Polar Solutes Research Articles

Probing the retention mechanism of small hydrophilic molecules in hydrophilic interaction chromatography using saturation transfer difference nuclear magnetic resonance spectroscopy

The interactions and dynamic behavior of a select set of polar probe solutes have been investigated on three hydrophilic and polar commercial stationary phases using saturation transfer difference 1H nuclear magnetic resonance (STD-NMR) spectroscopy under magic angle spinning conditions. The stationary phases were equilibrated with a select set of polar solutes expected to show different interaction patterns in mixtures of deuterated acetonitrile and deuterium oxide, with ammonium acetate added to a total concentration that mimics typical eluent conditions for hydrophilic interaction chromatography (HILIC). The methylene groups of the stationary phases were selectively irradiated to saturate the ligand protons, at frequencies that minimized the overlaps with reporting protons in the test probes. During and after this radiation, the saturation rapidly spreads to all protons in the stationary phase by spin diffusion, and from those to probe protons in contact with the stationary phase. Probe protons that have been in close contact with the stationary phase and subsequently been released to the solution phase will have been more saturated due to a more efficient transfer of spin polarization by the nuclear Overhauser effect. They will therefore show a higher signal after processing of the data. Saturation transfers to protons in neutral and charged solutes could in some instances show clear orientation patterns of these solutes towards the stationary phases. The saturation profile of formamide and its N-methylated counterparts showed patterns that could be interpreted as oriented hydrogen bond interaction. From these studies, it is evident that the functional groups on the phase surface have a strong contribution to the selectivity in HILIC, and that the retention mechanism has a significant contribution from oriented interactions.

Electrosprayed polydopamine membrane: Surface morphology, chemical stability and separation performance study

Polydopamine (PDA) surface coating has attracted intensive attentions in membrane surface engineering. Traditional immersion dopamine polymerization (iPDA) strategy has several limitations in morphology control, low chemical stability, low dopamine conversion and wastewater discharge. In this study, we proposed an electrosprayed polydopamine coating (ePDA) strategy exhibiting advantages over iPDA in terms of coating performance and coating efficiency. A comprehensive comparison between ePDA and iPDA for PDA coating construction was made to show the difference in PDA deposition, morphology, chemical stability and separation performance. Results demonstrated that ePDA produced PDA membrane showed relatively smooth surface, enhanced chemical stability (especially in basic and polar organic solvents, e.g., NaOH solution, N,N-dimethylformamide and dimethyl sulfoxide), well-arranged uniform and symmetric structure, high water flux and better dye/salt selectivity. The current study might supply more ideas for novel PDA formation and advance practical PDA applications in a greener way.

Dynamic Modeling of CHO Cell Metabolism Using the Hybrid Cybernetic Approach With a Novel Elementary Mode Analysis Strategy.

Chinese hamster ovary (CHO) cell culture has a major importance on the production of biopharmaceuticals, including recombinant therapeutic proteins such as monoclonal antibodies (MAb). Mathematical modeling of biological systems can successfully assess metabolism complexity while providing logical and systematic methods for relevant genetic target and culture parameter identification toward cell growth and productivity improvements. Most modeling approaches on CHO cells have been performed under stationary constraints, and only a few dynamic models have been presented on simplified reaction sets, due to substantial overparameterization problems. The hybrid cybernetic modeling (HCM) approach has been recently used to describe the dynamic behavior by incorporating regulation between different metabolic states by elementary mode participation control, with sets of equations evaluated by objective functions. However, as metabolic networks evaluated are constructed toward a genomic scale, and cell compartmentalization is considered, identification of the active set becomes more difficult as EM number exponentially grows. Thus, the development of robust approaches for EM active set selection and analysis with smaller computational requirements is required to impulse the use of cybernetic modeling on larger up to genome-scale networks. In this report, a novel elementary mode selection strategy, based on a polar representation of the convex solution space is presented and coupled to a cybernetic approach to model the dynamic physiologic and metabolic behavior of CHO-S cell cultures. The proposed Polar Space Yield Analysis (PSYA) was compared to other reported elementary mode selection approaches derived from Common Metabolic Objective Analysis (CMOA) used in Flux Balance Analysis (FBA), Yield Space Analysis (YSA), and Lumped Yield Space Analysis (LYSA). For this purpose, exponential growth phase dynamic metabolic models were calculated using kinetic rate equations based on previously modeled growth parameters. Finally, complete culture dynamic metabolic flux models were constructed using the HCM approach with selected elementary mode sets. The yield space elementary mode- and the polar space elementary mode- hybrid cybernetic models presented the best fits and performances. Also, a flux reaction perturbation prediction approach based on the polar yield solution space resulted useful for metabolic network flux distribution capability analysis and identification of potential genetic modifications targets.

Widely tunable polarization conversion in low-doped graphene-dielectric metasurfaces based on phase compensation.

We propose a tri-band half-wave plate in the reflection mode, composed of rectangular silicon bar arrays on a 10-layer graphene substrate. By merely varying the Fermi energy of graphene from 0 to 0.25 eV, the three frequency bands shift in step and merge to a continuous dynamic bandwidth from 0.88 to 1.81 terahertz (THz). In addition, it can also dynamically switch the reflected wave among cross-linear polarization, right-handed and left-handed circular polarization in 0.93-1.35 THz. We found that the large dynamic bandwidth originates from the tunable reflection phase from the graphene layers. As it no longer depends on the plasmonic resonance in graphene, the proposed hybrid metasurface offers an alternative solution for active THz polarization devices with low biasing voltages.

Development of a solvent-polarizable three-dimensional reference interaction-site model theory.

Solvent polarization around a polar solute molecule plays an essential role in determining the electronic and thermodynamic properties of solutions. In this study, a solvent-polarizable model in response to solute polarization is proposed, which is coupled with a three-dimensional reference interaction-site model theory. The charge-response kernel is used to describe solvent polarizability, and four different coupling schemes are assessed. The most feasible behavior scheme among them is the one that incorporates responses not only to solute polarization but also to solute-induced solvent polarization. The numerical results indicated that solvent molecules near the polar solute show significant polarization, and therefore, the model proposed here is useful for considering the solvation process and thermodynamics of polar solute molecules.

Simulating the Nonadiabatic Relaxation Dynamics of 4-(N,N-Dimethylamino)benzonitrile (DMABN) in Polar Solution.

The compound 4-(N,N-dimethylamino)benzonitrile (DMABN) represents the archetypal system for dual fluorescence, a rare photophysical phenomenon in which a given fluorophore shows two distinct emission bands. Despite extensive studies, the underlying mechanism remains the subject of debate. In the present contribution, we address this issue by simulating the excited-state relaxation process of DMABN as it occurs in polar solution. The potential energy surfaces for the system are constructed with the use of the additive quantum mechanics/molecular mechanics (QM/MM) method, and the coupled dynamics of the electronic wave function and the nuclei is propagated with the semiclassical fewest switches surface hopping method. The DMABN molecule, which comprises the QM subsystem, is treated with the use of the second-order algebraic diagrammatic construction (ADC(2)) method with the imposition of spin-opposite scaling (SOS). It is verified that this level of theory achieves a realistic description of the excited-state potential energy surfaces of DMABN. The simulation results qualitatively reproduce the main features of the experimentally observed fluorescence spectrum, thus allowing the unambiguous assignment of the two fluorescence bands: the normal band is due to the near-planar locally excited (LE) structure of DMABN, while the so-called "anomalous" second band arises from the twisted intramolecular charge transfer (TICT) structure. The transformation of the LE structure into the TICT structure takes place directly via intramolecular rotation, and is not mediated by another excited-state structure. In particular, the oft-discussed rehybridized intramolecular charge transfer (RICT) structure, which is characterized by a bent nitrile group, does not play a role in the relaxation process.

Response Theory for Static and Dynamic Solvation of Ionic and Dipolar Solutes in Water

The response of polar solvents to ions and polar molecules dictates many fundamental molecular processes. To understand such electrostatically-driven solvation processes, one ideally would probe the dielectric response of a solvent to an idealized point test charge or dipole solute, as envisioned in classic continuum treatments of the problem. However, this is difficult in simulations using standard atomically-detailed solvent models with embedded point charges due to possible overlap with the test charge that lead to singular interaction energies. This problem is traditionally avoided for a realistic charged solute by introducing an excluded volume core that shields its embedded point charge or dipole from the charges in the solvent. However, this core introduces additional molecular-scale perturbations of the solvent density that complicate the interpretation of solvent dielectric response. In this work, we avoid these complications through the use of Gaussian-smoothed test charges and dipoles. Gaussian charges and dipoles can be readily inserted anywhere into an atomistic solvent model without encountering infinite energies. If the Gaussian-smoothing is on the scale of molecular correlations in the solvent, both the thermodynamic and dynamic solvation response is linear. Using this observation, we construct accurate predictive theories for solvation free energies and solvation dynamics for insertion of Gaussian charges and dipoles in polar solvents and demonstrate the accuracy of the theories for a widely-used model of water. Our results suggest that Gaussian test charge distributions can be used as an informative probe of dielectric response in molecular models, and our theories can be used to analytically predict the largest component of solvation free energies of charged and polar solutes.

Analytical solution of spontaneous polarization based on a Landau-Devonshire eight-order potential

The analytical solutions of spontaneous polarization, phase transition temperature TC, and ferroelectric limit temperature Th have been solved based on the Landau-Devonshire eight-order potential. According to the analytical solutions, the eighth-order potential gives a more reasonable and thinner superheating zone (Th-TC). The analytical solutions can be applied to deduce other analytical solutions of the functional properties directly, e. g., dielectric susceptibility and pyroelectric coefficient. It can also be used to evaluate different Landau-Devonshire potentials as demonstrated for BaTiO3.

Formation of Enantiomerically Pure Luminescent Triple-Stranded Dimetallic Europium Helicates and Their Corresponding Hierarchical Self-Assembly Formation in Protic Polar Solutions.

Ditopic helicate ligands 1 and 2 were synthesized for the formation of dinuclear EuIII luminescent chiral helical assemblies (Eu2·L3) in competitive organic and protic solvent media. Spectroscopic analysis revealed formation of the 2:3 (Eu2·L3) and 2:2 (Eu2·L2) species in methanolic solutions. Circular dichroism and circularly polarized luminescence (CPL) spectroscopy confirmed the chiral purity of the helical systems, while scanning electron microscopy imaging demonstrated the formation of hierarchical self-assemblies with spherical morphologies.

Spectroscopic and quantum-chemical study of molecular interactions of iso-quinolinium ylids in polar solutions

Three iso-quinolinium ylids are studied by visible electron absorption spectroscopy from the point of view of their interactions with solvent molecules. The quantum mechanical calculations with Spartan 14 Program and solvatochromism of the intramolecular charge transfer visible absorption band of the studied molecules emphasized the prevalence of universal orientation-induction interactions in aprotic solvents and additionally the presence of hydrogen bond between the ylid molecules and the hydroxyl groups of the solvent molecules. The contribution of each type of interactions in the studied solutions is finally established by a multilinear regression applied to solvatochromic data.

Amplified luminescence quenching effect upon binding of nitrogen doped carbon nanodots to transition metal ions.

There is a significant drive to identify a unified emission mechanism hidden behind carbon nanodots (CDs) to attain reliable control over their photoluminescence properties. This issue is addressed here by investigating the fluorescence response of citric acid and urea-based nitrogen doped carbon nanodots (NCDs) towards transition metal ions in solutions of different polarities/viscosities/hydrogen bonding strengths. The photoluminescence from NCDs upon excitation at 400 nm is quenched by metal ions such as chromium(vi), ruthenium(iii) and iron(iii) in two different polar solvents, protic water and aprotic dimethylsulphoxide (DMSO). This amplified luminescence quenching in polar solutions showed significant static quenching contributions. The quenching phenomenon highly depends on the excitation wavelength and solvent environment. The fluorescence quenching sequence reveals that pyridinic nitrogen-bases have a dominant influence on J-like emissive aggregates of NCDs. Similarly, oxygen-containing functional groups play a significant role in constructing H-aggregates of NCDs. The most intense emission is contributed by the J-like assembly of H-aggregates.

Systematically Improving Espresso: Insights from Mathematical Modeling and Experiment

Summary Espresso is a beverage brewed using hot, high-pressure water forced through a bed of roasted coffee. Despite being one of the most widely consumed coffee formats, it is also the most susceptible to variation. We report a novel model, complimented by experiment, that is able to isolate the contributions of several brewing variables, thereby disentangling some of the sources of variation in espresso extraction. Under the key assumption of homogeneous flow through the coffee bed, a monotonic decrease in extraction yield with increasingly coarse grind settings is predicted. However, experimental measurements show a peak in the extraction yield versus grind setting relationship, with lower extraction yields at both very coarse and fine settings. This result strongly suggests that inhomogeneous flow is operative at fine grind settings, resulting in poor reproducibility and wasted raw material. With instruction from our model, we outline a procedure to eliminate these shortcomings.

Double-layer packed bed used for heating non-polar liquid under microwave irradiation

There are some reports showing that microwave heating has a positive effect on the non-polar reaction liquid with polar solute. For the continuous-flow microwave heating of non-polar reaction liquid, the methods such as the addition of a high-loss dielectric material are generally used, but there is a problem that the temperature of the fluid will continue to rise, which cannot be maintained within a stable range. In this paper, a novel double-layer packed bed is designed in order to solve the above problem. The double-layer packed bed is divided into a heating layer and a thermostatic layer: the packing of heating layer is composed of the high-loss dielectric material; the packing of thermostatic layer is composed of a mixture of the high-loss and low-loss dielectric material in a certain proportion. Both the experimental and simulation results verified that the non-polar liquid temperature can rapidly rise to the preheating temperature in the heating layer and remain stable in the thermostatic layer while passing through the double-layer packed bed under microwave irradiation. The practicality of the double-layer packed bed was exemplified in the continuous synthesis of geranyl butyrate that proceeded more rapidly under microwave irradiation than conventional heating.

Buried Liquid Interfaces as a Form of Chemistry in Confinement: The Case of 4-Dimethylaminobenzonitrile at the Silica-Aqueous Interface.

Time-resolved fluorescence emission and resonance-enhanced second harmonic generation (SHG) spectra were collected from 4-dimethylaminobenzonitrile (DMABN) adsorbed to the aqueous-silica interface in order to identify how strongly associating solvent-substrate interactions change DMABN's photoisomerization properties. In bulk polar solution, DMABN forms an excited twisted intramolecular charge-transfer (TICT) state that emits with a distinctive, solvatochromic fluorescent signature. At the silica-aqueous interface, the TICT fluorescence disappears, similar to DMABN's behavior in nonpolar environments. SHG spectra confirm that the interface is, in fact, polar, and DMABN's unusual fluorescence emission acquired from the interface is attributed to strong hydrogen bonding associations between the water molecules and the silica surface that prevent adsorbate isomerization. Additionally, SHG spectra show a strong resonance at long wavelengths that is unexpected based on bulk absorbance spectra and selection rules for nonlinear hyperpolarizabilities. Using both Zerner's INDO semiempirical and TD-DFT calculations, this spectroscopic behavior is attributed to a combination of strong electric fields present at the aqueous-silica interface and surface-induced changes to DMABN's ground-state molecular structure.

Polar molecule filtration using charged cellulose nanofiber membrane on the nanoporous alumina support for high rejection efficiency

In this study, we propose a charged cellulose nanofiber membrane on nanoporous alumina support (c-CNFNA), which consists of eco-friendly materials for polar molecule filtration. The CNFs were extracted from the cell walls of a tree and oxidized by TEMPO ((2,2,6,6-Tetramethylpiperidin-1-yl)oxyl) to exhibit a negative charge on its surface. The nanoporous alumina support (NAS) with high aspect ratio was fabricated by anodic aluminum oxidation process and chemical wet etching process. The charged CNFs were coated on the NAS surface for fabrication of c-CNFNA, and negatively-charged polar molecules would be rejected by the equivalent charge of c-CNFNA. To investigate the polar molecule rejection performance of c-CNFNA, a polar molecule solution was injected into the surface of c-CNFNA. Rejection efficiency was calculated by measuring the concentration of the output solution, and hydraulic resistance was calculated from the pressure loss and flow rate. The results show that the rejection efficiency of c-CNFNA is 88–99% in the first rejection. In the second rejection, for almost all cases, approximately 100% rejection efficiency was achieved.

A green chemistry approach for facile synthesis of functionalized boron nitride nanosheets

The lack of a high-yield, renewable and low-cost synthesis method limits the potential applications of boron nitride with impressive characterizations. In this study, a facile method is developed for the preparation of chemically functionalized boron nitride nanosheets (BNNSs) by considering the quantity and quality of chemical materials involved in the synthesis process. The proposed green method is a suitable and high-efficiency method for replacing other production methods of BNNSs. Ultrathin BNNSs is produced by chemical reactions and subsequent liquid exfoliation. The possibility of chemical reaction is the highest at the defect sites especially at the upper/lower surfaces as well as the edge of bulk material. Due to hydroxyl functional groups that are coupled to the surface during the synthesis, the obtained products can well be dispersed in polar solutions such as water, ethanol, acetone and isopropyl alcohol. AFM, TEM, and SEM techniques are utilized to confirm the quality of the used method and illustrated that the produced-BNNSs have minimum thicknesses in the range of 1–5.6 nm and with lateral sizes ranging from 0.8–2.5 μm. The existence of functional groups and the structure of the BNNSs are verified by FTIR, EDX, XPS, XRD and Raman analyses. It was seen that the hexagonal structure was retained during the functionalization procedure. One can expect that the functionalization and sonication process introduces functional groups onto the surface of BNNSs. By this method, the obtained yield of BN dispersion is improved up to 17-20%.

New anticandidal Cu(i) complexes with neocuproine and ketoconazole derived diphenyl(aminomethyl)phosphane: luminescence properties for detection in fungal cells.

The search for new antifungals is very important because the large genetic variation of pathogenic organisms has resulted in the development of increasingly effective defense mechanisms by microorganisms. Metal complexes as potential drugs are nowadays gaining interest, because they are characterized by accessible redox states of metal centers and a plethora of easily modifiable geometries. In this work we present two new copper(i) iodide or thiocyanide complexes with 2,9-dimethyl-1,10-phenanthroline (dmp) and a diphenylphosphane derivative of ketoconazole (KeP), where a ketoconazole acetyl group is replaced by the -CH2PPh2 unit, [CuI(dmp)KeP] (1-KeP) and [CuNCS(dmp)KeP] (2-KeP) - their synthesis and structural characteristics. The analysis of the intrinsic fluorescence of the ketoconazole moiety in the coordinated KeP molecule revealed that the copper(i) central atom does not act as a quencher and the observed decrease of fluorescence intensity is a result of a strong inner filter effect caused by the presence of the CuXdmp unit. Moreover, the complexes exhibit a remarkable MLCT (metal-ligand charge transfer) based phosphorescence with the emission maximum at 600-615 nm in aqueous media, which probably results from the formation of dimers and higher order oligomers in the most polar solutions. Both complexes proved to be promising antifungal agents towards Candida albicans, showing a relatively high efficiency towards the fluconazole resistant strains with -CDR1 and CDR2 or MDR1 efflux pump overexpression, which suggests that they overcome at least partially these defense mechanisms. Simulations of docking to the cytochrome P450 14α-demethylase (the azoles' primary molecular target) suggested that the compounds studied were rather incapable of competitively inhibiting this enzyme, unlike ketoconazole and the KeP ligand. On the other hand, the phosphorescence in aqueous solutions allowed recording the confocal micrographs of the complexes which showed that both of them are situated in spherical structures inside the cells, most likely in the vacuoles.

Swelling properties of graphite oxides and graphene oxide multilayered materials.

Graphite oxide (GtO) and graphene oxide (GO) multilayered laminates are hydrophilic materials easily intercalated by water and other polar solvents. By definition, an increase in the volume of a material connected to the uptake of a liquid or vapour is named swelling. Swelling is a property which defines graphite oxides and graphene oxides. Less oxidized materials not capable of swelling should be named oxidized graphene. The infinite swelling of graphite oxide yields graphene oxide in aqueous dispersions. Graphene oxide sheets dispersed in a polar solvent can be re-assembled into multilayered structures and named depending on applications as films, papers or membranes. The multilayered GO materials exhibit swelling properties which are mostly similar to those of graphite oxides but not identical and in some cases surprisingly different. Swelling is a key property of GO materials in all applications which involve the sorption of water/solvents from vapours, immersion of GO into liquid water/solvents and solution based chemical reactions. These applications include sensors, sorption/removal of pollutants from waste waters, separation of liquid and gas mixtures, nanofiltration, water desalination, water-permeable protective coatings, etc. Swelling defines the distance between graphene oxide sheets in solution-immersed GO materials and the possibility for penetration of ions and molecules inside of interlayers. A high sorption capacity of GO towards many molecules and cations is defined by swelling which makes the very high surface area of GO accessible. GtO and GO swelling is a surprisingly complex phenomenon which is manifested in a variety of different ways. Swelling is strongly different for materials produced using the most common Brodie and Hummers oxidation procedures; it depends on the degree of oxidation, ad temperature and pressure conditions. The value of the GO interlayer distance is especially important in membrane applications. Diffusion of solvent molecules and ions is defined by the size of "permeation channels" provided by the swelled GO structure. According to extensive studies performed over the last decade the exact value of the inter-layer distance in swelled GO depends on the nature of solvent, temperature and pressure conditions, and the pH and concentration of solutions and exhibits pronounced aging effects. This review provides insight into the fundamental swelling properties of multilayered GO and demonstrates links to advanced applications of these materials.

Functional group interaction profiles: a general treatment of solvent effects on non-covalent interactions.

Solvation has profound effects on the behaviour of supramolecular systems, but the effects can be difficult to predict even at a qualitative level. Functional group interaction profiles (FGIPs) provide a simple visual method for understanding how solvent affects the free energy contribution due to a single point interaction, such as a hydrogen bond, between two solute functional groups. A generalised theoretical approach has been developed, which allows calculation of FGIPs for any solvent or solvent mixture, and FGIPs for 300 different solvents have been produced, providing a comprehensive description of solvent effects on non-covalent chemistry. The free energy calculations have been validated using experimental measurements of association constants for hydrogen bonded complexes in multiple solvent mixtures. The calculated FGIPs provide good descriptions of the solvation of polar solutes, solvophobic interactions between non-polar solutes in polar solvents like water, and preferential solvation in solvent mixtures. Applications are explored of the use of FGIPs in drug design, for optimising receptor-ligand interactions, and in enantioselective catalysis for solvent selection to optimise selectivity.

Cultivation at high osmotic pressure confers ubiquinone 8–independent protection of respiration on Escherichia coli

Cultivation at high osmotic pressure confers ubiquinone 8–independent protection of respiration on Escherichia coli