Effect of Glycine Substitution on Fmoc–Diphenylalanine Self-Assembly and Gelation Properties

We have investigated the self-assembly behavior of fluorenyl-9-methoxycarbonyl (Fmoc)–FG, Fmoc–GG, and Fmoc–GF and compared it to that of Fmoc–FF using potentiometry, fluorescence and infrared spectroscopy, transmission electron microscopy, wide-angle X-ray scattering, and oscillatory rheometry. Titration experiments revealed a substantially shifted apparent p<i>K</i>_a transition for Fmoc–FG, Fmoc–GG, and Fmoc–GF. The apparent p<i>K</i>_a values observed correlated with the hydrophobicity (log <i>P</i>) of the Fmoc–dipeptide molecules. Fmoc–GG and Fmoc–GF were found to self-assemble only in their protonated form (below their apparent p<i>K</i>_a), while Fmoc–FG formed self-assembled structures above and below its apparent p<i>K</i>_a. Fmoc–GG and Fmoc–FG were found to form hydrogels below their apparent p<i>K</i>_a transitions in agreement with the entangled fibers morphologies revealed by TEM. Unlike Fmoc–FF and Fmoc–GG, Fmoc–FG showed unusual gelation behavior as gels were found to form upon heating. Fmoc–GF formed precipitates instead of a hydrogel below its apparent p<i>K</i>_a in agreement with the formation of micrometer scale sheetlike structures observed by TEM. The fact that all four Fmoc–dipeptides were found to self-assemble suggests that the main driving force behind the self-assembly process is a combination of the hydrophobic and π–π interactions of the fluorenyl moieties with a secondary role for hydrogen bonding of the peptidic components. The nature of the peptidic tail was found to have a pronounced effect on the type of self-assembled structure formed. This work indicates that the substitution of phenylalanine by glycine significantly impacts on the mode of assembly and illustrates the versatility of aromatic peptide amphiphiles in the formation of structurally diverse nanostructures

One-Step Preparation of Uniform Cane-Ball Shaped Water-Swellable Microgels Containing Poly(<i>N</i>-vinyl formamide)

In this study we report the preparation of a new family of core–shell microgels that are water-swellable and have a morphology that is controllable by particle composition. Here, nearly monodisperse core–shell PNVF-<i>x</i>GMA [poly­(<i>N</i>-vinylformamide-<i>co</i>-glycidyl methacrylate)] particles (where <i>x</i> is the weight fraction of GMA used) were prepared via nonaqueous dispersion (NAD) polymerization in one step. The shells were PGMA-rich and were cross-linked by reaction of epoxide groups (from GMA) with amide groups (from NVF). The core of the particles was PNVF-rich. A bifunctional cross-linking monomer was not required to prepare these new microgels. The particles had a remarkable “cane-ball”-like morphology with interconnected ridges, and this could be controlled by the value for <i>x</i>. The particle size was tunable over the range 0.8–1.8 μm. Alkaline hydrolysis was used to hydrolyze the PNVF segments to poly­(vinylamine), PVAM. The high swelling pressure of the cationic cores caused shell fragmentation and release of some of the core polymer when the hydrolyzed particles were dispersed in pure water. The extent to which this occurred was controllable by <i>x</i>. Remarkably, the PGMA-rich shells could be detached from the hydrolyzed particles by dispersion in water followed by drying. The hydrolyzed PNVF-0.4GMA particles contained both positively and negatively charged regions and the dispersions appeared to exhibit charge-patch aggregation at low ionic strengths. The new cross-linking strategy used here to prepare the PNVF-<i>x</i>GMA particles should be generally applicable for amide-containing monomers and may enable the preparation of a range of new water-swellable microgels

Virtual Screening for Dipeptide Aggregation: Toward Predictive Tools for Peptide Self-Assembly

Several short peptide sequences are known to self-assemble into supramolecular nanostructures with interesting properties. In this study, coarse-grained molecular dynamics is employed to rapidly screen all 400 dipeptide combinations and predict their ability to aggregate as a potential precursor to their self-assembly. The simulation protocol and scoring method proposed allows a rapid determination of whether a given peptide sequence is likely to aggregate (an indicator for the ability to self-assemble) under aqueous conditions. Systems that show strong aggregation tendencies in the initial screening are selected for longer simulations, which result in good agreement with the known self-assembly or aggregation of dipeptides reported in the literature. Our extended simulations of the diphenylalanine system show that the coarse-grain model is able to reproduce salient features of nanoscale systems and provide insight into the self-assembly process for this system

Tuning Supramolecular Chirality in Iodinated Amphiphilic Peptides Through Tripeptide Linker Editing

Protease-cleavable supramolecular oligopeptide nanofilaments are promising materials for targeted therapeutics and diagnostics. In these systems, single amino acid substitutions can have profound effects on the supramolecular structure and consequent proteolytic degradation, which are critical parameters for their intended applications. Herein, we describe changes to the self-assembly and proteolytic cleavage of iodine containing sequences for future translation into matrix metalloprotease (MMP-9)-activated supramolecular radio-imaging probes. We use a systematic single amino acid exchange in the tripeptide linker region of these peptide amphiphiles to provide insights into the role of each residue in the supramolecular assemblies. These modifications resulted in dramatic changes in the nature of the assembled structures formed, including an unexpected chiral inversion. By using circular dichroism, atomic force microscopy, Fourier transform infrared spectroscopy, and molecular dynamics simulations, we found that the GD loop, a common motif in β-turn elements, induced a reversal of the chiral orientation of the assembled nanofibers. In addition to the impact on peptide packing and chirality, MMP-9-catalyzed hydrolysis was evaluated for the four peptides, with the β-sheet content found to be a stronger determinant of enzymatic hydrolysis than supramolecular chirality. These observations provide fundamental insights into the sequence design in protease cleavable amphiphilic peptides with the potential for radio-labeling and selective biomedical applications

Pickering Stabilized Peptide Gel Particles as Tunable Microenvironments for Biocatalysis

We demonstrate the preparation of peptide gel microparticles that are emulsified and stabilized by SiO₂ nanoparticles. The gels are composed of aromatic peptide amphiphiles 9-fluorenyl­methoxy­carbonyl­diphenylalanine (Fmoc-FF) coassembled with Fmoc-amino acids with different functional groups (S: serine; D: aspartic acid; K: lysine; and Y: tyrosine). The gel phase provides a highly hydrated matrix, and peptide self-assembly endows the matrix with tunable chemical environments which may be exploited to support and stabilize proteins. The use of Pickering emulsion to stabilize these gel particles is advantageous through avoidance of surfactants that may denature proteins. The performance of enzyme lipase B immobilized in pickering/gel microparticles with different chemical functionalities is investigated by studying transesterification in heptane. We show that the use of Pickering particles enhances the performance of the enzyme, which is further improved in gel-phase systems, with hydrophilic environment provided by Fmoc-FF/S giving rise to the best catalytic performance. The combination of a tunable chemical environment in gel phase and Pickering stabilization described here is expected to prove useful for areas where proteins are to be exploited in technological contexts such as biocatalysis and also in other areas where protein performance and activity are important, such as biosensors and bioinspired solar fuel devices

Stable Emulsions Formed by Self-Assembly of Interfacial Networks of Dipeptide Derivatives

We demonstrate the use of dipeptide amphiphiles that, by hand shaking of a biphasic solvent system for a few seconds, form emulsions that remain stable for months through the formation of nanofibrous networks at the organic/aqueous interface. Unlike absorption of traditional surfactants, the interfacial networks form by self-assembly through π-stacking interactions and hydrogen bonding. Altering the dipeptide sequence has a dramatic effect on the properties of the emulsions formed, illustrating the possibility of tuning emulsion properties by chemical design. The systems provide superior long-term stability toward temperature and salts compared to with sodium dodecyl sulfate (SDS) and can be enzymatically disassembled causing on-demand demulsification under mild conditions. The interfacial networks facilitate highly tunable and stable encapsulation and compartmentalization with potential applications in cosmetics, therapeutics, and food industry

Assessing the Utility of Infrared Spectroscopy as a Structural Diagnostic Tool for β‑Sheets in Self-Assembling Aromatic Peptide Amphiphiles

β-Sheets are a commonly found structural motif in self-assembling aromatic peptide amphiphiles, and their characteristic “amide I” infrared (IR) absorption bands are routinely used to support the formation of supramolecular structure. In this paper, we assess the utility of IR spectroscopy as a structural diagnostic tool for this class of self-assembling systems. Using 9-fluorene-methyloxycarbonyl dialanine (Fmoc-AA) and the analogous 9-fluorene-methylcarbonyl dialanine (Fmc-AA) as examples, we show that the origin of the band around 1680–1695 cm^–1 in Fourier transform infrared (FTIR) spectra, which was previously assigned to an antiparallel β-sheet conformation, is in fact absorption of the stacked carbamate group in Fmoc-peptides. IR spectra from ¹³C-labeled samples support our conclusions. In addition, DFT frequency calculations on small stacks of aromatic peptides help to rationalize these results in terms of the individual vibrational modes

Utveckling av ett konfigurerbart system som utvärderar kritiskt material på företagsnivå

The use of different materials is a central part of our development, especially in the electronics industry since it is dependent on materials such as gold, silver and copper etc. to achieve the required performance. The material consumption is increasing, while material production is limited to a few countries. Industries and companies that consume unusual or large amounts of material are most exposed to this problem. Therefore it is important for companies to be able to identify their critical materials. There is a lack of systems that can identify different materials criticality at a company level. This report proposes a system that can identify critical materials at a company level, regardless of the company's industry and size. By combining a literature study with a case study in a leading electronic company, a system that identifies materials criticality at a company level was developed. The theoretical study consisted of a comparison between three existing systems for evaluating critical materials, combined with a qualitative study, interviews, that were conducted at the electronic company Ericsson. The developed system evaluates a material's criticality based on two parameters; supply risk and corporate importance. Each parameter includes several categories and indicators that measure the materials criticality. By testing the system on Ericsson's most important and used materials such as; Al, Au, Ag, Cu, etc., it was found that the company do not have any critical materials. The developed systems corporate importance part is configurable, which makes it company-specific. It is up each company to customize it for their own business and situation. The case study also showed that a nation´s critical material doesn’t necessarily need to be company critical just because the company operates within the nation, it mainly depend on the material usage. Companies that manufacture end products so called OEMs in the electronics industry don’t usually buy materials directly from the mine, but components containing these materials. This makes it difficult for OEMs to trace the material origin. Apart from the material production concentration that is limited to a few countries, the knowledge of how to manufacture certain components may also be limited, by being concentrated in few countries. This factor makes the OEMs to become more dependent on certain suppliers, which can affect the business

Investigation of the Ultrafast Dynamics Occurring during Unsensitized Photocatalytic H₂ Evolution by an [FeFe]-Hydrogenase Subsite Analogue

Biomimetic compounds based upon the active subsite of the [FeFe]-hydrogenase enzyme system have been the focus of much attention as catalysts for hydrogen production: a clean energy vector. Until recently, use of hydrogenase subsite systems for <i>light-driven</i> hydrogen production has typically required the involvement of a photosensitizer, but the molecule [(μ-pdt)­(μ-H)­Fe₂(CO)₄(dppv)]⁺, (<b>1</b>; dppv = <i>cis</i>-1,2-C₂H₂(PPh₂)₂; pdt = 1,3-propanedithiolate) has been reported to catalyze the evolution of hydrogen gas under sensitizer-free conditions. Establishing the molecular mechanism that leads to photohydrogen production by <b>1</b> is thus an important step that may enable further development of this family of molecules as solar fuel platforms. Here, we report ultrafast UV_pump–IR_probe spectroscopy of <b>1</b> at three different excitation wavelengths and in a range of solvents, including under the conditions required for H₂ production. Combining spectroscopic measurements of the photochemistry and vibrational relaxation dynamics of <b>1</b> with ground-state density functional theory (DFT) calculations shows that, irrespective of experimental conditions, near-instantaneous carbonyl ligand loss is the main photochemical channel. No evidence for a long-lived excited electronic state was found. These results provide the first time-resolved data for the photochemistry of <b>1</b> and offer an alternative interpretation of the underlying mechanism of light-driven hydrogen generation