Non-electrostatic Interactions Research Articles

Understanding the Directed Evolution of a Natural-like Efficient Artificial Metalloenzyme.

The artificial metalloenzyme containing iridium in place of iron along with four directed evolution mutations C317G, T213G, L69V, and V254L in a natural cytochrome P450 presents an important milestone in merging the extraordinary efficiency of biocatalysts with the versatility of small molecule chemical catalysts in catalyzing a new-to-nature carbene insertion reaction. This is a show-stopper enzyme, as it exhibits a catalytic efficiency similar to that of natural enzymes. Despite this remarkable discovery, there is no mechanistic and structural understanding as to why it displays extraordinary efficiency after the incorporation of the four active site mutations by directed evolution methods, which so far has been intractable to any experimental methods. In this study, we have deciphered how directed evolution mutations gradually alter the protein conformational ensemble to populate a catalytically active conformation to boost a multistep catalysis in a natural-like artificial metalloenzyme using large-scale molecular dynamics simulations, rigorous quantum chemical (QM), and multiscale quantum chemical/molecular mechanics (QM/MM) calculations. It reveals how evolution precisely positions the cofactor-substrate in an unusual but effective orientation within a reshaped active site in the catalytically active conformation stabilized by C-H···π interactions from more ordered mutated L69V and V254L residues to achieve preferential transition state stabilization compared to the ground state. This work essentially tracks down in atomistic detail the shift in the conformational ensemble of the highly active conformation from the less efficient single mutant to the most efficient quadruple mutant and offers valuable insights for designing better enzymes. The active conformation correctly reproduces the experimental barrier height and also accounts for the catalytic effect, which is in good agreement with experimental observations. Moreover, this conformation features an unusual bonding interaction in a metal-carbene species that preferentially stabilizes the rate-determining formation of an iridium porphyrin carbene intermediate to render the observed high catalytic rate acceleration. Our study provides crucial insights into the underlying rationale for directed evolution, reports the major catalytic role of nonelectrostatic interactions in enzyme catalysis different from the electrostatic model, and suggests a crucial principle toward designing enzymes with natural efficiency.

Physics-Based Machine Learning Trains Hamiltonians and Decodes the Sequence-Conformation Relation in the Disordered Proteome.

Intrinsically disordered proteins and regions (IDPs) are involved in vital biological processes. To understand the IDP function, often controlled by conformation, we need to find the link between sequence and conformation. We decode this link by integrating theory, simulation, and machine learning (ML) where sequence-dependent electrostatics is modeled analytically while nonelectrostatic interaction is extracted from simulations for many sequences and subsequently trained using ML. The resulting Hamiltonian, combining physics-based electrostatics and machine-learned nonelectrostatics, accurately predicts sequence-specific global and local measures of conformations beyond the original observable used from the simulation. This is in contrast to traditional ML approaches that train and predict a specific observable, not a Hamiltonian. Our formalism reproduces experimental measurements, predicts multiple conformational features directly from sequence with high throughput that will give insights into IDP design and evolution, and illustrates the broad utility of using physics-based ML to train unknown parts of a Hamiltonian, rather than a specific observable, in combination with known physics.

Structure-selectivity relationship of anion exchange resins with different quaternary amine functional groups for highly selective removal of PFAS from chromium-plating wastewater

Anion exchange resin (AER) adsorption is an effective technology for the removal of per- and polyfluoroalkyl substances (PFAS) from wastewater. However, existing AERs with tributylamine functional groups have poor adsorption selectivity for perfluorinated carboxylic acids (PFCAs) and 6:2 fluorotelomer sulfonate (6:2 FTS), and the structure-selectivity relationship is still unclear. In this study, several novel gel AERs with long-chain amine groups were prepared. It was found that their adsorption selectivity for 6:2 FTS was 3.3–5.1 times that of commercial AERs, and the adsorption amount for 6:2 FTS in chromium-plating wastewater was 2.1 times that of the commercial PFA694E. On this basis, we synthesized 16 AERs with different quaternary amine functional groups, and explored the structure-selectivity relationship through the selectivity coefficients and adsorption energies of different AERs for seven typical PFAS. The order of adsorption selectivity of AERs with different quaternary amine groups for PFAS was AER-(12–1-1) > AER-(8–1-1) > AER-(4–4-4) > AER-(4–1-1) ≈ AER-(2–2-2) > AER-(1–1-1), where the three numbers are the carbon-chain lengths of the three alkyl groups attached to the nitrogen atom of the quaternary amine group. Density functional theory (DFT) calculations confirmed the enhanced adsorption selectivity and contribution of both non-electrostatic and electrostatic interactions by the long-chain amine groups, and a quantitative relationship between theoretical calculations and experimental results was established. These results could provide guidance for the development of efficient adsorbents for PFAS removal from wastewater.

Quinine-Based Polymers Are Versatile and Effective Vehicles for Intracellular pDNA, mRNA, and Cas9 Protein Delivery.

Quinine-based polymers have previously demonstrated promising performance in delivering pDNA in cells owing to their electrostatic as well as the nonelectrostatic interactions with pDNA. Herein, we evaluate whether quinine-based polymers are versatile for delivery of mRNA and Cas9-sgRNA complexes, especially in a serum-rich environment. Both mRNA and the Cas9-sgRNA complex are potent therapeutics that are structurally, chemically, and functionally very different from pDNA. By exploring a family of 7 quinine-based polymers that vary in monomer structure and polymer composition, we tested numerous formulations (42 with pDNA, 96 with mRNA, and 48 with Cas9-sgRNA) for payload-polymer complexation and delivery to compare payload-dependent structure-activity relationships. Several formulations demonstrated performance comparable to or better than the commercially available transfection agent jetPEI. The results of this study demonstrate the potential of quinine-based as a versatile carrier platform for delivering a wide range of nucleic acid therapeutics and serving the drug delivery needs in the field genetic medicine.

Activated carbons from Brazilian lignocellulosic residues from baru and jurubeba as adsorbents for removal of diethyl phthalate in aqueous phase

New insights were achieved for the removal of plasticizer in the aqueous phase, through adsorption by H3PO4 and H2SO4 activated carbons. The preparation was made from Brazilian lignocellulosic residues from of the baru shell (Dipteryx alata) and the jurubeba fruit (Solanum paniculatum). Such residues were characterized by biochemical, elemental, thermogravimetric, Fourier Transform Infrared analyses. Subsequently, the influence of the biomass/acidity ratio (1/2; 1/3) was analyzed by applying adsorption kinetics for a diethyl phthalate concentration of 0.2 g L‐1, isotherms, and modeling. Chemical activation was carried out at 80 ºC 30 min‐1, drying at 110 ºC 15 h‐1 and carbonization under N2 flow at 800 ºC 60 min‐1 at a heating rate of 20 ºC min‐1. Precursors and ACs were characterized by nitrogen isotherm at 77 K, TGA-DTG, FT-IR, pHPZC. The reaction mechanisms, applicability of ACs were analyzed. ACs' yields varied: 31.7–50.4% (baru); 30–41.7% (jurubeba). The ACs exhibited a range of textural properties from: specific surface area (SBET): 2–269 m² g‐1, micropore volume (W0): 0.10–0.56 cm3 g‐1, micropore width (L0): 9.3–17.6 Å. Results revealed high thermal resistance, amorphous structure, mesoporous surfaces for baru ACs, microporous surfaces for jurubeba ACs, both predominantly acidic: pHPZC 1.8–3.9. This acidity facilitated non-electrostatic interactions during the adsorption.

Critical adsorption and charge reversal in polyelectrolyte solutions: Analytical mean-field theory.

An analytical linearized mean-field theory is presented to describe the adsorption behavior of polyelectrolytes near charged colloidal surfaces with additional short-ranged non-electrostatic interactions. The coupling between the polyelectrolyte segment density and electrostatic potential is explicitly accounted for in a self-consistent manner. This coupling gives rise to highly non-linear behavior, such as oscillations of the electrostatic potential. We derive analytical expressions for the critical surface charge density σc, after which adsorption takes place, and recover the well-known σc∼ns3/2 scaling regime, where ns is the salt concentration. In addition, the theory yields a new ns1 scaling regime if the surface is hard and a unified ns1 scaling regime if the surface also possesses some short-ranged attraction with the polyelectrolyte. Furthermore, we derive an analytical expression to describe the critical polyelectrolyte concentration φc to achieve complete charge reversal, which is found to scale as φc ∼ σ2/(f2c2), where c is related to the magnitude of short-ranged interactions and f is the average charge per monomer of the polyelectrolyte. It is observed that within our theory, complete charge reversal can only take place if the short-ranged interactions are sufficiently strong to completely compensate for the entropy loss of adsorption.

MnO2 decoration onto the guava leaves: A sustainable and cost-effective material for methylene blue dye removal

Excessive number of dyes in water is becoming the main cause of water pollution, which is very important to remove because it is harmful. Dye contaminated water is being treated by various methods. Adsorption method can be considered best for the study of dye removal due to several technological reasons. The adsorption method has also been emphasized in this study. In the present work, a nano-bio-composite was fabricated by growing manganese oxide nanoparticles on abundant cellulosic guava leaf powder. This allows nanocomposite to be prepared in large quantities at nominal cost. The characterization technique confirmed the irregular growth of manganese oxide nanoparticles onto the guava leaf powder. The electrostatic and non-electrostatic interactions was confirmed in between manganese oxide nanoparticles and the carbon structure of guava leaf powder. The massive functional groups were found to be in the prepared nano-bio-composite. The grain size of prepared material was in nano range. The developed nano-bio-composite was used to remove methylene blue from water. This showed a very good adsorptive capacity for methylene blue. The analyzed adsorption data was modelled through isotherms, kinetics and thermodynamics models. The nature of the adsorption process was determined to be spontaneous and exothermic. The reusability test was carried out for five adsorption-desorption cycles. The reusability results suggested the better removal efficiency (%) in the first two cycles with only 20 % reduction in removal efficiency (%). The leaching test result revealed the good stability of MnO2/GL at neutral pH. It was a unique and cheap adsorbent of its kind, which had not been noticed anywhere before.

Highly adsorptive removal of ciprofloxacin and E. coli inactivation using amino acid tryptophan modified nano-gibbsite

Adsorption of essential amino acid, Tryptophan (Tryp) on synthesized gibbsite nanoparticles and their applications in eliminating of antibiotic ciprofloxacin (CFX) and bacteria Escherichia coli (E. coli) in aqueous solution. Nano-gibbsite which was successfully fabricated, was characterized by XRD, TEM-SAED, FT-IR, SEM-EDX and zeta potential measurements. The selected parameters for Tryp adsorption on nano-gibbsite to form biomaterial, Tryp/gibbsite were pH 11, gibbsite dosage 20 mg/mL and 1400 mg/L Tryp. The optimum conditions for CFX removal using Tryp/gibbsite were adsorption time 60 min, pH 5, and 20 mg/mL Tryp/gibbsite dosage. The CFX removal significantly raised from 63 to 90% when using Tryp/gibbsite. The Freundlich and pseudo-second-order models achieved the best fits for CFX adsorption isotherm and kinetic on Tryp/gibbsite, respectively. The amount of CFX increased with increasing ionic strength, suggesting that both electrostatic and non-electrostatic interactions were important. After four reused time, CFX removal was greater than 66%, demonstrating that Tryp/gibbsite is reusable with high performance in removing CFX. The application in bacterial activity in term of E. coli reached greater than 98% that was the best material for bacteria inactivation. The present study reveals that Tryp/gibbsite is an excellent bio-material for removing CFX and E. coli.

Effect of solvent depletion on electrokinetic energy conversion in viscoelastic fluids

We analyze the electrokinetic energy conversion from the pressure-driven flow of viscoelastic fluids akin to dilute polymer solutions. In contrast to the previously reported results, we account for the reduced differential capacitance over the interfacial layer and the solvent-mediated non-electrostatic interactions, cumulatively represented in an extended continuum framework. We attribute a physical basis of our consideration from the perspective of the formation of a polymer-depleted layer at the channel interface, where the explicit role of the solvent appears to dictate the electromechanics–hydrodynamics coupling over the interfacial scales. By adapting a “box-model” depicting the alterations in the solvent permittivity across the interfacial layer and accommodating a non-electrostatic interaction coefficient concomitantly, the interfacial electrokinetics are coupled with the bulk flow of the polymer-rich medium using the simplified Phan-Thien–Tanner (sPTT) constitutive model. A closed-form theory is obtained that includes only two fitting parameters, namely, the span of the interfacial layer and the strength of the non-electrostatic interactions. These parameters are estimated from comprehensive molecular simulation data. The results of the investigation are analytically tractable and enable rationalizing the “electrokinetic” implications of the polymer-depleted interfacial layer and the possibility that the electrokinetic parameters can be extracted from measurements obtained from experiments. This paves the way toward optimizing the induced streaming potential for the conversion of hydraulic energy to electrical power in polymeric solutions.

Algae polysaccharide-induced transport transformation of nanoplastics in seawater-saturated porous media

This study examined the distinct effects of algae polysaccharides (AP), namely sodium alginate (SA), fucoidan (FU), and laminarin (LA), on the aggregation of nanoplastics (NP) in seawater, as well as their subsequent transport in seawater-saturated sea sand. The pristine 50 nm NP tended to form large aggregates, with an average size of approximately 934.5 ± 11 nm. Recovery of NP from the effluent (Meff) was low, at only 18.2 %, and a ripening effect was observed in the breakthrough curve (BTC). Upon the addition of SA, which contains carboxyl groups, the zeta (ζ)-potential of the NP increased by 2.8 mV. This modest enhancement of electrostatic interaction with NP colloids led to a reduction in the aggregation size of NP to 598.0 ± 27 nm and effectively mitigated the ripening effect observed in the BTC. Furthermore, SA's adherence to the sand surface and the resulting increase in electrostatic repulsion, caused a rise in Meff to 27.5 %. In contrast, the introduction of FU, which contains sulfate ester groups, resulted in a surge in ζ-potential of the NP to -27.7 ± 0.76 mV. The intensified electrostatic repulsion between NP and between NP and sand greatly increased Meff to 45.6 %. Unlike the effects of SA and FU, the addition of LA, a neutral compound, caused a near disappearance of ζ-potential of NP (-3.25 ± 0.68 mV). This change enhanced the steric hindrance effect, resulting in complete stabilization of particles and a blocking effect in the BTC of NP. Quantum chemical simulations supported the significant changes in the electrostatic potential of NP colloids induced by SA, FU and LA. In summary, the presence of AP can induce variability in the mobility of NP in seawater-saturated porous media, depending on the nature of the weak, strong, or non-electrostatic interactions between colloids, which are influenced by the structure and functionalization of the polysaccharides themselves. These findings provide valuable insights into the complex and variable behavior of NP transport in the marine environment.

Time-Dependent Multilevel Density Functional Theory.

We present a novel three-layer approach based on multilevel density functional theory (MLDFT) and polarizable molecular mechanics to simulate the electronic excitations of chemical systems embedded in an external environment within the time-dependent DFT formalism. In our method, the electronic structure of a target system, the chromophore, is determined in the field of an embedded inactive layer, which is treated as frozen. Long-range interactions are described by employing the polarizable fluctuating charge (FQ) force field. The resulting MLDFT/FQ thus accurately describes both electrostatics (and polarization) and non-electrostatic target-environment interactions. The robustness and reliability of the approach are demonstrated by comparing our results with experimental data reported for various organic molecules in solution.

Do Electrostatics Control the Diffusive Dynamics of Solitary Water? NMR and MD Studies of Water Translation and Rotation in Dipolar and Ionic Solvents.

NMR-based measurements of the diffusion coefficients and rotation times of solitary water and benzene at 300 K are reported in a diverse collection of 13 conventional organic solvents and 10 imidazolium ionic liquids. Proton chemical shifts of water are found to be correlated to water OH-stretching frequencies, confirming the importance of electrostatic interactions in these shifts. However, the influence of magnetic interactions in aromatic solvents renders chemical shifts a less reliable indicator of electrostatics. Diffusion coefficients (DB) and rotational correlation times (τB) of benzene in the solvents examined are accurately described as functions of viscosity (η) by DB ∝ η-0.81 and τB ∝ η0.64. Literature values of DB and τB in alkane and normal alcohols, which were not included among the solvents studied here, are systematically faster than predicted by these correlations, indicating that factors beyond solvent viscosity play a role in determining the friction on benzene. In contrast to benzene, water diffusion and rotation are poorly described in terms of viscosity alone, even in the dipolar and ionic solvents measured here. The present data and the substantial literature data already available on dilute water diffusion show a systematic dependence of DW on solvent polarity among isoviscous solvents. The aspect of solvent polarity most relevant to water dynamics is the ability of a solvent to accept hydrogen bonds from water, as conveniently quantified by the frequency of water's OH stretching band, ΔνOH. The friction on translation, ζtr = kBT/DW, and rotation, ζrot = kBTτW, are both well correlated by functions of the form ζ(η, ΔνOH) = a1ηa2 exp (a3ΔνOH), where the ai are adjustable parameters. Molecular dynamics simulations reveal a strong coupling between electrostatic and nonelectrostatic water-solvent interactions, which makes it impossible to dissect the friction on water into additive dielectric and hydrodynamic components. Simulations also provide a tentative explanation for the unusual form of the correlating function ζ(η, ΔνOH), at least in the case of ζrot.

Adsorption equilibrium, kinetics and dynamic process of polyphenols from orange peel extract on mixed‐mode adsorption resin HD‐1

AbstractBACKGROUNDThe extraction and separation of natural polyphenols are attractive. Many researchers used high‐speed counter‐current chromatography to separate and purify polyphenols. However, it requires a long operating time, a large amount of organic solvent consumption, and high operating costs. In this work, the adsorption behaviors of polyphenols from orange peel extract on mixed‐mode resins were studied. The adsorption capacities and selectivities of different resins to the main polyphenols in the extract including gallic acid, p‐coumaric acid and ferulic acid were compared. The adsorption mechanism was analyzed by adsorption equilibrium and kinetics studies as well as molecular docking. The fixed‐bed adsorption was studied experimentally and theoretically.RESULTSHD‐1 resin has excellent adsorption selectivities among the resins. The yield of polyphenols from orange peel by integrated extraction‐adsorption increased by 82.94% compared with that of extraction without adsorption. The adsorption isotherms agreed with the Freundlich model. Dubinin–Radushkevich model results indicated that the adsorption of gallic acid mainly depends on nonelectrostatic interaction. The adsorption of the other two polyphenols involves electrostatic and nonelectrostatic interaction. The adsorption kinetics curves accorded with the pseudo‐second‐order model, and the adsorption rate of gallic acid was the highest among the polyphenols. Adsorption of polyphenols involves both physical and chemical adsorption. The breakthrough curves could be closely simulated by Yoon–Nelson and Thoms models. Significant differences existed in times for 50% breakthrough.CONCLUSIONMixed‐mode chromatography with HD‐1 resin as stationary phase is applicable to the separation of polyphenols. © 2024 Society of Chemical Industry (SCI).

Electrophoretic Mobility of Nanoparticles in Water.

Classical equations for colloidal mobility anticipate linear proportionality between the nanoparticle mobility and zeta potential caused by the combined electrostatics of free charges at the nanoparticle and screening bound charges of the polar solvent. Polarization of the interfacial liquid, either spontaneous due to molecular asymmetry of the solvent (water) or induced by nonelectrostatic (e.g., charge-transfer) interactions, is responsible for a static interface charge adding to the overall electrokinetic charge of the nanoparticle. The particle mobility gains a constant offset term that is formally unrelated to the zeta potential. The static charge is multiplied by the static dielectric constant of the solvent in the expression for the electrokinetic charge and is sufficiently large in magnitude to cause electrophoretic mobility of even neutral particles. At a larger scale, nonlinear electrophoresis linked to the interface quadrupole moment can potentially contribute a sufficiently negative charge to a micrometer-size nanoparticle.

Modelling of selective ion partitioning between ion-exchange membranes and highly concentrated multi-ionic brines

In recent years, the growing interest in the use of Ion-Exchange Membranes, in the treatment of highly concentrated multi-ionic brines for the selective recovery of critical elements, has prompted the research of fundamental models capable of predicting the IEMs selectivity towards like-charged species. Prior studies have proposed ion partitioning models limited to single-salt solutions that were validated only up to moderate salt concentrations. In this work, we developed a novel multi-ionic extension of the Manning counter-ion condensation model, aiming to predict the sorption selectivity of like-charged counter-ions. Furthermore, the peNRTL model was coupled with the extended Manning model to broaden its applicability range, encompassing membrane equilibrated with very highly concentrated solutions. Novel experimental ion sorption tests with single-salt and binary solutions including NaCl, KCl, MgCl2, and CaCl2 at high concentrations were performed with the commercial cation-exchange membrane Fumasep FKE-50. To the best of Authors’ knowledge, the proposed model for the first time successfully provided quantitative predictions of multi-ionic ion partitioning for all the systems investigated up to extremely high external salt concentrations. The outcomes of this work suggest a strong influence of the local non-electrostatic interactions on the activity coefficients in the membrane phase at high external concentration and highlight the key role of counter-ions hydration state in the condensation phenomenon.

Ciprofloxacin adsorption onto CNT loaded Pumice: Adsorption Modelling, kinetics, equilibriums and reusability studies

A novel CNT-derived Pumice adsorbent (P-CNT3) was successfully synthesized as an efficient adsorbent for Ciprofloxacin (CIP) removal from aqueous solutions. In present study, P-CNT3 composite synthesized by hydrothermal technique was loaded with multiwalled carbon nanotube (CNT) using sonification to remove CIP antibiotic. P-CNT3 composite were characterized by Fourier transform infrared spectroscopy (FTIR), X-Ray diffraction (XRD), Brunauer–Emmett–Teller (BET), Thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analyses. Adsorption performance was studied by adjusting the pH, contact time, initial CIP concentration, temperature and adsorbent dosage in a batch reactor to obtain the maximum adsorption capacity (qm). The maximum adsorption capacity (qm) was achieved in 240 min at pH ≤ 5).The adsorption process of P-CNT3 followed the pseudo-first-order kinetic model (R2 = 0.989) and sips isotherm model (R2 = 0.991), and qm to adsorb CIP was 28.6 mg/g. The illustrated adsorption mechanism shows that hydrophobic interactions, electrostatic and non-electrostatic interactions, suggests CIP adsorption. Over the temperature range of 298–318 K, the thermodynamic parameters ΔG°, ΔS° and ΔH° were calculated. The adsorption reactions were shown to be spontaneous and endothermic. Furthermore, activation energy suggested a physisorption mechanism for P-CNT3. In addition, regeneration study shows that the P-CNT3 can be reused five times with excellent results in CIP adsorption. Based on these findings, P-CNT3 can be considered a feasible low-cost adsorbent for CIP removal. Hence, the prepared P-CNT3 composite can be used as an inexpensive and a promising adsorbent for the removal of other pharmaceutical compounds.

Interpolyelectrolyte complexes of a biguanide cationic polyelectrolyte: formation of core/corona nanoparticles with double-hydrophilic diblock polyanion.

Biguanide-based cationic polyelectrolytes are used as key components of interpolyelectrolyte complexes bolstering alginate hydrogel microcapsules employed in cell therapies. Nevertheless, electrostatic complexation of these unique polycations has not been studied before. In this study, the interaction between biguanide condensates and anionic polyelectrolytes with carboxylate groups was studied on a model system of a metformin condensate (MFC) and an anionic diblock polyelectrolyte poly(methacrylic acid)-block-poly(ethylene oxide) (PMAA-PEO). The formation of MFC/PMAA-PEO core-corona nanoparticles was followed by static, dynamic and electrophoretic light scattering and by isothermal titration calorimetry and their internal structure was investigated by small angle neutron scattering and cryogenic transmission electron microscopy. It was found that the aggregation of PMAA-PEO chains induced by MFC occurred at much lower MFC/PMAA-PEO ratios that would correspond to the isoelectric point, thus yielding strongly negatively charged nanoparticles, suggesting the role of specific (non-electrostatic) interactions in the stabilization of the complex between PMAA and MFC.

Organic micropollutant removal and phosphate recovery by polyelectrolyte multilayer membranes: Impact of buildup interactions

Polyelectrolyte multilayer (PEM) deposition conditions can favorably or adversely affect the membrane filtration performance of various pollutants. Although pH and ionic strength have been proven to alter the characteristics of PEM, their role in determining the buildup interactions that control filtration efficacy has not yet been conclusively proved. A PEM constructed using electrostatic or non-electrostatic interactions from controlled deposition of a weak polyelectrolyte could retain both charged and uncharged pollutants from water. The fundamental relationship between polyelectrolyte charge density, PEM buildup interaction, and filtration performance was explored using a weak-strong electrolyte pair consisting of branching poly (ethyleneimine) and poly (styrene sulfonate) (PSS) across pH ranges of 4–10 and NaCl concentrations of 0 M–0.5 M. PEI/PSS multilayers at acidic pH were dominated by electrostatic interactions, which favored the selective removal of a charged solute, phosphate over chloride, while at alkaline pH, non-electrostatic interactions dominated, which favored the removal of oxybenzone (OXY), a neutral hydrophobic solute. The key factor determining these interactions was the charge density of PEI, which is controlled by pH and ionic strength of the deposition solutions. These findings indicate that the control of buildup interactions can largely influence the physico-chemical and transport characteristics of PEM membranes.

Multiscale Frozen Density Embedding/Molecular Mechanics Approach for Simulating Magnetic Response Properties of Solvated Systems.

We present a three-layer hybrid quantum mechanical/quantum embedding/molecular mechanics approach for calculating nuclear magnetic resonance (NMR) shieldings and J-couplings of molecular systems in solution. The model is based on the frozen density embedding (FDE) and polarizable fluctuating charges (FQ) and fluctuating dipoles (FQFμ) force fields and permits the accurate ab initio description of short-range nonelectrostatic interactions by means of the FDE shell and cost-effective treatment of long-range electrostatic interactions through the polarizable force field FQ(Fμ). Our approach's accuracy and potential are demonstrated by studying NMR spectra of Brooker's merocyanine in aqueous and nonaqueous solutions.

Reversible surface modification of PAN-based carbon fibers by a ferrocene-based surfactant

The surface of carbon fibers (CFs) was modified by a surfactant (ferrocenemethyl)dodecyldimethylammonium bromide (FDDA) to enhance the interfacial ashesion between the CFs and surrounding matrix. Results showed that it could be electrochemically desorbed by a potentiostatic electro-oxidation method. The FDDA adsorption isotherm was attributed to the formation of multi-molecular layers mainly by non-electrostatic interactions. The adsorption and desorption of FDDA on the CFs have little effect on their tensile strength. The effects of FDDA modification on the interfacial properties of CF/epoxy composites were evaluated by a single-filament fragmentation test. Compared with the un-modified CFs, the FDDA-modified ones had significantly improved interfacial adhesion properties in the composites. This method provides a potential approach for preparing recyclable CF/resin composites.