Regions Of Isotherms Research Articles

Adsorption of Natural 3-Phenylpropenic Acids on Cerium Dioxide Surface

It has been shown that adsorption of natural antioxidants, such as 3-phenylpropenic (cinnamic), 3-(4-hydroxyphenyl)propenic (coumaric), and 3-(3-methoxy-4-hydroxyphenyl)propenic (ferulic) acids, on the surface of cerium dioxide is characterized by S-type isotherms, while adsorption of 3-(3,4-dihydroxyphenyl)propenic (caffeic) acid is described by an H-type isotherm. A linear correlation between adsorption values and hydrophobicity parameter logP has been found in initial regions of the S-type isotherms, with such correlation being typical for parallel orientation of adsorbed molecules relative to an adsorbent surface. The maximum adsorption values (≈2.9 × 10–4 mol/g), as well as dissociation constants (pKCOOH = 4.4–4.6), are almost identical for all acids, thereby suggesting that adsorbate molecules are predominantly bound to the adsorbent surface via carboxyl groups. The presence of hydroxyl groups in molecules of coumaric, ferulic, and caffeic acids widens the рН range of their adsorption as compared with cinnamic acid and promotes their oxidation on the cerium dioxide surface.

Fluorescence Resonance Energy Transfer, Small-Angle Neutron Scattering, and Dynamic Light Scattering Study on Interactions of Gemini Surfactants Having Different Spacer Groups with Protein at Various Regions of Binding Isotherms.

The binding interactions of three gemini surfactants having different spacer groups (12-4-12, 12-8-12, and 12-4(OH)-12) with a high concentration (150 μM) of bovine serum albumin (BSA) at various regions of binding isotherms have been studied by means of steady-state fluorescence and fluorescence anisotropy, time-correlated single-photon counting fluorescence of trans-2-[4-(dimethylamino)styryl]benzothiazole, small-angle neutron scattering (SANS), and dynamic light scattering (DLS) measurements. The fluorescence resonance energy transfer phenomenon between the twisted intramolecular charge transfer fluorescent molecule, trans-2-[4-(dimethylamino)styryl]benzothiazole as an acceptor, and tryptophan 213 (Trp-213) of BSA as a donor has been successfully used to probe the binding interactions of gemini surfactants with protein at all regions of binding isotherms. The increasing order of energy transfer efficiency at a higher concentration range of surfactants is 12-8-12 > 12-4-12 > 12-4(OH)-12. Stronger binding of micelles of gemini surfactant molecules having a comparatively more hydrophobic spacer group with the hydrophobic segments of the protein results in closer approach of trans-2-[4-(dimethylamino)styryl]benzothiazole molecules solubilized in micelles to Trp-213. The average excited-state lifetimes become shorter with a trend of increase in contribution from the fast component and decrease in contribution from the slow component to the decay with increasing concentration of a surfactant. The nonradiative rate constant of trans-2-[4-(dimethylamino)styryl]benzothiazole increases with increasing concentration of a surfactant because the average microenvironment around it in protein–surfactant aggregates is more polar as compared to that in native protein. SANS and DLS measurements were carried out for the study of the structural deformations in the protein, on enhancement of the concentration of the gemini surfactants. The necklace and bead model has been used for the analysis of SANS data for the protein–surfactant complexes. At a higher concentration range, 12-8-12 and 12-4-12 have a slightly smaller fractal dimension and a larger correlation length as compared to 12-4(OH)-12. DLS data show that the increasing order of hydrodynamic diameter for the complexes of protein with three gemini surfactants in their high concentration range is 12-4(OH)-12 < 12-4-12 < 12-8-12.

The effect of the surface chemistry of silica nanoparticles on sorption of polystyrene macromolecules

Adsorption isotherms of polystyrene from its solutions in tetrachloromethane and toluene on the hydroxylated, dehydroxylated, and silanized surfaces of nanoparticles of nonporous silica aerosil were measured. The adsorption equilibrium constants were calculated from the initial linear regions of the adsorption isotherms of polystyrene. The coefficients of distribution of polystyrene molecules between the surface and bulk phases and the changes in the free energy during the interaction between polystyrene macromolecules and hydroxylated, dehydroxylated, and silanized surfaces of aerosil nanoparticles were determined using the model of an adsorbed layer of constant thickness. The comparison of the experimental isotherms and the computed thermodynamic parameters of adsorption enabled revealing the effect of the surface state of aerosil nanoparticles and chemical nature of the solvent on the behavior of polystyrene macromolecules at the interface.

Influence of hydrogen absorption–desorption on structural properties ofDy1−xMmxCo2 alloys

The effect of hydrogen absorption–desorption on the structural properties of Laves phaseDy1−xMmxCo2 (x = 0.1, 0.3and 0.5; Mm = mischmetal, a natural mixture of the light rare earth metals containing 50 wt% Ce, 35 wt%La, 8 wt% Pr, 5 wt% Nd and 1.5 wt% of other rare earth elements and 0.5 wt%Fe) alloys has been investigated by means of hydrogen absorption–desorptionpressure-composition (PC) isotherms, kinetics of hydrogen absorption and powderx-ray diffraction (XRD). The PC isotherms and kinetics of hydrogen absorptionhave been studied in the pressure range 0.001–1 bar and temperature range50–200 °C using Sieverts-type apparatus. The experimental results of the kineticcurves are interpreted using the Johnson–Mehl–Avrami (JMA) modeland the reaction order and reaction rate have been determined. Theα-,(α+β)- and β-phase regions have been identified from the different slope regions of thePC isotherms and first-order type kinetic plots. The dependence of thereaction rate parameter upon hydriding pressure and temperature in the(α+β)-phase region has been discussed. The effect of hydrogenation pressure, temperatureand Mm concentration on the hydrogen-induced transformation from crystallineDy1−xMmxCo2–H toamorphous Dy1−xMmxCo2–H and decomposition into crystalline (Dy,Mm)H2 and Co have been discussed in detail. Further, the effect ofdehydrogenation on the recovery of the crystalline Laves phase structure ofDy1−xMmxCo2 fromits decomposed state is presented. This hydrogenation–disproportionation–desorption–recombination(HDDR) process can be conveniently used in powder metallurgy.

Physical Adsorption Analysis of Intact Supported MFI Zeolite Membranes

We compare the adsorption properties of intact supported silicalite membranes with those of silicalite powder and of alumina supports using nitrogen and argon as adsorbates at 77 K. We disentangle contributions from the membrane and support and find that the support contributes significantly to the total quantity adsorbed due to its relative thickness. The micropore-filling regions of the adsorption isotherms of the powder and the supported membrane are nearly identical for the membranes studied, but the isotherms differ at higher pressures--the supported membranes exhibit a much higher quantity adsorbed than the powders. Despite this difference, no hysteresis is observed in the membrane isotherms, indicating a lack of mesoporosity (pores in the 2-50 nm range) in either membrane or support for this preparation. We estimate argon transport fluxes at steady state by assuming surface diffusion with both a constant and concentration-dependent Maxwell-Stefan diffusion coefficient in the zeolite and the support. Further, we use the respective adsorption isotherms to determine the thermodynamic correction factors--that is, the ratios of the Fick and Maxwell-Stefan diffusion coefficients--required to solve the diffusion equation. The estimated argon flux is virtually the same using adsorption data from powders and membranes. For the relatively thick supports used in our study (approximately 2 mm), we find that the support exerts a much greater influence on the predicted fluxes for a wide range of values of the ratio of the support to zeolite diffusion coefficients. We emphasize that the results are specific to the architecture of the supported membranes studied, and thus, the results should be interpreted accordingly.

Adsorption Reaction Constants between Nanosilica/Nanodiamond and Lysozyme Molecule at pH = 11.0

Abstract Adsorption reaction constants of chicken egg lysozyme of 0–1000 nM prepared with potassium phosphate buffer solution (PPBS) of 7.0 mM and at pH = 11.0 on the surfaces of nanosilica and nanodiamond of diameter 100 nm by fluorescence method have been determined as 4.0 × 107 and 1.5 × 108 nM−1, respectively. The Langmuir isotherm can be well followed under the assumption of monolayer adsorption on both surfaces. The available surface areas per individual lysozyme molecule adsorbed on nanosilica and nanodiamond within the linear regions of Langmuir isotherms can be approximated with 2 and 10 nm2, respectively.

Experimental Evidences of Self-Assembly in Foam Films from Amphiphilic Solutions

Systematic foam film experiments are performed with amphiphile solutions. Specific film parameters are extracted which are related to the film lifetimes and reflect the coupling of film dynamics and the reorganization of surfactant assemblies present both in the film bulk and in the adsorption layers on its interfaces. A distinct qualitative sign of the above-stated coupling is the onset of peculiar unstable black patterns (black dots and “black spots”). Their occurrence is correlated with the plateau regions of the surface tension isotherms of the initial surfactant systems. The enhanced onset of the unstable black formations results in a sharp increase of the foam film lifetimes. This effect is interpreted as related to the disintegration of the amphiphilic structures in the process of film drainage. These experimental results are viewed as experimental evidences for the presence of amphiphilic structures in the primary surfactant solutions.

Adsorption of organic substances with different physicochemical properties

The linear regions of the adsorption isotherms of freon 13B1 (CF3Br) on active carbons with different porous structures were studied by gas chromatography at 343–573 K. The Henry's constants were determined, and the isosteric heats of adsorption (Q) were calculated in the region of zero filling. It was established that theQ values for active carbons with different pore size distributions are almost the same and vary within 38–41 kJ mol−1. This coincidence can be explained assuming that the interaction between the adsorbed molecules and the active carbons occurs in the pores whose sizes are comparable with those of the adsorbed molecules.

TIRF of salt and surface effects on protein adsorption: I. Equilibrium

Total internal reflectance fluorescence spectroscopy was used to study protein adsorption under conditions relevant to those used in liquid chromatography, particularly hydrophobic interaction chromatography. The effects of surface characteristics (butylated or aminopropylated) and solution salt conditions (concentration of NaCl or (NH 4) 2SO 4) on the extent of adsorption of lysozyme and chymotrypsinogen A on modified quartz surfaces were studied. An internal calibration technique was used to relate the intrinsic fluorescence intensity of the proteins to surface concentration. The two proteins displayed similar adsorption characteristics. Adsorption was found to be largely irreversible on the butylated slides but more readily reversible on the aminopropylated slides. Both proteins adsorbed on aminopropylated surfaces despite the expected electrostatic repulsion between the positively charged surface and the proteins, both of which bear a net positive charge at pH 7. Salt strength affected the extent of surface coverage, even in the plateau regions of adsorption isotherms; thus monolayer coverage was not attained under all conditions at high bulk protein concentrations. Salt effects on adsorption on butylated surfaces appeared to be due largely to those on solubility, but on aminopropylated surfaces the interaction of salt with the charged surface was apparent in adsorption behavior.

A comparison of the adsorption behaviour of nitrogen, alcohols and water towards active carbons

The adsorption behaviour of a range of vapours, of varying polarity, for two commercial carbons is reported. Type 5 (BDDT) isotherms are observed for water vapour adsorption where polar interactions predominate. Nitrogen gives type 1 isotherms, indicating that the major interaction is of the dispersion type. The initial regions of isotherms for the alcohols methanol to butanol suggest an increase in the relative dispersion to polar interaction with increasing molar volume, although the dispersion interaction appears dominant in all cases and the overall isotherms are all of type 1 character. Saturation volumes and Dubinin-Radushkevich micropore volumes from N 2 and the alcohols are consistent for each carbon. Saturation volumes for water adsorption are much lower than those from the other vapours. The high pressure regions of Polanyi characteristic curves for N 2 and the alcohols can be superimposed using β shifting factors based on molar volume or parachor data, low pressure deviations cannot be explained by molecular sieve effects and are most likely due to differential packing of adsorbate within the micropores. The Dubinin-Astakhov equation does not appear to offer any advantages for analysis of the data presented.

Physical Properties of Lipid Monolayers on Alkylated Planar Glass Surfaces

A method for transferring a lipid monolayer from an air-water interface to an alkylated glass slide is described. Specific antibodies bind tightly to lipid haptens contained in these monolayers on the glass slides. We conclude that the polar head groups of the lipids face the aqueous phase. A monolayer containing a fluorescent lipid was used to show that the monolayer is homogeneous as observed with an epifluorescence microscope. A periodic pattern photobleaching technique was used to measure the lateral diffusion of this fluorescent lipid probe in monolayers composed of dipalmitoyl phosphatidylcholine and dimyristoyl phosphatidylcholine. Different regions of the pressure-area isotherms of the monolayers at the air-water interface can be correlated with the diffusion of the fluorescent probe molecules on the monolayer-coated glass slide. Monolayers derived from the so-called "solid-condensed" state of a monolayer at the air-water interface showed a very low probe diffusion coefficient in this monolayer when placed on a glass slide, D </= 10(-10) cm(2)/s. Monolayers derived from the "liquid condensed/liquid expanded" (LC/LE) region of the monolayer isotherms at the air-water interface showed rapid diffusion (D > 10(-8) cm(2)/s) when these same monolayers were observed on an alkylated glass slide. The monolayers attached to the glass slide appear to be homogeneous when derived from monolayers in the LC/LE region of monolayers at the air-water interface. There is no major variation of the diffusion coefficient of a fluorescent lipid probe when this diffusion is measured on a lipid monolayer on a glass slide, for monolayers derived from various regions of the LC/LE monolayers at the air-water interface. This is consistent with the view that the LC/LE region is most likely a single fluid phase. Monolayers supported on a planar glass substrate are of much potential interest for biophysical and biochemical studies of the interactions between model membranes and cellular membranes, and for physical chemical studies relating the properties of lipid monolayers to the properties of lipid bilayers.

Two-component monolayers. III. Evaporation resistances of the octadecanol—docosyl sulphate system

The evaporation resistances of monolayers of the octadecanol-docosyl sulphate system have been measured by the Langmuir-Schaefer technique. Eleven different compositions spanning the entire composition range were studied. At surface pressures above 15 mN m −1 evaporation resistances of the mixed monolayers were greater than resistances calculated from the Barnes-La Mer logarithmic addition rule. At lower surface pressures the pattern was more complex, but of special note was a sharp drop in resistance from the high value of a pure octadecanol monolayer to the low values of the various mixtures. These results are discussed in terms of the energy barrier theory and excess free energies of activation ( ΔG ≠E) are reported. A relationship between these values and the excess free energies of mixing ( ΔG E): ΔG ≠E = − KΔG E, is established, provided allowance is made for the (unmeasured) contributions of the high area regions of the surface pressure-area isotherms to AGE. When the evaporation resistance data are plotted against molecular area, as suggested by the accessible area theory, all of the points fall roughly on the same curve except for the points for pure octadecanol monolayers. The high resistances of octadecanol are attributed to a low value of the evaporation coefficient.