide is described. 

Proposed conformational change of [Z-His-NHC5H4]Fe(C5H4CO-Asp-NH-r-Bu)] by deprotonation. In the sheet structure, two inter-chain NH - 0=C hydrogen bonds exist (left). When the carboxyl group releases a proton, ImNH--O C is formed instead of terminal NH - O C hydrogen bond to form a turn structure (right). 

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Fig. 3.36 (a) Schematic drawing ferrocene-peptide complex. The peptide chains are oriented in the... 

Mori M (2005) Synthesis and Reactivity of Zirconium-Silene Complexes. 10 41-62 Moriuchi T, Hirao T (2006) Ferrocene-Peptide Bioconjugates. 17 143-175 Morokuma K, see Musaev G (2005) 12 1-30... 

R681 T. Okamura and K. Ueyama, Synthesis and Properties of New Peptide Complex Having Ferrocene Structure as Main Chain , Kobunshi Kako, 2000, 49, 261... 

Transition Metal Complexes of Ferrocene-Peptide Bioconjugates. 160... 

The 2 1 irani-palladium complex 16 is formed by the complexation of the ferrocene-peptide bioconjugate 12 bearing the one dipeptide chain of the homochiral seqnence (-L-Ala-L-Pro-NH-2-Py) with 0.5 equiv. of PdCl2(MeCN)2 [35]. 

The ferrocene-peptide bioconjugate ferrocene 14 forms the 4 1 palladium complex 18 with 0.25 equiv. of [Pd(MeCN)4](BF4)2 [36]. The crystal structure of 18 shows that the four chirality-organized ferrocene-dipeptide conjugates are assembled around a palladium center in the same direction to form a chiral pocket surrounded by the dipeptide chains, wherein one BF4 counter anion is accommodated (Fig. 4.12). 

The ubiquitous electrochemical behavior of ferrocene and its relative chemical stability have made this organometallic complex a useful group for the preparation of redox-active devices. The incorporation of ferrocene-modified amino acids into larger polypeptide structures can therefore lead to electrochemically active de novo designed proteins. In addition, the attachment of ferrocene derivatives to peptides make them electroactive and eligible to electrochemical detection. Hence, it is not surprising that the first synthesis of a ferrocene-modified amino acid dates back to the 1950s. 

In contrast to the amino acid, peptide, and protein conjugates, where a number of different organometallic complexes were used for labeling, DNA derivatives are by and large limited to ferrocene. This is very likely due to the attractive electrochemical properties of ferrocene. Indeed, electrochemical DNA sensors are covered in more detail in Section 1.31.5.2. Two recent reviews cover the ferrocene conjugates with nucleobases, nucleosides and nucleotides,... 

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