Poly(vinyl alcohol) Chains Grafted onto the Surface of Copper Oxide Nanoparticles: Application in Synthesis and Characterization of Novel Optically Active and Thermally Stable Nanocomposites Based on Poly(amide-imide) Containing N-trimellitylimido-L-valine Linkage

Green polymer nanocomposites (NCs) show unique properties of combining the advantages of nanofillers and organic polymers. In this study, in order to control the dispersion of nanoparticles (NPs) in a polymer matrix, first, poly(vinyl alcohol) (PVA) as a green modifier was grafted on the surface of the CuO NPs to obtain CuO-PVA nanohybrid. Then poly(amide-imide) (PAI) was synthesized by the direct step growth polymerization of N-trimellitylimido-L-valine and 4,4′-methylenebis(3-chloro-2,6-diethylaniline) in ionic liquid medium. Finally, CuO-PVA hybrids were incorporated into the PAI matrix using ultrasonic technique for the preparation of PAI/CuO-PVA NCs. The obtained PAI/CuO-PVA NCs were characterized by different methods. The results of thermogravimetric analysis showed that thermal stability of the NCs was enhanced by incorporation of CuO-PVA nanohybrid compared to the pure PAI.     

Radiation synthesis of copper sulphide/poly(vinyl alcohol) nanocomposites films: an efficient and reusable catalyst for p-nitrophenol reduction

ABSTRACT

Copper sulphide nanoparticles (CuS NPs) were in situ synthesised via irradiation process, using Poly (vinyl alcohol) (PVA) as host polymeric matrices. The as-prepared CuS/PVA nanocomposite films were characterised by X-ray diffraction (XRD) spectroscopy, ultraviolet-visible (UV-VIS) spectroscopy, Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). Both UV-VIS spectra and X-ray diffraction patterns confirmed the formation of CuS nanoparticles. The FTIR spectrum indicates the coordination between CuS nanoparticles and the OH groups of the PVA chains. The TEM image showed that the obtained CuS nanoparticles have spherical shape, monodispersed and uniform particle size distribution. The CuS/PVA nanocomposite film was successfully applied in the reduction of p-nitrophenol into p-aminophenol as a catalyst using NaBH₄ as reducing agent. The catalytic test indicates that CuS/PVA nanocomposite film has high activity for the conversion of P-NP into P-AP and effectively recycled and reused for several times.     

L-Malate Determination in Wines and Fruit Juices by Flow Injection Analysis Adaptation of a Coupled Dehydrogenase/Transferase System

Abstract

A flow injection system for the enzymatic determination of L-malate is described. It is adapted for the analysis of wines and fruit juices by in-line sample dilution. Malate dehydrogenase (MDH) and aspartate aminotransferase (AST) were coimmobilized on controlled pore glass. The NADH generated in the packed bed bienzyme reactor was detected fluorimetrically. Sufficient L-malate conversion could be achieved using the coupled transferase reaction to transform the reaction product oxaloacetate. The linear range of the unmodified flow injection system, 5 – 100 μ M of L-malate, could be increased up to 50 mM by means of zone sampling so that untreated samples could be analyzed directly. From 12 – 20 samples per hour could be analyzed with a standard deviation of less than 2 % depending on variation in the degree of dilution. The activity of the bienzyme reactor decreased less than 4% over an analysis period of 3 weeks with more than 1200 injections.     

Stable physically adsorbed coating of poly-vinyl alcohol for the separation of basic proteins

In aqueous capillary electrophoresis, the electroosmotic flow can be strongly suppressed by coating the inner surface of the capillary. In the present work hydrophilic coating of 4% polyvinyl alcohol (PVA) has been used for the analysis of basic proteins. The coating is simple and easy to obtain. The separation of ribonuclease and α-chymotrypsin has been uniquely done with other three basic proteins (lysozyme, cytochrome-c and trypsin) using a buffer 11.60 mM sodium acetate and 18.40 mM acetic acid at pH 4.5 in addition to positive power supply of 20 kV at 25°C. Detection was performed using UV detector at 230 nm. The proposed PVA coated capillary provides reproducible separation of five basic proteins within 10 min with RSD values for mobility bellow 1.4% (n = 6) for all the five basic proteins. The stability of coated capillary has been checked up to 40 runs. The viscosity measurement for 4% PVA have been studied and scanning electron microscope (SEM) images obtained to make it compatible with future micro-chip applications.     

Sol–gel polydimethylsiloxane/poly(vinylalcohol)‐coated stir bar sorptive extraction of organophosphorus pesticides in honey and their determination by large volume injection GC

A PDMS/poly(vinylalcohol) (PDMS/PVA) film prepared through a sol–gel process was coated on stir bars for sorptive extraction, followed by liquid desorption and large volume injection–GC–flame photometric detector (LVI–GC–FPD) for the determination of five organophosphorus pesticides (OPPs) (phorate, fenitrothion, malathion, parathion, and quinalphos) in honey. The preparation reproducibility of PDMS/PVA‐coated stir bar ranged from 4.3 to 13.4% (n = 4) in one batch, and from 6.0 to 12.6% (n = 4) in batch to batch. And one prepared stir bar can be used for more than 50 times without apparent coating loss. The significant parameters affecting stir bar sorptive extraction (SBSE) were investigated and optimized. The LODs for five OPPs ranged from 0.013 (parathion) to 0.081 μg/L (phorate) with the RSDs ranging from 5.3 to 14.2% (c = 1 μg/L, n = 6). The proposed method was successfully applied to the analysis of five OPPs in honey.     

A tetraester derivative of fluorescent calix[4]arene bearing a proton-ionizable moiety for highly sensitive extraction-fluorometric determination of sodium ion

In this study, we report the highly sensitive extraction-fluorometric detection system of Na⁺ using flow injection analysis with a tetraester derivative of fluorescent calix[4]arene. In liquid-liquid extraction experiments, the fluorescent intensity of calix[4]arene derivative 1 bearing a p-nitrophenol moiety was highly dependent on pH and the Na⁺ concentration in the aqueous phase. On the other hand, such phenomenon was not observed in the case of calix[4]arene derivative 2, which is almost the same structure as 1 except for a p-nitrophenol moiety. These results show that the proton dissociation of the p-nitrophenol moiety decisively affects the fluorescence intensity of 1. Owing to these fluorescence responsiveness, a calibration graph of the Na⁺ concentration could be successfully prepared using flow injection analysis with good linearity at the tens of nanomolar level. The tetraester scaffold of calix[4]arene was essential to the detection of Na⁺ in such a very low concentration range.     

Electrogenerated Chemiluminescence of Tris(2,2′‐bipyridyl)ruthenium(II) Immobilized in Humic Acid‐Silica‐Poly(vinyl alcohol) Composite Films

In this paper, we report the first attempt to use humic acid (HA) as modifiers to prepare the organic‐inorganic hybrid modified glassy carbon electrodes based on HA‐silica‐PVA (poly(vinyl alcohol)) sol‐gel composite. Electroactive species of tris(2,2′‐bipyridyl)ruthenium(II) (Ru(bpy) ) can easily incorporate into the HA‐silica‐PVA films to form Ru(bpy) modified electrodes. The amount of Ru(bpy) incorporated in the composite films strongly depends on the amount of HA in the hybrid sol. Electrochemical and electrogenerated chemiluminescence (ECL) of Ru(bpy) immobilized in HA‐silica composite films coated on a glassy carbon electrode have been studied with tripropylamine (TPA) as the coreactant. The analytical performance of this modified electrode was evaluated in a flow injection analysis (FIA) system with a homemade flow cell. The as‐prepared electrode showed good stability and high sensitivity. The detection limits (S/N=3) were 0.050 μmol L^?1 for TPA and 0.20 μmol L^?1 for oxalate, and the linear ranges were from 0.10 μmol L^?1 to 1.0 mmol L^?1 for TPA and from 1.0 μmol L^?1 to 1.0 mmol L^?1 for oxalate, respectively. The resulting electrodes were stable over two months.     

Pyrene functional poly(vinyl alcohol) by “click” chemistry

Side‐chain pyrene functional poly(vinyl alcohol) (PVA) was synthesized by using “click chemistry” strategy. First, partial tosylation of PVA with p‐toluene sulfonyl chloride were performed. The resulting PVA‐Ts polymer was then quantitatively converted into poly(vinyl alcohol)‐azide (PVA‐N₃) in the presence of NaN₃/DMF at 60 °C. Propargyl pyrene was prepared independently as a photoactive click component. Finally, azido functionalized PVA was coupled to propargyl pyrene with high efficiency by click chemistry. Incorporation of pyrene functionality in the resulting polymer was confirmed by spectral analysis. It is also shown that pyrene functionalized PVA (PVA‐Py) exhibited characteristic fluorescence properties and improved solubility in highly polar solvents such as water, DMSO, and DMF as well as less polar solvent such as THF compared with pristine PVA. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1317–1326, 2009     

Amplified Detection of NAD+ and NADH by the Enzymatic Cycling with the Use of Immobilized Enzymes in a Flow System

Abstract

The enzymatic cycling for the detection of NAD⁺ and NADH in low level was carried out in the flow system with immobilized enzymes. Alcohol dehydrogenase and glutamate dehydrogenase immobilized on Sepharose 4B were used for the cycling reaction. The compound produced in the enzymatic cycling reaction was subjected to an enzymatic reaction to yield NADH, which was detected fluorometrically.     

Flow Injection Analysis of Benzoyl Peroxide Using N,N,N,N-Tetramethyl-p-phenylenediamine (TMPDA) and Surfactants

Abstract

The flow injection analysis of benzoyl peroxide using N,N,N,N-tetramethyl-p-phenylenediamine (TMPDA, also known as Wurster's reagent) and a solvent system including the surfactant sodium dodecyl sulfate (SDS) and cerium(IV) as a catalyst at pH 6.0 at 612 nm was investigated. The method was applied to the analysis of acne cream and flour. The study included a 26-metal-ion search for other possible methods of catalysis and a buffer study of SDS and cetyltrimethyl ammonium bromide (CTAB).     

Study of the Electrochemical Behavior of Disperse Blue 1‐Modified Graphite Electrodes. Application to the Flow Determination of NADH

The preparation and the electrochemical study of Disperse Blue 1‐chemically modified electrodes (DB1‐CME), as well as their efficiency for the electrocatalytic oxidation of NADH is described. The proposed mediator was immobilized by physical adsorption onto graphite electrodes. The electrochemical behavior of DB1‐CME was studied with cyclic voltammetry. The electrochemical redox reaction of DB1 was found to be reversible, revealing two well‐shaped pair of peaks with formal potentials 152 and ?42 mV, respectively, (vs. Ag/AgCl/3M KCl) at pH 6.5. The current I_p has a linear relationship with the scan rate up to 800 mV s^?1, which is indicative for a fast electron transfer kinetics. The dissociation constants of the immobilized DB1 redox couple were calculated pK₁=4 and pK₂=5. The electrochemical rate constants of the immobilized DB1 were calculated k₁°=18 s^?1 and k₂°=23 s^?1 (Γ=2.36 nmol cm^?2). The modified electrodes were mounted in a flow injection manifold, poised at +150 mV (vs. Ag/AgCl/3M KCl) and a catalytic current due to the oxidation of NADH was measured. The reproducibility was 1.4% RSD (n=11 for 30 μM NADH) The behavior of the sensor towards different reducing compounds was investigated. The sensor exhibited good operational and storage stability.     

Viscoelastic behaviors and molecular motions of highly syndiotactic poly(vinyl alcohol) fibers

The viscoelastic behavior and molecular motion of highly syndiotactic poly(vinyl alcohol) (S‐PVA) fibers with a dyad syndiotacticity (r) of 69% were studied by dynamic mechanical thermal analysis and wide‐angle X‐ray diffraction and compared with those of atactic poly(vinyl alcohol) (A‐PVA) fibers with r = 54%. The β_c dispersion, based on the molecular motion of the chain molecules in the crystalline regions, was observed for A‐PVA around 120–140 °C, and the only primary (α_c) dispersion was observed for S‐PVA around 180 °C. The thermal expansion coefficients for the a and c axes of the A‐PVA crystal changed discontinuously around 120 °C, which corresponded to the β_c dispersion. For S‐PVA, the coefficient for the (002) plane changed discontinuously around 100 °C, similarly to A‐PVA, but that for the (100) plane remained unchanged between 20 and 220 °C. These results showed that the intermolecular hydrogen bonding of S‐PVA was stronger in the direction of the a axis than in the other directions, suppressing the β_c dispersion. The storage modulus and thermal expansion coefficient of the (020) plane (molecular axis) of S‐PVA decreased markedly around 180 °C, and this indicated that the α_c dispersion was due to the torsional motion of the molecular chains in the crystalline regions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 800–808, 2004     

A novel method to prepare microporous and nanofibrous hydrogel scaffolds as neural tissue engineering

A new method to prepare poly (vinyl alcohol) hydrogels by nebulization method.is introduced. A blend of Poly (vinyl alcohol) (PVA), sodium gum malate (SGM) and cellulose nanofibers (CNFs) originated from Catha Edulis was prepared and tested as neural tissue substitutes. Glutaraldehyde (GLA) was used as a crosslinker. Presence of SGM and CNFs in the formulation improved the nebulization process of PVA solution as well as mechanical properties of the fabricated hydrogels. The tensile strength of neat PVA films attains 46.7 MPa, while the tensile strength was 94.23 MPa for crosslinked-PVA. The tensile strength was found to increase with the increase in the CNFs content in the PVA compared with PVA/SGM. These soft tissues were characterized by using FTIR, SEM, and DSC. Scanning electron microscopy (SEM) results showed that PVA/SGM/CNFs blends has a diameter about 50 ± 8µm. The hydrogels were tested also for antimicrobial activities against pathogenic bacteria like Candida albicans (fungus), Bacillus subtilis (G + Ve), Staphylococcus aureus (G + Ve), Proteus vulgaris (G ? Ve) and Erwinia carotovora (G ? Ve). Favorable mechanical, thermal properties and biodegradation nature of the hydrogels, as well as antimicrobial property indicate that prepared hydrogels are suitable for tissue engineering applications.     

Preparing of Iridium Oxide Film Modified Microelectrode as an Amperometric Detector in FIA for Determination of Epinephrine

Abstract

Iridium oxide film modified microelectrode with a tip diameter of 25 µm was constructed using anodically grown iridium oxide film. The iridium oxide film, which was formed at the tip of the iridium wire by cyclic voltammetry in dilute sulfuric acid, showed excellent catalytic activity towards the oxidation of epinephrine. The stability and electrochemical properties of iridium oxide film modified microelectrode along with catalytic oxidation of epinephrine was studied. An oxidation peak was observed at 0.28 V. The electron‐transfer number (n) was 2. The iridium oxide film modified microelectrode was used as a detector in flow injection system for determination of epinephrine. Under the optimized conditions, the calibration curve was linear in the concentration range of 1.0×10^?8 to 1.0×10^?5 mol/l for epinephrine, with a detection limit of 1.0×10^?9 mol/l. The iridium oxide film modified microelectrode was used for direct determination of the epinephrine in human serum samples. The flow injection analysis was precise detection method of epinephrine and time saving device.     

A study on optical limiting properties of Eosin-Y and Eriochrome Black-T dye-doped poly (vinyl alcohol) composite film

A poly (vinyl alcohol) PVA/Eriochrome Black-T (EBT) dye, and PVA/Eosin-Y (EY) dye composite film was prepared using a solution casting process. The dye-doped composite polymer films were characterized by UV–vis spectroscopy. An optical band gap (E_g) of pure PVA reduced from 4.22?eV to 2.80?eV for PVA/EBT film and 2.14?eV for PVA/EY film respectively. This result indicates the occurrence of inter-molecular hydrogen bonding between the –OH functional group in PVA chains and sulfonate (EBT) and carboxyl group (EY) in dye molecules, respectively. Moreover, the experimental result of PVA/EBT and PVA/EY composite film showed the excellent properties of a large scale cut-off filter in the ultraviolet and visible range region.     

Chemical modification of hydroxyl groups of poly(vinyl alcohol) by a glycosidation reaction

A new procedure for chemical modification of poly(vinyl alcohol) (PVA) was established by a glycosidation reaction of hydroxyl groups in PVA with triacetylated sugar oxazoline 1 . ¹H and ¹³C NMR analyses indicated that triacetylated N‐acetyl‐D‐glucosamine (GlcNAc) was introduced onto a PVA backbone selectively via a β‐O‐glycoside linkage. Deacetylation of triacetylated GlcNAc‐substituted PVA 2 resulted in GlcNAc‐substituted PVA 3 in good yield. These modified PVAs 2 and 3 exhibited solubilities and thermal properties different from the original PVA.     

Measurement of size‐dependent glass transition temperature in electrospun polymer fibers using AFM nanomechanical testing

The glass transition temperature (T_g) of individual electrospun polymer polyvinyl alcohol fibers of varying diameter was measured using atomic force microscopy (AFM) based nanomechanical thermal analysis. Indentation and bending of individual electrospun fibers using AFM allowed the calculation of the elastic modulus of the polyvinyl alcohol (PVA) fibers across a range of different temperatures. The elastic modulus of electrospun PVA fibers was observed to decrease significantly when passing through T_g, which allowed accurate determination of T_g. The T_g of electrospun PVA fibers was shown to decrease for smaller fiber diameters especially for fiber diameters below 250 nm. This size‐dependent glass transition behavior of electrospun PVA fibers is indicated as being due to polymer chain confinement. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Enzyme Electrode for Amplification of NAD+/NADH Using Glycerol Dehydrogenase and Diaphorase with Amperometric Detection

Abstract

An enzyme electrode is made from a glassy carbon electrode covered with a gelatin membrane containing entrapped glycerol dehydrogenase (GDH) and diaphorase, and protected with a dialysis membrane. Based on amplification by the recycling reaction catalyzed by the two-enzyme systems, NAD⁺ and NADH can be determined with 800–1200 times higher sensitivity than for the same electrode in a substrate sensing mode when the flow rate was 0.08 ml/min. The detection limit was about 0.03 μM for NADH. The amplification factors were around 1000 for 0.08 ml/min, with quite large variations between electrodes. They had decreased to about 70% of the original value after 7 days. The biosensor is intended for detection in immunoassays with alkaline phosphatase as a marker.     

Methylated Azopyridine as a New Electron Transfer Mediator for the Electrocatalytic Oxidation of NADH

Carbon ionic liquid electrode (CILE) has been modified with a new synthesized mediator i.e. N,N′‐dimethyl‐4,4′‐azopyridinium hexafluorophosphate (MAZPHP) via sol process and the electron transfer mediating characteristics of this mediator has been evaluated. 4,4′‐Azopyridine (AZP) did not show any electrocatalytic activity toward the selected probe, NADH, while its synthesized methylated derivative, MAZPHP, is a very efficient mediator for the electrocatalytic NADH oxidation. Cyclic voltammetry of MAZPHP/Sol/CILE exhibited a pair of reversible peaks corresponding to incorporated mediator with a formal potential of about 221 mV vs. Ag/AgCl. MAZPHP/Sol/CILE is free from fouling effects by the oxidation products of NADH which generally give hindrance to amperometric detection of NADH. Using amperometric technique, NADH can be determined in the range of 1.0×10^?5 M to 1.4×10^?3 M with a detection limit of 2.0×10^?6 M.     

In situ Electroreduction of Graphene Oxide: Increased Sensitivity for the Determination of NADH

A novel and useful method to catalyze the electro‐oxidation of nicotinamide adenine dinucleotide (NADH) over a glassy carbon electrode (GCE) modified with graphene oxide (GO) is presented. Based on the presence of oxygen moieties in GO, which can be easily reduced, an in situ electrochemical generation of reduced graphene oxide (denoted as erGO) applying a sufficient negative potential. A potential of ?1.000 V was selected to generate the erGO/GCE as a pretreatment potential before the detection of NADH. The in situ generated erGO/GCE system produces a decrease in the overpotential of NADH oxidation from +0.720 V to +0.230 V compared with GCE. The process also produced an important increase in current signals. The modified electrode was characterized by scanning electron (SEM) and electrochemical microscopies (SECM), cyclic voltammetry and by Raman spectroscopy. Amperometric detection of NADH via this straightforward electrocatalytic method provides a wide linear range between 10 and 100 μM, a lower detection limit of 0.36 μM and an excellent sensitivity of (1.47±0.09) μA mM^?1.