Influence of temperature on the adsorption of α-tocopherol from ethanol solutions on acid-activated clinoptilolite tuff

Patterns in the adsorption of α-tocopherol on acid-activated clinoptilolite tuff at 283, 295, 305, and 333 K are established and explained. It is found that the selectivity of the sorbent toward the vitamin rises as the temperature of the process falls. The adsorption of α-tocopherol from dilute solutions is described in terms of the Langmuir adsorption theory. It is shown that the fixing of vitamin E monolayers in the structural matrix of clinoptilolite tuff is due to the formation of hydrogen bonds between isolated silanol groups of the adsorbent and oxygen atoms of the chromane ring and the phenol residue of α-tocopherol. The thermodynamic functions of monolayer adsorption of the vitamin are estimated. It is concluded that the formation of polymolecular layers in the form of associates is due to hydrophobic interactions between side substituents of α-tocopherol.     

Influence of the surface structure of β-cyclodexrin-containing silica on the adsorption of mercury nitrate from dilute solutions

The construction of adsorption sites for mercury(II) by chemical immobilization of β-cyclodextrin and its functional derivatives on a surface of macroporous amorphous silica is proposed. It is shown that the adsorption of mercury(II) is adequately described by the Langmuir isotherm equation for monolayer adsorption on localized sites of energetically homogeneous surfaces. It is established that the considerably increased sorption of mercury nitrate on silica modified by different β-cyclodextrins is due to the formation of 1: 1 β-cyclodextrin-nitrate ion inclusion complexes on the surface and the participation of side functional groups of the upper edge of immobilized β-cyclodextrin molecules in the formation of mixed-ligand mercury(II) complexes.     

Infrared spectrum of α-cyanoacrylate adhesive in the first monolayer on a bulk aluminum surface

The i.r. spectrum of α-cyanoacrylate adhesive molecule in the first monolayer on anodically oxidized aluminum has been obtained with a reflection method. A lowering of CO stretching frequency and a shift of antisymmetric stretching vibration of COC group to a higher frequency were observed in the molecule interacting with surface oxide of aluminum, suggesting hydrogen bond formation between the oxide and the adhesive molecule.     

Density functional theory for adsorption of HCHO on the FeO（100） surface

The density functional theory (DFT) and periodic slab model were used to get information concerning the adsorption of HCHO on the FeO(100) surface. A preferred η2-(C,O)-di-σ four-membered ring adsorption conformation on the Fe-top site was found to be the most favorable structure with the predicted adsorption energy of 210.7 kJ/mol. The analysis of density of states, Mulliken population, and vibrational frequencies before and after adsorption showed clear weakening of the carbonyl bond, and high sp3 charact...     

The adsorption of mercury(II) on the surface of silica modified with β-cyclodextrin

Multistage chemical modification of the surface of silica with β-cyclodextrin was performed. IR spectroscopy and quantitative analysis of surface compounds were used to prove the structure of modified silica. The adsorption of Hg(II) from dilute solutions was studied. The adsorption affinity of silica for mercury ions increased because of the formation of supramolecular structures with chemically immobilized β-cyclodextrin.     

Features of the adsorption of aryl- and hetaryl-substituted 1,3,4-oxadiazoles from solutions on the surface of porous graphitic carbon in Henry’s range

Adsorption in Henry’s range of structurally related aryl- and hetaryl-substituted 1,3,4-oxadiazoles from n-hexane-dichloromethane and water-acetonitrile solutions on the surface of porous graphitic carbon (PGC) under the conditions close to equilibrium is studied by high-performance liquid chromatography. The characteristics of sorption of 1,3,4-oxadiazoles from solutions on the surface of this adsorbent, octadecyl silica gel, and on hypercrosslinked polystyrene are compared. It is shown that the structure of the molecules and their Van der Waals surface area and polarity affect adsorption on a PGC surface. A variant of the mechanism of adsorption of the polar molecules on the PGC surface, explaining the anomalously high values of their Henry constants of adsorption and based on the planar location of the 1,3,4-oxadiazoles molecules with respect to the adsorbent surface and the specific adsorbate-adsorbent intermolecular interaction in addition to the background dispersion interactions, is proposed. It is established that the linear the Gibbs energy relationship upon the adsorption of the studied compounds from n-hexane-dichloromethane and water-acetonitrile solutions on the PGC surface holds.     

A HREELS study of the adsorption of formic acid on slightly oxidized Nb(110) surface

An investigation has been made on the adsorption and decomposition of formic acid on slightly oxidized Nb(110) surface (0/Nb atom ratio = 0.2) using high resolution electron energy loss spectroscopy (HREELS),and a corresponding surface reaction mode is given.At 140 K,formic acid of low exposure on such an Nb(110) surface decomposed to formate,which bonded on Nb in monodentate configuration,simultaneously some formate decomposed to CO,which adsorbed on the surface.Formic acid multilayers formed when the exposure was high.While the temperature was increased to above 190 K,multilayer formic acid desorbed,and the surface was covered with mon-odentate-bonded formate and CO.In the temperature range of 250-300 K,chemisorbed formate changed from monodentate configuration into bridging configuration and CO molecules disappeared.The decomposition of formate at higher temperatures led to the oxidation of Nb.The formate formed in the high exposure case was so stable that it did not decompose even the temperature wa     

Studies of temperature influence on adsorption behaviour of nonionic polymers at the zirconia–solution interface

The temperature influence (15–35 °C) on the adsorption mechanism and conformation of nonionic polymers (polyethylene glycol (PEG), polyethylene oxide (PEO) and polyvinyl alcohol (PVA)) on the zirconium dioxide surface was examined. The applied techniques (spectrophotometry, viscosimetry, potentiometric titration and microelectrophoresis) allowed characterization of the changes in structure and thickness of polymer adsorption layers with the increasing temperature. The rise of temperature favours more stretched conformation of polymer chains on the ZrO₂ surface, which results in higher adsorption and thicker adsorption layer. Moreover, these conformational changes of adsorbed macromolecules affect the electric (solid surface charge density) and electrokinetic (zeta potential) properties of the zirconia–polymer interface. The obtained data indicate that the polyvinyl alcohol adsorption has a greater influence on zirconia properties in comparison to that of PEG and PEO. It is due to the presence of acetate groups in the PVA macromolecules (degree of hydrolysis 97.5%), which undergo dissociation.     

Catalytic and antimicrobial properties of α-amylase immobilised on the surface of metal oxide nanoparticles

New methods of obtaining products containing enzymes reduce the costs associated with obtaining them, increase the efficiency of processes and stabilize the created biocatalytic systems. In the study a catalytic system containing the enzyme α-amylase immobilized on ZnO nanoparticle and Fe₃O₄ nanoparticles was created. The efficiency of the processes was obtained with variables: concentrations of enzymes, temperatures and times, to define the best conditions for running the process, for which were determined equilibrium and kinetics of adsorption. The most effective parameters of α-amylase immobilization on metal oxides were determined, obtaining 100.8 mg/g sorption capacity for ZnO and 102.9 mg/g for Fe₃O₄ nanoparticles. Base on the best parameters, ZnO-α-amylase was investigated as an antimicrobial agent and Fe₃O₄-α-amylase was tested as a catalyst in the process of starch hydrolysis. As a result of the conducted experiments, it was found that α-amylase immobilized on Fe₃O₄ nanoparticles maintained high catalytic activity (the reaction rate constant K_M?=?0.7799 [g/dm³] and the maximum reaction rate V_max?=?8.660 [g/(dm³min)]).

     

Electrochemical and in situ spectroelectrochemical properties of metal-free and metallophthalocyanines containing α-naphtholbenzein groups on the peripheral positions

Phthalocyanine (Pc) compounds-containing α-naphtholbenzein units have been synthesized and characterized by spectroscopic data and elemental analysis. The redox properties of the compounds were investigated by cyclic and square wave voltammetry, controlled-potential coulometry and in situ spectroelectrochemistry in DMSO and compared with the free phthalonitrile ligand. The Pc compounds displayed common metal and/or ring-based reduction and oxidation processes. However, electrochemical measurements clearly suggested that the substituents involving anthraquinone units are redox active and so have a considerable effect on the redox processes of these compounds.     

Simulation analysis of the cellulase Cel7A carbohydrate binding module on the surface of the cellulose Iβ

The Family 7 cellobiohydrolase (Cel7A) from Trichoderma reesei consists of a carbohydrate-binding module (CBM) joined by a linker to a catalytic domain. Cellulose hydrolysis is limited by the accessibility of Cel7A to crystalline substrates, which is perceived to be primarily mediated by the CBM. Here, the binding of CBM to the cellulose Iβ fiber is characterized by combined Brownian dynamics (BD) and molecular dynamics (MD) simulations. The results confirm that CBM prefers to dock to the hydrophobic than to the hydrophilic fiber faces. Both electrostatic (ES) and van der Waals (VDW) interactions are required for achieving the observed binding preference. The VDW interactions play a more important role in stabilizing the CBM-fiber binding, whereas the ES interactions contribute through the formation of a number of hydrogen bonds between the CBM and the fiber. At long distances, an ES steering effect is also observed that tends to align the CBM in an antiparallel manner relative to the fiber axis. Furthermore, the MD results reveal hindered diffusion of the CBM on all fiber surfaces. The binding of the CBM to the hydrophobic surfaces is found to involve partial dewetting at the CBM-fiber interface coupled with local structural arrangements of the protein. The present simulation results complement and rationalize a large body of previous work and provide detailed insights into the mechanism of the CBM-cellulose fiber interactions.     

A calorimetric adsorption study on the interaction of water with hydroxylated surface of γ-Al2O3

The curve for the differential heat of adsorption of water on γ aluminum oxide has parts related to the interaction of the adsorbed water molecules with surface molecules of coordinated water and with acid and basic hydroxyl groups. Estimates have been made of the effective charges and hydration numbers for three of these adsorption centers. Textural changes have been observed in the γ-Al₂O₃ particles related to interplate swelling in the secondary sorbent packets into which the primary particles are linked. A. V. Dumanskii Institute for Colloid and Water Chemistry, National Academy of Sciences of Ukraine, 42 Prospekt Akademika Vernadskogo, Kiev-142 03680, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 36, No. 2, pp. 121–125, March–April, 2000.     

Effect of Lead(II) Complexation on Solubility of β-PbO in Alkaline Solutions in the Presence of Certain Alcohols

Complex formation of lead(II) was studied, and the solubility of -PbO was determined by potentiometric titration in solutions containing sodium hydroxide (0.3-4 M) and a series of mono- and polyhydric alcohols. A correlation between the lead monoxide solubility and Pb(II) complex formation function was considered.     

Influence of impurity elements on the corrosion of α-uranium surface: a density functional theory study

Journal of Radioanalytical and Nuclear Chemistry - Influence of substitutional Fe, Al and Mg atoms on the corrosion of α-U(110) surface was studied by DFT?+?U method. The...     

Molecular oxygen adsorption behaviors on the rutile TiO2(110)-1×1 surface: an in situ study with low-temperature scanning tunneling microscopy

A knowledge of adsorption behaviors of oxygen on the model system of the reduced rutile TiO(2)(110)-1×1 surface is of great importance for an atomistic understanding of many chemical processes. We present a scanning tunneling microcopy (STM) study on the adsorption of molecular oxygen either at the bridge-bonded oxygen vacancies (BBO(V)) or at the hydroxyls (OH) on the TiO(2)(110)-1×1 surface. Using an in situ O(2) dosing method, we are able to directly verify the exact adsorption sites and the dynamic behaviors of molecular O(2). Our experiments provide direct evidence that an O(2) molecule can intrinsically adsorb at both the BBO(V) and the OH sites. It has been identified that, at a low coverage of O(2), the singly adsorbed molecular O(2) at BBO(V) can be dissociated through an intermediate state as driven by the STM tip. However, singly adsorbed molecular O(2) at OH can survive from such a tip-induced effect, which implies that the singly adsorbed O(2) at OH is more stable than that at BBO(V). It is interesting to observe that when the BBO(V)s are fully filled with excess O(2) dosing, the adsorbed O(2) molecules at BBO(V) tend to be nondissociative even under a higher bias voltage of 2.2 V. Such a nondissociative behavior is most likely attributed to the presence of two or more O(2) molecules simultaneously adsorbed at a BBO(V) with a more stable configuration than singly adsorbed molecular O(2) at a BBO(V).     

Effect of the concentration of organic modifier in an aqueous-ethanol mobile phase on the chromatographic retention and thermodynamic characteristics of the adsorption of enantiomers of α-phenylcarboxylic acids on silica gel with immobilized eremomycin antibiotic

Regularities of the chromatographic retention and thermodynamics of the adsorption of enantiomers of α-phenylcarboxylic acids on a chiral stationary phase with immobilized macrocyclic antibiotic eremomycin under conditions of reversed-phase liquid chromatography with aqueous-ethanol mobile phases are studied. Relationships between the retention characteristics of the acids, the enantioselectivity of their separation, and the concentration of organic modifier in the mobile phase are found. It is shown that the sterical structure of substituents on the chiral atoms of the acids affect the mechanism of retention. The compensation effect in the studied systems is considered.     

Synthesis of Highly Oriented α-PbO2 Layers on the Surfaces of Single-Crystal Silicon and Quartz by Successive Ionic Layer Deposition

Conditions for the synthesis of -PbO₂ layers on silica surfaces by successive ionic layer deposition were determined. These layers were studied by X-ray spectral microanalysis, X-ray diffraction, IR Fourier spectroscopy, UV-Vis spectroscopy, and ellipsometry.     

Statistical analysis of the impact of spectral correlation on observed formation constants from UV–visible spectroscopic measurements

Information retrieved from UV–visible spectroscopic data by application of a self-modelling factor analysis algorithm showed apparently systematically shifted thermodynamic properties for the same chemical system as a function of spectral slit widths. This empirical observation triggered a systematic investigation into the likely effects of residual and spectral correlation on the numerical results from quantitative spectroscopic investigations. If slit width was a nuisance factor it would reduce the comparability of information evaluated from spectroscopic data. The influence of spectral slit width was investigated by simulation, i.e. by generating and evaluating synthetic spectra with known properties. The simulations showed that increasing spectral correlation may introduce bias into factor analysis evaluations. By evaluation of the complete measurement uncertainty budget using threshold bootstrap target factor (TB CAT) analysis, the apparent shifts are insignificant relative to the total width of the quantitys measurement uncertainty. Increasing the slit widths causes some systematic effects, for example broadening of the registered spectral bands and reduction of spectral noise, because of higher light intensity passing to the detector. Hence, the observed systematic shifts in mean values might be caused by some latent correlation. As a general conclusion, slit width does not affect bias. However, the simulations show that spectral correlation and residual correlation may cause bias. Residual correlation can be taken into account by computer-intensive statistical methods, for example moving block or threshold bootstrap analysis. Spectral correlation is a property of the chemical system under study and cannot be manipulated. As a major result, evidence is given showing that stronger spectral correlation (r<–0.7) causes non-negligible bias in the evaluated thermodynamic information from such a system.