Nonpolar Sites Research Articles

Utilization of the mixture of ethylene tar and different petrochemical by-products as collectors for coal flotation

ABSTRACT The ethylene tar and mixtures of ethylene tar with other petrochemical by-products were used as collectors for coal flotation. The results showed that the 1# compound collector was better than kerosene in terms of selectivity and collectibility for coal flotation. When the collector dosage was 1500 g/t, the yield of clean coal using the 1# compound collector increased by 4.05%, and the reduction in ash content was 0.36% lower compared to using kerosene. The mechanism of action of 1# compound collector on the coal surface was analyzed in combination with GC-MS tests and FTIR tests. The 1# compound collector contains more aromatics, olefins and heteropolar substances than kerosene. When the aromatics in the 1# compound collector interact with the nonpolar sites on the coal surface via π–π stacking interactions, some of the polar sites sandwiched between the aromatic compound molecules are covered. The olefins contained therein engage with the nonpolar sites on the surface experiences interactions attributable to van der Waals forces. The oxygenated functional groups of alcohols, acids, esters and carbonyl compounds engage with the polar sites on the surface of the particles through hydrogen bonding.

Leveraging synergistic polar and nonpolar binding sites in a fluorinated metal–organic framework for efficient ethane/ethylene separation

Constructing favorable C2H6-selective adsorbents for one-step C2H4 purification from C2H6/C2H4 mixtures is a matter of considerable significance, but is still a very challenging task in the field of petrochemical industry. Herein, we report a well-designed ant-type metal–organic framework (NUM-16) with appropriate pore size and pore environment for preferential trapping C2H6. NUM-16a (activated NUM-16) performs a high C2H6 uptake of 4.39 mmol/g and a good adsorption selectivity for C2H6/C2H4 (10:90, v/v) mixture at 298 K and 1 bar. The separation mechanism, as unveiled by the grand canonical Monte Carlo simulations and density functional theory calculations, is mainly attributed to synergistic polar and nonpolar binding sites on the pore surface of NUM-16a, which provide stronger affinities to C2H6 than C2H4. Under ambient conditions, dynamic breakthrough experiments revealed that NUM-16a demonstrates the enormous potential for actual C2H6/C2H4 separation and is expected to be applied to the correlative industrial process. Both experiments and theoretical calculations distinctly demonstrated that the reasonable integration of polar and nonpolar binding sites in C2H6-preferred MOFs is a feasible strategy for efficient C2H6/C2H4 separation. This work afforded some useful insights into designing and developing high-powered MOF adsorbents to solve tricky industrial separation challenges.

Porous Supramolecular Crystalline Probe that Detects Non-Covalent Interactions Involved in Molecular Recognition of Furanic Compounds.

Selective separation and conversion of furan-based biomass-derived compounds, which are closely related to biorefineries, is currently an important issue. To improve their performance, it is important to deepen the understanding of non-covalent interactions that act on the molecular recognition of furanic compounds on separation or catalyst matrices. Here, a new method is reported to comprehensively visualize such intermolecular interactions using a porous supramolecular crystalline probe with polar and non-polar binding sites within a low-symmetric nanochannel consisting of four isomeric PdII 3-macrocycles. Single-crystal X-ray diffraction analysis of the crystals including 5-hydroxymethylfurfural, furfural, furfuryl alcohol, or 2-acetylfuran reveals a variety of interactions involving their furan rings and polar substituents. It is also found that cooperative and competitive effects between guest and solvent molecules significantly change their recognition mode.

Preparation and investigation of the structural and mechanical properties of biodegradable gelatin- based films

Biodegradable gelatin-based films have been obtained in the presence of carboxymethylcellulose (CMC) additives intended for use as packaging of food products and drug carriers. By methods of scanning electron microscopy and measurement of film roughness, it was found that films obtained from a mixture of CMC and gelatin have the greatest roughness. It is shown that the introduction of CMC into the composition of gelatin films leads to a sharp decrease in the strength and modulus of elasticity of the films, however, the deformation has maximum values at a mass ratio of CMC / gelatin equal to 0.7. This is explained by the formation of associates due to H-bonds and electrostatic interactions between functional groups of gelatin proteins and polysaccharide macromolecules, stabilized by hydrophobic interactions between their nonpolar sites. The barrier properties of films based on CMC and gelatin have been studied. It is shown that CMC-based films have the highest air permeability and the lowest water resistance, which is due to the texture of the film material. Based on IR spectroscopy data, it was found that films obtained from a mixture of CMC and gelatin are the most stable. Glycerin was used to regulate the deformation of the films.

Decoding wettability in coal-water-CO2 system for enhanced sequestration security

The injection of CO2 into deep unminable coal seam is a most promising carbon storage method that can simultaneously achieve the dual objectives of mitigating CO2 emission and enhancing coalbed methane recovery. In this context, the wettability of the coal-water-CO2 system plays an important role in the CO2 injection rate, storage capacity, and sequestration security. However, the factors affecting wettability alternation in the coal-water-CO2 system are still unclear until now. In this study, the sessile drop method was used to measure the contact angle (CA) in the coal-water-CO2 system under different pressures (3 – 8 MPa) and temperatures of (40–70 °C) with four different rank coals. Results indicate that with increasing pressure, the CA shows a steady increase below 5 MPa followed by a rapid increase at 5 – 8 MPa. The CA decreases with increasing temperature and coal rank. The CA is negatively correlated with the mes- and macro-pores, but positively correlated with micropores. It was found that these relationships are attributed to the CO2 density and CO2 adsorption capacity of coal. As the CO2 density increases, the coal-CO2 interaction force intensifies, leading to a tendency towards CO2 wetting for the coal-water-CO2 system. The adsorption capacity illustrates the strength of the coal-CO2 interaction, where the affinity of polar adsorption sites for CO2 molecules exceeds that of nonpolar adsorption sites. Finally, we conducted a comprehensive assessment of the wettability of the coal-water-CO2 system as it varies with burial depth by developing an integrated model that considers four influential factors, including pressure, temperature, coal rank, and pore structure. The findings of this study can be utilized to determine the optimal CO2 injection pressure in CO2-ECBM projects and enhance sequestration safety.

Facile and efficient preparation of hemicellulose-assisted MoS2 nanosheets via green liquid-phase exfoliation method

A facile, environmental-friendly and efficient exfoliation process has been reported to produce MoS2 nanosheets at room temperature via liquid-phase exfoliation method using hemicellulose as an assistant in aqueous solution. It is found that bulk MoS2 has been successfully exfoliated into few-layered MoS2 nanosheets. The non-polar sites of hemicellulose can firmly adhere to MoS2 surface, whereas the hydrophilic branches can facilitate the dispersion, resulting in the effective exfoliation in aqueous solution. The exfoliated dispersions of MoS2 nanosheets are homogeneous and highly stable over 7 months, even stored at ambient conditions. The optical properties of exfoliated MoS2 nanosheets were investigated by UV–Vis, and the morphological characterizations were examined by SEM, TEM, AFM, XRD and Raman. The results show that the hemicellulose-assisted MoS2 nanosheets produced by 10 mg/ml initial concentration have approximately 8–9 layers. Also, the surface-enhanced Raman scattering (SERS) capability of as-prepared MoS2 nanosheets is observable with the enhancement factor (EF) of about 4 × 104, indicating that the hot-spots can be generated on nanosheets. It demonstrates a plausible application of exfoliated MoS2 nanosheets as a SERS substrate as well as a great potential for other solution-based device fabrication. This present liquid-phase exfoliation method is a green, simple and effective process for mass production of MoS2 nanosheets.

An atomic surface site interaction point description of non-covalent interactions.

Molecular electrostatic potential surfaces (MEPS) calculated using density functional theory have been used to develop a simplified description of the non-covalent interaction properties of organic molecules. The Atomic Interaction Point (AIP) model introduced here represents an evolution of the Surface Site Interaction Point (SSIP) model described previously, in which a molecule is represented by a discrete set of interaction points that define sites of interaction with other molecules. The interaction sites are described by interaction parameters that are equivalent to the experimentally determined H-bond donor and acceptor parameters α and β. By using high electron density MEPS that lie inside the van der Waals surface, it is possible to obtain accurate interaction parameters and locations for polar sites (s-holes, H-bond donors and acceptors), which are identified as local maxima and minima on the MEPS. For non-polar sites that represent π-systems and halogens, an approach based on molecular orbitals was used to assign the locations of the AIPs, and the interaction parameters were obtained using a lower electron density MEPS that lies close to the van der Waals surface. The AIP descriptions can be implemented directly in the Surface Site Interaction Point Model for Liquids at Equilibrium (SSIMPLE) to calculate solvation free energies, and the free energy of transfer of 1504 compounds from n-hexadecane to water was predicted with a root mean square error of 5 kJ mol-1. AIPs also provide a useful tool for mapping non-covalent interactions in intermolecular complexes, and examples are provided showing how X-ray crystal structures can be converted into AIP interaction maps that allow quantification of the free energy contributions of both polar and non-polar interactions to the stabilities of complexes in solution.

Control of the flagellation pattern in Helicobacter pylori by FlhF and FlhG.

FlhF and FlhG control the location and number of flagella, respectively, in many polar-flagellated bacteria. The roles of FlhF and FlhG are not well characterized in bacteria that have multiple polar flagella, such as Helicobacter pylori. Deleting flhG in H. pylori shifted the flagellation pattern where most cells had approximately four flagella to a wider and more even distribution in flagellar number. As reported in other bacteria, deleting flhF in H. pylori resulted in reduced motility, hypoflagellation, and the improper localization of flagella to nonpolar sites. Motile variants of H. pylori ∆flhF mutants that had a higher proportion of flagella localizing correctly to the cell pole were isolated, but we were unable to identify the genetic determinants responsible for the increased localization of flagella to the cell pole. One motile variant though produced more flagella than the ΔflhF parental strain, which apparently resulted from a missense mutation in fliF (encodes the MS ring protein), which changed Asn-255 to aspartate. Recombinant FliFN255D, but not recombinant wild-type FliF, formed ordered ring-like assemblies in vitro that were ~50 nm wide and displayed the MS ring architecture. We infer from these findings that the FliFN225D variant forms the MS ring more effectively in vivo in the absence of FlhF than wild-type FliF. IMPORTANCE Helicobacter pylori colonizes the human stomach where it can cause a variety of diseases, including peptic ulcer disease and gastric cancer. H. pylori uses flagella for motility, which is required for host colonization. FlhG and FlhF control the flagellation patterns in many bacteria. We found that in H. pylori, FlhG ensures that cells have approximately equal number of flagella and FlhF is needed for flagellum assembly and localization. FlhF is proposed to facilitate the assembly of FliF into the MS ring, which is one of the earliest structures formed in flagellum assembly. We identified a FliF variant that assembles the MS ring in the absence of FlhF, which supports the proposed role of FlhF in facilitating MS ring assembly.

Indistinguishable telecom band photons from a single Er ion in the solid state.

Atomic defects in the solid state are a key component of quantum repeater networks for long-distance quantum communication1. Recently, there has been significant interest in rare earth ions2-4, in particular Er3+ for its telecom band optical transition5-7 that allows long-distance transmission in optical fibres. However, the development of repeater nodes based on rare earth ions has been hampered by optical spectral diffusion, precluding indistinguishable single-photon generation. Here, we implant Er3+ into CaWO4, a material that combines a non-polar site symmetry, low decoherence from nuclear spins8 and is free of background rare earth ions, to realize significantly reduced optical spectral diffusion. For shallow implanted ions coupled to nanophotonic cavities with large Purcell factor, we observe single-scan optical linewidths of 150 kHz and long-term spectral diffusion of 63 kHz, both close to the Purcell-enhanced radiative linewidth of 21 kHz. This enables the observation of Hong-Ou-Mandel interference9 between successively emitted photons with a visibility of V = 80(4)%, measured after a 36 km delay line. We also observe spin relaxation times T1,s = 3.7 s and T2,s > 200 μs, with the latter limited by paramagnetic impurities in the crystal instead of nuclear spins. This represents a notable step towards the construction of telecom band quantum repeater networks with single Er3+ ions.

Diphenylsulfoxide exhibits an outstanding solubility in Methanol: Physicochemical and quantum chemical evidences. Comparison to acetonitrile

Diphenylsulfoxide (Ph2SO) represents a noteworthy organic substance composed of bulky amphiphilic molecules. The chemical interest in Ph2SO arises from a peculiar combination of the strongly polar and strongly nonpolar moieties which are uniquely packed. The solubility of Ph2SO in conventional organic solvents is a cornerstone of its prospective applications. In the present work, the full concentration ranges of the possible homogeneous solutions of diphenylsulfoxide (Ph2SO) in acetonitrile (ACN) and methanol (MEOH) have been investigated by densitometry, UV–vis, FTIR spectroscopy, and quantum-chemical calculations. For the first time, we unraveled an outstanding solubility of Ph2SO in MEOH. The homogeneous solutions form up to the molality of 0.9 mol kg−1. This observation is unexpected from the conventional chemical wisdom because Ph2SO contains twenty-two non-polar interaction sites vs. two polar interaction sites. Based on the volumetric measurements, we revealed that the partial molar volumes of Ph2SO depend somewhat on solvent (MEOH, ACN) peculiarities. The effects of solvent on the spectral characteristics of diphenylsulfoxide have been considered. The numerical simulations based on the systematic potential landscape exploration corroborate the existence of several types of supramolecular species involving Ph2SO and solvent molecules simultaneously. The peculiar anisotropic Ph2SO-MEOH coupling, which is a strong hydrogen bonding, along with the small size of the solvent molecules is responsible for the recorded outstanding solubility in the methanol media. In turn, the performance of ACN is somewhat less encouraging notwithstanding the way higher dipole moment of its molecules. As an amphiphilic solute, Ph2SO may boost the solubilities of hydrophobic solutes by interfacing its coupling with polar media. The reported results inspire further explorations of Ph2SO to design task-specific liquid systems.

The Surface acidity of freshly synthesized microplastics particles in simple electrolyte

The surface chemistry of sub-micron microplastics (MP) particles, specifically, the pH-dependent surface charge (or surface acidity), plays a role on the transport, transformation, and effect of contaminants in the aquatic environment. Little is known on the origin of surface charge and the quantification of surface acidity of MP. In this study, the surface charge of submicron particles of six major polymers, including low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), and polyethylene terephthalate (PET), was characterized in inert electrolytes, namely, NaClO4, NaCl, and NaNO3 for the elucidation of surface acidity. IR absorbance revealed that oxygen-rich functional groups were introduced during the resynthesis of MP particles, whose surface chemical structure consists of three main functional groups, i.e., carboxylic/ester, ether/alcohol, and aliphatic. Results show clearly that the zeta potential of MP particles was negatively charged in simple electrolytes at pH greater than ca. 2.0. Hydroxide ions adsorption on the non-polar aliphatic sites, and deprotonation of surface hydroxy group on the polar carboxylic/ester and ether/alcohol sites, contributed to the negative charges on MP surface. The surface acidity of selected MP particles was established in terms of acid strength (intrinsic acidity constants) and capacity (total surface site concentration) for the three distinct surface sites. Results also show the surface acid site density increases with hydration/hydrolysis time with rate constants of the polar surface sites, i.e., carboxylic/ester and ether/alcohol being 2.3 times greater than that of the non-polar aliphatic group.

Using HPMC to improve sensory properties of vegan omelet analogue: Effect of HPMC on water retention, oil adsorption, and thermal gelation

There is a growing need throughout the world for vegan egg analogues in recent years. In this study, the impact of hydroxypropyl methylcellulose (HPMC) on the mouthfeel perception of the vegan omelets was evaluated. Additionally, the effects of HPMC on water retention, oil adsorption, thermal gelation, intermolecular interactions, microstructures, and in vitro digestion of the vegan eggs were investigated. The formulation with 1.5% HPMC (1.5HPMC) approached the sensory perception of egg omelet, in terms of fluffiness (6.8 vs. 7.4), softness (7.3 vs. 6.1), smoothness (5.8 vs. 6.8), crispiness (6.3 vs. 7.9), and silkiness (6.4 vs. 7.0). This could be attributed to the gelling and water holding capacities of HPMC that hindered moisture diffusion within the omelet matrix. Moreover, HPMC could induce the increasing exposure of non-polar sites, thereby improving oil adsorption as well as oil-related sensory attributes. On the other hand, the added HPMC may wrap the protein, starch, and oil components through the hydrogen bonding and/or hydrophobic interactions and compete with them for free water. This would affect the thermal gelation process and textural profiles of the vegan eggs. The matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS)- and nuclear magnetic resonance (NMR) spectroscopy-based metabolomic analyses verified the above findings. It was reported that the 1.5HPMC omelet released less amino acid, fatty acid, and saccharide metabolites than the non-HPMC-modified omelet after in vitro digestion. Through understanding the mechanisms on how HPMC improved the mouthfeel sensation of vegan omelets, this study advises more conceivable roles of HPMC in novel food development.

Molecular insights into dissolution of lignin bunch in ionic liquid-water mixture for enhanced biomass conversion

Globally, the shift towards lignocellulosic biorefinery has opened avenues for valorizing lignin, a majorly accumulated recalcitrant by-product. A targeted lignin processing by ionic liquid-cosolvent mixtures can be an effective biomass conversion strategy. An understanding of lignin-ionic liquid dissolution can enable in designing a significant lignin processing technique to synthesis lignin-based renewable products. Here, we explored the molecular interaction during the dissolution of lignin containing five guaiacyl decamer chains in various (1-Ethyl-3-Methylimidazolium Acetate) EmimOAc-water mixtures using molecular dynamics simulation. The analysis showed that in only water, lignin formed a compact aggregate. Nevertheless, in 50%, 80%, and 100% EmimOAc-water, lignin underwent a segregated chain disentanglement with widespread dynamic motion. A detailed multifaceted analysis of Emim+, OAc− and water distribution on the polar and non-polar sites of lignin units was illustrated. An effective lignin dissolution was observed for 50% and 80% EmimOAc-water systems. The OAc− distribution was stronger around lignin's alkyl chains and alcoholic hydroxy groups. The Emim+ tails significantly impacted the benzene ring, whereas Emim+ heads were distributed around methoxy and hydroxy groups. Altogether, this study explores the lignin dissolution at atomistic level in EmimOAc-water mixtures; these understanding could serve as a cornerstone for engineering new ionic liquid-mediated lignin biorefinery.

Distribution and solvent exposure of Hsp70 chaperone binding sites across the Escherichia coli proteome.

Many proteins must interact with molecular chaperones to achieve their native state in the cell. Yet, how chaperone binding-site characteristics affect the folding process is poorly understood. The ubiquitous Hsp70 chaperone system prevents client-protein aggregation by holding unfolded conformations and by unfolding misfolded states. Hsp70 binding sites of client proteins comprise a nonpolar core surrounded by positively charged residues. However, a detailed analysis of Hsp70 binding sites on a proteome-wide scale is still lacking. Further, it is not known whether proteins undergo some degree of folding while chaperone bound. Here, we begin to address the above questions by identifying Hsp70 binding sites in 2258 Escherichia coli (E. coli) proteins. We find that most proteins bear at least one Hsp70 binding site and that the number of Hsp70 binding sites is directly proportional to protein size. Aggregation propensity upon release from the ribosome correlates with number of Hsp70 binding sites only in the case of large proteins. Interestingly, Hsp70 binding sites are more solvent-exposed than other nonpolar sites, in protein native states. Our findings show that the majority of E. coli proteins are systematically enabled to interact with Hsp70 even if this interaction only takes place during a fraction of the protein lifetime. In addition, our data suggest that some conformational sampling may take place within Hsp70-bound states, due to the solvent exposure of some chaperone binding sites in native proteins. In all, we propose that Hsp70-chaperone-binding traits have evolved to favor Hsp70-assisted protein folding devoid of aggregation.

Bifunctional Ionic Deep Eutectic Electrolytes for CO2 Electroreduction.

CO2 is a low-cost monomer capable of promoting industrially scalable carboxylation reactions. Sustainable activation of CO2 through electroreduction process (ECO2R) can be achieved in stable electrolyte media. This study synthesized and characterized novel diethyl ammonium chloride−diethanolamine bifunctional ionic deep eutectic electrolyte (DEACl–DEA), using diethanolamine (DEA) as hydrogen bond donors (HBD) and diethyl ammonium chloride (DEACl) as hydrogen bond acceptors (HBA). The DEACl–DEA has −69.78 °C deep eutectic point and cathodic electrochemical stability limit of −1.7 V versus Ag/AgCl. In the DEACl–DEA (1:3) electrolyte, electroreduction of CO2 to CO2•– was achieved at −1.5 V versus Ag/AgCl, recording a faradaic efficiency (FE) of 94%. After 350 s of continuous CO2 sparging, an asymptotic current response is reached, and DEACl–DEA (1:3) has an ambient CO2 capture capacity of 52.71 mol/L. However, DEACl–DEA has a low faradaic efficiency <94% and behaves like a regular amine during the CO2 electroreduction process when mole ratios of HBA–HBD are greater than 1:3. The electrochemical impedance spectroscopy (EIS) and COSMO-RS analyses confirmed that the bifunctional CO2 sorption by the DEACl–DEA (1:3) electrolyte promote the ECO2R process. According to the EIS, high CO2 coverage on the DEACl–DEA/Ag-electrode surface induces an electrochemical double layer capacitance (EDCL) of 3.15 × 10–9 F, which is lower than the 8.76 × 10–9 F for the ordinary DEACl–DEA/Ag-electrode. COSMO-RS analysis shows that the decrease in EDCL arises due to the interaction of CO2 non-polar sites (0.314, 0.097, and 0.779 e/nm2) with that of DEACl (0.013, 0.567 e/nm2) and DEA (0.115, 0.396 e/nm2). These results establish for the first time that a higher cathodic limit beyond the typical CO2 reduction potential is a criterion for using any deep eutectic electrolytes for sustainable CO2 electroreduction process.

Peculiarities of adsorption of Cr (VI) ions on the surface of Chlorella vulgaris ZBS1 algae cells

Cr (VI) compounds are the most dangerous for human health and the environment, therefore, the study of their adsorption features is of great interest. A comprehensive study of the adsorption of Cr (VI) ions on the surface of Chlorella vulgaris ZBS1 algae cells was carried out evaluating the effect of the pH of the medium on the degree of removal of Cr (VI) ions from solutions and on the zeta potential of the cell surface was. The highest values of the degree of removal of Cr (VI) ions equal to 94.6–95.4% are achieved in the pH range of 1–2, being the result of the electrostatic attraction of HCrO4− groups to protonated amino groups of the cell surface and the possibility of reducing Cr (VI) ions to Cr (III) in an acidic medium, followed by the formation of Cr (III) ions of coordination bonds with amine and carboxyl groups of algae cells.The adsorption data were processed within the framework of Langmuir, Freundlich, Dubinin-Radushkevich and Temkin models. It was shown that the maximum Langmuir adsorption value was 74.63 mg/g. The values of the adsorption parameters 1/n and Kf in the Freundlich model were equal to 0.713 and 2.82 mg/g. In the Dubinin-Radushkevich model, the maximum adsorption capacity (qm) and free energy (E) were equal to 39.73 mg/g and 2.604 kJ/mol, respectively. Whereas, according to the Temkin model, the constant A was equal to 18.215 L/mg, and bT was equal to 0.023 kJ/mol. Taking into account the low values of free energy, it is concluded that adsorption is caused by non-covalent interactions.The study of adsorption kinetics showed that the adsorption of Cr (VI) ions on the surface of Chlorella vulgaris ZBS1 algae cells is described in the framework of the pseudo-second order model. The kinetic behavior of the process is discussed in the framework of the IPDM and ELM models. With increasing temperature, the constant of intraparticle diffusion of Cr (VI) ions decreases, which is explained with increasing of hydrophobic interactions between nonpolar sites of protein macromolecules and polysaccharides in the composition of algae cells. The increase in the adsorption of Cr (VI) ions at pH 8.62 in the temperature range of 298–353 K is justified by the shrinkage of the biosorbent volume, which leads to the blocking of a part of the anionic groups on the surface of algae cells. Therefore, the decrease in the electrostatic repulsion between the negatively charged surface of the adsorbent and Cr (VI) oxyanions is observed.

Effects of catanionic surfactant mixture adsorption on the wettability of PTFE and PMMA

Surfactants can regulate the wettability of a liquid on a solid substrate as they adsorb to solid-liquid and gas-liquid interfaces. In the present work, a catanionic surfactant mixture, sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (C12TAB) mixed at a molar ratio of 2:1, showed outstanding synergistic effect in improving the wettability of low energy substrates (PTFE and PMMA). The adsorption behaviors of the catanionic surfactant mixture on PTFE and PMMA substrates were studied. The surface tensions and contact angles of aqueous solutions of SDS, C12TAB, and their mixture on PTFE and PMMA were measured, and the adhesion tension and adhesion work were calculated. Compared to individual SDS and C12TAB, the SDS-C12TAB mixture formed a compactly arranged layer at the PTFE-aqueous interface, thereby leading to a more significant hydrophilic modification of PTFE. In the PMMA system, the SDS-C12TAB mixture adsorbed to the PMMA-aqueous interface through acid-base interactions between the positively charged surfactant headgroups and the basic groups at PMMA surface and increased the hydrophobicity of the PMMA substrate at low surfactant concentrations. When the surfactant concentration exceeded the critical micelle concentration (CMC), the surfactant started to adsorb to the PMMA-aqueous interface through hydrophobic interactions between the hydrophobic surfactant tails and the nonpolar sites at PMMA surface, which further improved the wettability of PMMA. Overall, the wettability of low energy substrates can be significantly improved under the strong synergistic effect of commercial anionic and cationic surfactants without need of complex synthesis of new amphiphiles. Therefore, the catanionic surfactant mixtures may be a very promising system for regulating wettability.

Study of Interaction of Glycerol Cryoprotectant and Its Derivatives with Dimethylacetamide in Aqueous Solution Using Fluorescent Probes

In this paper we have studied the interaction of the mixtures of glycerol (GL) and its oxyethylated derivatives (OEG) with polymerization degree n = 3, 25 and 30 with dimethylacetamide (DMAc) in aqueous solution using 3-hydroxy-4´-(N, N dimethylaminoflavone) fluorescent probe. The combination of GL and its oxyethylated derivatives with DMAc was found to reduce the membranotropy of certain cryoprotective agents, forming a mixture. The combination of both GL and its low molecular weight derivative (OEGn=3) with DMAc reduced the membranotropy of the latter. At the same time, combining GL derivatives of high molecular weight (OEGn=25 and OEGn=30) with DMAc diminished the membranotropy of OEG. The OEGn=30 at concentrations above 1 wt.% was shown to form the micellar-type structures or micellar associates in aqueous solution. This enabled suggesting the membranotropic ability of high molecular weight OEG associates to be stipulated by possible interaction of their nonpolar segments with nonpolar sites on biomembrane surface. Structural rearrangements of molecular associates in aqueous solutions of low and high molecular weight cryoprotectant mixtures were designated as the experimentally established mechanism of cytotoxicity reduction in combined cryoprotective media.

Dual Binding Modes of a Small Cavitand

ABSTRACT The small size and high cohesiveness of water means that water-mediated interactions are strongly context dependent.As a result, there is still much to learn about how non-polar solutes and ions interact with themselves or each other.To help address this issue, we report here on a cavitand host, TMAX-Cl (2). Possessing two different binding sites, a shallow non-polar dish that binds hydrophobes, and a crown of ammoniums that bind anions, TMAX-Cl (2) provides insight into the hydrophobic and Hofmeister effects.We find that binding to the non-polar site is weak, suggesting that a larger surface area is needed for substantial binding.In contrast, binding to the crown of ammoniums is relatively strong, despite the high dielectric of water.These findings provide a better understanding of water-mediated interactions, and define the supramolecular properties of TMAX-Cl 2 as we continue our studies of this host and related water-soluble cavitands.

Zinc protoporphyrin-trimethylamine-N-oxide complex involves cholesterol oxidation causing atherosclerosis.

Metabolism of food protein by gut microbes produce trimethylamine which on oxidation by hepatic flavin-containing monooxygenases is transformed to trimethylamine-N-oxide (TMAO). TMAO has recently been implicated as a biomarker for atherosclerosis. TMAO, as (CH3)3N+-O-), is ionic and so a hydrophilic molecule that is freely available in blood plasma. For the effective interaction with lipid-soluble molecules, TMAO should be phase transferred to the lipid site. We show that the free TMAO is effectively bonded to zinc protoporphyrin IX dimethyl ester [ZnPPDME] to yield [TMAOZnPPDME] using phase transfer reaction. The zinc protoporphyrin IX, [ZnPP], in general, available in blood may form [TMAOZnPP] complex. The nature of such interaction between TMAO and [ZnPP] has been structurally shown using a model complex, [TMAOZnTPP] (TPP = tetraphenylporphyrin). These complexes readily move from the polar plasma to the non-polar (lipid) site to act as the oxo-transfer agent to oxidize cholesterol causing atherosclerosis. Chromatographic and circular dichroism (CD) studies show that either TMAO or [ZnPP] alone cannot oxidize cholesterol. Free TMAO bonded with zinc-protoporphyrin IX, [ZnPP], in blood plasma as [TMAOZnPP] is transported to the lipid site and this is the reacting species to oxidize cholesterol causing atherosclerosis.