Electronic Structures and Conductivity in Peptide Nanotubes

Abstract

Self-assembling cyclic D,L-peptide nanotubes are electronically insulating and possess wide band gaps (E(g) > 4 eV). Our ab initio electronic structure calculations indicate that the presence of aromatic rings in the side chain of peptide nanotubes significantly reduces the band gap. We investigate the conductivity of the modified peptide nanotubes through calculations of the electron tunneling probability. The electron tunneling probability through a molecule depends on the length of the molecule, L, as e-beta(E)L, where the tunneling beta(E)-factor is strongly energy-dependent. We have calculated beta(E) in three types of peptide nanotubes that have different sequences of amino acid residue, (L-Gln, D-Ala)(4), (L-Gln, D-Leu)(4) and (L-Gln, D-Phe)(4), using the complex band structure approach. We find large beta values near midgap, making these peptide nanotubes a poor tunneling conductor.

Photo-induced surface-enhanced Raman spectroscopy from a diphenylalanine peptide nanotube-metal nanoparticle template

“…S2 ) in resonance with the Raman laser excitation wavelength, resulting in surface-enhanced resonance Raman spectroscopy (SERRS). The sample was then irradiated for 5 minutes using light with an energy (4.8 eV) greater than the bandgap of the FF-PNTs ( E g ~ 4.6 eV) 39 – 41 . With the UV lamp off, Raman measurements were again performed and the process was repeated until the total irradiation time was 45 minutes.…”

“…Photogenerated electrons are thus transferred from the FF-PNTs to the Ag NPs as the two systems undergo charge equilibration 17 , 39 – 41 , 45 – 47 . To further understand the charge transfer process between FF-PNTs and Ag NPs, we have estimated the workfunction of FF-PNTs based on previously reported Kelvin probe force microscopy (KPFM) data 63 .…”

“…Self-assembly of organic semiconductor peptide-based materials has emerged as a new approach for the fabrication of SERS substrates, offering an alternative to more traditionally used semiconductor materials such as TiO 2 2 , 7 , 18 – 24 . Diphenylalanine peptide nanotubes (FF-PNTs) are particularly interesting due to their high thermal stability 25 – 32 , high stiffness and elastic modulus 31 , 32 , ease of preparation 25 – 28 , biocompatibility 33 , piezoelectricity 34 , ability to bind with metal ion residues at specific locations 35 – 38 , and wide bandgap ( E g ~ 4.6 eV) 39 – 41 . FF-PNTs are almost transparent to visible (380–750 nm) and near-UV (300–380 nm) light, and they strongly absorb light in the middle-UV spectral region (200–300 nm) 41 – 44 , making them suitable for a variety of light harvesting and catalytic applications 45 – 47 .…”

“…FF-PNTs have been shown to enhance the photo luminescent properties of photosensitizer molecules via a cascaded energy transfer process 44 and to mediate the transfer the energy from photo-excited molecules or chromophores to catalytic centers 44 , 48 . Such charge transfer processes in FF-PNTs have been reported to be strongly affected by structural changes, heat, and UV irridiation 39 – 41 . The described properties make FF-PNTs an attractive alternative material to more traditional semiconductors such as TiO 2 or CNTs for SERS-based applications 9 , 10 , 14 – 16 .…”

Evaluating the Conductive Properties of Melanin-Producing Fungus, Curvularia lunata, after Copper Doping

“…The roles that melanins play in organisms are still under investigation, including metal chelation (Meredith and Sarna 2006), radiation and radionuclide protection (Kunwar et al 2012), photoreception and photoconductivity (Jeffery et al 1994;Capozzi et al 2006), tensile strength (Roy and Rhim 2019), optical tunability (Wang et al 2018), supercapacitor properties (Kumar et al 2016), and electrical conductance (Jastrzebska et al 1996;Mostert, Powell, Pratt, et al 2012;Mostert, Powel, Gentle, et al 2012;McGinness et al 1974) (Figure 2). (Ashkenasy et al 2006;Takahashi et al 2007;Waleed et al 2010;Ing et al 2018). However, melanin is unique as it has tunable conductive properties primarily controlled by its hydration state (Jastrzebska et al 1996, Wunsche et al 2015 and the method of polymerization (Solano 2014;Ambrico et al 2015).…”