Single Amino Acid Modifications for Controlling the Helicity of Peptide-Based Chiral Gold Nanoparticle Superstructures.

Assembling nanoparticles (NPs) into well-defined superstructures can lead to emergent collective properties that depend on their 3-D structural arrangement. Peptide conjugate molecules designed to both bind to NP surfaces and direct NP assembly have proven useful for constructing NP superstructures, and atomic- and molecular-level alterations to these conjugates have been shown to manifest in observable changes to nanoscale structure and properties. The divalent peptide conjugate, C16-(PEPAu)2 (PEPAu = AYSSGAPPMPPF), directs the formation of one-dimensional helical Au NP superstructures. This study examines how variation of the ninth amino acid residue (M), which is known to be a key Au anchoring residue, affects the structure of the helical assemblies. A series of conjugates of differential Au binding affinities based on variation of the ninth residue were designed, and Replica Exchange with Solute Tempering (REST) Molecular Dynamics simulations of the peptides on an Au(111) surface were performed to determine the approximate surface contact and to assign a binding score for each new peptide. A helical structure transition from double helices to single helices is observed as the peptide binding affinity to the Au(111) surface decreases. Accompanying this distinct structural transition is the emergence of a plasmonic chiroptical signal. REST-MD simulations were also used to predict new peptide conjugate molecules that would preferentially direct the formation of single-helical AuNP superstructures. Significantly, these findings demonstrate how small modifications to peptide precursors can be leveraged to precisely direct inorganic NP structure and assembly at the nano- and microscale, further expanding and enriching the peptide-based molecular toolkit for controlling NP superstructure assembly and properties.

Using Nitroxides to Enhance Carbon Fiber Interfacial Adhesion and as an Anchor for "Graft to" Surface Modification Strategies.

Nitroxide groups covalently grafted to carbon fibers are used as anchoring sites for TEMPO-terminated polymers (poly-n-butylacrylate and polystyrene) in a "graft to" surface modification strategy. All surface-modified fibers are evaluated for their physical properties, showing that several treatments have enhanced the tensile strength and Young's modulus compared to the control fibers. Up to an 18% increase in tensile strength and 12% in Young's modulus are observed. Similarly, the evaluation of interfacial shear strength in an epoxy polymer shows improvements of up to 144% relative to the control sample. Interestingly, the polymer-grafted surfaces show smaller increases in interfacial shear strength compared to surfaces modified with a small molecule only. This counterintuitive result is attributed to the incompatibility, both chemical and physical, of the grafted polymers to the surrounding epoxy matrix. Molecular dynamics simulations of the interface suggest that the diminished increase in mechanical shear strength observed for the polymer grafted surfaces may be due to the lack of exposed chain ends, whereas the small molecule grafted interface exclusively presents chain ends to the resin interface, resulting in good improvements in mechanical properties.

Accelerated lithium-ion diffusion via a ligand 'hopping' mechanism in lithium enriched solvate ionic liquids.

Solvate ionic liquids (SILs), equimolar amounts of lithium salts and polyether glymes, are well studied highly customisable "designer solvents". Herein the physical, thermal and ion mobility properties of SILs with increased LiTFSI (LiTFSA) concentration, with ligand 1 : >1 LiTFSI stoichiometric ratios, are presented. It was found that between 60-80 °C, the lithium cation diffuses up to 4 times faster than the corresponding anion or ligand (glyme). These systems varied from viscous liquids to self-supporting gels, though were found to thin exponentially when heated to mild temperatures (50-60 °C). They were also found to be thermally stable, up to 200 °C, well in excess of normal operating temperatures. Ion mobility, assessed under an electric potential via ionic conductivity, showed the benefit of SIL optimisation for attaining greater concentrations of Li+ cations to store charge during supercapacitor charging and discharging. Molecular dynamics simulations interrogate the mechanism of enhanced diffusion at high temperatures, revealing a lithium hopping mechanism that implicates the glyme in bridging two lithiums through changes in the denticity.

ContactAngleCalculator: An Automated, Parametrized, and Flexible Code for Contact Angle Estimation in Visual Molecular Dynamics.

Accurate, fast, and flexible approaches for contact angle estimation in molecular dynamics simulations are of great importance for characterization of surface wettability, especially for machine learning approaches which would usually require thousands of computational contact angle evaluations for training and prediction purposes. However, evaluation of the contact angle from molecular simulations is typically a human-intensive process, which hinders the required fast throughput. To address this challenge, here a flexible and automated contact angle estimation tool, ContactAngleCalculator, is developed to meet these new requirements. In contrast to the current widely used computational approaches that are laborious and human intensive, this code is based on the concepts of the coarse-graining technique and equivalent contact area and volume of the droplet. Once the parameters are determined for a target liquid, it can automatically estimate the contact angle of different time points of one case or multiple cases by only one click. This tool is targeted for integration with machine learning methods, in which it can substantially streamline and reduce human labor and time in a computational contact angle estimation.

From graphene to graphene oxide: the importance of extended topological defects.

Graphene oxide (GO) represents a complex family of materials related to graphene: easy to produce in large quantities, easy to process, and convenient to use as a basis for further functionalization, with the potential for wide-ranging applications such as in nanocomposites, electronic inks, biosensors and more. Despite their importance, the key structural traits of GO, and the impact of these traits on properties, are still poorly understood due to the inherently berthollide character of GO which complicates the establishment of clear structure/property relationships. Widely accepted structural models of GO frequently neglect the presence of extended topological defects, structural changes to the graphene basal plane that are not removed by reduction methods. Here, a combination of experimental approaches and molecular simulations demonstrate that extended topological defects are a common feature across GO and that the presence of these defects strongly influences the properties of GO. We show that these extended topological defects are produced following even controlled 'gentle' functionalization by atomic oxygen and are comparable to those obtained by a conventional modified Hummers' method. The presence of the extended topological defects is shown to play an important role in the retention of oxygen functional groups after reduction. As an exemplar of their effect on the physical properties, we show that the GO sheets display a dramatic decrease in strength and stiffness relative to graphene and, due to the presence of extended structural defects, no improvement is seen in the mechanical properties after reduction. These findings indicate the importance of extended topological defects to the structure and properties of functionalized graphene, which merits their inclusion as a key trait in simple structural models of GO.

Identification of Parameters Controlling Peptide-Driven Graphene Exfoliation in Aqueous Media.

Bio-inspired approaches represent potentially transformational methods to fabricate and activate non-natural materials for applications ranging from biomedical diagnostics to energy harvesting platforms. Recently, bio-based methods for the exfoliation of graphene in water have been developed, resulting in peptide-capped nanosheets; however, a clear understanding of the reaction system and peptide ligand structure remains unclear, limiting the advance of such approaches. Here the effects of reaction solution conditions and peptide ligand structure were systematically examined for graphene exfoliation, identifying key parameters to optimize material production. For this, the P1 peptide, identified with affinity for graphene, was exploited to drive exfoliation of bulk graphite to generate the final materials. The peptide was modified at both the N- and C-terminus with a 10-carbon chain fatty acid to explore the effects of a hydrophobic domain on the exfoliation process. The system was examined as a function of sonication time, pH, reagent concentration, and graphite source, where the final materials were fully characterized using a suite of approaches. Collectively, these results demonstrated that maximum graphene production was achieved using the parent P1 peptide after 12 h of sonication under basic conditions. While the exfoliation efficiency was slightly lower for the fatty acid modified peptides, the graphene produced using these biomolecules had fewer defects incorporated, potentially from the wrapping of the nanosheet edge by the aliphatic domain. Such results are important to provide key reaction designs to optimize the reproducibility of graphene exfoliation using biomimetic approaches.

Dynamical Water Ingress and Dissolution at the Amorphous-Crystalline Cellulose Interface.

The use of cellulose has considerable promise in a wide range of industrial applications but is hampered by degradation in mechanical properties due to ambient moisture uptake. Existing models of equilibrium moisture content can predict the impact of these effects, but at present, the dynamical, atomic-scale picture of water ingress into cellulose is lacking. The present work reports nonequilibrium molecular simulations of the interface between cellulose and water aimed at capturing the initial stages of two simultaneous dynamical processes, water ingress into cellulose and cellulose dissolution into water. These simulations demonstrate that the process depends on the temperature and chain length in the amorphous region, where high temperatures can induce more mass exchange and short chains can easily detach from amorphous cellulose. A cooperative mechanism that involves both chemical and physical aspects, namely, hydrogen bonding and chain intertwining, respectively, is proposed to interpret the incipient dual ingress/dissolution process. Outcomes of this work will provide a foundation for cellulose functionalization strategies to impede moisture uptake and preserve the mechanical properties of nanocellulose in applications.

Predictions of Pattern Formation in Amino Acid Adlayers at the In Vacuo Graphene Interface: Influence of Termination State.

Controlled self-assembly of biomolecules on graphene offers a pathway for realizing its full potential in biological applications. Microscopy has revealed the self-assembly of amino acid adlayers into dimer rows on nonreactive substrates. However, neither the spontaneous formation of these patterns, nor the influence of amino acid termination state on the formation of patterns has been directly resolved to date. Molecular dynamics simulations, with the ability to reveal atomic level details and exert full control over the termination state, are used here to model initially disordered adlayers of neutral, zwitterionic, and neutral-zwitterionic mixtures for two types of amino acids, tryptophan and methionine, adsorbed on graphene in vacuo. The simulations of the zwitterion-containing adlayers exhibit the spontaneous emergence of dimer row ordering, mediated by charge-driven intermolecular interactions. In contrast, adlayers containing only neutral species do not assemble into ordered patterns. It is also found that the presence of trace amounts of water reduces the interamino acid interactions in the adlayers, but does not induce or disrupt pattern formation. Overall, the findings reveal the balance between the lateral interamino acid interactions and amino acid-graphene interactions, providing foundational insights for ultimately realizing the predictable pattern formation of biomolecules adsorbed on unreactive surfaces.

Tuning the Structure and Chiroptical Properties of Gold Nanoparticle Single Helices via Peptide Sequence Variation.

Just as peptide function is determined by the position, sequence, and overall arrangement of constituent amino acids, the optical properties of nanoparticle (NP) assemblies are influenced by the size, dimensions, and arrangement of constituent NPs. In this work, we demonstrate that peptide sequence can be programmed to direct the structure and chiroptical activity of chiral helical gold NP (AuNP)superstructures, a growing class of chiral nanomaterials with potential in sensing, detection, and optics-based applications. Gold-binding peptide conjugate families, C18-(PEPAuM,x)2 and C18-(PEPAuM-ox,x)2, that differ in the position (x = 7, 9, and 11) of methionine (M)/methionine sulfoxide (M-ox) within the peptide sequences (PEPAu = AYSSGAPPMPPF/PEPAuM-ox = AYSSGAPPMoxPPF) are employed to control the aspect ratio and size of AuNPs within helical NP assemblies. Computational modeling reveals that the amino acid variations have a profound effect on peptide-AuNP interactions that ultimately lead to control over NP size. C18-(PEPAuM,x)2 (x = 7, 9, and 11) yield irregular double-helical superstructures comprising spherical AuNPs, while C18-(PEPAuM-ox,x)2 (x = 9, 11) yield single-helical assemblies comprising oblong or rod-shaped AuNPs. Further, component AuNPs are larger when M/M-ox is placed at x = 11, while smaller component AuNPs are observed when M/M-ox is placed at x = 7. Changes in nanoscale structures manifest themselves in observable differences in chiroptical signal intensity. Ultimately, we achieve dramatic variance in the structure and properties of chiral AuNP superstructures via simple molecular-level tuning of peptide primary sequence.

Biomolecular Material Recognition in Two Dimensions: Peptide Binding to Graphene, h-BN, and MoS2 Nanosheets as Unique Bioconjugates.

Two-dimensional nanosheet-based materials such as graphene, hexagonal boron nitride, and MoS2 represent intriguing structures for a variety of biological applications ranging from biosensing to nanomedicine. Recent advances have demonstrated that peptides can be identified with affinity for these three materials, thus generating a highly unique bioconjugate interfacial system. This Review focuses on recent advances in the formation of bioconjugates of these types, paying particular attention to the structure/function relationship of the peptide overlayer. This is achieved through the amino acid composition of the nanosheet binding peptides, thus allowing for precise control over the properties of the final materials. Such bioconjugate systems offer rapid advances via direct property control that remain difficult to achieve for biological applications using nonbiological approaches.

A Bespoke Force Field To Describe Biomolecule Adsorption at the Aqueous Boron Nitride Interface.

Reliable manipulation of the interface between 2D nanomaterials and biomolecules represents a current frontier in nanoscience. The ability to resolve the molecular-level structures of these biointerfaces would provide a fundamental data set that is needed to enable systematic and knowledge-based progress in this area. These structures are challenging to obtain via experiment alone, and molecular simulations offer a complementary approach to address this problem. Compared with graphene, the interface between hexagonal boron nitride (h-BN) and biomolecules is relatively understudied at present. While several force fields are currently available for modeling the h-BN/water interface, there is a lack of a suitable force field that can describe the interactions between h-BN, liquid water, and biomolecules. Here, we use density functional theory calculations to create a force field, BoNi-CHARMM, to describe biomolecular interactions at the aqueous h-BN interface. Verifying our force field presents an additional challenge, given the scarcity of available experimental data for these interfaces. We test our force field against experimental evidence regarding the water/surface contact angle and confirm that the force field provides experimentally consistent values. We also present preliminary data regarding predictions of the free energy of adsorption of a selection of amino acids at the aqueous h-BN interface, revealing arginine and tryptophan to be among the strongest binders. This force field provides an opportunity to initiate a systematic progression in our current understanding of how to capture the intermolecular interactions at the h-BN biointerface.

Biointerface Structural Effects on the Properties and Applications of Bioinspired Peptide-Based Nanomaterials.

Peptide sequences are known to recognize and bind different nanomaterial surfaces, which has resulted in the screening and identification of hundreds of peptides with the ability to bind to a wide range of metallic, metal oxide, mineral, and polymer substrates. These biomolecules are able to bind to materials with relatively high affinity, resulting in the generation of a complex biointerface between the biotic and abiotic components. While the number of material-binding sequences is large, at present, quantitative materials-binding characterization of these peptides has been accomplished only for a relatively small number of sequences. Moreover, it is currently very challenging to determine the molecular-level structure(s) of these peptides in the materials adsorbed state. Despite this lack of data related to the structure and function of this remarkable biointerface, several of these peptide sequences have found extensive use in creating functional nanostructured materials for assembly, catalysis, energy, and medicine, all of which are dependent on the structure of the individual peptides and collective biointerface at the material surface. In this Review, we provide a comprehensive overview of these applications and illustrate how the versatility of this peptide-mediated approach for the growth, organization, and activation of nanomaterials could be more widely expanded via the elucidation of biointerfacial structure/property relationships. Future directions and grand challenges to realize these goals are highlighted for both experimental characterization and molecular-simulation strategies.

Pathways to Structure-Property Relationships of Peptide-Materials Interfaces: Challenges in Predicting Molecular Structures.

An in-depth appreciation of how to manipulate the molecular-level recognition between peptides and aqueous materials interfaces, including nanoparticles, will advance technologies based on self-organized metamaterials for photonics and plasmonics, biosensing, catalysis, energy generation and harvesting, and nanomedicine. Exploitation of the materials-selective binding of biomolecules is pivotal to success in these areas and may be particularly key to producing new hierarchically structured biobased materials. These applications could be accomplished by realizing preferential adsorption of a given biomolecule onto one materials composition over another, one surface facet over another, or one crystalline polymorph over another. Deeper knowledge of the aqueous abiotic-biotic interface, to establish clear structure-property relationships in these systems, is needed to meet this goal. In particular, a thorough structural characterization of the surface-adsorbed peptides is essential for establishing these relationships but can often be challenging to accomplish via experimental approaches alone. In addition to myriad existing challenges associated with determining the detailed molecular structure of any molecule adsorbed at an aqueous interface, experimental characterization of materials-binding peptides brings new, complex challenges because many materials-binding peptides are thought to be intrinsically disordered. This means that these peptides are not amenable to experimental techniques that rely on the presence of well-defined secondary structure in the peptide when in the adsorbed state. To address this challenge, and in partnership with experiment, molecular simulations at the atomistic level can bring complementary and critical insights into the origins of this abiotic/biotic recognition and suggest routes for manipulating this phenomenon to realize new types of hybrid materials. For the reasons outlined above, molecular simulation approaches also face challenges in their successful application to model the biotic-abiotic interface, related to several factors. For instance, simulations require a plausible description of the chemistry and the physics of the interface, which comprises two very different states of matter, in the presence of liquid water. Also, it is essential that the conformational ensemble be comprehensively characterized under these conditions; this is especially challenging because intrinsically disordered peptides do not typically admit one single structure or set of structures. Moreover, a plausible structural model of the substrate is required, which may require a high level of detail, even for single-element materials such as Au surfaces or graphene. Developing and applying strategies to make credible predictions of the conformational ensemble of adsorbed peptides and using these to construct structure-property relationships of these interfaces have been the goals of our efforts. We have made substantial progress in developing interatomic potentials for these interfaces and adapting advanced conformational sampling approaches for these purposes. This Account summarizes our progress in the development and deployment of interfacial force fields and molecular simulation techniques for the purpose of elucidating these insights at biomolecule-materials interfaces, using examples from our laboratories ranging from noble-metal interfaces to graphitic substrates (including carbon nanotubes and graphene) and oxide materials (such as titania). In addition to the well-established application areas of plasmonic materials, biosensing, and the production of medical implant materials, we outline new directions for this field that have the potential to bring new advances in areas such as energy materials and regenerative medicine.

Facet-Specific Adsorption of Tripeptides at Aqueous Au Interfaces: Open Questions in Reconciling Experiment and Simulation.

The adsorption of three homo-tripeptides, HHH, YYY, and SSS, at the aqueous Au interface is investigated, using molecular dynamics simulations. We find that consideration of surface facet effects, relevant to experimental conditions, opens up new questions regarding interpretations of current experimental findings. Our well-tempered metadynamics simulations predict the rank ordering of the tripeptide binding affinities at aqueous Au(111) to be YYY > HHH > SSS. This ranking differs with that obtained from existing experimental data which used surface-immobilized Au nanoparticles as the target substrate. The influence of Au facet on these experimental findings is then considered, via our binding strength predictions of the relevant amino acids at aqueous Au(111) and Au(100)(1 × 1). The Au(111) interface supports an amino acid ranking of Tyr > HisA ≃ HisH > Ser, matching that of the tripeptides on Au(111), while the ranking on Au(100) is HisA > Ser ≃ Tyr ≃ HisH, with only HisA showing non-negligible binding. The substantial reduction in Tyr amino acid affinity for Au(100) vs Au(111) offers one possible explanation for the experimentally observed weaker adsorption of YYY on the nanoparticle-immobilized substrate compared with HHH. In a separate set of simulations, we predict the structures of the adsorbed tripeptides at the two aqueous Au facets, revealing facet-dependent differences in the adsorbed conformations. Our findings suggest that Au facet effects, where relevant, may influence the adsorption structures and energetics of biomolecules, highlighting the possible influence of the structural model used to interpret experimental binding data.

Adsorption of DNA Fragments at Aqueous Graphite and Au(111) via Integration of Experiment and Simulation.

We combine single molecule force spectroscopy measurements with all-atom metadynamics simulations to investigate the cross-materials binding strength trends of DNA fragments adsorbed at the aqueous graphite C(0001) and Au(111) interfaces. Our simulations predict this adsorption at the level of the nucleobase, nucleoside, and nucleotide. We find that despite challenges in making clear, careful connections between the experimental and simulation data, reasonable consistency between the binding trends between the two approaches and two substrates was evident. On C(0001), our simulations predict a binding trend of dG > dA ≈ dT > dC, which broadly aligns with the experimental trend. On Au(111), the simulation-based binding strength trends reveal stronger adsorption for the purines relative to the pyrimadines, with dG ≈ dA > dT ≈ dC. Moreover, our simulations provide structural insights into the origins of the similarities and differences in adsorption of the nucleic acid fragments at the two interfaces. In particular, our simulation data offer an explanation for the differences observed in the relative binding trend between adenosine and guanine on the two substrates.

Molecular Modelling of Peptide-Based Materials for Biomedical Applications.

The molecular-level interactions between peptides and medically-relevant biomaterials, including nanoparticles, have the potential to advance technologies aimed at improving performance for medical applications including tissue implants and regenerative medicine. Peptides can possess materials-selective non-covalent adsorption properties, which in this instance can be exploited to enhance the biocompatibility and possible multi-functionality of medical implant materials. However, at present, their successful implementation in medical applications is largely on a trial-and-error basis, in part because a deep comprehension of general structure/function relationships at these interfaces is currently lacking. Molecular simulation approaches can complement experimental characterisation techniques and provide a wealth of relevant details at the atomic scale. In this Chapter, progress and prospects for advancing peptide-mediated medical implant surface treatments via molecular simulation is summarised for two of the most widely-found medical implant interfaces, titania and hydroxyapatite.

Sequence-Dependent Structure/Function Relationships of Catalytic Peptide-Enabled Gold Nanoparticles Generated under Ambient Synthetic Conditions.

Peptide-enabled nanoparticle (NP) synthesis routes can create and/or assemble functional nanomaterials under environmentally friendly conditions, with properties dictated by complex interactions at the biotic/abiotic interface. Manipulation of this interface through sequence modification can provide the capability for material properties to be tailored to create enhanced materials for energy, catalysis, and sensing applications. Fully realizing the potential of these materials requires a comprehensive understanding of sequence-dependent structure/function relationships that is presently lacking. In this work, the atomic-scale structures of a series of peptide-capped Au NPs are determined using a combination of atomic pair distribution function analysis of high-energy X-ray diffraction data and advanced molecular dynamics (MD) simulations. The Au NPs produced with different peptide sequences exhibit varying degrees of catalytic activity for the exemplar reaction 4-nitrophenol reduction. The experimentally derived atomic-scale NP configurations reveal sequence-dependent differences in structural order at the NP surface. Replica exchange with solute-tempering MD simulations are then used to predict the morphology of the peptide overlayer on these Au NPs and identify factors determining the structure/catalytic properties relationship. We show that the amount of exposed Au surface, the underlying surface structural disorder, and the interaction strength of the peptide with the Au surface all influence catalytic performance. A simplified computational prediction of catalytic performance is developed that can potentially serve as a screening tool for future studies. Our approach provides a platform for broadening the analysis of catalytic peptide-enabled metallic NP systems, potentially allowing for the development of rational design rules for property enhancement.

A robust and reproducible procedure for cross-linking thermoset polymers using molecular simulation.

Molecular simulation can provide valuable guidance in establishing clear links between structure and function to enable the design of new polymer-based materials. However, molecular simulation of thermoset polymers in particular, such as epoxies, present specific challenges, chiefly in the credible preparation of polymerised samples. Despite this need, a comprehensive, reproducible and robust process for accomplishing this using molecular simulation is still lacking. Here, we introduce a clear and reproducible cross-linking protocol to reliably generate three dimensional epoxy cross-linked polymer structures for use in molecular simulations. This protocol is sufficiently detailed to allow complete reproduction of our results, and is applicable to any general thermoset polymer. Amongst our developments, key features include a reproducible procedure for calculation of partial atomic charges, a reliable process for generating and validating an equilibrated liquid precursor mixture, and establishment of a novel, robust and reproducible protocol for generating the three-dimensional cross-linked solid polymer. We use these structures as input to subsequent molecular dynamics simulations to calculate a range thermo-mechanical properties, which compare favourably with experimental data. Our general protocol provides a benchmark for the process of simulating epoxy polymers, and can be readily translated to prepare and model epoxy samples that are dynamically cross-linked in the presence of surfaces and nanostructures.

Elucidating the mechanisms of nanodiamond-promoted structural disruption of crystallised lipid.

The removal or structural disruption of crystallised lipid is a pivotal but energy-intensive step in a wide range of industrial and biological processes. Strategies to disrupt the structure of crystallised lipid in aqueous solution at lower temperatures are much needed, where nanoparticle-based strategies show enormous promise. Using the aqueous tristearin bilayer as a model for crystallised lipid, we demonstrate that the synergistic use of surfactant and detonation nanodiamonds can depress the onset temperature at which disruption of the crystallised lipid structure occurs. Our simulations reveal the molecular-scale mechanisms by which this disruption takes place, indicating that the nanodiamonds serve a dual purpose. First, the nanodiamonds are predicted to facilitate delivery of surfactant to the lipid/water interface, and second, nanodiamond adsorption acts to roughen the lipid/water interface, enhancing ingress of surfactant into the bilayer. We find the balance of the hydrophobic surface area of the nanodiamond and the nanodiamond surface charge density to be a key determinant of the effectiveness of using nanodiamonds to facilitate lipid disruption. For the nanodiamond size considered here, we identify a moderate surface charge density, that ensures the nanodiamonds are neither too hydrophobic nor too hydrophilic, to be optimal.

Non-covalent adsorption of amino acid analogues on noble-metal nanoparticles: influence of edges and vertices.

The operation of many nanostructured biomolecular sensors and catalysts critically hinges on the manipulation of non-covalent adsorption of biomolecules on unfunctionalised noble-metal nanoparticles (NMNPs). Molecular-level structural details of the aqueous biomolecule/NMNP interface are pivotal to the successful realisation of these technologies, but such experimental data are currently scarce and challenging to obtain. Molecular simulations can generate these details, but are limited by the assumption of non-preferential adsorption to NMNP features. Here, via first principles calculations using a vdW-DF functional, and based on nanoscale sized NMNPs, we demonstrate that adsorption preferences to NP features vary with adsorbate chemistry. These results show a clear distinction between hydrocarbons, that prefer adsorption to facets over edges/vertices, over heteroatomic molecules that favour adsorption onto vertices over facets. Our data indicate the inability of widely used force-fields to correctly capture the adsorption of biomolecules onto NMNP surfaces under aqueous conditions. Our findings introduce a rational basis for the development of new force-fields that will reliably capture these phenomena.