• Biocatalytic Amide Condensation and Gelation Controlled by Light

      Sahoo, J.K.; Nalluri, S.K.M.; Javid, Nadeem; Webb, H.; Ulijn, R.V. (2014-03-25)
      We report on a supramolecular self-assembly system that displays coupled light switching, biocatalytic condensation/hydrolysis and gelation. The equilibrium state of this system can be regulated by light, favouring in situ formation, by protease catalysed peptide synthesis, of self-assembling trans-Azo-YF-NH2 in ambient light; however, irradiation with UV light gives rise to the cis-isomer, which readily hydrolyzes to its amino acid derivatives (cis-Azo-Y + F-NH2) with consequent gel dissolution.
    • Biocatalytic Self-Assembly of Supramolecular Charge Transfer Nanostructures Based on n-Type Semiconductor-Appended Peptide

      Nalluri, S.K.M.; Berdugo, C.; Javid, Nadeem; Frederix, P.W.J.M.; Ulijn, R.V. (2014-05-30)
      The reversible in situ formation of a self-assembly building block (naphthalenediimide (NDI)–dipeptide conjugate) by enzymatic condensation of NDI-functionalized tyrosine (NDI-Y) and phenylalanine-amide (F-NH2) to form NDI-YF-NH2 is described. This coupled biocatalytic condensation/assembly approach is thermodynamically driven and gives rise to nanostructures with optimized supramolecular interactions as evidenced by substantial aggregation induced emission upon assembly. Furthermore, in the presence of di-hydroxy/alkoxy naphthalene donors, efficient charge-transfer complexes are produced. The dynamic formation of NDI-YF-NH2 and electronic and H-bonding interactions are analyzed and characterized by different methods. Microscopy (TEM and AFM) and rheology are used to characterize the formed nanostructures. Dynamic nanostructures, whose formation and function are driven by free-energy minimization, are inherently self-healing and provide opportunities for the development of aqueous adaptive nanotechnology.
    • Biocatalytically Triggered Co‐Assembly of Two‐Component Core/Shell Nanofibers

      Abul-Haija, Y.M.; Roy, S.; Frederix, P.W.J.M.; Javid, Nadeem; Jayawarna, V.; Ulijn, R.V. (2014-03-05)
      For the development of applications and novel uses for peptide nanostructures, robust routes for their surface functionalization, that ideally do not interfere with their self‐assembly properties, are required. Many existing methods rely on covalent functionalization, where building blocks are appended with functional groups, either pre‐ or post‐assembly. A facile supramolecular approach is demonstrated for the formation of functionalized nanofibers by combining the advantages of biocatalytic self‐assembly and surfactant/gelator co‐assembly. This is achieved by enzymatically triggered reconfiguration of free flowing micellar aggregates of pre‐gelators and functional surfactants to form nanofibers that incorporate and display the surfactants’ functionality at the surface. Furthermore, by varying enzyme concentration, the gel stiffness and supramolecular organization of building blocks can be varied.
    • Differential Self-Assembly and Tunable Emission of Aromatic Peptide Bola-Amphiphiles Containing Perylene Bisimide in Polar Solvents Including Water

      Bai, S.; Debnath, S.; Javid, Nadeem; Frederix, P.W.J.M.; Fleming, S.; Pappas, C.G.; Ulijn, R.V. (2014-07-01)
      We demonstrate the self-assembly of bola-amphiphile-type conjugates of dipeptides and perylene bisimide (PBI) in water and other polar solvents. Depending on the nature of the peptide used (glycine-tyrosine, GY, or glycine-aspartic acid, GD), the balance between H-bonding and aromatic stacking can be tailored. In aqueous buffer, PBI-[GY]2 forms chiral nanofibers, resulting in the formation of a hydrogel, while for PBI-[GD]2 achiral spherical aggregates are formed, demonstrating that the peptide sequence has a profound effect on the structure formed. In water and a range of other polar solvents, self-assembly of these two PBI-peptides conjugates results in different nanostructures with highly tunable fluorescence performance depending on the peptide sequence employed, e.g., fluorescent emission and quantum yield. Organogels are formed for the PBI-[GD]2 derivative in DMF and DMSO while PBI-[GY]2 gels in DMF. To the best of our knowledge, this is the first successful strategy for using short peptides, specifically, their sequence/structure relationships, to manipulate the PBI nanostructure and consequent optical properties. The combination of controlled self-assembly, varied optical properties, and formation of aqueous and organic gel-phase materials may facilitate the design of devices for various applications related to light harvesting and sensing.
    • Discovery of Catalytic Phages by Biocatalytic Self-Assembly

      Maeda, Y.; Javid, Nadeem; Duncan, K.; Birchall, L.; Gibson, K.F.; Cannon, D.; Kanetsuki, Y.; Knapp, C.; Tuttle, T.; Ulijn, R.V.; et al. (2014-10-24)
      Discovery of new catalysts for demanding aqueous reactions is challenging. Here, we describe methodology for selection of catalytic phages by taking advantage of localized assembly of the product of the catalytic reaction that is screened for. A phage display library covering 109 unique dodecapeptide sequences is incubated with nonassembling precursors. Phages which are able to catalyze formation of the self-assembling reaction product (via amide condensation) acquire an aggregate of reaction product, enabling separation by centrifugation. The thus selected phages can be amplified by infection of Escherichia coli. These phages are shown to catalyze amide condensation and hydrolysis. Kinetic analysis shows a minor role for substrate binding. The approach enables discovery and mass-production of biocatalytic phages.
    • Dynamic Peptide Library for the Discovery of Charge Transfer Hydrogels

      Berdugo, C.; Nalluri, S.K.M.; Javid, Nadeem; Escuder, B.; Miravet, J.F.; Ulijn, R.V. (2015-11-25)
      Coupling of peptide self-assembly to dynamic sequence exchange provides a useful approach for the discovery of self-assembling materials. In here, we demonstrate the discovery and optimization of aqueous, gel-phase nanostructures based on dynamically exchanging peptide sequences that self-select to maximize charge transfer of n-type semiconducting naphthalenediimide (NDI)-dipeptide bioconjugates with various π-electron-rich donors (dialkoxy/hydroxy/amino-naphthalene or pyrene derivatives). These gel-phase peptide libraries are characterized by spectroscopy (UV–vis and fluorescence), microscopy (TEM), HPLC, and oscillatory rheology and it is found that, of the various peptide sequences explored (tyrosine Y-NDI with tyrosine Y, phenylalanine F, leucine L, valine V, alanine A or glycine G-NH2), the optimum sequence is tyrosine-phenylalanine in each case; however, both its absolute and relative yield amplification is dictated by the properties of the donor component, indicating cooperativity of peptide sequence and donor/acceptor pairs in assembly. The methodology provides an in situ discovery tool for nanostructures that enable dynamic interfacing of supramolecular electronics with aqueous (biological) systems.
    • Exploring the Sequence Space for (tri-) Peptide Self-assembly to Design and Discover New Hydrogels

      Frederix, P.W.J.M.; Scott, G.G.; Abul-Haija, Y.M.; Kalafatovic, D.; Pappas, C.G.; Javid, Nadeem; Hunt, N.T.; Ulijn, R.V.; Tuttle, T. (2015-01-05)
      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.
    • MMP-9 triggered micelle-to-fibre transitions for slow release of doxorubicin

      Kalafatovic, D.; Nobis, M.; Javid, Nadeem; Frederix, P.W.J.M.; Anderson, K.I.; Saunders, B.R.; Ulijn, R.V. (2014-10-28)
      Phenylacetyl-peptide amphiphiles were designed, which upon cleavage by a disease-associated enzyme reconfigure from micellar aggregates to fibres. Upon this morphological change, a doxorubicin payload could be retained in the fibres formed, which makes them valuable carriers for localised formation of nanofibre depots for slow release of hydrophobic anticancer drugs.
    • Pathway-dependent gold nanoparticle formation by biocatalytic self-assembly

      Sahoo, J.K.; Roy, S.; Javid, Nadeem; Duncan, K.; Aitken, L.; Ulijn, R.V. (2017-09)
      We report on the use of non-equillibrium biocatalytic self-assembly and gelation to guide the reductive synthesis of gold nanoparticles. We show that biocatalytic rates simultaneously dictate supramolecular order and presentation of reductive phenols which in turn results in size control of nanoparticles that are formed.
    • Tunable supramolecular gel properties by varying thermal history

      Debnath, S.; Roy, S.; Abul-Haija, Y.M.; Frederix, P.W.J.M.; Ramalhete, S.M.; Hirst, A.R.; Javid, Nadeem; Hunt, N.T.; Kelly, S.M.; Angulo, J.; et al. (2019-06-12)
      The possibility of using differential pre‐heating prior to supramolecular gelation to control the balance between hydrogen‐bonding and aromatic stacking interactions in supramolecular gels and obtain consequent systematic regulation of structure and properties is demonstrated. Using a model aromatic peptide amphiphile, Fmoc‐tyrosyl‐leucine (Fmoc‐YL) and a combination of fluorescence, infrared, circular dichroism and NMR spectroscopy, it is shown that the balance of these interactions can be adjusted by temporary exposure to elevated temperatures in the range 313–365 K, followed by supramolecular locking in the gel state by cooling to room temperature. Distinct regimes can be identified regarding the balance between H‐bonding and aromatic stacking interactions, with a transition point at 333 K. Consequently, gels can be obtained with customizable properties, including supramolecular chirality and gel stiffness. The differential supramolecular structures also result in changes in proteolytic stability, highlighting the possibility of obtaining a range of supramolecular architectures from a single molecular structure by simply controlling the pre‐assembly temperature.
    • Tunable Supramolecular Hydrogels for Selection of Lineage-Guiding Metabolites in Stem Cell Cultures

      Alakpa, E.V.; Jayawarna, V.; Lampel, A.; Burgess, K.V.; West, C.C.; Bakker, S.C.J.; Roy, S.; Javid, Nadeem; Fleming, S.; Lamprou, D.A.; et al. (2016-08-11)
      Stem cells are known to differentiate in response to the chemical and mechanical properties of the substrates on which they are cultured. Thus, supramolecular biomaterials with tunable properties are well suited for the study of stem cell differentiation. In this report, we exploited this phenomenon by combining stem cell differentiation in hydrogels with variable stiffness and metabolomics analysis to identify specific bioactive lipids that are uniquely used up during differentiation. To achieve this, we cultured perivascular stem cells on supramolecular peptide gels of different stiffness, and metabolite depletion followed. On soft (1 kPa), stiff (13 kPa), and rigid (32 kPa) gels, we observed neuronal, chondrogenic, and osteogenic differentiation, respectively, showing that these stem cells undergo stiffness-directed fate selection. By analyzing concentration variances of >600 metabolites during differentiation on the stiff and rigid gels (and focusing on chondrogenesis and osteogenesis as regenerative targets, respectively), we identified that specific lipids (lysophosphatidic acid and cholesterol sulfate, respectively), were significantly depleted. We propose that these metabolites are therefore involved in the differentiation process. In order to unequivocally demonstrate that the lipid metabolites that we identified play key roles in driving differentiation, we subsequently demonstrated that these individual lipids can, when fed to standard stem cell cultures, induce differentiation toward chondrocyte and osteoblast phenotypes. Our concept exploits the design of supramolecular biomaterials as a strategy for discovering cell-directing bioactive metabolites of therapeutic relevance.