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

Disordered fibre networks are ubiquitous in nature and have a wide range of industrial applications as novel biomaterials. Predicting their viscoelastic response is straightforward for affine deformations that are uniform over all length scales, but when affinity fails, as has been observed experimentally, modelling becomes challenging. Here we introduce a numerical methodology to predict the steadystate viscoelastic spectra and degree of affinity for disordered fibre networks driven at arbitrary frequencies. Applying this method to a peptide gel model reveals a monotonic increase of the shear modulus as the soft, non-affine normal modes are successively suppressed as the driving frequency increases. In addition to being dominated by fibril bending, these low frequency network modes are also shown to be delocalised. The presented methodology provides insights into the importance of non-affinity in the viscoelastic response of peptide gels, and is easily extendible to all types of fibre networks. [5]. Nature employs protein fibre networks in the multi-functional cellular cytoskeleton [6,7]. The mechanical stiffness of fibre networks is often central to their function, and although static properties come under most scrutiny, they often exist in dynamic environments subject to temporally-varying mechanical loads, including the cytoskeleton of motile cells [7], and scaffolds for tendon and ligament regeneration, where habitual loading propagating through the network influences the viability of embedded stem cells [8][9][10]. Understanding the dynamical network response is essential to design novel materials with properties suited for such situations.A key modelling challenge is to determine the degree to which the deformation is affine [11], i.e. uniform over all relevant length scales; see Fig. 1. If affinity holds, extrapolating the macroscopic response from a putative microstructure is straightforward, and a range of thermal and athermal affine models for fibre networks have been developed [12,13]. When affinity fails, however, as experimentally observed over broad parameter ranges [14][15][16][17], it is necessary to determine the microscopic deformation field, which typically requires numerical solution for explicit network realisations. This has thus far been limited to the elastic plateau amenable to energy minimization algorithms [18][19][20][21], or computationally-intensive particle methods that only access short times [22,23]. Without a more general understanding of fibre networks dynamics, we lack the capability to predict potentially large changes in viscoelastic properties over experimentally relevant time scales.Here we present a methodology which allows the numerical calculation of the viscoelastic spectra for any type of disordered fibre network driven at arbitrary oscillation frequencies. The method is based on normal modes which ensures linear response, and since no thermal effects or crosslink dynamics are included by construction, all measured variation in affinity and viscoelasticity can be as...

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“…These values are comparable to measurements for peptide gels such as amyloid tapes [32][33][34] and spider silk [35,36]. Fig.…”

supporting

confidence: 86%

Importance of non-affine viscoelastic response in disordered fibre networks

2016

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“…86 This is perhaps surprisingly high for the terminal carboxylic acid of a dipeptide, but this is a common observation for this kind of gelator. [86][87][88] In fact, the apparent pK a depends on the hydrophobicity of the gelator, the concentration in solution, and the solution temperature, and should probably be interpreted as the apparent pK a of the self-assembled aggregate. In analogy with other systems, close packing of carboxylates and carboxylic acids results in an increase in the pK a .…”

Section: Process Of Assemblymentioning

confidence: 99%

“…As mentioned above, for gelators such as 2NapFF, where the gelation can be controlled by the protonation of the terminal carboxylic acid, we and others have observed that the apparent pK a of this carboxylic acid is affected by the hydrophobicity of the gelator; the higher the hydrophobicity, the higher the apparent pK a . 87 Hence, if two gelators with sufficiently different pK a are mixed and the pH can be decreased in a controlled manner, self-sorting should be favored. Using the hydrolysis of GdL to slowly lower the pH allowed us to produce self-sorted systems.…”

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confidence: 99%

Low-Molecular-Weight Gels: The State of the Art

Draper

Adams

2017

Chem

517

469

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Low-molecular-weight gels are currently a hugely important class of materials that are attracting significant interest. These gels are formed when small molecules self-assemble into one-dimensional structures that entangle and cross-link to form a network that is capable of immobilizing the solvent. Here, we critically discuss the current state of the art and highlight two key areas where we believe there is significant untapped potential. The first is the observation that the properties of the gels are highly process dependent, which means that it is possible to access materials with very different properties from a single gelator. Second, using multiple gelators offers the opportunity to prepare materials with a high degree of information content and with a wider range of properties. We aim to spark thought and discussion on these aspects. INTRODUCTIONLow-molecular-weight gels (LMWGs), or supramolecular gels, are a fascinating and useful class of material. The gels arise from the self-assembly of small molecules into long, anisotropic structures, most commonly fibers. [1][2][3][4][5] At a sufficiently high concentration, these fibers entangle or otherwise form cross-links, leading to the network that is able to immobilize the solvent through surface tension and capillary forces. 1,2 These gels differ from permanently covalently cross-linked polymer gels because the cross-linking can be reversed by the input of energy, for example, by heating. 6 LMWGs have been around for many years but are receiving considerable current interest. 4 They are also used in industrial products, 7 although this seems rarely discussed in the academic literature.In addition to the industrial applications, many recent advances and uses are being described. [8][9][10][11][12] The specific self-assembly leading to gel formation can be exploited. For example, the fiber formation is a result of molecular stacking, meaning that the self-assembly leads to aggregates that can be suitable for optoelectronic applications. 13,14 The ready reversibility of gelation can be exploited, for example, to release cells from gels on demand in a manner that does not lead to cell death. 15 Ready gel formation by a simple trigger can also be used to allow easy and efficient gel loading. [16][17][18] Unsurprisingly, therefore, there is significant interest in these materials ( Figure 1). This is a fascinating area and in many ways holds attention because of the difficulties in probing and understanding the gels. The gels arise from assembly across many length scales, and understanding all of these is difficult. At the molecular level, the molecules must interact in a manner that leads to the formation of suitable aggregates that can eventually entangle. Thus, one-dimensional growth must be favored. From this perspective, it is very frustrating that it is often extremely difficult to predict whether a molecule will form a gel or not; indeed, gelation has been described as an empirical science. 4 Structurally similar small molecules can exhibitThe Bigger Pict...

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“…[15][16][17][18] A number of chemical and physical means have been used as a trigger to initiate self-assembly and to influence the produced nanostructures. [19][20][21][22][23][24] In particular, the biocatalytically triggered self-assembly of aromatic peptide amphiphiles enables control of the self-assembly process under constant and physiological conditions. 25 Xu et al was the first to exploit enzymatic self-assembly of Fmoc-amino acid using an alkaline phosphatase to dephosphorylate Fmoc-tyrosine phosphate (Fmoc-Yp) under basic conditions, forming a hydrogel, 26 but many more followed.…”

Section: Introductionmentioning

confidence: 99%

Enzymatically activated emulsions stabilised by interfacial nanofibre networks

et al. 2016

Self Cite

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This version is available at https://strathprints.strath.ac.uk/55388/ Strathprints is designed to allow users to access the research output of the University of Strathclyde. Unless otherwise explicitly stated on the manuscript, Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Please check the manuscript for details of any other licences that may have been applied. You may not engage in further distribution of the material for any profitmaking activities or any commercial gain. You may freely distribute both the url (https://strathprints.strath.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge.Any correspondence concerning this service should be sent to the ABSTRACTWe report on the on-demand formation of emulsions stabilized by interfacial nanoscale networks by biocatalytic self-assembly of Fmoc (9-fluorenylmethoxycarbonyl) dipeptide amphiphiles in aqueous/organic mixtures. The use of an alkaline phosphatase to transform phosphorylated precursors into self-assembling aromatic peptide amphiphiles (Fmoc-tyrosine-leucine, Fmoc-YL) provides a route to trigger self-assembly of nanofibrous networks and gels. In biphasic organic/aqueous systems, these networks form preferentially at the interface. This gives rise to the possibility of on-demand activation of emulsifying ability, producing switchable emulsions that may be activated by enzyme addition, even after storage of the biphasic mixture for several weeks. Experimental (Fluorescence and FTIR spectroscopy) and computational techniques (Atomistic Molecular Dynamics) are combined to show that the self-assembly process of Fmoc-YL occurs through aromatic interactions and hydrogen bonding to generate an interfacial nanofibrous network.

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

Cited by 179 publications

References 52 publications

Importance of non-affine viscoelastic response in disordered fibre networks

Importance of non-affine viscoelastic response in disordered fibre networks

Low-Molecular-Weight Gels: The State of the Art

Enzymatically activated emulsions stabilised by interfacial nanofibre networks

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