Changes In Thermodynamic Quantities Research Articles

Production of CNT Yarns from Methane Gas for Use as Filaments in Incandescent Bulbs: Thermodynamic Properties of As-spun CNT Yarns

Energy efficiency is a minimal cost energy resource. It is critical in bridging the gap via reducing overall demand, allowing electricity supply to be expanded to meet increasing demand in a timely and sustainable way. Incandescent bulbs with tungsten filaments convert only about 10% of the input energy into light with the rest wasted as heat and resultant carbon dioxide gas emissions. This results in high energy and environmental inefficiency. Carbon nanotubes (CNT) yarns as filaments for replacement of tungsten in incandescent bulbs represent an economic option boosting high energy and environmental efficiency. In this study, CNT yarns were produced from methane, an abundant greenhouse gas currently flared in Africa. Synthesis of CNT yarns were carried out in a Floating Catalyst Chemical Vapour Deposition (FCCVD) reactor using ferrocene as the catalyst with direct spinning of CNT into yarn. The quality and morphology of the produced yarns at different temperatures (900 – 1000°C) were determined using Scanning Electron Microscope (SEM) and Raman Spectroscopy. The optimum temperature to produce CNT yarns was found to be at reactor temperature of 950°C. The thermodynamics associated with the production of the as-spun CNT yarns were determined by Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). Heat capacity of CNT yarns was calculated based on the measured heat flow at thermal stable state. A polynomial regression of the form: Cp=0.002T2 – 0.4512T+66.099 was proposed for the prediction of the thermodynamic values. Change in thermodynamic quantities of yarn such as entropy and enthalpy were determined based on the heat capacities calculated from fitted polynomial models using relationship of thermodynamic function.

Essential Roles of Water in Actin-Myosin Binding

Though the binding of actin and myosin is one of the most important biological self-assembly processes, its mechanism is still controversial. In a prevailing view, which claims that the binding is driven by the actin-myosin electrostatic attractive interaction, the effect of surrounding water molecules (i.e., hydration effect) is not suitably taken into account. Here we investigate the water roles in the binding using a statistical-mechanical approach combined with molecular models for water. The hydration energies and entropies of actin, myosin, and their complex are calculated by the three-dimensional reference interaction site model theory and by the angle-dependent integral equation theory combined with our morphometric approach, respectively. In this theory, the changes in thermodynamic quantities upon the binding can be decomposed into physically insightful components. The actin-myosin binding brings a large gain of their electrostatic attractive interaction. However, it accompanies an even larger loss of actin-water and myosin-water electrostatic attractive interactions. The net change in the electrostatic component of system energy is positive. We find that the binding is driven by a large gain of configurational entropy of water which should surpass the positive change in system energy and the conformational-entropy loss occurring for actin and myosin. The physical origin of the large water-entropy gain is as follows: The actin-myosin interface is closely packed with the achievement of high shape complementarity on the atomic level, leading to a large increase in the total volume available to the translational displacement of water molecules in the system.

Mechanism of One-to-Many Molecular Recognition Accompanying Target-Dependent Structure Formation: For the Tumor Suppressor p53 Protein as an Example.

The new type of molecular recognition, in which an intrinsically disordered region (IDR) of a protein binds to many different target proteins with target-dependent structure formation, is indispensable to the expression of life phenomena and also implicated in a number of diseases. According to the prevailing view, the physicochemical factors responsible for the binding are also target dependent. Here we consider an IDR of the tumor suppressor p53 protein, p53CTD, as an important example related to carcinogenesis and analyze its binding to four targets accompanying the formation of target-dependent structures (i.e., helix, sheet, and two different coils) using our statistical-mechanical method combined with molecular models for water. We find that all of the seemingly different binding processes are driven by a large gain of the translational, configurational entropy of water in the system. The gain originates from sufficiently high shape complementarity on the atomic level within the p53CTD-target interface. It is also required that the electrostatic complementarity be ensured as much as possible to compensate for the dehydration. Such complementarities are achieved in harmony with the portion of the target to which p53CTD binds, leading to a large diversity of structures of p53CTD formed upon binding: If they are not achievable, the binding does not occur. This finding is made possible only by calculating the changes in thermodynamic quantities upon binding and decomposing them into physically insightful components.

Solubility of diazepam in water + tert-butyl alcohol solvent mixtures: Part 1. Experimental data and thermodynamic analysis

The aim of this work is to provide solubility data of a poorly water-soluble drug, diazepam, in water + tert-butyl alcohol solvent mixtures that could be used to train existing cosolvency models and to identify the forces driving the drug solubility variation with the cosolvent content in the solvent mixture. The solubility of diazepam was determined in nine binary solvent mixtures and in both neat solvents at temperatures ranging from 293.15 to 313.15 K under atmospheric pressure. The density of diazepam-free and diazepam-saturated solvent mixtures were also determined as well as the thermophysical properties of original drug crystals and excess solid phases from solid–liquid equilibria. The thermodynamic quantities relative to the dissolution process of diazepam under saturation condition were obtained from solubility temperature dependence using the van't Hoff plot. From these data, the changes in thermodynamic quantities of diazepam upon fusion and mixing as well as the excess thermodynamic quantities of the drug in the different saturated solvent compositions over the temperature range investigated were determined using classical thermodynamic approaches. The mole fraction solubility of diazepam increases with the tert-butyl alcohol content in the solvent mixture to reach a maximum in the solvent mixture with a cosolvent mass fraction of 0.90. For every solvent compositions investigated, the transfer of the drug molecules from the pure crystalline solid to the saturated liquid mixtures was found to be endothermic so that the solubility of the drug increases with the temperature. Moreover, for every solvent compositions investigated, enthalpy is the main contributor to the deviation of the systems from ideal behavior, with noticeable exception of neat water. The solubility enhancement of the drug upon increase of the tert-butyl alcohol content in the solvent is then linked to a simultaneous evolution of the partial molar excess entropy and enthalpy of the drug with respect to the solvent composition.

Statistical Thermodynamics of One-To-Many Molecular Recognition Accompanied by Partner-Dependent Folding: In the Case of a Tumor Suppressor Protein p53

A tumor suppressor protein p53 recognizes over 100 biomolecules. Here we investigate the mechanism of its molecular recognition accompanied by partner-dependent folding of its partial peptide, the p53 C-terminal domain (p53-CTD). The p53-CTD lacks a well-defined tertiary structure without a partner, form a helix in binding to S100ββ, a sheet in binding to sirtuin, and a coil with two distinct backbone conformations in binding to CBP or cyclin A. We calculate changes in thermodynamic quantities upon these binding processes using a statistical-mechanical approach combined with molecular models for water. The hydration entropy is calculated by our hybrid method in which the angle-dependent integral equation theory applied to a multipolar water model is combined with the morphometric approach. The three-dimensional reference interaction site model theory is employed for calculation of the hydration energy. This approach is the cutting edge of studies on the biomolecule hydration and on a variety of biological self-assembly processes. It is shown that a common driving force for the p53-CTD binding is a large gain of the water entropy, which originates primarily from an increase in the total volume available to the translational displacement of water molecules in the system and the reduction in the water crowding. We discuss the several characteristics of the one-to-many molecular recognition by p53-CTD from the viewpoint of hydration thermodynamics.

Binding of an RNA aptamer and a partial peptide of a prion protein: crucial importance of water entropy in molecular recognition.

It is a central issue to elucidate the new type of molecular recognition accompanied by a global structural change of a molecule upon binding to its targets. Here we investigate the driving force for the binding of R12 (a ribonucleic acid aptamer) and P16 (a partial peptide of a prion protein) during which P16 exhibits the global structural change. We calculate changes in thermodynamic quantities upon the R12–P16 binding using a statistical-mechanical approach combined with molecular models for water which is currently best suited to studies on hydration of biomolecules. The binding is driven by a water-entropy gain originating primarily from an increase in the total volume available to the translational displacement of water molecules in the system. The energy decrease due to the gain of R12–P16 attractive (van der Waals and electrostatic) interactions is almost canceled out by the energy increase related to the loss of R12–water and P16–water attractive interactions. We can explain the general experimental result that stacking of flat moieties, hydrogen bonding and molecular-shape and electrostatic complementarities are frequently observed in the complexes. It is argued that the water-entropy gain is largely influenced by the geometric characteristics (overall shapes, sizes and detailed polyatomic structures) of the biomolecules.

Statistical mechanics of Roskilde liquids: Configurational adiabats, specific heat contours, and density dependence of the scaling exponent

We derive exact results for the rate of change of thermodynamic quantities, in particular, the configurational specific heat at constant volume, CV, along configurational adiabats (curves of constant excess entropy Sex). Such curves are designated isomorphs for so-called Roskilde liquids, in view of the invariance of various structural and dynamical quantities along them. The slope of the isomorphs in a double logarithmic representation of the density-temperature phase diagram, γ, can be interpreted as one third of an effective inverse power-law potential exponent. We show that in liquids where γ increases (decreases) with density, the contours of CV have smaller (larger) slope than configurational adiabats. We clarify also the connection between γ and the pair potential. A fluctuation formula for the slope of the CV-contours is derived. The theoretical results are supported with data from computer simulations of two systems, the Lennard-Jones fluid, and the Girifalco fluid. The sign of dγ∕dρ is thus a third key parameter in characterizing Roskilde liquids, after γ and the virial-potential energy correlation coefficient R. To go beyond isomorph theory we compare invariance of a dynamical quantity, the self-diffusion coefficient, along adiabats and CV-contours, finding it more invariant along adiabats.

Spectral analysis, structural elucidation, and evaluation of both nonlinear optical properties and chemical reactivity of a newly synthesized ethyl-3,5-dimethyl-4-[(toluenesulfonyl)-hydrazonomethyl]-1H-pyrrole-2-carboxylate through experimental studies and quantum chemical calculations

As part of study of hydrazide–hydrazones, we have synthesized ethyl-3,5-dimethyl-4-[(toluenesulfonyl)-hydrazonomethyl]-1H-pyrrole-2-carboxylate (EDTHMPC) and characterized by elemental analysis, FT-IR, UV–Vis, 1H, 13C NMR and Mass spectroscopy. The structure, spectral and thermodynamic parameters of EDTHMPC were quantum chemically calculated performing density functional level theory (DFT) with B3LYP functional and 6-31G (d,p) basis set. Electrophilic charge transfer (ECT) values of interacting molecules indicate that charge flows from p-toluene sulphonyl-hydrazide to ethyl-3,5-dimethyl-4-formyl-1H-pyrrole-2-carboxylate confirming the formation of product by nucleophilic attack. The calculated and experimental wavenumbers analysis confirms the formation of dimer. The calculated changes in thermodynamic quantities during dimer formation in gaseous phase have the negative values for ΔH, ΔG (kcal/mol) and ΔS (cal/mol-K) indicating that the dimer formation is exothermic and will proceed only at low temperature. The strength and nature of hydrogen bonding and weak interactions in dimer have been analyzed by ‘Quantum theory of atoms in molecules’ (QTAIM) and found to be five types of interactions in which three types are (C⋯N, CH⋯O and CH⋯HC) intramolecular and two types are (CO⋯HN and CH⋯OC) intermolecular. The calculated binding energy of dimer using DFT and QTAIM theory are 14.32 and 15.41kcal/mol, respectively. The β0 value for monomer is calculated as 11.54 x 10–30 esu indicating microscopic nonlinear optical (NLO) behavior with non–zero values.

MAGNETIC FIELD DEPENDENCE OF ENTROPY AND SPECIFIC HEAT OF YBa2Cu3O7-δ SUPERCONDUCTORS

The change in thermodynamic quantities (e.g., entropy, specific heat etc.) by the application of magnetic field in the case of the high-Tc superconductor YBCO system is examined phenomenological by the Ginzburg–Landau theory of anisotropic type-II superconductors. An expression for the change in the entropy (ΔS) and change in specific heat (ΔC) in a magnetic field for any general orientation of an applied magnetic field Ba with respect to the crystallographic c-axis is obtained. The observed large reduction of specific heat anomaly just below the superconducting transition and the observed variation of entropy with magnetic field are explained quantitatively.

Incommensurate spin-density wave and magnetic lock-in transition inCaFe4As3

The magnetic structure for the recently synthesized iron-arsenide compound ${\text{CaFe}}_{4}{\text{As}}_{3}$ has been studied by neutron-powder diffraction. Long-range magnetic order is detected below 85 K, with an incommensurate modulation described by the propagation vector $k=(0,\ensuremath{\delta},0)$, $\ensuremath{\delta}\ensuremath{\sim}0.39$. Below $\ensuremath{\sim}25\text{ }\text{K}$, our measurements detect a first-order phase transition where $\ensuremath{\delta}$ locks into the commensurate value $\frac{3}{8}$. A model of the magnetic structure is proposed for both temperature regimes, based on Rietveld refinements of the powder data and symmetry considerations. The structures correspond to longitudinal spin-density waves with magnetic moments directed along the $b$ axis. A Landau analysis captures the change in thermodynamic quantities observed at the two magnetic transitions, in particular, the drop in resistivity at the lock-in transition.

Thermodynamics and Biological Properties of the Aqueous Solutions of New Glucocationic Surfactants

Thermodynamic properties of aqueous solutions of newly synthesized compounds, namely, N-[2-(beta-D-glucopyranosyl)ethyl]-N,N-dimethyl-N-alkylammonium bromides with hydrophobic tails of 12 (C12DGCB) and 16 (C16DGCB) carbon atoms, determined as a function of concentration by means of direct methods, are reported here. Dilution enthalpies, densities, and sound velocities were measured at 298 K, allowing for the determination of apparent and partial molar enthalpies, volumes, and compressibilities. Changes in thermodynamic quantities upon micellization were derived using a pseudophase-transition approach. From a comparison with the corresponding acetylated compounds N-[2-(2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl)ethyl]-N,N-dimethyl-N-dodecylammonium bromide (C12AGCB) and N-[2-(2,3,4,6-tetra-O-acetyl-beta-D-glucopyanosyl)ethyl]-N,N-dimethyl-N-hexadecylammonium bromide (C16AGCB), the role played in the micellization process by the acetylated glycosyl moiety was inferred: it enhances the hydrophobic character of the molecule and lowers the change in enthalpy of micelle formation by about 1.5 kJ mol(-1). By comparing the volume of C12DGCB with those of DEDAB and DTAB, the volumes taken up by the (beta- d-glucopyranosyl)ethyl and beta- d-glucopyranosyl groups were found to be 133 and 99 cm3 mol(-1), respectively. Regarding the interaction with DPPC membranes, it seems that the sugar moiety of the hexadecyl deacetylated compound gives rise to hydrogen bonds with the oxygen atoms of the lipid phosphates, shifting the phase transition of DPPC from a bilayer gel to a bilayer liquid crystal to lower temperatures. C16AGCB induces significantly greater changes than C16DGCB in the structure of liposomes, suggesting the formation of domains. The interaction is strongly enhanced by the presence of water. Neither compound interacts strongly with DNA or compacts it, as shown by EMSA assays and AFM images. Only C16AGCB is able to deliver little DNA inside cells when coformulated with DOPE, as shown by the transient transfection assay. This might be related to the ability of C16AGCB to form surfactant-rich domains in the lipid structure.

Monte Carlo Study of First-Order Phase Transitions of a Bulk Lennard–Jones Fluid System in the Isobaric–Multithermal Ensemble

Abstract A Monte Carlo (MC) simulation in the isobaric–multithermal (MUTH) ensemble has been carried out for a bulk Lennard–Jones fluid system that consists of 108 particles to investigate the validity of the algorithm. After we obtain the best estimate of the MUTH (isobaric–multithermal) weight factor, the probability distributions, the expectation values of some physical quantities, and the radial distribution functions are calculated for the temperature range between T*=0.417 and 1.00 under the pressure of P*=2.42×10−3 from the MUTH MC production run by adopting reweighting techniques. The thermodynamic quantities exhibit the characteristics of first-order phase transitions at T*=0.726, which correspond to the transition from face-centered-cubic (f.c.c.) solid to liquid by judging from the radial distribution functions and the snapshots. The obtained contour representation of the probability distribution at T*=0.726 and P*=2.42×10−3 shows two distinct configurational spaces. The changes in thermodynamic quantities at the phase-transition temperature of Lennard–Jones argon (at 87 K under 1 atm) were also compared with those of real argon.

Density functional theory investigations on boronyl-substituted ethylenes C 2H 4− m(BO) m ( m = 1–4) and acetylenes C 2H 2− m(BO) m ( m = 1, 2)

The geometrical and electronic structures and electron detachment energies of boronyl-substituted ethylenes C 2H 4− m (BO) m ( m = 1–4) and acetylenes C 2H 2− m (BO) m ( m = 1, 2) have been comparatively studied with the corresponding cyano substitutes at density functional theory level. B O boronyl groups are found to serve basically as σ-radicals in these covalent systems, similar to H in hydrocarbons and C N in cyanocarbons. The electron affinities of boronyl dimer (BO) 2 and boronyl-substituted ethylenes and acetylenes and the first and second vertical detachment energies of their anions have been predicted for the first time. The thermodynamic quantity changes of carbon boronyls turned out to be parallel with the corresponding values of cyanocarbons. The typical symmetrical stretching frequencies of B O functional groups at about 2000 cm −1 feature the vibrational properties of boronyl compounds. The results obtained in this paper and our previous work [S.-D. Li, C.-Q. Miao, J.-C. Guo, G.-M. Ren, J. Comp. Chem. 26 (2005) 799] complete the C n (BO) n carbon boronyl series with n = 2–7 and provide more partially BO-substituted ethylene and acetylene species possible to be synthesized in future experiments.

Theoretical analysis on changes in thermodynamic quantities upon protein folding: Essential role of hydration

The free energy change associated with the coil-to-native structural transition of protein G in aqueous solution is calculated by using the molecular theory of solvation, also known as the three-dimensional reference interaction site model theory, to uncover the molecular mechanism of protein folding. The free energy is decomposed into the protein intramolecular energy, the hydration energy, and the hydration entropy. The folding is accompanied with a large gain in the protein intramolecular energy. However, it is almost canceled by the correspondingly large loss in the hydration energy due to the dehydration, resulting in the total energy gain about an order of magnitude smaller than might occur in vacuum. The hydration entropy gain is found to be a substantial driving force in protein folding. It is comparable with or even larger than the total energy gain. The total energy gain coupled with the hydration entropy gain is capable of suppressing the conformational entropy loss in the folding. Based on careful analysis of the theoretical results, the authors present a challenging physical picture of protein folding where the overall folding process is driven by the water entropy effect.

BEHAVIOR STUDY OF SOME COMMERCIAL NONIONIC COMPOUNDS IN COMPARISON WITH ANIONIC SURFACTANT

The surface tension of aqueous surfactant solutions was measured as a function of temperature at various bulk concentrations for homogeneous series of polyoxyethylene (n) cotton seed fatty acid [Co(EO)n] (where n = 20, 40, and 80 units) as nonionic surfactants and the anionic sodium oleic sulfonate (SOS). The critical micelle concentration (CMC), surface density ΓH, and thermodynamic quantity changes associated with the adsorption and micellization were deduced. CMC values were influenced by both hydrophilic chain length and temperature. It has been found that the trend of ΓH of the tested nonionic samples resembles that of the anionic SOS due to their huge polar head groups. values of the tested nonionic surfactants are lower than that of the anionic surfactant due to the dehydration of the EO chains of the former in addition to the electrostatic repulsion acting between the head groups of the latter. possesses lower values than due to the crowding of the hydrocarbon chains acting inside the micelle. The variations of surface tension with temperature as well as entropy with concentration show the probability of nonionic surfactants (with long EO chains) behaving the same as ionic surfactants.

Changes in thermodynamic quantities upon contact of two solutes in solvent under isochoric and isobaric conditions

The changes in excess thermodynamic quantities upon the contact of two solutes immersed in a solvent are analyzed using the radial-symmetric and three-dimensional versions of the integral equation theory. A simple model mimicking a solute in water is employed. The solute-solute interaction energy is not included in the calculations. Under the isochoric condition, the solute contact always leads to a positive entropy change irrespective of the solute solvophobicity or solvophilicity. The energy change is negative for solvophobic solutes while it is positive for solvophilic ones. Under the isobaric condition, the contact of solvophobic solutes results in system-volume compression but that of solvophilic ones gives rise to expansion. Effects of the compression and expansion on the changes in enthalpy and entropy are enlarged with rising temperature. When the solute solvophobicity is sufficiently high, the entropy change (multiplied by the absolute temperature) can become negative due to the compression, except at low temperatures with the result of an even larger, negative enthalpy change. The expansion in the case of solvophilic solutes leads to a large, positive entropy change accompanied by an even larger, positive enthalpy change. The changes in enthalpy and entropy are strongly dependent on the temperature. However, the changes in enthalpy and entropy are largely cancelled out and the temperature dependency of the free-energy change is much weaker. The authors also discuss possible relevance to the enthalpy-entropy compensation experimentally known for a variety of physicochemical processes in aqueous solution such as protein folding.

Thermodynamic properties of aqueous micellar solutions of some new acetylated gluco-cationic surfactants

Thermodynamic properties of the aqueous solutions of a newly synthesized homologous series of N-[2-(2,3,4,6-tetra- O-acetyl-β- d-glucopyranosyl)ethyl]- N, N-dimethyl- N-alkylammonium bromides with hydrophobic tails of 8, 12 and 16 carbon atoms, determined as a function of concentration by means of direct methods, are here reported for the first time. Dilution enthalpies, densities and sound velocities were measured at 298 K, allowing for the determination of apparent and partial molar enthalpies, volumes and compressibilities. Changes in thermodynamic quantities upon micellization were derived using a pseudo-phase transition approach. The trends of apparent and partial molar enthalpies versus m confirm the increase in global hydrophobicity of the molecule, already suggested by the value of the cmc of C 12AGCB, lower than that of DTAB, and show that, also in the case of surfactants with a bulky substitution on the polar head, the group contribution of the –CH 2– is additive both in the plateau (−1.3 kJ mol −1 group −1) and in the micellization enthalpy changes (−1.5 kJ mol −1 group −1). The determination of apparent molar volumes and compressibilities presents some experimental problems, due to the strong tendency of this class of surfactants to adsorb on the glass surfaces. Even so, the group contribution of the methylene group results as being additive and comparable to that of other cationic and anionic surfactants. From the comparison with DTAB, the volume of (2,3,4,6-tetra- O-acetyl-β- d-glucopyranosyl)ethyl group results as 291 cm 3 mol −1.

Thermodynamics of aqueous solutions of dodecyldimethylethylammonium bromide

The thermodynamic properties of the aqueous solutions of dodecyldimethylethylammonium bromide (DEDAB) were determined as a function of concentration by means of direct methods. Dilution enthalpies at 298 and 313 K, densities and sound velocities at 298 K were measured, allowing the determination of apparent and partial molar enthalpies, volumes, heat capacities and compressibilities. Changes in thermodynamic quantities upon micellization were derived using a pseudo-phase transition approach. These data allow for the determination of the effect of the CH 2 group, when added to the polar head of alkyltrimethylammonium bromides. The properties mainly affected by this addition are the enthalpies and, as a consequence, the entropies. The lowering of the charge density on the quaternary nitrogen due to the inductive effect of the ethyl group, greater than that of the methyl one, raises the plateau value of apparent and molar enthalpy by a quantity similar to that due to the removing of a methylene group from the hydrophobic chain. This effect does not play a great role in the value of the cmc (i.e. on the free energy of micelle formation), since the small decrease in cmc of DEDAB compared to DTAB reflects the increase in the overall hydrophobicity of the molecule. Volumes of DEDAB are greater than those of DTAB by about 15 cm 3 mol −1, both at infinite dilution and at micellar phase, a value in agreement with that generally accepted for a methylene group. The trends of apparent molar heat capacities and compressibilities vs m are the same as for DTAB: in fact, these quantities are related to the number of water molecules involved in the hydrophobic processes in solution, not very greatly affected by the substitution of a methyl group by an ethyl one on the polar head. In summary, this substitution affects to a significant extent the first derivatives of the free energy, but does not affect the second derivatives.

The influence of Coulomb interaction on the equation of state under nuclear statistical equilibrium conditions

In the domain of thermodynamic parameters characteristic of the initial collapse of iron stellar cores, we studied the influence of Coulomb interaction on the thermodynamic functions of a plasma under nuclear statistical equilibrium conditions. Our attention was focused on the nuclear component of the matter. We established that including the interaction shifts the equilibrium toward the nuclei with larger charges. However, this effect and the changes in thermodynamic quantities are noticeable only at high densities (ρ ≳ 1011 g cm−3), i.e., at an advanced stage of gravitational collapse. We also showed that the mean ion model is inadequate in regions with a coupling parameter Γ ∼ 1. We point out a method for modifying the linear mixing model to properly pass to the Debye limit and discuss other multicomponent plasma models.

Retention of 3,5-dinitrobenzoyl derivatives of linear alcohol polyethoxylates in reversed-phase liquid chromatographic system with acetonitrile–water mobile phase

The influence of mobile phase composition (acetonitrile–water ratio) on the separation of derivatised linear alkyl polyethoxylates (LAEs) is evaluated using thermodynamic quantities (Gibbs energy, enthalpy and entropy). In comparison to homologue series of alcohols oligomers of LAEs show irregular chromatographic behaviour that is demonstrated in irregular changes of thermodynamic quantities. It might be explained considering an influence of some of the following processes or their combinations on the retention of LAEs. These processes are solvation of oxyethylene chains in mobile phase, their interaction with silanols on silica surface of stationary phase and possibly their conformation changes. The composition of a mobile phase affects the mentioned processes and that is why the retention of LAEs is strongly (for the reversed-phase system unusually) sensitive to this composition in the studied range (volume fraction of acetonitrile ϕ=0.90, 0.96 and 0.98). The experimental data also support the idea of the active role of stationary phase in the reversed-phase system.