Deposition of silver nanoparticles on cellulosic fibers via stabilization of carboxymethyl groups

The stabilizing role of carboxymethyl groups on the conformal deposition of Ag NPs over cellulosic fibers was elucidated while developing a method for the deposition of silver nanoparticles (NPs) on cellulose acetate (CA), cellulose and partially carboxymethylated cellulose (CMC) electrospun fibers. CMC fibers were prepared through judicious anionization of deacetylated cellulose acetate fibers. Ag NPs were chemically reduced from silver nitrate using sodium borohydride and further stabilized using citrate. Ag NPs were directly deposited onto CA, cellulose and CMC electrospun fibers at pH conditions ranging from 2.5 to 9.0. The resulting composites of Ag/fiber were characterized by field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDX). The results revealed that the amount of Ag agglomerates and NPs deposited on CMC fibers was higher than that deposited on cellulose fibers at similar pH conditions, and that barely any Ag agglomerates or NPs were deposited on the CA fibers. These results implied that functional groups on the cellulose backbone played two important roles in the deposition of NPs as follows: (1) Hydrogen bonding was the main driving force for agglomeration of NPs when the medium pH was below 4.4, which corresponds to the pKa of carboxylic acid groups; (2) Carboxymethyl groups could replace citrate groups as stabilizers allowing the fabrication of a uniform and evenly distributed Ag NPs layer over CMC fibers at higher pH values. This report also highlights the importance of the substrate’s surface charge and that of the pH of the medium used, on the deposition of NPs. The composite of Ag NPs on CMC electrospun fibers appears to be a promising candidate for wound dressing applications due to its superior antibacterial properties originated by the uniform and even distribution of Ag NPs on the surface of the fibers and the wound healing aptness of the CMC fibers.     

Direct synthesis of nitriles by Cu/DMEDA/TEMPO-catalyzed aerobic oxidation of primary amines with air

By screening the copper catalysts, ligands, and the reaction conditions, a simple CuCl/DMEDA/TEMPO catalyst system readily available from commercial sources is developed for a direct and selective synthesis of the useful nitriles by an aerobic oxidation reaction of primary amines using air as an advantageous oxidant under mild conditions.     

Adsorption of octadecyltrimethylammonium chloride and adsolubilization on to cellulosic fibers

The coadsorption of different organic solutes on cellulosic fibers treated with octadecyltrimethylammonium chloride (ODTMA) has been studied. In the absence of ODTMA cellulosic fibers had little tendency to retain organic compounds. The enhanced solute incorporation was ascribed to the adsolubilization of these compounds on the aggregated domains of the adsorbed surfactant molecules at the solid/liquid interface. The specific shape of solute coadsorption isotherms indicated that the adsolubilization process may be regarded as a partition phenomenon between the aqueous bulk phase and the adsorbed surfactant aggregates. The decrease in solute uptake at the cellulose/water interface above the CMC of ODTMA was ascribed to micelle formation in the bulk solution and to the ensuing micellar solubilization of organic solutes. Preliminary experiments performed using vertical fixed bed columns showed that modified cellulosic fibers can be conveniently used as substrate for treating organic pollutants.     

Synthesis of aromatic polyesters having pendant carboxyl groups in the side chains and conversion of the carboxyl groups to other reactive groups

Aromatic polyester, copolyester, and poly(ester-amide-thioester) having pendant carboxyl groups are directly synthesized by the organic phase/water phase interfacial polyconden-sation using low-molecular and polymeric phase transfer catalysts. Spectral analysis of the resulting polymers indicates that the nucleophilicity of salts of phenols to diacid chloride is far higher than that of salts of carboxylic acids and chemoselective esterification occurs in a 100% yield. Even if the polymeric catalyst having amino acid moiety as a nucleophilic group is used in the polycondensation, the polymers do not contain anhydride groups. The polyester can be almost quantitatively converted to polymers with different reactive groups by reacting the pendant carboxyl groups with alkyl halides in a DMA_c-H₂O mixture con-taining K₂CO₃. A bifunctional catalytic mechanism is proposed for the chemical modification of the polyesters. © 1995 John Wiley & Sons, Inc.     

Hydrogen bonding of carboxyl and amide groups to nucleosides

Carboxylic acid-nucleoside systems are studied by infrared spectroscopy. Intermolecular interactions of these systems in aqueous solution are investigated as a function of the degree of hydration and ΔpK_a. On the other hand, thermodynamic parameters for the association of N-methyl-acetamide with lactams in organic solvents have been determined by infrared spectroscopy. The low enthalpy values suggest open dimers formation.     

TEMPO-catalyzed aerobic oxidation of alcohols to aldehydes and ketones in ionic liquid [bmim][PF6

[reaction: see text]. A simple and mild TEMPO-CuCl catalyzed aerobic oxidation of primary and secondary alcohols to the corresponding aldehydes and ketones in ionic liquid [bmim][PF6] with no trace of overoxidation to carboxylic acids has been developed. The product can be isolated by a simple extraction with organic solvent, and the ionic liquid can be recycled or reused.     

Influence of spatial effects on the oxidation of cardenolides and bufadienolides containing aldehyde groups

The reactivity of a number of aglycones and glycosides with a cardiac action containing a carbonyl group at C₁₀ is considered. The study was based on the use of the oxidation reaction in the presence of diethylamine, the excess of which after the binding of the hydrochloric acid liberated in the reaction was backtitrated with percholoric acid in methanol. The rate constants of 15 compounds have been determined and it has been established that their reactivity depends on their structure: the nature of the linkage of the A/B rings of the steroid skeleton, the position of a double bond in it, the introduction of a sugar or acetyl group in position 3 of the aglycon, and the nature of the sugar.All-Union Scientific-Research Institute of Drug Chemistry and Technology, Khar'kov. Translated from Khimiya Prirodnykh Soedinenii, Nö. 5, pp. 602–607, September–October, 1986.     

Influence of spatial effects on the oxidation of cardenolides and bufadienolides containing aldehyde groups

The reactivity of a number of aglycones and glycosides with a cardiac action containing a carbonyl group at C₁₀ is considered. The study was based on the use of the oxidation reaction in the presence of diethylamine, the excess of which after the binding of the hydrochloric acid liberated in the reaction was backtitrated with percholoric acid in methanol. The rate constants of 15 compounds have been determined and it has been established that their reactivity depends on their structure: the nature of the linkage of the A/B rings of the steroid skeleton, the position of a double bond in it, the introduction of a sugar or acetyl group in position 3 of the aglycon, and the nature of the sugar.     

Analysis of CMC attachment onto cellulosic fibers by infrared spectroscopy

Infrared spectroscopy has been used to measure the amount of carboxymethyl cellulose (CMC) attached to cellulosic fibers. CMC was attached to an unbleached kraft pulp in aqueous conditions. Isotropic handsheets were then prepared and ATR spectroscopy was used to measure the intensity of the carboxyl vibration, which correlates to the amount of attached CMC that was determined using a wet chemical approach. The ATR method is rather time consuming as several measurement points on the sample have to be averaged, although it is still much faster than the wet chemical approach. Infrared reflection absorption spectroscopy (IRRAS) using polarized light was further used to measure the amount of attached CMC. In this method the intensity of an electromagnetic wave confined to the thin layer is used to correlate the spectroscopy to the amount of CMC on the fiber surface in the paper sample. The measurement time is shorter than with the ATR method. The proposed IRRAS method could be employed as a fast and reliable way to quantify adsorption of chemicals on pulp fibers.     

Aerobic copper/TEMPO-catalyzed oxidation of primary alcohols to aldehydes using a microbubble strategy to increase gas concentration in liquid phase reactions

An efficient method for the synthesis of aldehydes was achieved by using air-microbubble techniques in aerobic copper/TEMPO-catalyzed oxidation of primary alcohols. Use of air-microbubbles to improve gas absorption into liquid phase is proven to be highly beneficial for gas/liquid phase reactions.     

Catalysis of novel enzymatic iodide oxidation by fungal laccase

A fungal laccase (Myceliophthom thermophila) has been shown to function as an iodide oxidase. Unlike other halides which interact with the type 2 copper site and are inhibitors for the laccase, iodide interacts with the type 1 copper site and serves as a substrate capable of donating an electron to the laccase. Under anaerobic conditions, the interaction between the laccase and iodide results in the reduction of the laccase type 1 copper and the concomitant oxidation of iodide to form iodide. In aerated solutions, the laccase catalyzes the oxidation of iodide to iodine and the concomitant reduction of dioxygen to water. The reaction exhibits typical Michaelis kinetics with aK _m of 0.16 ± 0.02M and ak _cat of 2.7 ± 0.2 turnovers per min at the optimal pH (3.4). The catalysis can be enhanced by 2,2′-azino-bis-(3-ethylbenz-thiazoline-6-sulfonic acid), which shuttles electrons rapidly between iodide and the laccase. Bilirubin oxidase also demonstrates significant iodide oxidase activity, suggesting that the property could be a common feature for copper-containing oxidases. Possible industrial and medicinal applications for a laccase-based iodine production system are discussed.     

Efficient and highly aldehyde selective Wacker oxidation

A method for efficient and aldehyde-selective Wacker oxidation of aryl-substituted olefins using PdCl(2)(MeCN)(2), 1,4-benzoquinone, and t-BuOH in air is described. Up to a 96% yield of aldehyde can be obtained, and up to 99% selectivity can be achieved with styrene-related substrates.     

Functional polymer nanocomposites containing triazole and carboxyl groups

New water-soluble functional polymer nanocomposites with nanoparticles of metallic silver in a matrix of 1-vinyl-1,2,4-triazole copolymers with crotonic acid have been synthesized. The resulting nanocomposites contain isolated silver nanoparticles 2–12 nm in diameter, preferably spherical in shape, and uniformly distributed in the polymer matrix. ATR IR spectroscopy has revealed that the nanoparticles affect the state of the carboxyl groups in the polymer matrix. It has been found that the size of zero-valent silver nanoparticles depends on the ratio of monomer units in the polymer matrix. The thermo-oxidative stabilities of the synthesized copolymers and polymer nanocomposites produced on their basis have been examined.     

Superhydrophobic,strong and transparent paper made from cellulosic fibers

Cellulose - Superhydrophobic and strong cellulosic paper was fabricated in a two-step process consisting of heavy refining and dip coating with PDMS (trimethylsiloxy-terminated poly...     

Enhancing the inter-fiber bonding properties of cellulosic fibers by increasing different fiber charges

Cellulosic fiber has been increasingly used in many fields. The fiber charge, including the surface charge and inner charge, affects the properties of cellulosic fiber and fiber-based materials significantly. In this study, the cellulosic fiber was subjected to different treatments, including 2,2,6,6-tetramethyl-piperidine-1-oxyl radical-mediated oxidation, carboxymethyl cellulose attachment and mechanical refining, to alter the fiber charge selectively. The effects of the fiber surface charge and inner charge on fiber performances and inter-fiber bonding strength for improving the high-value application of cellulosic fibers, respectively, were discussed. The results showed that the performances of cellulosic fiber can be improved with the increase of either surface or inner fiber charges, including the increased water retention value, flexibility and inter-fiber bonding strength, but with slightly decreased drainability. An increasing bulk fiber charge showed more significant enhancement of the inter-fiber bonding strength than only an increase of the fiber surface charge on cellulosic fiber. This was because the fiber inner charge contributed to the increase of fiber flexibility and deformability, which could benefit the inter-fiber bonding indirectly. As a consequence, the bulk fiber charge enhancement was better for tensile strength improvement of handsheets (fiber-based material) than only fiber surface charge enhancement. Increasing both the surface charge and inner charge improved the tensile strength effectively with less change of the bulky fiber network than the refining treatment.     

Kinetic resolution in the oxidation of iminium ion to lactam catalysed by aldehyde oxidase

A rabbit liver enzyme preparation oxidised racemic iminium ions 1 and 2 to optically active lactams 3 and 4 with enantiomer ratios ER/S = 5.5 and 0.14, respectively.     

Practical Cu(OAc)2/TEMPO-catalyzed selective aerobic alcohol oxidation under ambient conditions in aqueous acetonitrile

We reported a ligand- and additive-free Cu(OAc)₂/TEMPO catalyst system that enables efficient and selective aerobic oxidation of a broad range of primary and secondary benzylic alcohols, primary and secondary 1-heteroaryl alcohols, cinnamyl alcohols, and aliphatic alcohols to the corresponding aldehydes and ketones. This ambient temperature oxidation protocol is of practical features like aqueous acetonitrile as solvent, ambient air as the terminal oxidant, and low catalyst loading, presenting a potential value in terms of both economical and environmental considerations. Based on the experimental observations, a plausible reaction mechanism was proposed.     

Splitting tendency of cellulosic fibers. Part 3: splitting tendency of viscose and modal fibers

The splitting tendency of viscose and modal fibers in aqueous alkali solutions of LiOH, NaOH, KOH and TMAH was investigated. The viscose fibers splitted up to 5–7 fibrils, whereas modal fibers splitted up to 2–4 fibrils depending on alkali type and concentration. The fibrillar structure of lyocell enables it to split more (15–20 fibrils) than viscose and modal fibers. Splitting occurs where internal stress of fiber is high due to different alkali or void distribution inside fiber. The splitting test couldn’t be achieved for viscose and modal fibers between 1 and 5 M concentration of NaOH and TMAH solutions due to breakage of fibers during test. Above 5 M concentration, no split can be observed due to even distribution of alkali inside fiber. Paper presented at the 7th World Textile Conference, AUTEX 2007, Tampere, Finland, 26–28 June 2007. Christian-Doppler Laboratory of Textile and Fiber Chemistry of Cellulosics is a Member of European Polysaccharide Network of Excellence (EPNOE), www.epnoe.org