Adsorption Conformation Research Articles

Plasmon-driven oxidative coupling of aniline-derivative adsorbates: A comparative study of para-ethynylaniline and para-mercaptoaniline.

Plasmon-driven photocatalysis has emerged as a paradigm-shifting approach, based on which the energy of photons can be judiciously harnessed to trigger interfacial molecular transformations on metallic nanostructure surfaces in a regioselective manner with nanoscale precision. Over the past decade, the formation of aromatic azo compounds through plasmon-driven oxidative coupling of thiolated aniline-derivative adsorbates has become a testbed for developing detailed mechanistic understanding of plasmon-mediated photochemistry. Such photocatalytic bimolecular coupling reactions may occur not only between thiolated aniline-derivative adsorbates but also between their nonthiolated analogs. How the nonthiolated adsorbates behave differently from their thiolated counterparts during the plasmon-driven coupling reactions, however, remains largely unexplored. Here, we systematically compare an alkynylated aniline-derivative, para-ethynylaniline, to its thiolated counterpart, para-mercaptoaniline, in terms of their adsorption conformations, structural flexibility, photochemical reactivity, and transforming kinetics on Ag nanophotocatalyst surfaces. We employ surface-enhanced Raman scattering as an in situ spectroscopic tool to track the detailed structural evolution of the transforming molecular adsorbates in real time during the plasmon-driven coupling reactions. Rigorous analysis of the spectroscopic results, further aided by density functional theory calculations, lays an insightful knowledge foundation that enables us to elucidate how the alteration of the chemical nature of metal-adsorbate interactions profoundly influences the transforming behaviors of the molecular adsorbates during plasmon-driven photocatalytic reactions.

Experiment and molecular dynamics simulation of functionalized cellulose nanocrystals as reinforcement in cement composites

This study evaluated the potential effect of cellulose nanocrystal and coated polyethylene fiber on the mechanical properties of mortar. Two kinds of cellulose nanocrystals (CNC) directly as Nano-materials, and indirectly as film coated onto the polypropylene fibers were employed as cement-based reinforcement materials. The fluidity, flexural and compressive strength, and the microstructure of each specimen were measured. In the direct method, mortar mixed with the CNC containing carboxyl groups (CNC-C) showed superior properties compared to the CNC containing sulfo groups (CNC-S). The addition of CNC impacted the process of hydration and compactness of hydration products. The results of X-Ray polycrystalline diffractometer (XRD) and heat of hydration showed that CNC accelerated hydration process. Energy spectrum analysis (EDS) measured ratio of calcium to silicon (C/S) of calcium silicate hydrate (C-S-H) and proved that CNC-C increased the tightness of C-S-H while CNC-S decreased. The results of scanning electron microscopy (SEM) indicated that cellulose nanocrystals were interspersed in C-S-H, forming Nano-bridge and arresting Nano-crack. In the indirect method, the maximum increase in flexural strength of sample between all groups was the specimen that adding 0.3% (volume ratio of fiber to mortar) of CNC-C coated polypropylene fibers. The flexural and compressive strength of the mortar were increased by 22.81% and 10.65% compared to the control, respectively. The results of SEM indicated that coating enhanced bond of the fibers/matrix. Molecular dynamics simulation (MD) analyzed the binding energy, microstructure, dynamic characteristics and adsorption conformation between two CNCs and C-S-H at the molecular scale. MD presented clearly that the adsorption energy between CNC-S and C-S-H was much smaller than CNC-C and C-S-H. This was identical with CNC-C enhancing the mechanical properties of the mortar and CNC-S reducing the mechanical properties.

Orientation and Conformation of Hydrophobin at the Oil–Water Interface: Insights from Molecular Dynamics Simulations

Hydrophobins, a new class of potential protein emulsifiers, have been extensively employed in the food, pharmaceutical, and chemical industries. However, the knowledge of the underlying molecular mechanism of protein adsorption at the oil-water interface remains elusive. In this study, all-atom molecular dynamics simulations were performed to probe the adsorption orientation and conformation change of class II hydrophobin HFBI at the cyclohexane-water interface. It was proposed that a hydrophobic dipole of the protein could be used to quantitatively predict the orientation of the adsorbed HFBI. Simulation results revealed that HFBI adsorbed at the interface with the patch-up orientation toward the oil phase, regardless of its initial orientations. HFBI's secondary structure was maintained to be intact in the course of simulations despite relatively significant variations in the tertiary structure observed, which could well preserve the bioactivity of HFBI. From the energy analysis, the driving force for interface adsorption was primarily determined by van der Waals interactions between HFBI and cyclohexane. Further analysis indicated that the adsorption orientation and conformation of HFBI at the oil-water interface were typically regulated by the hydrophobic patch and some key residues. This study provides some insights into the orientation, conformation, and adsorption mechanism of proteins at the oil-water interface and theoretical guidelines for the design and development of novel biological emulsifiers involved in the food, pharmaceutical, and chemical industries.

Adsorption behavior of sodium oleate on iron minerals and its effect on flotation kinetics

This work systematically studied the adsorption behavior of sodium oleate (NaOL) on hematite, limonite, and siderite and their corresponding flotation performance at alkaline pH. The adsorption behavior and conformation of NaOL on mineral surfaces were investigated using zeta potential analysis, Fourier-transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy spectra (XPS), and atomic force microscopy (AFM) imaging characterization. The effect of NaOL adsorption on the surface wettability and bubble-particle attachment was further analyzed by contact angle measurement, attachment time tests, and wrap angle tests. Finally, batch flotation tests and kinetic analysis were carried out to evaluate three mineral flotation behaviors. The results revealed that NaOL could chemically adsorb on hematite, limonite, and siderite and caused the significant negative mobility in their zeta potentials. It was found that Fe atoms exposed on their surface were the main active centers for the chemisorption of NaOL. Hematite and limonite had more active sites for NaOL adsorption than siderite, and Fe(III) on hematite and limonite surface could interact more strongly with NaOL than Fe(II) on siderite, which resulted in the higher adsorption density and intensity of NaOL on hematite and limonite than that on siderite. This further contributed to the stronger hydrophobicity on their surface than that on siderite surface. The enhancement of hydrophobicity could increase the attachment efficiency of bubble-particle (Ea). Therefore, hematite and limonite particles had more and faster attachment with bubbles than siderite particles. As such, much higher cumulative ultimate recoveries (R∞) and flotation rate constants (k) of hematite and limonite than those of siderite were obtained.

Molecular modeling of chemical admixtures; opportunities and challenges

Chemical admixtures are an essential ingredient of modern concrete mix, but many of their molecular scale working mechanisms remain poorly described. In this respect, recent advances in computational methods, provide a unique opportunity to gain the needed molecular level insights into the mechanism of action of chemical admixtures in cementitious systems. Such studies are slowly increasing in number and this paper proposes a review on approaches that deal with molecular simulations of chemical admixtures. The key properties studied so far are mainly adsorption behaviors and conformations of monomers, oligomers and polymers (molecular weight ~ 10,000 g/mol). Our aim is to identify opportunities, challenges and give perspectives on the future of molecular modeling of chemical admixture-cement interactions.

Physicochemical properties and slurry ability changes of lignite after microwave upgrade with the assist of lignite semi-coke

Microwave pyrolysis is a promising technique for the clean and effective utilization of low-rank coal, which has aroused widespread concern during the past decades. This paper applied microwave energy with the assist of 10 wt% lignite semi-coke (LSC) to upgrade lignite and prepared the solid residue into lignite water slurry (LWS). The physicochemical property and slurry ability changes of upgraded lignite were analyzed. The micro-mechanisms on interactions between dispersant molecules and upgraded lignite particles were investigated through Molecular Dynamics (MD) simulations. It turns out that LSC could effectively prompt the rapid heating of lignite in the microwave field. And after microwave upgrade the coal quality of lignite was improved, the oxygen-containing functional groups was removed remarkably. The adsorption conformation of dispersant on the lignite-water interface exhibited a double adsorption, while that on upgraded lignite-water interface gradually showed single-layer and multi-point adsorptions. Besides, the physicochemical property changes varied most when lignite was upgraded under 800 W, which leads to the maximum solid concentration of LWS improved most, from 51.84 wt% to 61.45 wt%. It further increased to 62.43 wt% as the LWS was directly prepared from the solid residues after microwave irradiation. Morever, the pseudoplasticity of LWS became weaker, but the static stability became better. Therefore, LSC, a self-product of lignite, exerted an enormous function on improving the slurry ability of lignite.

Adsorption of hyaluronan saccharides on the surface of a single walled carbon nanotube. A computational study

Adsorption of β-d-glucopyranuronic acid (GlcA), N-acetyl-β-d-glucosamine (GlcNAc), two disaccharides composed of GlcA and GlcNAc and hyaluronic acid (HA) on single walled carbon nanotube (CNT) was studied using molecular dynamics simulations based on the GLYCAM-06j force field and quantum chemical approach based on DFT method and ωB97X-D functional. It was found that both monosaccharides adsorb on the (17,0) single walled carbon nanotube with adsorption energy strongly dependent on the number of molecules. Single molecule adsorption was stable only for GlcNAc molecule while the GlcA molecule revealed energetically quite complex picture involving the assumption of energy barrier for desorption. Hetero-disaccharides composed of GlcNAc and GlcA revealed stable surface layers. Most uniform surface layer with highly specific orientation towards surface was found for GlcNAc. Adsorption of monosaccharides weakly affects their conformation: disaccharides display only moderate reduction in the flexibility of glycosidic linkages but oligosaccharides can be more significantly deformed, exhibiting conformationally-locked kinks along the chain that impose tighter CNT-HA contact. Results from quantum chemical studies concerning conformation and energetics of monosaccharides adsorption on the same CNT type are consistent with molecular dynamics studies based on the GLYCAM-06j force field at the limit of absolute zero temperature.

Real-time changes of the adsorption process and conformation of marine dissolved organic matters on the solid-liquid interface

In this study, the adsorption characteristics of marine dissolved organic matters (MDOMs) on the solid-liquid interface in the coastal waters was investigated. The results showed that the organic macromolecules with adsorption ability in MDOMs are not rigid molecules. However, the macromolecules have viscoelasticity properties. At different dilution ratios, the MDOMs adsorption process includes rapid (0–200 s) and slow adsorption (200 s later) periods. MDOMs adsorption in the solid-liquid interface is a dynamic process in which adsorption and hydration occur simultaneously. MDOMs concentration is an important driving force for adsorption. The three macromolecules of acid polysaccharides, protein-like, and polycarboxylate-type humic acids in MDOMs are rich in functional groups and they have the ability to absorb to solid surface. Acidic polysaccharides exhibit a sustained adsorption ability, while the adsorption of other macromolecules occurred only in the initial rapid adsorption period. In addition, the acid polysaccharides show weak thixotropy during the adsorption process. It would cause the stretching of macromolecular structure of the adsorption layer, enhancing the hydration of the adsorption layer. The study shows the adsorption process of MDOMs at the solid-liquid interface and the structural characteristics of the adsorption layer. It can provide helpful information for the inhibition and removal of MDOMs pollution during the actual development of marine resources.

Steering Metal-Organic Network Structures through Conformations and Configurations on Surfaces.

Molecular adsorption conformations and arrangement configurations on surfaces are important structural aspects of surface stereochemistry, but their roles in steering the structures of metal-organic networks (MONs) remain vague and unexplored. In this study, we constructed MONs by the coordination self-assembly of isocyanides on Cu(111) and Ag(111) surfaces and demonstrated that the MON structures can be steered by surface stereochemistry, including the adsorption conformations of the isocyanide molecules and the arrangement configurations of the coordination nodes and subunits. The coordination self-assembly of 1,4-phenylene diisocyanobenzene afforded a honeycomb MON consisting of 3-fold (isocyano)3-Cu motifs on a Cu(111) surface. In contrast, geometrically different chevron-shaped 1,3-phenylene diisocyanobenzene (m-DICB) failed to generate a MON, which is ascribable to its standing conformation on the Cu(111) surface. However, m-DICB was adsorbed in a flat conformation on a Ag(111) surface, which has a larger lattice constant than a Cu(111) surface, and smoothly underwent coordination self-assembly to form a MON consisting of (isocyano)3-Ag motifs. Interestingly, only C3-Ag nodes with heterotactic configurations could grow into larger subunits; those subunits with heterotactic configurations further grew into Sierpiński triangle fractals (up to fourth order), while subunits with homotactic configurations afforded a triangular MON.

Boosting the Rate Performance of Li–S Batteries via Highly Dispersed Cobalt Nanoparticles Embedded into Nitrogen-Doped Hierarchical Porous Carbon

Boosting the Rate Performance of Li–S Batteries via Highly Dispersed Cobalt Nanoparticles Embedded into Nitrogen-Doped Hierarchical Porous Carbon

SARS-CoV-2 Unrevealed: Ultrastructural and Nanomechanical Analysis.

The ongoing outbreak of the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) started in late 2019 and spread across the world, infecting millions of people, with over 3.3 million deaths worldwide. To fight back the virus, it is necessary to understand how the main structures work, especially those responsible for the virus infectivity pathogenicity. Here, using the most advanced atomic force microscopy techniques, SARS-CoV-2 viral particles were analyzed, with a special focus on their ultrastructure, adsorption conformation, and nanomechanical behavior. The results uncovered the aspects of the organization and the spatial distribution of the proteins on the surface of the viral particles. It also showed the compliant behavior of the membrane and ability to recover from mechanical injuries. At least three layers composing the membrane and their thickness were measured, protecting the virus from external stress. This study provides new insight into the ultrastructure of SARS-CoV-2 particles at the nanoscale, offering new prospects that could be employed for mapping viral surfaces. The understanding of the viruses’ capacity to survive mechanical disruptions at any level and their ability to recover from such injuries can shed a light on the structure–function relationship and help us to find targets for drug action, especially for this virus that, to this day, has no course of treatment approved.

Partial Order–Disorder Transformation of Interpenetrated Porous Coordination Polymers

Controlling interpenetration and flexibility behaviors is intriguing and fundamental for porous coordination polymers. We report exceptional interpenetration behaviors involving controllable partia...

DFT study of the fouling deposition process in the steam generator by simulating the adsorption of Fe2+ on Fe3O4 (0 0 1)

In order to reveal the fouling problem on the outer surface of the steam generator (SG) tube in the secondary circuit condition of pressurized water reactor (PWR) nuclear power plant, based on the density functional theory (DFT) method, the Cambridge sequential total energy program package (CASTEP) is used to simulate seven kinds of highly symmetric adsorption structure models of termination with tetrahedral Fe (A termination) and termination with octahedral Fe (B termination) on Fe3O4 (0 0 1) surface. The adsorption energies and stable adsorption conformations are calculated. The results show that the most stable adsorption structures of the Fe2+/Fe3O4 (0 0 1) configurations are Fe2+ above Fe-O bond of B layer termination (Fe3O4(001) A-b). During the adsorption, the Fe-Fe, Fe-O bond length, and Fe-Fe-O bond angle of (0 0 1) surface change, and the atomic positions parallel and perpendicular to (0 0 1) surface change correspondingly. The change happened to the surface layer is the most drastic one. The calculation of charge population, the density of states (DOS), and electron local function of Fe2+/Fe3O4 (0 0 1) optimal adsorption configuration show that there is electron transfer between Fe2+ and Fe3O4 (0 0 1), and the adsorption type is chemisorption. Among them, Fe (Fe2+)-Fe (Fe3O4) forms a metal bond, and Fe (Fe2+)-O (Fe3O4) forms the ionic bond. The results illustrate the interaction between free Fe2+ and Fe3O4 is the reason of the nucleation and agglomeration of Fe3O4 scale and it provides the foundation for the further research on Fe3O4 scale deposition.

Comparison of Adsorption Conformation of Comb‐Shaped Polycarboxylate on Tricalcium Aluminate (100) and Ettringite (100) Surfaces: A Molecular Dynamics Study

AbstractThe adsorption conformations of three comb‐shaped polycarboxylate (PCE) with different numbers of grafted side‐chains on the tricalcium aluminate (C3A) and ettringite surface is studied by all‐atom molecular dynamics (MD) simulations with INTERFACE‐PCFF forcefield. The similarity of absorbed PCEs on both surfaces is backbones of PCEs absorbed on the surface and the side‐chains extended to liquid phase. The difference is that side‐chains of PCEs keep a tilt angle with the C3A crystal but maintain parallel and closer to ettringite crystals. The absolute value of adsorption energy of PCEs on C3A surface is greater than that on ettringite surface, which indicate the stronger interaction between PCEs and C3A than ettringite. PCE with less side chains is favorable for the adsorption due to stronger electrostatic interaction with surface. Adsorption capacity and water‐reducing ability of PCEs are contradictory. Density of water near the solid–liquid interface is more severely decreased by PCE with more side chains. Correlation of the adsorption conformation of PCEs with the flow behaviors of fresh cement paste is summarized.

A periodic density functional theory study on methanol adsorption in HSAPO-34 zeolites

Methanol-to-olefins is a successful alternative route to produce the low-carbon olefins. The methanol adsorption in HSAPO-34 was investigated by the periodic density functional theory method. Several possible adsorption conformations were obtained, as well as the spatial orientation and the free energy. Methanol could be adsorbed on the Brönsted acid (BA) site in either the hydrogen bonding or in the protonation. The adsorption configurations coexist, slightly varying with the channel. When two CH3OH molecules were considered, they were likely located at both ends of the eight-ring window via the strong and the weak hydrogen bonding.

Nano-size dependence in the adsorption by the SARS-CoV-2 spike protein over gold colloid

Gold nano-particles were coated with the spike protein (S protein) of SARS-CoV-2 and exposed to increasingly acidic conditions. Their responses were investigated by monitoring the surface plasmon resonance (SPR) band shift. As the external pH was gradually changed from neutral pH to pH ∼2 the peak of the SPR band showed a significant red-shift, with a sigmoidal feature implying the formation of the gold-protein aggregates. The coating of S protein changed the surface property of the gold enough to extract the coverage fraction of protein over nano particles, Θ, which did not exhibit clear nano-size dependence. The geometrical simulation to explain Θ showed the average axial length to be a = 7. 25 nm and b =8.00 nm when the S-protein was hypothesized as a prolate shape with spiking-out orientation. As the pH value externally hopped between pH∼3 and pH∼10, a behavior of reversible protein folding was observed for particles with diameters >30 nm. It was concluded that S protein adsorption conformation was impacted by the size (diameter, d) of a core nano-gold, where head-to-head dimerized S protein was estimated for d ≤ 80 nm and a parallel in opposite directions formation for d = 100 nm.

Ultrasmall and Stable Pd and Pt Nanoparticles Within Zeolite HY Through Impregnated Method with Enhanced Semihydrogenation Selectivity

In this study, with zeolite HY as support, ultrasmall Pd and Pt nanoparticles were successfully immobilized into zeolite HY crystals through an optimized impregnation approach. The success of this new approach mainly relied on the selecting appropriate metal precursor to make Pd and Pt element exists with the cation forms, which can facilitate their diffusion into inner channels of zeolite HY through electrostatic attraction and capillary force. Integration of confinement effect of zeolite HY, taking zeolite HY (Si/Al = 3) encapsulation of ultrasmall Pd NPs (Pd@HY-3) as an instance, Pd@HY-3 catalyst exhibited enhanced catalytic selectivity in semihydrogenation of alkynes, in comparison with Pd/HY, Pd/C, Pd/Al2O3 and lindlar catalysts. This improved catalytic selectivity can be attributed to the constrained upright adsorption conformation of reactant alkyne and corresponding product alkene on encapsulated Pd surface to make alkyne adsorption on Pd surface with larger adsorption energy than that of alkene, thus achieving the high catalytic selectivity.

Synthesis optimization of metal-organic frameworks MIL-125 and its adsorption separation on C8 aromatics measured by pulse test and simulation calculation

The metal-organic frameworks (MIL-125) were synthesized by the solvothermal method and the experimental parameters of preparation, purification and activation were optimized and the physicochemical properties were characterized. The adsorption capacity of MIL-125 on C8 aromatics was tested by the intelligent gravimetric analyzer (IGA) and the toluene vapor static adsorption device. The adsorption selectivity was studied by liquid static adsorption equilibrium experiment and large-scale pulse test. The C8 aromatics adsorption conformation and adsorption heat in MIL-125 was simulated by Materials Studio software. The characterization results show that the synthesized sample has excellent crystallinity, regular morphology with a grain size of about 1 ​μm, surface area of 1315 ​m2/g, micropore volume of 0.601 ​mL/g and a bulk density of 0.45 ​g/mL. Moreover, the vapor static adsorption results show that the synthesized sample has almost three times of adsorption capacity as large as BaX zeolite and the liquid dynamic adsorption results indicate the synthesized sample is preferentially selective to pare-xylene with the alkane desorbent. The simulation results show that the adsorption heat of pare-xylene in the synthesized sample and the binding energy of pare-xylene in the tetrahedral cage are the largest among these four isomers.

Chiral Adsorption Conformations of Long-Chain n-Alkanes Induced by Lattice Mismatch

The adsorption and self-assembly of n-alkanes on graphite not only find value in applications related to lubrication and surface passivation but are also of fundamental importance in the study of molecule/substrate interactions. Their adsorption is classically described by Groszek’s model of commensurate registry, which is confirmed by high-resolution scanning tunneling microscopy studies. Nonetheless, the role of the chain length-dependent lattice mismatch between n-alkanes and graphite has not been considered. Here, a systematic study of various length n-alkanes at the liquid/graphite interface reveals the existence of a stability limit for the classical straight chain conformation postulated by Groszek’s model. Once the critical length is reached, the increasing lattice mismatch induces a swerved chain conformation that is chiral. Experimentally, as well as computationally, the crossover from a straight to a swerved chain conformation is determined to be between 40 and 50 carbon atoms.

Chemically modified guar gum and ethyl acrylate composite as a new corrosion inhibitor for reduction in hydrogen evolution and tubular steel corrosion protection in acidic environment

The paper deals with the synthesis of Guar gum and ethyl acrylate (GG-EEA) composite. The synthesized natural polysaccharide composite was used as a corrosion inhibitor to reduce hydrogen evolution and P110 steel corrosion protection in 15% HCl (Hydrochloric acid). The primary corrosion techniques like weight loss, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP) was used to analyze the corrosion inhibition process. The PDP proposed that GG-EEA composite is a mixed-type corrosion inhibitor and inhibits corrosion by blocking the active sites presenting over the metal surface. The corrosion inhibition performance of GG alone is 77.5%, and that of GG-EEA is 92.3% at 500 mg/L. The adsorption of GG-EEA onto P110 steel is spontaneous and mixed type, i.e., both physical and chemical. The conformation of GG-EEA molecule adsorption was done using a scanning electron microscope (SEM), Energy dispersive x-ray spectroscopy (EDX), Atomic force microscopy (AFM), and X-ray photoelectron spectroscopy studies. Density functional theory (DFT) analysis was done to explore the active sites over the inhibitor in metal-inhibitor interaction. Molecular dynamic simulation (MD) simulations study reveals that GG-EEA has more adsorption capacity than GG alone.