Carla W. Scheeren

A novel support for laccase immobilization: Cellulose acetate modified with ionic liquid and application in biosensor for methyldopa detection

A material based on cellulose acetate (CA) and the room temperature ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMI·N(Tf)(2)) was developed and characterized by scanning electron microscopy, electron dispersive spectroscopy and infrared analysis. Laccase (Lac) from Aspergillus oryzae was immobilized in this material to investigate the behavior of methyldopa by square-wave voltammetry. Under optimized conditions, the Lac biosensor based on CA/BMI·N(Tf)(2) exhibited an excellent electrocatalytic performance: the analytical curve showed good linear range for methyldopa concentrations from 34.8 to 370.3 μM with a detection limit of 5.5 μM. This sensor demonstrated acceptable stability (ca. 60 days; at least 350 determinations), good repeatability and reproducibility (relative standard deviations of 1.5 and 4.3%, respectively). The recovery study of methyldopa in pharmaceutical formulations ranged from 94.1 to 105.9%. The determination of this substance using the biosensor compared favorably with that using a spectrophotometry procedure at the 95% confidence level, and indicated potential application to methyldopa determination in pharmaceutical samples.

Biosensor for chlorogenic acid based on an ionic liquid containing iridium nanoparticles and polyphenol oxidase.

A biosensor based on the ionic liquid, 1-n-butyl-3-methylimidazolium hexafluorophosphate containing dispersed iridium nanoparticles (Ir-BMI.PF(6)) and polyphenol oxidase was constructed. This enzyme was obtained from the sugar apple (Annona squamosa), immobilized in chitosan ionically crosslinked with oxalate. The biosensor was used for determination of chlorogenic acid by square wave voltammetry. The polyphenol oxidase catalyzes the oxidation of chlorogenic acid to the corresponding o-quinone, which is electrochemically reduced back to this substance at +0.25V vs. Ag/AgCl. Under optimized operational conditions the chlorogenic acid concentration was linear in the range of 3.48x10(-6) to 4.95x10(-5)mol L(-1) with a detection limit of 9.15x10(-7)mol L(-1). The biosensor was applied in the determination of chlorogenic acid in organic and decaffeinated coffee and the results compared with those obtained using the capillary electrophoresis method. The recovery study for chlorogenic acid in these samples gave values of 93.2-105.7%.

Palladium nanoparticles supported in a polymeric membrane: an efficient phosphine-free “green” catalyst for Suzuki–Miyaura reactions in water

Palladium(0) nanoparticles supported on a polymeric membrane, CA/Pd(0), were found to be a highly efficient “dip catalyst” (heterogeneous catalyst) for Suzuki–Miyaura cross-coupling reactions. Iodo-, bromo- and electron-poor chloroarenes coupled with phenylboronic acid under eco-friendly conditions (i.e., phosphine-free and with water as the solvent) to give excellent yields. The CA/Pd(0) was prepared initially via the synthesis of Pd(0) by hydrogen decomposition of Pd(acac)2 dissolved in BMI·BF4 ionic liquid at 75 °C for 1.0 hour to yield a black suspension (nanoparticles with a diameter of 2.7 ± 0.4 nm). These nanoparticles were washed with acetone and dried under reduced pressure. The Pd(0) nanoparticles were subsequently added to a cellulose acetate solution with acetone to generate the CA/Pd(0) polymeric membrane. The CA/Pd(0) “dip catalyst” was characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), electron-dispersive spectroscopy (EDS) and transmission electron microscopy (TEM).

Metal Nanoparticle/Ionic Liquid/Cellulose: New Catalytically Active Membrane Materials for Hydrogenation Reactions

Transition metal-containing membrane films of 10, 20, and 40 μm thickness were obtained by the combination of irregularly shaped nanoparticles with monomodal size distributions of 4.8 ± 1.1 nm (Rh(0)) and 3.0 ± 0.4 nm (Pt(0)) dispersed in the ionic liquid (IL) 1-n-butyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide (BMI·(NTf)(2)) with a syrup of cellulose acetate (CA) in acetone. The Rh(0) and Pt(0) metal concentration increased proportionally with increases in film thickness up to 20 μm, and then the material became metal saturated. The presence of small and stable Rh(0) or Pt(0) nanoparticles induced an augmentation in the CA/IL film surface areas. The augmentation of the IL content resulted in an increase of elasticity and decrease in tenacity and toughness, whereas the stress at break was not influenced. The introduction of IL probably causes an increase in the separation between the cellulose macromolecules that results in a higher flexibility, lower viscosity, and better formability of the cellulose material. The nanoparticle/IL/CA combinations exhibit an excellent synergistic effect that enhances the activity and durability of the catalyst for the hydrogenation of cyclohexene. The nanoparticle/IL/cellulose acetate film membranes display higher catalytic activity (up to 7353 h(-1) for the 20 μm film of CA/IL/Pt(0)) and stability than the nanoparticles dispersed only in the IL.

Silica-alumina-niobia (SiO2/Al2O3/Nb2O5) matrix obtained by the sol-gel processing method: new material for online extraction of zinc ions

In the present work, a new material, SiO2/Al2O3/Nb2O5 (designated as SiAlNb), was evaluated as an adsorbent in a flow injection spectrophotometric method for online preconcentration and determination of trace amounts of Zn2+ ions. The preconcentration method is based on Zn2+ adsorption onto the surface of SiAlNb in alkaline medium (pH 9.0). The elution step is carried out using HNO3 solution, followed by reaction of the Zn2+ ions with 1-(2-piridylazo)-2-naphtol (pan) in ammoniacal buffer solution (pH 9.3) containing Tween-80. The [Zn(pan)2] complex formed is determined at 560 nm. The method presented a linear range between 7.6 and 180.0 µg L-1 (r = 0.9992) and limits of detection and quantification of 2.3 and 7.6 µg L-1, respectively. According to the Langmuir linear model, the maximum adsorption capacity was found to be 7.0 mg of Zn2+ g-1 of SiAlNb. The proposed method was successfully applied to the Zn2+ determination in water samples (lake, mineral, tap) and certified reference material (TORT-2 Lobster Hepatopancreas).

Gold nanoparticles in an ionic liquid phase supported in a biopolymeric matrix applied in the development of a rosmarinic acid biosensor.

Gold nanoparticles dispersed in 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid (Au-BMI·PF(6)) were supported in chitin (CTN) chemically crosslinked with glyoxal and epichlorohydrin to obtain a new supported ionic liquid phase (SILP) catalyst with high catalytic activity, and providing an excellent environment for enzyme immobilization. This modified biopolymer matrix (Au-BMI·PF(6)-CTN) was used as a support for the immobilization of the enzyme peroxidase (PER) from pea (Pisum sativum), and employed to develop a new biosensor for rosmarinic acid (RA) determination in pharmaceutical samples by square-wave voltammetry. In the presence of hydrogen peroxide, the PER catalyzes the oxidation of RA to the corresponding o-quinone, which is electrochemically reduced at a potential of +0.14 V vs. Ag/AgCl. Under optimized conditions, the resulting peak current increased linearly for the RA concentration range of 0.50 to 23.70 μM with a detection limit of 70.09 nM. The biosensor demonstrated high sensitivity, good repeatability and reproducibility, and long-term stability (15% decrease in response over 120 days). The method was successfully applied to the determination of RA content in pharmaceutical samples, with recovery values being in the range of 98.3 to 106.2%. The efficient analytical performance of the proposed biosensor can be attributed to the effective immobilization of the PER enzyme in the modified CTN matrix, the significant contribution of the high conductivity of the ionic liquid, the facilitation of electron transfer promoted by gold nanoparticles, and the inherent catalytic ability of these materials.

Platinum nanoparticles supported on ionic liquid-modified-silica gel: hydrogenation catalysts

Platinum nanoparticles (ca. 2.3 nm) dispersed in ionic liquids and functionalized ionic liquids were supported within a silica network by the sol–gel method. The effect of the sol–gel catalyst (acid or base) on the encapsulated ionic liquid and on the platinum content was studied, and the silica morphology, the texture of the support material, and the hydrogenation activity were investigated. The Pt(0) content in the resulting xerogels (ca. 0.2 wt% Pt/SiO2) was shown to be independent of the sol–gel process. The acidic conditions resulted in xerogels with larger pore diameters, which in turn might be responsible for the higher catalytic activity in hydrogenation of the alkenes and arenes obtained with the heterogeneous catalyst (Pt(0)/SiO2).

Chitosan/Carboxymethylcellulose/Ionic Liquid/Ag(0) Nanoparticles Form a Membrane with Antimicrobial Activity

Silver metal nanoparticles were immobilized in chitosan/carboxymethylcellulose/BMI.BF4(1-n-butyl-3-methylimidazolium tetrafluoroborate ionic liquid) (CS/CMC/IL) to form polymeric membrane with 20 μm thickness. The CS/CMC/IL polymeric membrane was prepared using a simple solution blending method. Irregularly shaped Ag(0) nanoparticles with monomodal size distributions of  nm Ag(0) were immobilized in the membrane. The presence of small Ag(0) nanoparticles induced an augmentation in the CS/CMC/IL film surface areas. The CS/CMC/IL membrane containing Ag(0) showed increase antimicrobial activity the Ag(0) concentration increased up to saturation at 10 mg. CS/CMC/IL membrane that contains Ag(0) nanoparticles has enhanced durability of the membrane and exhibited stronger antimicrobial activity against Escherichia coli and Staphylococcus aureus.

Iridium nanoparticles supported in polymeric membranes: a new material for hydrogenation reactions

Iridium nanoparticles (Ir(0) NPs) of 2.1 ± 0.5 nm were synthesized from [Ir(cod)Cl]2 (cod = 1,5-cyclooctadiene) in the ionic liquid (IL) 1-n-butyl-3-methylimidazolium hexafluorophosphate [BMI.PF6]. The Ir(0) NPs were subsequently supported on polymeric membranes using cellulose acetate (CA) in acetone and the IL 1-n-butyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide [BMI.N(Tf)2]. Polymeric membranes with thicknesses of 20 μm were prepared with 10 mg of Ir(0) NPs. The polymeric membranes were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM). The analysis showed that the Ir(0) NPs are homogeneously distributed over the entire membrane, which has a compact structure. The presence of small Ir(0) NPs induced increases in the surface areas of the ​​polymeric membranes. The presence of the IL in the membrane structure increases the separation between the cellulose macromolecules, which results in greater flexibility and durability of the polymeric membranes. The CA/LI/Ir(0) combination exhibits excellent synergistic effects that increase the activity of the catalyst in hydrogenation reactions.

NANOPARTÍCULAS DE Au EM LÍQUIDO IÔNICO SUPORTADAS EM FILMES BIOPOLIMÉRICOS: UMA AULA PRÁTICA PARA INVESTIGAÇÃO DA ATIVIDADE ANTIMICROBIANA

The synthesis of Au nanoparticles (NPs) in ionic liquid (IL) supported on biopolymers films applied in the investigation of antimicrobial activity was introduced as a new experimental practice for undergraduates in the nanotechnology discipline at the Department of chemistry, at University Federal of Rio Grande- FURG. The Au NPs were synthesized by reduction of tetrachloroauric acid complex trihydrate (HAuCl4.3H2O) in IL 1-n-butyl-3-methyl-imidazolium hexafluorophosphate (BMI.PF6) using sodium borohydride at room temperature. Subsequently, the Au NPs were supported in the biopolymers films using a solution of cellulose acetate dissolved in acetone. The biopolymers films containing supported Au NPs were applied in the investigation of antimicrobial activity against bacteria Escherichia coli e Staphylococcus aureus.