Kinetic study of adsorption of some biocompounds at the oil/water interface

The adsorption kinetics of some local anesthetics, like dibucaine and tetracaine, and of stearic acid from bulk solutions at the oil/water interface was studied by using the pendent drop and ring methods. The anesthetics were dissolved in aqueous solutions (pH 2), and the fatty acid was dissolved in benzene, each biocompound at several different concentrations in bulk solutions. Kinetic equations for Langmuir mechanism of adsorption at oil/water interface were tested. The kinetic analysis shows that Langmuir kinetic approach describes the dynamic interfacial pressures within the limits of the experimental errors over a wide range of time and for different surfactant concentrations in bulk solutions. It is also concluded that this approach allows the calculation of the ratio of the adsorption and desorption rate constants of these biocompounds at the oil/water interface. Obtained results are in substantial agreement with earlier reported data for the surfactant adsorption as, well as with their molecular structure.     

Chemometric study of soil analysis data

The present paper deals with chemometric interpretation of soil analysis data collected from 31 sampling sites in the region of Kavala and Drama, Northern Greece. The determination of 16 different chemical and physicochemical characteristics is principally needed for prognosis of the land treatment and fertilizing. The study carried out indicates that the application of multivariate statistical approaches could reveal new and specific information about sampling sites. It has been found that they could be divided into four general patterns: pattern 1 contains dominantly inorganic and alkaline soil samples from semi-mountainous regions in close proximity to the seacoast; pattern 2 indicates the same soil sample type and regional location as pattern 1 but is far from the coastal line; pattern 3 includes samples from sites from the plains with organic and alkaline soils with close proximity to the coast; pattern 4 resembles pattern 3 as soil type but involves samples from sites far from the shore. Further, six latent factors were identified, conditionally named “structural”, “acidic”, “nutritional”, “salt”, “microcomponents” and “organic”. Finally, an apportioning procedure was carried out to find the source contributions in the measured analytical values. In this way the routine estimation of the soil quality could be improved.     

One-step synthesis of α-hydroxy-α-azinylcyanoacetic esters from α-nitro derivatives of α-azinylcyanoacetic esters

When boiled in aromatic hydrocarbons, solutions of α-nitro-α-azinylcyanoacetic esters of the pyrimidine, pyrazine, ands-triazine series gave the corresponding α-hydroxy derivatives of α-azinylcyanoacetic esters in high yields. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1407–1409, July, 1997.     

Gas adsorption by a crystalline silicic acid

Crystalline silicic acids are prepared from alkali layer silicates by exchanging protons for the alkali ions. The acid H₂Si₂₀O₄₁ · xH₂O (parent material K₂Si₂₀O₄₁ · xH₂O) exhibits some outstanding gas adsorption properties which are related to the layer structure and the interlamellar microporosity. The external surface, about 20 m² g^–1, is estimated from nitrogen adsorption data after blocking the micropores. Slit-shaped ultramicropores (with diameters similiar to that of the nitrogen molecule) between the layers are widened to supermicropores near the crystal edges. During an adsorption run the nitrogen molecules penetrate more deeply into the ultramicropores. Nitrogen molecules strongly adsorbed in the ultramicropores are not desorbed at 77 K. Additional amounts of nitrogen are adsorbed by widening of the slit-shaped micropores at the crystal edges when pressure increases. This process proceeds slowly and is reversible.     

The Structure of Tris(3',5'-dimethylpyrazol-1-yl)-s-triazine and Its Use as a Ligand in Coordination Chemistry

The crystal and molecular structure of the title compound (Me₂-TPzT) has been determined by X-ray analysis. The observed molecular conformation presents the nitrogen atoms of three pyrazole rings in the same relative positions. The molecules are joined through intermolecular contacts forming chains that are arranged in a distorted hexagonal symmetry. Two complexes containing this ligand have been prepared: [{Pd(en)}₃(Me₂-TPzT)](PF₆)₆ and [{Ag(PPh₃)}3(Me₂-TPzT)](ClO₄)₃, which, due to their insolubility, have been characterized only by microanalysis, IR, ¹H NMR and, in the latter case, by mass spectrometry.     

Application of a partially mobile model of monolayer adsorption to multilayer phenomena

Two multilayer adsorption models are discussed, assuming partially mobile adsorption in the first layer, and theBET orKim-Oh (KO) mechanisms for formation of higher layers. The theoretical multilayer adsorption isotherms corresponding to these models have been calculated for differing degrees of mobility of the first layer.

---

Anwendung eines partiell mobilen Modells der Adsorption der ersten Schicht bei Mehrschicht-Phenomenen

Zusammenfassung Zwei Mehrschicht-Modelle, bei der Annahme einer partiell mobilen Adsorption der Erst-Schicht, und desBET, bzw.Kim-Oh (KO) Mechanismus für die Ausbildung höherer Schichten, werden diskutiert. Die theoretischen Mehrschicht-Adsorptionsisothermen, die diesen Modellen entsprechen, werden für verschiedene Grade von Mobilität der ersten Schicht berechnet.

     

Multilayer adsorption from multicomponent liquid mixtures on solid surfaces

Multilayer adsorption of multicomponent liquid mixtures on homogeneous and heterogeneous solid surfaces is discussed. Heterogeneity effects of the adsorbent surface have been taken into account in calculation of mole fractions of the components in the first adsorbed layer. The model calculations, illustrating multilayer and heterogeneity effects, have been performed for adsorption of ternary liquid mixtures.

---

Mehrschicht-Adsorption von flüssigen Mehrkomponentenmischungen auf festen Oberflächen

Zusammenfassung Es wird die Mehrschichtadsorption auf homogenen und heterogenen Oberflächen diskutiert. Bei der Berechnung der Molbrüche der Komponenten der ersten adsorbierten Schicht wurden Heterogenitäts-Effekte berücksichtigt. Die Modellrechnungen wurden an ternären flüssigen Mischungen vorgenommen.

     

Statistical thermodynamics of adsorption from multicomponent liquid mixtures on heterogeneous solid surfaces

The statistical thermodynamics of adsorption from multicomponent liquid mixtures on heterogeneous solid surfaces is discussed by assuming the cell adsorption model and ideal adsorbed phase.Two integral representations for the adsorption isotherm are proposed: one based onn-dimensional energy distribution function (i.e., each adsorption site is characterized by adsorption energies of all components), and the other based on distribution of differences of adsorption energies ofn-1 components in relation to adsorption energy of the chosen component (i.e., each adsorption site is characterized byn-1 differences of adsorption energies of the components in relation to adsorption energy of the chosen component).The expressions for differential adsorption heat for adsorption from binary liquid mixtures have been derived from both integral equations.

---

Statistische Thermodynamik der Adsorption aus flüssigen Mehrkomponentenmischungen auf heterogenen festen Oberflächen

Zusammenfassung Die statistische Thermodynamik der Adsorption von aus mehreren Komponenten bestehenden flüssigen Mischungen auf heterogenen festen Oberflächen wird für das Modell der Zellenadsorption bei ideal adsorbierter Phase diskutiert.Zwei Integraldarstellungen der Adsorptionsisotherme werden vorgeschlagen: eine auf einen-dimensionale Verteilungsfunktion der Energie gestützte (das heißt, jede Adsorptionsstelle wird durch Adsorptionsenergien von allen Komponenten charakterisiert); die andere basiert auf der Verteilung der Unterschiede von Adsorptionsenergien dern-1-Komponenten in bezug auf die Adsorptionsenergie der ausgewählten Komponente (das heißt, jede Adsorptionsstelle wird durchn-1-Unterschiede charakterisiert. Formeln für differentiale Adsorptionswärmen für die Adsorption aus binären flüssigen Mischungen sind von beiden Integral-Gleichungen abgeleitet worden.

     

MRINDO/S-CI calculation on the electronic spectra of higher azines

Summary MRINDO/S calculation completed by singly excited configuration interaction was performed on the higher aziness-triazine,s-tetrazine and pentazine. The results enable the main characteristics of the observed electronic spectra to be interpreted. The importance of outer (Rydberg) atomic orbitals is stressed and it is found that a few singlet-singlet transitions of the higher azines lead to an excited state with considerable Rydberg character.     

UV-Vis spectroscopic study on effects of pressure for adsorption ofp-nitrotoluene at liquid-solid interface

The behavior ofp-nitrotoluene adsorbed at zeolite/n-heptane interface has been investigated by the electronic spectroscopy under pressure up to 300 MPa. The uv-vis absorption bands of adsorbedp-nitrotoluene were deconvoluted into ones for the species adsorbed on the cation sites, and one for that on the pore wall of zeolite. The peak of adsorbed species on the cation site red-shifted by 20–80 nm from the position of the same species in the liquid phase, and their magnitudes of shift depended on the strength of electric field generated by the cation in zeolites. The peak intensities of adsorbed species on the cation site were enhanced but these or the pore wall site were reduced with the increase in pressure, suggesting that a part ofp-nitroluene molecules on the pore wall site desorbed and the adsorption on the cation site was enhanced by compression. The pressure dependence of peak intensity indicated that the behavior of this adsorption system was strongly governed by the solvation structure of the adsorbate in the zeolite pore. In particular, it was found that the adsorption of solvent molecules on the cation site strongly affected the volume change of the adsorption system.     

A new way for calculating the adsorption capacity from surface excess isotherms

 Adsorption of n-butanol and water from butanol–water mixtures is studied on adsorbents of different hydrophobicity (activated carbon and hydrophobized montmorillonites). The shape of the adsorption isotherms of the hydrophobized clay minerals does not indicate preferential adsorption of butanol. Therefore, the adsorption capacity cannot be determined on the basis of the Langmuir isotherm. A new equation for determining the adsorption capacity is derived by combining the free enthalpy of adsorption with the adsorption excess amount. Both collections of data are obtained from the surface excess isotherm. The reliability of the adsorption capacity is checked by X-ray diffraction measurements. Received: 1 November 1997 Accepted: 19 February 1998     

The adsorption of CaOH+ on (001) basal and (010) edge surface of Na‐montmorillonite: a DFT study

Ca²⁺ cations were generally added to facilitate the coagulation of stable fine clay mineral dispersion due to the specific adsorption of their first hydrolysis CaOH⁺ species at pH near 10. The adsorption of CaOH⁺ on dry and hydrated (001) basal surface and (010) surface of Na‐montmorillonite was investigated by using density functional theory method combined with the periodic slab model method. The adsorption energies and geometries, Mulliken charge, electron density difference, and density of state were presented and discussed. It was found that the adsorption energy of CaOH⁺ on (010) edge surface of Na‐montmorillonite (?328.8 kJ/mol) was much larger than that (?126.9 kJ/mol) on (001) basal surface. The presence of waters could increase the adsorption energy of CaOH⁺ on (001) surface but affect that on (010) surface slightly. The protons in Si–OH and Al–OH₂ groups as well as the OH₂ ligands in Al–OH₂ group on (010) edge surface were easily dissociated and coordinated to CaOH⁺ to form new waters. CaOH⁺ was the most steady adsorption species among CaOH⁺, Ca²⁺ cation, and H₂O molecule on both (001) and (010) surfaces. Copyright © 2016 John Wiley & Sons, Ltd.     

Microwave-assisted synthesis and reversed-phase high-performance liquid chromatographic separation of diastereomers of (R,S)-baclofen using ten chiral derivatizing reagents designed from trichloro-s-triazine

Four dichloro-s-triazine (DCT) and five monochloro-s-triazine (MCT) chiral derivatizing reagents (CDRs) were synthesized by incorporating amino acid amide moieties as chiral auxiliaries in trichloro-s-triazine and its 6-methoxy derivative, respectively. Another MCT reagent was synthesized by substitution of two chlorine atoms with two different amino acid amides in trichloro-s-triazine. These reagents were used for synthesis of diastereomers of (R,S)-baclofen under microwave irradiation (i.e. 60 s at 85% power using DCT reagents and 90 s at 85% power using MCT reagents). The diastereomers were separated on a reversed-phase C18 column using mixtures of methanol with aqueous trifluoroacetic acid (TFA) with UV detection at 230 nm. The separation behavior in terms of retention times and resolutions obtained for the two sets of diastereomers prepared with DCT and MCT reagents were compared among themselves and among the two groups. Longer retention times and better resolutions were observed with DCT reagents as compared to MCT reagents. The calibration curves were linear for both (R)- and (S)-baclofen in the concentration range 50-500 μg/ml. The average regression was 0.999 for both (R)- and (S)-baclofen. The RSD for (R)-baclofen was 0.40-0.86% for intra-day precision and 0.60-1.40% for inter-day precision and these values for (S)-baclofen were 0.52-0.75% and 0.64-1.32%, respectively. The recovery was 97.2-98.9% for (R)- and 97.0-98.9% for (S)-baclofen. The limit of detection was 1.63ng/ml and 1.52ng/ml for (R)- and (S)-baclofen, respectively.     

Kinetics of adsorption and desorption of sodium alkyl sulfates to and from nylon particles

The desorption rate of surfactant ions from nylon particles was investigated at the concentrations below the critical micelle concentration by applying the stopped-flow method. A mixing cell of stopped-flow spectrophotometer was modified with platinum electrodes for electric conductivity detection. The change in electric conductivity with time in the desorption process was monitored by a memory-recorder system. The surfactants used were sodium decyl, sodium dodecyl, sodium tetradecyl, and sodium hexadecyl sulfates. The desorption rate was independent of the surfactant concentration and the rate constants were obtained by applying the first-order reaction scheme. The adsorption rate constants were estimated from the experimental desorption rate constants and equilibrium constants assuming the second-order kinetics. The desorption rate constants were determined to be 1–6 sec^–1 and the adsorption rate constants to be 2–8×10⁴ mol^–1 dm³ sec^–1; the former decreased and the latter increased with increasing number of carbon atoms in alkyl chain of the surfactants.     

Role played by the head size of some non‐ionic surfactants on their adsorption onto montmorillonite clay

Sorption behavior of polyoxethylene(n)monooleate series [Ol(EO)_n] onto montmorillonite clay was studied at 25°C to investigate the influence of the surfactant's head size on the sorption process. All the tested surfactants exhibited L‐shaped isotherms that means a strong interaction between the adsorbent and the adsorbate. Also, all the obtained isotherms ended with a drastic increase in the isotherm slope at nearly constant equilibrium concentration. This abrupt increase reflected the fairly high affinity of the tested surfactants to the clay surface at high bulk concentration region. The maximum amount adsorbed at the plateau region, Γ_max, was calculated according to the Langmuir adsorption theory and followed the order: Ol(EO)₁₄ > Ol(EO)₂₀ < Ol(EO)₄₀ < Ol(EO)₈₀. In case of short ethylene oxide (EO) chain, Γ_max decreased with the increase in the chain length; but a reverse result was obtained in case of surfactants with longer EO chain length (20 to 80 units). The free energy of adsorption, ΔG°_ad, had negative values indicating the spontaneous adsorption of surfactant molecules onto clay. The values of ΔG°_ad increased with increasing EO units from 14 to 20 units and decreased with further elongation in the EO chain from 20 to 80 units. Copyright © 2004 John Wiley & Sons, Ltd.     

Extension of theHüttig isotherm on mixed gas adsorption

Hüttig's theory was extended for mixed gas adsorption. The derived equation is the same as the one that has been obtained byGonzalez andHolland for bilayer adsorption.

---

Erweiterung der Hüttig-Isotherme für Gasmischungen (Kurze Mitteilung)

Zusammenfassung Die Theorie vonHüttig wurde auf gemischte Gase ausgedehnt. Die dabei abgeleitete Gleichung ist dieselbe wie die vonGonzalez undHolland für Zweischichtadsorption.

     

亚硝胺在小微孔沸石上的“嵌入式”吸附探讨

通过结构计算分析了大体积的六亚甲基亚硝胺（NHMI）和N’-亚硝基去甲烟碱（NNN）在小微孔沸石上各种可能的吸附方式,结合实验事实推断出它们以－N－N=O官能团嵌入沸石孔道进行吸附的几率最大.这种“嵌入式”吸附方式是小微孔沸石得以吸附、分离那些体积远远大于其孔径的毒物分子的重要原因,可用以拓宽沸石在生态环境保护中的应用.     

Reversed-phase high-performance liquid chromatographic separation of diastereomers of (R,S)-mexiletine prepared by microwave irradiation with four new chiral derivatizing reagents based on trichloro-s-triazine having amino acids as chiral auxiliaries and 10 others having amino acid amides

A new series of chiral derivatizing reagents (CDRs) consisting of four dichloro-s-triazine reagents was synthesized by nucleophilic substitution of one chlorine atom in trichloro-s-triazine with amino acids, namely L-Leu, D-Phg, L-Val and L-Ala as chiral auxiliaries. Two other sets of CDRs consisting of four dichloro-s-triazine (DCT) and six monochloro-s-triazine (MCT) reagents were also prepared by nucleophilic substitution of chlorine atom(s) with different amino acid amides as chiral auxiliaries in trichloro-s-triazine and its 6-methoxy derivative, respectively. These 14 CDRs were used for the synthesis of diastereomers of (R,S)-mexiletine under microwave irradiation (i.e. 60s and 90 s at 85% power (of 800 W) using DCT and MCT reagents, respectively), which were resolved by reversed-phase high-performance liquid chromatography using C18 column and gradient eluting mixtures of methanol with aqueous trifluoroacetic acid (TFA) with UV detection at 230 nm. The resolution (R(s)), difference between retention times of resolved diastereomers (Δt) and retention factors (k) obtained for the three sets of diastereomers were compared among themselves and among the three groups. Explanations have been offered for longer retention times and better resolution of diastereomers prepared with DCT reagents in comparison of their MCT counterparts and, for the influence of hydrophobicity of the side chain R of the amino acid in the CDRs on retention times and resolution. The newly synthesized CDRs were observed to be superior as compared to their amide counterparts in terms of providing better resolution and cost effectiveness. The method was validated for limit of detection, linearity, accuracy and precision.     

Pyrazoles as molecular probes to study the properties of co-crystals by solid state NMR spectroscopy

Equimolar mixtures of 3,5-dimethylpyrazole (1) with four NH-imidazoles (2–5) have been studied by¹³C and ¹⁵N CPMAS NMR and by DSC. In three cases, the solid mixture behaves as the sum of the individual components [imidazole (2), 2-methylimidazole (3) and 2,4(5)-dimethylimidazole (5)]. In one case [4,5-dimethylimidazole (4)], the mixture corresponds to a new species in which the dynamic behavior of1 no longer exists.     

Protease production by Streptomyces sp. isolated from brazilian cerrado soil

Streptomyces are important microorganisms because of their capacity to produce numerous bioactive molecules. In the present work protease production, by Streptomyces sp. 594 isolated from a Brazilian Cerrado soil, was maximized by optimizing a low-cost culture medium composition (casitone and sugarcane molasses) using statistical experimental design. The final protease activity (56 U/mL) was 2.8-fold and 58-fold higher than that obtained in the beginning of this study, and in a previous work, using an actinomycete selection medium, respectively. Protease production, not growth associated, appeared to be modulated by an inducer system, whereby the C/N ratio seemed to play a significant role.