Amyloid-derived peptide forms self-assembled monolayers on gold nanoparticle with a curvature-dependent β-sheet structure

Curved Nanointerface Controls the Chiral Effect on Peptide Fibrillation

Nanostructures with varying functionalities have been engineered to modulate the fibrillation of amyloid-β (Aβ) peptides. Nevertheless, the chirality effect at the curved nanointerfaces is seldom dissected. In this study, we systematically explored the curvature-modulated chiral effect on the regulation of Aβ1-42 fibrillation by using l/d-penicillamine-gold nanoparticles (l/d-PGNPs). According to the microscopic and spectroscopic analyses, Aβ1-42 fibrillation can be effectively suppressed by more curved (0.2 nm-1, 1/r) d-nanointerface (d-PGNPs5) with notable chiral selectivity, even at a low inhibitor/peptide (I/P) molar ratio (1:100). A greatly alleviated cytotoxic effect of Aβ1-42 peptides after the inhibition process is also revealed. The highly curved nanointerface drives the formation of multiple hydrogen bonds and promotes electrostatic interactions with Aβ1-42. Importantly, the curved d-nanointerface controls well the spatial arrangement of Pen motifs, making it incompatible with the fibrillation direction of Aβ1-42 and thus gaining enhanced efficiency on amyloid fibrillar modulation. This study provides valuable insights into the interactions between chirality and peptide-nanointerface effects, which are crucial for the development of inhibitors in anti-β-amyloidosis.

Noble Metal Nanoparticles with Nanogel Coatings: Coinage Metal Thiolate-Stabilized Glutathione Hydrogel Shells

Developing biocompatible nanocoatings is crucial for biomedical applications. Noble metal colloidal nanoparticles with biomolecular shells are thought to combine diverse chemical and optothermal functionalities with biocompatibility. Herein, we present nanoparticles with peptide hydrogel shells that feature an unusual combination of properties: the metal core possesses localized plasmon resonance, whereas a few-nanometer-thick shells open opportunities to employ their soft framework for loading and scaffolding. We demonstrate this concept with gold and silver nanoparticles capped by glutathione peptides stacked into parallel β-sheets as they aggregate on the surface. A key role in the formation of the ordered structure is played by coinage metal(I) thiolates, i.e., Ag(I), Cu(I), and Au(I). The shell thickness can be controlled via the concentration of either metal ions or peptides. Theoretical modeling of the shell's molecular structure suggests that the thiolates have a similar conformation for all the metals and that the parallel β-sheet-like structure is a kinetic product of the peptide aggregation. Using third-order nonlinear two-dimensional infrared spectroscopy, we revealed that the ordered secondary structure is similar to the bulk hydrogels of the coinage metal thiolates of glutathione, which also consist of aggregated stacked parallel β-sheets. We expect that nanoparticles with hydrogel shells will be useful additions to the nanomaterial toolbox. The present method of nanogel coating can be applied to arbitrary surfaces where the initial deposition of the seed glutathione monolayer is possible.

Improvements of Solubility and Bioavailability of Lutein Through Grafting with Hydrophilic Polyacrylic Acid

In this study, polyacrylic acid grafted lutein (PAA-g-lutein) was prepared by hydrophilic modification of lutein with polyacrylic acid (PAA) through Steglish esterification method. The unreacted lutein was loaded in micelles formed by self-assembly of graft copolymers in water to form composite nanoparticles. The bioaccessibility and bioavailability of lutein nanoparticles were studied by in vitro and in vivo digestion experiments. Compared with free lutein, the saturated solubility and bioaccessibility of lutein nanoparticles were increased by 78 times and 3.6 times, respectively. The pharmacokinetics results in the mice model showed that the maximum concentration (Cmax) and area under concentration-time curve (AUC) of plasma of mice were increased by 3.05 and 6.07 times with lutein nanoparticles compared with free lutein. Meanwhile, the prepared lutein nanoparticles also promoted the accumulation of lutein in the liver, mesenteric adipose, and eyeballs. These results indicate that graft copolymerization of lutein with water-soluble polymers to form nanoparticles is an effective method to promote the bioavailability of lutein in vivo. Moreover, this method is simple and applicable, and can also be used for the modification of other bioactive molecules.

Mechanistic insights into the size-dependent effects of nanoparticles on inhibiting and accelerating amyloid fibril formation

The aggregation of peptides into amyloid fibrils has been linked to ageing-related diseases, such as Alzheimer's and type 2 diabetes. Interfaces, particularly those with large nanostructured surfaces, can affect the kinetics of peptide aggregation, which ranges from complete inhibition to strong acceleration. While a number of physiochemical parameters determine interfacial effects, we focus here on the role of nanoparticle (NP) size and curvature. We used thioflavin T (ThT) fluorescence assays to demonstrate the size-dependent effects of NPs on amyloid fibril formation for the peptides Aβ₄₀, NNFGAIL, GNNQQNY and VQIYVK. While 5 nm gold NPs (AuNP-5) retarded or inhibited the aggregation of all peptides except NNFGAIL, larger 20 nm gold NPs (AuNP-20) tended to accelerate or not influence peptide aggregation. Differences in the NP effects for the peptides resulted from the different peptide properties (size, tendency to aggregate) and associated surface binding affinities. Additional dynamic light scattering (DLS), electron microscopy, and atomic force microscopy (AFM) experiments with the Aβ₄₀ peptide confirmed size-dependent NP effects on peptide aggregation, and also suggested a structural influence on the formed fibrils. NPs can serve as a surface for the adsorption of peptide monomers and enable nucleation to oligomers and fibril formation. However, molecular dynamics (MD) simulations showed that peptide oligomers were less stable at smaller NPs. High surface curvatures destabilized prefibrillar structures, which provides a possible explanation for inhibitory effects on fibril growth, provided that peptide-NP surface binding was relevant for fibril formation. These mechanistic insights can support the design of future nanostructured materials.

Phosphorylation of covalent organic framework nanospheres for inhibition of amyloid-β peptide fibrillation

The development and exploration of new nanostructural inhibitors against Alzheimer's disease (AD)-associated amyloid-β (Aβ) fibrillation have attracted extensive attention and become a new frontier in nanomedicine. However, focusing on finding an effective nanostructure is one of the most challenging parts of the therapeutics task. Herein, nanoscale spherical covalent organic frameworks (COFs) via post-synthetic functionalization with sodium phosphate (SP) groups on the channel networks were found to efficiently inhibit Aβ fibrillation. The as-prepared uniform SP-COF nanospheres with high surface area, good crystallinity, and chemical stability were characterized by multifarious microscopic and spectroscopic techniques. Moreover, molecular dynamics simulation together with fibrillation kinetics and cytotoxicity assay experiments shows that there were restricted-access adsorption channels in the SP-COFs which were formed by the cavities with size and functional groups accommodated to the Aβ peptide sequence and significantly affected the fibrillation and cytotoxicity of Aβ. Transmission electron microscopy (TEM), dynamic light scattering (DLS) monitoring, isothermal titration calorimetry (ITC), Fourier transform infrared (FT-IR) and circular dichroism (CD) spectra measurements, and confocal imaging observation were performed to understand the inhibition mechanism and influencing factors of the SP-COFs. To our knowledge, our strategy is the first exploration of COF-based anti-amyloidogenic nanomaterials with high affinity and specific targeting, which are crucial for the inhibition of Aβ fibrillation for AD prevention and treatment.

Nanoscale spherical COFs via phosphorylation functionalization were found to efficiently inhibit fibrillation of the Alzheimer's disease-associated Aβ peptide.

Influencing factors and characterization methods of nanoparticles regulating amyloid aggregation

Human disorders associated with amyloid aggregation, such as Alzheimer's disease and Parkinson's disease, afflict the lives of millions worldwide. When peptides and proteins in the body are converted to amyloids, which have a tendency to aggregate, the toxic oligomers produced during the aggregation process can trigger a range of diseases. Nanoparticles (NPs) have been found to possess surface effects that can modulate the amyloid aggregation process and they have potential application value in the treatment of diseases related to amyloid aggregation and fibrillary tangles. In this review, we discuss recent progress relating to studies of nanoparticles that regulate amyloid aggregation. The review focuses on the factors influencing this regulation, which are important as guidelines for the future design of NPs for the treatment of amyloid aggregation. We describe the characterization methods that have been utilized so far in such studies. This review provides research information and characterization methods for the rational design of NPs, which should result in therapeutic strategies for amyloid diseases.

Study on physicochemical characteristics of lutein nanoemulsions stabilized by chickpea protein isolate-stevioside complex

BACKGROUND

Chickpea protein isolate (CPI) originating from chickpeas has the advantages of facilitating the stability of food emulsions. Stevioside (STE) exhibits a notable surface activity and can improve the water solubility of numerous hydrophobic nutrients. STE and protein mixtures show great potential as emulsions stabilizers. The present study aimed to prepare a novel nanoemulsion for encapsulating lutein (LUT) by ultrasonic homogenization using chickpea protein isolate-stevioside complex (CPI-STE) as a stabilizer and also to investigate the physicochemical characteristics.

RESULTS

The results obtained showed that different preparation conditions demonstrated significant influences on the physicochemical properties of CPI-STE-LUT nanoemulsions. Under the optimal condition, the average particle size of CPI-STE-LUT nanoemulsions was 195.1 nm, and the emulsifying and encapsulation efficiencies of lutein were 91.04% and 87.56%, respectively. CPI-STE-LUT nanoemulsions stabilized by CPI-STE could significantly increase the emulsifying and encapsulation efficiencies of lutein compared to that stabilized by CPI. Fourier transform infrared spectroscopy revealed that hydrogen bond was the main binding force of CPI and lutein, and there was a covalent bond between the two molecules. Furthermore, the stability of CPI-STE-LUT nanoemulsions in gastrointestinal phase was higher than that of CPI-LUT nanoemulsions, which could load lutein more effectively and be more resistant to digestive enzymes.

CONCLUSION

The present study reports the physicochemical characterization of CPI-STE-LUT nanoemulsions for the first time. CPI-STE-LUT nanoemulsions were characterized by a small average particle size lower than 200 nm, as well as high emulsifying and encapsulation efficiencies, and good stability. © 2021 Society of Chemical Industry.

Coating Gold Nanorods with Self-Assembling Peptide Amphiphiles Promotes Stability and Facilitates in vivo Two-Photon Imaging

Gold nanorods (GNRs) are versatile asymmetric nanoparticles with unique optical properties. These properties makes GNRs ideal agents for applications such as photothermal cancer therapy, biosensing, and in vivo imaging. However,...

Zinc oxide nanoparticle interface moderation with tyrosine and tryptophan reverses the pro-amyloidogenic property of the particle

Zinc oxide nanoparticle with negative surface potential (ZnONP) enhances bovine insulin fibrillation. Here, we are exploring ZnONP with positive surface potential (ZnONP_Unc) and surface functionalized with tyrosine and tryptophan amino acids to observe the effects of surface potential and surface functional groups on the fibrillation. ZnONP_Unc, despite of inversed surface potential, enhances the insulin fibrillation with increase in the interface concentration at physiological pH. Whereas, the interface moderation with the amino acids mitigates the surface-mediated insulin fibrillation propensity. Additionally, the study indicates that the change in interfacial functional groups at ZnONP_Unc significantly reverses the interface-mediated destabilization of insulin conformation. The functional groups from the amino acids, like CO, N-H and aromatic functional groups, are anticipated to further stabilize the insulin conformation by forming hydrogen bond and van der Waals interactions with the key amyloidogenic sequences of insulin, A13-A20 from A-chain and B9-B20 from B-chain. Hence, the altered interaction profile, with change in interfacial functional groups, mitigates the interface-mediated insulin fibrillation and the ZnONP_Unc-/fibril-mediated cytotoxicity.

Exploiting Ultrashort α,β-Peptides in the Colloidal Stabilization of Gold Nanoparticles

Colloidal gold nanoparticles (GNPs) have found wide-ranging applications in nanomedicine due to their unique optical properties, ease of preparation, and functionalization. To avoid the formation of GNP aggregates in the physiological environment, molecules such as lipids, polysaccharides, or polymers are employed as GNP coatings. Here, we present the colloidal stabilization of GNPs using ultrashort α,β-peptides containing the repeating unit of a diaryl β^2,3-amino acid and characterized by an extended conformation. Differently functionalized GNPs have been characterized by ultraviolet, dynamic light scattering, and transmission electron microscopy analysis, allowing us to define the best candidate that inhibits the aggregation of GNPs not only in water but also in mouse serum. In particular, a short tripeptide was found to be able to stabilize GNPs in physiological media over 3 months. This new system has been further capped with albumin, obtaining a material with even more colloidal stability and ability to prevent the formation of a thick protein corona in physiological media.

Study on the bioavailability of stevioside-encapsulized lutein and its mechanism

This study aims to develop novel lutein nanoparticles encapsulized by stevioside (LUT-STE, 165 ± 2 nm average particles size) and systematically evaluate its bioavailability. Multiple spectroscopy and NMR analyses showed lutein and stevioside could interact through hydrogen bonds, CHπ interaction and van der Waals forces. Molecular docking simulation showed lutein was well distributed in the hydrophobic cavity of stevioside. Analyzed by Caco-2 cellular models, the transported amount of LUT-STE was 2.39 times that of lutein in 120 min with a P_app (B → A)/P_app (A → B) value of 0.63 ± 0.04. Nystatin and dynasore significantly reduced the cellular uptake of LUT-STE by 41.3% and 57.7%, respectively. Compared with free lutein, LUT-STE increased the C_max in mice plasma by 5.01-fold and promoted the accumulation in multiple organs. LUT-STE promoted the protein expressions of CD36, NPC1L1 and PPARγ in both cell and animal models. In conclusion, stevioside entrapment significantly promote the bioavailability of lutein through multiple transmembrane pathways.

The role of surfaces on amyloid formation

Interfaces can strongly accelerate or inhibit protein aggregation, destabilizing proteins that are stable in solution or, conversely, stabilizing proteins that are aggregation-prone. Although this behaviour is well-known, our understanding of the molecular mechanisms underlying surface-induced protein aggregation is still largely incomplete. A major challenge is represented by the high number of physico-chemical parameters involved, which are highly specific to the considered combination of protein, surface properties, and solution conditions. The key aspect determining the role of interfaces is the relative propensity of the protein to aggregate at the surface with respect to bulk. In this review, we discuss the multiple molecular determinants that regulate this balance. We summarize current experimental techniques aimed at characterizing protein aggregation at interfaces, and highlight the need to complement experimental analysis with theoretical modelling. In particular, we illustrate how chemical kinetic analysis can be combined with experimental methods to provide insights into the molecular mechanisms underlying surface-induced protein aggregation, under both stagnant and agitation conditions. We summarize recent progress in the study of important amyloids systems, focusing on selected relevant interfaces.

Understanding the Factors Influencing Chitosan-Based Nanoparticles-Protein Corona Interaction and Drug Delivery Applications

Chitosan is a polymer that is extensively used to prepare nanoparticles (NPs) with tailored properties for applications in many fields of human activities. Among them, targeted drug delivery, especially when cancer therapy is the main interest, is a major application of chitosan-based NPs. Due to its positive charges, chitosan is used to produce the core of the NPs or to cover NPs made from other types of polymers, both strategies aiming to protect the carried drug until NPs reach the target sites and to facilitate the uptake and drug delivery into these cells. A major challenge in the design of these chitosan-based NPs is the formation of a protein corona (PC) upon contact with biological fluids. The composition of the PC can, to some extent, be modulated depending on the size, shape, electrical charge and hydrophobic / hydrophilic characteristics of the NPs. According to the composition of the biological fluids that have to be crossed during the journey of the drug-loaded NPs towards the target cells, the surface of these particles can be changed by covering their core with various types of polymers or with functionalized polymers carrying some special molecules, that will preferentially adsorb some proteins in their PC. The PC's composition may change by continuous processes of adsorption and desorption, depending on the affinity of these proteins for the chemical structure of the surface of NPs. Beside these, in designing the targeted drug delivery NPs one can take into account their toxicity, initiation of an immune response, participation (enhancement or inhibition) in certain metabolic pathways or chemical processes like reactive oxygen species, type of endocytosis of target cells, and many others. There are cases in which these processes seem to require antagonistic properties of nanoparticles. Products that show good behavior in cell cultures may lead to poor in vivo results, when the composition of the formed PC is totally different. This paper reviews the physico-chemical properties, cellular uptake and drug delivery applications of chitosan-based nanoparticles, specifying the factors that contribute to the success of the targeted drug delivery. Furthermore, we highlight the role of the protein corona formed around the NP in its intercellular fate.

Surface-Directed Disparity in Self-Assembled Structures of Small-Peptide l-Glutathione on Gold and Silver Nanoparticles

Despite the key roles of l-glutathiones (GSHs) inbiology and nano-biotechnology, understanding their labile structures and hydrogen bond interactions with nanoparticles has posed a critical challenge to the scientific community. The structural conformation of GSH as a capping layer on gold nanoparticle (AuNP) and silver nanoparticle (AgNP) surfaces is investigated. In this report, we attempt to explore the material-dependent interaction of GSH with different spherical nanoparticle surfaces by employing Fourier transform infrared (FTIR) spectroscopy. The infrared signal of amide I of GSH is studied as a function of different materials' spherical nanoparticles with comparable size. We revealed the β-sheet secondary structure of GSH on AgNPs and the random structure on AuNPs even though both the nanoparticles have comparable shapes and sizes and belong to the same group of the periodic table. The GSH is firmly anchored on the gold and silver surface via the thiol of the cys part. However, our experimental data designate a further interaction with the AgNP surface via the carboxylic acid group of the gly- and glu- end of the molecule. It is observed that enhancement of IR absorption of amide I of GSH is pronounced by a factor of 10 on AuNP but, in contrast, on the same-sized AgNP, the suppression is perceived by a factor of 2, even though both are plasmonic materials with respect to free GSH. This study can be used as a point of reference for understanding the structural conformation of the capping layer on nanoparticle surfaces as well as surface enhancement of the IR absorption of amide I. We would like to emphasize that molecular self-assembly on the nanoparticle surfaces is definitely of very broad interest for chemists working in nearly any subdiscipline, spanning from the nanoparticle-based medicine to surface-enhanced spectroscopy to heterogeneous catalysis, etc.

Probing the binding modes and dynamics of histidine on fumed silica surfaces by solid-state NMR

Silica nanoparticles can be designed to exhibit a diverse range of morphologies (e.g. non-porous, mesoporous), physical properties (e.g. hydrophobic, hydrophilic) and a wide range of chemical and biomolecular surface functionalizations. In the present work, the adsorption complex of histidine (His) and fumed silica nanoparticles (FSN) is probed using thermal analysis (TGA/DTG) and a battery of solid-state (SS) NMR methods supported by DFT chemical shift calculations. Multinuclear (1H/13C/15N) one- and two-dimensional magic angle spinning (MAS) SSNMR experiments were applied to determine site-specific interactions between His and FSN surfaces as a function of adsorption solution concentration, pH and hydration state. By directly comparing SSNMR observables (linewidth, chemical shift and relaxation parameters) for His-FSN adsorption complexes to various crystalline, amorphous and aqueous His forms, the His structural and dynamic environment on FSN surfaces could be determined at an atomic level. The observed 13C and 15N MAS NMR chemical shifts, linewidths and relaxation parameters show that the His surface layer on FSN has a significant dependence on pH and hydration state. His is highly dynamic on FSN surfaces under acidic conditions (pH 4) as evidenced by sharp resonances with near isotropic chemical shifts regardless of hydration level indicating a non-specific binding arrangement while, a considerably more rigid His environment with defined protonation states is observed at near neutral pH with subtle variations between hydrated and anhydrous complexes. At near neutral pH, less charge repulsion occurs on the FSN surface and His is more tightly bound as evidenced by considerable line broadening likely due to chemical shift heterogeneity and a distribution in hydrogen-bonding strengths on the FSN surface. Multiple His sites exchange with a tightly bound water layer in hydrated samples while, direct interaction with the FSN surface and significant chemical shift perturbations for imidazole ring nitrogen sites and some carbon resonances are observed after drying. The SSNMR data was used to propose an interfacial molecular binding model between His and FSN surfaces under varying conditions setting the stage for future multinuclear, multidimensional SSNMR studies of His-containing peptides on silica nanoparticles and other nanomaterials of interest.

Chiral gold nanoparticles enantioselectively rescue memory deficits in a mouse model of Alzheimer's disease

Preventing aggregation of amyloid beta (Aβ) peptides is a promising strategy for the treatment of Alzheimer’s disease (AD), and gold nanoparticles have previously been explored as a potential anti-Aβ therapeutics. Here we design and prepare 3.3 nm L- and D-glutathione stabilized gold nanoparticles (denoted as L3.3 and D3.3, respectively). Both chiral nanoparticles are able to inhibit aggregation of Aβ42 and cross the blood-brain barrier (BBB) following intravenous administration without noticeable toxicity. D3.3 possesses a larger binding affinity to Aβ42 and higher brain biodistribution compared with its enantiomer L3.3, giving rise to stronger inhibition of Aβ42 fibrillation and better rescue of behavioral impairments in AD model mice. This conjugation of a small nanoparticle with chiral recognition moiety provides a potential therapeutic approach for AD.

Nanoparticles are being explored as a potential method to target Aβ aggregation in Alzheimer’s disease. Here, the authors develop gold nanoparticles that were capped with chiral L or D-glutathione which has been shown to improve BBB permeability and demonstrate their ability to improve cognitive function in a mouse model of AD.

Alzheimer's Therapeutic Strategy: Photoactive Platforms for Suppressing the Aggregation of Amyloid β Protein

Neurodegenerative diseases such as Alzheimer's disease (AD) have become a public health problem. Progressive cerebral accumulation of amyloid protein (Aβ) was widely considered as the cause of AD. One promising strategy for AD preclinical study is to degrade and clear the deposited amyloid aggregates with β-sheet-rich secondary structure in the brain. Based on the requirement, photo-active materials with the specific excitation and the standardization of the photosensitizer preparation and application in clinics, have attracted increased attention in the study and treatment of neurodegenerative disease as a novel method termed as photodynamic therapy (PDT). This review will focus on the new photosensitizing materials and discuss the trend of PDT techniques for the possible application in the treatment strategy of amyloid-related diseases.

Solid-state nuclear magnetic resonance studies of nanoparticles

In this trends article, we review seminal and recent studies using static and magic-angle spinning solid-state NMR to study the structure of nanoparticles and ligands attached to nanoparticles. Solid-state NMR techniques including one-dimensional multinuclear NMR, cross-polarization, techniques for measuring dipolar coupling and internuclear distances, and multidimensional NMR have provided insight into the core-shell structure of nanoparticles as well as the structure of ligands on the nanoparticle surface. Hyperpolarization techniques, in particular solid-state dynamic nuclear polarization (DNP), have enabled detailed studies of nanoparticle core-shell structure and surface chemistry, by allowing unprecedented levels of sensitivity to be achieved. The high signal-to-noise afforded by DNP has allowed homonuclear and heteronuclear correlation experiments involving nuclei with low natural abundance to be performed in reasonable experimental times, which previously would not have been possible. The use of DNP to study nanoparticles and their applications will be a fruitful area of study in the coming years as well.

One Peptide for Them All: Gold Nanoparticles of Different Sizes Are Stabilized by a Common Peptide Amphiphile

The functionalization of gold nanoparticles (GNPs) with peptidic moieties can prevent their aggregation and facilitate their use for applications both in vitro and in vivo. To date, no peptide-based coating has been shown to stabilize GNPs larger than 30 nm in diameter; such particles are of interest for applications including vaccine development, drug delivery, and sensing. Here, GNPs with diameters of 20, 40, and 100 nm are functionalized with peptide amphiphiles. Using a combination of transmission electron microscopy, UV-vis spectroscopy, and dynamic light scattering, we show that GNPs up to 100 nm in size can be stabilized by these molecules. Moreover, we demonstrate that these peptide amphiphiles form curvature-dependent, ordered structures on the surface of the GNPs and that the GNPs remain disperse at high-salt concentrations and in the presence of competing thiol-containing molecules. These results represent the development of a peptide amphiphile-based coating system for GNPs which has the potential to be beneficial for a wide range of biological applications, in addition to image enhancement and catalysis.

Peptide–Gold Nanoparticle Conjugates as Artificial Carbonic Anhydrase Mimics

We herein describe the design and synthesis of a catalytically active peptide–gold nanoparticle conjugate (Pep-Au-NP) that binds Zn(II) within its peptide monolayer and develops carbonic anhydrase activity. Specifically, a modified variant of the β-sheet forming IHIHIQI-peptide (IHQ), which forms an interstrand 3-His Zn(II)-binding site, was used as a ligand for spherical gold nanoparticles (Au-NPs). The resulting immobilized peptide maintains its ability to form β-sheets, as determined by circular dichroism (CD)-spectroscopy and, thus, maintains its ability to form Zn(II)-binding sites. The addition of Zn(II)-ions to the peptide–gold nanoparticle conjugates (Au@IHQ-NP) resulted in significant improvements in rates of ester hydrolysis of 4-nitrophenyl acetate (4-NPA) and the hydration of CO2 compared to the unconjugated peptide variants. Recycling of the catalyst revealed that Au@IHQ-NP remains intact with at least 94% of its initial activity after five rounds of CO2 hydration. The herein reported results reveal that Pep-Au-NPs are able to perform reactions catalyzed by natural metalloenzymes and open up new possibilities for the implementation of these conjugates.

Magnesium matrix nanocomposites for orthopedic applications: A review from mechanical, corrosion, and biological perspectives

Magnesium (Mg) and some of its alloys have attracted extensive interests for biomedical applications as they exhibit biodegradability and low elastic modulus that is closer to natural bones than the currently used metallic implant materials such as titanium (Ti) and its alloys, stainless steels, and cobalt-chromium (Co-Cr) alloys. However, the rapid degradation of Mg alloys and loss of their mechanical integrity before sufficient bone healing impede their clinical application. Our literature review shows that magnesium matrix nanocomposites (MMNCs) reinforced with nanoparticles possess enhanced strength, high corrosion resistance, and good biocompatibility. This article provides a detailed analysis of the effects of nanoparticle reinforcements on the mechanical properties, corrosion behavior, and biocompatibility of MMNCs as promising biodegradable implant materials. The governing equations to quantitatively predict the mechanical properties and underlying synergistic strengthening mechanisms in MMNCs are elucidated. The potential, recent advances, challenges and future research directions in relation to nanoparticles reinforced MMNCs are highlighted. STATEMENT OF SIGNIFICANCE: Critically reviewing magnesium metal matrix nanocomposites (MMNCs) for the biomedical application. Clear definitions of strengthening mechanisms using reinforcement particle in the magnesium matrix, as there were controversial in governing equations of strengthening parameters. Providing better understanding of the effect of particle size, volume fraction, interfacial bonding, and uniform dispersion of reinforcement particles on MMNCs.

One Step Preparation of Peptide-Coated Gold Nanoparticles with Tunable Size

Gold nanoparticles (AuNPs) made from self-assembling peptides have been used in many research fields and attracted a great deal of attention due to their high stability, biocompatibility and functionality. However, existing preparation methods for peptide-coated AuNPs are post-synthesis processes, which are complicated and time consuming. Therefore, a one-step preparation method for peptide-coated AuNPs is proposed here. The AuNPs obtained by this method exhibit good stability. Importantly, peptide-coated AuNPs with precise different sizes can be prepared by this method through pH control of reducing reagent tyrosine in range of 10.0~12.7. Thus, the one-step preparation method proposed here provides a significant tool for the research in different fields concerning NP size, stability and biocompatibility.

Modulation of β-amyloid aggregation by graphene quantum dots

Misfolding and abnormal aggregation of β-amyloid peptide is associated with the onset and progress of Alzheimer's disease (AD). Therefore, modulating β-amyloid aggregation is critical for the treatment of AD. Herein, we studied the regulatory effects and mechanism of graphene quantum dots (GQDs) on 1-42 β-amyloid (Aβ_1-42) aggregation. GQDs displayed significant regulatory effects on the aggregation of Aβ_1-42 peptide as detected by thioflavin T (ThT) assay. Then, the changes of confirmations and structures induced by GQDs on the Aβ_1-42 aggregation were monitored by circular dichroism (CD), dynamic light scattering (DLS) and transmission electron microscope (TEM). The in vitro cytotoxicity experiments further demonstrated the feasibility of GQDs on the regulation of Aβ_1-42 aggregation. Meanwhile, the structural changes of a Aβ_1-42/GQDs mixture in different pH revealed that electrostatic interaction was the major driving force in the co-assembly process of Aβ_1-42 and GQDs. The proposed mechanism of the regulatory effects of GQDs on the Aβ_1-42 aggregation was also deduced reasonably. This work not only demonstrated the potential feasibility of GQDs as therapeutic drug for AD but also clarified the regulatory mechanism of GQDs on the Aβ_1-42 aggregation.

Two-Dimensional Infrared Spectroscopy Reveals Molecular Self-Assembly on the Surface of Silver Nanoparticles

The conformation of molecules, peptides, and proteins, self-assembled into structured monolayers on the surface of metal nanoparticles (NPs), can strongly affect their properties and use in chemical or nanobiomedical applications. Elucidating molecular conformations on the NP surface is highly challenging, and the microscopic details mostly remain elusive. Using polarization-selective third-order two-dimensional ultrafast infrared spectroscopy, we revealed the highly ordered intermolecular structure of γ-tripeptide glutathione on the surface of silver NPs in aqueous solution. Glutathione is an antioxidant thiol abundant in living cells; it is extensively used in NP chemistry and related research. We identified conditions where the interaction of glutathione with the NP surface facilitates formation of a β-sheet-like structure enclosing the NPs. A spectroscopic signature associated with the assembly of β-sheets into an amyloid fibril-like structure was also observed. Remarkably, the interaction with the metal surface promotes formation of a fibril-like structure by a small peptide involving only two amino acids.

Chiral Effect at Nano-Bio Interface: A Model of Chiral Gold Nanoparticle on Amylin Fibrillation

Protein/Peptide amyloidosis is the main cause of several diseases, such as neurodegenerative diseases. It has been widely acknowledged that the unnatural fibrillation of protein/peptides in vivo is significantly affected by the physical and chemical properties of multiscale biological membranes. For example, previous studies have proved that molecule chirality could greatly influence the misfolding, fibrillation and assembly of β-Amyloid peptides at the flat liquid-solid surface. However, how the nanoscale chirality influences this process remains unclear. Here we used gold nanoparticles (AuNPs, d = 4 ± 1 nm)-modified with N-isobutyl-L(D)-cysteine (L(D)-NIBC) enantiomers-as a model to illustrate the chiral effect on the amylin fibrillation at nano-bio interface. We reported that both two chiral AuNPs could inhibit amylin fibrillation in a dosage-dependent manner but the inhibitory effect of L-NIBC-AuNPs was more effective than that of D-NIBC-AuNPs. In-situ real time circular dichroism (CD) spectra showed that L-NIBC-AuNPs could inhibit the conformation transition process of amylin from random coils to α-helix, while D-NIBC-AuNPs could only delay but not prevent the formation of α-helix; however, they could inhibit the further conformation transition process of amylin from α-helix to β-sheet. These results not only provide interesting insight for reconsidering the mechanism of peptides amyloidosis at the chiral interfaces provided by biological nanostructures in vivo but also would help us design therapeutic inhibitors for anti-amyloidosis targeting diverse neurodegenerative diseases.

Carbon Nanotubes and Graphene as Nanoreinforcements in Metallic Biomaterials: a Review

Current challenges in existing metallic biomaterials encourage undertaking research in the development of novel materials for biomedical applications. This paper critically reviews the potential of carbon nanotubes (CNT) and graphene as nanoreinforcements in metallic biomaterials for bone tissue engineering. Unique and remarkable mechanical, electrical, and biological properties of these carbon nanomaterials allow their use as secondary-phase reinforcements in monolithic biomaterials. The nanoscale dimensions and extraordinarily large surface areas of CNT and graphene make them suitable materials for purposeful reaction with living organisms. However, the cytocompatibility of CNT and graphene is still a controversial issue that impedes advances in utilizing these promising materials in clinical orthopedic applications. The interaction of CNT and graphene with biological systems including proteins, nucleic acids, and human cells is critically reviewed to assess their cytocompatibity in vitro and in vivo. It is revealed that composites reinforced with CNT and graphene show enhanced adhesion of osteoblast cells, which subsequently promotes bone tissue formation in vivo. This potential is expected to pave the way for developing ground-breaking technologies in regenerative medicine and bone tissue engineering. In addition, current progress and future research directions are highlighted for the development of CNT and graphene reinforced implants for bone tissue engineering.

Effects of Gold Nanospheres and Nanocubes on Amyloid-β Peptide Fibrillation

Direct exposure or intake of engineered nanoparticles (ENPs) to the human body will trigger a series of complicated biological consequences. Especially, ENPs could either up- or downregulate peptide fibrillation, which is associated with various degenerative diseases like Alzheimer's and Parkinson's diseases. This work reports the effects of gold nanoparticles (AuNPs) with different shapes on the aggregation of an amyloid-β peptide (Aβ(1-40)) involved in Alzheimer's disease. Two kinds of AuNPs were investigated, i.e., gold nanospheres (AuNSs, ∼20 nm in diameter) and gold nanocubes (AuNCs, ∼20 nm in edge length). It was found that AuNPs play a catalytic role in peptide nucleation through interfacial adsorption of Aβ(1-40). AuNSs with hybrid facets have higher affinity to Aβ(1-40) because of the higher degree of surface atomic unsaturation than the {100}-faceted AuNCs. Therefore, AuNSs exert a more significant acceleration effect on the fibrillation process of Aβ(1-40) than AuNCs. Besides, a shape-dependent secondary structure transformation of Aβ(1-40) with different AuNPs was observed using Fourier transform infrared spectroscopy. The variation of peptide-NP and peptide-peptide interactions caused by the shape alteration of AuNPs influences the equilibrium of inter- and intramolecular hydrogen bonds, which is believed to be responsible for the shape-dependent secondary structure transformation. The study offers further understanding on the complicated NP-mediated Aβ aggregation and also facilitates further development on designing and synthesizing task-specific AuNPs for amyloid disease diagnosis and therapy.

Resistance of Zwitterionic Peptide Monolayers to Biofouling

Self-assembled monolayers (SAMs) are widely used in science and engineering, and recent progress has demonstrated the utility of zwitterionic peptides with alternating lysine (K) and glutamic acid (E) residues for antifouling purposes. Aiming at developing a peptide-based fouling-resistant SAM suitable for presentation of surface-attached pheromones for barnacle larvae, we have investigated five different peptide SAMs, where four are based on the EK motif, and the fifth was designed based on general principles for fouling resistance. The SAMs were formed by self-assembly onto gold substrates via cysteine residues on the peptides, and formation of SAMs was verified via ellipsometry, wettability, infrared reflection-absorption spectroscopy and cyclic voltammetry. Settlement of cypris larvae of the barnacle Balanus (=Amphibalanus) amphitrite, the target of pheromone studies, was tested. SAMs were also subjected to fouling assays using protein solutions, blood serum, and the bacterium Mycobacterium marinum. The results confirm the favorable antifouling properties of EK-containing peptides in most of the assays, although this did not apply to the barnacle larvae settlement test, where settlement was low on only one of the peptide SAMs. The one peptide that had antifouling properties for barnacles did not contain a pheromone motif, and would not be susceptible to degredation by common serine proteases. We conclude that the otherwise broadly effective antifouling properties of EK-containing peptide SAMs is not directly applicable to barnacles, and that great care must be exercised in the design of peptide-based SAMs for presentation of barnacle-specific ligands.

A repertoire of biomedical applications of noble metal nanoparticles

The emerging properties of noble metal nanoparticles are attracting huge interest from the translational scientific community. In this feature article, we highlight recent advances in the adaptation of noble metal nanomaterials and their biomedical applications in therapeutics, diagnostics and sensing.

Defragmentation of lysozyme derived Amyloid β fibril using Biocompatible Magnetic fluid

We present here a modulating effect on lysozyme derived Amyloid β fibrils by aqueous magnetic fluid. This non-conventional approach of treatment of lysozyme derived Amyloid β fibrils showed lysing of Amyloid fibrils to its secondary structures which can be seen using optical microscope and scanning electron microscopic image. The size of lysozyme derived amyloid fibrils before and after treatment was measured using dynamic light scattering technique. The mechanism of defragmentation of lysozyme derived Amyloid β fibrils by magnetic fluid is explained. This is a first report to identify the secondary structure of protein using Fourier Transform Infrared (FTIR) and Circular Dichroism (CD) spectra after lysing. The cyto-toxicity study of this magnetic fluid on neuronal (SH-SY5Y) and non-neuronal (NRK) cell lines shows non-toxicity up to a concentration of 250 μg/mL. The study indicates a novel and unique complementary approach to treat the amyloidogenic brain diseases.

Controlling Protein Adsorption through Nanostructured Polymeric Surfaces

The initial host response to healthcare materials' surfaces after implantation is the adsorption of proteins from blood and interstitial fluids. This adsorbed protein layer modulates the biological/cellular responses to healthcare materials. This stresses the significance of the surface protein assembly for the biocompatibility and functionality of biomaterials and necessitates a profound fundamental understanding of the capability to control protein-surface interactions. This review, therefore, addresses this by systematically analyzing and discussing strategies to control protein adsorption on polymeric healthcare materials through the introduction of specific surface nanostructures. Relevant proteins, healthcare materials' surface properties, clinical applications of polymer healthcare materials, fabrication methods for nanostructured polymer surfaces, amorphous, semicrystalline and block copolymers are considered with a special emphasis on the topographical control of protein adsorption. The review shows that nanostructured polymer surfaces are powerful tools to control the amount, orientation, and order of adsorbed protein layers. It also shows that the understanding of the biological responses to such ordered protein adsorption is still in its infancy, yet it has immense potential for future healthcare materials. The review, which is-as far as it is known-the first one discussing protein adsorption on nanostructured polymer surfaces, concludes with highlighting important current research questions.

Stereochemistry and amyloid inhibition: Asymmetric triplex metallohelices enantioselectively bind to Aβ peptide

Stereochemistry is vital for pharmaceutical development and can determine drug efficacy. Herein, 10 pairs of asymmetric triplex metallohelix enantiomers as a library were used to screen inhibitors of amyloid β (Aβ) aggregation via a fluorescent cell-based high-throughput method. Intriguingly, Λ enantiomers show a stronger inhibition effect than Δ enantiomers. In addition, the metallohelices with aromatic substituents are more effective than those without, revealing that these groups play a key role in the Aβ interaction. Fluorescence stopped-flow kinetic studies indicate that binding of the Λ enantiomer to Aβ is much faster than that of the Δ enantiomer. Furthermore, studies in enzyme digestion, isothermal titration calorimetry, nuclear magnetic resonance, and computational docking demonstrate that the enantiomers bind to the central hydrophobic α-helical region of Aβ13-23, although with different modes for the Λ and Δ enantiomers. Finally, an in vivo study showed that these metallohelices extend the life span of the Caenorhabditis elegans CL2006 strain by attenuating Aβ-induced toxicity. Our work will shed light on the design and screening of a metal complex as an amyloid inhibitor against Alzheimer's disease.

Gold Nanoparticles as a Probe for Amyloid-β Oligomer and Amyloid Formation

The process of amyloid-β (Aβ) amyloid formation is pathologically linked to Alzheimer's disease (AD). The identification of Aβ amyloids and intermediates that are crucial players in the pathology of AD is critical for exploring the underlying mechanism of Aβ aggregation and the diagnosis of the disease. Herein, we performed a gold nanoparticle (AuNP)-based study to detect the formation of Aβ amyloid fibrils and oligomers. Our results demonstrate that the intensity of the surface plasmon resonance (SPR) absorption band of the AuNPs is sensitive to the quantity of Aβ40 amyloids. This allows the SPR assay to be used for detection and semi-quantification of Aβ40 amyloids, and characterization of the kinetics of Aβ amyloid formation. Furthermore, our study demonstrates that the SPR band intensity of the AuNPs is sensitive to the presence of oligomers of both Aβ40 and an Aβ40 mutant, which forms more stable oligomers. The kinetics of the stable oligomer formation of the Aβ40 mutant can also be monitored following the SPR band intensity change of AuNPs. Our results indicate that this nanoparticle based method can be used for mechanistic studies of early protein self-assembly and fibrillogenesis.

Using Multifunctional Peptide Conjugated Au Nanorods for Monitoring β-amyloid Aggregation and Chemo-Photothermal Treatment of Alzheimer's Disease

Development of sensitive detectors of Aβ aggregates and effective inhibitors of Aβ aggregation are of diagnostic importance and therapeutic implications for Alzheimer's disease (AD) treatment. Herein, a novel strategy has been presented by self-assembly of peptide conjugated Au nanorods (AuP) as multifunctional Aβ fibrillization detectors and inhibitors. Our design combines the unique high NIR absorption property of AuNRs with two known Aβ inhibitors, Aβ15-20 and polyoxometalates (POMs). The synthesized AuP can effectively inhibit Aβ aggregation and dissociate amyloid deposits with NIR irradiation both in buffer and in mice cerebrospinal fluid (CSF), and protect cells from Aβ-related toxicity upon NIR irradiation. In addition, with the shape and size-dependent optical properties, the nanorods can also act as effective diagnostic probes to sensitively detect the Aβ aggregates. This is the first report to integrate 3 segments, an Aβ-targeting element, a reporter and inhibitors, in one drug delivery system for AD treatment.

Self-assembly of two hydrophobins from marine fungi affected by interaction with surfaces

Hydrophobins are amphiphilic fungal proteins endowed with peculiar characteristics, such as a high surface activity and an interface triggered self-assembly. Several applications of these proteins have been proposed in the food, cosmetics and biomedical fields. Moreover, their use as proteinaceous coatings can be effective for materials and nanomaterials applications. The discovery of novel hydrophobins with diverse properties may be advantageous from both the scientific and industrial points of view. Stressful environmental conditions of fungal growth may induce the production of proteins with peculiar features. Two Class I hydrophobins from fungi isolated from marine environment have been recently purified. Herein, their propensity to aggregate forming nanometric fibrillar structures has been compared, using different techniques, such as circular dichroism, dynamic light scattering and Thioflavin T fluorescence assay. Furthermore, TEM and AFM images indicate that the interaction of these proteins with specific surfaces, are crucial in the formation of amyloid fibrils and in the assembly morphologies. These self-assembling proteins show promising properties as bio-coating for different materials via a green process. Biotechnol. Bioeng. 2017;114: 2173-2186. © 2017 Wiley Periodicals, Inc.

Understanding Surface and Interfacial Chemistry in Functional Nanomaterials via Solid-State NMR

Surface and interfacial chemistry is of fundamental importance in functional nanomaterials applied in catalysis, energy storage and conversion, medicine, and other nanotechnologies. It has been a perpetual challenge for the scientific community to get an accurate and comprehensive picture of the structures, dynamics, and interactions at interfaces. Here, some recent examples in the major disciplines of nanomaterials are selected (e.g., nanoporous materials, battery materials, nanocrystals and quantum dots, supramolecular assemblies, drug-delivery systems, ionomers, and graphite oxides) and it is shown how interfacial chemistry can be addressed through the perspective of solid-state NMR characterization techniques.

Protein bio-corona: critical issue in immune nanotoxicology

With the expansion of the nanomedicine field, the knowledge focusing on the behavior of nanoparticles in the biological milieu has rapidly escalated. Upon introduction to a complex biological system, nanomaterials dynamically interact with all the encountered biomolecules and form the protein "bio-corona." The decoration with these surface biomolecules endows nanoparticles with new properties. The present review will address updates of the protein bio-corona characteristics as influenced by nanoparticle's physicochemical properties and by the particularities of the encountered biological milieu. Undeniably, bio-corona generation influences the efficacy of the nanodrug and guides the actions of innate and adaptive immunity. Exploiting the dynamic process of protein bio-corona development in combination with the new engineered horizons of drugs linked to nanoparticles could lead to innovative functional nanotherapies. Therefore, bio-medical nanotechnologies should focus on the interactions of nanoparticles with the immune system for both safety and efficacy reasons.

Facet-Dependent Interactions of Islet Amyloid Polypeptide with Gold Nanoparticles: Implications for Fibril Formation and Peptide-Induced Lipid Membrane Disruption

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.

Computational and Experimental Investigation of the Structure of Peptide Monolayers on Gold Nanoparticles

The self-assembly and self-organization of small molecules on the surface of nanoparticles constitute a potential route toward the preparation of advanced proteinlike nanosystems. However, their structural characterization, critical to the design of bionanomaterials with well-defined biophysical and biochemical properties, remains highly challenging. Here, a computational model for peptide-capped gold nanoparticles (GNPs) is developed using experimentally characterized Cys-Ala-Leu-Asn-Asn (CALNN)- and Cys-Phe-Gly-Ala-Ile-Leu-Ser-Ser (CFGAILSS)-capped GNPs as a benchmark. The structure of CALNN and CFGAILSS monolayers is investigated using both structural biology techniques and molecular dynamics simulations. The calculations reproduce the experimentally observed dependence of the monolayer secondary structure on the peptide capping density and on the nanoparticle size, thus giving us confidence in the model. Furthermore, the computational results reveal a number of new features of peptide-capped monolayers, including the importance of sulfur movement for the formation of secondary structure motifs, the presence of water close to the gold surface even in tightly packed peptide monolayers, and the existence of extended 2D parallel β-sheet domains in CFGAILSS monolayers. The model developed here provides a predictive tool that may assist in the design of further bionanomaterials.

Modeling and simulation of protein-surface interactions: achievements and challenges

Understanding protein-inorganic surface interactions is central to the rational design of new tools in biomaterial sciences, nanobiotechnology and nanomedicine. Although a significant amount of experimental research on protein adsorption onto solid substrates has been reported, many aspects of the recognition and interaction mechanisms of biomolecules and inorganic surfaces are still unclear. Theoretical modeling and simulations provide complementary approaches for experimental studies, and they have been applied for exploring protein-surface binding mechanisms, the determinants of binding specificity towards different surfaces, as well as the thermodynamics and kinetics of adsorption. Although the general computational approaches employed to study the dynamics of proteins and materials are similar, the models and force-fields (FFs) used for describing the physical properties and interactions of material surfaces and biological molecules differ. In particular, FF and water models designed for use in biomolecular simulations are often not directly transferable to surface simulations and vice versa. The adsorption events span a wide range of time- and length-scales that vary from nanoseconds to days, and from nanometers to micrometers, respectively, rendering the use of multi-scale approaches unavoidable. Further, changes in the atomic structure of material surfaces that can lead to surface reconstruction, and in the structure of proteins that can result in complete denaturation of the adsorbed molecules, can create many intermediate structural and energetic states that complicate sampling. In this review, we address the challenges posed to theoretical and computational methods in achieving accurate descriptions of the physical, chemical and mechanical properties of protein-surface systems. In this context, we discuss the applicability of different modeling and simulation techniques ranging from quantum mechanics through all-atom molecular mechanics to coarse-grained approaches. We examine uses of different sampling methods, as well as free energy calculations. Furthermore, we review computational studies of protein-surface interactions and discuss the successes and limitations of current approaches.