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The immobilization of enzymes on solid supports is an important challenge in biotechnology and biomedicine. In contrast to other methods, enzyme deposition in polymer brushes offers the benefit of high protein loading that preserves enzymatic activity in part due to the hydrated 3D environment that is available within the brush structure. The authors equipped planar and colloidal silica surfaces with poly(2-(diethylamino)ethyl methacrylate)-based brushes to immobilize Thermoplasma acidophilum histidine ammonia lyase, and analyzed the amount and activity of the immobilized enzyme. The poly(2-(diethylamino)ethyl methacrylate) brushes are attached to the solid silica supports either via a "grafting-to" or a "grafting-from" method. It is found that the grafting-from method results in higher amounts of deposited polymer and, consequently, higher amounts of Thermoplasma acidophilum histidine ammonia lyase. All polymer brush-modified surfaces show preserved catalytic activity of the deposited Thermoplasma acidophilum histidine ammonia lyase. However, immobilizing the enzyme in polymer brushes using the grafting-from method resulted in twice the enzymatic activity from the grafting-to approach, illustrating a successful enzyme deposition on a solid support.

Surface of Lactobacillus crispatus DSM 20584 (LBC) and Lactobacillus rhamnosus GG (LGG) from stationary and exponential phase were chemically modified using hexanoic anhydride (HA) and octanal via grafting hydrophobic moieties onto the bacterial surface hydroxyl and amine groups. The physicochemical properties of the bacteria were measured using a range of surface-sensitive methods including x-ray photoelectron spectroscopy (XPS), zeta potential measurement, contact angle measurement (CAM) and microbial adhesion to solvents (MATS). Before modification, the surface of two strains was distinctly different, where LBC was covered by hydrophobic surface-layer proteins (SLPs) while LGG was hydrophilic with the rich presence of polysaccharides. Surface hydrophilic polymers rendered steric hindrance of LGG against autoaggregation, whereas LBC lacking polysaccharides showed strong autoaggregation. After HA and octanal modifications, the intrinsic surface differences between two strains were reduced according to the Principal Component Analysis (PCA). The enhancement of hydrophobicity by HA and octanal was most likely derived from the lowered Lewis acid-base characters via elimination of hydroxyl and amine groups. Chemical modification using the two treatments can be a useful tool to tune the surface of lactic acid bacteria, which might be further applied to other microorganisms, enabling applications such as altered bacterial adhesive behaviors and biofilm formation.

Nano/micromotors are self-propelled particles that use external stimuli to gain locomotion outperforming Brownian motion. Here, three different polymers are employed that are conjugated to silica particles through a pH-labile linker. At slightly acidic pH, the linkers hydrolyze and release the polymeric chains, resulting in enhanced locomotion. The motors show a maximum velocity of approximate to 3 mu m s(-1) in cell media when poly(ethylene glycol) methyl ether methacrylate is asymmetrically distributed on the surface of the particles. Further, the motor internalization by RAW 264.7 macrophages was compared between motors, which have the polymer conjugated via a pH-labile linker, and the irresponsive particles. Preliminary data indicate enhanced uptake, but further efforts are required to use responsive polymers to propel motors inside mammalian cells.

Electrochemical CO2 reduction to valuable chemicals represents a greenand sustainable approach to close the anthropogenic carbon cycle, but hasbeen impeded by low efficiency and high cost of electrocatalysts. Here, acost-effective hybrid catalyst consisting of hemin (chloroprotoporphyrin IXiron(III)), a product recovered from bovine blood, adsorbed onto commercialVulcan carbon is reported. Upon heat treatment, this material shows significantlyimproved activity and selectivity for CO2 reduction in water whileexhibiting good stability for more than 10 h. The heat treatment leads toconsecutive removal of the axial chlorine atom and decomposition of the ironporphyrin ring, restructuring to form atomic Fe sites. The optimized hybridcatalyst obtained at 900 °C shows near-unity selectivity for reduction of CO2to CO at a small overpotential of 310 mV. The insight into transformation ofadsorbed Fe complexes into single Fe atoms upon heat treatment providesguidance for development of single atom catalysts.

Interactions between graphene oxide (GO) and organic molecules play a role in processes such as environmental remediation and water treatment. However, little is known about underlying molecular level processes with the presence of ions. In this study, we utilized atomic force microscopy (AFM) in chemical force mapping (CFM) mode to directly probe their adhesion interactions. AFM tips were functionalised to serve as models for nonpolar and polar organic molecules, i.e. with alkyl, –CH3, and carboxyl, –COO(H). For experiments with –COO(H) tips, adhesion between GO and tips decreased in the order: Ba2+ > Ca2+ > Mg2+ > Na+, whereas for the –CH3 tips, ion dependent adhesion was relatively low but followed the same: Ba2+ > Ca2+ > Mg2+ ≈ Na+. Calculations with Derjaguin–Landau–Verwey–Overbeek (DLVO) theory and the Schulze–Hardy rule could not account for the observations. We propose that ion bridging plays a definitive role in adhesion between –COO(H) tips and the GO surface. This is consistent with proposed models with density functional theory (DFT) calculations. Adhesion of –CH3 tips is a response to the hydrophilic interactions and the ion dependent part is suggested to arise from ion bridging between slightly negative charged –CH3 tips and the GO surface. High pH had a notable influence on the adhesion of the –COO(H) tip but a negligible effect on the –CH3 tip. These results offer important insights into interactions between solutions and mineral surfaces with adsorbed organic molecules.

Simultaneous retention of SMM behaviour and of optical activity is demonstrated upon surface deposition for a chiral SMM., The synthesis and characterization of a chiral, enneanuclear Mn(iii)-based, Single-Molecule Magnet, [Mn9O4(Me-sao)6(L)3(MeO)3(MeOH)3]Cl (1; Me-saoH2 = methylsalicylaldoxime, HL = lipoic acid) is reported. Compound 1 crystallizes in the orthorhombic P212121 space group and consists of a metallic skeleton describing a defect super-tetrahedron missing one vertex. The chirality of the [MnIII9] core originates from the directional bridging of the Me-sao2– ligands via the –N–O– oximate moieties, which define a clockwise (1ΔΔ) or counter-clockwise (1ΛΛ) rotation in both the upper [MnIII3] and lower [MnIII6] subunits. Structural integrity and retention of chirality upon dissolution and upon deposition on (a) gold nanoparticles, 1@AuNPs, (b) transparent Au(111) surfaces, 1ΛΛ@t-Au(111); 1ΔΔ@t-Au(111), and (c) epitaxial Au(111) on mica surfaces, 1@e-Au(111), was confirmed by CD and IR spectroscopies, mass spectrometry, TEM, XPS, XAS, and AFM. Magnetic susceptibility and magnetization measurements demonstrate the simultaneous retention of SMM behaviour and optical activity, from the solid state, via dissolution, to the surface deposited species.

The Au-C linkage has been demonstrated as a robust interface for coupling thin organic films on Au surfaces. However, the nature of the Au-C interaction remains elusive up to now. Surface-enhanced Raman spectroscopy was previously used to assign a band at 412 cm(-1) as a covalent sigma Au-C bond for films generated by spontaneous reduction of the 4-nitrobenzenediazonium salt on Au nanoparticles. However, this assignment is disputed based on our isotopic shift study. We now provide direct evidence for covalent Au-C bonds on the surface of Au nanoparticles using C-13 crosspolarization/magic angle spinning solid-state NMR spectroscopy combined with isotope substitution. A C-13 NMR shift at 165 ppm was identified as an aromatic carbon linked to the gold surface, while the shift at 148 ppm was attributed to C-C junctions in the arylated organic film. This demonstration of the covalent sigma Au-C bond fills the gap in metal-C bonds for organic films on surfaces, and it has great practical and theoretical significance in understanding and designing a molecular junction based on the Au-C bond.

The design of selective and efficient catalysts for electrochemical CO2 reduction is highly desirable yet still challenging, in particular, if the aim is to make them binder-free and self-standing. Here, we report a new and straightforward strategy to incorporate Ni single atoms into a commercially available carbon paper to prepare a self-standing electrode. This is accomplished by consecutive acid activation, adsorption of Ni2+ ions, and pyrolysis steps. Structural characterizations and calculations based on density functional theory consistently suggest that the Ni single atoms are coordinated with three N and one S atoms on the carbon paper. When used for CO2 electroreduction, the electrode exhibits an optimal selectivity (91%), activity (3.4 mA cm-2), and stability (at least 14 h) for CO production in water at an overpotential of 660 mV. This report may inspire the design and incorporation of single atoms of various metal types into carbon papers, or other kinds of carbon substrates, for a wide range of electrocatalytic processes. This journal is

The stability of phenol-urea-formaldehyde (PUF) binder and 3-aminopropylsilane (APS) on composite silicate materials (fibers and wafers) was studied with surface sensitive techniques (X-ray photoelectron spectroscopy (XPS) and streaming potential) through a wide range of humidity and temperature and ab initio modelling complemented the results. Behavior was compared for wettability properties, determined by vapor adsorption and contact angle analysis. APS and PUF, deposited on the silicate surfaces, decrease surface energy and wettability but water adsorption remains high, facilitating hydrolytic decomposition of the composite material. Deposited APS is unstable at T>50 degrees C and 75% RH, while PUF is less sensitive to high humidity and temperature. Molecular dynamics confirmed APS sensitivity to humidity. Water adsorption and surface energy decrease, and material stability increases when a hydrophobization agent is applied to APS/PUF treated surfaces. The direct correlation between wettability and stability of PUF/APS/fiber composites can contribute in designing new materials with controlled hydrophobic properties. (C) 2020 Elsevier Ltd. All rights reserved.

Lignin is currently an underutilized part of biomass, thus, further research into lignin could benefit both scientific and commercial endeavors. The present study investigated the potential of kraft lignin as a support material for the removal of hydrogen sulfide (H2S) from gaseous streams, such as biogas. The removal of H2S was enabled by copper ions that were previously adsorbed on kraft lignin. Copper adsorption was based on two different strategies: either directly on lignin particles or by precipitating lignin from a solution in the presence of copper. The H2S concentration after the adsorption column was studied using proton-transfer-reaction mass spectrometry, while the mechanisms involved in the H2S adsorption were studied with X-ray photoelectron spectroscopy. It was determined that elemental sulfur was obtained during the H2S adsorption in the presence of kraft lignin and the differences relative to the adsorption on porous silica as a control are discussed. For kraft lignin, only a relatively low removal capacity of 2 mg of H2S per gram was identified, but certain possibilities to increase the removal capacity are discussed.

The production of novel composite materials, assembled using biomimetic polymers known as peptoids (N-substituted glycines) to nucleate CaCO3, can open new pathways for advanced material design. However, a better understanding of the heterogeneous CaCO3 nucleation process is a necessary first step. We determined the thermodynamic and kinetic parameters for calcite nucleation on self-assembled monolayers (SAMs) of nanosheet-forming peptoid polymers and simpler, alkanethiol analogues. We used nucleation rate studies to determine the net interfacial free energy (γnet) for the peptoid–calcite interface and for SAMs terminated with carboxyl headgroups, amine headgroups, or a mix of the two. We compared the results with γnet determined from dynamic force spectroscopy (DFS) and from density functional theory (DFT), using COSMO-RS simulations. Calcite nucleation has a lower thermodynamic barrier on the peptoid surface than on carboxyl and amine SAMs. From the relationship between nucleation rate (J0) and saturation state, we found that under low-saturation conditions, i.e., We have combined nucleation studies, dynamic force spectroscopy, and density functional theory and determined the thermodynamic and kinetic parameters for calcite nucleation on self-assembled monolayers (SAMs) of nanosheet-forming peptoid polymers and simpler, alkanethiol analogues. Our results show insight into biopolymeric influence on nucleation and growth of a mineral phase during biomineralization processes and are directly applicable to nacre mimicry.

To establish an approach for a bulk upscaling of a composit material consisting of calcium carbonate and tunable peptoids we here combined three distinct approaches to thoroughly access the underlying kinetic and thermodynamic driving forces for CaCO3 formation on peptoid polymers. We derived the net interfacial free energy for calcite formation on the nanosheets and self-assemblage monolayers of the sheets constituent functional groups (carboxyl, amine and a 1:1 mix) using: nucleation experiments, dynamic force spectroscopy and theoretical modeling (COSMO-RS). We applied nucleation theory to the results and obtain insight into conditions were we can obtain favorable nucleation conditions on the polymers in a highly controlled manner.

Flooding sandstone oil reservoirs with low salinity water can lead to a significant increase in oil recovery, a phenomenon called “the low salinity effect”. Although there are many factors that contribute to this response, the surface tension on the pore walls is an important one. Sandstone is composed predominantly of quartz with some clay, but feldspar grains are often also present. While the wettability of quartz and clay surfaces has been thoroughly investigated, little is known about the adhesion properties of feldspar. We explored the interaction of model oil compounds, molecules that terminate with carboxyl, −COO(H), and alkyl, −CH3, with freshly cleaved, museum quality perthitic microcline, KxNa(1–x)AlSi3O8, a K-feldspar. Microcline is a member of the orthoclase family, a type of feldspar that weathers more slowly than the plagioclase series, and thus is more likely to be preserved in well sorted sandstone. Adhesion forces, measured with the chemical force mapping (CFM) mode of atomic force micros...

The unambiguous determination of the chemical functionality over graphene oxide (GO) is important to unleash its potential applications. However, the mapping of oxygen functionalities distribution remains to be unequivocally determined because of highly inhomogeneous non-stoichiometric structures and ultra-thin layers of GO. In this study, we report an experimental observation of the spatial distribution of oxygen functional groups on monolayer and multilayer GO using AFM-IR, atomic force microscopy coupled with infrared spectroscopy. Overcoming conventional IR diffraction limit for several micrometers, the novel AFM-IR reaches high spatial resolution ∼20 nm and could detect IR absorption on ∼1 nm thickness of monolayer GO. With nanoscale chemical mapping, the distribution of different oxygen functional groups is distinguished with AFM-IR over the GO surface. It allows us to observe that these oxygen functional groups prefer to sit on the fold areas, in discrete domains and on the edges of GO, which gave more insights into its chemical nature. The determination of the position of functional groups through precise imaging contributes to our understanding of GO structure-properties relations and paves the way for targeted tethering of polymers, biomaterials, and other nanostructures.

Understanding the adsorption behavior of nitrogen heterocyclic compounds (NHCs) on soil minerals underlies more effective design of wastewater treatment and soil/groundwater remediation. We investigated adsorption of quinoline, a representative NHC, on quartz sand (using Berea sandstone as a model), at 3 < pH < 9, in low (0.05 M) and high (0.7 M) ionic strength solutions where NaCl was the background electrolyte. Minor clay (kaolinite) in the sandstone contributed significantly to quinoline uptake. Adsorption peaked at pH∼6. It decreased from 2 equivalent monolayers at low ionic strength to a monolayer at NaCl activity approaching that of seawater. A triple layer surface complexation model fits the data well, where quartz and kaolinite contributed sites for three types of quinoline (Q) complexes: 1) innersphere ≡SiOHQ; 2) outersphere ≡SiO-QH+ and 3) innersphere ≡AlOHQ2. Aluminol kaolinite sites promote multilayer quinoline adsorption, whereas only monolayers form on silanol sites. Site density calculations and molecular dynamics (MD) confirmed that quinoline adsorbs upright, on edge, and multilayer adsorption follows formation of the initial monolayer. Our results confirm the effectiveness of sand(stones) and clays for removing NHCs from waste and groundwaters.

Graphene oxide (GO) is an interesting material that has the potential for a wide range of applications. Critical for these applications are the type of oxygen bond and its spatial distribution on the individual GO sheets. This distribution is not yet well understood. Few techniques offer a resolution high enough to unambiguously identify oxygen configuration. We used a new, label free spectroscopic technique to map oxygen bonding on GO, with spatial resolution of nanometres and high chemical specificity. AFM-IR, atomic force microscopy coupled with infrared spectroscopy, overcomes conventional IR diffraction limits, producing IR spectra from specific points as well as chemical maps that are coupled to topography. We have directly observed oxygen bonding preferentially on areas where graphene is folded, in discrete domains and on edges of GO. From these observations, we propose an updated structural model for GO, with C O on its edge and plane, which confirms parts of earlier proposed models. The results have interesting implications. Determining atomic position and configuration from precise imaging offers the possibility to link nanoscale structure and composition with material function, paving the way for targeted tethering of ions, polymers and biomaterials.

Phenol-urea-formaldehyde (PUF) resin is one of the most important thermosetting polymers. It is widely used in many industrial and construction applications as an organic coating and adhesive. For example, in production of mineral wool for insulation, PUF is used together with the coupling agent (3-aminopropylsilane, APS) and serves as a binder for attaching mineral fibers to each other and to create the necessary mechanical integrity and shape of the final product. However, during ageing under high humidity (95%) and temperature (70 °C), hydrolysis can degrade PUF, decreasing product quality. A better understanding of the chemical processes caused by hydrolysis would promote development of more stable PUF binders. We investigated the composition and stability changes during ageing of cured PUF powder binder and mineral wool fibers where PUF binds the fibers together. We aged the samples in hot water (80 °C) or in a controlled climate chamber (70 °C; 91% RH) and analyzed them using X-ray photoelectron spectroscopy (XPS), element analysis and thermogravimetric (TG) analysis. We investigated the composition of species released from PUF during hydrolysis by electrospray ionization (ESI) of the aqueous solutions. The results show that the extent of PUF curing and the presence of APS as the coupling agent have an important impact on its stability. XPS revealed that poorly cured PUF contains a high fraction of –NH–CH2–O–CH2–NH– bonds which are easily hydrolyzed, while longer curing results mostly in more stable methylene bridges, –NH–CH2–NH–. We also observed evidence for urea –NH–CO– bond decomposition by ESI analysis. Mineral wool fiber ageing studies showed that PUF rearranges on the fiber surface and detaches from it, together with the APS coupling agent. This improved understanding of the effects of ageing provides clues for designing a more robust binder, leading to increased quality and stability of mineral wool insulation.