Tuning Supramolecular Structure and Functions of Peptide bola

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Tuning Supramolecular Structure and Functions of Peptide bola-Amphiphile by Solvent Evaporation-Dissolution Anhe Wang, Lingyun Cui, Sisir Debnath, Qianqian Dong, Xuehai Yan, Xi Zhang, Rein V. Ulijn, and Shuo Bai ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 07 Jun 2017 Downloaded from http://pubs.acs.org on June 8, 2017

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ACS Applied Materials & Interfaces

Tuning Supramolecular Structure and Functions of Peptide bola-Amphiphile by Solvent Evaporation-Dissolution Anhe Wang,†,¶ Lingyun Cui,†,¶ Sisir Debnath,‡ Qianqian Dong,† Xuehai Yan,† Xi Zhang,§Rein V. Ulijn*,‡,ǁ,■,▲ and Shuo Bai*,† †

State Key Laboratory of Biochemical Engineering, Institute of Process Engineering, Chinese

Academy of Sciences, 100190 Beijing, China. ‡

WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde, Glasgow

G1 1XL, U.K. §

MOE Key Lab of Organic Optoelectronics & Molecular Engineering, Department of Chemistry,

Tsinghua University, 100084 Beijing, China. ǁ

Advanced Science Research Center (ASRC), City University of New York, New York,

NY10031, USA. ■

Hunter College, Department of Chemistry and Biochemistry, 695 Park Avenue, New York,

New York 10065, USA. ▲

The Graduate Center of the City University of New York, New York 10016, USA.

¶

These authors contributed equally to this work.

ACS Paragon Plus Environment

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KEYWORDS: trace solvent, peptide self-assembly, nanostructure, white light emission, cell staining

ABSTRACT: Solvent molecules significantly affect the supramolecular self-assembly, for example in forming solvent-bridged hydrogen bonding networks. Even small changes in solvent composition can have dramatic impact on supramolecular assembly. Herein, we demonstrate the use of trace solvents (as low as 0.04%) to tune the morphology and consequent functions of supramolecular nanostructures based on an aromatic peptide bola-amphiphile. Specifically, perylene bisimide-(di-)glycine-tyrosine (PBI-[GY]2) bola-amphiphile were shown to give rise to red emitting nanofibers when assembled in water, while exposure to trace organic solvents such as tetrahydrofuran (THF) et al. via solvent-evaporation followed by aqueous assembly gave rise to white light emitting nanospheres. Differential hydrogen bonding between water (donor and acceptor) and THF (acceptor only) impacts on the supramolecular organization, which was verified using a density functional theory (DFT) simulation. The tunable consequent surface hydrophobicity was utilized in staining the cytoplasm and membrane of cells, respectively. The trace-solvent effect achieved through evaporation-dissolution provides methodology to mediate the morphologies and consequent functions for supramolecular biomaterials controlled by the self-assembly pathway.

1. Introduction Supramolecular self-assembly is indispensable in living systems where molecular arrangements dictate function, as seen in proteins, DNA, cell and organelle membranes. The formation and transformation of these structures are key to life’s functions, what's more, the irregularities in these processes can cause various disease states.1,2 Intermolecular non-covalent


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interactions (hydrogen bonds, electrostatic interactions, π-π stacking and hydrophobic forces et al.) synergistically control the self-assembly processes and final morphologies.3-6 Among these weak interactions, the formation of hydrogen bonding between biomolecules and solvent molecules is considered to be a dominant factor.7 Solvents with different polarity, and hydrogen bonding ability can dramatically influence supramolecular self-assembly.8,9 Even trace solvents can disturb the interactions among molecules leading to changes of self-assembly arrangement.7 For example, proteins can be denatured when exposed to a small amount of solvent and selfassemble into a variety of aggregates including amyloid fibrils which are the cause of some diseases, such as Alzheimer’s and diabetes II.1,2 Thus, changes in self-assembly by trace solvents can dramatically influence supramolecular functionality. Peptides and peptide derivatives have attracted considerable attention as a class of selfassembling supramolecules to create functional nano-architectures not only relevant in biological processes but also in the design of smart nanomaterials with promising applications as cell scaffolds, drug release vehicles and imaging agents in biomedicine.10-12 In order to achieve selective biological interactions and targeting within the biological context, their fate in biological environment may be influenced by chemical properties of the structure’s surface.13 In here, we demonstrate the ability of trace organic solvent (THF and ethanol) to influence aqueous self-assembly behavior of a bola-peptide amphiphile as a new processing methodology. We demonstrate simultaneous control of fluorescence emission (red to white), morphology (fiber to sphere), hydrophobicity and access to either cytoplasm or cell membranes when exposed to cells.


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Scheme 1. Schematic illustration of the pathway-dependent self-assembly behavior of bolaamphiphiles (PBI-[GY]2) and the simultaneous control of morphology (fiber to sphere) and fluorescence emission (red to white) via solvent evaporation-dissolution method. Our system is a bola-amphiphile version of aromatic peptide amphiphiles, which are typically composed of aromatic groups forming π-stacking interactions and short (e.g., di-) peptide segments suitable for the formation of hydrogen bonding and introduction of supramolecular chirality.13-17 The use of functional aromatic moieties such as perylene bisimide (PBI), a dye with outstanding photostability, will endow the self-assembled structures with optical properties and potential use in photonic devices and solar cells.18-25 In our previous work, we prepared PBI-(di)peptide bola-amphiphiles which were shown to self-assemble with solvent-tunable morphology.26 It is increasingly appreciated that the nature of peptide amphiphiles self-assembly can not only be influenced by solvent environment, but also strongly affected by the pathways of sample preparation and structure formation under kinetic control.27-29 Herein, we certify the


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pathway-dependent self-assembly of peptide bola-amphiphiles in water with trace THF, where the samples were prepared by evaporation of peptide THF solution followed by dissolution in water (Scheme 1). The presence of trace THF (as a proton acceptor) changes the H-bonding network giving rise to tuned morphologies from long fibers to spherical aggregates and consequent functions, in particular dramatic shifts in luminescence, hydrophobicity and partitioning behavior within biological cells. 2. Experimental Section 2.1.

Materials.

Trifluoroacetic

acid

(99%),

Boc-Gly-OH

(≥

99.0

%),

N,N-

Diisopropylethylamine (DIPEA) (>99.5%), Perylene-3,4,9,10-tetracarboxylic dianhydride (97 %), L-Tyrosine imidazole (≥99%), tert-butyl ester hydrochloride (>99%), Sodium hydrogencarbonate (≥ 95%), Sodium hydroxide and all solvents were obtained from SigmaAldrich and used without purification. 2-(1H-Benzotriazole-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate (HBTU) was get from Novabiochem. Phosphate buffer solution (PBS, pH 8) was prepared by adding NaH2PO4·H2O (94 mg) and Na2HPO4·7H2O (2.5 g) into 100 mL water. The water applied in all experiments was purified in a Milli-Q plus 185-purification system with a resistivity higher than 18.2 MΩ. 2.2. Cell culture. MCF-7 cells (human breast adenocarcinoma cells) and 3T3 cells (mouse embryonic fibroblast cells) were cultured at 37 °C in a DMEM medium (Gibco BRL, USA) which was complemented with fetal bovine serum (FBS, 10%), L-glutamine (2 mM), penicillin (100 U·mL-1) and streptomycin (25 mg·mL-1), and put in an incubator (Thermo Forma 3111, humidified atmosphere with 5% CO2). Standard digestion procedure for isolating cells from culture flasks was performed using EDTA (ethylenediaminetetraacetic acid, 0.02%)-trypsin


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(0.05%) mixture PBS solution and seeded to 96-well plates (105 cells well-1) for the subsequent experiments. 2.3. Cellular internalization. Cellular internalization behavior of the peptide nanoparticles was studied by CLSM (confocal laser scanning microscope). In brief, cells were incubated with a concentration of peptide aggregates (0.04 mg·mL-1) for 12 h, and washed with cell medium for 3 times before observation. To determine the location of peptide aggregates (the concentration was 0.005 mg mL-1) over the cells, the cell nuclei was stained with Hoechst 33342 and membrane was labeled with Alexa 488 WGA, (0.025 mg·mL-1, 10 µL). Finally, the cells were rinsed using PBS for 3 times and supplemented with DMEM medium. 2.4. Biocompatibility of PBI-[GY]2. Biocompatibility assessments were conducted on MCF-7 and 3T3 cells in 96-well plates. Cells were incubated in triplicate with preselected concentrations of the peptide aggregates (0.005, 0.01, 0.015, 0.02, 0.03, 0.04 mg mL-1) with and without trace THF in 10% FBS DMEM medium (Dulbecco's Modified Eagle Medium) for 24 h. After that, cells were washed for 3 times with cell medium. Then 10 µL of sterile filtered CCK-8 (Cell Counting Kit-8) in PBS was dropped into each well of 96-well plates and co-incubated for 1 h at 37 °C. The viability of cells were determined by measuring the absorbance at 490 nm with a UVVis spectrophotometer. 2.5. Characterization and instrumentation. JAS.C.O V-660 spectrophotometer (scanning speed of 400 nm·min−1) was used to measure the spectra of UV-Vis in the range from 300 to 700 nm. Data of emission fluorescence were recorded by a JAS.C.O FP-6500 spectrofluorometer, which measured the light orthogonally to the excitation light with bandwidth and data pitch of 3 nm. DMSO-d6 (perdeuterated solvents) was taken as internal standards in NMR measurement by


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a Brucker Avance 400 spectrometer at room temperature. The FTIR (Fourier Transform Infrared Spectroscopy) data was obtained from a Bruker Vertex 70 spectrometer with a resolution of 1 cm-1. To prepare the samples for FTIR, peptide aggregates were placed in the space formed by two CaF2 plates (size 2 mm) taken a polytetrafluoroethylene (PTFE, 50 µm) as spacer. For the AFM (Atomic Force Microscopy) measurement, Veeco diINNOVA Scanning Probe Microscope (VEECO/BRUKER, Santa Barbara, CA, USA) were performed in tapping mode under ambient conditions with 512 x 512 pixels resolution. 20 µl of samples were dropped on a freshly cleaved mica sheet (G250-2 Mica sheets 1" x 1" x 0.006"; Agar Scientific Ltd, Essex, UK) which was placed on an AFM stage and kept in a dust free environment overnight. For a typical AFM operation, the parameters were set as integral and proportional gains 0.3 and 0.5 respectively, tapping frequency 308 kHz, set point 0.5-0.8 V and scanning speed 1.0 Hz. TEM (JEMO 2010 electron microscope, acceleration voltage of 110 kV) was operated to observe the morphology of samples which were prepared by dropping 5 µl of aqueous solution of sample on the carbon-coated copper grid and leaving to air-dry. The DLS (The dynamic light scattering) experiments were conducted at 25 oC by a 3 DDLS spectrophotometer (LS instruments, Fribourg, Switzerland) equipped with a vertically polarized He-Ne laser source (25 mW, wavelength: 632.8 nm) and an avalanche photodiode detector (angle of 90°). To determine the D (intensity weighted diffusion coefficients) and Rh (average hydrodynamic radius), intensity autocorrelation functions were assayed through the cumulant method by using Rh = kBT/6πηD equation, in which kB, T and η are the Boltzmann constant, absolute temperature and solvent viscosity at the given temperature, respectively.


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Density-functional-theory (DFT) simulation. The B3LYP level of theory with the Gaussian 09 computer code was run in all computations, which is a widely used density functional in quantum chemistry and get great success in solving chemical problems. The 6-31G(d,p) basis set has been used for geometry optimization. Frequency calculations were performed to verify the minima nature of reactant and product. Different amount of PBI-[GY]2 molecules and solvent molecules have been chosen. THF molecules could only be the proton acceptor in the hydrogen bond and occupy the proton donors in PBI molecules. Water molecules could be both proton donor and acceptor forming hydrogen bond network. All of these structures were optimized with explicit solvent model in periodical boxes of 40Å×40Å×40Å employing COMPASS force field. Amorphous Cell, Discovery, and Blends modules in Materials Studio software (Accelrys Inc.) was used to calculate coordination numbers and binding energies considering the inter- and intra-molecular interactions (electronic, van der waals, and hydrogen bonding et al.). The densities of the boxes were set at 1.0000 g mL-1 for aqueous solvent and 0.8892 g mL-1 for the THF solvent. In the Figures, solvent molecules are omitted, except for the close contact ones direct linked to PBI-[GY]2 molecules via hydrogen bonds. 3. Results and Discussion Perylene bisimide-(di-)glycine-tyrosine (PBI-[GY]2) bola-amphiphiles were prepared by coupling GY (di-peptide glycine-tyrosine) at both ends of the perylene moiety (chemical structure, see Scheme 1; for details on synthesis, see Supporting Information Scheme S1). Our interest in studying trace-solvent effect on PBI-[GY]2 amphiphiles started from the investigation of self-assembly behavior of amphiphiles in a number of solvents with different polarity including water.26 PBI-[GY]2 self-assembled into microns long fibrous nanostructure in PBS


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(phosphate buffer solution) at 1x10-4 M (Figure 1a). When changing of solvent from water to THF at the same concentration, the self-assembled morphologies tuned from long fibers to short rod like aggregates with length below 300 nm (Figure S1) due to the change of interactions between amphiphiles and solvent molecules. When the THF solution was evaporated via rotary evaporation in vacuum at 50 ºC, a purple film was obtained in glass vial. The film could be readily redispersed into PBS solution giving rise to an opaque, pinkish solution at 1x10-4 M which was stable for several weeks (Figure 1b insert). Figure 1b showed that the self-assembled morphology of PBI-[GY]2 amphiphiles was composed of nanospheres. DLS (Dynamic light scattering) experiments showed that the particles possessed an average diameter around 200 nm with narrow distribution (Figure S2) agreeing well with those observed by TEM (Transmission Electron Microscope) and AFM (Atomic Force Microscope) after drying. The evaporationdissolution procedure could be used to enhance the interactions between supramolecular amphiphiles. During the evaporation process, bound THF molecules remain associated with amphiphiles, resulting in the formation of nanospheres. Nuclear magnetic resonance (NMR) was used to quantify THF molecules (H1 NMR, δ 3.59-3.62) 30 that remained bound to PBI-[GY]2 amphiphiles. The molar ratio of THF molecules to PBI-[GY]2 molecules is 60:1 (The weight fraction of trace THF in water is around 0.04 w%). FTIR (Fourier Transform Infrared Spectroscopy) measurement was then carried out to certify the hydrogen bonding interactions that underpin self-assembly of PBI-[GY]2 structures. Figure S3 shows the FTIR spectra of PBI-[GY]2 structures with or without trace THF in D2O for comparison. The peak at 1594 cm-1 relates to the contribution of –COOH groups of peptides in PBI-[GY]2 molecule and the peak of 1697 cm-1 is assigned to PBI moieties in the molecule. The disappearance of absorption of amide groups at 1632 cm-1 with trace THF indicates the less


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ordered β sheet-like arrangement of H-bonding network compared with absolute PBI-[GY]2 aggregates in water, resulting in the morphology change from fibers to spheres.31

Figure 1. TEM (left) and AFM (right) images of aggregates of PBI-[GY]2 self-assembled in PBS solution a) and co-assembled with trace THF in PBS solution via solvent-evaporation treatment b). The concentration is 1x10-4 M. Scale bar of TEM images are 200 and 100 nm, respectively. Scale bars of AFM images are 500 nm. Inserts: photographs of PBI-[GY]2 PBS solution with the same concentration. The detailed hydrogen bonding and self-assembled structures were further investigated using a computational model. The optimized structure of different amount of PBI-[GY]2 molecules (stick model) with water or THF (ball model) obtained by density functional theory (DFT) simulation


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is shown in Figure 2 (for the calculation method, see supporting information). The binding sites of hydrogen bonds (dashed cyan line) were determined based on the optimized structure of single PBI-[GY]2 molecule and the self-assembled structures were determined by molecular structures and tightly bounded solvent molecules. THF molecule is a proton acceptor and can occupy the proton donors in PBI-[GY]2 molecules such as carboxylic and phenolic hydroxyl groups forming spherical self-assembled structures with less close packed PBI moieties. By contrast, water can be both proton donor and acceptor giving rise to long-range ordered β sheet-like hydrogen bond network resulting in fibrous structures.


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Figure 2. Optimized hydrogen-bonding and self-assembled structures of different amount (Left: 4 molecules; Right: 32 molecules) of PBI-[GY]2 (stick model) with water a) or THF b) (ball model) molecules. The functions of PBI derivatives such as luminescent properties are strongly depended on the supramolecular interactions and solvent environment.19,20 To investigate the trace solvent effect of THF on the functions of PBI-[GY]2, we measured UV-Vis and fluorescent data of PBI-[GY]2 aggregates in PBS solution at a concentration of 1x10-4 M for the two systems. Figure 3a shows


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the absorption spectral shape of PBI-[GY]2 in aqueous media with or without trace THF indicating that there is no clear change depending on solvent environment.26 The emission of PBI-[GY]2 aggregates excited at 365 nm in PBS solution exhibited emission maxima at 436 nm with blue emission and 595 nm with red emission (black curve), readily observable as red color under UV-lamp as shown in Figure 3b. However, PBI-[GY]2 with trace THF exhibited additional enhanced emissions at 476 and 505 nm with green emission, which was attributed to the isolated chromophores of PBI-[GY]2 in the presence of trace THF (Figure S4),26 leading to a change of color from red to white light emission under UV-lamp. The Commission Internationale de L'Eclairage (CIE) colour coordinates of PBI-[GY]2 with trace THF are (0.38, 0.30), close to pure white light (0.33, 0.33) compared with that of PBI-[GY]2 in water (0.38, 0.24) and in THF (0.36, 0.56). As far as we know, it is the first time to observe the tuning luminescent property of one compound to white light emission by trace-solvent effect. With less close packed aggregation of PBI moieties caused by trace THF, the intensity of fluorescent emission increased dramatically and subsequently the quantum yield was enhanced from 6% to 9.6% compared with PBI-[GY]2 in PBS solution at the same concentration.


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Figure 3. a) UV-Vis and b) fluorescence emission spectra of PBI-[GY]2 with (red curve) or without (black curve) trace THF in PBS solution. The concentration is 1x10-4 M. The excitation wavelength is 365 nm. Inserts: photographs of PBI-[GY]2 without (left) or with (right) trace THF in PBS solution with the same concentration irradiated by UV lamp (365 nm). To assess whether the observed effects are dictated by the self-assembly pathway or by thermodynamics, the role of THF was studied further, we directly added varying amounts of THF from weight fraction 0.1% to 10% into PBI-[GY]2 PBS solution at the same concentration demonstrated previously. Figure S5 shows that the properties of PBI-[GY]2 aggregates with 0.1% and 1% THF including morphologies and luminescent property are identical to those of PBI[GY]2 in pure PBS solution. When the amount of THF reached 10%, the intensity of fluorescent emission increased dramatically but the spectral shape did not change significantly. These results indicate that the solvent-evaporation procedure is essential to achieve the co-assembly of peptide amphiphiles and solvent molecules leading to tunable PBI-[GY]2 aggregates.27-29 THF was replaced with ethanol which has different hydrogen bonding ability (in between water and THF) to assess the effect of solvent properties on the evaporation-dissolution experiment. Figure S6 shows a similar PBI-[GY]2 aggregates change in morphology from fibers to spherical structures and inherent luminescent property affected by trace ethanol. It indicates that the tracesolvent effect achieved through evaporation-dissolution method on the formation of hydrogen bonding between peptides and solvent molecules is the dominant factor in mediating the selfassembled structures and consequent functions. As a valuable dye, PBI displays outstanding photostability and optical properties, while the bola- peptide chains provide a suitable interface for interacting synthetic systems with biology,


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which are of potential use in bio-imaging such as cell staining in vitro.32 To assess the cytocompatibility of PBI-[GY]2 aggregates, the viability of MCF-7 cells (human breast adenocarcinoma cells) was firstly analyzed with varying concentrations of PBI-[GY]2 aggregates with (green bar) or without (red bar) trace THF (Figure 4a). No obvious cytotoxicity in vitro was observed when the concentration was lower than 0.04 mg·mL-1. These results indicate that PBI[GY]2 in the presence of trace THF do not negatively impact cell viability in vitro, which could render them useful as supramolecular dyes for staining of cells.13 We first introduced PBI-[GY]2 nanofibers into MCF-7 cells. The PBI-[GY]2 nanofibers were added to the Cells at a concentration of 0.04 mg·mL-1 and incubated for 12 h and then washed with cell medium for three times. Cellular internalization of peptide aggregates was studied by CLSM. As shown in Figure 4b, the PBI-[GY]2 nanofibers (red fluorescent dots excited at 559 nm) tend to accumulate in the cytoplasm of cells.33 Interestingly, PBI-[GY]2 nanoparticles co-assembled with trace THF are co-localized into the membrane of treated MCF-7 cells and no signals could be observed within cells as Figure 4c depictured. For the cell accumulation, the spherical nanoparticles with smaller size have higher penetration efficiency than the fibrous structures with micron- length. This differential behaviour of PBI-[GY]2 aggregates for cellular internalization is attributed to the change of surface hydrophobicity

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PBI-[GY]2 nanostructures assembled through

evaporation-dissolution result in aggregates with more hydrophobic surfaces, which could be trapped by the hydrophobic phospholipid membrane of cells.35-37 As 3T3 cells ( mouse embryonic fibroblast cells) were taken as another model cells, similar results were obtained as shown in Figure S7. Altogether, depending on processing, PBI-[GY]2 aggregates could be used to stain the cytoplasm and membrane of cells, respectively.


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Figure 4. a) MCF-7 cells viability by CCK-8 method in the presence of PBI-[GY]2 aggregates with or without trace THF in vitro. The excitation wavelength is 490 nm. Cell staining experiments by using PBI-[GY]2 aggregates self-assembled without b) or with c) trace THF. CLSM fluorescent images (left), the corresponding overlapped images of fluorescence and optical transmitted-light images (middle) and 3D fluorescent images (right) of MCF-7 cells incubated with PBI-[GY]2 aggregates without and with THF (red emission) for 12 h, respectively. The concentration of PBI-[GY]2 was 0.04 mg mL-1. In 3D images, x-z (bottom) and y-z (right) views along the two yellow lines, which represent the position where the stack is cut to form x-z and y-z sections, respectively. The nuclei and membrane of MCF-7 was stained by Hoechst 33342 (blue) and Alexa Fluor 488 (green), respectively. 4. Conclusions In conclusion, we demonstrate the pathway-dependent trace solvent effect on the self-assembly and consequent functions of aromatic peptide amphiphiles in aqueous media. The PBI-based peptide amphiphiles formed in the presence of bound trace THF achieved via evaporationdissolution procedure, gives rise to different H-bonding network observed in water. This resulted


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in change in balance between H-bonding and aromatic stacking interactions that was retained, even upon dilution into cell culture media. This resulted in tunable luminescence property from red to white light emission and the hydrophobicity of peptide aggregates which is utilized in staining the cytoplasm and membrane of cells, respectively. The observation of trace-solvent effect on the bio-molecular self-assembly process in mediating the morphologies and consequent functions provides new supramolecular processing methodology, which could be used to influence the performance of supramolecular systems in complex biological systems. ASSOCIATED CONTENT Supporting Information. Experimental procedures, product characterization and contrast experiments. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]; [email protected]. Author Contributions Anhe Wang and Lingyun Cui contributed equally. Notes The authors declare no competing financial interest ACKNOWLEDGMENT


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We thank Linyin Yan for computational simulation, Qianli Zou for NMR measurement and Huifeng Ren, Guanglu Wu, Kai Liu for TEM measurement. The authors acknowledge financial support from the National Natural Science Foundation of China (Project No. 21644007) and the Talent Fund of the Recruitment Program of Global Youth Experts. ABBREVIATIONS PBI-[GY]2, Perylene Bisimide-(di-)glycine-tyrosine; THF, Tetrahydrofuran; DFT, Density Functional Theory; NMR, Nuclear Magnetic Resonance; CIE, Commission Internationale de L'Eclairage; MCF-7 cells, Human Breast Adenocarcinoma Cells; CLSM, Confocal Laser Scanning Microscopy; DIPEA, Diisopropylethylamine; HBTU, 2-(1H-Benzotriazole-1-yl)1,1,3,3-tetramethyluronium hexafluorophosphate; PTFE, Polytetrafluoroethylene; AFM, Atomic Force Microscopy; DLS, Dynamic Light Scattering Measurements; kB, Boltzmann Constant; PBS, Phosphate Buffer Solution; 3T3 cells, Mouse Embryonic Fibroblast cells; FBS, Fetal Bovine Serum; DMEM medium, Dulbecco's Modified Eagle Medium; TEM, Transmission Electron Microscope; SEM, Scanning Electron Microscope; EDTA, Ethylenediaminetetraacetic Acid; FTIR, Fourier Transform Infrared Spectroscopy. REFERENCES (1) Knowles, T. P.; Fitzpatrick, A. W.; Meehan, S.; Mott, H. R.; Vendruscolo, M.; Dobson, C. M.; Welland, M. E. Role of Intermolecular Forces in Defining Material Properties of Protein Nanofibrils. Science 2007, 318, 1900-1903. (2) Krone, M. G.; Hua, L.; Soto, P.; Zhou, R.; Berne, B. J.; Shea, J. E. Role of Water in Mediating the Assembly of Alzheimer Amyloid-β Aβ16−22 Protofilaments. J. Am. Chem. Soc. 2008, 130, 11066-11072.


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Table of contents


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Tuning Supramolecular Structure and Functions of Peptide bola

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