Unusually Conductive Organic–Inorganic Hybrid Nanostructures Derived from Bio-Inspired Mineralization of Peptide/Pi-Electron Assemblies

Abstract

Supramolecular materials derived from pi-conjugated peptidic macromolecules are well-established to selfassemble into 1D nanostructures. In the presence of KOH, which was used to more fully dissolve the peptide macromolecules prior to triggering the self-assembly by way of exposure to HCl vapor, we report here an unexpected mineralization of KCl as templated presumably by the glutamic acid residues that were present along the backbone of the peptide macromolecules. In order to decouple the peptidic side chains from the central pi-electron unit, three-carbon spacers were added between them on both sides. The assembled structures that resulted from the collective formation of β-sheets, π-orbital overlaps, and mineralization resulted in highly interconnected dendritic structures under suitable KOH concentrations. Electrical measurements indicated that when wellinterconnected, these dendritic structures maintained conductivities comparable to those of metals at around 1800 S/cm. About 50 mA current was measured for 0.5 V/37.5 μm. Varying the gate voltage in a transistor configuration had no effect on the current levels, indicating a conductive instead of a semiconducting pathway. Control experiments without the peptide, measurements of conductivity over time, and conductivity quenching by ammonia suggested the conductivity of these dendritic networks was derived from proton doping of the central π-electron units in a strong acid environment and was facilitated by closely spaced chromophores, as suggested in the literature, leading to facile π-electron transfer along the interconnected dendritic pathways. Our findings suggest that mineralization templated by appropriate amino acids combined with peptide/π-electron self-assembly can lead to highly conductive dendritic macrostructures as well as control of nanowire growth in specific directions.

Self-Assembling Hydrogel Structures for Neural Tissue Repair

“…π-stacking has been shown to have profound effects on the conductivity of self-assembled structure metal–organic frameworks, , we can therefore infer that conductive peptide packing will be affected by the AA sequence leading to changes in conductivity. This is further reinforced by Lee et al’s recent report of very high conductivity in a self-assembly system composed of a π-chromophore core flanked by an alkyl spacer and pentapeptide on both sides. Unexpected mineralization of KCl along the glutamic AA in HCl vapor deposition was obtained following KOH treatment, which is thought to have led to proton doping along with very strong packing and stability .…”

“…This is further reinforced by Lee et al’s recent report of very high conductivity in a self-assembly system composed of a π-chromophore core flanked by an alkyl spacer and pentapeptide on both sides. Unexpected mineralization of KCl along the glutamic AA in HCl vapor deposition was obtained following KOH treatment, which is thought to have led to proton doping along with very strong packing and stability . This method yielded conductivities as high as 1800 S cm –1 when incorporating alkyl spacers between the peptides and π-conjugation .…”

“…381 This method yielded conductivities as high as 1800 S cm −1 when incorporating alkyl spacers between the peptides and πconjugation. 381 Obtaining such conductivity values demonstrates the potential for the application of molecular selfassembly to form conductive networks. 4.2.…”

“…Unexpected mineralization of KCl along the glutamic AA in HCl vapor deposition was obtained following KOH treatment, which is thought to have led to proton doping along with very strong packing and stability . This method yielded conductivities as high as 1800 S cm –1 when incorporating alkyl spacers between the peptides and π-conjugation . Obtaining such conductivity values demonstrates the potential for the application of molecular self-assembly to form conductive networks.…”

Aqueous Self-Assembly of Peptide–Diketopyrrolopyrrole Conjugates with Variation of N-Alkyl Side Chain and π-Core Lengths

“…Collectively, the entire ensemble can participate in more generalized electrostatic interactions such as induced dipole/van der Waals/dispersion interactions within a supramolecular assembly. A range of π-electron moieties was installed within these triblock constructs ranging from linear oligothiophenes and oligophenylenes 14,17 to more 'two-dimensional' perylenediimide, 12 benzotrithiophene and porphyrin 18 groups. The emergent optoelectronic and electrical properties depend on the specific amino acids in the peptidic wings and on the installed π-electron groups.…”