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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.

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]

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]

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]

Light is an attractive source of energy for regulating stimulus-responsive chemical systems. Here, we use light as a gating source to control the redox state, the localized surface plasmonic resonance (LSPR) peak, and the structure of molybdenum oxide (MoO 3 ) nanosheets, which are important for various applications. However, the light excitation is not that of the MoO 3 nanosheets but rather that of pyranine (HPTS) photoacids, which in turn undergo an excited-state proton transfer (ESPT) process. We show that the ESPT process from HPTS to the nanosheets and the intercalation of protons within the MoO 3 nanosheets trigger the reduction of the nanosheets and the broadening of the LSPR peak, a process that is reversible, meaning that in the absence of light, the LSPR peak diminishes and the nanosheets return to their oxidized form. We further show that this reversible process is accompanied by a change in the nanosheet size and morphology.

Neural tissue engineering (TE) represents a promising new avenue of therapy to support nerve recovery and regeneration. To recreate the complex environment in which neurons develop and mature, the ideal biomaterials for neural TE require a number of properties and capabilities including the appropriate biochemical and physical cues to adsorb and release specific growth factors. Here, we present neural TE constructs based on electrospun serum albumin (SA) fibrous scaffolds. We doped our SA scaffolds with an iron-containing porphyrin, hemin, to confer conductivity, and then functionalized them with different recombinant proteins and growth factors to ensure cell attachment and proliferation. We demonstrated the potential for these constructs combining topographical, biochemical, and electrical stimuli by testing them with clinically relevant neural populations derived from human induced pluripotent stem cells (hiPSCs). Our scaffolds could support the attachment, proliferation, and neuronal differentiation of hiPSC-derived neural stem cells (NSCs), and were also able to incorporate active growth factors and release them over time, which modified the behavior of cultured cells and substituted the need for growth factor supplementation by media change. Electrical stimulation on the doped SA scaffold positively influenced the maturation of neuronal populations, with neurons exhibiting more branched neurites compared to controls. Through promotion of cell proliferation, differentiation, and neurite branching of hiPSC-derived NSCs, these conductive SA fibrous scaffolds are of broad application in nerve regeneration strategies.

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.

Solid-state electron transport (ETp) via a monolayer of immobilized azurin (Az) was examined by conducting probe atomic force microscopy (CP-AFM), as a function of both temperature (248-373K) and applied tip force (6-15 nN). At low forces, ETp via holo-Az (with Cu(2+)) is temperature-independent, but thermally activated via the Cu-depleted form of Az, apo-Az. While this observation agrees with those of macroscopic-scale measurements, we find that for holo-Az the mechanism of ETp at high temperatures changes upon an increase in the force applied by the tip to the proteins; namely, above 310 K and forces >6 nN ETp becomes thermally activated. This is in contrast to apo-Az, where increasing applied force causes only small monotonic increases in currents due to decreased electrode separation. The distinct ETp temperature dependence of holo- and apo-Az is assigned to a difference in structural response to pressure between the two protein forms. An important implication of these CP-AFM results (of measurements over a significant temperature range) is that for reliable ETp measurements on flexible macromolecules, such as proteins, the pressure applied during the measurements should be controlled or at least monitored.

Steady-state and time-resolved emission techniques have been employed to study the fluorescence properties of thioflavin-T (ThT) adsorbed on oxidized porous silicon (PSi) surfaces, with an average pore size of ∼10 nm. We found that the average fluorescence decay time of ThT, when it is adsorbed on the PSi surface, is rather long, τ(av) = 1.3 ns. We attribute this relatively long emission lifetime to the effect of the immobilization of ThT on the PSi surface, which inhibit the rotation of the aniline with respect to the benzothiazole moieties of ThT. We also measured the fluorescence properties of ThT in PSi samples in equilibrium with vapors of several liquids, such as methanol, acetonitrile, and water. We found that the fluorescence intensity drops by a factor of 10, and the average decay time, measured by a time-correlated single-photon counting technique, decreases by a factor of 3. We explain these results in terms of liquid condensation of the vapors in the PSi pores, which leads to partial dissolution of the ThT molecules in the liquid pools., (© 2011 American Chemical Society)

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.

Steady-state and time-resolved emission techniques were employed to study the nonradiative process of Thioflavin-T (ThT) in 1-propanol as a function of temperature. We found that the nonradiative rate, k(nr), decreased by about 3 orders of magnitude when the temperature was lowered to 88 K. We found remarkably good correspondence between the temperature dependence of k(nr) of ThT and the dielectric relaxation times of the 1-propanol solvent.

We show anomalously strong shear piezoelectric activity in self-assembled diphenylalanine peptide nanotubes (PNTs), indicating electric polarization directed along the tube axis. Comparison with well-known piezoelectric LiNbO(3) and lateral signal calibration yields sufficiently high effective piezoelectric coefficient values of at least 60 pm/V (shear response for tubes of approximately 200 nm in diameter). PNTs demonstrate linear deformation without irreversible degradation in a broad range of driving voltages. The results open up a wide avenue for developing new generations of "green" piezoelectric materials and piezonanodevices based on bioactive tubular nanostructures potentially compatible with human tissue.

We report on observation of photoluminescence (PL) in blue and UV regions of exciton origin in bioinspired material-peptide nanotubes (PNTs). Steplike optical absorption and PL measurements have allowed finding quantum confined (QC) phenomenon in PNTs. The estimations show that QC in these nanotubes occurs due to a crystalline structure of subnanometer scale dimension formed under the self-assembly process. Our new findings pave the way for the integration of PNT in a new generation of optical devices. A blue PL array of a PNT-patterned device is demonstrated.