Direct synthesis of surface molecularly imprinted polymers based on vinyl–SiO2 nanospheres for recognition of bisphenol A

Molecularly imprinted polymers (MIP) with high performance in selectively recognizing bisphenol A (BPA) were prepared by using a novel and facile surface molecular‐imprinting technique. Vinyl‐functionalized, monodispersed silica spheres were synthesized by a one‐step emulsion reaction in aqueous solution. Then, BPA surface molecularly imprinted polymers (SMIP) were prepared by polymerization with 4‐vinylpyridine as the functional monomer and ethylene glycol dimethacrylate as the crosslinker. Maximal sorption capacity (Q_max) of the resulting SMIP was up to 600 μmol g^?1, while that of nonimprinted polymers was only 314.68 μmol g^?1. Kinetic binding study showed that sorption capacity reached 70% of Q_max in 20 min and sorption equilibrium at 80 min. SMIP had excellent accessibility and affinity toward BPA, for the selectivity coefficients of SMIP for BPA in respect to phenol, p‐tert‐butylphenol, and o‐phenylphenol were 3.39, 3.35, and 3.02, respectively. The reusage process verified the SMIP owning admirably stable adsorption capacity toward BPA for eight times. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

The essential oil fromTagetes minuta L. modulates the binding of [3H]flunitrazepam to crude membranes from chick brain

The hypothesis that the essential oil fromTagetes minuta L. can interact with biological membranes was investigated by assessing its ability of perturbing the binding of a benzodiazepine [flunitrazepam (FNTZ)] to crude membranes from chick brains. The essential oil fromT. minuta L. inhibited [³H]FNTZ specific binding to chick brain membranes. These values were obtained from the analysis of the saturation curve for the kinetic parameters: dissociation equilibrium constant (K_d)=2.47±0.32 nM, maximal binding (B_max)=556±5 fmoles/mg protein, and Hill coefficient (n)=1.00±0.07 in the absence, and K_d=6.73±1.4 nM, B_max=583±69 fmoles/mg protein, and n=1.02±0.08 in the presence of 29 μg/mL of essential oil. The essential oil could self-aggregate with a critical micellar concentration (CMC) of 60 μg/mL. The marked increase in [³H]FNTZ nonspecific binding starting at 60 μg of essence per mL was due to that phenomenon and revealed the ability of self-aggregated structures to interact with membranes. [³H]FNTZ specific binding decrement as a function of essence concentration cannot be ascribed merely to oil's micelles ability of trapping the lipophilic radioligand molecules, because the discontinuous behavior that characterizes a monomer-aggregate phase transition was not shown. Oil's components might behave as competitive inhibitors or allosteric modulators of FNTZ specific binding. However, their ability to increase FNTZ nonspecific binding at concentrations below oil's CMC suggests that this effect may be due to oil's partitioning into the lipid bilayer. This latter phenomenon would induce an increment in membrane fluidity and a change on FNTZ binding site toward a lower affinity conformation. Therefore, the essential oil components can interact with brain membranes either as monomers, by partitioning into the lipid bilayer, or as self-aggregated structures, through an adsorption to the membrane surface.     

Physicochemical characterization of ATP binding to human 5-lipoxygenase

Human 5-lipoxygenase requires ATP as a stimulatory factor. At the two preferred concentrations of the free Ca²⁺, 0.02 μM with a resting cell and 20 μM with a stimulated cell, Scatchard analysis revealed that 5-lipoxygenase has one affinity ATP binding site with aK _d of 4.6 μM at the low Ca²⁺ concentration but has two affinity ATP binding sites with a higherK _d of 4.4 μM and a lowerK _d of 14.5 μM at the high Ca²⁺ concentration. In contrast, in a Tween 20 reaction system, 5-lipoxygenase had similar activation coefficients for ATP at both Ca²⁺ concentrations; these were 12.7 μM at the low Ca²⁺ concentration and 12.0 μM at the high Ca²⁺ concentration. These results showed that 5-lipoxygenase has an ATP binding site and suggest that self-association of 5-lipoxygenase in 20 μM Ca²⁺ may affect ATP binding affinity as measured by Scatchard analysis.     

Precipitation polymerization of molecularly imprinted polymers for recognition of melamine molecule

Molecular imprinted polymer microspheres (MIPs) were prepared by precipitation polymerization using melamine as template molecule, methacrylic acid (MAA) as functional monomer, trimethylol‐propane trimethacrylate (TRIM) as crosslinking agent, acetonitrile as solvent and dispersion medium. Release of the template was performed by continuous extraction with methanol containing 10% acetic acid. The microspheres were observed by scanning electron microscopy (SEM). The perfect microspheres were produced when the addition of crosslinker was 7.48 mmol. The binding capacity of MIPs was examined, Q_max = 68.36 μmol g^?1, and the dissociation constant at binding site of MIPs, K_d = 0.761, was estimated. Compared with the performance of conventional imprinted polymer, the imprinted microspheres showed high selectivity in special binding to template molecule. The imprinted microspheres could be used as the stationary phase in HPLC or SPE for selective extraction of melamine in daily products. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Water‐compatible imprinted polymers based on CS@SiO2 particles for selective recognition of naringin

Molecularly imprinted polymers are being proposed for the development of novel biorecognition elements for active components. In this study, an imprinted chitosan coated silica nanoparticles (I‐CS@SiO₂) polymer was prepared by a simple procedure, in which, naringin (NG) with antioxidant activity, acted as a template, silica as a matrix and CS as a functional polymer. The binding properties were discussed by the equilibrium binding experiment method. Experiments show that the adsorption characteristics of I‐CS@SiO₂ are better than that of nonimprinted polymer. It exhibited high selectivity for NG when compared with the nonimprinted polymer, with an imprinting factor α of 1.74. Scatchard analysis of the I‐CS@SiO₂ indicated that there was a class of binding sites during the I‐CS@SiO₂ recognizing NG: The dissociation constant of K_D is 0.016 mmol L^?1, the maximum apparent binding capacity of B_max is 6.56 μmol g^?1. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40491.     

Lack of specificity in accumulation of sterols byPhytophthora cactorum

The kinetics of sterol uptake inPhytophthora cactorum were examined. A V_max of 4.81×10⁻⁵ μmol/min/mg dry wt and an average apparent Km of 18.0 μM were determined for both cholesterol and sitosterol accumulation. Selectivity for specific sterols was not apparent in the accumulation, esterification, or distribution of sterols byPhytophthora cactorum.     

PC and PE synthesis: mixed micellar analysis of the cholinephosphotransferase and ethanolaminephosphotransferase activities of human choline/ethanolamine phosphotransferase 1 (CEPT1)

The human choline/ethanolamine phosphotransferase 1 (CEPT1) gene codes for a dual-specificity enzyme that catalyzes the de novo synthesis of the two major phospholipids through the transfer of a phosphobase from CDP-choline or CDP-ethanolamine to DAG to form PC and PE. We used an expression system devoid of endogenous cholinephosphotransferase and ethanolaminephosphotransferase activities to assess the diradylglycerol specificity of CEPT1. A mixed micellar assay was used to ensure that the diradylglycerols delivered were not affecting the membrane environment in which CEPT1 resides. The CEPT1 enzyme displayed an apparent K _m of 36 μM for CDP-choline and 4.2 mol% for di-18∶1 DAG with a V _max of 14.3 nmol min⁻¹ mg⁻¹. When CDP-ethanolamine was used as substrate, the apparent K _m was 98 μM for CDP-ethanolamine and 4.3 mol% for di-18∶1 DAG with a V _max of 8.2 nmol min⁻¹ mg⁻¹. The preferred diradylglycerol substrates used by CEPT1 with CDP-choline as the phosphobase donor were di-18∶1 DAG, di-16∶1 DAG, and 16∶0/18∶1 DAG. A major difference between previous emulsion-based assay results and the mixed micelle results was a complete inability to use 16∶0(O)/2∶0 as a substrate for the de novo synthesis of platelet-activating factor when the mixed micelle assay was used. When CDP-ethanolamine was used as the phosphobase donor, 16∶0/18∶1 DAG, di-18∶1 DAG, and di-16∶1 DAG were the preferred substrates. The mixed micelle assay also allowed the lipid activation of CEPT to be measured, and both the cholinephosphotransferase and ethanolaminephosphotransferase activities displayed the unusual property of product activation at 5 mol%, implying that specific lipid activation binding sites exist on CEPT1. The protein kinase C inhibitor chelerythrine and the human DAG kinase inhibitor R59949 both inhibited CEPT1 activity with IC₅₀ values of 40 μM.     

Determination of the phospholipase activity of patatin by a continuous spectrophotometric assay

Patatin is a family of glycoproteins that accounts for 30–40% of the total soluble protein in potato (Solanum tuberosum L.) tubers. This protein has been reported to serve as a storage protein and also to exhibit lipid phospholipase activity. This paper describes a simple continuous spectrophotometric method for assaying patatin phospholipase activity. The procedure is based on a coupled enzymatic assay using [1,2-dilinoleoyl]PC as the phospholipase substrate and lipoxygenase as the coupling enzyme. In the procedure developed in this work, lipoxygenase oxidizes the linoleic acid released by the phospholipase activity of patatin. This activity can then be followed spectrophotometrically by recording the increase in absorbance at 234 nm that results from the formation of the corresponding hydroperoxide from linoleic acid by the action of lipoxygenase. The optimal assay concentrations of patatin and lipoxygenase were established. Phospholipase activity varied with pH, reaching its optimal value at pH 9.5. Scans of the deoxycholate concentration pointed to an optimal detergent concentration of 3 mM. Phospholipid hydrolysis followed classical Michaelis-Menten kinetics (V _m=9.8×10⁻³ μmol/min·μg protein, K _m=7.8 μM, V _m/K _m=1.3 min⁻¹·μg protein). This method proved to be specific since there was no activity in the absence of patatin. It also had the advantages of a short analysis time and the use of commercially nonradiolabeled and inexpensive substrates, which are, furthermore, natural substrates of phospholipase.     

Synthesis of novel photoresponsive molecularly imprinted polymer microspheres with special binding properties

An azobenzene‐containing molecularly imprinting polymer microsphere with photoresponsive binding properties toward 2,4‐dichlorophenoxyacetic acid (2,4‐D) was successful prepared via silica surface polymerization. The number‐average diameters of silica and imprinting polymer microsphere are 0.5 and 0.7 μm, respectively. The static adsorption, binding and selectivity experiments were performed to investigate the adsorption properties and recognition characteristics of the polymers for 2,4‐D. The equilibrium adsorptive experiments indicated that 2,4‐D‐SMIP(surface molecularly imprinted polymers) has significantly higher adsorption capacity for 2,4‐D than its nonimprinted polymers (SNIP).The binding constant K_d and apparent maximum number Q_max of the imprinted polymer were determined by Scatchard analysis as 0.054 mmol L^?1 and 0.167 mmol g^?1_, respectively. The result of photoregulated release and uptake of 2,4‐D experiment demonstrated that azo‐containing SMIP can make use of light and change it into mechanical properties to release and take up the template molecules. It means that the SMIP can be controlled by light. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 869‐876, 2013     

Structures,Stabilities and Electronic Properties of Endo- and Exohedral Dodecahedral Silsesquioxane (T<Subscript>12</Subscript>-POSS) Nanosized Complexes with Atomic and Ionic Species

The structures of endohedral complexes of the polyhedral oligomeric silsesquioxane (POSS) cage molecule (HSiO_3/2)₁₂, with both D _2d and D _6h starting cage symmetries, containing the atomic or ionic species: Li⁰, Li⁺, Li⁻, Na⁰, Na⁺, Na⁻, K⁰, K⁺, K⁻, F⁻, Cl⁻, Br⁻, He, Ne, Ar were optimized by density functional theory using B3LYP and the 6-311G(d,p) and 6-311 ++G(2d,2p) basis sets. The exohedral Li⁺, Na⁺, K⁺, K⁻, F⁻, Cl⁻, Br⁻, He, Ne, Ar complexes, were also optimized. The properties of these complexes depend on the nature of the species encapsulated in, or bound to, the (HSiO_3/2)₁₂ cage. Noble gas (He, Ne and Ar) encapsulation in (HSiO_3/2)₁₂ has almost no effect on the cage geometry. Alkali metal cation encapsulation, in contrast, exhibits attractive interactions with cage oxygen atoms, leading to cage shrinkage. Halide ion encapsulation expands the cage. The endohedral X@(HSiO_3/2)₁₂ (X = Li⁺, Na⁺, K⁺, F⁻, Cl⁻, Br⁻, He and Ne) complexes form exothermically from the isolated species. The very low ionization potentials of endohedral Li⁰, Na⁰, K⁰ complexes suggest that they behave like “superalkalis”. Several endohedral complexes with small guests appear to be viable synthetic targets. The D _2d symmetry of the empty cage was the minimum energy structure in accord with experiment. An exohedral fluoride penetrates the D _6h cage to form the endohedral complex without a barrier.     

Poly(acrylamide/maleic acid)–sepiolite composite hydrogels for immobilization of invertase

Poly(acrylamide/maleic acid) and sepiolite (PAMS) composite hydrogel was prepared and used for the immobilization of invertase. In FTIR analysis, the characteristic bands of composite such as –OH, –COOH, Si–OH show the evidence of sepiolite and maleic acid. In TGA analysis, water loss, decomposition of amide side groups and breakdown of main chain regions of the composite were found. The parameters of equilibrium swelling, initial swelling rate, diffusional exponent, and diffusion coefficient were calculated and evaluated from swelling experiments in distilled water. Invertase was immobilized onto PAMS by adsorption and poly(acrylamide/maleic acid)–sepiolite–invertase (PAMSI) was prepared. Optimum pH, optimum temperature values for free invertase and PAMSI were found. It was found that K _m values of free invertase and PAMSI were 11.3 and 34.1 mM, respectively. V _max value was found that 2.0 μmol min⁻¹ for free invertase and 13.9 μmol min⁻¹ for PAMSI, respectively. PAMSI showed excellent temperature, operational and storage stability.     

Growth and eicosapentaenoic acid production byPhaeodactylum tricornutum in batch and continuous culture systems

Maximum specific growth rate (μ_max) ofPhaeodactylum tricornutum increased with increasing culture reactor surface-to-volume ratio. Values for μ_max of 0.647, 0.377 and 0.339 day⁻¹ were observed for the 75-mL tube, 5.6-L tank and the 16-L tank, respectively. Higher biomass was achieved in the 75-mL batch culture tube under continuous light as compared with light cycle conditions. Palmitic acid, palmitoleic acid and eicosapentaenoic acid (EPA) accounted for over 60% of total fatty acids in the batch tube culture, with EPA content increasing to a maximum after three days. In chemostat cultures, run at dilution rates of 0.15 day⁻¹ (0.45 of μ_max) and 0.3 day⁻¹ (0.9 of μ_max), cell concentration reached a steady state of 2.18 and 0.7 g/L, respectively, while contents of EPA per liter of culture at steady state were 100.9 and 82.5 mg/L, respectively. At both dilution rates, EPA content of total fatty acids was the same (35.0–35.2%). At a dilution rate of 0.3 day⁻¹, the continuous culture system manifested productivities of 0.51 g/L/d and 25.1 mg/L/d for biomass and EPA, respectively.     

Isolation and identification of acetyl-CoA carboxylase from rainbow trout (Salmo gairdneri) liver

Acetyl-CoA carboxylase is the pivotal enzyme in the de novo synthesis of fatty acids and is the only carboxylase with a biotin-containing subunit greater than 200,000 daltons. The biotin moiety is covalently linked to the active site and has a high affinity (K_d=10⁻¹⁵ M) for the protein avidin. This relationship has been used in previous studies to identify acetyl-CoA carboxylase isolated from mammalian species. However, acetyl-CoA carboxylase has not been isolated and characterized in a poikilothermic species such as the rainbow trout. The present study describes the isolation and identification of acetyl-CoA carboxylase in the cytosol of rainbow trout (Salmo gairdneri) liver. The enzyme was isolated using two distinct procedures—polyethylene glycol precipitation and avidin-Sepharose affinity chromatography. Identification of the isolated protein as acetyl-CoA carboxylase was made by the following: (1) sodium dodecyl sulfate-polyacrylamide gel electrophoresis; (2) avidin binding; (3) in vivo labeling with [¹⁴C]biotin; and (4) acetyl-CoA carboxylase-specific activity. The subunit molecular weight of the major protein was 230,000 daltons ±3.3%. This protein was shown to bind avidin (M_r=16,600) prior to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, indicating the presence of biotin. In addition, protein isolated from fish that had previously received intraperitoneal injections of [¹⁴C]biotin, showed the majority of radioactivity associated with the 230,000 dalton protein. The polyethylene glycol precipitation yielded 200 μg protein (4.4 μg/g liver), with a specific activity of 5 nmol malonyl-CoA/min/mg protein, whereas avidin affinity chromatography yielded 1.75±1.1 mg protein (9.0 μg/g liver), with a specific activity of 1.37±0.18 μmol malonyl-CoA/min/mg protein. The enzyme was citrate dependent showing maximum activity between 10 and 20 mM. Acetyl-CoA carboxylase-specific activity decreased by 50% in the presence of 0.2 M NaCl. These findings suggest that the major protein (M_r=230,000) purified from rainbow trout liver is acetyl-CoA carboxylase with enzyme characteristics comparable to mammalian acetyl-CoA carboxylase.     

Removal of arsenic from aqueous solution using polyaniline/rice husk nanocomposite

The present study deals with the adsorption of arsenic ions from aqueous solution on polyaniline/rice husk (PAn/RH) nanocomposite. Batch studies were performed to evaluate the influence of various experimental parameters like pH, adsorbent dosage, contact time and the effect of temperature. Optimum conditions for arsenic removal were found to be pH 10, adsorbent dosage of 10 g/L and equilibrium time 30 minutes. Adsorption of arsenic followed pseudo-second-order kinetics. The equilibrium adsorption isotherm was better described by Freundlich adsorption isotherm model. The adsorption capacity (q _max ) of PAn/RH for arsenic ions in terms of monolayer adsorption was 34.48 mg/g. The change of entropy (ΔS⁰) and enthalpy (ΔH⁰) was estimated at −0.066 kJ/(mol K) and −22.49 kJ/mol, respectively. The negative value of the Gibbs free energy (ΔG⁰) indicates feasible and spontaneous adsorption of arsenic on PAn/RH.     

Amperometric hydrogen peroxide biosensor based on a modified gold electrode with silver nanowires

A novel amperometric biosensor for the detection of hydrogen peroxide (H₂O₂) was prepared by immobilizing horseradish peroxidase (HRP) on highly dense silver nanowire (Ag-NW) film. The modified electrode was characterized using UV–Vis spectroscopy, scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. The electrochemical performances of the electrode were studied by cyclic voltammetry and chronoamperometry. The HRPs immobilized on the surface of Ag-NWs exhibited an excellent electrocatalytic response toward reduction of H₂O₂. The resulting Ag-NW modified sensor showed a sensitivity of ~2.55 μA μM⁻¹ (correlation coefficient r = 0.9969) with a linear range of 4.8 nM–0.31 μM. Its detection limit was 1.2 nM with a signal-to-noise ratio of 3. The Michaelis–Menten constant K_M^app and the maximum current density I _max of the modified electrode were 0.0071 mM and 8.475 μA, respectively. The preparation process of the proposed biosensor was convenient, and the resulting biosensor showed high sensitivity, low detection limit and good stability.     

A new molecularly imprinted polymer prepared by surface imprinting technique for selective adsorption towards kaempferol

A new molecularly imprinted polymer (KAE-MPS/SiO₂) with high performance for recognizing kaempferol (KAE) was prepared by adopting the surface molecular imprinting technique with silica nanoparticles modified with 3-methacryloxypropyltrimethoxysilane (MPS) as a carrier material, 2-vinylpridine as the functional monomer and ethylene glycol dimethacrylate as the crosslinker. The static adsorption experiments indicated that KAE-MPS/SiO₂ had significantly higher adsorption capacity for KAE than its non-imprinted polymers. Scatchard analysis revealed that two classes of binding sites were formed in KAE-MPS/SiO₂ with dissociation constants of 0.26 and 2.34 μmol/mL, and the maximum apparent binding capacity was 3.33 and 16.16 μmol/g, respectively. The selectivity coefficients of KAE-MPS/SiO₂ for KAE in relation to competition species myricetin and chlorogenic acid were 2.51 and 4.24, respectively, which suggested that KAE-MPS/SiO₂ had high recognition selectivity and binding affinity for the template KAE. Dynamic binding study showed that the KAE-MPS/SiO₂ had good site accessibility and mass transport for KAE. The KAE-MPS/SiO₂ can be reused many times without decreasing their adsorption capacities significantly.     

Properties and catalytic mechanism of γ-glutamyltranspeptidase from B.subtilis NX-2

Since γ-glutamyltranspeptidase (GGT) especially catalyses the transfer of the γ-glutamyl moiety to a variety of amino acids and short peptides, GGT has important practical value for enzymatic synthesis of γ-glutamyl compounds. In this paper, the GGT produced from Bacillus subtilis NX-2 was purified by a combination of ammonium sulfate fractionation and ion exchange chromatography, and the properties of purified GGT were investigated. At the conditions of pH 10.0, D-glutamine (D-Gln)/L-tryptophan (L-Trp) with a molar ratio of 5: 7, a temperature 40°C and a reaction time of 4 h, a higher conversion rate of 42% was obtained. According to the time course, the catalytic mechanism of enzymatic synthesis of γ-D-glutamyl-L-tryptophan (γ-D-Gln-L-Trp) was discussed. It was demonstrated that the GGT can catalyze not only the reaction of transpeptidation, but also the irreversible hydrolysis of the products which results in the decrease of the yield of the products. The affinity parameter of GGT to D-Gln (Km) was 5.08 mmol·L⁻¹ and the maximum reaction rate of transpeptidation (r _max) was determined as 0.034 mmol·min⁻¹·L⁻¹, while the affinity parameter of GGT to γ-D-Gln-L-Trp (K’_m) was 2.267 mmol·L⁻¹, and the maximum reaction rate of hydrolysis (r’_max) was 0.012 mmol·min⁻¹·L⁻¹. __________ Translated from Journal of Chemical Engineering of Chinese Universities, 2008, 22(2): 288–293 [译自: 高校化学工程学报]     

In situ synthesis of monolithic molecularly imprinted stationary phases for liquid chromatographic enantioseparation of dibenzoyl tartaric acid enantiomers

A monolithic molecularly imprinted polymer (monolithic MIP) for dibenzoyl-D-tartaric acid (D-DBTA) was prepared in a stainless-steel chromatographic column tube (50?mm?×?4.6?mm I.D.) as HPLC stationary phase through in situ polymerization. By optimizing polymeric and chromatographic conditions, the chiral separation of DBTA enantiomers was successfully achieved in the obtained MIP in less than 25?min with a resolution Rs?=?1.25, whereas no enantioseparation effect was found on the monolithic non-imprinted polymer (NIP). Thermodynamic data of the enantioseparation were calculated. The results revealed that two different thermodynamic processes existed within the temperature range investigated, moreover, just at the transition temperature (50?°C) of the two processes, separation factor ?? reached its maximum. Scathcard analysis indicated that only one class of binding sites existed in the obtained MIP, with its K _d and Q _max estimated to be 5.457?×?10^?4?mol?L^?1 and 229.6???mol?g^?1, respectively. Nitrogen adsorption experiment proved that the prepared MIP had a large specific surface area of 105?m²?g^?1. Scanning electron microscopy showed that large flow-through pores were present in the prepared monolith. As a consequence, the column backpressure was only 1.2?MPa with acetonitrile as mobile phase at a flow rate of 1.0?mL?min^?1.     

Immobilization and stabilization of <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> SRT9 lipase on tri(4-formyl phenoxy) cyanurate

Lipase was extracted and purified from Pseudomonas aeruginosa SRT9. Culture conditions were optimized and highest lipase production amounting to 147.36 U/ml was obtained after 20 h incubation. The extracellular lipase was purified on Mono QHR5/5 column, resulting in a purification factor of 98-fold with specific activity of 12307.81 U/mg. Lipase was immobilized on tri (4-formyl phenoxy) cyanurate to form Schiff’s base. An immobilization yield of 85% was obtained. The native and immobilized lipases were used for catalyzing the hydrolysis of olive oil in aqueous medium. Comparative study revealed that immobilized lipase exhibited a shift in optimal pH from 6.9 (free lipase) to 7.5 and shift in optimal temperature from 55 °C to 70 °C. The immobilized lipase showed 20–25% increase in thermal stability and retained 75% of its initial activity after 7 cycles. It showed good stability in organic solvents especially in 30% acetone and methanol. Enzyme activity was decreased by ∼60% when incubated with 30% butanol. The kinetic studies revealed increase in K _M value from 0.043 mM (native) to 0.10 mM for immobilized lipase. It showed decrease in the V _max of immobilized enzyme (142.8 μmol min⁻¹ mg⁻¹), suggesting enzyme activity decrease in the course of covalent binding. The immobilized lipase retained its initial activity for more than 30 days when stored at 4 °C in Tris-HCl buffer pH 7.0 without any significant loss in enzyme activity.     

Adsorption equilibrium constants of methyl oleate and methyl linoleate in vapor phase on supported copper and nickel catalysts

Adsorption equilibrium constants for methyl oleate and methyl linoleate in vapor phase on supported copper and nickel catalysts have been determined using the technique of pulse gas chromatography. The results are discussed in relation to selectivity in fat hydrogenation. Notation: A, column cross-section, m₂ ; a_n,b_n, nth Fourier coefficients; c, concentration of adsorbate in bulk flow, mol/m³ ; c^* = c/ ∫ ₀ ^∞ cdt, normalized concentration of adsorbate in bulk flow; C_i, concentration of adsorbate in catalyst pores, mol/m³ ; c_a, concentration of adsorbate on catalyst surface, mol/kg; c_TOT, active area of catalyst as measured by hydrogen adsorption, mol/kg; D_e, effective diffusion coefficient of adsorbate in catalyst, m²/s; D_ea, axial dispersion coefficient based on void cross-section, m²/s; h_n, nth coefficient in Hermite polynomial expansion; H_n nth Hermite polynomial; ΔH_A, adsorption enthalpy, kJ/mol; ΔH_vap , heat of vaporization, kJ/moll; k_a, adsorption rate constant, m³/kgs;K_A, adsorption equilibrium constant, m³/kg; K₀ , preexponential factor defined in Eqn. 8, m³/kg; k_f, mass transfer coefficient, m/s; L, bed length, m; q, flow rate, m³/s; R, particle radius, m; R_g, gas constant; t, time, s; T, temperature, K; T_F, period of Fourier expansion, s; u = q/A, linear velocity, m/s; z, length coordinate in packed column, m. Greek symbols: δ(t), Dirac delta function; ∈_B, void fraction of bed; ∈_-p, particle void fraction, ρ_rp, particle density, kg/m³ ; ξ, radial coordinate in particle, m; μ₁, first absolute moment, μ₂, second central moment.