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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]

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]

Proton diffusion (PD) across biological membranes is a fundamental process in many biological systems, and much experimental and theoretical effort has been employed for deciphering it. Here, we report on a spectroscopic probe, which can be tightly tethered to the membrane, for following fast (nanosecond) proton transfer events on the surface of membranes. Our probe is composed of a photoacid that serves as our light-induced proton source for the initiation of the PD process. We use our probe to follow PD, and its pH dependence, on the surface of lipid vesicles composed of a zwitterionic headgroup, a negative headgroup, a headgroup that is composed only from the negative phosphate group, or a positive headgroup without the phosphate group. We reveal that the PD kinetic parameters are highly sensitive to the nature of the lipid headgroup, ranging from a fast lateral diffusion at some membranes to the escape of protons from surface to bulk (and vice versa) at others. By referring to existing theoretical models for membrane PD, we found that while some of our results confirm the quasi-equilibrium model, other results are in line with the nonequilibrium model. [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]

Electron transfer (ET) across proteins is one of the fundamental processes in nature. While trying to decipher and understand natural ET, much scientific effort has been employed in scaling down the process to the role of the elementary secondarystructure units of proteins, that is, β sheets and α helices. Among these two motifs, the vast majority of studies have focused on α-helical peptides because they require fewer amino acids for formation, they can be easily assembled on surfaces, and they can be easily functionalized. Herein, the focus is only on ET across α-helical peptides, not only because of the reasons discussed, but also because they are one of the most promising biological molecules for integration into ET-based bioelectronic devices. The different methodologies used to follow ET across the peptides, namely, photoinduced ET, electrochemistry, and solid-state conductivity measurements (referred to as electron transport, ETp), are reviewed and discussed. In this context, the fundamental differences between the different methodologies, the appropriate interpretation of the results, and possible mechanisms to describe the ET(p) process in each methodology are discussed. Furthermore, possible functionalization of the helical peptides to modify and control their (opto-)electronic properties is reviewed. [ABSTRACT FROM AUTHOR]

Electron transfer (ET) proteins are biomolecules with specific functions, selected by evolution. As such they are attractive candidates for use in potential bioelectronic devices. The blue copper protein azurin (Az) is one of the most‐studied ET proteins. Traditional spectroscopic, electrochemical, and kinetic methods employed for studying ET to/from the protein's Cu ion have been complemented more recently by studies of electrical conduction through a monolayer of Az in the solid‐state, sandwiched between electrodes. As the latter type of measurement does not require involvement of a redox process, it also allows monitoring electronic transport (ETp) via redox‐inactive Az‐derivatives. Here, results of macroscopic ETp via redox‐active and ‐inactive Az derivatives, i.e., Cu(II) and Cu(I)‐Az, apo‐Az, Co(II)‐Az, Ni(II)‐Az, and Zn(II)‐Az are reported and compared. It is found that earlier reported temperature independence of ETp via Cu(II)‐Az (from 20 K until denaturation) is unique, as ETp via all other derivatives is thermally activated at temperatures >≈200 K. Conduction via Cu(I)‐Az shows unexpected temperature dependence >≈200 K, with currents decreasing at positive and increasing at negative bias. Taking all the data together we find a clear compensation effect of Az conduction around the Az denaturation temperature. This compensation can be understood by viewing the Az binding site as an electron trap, unless occupied by Cu(II), as in the native protein, with conduction of the native protein setting the upper transport efficiency limit. [ABSTRACT FROM AUTHOR]

Theinteraction between a photoacid (8-hydroxy-1,3,6-pyrenetrisulfonate,HPTS) and the surfaces of biomaterials and the diffusion of protonsalong the biomaterial surfaces were examined by following the excited-stateproton transfer (ESPT) from the photoacid, adsorbed on the surfaces,to water molecules next to it. We chose two different types of biomaterialsurfaces, hydrophobic insulin amyloid fibrils and hydrophilic cellulosesurfaces. With the help of steady-state and time-resolved fluorescencetechniques, we found that the rate of ESPT from HPTS on insulin fibrilsto adjacent water molecules is about 1/10thatin bulk water. However, the proton geminate recombination takes placewith an efficiency similar to that in bulk water. ESPT from HPTS inwet cellulose to water depends on the weight percentage of water adsorbedby the cellulose. In a semidry sample (<100% weight percentageof water), the ESPT rate is rather low and thus the quantum efficiencyof the ESPT is also low within the excited-state lifetime. When thewater content is higher, the ESPT rate is almost that of bulk water.We explain these results by the existence of pools of water in celluloseof high water content, in which the triple-negatively charged HPTSmolecules desorb from the cellulose surface to these pools. The useof HPTS has allowed us to examine the biological surface and its interactionwith water molecules, while obtaining important information regardingthe hydration state of the surface that otherwise could not have beenobtained. The model that we propose here for the use of photoacids to followthe hydrated state of a given surface is a promising new method ofexamining the interaction of water molecules with biological surfaces. [ABSTRACT FROM AUTHOR]

Monolayers of the redox protein Cytochrome C (CytC) can be electrostatically formed on an H-terminated Si substrate, if the protein- and Si-surface are prepared so as to carry opposite charges. With such monolayers we study electron transport (ETp) via CytC, using a solid-state approach with macroscopic electrodes. We have revealed that currents via holo-CytC are almost 3 orders of magnitude higher than via the heme-depleted protein (→ apo-CytC). This large difference in currents is attributed to loss of the proteins' secondary structure upon heme removal. While removal of only the Fe ion (→ porphyrin-CytC) does not significantly change the currents via this protein at room temperature, the 30-335 K temperature dependence suggests opening of a new ETp pathway, which dominates at high temperatures (>285 K). These results suggest that the cofactor plays a major role in determining the ETp pathway(s) within CytC. [ABSTRACT FROM AUTHOR]

Measuring solid-state electron transport (ETp) across proteins allows studying electron transfer (ET) mechanism(s), while minimizing solvation effects on the process. ETp is, however, sensitive to any static (conformational) or dynamic (vibrational) changes in the protein. Our macroscopic measurements allow extending ETp studies to low temperatures, with the concomitant resolution of lower current densities, because of the larger electrode contact areas. Thus, earlier we reported temperature-independent ETp via the copper protein azurin (Az), from 80 K until denaturation, whereas for apo-Az ETp was temperature dependent above 180 K. Deuteration (H/D substitution) may provide mechanistic information on the question of whether the ETp involves H-bonds in the solid state. Here we report results of kinetic deuterium isotope effect (KIE) measurements on ETp through holo-Az as a function of temperature (30-340 K). Strikingly, deuteration changed ETp from temperature independent to temperature dependent above 180 K. This H/D effect is expressed in KIE values between 1.8 (340 K) and 9.1 (⩽180 K). These values are remarkable in light of the previously reported inverse KIE on ET in Az in solution. We ascribe the difference between our KIE results and those observed in solution to the dominance of solvent effects in the latter (larger thermal expansion in H2O than in D2O), whereas in our case the KIE is primarily due to intramolecular changes, mainly in the low-frequency structural modes of the protein caused by H/D exchange. The observed high KIE values are consistent with a transport mechanism that involves through-H-bonds of the β-sheet structure of Az, likely also those in the Cu coordination sphere. [ABSTRACT FROM AUTHOR]

Both auramine-O (AuO) and thioflavin-T (ThT) behave asfluorescentmolecular rotors, meaning that their (non)radiative properties aremarkedly affected by the intramolecular rotation of the molecule.In this article, steady-state and time-resolved fluorescence of AuOand ThT were measured in three alcohols, 1-propanol, 1-butanol, and1-pentanol, over a wide range of temperatures (86–260 K). Thesesolvents are glass-forming liquids, and their viscosity and dielectricrelaxation time increase by more than 10 orders of magnitude as thetemperature is lowered from room temperature to ?100 K. Accordingly,the fluorescence nonradiative rates constants of AuO and ThT in thesesolvents decrease by about 3 orders of magnitude at the latter temperaturerange. We found very good correspondence between the temperature dependenceof the nonradiative rate constant, knr, of both molecules and the dielectric relaxation rate of the solvents.The knrvalues of AuO are twice thoseof ThT along the whole temperature range. The temperature dependenceof knris consistent with the nonradiativemodel suggested by Glasbeek and co-workers.(1) [ABSTRACT FROM AUTHOR]

There is an indispensable need for a fluorescence markerfor thedetection of amyloid fibrils, where, at present, the most used markeris thioflavin-T (ThT). Here, we present the use of auramine-O (AuO)as a possible alternative to ThT. As with ThT, the increase in theemission of AuO upon binding to amyloid fibrils is the result of inhibitionof the free rotation of the two dimethylamino arms of the molecule.This inhibition prevents the excited-state electronic wave functionfrom moving from the emissive locally excited state to the dark charge-transferstate. We further show that not only AuO is comparable to ThT as afluorescent marker for amyloid fibrils but also it has a unique spectroscopicsignature. AuO has distinct two modes that are characterized by alarge shift in the absorption and emission peak positions betweenits unbound and bound states (before and after the fibrils formation,respectively). In this context, we show that, whereas the emissionband position is red-shifting, the absorption peak shifts to the blueand the spectrum exhibits an isosbestic point. The large shifts inemission and absorption peak positions can be explained by the photoacidactivity of AuO exhibiting an excited-state proton-transfer process. [ABSTRACT FROM AUTHOR]

Electrons can migrate via proteins over distances that are considered long for nonconjugated systems. The nanoscale dimensions of proteins and their enormous structural and chemical flexibility makes them fascinating subjects for exploring their electron transport (ETp) capacity. One particularly attractive direction is that of tuning their ETp efficiency by "doping" them with small molecules. Here we report that binding of retinoate (RA) to human serum albumin (HSA) increases the solid-state electronic conductance of a monolayer of the protein by >2 orders of magnitude for RA/HSA ≥ 3. Temperature-dependent ETp measurements show the following with increasing RA/HSA: (a) The temperature-independent current magnitude of the low-temperature (<190 K) regime increases significantly (>300-fold), suggesting a decrease in the distance-decay constant of the process. (b) The activation energy of the thermally activated regime (>190 K) decreases from 220 meV (RA/HSA = 0) to 70 meV (RA/HSA ≥ 3). [ABSTRACT FROM AUTHOR]

Thioflavin-T (ThT) can bind to amyloid fibrils and is frequentlyused as a fluo-rescent marker for in vitrobiomedicalassays of the potency of inhibitors for amyloid-related diseases,such as Alzheimer’s disease, Parkinson’s disease, andamyloidosis. Upon binding to amyloid fibrils, the steady-state (time-integrated)emission intensity of ThT increases by orders of magnitude. The simplicityof this type of measurement has made ThT a common fluorescent markerin biomedical research over the last 50 years. [ABSTRACT FROM AUTHOR]

Abstract: Insulin, as other amyloid proteins, can form amyloid fibrils at certain conditions. The self-assembled aggregation process of insulin can result in a variety of conformations, starting from small oligomers, going through various types of protofibrils, and finishing with bundles of fibrils. One of the most common consensuses among the various self-assembly processes that are suggested in the literature is the formation of an early stage nucleus conformation. Here we present an additional insight for the self-assembly process of insulin. We show that at the early lag phase of the process (prior to fibril formation) the insulin monomers self-assemble into ordered nanostructures. The most notable feature of this early self-assembly process is the formation of nanocrystalline nucleus regions with a strongly bound electron–hole confinement, which also change the secondary structure of the protein. Each step in the self-assembly process is characterized by an optical spectroscopic signature, and possesses a narrow size distribution. By following the spectroscopic signature we can measure the potency of amyloid fibrils inhibitors already at the lag phase. We further demonstrate it by the use of epigallocatechin gallate, a known inhibitor for insulin fibrils. The findings can result in a spectroscopic-based application for the analysis of amyloid fibrils inhibitors. [Copyright &y& Elsevier]

In this letter we present a variation in the optical properties of bio-organic peptide nanostructures, which are induced by molecular transformation. The self-assembled tubular structures are formed from short aromatic di-peptides. Upon thermal induction, the structure changes its molecular conformation, and the linear di-peptide closes into a cyclic peptide. This irreversible transition changes the molecular packing at the nanoscale, which results in reconstruction of the native quantum dot-like packing to quantum well-like packing and the generation of blue luminescence. We further show that the same cyclic peptide can exhibit different photoluminescence properties according to the formed structure. [ABSTRACT FROM AUTHOR]

Time-resolved emission techniques were employed to study the non-radiative process of thioflavin-T (ThT) in 1-propanol, 1-butanol, and 1-pentanol as a function of the hydrostatic pressure. Elevated hydrostatic pressure increases the alcohol viscosity, which in turn strongly influences the nonradiative rate of ThT. A diamond-anvil cell was used to increase the pressure up to 2.4 GPa. We found that the nonradiative rate constant, knr, decreases with pressure. We further found a remarkable linear correlation between a decrease in knr (increase in the nonradiative lifetime, τnr) and an increase in the solvent viscosity. The viscosity was varied by a factor of 1000 and knr was measured at high pressures, at which the nonradiative rate constant of the molecules decreased from (7 ps)-1 to (13 ns)-1, (13 ps)-1 to (17 ns)-1 and (17 ps)- 1 to (IS ns)-1 for 1-propanol, 1-butanol, and 1-pentanol, respectively. The viscosity-dependence of knr is explained by the excited-state rotation rate of the two-ring systems, with respect to each other. [ABSTRACT FROM AUTHOR]

In the world of biology, "self-assembly" is the ability of biological entities to interact with one another to form supramolecular structures. One basic group of self-assembled structures is peptide nanotubes (PNTs). However, the self-assembly mechanism, with its special characteristics, is not yet fully understood. An exceptional quantum-confined approach is shown here for the self-assembly mechanism in bio-inspired materials. We found the elementary building block of the studied PNT, which is self-assembled from short peptides composed of two phenylalanine residues, to be 0D-quantum-confined (can be related to confinement in 3D), also called a quantum dot (QD). This elementary building block can further self- assemble to a PNT formation. It has been observed that the assembly process of dots to tubes and the disassembly process of tubes to dots are reversible. We further show that a similar dipeptide can also self-assemble to a QD-like structure, with different dimensions. The presented peptide QD structures are nanometer-sized structures, with pronounced exciton effects, which may promote the use of an entirely new kind of organic QDs. [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]

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]

Review: 190 refs. [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]

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]

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]

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]

A computational model of nonradiative decay is developed and applied to explain the time-dependent emission spectrum of thioflavin T (ThT). The computational model is based on a previous model developed by Glasbeek and co-workers (van der Meer, M. J.; Zhang, H.; Glasbeek, M ; J. Chem. Phys. 2000, 112, 2878) for auramine O, a molecule that, like ThT, exhibits a high nonradiative rate. The nonradiative rates of both auramine O and ThT are inversely proportional to the solvent viscosity. The Glasbeek model assumes that the excited state consists of an adiabatic potential surface constructed by adiabatic coupling of emissive and dark states. For ThT, the twist angle between the benzothiazole and the aniline is responsible for the extensive mixing of the two excited states. At a twist angle of 90°, the S1 state assumes a charge-transfer-state character with very small oscillator strength, which causes the emission intensity to be very small as well. In the ground state, the twist angle of ThT is rather small. The photoexcitation leads first to a strongly emissive state (small twist angle). As time progresses, the twist angle increases and the oscillator strength decreases. The fit of the experimental results by the model calculations is good for times longer than 3 ps. When a two-coordinate model is invoked or a solvation spectral-shift component is added, the fit to the experimental results is good at all times. [ABSTRACT FROM AUTHOR]

• BiVO4: negative correlation between photoactivity and O vacancies. • BiVO4: transient changes in FTIR for dozens of nanoseconds. • BiVO4: Changes in transient IR spectroscopy correlate with photoactivity. Bismuth vanadate is an appealing candidate for photocatalysis. In a quest to clarify the effect of phase and shape on its photocatalytic activity, four types of particles, differing in phase and shape, were prepared, characterized and studied. Monoclinic particles having a prismatic shape as well as tetragonal particles were found to be more active towards Cr(VI) reduction than a mixed phase or octahedron-shaped monoclinic particles. A negative correlation was found between the activity and the concentration of oxygen vacancies near the surface. Transient IR measurements following pulsed excitation revealed temporal changes in the spectra, prevailing for dozens of nanoseconds. A negative correlation between the duration of the IR transient signal and the photocatalytic activity was found. The observations made by the transient step-scan FTIR technique clearly demonstrate the potential of this technique as a tool for understanding, rationalizing, or even predicting the activity of photocatalytic materials. [ABSTRACT FROM AUTHOR]

The fundamental biological process of electron transfer (ET) takes place across proteins with common ET pathways of several nanometers. Recent discoveries push this limit and show long-range extracellular ET over several micrometers. Here, we aim in deciphering how protein-bound intramolecular cofactors can facilitate such long-range ET. In contrast to natural systems, our proteinbased platform enables us to modulate important factors associated with ET in a facile manner, such as the type of the cofactor and its quantity within the protein. We choose here the biologically relevant protoporphyrin molecule as the electron mediator. Unlike natural systems having only Fe-containing protoporphyrins, i.e., heme, as electron mediators, we use here porphyrins with different metal centers, or lacking a metal center. We show that the metal redox center has no role in ET and that ET is mediated solely by the conjugated backbone of the molecule. We further discuss several ET mechanisms, accounting to our observations with possible contribution of coherent processes. Our findings contribute to our understanding of the participation of heme molecules in long-range biological ET. [ABSTRACT FROM AUTHOR]

Amyloid fibrillation is a nucleation-dependent process known be involved in the development of more than 20 progressive and chronic diseases. The detection of amyloid formation at the nucleation stage can greatly advance early diagnoses and treatment of diseases. In this work, we developed a new assay for the early detection of amylin fibrillation using the biarsenical dye 4,5-bis(1,3,2-dithiarsolan-2-yl)fluorescein (FlAsH), which could recognise tetracysteine motifs and transform from non-fluorescent form into strongly fluorescent complexes. Due to the close proximity of two cysteine residues within the hydrophilic domain of amylin, a non-contiguous tetracysteine motif can form upon amylin dimerisation or oligomerisation, which can be recognised by FlAsH and emit strong fluorescence. This enables us to report the nucleation-growth process of amylin without modification of the protein sequence. We showed that the use of this assay not only allowed the tracking of initial nucleation events, but also enabled imaging of amyloid fibrils and investigation of the effects of amyloid inhibitor/modulator toward amylin fibrillation. [ABSTRACT FROM AUTHOR]

A comprehensive understanding of the mechanisms of interaction between proteins or peptides and nanomaterials is crucial for the development of nanomaterial-based diagnostics and therapeutics. In this work, we systematically explored the interactions between citrate-capped gold nanoparticles (AuNPs) and islet amyloid polypeptide (IAPP), a 37-amino acid peptide hormone co-secreted with insulin from the pancreatic islet. We utilized diffusion-ordered spectroscopy, isothermal titration calorimetry, localized surface plasmon resonance spectroscopy, gel electrophoresis, atomic force microscopy, transmission electron microscopy (TEM), and molecular dynamics (MD) simulations to systematically elucidate the underlying mechanism of the IAPP-AuNP interactions. Because of the presence of a metal-binding sequence motif in the hydrophilic peptide domain, IAPP strongly interacts with the Au surface in both the monomeric and fibrillar states. Circular dichroism showed that AuNPs triggered the IAPP conformational transition from random coil to ordered structures (α-helix and β-sheet), and TEM imaging suggested the acceleration of IAPP fibrillation in the presence of AuNPs. MD simulations revealed that the IAPP-AuNP interactions were initiated by the N-terminal domain (IAPP residues 1-19), which subsequently induced a facet-dependent conformational change in IAPP. On a Au(111) surface, IAPP was unfolded and adsorbed directly onto the Au surface, while for the Au(100) surface, it interacted predominantly with the citrate adlayer and retained some helical conformation. The observed affinity of AuNPs for IAPP was further applied to reduce the level of peptide-induced lipid membrane disruption. [ABSTRACT FROM AUTHOR]

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]

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]

Soluble oligomeric assemblies of amyloidal proteins appear to act as major pathological agents in several degenerative disorders. Isolation and characterization of these oligomers is a pivotal step towards determination of their pathological relevance. Here we describe the isolation of Type 2 diabetes-associated islet amyloid polypeptide soluble cytotoxic oligomers; these oligomers induced apoptosis in cultured pancreatic cells, permeated model lipid vesicles and interacted with cell membranes following complete internalization. Moreover, antibodies which specifically recognized these assemblies, but not monomers or amyloid fibrils, were exclusively identified in diabetic patients and were shown to neutralize the apoptotic effect induced by these oligomers. Our findings support the notion that human IAPP peptide can form highly toxic oligomers. The presence of antibodies identified in the serum of diabetic patients confirms the pathological relevance of the oligomers. In addition, the newly identified structural epitopes may also provide new mechanistic insights and a molecular target for future therapy. [ABSTRACT FROM AUTHOR]

Abstract: Steady-state and time-resolved emission spectra were measured to study the relaxation of all-trans retinoic acid (ATRA) from its excited-states in a number of solvents. We found that the time-resolved emission signal is composed of three decay components arising from three different excited-states. The ultrafast component that is shorter than 80fs is dominant at λ ≤500nm, whereas the intermediate component is dominant at longer wavelengths and its lifetime is solvent dependent. For acetonitrile, methanol and 1-pentanol the average decay times of the intermediate component are 0.9, 1.3 and 4ps respectively, and the overall decay is non-exponential. The third decay component has a very small amplitude of ∼0.05 in polar solvents and a longer lifetime of ∼10ps. We assign the fast decaying emission component to the allowed transition from the upper 1 B u + state to the ground 1 A g state. The intermediate lifetime component is assigned to the forbidden transition from the excited 1 A g ππ* state to the ground-state. In n-octane, a non-polar solvent, the amplitude of the intermediate time component is smaller than in polar solvents, and its lifetime is 600fs. This lifetime is shorter than in acetonitrile, whose viscosity is half that of n-octane. Moreover, the amplitude of the long time component in this solvent at long wavelengths is dominant. We therefore propose that the excited state ordering may be different in non-polar solvents. We also conducted a temperature dependence study on ATRA emission in 1-propanol and 1-pentanol, both of which are glass forming liquids. We found that the average emission lifetime increases as the temperature decreases. The value of the activation energy of the non-radiative process is half that of the dielectric relaxation process of the solvent. [Copyright &y& Elsevier]

Nanoscale bioimaging is a highly important scientific and technological tool, where fluorescent (FL) proteins, organic molecular dyes, inorganic quantum dots, and lately carbon dots are widely used as light emitting biolabels. In this work, a new class of visible FL bioorganic nanodots, self‐assembled from short peptides of different composition and origin, is introduced. It is shown that the electronic energy spectrum of native nonfluorescent peptide nanodots (PNDs) is deeply modified upon thermally mediated refolding of their biological secondary structure from native metastable to stable β‐sheet rich structure. This refolding leads to the appearance of a broadband optical absorption across visible region and tunable, excitation‐dependent visible FL of the nanodots with a high quantum yield of ≈30%. It is shown that this intriguing biophotonic effect appears in several peptides/proteins and does not require the presence of aromatic residues. It is assumed that the origin of the phenomenon is related to proton transfer along network of reconstructed intermolecular hydrogen bonds, stabilizing the thermally induced supramolecular β‐sheet structure. The biocompatible FL PNDs can be potentially applied as high‐resolution bioimaging labels toward advanced biotechnology and biomedical theranostics. A new class of fluorescent bioorganic nanodots self‐assembled from different short peptides is presented. The electronic energy spectrum of native non‐fluorescent nanodots is deeply modified upon thermally mediated refolding of their biological secondary structure from initial metastable to stable b‐sheet rich structure. This refolding leads to the tunable excitation dependent visible fluorescence of the nanodots. [ABSTRACT FROM AUTHOR]