Steric Forces Research Articles

Study of the Electronic Properties of a Fluoropyrazolecarbonitrile Derivative and Enhancement of Spectral Properties on Adsorption with Fullerene

The molecule 5-amino-1-(2,6-dichloro-4-(trifluoromethyl)phenyl)-1H-pyrazole-3-carbonitrile is a pyrazole derivative with five different functional points. The main aim of this manuscript is to identify whether the compound interacts with fullerene molecules. The molecule's structure was simulated DFT- B3LYP/6-311+G (2d, p). The electronic spectra were generated using RCAM-B3LYP functional and the same basis sets with different solvents. Physical and chemical properties like active sites, biological activities, stabilities, solvation energy, electrons' occupancies in bonding orbitals, weak and strong hydrogen bonds, the steric force of interactions, delocalization of electrons, and reactive sites identification are reported. PASS and subsequent docking studies indicate the antiarthritic property. This molecule has good absorption energy (ΔH) -71.84 kcal/mol with a fullerene complex. Also, we found an enhancement of Raman activity of the compound when adsorbed with fullerene.

Effects of inorganic cations on the steric force between polyacrylamide layer physically adsorbed on SiO2 wafer and poly (ethylene oxide) layer

The physical adsorption of polyacrylamide on the SiO2 wafer in high salty solutions was investigated by an improved AFM steric force measurement. The colloid probe was modified by poly (ethylene oxide) layer and used to determine the steric force between adsorbed polyacrylamide and poly (ethylene oxide) layer in NaCl, KCl, MgCl2 and CaCl2 solutions. Assuming the adsorbed polyacrylamide complies with the self-similar model, the surface excesses, the thicknesses of the proximal regions, and "free energies of sticking" were estimated. Take the case of 5000 mg/L NaCl for example. The concentration profile was deduced from the corresponding steric force profile. The polyacrylamide concentration next to the SiO2 wafer was estimated to be about 147 g/L and the average concentration in the proximal region was estimated to be about 100 g/L. Based on the above estimations, interaction strength between the adsorbed cations and polyacrylamide was established, Mg2+ > Ca2+ > K+ > Na+. Moreover, the conformations of the adsorbed polyacrylamide were changed from "lying flat" to folded ones by the stronger interactions between the adsorbed cations and polyacrylamide.”

Effects of soil colloids on the aggregation and degradation of engineered nanoparticles (Ti3C2Tx MXene)

Soil colloid is a nonnegligible factor when evaluating the environmental risk of engineered nanoparticles (ENPs) in the groundwater. In this study, the environmental fate of an emerging ENP (Ti3C2Tx MXene) in the groundwater was investigated for the first time, which currently poses a severe environmental risk due to its cytotoxicity but has received little attention. The colloidal dispersion stability and degradation kinetics of Ti3C2Tx MXene in the groundwater were evaluated by considering the effects of soil colloids prepared from sodium humate (SH), montmorillonite (MT), and a natural soil (NS) under variable solution chemistry. The results showed that the affinity of soil colloids with Ti3C2Tx followed an SH > MT > NS sequence. Increasing SH concentration led to Ti3C2Tx disaggregation by enhancing the electrical and steric repulsive forces, while MT and NS resulted in hetero-aggregation because of the elevated collision frequency. SH and MT enhanced the critical coagulation concentrations of Ti3C2Tx by 100 and 10 folders, respectively, via surface coating process, while NS slightly reduced due to the bridging effects induced by the soluble cations. The soil colloids promoted Ti3C2Tx degradation compared with their absence and in an SH > MT ≫ NS sequence. SH and MT were through forming Ti–O–C and Si–O–Ti bonds with Ti3C2Tx via their carboxyl and hydroxyl groups, respectively, rendering the Ti3C2Tx surface more reactive and faster degradation. NS showed a weak promotion effect because of its less affinity with Ti3C2Tx and limited organic matter and clay contents with hydroxyl and carboxyl groups. This study demonstrated the unstable environmental behaviors of Ti3C2Tx in the groundwater and mitigated its environmental risk concerns.

Regulation of nano-biological interface adhesion through grafted polymers

<p indent="0mm">The employment of grafted polymers to modulate the adhesion behavior of nano-biological interfaces has a wide range of applications in the field of biomedicine, and related research has important theoretical significance, thus gaining continuous attention. In this paper, the physicochemical mechanisms involved in the regulation of the adhesion behaviors of the nano-biological interface by grafted polymers are reviewed. There are two key challenges in the field of nanomedicine: Suppressing of immune responses and enhancing the drug retention at disease sites. In the both aspects, grafted polymers play an increasingly important role. By grafting polymers on the surface of nano-drugs, the random adhesion of small biomolecules can be suppressed, thereby decreasing the thickness of protein coronas, reducing the immune response, and prolonging the <italic>in vivo</italic> circulation time. Reduced adhesion also alleviates the dissipation of nano-drugs. In addition, grafted polymers can alter the surface mechanical property, endowing a moderate stiffness and altering collision behaviors, thus enhancing the transport efficiency and nano-drugs in physiological tissues and nano-drug retention at disease sites. The involved mechanisms in this paper are divided into two categories: Interfacial physics and interfacial chemistry. The former group mainly focuses on the microstructure and morphology, which can be adjusted through grafting density, grafting length, chain topology, etc. This paper focuses on two physical mechanisms closely related to the high entropy properties of grafted polymers: Entropic steric hindrance and chain segment dynamics. With increasing grafting density, the repulsive interactions between grafted chains increase, and the chains are stretched further resulting in a thicker grafting layer. Meanwhile, the conformation of grafting polymers experiences a mushroom-to-brush transition. In addition to less free volume, a higher grafting density also enhances chain stiffness, making biomolecules encounter a higher steric repulsive force when colliding with grafting polymer chains and thus less biomolecule adhesion. A high mobility of segmental chains also suppresses adhesion. According to this mechanism, increasing grafting density decreases segmental chain dynamics and promotes adhesion. The two mechanisms compete with increasing grafting density. Entropic steric hindrance dominates in low grafting density regime, while chain segment dynamic plays a larger role in high grafting density regime. A moderate high grafting density has maximal inhibiting ability on adhesion. The regulation of biomolecule adhesion based on interfacial physics combines structural and dynamical factors, and is usually nonspecific, although specific regulation is also possible. This group of mechanisms is independent of specific chemical groups, thus having a certain degree of universality. The mechanisms based on interfacial chemistry depend on special chemical groups, especially the hydrophilicity of functional groups. Most grafted polymers having good anti-fouling properties are hydrophilic, for example, polyethylene glycol (PEG). Hydrophilic functional groups promote the formation of hydrated surface layers, which inhibit biomolecule adhesion. PEG is the most widely used by now. However, its stability and anti-fouling ability are limited. By finding and modifying with appropriate chemical groups on the grafted chains, a better stability and stronger inhabitation of biomolecule adhesion can be achieved. On the other hand, through adjusting the temperature, light or pH dependence of chemical groups, the bio-adhesion of the grafting polymer layer can be dynamically tuned, realizing intelligent response to external stimuli and thus smart coating surfaces. This paper is expected to provide a reference for future fundamental theoretical research and advanced material development in this field.

Nano-SiO2 transport and retention in saturated porous medium: Influence of pH, ionic strength, and natural organics

Nano silica (nSiO2), induces potential harmful effects on the living environment and human health. It is well established that SiO2 facilitates the co-transport of a variety of other contaminants, including heavy metals and pesticides. The current study focused on the systematic evaluation of the effects of multiple physicochemical parameters such as pH (5, 7, and 9), ionic strength (10, 50, and 100 mM), and humic acid (0.1, 1, and 10 mg/L) on the transport and retention of nSiO2 in saturated porous medium. Additionally, the influent concentration of nSiO2 (10, 50, and 100 mg/L) was also varied. Our experimental findings indicate that the size of nSiO2 aggregates was directly related to the pH, ionic strength, HA, and particle concentration had a significant impact on the breakthrough curves (BTCs). The stability provided by the varying concentrations of pH and humic acid had a significant effect on the size of nSiO2 aggregates and transport (C/C0 > 0.7). The presence of a greater magnitude of negative charge on the surface of both nSiO2 and quartz sand resulted in less aggregation and enhanced flow of nSiO2 through the sand column. The Electrostatic and steric repulsion forces were the primary governing mechanisms in relation to the size of nSiO2 aggregates, affecting the single-collector efficiency and attachment efficiency, which determined the maximal transport of nSiO2. Conversely, a probable increase in Van der Waals force of attraction exacerbated the particle deposition and reduced their mobility for high ionic strength, and particle concentrations (C/C0 < 0.1). The formation of large nSiO2 aggregates, in particular, was principally responsible for the enhancement of nSiO2 retention in sand columns over a broad range of IS and particle concentration. The interaction energy profiles based on the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory were determined to understand the mechanism of nSiO2 deposition. Aditionally, all the experimental BTCs were mathematically simulated and justified by the colloidal filtration theory (CFT). Considering the environmental ramifications, the transport behavior of nSiO2 was further evaluated in various natural matrices such as river, lake, ground, and tap water. The nSiO2 suspended in the river, lake, and tap water had significantly higher mobility (C/C0 > 0.7), whereas groundwater indicated higher retention (C/C0 < 0.3). The study advances our collective knowledge of physicochemical and environmental parameters that can affect particle mobility.

Stabilization activity of a new protein-carbohydrate complex in sesame paste: rheology, microstructure, and particle size analysis.

Sesame protein concentrate is a by-product of sesame processing with great nutritional and functional value. In the present study, sesame protein concentrate and a conjugated form of the protein with maltodextrin were applied to improve stability and texture of sesame paste. The rheological properties of samples were studied using dynamic measurement, controlled rate and controlled stress rheological analysis, and creep analysis to investigate the sesame paste structure and to illustrate the mechanism of their stability against oil separation. Samples containing the conjugate showed good stability, low average droplet size and uniform microstructure. Creep analyses showed as the conjugate was added to sesame paste, μ0 and μ1 values (corresponding dashpot viscosities) were higher than that of G0 and G1 (shear moduli of Maxwell and Kelvin-Voigt springs). Dynamic shear test exhibited increased storage modulus (G') and loss modulus (G″) by the increase in frequency and elastic structure of sesame paste converted to viscose behavior with the contribution of conjugate. Particle interaction in sesame protein concentrate (SPC)-maltodextrin conjugate (SMC), may be overcome by steric repulsion force. Furthermore, impression of a weak network structure can be observed. These phenomenon could resolve the phase separation problem of traditional sesame paste. © 2022 Society of Chemical Industry.

Phosphate and humic acid inhibit corrosion of green-synthesized nano-iron particles to remove Cr(VI) and facilitate their cotransport

Green tea synthesized nano-zero-valent iron (GT-nZVI), composed of a Fe0 core and tea polyphenols (TPs), has been attracting attention for effective removal of hexavalent chromium (Cr(VI)) from water and soils. However, the relevant environmental factors which may affect GT-nZVI removal of Cr(VI) are still unclear. Thus, it is necessary to investigate the interplay of naturally occurring phosphate and HA on the reactions and stability of GT-nZVI with Cr(VI) in water-saturated porous media to mimic soils and groundwater. The inherent mechanisms were revealed using multiple technologies, including TEM, SEM-EDS, FTIR, XPS, and a transport model. We found that the Cr(OH)3 and Cr2O3 were formed on GT-nZVI upon reacting with Cr(VI). When phosphate and HA were present, their adsorption inhibited the Fe0 core corrosion and the release of TPs from GT-nZVI at pH ≤ 6.0. Thus, the generation of soluble Cr(III) was reduced by 39.9% (6.7 mg∙g−1) and 70.6% (11.9 mg∙g−1) at pH 3.0, respectively. In particular, HA favors the formation of Cr2O3, and then facilitates the cotransport with GT-nZVI, forming Fe(III)–HA–Cr2O3 complex due to the steric repulsive forces of HA. In contrast, phosphate ion dereases Cr(VI) adsorption and subsequent generation of Cr2O3 on GT-nZVI and accordingly increased the Cr(VI) mobility through water-saturated porous media. To our knowledge, this is the first study unraveling the mechanisms regarding the impact of phosphate and HA on the change of physicochemical properties of GT-nZVI coupling with Cr(VI)/Cr(III) transformation. Our discovery informs a better strategy for in situ remediation of Cr(VI) by GT-nZVI where phosphate and HA commonly cooccur.

Aggregation kinetics of biochar nanoparticles in aqueous environment: Interplays of anion type and bovine serum albumin

The colloidal particles, especially those at the nanoscale, are the most active part of the pyrogenic carbon (biochar). Increasingly applied biochar has resulted in a large number of biochar nanoparticles (NPs) being released into the environment. The aggregation of biochar NPs affects their environmental behavior and fate. The complex effects of anion type (Cl−, SO42−) and protein (bovine serum albumin, BSA) on the aggregation of wheat straw biochar (WB) and pinewood biochar (PB) NPs in solutions were investigated by the time-resolved dynamic light scattering method. The critical coagulation concentration (CCC) of WB and PB NPs in Na2SO4 solution was higher than their CCCs in NaCl solution, which was consistent with the Hofmeister series that SO42−, a kosmotrope anion, increased the interaction between water molecules, thus enhancing the hydrophobic interactions between biochar NPs in solution and promoting their aggregation, while Cl−, a chaotropic agent, exhibited the opposite effect. When BSA was added into the solution, BSA was adsorbed on the surface of biochar NPs and BSA corona was formed, which inhibited the aggregation of biochar NPs by inducing steric force. The enhanced stability of biochar NPs by BSA was more significant in NaCl than in Na2SO4 solution because BSA corona had a more negatively charged surface and a more steric structure in NaCl solution, thus generating stronger electrical repulsion and steric hindrance. The classical DLVO theory and the XDLVO theory incorporating the steric repulsion (in the presence of BSA) were used to interpret the aggregation and dispersion of biochar NPs. Through this study, we found that anion type indirectly affected the aggregation of biochar NPs by influencing the interaction between water molecules, while the aggregation of BSA-biochar NPs conjugates is mainly influenced by the surface charge and structure of BSA corona.

A comparative study on aggregation and sedimentation of natural goethite and artificial Fe3O4 nanoparticles in synthetic and natural waters based on extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory and molecular dynamics simulations

Natural iron oxides nanomaterials have important roles in biogeochemical processes. In this study, the effects of pH, natural organic matter, and cations on aggregation and sedimentation of natural goethite and artificial Fe3O4 nanoparticles in water were investigated to learn more about the environmental behaviors of engineered and natural nanomaterials and how they differ. In addition, a novel extended DLVO theory that considered steric, gravitational, and magnetic attraction forces concurrently was specifically developed to provide mechanisms explanations. Specifically, Fe3O4 NPs were more likely than bulk goethite to aggregate (because of magnetic attraction interactions) at low HA concentrations and disperse at high HA concentrations. Besides, goethite was less prone to settle with the same concentration of NaCl than Fe3O4 NPs, but the opposite trend was found for the same concentration of CaCl2 because of the difference in maximum net energy (barrier) and strong Ca2+ bridging effectiveness of goethite in CaCl2 solution. Statistical models were established to evaluate colloidal stability of the particles. XPS and molecular dynamics simulation results suggested that ions were adsorbed onto particles via ionic polarization and that the binding free energies at high coverage followed the order Ca2+ > Na+ > Cl- and presence of cation bridging between particles.

Colloidal stability and aggregation kinetics of nanocrystal CdSe/ZnS quantum dots in aqueous systems: Effects of ionic strength, electrolyte type, and natural organic matter

Understanding the stability and aggregation of nanoparticles in aqueous milieu is critical for assessing their behavior in the natural and engineered environmental systems and establishing their threat to human and ecosystems health. In this study, the colloidal stability and aggregation kinetics of nanocrystal quantum dots (QDs) —CdSe/ZnS QDs—were thoroughly explored under a wide range of aqueous environmental conditions. The z-average hydrodynamic diameters (z-avg. HDs) and zeta potential (ξ potential) of CdSe/ZnS QDs were measured in monovalent electrolyte (NaCl) and divalent electrolyte (CaCl2) solutions in both the absence and presence of natural organic matter (NOM)—Suwannee River natural organic matter, SRNOM to assess the dynamic growth of these nanoaggregate-QD-complexes, and the evaluation of their colloidal stability. Results show that CaCl2 was more effective to destabilize the QDs compared to NaCl at similar concentrations. An increase in NaCl concentration from 0.01 to 3.5 M increased the z-avg. HD of QD aggregates from 61.4 nm to 107.2 nm. The aggregation rates of QDs increased from 0.007 to 0.042 nm·s−1 with an increase in ionic strength from 0.5 to 3.5 M NaCl solutions, respectively. In the presence of Na+ cations, the aggregation of QDs was limited as steric forces generated by the original surface coating of QDs prevailed. In the presence of CaCl2, the aggregation of QDs was observed at a low concentration of CaCl2 (0.0001 M) with a z-avg. HD of 74.2 nm that significantly increased when the CaCl2 was higher than 0.002 M. Larger sizes of QD aggregates were observed at each level of CaCl2 concentration in suspensions of 0.002–0.1 M, as the z-avg. HDs of QDs increased from 125.1 to 560.4 nm, respectively. In the case of CaCl2, an increase in aggregation rates occurred from 0.035 to 0.865 nm·s−1 with an increase in ionic strength from 0.0001 M to 0.004 M, respectively. With Ca2+ cations, the aggregation of QDs was enhanced due to the bridging effects from the formation of complexes between Ca2+ cations in solution and the carboxyl group located on the surface coating of QDs. In the presence of SRNOM, the aggregation of QDs was enhanced in both monovalent and divalent electrolyte solutions. The degree of aggregation formation between QDs through cation-NOM bridges was superior for Ca2+ cations compared to Na+ cations. The presence of SRNOM resulted in a small increase in the size of the QD aggregates for each of NaCl concentrations tested (i.e., 0.01 to 3.5 M, except 0.1 M), and induced a monodispersed and narrower size distribution of QDs suspended in the monovalent electrolyte NaCl concentrations. In the presence of SRNOM, the aggregation rates of QDs increased from 0.01 to 0.024 nm 1 with the increase of NaCl concentrations from 0.01 to 2 M, respectively. The presence of SRNOM in QDs suspended in divalent electrolyte CaCl2 solutions enhanced the aggregation of QDs, resulting in the increase of z-avg. HDs of QDs by approximately 19.3%, 42.1%, 13.8%, 1.5%, and 24.8%, at CaCl2 concentrations of 0.002, 0.003, 0.005, 0.01, and 0.1 M, respectively. In the case of CaCl2, an increase in aggregation rates occurred from 0.035 to 0.865 nm·s−1 with an increase in ionic strength from 0.0001 to 0.004 M, respectively. Our findings demonstrated the colloidal stability of QDs and cations-NOM-QD nanoparticle complexes under a broad spectrum of conditions encountered in the natural and engineered environment, indicating and the potential risks from these nanoparticles in terms of human and ecosystem health.

Study of the structural features and solvent effects using ab initio molecular dynamics and energy decomposition analysis of atogepant in water and ammonia

Atogepant is a new drug developed for treating migraine in adults, marking it active with a calcitonin gene-related peptide (CGRP) receptor antagonist, which can be used to prevent migraine. The main objective of this manuscript is to study the structure and interaction of atogepant with solvents like water and ammonia. We optimized the molecule using the DFT method and did the conformational analysis. A potential energy scan was conducted to ascertain the conformation preference of the compound and found that global minima are at the angles 60, 180, and 300 0 with respect to the C30-C38 bond. The electronic spectra were produced using RCAM-B3LYP functional and identical basis sets with different polar and nonpolar solvents. Methanol showed excellent solvation energy –33.5448 kcal/mol and more interactions in implicit studies. Qualitative studies indicated that the compound has more non-covalent interactions with water when compared to ammonia. Local energy decomposition analysis using DLPNO/CCSD(T) level revealed the exact type of interaction between the drug and water/ammonia. Later we studied the interaction between the molecule and explicit solvent molecules using ab initio molecular dynamics simulations and found that the drift velocity is more complex with water. Physico-chemical properties like reactive sites, bioactivities, stabilities, solvation energy, occupancies of electrons in atomic and bonding orbitals, different types of hydrogen bonds, the steric force of interactions, delocalization of electrons, and reactive sites of nucleophiles, and electrophiles are also reported.

Planar in Brooker's mode and twisted in Reichardt's mode: defying the steric forces in biphenyl types of zwitterionic systems through metameric resonance stabilizations.

To be planar or to be twisted at the bridge junctions in biphenyls or biaryl types of molecular systems depends on two conflicting forces: (1) steric repulsions (destabilizations) and (2) conjugation assisted electron delocalizations (resonance stabilizations). This work reports an unfamiliar kind of behaviour shown by metamers of a zwitterionic biphenyl type of system, where the Reichardt's metamer was found to be in an usual twisted conformation (delicate balance of conflicting forces), but the Brooker's metamer was found to be in a fully planar conformation. Interestingly, at the ωB97xD/aug-cc-pVDZ level, energetically (ΔE) the planar Brooker's metamer was found to be 16.7 kcal mol-1 lower (22.9 kcal mol-1 lower in the CASSCF method) in energy (more stable) than the isoelectronic twisted Reichardt's metamer, and also thermodynamic ΔG values were found to be close to ΔE values for various methods (for example, 15.6 kcal mol-1 in the above case using the ωB97xD method). When the steric repulsions are in their full potentials at the ring junction site, attainment of a conformational planarity by any biaryl type of system has not been reported previously. Without reducing the steric constraints or even without inducing any attractive forces, determining what other factors were responsible for defying the steric forces is the main focus of this investigation. Using the results of quantum mechanical computations of NBO, rotational barriers, and other saddle points (metastable conformations in singlet and triplet surfaces) in the potential energy surfaces, the dominant contribution of the resonance stabilized quinonoid form to the ground state was delineated as the possible reason for this unusual behaviour.

Mechanisms for efficient clay dispersing effect with tannins and sodium hydroxide

Substituting the industrial additives in building materials with natural ones can reduce the embodied carbon in the construction sector. In this paper, the dispersing effect of oak tannin as natural dispersant on clay materials is studied in combination with sodium hydroxide. Through rheological measurements, adsorption tests, and zeta potential measurements, the deflocculation mechanism of tannin under varied NaOH environments has been highlighted. The results show that the dispersing ability of tannin can be increased greatly with the incorporation of NaOH. By adding NaOH in the system, the kaolinite deflocculation mechanism of tannin is changed from steric hindrance to combined steric hindrance and electrostatic repulsion forces. This shift stems from two aspects: the transformation of the tannin chemical structure and the modification of kaolinite by NaOH. The results indicate that tannin coupled with NaOH can be a promising superplasticizer for earthen materials, with the potential of producing poured earth based on this combination. • Oak tannin is an efficient and natural dispersant for clay materials. • In combination with sodium hydroxide, the deflocculation action of tannin is amplified. • Oak tannin and NaOH disperse clay particles via combined steric repulsion forces and electrostatic repulsive forces. • Oak tannin coupled with NaOH is a promising superplasticizer for earthen materials and an environmentally friendly alternative to industrial product.

Role of sodium hexametaphosphate in ultra-fine grinding of alumina-doped titanium dioxide

In wet stirred milling of Al-doped TiO2, sodium hexametaphosphate (SHMP) is used as a small molecule dispersant to improve milling performance. In both acidic and basic conditions, SHMP interacts strongly with Al-doped TiO2 and remains stable during milling. Considering the apparent and true particle breakage performance, at pH 10.3, the optimal dosing concentration was 0.16 wt% (0.33θ, sub-monolayer coverage), which is consistent for both dilute (5 vol%) and concentrated (≥ 19.1 vol%) suspensions. At higher SHMP concentration (0.77θ), the increased solution conductivity compromised milling performance by weakly destabilizing the Al-doped TiO2 particles. At the optimal dose concentration of 0.33θ SHMP, particle dispersion is maintained through electrostatic and steric forces which contribute to moderating changes in suspension viscosity (~10% increase) as the particle size is reduced.

Accurate prediction of mutation-induced frequency shifts in chlorophyll proteins with a simple electrostatic model.

Photosynthetic pigment-protein complexes control local chlorophyll (Chl) transition frequencies through a variety of electrostatic and steric forces. Site-directed mutations can modify this local spectroscopic tuning, providing critical insight into native photosynthetic functions and offering the tantalizing prospect of creating rationally designed Chl proteins with customized optical properties. Unfortunately, at present, no proven methods exist for reliably predicting mutation-induced frequency shifts in advance, limiting the method's utility for quantitative applications. Here, we address this challenge by constructing a series of pointmutants in the water-soluble chlorophyll protein of Lepidium virginicum and using them to test the reliability of a simple computational protocol for mutation-induced site energy shifts. The protocol uses molecular dynamics to prepare mutant protein structures and the charge density coupling model of Adolphs et al. [Photosynth. Res. 95, 197-209 (2008)] for site energy prediction; a graphical interface that implements the protocol automatically is published online at http://nanohub.org/tools/pigmenthunter. With the exception of a single outlier (presumably due to unexpected structural changes), we find that the calculated frequency shifts match the experiment remarkably well, with an average error of 1.6nm over a 9nm spread in wavelengths. We anticipate that the accuracy of the method can be improved in the future with more advanced sampling of mutant protein structures.

One-Pot Synthesis of Al-P-O Catalysts and Their Catalytic Properties for O-Methylation of Catechol and Methanol.

A series of Al-P-O catalysts (Al-xP-O) were prepared using a P123-assisted one-pot method at different P/Al molar ratios and used for O-methylation of catechol and methanol. The influences of the P/Al molar ratio and P123 addition on catalyst structure and surface acid-base characteristics were investigated in detail. Increasing the P/Al molar ratio more favored crystalline aluminophosphate. The P123-assisted Al3+ and PO43− are known to be stabilized through weak steric force so that the formation of crystalline aluminophosphate could be inhibited at higher P/Al molar ratios. The results showed that the prepared Al-P-O catalysts possessed appropriate weak acid and weak base sites, which was beneficial to the reaction of catechol and methanol. The Al-1.1P-O catalyst synthesized with the assistance of P123 exhibited superior catalytic performances, with 52.5% catechol conversion and higher guaiacol selectivity of 97.6%.

Interparticle Forces of a Native and Encapsulated Metal-Organic Framework and Their Effects on Colloidal Dispersion.

The colloidal properties of suspended metal-organic frameworks (MOFs) are critical for device fabrication and application. Herein, van der Waals attractive, electric double layer repulsive, and steric repulsive forces of a native and encapsulated MOF are quantified for the first time. The van der Waals attractive forces were investigated by conducting environmental ellipsometric porosimetry (EEP) and spectroscopic ellipsometry (SE) on submicron, optical-quality nanoparticle films. The repulsive forces were determined from colloid and material characterization measurements. These data were used to predict suspension properties via extended Derjaguin, Landau, Verwey, and Overbeek theory. The state of dispersion was quantified for comparison with theoretical predictions for nine solvents. The MOF encapsulated with a surface-selective modification showed superior suspension in hydrophobic solvents. These findings should expedite the formulation of MOF colloidal suspensions for future works.

Hydration Forces Dominate Surface Charge Dependent Lipid Bilayer Interactions under Physiological Conditions.

Lipid bilayer interactions are essential to a vast range of biological functions, such as intracellular transport mechanisms. Surface charging mediated by concentration dependent ion adsorption and desorption on lipid headgroups alters electric double layers as well as van der Waals and steric hydration forces of interacting bilayers. Here, we directly measure bilayer interactions during charge modulation in a symmetrically polarized electrochemical three-mirror interferometer surface forces apparatus. We quantify polarization and concentration dependent hydration and electric double layer forces due to cation adsorption/desorption. Our results demonstrate that exponential hydration layer interactions effectively describe surface potential dependent surface forces due to cation adsorption at high salt concentrations. Hence, electric double layers of lipid bilayers are exclusively dominated by inner Helmholtz charge regulation under physiological conditions. These results are important for rationalizing bilayer behavior under physiological conditions, where charge and concentration modulation may act as biological triggers for function and signaling.

Atomic Force Microscopy Measurement in the Lignosulfonate/Inorganic Silica System: From Dispersion Mechanism Study to Product Design

Designing and preparing high-performance lignin-based dispersants are crucial steps in realizing the value-added utilization of lignin on an industrial scale. Such process depends heavily on an understanding of the dispersion mechanism of lignin-based dispersants. Here, atomic force microscopy (AFM) is employed to quantitatively investigate the dispersion mechanism of a lignosulfonate/silica (LS/SiO2) system under different pH conditions. The results show that the repulsive force between SiO2 particles in LS solution is stronger than it is in water, resulting in better dispersion stability. The Derjaguin–Landau–Verwey–Overbeek (DLVO) formula as well as the DLVO formula combined with steric repulsion is utilized for the fitting of the AFM force/distance (F/D) curves between the SiO2 probe and substrate in water and in LS solution. Based on these fitting results, electrostatic and steric repulsive forces are respectively calculated, yielding further evidence that LS provides strong steric repulsion between SiO2 particles. Further studies indicate that the adsorbance of LS on SiO2 (Q), the normalized interaction constant (A), and the characteristic length (L) are the three critical factors affecting steric repulsion in the LS/SiO2 system. Based on the above conclusions, a novel quaternized grafted-sulfonation lignin (QAGSL) dispersant is designed and prepared. The QAGSL dispersant exhibits good dispersing performance for SiO2 and real cement particles. This work provides a fundamental and quantitative understanding of the dispersion mechanism in the LS/inorganic particle system and provides important guidance for the development of high-performance lignin-based dispersants.

Comparison of acidic and basic ionic liquids effects on dispersion of alumina particles in Pebax composite membranes for CO2/N2 separation: Experimental study and molecular simulation

In this study, two types of acidic and basic ionic liquids (ILs) were used to modify the γ-Al2O3 particles. Different amounts of modified particles were added to the poly (ether-block-amide) (Pebax) polymeric matrix, and various composite membranes were prepared. FTIR (Fourier transform infrared), SEM (scanning electron microscopy), XRD (X-ray diffraction), DSC (differential scanning calorimetry), tensile and gas permeation analyses, as well as molecular simulations, were used to study the effect of ILs on the structure of membranes and their performances. The results indicated that ILs prevented well the sedimentation and agglomeration of particles through the electrostatic and steric forces. The electrostatic forces were more effective than steric forces. In addition to improving membrane separation performance and overcoming the trade-off limit, the modification of γ-Al2O3 particles has improved membranes mechanical strength. The comparison of ILs performances showed that the acidic IL had a better effect on the particle dispersion than the basic one. The CO2 permeability and CO2/N2 selectivity in the membrane containing 10 wt% acidic IL-modified particles increased about 47% and 124%, respectively, compared to the pure Pebax membrane. The molecular simulation confirmed the experimental results and showed that the employed ILs had different effects on the diffusivity and solubility coefficients of CO2 molecules in the membranes. Based on simulation results, the acidic IL improved the solubility coefficient by 95%, and the basic IL enhanced the diffusivity coefficient by 71%.