Non-polar Probes Research Articles

Characterization of biosurfactants’ micelles formation using fluorescence measurements: sodium taurocholate as case of study

Background and purpose: The evaluation of micellization parameters of surfactants that aggregate gradually, such as bile salts, is not trivial. In this work, different probes and data treatment models are tested to set up an analytical method based on fluorescence measurements to determine the critical micelle concentration (CMC) and micellization range (DC) of biosurfactants. Sodium taurocholate (NaTc) is used as example. Experimental approach: The fluorescence intensity of five fluorophores has been monitored upon the addition of a concentrated NaTc solution in two different media: water and a biorelevant buffer (maleic buffer pH 6.5, I = 120 mM). Four different data treatment methods have been tested. Key results; The micellization process can be evaluated satisfactorily using fluorescent probes such as propranolol and tetracaine, and also monitoring directly the intrinsic fluorescence of NaTc. However, the results obtained with nonpolar probes (pyrene and naphthalene) are more complex to evaluate due to the presence of confluent processes. Although the four models tested for the data treatment are commonly used for this purpose, Carpena’s method is the most appropriate as it provides the most accurate CMC and ΔC values. The micellization process is faster in a biorelevant buffer than in water. Conclusion: The study of the micellization of bile salts is not an evident process. After the selection of adequate probes and data treatment methods, the CMC values for NaTC in water and maleic buffer reveal that the biorelevant conditions favour micellization, which in turn may allow faster solubilization of ingested compounds.

An inverse gas chromatography study of the adsorption of organics on zeolite and zeolite/iron oxyhydroxide composite at the infinite and finite surface coverage

The surfaces of natural (NZ) and zeolite/iron oxyhydroxide composite (ZFe) samples were analysed by means of inverse gas chromatography (IGC) using the adsorption data of organic non-polar and polar probes, in the infinite and finite-dilution regimes, in the temperature range 483?513 K. The dispersive components of the free energy of adsorption, ?S, determined by the Gray method, decreased with increasing temperature for both zeolites. The specific interactions were characterised by the specific free adsorption energy change, ?Ga S, the specific enthalpy change of adsorption, ?Ha S, as well as the donor and acceptor interaction parameters (KA, KD) and the basic character of the NZ and ZFe was evidenced. The adsorption isotherms of n-hexane, benzene, chloroform and tetrahydrofuran (THF) were determined under finite surface coverage and used to estimate the specific surface area and the adsorption energy distribution. The adsorption capacity of the ZFe was higher than for NZ for all the investigated adsorbates. The specific surface areas and pore size distributions were also determined using nitrogen adsorption?desorption isotherms, i.e., the BET method. It was observed that the nature of the adsorbate and the properties of the solid surface of the initial and modified samples governed the uptake of adsorbates.

Surface Properties of Fluorine-Functionalized Metal-Organic Frameworks Based on Inverse Gas Chromatography.

The introduction of the concept of surface properties can help us to better analyze the basic physicochemical property changes of metal-organic framework (MOF) materials before and after fluorine functional group treatment. In this study, several polar and nonpolar probes were selected to determine the surface properties, including surface-dispersive free energy, Lewis acid-base constants of Ni-MOF-74, and perfluoro carboxylic acid-modified Ni-MOF-74-Fn (n = 3, 5, and 7) in the range of 343.15-383.15 K by inverse gas chromatography (IGC). It was observed that the surface energy of the treated Ni-MOF-74-Fn showed a substantial decrease with the growth of the perfluorocarbon alkyl chains and the increase in surface roughness. In addition, Lewis acidic sites exposed by the Ni-MOF-74 material after adopting modification with fluorine functional groups increased with the increase of perfluorinated carboxylic acid chains, and their surface properties changed from amphiphilic acidic to strongly acidic. These results not only enrich the basic physical property data of Ni-MOF-74 but also provide more theoretical basis for the fluorinated functionalized custom-designed MOFs and enrich their applications in the fields of multiphase catalysis, gas adsorption, and chromatographic separation.

Cosolvent and Dynamic Effects in Binding Pocket Search by Docking Simulations.

The lack of conformational sampling in virtual screening projects can lead to inefficient results because many of the potential drugs may not be able to bind to the target protein during the static docking simulations. Here, we performed ensemble docking for around 2000 United States Food and Drug Administration (FDA)-approved drugs with the RNA-dependent RNA polymerase (RdRp) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as a target. The representative protein structures were generated by clustering classical molecular dynamics trajectories, which were evolved using three solvent scenarios, namely, pure water, benzene/water and phenol/water mixtures. The introduction of dynamic effects in the theoretical model showed improvement in docking results in terms of the number of strong binders and binding sites in the protein. Some of the discovered pockets were found only for the cosolvent simulations, where the nonpolar probes induced local conformational changes in the protein that lead to the opening of transient pockets. In addition, the selection of the ligands based on a combination of the binding free energy and binding free energy gap between the best two poses for each ligand provided more suitable binders than the selection of ligands based solely on one of the criteria. The application of cosolvent molecular dynamics to enhance the sampling of the configurational space is expected to improve the efficacy of virtual screening campaigns of future drug discovery projects.

Application of inverse gas chromatography in the surface characterization of diethanol amine modified polystyrene based polymer.

In the present work, diethanol amine modified polystyrene based polymer (PVBC-Diethanol amine) was synthesized and characterized, then surface properties of the polymer were examined by inverse gas chromatography method at infinite dilution. The retention diagrams obtained based on the interaction of polar and nonpolar probes with the polymer were drawn over a temperature range from 30 to 55 °C. Through the diagrams, the dispersive component of the surface free energy, g S D of the polymer surface, and the specific enthalpy of adsorption, DH A S , of probes on the polymer were also calculated. Lewis acid, K A , and Lewis base, K D , parameters of PVBC-Diethanol amine surface were determined. The values of K A and K D indicated that PVBC-Diethanol amine surface exhibited a basic behavior.

Mass Cytometry Tags: Where Chemistry Meets Single-Cell Analysis.

Mass cytometry is a highly multiparametric proteomic technology that allows the measurement and quantification of nearly 50 markers with single-cell resolution. Mass cytometry reagents are probes tagged with metal isotopes of defined mass and act as reporters. Metals are detected using inductively coupled plasma time-of-flight mass spectrometry (ICP-TOF-MS). Many different types of mass-tag reagents have been developed to afford myriad applications. We have classified these compounds into polymer-based mass-tag reagents, nonpolymer-based mass-tag reagents, and inorganic nanoparticles. Metal-chelating polymers (MCPs) are widely used to profile and quantify cellular biomarkers; however, both the range of metals that can be detected and the metal signals have to be improved. Several strategies such as the inclusion of chelating agents or highly branched polymers may overcome these issues. Biocompatible materials such as polystyrene and inorganic nanoparticles are also of profound interest in mass cytometry. While polystyrene allows the inclusion of a wide variety of metals, the high metal content of inorganic nanoparticles offers an excellent opportunity to increase the signal from the metals to detect low-abundance biomarkers. Nonpolymer-based mass-tag reagents offer multiple applications: cell detection, cell cycle property determination, biomarker detection, and mass-tag cellular barcoding (MCB). Recent developments have been achieved in live cell barcoding by targeting proteins (CD45, b2m, and CD298), by using small and nonpolar probes or by ratiometric barcoding. From this perspective, the principal applications, strengths, and shortcomings of mass-tag reagents are highlighted, summarized, and discussed, with special emphasis on mass-tag reagents for MCB. Thereafter, the future perspectives of mass-tag reagents are discussed considering the current state-of-the-art technologies.

On surface energy and acid–base properties of highly porous parent and surface treated activated carbons using inverse gas chromatography

This study provides the surface characteristics (surface energy and the acid–base properties) of surface treated activated carbons (ACs) using inverse gas chromatography. The surface energy and the acid–base characteristic of studied adsorbents are determined by the retention time using several non-polar and polar probes at 140°C. It is observed that the dispersive surface energy dominates for all AC samples. The treatment of Maxsorb III with H2 exhibits the highest basicity due to lower oxygen content on the surface. The presented results express further insights and useful information in functionalizing the activated carbon for various industrial applications.

Isosteric Heats of Adsorption of Gases and Vapors on a Microporous Carbonaceous Material

High-resolution, multiple temperature adsorption isotherms of ten adsorptives classified into highly polar (1.7 ± 0.1 D) and nonpolar (0 D) probes with increasing kinetic diameters were measured on a well-characterized poly(furfuryl alcohol)-based microporous carbon. The Clausius–Clapeyron equation was applied to each, resulting in isosteric heats of adsorption. Fluid–fluid interactions, nonspecific fluid–solid interactions, and specific fluid–high energy site interactions were identified and discussed as variables contributing to the total isosteric heat of adsorption. Each isosteric heat was compared against its position relative to adsorption heat by a flat surface, twice this heat, and adsorptive latent heat of condensation. The shape of each curve was analyzed via the contribution of each interaction to the total across the fractional filing range, leading to identification of fillings as Zero Coverage, Low Coverage, and High Coverage. This systematic investigation provided a detailed analysis of the...

The effect of water addition on the surface energy, bulk and flow properties of lignite

In this paper, the relationship between angle of repose, surface energy and bulk and shear properties of different particle size distribution lignite pulverized coal with different moisture content was experimentally investigated. The dry sample and wet sample were prepared under relative humidity 0% and 90%. The interactions between coal samples and polar or non-polar gaseous probes were investigated by the surface energy test with an inverse gas chromatography (IGC) technique. The compressibility test and shear test were taken by the FT4 Powder Rheometer. The changes in bulk and flow properties of different particle size distribution samples were collected as a function of water content. The results show that water content plays a significant role on the packing and flow behaviors and surface energy of the dry and wet different particle size lignite pulverized coal. The IGC tests results showed that for the relative humidity 90% samples, the water was the interior water, which played a role of improving the flowability. In the end, a model was proposed to study the relationship between angle of repose and surface energy and flowability. The model could easily predict the relationship between angle of repose with wet and dry particles. This research will provide a better understanding on how water content affects surface characteristic and the flow properties of lignite particles and will benefit to optimize the relevant unit operations.

Determination of the surface properties of kaolinite by inverse gas chromatography.

Inverse gas chromatography (IGC) was applied to characterize the surface of kaolinite. The adsorption thermodynamic parameters (the standard enthalpy (∆H0), entropy (∆S0) and free energy of adsorption (∆G0), the dispersive component of the surface energy (γsd), and the acid/base character of kaolinite surface were estimated by using the retention time of different non-polar and polar probes at infinite dilution region. The specific free energy of adsorption (∆Gsp), the specific enthalpy of adsorption (∆Hsp), and the specific entropy of adsorption (∆Ssp) of polar probes on kaolinite were determined. (∆Gsp) values were correlated with the donor and modified acceptor numbers of the probes to quantify the acidic (KA) and the basic (KD) parameters of the kaolinite surface. The values obtained for the parameters KA and KD indicated a basic character for kaolinite surface.

Surface Properties of Hyper-Cross-Linked Polymeric Resins Using Inverse Gas Chromatography: Effect of Post-Cross-Linking Solvents

Two series of hyper-cross-linked polymeric resins (hyper-resins) were prepared via post-cross-linking of low-cross-linked macroporous poly(vinylbenzyl chloride-divinylbenzene) (poly(CDVB)) or poly(styrene-divinylbenzene) (poly(DVB)) swollen in the solution of 1,2-dichloroethane or nitrobenzene, respectively. Inverse gas chromatography was used to investigate the effect of post-cross-linking solvents on the surface chemistry of hyper-resins. The dispersive component of the surface free energy (γsd) and surface acid–base character of hyper-resins were estimated using the retention time of different nonpolar and polar probes at the infinite dilution region. Results showed that the values of γsd were basically identical for the hyper-resins prepared using the same precursor; the acidity and basicity constants KA and KD confirmed that the surface of four hyper-resins were Lewis amphoteric with predominantly basic character, but the strength of the surface acidic and basic sites of hyper-resins synthesized usin...

Characterization of Thermodynamic Properties of 3-N-Butyl-6-(1-Decyl Olefinic Acid Base)-4-Cyclohexene Diacid by Inverse Gas Chromatography

The dispersive-free energy and acid–base forces of 3-n-butyl-6-(1-decyl olefinic acid base)-4-cyclohexene diacid were investigated by inverse gas chromatography. Five nonpolar and 5 polar solvents were used between 353 K and 413 K. By using the retention times of nonpolar and polar probes in the infinite dilution region, adsorption thermodynamic parameters, including the adsorption enthalpy by acid-base interactions and the molar-free adsorption energy of acid-base interaction were evaluated. The results showed that 3-n-butyl-6-(1-decyl olefinic acid base)-4-cyclohexene diacid has low surface energy dispersion and is a Lewis amphoteric material with predominantly basic character. These results were confirmed by the Lewis acidity and basicity constants. Because the surface energy dispersion of inorganic fillers was higher than modified inorganic fillers, and the compatibility of inorganic fillers with the polymers was poor, the inorganic fillers should be modified with 3-n-butyl-6-(1-decyl olefinic acid base)-4-cyclohexene diacid to reduce the surface energy.

Relationship between processing, surface energy and bulk properties of ultrafine silk particles

Silk particles of different sizes and shapes were produced by milling and interactions with a series of polar and non-polar gaseous probes were investigated using an inverse gas chromatography technique. The surface energy of all silk materials is mostly determined by long range dispersive interactions such as van der Waals forces. The surface energy increases and surface energy heterogeneity widens after milling. All samples have amphoteric surfaces and the concentration of acidic groups increases after milling while the surfaces remain predominantly basic. We also examined powder compression and flow behaviours using a rheometer. Increase in surface energy, surface area, and static charges in sub-micron air jet milled particles contributed to their aggregation and therefore improved flowability. However they collapse under large pressures and form highly cohesive powder. Alkaline hydrolysis resulted in more crystalline fibres which on milling produced particles with higher density, lower surface energy and improved flowability. The compressibility, bulk density and cohesion of the powders depend on the surface energy as well as on particle size, surface area, aggregation state and the testing conditions, notably the consolidated and unconsolidated states. The study has helped in understanding how surface energy and flowability of particles can be changed via different fabrication approaches.

Luminescence quenching by heavy metal ions of probes based on anthracene, pyrene, and eosin in human serum albumin

UDC 535.373.4 Fluorescence and phosphorescence quenching processes of polar and non-polar luminescent probes associated with human serum albumin (HSA) in phosphate buffer at pH 7.4 were studied. Stern–Volmer quenching constants of anthracene and pyrene fl uorescence and eosin phosphorescence and rate constants for quenching of eosin triplet states were determined. The polarity index of pyrene bound to HSA was obtained as a function of thallium nitrate concentration. The infl uences of structural changes in the proteins that were stimulated by heavy-metal salts and of screening of protein charges by salt ions on quenching processes of singlet and triplet states of the probes were found.

Determination of Surface Characteristics of Epoxidized Soybean Oil by Inverse GC

The dispersive free energy and acid–base forces of epoxidized soybean oil (ESO) were determined by inverse gas chromatography (IGC). Eight non-polar and polar solvents were used as the probes in the temperature range between 303.15 and 343.15 K. The IGC characterization encompassed the adsorption thermodynamic parameters, including the standard enthalpy ( $$ \Updelta H_{\text{a}}^{\text{s}} $$ ) and the free energy change of adsorption ( $$ \Updelta G_{\text{a}}^{\text{s}} $$ ), using the retention time of different non-polar and polar probes at the infinite dilution region. Surface characterization showed that ESO has low $$ r_{\text{s}}^{\text{d}} $$ value, even at 303.15 K, and is a Lewis amphoteric material with predominantly basic character, as confirmed by the Lewis acidity and basicity constants K a and K b, respectively.

Synthesis of OMS Materials and Investigation of Their Acceptor–Donor Characteristics

Three ordered mesoporous siliceous (OMS) materials known as MCM41s—unmodified MCM-41C16 (“C16”), and two MCM41s with different surface functionalities: MCM-41C16-SH (“C16-SH”) and MCM-41C16-NH2 (“C16-NH2”)—were synthesized and studied by inverse gas chromatography in order to determine their acceptor–donor properties. The specific retention volumes of nonpolar and polar probes that were chromatographed on these ordered mesoporous silica adsorbents were evaluated under infinite dilution conditions. Two methods were employed to calculate the standard free energy of adsorption, ΔG ads, of each chromatographed probe on the basis its specific retention volume. These ΔG ads values were then employed to estimate the van der Waals contribution and the specific contribution of the free surface energy for each MCM41. DN values (donor numbers, based on the Gutmann scale) and AN* values (acceptor numbers, based on the Riddle–Fowkes scale) were employed to determine the values of parameters that characterize the ability of the MCM41s to act as electron acceptors (parameter: K A) and donors (parameter: K D). Considering the different compositions of the probes, each of which has different acceptor–donor properties, a new chromatographic test to supplement the Grob test is suggested.

Surface characterization of urushiol-titanium chelate polymers by inverse gas chromatography

Urushiol-titanium chelate polymer (UTP), the reaction product of urushiol with titanium compound, is a special eco-friendly polymer with excellent performances, such as strong acids-resistance, strong alkalis-resistance, salt solution-resistance and several organic solvent-resistance. Inverse gas chromatography (IGC) was used to measure the dispersive component of surface free energy (gamma(s)d) and the Lewis acid-base parameters of UTP in this work. The gamma(s)d and the acid/base characters of UTP' surfaces were estimated by the retention time with different non-polar and polar probes at infinite dilution region. n-Pentane (C5), n-hexane (C6), n-heptane (C7), n-octane (C8) and n-nonane (C9) were chosen as the non-polar probes to characterize the gamma(s)d. Trichloromethane (CHCl3), tetrahydrofuran (THF) and acetone were chosen as polar probes to detect the Lewis acid-base parameters. The specific free energy (deltaG(a)AB) and the enthalpy (deltaH(a)AB) of adsorption corresponding to acid-base surface interactions were determined. By correlating deltaH(a)AB with the donor and acceptor numbers of the probes, the acidic (K(a)) and the basic (K(b)) parameters of the samples were calculated. The results showed that the dispersive components of the free energy of UTP were 37.68, 33.53, 35.92, 24.01 and 31.32 mJ/m2 at 70, 80, 90, 100 and 110 degrees C, respectively. The Lewis acidic number K(a) of UTP was 0.185 3, and the Lewis basic number K(b) was 0.966 2. The results were of great importance to the study of the surface properties and the applications for urushiol-metal chelate polymers.

Surface modification of high-performance polymeric fibers by an oxygen plasma. A comparative study of poly( p-phenylene terephthalamide) and poly( p-phenylene benzobisoxazole)

Poly( p-phenylene terephthalamide) (PPTA) and poly( p-phenylene benzobisoxazole) (PBO) fibers were exposed to an oxygen plasma under equivalent conditions. The resulting changes in the surface properties of PPTA and PBO were comparatively investigated using inverse gas chromatography (IGC) and atomic force microscopy (AFM). Both non-polar ( n-alkanes) and polar probes of different acid–base characteristics were used in IGC adsorption experiments. Following plasma exposure, size-exclusion phenomena, probably associated to the formation of pores (nanoroughness), were detected with the largest n-alkanes (C 9 and C 10). From the adsorption of polar probes, an increase in the number or strength of the acidic and basic sites present at the fiber surfaces following plasma treatment was detected. The effects of the oxygen plasma treatments were similar for PPTA and PBO. In both cases, oxygen plasma introduces polar groups onto the surfaces, involving an increase in the degree of surface nanoroughness. AFM measurements evidenced substantial changes in the surface morphology at the nanometer scale, especially after plasma exposure for a long time. For the PBO fibers, the outermost layer – contaminant substances – was removed thanks to the plasma treatment, which indicates that this agent had a surface cleaning effect.

Surface Analysis of Poly (Ethylene Glycol) Methyl Ether by Inverse Gas Chromatography

The surface characterization of poly (ethylene glycol) methyl ether (PEGME) was carried out using inverse gas chromatography (IGC) in the temperature range 393.15 to 443.15 K. The thermodynamic parameters, the dispersive component of the surface energy, , and the acid-base character of the surface of the PEGME were estimated using the retention time of different nonpolar and polar probes at infinite dilution. The specific free energy of adsorption, ΔG a , the specific enthalpy of adsorption, ΔH a , and the specific entropy of adsorption, ΔS a , of polar probes on polymer were determined. The values of ΔH a were correlated with both the donor and the modified acceptor numbers of the probes to quantify the acidic Ka and the basic Kb parameters of the PEGME surface. The values obtained for the Ka and Kb parameters indicate that the PEGME surface has basic character.

Triplet-triplet energy transfer between luminescent probes bound to albumins

The interaction of polar and nonpolar luminescent probes with human blood serum albumins is studied by absorption and luminescence spectroscopy. It is found that the probes (polar eosin and nonpolar anthracene) can efficiently bind to proteins. The radii of the quenching spheres of energy-donor (eosin) triplet states in the presence of an acceptor (anthracene) in the process of the triplet-triplet energy transfer in proteins are determined for homogeneous and inhomogeneous distributions of acceptor molecules over the solution volume. It is shown that a decrease in the radius of the quenching sphere observed upon the addition of sodium dodecylsulfate surfactant is caused by structural changes in the protein.