Regulation of catalytic behaviour of hydrolases through interactions with functionalized carbon-based nanomaterials

The interaction of enzymes with carbon-based nanomaterials (CBNs) is crucial for the function of biomolecules and therefore for the design and development of effective nanobiocatalytic systems. In this study, the effect of functionalized CBNs, such as graphene oxide (GO) and multi-wall carbon nanotubes (CNTs), on the catalytic behaviour of various hydrolases of biotechnological interest was monitored and the interactions between CBNs and proteins were investigated. The enzyme–nanomaterial interactions significantly affect the catalytic behaviour of enzymes, resulting in an increase up to 60 % of the catalytic efficiency of lipases and a decrease up to 30 % of the esterase. Moreover, the use of CNTs and GO derivatives, especially those that are amine-functionalized, led to increased thermal stability of most the hydrolases tested. Fluorescence and circular dichroism studies indicated that the altered catalytic behaviour of enzymes in the presence of CBNs arises from specific enzyme–nanomaterial interactions, which can lead to significant conformational changes. In the case of lipases, the conformational changes led to a more active and rigid structure, while in the case of esterases this led to destabilization and unfolding. Kinetic and spectroscopic studies indicated that the extent of the interactions between CBNs and hydrolases can be mainly controlled by the functionalization of nanomaterials than by their geometry.     

From the soft matter-hard matter interface to bio-self-organization and hybrid systems

The molecular investigation of the interaction of charged and neutral biomolecules with 2D-nanostructures of aluminum oxyhydroxide characterized by curvature and defects is performed. Steered molecular dynamics and the potential of mean force analysis are used for quantitative assessment of adsorption properties of the aluminum oxyhydroxide (AlOOH) nanosheet surface for typical representatives of anionic, cationic and uncharged biomolecules—amino acid residues. The results are analyzed and compared with the literature data and own previous results. Unbiased molecular dynamics is employed to estimate radial distribution functions of different atom pairs of the AlOOH nanosheet surface and adsorbate surface as well as to study how curvature and surface defects in the form of vacancies of hydroxyl groups influence the interaction of the nanomaterial with monovalent ions. The combined molecular dynamics and quantum mechanical calculation reveals characteristic structural elements with different curvature of the AlOOH nanosheet and enables an estimation of the effect of edge zones in the form of folds on local electrostatic properties of the nanomaterial. The role of these factors in the selective adsorption of nanomaterials and future directions of numerical and experimental studies are discussed. The work is a further investigation into the synthesis, characterization, and application of low-dimensional nanostructures with complex morphology based on layered aluminum (oxy)hydroxide in biomedicine and materials science.     

Cl原子在γ-TiAl(111)表面吸附的第一性原理研究

基于密度泛函理论,在广义梯度近似下研究了Cl在γ-TiAl(111)表面的吸附.计算结果表明:γ-TiAl(111)表面的面心立方位置(fcc)和六角密排位置(hcp)为Cl吸附的稳定位置,当覆盖度Θ小于一个单层(ML)时,Cl原子倾向于吸附在γ-TiAl(111)表面近邻为多Ti的位置.电子结构分析发现,Cl原子同表面金属原子形成较强的离子键,并且成键具有一定的方向性.当Cl原子和O原子共同在γ-TiAl(111)表面吸附时,二者都趋     

A risk forecasting process for nanostructured materials, and nanomanufacturing

Nanomaterials exhibit novel properties that enable new applications ranging from molecular electronics to energy production. Proactive consideration of the potential impacts on human health and the environment resulting from nanomaterial production and use requires methods for forecasting risk associated with of these novel materials. However, the potential variety of nanomaterials is virtually infinite and a case-by-case analysis of the risks these materials may pose is not possible. The challenge of forecasting risk for a broad number of materials is further complicated by large degrees of uncertainty concerning production amounts, the characteristics and uses of these materials, exposure pathways, and a scarcity of data concerning the relationship between nanomaterial characteristics and their effects on organisms and ecosystems. A traditional risk assessment on nanomaterials is therefore not possible at this time. In its place, an evolving process is needed for analyzing the risks associated with emerging nanomaterials-related industries.In this communication, we propose that such a process should include the following six key features: (1) the ability to generate forecasts and associated levels of uncertainty for questions of immediate concern; (2) a consideration of all pertinent sources of nanomaterials; (3) an inclusive consideration of the impacts of activities stemming from nanomaterial use and production that extends beyond the boundaries of toxicology and include full life cycle impacts; (4) the ability to adapt and update risk forecasts as new information becomes available; (5) feedback to improve information gathering; and (6) feedback to improve nanomaterial design. Feature #6 implies that the potential risks of nanomaterials must ultimately be determined as a function of fundamental, quantifiable properties of nanomaterials, so that when these properties are observed in a new material, they can be recognized as indicators of risk. Thus, the required risk assessment process for nanomaterials addresses needs that span from urgent, short-term questions dealing with nanomaterials currently in commerce, to longer-term issues that will require basic research and advances in theory. In the following sections we outline issues surrounding each of these six features and discuss.     

Permeation of nanocrystals across lipid membranes

Biological membranes are one of the major structural elements of cells, and play a key role as a selective barrier and substrate for many proteins that facilitate transport and signaling processes. Understanding the structural and mechanical properties of lipid membranes during permeation of nanomaterials is of prime importance in determining the toxicity of nanomaterials to living cells. It has been shown that the interaction between lipid membranes and nanomaterials and the disruption of lipid membranes are often determined by physicochemical properties of nanomaterials, such as size, shape and surface composition. In this work, molecular dynamic simulations were carried out using various sizes of nanocrystals as a probe to explore the transport of nanomaterials across dipalmitoylphosphatidylcholine (DPPC) bilayers and the changes in the structural and mechanical properties of DPPC bilayers during the permeation. A coarse-grained model was used to provide insight at large time and length scales. In this work, an external driving force helps the nanocrystals across the lipid bilayer. The minimum forces needed to penetrate the model membrane and the interaction of nanocrystals and lipid bilayers were investigated in simulations. The elastic and dynamic properties of lipid bilayers, including the local and bulk properties during the permeation of the nanocrystals, which are of considerable fundamental interest, were also studied. The findings described will lead to better understanding of nanomaterial–lipid membrane interactions and the mechanical and dynamic properties of lipid membranes under permeation.     

Surface interactions of Au(I) cyclo-trimer with Au(111) and Al(111) surfaces: A computational study

A plane-wave density functional theory (DFT) study on surface interactions of a cyclo-[Au(μ-Pz)]₃ monolayer (denoted as T), Pz = pyrazolate, with Au(111) and Al(111) surfaces (denoted as M′) has been performed. Structural and electronic properties at the M′–T interfaces are determined from individually optimized structures of M′, T and M′–T. Results show that the gold pyrazolate trimer (T) binds more strongly on the Au(111) surface than on Al(111). Charge redistribution has been observed at both M′–T interfaces, where charge is “pushed” back towards the Au(111) surface from the trimer monolayer in Au(111)–T system, while the opposite happens in the Al(111)–T system where the charge is being pushed toward the trimer monolayer from the Al(111) surface. Considerable changes to the work function of Au(111) and Al(111) surfaces upon the trimer adsorption which arise from monolayer vacuum level shifts and dipole formation at the interfaces are calculated. The interaction between cyclo-[Au(μ-Pz)]₃ with metal surfaces causes band broadening of the gold pyrazolate trimer in M′–T systems. The present study aids better understanding of the role of intermolecular interactions, bond dipoles, energy-level alignment and electronic coupling at the interface of metal electrodes and organometallic semiconductor to help design metal–organic field effect transistors (MOFETs) and other organometallic electronic devices.     

Improving the charge transfer performance of Si nanomaterial through C surface modification: A first-principles study

Models of oxidized Si (111) surface under different C coverage were established to study the charge transfer ability of Si nanomaterial from strategy of C surface modification using first-principles calculation. The calculated formation energies show that structures of C surface-modified oxidized Si (111) surface are stable. The electronic properties present that the interaction between C and Si atoms is mainly contributed by the hybridization of C-2p and Si-3p states. And the interaction between C and Si atoms increases firstly and then decreases with the increasing C coverage rate. The transfer charge between C and Si reaches a maximum when C coverage rate is 0.5. We speculate that the conductivity of experimentally prepared Si nanomaterial does not monotonously enhance with the increasing C concentration, which would reach a maximum at a certain C concentration, and then decreases.     

Oxidation degree dependent adsorption of ssDNA onto graphene-based surface

DNA/GO composite plays a significant role in the research field of biotechnology and nanotechnology, and attracts a great deal of interest. However, it is still unclear how the oxidation degree of the graphene-based surface affects the adsorption process of single-strand DNA(ss DNA). In this paper, based on the molecular dynamics simulations, we find that ss DNA molecule is absorbed on the GO surface in the most stable state with the oxidation degree around 15%. The microscopic mechanism is attributed to the van Der Walls and the electrostatic interactions between the ss DNA molecule and the graphene-based surface, which is accompanied with the π–π stacking and hydrogen bond formation. The number of π–π stacking between ss DNA and GO reaches the maximum value when the oxidation degree is around 15% among all the GO surfaces. Our simulation results also reveal the coexistence of stretched and curved configurations as well as the adsorption orientation of ss DNA on the GO surface. Furthermore, it is found that the absorbed ss DNA molecules are more likely to move on the graphene-based surface of low oxidation degree, especially on pristine graphene. Our work provides the physics picture of ss DNA's physisorption dynamics onto graphene-based surface and it is helpful in designing DNA/GO nanomaterials.     

Safety assessment of nanomaterials using an advanced decision-making framework,the DF4nanoGrouping

As presented at the 2016 TechConnect World Innovation Conference on 22–25 May 2016 in Washington DC, USA, the European Centre for Ecotoxicology and Toxicology of Chemicals (ECETOC) ‘Nano Task Force’ proposes a Decision-making framework for the grouping and testing of nanomaterials (DF4nanoGrouping) consisting of three tiers to assign nanomaterials to four main groups with possible further subgrouping to refine specific information needs. The DF4nanoGrouping covers all relevant aspects of a nanomaterial’s life cycle and biological pathways: intrinsic material properties and system-dependent properties (that depend upon the nanomaterial’s respective surroundings), biopersistence, uptake and biodistribution, and cellular and apical toxic effects. Use, release, and exposure route may be applied as ‘qualifiers’ to determine if, e.g., nanomaterials cannot be released from products, which may justify waiving of testing. The four main groups encompass (1) soluble, (2) biopersistent high aspect ratio, (3) passive, and (4) active nanomaterials. The DF4nanoGrouping foresees a stepwise evaluation of nanomaterial properties and effects with increasing biological complexity. In case studies covering carbonaceous nanomaterials, metal oxide, and metal sulfate nanomaterials, amorphous silica and organic pigments (all nanomaterials having primary particle sizes below 100 nm), the usefulness of the DF4nanoGrouping for nanomaterial hazard assessment was confirmed. The DF4nanoGrouping facilitates grouping and targeted testing of nanomaterials. It ensures that sufficient data for the risk assessment of a nanomaterial are available, and it fosters the use of non-animal methods. No studies are performed that do not provide crucial data. Thereby, the DF4nanoGrouping serves to save both animals and resources.     

Structural and electronic properties of Na/Cu(111) at different coverages by first principles

Nanostructures are presently enjoying an increasing interest in the field of materials science. In particular, importance is given to ordered monolayers prepared by deposition of atoms on a crystalline surface. The growth of these superlattices can be controlled so as to obtain an ordered structure by means of the lateral interaction of adatoms lying on the metal surface. The objective of our study is to investigate the structural and electronic properties using DFT total-energy calculations; we employ a jellium-like model to describe the substrate but we also take into account the presence of discrete surface states that are known to affect the lateral interaction. Our treatment of the substrate is based on the model proposed by E.V. Chulkov et al. [Surf. Sci. 437, 330 (1999)]; in this model one constructs a mono-dimensional potential so as to reproduce some important electronic properties of the metal surface, such as i) the energy gap in the projected bulk band-structure and ii) the energy position of surface states. We put into practice Chulkov potential implementing into an existing plane-waves code (ABINIT, URL http://www.abinit.org) an ionic potential, so as to obtain a self-consistent Kohn-Sham effective potential which corresponds to the Chulkov one. Using this effective potential in a fully three-dimensional code we are able to study the adsorption process and the interaction between adsorbates. We illustrate some details of our implementation of the Chulkov model and we present our results about the simple system of Na adatoms on a Cu(111) surface for different coverages. In particular, we compare electronic properties and adsorption energies with those obtained within a standard jellium model substrate and with those obtained for Na adsorption on a realistic Cu(111) surface.     

Effect of the electronic structure of a substrate on the photoinduced behavior of adsorbed NO and CO molecules

Photoprocesses in systems produced by adsorption of NO and CO molecules on the Pt(111) and Ni(111) surfaces, as well as on the (111) surface of Pt-Ge alloy, is studied by the IR absorption spectroscopy, resonant multiphoton ionization, and UV photoelectron spectroscopy methods. The energy of photons varies between 2.3 and 6.4 eV. The character of the processes depends on the type of the metallic substrate. On the Pt(111) surface, NO molecules dissociate or are desorbed, depending on the degree of coverage. On the Ni(111) surface, the molecules only dissociate. Conversely, NO molecules adsorbed on the (111) surface of the Pt-Ge alloy are only desorbed from the surface. In the CO/Pt(111) and CO/Pt(111)-Ge systems, CO molecules adsorbed on on-top adsorption sites are desorbed under the action of the photons, while those occupying bridging adsorption sites change their properties insignificantly. A model of photoinduced processes is suggested. According to this model, the lifetime of a state excited by charge transfer between the valence band of the metal and the 2π-antibonding molecular orbital plays a decisive part in the occurrence of one or the other of these processes.     

The effect of Ti on the wetting of CaF<Subscript>2</Subscript> substrate by In–Ti and Ga–Ti alloys. Ab-initio consideration

CaF₂ is a thermodynamically stable, non-reactive compound, displaying a relatively high contact angle with pure liquid metal melts. A remarkable decrease of this contact angle takes place when small amounts of Ti are added to liquid In (a decrease from 125 to 20°) or to liquid Ga (from 118 to 60°). Thermodynamic analysis indicates that this feature cannot be attributed to chemical reactions between the substrate and the melt. It was suggested that the reason for this behavior may be a preferential titanium adsorption from the liquid In–Ti or Ga–Ti solution at the substrate surface. In order to understand the nature of the In–Ti or Ga–Ti bonding in the vicinity of the CaF₂ surface, the adsorption energy of 0.5 monolayer of In and Ga was computed for three different surface conditions: (i) clean CaF₂(111), (ii) CaF₂(111) with In or Ga adatoms, and (iii) CaF₂(111) with Ti adatoms. The differences in adsorption energies for these configurations are related to the electron charge redistribution in the vicinity of the interface, and to the density of states of the electronic subsystems. It was found that the adsorption energy of In or Ga increases due to the lateral interactions with the adatoms. According to the analysis, a strong lateral interaction exists between Ti adatoms and Me, while relatively weak interaction exists between Me and Me adatoms. The difference of the lateral interactions was considered in order to explain the improvement of the wetting of CaF₂ substrate by Ti alloying of In and Ga.     

Adsorption studies on a stepped Pt(111) surface: O2, CO,C2H4, C2N2

A comparative study of the adsorption of several gases on a Pt(S)-[9(111) × (111)] surface was performed using LEED, Auger spectroscopy, flash desorption mass spectrometry and work function changes as surface sensitive techniques. Adsorption was found to be generally less ordered on the stepped surface than on the corresponding flat surface with the exception of the oxygen, where r well ordered overlayer in registry over many terraces was found. Absolute coverages were determined from flash desorption experiments for O₂, CO and C₂N₂. Similar values were obtained as on flat Pt surfaces. Two different surface species seem to be formed upon adsorption of C₂H₄ depending on the adsorption temperature. Contrary to reports from Pt(111) surfaces conversion between the two surface species is heavily restricted on the stepped surface. Work function changes revealed nonlinear adsorbate effects where the adsorbate is electronegative with respect to the substrate. Various adsorption models are discussed in the light of complementary experimental evidence. The results of this study are compared with data available from flat Pt surfaces and possible influences of steps are discussed. No general trends, however, emerge from this comparison and it seems that eventual influences of steps have to be considered individually for every adsorbate.     

环氧树脂基碳纳米复合电磁屏蔽材料研究

基于碳纳米材料有序结构优异的结构与功能特点,研究了其在新型电磁防护材料中的应用,结合环氧树脂与碳纳米有序结构在电磁屏蔽效能和力学性能方面表现出的显著优势,论述了环氧树脂基碳纳米管复合电磁屏蔽材料和碳纳米管有序纳米结构研究,通过电磁仿真优化设计构筑三维导电网络结构,得出8~12 GHz电磁波段屏蔽效能≥82.96 dB的理想结构模型,为环氧树脂基碳纳米复合电磁屏蔽材料研究开发提供了指导,有利于该新型电磁屏蔽材料在国防、国民经济各领域的应用。     

Risk-based classification system of nanomaterials

Various stakeholders are increasingly interested in the potential toxicity and other risks associated with nanomaterials throughout the different stages of a product’s life cycle (e.g., development, production, use, disposal). Risk assessment methods and tools developed and applied to chemical and biological materials may not be readily adaptable for nanomaterials because of the current uncertainty in identifying the relevant physico-chemical and biological properties that adequately describe the materials. Such uncertainty is further driven by the substantial variations in the properties of the original material due to variable manufacturing processes employed in nanomaterial production. To guide scientists and engineers in nanomaterial research and application as well as to promote the safe handling and use of these materials, we propose a decision support system for classifying nanomaterials into different risk categories. The classification system is based on a set of performance metrics that measure both the toxicity and physico-chemical characteristics of the original materials, as well as the expected environmental impacts through the product life cycle. Stochastic multicriteria acceptability analysis (SMAA-TRI), a formal decision analysis method, was used as the foundation for this task. This method allowed us to cluster various nanomaterials in different ecological risk categories based on our current knowledge of nanomaterial physico-chemical characteristics, variation in produced material, and best professional judgments. SMAA-TRI uses Monte Carlo simulations to explore all feasible values for weights, criteria measurements, and other model parameters to assess the robustness of nanomaterial grouping for risk management purposes.     

Ar adsorptions on Al (111) and Ir (111) surfaces: a first-principles study

We investigate the adsorptions of Ar on Al (111) and Ir (111) surfaces at the four high symmetry sites, i.e., top, bridge, fcc- and hcp-hollow sites at the coverage of 0.25 monolayer (ML) using the density functional theory within the generalized gradient approximation of Perdew, Burke and Ernzerhof functions. The geometric structures, the binding energies, the electronic properties of argon atoms adsorbed on Al (111) and Ir (111) surfaces, the difference in electron density between on the Al (111) surface and on the Ir (111) surface and the total density of states are calculated. Our studies indicate that the most stable adsorption site of Ar on the Al (111) surface is found to be the fcc-hollow site for the (2 × 2) structure. The corresponding binding energy of an argon atom at this site is 0.538 eV/Ar atom at a coverage of 0.25 ML. For the Ar adsorption on Ir (111) surface at the same coverage, the most favourable site is the hcp-hollow site, with a corresponding binding energy of 0.493 eV. The total density of states (TDOS) is analysed for Ar adsorption on Al (111) surface and it is concluded that the adsorption behaviour is dominated by the interaction between 3s, 3p orbits of Ar atom and the 3p orbit of the base Al metal and the formation of sp hybrid orbital. For Ar adsorption on Ir (111) surface, the conclusion is that the main interaction in the process of Ar adsorption on Ir (111) surface comes from the 3s and 3p orbits of argon atom and 5d orbit of Ir atom.     

Static sims studies of adsorbate structure: II. CO adsorption on Pd(111); adsorbate-adsorbate interactions on Ru(001), Ni(111) and Pd(111)

In a study of CO adsorption on Pd(111) it is shown that the secondary ion mass spectrum contains information on both adsorbate site geometry and adsorbate coverage. The fractional yields of PdCO⁺, Pd₂CO⁺ and Pd₃CO⁺, as a function of CO coverage are correlated with the changing site geometries suggested by reflection IR data. A relationship between secondary ion emission and the adsorbate-adsorbate interactions revealed by IR and EELS is also demonstrated for CO adsorption on Ru(001), Ni(111) and Pd(111).     

Study of chemisorption on silver surfaces using ultraviolet photoelectron spectroscopy (UPS)

Ultraviolet photoelectron spectroscopy (UPS) was used to study the chemisorption of halogens on stepped [3(111) × (100)] and low-index (111) silver surfaces. The initial rate of halogen adsorption using CHCl₃ exposure on the silver stepped surface is approximately twice that on the low-index surface. This indicates that steps play an important role in chemisorption even on metals with a low density of states at the Fermi level. The adsorbate-induced levels on silver were correlated with halogen p valence orbitals using model extended Hückel calculations. Changes in the silver d band are interpreted as due to p?d orbital interactions.     

纳米尺度物质的生物效应和安全性

纳米尺度的物质包括碳纳米管、纳米二氧化碳、纳米三氧化铁和四氧化三铁等，它们与包括氨基酸在内的生物分子和细胞以及动物整体的相互作用受到广泛关注和研究．结果表明这些纳米材料都能和这些生物成分和生物体相互作用，具有明显的生物效应，能够影响生物分子的结构或构象、细胞的生长，且它们的毒性都较小．但从我们获得的资料看，有些纳米物质对生物的整体特性和人的健康有较重的影响．这是我们应该引起严重注意的．