Molecular Solvents Research Articles

Loosely Sandwich-Structured Membranes Decorated with UiO-66-NH2 for Efficient Antibiotic Separation and Organic Solvent Resistance

Thin-film nanocomposite (TFN) membranes with efficient molecular separation and organic solvent resistance are active in demand in wastewater treatment and resource reclamation, meeting the goal of emission peaks and carbon neutrality. In this work, a simple and rational design strategy has been employed to construct a sandwich-structured membrane for removing fluoroquinolone antibiotics and recycling organic solvents. The sandwich-structured membrane is composed of a porous substrate, a hydrophilic tannic acid-polyethyleneimine (TA-PEI) interlayer, and a polyamide (PA) selective layer decorated with metal-organic framework (PA-MOF). Results manifest that the hydrophilic TA-PEI interlayer played a bridging and gutter effect to achieve effective control in amide storage, amine diffusion, and nanomaterial downward leakage at the immiscible interface. The PA-MOF selective layer has been changed to a loosely crumpled surface, endowing functionalities on the sandwich-structured membrane that included limited pores, strengthened electronegativity, and stronger hydrophilicity. Thus, an enhanced water flux of 87.23 ± 7.43 LMH was achieved by the TFN-2 membrane (0.04 mg·mL-1 UiO-66-NH2), which is more than five times that of the thin-film composite membrane (17.46 ± 3.88 LMH). The rejection against norfloxacin, ciprofloxacin, and levofloxacin is 92.94 ± 1.60%, 94.62 ± 1.29%, and 96.92 ± 1.05%, respectively, effectively breaking through the "trade-off" effect between membrane permeability and rejection efficiency. Further antifouling results showed that the sandwich-structured membrane had lower flux decay ratios (3.36∼7.07%) and higher flux recovery ratios (93.40∼98.40%), as well as superior long-term stability after 30 days of filtration. Moreover, organic solvent resistance testing confirms that the sandwich-structured membrane maintained stable solvent flux and better recovery rates in ethanol, acetone, isopropanol, and N,N-dimethylformamide. Detailed nanofiltration mechanism studies revealed that these outstanding performances are based on the joint effect of the TA-PEI interlayer and PA-MOF selective layer, proposing a new perspective to break through the bottleneck of nanofiltration application in a complex environment.

The catalytic performance of acid-modified Hβ molecular sieves for environmentally friendly acylation of 2-methylnaphthalene

Abstract 2,6-Methylacylnaphthalene is an important organic chemical raw material, mainly used as a precursor for synthesizing polyethylene 2,6-naphthalene dicarboxylate (PEN). The heterogeneous catalyst molecular sieve catalyzes the acylation of 2-methylnaphthalene to synthesize β,β-methylacylnaphthalene, which has good activity, is green and environmentally friendly, with simple post-treatment. Different molecular sieves and reaction solvents were selected, and Hβ molecular sieves were more suitable for the acylation reaction of 2-methylnaphthalene. The reaction results were better when sulfolane was used as a solvent in this paper. The catalytic performances of citric acid-modified Hβ molecular sieve (SiO2/Al2O3 of 25) and unmodified molecular sieve were investigated and compared. The results showed that modification with low-concentration citric acid increased the amount of mediate strong acid and Bronsted acid, the specific surface area, pore volume, and pore size of Hβ zeolite. When the concentration of citric acid was 0.3 mol·L−1, the modification time was 48 h and the calcination at 550°C for 3 h had the best catalytic activity. By further optimizing the acylation process, the conversion rate of 2-methylnaphthalene increased to 88.82%, and the yield of β,β-methyl propyl naphthalene increased to 82.12%.

Analysis of amyloidogenic transthyretin mutations using continuum solvent free energy calculations.

Many proteins can undergo pathological conformational changes that result in the formation of amyloidogenic fibril structures. Various neurodegenerative diseases are associated with such pathological fibril formation of specific proteins. Transthyretin (TTR) is a tetrameric globular transport protein in the blood plasma that can dissociate, unfold, and form long and stable fibrils. Many TTR mutations are known that promote (TTR) amyloidosis and cause severe diseases. TTR amyloidosis has been studied extensively using biochemical methods and structures of various mutations in the globular form have been characterized. Recently, also the structure of a TTR fibril has been determined. In an effort to better understand why some mutations increase or decrease the tendency of amyloid formation, we have applied a combined molecular dynamics and continuum solvent approach to calculate the energetic influence of residue changes in the globular versus fibril form. For 29 out of 36 tested TTR single residue mutations, the approach correctly predicts the increased or decreased tendency for amyloidosis allowing us also to elucidate the origins of the tendency. We find that indeed the destabilization of the globular monomer or changes in dimer and tetramer stability due to mutation has a dominant influence on the amyloidogenic tendency. The continuum solvent model predicts a significantly more favorable mean energy per residue of the fibril form compared to the globular form. This effect is only slightly modulated by single-point mutations preserving the energetic preference for fibril formation upon protein unfolding. It explains why no correlation between experimental amyloidosis and calculated change in fibril stability was observed.

Theoretical study of the non-linear optical properties of colloids formed by different Au and Ag nanocluster morphologies and molecular organic solvents

• Colloidal systems formed by gold and silver nanoclusters. • Theoretical study using density functional theory. • Effects of solvents as water, diethyl ether, benzene, vacuum and, tetrahydrofuran. • Nonlinear optical properties as polarizability, first hyperpolarizability, and second hyperpolarizability. The structural, electronic, and nonlinear optical properties of colloidal systems formed by gold and silver nanoclusters in different molecular organic solvents: water, benzene, diethylether, and tetrahydrofuran were studied from the theoretical point of view by the self-consistent reactions field theory using the polarizable continuum model, under the framework of the density functional theory. The analysis was developed to clarify the effects of the selected solvents in combination with a specific nanocluster structure: cubic, octahedral, tetrahedral, and pentagonal rod. By the discussion of the results, it is exposed that a variety of variables are involved in the obtained nonlinear optical values, such as the macroscopic solvent parameters used by the employed model, where the dielectric constant value is the most significant to describe the behavior of properties as the polarizability and the first and second hyperpolarizabilities. Besides, in the case of morphology, the symmetry of each structure is the most critical factor to consider in tailoring the desired nonlinear optical response. Our results can be used as a reference to the experimental development of non-linear optical devices based on colloids.

Transitioning from a lab-scale PLGA microparticle formulation to pilot-scale manufacturing.

The complexity of scale-up manufacturing of PLGA microparticles creates a significant challenge when transitioning from benchtop-scale formulation development into larger clinical scale batches. Minor changes in the initial formulation composition (e.g., PLGA molecular weight, solvent type, and drug concentration) and processing parameters (e.g., extraction kinetics and drying condition) during scale-up production can result in significantly different performance of the prepared microparticles. The objectives of the present study were to highlight the in vitro and in vivo performance of a candidate benchtop-scale batch created with a rotor-stator mixer, transitioned into an in-line manufacturing process at ~15× scale of a long-acting naltrexone formulation. Physicochemical properties (such as drug loading, residual benzyl alcohol content, and morphology) as well as the in vitro release characteristics of the prepared naltrexone microparticles between the benchtop-scale and in-line process pilot-scale were determined. The pharmacokinetics of the naltrexone microspheres were investigated using the rat model. The results demonstrate that while the morphologies of the particles were different from a visual assessment and slight differences were observed in the in vitro release profiles, the in vivo pharmacokinetics illustrate similar kinetics. Our study shows that scale-up production having the same drug release kinetics can be made by controlling the formulation and processing parameters.

Hydrogen bonding between 1-ethyl-3-methyl-imidazolium dicyanamide ionic liquid and selected co-solvents with varying polarity: A DFT study

A theoretical study was performed to investigate the solute-solvent interactions between 1-ethyl-3-methyl-imidazolium ([EMIM]+) dicyanamide ([DCA]-) ionic liquid (IL) and each of the three traditional molecular solvents, namely, water, methanol and chloroform, to elucidate the geometry of the stable IL⋯co-solvent structures as well as the interaction strength at different possible sites. The study was performed by utilising a simplified structure approach in which one solvent molecule interacts with the IL at different possible interaction sites. Geometry optimisations were performed by using the density functional theory (DFT) method in combination with the 6-31++G(d,p) basis set; the energy was improved by using the B3LYP/6-311++G(3df,3pd)// B3LYP/6-31++G(d,p) approach to eliminate the basis set superposition error on the energies. The results of the study show that IL forms a strong interaction with the co-solvent at nearly all possible interaction sites. The C–H⋯N intermolecular interactions between the cation and the anion units of the IL are weakened when the solvent molecule interacts simultaneously with the hydrogen bond donor involved between the cation and the anion units of the IL. The polar solvents (methanol and water) interact more strongly with the IL than the nonpolar chloroform solvent. The results presented herein have fundamentally advanced the understanding of the specific structural, energetic and electronic changes induced on [EMIM]DCA cation–anion units by the selected co-solvents and provided a detailed description of the interaction patterns between [EMIM]DCA and the selected co-solvent molecules. Such information, which had not previously been provided, could serve as a basis for further studies on derivatives of [EMIM]DCA with the selected co-solvents or with other solvents not considered in this work.

Density, viscosity and electrical conductivity of four amino acid based ionic liquids derived from l-Histidine, l-Lysine, l-Serine, and Glycine

Amino acid ionic liquids (AAILs), as a kind of renewable and biocompatible ionic liquids, show special properties of strong polarity, strong hydrogen bonding ability, stable chiral center and excellent biodegradability, and share huge application potentials in almost all of the biological, medical, pharmaceutical and biotechnological processes. The investigation of physico-chemical properties of AAILs both in purity and interacting with molecular solvents highly contributes to understanding the huge application potential of AAILs in different fields of the chemical, pharmaceutical and petrochemical industries. This paper synthesized several AAILs of [VilmC3][His], [VilmC3][Lys], [VilmC3][Ser] and [VilmC3][Gly], by using l-Histidine, l-Lysine, l-Serine, and Glycine as anions, respectively. The obtained AAILs were characterized by 1H NMR analysis and TG-DTG analysis. The basic physical properties of density, dynamic viscosity, and conductivity were systemically measured. The apparent molar volume, limiting apparent molar volume, excess molar volume, isobaric expansivity coefficient and apparent molar expansivity were estimated from density. The viscosity deviation, the molar and limiting conductivities were calculated from dynamic viscosity and conductivity, respectively. Various models were used to correlate the experimental data, and the molecular interactions were discussed. The information obtained from this work serves as the basement to the AAILs application.

Solvents and Stabilization in Ionic Liquid Films.

We report the interfacial structures and chemical environments of ionic liquid films as a function of dilution with molecular solvents and over a range of film thicknesses (a few micrometers). Data from spectroscopic ellipsometry and infrared spectroscopy measurements show differences between films comprised of neat ionic liquids, as well as films comprised of ionic liquids diluted with two molecular solvents (water and acetonitrile). While the water-diluted IL films follow thickness trends predicted by the Landau-Levich model, neat IL and IL/MeCN films deviate significantly from predicted behaviors. Specifically, these film thicknesses are far greater than the predicted values, suggesting enhanced intermolecular interactions or other non-Newtonian behaviors not captured by the theory. We correlate film thicknesses with trends in the infrared intensity profiles across film thicknesses and IL-solvent dilution conditions and interpret the changes from expected behaviors as varying amounts of the film volume existing in isotropic (bulk) vs anisotropic (interfacial) states. The hydrogen bonding network of water-diluted ionic liquids is implicated in the agreement of this system with the Landau-Levich model's thickness predictions.

Molecular Mechanism of Organic Crystal Nucleation: A Perspective of Solution Chemistry and Polymorphism

Crystal nucleation determining the formation and assembly pathway of first organic materials is the central science of various scientific disciplines such as chemical, geochemical, biological, and synthetic materials. However, our current understanding of the molecular mechanisms of nucleation remains limited. Over the past decades, the advancements of new experimental and computational techniques have renewed numerous interests in detailed molecular mechanisms of crystal nucleation, especially structure evolution and solution chemistry. These efforts bifurcate into two categories: (modified) classical nucleation theory (CNT) and non-classical nucleation mechanisms. In this review, we briefly introduce the two nucleation mechanisms and summarize current molecular understandings of crystal nucleation that are specifically applied in polymorphic crystallization systems of small organic molecules. Many important aspects of crystal nucleation including molecular association, solvation, aromatic interactions, and hierarchy in intermolecular interactions were examined and discussed for a series of organic molecular systems. The new understandings relating to molecular self-assembly in nucleating systems have suggested more complex multiple nucleation pathways that are associated with the formation and evolution of molecular aggregates in solution.

Stable Formulations for the Lithium and Sodium Metal Interfaces in Alkali Metal-Oxygen Batteries

The high reactivity of both positive and negative interfacial regions in metal-oxygen (M-O2) batteries leads to a variety of parasitic degradation reactions that reduce reversibility on charge/discharge and can lead to rapid cell failure. To reversibly access the high theoretical specific energies these chemistries promise (3456 and 1602 Wh·kg-1 for Li-O2 and Na-O2, respectively), reducing charging overpotentials and the design of new electrode and electrolyte materials with improved stabilities are key targets. Considering the M|electrolyte interface, where decomposition reactions and dendrite formation generates severe safety concerns as well as reduced cycling stabilities, surface protection of the alkali metal anode by pre-treatment techniques or additive formulation has been among the more successful methodologies.1 In this work, we present a formulation strategy targeting enhanced cycling stabilities of the metal anode in M-O2 cells. Initially demonstrated in the Li-O2 chemistry, we report on an in-depth investigation into the electrochemical performance and the spectroscopic and diffusional properties of ternary ionic liquid (IL)-molecular solvent blend electrolytes.2 By introduction of the IL and exploring a wide formulation range (Figure 1a), we attain significant enhancements in the stability of practically-relevant electrolyte materials that otherwise fail rapidly at alkali metal anodes (Figure 1b), achieving the highest Coulombic efficiencies for Li plating/stripping in this solvent. The optimized formulations consequently displayed enhanced performances in Li-O2 full cells and ex situ characterization of Li surfaces also revealed the suppression of dendrite formation and important changes in the solid electrolyte interphase as a result of modulating solvent reactivity. Using Raman spectroscopy and diffusional analyses, we relate this closely to the local solvation environments involving the reactive solvent component in optimized formulations and, therefore, elucidate critical solvent/Li-salt ratios for improved stability.By understanding key shifts in Raman spectra relating to solvation effects in concentrated Li formulations, and how this modulates cycling performances, we further demonstrate the applicability of this relationship and formulation strategy to the Na-O2 battery chemistry. Therein, the Na metal interface is comparably more reactive and, therefore, presents greater stability challenges, with decomposition reactions in non-optimized formulations more rapidly causing plating and stripping at the anode to fail. However, we demonstrate the plating/stripping of Na (Figure 1c) and cycle lifetime in Na-O2 cells can be hugely improved by applying the above strategy and understandings of critical solvation interactions to equivalent formulations based on Na-salts. Y. Yu, G. Huang, J.-Z. Wang, K. Li, J.-L. Ma, and X.-B. Zhang, Adv. Mater. (Weinheim, Ger.), 32 (38), 2004157 (2020). A. R. Neale, R. Sharpe, S. R. Yeandel, C.-H. Yen, K. V. Luzyanin, P. Goddard, E. A. Petrucco, and L. J. Hardwick, Adv. Funct. Mater., 31 (27), 2010627 (2021). Figure 1. (a) Ternary plot highlighting the changes in stability of Li/Na metal anode cycling as a function of the studied formulation ranges and example voltage profiles of symmetric (b) Li|Li cells and (c) Na|Na cells with non-optimized (navy/purple) and optimized (orange) electrolyte formulations. Figure 1

A DENSITY FUNCTIONAL THEORY (DFT) STUDY ON SILICON DOPED CARBON NANOTUBE Si-CNT AS A CARRIER FOR BMSF-BENZ DRUG USED FOR OSTEOPOROSIS DISEASE

This study aims to investigate the capability of Silicon-Doped Carbon Nanotube (Si-CNT) to detect and adsorb the BMSF-BENZ ((4-Bromo-7-methoxy-1-(2-methoxyethyl)-5-{[3-(methylsulfonyl)phenyl]methyl}-2-[4- (propane-2-))yl)phenyl]-1H-1,3-benzothiazole) molecular. For this purpose, we considered different configurations for adsorbing BMSF-BENZ drugs on the surface of the Si-CNT nanotube. All considered configurations are optimized using the density functional theory (DFT) at the 6-31G∗∗ basis set and B3LYP-B97D level of theory. Then from optimized structures, for each nanoparticle, we selected seven stable locations for the adsorption of BMSF-BENZ in (Br, N8, N9, N58, O35, O41 and S) active atoms on the surface of the selected nanoparticle. The quantum theory of atoms in molecules (QTAIM), reduced density gradient (RDG) analysis, and molecular orbital (MO) analysis were also established. The calculated results indicate that the distance between nanotube and drug from the N8 site is lower than from all other locations sites for all investigated complexes, and adsorption of BMSF-BENZ from the N8 site is more favorable for the Si-CNT nanotube. The adsorption energy, hardness, softness, and fermi energy results reveal that the interaction of BMSF-BENZ with Si-CNT is a promising adsorbent for this drug as Adsorption energy Eads of BMSF-BENZ/Si-CNT complexes are (-13.08, -43.50, -17.90, -31.29, -25.57, -16.56, and -28.05) kcal/mol in the gas phase. As well, the appropriate and spontaneous interaction between the BMSF-BENZ drug and Si-CNT nanoparticle was confirmed by investigating the quantum chemical molecular descriptors and solvation Gibbs free energies of all atoms.

Front Cover: Solvated Actinoids: Methanol, Ethanol, and Water Adducts of Thorium and Uranium Tetrachloride (Eur. J. Inorg. Chem. 21/2022)

The Front Cover shows that there are occasions on which chemistry shows its human face. Thorium(IV) and uranium(IV), both of which share a love for chloride, saturate themselves quite literally when given the opportunity to take up some alcohol or water, i.e. polar-protic solvents. When either ThCl4 or UCl4 is treated with methanol or ethanol, the molecular solvent adducts [ThCl4(MeOH)4], [UCl4(MeOH)4], [ThCl4(EtOH)4] and [UCl4(EtOH)4] form. The tendency to form the water adduct is so strong that, when a Th adduct is dissolved in hydrochloric acid, two Th−Cl bonds break up and [ThCl2(H2O)7](Cl)2(H2O)2, which is isotypic with the already known [UCl2(H2O)7](Cl)2(H2O)2, forms. At elevated temperature, the materials decompose to form their respective oxides. More information can be found in the Research Article by M. Zegke and co-workers.

Molecular-Based Description of the Osmotic Second Virial Coefficients of Electrolytes: Rigorous Formal Links to Solute-Solvent Interaction Asymmetry, Virial Expansion Paths, and Experimental Evidence.

We introduce a molecular-based route to the evaluation of the osmotic second virial coefficients of dissociative solutes in dilute binary solutions, according to a general molecular thermodynamic solvation formalism of electrolyte solutions. We discuss the underlying solvation fundamentals and derive rigorous expressions leading to (i) the functional relationship among the osmotic second virial coefficients and the limiting composition behavior of the non-Coulombic contribution to the Kirkwood-Buff integral of the solute-solute interactions, the corresponding composition slope of the mean activity coefficient of the electrolyte solute, and a precisely defined solute-solvent intermolecular interaction asymmetry that characterizes unambiguously the solution non-ideality; (ii) the self-consistent calculation of the osmotic second virial coefficients of electrolytes as defined by the composition expansion along different thermodynamic paths and/or composition variables; (iii) the microstructural interpretation of Hill's isobaric-isothermal osmotic second virial coefficient in terms of Kirkwood-Buff correlation function integrals and its relationships to other osmotic coefficients from composition expansions along alternative thermodynamic paths; and (iv) the identification of drawbacks in the implementation of previous methods, originally intended for non-electrolyte systems, to systems involving dissociative solutes. The proposed formalism provides the fundamentally based foundations to the determination of the osmotic second virial coefficients of any type of electrolyte solute, whose thermodynamic expressions converge naturally to the non-electrolyte ones by setting to unity the solute stoichiometric coefficient ν. Following the formal results, we illustrate the formalism with the calculation of a variety of osmotic second virial coefficients involving a wide selection of aqueous solutions at ambient conditions and comprising a wide range of anion-cation type combinations characterized by 2 ≤ ν ≤ 6. Finally, we interpret the behavior of the resulting osmotic virial coefficients in terms of the solute-solvent intermolecular interaction asymmetry, discuss the experimental data requirements for the accurate evaluation of the osmotic second virial coefficients, and provide some observations as well as their modeling implications.

OzTracs: Optical Osmolality Reporters Engineered from Mechanosensitive Ion Channels.

Interactions between physical forces and membrane proteins underpin many forms of environmental sensation and acclimation. Microbes survive osmotic stresses with the help of mechanically gated ion channels and osmolyte transporters. Plant mechanosensitive ion channels have been shown to function in defense signaling. Here, we engineered genetically encoded osmolality sensors (OzTracs) by fusing fluorescent protein spectral variants to the mechanosensitive ion channels MscL from E. coli or MSL10 from A. thaliana. When expressed in yeast cells, the OzTrac sensors reported osmolality changes as a proportional change in the emission ratio of the two fluorescent protein domains. Live-cell imaging revealed an accumulation of fluorescent sensors in internal aggregates, presumably derived from the endomembrane system. Thus, OzTrac sensors serve as osmolality-dependent reporters through an indirect mechanism, such as effects on molecular crowding or fluorophore solvation.

Dynamic self-stabilization in the electronic and nanomechanical properties of an organic polymer semiconductor

The field of organic electronics has profited from the discovery of new conjugated semiconducting polymers that have molecular backbones which exhibit resilience to conformational fluctuations, accompanied by charge carrier mobilities that routinely cross the 1 cm2/Vs benchmark. One such polymer is indacenodithiophene-co-benzothiadiazole. Previously understood to be lacking in microstructural order, we show here direct evidence of nanosized domains of high order in its thin films. We also demonstrate that its device-based high-performance electrical and thermoelectric properties are not intrinsic but undergo rapid stabilization following a burst of ambient air exposure. The polymer’s nanomechanical properties equilibrate on longer timescales owing to an orthogonal mechanism; the gradual sweating-out of residual low molecular weight solvent molecules from its surface. We snapshot the quasistatic temporal evolution of the electrical, thermoelectric and nanomechanical properties of this prototypical organic semiconductor and investigate the subtleties which play on competing timescales. Our study documents the untold and often overlooked story of a polymer device’s dynamic evolution toward stability.

Facile fabrication and SERS performance of polymer/Ag core-shell microspheres via the reverse breath figure accompanied by in situ reduction

A new facile fabrication process of the polymer/Ag core-shell microspheres is demonstrated via the reverse breath figure method accompanied by in situ reduction. In contrast to traditional approaches, which require the prior preparation of polymer microspheres, the star-shaped polyhedral oligomeric silsesquioxane (POSS) amphiphilic block copolymers solution containing AgNO3 is cast under ethanol vapor for the formation of polymer/AgNO3 core-shell microspheres in one step. The influence of polymer molecular structures, solvent, non-solvent and metal salt on the morphology of polymer microspheres was analyzed. Then the AgNO3 can be reduced in situ to form Ag nanoparticles on the surface of polymer microspheres, which resulted in the formation of polymer/Ag core-shell microspheres. The reduced Ag nanoparticles were homogeneously deposited on the surfaces of polymer microspheres, which can exhibit good performance in the surface-enhanced Raman scattering (SERS). The polymer/Ag core-shell microspheres substrate showed a high detection sensitivity (enhancement factor 2.49 × 106) with excellent uniformity and reproducibility for Rhodamine 6G (R6G) (relative standard deviation of the intensity at 612 cm−1 was 6.19%＜20%). The proposed strategy is facile to implement and thus a promising new method for the preparation of polymer/metal core-shell microspheres.

Mixtures of Diethyl Sulfoxide and Methanol: Structure and Thermodynamics

Mixtures of sulfoxides with molecular solvents possess interesting physicochemical properties and may have applications in chemical synthesis. Hereby we confirm and rationalize the previously reported excellent miscibility of diethyl sulfoxide (DESO) with methanol (MeOH). By performing a comprehensive potential energy surface investigation we identified a global minimum for each system and a significant number of local minima described at the hybrid density functional level of theory. A strong 0.18 nm long hydrogen bond forming between the oxygen atom of DESO and the polarized hydrogen atom of MeOH was evidenced both via the structural and spectral analyses. Our results robustly explain negative deviations in the DESO–MeOH mixtures from ideal behavior and interpret the experimental observations with microscopic precision.Graphical Abstract

Stabilized convection in a ternary mixture with two Soret coefficients of opposite sign

We performed ground-based experiments on the sample polystyrene–toluene–cyclohexane in order to complement the experimental activities in microgravity conditions related to the ESA projects DCMIX4 and Giant Fluctuations. After applying a stabilizing thermal gradient by heating from above a layer of the fluid mixture, we studied over many hours the density variations in the bidimensional horizontal field by means of a Shadowgraph optical setup. The resulting images evidence the appearance of convective instability after a diffusive time associated with the binary molecular solvent consisting of toluene and cyclohexane, confirming the negative sign of the Soret coefficient of this mixture. After a larger diffusive time related to mass diffusion of the polystyrene in the binary solvent, convection was suppressed by the increasing stabilizing density gradient originated by the Soret-induced concentration gradient of the polymer. This is compatible with a positive sign of the Soret coefficient of the polymer in the binary solvent.Graphic

Accelerating the 3D reference interaction site model theory of molecular solvation with treecode summation and cut-offs.

The 3D reference interaction site model (3D-RISM) of molecular solvation is a powerful tool for computing the equilibrium thermodynamics and density distributions of solvents, such as water and co-ions, around solute molecules. However, 3D-RISM solutions can be expensive to calculate, especially for proteins and other large molecules where calculating the potential energy between solute and solvent requires more than half the computation time. To address this problem, we have developed and implemented treecode summation for long-range interactions and analytically corrected cut-offs for short-range interactions to accelerate the potential energy and long-range asymptotics calculations in non-periodic 3D-RISM in the AmberTools molecular modeling suite. For the largest single protein considered in this work, tubulin, the total computation time was reduced by a factor of 4. In addition, parallel calculations with these new methods scale almost linearly and the iterative solver remains the largest impediment to parallel scaling. To demonstrate the utility of our approach for large systems, we used 3D-RISM to calculate the solvation thermodynamics and density distribution of 7-ring microtubule, consisting of 910 tubulin dimers, over 1.2 million atoms.

Effect of polar molecular organic solvents on non-aqueous solvent extraction of rare-earth elements

The extraction and separation of five different rare-earth elements, La, Nd, Eu, Dy and Yb, from an aqueous chloride solution and from different chloride non-aqueous solutions using the solvating extractant Cyanex 923 was investigated. As previous studies had demonstrated the potential of non-aqueous solvent extraction (NASX) to refine rare earths from ethylene glycol, structural analogues of ethylene glycol (1,2-propanediol and 1,3-propanediol) and to other polar organic solvents (triethylene glycol, dimethylsulfoxide, methanol, N,N-dimethylformamide and N,N-dimethylacetamide) were studied. The extraction data were interpreted in terms of different solvent properties: dielectric constant, Gutmann donor number, molecular structure and hydrogen-bonding capabilities. Remarkable differences were observed between the extraction behaviour from ethylene glycol, 1,2-propanediol and 1,3-propanediol. Therefore, these solvent systems were further studied to elucidate the speciation of the rare-earth elements by optical absorption and luminescence spectroscopy. Based on these studies, both contact-ion-pair formation and solvation strength are assumed to play an important role in the extraction of rare earths by Cyanex 923 from different polar organic solvents. The differences in extraction behaviour can be exploited to fine-tune the separation of rare earths.