Adsorption behaviors of recombinant proteins on hydroxyapatite-based immobilized metal affinity chromatographic adsorbents

The equilibrium adsorption of three homo-oligomeric model recombinant proteins containing up to 8 poly(histidine) affinity tags on a hydroxyapatite-based immobilized metal affinity chromatography (IMAC) adsorbent is reported in this study. The experimental data are well fitted with the three-parameter Langmuir-Freundlich isotherm model, indicating the presence of positive cooperativity for the adsorption of these model proteins. The maximum capacity and the binding affinity of the IMAC adsorbent for the model proteins are in principle dependent on the size and the number of affinity tags of proteins, respectively. The exceptionally high association constant of the octameric racemase, probably due to simultaneous multipoint attachment, make it difficult to elute racemase from the adsorbent. The adsorption isotherms under denaturing conditions are well fitted with the Langmuir model. Results of Scatchard analysis further suggest the homogeneous adsorption of the model protein subunits under denaturing conditions. The binding capacities and affinities of the adsorbent under denaturing conditions for the three unfolded protein subunits become essentially identical because the molecular size and number of poly(His) tags of the unfolded polypeptide chains of the three protein subunits are the same. The significant reduction in association constants under denaturing conditions suggests that high concentration of urea could interfere with the binding of proteins on the hydroxyapatite-based adsorbent.     

Comparison between extraction of lipids and fatty acids from microalgal biomass

Seven solvent mixtures have been used to extract the lipid fraction of lyophilized biomass ofIsochrysis galbana. Six of them were composed of biocompatible solvents. Each method was carried out under relaxed operating conditions (i.e., one hour at room temperature) with extraction in a nitrogen atmosphere to prevent autooxidation and degradation of polyunsaturated fatty acids (PUFAs). Apart from the well-established Bligh and Dyer method [Can. J. Biochem. Physiol. 37:911 (1959)] (Cl₃CH/MeOH/H₂O, 1∶2∶0.8, vol/vol/vol), which rendered the highest yield of lipids (93.8%), ethanol (96%) and hexane/ethanol (96%), 1∶2.5 vol/vol produced the best results (84.4 and 79.6%, respectively). To obtain free fatty acids, KOH was added to the solvent mixtures used to extract the total lipids, except for Cl₃CH/MeOH/H₂O, and direct saponification was carried out at 60°C for 1 h or at room temperature for 8 h. The highest yields obtained by direct saponicification were 81% with hexane/ethanol (96%), 1∶2.5, vol/vol and 79.8% with ethanol (96%). Partial yields of the mainn-3 PUFAs found inI. galbana, stearidonic acid (SA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), were calculated for both extraction methods. For lipid extraction with ethanol (96%), yields of 91, 82 and 83% were obtained for SA, EPA and DHA, respectively. When direct saponification was used, hexane/ethanol (96%; 1∶2.5, vol/vol) produced the best yields of (91, 79 and 69% for SA, EPA and DHA, respectively).     

Tannin-based adsorbents from green tea for removal of monoaromatic hydrocarbons in water: Preliminary investigations

In this study, we report the adsorption of benzene and toluene from water using rarely reported tannin adsorbents. Tannin gel and tannin powder were synthesized by adding formaldehyde to green tea extract, while iron nanoparticles were synthesized by the addition of FeSO₄?·?7H₂O. The surface morphology of the synthesized adsorbents was determined using SEM and FTIR prior to application to contaminated water. The results show up to 88% removal of benzene and toluene in a batch system after 30?min of reaction time, with a higher rate of removal of toluene compared to benzene. A low pH value of 2 had an adverse effect on the tannin gel, reducing the total adsorption of benzene to approx. 37.5%. On the other hand, iron nanoparticles were least affected by the pH with an adsorption of 62.9% for benzene and 83.3% for toluene.     

Adsorption of tannic acid on chitosan-montmorillonite as a function of pH and surface charge properties

Chitosan, a natural biopolymeric cation, is a candidate to modify montmorillonite for the adsorption of anions. As an anionic organic pollutant the adsorption of tannic acid was studied. Because of protonation/deprotonation reactions of both chitosan-montmorillonite and tannic acid, the adsorption process is strongly pH-dependent. The objective of this work is to characterize the pH dependency of adsorption in combination with surface charge determinations.Montmorillonite was modified with different amounts of chitosan, corresponding to 20–1000% of the cation exchange capacity (CEC). The deacetylation degree of chitosan was determined by polyelectrolyte titration and was found to be 74%. The uptake of chitosan was determined by the C-content. The interlayer expansion was investigated by X-ray powder diffraction. The adsorption capacity for tannic acid was investigated with the batch technique at pH 3, 4, 5 and 8. As a measure for the adsorption properties, the electrokinetic surface charge was determined with a particle charge detector.The uptake of chitosan by montmorillonite is up to 152% (1.69 mol_c kg^− 1) of the CEC. The resulting anion exchange capacity of chitosan-montmorillonite calculated from C-content is 0.43 mol_c kg^− 1. At low loadings with chitosan (24.7 and 49.5% uptake), a monolayer is formed in montmorillonite. At an uptake of 96.8%, a bilayer structure is observed, which becomes more dominant at higher loadings. On the external surface, a monolayer of chitosan was formed. From pH 4 to 8, the surface charge of all modified montmorillonites is with − 9 to 8 mmol_c kg^− 1 close to the point of zero charge. The maximal adsorption capacity for tannic acid is found with 240 g kg^− 1 (0.14 mol_c kg^− 1) at pH 4. The adsorption process fits in well with the Freundlich isotherm. At lower as well as higher pH values the adsorption capacity decreases up to about 25%. Most probably the exchange sites in the interlayer do not contribute to the adsorption of tannic acid. The observed surface charge is lower than the adsorbed amount of tannin. It is thought that tannin is adsorbed also by van der Waals forces besides ionic forces.     

An improved reversed-phase thin-layer chromatography method for separation of fatty acid methyl esters

Resolution of fatty acid methyl esters (FAME) by thin-layer chromatography often is complicated by co-migration of certain acyl-isomers in heterogeneous mixtures. However, a novel reversed-phase thin-layer chromatography method which employs 10% (wt/vol) silver nitrate in a mobile phase containing acetonitrile/1,4-dioxane/acetic acid (80:20:1, vol/vol/vol) allows one-dimensional resolution of a wide range of acyl-methyl esters. This innovation enables improved separation of saturated FAME ranging from C₁₂ to C₂₂, and geometric isomers of C₁₄ to C₂₂ unsaturated FAME by thin-layer chromatography.     

Adsorption isotherms of fatty acids on rice hull ash in a model system

The adsorption of lauric, myristic and stearic acids on rice hull ash (RHA) from isooctane as solvent was studied and conformed to a Langmuir isotherm. Monolayer coverage was determined to be 35.7±2.5, 43.5±2.2 and 36±5 mg/g, respectively. The free energy of adsorption, †G°, for the adsorption was determined to be-6.64,-6.23 and-6.49 kcal mol⁻¹ for the adsorbates, respectively. The equilibrium parameter indicated that RHA is a good adsorbent for the three fatty acids examined.     

Adsorption equilibria of benzoic acid on silica gel from supercritical carbon dioxide

Supercritical fluids, especially carbon dioxide, are increasingly used as carriers for adsorption-desorption processes, particularly in the pharmaceutical industry. Nevertheless, equilibria data for such processes are rather limited. Therefore, in this work, the adsorption equilibria of benzoic acid onto non-modified silica gel from scCO₂ were evaluated by Supercritical Fluid Chromatography applying the Peak Maxima method. Solubility of benzoic acid in scCO₂ was enhanced by addition of 2-propanol.The effects of modifier content, temperature and pressure on the solute loading were investigated. Experimental data were best described by the cubic Hill isotherm model, which accounted for the change of curvature of the elution profiles observed as concentrations in the mobile phase increased. For the concentration range reached in this study (up to 6 mg/mL), adsorption of benzoic acid was favoured at low modifier contents, high temperatures and low pressures, conditions at which the solvating power of the modified scCO₂ decreased.     

Sorption equilibrium of Cr(VI) ions on oak wood charcoal (Carbo Ligni) and charcoal ash as low-cost adsorbents

The aim of this study is to demonstrate the potential of oak wood charcoal (WC) and oak wood charcoal ash (WCA) as a low-cost adsorbent for environmental protection applications of Cr(VI) ion. The influence of contact time, solution pH, initial metal concentration, amount of adsorbent and ionic strength on the removal of Cr(VI) ion was studied. The adsorption of Cr(VI) with (WC) and (WCA) was investigated in a batch arrangement. The Cr(VI) ions sorbed onto the adsorbents were determined by a UV-Visible Spectrophotometer. The sorption of Cr(VI) on the adsorbent surface depends strongly on the pH and Cr(VI) ion-sorption increased with a decreasing pH until pH 2 and increase in the concentration of this metal in solution phase. The adsorption of Cr(VI) was higher between pH 2.0 and 2.5 for both adsorbents. The Freundlich adsorption isotherm was used to describe observed sorption phenomena. The maximum adsorption capacity of 30.10 mg of Cr(VI)/g for (WC) and 46.17 mg of Cr(VI)/g for (WCA) was obtained at pH of 2 and 2.5 respectively.     

Adsorption and electrothermal desorption of organic vapors using activated carbon adsorbents with novel morphologies

Novel morphologies of activated carbons such as monolith, beads and fiber cloth can effectively capture organic vapors from industrial sources. These adsorbent materials are also unique because they can undergo direct electrothermal regeneration to recover the adsorbed organic vapors for potential re-use. This investigation compares and contrasts the properties of these adsorbents when using electrothermal-swing adsorption. The adsorption systems consisted of an organic vapor generation system, an electrothermal-swing adsorption vessel, a gas detection unit, and a data acquisition and control system. The activated carbon monolith (ACM) had the lowest pressure drop, highest permeability, highest electrical resistivity and lowest cost as compared to the activated carbon beads (ACB) and the activated carbon fiber cloth (ACFC). ACB had the largest throughput ratio and lowest length of unused bed as compared to the other adsorbents. However, ACFC had the largest adsorption capacity for toluene when compared to ACM and ACB. ACFC was also faster to regenerate and had a larger concentration factor than ACM and ACB. These results describe relevant physical, electrical, adsorption and cost properties for specific morphologies of the adsorbents to more effectively capture and recover organic vapors from gas streams.     

A rapid method for determining the oxidation of n-3 fatty acids

The stability of unsaturated fatty acids to oxidation was monitored by following gas chromatographic (GC) analyses of headspace volatiles in comparison to changes in polyunsaturated fatty acids (PUFA) and increases in malonaldehydevia the 2-thiobarbituric (TBA) assay. Pure standards of linoleic acid (Lo) and n-3 fatty acids [eicosapentaenoic (EPA) and docosahexaenoic acid (DHA)] were added to headspace vials, equilibrated in air for 10 min, followed by heating at 80°C in teflon-capped vials for different time intervals. Headspace analysis showed increases in acetaldehyde, propenal, and propanal, corresponding to the oxidation of n-3 fatty acids, whereas hexanal production corresponded to losses of linoleic acid. The analysis of propanal by GC-headspace after only five minutes of heating appeared to be the most effective method of monitoring the oxidation of n-3 fatty acids, as indicated by correlations between TBA values and loss of PUFA. The oxidation of Lo, EPA and DHA appeared to be a function of the number of double bonds. Correlations between PUFA depletion, TBA values and volatile formation indicate that under the prescribed conditions of this experiment, GC-headspace analysis of propanal and pentane/hexanal is an excellent method for following the oxidation of selected n-3 fatty acids and linoleic acid.     

Development of adsorbents from used tire rubber: Their use in the adsorption of organic and inorganic solutes in aqueous solution

Using used tire rubber (UTR), carbonaceous adsorbents (CAs) were prepared by chemical treatment of the material with HCl, HNO₃ and NaOH aqueous solutions and by heat treatment at 900 °C for 2 h in N₂ atmosphere (H900). UTR and the UTR-derived products were first characterized in terms of texture by N₂ adsorption at − 196 °C and of oxygen surface groups by FT-IR spectroscopy and pH of the point of zero charge (pH_pzc). Then, the products were tested as adsorbents of phenol, p-aminophenol, p-nitrophenol, and p-chlorophenol and of chromium, cadmium, mercury and lead in aqueous solution. The development of porosity is very poor in UTR and in the chemically treated products. H900 is the only CA with a better developed porosity, mainly in the regions of meso and macropores. pH_pzc is close to 7.0 for most of the CAs. As an exception to the rule, pH_pzc is 8.4 for H900. For this CA, the adsorption of all the adsorptives is greater. Usually, adsorption kinetics are fast. This is so in particular for p-nitrophenol and p-chlorophenol, on the one side, and for mercury and lead, on the other side. Adsorption is much higher for mercury and lead than for the remaining adsorptives.     

Adsorption properties of a Pd/γ-Al2O3 catalyst using inverse gas chromatography

The adsorption properties of a commercial Pd/Al₂O₃ catalyst were studied and compared with those of the Al₂O₃ support of the same specific surface area. Inverse gas chromatography (IGC) was used to determine the adsorption isotherms of five n-alkanes (C₈–C₁₂) in the 200–230 °C temperature range. Moreover, heats of adsorption, solubility coefficients and free energy of adsorption, are also reported. Interaction parameters of polar molecules with the stationary phase have also been determined and compared with those for the n-alkanes. Experiments with both the reduced and oxidized catalyst have been carried out by IGC and the results compared with those obtained by temperature programmed reduction (TPR) experiments.     

Liver lipids and fatty acids of the sting ray Dasyatis bleekeri (Blyth)

The sting ray, Dasyatis bleekeri (Blyth), has been studied for lipids and fatty acids of its liver. The neutral lipids identified were hydrocarbons, wax esters, steryl esters, 1-O-alkyl-2,3-diacylglycerols, triacylglycerols, and sterols. Neutral lipids were predominant (91.8%), major components being triacylglycerols (92.7%). Polyenoic fatty acids of n-3 series, viz. eicosapentaenoic acid and docosahexaenoic acid, were high in the phospholipid and neutral lipid fractions. Cholesterol was the major component (67.9%) in the steryl ester fraction. Glyceryl ethers, with chainlengths up to 30 carbons, were recorded with unsaturated, anteiso, iso, and normal chains. In wax ester alcohols, up to 32-carbon chains were recorded. Hydrocarbons were up to 36-carbon chains with anteiso, iso, and normal chains. Among branched chain hydrocarbons, pristane was the major component (6.7%) and squalene was present at the level of 3.5%. Chimyl and batyl alcohol backbones were the major components found in 1-O-alkyl-diacylglycerols.     

Moisture Adsorption Isotherms of Watermelon Seed and Kernels

The moisture adsorption isotherms of watermelon seeds and kernels from Citrullus lanatus Cv Mateera and Citrullus vulgaris Cv Sugar baby were obtained using standard static method with saturated salt solutions over a range of water activities from 0.113 to 0.92 at 20–60°C. The adsorption capacity of seeds decreased with the increase in temperature at constant water activity. Sorption models were used to explain the adsorption behavior involving water activity and moisture content (Type I) and also temperature (Type II). Oswin's models gave best fit among Type I with coefficient of determination of 0.953–0.995, standard error of 0.031–0.0571, mean relative error of 0.071–0.152, and scattered residual plots. Modified Oswin was the best fit model among Type II for the seeds and kernels of both the cultivars with coefficient of determination of 0.997–0.999, standard error of 0.151–0.255, mean relative error of 0.018–0.244, and scattered residual plots. The net isoelectric heat of adsorption, estimated from Clausius-Clapeyron decreased from about 27.0 to 0.5 kJ/mol in kernels and 18.0 to 0.5 kJ/mol in seeds of both the cultivars as the moisture content increased from 5 to 25% (dry basis).     

Moisture Adsorption Isotherms of Watermelon Seed and Kernels

The moisture adsorption isotherms of watermelon seeds and kernels from Citrullus lanatus Cv Mateera and Citrullus vulgaris Cv Sugar baby were obtained using standard static method with saturated salt solutions over a range of water activities from 0.113 to 0.92 at 20-60°C. The adsorption capacity of seeds decreased with the increase in temperature at constant water activity. Sorption models were used to explain the adsorption behavior involving water activity and moisture content (Type I) and also temperature (Type II). Oswin's models gave best fit among Type I with coefficient of determination of 0.953-0.995, standard error of 0.031-0.0571, mean relative error of 0.071-0.152, and scattered residual plots. Modified Oswin was the best fit model among Type II for the seeds and kernels of both the cultivars with coefficient of determination of 0.997-0.999, standard error of 0.151-0.255, mean relative error of 0.018-0.244, and scattered residual plots. The net isoelectric heat of adsorption, estimated from Clausius-Clapeyron decreased from about 27.0 to 0.5 kJ/mol in kernels and 18.0 to 0.5 kJ/mol in seeds of both the cultivars as the moisture content increased from 5 to 25% (dry basis).     

Oxidative stability of polyunsaturated fatty acids and soybean oil in an aqueous solution with emulsifiers

The oxidative stability of polyunsaturated fatty acids (PUFA) and soybean oil homogenized with emulsifiers was investigated. Model emulsions were prepared from PUFA, including linoleic acid (LA), arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), and from soybean oil emulsified with different emulsifiers: three Tween emulsifiers (Tween 20, Tween 60, Tween 80) and two sucrose esters (S-1170 and S-1570) were used. The results showed that the emulsions prepared from LA and the various emulsifiers, oxidized at 40°C, were unstable. However, the corresponding AA, EPA, and DHA emulsions were stable, indicating that PUFA with a higher degree of unsaturation were more stable with emulsifiers than without the emulsifiers. In the soybean oil-in-water model system, the oxidation of soybean oil with various emulsifiers was less than without the emulsifiers.     

Kinetics,Isotherms and Equilibrium Study of Co(II) Adsorption from Single and Binary Aqueous Solutions by Acacia nilotica Leaf Carbon

The removal of cobalt ion from aqueous solution by Acacia nilotica leaf carbon (HAN), is described. Effect of pH, agitation time and initial concentration on adsorption capacities of HAN was investigat...     

Evaluation of chromatographic separation of free lutein and fatty acids in de-esterified marigold lutein

In this study, chromatographic purification of de-esterified marigold lutein was evaluated to obtain high purity free lutein. The quantification and identification of fatty acid in the de-esterified marigold lutein, which have not been reported before, were determined. The amount of fatty acid, mostly palmitic acid, was 49.12 mg/g oleoresin. The separation of free lutein and fatty acid was then performed. The high purity and recovery of free lutein were observed to be 99.2% and 95.2%, respectively, for the suitable chromatographic separation condition, i.e., step-gradient of hexane-ethyl acetate mixture at 85:15 v/v in the first 12 min, followed by 70:30 v/v.     

Structured lipids from high-laurate canola oil and long-chain omega-3 fatty acids

The lipase-assisted acidolysis of high-laurate canola oil (HLCO; Laurical 25) with long-chain n−3 FA (DHA and EPA) was studied. Response surface methodology was used to obtain a maximal incorporation of DHA or EPA into HLCO. The studied process variables were the amount of enzyme (2–6%), reaction temperature (35–55°C), and incubation time (12–36 h). The amount of water added and the mole ratio of substrates (oil to DHA or EPA) were kept at 2% and 1∶3, respectively. All experiments were conducted according to a face-centered cube design. Under optimal conditions (4.79% of enzyme; 46.1°C; 30.1 h), the incorporation of DHA into HLCO was 37.3%. The corresponding maximal incorporation of EPA (61.6%) into Laurical 25 was obtained using 4.6% enzyme, a reaction temperature of 39.9°C, and a reaction period of 26.2 h. Examination of the positional distribution of FA on the glycerol backbone of modified HLCO with DHA showed that the DHA was primarily located in the sn-1,3 positions of the TAG molecules. However, lauric acid also remained mainly in the sn-1,3 positions of the modified oil. For EPA-modified Laurical 25, lauric acid was present mainly in the sn-1,3 positions, whereas EPA was randomly distributed over the three positions.