Raman Spectra of Diphenylalanine Microtubes: Polarisation and Temperature Effects (original) (raw)
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Pyroelectric effect and polarization instability in self-assembled diphenylalanine microtubes
Applied Physics Letters, 2016
The natural ability of peptides and proteins to self-assemble into elongated fibrils is associated with several neurogenerative diseases. Diphenylalanine (FF) tubular structures that have the same structural motif as in Ab-amyloid peptide (involved in Alzheimer's disease) are shown to possess remarkable physical properties ranging from piezoelectricity to electrochemical activities. In this work, we also discover a significant pyroelectric activity and measure the temperature dependence of the pyroelectric coefficient in the temperature range of 20 100 C. Pyroelectric activity decreases with temperature contrary to most ferroelectric materials and significant relaxation of pyrocurrent is observed on cooling after heating above 50 C. This unusual behavior is assigned to the temperature-induced disorder of water molecules inside the nanochannels. Pyroelectric coefficient and current and voltage figures of merit are estimated and future applications of pyroelectric peptide nanostructures in biomedical applications are outlined. Published by AIP Publishing.
Structural Transition-Induced Raman Enhancement in Bioinspired Diphenylalanine Peptide Nanotubes
Semiconducting materials are increasingly proposed as alternatives to noble metal nanomaterials to enhance Raman scattering. We demonstrate that bioinspired semiconducting diphenylalanine peptide nanotubes annealed through a reported structural transition can support Raman detection of 10 −7 M concentrations for a range of molecules including mononucleotides. The enhancement is attributed to the introduction of electronic states below the conduction band that facilitate charge transfer to the analyte molecule. These results show that organic semiconductor-based materials can serve as platforms for enhanced Raman scattering for chemical sensing. As the sensor is metal-free, the enhancement is achieved without the introduction of electromagnetic surface-enhanced Raman spectroscopy.
Temperature-driven phase transformation in self-assembled diphenylalanine peptide nanotubes
Journal of Physics D: Applied Physics, 2010
Diphenylalanine (FF) peptide nanotubes (PNTs) represent a unique class of self-assembled functional biomaterials owing to a wide range of useful properties including nanostructural variability, mechanical rigidity and chemical stability. In addition, strong piezoelectric activity has recently been observed paving the way to their use as nanoscale sensors and actuators. In this work, we fabricated both horizontal and vertical FF PNTs and examined their optical second harmonic generation and local piezoresponse as a function of temperature. The measurements show a gradual decrease in polarization with increasing temperature accompanied by an irreversible phase transition into another crystalline phase at about 140-150 • C. The results are corroborated by the molecular dynamic simulations predicting an order-disorder phase transition into a centrosymmetric (possibly, orthorhombic) phase with antiparallel polarization orientation in neighbouring FF rings. Partial piezoresponse hysteresis indicates incomplete polarization switching due to the high coercive field in FF PNTs.
Probing nonlinear optical coefficients in self-assembled peptide nanotubes
Self-assembled L,L-diphenylalanine (FF) peptide micro/nanotubes represent a class of biomimetic materials with a non- centrosymmetric crystal structure and strong piezoelectricity. The peptide nanotubes synthesized by liquid phase method yield tube lengths in the hundreds of micron range, inner diameters in the few hundred nanometer range, and outer diameters in the 5-15 μm range. Second harmonic generation (SHG) polarimetry from individual self-assembled FF nanotubes is used to obtain the nonlinear (NLO) optical coefficients as a function of the tube diameter and thermal treatment. The ratio of the shear to the longitudinal component (d15/d33) of the NLO coefficient increases with the diameter of the tubes. One of the transverse components of the nonlinear coefficient is found to be negative, and its magnitude with respect to the longitudinal component increases with the tube diameter. Thermal treatment of individual FF tubes has a similar effect as increasing the diameter of the tubes in SHG polarimetry. Concurrent Raman scattering measurements from individual FF tubes show a distinct change in the low frequency (100 cm-1) region with the diameter of the tubes, reflecting subtle effects of water.
Water‑driven stabilization of diphenylalanine nanotube structures
L,L-diphenylalanine has been employed in the formation of self-assembled peptide nanotubes with great potential for the development of biosensors, molecular car- riers, and optoelectronic devices. They are usually formed in an aqueous solution, and it is well known that water remains con ned inside the structure. However, the role played by water in the overall stability of the nanotube is still unknown at the microscopic level. In this work, we investigate the stability of peptide structures after assem- bly due to the interaction with water molecules. We dem- onstrate, using molecular dynamics based on density func- tional tight-binding techniques, that water is fundamental in keeping the nanotube structure. It interacts with the nanotube walls as well as with other water molecules via hydrogen bonds keeping the structure stable. We identify and quantify the interaction between water and the relevant groups, and, upon increasing the solvent concentration, we show there is a transition region where there is a competi- tion between the formation of water/water hydrogen bonds, and steric effects.
Langmuir, 2006
The diphenylalanine peptide, the core recognition motif of the -amyloid polypeptide, efficiently self-assembles into discrete, well-ordered nanotubes. Here, we describe the notable thermal and chemical stability of these tubular structures both in aqueous solution and under dry conditions. Scanning and transmission electron microscopy (SEM and TEM) as well as atomic force microscopy (AFM) revealed the stability of the nanotubes in aqueous solution at temperatures above the boiling point of water upon autoclave treatment. The nanotubes preserved their secondary structure at temperatures up to 90°C, as shown by circular dichroism (CD) spectra. Cold field emission gun (CFEG) high-resolution scanning electron microscope (HRSEM) and thermogravimetric analysis (TGA) of the peptide nanotubes after dry heat revealed durability at higher temperature. It was shown that the thermal stability of diphenylalanine peptide nanotubes is significantly higher than that of a nonassembling dipeptide, dialanine. In addition to thermal stability, the peptide nanotubes were chemically stable in organic solvents such as ethanol, methanol, 2-propanol, acetone, and acetonitrile, as shown by SEM analysis. Moreover, the acetone environment enabled AFM imaging of the nanotubes in solution. The significant thermal and chemical stability of the peptide nanotubes demonstrated here points toward their possible use in conventional microelectronic and microelectromechanics processes and fabrication into functional nanotechnological devices.
Low temperature Raman study of dimethylacetylene
Journal of Molecular Structure, 1999
On the basis of low temperature Raman spectra from 10 to 170 K of polycrystalline dimethylacetylene (DMA), two stable and two metastable crystalline phases were detected. One can be identified with a previously reported metastable phase [N. Prasad, R. Kopelman, Chem. Phys. Lett. 20 (1973) 513-516] and can be observed from 10 to 75 K, when it transforms into another metastable phase. This one, in turn, transforms at 115 K into the stable C2/m phase. To enable better assignment of the observed internal modes, especially those involving methyl group, matrix isolation of DMA at 10 K was performed. In the recorded Raman spectra at matrix ratios of 1:100, 1:50 and 1:25, the strongest bands observed are of a 1s symmetry. Besides them, we were able to detect bands at 218 and 1040 cm Ϫ1 of e 1d symmetry, which are only infrared active when no intermolecular interactions are present. The Raman spectrum of DMA as a thin solid film was also recorded. The bands' positions are found not to deviate significantly in comparison with the spectra of the matrix isolated sample, and thanks to the better signal to noise ratio, several additional bands were detected. Among those is the n 8 at 1147 cm Ϫ1 of a 4s symmetry. ᭧