Immobilization of hexokinase onto chitosan decorated particles

Chitosan (CH) decorated polystyrene (PS) particles were synthesized within complexes of CH, a polycation under acid conditions, and tiny amounts of sodium dodecylsulfate (SDS). Particle characterization was performed by means of dynamic light scattering, zeta potential measurements, and transmission electron microscopy. All dispersions were stable in the ionic strength of 2.0 mol L-1 NaCl during 2 months. The outstanding colloidal stability was attributed to the presence of a hydrated CH layer around the particles. CH decorated PS particles were attached to atomic force microscopy cantilevers and probed against Si wafers in water and in NaCl 0.01 mol/L. The mean thickness of CH layer amounted to 35 +/- 11 and 16 +/- 6 nm, when the medium was water and NaCl 0.01 mol/L, respectively. Adsorption isotherm of hexokinase (HK) onto PS/CH particles studied by means of spectrophotometry showed three regions: an initial step; adsorption plateau and multilayer formation. Enzymatic activity of free HK and immobilized HK was monitored by means of spectrophotometry as a function of storing time and reuse. After 3 days, storing HK free in solution dramatically lost its catalytic properties. On the contrary, HK-covered PS/CH particles retained enzymatic activity over 1 month. Moreover, HK-covered PS/CH particles could be reused in the determination of glucose two times consecutively, without losing activity. These interesting findings were discussed in light of the role of water in enzyme conformation.     

An Easy Way Toward ε‐Caprolactone Macromonomers by Microwave Irradiation Using Early Lanthanide Halides as Catalysts

Poly(ε‐caprolactone) macromonomers were synthesized under microwave irradiation from commercial caprolactone, using commercial hydrated lanthanide halides as catalysts. The molecular weight of the polymers was in the range 3 000–5 000. Higher molecular weights (5 000–20 000) and lower polydispersity indices were obtained with THF adducts of the lanthanide halides as catalysts and also by applying longer reaction times or using diethylene glycol as a coupling reagent.     

Effect of sorbitan-based surfactants on glass transition temperature of cellulose esters

Thermal behavior of mixtures composed of cellulose acetate butyrate (CAB), carboxymethylcellulose acetate butyrate (CMCAB), or cellulose acetate phthalate (CAPh), and sorbitan-based surfactants was investigated as a function of mixture composition by means of differential scanning calorimetry (DSC). Surfactants with three different alkyl chain lengths, namely, polyoxyethylenesorbitan monolaurate (Tween 20), polyoxyethylenesorbitan monopalmitate (Tween 40), and polyoxyethylene sorbitan monostearate (Tween 60) were chosen. DSC measurements revealed that Tween 20, 40, and 60 act as plasticizers for CAB, CMCAB, and CAPh (except for Tween 60), leading to a dramatic reduction of glass transition temperature (T _g). The dependence of experimental T _g values on the mixture composition was compared with theoretical predictions using the Fox equation. Plasticization was strongly dependent on mixture composition, surfactant hydrophobic chain length, and type of cellulose ester functional group.     

Hydrolysis of new phthalimide-derived esters catalyzed by immobilized lipase

The last step of the production of four phthalimide-derived acids, designed to act as antiasthma drugs, was performed by enzymatic hydrolysis of the respective methyl or ethyl esters. The esters 4-ethyl-[2-(1,3-dioxo-1,3-dihydro-2-isoindoylyl)]-phenoxyacetic methyl ester (PHT-MET), 4-ethyl-[2-(1,3-dioxo-1,3-dihydro-2-isoindoylyl)]-phenoxyacetic ethyl ester, 4-(1,3-dioxo-1,3-dihydro-2-isoindoylyl)-phenoxyacetic ethyl ester, and 2-(1,3-dioxo-1, 3-dihydro-2-isoindoylyl)-phenoxyacetic ethyl ester were hydrolyzed by immobilized lipase. The enzymatic reaction could be used only to produce the desired 4-substituted compounds. The best result that was found to hydrolysis of PHT-MET, and, therefore, that ester was selected for optimization experiments in a three-phase system. Reactions were performed with solid biocatalyst (Lipozyme® RM IM), organic solvent phase (ethyl acetate), and aqueous phase (saturated Na₂CO₃ solution). To optimize the reaction conditions, an experimental design optimization procedure was used. The variables studied were the amount of enzyme, the temperature, and the volume of the aqueous solution. Time course experiments were then performed for different initial enzyme concentrations (0.5, 0.9, and 1.4 U_H/mL of solvent). The optimized reaction conditions found were 20 mg of Lipozyme (0.9 U_H/mL_solvent) and 5.0 mL of Na₂CO_3(sat) at 40°C for 6 h.     

Calix[4]azulene

Azulene reacts with paraformaldehyde in the presence of florisil to give excellent yields of calix[4]azulene.     

Internal standard in flow injection analysis with amperometric detection

In this work, we describe for the first time the use of the internal standard method in flow injection analysis (FIA) with amperometric detection. The method is based on the application of sequential potential pulses to the working electrode in an electrochemical flow cell. The sequence of potential pulses is selected in such a way that the analyte and internal standard compound are detected and monitored individually and independently at the same working electrode. This approach compensates for random errors associated with variations of flow rate, injection volume, ionic strength difference between standards and samples, and accidental insertion or formation of air bubbles in the carrier stream. In addition, this method can overcome the major drawback of amperometric detection using solid electrodes, which is gradual electrode passivation. To illustrate the potential of this method, the flow-injection amperometric detection of uric acid using [Fe(CN)₆]^3? as an internal standard (IS) is presented as an example.     

The effects of gamma irradiation on the microbiological, physical and sensory qualities of diced tomatoes

Diced Roma tomatoes were treated with gamma irradiation and evaluated for changes in microbial, physical, chemical and sensory properties. Dosages for Trial 1 were 0.0, 0.39, 0.56 and 1.82 kGy and in Trial 2, 0.0, 0.50, 1.24 and 3.70 kGy. Irradiation at 3.70 kGy resulted in no aerobic populations through day 12 and significantly fewer colonies through day 15 whereas yeast and mold populations experienced a 2 log reduction through day 12. Color, titratable acidity, and °Brix were not significantly affected by irradiation. Tissue firmness decreased with increasing dose but not with storage time. Treatment with 3.7 kGy decreased firmness by 50% and 20% with 0.5 kGy, however, the reduced firmness induced by 0.50 kGy was undetected by a 9 member trained sensory panel. A significant (p0.05) inverse correlation between changes in texture and water-soluble pectin (WSP) was determined while total pectin remained relatively constant and oxalate soluble pectin content decreased slightly with irradiation dose. The significant inverse correlation between the loss of firmness and WSP indicates that the changes in WSP play an important role in the tissue softening of tomatoes, This study indicates that irradiation at 0.5 kGy can reduce microbial counts substantially to improve microbial shelf life without adverse effects on sensory qualities.     

Cellulosic Films Obtained from the Treatment of Sugarcane Bagasse Fibers with N-methylmorpholine-N-oxide (NMMO)

Ethanol/water organosolv pulping was used to obtain sugarcane bagasse pulp that was bleached with sodium chlorite. This bleached pulp was used to obtain cellulosic films that were further evaluated by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). A good film formation was observed when temperature of 74 °C and baths of distilled water were used, which after FTIR, TGA, and SEM analysis indicated no significant difference between the reaction times. The results showed this to be an interesting and promising process, combining the prerequisites for a more efficient utilization of agro-industrial residues.