Molecular Interaction Parameters Research Articles

Equilibrium curves and modeling of binary systems for the carbon di-oxide + benzyl acetoacetate and carbon di-oxide + benzyl acetate mixtures under high pressure

The solution phase behavior of the binary systems of supercritical carbon di-oxide (SU-CO2) + benzyl acetoacetate and SU-CO2 + benzyl acetate was investigated in a synthetic high-pressure apparatus at five temperatures from 313.2 to 393.2 K and pressure up to 33.53 MPa for the industrial benefit of food, pharmaceutical and cosmetics application. The solubility of benzyl acetoacetate and benzyl acetate in the SU-CO2 + benzyl acetoacetate and SU-CO2 + benzyl acetate systems were increased with increasing temperature at constant pressure, respectively. Both system isotherms were exhibited in the simple Type-I category phase behavior. Besides, the Peng-Robinson equation of state has been successfully applied to predict the phase behavior of the SU-CO2 + benzyl ester systems using adjustable molecular interaction parameters (kij and ηij). Neither system shows a three-phase behavior at any point of temperature and pressure. A one-fluid-phase locale was ascertained above and throughout the solubility curve whereas a two-phase locale was exhibited inside the critical curve for both binary systems. The critical mixture curve provides the fingerprint for the phase behavior study of any binary system since it is used to understand and calculate thermodynamic properties effectively. The accuracy of the studied model was tested by evaluating the percentage of root mean square deviation utilizing optimized temperature-dependent mixture parameters. Indeed, this is the first reference point for the prediction of phase transition behavior for benzyl acetoacetate and benzyl acetate in SU-CO2 and the findings make a remarkable impression on industrial applications.

Chemically reactive and aging macromolecular mixtures. I. Phase diagrams, spinodals, and gelation

Multicomponent macromolecular mixtures often form higher-order structures, which may display non-ideal mixing and aging behaviors. In this work, we first propose a minimal model of a quaternary system that takes into account the formation of a complex via a chemical reaction involving two macromolecular species; the complex may then phase separate from the buffer and undergo a further transition into a gel-like state. We subsequently investigate how physical parameters such as molecular size, stoichiometric coefficients, equilibrium constants, and interaction parameters affect the phase behavior of the mixture and its propensity to undergo aging via gelation. In addition, we analyze the thermodynamic stability of the system and identify the spinodal regions and their overlap with gelation boundaries. The approach developed in this work can be readily generalized to study systems with an arbitrary number of components. More broadly, it provides a physically based starting point for the investigation of the kinetics of the coupled complex formation, phase separation, and gelation processes in spatially extended systems.

Physico-chemical analysis in ternary organic mixtures at various temperatures with an acoustical approach

Thermo-dynamical analyses of organic mixtures are essential across industries. Ultrasonic sound velocity (U) measurements in the ternary organic mixtures of Toluene, Chloroform, and Cyclohexane have been conducted between 303.15, 308.15 and 313.15 K. The experimental/derived data were utilised to compute deviations for their excess values such as adiabatic compressibility (βE), free length (LfE), free volume (VfE), impedance (ZE), internal pressure (πiE) and enthalpy (HE) to investigate and confirm the types of interactions. Using these derived parameters, excess parameters were calculated to further reaffirm the type, strength, magnitude, and potential interactions such as complex formation, dipole-dipole, and dispersive types. Moreover, both ideal and non-ideal behaviours were analysed. The ultrasonic velocity data were validated against some contemporary and well-known models like Namoto’s relation (NR), Ideal mixture relation (IMR), Impedance dependence relation (IDR), Collision factor theory (CFT) and Nutch-Kunkies (NK) theorem. From the IMR and IDR are gives well approach to experimental one. And a comparative study of these models was conducted to ascertain the possible types of interactions within the mixtures through their molecular interaction parameter, percentage deviation, standard percentage error deviation.

Interactions at the interfaces of the H2-brine-cement systems at elevated pressures for H2 storage

There is a global demand on assessment of potential subsurface gas storage sites in view of safely injecting hydrogen or carbon dioxide. One relevant aspect that has already been subject to thorough investigation is the mutual interaction of all participating compounds in terms of the wetting behaviour that on its turn is directly related to the predominating capture mechanisms. Given the diversity of the geophysical and geochemical circumstances, transferability of results from work conducted on one geological site to another location is limited. For instance, there is a large number of publications on wettability of many different rock types in hydrogen atmosphere that are partly controversal and strictly applicable only to the respective reported system. Hence, there is a gap in finding general model approaches that serve for a holistic understanding of predominating mechanisms and building the fundamentals for predicting the behaviour of systems that have not been studied so far. The presented work addresses this gap by quantifying mutual interactions of the participating phases in a solid-liquid-gas systems and determining the respective interfacial tensions, γSV (solid-vapor), γLV, (liquid-vapor) and γSL (solid-liquid).Neumann and Good demonstrated how to determine the solid-fluid interfacial tension based on the contact angle and the liquid-gas interfacial tension by calculating a so-called molecular interaction parameter. Up to date, this method has been applied, among others, for systems containing CO2 and solids such a teflon, glass, and steel. The methodology could be confirmed by testing systems comprising steel - H2O - CH4 /H2 and comparing the results to the aforementioned literature data.As one of the critical parts in H2 underground storage, the completion system containing a common well cement, H2 and brine was subject to this work. The interfacial tension between H2 and brine as well as the contact angle between the fluid phases and the cement were investigated experimentally up to 20 MPa, temperatures from 313.15 to 353.15 K and NaCl – concentrations of up to 10% wt. As a theoretical approach, the interfacial tension of the system H2O+H2 was investigated using the density gradient theory (DGT) in combination with the perturbed chain statistical associating fluid theory equation of state (PC-SAFT). Finally, the H2-cement interfacial tension is determined through the calculation of a so-called molecular interaction parameter. The interfacial tension data of H2O+H2 experimentally and theoretically determined in this work agree among each other as well as with previous literature data. Likewise, agreement was found between the brine+H2 interfacial tension and previous studies. The contact angle appears to be influenced mostly by pressure, producing a less H2O/brine-wet system as pressure increases. The H2-cement interfacial tension decreases from approximately 150 mN/m down to 100 mN/m, as the pressure increases from 0.1 to 20 MPa. The presented data suggest H2 to be slightly adsorbed on the one hand but the capillary entry pressure to decrease on the other, causing concerns regarding the integrity of the completion system.

Study of molecular interactions by nonequilibrium capillary electrophoresis of equilibrium mixtures: Originations, developments, and applications.

Molecular interactions play a vital role in regulating various physiological and biochemical processes in vivo. Kinetic capillary electrophoresis (KCE) is an analytical platform that offers significant advantages in studying the thermodynamic and kinetic parameters of molecular interactions. It enables the simultaneous analysis of these parameters within an interaction pattern and facilitates the screening of binding ligands with predetermined kinetic parameters. Nonequilibrium capillary electrophoresis of equilibrium mixtures (NECEEM) was the first proposed KCE method, and it has found widespread use in studying molecular interactions involving proteins/aptamers, proteins/small molecules, and peptides/small molecules. The successful applications of NECEEM have demonstrated its promising potential for further development and broader application. However, there has been a dearth of recent reviews on NECEEM. To address this gap, our study provides a comprehensive description of NECEEM, encompassing its origins, development, and applications from 2015 to 2022. The primary focus of the applications section is on aptamer selection and screening of small-molecule ligands. Furthermore, we discuss important considerations in NECEEM experimental design, such as buffer suitability, detector selection, and protein adsorption. By offering this thorough review, we aim to contribute to the understanding, advancement, and wider utilization of NECEEM as a valuable tool for studying molecular interactions and facilitating the identification of potential ligands and targets.

Experimental Study and Modeling of Solid-liquid Equilibrium for Binary and Ternary Pharmaceutical and Food Systems

Background: The experimental measurement of the solubility of a solute in a given solvent is a difficult task; hence, there is a need for reliable thermodynamic models for its prediction. However, these models require either molecular or group interaction parameters, which are not always available. Objective: The objective of the present study is to measure experimentally the solubility of different solutes in solvents selected from pharmaceutical or food fields on the basis that not all the required model interaction parameters are available to use the obtained experimental data for their determination. Methods: The experimental study of solid-liquid equilibrium for chosen binary and ternary systems at different temperatures was carried out using differential scanning calorimetry to determine the essential thermophysical properties like melting temperature and enthalpy. The modeling of these phase equilibrium data was performed using thermodynamic models like Random Two Liquids (NRTL) and Universal Functional Activity Coefficient (UNIFAC). The required NRTL interaction parameters were determined by minimizing a well-defined objective function using the simplex method. Results: The solubilities of the solutes in the different considered solvents at different temperatures obtained experimentally provided the required NRTL molecular interaction parameters. Solute solubilities were obtained using NRTL, UNIFAC, and ideal models. The comparisons showed an excellent agreement between the experimental values and the NRTL results, contrary to UNIFAC and ideal case models. Conclusion: This study shows the importance of thermodynamic modeling to predict solubility data that may be difficult, time-consuming, and costly to obtain experimentally.

Multi-objective optimization of equation of state molecular parameters: SAFT-VR Mie models for water

The determination of a suitable set of molecular interaction parameters for use with an equation of state (EoS) can be viewed as a multi-objective optimization (MOO) problem, where each objective quantifies the quality of the description for a particular type of thermodynamic property. We outline a methodology for the determination of a set of Pareto-optimal interaction parameters. The Pareto front is generated efficiently using a sandwich algorithm where one solves a sequence of weighted-sum scalarized single objective optimization problems. The algorithm presented can be used for any number of objective functions, allowing for the consideration of multiple thermodynamic property types as competing objectives in the MOO. The methodology is applied to the determination of suitable parameter sets for models of water within the SAFT-VR Mie framework. Three competing property targets are considered as objective functions: saturated-liquid density, vapour pressure and isobaric heat capacity. Two different types of molecular models are considered: spherical models of water, and non-spherical model of water. We analyse the two- and three-dimensional Pareto surfaces and parameter sets obtained for different property combinations in the MOO. The proposed methodology can be used to provide a rigorous comparison between different model types. Numerous Pareto-optimal parameter sets for SAFT-VR Mie water models are documented, and we recommend two new models (one spherical model and one non-spherical model) with an appropriate compromise between the competing objectives.

Transport properties of binary Lennard-Jones mixtures: Insights from entropy scaling and conformal solution theory

The relation of transport properties and the molecular interactions in binary mixtures was studied. The self-diffusion coefficient, Maxwell–Stefan as well as Fickian mutual diffusion coefficient, shear viscosity, and thermal conductivity of liquid binary simple mixtures were therefore sampled using molecular dynamics simulations. The mixtures were described by the Lennard-Jones potential. The molecular interaction parameters were chosen such that a large variety of mixture behavior was covered. The two components had the same size parameter in all cases, but different dispersion energies. Moreover, the cross-interaction parameter used in the modified Lorentz-Berthelot combination rule was varied such that the resulting mixtures showed different types of phase behavior: ideal, high- and low-boiling azeotrope. The results are discussed using conformal solution theory as a link between the molecular interactions in the mixtures and the macroscopic properties. Moreover, the applicability of Rosenfeld’s entropy scaling is tested. Despite the important differences of the studied mixtures regarding their molecular interactions and the large pressure, temperature, and composition range considered, a practically monovariate relation of these properties with respect to the configurational entropy is observed. Yet, the quality of the approximation differs for the studied properties.

Molecular docking studies on the binding interaction and stability of ovalbumin with an intramolecular charge transfer dye 4-dicyanomethylene-2,6-dimethyl-4H-pyran in the presence of an antibiotic: Tetracycline

Molecular docking (MD) studies of an Intramolecular Charge Transfer (ICT) dye, 4-Dicyanomethylene2,6-Dimethyl-4-Hpyran (DDP) dye with a globular protein, ovalbumin (OVA) were carried out in the presence of antibiotic drug, tetracycline (TTC). OVA is classified as a globular protein and the binding stability of OVA-DDP versus OVA-TTC was ascertained from energetics (docking of protein-dye/drug) and molecular interaction parameters existing between the host and guest molecule. OVA is the host molecule and the drug and dye are the guest molecule under considerations. MD studies reveals the location of DDP dye in five distinguishably different active binding sites of OVA corresponding to various sub domains and the binding energy of dye differs significantly based on the conformers generated. Similarly, the drug is bound to several sub domains of OVA such the co-existence of eight different unique conformers is visualized among which TTC is bound to four active sites. Docking studies reveals TTC-OVA complex is relatively less stable than DDP-OVA complex even though the stability is attributed to several conventional hydrogen-bonding (HB) interactions existing between TTC and amino acid (AA) residues of OVA. TTC predominantly acts as a HB acceptor and the AA residues as the donor. The extent of HB interactions predominates over hydrophobic interactions in TTC-OVA compared to DDP-OVA complex. Interestingly, docking of TTC to DDP-OVA complex results in an enhanced stability of the dye-protein complex. Interestingly, there exist no direct binding of dye with drug when docked simultaneously. Both dye and drug reside far apart from each other in conformationally distinct active sites of OVA is authenticated. MD studies further, elucidates that DDP dye is bound to several AA residues through conventional and non-conventional HB interactions accompanied with hydrophobic interactions, π -π, π -alkyl interactions and weak van der Waals forces such that the presence of drug does not destabilize the complex, rather promote more binding interactions. MD is used as an efficient tool and non-evasive technique in establishing the stability of two distinct guest molecules competing with same host molecule (protein) is imparted in the present study.

Multi-technique approach to explore the mixed micellization behavior of promazine hydrochloride drug and cetyltrimethylammonium bromide surfactant in aqueous glycine, glycylglycine (dipeptide) and glycylglycylglycine (tripeptide) solutions

The aggregation properties of amphiphiles and their mixtures are of theoretical and applied importance. Therefore, mixed micellization behavior of promazine hydrochloride (PMZ) drug and cetyltrimethylammonium bromide (CTAB) surfactant at different mole fractions, α PMZ = (0.2, 0.4, 0.6 and 0.8) has been scrutinized in water and (0.025, 0.050 and 0.100) mol·kg −1 aqueous solutions of glycine, glycylglycine (dipeptide) and glycylglycylglycine (tripeptide) at T = (298.15 to 318.15) K, by means of multiple techniques. Thermodynamic parameters of micellization (ΔG°m, ΔH°m, and ΔS°m) along with excess Gibbs free energy of mixing (ΔG m ex), the molecular interaction parameter (β int), and the degree of ionization (α), have been attained from the conductivity measurements. The partial specific volumes (φ v), partial specific isentropic compression (φ κ) as well as isentropic compressibilities (κ s) were computed from the measured density and speed of sound data. UV-Visible absorption, fluorescence emission and proton (1H) NMR spectra were recorded for the pure PMZ and mixed (PMZ + CTAB) system in the presence of glycine(aq), glycylglycine(aq) and glycylglycylglycine(aq) solutions. Dynamic light scattering (DLS) study was carried out to measure the hydrodynamic diameters (D H) of mixed micellar systems. The prevalence of hydrophobic-hydrophobic interactions amid the hydrophobic groups of PMZ drug (tricyclic scaffolding), CTAB (–C16H33), glycine, di- and tri-peptides (–CH2), and electrostatic interactions amid the hydrophilic/ionic groups of PMZ{tertiary amine part and +NH (CH3)2, Cl−}, CTAB (–N (CH3)3 +, Br‒) and glycine, di- and tri-peptides {zwitterion (NH3 +, COO−} have been depicted from the aforementioned studies.

VUV–VIS FT spectroscopy of the rare 13C18O isotopologue of carbon monoxide: Analysis of the A1Π(v = 1) multiply-perturbed level

Ro-vibronic spectra of the 13C18O carbon monoxide isotopologue were obtained with (i) emission spectroscopy in the visible region using a Bruker IFS 125HR spectrometer (University of Rzeszów) and (ii) vacuum-ultraviolet absorption spectroscopy using the wave-front-division spectrometer on the DESIRS beamline of the SOLEIL synchrotron. A deperturbation analysis of the 13C18O A1Π(v = 1) level was conducted from 598 observed transitions from the B1Σ+ - A1Π(0, 1), C1Σ+ - A1Π(0, 1), A1Π - X1Σ+(1, 0), B1Σ+ - X1Σ+(0, 0), C1Σ+ - X1Σ+(0, 0), I1Σ– - X1Σ+(2, 0) bands and five further nominally forbidden bands. An effective Hamiltonian and term-value fitting analysis was implemented. Consequently, 135 parameters were floated: 23 molecular parameters, including molecular constants for A1Π(v = 1), I1Σ–(v = 2), d3Δ(v = 6), e3Σ–(v = 3) and D1Δ(v = 1); rotation-electronic (L-uncoupling) mixing of A1Π(v = 1) ∼ [D1Δ(v = 1), I1Σ–(v = 1), I1Σ–(v = 2)] and spin–orbit interaction parameters for A1Π(v = 1) ∼ [d3Δ(v = 6), e3Σ–(v = 3), aʹ3Σ+(v = 11)]; the spin–orbit/spin-electronic/L-uncoupling a3Π(v = 12) ∼ d3Δ(v = 5) and spin–orbit a3Π(v = 12) ∼ [D1Δ(v = 1), I1Σ–(v = 2)] perturbation parameters; as well as 112 ro-vibronic term values of B1Σ+(v = 0) up to J = 50 and C1Σ+(v = 0) up to J = 60. The significant, indirect a3Π(v = 12) ∼ [e3Σ–(v = 2, 3), d3Δ(v = 5, 6)] ∼ A1Π(v = 1) spin–orbit/spin-electronic/L-uncoupling interaction and a3Π(v = 12) ∼ [I1Σ–(v = 2), D1Δ(v = 1)] ∼ A1Π(v = 1) spin–orbit/L-uncoupling interaction were detected and analysed. Thus, this study, using modern experimental methods and deperturbation analysis, leads to a much improved description in terms of molecular constants and interaction parameters, compared to previous studies of the A1Π(v = 1) energy region in the 13C18O isotopologue. This research is a continuation of the studies on the A1Π state and its numerous perturbers in the CO isotopologues made by our team.

Interaction of methylene blue with SDS in the premicellar solution of CPC in the aqueous and methanol-water system

Interactions between sodium dodecyl sulfate (SDS) and methylene blue (MB) have been studied in presence of cetylpyridinium chloride (CPC) in aqueous and methanol-water binary solvents via conductometric and tensiometric methods. The experiment was conducted to see the possibility of a synergistic effect of the SDS+CPC system and changes in the interactional behavior of SDS with MB in presence of CPC. The value of the molecular interaction parameter for micellization (βM) was found to be negative from the experimental results and the value of |βM| was found to be greater than ln(CMCSDS / CMCCPC), which didn’t describe synergism completely but indicated the strong striking interactions between the oppositely charged surfactants. However, the CMC of the SDS+CPC system was found to be very low as compared to the CMC of SDS alone. This result of CMC based on striking interactions between oppositely charged surfactants was used to calculate various parameters like Gibb’s free energy of micellization (∆Gmo), surface excess(Γmax), minimum surface area (Amin), surface pressure πCMC, standard free energy of adsorption (∆Gadso), pC20, minimum surface free energy (Gmins), packing parameter (P) and association equilibrium constant (K). The addition of methanol as a cosolvent enhances the CMC and α value of the SDS+CPC as well as the SDS+CPC-MB system. Correlation of ∆Gmo with different solvent parameters namely Gordon parameter (G), Reichardt's parameter (ET (30)), viscosity (ηo), and solvophobic parameter (SP) has also been evaluated.

Molecular docking approach on the molecular interactions involving beta-lactoglobulin (βLG)-4-Dicyanomethylene2,6-Dimethyl-4-Hpyran (DDP) dye in the presence of an antibiotic, norfloxacin

Molecular docking (MD) techniques were employed in the determination of binding stability of Beta-lactoglobulin (βLG) with 4-Dicyanomethylene2,6-Dimethyl-4-Hpyran (DDP) dye in the presence of quinolone-based antibiotic, norfloxacin (NOR). βLG acts as the host and drug/dye is employed as the guest molecule. The energetics and molecular interaction parameters of βLG-DDP were found to be stable than βLG-NOR. DDP resides in three distinguishably different binding sites of βLG, however the binding energies does not differ considerably. Interestingly, the energetics of βLG-NOR conformers differs significantly and reveals the existence of two distinguishable conformers. NOR acts as a hydrogen-bonding (HB) acceptor and the amino acid (AA) residues of βLG as the donor. The extent of HB interactions predominates over hydrophobic interactions in βLG-NOR than βLG-DDP complex. MD studies authenticates no direct binding of dye-drug inside the domains of βLG, when docked simultaneously. On the contrary, docking of dye to βLG-NOR complex enhances the binding stability. Several molecular interactions govern the stability of the complex and play a major role on the binding affinity of the host-guest complex in the presence of two competitive ligands. MD techniques authenticate that DDP/NOR is bound to several AA residues through conventional and non-conventional HB interactions accompanied with hydrophobic, pi-pi, pi-alkyl and van der Waals forces of interactions. Further, MD methods is employed as an efficient tool and a non-evasive technique in establishing the stability of 1:1complex of drug/dye with βLG in the present study.

Micellar and Surface Properties of Cationic-Cationic Binary Surfactant Mixtures: Synergistic Interactions and Solubility Enhancement of Anthracene

The micellar and surface behaviors of decylammonium chloride (DACl) in presence of L-alanine hydrochloride decylester (L-ADE) and L-alanine hydrochloride dodecylester (L-ADDE) at various mole fractions were investigated by conductivity and surface tension measurements. From the conductivity measurements, the critical micelle concentration (CMC), the degree of counter-ion ionization (α) and standard Gibbs energy of micellization (ΔG°mic) were investigated for both pure and binary mixtures. The molecular interaction parameter (β) and the micellar mole fraction (XmDACl) for mixed micelle formation by DACl/L-ADE (C10-C10) and DACl/L-ADDE (C10-C12) were calculated using the regular solution equation proposed by Rubingh. The ideal values of CMC (CMCideal) and the micellar mole fraction (XmDACl(ideal)) were also obtained for mixed micelle according to the pseudo phase theoretical models. The negative β values showed that there were synergistic interactions for all compositions of DACl/L-ADE and DACl/L-ADDE mixed systems. From the surface tension measurements, adsorption parameters such as the surface excess concentration (Γmax), minimum surface tension at the CMC, efficiency in the surface tension reduction (pC20), standard Gibbs energy of adsorption (ΔG°ads), and minimum area per head group of a molecule (Amin) in pure, mixed and their ideal values were also determined. The results indicated that the synergism and attractive interactions in the studied binary mixtures depend on the chain length of the cationic L-alanine ester and their mole fractions in the mixed system. The solubilization capacity of pure DACl and its mixed system with L-ADE and L-ADDE towards anthracene were determined and discussed in terms of molar solubilization ratio (MSR). Based on the MSR values, the solubility enhancement was found for anthracene in DACl/L-ADE and DACl/L-ADDE mixed systems.

An analytical model for evaluating fluid flux across carbon-based membrane

A mass transfer model of fluid across membranes is developed by taking into account the entrance/exit effect and molecular slipping in nanopores. This model, involving the molecular interaction parameters between fluid and nanopore, can accurately predict water fluxes across different practical membranes, and the discrepancy between predictions and reported experimental measurements can be reduced to 2.45%. By analyzing the flux dependence on membrane thickness and pore size, a physical correspondence is unraveled that an optimal flux can be achieved when the pore size of a membrane takes about 5 times the involved fluid molecule diameter (∼1.50 nm for water flux). In addition, an upper bound of the water flux across CNT membranes is identified by regulating the entrance/exit resistance, and we find a thin membrane with neutrally wettable exterior surface (with contact angle θ ≈ 60°) can greatly boost the water flux. This work not only provides a workhorse for predicting fluid flux but also casts insights for designing high-performance membranes. • An analytical and convenient flux model of fluid across membranes is developed. • The predicted fluxes are of the same order of magnitude with the measured ones. • Optimal flux exists when pore diameter is about 5 times the fluid molecule size. • An upper bound of the water flux across CNT membranes is identified.

Binding studies of dopamine HCl drug with the mixed {sodium bis(2-ethylhexyl) sulfosuccinate + sodium dodecylsulfate} micelles: Physicochemical, spectroscopic, calorimetric and computational approach

Taking into consideration the importance of dopamine HCl as neurotransmitter in controlling central nervous system activities, the studies of binding interactions of dopamine HCl drug with micellar system (imitator of biomembranes) have been conducted by utilizing experimental as well as computational techniques. The systematic knowledge of physicochemical, spectroscopic and calorimetric properties is helpful to understand the physiological actions of biologically active additives in the living organisms. Therefore, mixed aggregation behavior of sodium bis(2-ethylhexyl) sulfosuccinate, AOT and sodium dodecylsulfate, SDS has been explored at diverse mole fractions of AOT, αAOT = 0.25, 0.39 and 0.50 in (1, 2 and 3) × 10−3 mol kg−1 dopamine HCl(aq) solutions by employing different techniques. From conductivity studies, the thermodynamic parameters (∆G°m, ∆H°m and ∆S°m), the molecular interaction parameter (βint) and the excess Gibbs free energy of micellization (∆Gmex) were ascertained at T = (298.15, 308.15, and 318.15) K. Isentropic compressibility (κs), partial specific volume (φv) and partial specific isentropic compressibility (φκ) parameters were computed from the density and sound velocity studies. Binding constant (Kb) and standard Gibbs free energy of binding (∆Gbο) have been evaluated from UV–visible absorption studies for dopamine HCl(aq) solutions at all the studied mole fractions of surfactant mixtures. Through dynamic light scattering (DLS) measurements, the hydrodynamic diameters (Dh) of mixed micellar aggregates have been acquired. Isothermal titration calorimetric (ITC) studies were executed to obtain the values of partitioning constant / binding constant (K), standard molar enthalpy of binding (ΔrHᴼ), standard molar entropy of binding (ΔrSᴼ), and stoichiometry of partitioning / binding (n) of drug with micellar system. Through density functional theory (DFT) calculations, the band gap between HOMO and LUMO for the dopamine-HCl bound mixed micelle system, and interactive features have been obtained. Aforementioned studies favor the supremacy of hydrophilic-hydrophilic / ionic and electrostatic interactions causing the binding among the hydrophilic / ionic groups of dopamine HCl (−OH, H+, Cl−), AOT (–SO3−, –OCO, Na+), and SDS (–OSO3−, Na+).

Phase behavior of carbon dioxide/tetrapropyl orthosilicate and tetrabutyl orthosilicate systems

Alkyl groups of tetraalkoxysilane have different chain lengths, which results in different reactivity of the sol–gel reaction. Hence, it is essential to understand the phase behavior for designing chemical processes using the sol–gel reaction. The phase behavior of CO2/tetrapropyl orthosilicate (TPOS) and CO2/tetrabutyl orthosilicate (TBOS) binary systems was measured. The experiments were performed using a synthetic method combined with a laser displacement measurement wherein the movement of the piston inside the high-pressure vessel was measured. The phase boundaries were determined at 313–373 K and CO2 molar fractions of 0.1–0.9. No significant difference was observed in the phase behavior of tetraalkoxysilanes, which have alkyl groups of different chain lengths. The experimentally obtained vapor–liquid equilibria of the two binary systems were correlated by the Sanchez–Lacombe equation of state using the original mixing rule reported by Sanchez et al. The results showed that molecular interaction parameter kij exhibits a clear temperature dependence.

Tensiometry and FTIR study of the synergy in mixed SDS:DDAO surfactant solutions at varying pH

The interactions between a model anionic and amphoteric surfactant pair in aqueous solution are examined as a function of composition, at floating and fixed pH, employing a combination of tensiometry, regular solution theory analysis, and FTIR spectroscopy. An extensive series of pure and mixed ratios of sodium dodecyl sulfate (SDS) and N,N-dimethyldodecylamine N-oxide (DDAO), ranging from 0.0016 to 100 mM, yielding 77 data points below and above the critical micelle concentrations (CMC), is investigated. Compared to either pure surfactant solutions, the CMC of mixed SDS:DDAO solutions is found to decrease by up to 20-fold, and the surface tension (γ) at CMC down to ≃ 23 mN/m. At all concentrations, the most prominent effects are observed at equimolar SDS:DDAO ratios. Further, the pH of mixed micellar solutions is found to increase with respect to the pure surfactant solutions (from ≃ 7 up to ≃ 9.5), which is attributed to the enhanced protonation of DDAO in the presence of SDS, and supported by FTIR frequency shifts of isolated O‒H stretching vibrations. Vibrational responses from CH2 stretching of the methylene tails, and the S‒O stretching modes for the sulfate headgroups indicate strong lateral interaction and enhanced packing between SDS and DDAO. From regular solution theory analysis of tensiometry data, the molecular interaction parameters are found to have a larger magnitude (i.e., more negative) at the interface as compared to within micelles. At fixed solution pH, a decrease from pH 9.5 to 7.5 results in minimal changes in both interfacial and micellar parameters, indicating the intrinsic origin of these pairwise interactions. Overall, our findings demonstrate a pronounced synergistic interaction between SDS and DDAO, arising from diminished electrostatic and steric repulsions in, respectively, SDS and DDAO, accompanied by enhanced lateral surfactant packing.

Electronic structure parameter of nuclear magnetic quadrupole moment interaction in metal monofluorides.

The electronic structure parameter (WM) of the nuclear magnetic quadrupole moment (MQM) interaction in numerous open-shell metal monofluorides (viz., MgF, CaF, SrF, BaF, RaF, and PbF) is computed in the fully relativistic coupled-cluster framework. The electron-correlation effects are found to be very important for the precise calculation of WM in the studied molecular systems. The molecular MQM interaction parameter scales nearly as Z2 in the alkaline earth metal monofluorides, where Z is the nuclear charge of metal. Our study identifies 223RaF as a good candidate for the experimental search of the nuclear MQM, which can help unravel the physics beyond the standard model in the hadron sector of matter.

Modelling the thermodynamic properties and fluid-phase equilibria of n-perfluoroalkanes and their binary mixtures with the SAFT-γ Mie group contribution equation of state

The SAFT-γ Mie group-contribution approach is extended to describe the thermodynamic properties and fluid-phase behaviour of n-perfluoroalkanes and their binary mixtures. New molecular interaction parameters characterising the functional chemical groups forming these molecules (CF4, CF3 and CF2) are estimated from experimental vapour pressure and saturated-density data of the pure compounds. The vapour–liquid equilibria of four mixtures are then described predictively and compared to recent experimental data from the literature. Additionally, new experimental data for the excess volume of the (n-C6F14 + n-C8F18) mixture is measured over the whole range of compositions, between 278.15 and 318.15 K. The mixture presents small negative excess volumes, which increase in absolute value with increasing temperature. The results are compared with the excess volume for the corresponding mixture of n-alkanes of the same chain length, and with the SAFT-γ Mie predictions. The theory provides a very good description of the properties of both the pure compounds and their binary mixtures.