Phase transitions in organic and inorganic materials are well-studied classical phenomena, where a change in the crystal space group symmetry induces a wide variation of physical properties, permitted by the crystalline symmetry in each phase. Here we observe a conformational induced transition in bioinspired peptide nanotubes (PNTs). We found that the PNTs change their original molecular assembly from a linear peptide conformation to a cyclic one, followed by a change of the nanocrystalline structure from a noncentrosymmetric hexagonal space group to a centrosymmetric orthorhombic space group. The observed transition is irreversible and induces a profound variation in the PNTs properties, from the microscopic to the macroscopic level. In this context, we follow the unique changes in the molecular, morphological, piezoelectric, second harmonic generation, and wettability properties of the PNTs.

Diphenylalanine (FF) peptide nanotubes (PNTs) present a unique class of selfassembled functional biomaterials owing to a wide range of useful properties including nanostructural variability, mechanical rigidity, and chemical stability. In addition, a strong piezoelectric activity has been recently 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 gradual decrease of polarization with increasing temperature accompanied by irreversible phase transition into another crystalline phase at about 140-150 ºC. The results are corroborated by the molecular dynamic simulations predicting order-disorder phase transition into centrosymmetric (possibly, orthorhombic) phase with antiparallel polarization orientation in neighboring FF rings. Partial piezoresponse hysteresis indicates incomplete polarization switching due to high coercive field in FF PNTs.

Synthetic peptide monomers can self-assemble into PNM such as nanotubes, nanospheres, hydrogels, etc. which represent a novel class of nanomaterials. Molecular recognition processes lead to the formation of supramolecular PNM ensembles containing crystalline building blocks. Such low-dimensional highly ordered regions create a new physical situation and provide unique physical properties based on electron-hole QC phenomena. In the case of asymmetrical crystalline structure, basic physical phenomena such as linear electro-optic, piezoelectric, and nonlinear optical effects, described by tensors of the odd rank, should be explored. Some of the PNM crystalline structures permit the existence of spontaneous electrical polarization and observation of ferroelectricity. The PNM crystalline arrangement creates highly porous nanotubes when various residues are packed into structural network with specific wettability and electrochemical properties. We report in this review on a wide research of PNM intrinsic physical properties, their electronic and optical properties related to QC effect, unique SHG, piezoelectricity and ferroelectric spontaneous polarization observed in PNT due to their asymmetric structure. We also describe PNM wettability phenomenon based on their nanoporous structure and its influence on electrochemical properties in PNM. The new bottom-up large scale technology of PNT physical vapor deposition and patterning combined with found physical effects at nanoscale, developed by us, opens the avenue for emerging nanotechnology applications of PNM in novel fields of nanophotonics, nanopiezotronics and energy storage devices.

Many peptide nanostructures, self-assembled from chemically synthesized biomolecules, have drawn much attention in the fi eld of nanotechnology due to their physical, chemical, and biological properties, which make them promising candidates for applications in bionanomedicine, [ 1 ] bionanotechnology, [ 2,3 ] electronics, [ 4,5 ] optics, [ 6 ] energy storage, [ 7,8 ] etc. Some of these properties, such as ferro-and piezoelectricity observed in diphenylalanine nanotubes (FF-PNT) [ 9 ] are directly related to the nanocrystalline structural asymmetry of the elementary building blocks comprising these supramolecular materials. [ 6,10 ] One basic physical effect that depends on both the crystalline symmetry and the electronic properties of dielectric materials is second harmonic generation (SHG). SHG is observed only in crystals with no center of symmetry [ 11 ] and is related to ferroelectric phenomena together with linear electrooptical and piezoelectric effects. Ferroelectric effects have been observed in many biological materials such as plants, animals, and human tissues (amino acids, pineal gland of brain, skin, tendon, etc.). [ 12 ] Today, the SHG effect is also exploited in optical microscopy, especially in medical and biological research. [ 13 ] It allows the detection of two-photon emission from biomaterials and biopolymers [ 14 ] lacking a center of symmetry. The effect has been used with quantitative metrics for diagnosing a wide range of diseases. [ 15 ] Recently, second-order responses have also been found in bioinspired aromatic FF-PNT with hexagonal space group P6 1 using nonlinear optical microscopy. [ 16 ] Both the elementary crystalline symmetry and the electronic structure of bioinspired peptide nanostructures can be significantly changed by deep reconstruction process, such as phase transformation at a nanoscale level, which results in the disappearance of an SHG response. [ 17 ] Another method to modulate these fundamental properties is to use different solvents, [18][19][20][21] which strongly infl uence the self-assembly process and defi ne peptide nanostructures' morphologies. Modifi cation of the physical properties in peptide nanomaterials is a new way to fabricate basic nanoscale units for future bottom-up nanotechnologies. [ 6 ] Bioinspired peptide nanostructures, much like other organic nanostructures, [ 22,23 ] have ultra-small sizes and are easily produced by a rapid self-assembly fabrication process. All these properties make them favorable for implementation in diverse applications, and especially in biophotonics devices.In this work, we have studied the SHG effect in bioorganic peptide nanostructures of different morphologies and symmetries, such as nanotubes, nanofi bers, nanobelts, and nanospheres. These nanostructures were self-assembled in different solvents from peptide precursors with a variable number of A nonlinear optical effect of a second harmonic generation (SHG) was fi rst observed in quartz and then found in many inorganic materials that have an asymmetric crystalline s...

The mechanism of dc-electric-field-induced second-harmonic generation ͑EISH͒ was studied at the buried Si͑111͒-SiO 2 interface in transmission through a planar Si-SiO 2 -Cr MOS structure. The second-harmonic contribution of the field-induced quadratic polarization generated in the space-charge region is determined. The role of the spatial distribution of the dc electric field inside the silicon space-charge region is demonstrated, as well as the influence of the oxide thickness. We have developed a phenomenological model of the EISH taking into account the interference between field-dependent and field-independent contributions to the nonlinear polarization ͑nonlinear interference͒ as well as the retardation of the EISH wave. We show that, due to these interference effects, the minima of the EISH curves do not coincide with the flatband voltage.