Adsorption and catalytic properties of peroxidase

The adsorption of peroxidase was studied on ten silicate adsorbents, aluminosilicate, and alumina. It was shown that its value depended on both the parameters of the porous structure and the nature of the adsorbent. The maximum adsorption values were obtained on biporous silicate adsorbents and biporous aluminosilicate. It was established that the adsorbed peroxidase layers on these adsorbents had the best catalytic properties as well. It was shown that the specific activity of the enzyme depended on the degree of the surface filling.     

Composite cryogel with immobilized concanavalin A for affinity chromatography of glycoproteins

Composite cryogels containing porous adsorbent particles were prepared under cryogelation conditions. The composites with immobilized concanavalin A (Con A) were used for capturing glycoproteins. Adsorbent particles were introduced into the structure in order to improve the capacity and to facilitate the handling of the particles. The monolithic composite cryogels were produced from suspensions of polyvinyl alcohol particles and porous adsorbent particles and cross‐linked under acidic conditions at sub‐zero temperature. The cryogels were epoxy activated and Con A was immobilized as an affinity ligand. Binding and elution of horseradish peroxidase (HRP) was studied in batch experiment and in a chromatographic setup. Increasing adsorbent concentration in composite cryogels will increase ligand density, which therefore enhances the amount of bound HRP from 0.98 till 2.9 (milligram enzyme per milliliter of gel) in the chromatographic system. The material was evaluated in 10 cycles for binding and elution of HRP.     

Numerical simulation of rapid pressurization and depressurization of a zeolite column using nitrogen

The required durations of pressurization and depressurization steps of a rapid pressure swing adsorption process are primarily governed by adsorbent particle size, adsorption kinetics, column pressure drop, column length to diameter ratio, and the valve constant of the gas inlet and outlet control valve attached to the adsorbent column. A numerical model study of the influence of these variables for an adiabatic LiX zeolite column is presented using pure N₂ as an adsorbate gas. An adsorbent particle size range of 200–350 μm was found to minimize (<1 s) the times required for the pressurization and depressurization steps.     

Photocatalytic Characterization of TiO_2 Supported on Active Carbon

Photocatalysis on TiO2, with a promising application to the elimination of organic contaminants from air and water, has been a particularly active area1. For such application, it is important to improve the efficiency of TiO_2 photocatalysts. In the most cases, the concentration of organic contaminants in water is extremely dilute (ppm level or below) and TiO_2 itself has low adsorbabilities for them, it usually takes a long time to complete their decomposition. One of the effective ways to …     

Synthesis and inhibition properties of conformational probes for the mutase-catalyzed UDP-galactopyranose/furanose interconversion

UDP-galactose mutase is a flavoenzyme that catalyzes the isomerization of UDP-galactopyranose into UDP-galactofuranose, a key step in the biosynthesis of important bacterial oligosaccharides. Several mechanisms for this unique ring-contraction have been proposed, one of them involving a putative 1,4-anhydrogalactopyranose as an intermediate in the reaction. The purpose of this study was to probe the mutase binding site with conformationally restricted analogues of its substrate. Thus, we describe the straightforward synthesis of two C-glycosidic UDP-galactose derivatives: analogue 1, presenting a galactose moiety locked in a bicyclic (1,4)B boat conformation, and UDP-C-Galf 2, where the galactose residue is locked in the conformation of the mutase substrate. The two molecules were found to be inhibitors of UDP-galactose mutase at levels depending on the redox state of the enzyme. Strong inhibition of the native enzyme, but a low one of the reduced mutase, were observed with UDP-C-Galf 2, whereas 1 displayed intermediate inhibition levels under both native and reducing conditions. These data provide evidence of a significant conformational difference of the mutase binding pocket in the reduced enzyme and in the native one, the enzyme switching from a low Galf-affinity state (reduced enzyme) to a very strong one (native enzyme). It is remarkable that the mutase binds the boat-locked analogue 1 with similar affinities in both its conformational states. These results support a mechanism involving the formation of 1,4-anhydrogalactopyranose as a low-energy intermediate. An alternative explanation would be that the distortion of the galactose moiety during the cycle contraction transiently brings the carbohydrate into a conformation close to a (1,4)B boat.     

Feasibility of using gravimetry to measure excess adsorption effects of a binary solvent system in a reversed-phase high-performance liquid chromatography column

A modified method for weighing HPLC columns filled with solvent is described. The method prevents the loss of traces of solvent from within the threads of the column. The method was tested by obtaining the weights of a C18 column filled with 10 different organic solvents, showing a standard deviation on the order of 0.1%. A plot of gross column weight versus solvent density showed excellent linearity. The method was then used to weigh a column filled with several acetonitrile–water mixtures. The gross column weights were lower than would have been predicted from the density of the acetonitrile–water mixtures. A likely explanation is the existence of an adsorbed acetonitrile-rich liquid on the surface of the C18 adsorbent, which caused the lower than expected weights due to the lower density of pure acetonitrile relative to the bulk mixtures. The volume of pure acetonitrile required for the observed weight discrepency was calculated. Based on the surface area of the column adsorbent, values of micromoles acetonitrile per square meter of surface area were determined. The values showed reasonable agreement with values obtained from published adsorption isotherm studies. This suggests that pycnometry may be a useful technique for adsorption studies. The limitations of the technique are discussed.     

High-performance liquid and gas-liquid chromatography of isomeric phenoxathiins. Use of organo-clay to increase selectivity

Summary Bentone-34, a selective adsorbent, has been studied for use in high-performance liquid chromatography (HPLC) to separate isomeric phenoxathiin derivatives. We have compared the performance of this adsorbent in gas chromatography and liquid chromatography. We have obtained better and faster analyses of these isomeric phenoxathiins by high-pressure liquid-solid chromatography. This method is more flexible, as we have the choice of a large variety of mobile phases, and analyses are achieved at ambient temperature. Moreover HPLC can be used for collecting the pure solutes.     

Synthesis of a carbasugar analogue of a putative intermediate in the UDP-galp-mutase catalyzed isomerization

[reaction: see text] The synthesis of the carbasugar analogue of 1,4-anhydro-beta-d-galactopyranose, a proposed intermediate in the reaction catalyzed by uridine diphosphate-alpha-d-Galp mutase, in racemic form via Diels-Alder and Barton decarboxylation chemistry is reported. This compound was found not to inhibit the mutase from Mycobacterium tuberculosis, indicating that the enzyme does not possess a 1,4-anhydro-beta-d-galactopyranose binding pocket.     

Heats of adsorption and adsorption heterogeneity for methane, ethane, and carbon dioxide in MCM-41

We report the adsorption isotherms and the isosteric heats of adsorption of pure methane, ethane, and CO2 and a mixture of methane and CO2 in the periodic mesoporous silica MCM-41 using a multicomponent adsorption calorimeter of the Tian-Calvet type, looking in particular at the degree of heterogeneity in the adsorption of these species. The adsorption of methane and ethane in MCM-41 was found to be essentially homogeneous, while the adsorption of pure CO2 and of CO2 from a CO2/methane mixture was found to be significantly heterogeneous, reflecting the electrostatic interactions between CO2 and the adsorbent.     

Simple and rapid method for the isolation of forskolin from Coleus forskohlii by charcoal column chromatography

A simple, safe, rapid and economical method was developed for the isolation of high-purity forskolin from Coleus forskohlii roots using activated charcoal as an adsorbent in a column. The elution was carried out under reduced pressure to make the process rapid. Activated charcoal acted as a reversed phase adsorbent and allowed elution of forskolin without much impurities. The residue, obtained from the eluate was purified and crystallized using different solvent mixtures to obtain pure forskolin. The forskolin isolated was analyzed and characterized by UV, IR, RP-HPLC, electrospray ionization MS, 1H NMR and 13C NMR. The yield was 0.097% w/w (RSD 5.6%). The purity was 96.9% w/w (RSD 0.3%) as determined by RP-HPLC. The present method enables researchers to produce high-purity forskolin in their labs by using common chemicals.     

Trapping Efficiencies of Various Adsorbents in Supercritical Fluid Extraction with Modified Carbon Dioxide

One way of collecting extracted analytes after a supercritical fluid extraction (SFE) is to pass the depressurized fluid through a trap composed of a solid adsorbent. The influence of the adsorbent nature on the trap efficiency has been studied. First, the retention factors of each compound of a polarity test mix (tetracosane, naphthalene, fluoranthene, acetophenone, N,N-dimethylaniline, 2-naphthol, decanoic acid) have been determined on five high specific area (greater than 800 m²/g) polymeric phases by supercritical fluid chromatography (SFC). The comparison of this values with those obtained on octadecyl silica (ODS) showed that polymeric phases have the greatest retention power. After that, the efficiency of a solid trap filled with the greatest retention power polymeric adsorbent was evaluated by using pure carbon dioxide and 2.5%, 5%, 10%, and 20% methanol-modified carbon dioxide. As expected, this trap permitted a quantitative collection of all the former compounds even when a content as high as 10% of methanol was implemented. A solid trap filled with ODS adsorbent allowed quantitative collection of all the compounds only at a methanol content lower than 2.5%.     

DFT investigation of NH3 physisorption on CuSO4 impregnated SiO2

In this quantum chemical investigation, NH(3) physisorption onto a model of copper sulfate impregnated silica is compared with pure silica and copper sulfate adsorbents. The physisorption process is modeled as direct binding of the NH(3) molecule to the adsorption site of the dry adsorbents and as displacement of a H(2)O molecule by NH(3) in the hydrated complexes. The surface of silica is represented by a hydroxyl group attached to a silsesquioxane cage, H(7)Si(8)O(12)(OH) and silica impregnated with CuSO(4) by the most stable configuration of the cluster containing a CuSO(4) ion pair placed adjacent to the silica cage. H(2)O is systematically added to the dehydrated adsorbents to investigate the role of water in NH(3) adsorption. Modeling hydrated environments of each type of adsorbent is focused on H(2)O molecules that directly coordinate with the active sites. The results indicate that the binding energy of adsorbing NH(3) onto the mixed adsorbent is greater than in pure silica. This enhanced binding in the mixed adsorbent is consistent with improved Br?nsted acidity of the silanol in the presence of CuSO(4).     

Purification of the coenzyme B12-containing 2-methyleneglutarate mutase from Clostridium barkeri by high-performance liquid chromatography.

Two methods are described by which the enzymes 2-methyleneglutarate mutase and 3-methylitaconate delta-isomerase from Clostridium barkeri have been separated by high-performance liquid chromatography on a much larger scale than reported previously. First, the mutase eluted before the delta-isomerase after incubation with the mild detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulphonate (CHAPS) followed by high-performance anion-exchange chromatography on Mono Q in the presence of the same detergent. Second, an even better separation, although with a lower yield of mutase, was obtained by hydrophobic interaction chromatography on phenyl-Sepharose HiLoad, whereby the enzymes were eluted in the reverse order. Final high-performance anion-exchange chromatography of the latter preparation on Mono Q at pH 8 gave highly purified 2-methyleneglutarate mutase (greater than 95% purity) which had a pink-orange colour (lambda max 280, 375, 470 and 532 nm). The enzyme was active in the absence of coenzyme B12 (adenosylcobalamin) and contained 2.1 mol of this coenzyme per homotetramer (molecular mass, m = 300 kilodalton).     

Direct capture of product from fermentation broth using a cell-repelling ion exchanger

A new technique for treating anion exchangers has been proposed allowing direct capture of the fermentation product, shikimic acid directly from the cell-containing fermentation broth. A layer of hydrophilic polymer, poly(acrylic acid) (PAA) has been physically adsorbed on the anion exchanger followed by a covalent cross-linking of PAA. The PAA layer is penetrable for small molecules despite being negatively charged as PAA is, but the polymer layer repels large negatively charged structures like cell debris and cells preventing them from adsorption to the chromatographic matrix. The binding capacity for pure shikimic was about 81 mg/ml adsorbent for both cross-linked PAA-Amberlite and native Amberlite in the fluidized mode of column operation. Binding capacity dropped to 17 and 15 mg per ml adsorbent, respectively, when using filtrated fermentation broth and to about 10 mg/ml adsorbent for cross-linked PAA-Amberlite when using directly the fermentation broth containing cells. Native Amberlite cannot be used for the direct capture of shikimic acid due to the immediate clogging of the column and the collapse of the expanded bed. The cross-linked PAA-Amberlite was used repeatedly for the direct adsorption of shikimic acid from the industrial fermentation broth.     

Application of Calcium Alginate–Starch Entrapped Bitter Gourd (<Emphasis Type="Italic">Momordica charantia</Emphasis>) Peroxidase for the Removal of Colored Compounds from a Textile Effluent in Batch as well as in Continuous Reactor

Calcium alginate–starch entrapped bitter gourd peroxidase has been employed for the treatment of a textile industrial effluent in batch as well as in continuous reactor. The textile effluent was recalcitrant to decolorization by bitter gourd peroxidase; thus, its decolorization was examined in the presence of a redox mediator, 1.0 mM 1-hydroxybenzotriazole. Immobilized enzyme exhibited same pH and temperature optima for effluent decolorization as attained by soluble enzyme. Immobilized enzyme could effectively remove more than 70% of effluent color in a stirred batch process after 3 h of incubation. Entrapped bitter gourd peroxidase retained 59% effluent decolorization reusability even after its tenth repeated use. The two-reactor system containing calcium alginate–starch entrapped enzyme retained more than 50% textile effluent decolorization efficiency even after 2 months of its operation. The absorption spectra of the treated effluent exhibited a marked difference in the absorption at various wavelengths as compared to untreated effluent. The use of a two-reactor system containing immobilized enzyme and an adsorbent will be significantly successful for treating industrial effluents at large scale, and it will help in getting water free from aromatic pollutants.     

Flow injection analysis of trace hydrogen peroxide using an immobilized enzyme reactor

Summary Flow Injection Analysis of Trace Hydrogen Peroxide Using an Immobilized Enzyme Reactor Sub-part-per-billion levels of aqueous hydrogen peroxide have been determined with a flow injection analysis system employing a single bead string reactor composed of horseradish peroxidase covalently bound to an animated macroporous polymeric adsorbent with glutaraldehyde and a passive cation exchange membrane reactor to alter pH. The chemistry relies on the peroxidase mediated oxidation of nonfluorescentp-hydroxyphenylacetate to its fluorescent dimer. The advantage of the system includes rapid throughout rates (40 samples/h), excellent detection limits (0.3 ppb H₂O₂) and large dynamic range of linear response (1 ppb-1 ppm). However, the immobilized enzyme is not useful for the analysis of organic peroxides which act as inhibitors.     

Desulfurization of Diesel over Ni/ZnO Adsorbent Prepared by Coprecipitation

Ni/ZnO adsorbents with various Ni/Zn molar ratios were prepared by coprecipitation; their adsorption capacity in reactive adsorption desulfurization (RADS) of diesel oil was investigated. Ni/ZnO exhibits much higher adsorption performance than pure Ni and pure ZnO. The Ni content plays a crucial role in determining RADS activity over Ni/ZnO; the sulfur capacity depends on the ZnO content in Ni/ZnO. The Ni₄/Zn₆ adsorbent shows the optimal performance; the sulfur content in diesel oil is reduced to less than 5 ppm in first 60 h and less than 15 ppm in next 68 h.     

Hemoglobin,horseradish peroxidase,and heme-bovine serum albumin as biocatalyst for the oxidation of dibenzothiophene

Hemoglobin, horseradish peroxidase, and bovine serum albumin incubated heme-catalyzed the oxidation of dibenzothiophene into sulfoxide in the presence of hydrogen peroxide. This reaction was carried out in an aqueous buffer containing 25% of water-miscible organic solvents. The observation of this transient state of hemoproteins during sulfoxidation showed heme degradation. None of the compounds usually involved in a classical peroxidative activity mechanism were detected. Furthermore, this activity did not appear to be based on a Fenton-type reaction. The highest degrees of sulfoxidation were obtained with hemoglobin. Under the best conditions of reaction, 100% of dibenzothiophene were converted into dibenzothiophene sulfoxide by hemoglobin. Heat-denatured hemoproteins did keep their sulfoxidation activity. With hemoglobin, a k_cat of 0.22 min^-1 was determined. Nearly the same values were obtained with heat-denatured hemoglobin and bovine serum albumin-adsorbed heme. With horseradish peroxidase, only 4% of conversion was attained. This percentage could be slightly increased by using a less pure peroxidase or heat-denatured peroxidase.     

Effect of pore size on the performance of composite adsorbent

Three kinds of commercial silica gels with pore size of 2–3, 4–7 and 8–10 nm respectively are used for preparing composite adsorbents by soaking them into the aqueous solution of calcium chloride. The test result indicates that both the water uptake and adsorption rate of composite adsorbents prepared from 4–7 and 8–10 nm silica gels improve greatly compared to pure silica gels, but they do not for 2–3 nm silica gels. The silica gel with pore size of 2–3 nm is not suitable for preparing the composite adsorbent by impregnation method due to the pore blockage because of the small pore size. The SCP and COP of the adsorption chiller with sample SA50 are 128.3 Wkg^?1 and 0.27 respectively at the hot source temperature of 90 °C, which are largely superior to that of SA0. Hence using the composite adsorbent instead of the pure silica gel can reduce the size of the adsorption chiller.     

The structure and properties of n-octadecanol film present on the surface of a carbon-silica adsorbent

Summary The properties of the n-octadecanol film on carbon-silica adsorbent (Carbosil) were investigated. It was found that n-octadecanol forms an oriented film on the Carbosil's surface. If the surface of the basic silica gel is not completely covered with carbon, then the phase transition takes place in this film at a temperature higher than the melting temperature of n-octadecanol. One may distinguish two forms of this film, characterised by the different structures and the temperatures of the phase transitions. The first exists on the surface of silica gel unblocked by carbon. This part of the film is a monolayer, in which the alcohol molecules are vertically oriented. The solid compact-liquid expanded type phase transition at the well-defined temperature occurs in this film. In the second part of the film formed on the carbon surface, there is a multilayer of n-octadecanol. Its molecules are probably parallely oriented in relationship to the adsorbent surface. This film desintegrates progressively when the temperature increase. Maximum temperature of this phase transition is lower than the temperature of its analogue on pure silica gel surface.