Detection of helical water flows in sub-nanometer channels.

Nanoscale flows of liquids can be revealed in various biological processes and underlie a wide range of nanofluidic applications. Though the integral characteristics of these systems, such as permeability and effective diffusion coefficient, can be measured in experiments, the behaviour of the flows within nanochannels is still a matter of speculation. Herein, we used a combination of quadrupolar solid-state NMR spectroscopy, computer simulation, and dynamic vapour sorption measurements to analyse water diffusion inside peptide nanochannels. We detected a helical water flow coexisting with a conventional axial flow that are independent of each other, immiscible, and associated with diffusion coefficients that may differ up to 3 orders of magnitude. The trajectory of the helical flow is dictated by the screw-like distribution of ionic groups within the channel walls, while its flux is governed by external water vapour pressure. Similar flows may occur in other types of nanochannels containing helicoidally distributed ionic groups and be exploited in various nanofluidic lab-on-a-chip devices.

Piezoactive Bioorganic Diphenylalanine Films: Mechanism of Phase Formation.

Self-organized peptides are unique materials with various applications in biology, medicine, and nanotechnology. Many of these applications require fabrication of homogeneous thin films having high piezoelectric effect and sufficiently low roughness. Recently, a facile method for the controlled deposition of flat solid films of the most studied peptide, diphenylalanine (FF), has been proposed, which is based on the crystallization of FF in the amorphous phase under the action of water vapor. This method is very advantageous compared with crystallization from a liquid phase reported previously. Here, we thoroughly investigate the mechanism of solid-state transformation from the amorphous to crystalline phase. The study revealed that the process proceeds in two distinct stages, maintaining clamped condition of self-assembling building blocks that preserve the films' morphology and high piezoelectric activity. We emphasize the critical role of water diffusion that governs two-dimensional growth of crystalline domains in FF films, merging in very dense, flat, and homogeneous films. These findings open a wide perspective for using this methodology for the direct fabrication of biofilms from the amorphous phase. We thus expect the application of these films to various nanotechnological applications of self-assembled structures.

Triboelectric Generator Based on Oriented Self-Assembled Peptide Microbelts.

Along with piezoelectric nanogenerators, triboelectric nanogenerators (TENGs) collecting energy from mechanical vibrations proved to be simple, low-cost, and efficient sources of electricity for various applications. In view of possible biomedical applications, the search for TENGs made of biomolecular and biocompatible materials is demanding. Diphenylalanine (FF) microstructures are promising for these applications due to their unique characteristics and ability to form various morphologies (microribbons, spherical vesicles, fibrils, micro- and nanotubes, nanorods, etc.). In this work, we developed a contact-separate mode TENG based on arrays of oriented FF microbelts deposited by dip-coating technique and studied their performance under various temperature treatments. We show that these TENGs outperform piezoelectric nanogenerators based on FF microbelts in terms of short-circuit current (ISC), open-circuit voltage (VOC), and output power. It was found that bound water captured in FF nanochannels mainly affects VOC, whereas mobile water increases ISC. We also found that the cyclization of FF molecules increases the performance of TENG likely due to an increase in surface energy and surface flattening.

Modeling of Self-Assembled Peptide Nanotubes and Determination of Their Chirality Sign Based on Dipole Moment Calculations.

The chirality quantification is of great importance in structural biology, where the differences in proteins twisting can provide essentially different physiological effects. However, this aspect of the chirality is still poorly studied for helix-like supramolecular structures. In this work, a method for chirality quantification based on the calculation of scalar triple products of dipole moments is suggested. As a model structure, self-assembled nanotubes of diphenylalanine (FF) made of L- and D-enantiomers were considered. The dipole moments of FF molecules were calculated using semi-empirical quantum-chemical method PM3 and the Amber force field method. The obtained results do not depend on the used simulation and calculation method, and show that the D-FF nanotubes are twisted tighter than L-FF. Moreover, the type of chirality of the helix-like nanotube is opposite to that of the initial individual molecule that is in line with the chirality alternation rule general for different levels of hierarchical organization of molecular systems. The proposed method can be applied to study other helix-like supramolecular structures.

Nanoscale Piezoelectric Properties and Phase Separation in Pure and La-Doped BiFeO3 Films Prepared by Sol-Gel Method.

Pure BiFeO3 (BFO) and doped Bi0.9La0.1FeO3 (BLFO) thin films were prepared on Pt/TiO2/SiO2/Si substrates by a modified sol-gel technique using a separate hydrolysis procedure. The effects of final crystallization temperature and La doping on the phase structure, film morphology, and nanoscale piezoelectric properties were investigated. La doping and higher crystallization temperature lead to an increase in the grain size and preferred (102) texture of the films. Simultaneously, a decrease in the average effective piezoelectric coefficient (about 2 times in La-doped films) and an increase in the area of surface non-polar phase (up to 60%) are observed. Phase separation on the films' surface is attributed to either a second phase or to a non-polar perovskite phase at the surface. As compared with undoped BFO, La-doping leads to an increase in the average grain size and self-polarization that is important for future piezoelectric applications. It is shown that piezoelectric activity is directly related to the films' microstructructure, thus emphasizing the role of annealing conditions and La-doping that is frequently used to decrease the leakage current in BFO-based materials.

Molecular modeling and computational study of the chiral-dependent structures and properties of the self-assembling diphenylalanine peptide nanotubes, containing water molecules.

DFT (VASP) and semi-empirical (HyperChem) calculations for the L- and D-chiral diphenylalanine (L-FF and D-FF) nanotube (PNT) structures, empty and filled with water/ice clusters, are presented and analyzed. The results obtained show that after optimization, the dipole moment and polarization of both chiral type L-FF and D-FF PNT and embedded water/ice cluster are enhanced; the water/ice cluster acquire the helix-like structure similar as L-FF and D-FF PNT. Ferroelectric properties of tubular water/ice helix-like-cluster obtained after optimization inside L-FF and D-FF PNT and total L-FF and D-FF PNT with embedded water/ice cluster are discussed.

Structures and Properties of the Self-Assembling Diphenylalanine Peptide Nanotubes Containing Water Molecules: Modeling and Data Analysis.

The structures and properties of the diphenylalanine (FF) peptide nanotubes (PNTs), both L-chiral and D-chiral (L-FF and D-FF) and empty and filled with water/ice clusters, are presented and analyzed. DFT (VASP) and semi-empirical calculations (HyperChem) to study these structural and physical properties of PNTs (including ferroelectric) were used. The results obtained show that after optimization the dipole moment and polarization of both chiral type L-FF and D-FF PNT and embedded water/ice cluster are enhanced; the water/ice cluster acquire the helix-like structure similar as L-FF and D-FF PNT. Ferroelectric properties of tubular water/ice helix-like cluster, obtained after optimization inside L-FF and D-FF PNT, as well of the total L-FF and D-FF PNT with embedded water/ice cluster, are discussed.

Efficient Water Self-Diffusion in Diphenylalanine Peptide Nanotubes.

Nanotubes of self-assembled dipeptides exemplified by diphenylalanine (FF) demonstrate a wide range of useful functional properties, such as high Young's moduli, strong photoluminescence, remarkable piezoelectricity and pyroelectricity, optical waveguiding, etc., and became the object of intensive research due to their ability to combine electronic and biological functions in the same material. Two types of nanoconfined water molecules (bound water directly interacting with the peptide backbone and free water located inside nanochannels) are known to play a key role in the self-assembly of FF. Bound water provides its structural integrity, whereas movable free water influences its functional response. However, the intrinsic mechanism of water motion in FF nanotubes remained elusive. In this work, we study the sorption properties of FF nanotubes directly considering them as a microporous material and analyze the free water self-diffusion at different temperatures. We found a change in the regime of free water diffusion, which is attributed to water cluster size in the nanochannels. Small clusters of less than five molecules per unit cell exhibit ballistic diffusion, whereas, for larger clusters, Fickian diffusion occurs. External conditions of around 40% relative humidity at 30 °C enable the formation of such large clusters, for which the diffusion coefficient reaches 1.3 × 10-10 m2 s-1 with an activation energy of 20 kJ mol-1, which increases to attain 3 × 10-10 m2 s-1 at 65 °C. The observed peculiarities of water self-diffusion along the narrow FF nanochannels endow this class of materials with a new functionality. Possible applications of FF nanotubes in nanofluidic devices are discussed.

Natural and Eco-Friendly Materials for Triboelectric Energy Harvesting.

Triboelectric nanogenerators (TENGs) are promising electric energy harvesting devices as they can produce renewable clean energy using mechanical excitations from the environment. Several designs of triboelectric energy harvesters relying on biocompatible and eco-friendly natural materials have been introduced in recent years. Their ability to provide customizable self-powering for a wide range of applications, including biomedical devices, pressure and chemical sensors, and battery charging appliances, has been demonstrated. This review summarizes major advances already achieved in the field of triboelectric energy harvesting using biocompatible and eco-friendly natural materials. A rigorous, comparative, and critical analysis of preparation and testing methods is also presented. Electric power up to 14 mW was already achieved for the dry leaf/polyvinylidene fluoride-based TENG devices. These findings highlight the potential of eco-friendly self-powering systems and demonstrate the unique properties of the plants to generate electric energy for multiple applications.

Molecular modeling and computational study of the chiral-dependent structures and properties of self-assembling diphenylalanine peptide nanotubes.

The structure and properties of diphenylalanine (FF) peptide nanotubes (PNT) based on phenylalanine were investigated by various molecular modeling methods. The main approach employed semi-empirical quantum-chemical methods (PM3 and AM1). Ab initio, density functional theory methods and molecular mechanical approaches were also used. Both model structures and structures extracted from experimental crystallographic databases obtained by X-ray methods were examined. A comparison of optimized model structures and structures obtained by natural self-assembly revealed important differences depending on chirality: D and L. In both the cases, the effect of chirality on the results of self-assembly of FF PNT was established: PNT based on the D-FF has large condensation energy E0 in the transverse direction, and form thicker and shorter PNT bundles than those based on L-FF. A topological difference was established: model PNT were optimized into structures consisting of rings, while naturally self-assembled PNT consisted of helical turns. The latter nanotubes differed from the original L-FF and D-FF and formed helix structures of different chirality signs in accordance with the alternation rule of chirality due to macromolecule hierarchy. A topological transition between ring and helix turn PNT structures is discussed: self-assembled natural helix structures are favorable and their energy is lower by a value of the order of one to several eV.

Effect of the Chloride Anions on the Formation of Self-Assembled Diphenylalanine Peptide Nanotubes.

Self-assembled peptide nanostructures are being intensively investigated due to their potential applications such as biosensors, piezotransducers, and microactuators. It was predicted that their formation and hence piezoelectric property strongly depend on the water content and acidity of the stock solution. In this paper, simple diphenylalanine (FF) tubular structures were fabricated from the solutions with added hydrochloric acid in order to understand the influence of chloride ions on the self-assembly process and resulting piezoelectricity. Low-frequency Raman scattering, atomic, and piezoresponse force microscopies were used to characterize both the morphology and piezoelectric properties of the grown samples. The mechanism of chloride anions' effect on the formation of self-assembled peptide nanostructures is discussed based on the acquired Raman data and quantum-chemical modeling. It is shown that the addition of chloride anions causes a significant reduction of the dipole moments of FF tubes accompanied with the concomitant decrease of tube dimensions and apparent shear piezoelectric coefficients.

Diphenylalanine-Based Microribbons for Piezoelectric Applications via Inkjet Printing.

Peptide-based nanostructures are very promising for nanotechnological applications because of their excellent self-assembly properties, biological and chemical flexibility, and unique multifunctional performance. However, one of the limiting factors for the integration of peptide assemblies into functional devices is poor control of their alignment and other geometrical parameters required for device fabrication. In this work, we report a novel method for the controlled deposition of one of the representative self-assembled peptides-diphenylalanine (FF)-using a commercial inkjet printer. The initial FF solution, which has been shown to readily self-assemble into different structures such as nano- and microtubes and microrods, was modified to be used as an efficient ink for the printing of aligned FF-based structures. Furthermore, during the development of the suitable ink, we were able to produce a novel type of FF conformation with high piezoelectric response and excellent stability. By using this method, ribbonlike microcrystals based on FF could be formed and precisely patterned on different surfaces. Possible mechanisms of structure formation and piezoelectric effect in printed microribbons are discussed along with the possible applications.

Molecular modeling of the piezoelectric properties of ferroelectric composites containing polyvinylidene fluoride (PVDF) and either graphene or graphene oxide.

Molecular modeling of ferroelectric composites containing polyvinylidene fluoride (PVDF) and either graphene (G) or graphene oxide (GO) were performed using the semi-empirical quantum approximation PM3 in HyperChem. The piezo properties of the composites were analyzed and compared with experimental data obtained for P(VDF-TrFE)-GO films. Qualitative agreement was obtained between the results of the modeling and the experimental results in terms of the properties of the measured effective piezoelectric coefficient d 33eff and its decrease in the presence of G/GO in comparison with the average computed piezoelectric coefficient . When models incorporating one or several G layers with 54 carbon atoms were investigated, the average piezoelectric coefficient was found to decrease to -9.8 pm/V for the one-sided model PVDF/G and to -18.98 pm/V for the sandwich model G/PVDF/G as compared with the calculated piezoelectric coefficient for pure PVDF ( = -42.2 pm/V computed in present work, and = -38.5 pm/V, obtained from J Mol Model 35 (2013) 19:3591-3602). When models incorporating one or several GO layers with 98 carbon atoms were considered, the piezoelectric coefficient was found to decrease to -14.6 pm/V for the one-sided PVDF/GO model and to -29.8 pm/V for the sandwich GO/PVDF/GO model as compared with the same calculated piezoelectric coefficient for pure PVDF.