Immobilization of glucose oxidase in polypyrrole/polytetrahydrofuran graft copolymers

Enzyme immobilization and molecular modeling studies on an organic–inorganic polypyrrole–titanium(iv)phosphate nanocomposite

A polypyrrole–titanium(iv)phosphate nanocomposite was synthesized by using facile chemical oxidative polymerization of pyrrole in the presence of titanium(iv)phosphate for YADH immobilization.

Pull-out bond strength of a self-adhesive resin cement to NaOCl-treated root dentin: effect of antioxidizing agents

Objectives

This study evaluated the effect of three antioxidizing agents on pull-out bond strengths of dentin treated with sodium hypochlorite.

Materials and Methods

Root canals of 75 single-rooted human teeth were prepared. Fifteen teeth were irrigated with normal saline for a negative control group, and the remaining 60 teeth (groups 2 - 5) with 2.5% NaOCl. The teeth in group 2 served as a positive control. Prior to post cementation, the root canals in groups 3 - 5 were irrigated with three antioxidizing agents including 10% rosmarinic acid (RA, Baridge essence), 10% hesperidin (HPN, Sigma), and 10% sodium ascorbate hydrogel (SA, AppliChem). Seventy-five spreaders (#55, taper .02, Produits Dentaires S.A) were coated with silica and silanized with the Rocatec system and ceramic bond. All the prepared spreaders were cemented with a self-adhesive resin cement (Bifix SE, Voco Gmbh) in the prepared canals. After storage in distilled water (24 h/37℃), the spreaders were pulled out in a universal testing machine at a crosshead speed of 1.0 mm/min. Pull-out strength values were analyzed by one-way ANOVA and Tukey's HSD test (α = 0.05).

Results

There were significant differences between study groups (p = 0.016). The highest pull-out strength was related to the SA group. The lowest strength was obtained in the positive control group.

Conclusions

Irrigation with NaOCl during canal preparation decreased bond strength of resin cement to root dentin. Amongst the antioxidants tested, SA had superior results in reversing the diminishing effect of NaOCl irrigation on the bond strength to root dentin.

Advances in Drug-delivery Systems Based on Intrinsically Conducting Polymers

Intrinsically conducting polymers (ICPs) are organic polymers with unique capabilities including the ability to conduct electricity. The release of drugs from ICP-based drug delivery systems can be controlled using electrical signaling to alter the redox state of the ICP, leading to subsequent changes in polymer charge and volume. The increasing use of ICPs in drug delivery systems can be attributed to their biocompatible nature and the ability to regulate drug release electrically. Drug can be easily incorporated into these polymers by physical and chemical means. As the release of the drugs from ICPs is in accordance with electrical stimulus the therapeutic effect can be maximized with a reduction in the side effects. In this chapter a general overview of ICPs, their electrochemical properties and the techniques used to characterize these materials with specifics pertaining to drug delivery is provided. Emphasis is given to advances in methods and technology to enhance the drug-loading capacity of these polymers and to achieve precise controlled therapy. The chapter discusses some of the exciting applications of ICPs as devices for controlled delivery of drugs to desired locations.

Effect of reducing agents on bond strength to NaOCl-treated dentin

OBJECTIVE

The purpose of this study was to evaluate the effect of three antioxidant/reducing agents with different application times on microtensile bond strengths to sodium hypochlorite-treated dentin.

METHODS

The occlusal surfaces of 24 extracted human third molars were horizontally cut to expose sound dentin. The teeth were divided into eight groups. The dentin surfaces of the teeth were treated as follows: group 1, no treatment; group 2, treated with 6% sodium hypochlorite (NaOCl) for 30s; groups 3-8, applications of 10% sodium ascorbate solution, 100 μM rosmarinic acid solution or Accel for 5 or 10s after the same treatment as in group 2. All treated dentin surfaces were bonded with a 2-step self-etching adhesive system (Clearfil Protect Bond) and restored with a resin composite (Clearfil AP-X). After storage in water for 24h, the bonded specimens were subjected to the microtensile bond test at a crosshead speed of 1.0 mm/min. Data were analyzed by a one-way ANOVA and Tukey test (p<0.05).

RESULTS

The NaOCl-treated group had significantly lower bond strength than the control group (p<0.05). The application of sodium ascorbate solution for 5 or 10s did not significantly increase the compromised bonding to NaOCl-treated dentin (p>0.05). On the other hand, Accel and rosmarinic acid solution had significant reversal effects with the same application times (p<0.05).

SIGNIFICANCE

The reversal effect on compromised bonding to NaOCl-treated dentin depended upon the type of antioxidant within the short application time. Applying Accel or rosmarinic acid for 5 or 10s improved bond strengths to NaOCl-treated dentin.

Enzymatic oxidation and separation of various saccharides with immobilized glucose oxidase

Glucose oxidase from Aspergillus niger, the specific enzyme for beta-D-glucose oxidation, can also oxidize other related saccharides at very slow or negligible rates. The present study aimed to compare the kinetics of D-glucose oxidation using immobilized glucose oxidase on bead cellulose for the oxidation of related saccharides using the same biocatalyst. The significant differences were observed between the reaction rates for D-glucose and other saccharides examined. As a result, k (cat)/K (M) ratio for D-glucose was determined to be 42 times higher than D-mannose, 61.6 times higher than D-galactose, 279 times higher than D-xylose, and 254 times higher than for D-fructose and D-cellobiose. On the basis of these differences, the ability of immobilized glucose oxidase to remove D-glucose from D-cellobiose, D-glucose from D-xylose, and D-xylose from D-lyxose was examined. Immobilized catalase on Eupergit and mixed with immobilized glucose oxidase on bead cellulose or co-immobilized with glucose oxidase on bead cellulose was used for elimination of hydrogen peroxide from the reaction mixture. The accelerated elimination of D-glucose and D-xylose in the presence of co-immobilized catalase was observed. The co-immobilized glucose oxidase and catalase were able to decrease D-glucose or D-xylose content to 0-0.005% of their initial concentrations, while a minimum decrease of low oxidized saccharides D-xylose, D-cellobiose, and D-lyxose, respectively, was observed.

Characterization of functionalized nanoporous supports for protein confinement

Here we characterize a highly efficient approach for protein confinement and enzyme immobilization in NH(2)- or HOOC- functionalized mesoporous silica (FMS) with pore sizes as large as tens of nanometres. We observed a dramatic increase of enzyme loading in both enzyme activity and protein amount when using appropriate FMS in comparison with unfunctionalized mesoporous silica and normal porous silica. With different protein loading density in NH(2)-FMS, the negatively charged glucose oxidase (GOX) displayed an immobilization efficiency (I(e), the ratio of the specific activity of the immobilized enzyme to the specific activity of the free enzyme in stock solution) in a range from 30% to 160%, while the same charged glucose isomerase (GI) showed an I(e) of 100% to 120%, and the positively charged organophosphorus hydrolase (OPH) exhibited I(e) of more than 200% in HOOC-FMS. The enzyme-FMS composite was stained with the charged gold nanoparticles and imaged by transmission electron microscopy (TEM). Fourier transform infrared (FTIR) spectroscopy showed no major secondary structural change for the enzymes entrapped in FMS. Thanks to the large, rigid, open pore structure of FMS, the reaction rate and K(m) of the entrapped enzymes in FMS were comparable to those of the free enzymes in solution. In principle, the general approach described here should be applicable to many enzymes, proteins, and protein complexes since both pore sizes and functional groups of FMS are controllable.

The effect of the layer structure on the activity of immobilized enzymes in ultrathin films

The molecular engineering capability of the layer-by-layer (LbL) method for fabricating thin films has been exploited in order to immobilize glucose oxidase (GOD) in films with alternating layers of chitosan. Chitosan was proven a good scaffolding material, as GOD molecules preserved their catalytic activity towards glucose oxidation. Using electrochemical measurements, we showed that chitosan/GOD LbL films can be used to detect glucose with a limit of detection of 0.2 mmol l-1 and an activity of 40.5 microA mmol-1 L microg-1, which is highly sensitive when compared to other sensors in previous reports in the literature. The highest sensitivity of the LbL film was achieved when only the top layer contained GOD, thus indicating that GOD in inner layers did not contribute to glucose oxidation, probably because it hampers analyte diffusion and electron transport through the deposited layers. This may be explained by the dense packing of GOD molecules in the LbL films with chitosan, as inferred from estimates of the amount of GOD adsorbed per layer using a quartz crystal microbalance.

Preventing inhibition of tyrosinase with modified electrodes

Wines, especially red wines, contain numerous biologically active compounds, the most important of which are polyphenols, whose nutritional importance is attributed to their antioxidant power. Because of this, the detection of the amount of phenolic compounds in red wines becomes extremely important. However, using free enzyme in the determination of phenolic compounds in wines cannot reflect the actual values since there are also naturally found inhibitors in red wines. In this study, benzoic acid, cinnamic acid, and sorbic acid were utilized to understand the behavior of immobilized polyphenol oxidase in the conducting polymer matrices toward inhibition. Cinnamic acid was found to be the most powerful inhibitor for both free and immobilized enzyme in copolymer matrix of poly(terephthalic acid bis-(2-thiophen-3-yl-ethyl) ester) (PTATE) with polypyrrole (PPy). In the case of immobilized enzyme in PPy matrix, it was observed that sorbic acid is a stronger inhibitor than cinnamic acid. The inhibitory effects of these inhibitors on PPO were compared with respect to both the structural differences of inhibitors and conducting polymer matrices.

Biosensing and drug delivery by polypyrrole

Conducting polypyrrole is a biological compatible polymer matrix wherein number of drugs and enzymes can be incorporated by way of doping. The polypyrrole, which is obtained as freestanding film by electrochemical polymerization, has gained tremendous recognition as sophisticated electronic measuring device in the field of sensors and drug delivery. In drug delivery the reversing of the potential 100% of the drug can be released and is highly efficient as a biosensor in presence of an enzyme. In this review we discuss the applications of conducting polypyrrole as biosensor for some biomolecules and drug delivery systems.

Glucose oxidase immobilization on a novel cellulose acetate–polymethylmethacrylate membrane

Glucose oxidase (GOD) was immobilized on cellulose acetate-polymethylmethacrylate (CA-PMMA) membrane. The immobilized GOD showed better performance as compared to the free enzyme in terms of thermal stability retaining 46% of the original activity at 70 degrees C where the original activity corresponded to that obtained at 20 degrees C. FT-IR and SEM were employed to study the membrane morphology and structure after treatment at 70 degrees C. The pH profile of the immobilized and the free enzyme was found to be similar. A 2.4-fold increase in Km value was observed after immobilization whereas Vmax value was lower for the immobilized GOD. Immobilized glucose oxidase showed improved operational stability by maintaining 33% of the initial activity after 35 cycles of repeated use and was found to retain 94% of activity after 1 month storage period. Improved resistance against urea denaturation was achieved and the immobilized glucose oxidase retained 50% of the activity without urea in the presence of 5M urea whereas free enzyme retained only 8% activity.