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Determining the structural origins of amyloid fibrillation is essential for understanding both the pathology of amyloidosis and the rational design of inhibitors to prevent or reverse amyloid formation. In this work, the decisive roles of peptide structures on amyloid self-assembly and morphological diversity were investigated by the design of eight amyloidogenic peptides derived from islet amyloid polypeptide. Among the segments, two distinct morphologies were highlighted in the form of twisted and planar (untwisted) ribbons with varied diameters, thicknesses, and lengths. In particular, transformation of amyloid fibrils from twisted ribbons into untwisted structures was triggered by substitution of the C-terminal serine with threonine, where the side chain methyl group was responsible for the distinct morphological change. This effect was confirmed following serine substitution with alanine and valine and was ascribed to the restriction of intersheet torsional strain through the increased hydrophobic interactions and hydrogen bonding. We also studied the variation of fibril morphology (i.e., association and helicity) and peptide aggregation propensity by increasing the hydrophobicity of the peptide side group, capping the N-terminus, and extending sequence length. We anticipate that our insights into sequence-dependent fibrillation and morphological diversity will shed light on the structural interpretation of amyloidogenesis and development of structure-specific imaging agents and aggregation inhibitors.

Light‐gated chemical reactions allow spatial and temporal control of chemical processes. Here, we suggest a new system for controlling pH‐sensitive processes with light using two photobases of Arrhenius and Brønsted types. Only after light excitation do Arrhenius photobases undergo hydroxide ion dissociation, while Brønsted photobases capture a proton. However, none can be used alone to reversibly control pH due to the limitations arising from excessively fast or overly slow photoreaction timescales. We show here that combining the two types of photobases allows light‐triggered and reversible pH control. We show an application of this method in directing the pH‐dependent reaction pathways of the organic dye Alizarin Red S simply by switching between different wavelengths of light, i. e., irradiating each photobase separately. The concept of a light‐controlled system shown here of a sophisticated interplay between two photobases can be integrated into various smart functional and dynamic systems. [ABSTRACT FROM AUTHOR]

Semiconducting single walled carbon nanotubes (SWCNTs) are promising materials for biosensing applications with electrolyte‐gated transistors (EGT). However, to be employed in EGT devices, SWCNTs often require lengthy solution‐processing fabrication techniques. Here, we introduce a simple solution‐based method that allows fabricating EGT devices from stable dispersions of SWCNTs/bovine serum albumin (BSA) hybrids in water. The dispersion is then deposited on a substrate allowing the formation of a SWCNTs random network as the semiconducting channel. We demonstrate that this methodology allows the fabrication of EGT devices with electric performances that allow their use in biosensing applications. We demonstrate their application for the detection of cortisol in solution, upon gate electrode functionalization with anti‐cortisol antibodies. This is a robust and cost‐effective methodology that sets the ground for a SWCNT/BSA‐based biosensing platform that allows overcoming many limitations of standard SWCNTs biosensor fabrications. [ABSTRACT FROM AUTHOR]

Light is a common source of energy in sustainable technologies for photocurrent generation. To date, in such light‐harvesting applications, the excited electrons generate the photocurrent. Here, we introduce a new mechanism for photocurrent generation that is based on excited state proton transfer (ESPT) of photoacids and photobases that can donate or accept a proton, respectively, but only after excitation. We show that the formed ions following ESPT can either serve as electron donors or acceptors with the electrodes, or modify the kinetics of mass transport across the diffuse layer, both resulting in photocurrent generation. We further show that control of the current polarity is obtained by switching the irradiation between the photoacid and the photobase. Our study represents a new approach in photoelectrochemistry by introducing ESPT processes, which can be further utilized in light‐responsive energy production or energy storage. [ABSTRACT FROM AUTHOR]

Mixed ionic–electronic conductive polymers are gaining high momentum for several electronic and bioelectronic applications. These polymers are composed of a synthetic conjugated polymer for electronic conduction and a synthetic ionomer for the ionic one. To make these materials more environmentally sustainable, much effort is being put in replacing synthetic polymers with biopolymers. However, to date, the only strategy for making mixed conductors with biopolymers is to blend them with synthetic polymers. Here, we show that by targeting certain amino acids of a protein-based biopolymer, we can modify them with naphthalenediimide (NDI) after polymerization, resulting in an improved electronic transport, which is in addition to the native ionic transport of the biopolymer. We further show that by reducing the NDI moieties we can reach conductivity values in the order of 40 mS cm−1, though NDI can re-oxidize depending on the environment of the biopolymer. The abundant nature of the protein building blocks together with the easy post-polymerization functionalization chemistry of NDI, which is very much different than any previous use of NDI in conductive polymers, is making our new strategy for making mixed ionic–electronic conductive biopolymers highly attractive. [ABSTRACT FROM AUTHOR]

Plastic items are an indispensable part of our society, but due to the high carbon footprint and limited degradability of many of the petrochemical-based plastics, they raise an immense ecological concern on our planet. One approach to replacing current plastics is switching to bioderived plastics (bioplastics), which are based on the use of biological materials for the making of bioplastics. While most bioplastics to date focused on replacing common thermoplastics, we show here the use of abundant biological materials for the making of the first ion-conductive bioplastic, for which we use the most commonly available casein protein in a one-pot process. We show that sulfonating the casein chains results in an enhanced ionic conductivity of the bioplastic. The final bioplastic shows attractive tunable mechanical (Young's modulus of 2–200 MPa) and electrical (0.01–0.4 mS cm−1) properties, and owing to the protein-based nature, the bioplastic is degradable upon disposal. Due to the abundance of the raw starting material and the lack of any purification stage, the final casein bioplastic has a low price tag of below 0.01 USD cm−2. [ABSTRACT FROM AUTHOR]

Many efforts have been directed towards elucidating the nitrogenase structure, its biocatalytic activity, and methods to artificially activate it by external stimuli. Here, we investigated how semiconductor nanoparticles (NPs) with sizes ranging between 2.3–3.5 nm form nano‐biohybrids with the nitrogenase enzyme and enable its photoinduced biocatalytic activity. We examined two homogenously synthesized quantum dots (QDs), CdS, CdSe, and two nitrogenase variants, the wild‐type and a cysteine‐mutated. We show that the cysteine‐mutated variant does not enhance the hydrogen generation amounts, as compared with the wild type. Nevertheless, we show that the 2.3 nm‐sized CdSe NPs facilitate an eightfold increase compared with larger CdSe NPs. The obtained results were investigated using electrochemical techniques, transmission electron microscopy, and further confirmed by time‐resolved spectroscopic measurements, which allow us to determine the electron tranfer rate constant (kET) of the different configurations. [ABSTRACT FROM AUTHOR]

Nature demonstrates many examples of response and adaptation to external stimuli. Here, this study focuses on self-propulsion (motion) while presenting several self-propelling droplet systems responsive to pH gradients. Light is used as the gating source to gain reversibility, avoid the formation of chemical wastes, and control the self-propulsion remotely. To achieve light-stimuli ultrafast response, photoacids and photobases are used, capable of donating or capturing a proton, respectively, in their excited state. The movement and directionality of the droplet's self-propulsion are controlled by introducing the photoacid/base either in bulk solution, on the surface of the droplet, or inside the droplet. It is shown that proton transfer between the photoacid/base and the droplet results in a rapid change in the droplet's surface tension, which induces the self-propulsion movement. The high versatility of the systems together with a record-breaking ultrafast response to light makes them highly attractive for the design of various controlled cargo-carrier systems. [ABSTRACT FROM AUTHOR]

Light is a convenient source of energy and the heart of light‐harvesting natural systems and devices. Here, we show light‐modulation of both the chemical nature and ionic charge carrier concentration within a protein‐based biopolymer that was covalently functionalized with photoacids or photobases. We explore the capability of the biopolymer‐tethered photoacids and photobases to undergo excited‐state proton transfer and capture, respectively. Electrical measurements show that both the photoacid‐ and photobase‐functionalized biopolymers exhibit an impressive light‐modulated increase in ionic conductivity. Whereas cationic protons are the charge carriers for the photoacid‐functionalized biopolymer, water‐derived anionic hydroxides are the suggested charge carriers for the photobase‐functionalized biopolymer. Our work introduces a versatile toolbox to photomodulate both protons and hydroxides as charge carriers in polymers, which can be of interest for a variety of applications. [ABSTRACT FROM AUTHOR]

Hydrogels are common platforms for drug delivery applications. Amongst the different loading and release methodologies, physisorption loading and passive release stand out for their straightforwardness. However, evaluating the inner environment and the surface of the polymer can be complicated, as they can be very different from the properties of the monomer composing the hydrogel. Here, we explore the inner environment of macroscopic bovine serum albumin (BSA) hydrogels, by using both the native Trp residues of the protein and the pyranine photoacid as fluorescent probes. Time-resolved fluorescence is used to follow the fast solvation dynamics of Trp and the excited-state proton dissociation of pyranine. The results show that upon gelation, the surface of the BSA within the hydrogel is less accessible to water, i.e., more hydrophobic, as compared to before gelation. This understanding is used to rationalize the different drug binding efficiencies of the anti-cancer drug doxorubicin to the hydrogel at different pH values, which changes the charge of the molecule. Finally, we give proof for the hydrogels capacity to effectively function as drug-carrier systems in vitro, using different cancer cell lines over a 7 day period. Our study shows that relatively simple spectroscopic measurements can result in a fundamental structural and chemical understanding of (protein) hydrogels. From an application point of view, our protein hydrogels are very easy to form, without any need of complex chemical modification, they are very low cost as compared to other hydrogels, and show slow and sustained drug release profiles, all very sought-after properties. [ABSTRACT FROM AUTHOR]

Fluorescent dyes are common tools for tracking biological membranes. In this work, we introduce a new ratiometric fluorescent probe for membranes based on a surface‐sensitive photoacid. As all other probes, it lights up within membranes, and furthermore, it has different ratios of fluorescent peaks for different membranes. The main unique feature of the probe is its ability to sense events taking place in the membrane far away from its actual location. This is due to the photoacidity of the probe, and the associated kinetics of its excited‐state proton release and capture that are highly sensitive to the lateral proton diffusion on the surface of the membrane. We show here that minor disruptions to the membrane integrity, induced by the Triton X‐100 surfactant at low concentration (surfactant:lipid ratio of 0.02), can be sensed by our probe using steady‐state fluorescence, while other probes are invisible to them. Time‐resolved fluorescence reveals that the surfactant insertion affects the lateral proton diffusion and accordingly the measured proton recombination of the photoacid. [ABSTRACT FROM AUTHOR]

Biological electron transfer (ET) is one of the most studied biochemical processes due to its immense importance in biology. For many years, biological ET was explained using the classical incoherent transport mechanism, i.e. sequential hopping. One of the relatively recent major observations in this field is long-range extracellular ET (EET), where some bacteria were shown to mediate electrons for extremely long distances on the micrometer length scales across individual nanowires. This fascinating finding has resulted in several suggested mechanisms that might explain this intriguing EET. More recently, the structure of a conductive G. sulfurreducens nanowire has been solved, which showed a highly ordered quasi-1D wire of a hexaheme cytochrome protein, named OmcS. Based on this new structure, we suggest here several electron diffusion models for EET, involving either purely hopping or several degrees of mixed hopping and coherent transport, in which the coherent part is due to a local rigidification of the protein structure, associated with a decrease in the local reorganization energy. The effect is demonstrated for two closely packed heme sites as well as for longer chains containing up to several dozens porphyrins. We show that the pure hopping model probably cannot explain the reported conductivity values of the G. sulfurreducens nanowire using conventional values of reorganization energy and electronic coupling. On the other hand, we show that for a wide range of the latter energy values, the mixed hopping-coherent model results in superior electron diffusion compared to the pure hopping model, and especially for long-range coherent transport, involving multiple porphyrin sites. [ABSTRACT FROM AUTHOR]

Tissue engineering is a promising therapeutic approach in medicine, targeting the replacement of a diseased tissue with a healthy one grown within an artificial scaffold. Due to the high prevalence of cardiac and brain‐related ailments that involve some necrosis of tissue, cardiac and neuronal tissue engineering are intensely studied fields in regenerative medicine. A growing trend in the use of conductive scaffolds for the growth of these tissues has been witnessed recently. While the results are irrefutable, the mechanism of how an electrically conducting scaffold interacts with an electroactive tissue remains has remained elusive. An up‐to‐date summary of all work done in the field is reported, with a special focus on the specific contribution of the conductive scaffold on the performance of the formed tissue. The cell–scaffold electronic interface is then explored from an electrical engineering perspective. The electronic configuration of the system and the mechanisms and governing factors controlling the ability of a conductive scaffold to support cardiac and neuronal tissues are discussed. Using several simulations, the required conductivity of the scaffold in order for it to be suitable for tissue engineering—which also depends on the nature of the charge carriers—is also discussed. [ABSTRACT FROM AUTHOR]

An exceptional quantum-confined approach is proposed to understand the self-assembly mechanism in bio-inspired materials such as peptide nanotubes (PNTs) which are self-assembled from short peptides composed of two phenylalanine residues, to be 0D-quantum-confined also called a quantum dot (QD). The proposed peptide QD structures are found to be nanometer-sized structures, with pronounced exciton effects, which might promote the use of an entirely new kind of organic QDs.

Supramolecular self-assembly is an important process that enables the conception of complex structures mimicking biological motifs. Herein, we constructed helical fibrils through chiral self-assembly of nucleobase-peptide conjugates (NPCs), where achiral nucleobases are helically displayed on the surface of fibrils, comparable to polymerized nucleic acids. Selective binding between DNA and the NPC fibrils was observed with fluorescence polarization. Taking advantage of metal-nucleobase recognition, we highlight the possibility of deposition/assembly of plasmonic nanoparticles onto the fibrillar constructs. In this approach, the supramolecular chirality of NPCs can be adaptively imparted to metallic nanoparticles, covering them to generate structures with plasmonic chirality that exhibit significantly improved colloidal stability. The self-assembly of rationally designed NPCs into nanohelices is a promising way to engineer complex, optically diverse nucleobase-derived nanomaterials. [ABSTRACT FROM AUTHOR]

It is reported that spiropyran-a widely investigated molecular photoswitch-can be stabilized in aqueous environments in the presence of a variety of proteins, including human serum albumin, insulin fibrils, lysozyme, and glucose oxidase. The optical properties of the complexed photoswitch are protein dependent, with human serum albumin providing the spiropyran with emission features previously observed for a photoswitch confined in media of high viscosity. Despite being bound to the protein molecules, spiropyran can undergo a ring-opening reaction upon exposure to UV light. This photoisomerization process can affect the properties of the proteins: here, it is shown that the electrical conduction through human serum albumin to which the spiropyran is bound increases following the ring-opening reaction. [ABSTRACT FROM AUTHOR]