No abstract

Bone tissue is a complex biocomposite material with a variety of organic (e.g., proteins, cells) and inorganic (e.g., hydroxyapatite crystals) components hierarchically organized with nano/microscale precision. Based on the understanding of such hierarchical organization of bone tissue and its unique mechanical properties, efforts are being made to mimic these organic–inorganic hybrid biocomposites. A key factor for the successful designing of complex, hybrid biomaterials is the facilitation and control of adhesion at the interfaces, as many current synthetic biomaterials are inert, lacking interfacial bioactivity. In this regard, researchers have focused on controlling the interface by surface modifications, but the development of a simple, unified way to biofunctionalize diverse organic and inorganic materials remains a critical challenge. Here, a universal biomineralization route, called polydopamine‐assisted hydroxyapatite formation (pHAF), that can be applied to virtually any type and morphology of scaffold materials is demonstrated. Inspired by the adhesion mechanism of mussels, the pHAF method can readily integrate hydroxyapatites on ceramics, noble metals, semiconductors, and synthetic polymers, irrespective of their size and morphology (e.g., porosity and shape). Surface‐anchored catecholamine moieties in polydopamine enriches the interface with calcium ions, facilitating the formation of hydroxyapatite crystals that are aligned to the c‐axes, parallel to the polydopamine layer as observed in natural hydroxyapatites in mineralized tissues. This universal surface biomineralization can be an innovative foundation for future tissue engineering.

The abnormal deposition and aggregation of beta-amyloid (Abeta) on brain tissues are considered to be one of the characteristic neuropathological features of Alzheimer's disease (AD). Environmental conditions such as metal ions, pH, and cell membranes are associated with Abeta deposition and plaque formation. According to the amyloid cascade hypothesis of AD, the deposition of Abeta42 oligomers as diffuse plaques in vivo is an important earliest event, leading to the formation of fibrillar amyloid plaques by the further accumulation of soluble Abeta under certain environmental conditions. In order to characterize the effect of metal ions on amyloid deposition and plaque growth on a solid surface, we prepared a synthetic template by immobilizing Abeta oligomers onto a N-hydroxysuccinimide ester-activated solid surface. According to our study using ex situ atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT-IR), and thioflavin T (ThT) fluorescence spectroscopy, Cu2+ and Zn2+ ions accelerated both Abeta40 and Abeta42 deposition but resulted only in the formation of "amorphous" aggregates. In contrast, Fe3+ induced the deposition of "fibrillar" amyloid plaques at neutral pH. Under mildly acidic environments, the formation of fibrillar amyloid plaques was not induced by any metal ion tested in this work. Using secondary ion mass spectroscopy (SIMS) analysis, we found that binding Cu ions to Abeta deposits on a solid template occurred by the possible reduction of Cu ions during the interaction of Abeta with Cu2+. Our results may provide insights into the role of metal ions on the formation of fibrillar or amorphous amyloid plaques in AD.

The self-assembly of peptide-based building blocks into nanostructures is an attractive route for fabricating novel bio-inspired materials because of their capacity for molecular recognition and functional flexibility as well as the mild conditions required in the fabrication process.[1-4] Among various peptide-based building blocks forming nanostructures, the simplest building blocks are aromatic dipeptides like diphenylalanine, which can readily self-assemble into nanotubes in aqueous solutions at ambient conditions. [2,[5][6][7] According to literature, the peptide nanotubes could be used in versatile applications for casting conducting metal nanowires, [8] enhancing the sensitivity of electrochemical detection of biomolecules, [9] and fabricating nano-fluidic channels [10] or peptide liquid crystals.[11]Although the self-assembly of peptides into nanostructured materials had been extensively studied, little progress had been made in the alignment and positioning of peptide nanostructures on a solid surface. Major obstacles include the complexity of current 'solution-based' approaches to peptide nanofabrication, causing dispersion and agglomeration problems, [6] which also require the chemical modification of surface and peptide nanostructures. [12] In the present study, we report a novel solid-phase growth of crystalline peptide nanowires at high temperatures driven by aniline vapor under anhydrous conditions. The formation of vertically well-aligned peptide nanowires on a solid surface were investigated through multiples tools, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), matrix-assisted laser desorption/ ionization time-of-flight (MALDI-TOF) mass spectrometry, and thermal analytical tools like the differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). We prepared an amorphous peptide thin film by drying a drop of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) solution containing diphenylalanine on a Si substrate. We conducted the experiment under strictly anhydrous conditions in a vacuum desiccator because water vapor could affect the final surface structure of the peptide thin film.[13] We could control the thickness of the film from a few mm down to $50 nm precisely by simply changing the diphenylalanine concentration in HFIP solution. According to our SEM and XRD analysis, the thin peptide film exhibited no surface features ( Fig. 1) and no characteristic diffraction peaks (Fig. 2), which indicate the 'amorphous' nature of the film. From the amorphous peptide film as a starting point, we were able to successfully grow vertically well-aligned peptide nanowires by aging the film at temperatures above 100 8C with aniline vapor. Figure 1 shows the electron micrographs of vertically wellaligned, rigid peptide nanowires. Peptide nanowires were uniformly formed over the entire region of the whole surface (10 mm  10 mm). The average diameter of the nanowires measured by SEM was found to be about 150 nm, but if we consider the effect of conductive coating for SEM, the act...

One of most unique and fascinating features of natural biomineralization processes is the controlled growth and hierarchical organization of inorganic minerals along with organic materials. Such marvels of nature give excellent physicochemical properties to natural biomaterials [1][2][3] and provide inspiration for the synthesis of novel functional nanomaterials to chemists and materials scientists. [4][5][6][7][8][9] For example, natural bones with excellent mechanical properties are a kind of organic/inorganic hybrid materials with organic collagen nanofi brils and inorganic calcium phosphate nanocrystals hierarchically organized on a nanoscale. [ 10 ] Researchers have found that the hierarchical organization of organic and inorganic components of natural biomaterials is due mainly to the repetitive display of acidic functional groups on the surface of organic materials [ 2 , 11 ] that can act as a nucleation site for the growth of inorganic materials. In this regard, numerous efforts have been made to synthesize novel hybrid nanomaterials by mimicking biomineralization processes especially for biomedical applications. [12][13][14][15] For example, Hartgerink and colleagues reported on synthesis and mineralization of peptideamphiphile nanofi bers displaying phosphate groups on their surface for bone regeneration. [ 13 ] To date, however, the synthesis of industrially important hybrid nanomaterials by mimicking biomineralization processes has been rarely reported despite many potential advantages of biomimetic approaches such as environmental compatibility and high controllability of shape and size.On the other hand, interest is growing in the fabrication of functional nanomaterials by self-assembly of peptide-based building blocks because of functional fl exibility and environmental compatibility. [ 16 , 17 ] Among numerous self-assembling peptides reported to date, diphenylalanine (Phe-Phe, FF) and its derivatives [18][19][20][21][22][23][24][25][26][27][28][29][30] are simplest peptides exhibiting unique mechanical, [ 19 ] electrochemical, [ 20 ] and optical properties [ 21 ] as well as high thermal and chemical stabilities. [ 23 ] It has been reported that they can readily form various nanostructures, including nanotubes, [18][19][20][21][22] nanowires, [23][24][25][26][27] nanospheres, [ 28 ] organogels, [ 29 ] and hydrogels [ 30 ] through a self-assembly process. Here, we fi rst report the synthesis of transition metal phosphate nanotubes for application as a cathode material for rechargeable lithium (Li) ion batteries by using a peptide hydrogel self-assembled from fl uorenylmethoxycarbonyl (Fmoc)-FF [ 30 ] as a template. The peptide hydrogel is composed of very thin nanofi bers (diameter about a few tens of nm) and displays numerous acidic and polar moieties on its surface (Figures S1 and S2 in the Supporting Information), which are highly benefi cial for the synthesis of novel organic/inorganic hybrid nanomaterials.We synthesized peptide/transition metal phosphate core/ shell nanofi bers, as schematic...

Photoluminescent peptide nanotubes are synthesized in an in situ incorporation of lanthanide complexes into peptide nanotubes through a self‐assembly process. We found that peptide nanotubes and photosensitizer molecules exhibited a high synergistic effect on the enhancement of lanthanide photoluminescence through a cascaded energy‐transfer mechanism.

Redox enzymes can catalyze complex synthesis reactions under mild conditions but conventional catalysts rarely accomplish this task. Despite the high potential of redox enzymes for the synthesis of valuable compounds (e.g., chiral alcohols and drug intermediates), [1][2][3][4][5] their application is hampered by the high cost of enzyme-specifi c cofactors that are required as a redox equivalent, such as nicotinamide adenine dinucleotide (NAD(P) H) and fl avin adenine dinucleotide (FADH). Thus, numerous efforts have been made over the past decades to accomplish in situ cofactor regeneration from their oxidized counterpart. [6][7][8][9] For example, researchers found that NAD(P)H can be successfully regenerated by introducing secondary enzymes [10][11][12] that reduce its oxidized counterpart (i.e., NAD(P) + ) or electrodes [13][14][15] with an external power supply into reaction media. However, these approaches present intrinsic drawbacks (e.g., by-product formation and requirement of secondary enzymes for biocatalytic regeneration, as well as extremely low yield and high overpotential for electrochemical regeneration) that hindered their practical application beyond the laboratory scale. [6][7][8] Herein, we report on the development of quantum-dotsensitized TiO 2 nanotube arrays for redox enzymatic synthesis coupled with the photoregeneration of nicotinamide cofactors via inspiration from natural photosynthesis. In natural photosynthesis, [ 16 , 17 ] incident light electronically excites a membranebound protein-pigment complexes called a photosystem. The photogenerated electrons are rapidly delivered to reaction centers along the electron transport chain for regenerating NADPH cofactors. These cofactors drive redox enzymatic reactions to synthesize organic compounds in the Calvin cycle. Its unique features (e.g., environmental compatibility and nearunity quantum yield) have fascinated scientists and provided inspiration to improve the effi ciency of solar cells and photoelectrochemical hydrogen production systems. [18][19][20][21][22][23][24] In the present study, the photosystem for in situ NAD(P)H regeneration consisted of TiO 2 -CdS nanotubes as a photoelectrode, triethanolamine (TEOA) as an electron donor, and pentamethylcyclopentadienyl rhodium bipyridine ([Cp * Rh(bpy)(H 2 O)] 2 + ) as an electron mediator and a hydride transfer catalyst ( Figure S1, Supporting Information). As a photoelectrode for non-enzymatic regeneration of NAD(P)H, a nanotubular TiO 2 -CdS fi lm has many advantages that include easy synthesis and morphology control, [ 25 , 26 ] effi cient charge separation, [ 24 , 27 ] and better diffusion of reaction species through nanotube channels. Due to the small size and more negative position of the conduction band (CB) edge of CdS compared to TiO 2 (at least 0.2 V more negative), photogenerated electrons can be rapidly injected from CdS to TiO 2 in a thermodynamically favorable manner ( Figure S1, Supporting Information). This injection suppresses electron-hole recombination, which is more...

Understanding the self-assembly of peptides into ordered nanostructures is recently getting much attention since it can provide an alternative route for fabricating novel bio-inspired materials. In order to realize the potential of the peptide-based nanofabrication technology, however, more information is needed regarding the integrity or stability of peptide nanostructures under the process conditions encountered in their applications. In this study, we investigated the stability of self-assembled peptide nanowires (PNWs) and nanotubes (PNTs) against thermal, chemical, proteolytic attacks, and their conformational changes upon heat treatment. PNWs and PNTs were grown by the self-assembly of diphenylalanine (Phe-Phe), a peptide building block, on solid substrates at different chemical atmospheres and temperatures. The incubation of diphenylalanine under aniline vapor at 150 degrees C led to the formation of PNWs, while its incubation with water vapor at 25 degrees C produced PNTs. We analyzed the stability of peptide nanostructures using multiple tools, such as electron microscopy, thermal analysis tools, circular dichroism, and Fourier-transform infrared spectroscopy. Our results show that PNWs are highly stable up to 200 degrees C and remain unchanged when incubated in aqueous solutions (from pH 1 to 14) or in various chemical solvents (from polar to non-polar). In contrast, PNTs started to disintegrate even at 100 degrees C and underwent a conformational change at an elevated temperature. When we further studied their resistance to a proteolytic environment, we discovered that PNWs kept their initial structure while PNTs fully disintegrated. We found that the high stability of PNWs originates from their predominant beta-sheet conformation and the conformational change of diphenylalanine nanostructures. Our study suggests that self-assembled PNWs are suitable for future nano-scale applications requiring harsh processing conditions.