Spectroscopic and Electrochemical Characterization of Cytochrome P450st‐DDAB Films on a Plastic‐Formed Carbon Electrode

We have studied the characterization of thermophilic cytochrome P450 (P450st)‐didodecyldimethylammonium bromide (DDAB) films by using UV‐vis absorption, resonance Raman spectroscopy, and electrochemical methods. The observed Raman spectrum indicated near‐native conformation of the heme iron in DDAB film on the surface of a glass slide, while on the surface of a plastic‐formed carbon (PFC) electrode, the conformation of P450st‐DDAB was very similar to that of heme‐DDAB film, suggesting the release of heme from P450st in DDAB films on PFC electrodes. When NaBr was added as salt to the casting solution, the result of Raman spectrum indicated near‐native conformation of P450st in DDAB film even on the PFC electrode, but no redox potential of P450st which has near native structure was observed. This study suggests the essential experimental conditions when working with heme protein‐DDAB films as, in some cases, heme iron from proteins is released on the surface of the electrode.     

Surface behavior and film formation analysis of sisal fiber coated by poly(methyl methacrylate) ultrathin film

Admicellar polymerization was used to modify a sisal fiber surface with poly(methyl methacrylate) (PMMA) in order to improve the compatibility between the sisal fiber and the surrounding polymeric matrix in a composite. The effect of the amount of monomer (methyl methacrylate) and initiator (sodium persulfate) on the hydrophobicity behavior and PMMA film formation of the admicellar-treated sisal surface was studied. The increase in the hydrophobicity of the admicellar-treated sisal fiber was examined by flotation testing, moisture absorption, and electrostatic charge or zeta (ζ) potential. The amount of PMMA film formed on the sisal surface was investigated by the weight loss of the admicellar-treated sisal extracted by acetone and chloroform; and the thermal degradation was studied by thermogravimetric analyses. The admicellar-treated sisal could float on the surface of water for longer than half an hour, and its moisture absorption decreased. The ζ potential of its surface also showed a significant change compared to the untreated sisal. The results from the weight loss indicated that the amount of PMMA formed on the sisal fiber surface depended on the amount of monomer and initiator. The Fourier transform infrared spectrum of the admicellar-treated sisal showed the characteristic peaks of PMMA and the scanning electron micrograph of the treated sisal was clearly different from the untreated sisal, confirming that there was a thin film coating on the admicellar-treated sisal fiber.     

Production of 2-O-α-glucopyranosyl l-ascorbic acid from ascorbic acid and β-cyclodextrin using immobilized cyclodextrin glycosyltransferase

Cyclodextrin glycosyltransferase (CGTase) isolated and purified from Paenibacillus sp. A11 was immobilized on various carriers by covalent linkage using bifunctional agent glutaraldehyde. Among tested carriers, alumina proved to be the best carrier for immobilization. The effects of several parameters on the activation of the support and on the immobilization of enzyme were optimized. The best preparation of immobilized CGTase retained 31.2% of its original activity. After immobilization, the enzymatic properties were investigated and compared with those of the free enzyme. The optimum pH of the immobilized CGTase was shifted from 6.0 to 7.0 whereas optimum temperature remained unaltered (60°C). Free and immobilized CGTase showed similar pH stability profile but the thermal stability of the immobilized CGTase was 20% higher. Kinetic data (K _M and V _max) for the free and immobilized enzymes were determined from the rate of β-CD formation and it was found that the immobilized form had higher K _M and lower V _max. The immobilized CGTase also exhibited higher stability when stored at both 4°C and 25°C for 2 months. The enzyme immobilized on alumina was further used in a batch production of 2-O-α-glucopyranosyl-l-ascorbic acid (AA-2G) from ascorbic acid and β-cyclodextrin. The yield of AA-2G was 2.92% and the immobilized CGTase retained its activity up to 74.4% of the initial catalytic activity after being used for 3 cycles. The immobilized CGTase would have a promising application in the production of various transglycosylated compounds and in the production of cyclodextrin by the hydrolysis of starch.     

Electrical response characterisation of poly(ethylene glycol) macromer (PEGM)/chitosan hydrogels in NaCl solution

Interpenetrating polymer network hydrogels composed of poly(ethylene glycol) macromer (PEGM) and chitosan were synthesised by UV irradiation of solutions in a mild aqueous media. The IPN hydrogels exhibited the equilibrium water content (EWC) in the range of 86-94%. The hydrogels were characterised using FT-IR, FT-Raman spectroscopy and differential scanning calorimetry (DSC). The results from DSC measurements indicate that the melting endotherms of PEGM, within the hydrogels, decreased in intensities and shifted to lower temperatures comparing with a linear PEGM. This was due to the decrease of the crystallinity in the IPN hydrogels with higher contents of PEGM. The electrical response of the IPN hydrogels was also investigated by applying electrical current to the hydrogels immersed in a NaCl solution. The extent of a bending degree of the IPN hydrogel depends on the IPN hydrogel composition and applied electric field strength.     

Colloidal crystals of core–shell-type spheres in deionized aqueous suspension

The structure, crystal growth kinetics and rigidity of colloidal crystals of core–shell-type latex spheres (diameters 280–330 nm) with differences in shell rigidity have been studied in aqueous suspension, mainly by reflection spectroscopy. The suspensions were deionized exhaustively for more than 2 years using mixed-bed ion-exchange resins. The five kinds of core–shell spheres examined form colloidal crystals, where the critical sphere concentrations, _c, of crystallization (or melting) are high and range from 0.01 to 0.06 in volume fraction. Nearest-neighbor intersphere distances in the crystal lattice agree satisfactorily with values calculated from the sphere diameter and concentration. The crystal growth rates are between 0.1 and 0.3 s^–1 and decrease slightly as the sphere concentration increases, indicating that the crystal growth rates are from the secondary process in the colloidal crystallization mechanism, corresponding to reorientation from metastable crystals formed in the primary process and/or Ostwald-ripening process. The rigidities of the crystals range from 2 to 200 Pa, and increase sharply as the sphere concentration increases. The g factor, the parameter for crystal stability, is around 0.02 irrespective of the sphere concentration and/or the kind of core–shell sphere. There are no distinct differences in the structural, kinetic and elastic properties among the colloidal crystals of the different core–shell-type spheres, showing that the internal sphere structure does not affect the properties of the colloidal crystals. The results show that colloidal crystals form in a closed container owing to long-range repulsive forces and the Brownian movement of colloidal spheres surrounded by extended electrical double layers and that their formation is not influenced by the rigidity and internal structure of the spheres.