The cationic grafting of cellulose with 2-methyl-2-oxazoline

Grafting of cellulosic materials, including bleached kraft pulp, has been achieved by electrophilic polymerization. The process involves two steps, (i) the tosylation of the cellulosic substrate by reaction with tosyl chloride, (ii) polymerization of 2-methyl-2-oxazoline in contact with the esterified cellulose. The grafting efficiency was generally in the range of 20 to 50 %, which was attributed to the occurrence of a transfer reaction specific to the cellulose.     

MANGANESE (IV)-INITIATED GRAFTING OF TRIMETHYLALLYLAMMONIUM CHLORIDE ONTO CARBOXYMETHYLCELLULOSE

Graft copolymerization of cationic monomer trimethylallylammonium chloride onto anionic carboxymethylcellulose has been investigated in aqueous medium using potassium permanganate/sulphuric acid redox system as initiator, involving the identification of grafting, the mechanism for grafting and various factors affecting grafting. The prepared cellulosic copolymers with amphoteric functional groups have been found to be effective to retard the hydration of clay minerals, showing a potential use as new clay-hydration suppressant for oilfields.     

Biomimetic Synthesis of Meroterpenoids by Dearomatization‐Driven Polycyclization

A biomimetic route to farnesyl pyrophosphate and dimethyl orsellinic acid (DMOA)‐derived meroterpenoid scaffolds has yet to be reported despite great interest from the chemistry and biomedical research communities. A concise synthetic route with the potential to access DMOA‐derived meroterpenoids is highly desirable to create a library of related compounds. Herein, we report novel dearomatization methodology followed by polyene cyclization to access DMOA‐derived meroterpenoid frameworks in six steps from commercially available starting materials. Furthermore, several farnesyl alkene substrates were used to generate structurally novel, DMOA‐derived meroterpenoid derivatives. DFT calculations combined with experimentation provided a rationale for the observed thermodynamic distribution of polycyclization products.     

Traversing Biosynthetic Carbocation Landscapes in the Total Synthesis of Andrastin and Terretonin Meroterpenes

Meroterpenes derived from dimethylorsellinic acid (DMOA) and farnesyl pyrophosphate have attracted much biosynthetic attention, yet only recently have synthetic solutions to any family members appeared. A key point of divergence in DMOA‐derived meroterpene biosynthesis is the protoaustinoid A carbocation, which can be diverted to either the berkeleyone, andrastin, or terretonin structural classes by cyclase‐controlled rearrangement pathways. Shown herein is that the protoaustinoid bicyclo[3.3.1]nonane nucleus can be reverted to either andrastin or terretonin ring systems under abiotic reaction conditions. The first total syntheses of members of these natural product families are reported as their racemates.     

Effects of Counter Ions in Ion-Pair Liquid Chromatography of Hydrophobic Amines on Non-Polar Bonded Phases

Abstract

The retention behaviour of alprenolol and related hydrophobic amines in ion-pair adsorption systems has been examined with particular emphasis on the influence of different mono-and divalent counter ions (dihydrogenphosphate, bromide, perchlorate, dimethylcyclohexyl sulphate, sulphate and ethylenediaminetetraacetate). N,N-dimethyloctylamine (DMOA) and 1-pentanol were used as modifiers in the aqueous eluent and LiChrosorb RP-8 as stationary phase.

The retention is evaluated according to a two-site adsorption model and equilibrium constants are given for ion pair adsorption of DMOA. The retention of alprenolol has been evaluated in terms of ion exchange with DMOA and the ion-exchange constants are shown to be of the same magnitude and independent of the nature of the counter ion used. The ion-pair adsorption and the ion-exchange approaches are analogous expressions for the distribution process governing the retention.     

Graft Copolymerization of Acrylonitrile on Bleached Holocellulose

The mechanism by which ceric ions interact with cellulosic materials in the presence of vinyl monomers to initiate graft copolymer formation is generally believed to involve propagation by radicals generated on the cellulosic substrate [1–5]. However, the relatively high levels of homopolymerization and low efficiencies of grafting associated with graft copolymerization suggest that loci of initiation other than radicals formed on the cellulosic materials may be important in graft copolymerization [6].     

Isolation and Identification of Residual Chromophores in Cellulosic Materials

A general procedure was developed for the isolation of residual chromophores in or on cellulosic material, which were hitherto inaccessible to structure elucidation due to their extremely low content in the ppb concentration scale. It is applicable to cellulosic pulp, cellulosic fibers (viscose, Lyocell) and cellulose derivatives (acetate, carbonyl-labeled cellulose) as well. The chromophore identification comprises treatment of the cellulosic material with boron trifluoride – acetic acid complex (BF₃*2HOAc) containing sulfite, chromatographic separation of the resulting chromophore-containing mixture, and structure determination of the main constituents by NMR / MS and comparison to authentic samples. Both adsorbed and covalently bound aromatic and quinoid compounds are selectively released by the treatment. Covalent ester, ether and secondary alkyl links between chromophore and cellulose are broken. Two cellulosic example substrates have been analyzed for their chromophore content: Lyocell fibers and non-bleached viscose fibers, and up to eleven chromophores per sample have been identified.     

Investigation of chiral recognition mechanism on chicken alpha(1)-acid glycoprotein using separation system

Chicken alpha1-acid glycoprotein (alpha1-AGP) consists of 183 amino acid residues and has only one Trp residue at the 26 position. In this study, the Trp26 residue was modified with 2-nitrophenylsulfenyl chloride and chiral separation of neutral, acidic and basic compounds was examined on chicken alpha1-AGP and Trp-modified chicken alpha1-AGP columns. Chiral separation of propranolol, alprenolol and oxprenolol was lost on the Trp-modified chicken alpha1-AGP column, while chlorpheniramine, ketoprofen and benzoin were still enantioseparated on the Trp-modified chicken alpha1-AGP column despite of lower enantioselectivity than that on the chicken alpha1-AGP column. These results suggest that the Trp26 residue could be responsible for chiral recognition of these compounds. Competition studies using N,N-dimethyl-n-octylamine (DMOA) as a competitor indicated that propranolol, alprenolol and oxprenolol competed with DMOA on a single binding site near the Trp26 region and that further bindings of chlorpheniramine, ketoprofen and benzoin occurred at the secondary binding site in a non-competitive fashion with DMOA.     

Corona discharge treatment route for the grafting of modified ��-cyclodextrin molecules onto cellulose

Corona discharge treatment (CDT) was implemented to attempt to graft a modified ??-cyclodextrin (??-CD) onto cellulose. The occurrence of grafting was indirectly proven by gravimetric analyses, X-ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscopy (SEM). Besides, the effect of CDT onto cellulosic substrate was studied using SEM and XPS. It appeared that surface roughness increased with the treatment time as a consequence of an etching effect and that surface oxidation took place as evidenced by the creation of hydroxyl and carboxyl groups. These functional groups are not responsible for chemical link between modified ??-CD and substrate. It was assumed that the grafting results from the reaction of double-bonds of modified ??-CD and radicals formed on treated surface, these ones being evidenced by DPPH radical trapping. Moreover the inclusion of a guest molecule is still possible in grafted modified ??-CD giving a new proof of grafting.     

Polypropylene/Cellulosic Fiber Composites Chemical Treatment of the Cellulose Assuming Compatibilization Between the Two Materials

Abstract

The present work deals with the realization of composites with a polypropylene (PP) matrix and cellulosic fibers as reinforcement. In order to achieve a good adhesion with the PP matrix, the modification of different cellulosic fibers has been performed with various chemical functions: carboxylic anhydrides, isocyanates, vinylsulfone, and chlorotriazine systems. All these compatibilizing agents carry an alkyl chain or a PP chain. Grafting is evidenced by infrared and ESCA spectroscopies, and the grafting rates for the different chemicals are determined by microweighing measurements. Modification of the surface characteristics is followed by wettability tests and inverse gas chromatography. Determination of the water sorption isotherm for the treated fibers shows an important decrease in water regain in the case of isocyanate treatments in swelling medium. Enhancement of adhesion between fibers and the matrix is demonstrated by mechanical tests: the interfacial shear stress obtained by the microbond test increases by 70% for cellulosic fibers treated with maleated PP. This may be the result of entanglements between PP chains, but for macrocomposites the effect is much more limited due to the predominance of external factors during development of the composite.     

Free Radical–Induced Graft Copolymerization onto Natural Fibers

Surface modification of a natural cellulosic polymer system is required to improve the physicochemical properties of the fibers to be used as reinforcement for green composite applications. Surface modification through graft copolymerization improves the existing properties of the cellulosic fibers for a number of applications. Therefore, in the present study, an attempt was made to synthesize butyl acrylate (BA)-g-Saccaharum cilliare fibers using a redox initiator. Graft copolymers were characterized through FT-IR/SEM/TGA/DTA/DTG techniques, and the effect of grafting percentage on the water absorption properties of raw as well as grafted fibers was also investigated.     

Effects of aliphatic amines on capillary electrochromatographic performance of tricyclic antidepressants on octadecylsilica

Adding aliphatic amines to the mobile phase improves peak symmetry and efficiency in capillary electrochromatography of tricyclic antidepressants on octadecylsilica. The most hydrophobic aliphatic amine studied, dimethyloctylamine (DMOA), was the most efficient. Despite the fact that the amine additives substantially reduced the electroosmotic flow, the retention of the analytes decreased indicating a strong competitive effect of the additives. DMOA gave the largest retention decrease, and simultaneously reduced the resolution, indicating that silanophilic interaction is significant to the separation. Highest efficiencies were obtained at the lowest pH (2.8). Acetonitrile influenced both efficiency and peak symmetry, and best results were obtained at 60%.     

Characterisation of reversed-phase stationary phases for the liquid chromatographic analysis of basic pharmaceuticals by thermodynamic data

This paper describes the characterisation of reversed-phase liquid chromatography (RPLC) columns using thermodynamic measurements. Retention versus 1/T data were used to construct Van't Hoff plots. The slope of these plots indicates the standard enthalpy of transfer of the analyte from the mobile to the stationary phase. The standard entropy can be calculated from the intercept. Van't Hoff plots were linear for the investigated RPLC columns, meaning that for basic analytes over the temperature range studied no changes in the retention mechanism occurred. Enthalpies and entropies of transfer of basic analytes from the mobile to the stationary phase revealed information about the types of interaction of protonated and neutral compounds with the stationary phases. However, a clear view using the present set of basic compounds on how these thermodynamic data may explain the observed substantial differences in peak symmetry cannot be given. It is considered that addition of N,N-dimethyloctylamine (DMOA) to the eluent will results in a dynamically coating of the stationary phase. Addition of DMOA to the eluent resulted for protonated basic compounds in a reduction of both enthalpy and entropy. In practice, with DMOA in the eluent symmetrical peaks were obtained. It is assumed that this is due to blocking residual silanols and/or ion exclusion effects.     

Synthesis and characterization of photosensitive cinnamate-modified cellulose acetate butyrate spin-coated or network derivatives

The photochemical behavior of photosensitive materials obtained by spin-coating or network synthesis of a cellulosic polymer bearing photo-cross-linkable cinnamate groups was investigated. First, cinnamate groups were grafted on a cellulose acetate butyrate polymer, with different grafting densities. The photochemical properties of the polymers were studied in solution by UV–visible and ¹H NMR spectroscopy. Then spin-coated films and networks were prepared and characterized as a function of the number of cinnamate groups per cellulosic unit. The water-wetting properties of both surfaces were studied by dynamic contact angle measurements, before and after photoirradiation, and subsequent heating. The surfaces obtained by the two methods have significantly different behaviors that can be assigned to the distinct photochemical pathways of the cinnamate groups upon irradiation depending on the sample preparation. Indeed, dimerization reaction is evidenced as the main process in the spin-coated films while the expected isomerization is predominant at the surface of the polymer networks.     

Competitive adsorption of anionic dyes onto DMOA modified MCM-41

Research on Chemical Intermediates - The single and binary adsorption of two anionic dyes Acid Yellow 17 (AY17) and Naphtol Green B (NGB) onto N–N–Dimethyl-n-octylamine (DMOA) modified...     

Effects of carbonyl and aldehyde groups in the graft copolymerization of methyl methacrylate on cellulose with a ceric salt

Graft copolymerization of methyl methacrylate on cellulosic materials of various carbonyl and aldehyde contents with the use of a ceric salt as an initiator was studied. It was found that the concentration of the ceric salt which gives the maximum per cent grafting is in good agreement with the equivalent of total carbonyl content in the cellulosic material, and the number of grafted chains in copolymers is roughly proportional to it. However, the molar ratio of the number of grafted chains to total carbonyl content is quite small, being approximately 1:50, and the graft copolymerization can be explained kinetically on the assumption that the number of radicals produced on cellulose by the ceric salt leading to branching is very much smaller than the number of radicals destroyed by the ceric salt, and growing radicals can be stabilized by the termination reaction with the ceric salt or with a cellulose radical. Although both aldehyde and carbonyl groups contribute to the formation of grafted chains, the former are effective mainly at low concentrations of the ceric salt; both groups participate in the production of graft copolymers showing the maximum per cent grafting.     

On the indirect polyelectrolyte titration of cellulosic fibers. Conditions for charge stoichiometry and comparison with ESCA

The effect of electrolyte (NaHCO3) concentration on the adsorption of poly-DADMAC (poly-diallyldimethylammonium chloride) onto cellulosic fibers with different charge profiles was investigated. Surface carboxymethylated fibers were obtained by grafting carboxymethyl cellulose (CMC) onto the fiber surface and bulk carboxymethylated fibers were obtained by reacting the fibers with monochloroacetic acid. It was shown that nonionic interactions do not exist between cellulose and poly-DADMAC, rather electrostatic interactions govern the adsorption. Charge stoichiometry prevails under electrolyte-free conditions, whereas surface charge overcompensation occurs at higher electrolyte concentrations. It was shown that charge stoichiometry prevails if the thickness of the electric double layer kappa(-1) was larger than the mean distance between the charges on the fiber surface, as predicted by polyelectrolyte adsorption theories, taking lateral correlation effects into account. In a second set of experiments the ESCA technique served to independently calibrate the polyelectrolyte titrations for determining the surface charge of cellulosic fibers. Various molecular masses of poly-DADMAC were adsorbed to carboxymethylated fibers having different charge profiles. The adsorption of low M(w) poly-DADMAC (7.0 x 10(3)), analyzed by polyelectrolyte titration, was about 10 times higher than that of the high M(w) poly-DADMAC (9.2 x 10(5)). Despite the difference in accessibility of these two polyelectrolytes to the fiber cell wall, ESCA surface analysis showed, as expected, only slight differences between the two polyelectrolytes. This gives strong credibility to the idea that surface charge content of cellulosic fibers can be analyzed by means of adsorption of a high-molecular-mass cationic polymer, i.e., by polyelectrolyte titration.     

The effect of grafting on the dyeability and properties of some modified celluloses

Summary Poly(acrylonitrile) and poly(methyl methacrylate) were grafted onto standard and chemically modified celluloses under various conditions using Ceric IV ion as a catalyst. Purified Chlorazol Sky Blue FF (C. I. Direct Blue 1) was used in dyeing the standard and modified cellulosic fabrics. Chemically modified celluloses were obtained by oxidation and cross-linking with various agents using standard procedures. Generally, grafting lowered the dye affinity, of standard and cross-linked celluloses.With 2 tables     

Construction of Bridged Polycyclic Systems by Polyene Cyclization

A stereoselective construction of bridged tri‐ and tetracyclic systems embedded in some 3,5‐dimethylorsellinic acid (DMOA)‐derived meroterpenoids was achieved by exploiting a polyene cyclization of suitably functionalized epoxyallylsilanes. Both the olefinic substituent on the epoxide and allylic trimethylsilyl (TMS) group were found to play pivotal roles in the success of the present reaction. The fact that the cyclization of monocyclized byproducts did not proceed strongly suggests that the reaction could be a concerted transformation.     

Study of new cellulosic dressing with enhanced antibacterial performance grafted with a biopolymer of chitosan and myrrh polysaccharide extract

The treatment of chronic wounds represents a major interest for public health both medically and economically. Hence the need for a modern wound dressing that actively promotes the physiological process specific to healing. In this perspective we have studied the development of a new dressing able to offer a serious contribution to the dilemma of the various chronic wounds. A dressing grafted with two natural polysaccharides known for their multiple biological effects, chitosan and a carbohydrate polymer extracted from Commiphora myrrha (CMP). We began by studying the grafting of the two natural biopolymers onto cellulose dressings, via a polyacrylic acid as a crosslinking agent. An optimization study, revealed the different grafting parameters, the polymer concentration as well as the heat-setting time and temperature. After, different characterization techniques were carried out in order to evaluate the effectiveness of our grafting. The swelling test revealed a hydrophilicity enhancement which increased with the degree of grafting, a desired property for effective dressings. Infrared characterization as well as thermogravimetric analysis (TGA and DTA) confirmed the binding mode and the permanence of our grafting. XRD and mechanical characterization showed no change in the crystallinity or in the original mechanical properties of the functionalized dressings. Morphological SEM study, confirmed the presence of our grafting as well as its mode of distribution. Finally, a bacteriological study conducted, showed a clear improvement of the antimicrobial behavior of cellulosic wound dressings functionalized by our combined natural biopolymers.