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.

Comparison of embedded atom method potentials for small aluminium cluster simulations.

In this paper, we present a comparison of the performance of a series of embedded atom method potentials for the evaluation of bulk and small aluminium cluster geometries and relative energies, against benchmark density functional theory calculations. In general, the non-pairwise potential-B (NP-B), which was parametrized against Al cluster data, performs the best.

Comparative study of insulin chain-B in isolated and monomeric environments under external stress.

We have conducted a series of theoretical simulations of insulin chain-B under different electric field conditions. This work extends our previous studies of the isolated chain-B by including chain-A and revealing the effects of chemical stress. For this complete protein, we observed increased stability under ambient conditions and under the application of thermal stress, compared to isolated chain-B. On the other hand, the presence of chain-A enhanced the effects of the applied electric field. Under the static field, the presence of chain-A lowered the strength of the field necessary to stretch the protein. Under the oscillating fields, there was relatively less stretching due to the competitive alignment process of the three helical regions with respect to the field. At high field strengths, we observed that the high frequency oscillating field caused less secondary structure disruption than a lower frequency field of the same strength.

Effect of frequency on insulin response to electric field stress.

There are many unanswered questions regarding the precise way in which proteins respond to external stress. Since the function of proteins is critically linked to their three-dimensional structures, exposure to any form of stress which may induce changes in conformation can potentially initiate severe cellular dysfunction. This is particularly relevant with regard to the increasing presence of electromagnetic devices in today's environment and the possible effects on human health. Previously, we investigated the effect of electric field of various strengths on insulin chain-B under static and oscillating conditions. This paper expands on our previous work by subjecting the peptide to an oscillating electric field of different frequencies. We observed a frequency-dependent effect where the application of lower-frequency oscillating fields resulted in static-field-like behavior of the peptide, whereby the intrinsic flexibility of the protein is constrained, thus potentially restricting access to the protein's active state.

Hydrolytic Stability of 3-Aminopropylsilane Coupling Agent on Silica and Silicate Surfaces at Elevated Temperatures.

3-Aminopropylsilane (APS) coupling agent is widely used in industrial, biomaterial, and medical applications to improve adhesion of polymers to inorganic materials. However, during exposure to elevated humidity and temperature, the deposited APS layers can decompose, leading to reduction in coupling efficiency, thus decreasing the product quality and the mechanical strength of the polymer-inorganic material interface. Therefore, a better understanding of the chemical state and stability of APS on inorganic surfaces is needed. In this work, we investigated APS adhesion on silica wafers and compared its properties with those on complex silicate surfaces such as those used by industry (mineral fibers and fiber melt wafers). The APS was deposited from aqueous and organic (toluene) solutions and studied with surface sensitive techniques, including X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), streaming potential, contact angle, and spectroscopic ellipsometry. APS configuration on a model silica surface at a range of coverages was simulated using density functional theory (DFT). We also studied the stability of adsorbed APS during aging at high humidity and elevated temperature. Our results demonstrated that APS layer formation depends on the choice of solvent and substrate used for deposition. On silica surfaces in toluene, APS formed unstable multilayers, while from aqueous solutions, thinner and more stable APS layers were produced. The chemical composition and substrate roughness influence the amount of deposited APS. More APS was deposited and its layers were more stable on fiber melt than on silica wafers. The changes in the amount of adsorbed APS can be successfully monitored by streaming potential. These results will aid in improving industrial- and laboratory-scale APS deposition methods and increasing adhesion and stability, thus increasing the quality and effectiveness of materials where APS is used as a coupling agent.

Electric field effects on insulin chain-B conformation.

The response of proteins to different forms of stress continues to be a topic of major interest, especially with the proliferation of electromagnetic devices conjectured to have detrimental effects on human health. In this paper, we have performed molecular dynamics simulations on insulin chain-B under the influence of both static and oscillating electric fields, ranging from 10(7) to 10(9) V/m. We have found that both variants have an effect on the normal behavior of the protein, with oscillating fields being more disruptive to the structure as compared to static fields of similar effective strength. The application of a static field had a stabilizing effect on the secondary structure, restricting the inherent flexibility that is crucial for insulin's biological activity.

Graphene field effect transistor as a probe of electronic structure and charge transfer at organic molecule-graphene interfaces.

The electronic structure of physisorbed molecules containing aromatic nitrogen heterocycles (triazine and melamine) on graphene is studied using a combination of electronic transport, X-ray photoemission spectroscopy and density functional theory calculations. The interfacial electronic structure and charge transfer of weakly coupled molecules on graphene is found to be governed by work function differences, molecular dipole moments and polarization effects. We demonstrate that molecular depolarization plays a significant role in these charge transfer mechanisms even at submonolayer coverage, particularly for molecules which possess strong dipoles. Electronic transport measurements show a reduction of graphene conductivity and charge carrier mobility upon the adsorption of the physisorbed molecules. This effect is attributed to the formation of additional electron scattering sites in graphene by the molecules and local molecular electric fields. Our results show that adsorbed molecules containing polar functional groups on graphene exhibit different coverage behaviour to nonpolar molecules. These effects open up a range of new opportunities for recognition of different molecules on graphene-based sensor devices.

Ab initio electronic properties of dual phosphorus monolayers in silicon.

IN THE MIDST OF THE EPITAXIAL CIRCUITRY REVOLUTION IN SILICON TECHNOLOGY, WE LOOK AHEAD TO THE NEXT PARADIGM SHIFT: effective use of the third dimension - in particular, its combination with epitaxial technology. We perform ab initio calculations of atomically thin epitaxial bilayers in silicon, investigating the fundamental electronic properties of monolayer pairs. Quantitative band splittings and the electronic density are presented, along with effects of the layers' relative alignment and comments on disordered systems, and for the first time, the effective electronic widths of such device components are calculated.

Ab initio calculation of valley splitting in monolayer δ-doped phosphorus in silicon.

: The differences in energy between electronic bands due to valley splitting are of paramount importance in interpreting transport spectroscopy experiments on state-of-the-art quantum devices defined by scanning tunnelling microscope lithography. Using vasp, we develop a plane-wave density functional theory description of systems which is size limited due to computational tractability. Nonetheless, we provide valuable data for the benchmarking of empirical modelling techniques more capable of extending this discussion to confined disordered systems or actual devices. We then develop a less resource-intensive alternative via localised basis functions in siesta, retaining the physics of the plane-wave description, and extend this model beyond the capability of plane-wave methods to determine the ab initio valley splitting of well-isolated δ-layers. In obtaining an agreement between plane-wave and localised methods, we show that valley splitting has been overestimated in previous ab initio calculations by more than 50%.