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Aqueous compatible supramolecular materials hold promise for applications in environmental remediation, energy harvesting and biomedicine. One remaining challenge is to actively select a target structure from a multitude of possible options, in response to chemical signals, while maintaining constant, physiological conditions. Here, we demonstrate the use of amino acids to actively decorate a self-assembling core molecule in situ, thereby controlling its amphiphilicity and consequent mode of assembly. The core molecule is the organic semiconductor naphthalene diimide, functionalized with D- and L- tyrosine methyl esters as competing reactive sites. In the presence of α-chymotrypsin and a selected encoding amino acid, kinetic competition between ester hydrolysis and amidation results in covalent or non-covalent amino acid incorporation, and variable supramolecular self-assembly pathways. Taking advantage of the semiconducting nature of the naphthalene diimide core, electronic wires could be formed and subsequently degraded, giving rise to temporally regulated electro-conductivity.

Peptides that self-assemble into nanostructures are of tremendous interest for biological, medical, photonic and nanotechnological applications. The enormous sequence space that is available from 20 amino acids probably harbours many interesting candidates, but it is currently not possible to predict supramolecular behaviour from sequence alone. Here, we demonstrate computational tools to screen for the aqueous self-assembly propensity in all of the 8,000 possible tripeptides and evaluate these by comparison with known examples. We applied filters to select for candidates that simultaneously optimize the apparently contradicting requirements of aggregation propensity and hydrophilicity, which resulted in a set of design rules for self-assembling sequences. A number of peptides were subsequently synthesized and characterized, including the first reported tripeptides that are able to form a hydrogel at neutral pH. These tools, which enable the peptide sequence space to be searched for supramolecular properties, enable minimalistic peptide nanotechnology to deliver on its promise. Peptides that self-assemble into nanostructures are of interest for many applications, including ones relevant to cosmetics, food, biomedicine and nanotechnology. Now, computational tools have been developed that enable peptide sequence space to be rapidly searched for supramolecular properties and this approach has been used to identify unprotected tripeptide hydrogelators.

Sequence-specific polymers, such as oligonucleotides and peptides, can be used as building blocks for functional supramolecular nanomaterials. The design and selection of suitable self-assembling sequences is, however, challenging because of the vast combinatorial space available. Here we report a methodology that allows the peptide sequence space to be searched for self-assembling structures. In this approach, unprotected homo- and heterodipeptides (including aromatic, aliphatic, polar and charged amino acids) are subjected to continuous enzymatic condensation, hydrolysis and sequence exchange to create a dynamic combinatorial peptide library. The free-energy change associated with the assembly process itself gives rise to selective amplification of self-assembling candidates. By changing the environmental conditions during the selection process, different sequences and consequent nanoscale morphologies are selected. Searchable dynamic peptide libraries, which are based on the sequence exchange of unprotected peptides under user-defined conditions, can be used to discover self-assembled peptide nanostructures.

Water-responsive materials undergo reversible shape changes upon varying humidity levels. These mechanically robust yet flexible structures can exert substantial forces and hold promise as efficient actuators for energy harvesting, adaptive materials and soft robotics. Here we demonstrate that energy transfer during evaporation-induced actuation of nanoporous tripeptide crystals results from the strengthening of water hydrogen bonding that drives the contraction of the pores. The seamless integration of mobile and structurally bound water inside these pores with a supramolecular network that contains readily deformable aromatic domains translates dehydration-induced mechanical stresses through the crystal lattice, suggesting a general mechanism of efficient water-responsive actuation. The observed strengthening of water bonding complements the accepted understanding of capillary-force-induced reversible contraction for this class of materials. These minimalistic peptide crystals are much simpler in composition compared to natural water-responsive materials, and the insights provided here can be applied more generally for the design of high-energy molecular actuators. Experiments and molecular dynamics simulations show that the dehydration-induced actuation of nanoporous tripeptide crystals is a result of pore contraction caused by the strengthening of the water hydrogen-bonding network inside the pore, which creates mechanical stress that deforms the crystal lattice.

Supramolecular gels, which demonstrate tunable functionalities, have attracted much interest in a range of areas, including healthcare, environmental protection and energy-related technologies. Preparing these materials in a reliable manner is challenging, with an increased level of kinetic defects observed at higher self-assembly rates. Here, by combining biocatalysis and molecular self-assembly, we have shown the ability to more quickly access higher-ordered structures. By simply increasing enzyme concentration, supramolecular order expressed at molecular, nano- and micro-levels is dramatically enhanced, and, importantly, the gelator concentrations remain identical. Amphiphile molecules were prepared by attaching an aromatic moiety to a dipeptide backbone capped with a methyl ester. Their self-assembly was induced by an enzyme that hydrolysed the ester. Different enzyme concentrations altered the catalytic activity and size of the enzyme clusters, affecting their mobility. This allowed structurally diverse materials that represent local minima in the free energy landscape to be accessed based on a single gelator structure. Supramolecular gels show promise in diverse areas, including healthcare and energy technologies, owing to tunable properties that arise directly from the organization of their building blocks. Researchers have now been able to control this behaviour by combining enzymatic catalysis with molecular self-assembly. Although it seems counter-intuitive, gels that assembled faster showed fewer defects.

Peptide-based liquid-liquid phase separated domains, or coacervates, are a biomaterial gaining new interest due to their exciting potential in fields ranging from biosensing to drug delivery. In this study, we demonstrate that coacervates provide a simple and biocompatible medium to improve nucleic acid biosensors through the sequestration of both the biosensor and target strands within the coacervate, thereby increasing their local concentration. Using the well-established polyarginine (R 9 ) – ATP coacervate system and an energy transfer-based DNA molecular beacon we observed three key improvements: i) a greater than 20-fold reduction of the limit of detection within coacervates when compared to control buffer solutions; ii) an increase in the kinetics, equilibrium was reached more than 4-times faster in coacervates; and iii) enhancement in the dye fluorescent quantum yields within the coacervates, resulting in greater signal-to-noise. The observed benefits translate into coacervates greatly improving bioassay functionality. Fluorescence-based oligonucleotide probes, also known as molecular beacons (MBs), are popular for detecting nucleic acids with high specificity. Here, the authors demonstrate self-sequestration of MB-based biosensors and target strands within peptide-based coacervates, increasing local concentrations and significantly increasing the sensitivity and kinetics of the DNA biosensors.

Skeletal stem cells (SSCs, or mesenchymal stromal cells typically referred to as mesenchymal stem cells from the bone marrow) are a dynamic progenitor population that can enter quiescence, self-renew or differentiate depending on regenerative demand and cues from their niche environment. However, ex vivo, in culture, they are grown typically on hard polystyrene surfaces, and this leads to rapid loss of the SSC phenotype. While materials are being developed that can control SSC growth and differentiation, very few examples of dynamic interfaces that reflect the plastic nature of the stem cells have, to date, been developed. Achieving such interfaces is challenging because of competing needs: growing SSCs require lower cell adhesion and intracellular tension while differentiation to, for example, bone-forming osteoblasts requires increased adhesion and intracellular tension. We previously reported a dynamic interface where the cell adhesion tripeptide arginine-glycine-aspartic acid (RGD) was presented to the cells upon activation by user-added elastase that cleaved a bulky blocking group hiding RGD from the cells. This allowed for a growth phase while the blocking group was in place and the cells could only form smaller adhesions, followed by an osteoblast differentiation phase that was induced after elastase was added which triggered exposure of RGD and subsequent cell adhesion and contraction. Here, we aimed to develop an autonomous system where the surface is activated according to the need of the cell by using matrix metalloprotease (MMP) cleavable peptide sequences to remove the blocking group with the hypothesis that the SSCs would produce higher levels of MMP as the cells reached confluence. The current studies demonstrate that SSCs produce active MMP-2 that can cleave functional groups on a surface. We also demonstrate that SSCs can grow on the uncleaved surface and, with time, produce osteogenic marker proteins on the MMP-responsive surface. These studies demonstrate the concept for cell-controlled surfaces that can modulate adhesion and phenotype with significant implications for stem cell phenotype modulation.

Differentiation of stem cells to chondrocytes in vitro usually results in a heterogeneous phenotype. This is evident in the often detected over expression of type X collagen which, in hyaline cartilage structure is not characteristic of the mid-zone but of the deep-zone ossifying tissue. Methods to better match cartilage developed in vitro to characteristic in vivo features are therefore highly desirable in regenerative medicine. This study compares phenotype characteristics between pericytes, obtained from human adipose tissue, differentiated using diphenylalanine/serine (F 2 /S) peptide hydrogels with the more widely used chemical induced method for chondrogenesis. Significantly higher levels of type II collagen were noted when pericytes undergo chondrogenesis in the hydrogel in the absence of induction media. There is also a balanced expression of collagen relative to aggrecan production, a feature which was biased toward collagen production when cells were cultured with induction media. Lastly, metabolic profiles of each system show considerable overlap between both differentiation methods but subtle differences which potentially give rise to their resultant phenotype can be ascertained. The study highlights how material and chemical alterations in the cellular microenvironment have wide ranging effects on resultant tissue type.

The paper describes guidelines for the planning, organization, and successful execution of virtual, global scientific conferences for global audiences. The guidelines are based on experience and lessons learned during the organization of the 3‐day 2020 Virtual Systems Chemistry Symposium hosted on Zoom webinar and Twitter, held on May 2020 with over 1000 registered participants from 46 different countries. This planning guide outlines ten steps that academic organizers can follow to successfully organize and execute virtual, global scientific symposia for global audiences. The authors have also included instructional guides, videos, and PowerPoint slides that can be used as templates or inspiration for hosting virtual symposia with oral presentations on Zoom webinar and poster presentations on Twitter.

The materials pipeline for biomaterials and tissue engineering applications is under continuous development. Specifically, there is great interest in the use of designed materials in the stem cell arena as materials can be used to manipulate the cells providing control of behavior. This is important as the ability to \"engineer\" complexity and subsequent in vitro growth of tissues and organs is a key objective for tissue engineers. This review will describe the nature of the materials strategies, both static and dynamic, and their influence specifically on mesenchymal stem cell fate.