Anhydroglucose Unit Research Articles

Investigation of endoglucanase selectivity on carboxymethyl cellulose by mass spectrometric techniques

The benefits of applying cellulose selective enzymes as analytical tools for chemical structure characterization of cellulose derivatives have been frequently addressed over the years. In a recent study the high selectivity of cellulase Cel45A from Trichoderma reesei (Tr Cel45A) was utilized for relating the chemical structure to the flow properties of carboxymethyl cellulose (CMC). However, in order to take full advantage of the enzymatic hydrolysis the enzyme selectivity on the cellulose substrate must be further investigated. Therefore, the selectivity of Tr Cel45A on CMC was studied by chemical sample preparation of the enzyme products followed by mass spectrometric chemical structure characterization. The results strongly suggest that, in accordance with recent studies, also this highly selective endoglucanase is able to catalyze hydrolysis of glucosidic bonds adjacent to mono-substituted anhydroglucose units (AGUs). Furthermore, the results also indicate that substituents on the nearby AGUs will affect the hydrolysis.

Graft copolymerization of acrylonitrile onto allylated caesarweed fibres by ceric ion in the presence of 2‐mercaptoethanol

AbstractPolyacrylonitrile was grafted onto caesarweed fibers and on the allyldervative in aqueous media by ceric ion‐2‐mercaptoethanol redox pair. The allylfibre was obtained by treatment of caesarweed fibers with sodium hydroxide followed by allylchloride in diisoproylether to yield an average degree of substitution of 3.24 allyl moieties per anhydroglucose unit (AGU). The graft yield dependence on 2‐mercaptoethanol concentration, in the range, 10.7–64.0 × 10−4M was characterized by a minimum followed by an enhanced yield. This suggested the existence of two initiating species, a thioglycol radical and mercaptoethoxyl radical. A fivefold increase in the concentration of 2‐mercaptoethanol was accompanied by reduction in the frequency of graft, Fg from 75.6–0.79 Ng/104 AGU and a concomitant increase, by two orders of magnitude, in the average molecular weight of grafted polymer Mv, with values of up to 11.78 × 105. Infrared spectroscopy of allylfibre‐g‐polyacrylonitrile copolymer showed evidence of radical coupling reaction involving thioglycol radical species and allylic macroradicals of the allylfibre. The unmodified fiber was more reactive than the allylfibre by as much as a factor of 2, and was ascribed to resonance stabilization of allylic macro radicals derived from the latter. For the allyl fiber, a 150% increase in monomer concentration resulted in nominal increase in graft yield, not higher than 7%. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Grafting of acrylonitrile onto allylated caesarweed fibers by potassium permanganate – N,N′‐dimethylacetamide redox pair

AbstractCaesarweed fiber, Urena lobata, was modified by successive treatment with sodium hydroxide and allylchloride in diethylether to yield an average degree of substitution of 2.73 allyl moieties per anhydroglucose unit. The presence of allyl moieties on the fiber was confirmed by infrared spectroscopy. Graft copolymerization of acrylonitrile onto the unmodified and allyl‐modified fibers was initiated by potassium permanganate –N,N′‐dimethylacetamide redox pair in aqueous medium. The allyl fiber was markedly less reactive than the unmodified fiber with graft yields for the latter a factor of 2.3 higher than those of the former. This was attributed to resonance stabilization of allylic macroradicals of the fiber. The graft yield showed positive dependence on N,N′‐dimethylacetamide concentration in the range, 9.0–45.0 × 10−4M with Pg/Pgo of up to 1.39 at the highest concentration. The conversion in graft yield was however characterized by a plateau at the latter concentration and was ascribed to termination of grafted polymer chains by methylacetylaminomethyl radical initiating species. Spectroscopic evidence in support of the latter was the absorption peak at 1680 cm−1 for the graft copolymers, characteristic of CO stretching vibration for tertiary amide. Acetic acid, at concentrations in the range 0.28–2.22M, was inimical to grafting of acrylonitrile onto allylfibre with Pg/Pgo, of less than one. Grafting onto allylfiber showed positive temperature dependence in the range, 30–50°C with calculated activation energy of 12.3 kcal mol−1 for the graft polymerization reaction. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Homogeneous Quaternization of Cellulose in NaOH/Urea Aqueous Solutions as Gene Carriers

Quaternized celluloses (QCs) were homogeneously synthesized by reacting cellulose with 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC) in NaOH/urea aqueous solutions. The structure and solution properties of the QCs were characterized by using elemental analysis, FTIR, (13)C NMR, SEC-LLS, viscometer, and zeta-potential measurement. The results revealed that water-soluble QCs, with a degree of substitution (DS) value of 0.20-0.63, could be obtained by adjusting the molar ratio of CHPTAC to anhydroglucose unit (AGU) of cellulose and the reaction time. The QC solutions in water displayed a typical polyelectrolyte behavior, and the intrinsic viscosity ([eta]) value determined from the Fuoss-Strauss method increased with increasing DS value. Moreover, two QC samples (DS = 0.46 and 0.63) were selected and studied as gene carriers. The results of gel retardation assay suggested that QCs could condense DNA efficiently. QCs displayed relatively lower cytotoxicity as compared with PEI, and QC/DNA complexes exhibited effective transfection compared to the naked DNA in 293T cells. The quaternized cellulose derivatives prepared in NaOH/urea aqueous solutions could be considered as promising nonviral gene carriers.

Influence of the functionalization pattern of ethyl cellulose on the interactions with polystyrene latex particles in aqueous mixtures

The interactions between polystyrene latex particles and ethyl cellulose (EC) with different functionalization pattern have been investigated. 3-Mono- O-EC and EC with statistical functionalization pattern in the anhydroglucose units were studied in aqueous solutions and dispersions. EC belongs to a group of polymers that phase separate upon heating. The two types of EC showed large differences in phase separation temperature, which was explained as an effect of different interactions with water due to different functionalization pattern. Both types of EC did adsorb on polystyrene particles, which indicated a favorable interaction between EC and polystyrene latex particles, however, in a different manner depending on the structure of EC. The conventionally synthesized ethyl cellulose with statistical functionalization pattern formed much stronger networks with polystyrene latex particles than 3-mono- O-EC did. The lower phase separation temperature and the slightly higher molecular weight of the conventional ethyl cellulose gave it higher preference for interacting with polystyrene latex particles to form network. Throughout the study, comparison is made with other cellulose derivatives like ethyl(hydroxyethyl) cellulose (EHEC) and carboxymethyl cellulose (CMC).

Influence of alkyl chains length on the conformation and solubilization properties of amphiphilic carboxymethylpullulans

The existence of inter- and/or intramolecular interactions in aqueous solutions of hydrophobically modified polysaccharides induces specific macromolecular conformations at the air–solution interface and in the bulk, where hydrophobic microdomains may be formed. The present work focuses on the interfacial and solubilizing properties of amphiphilic pullulans (CMP12C8, CMP7C14, and CMP4C16) differing in the length and percentage of alkyl chains grafted to the anhydroglucose units. The surface tension studies of these polymers evidence a marked difference between the interfacial properties of CMP12C8 on one hand and those of CMP7C14 and CMP4C16 on the other hand. Pyrene fluorescence spectroscopy and benzophenone solubilization experiments demonstrate a similar partition. Increasing alkyl chains length from eight up to 14 or 16 carbons improves the solubilization properties of nonpolar molecules, even though at the same time, the average number of grafted chains per 100 anhydroglucose units is decreased from 12 down to seven and four for the three compounds, respectively.

The synthesis conditions, characterizations and thermal degradation studies of an etherified starch from an unconventional source

Starch isolated from an under-utilized legume plant (pigeon pea) was carboxymethylated. Influences of reaction parameters were investigated on the degree of substitution (DS) and the reaction efficiency (RE). Studies showed that optimal DS of 1.12 could be reached at reaction efficiency of 80.6% in isopropanol–water reaction medium (40 °C, 3 h). Scanning electron microscopy showed that after carboxymethylation, the granular appearance of the native starch was distorted. Wide-angle X-ray diffractometry revealed that crystallinity was reduced significantly after carboxymethylation. The infrared spectra revealed new bands in the carboxymethyl starch at ν = 1600, 1426 and 1324 cm −1 which were attributed to carbonyl functional groups vibration, –CH 2 scissoring and OH bending vibration, respectively. Broad-band 13C NMR of carboxymethyl starch showed an intense peak at δ = 180.3 ppm which was assigned to carbonyl carbon on the carboxymethyl substituent on the AGU (Anhydroglucose Unit). DEPT (Distortionless Enhancement by Polarization Transfer) 135 NMR showed negative signals which correspond to methylene carbons on the AGU. Differential Scanning Calorimetry (DSC) suggests loss of crystallinity after carboxymethylation. Thermogravimetry (TG), Derivative Thermogravimetry (DTG) and Differential Thermal Analysis (DTA) show that thermal stability improved after carboxymethylation. The study provides information on the preparation and characterization of a biomaterial from a new source which could be used alone or in the preparation of other functional polymers for diverse polymer applications.

Structural analysis of polymer-brush-type cellulose β-ketoesters by molecular dynamics simulation

The reason for anomalous NMR patterns of cellulose β-ketoesters, which were prepared by reaction between cellulose and ketene dimers having long alkyl chains (AKDs) under homogeneous conditions using a cellulose solvent system, was studied by molecular dynamics simulation. Cellulose/AKD β-ketoester models with degree of substitution (DS) 2.0 and degree of polymerization (DP) 5, 10, 20 or 40, and cellulose/fatty acid ester models with DS 3.0 and DP 5, 10, 20 or 40 were assembled in the simulation. The calculated results were compared with those obtained by NMR and conformation analyses of the actually prepared cellulose derivatives. The molecular dynamics simulation data showed that the average velocities of anhydroglucose units in cellulose/AKD β-ketoesters were approximately one tenth of those in cellulose/fatty acid esters. Thus, cellulose chains in the cellulose/AKD β-ketoesters are extremely restricted in motion by the β-ketoester substituents. The solid-like behavior of cellulose chains in cellulose/AKD β-ketoesters in solution state is, therefore, explainable by strong restriction in motion of cellulose chains by long, branched and bulky substituents introduced into cellulose hydroxyls in high densities via β-ketoester bonds.

Efficient allylation of cellulose in dimethyl sulfoxide/tetrabutylammonium fluoride trihydrate

The cellulose solvent dimethyl sulfoxide (DMSO)/tetrabutylammonium fluoride trihydrate (TBAF) was successfully applied as reaction medium for the synthesis of allyl cellulose by conversion of the polymer with allyl chloride in the presence of solid NaOH. Samples with degree of substitution from 0.50 to 2.98 were accessible by varying the molar ratio anhydroglucose unit:allyl chloride:NaOH and reaction time. DMSO/TBAF was found to be an efficient reaction medium for the preparation of highly functionalized samples from spruce sulfite pulp with degree of polymerization of about 500 even in a scale of 50 g. The allyl cellulose samples were characterized by means of FTIR- and NMR spectroscopy. Size exclusion chromatography revealed negligible polymer degradation during synthesis and purification of the samples.

Starch hydroxyalkylation: Physicochemical properties and enzymatic digestibility of native and hydroxypropylated finger millet ( Eleusine coracana) starch

Starch was isolated from finger millet ( Eleusine coracana) and it was etherified with propylene oxide to produce hydroxypropylated derivative. The specific specie used in this study is African finger millet known as jeero. The yield of starch obtained from finger millet on dry weight basis was 52.4%. Progressive increases in molar substitution (MS) were observed as the volume of propylene oxide added to the reaction medium increased. The X-ray pattern of native finger millet starch conforms to the ‘A’ diffraction pattern characteristics of cereal starches. Prominent peaks were observed at around 2 θ=15°, 17°, 18° and 23° and weaker peaks at around 2 θ=20° and 26°. No pronounced differences were observed between the diffractograms of native starch and the hydroxypropyl derivatives. Hydroxypropylation improved the free swelling capacities of the native starch at all temperatures studied (30–90 °C). Turbidity of unmodified finger millet starch paste increased progressively as the days of storage increased. Turbidity reduced remarkably after hydroxypropylation and reduction in turbidity was observed as the MS of the modified starches increased. Hydroxypropylation reduced pasting temperature, increased peak viscosity but reduced setback value. In addition, hydroxypropylation reduced percentage syneresis of the unmodified starch. Retrogradation properties monitored with differential scanning calorimetry reveals that starch retrogradation reduced reasonably after hydroxypropylation. Carbon 13 NMR spectroscopy reveals that hydroxypropylation took place predominantly on carbon 6 on the anhydroglucose unit (AGU).

Dynamics of Cellulose−Water Interfaces: NMR Spin−Lattice Relaxation Times Calculated from Atomistic Computer Simulations

Solid-state nuclear magnetic resonance (CP/MAS 13C NMR) spectroscopy has often been used to study cellulose structure, but some features of the cellulose NMR spectrum are not yet fully understood. One such feature is a doublet around 84 ppm, a signal that has been proposed to originate from C4 atoms at cellulose fibril surfaces. The two peaks yield different T1, differing by approximately a factor of 2 at 75 MHz. In this study, we calculate T1 from C4-H4 vector dynamics obtained from molecular dynamics computer simulations of cellulose I beta-water interfacial systems. Calculated and experimentally obtained T1 values for C4 atoms in surface chains fell within the same order of magnitude, 3-20 s. This means that the applied force field reproduces relevant surface dynamics for the cellulose-water interface sufficiently well. Furthermore, a difference in T1 of about a factor of 2 in the range of Larmor frequencies 25-150 MHz was found for C4 atoms in chains located on top of two different crystallographic planes, namely, (110) and (10). A previously proposed explanation that the C4 peak doublet could derive from surfaces parallel to different crystallographic planes is herewith strengthened by computationally obtained evidence. Another suggested basis for this difference is that the doublet originates from C4 atoms located in surface anhydro-glucose units with hydroxymethyl groups pointing either inward or outward. This was also tested within this study but was found to yield no difference in calculated T1.

Substitution Patterns of Cellulose Ethers ‐ Influence of the Synthetic Pathway

AbstractCommercial cellulose ethers are usually prepared under heterogeneous reaction conditions. In contrast, this contribution also describes the derivatization under homogeneous conditions in N‐methylmorpholine‐N‐oxide monohydrate (NMMNO*H2O) and under heterogeneous conditions after converting native cellulose to amorphous cellulose. Amorphous cellulose is prepared by dissolving cellulose in NMMNO*H2O followed by precipitation in different media. The degree of order and the porosity of the regenerated cellulose is significantly influenced by the content of water in the precipitating agent. The differences are described by measurements using wide angle X‐ray scattering, solid‐state 13C‐NMR, mercury porosimetry, and water/liquid retention values. Three synthetic pathways (heterogeneous, heterogeneous with amorphous cellulose and homogeneous) are compared regarding the structure‐property relationship of the cellulose ethers formed. Carboxymethylation, hydroxyethylation, hydroxypropylation and sulfoethylation are considered in detail. The choice of synthetic pathway has a significant influence on the degree of substitution (DS), the distribution of substituents on the level of the anhydroglucose unit (AGU), solubility behavior, and the viscosity of aqueous solutions. In general an increasing solubility and an increasing viscosity are observed from heterogeneous to heterogeneous with amorphous cellulose to homogeneous reaction conditions. There is a remarkable difference between the heterogeneously produced cellulose ethers with a DS distribution C2 ≥ C6 > C3 and the strictly homogeneous etherification in NMMNO*H2O/organic solvent systems with a DS distribution of C3 > C2 ≫ C6. This high regioselectivity at the secondary OH‐groups of the AGU may be caused by the strong solvation behavior of NMMNO*H2O and thereby a protecting function at the C6‐OH‐group.

“Furan Endwise Peeling” of Celluloses: Mechanistic Studies and Application Perspectives of a Novel Reaction

AbstractThe mechanism of a novel reaction type, the “furan endwise peeling” reaction, has been studied. Making extensive use of experiments on model compounds, the structural prerequisites to the reaction were found to be a 2‐hydroxpyran β‐glycosidically linked to a 2‐(2‐furyl)ethyl moiety. Proceeding from the reducing end of the celluloses, the reaction causes the one‐by‐one loss of anhydroglucose units (AGUs) which are concomitantly converted into 2‐(tetrahydroxybutyl)furans (4) by co‐reacting with 1,3‐dicarbonyl compounds such as ethyl acetoacetate (1). The key step of the reaction is the formation of a furan at the reducing end followed by the attack of the 2‐OH group of the last‐but‐one AGU at this terminal furan. The intermediate, unstable dioxepane fragments by cleavage of the glycosidic bond. The terminal AGU is released as a substituted furan, the “new” reducing end reacting immediately with the 1,3‐dicarbonyl component to form a new terminal furan which, in turn, undergoes the same cycle. The “furan endwise peeling” reaction represents an interesting way to convert cellulosic biomass by an easy procedure into substituted furans that are valuable fine chemicals with multiple uses.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

New Possibilities of the Acetosulfation of Cellulose

AbstractRegioselectively substituted cellulose sulfates in C2/3‐, C2/6‐, or C6‐position of the anhydroglucose unit are accessible by certain synthesis routes. Thereby, products with different properties and various application areas are resulted. Important characteristics of cellulose sulfates regarding their applications are solubility (e.g. in water), rheological behavior, different interaction with low or high molecular cations, thermo reversible gel formation, enzymatic degradability, anticoagulant and antiviral activity. In C6‐position substituted cellulose sulfates can be synthesized in principle by acetosulfation. The acetosulfation is a quasi‐homogeneous synthesis proceeding under gradually dissolution of the cellulose by using different reactivity of the primary and secondary OH‐groups as soon as converting cellulose acetate sulfates. After precipitation of the polymer the acetyl groups are cleaved in alkaline solution. The focus of our study was firstly the investigation of the acetosulfation in different polar aprotic solvents by various sulfating and acetylating agents. In general it should be investigated if C6 substituted cellulose sulfates can be obtained by acetosulfation with different solvents and agents. The products were characterized by 13C‐NMR and Raman spectroscopy.

Alkaline treatment of diacetate fibers and subsequent cellulase degradation

AbstractThe work investigated the degradation behavior of cellulose acetate (CA) fibers in NaOH solutions in heterogeneous conditions and the effect of alkaline treatment on cellulase degradation of CA fibers. Weight analysis and IR spectra showed that the weight loss of CA fibers immersed in NaOH solution chiefly depended on acetylation. Alkaline treatment promoted the degradation of CA fibers in cellulase solution by reason of deacetylation, especially when the degree of substitution (DS) of CA fibers reached 0.8, cellulase degradation increased most markedly. SEM revealed a smooth surface except some thin holes in the CA fibers after immersion in NaOH solution with a lower concentration because of the formation of alkaline cellulose, and only in a higher concentration such as 5.0N, it could be observed that microfibers perpendicular to fiber axis distributed over the surfaces of the fibers. 1NMR spectra suggested that only in a lower NaOH concentration (≤0.25N), deacetylation reaction was affected by the reactivities of ester groups at position 2, 3, and 6 in anhydroglucose unit, but did not follow the theoretical trend in the three positions. Moreover, the DS for polymer molecules in CA fibers were dispersive after alkaline treatment in heterogeneous condition and the DS of the product increased during sequent cellulase degradation. This was also demonstrated by the result of IR analysis and X‐ray diffraction. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Homogenous modification of cellulose with acrylamide in NaOH/urea aqueous solutions

A series of cellulose polyelectrolytes, containing acylamino and carboxyl groups, were homogenously synthesized from cellulose with acrylamide in NaOH/urea aqueous solutions. The structure and solution properties of the polyelectrolytes were characterized with elemental analysis, FTIR, NMR, viscometer and zeta-potential measurement. The nitrogen content and total degree of substituent (DS) of the derivatives increased with increasing of the molar ratio of acrylamide to the anhydroglucose unit (AGU) and the cellulose concentration. The DS of carboxyl groups hardly changed because of the similar reaction and hydrolysis conditions, while the DS of acylamino groups increased with increasing of the total DS values of the products. The polyelectrolytes are soluble in water at a total DS as low as 0.36, and the zeta-potential values in pure water are in the range of −15 to −25 mV. The [ η] values of the polyelectrolytes in NaCl aqueous solutions increased apparently with an increase of the pH value in the lower pH region, and reached the maximum value at the pH range from 5 to 6, and while hardly changed at the pH range from 7 to 12. This work provided a facile method for the synthesis of cellulose polyelectrolytes with two different functional groups.

Fluorescently Labeled Cellulose Nanocrystals for Bioimaging Applications

Cellulose nanocrystals are promising candidates for applications in nanomedicine. To enable the use of fluorescence techniques in in vitro and in vivo studies, cellulose nanocrystals were labeled with fluorescein-5‘-isothiocyanate (FITC) via a three-step reaction, involving epoxy activation of the nanocrystal surface, opening of the epoxy rings with ammonium hydroxide, and coupling of FITC molecules to the primary amino groups. The FITC content of the labeled cellulose nanocrystals was determined by UV/vis spectroscopy. A FITC content of 0.03 mmol/g of cellulose, equivalent to 5 FITC moieties per 1000 anhydroglucose units, was obtained using the described method.

Novel cationic and amphiphilic pullulan derivatives I: Synthesis and characterization

Cationic amphiphilic modified pullulan’s were obtained in two steps: firstly the synthesis of diethylaminoethylpullulan (DEAE-Pullulan) with DS 0 = 0.80 in water (all degrees of substitution (DS) are calculated in anhydroglucose units (AGU)) followed by the incorporation of different alkyl chains (C 10, C 12 and C 16) using Hoffmann alkylation reaction. Three alkylated derivatives (Y-Cx-DEAE-Pullulan) were produced with a degree of substitution of alkyl chains (Y = 100 DS Cx) of 40 in the case of C10 and C12 and 20 in the case of C16. The three samples contained two functional types: an amine function (DS N), dependent on pH and a quaternary ammonium function (DS N+) linked to a hydrophobic alkyl chain (DS Cx). Chemical characterizations were carried out by conductimetric measurements, elemental analysis and 1H NMR. The amphiphilic and associative properties have been confirmed by flow field flow fractionation (F4) coupled on-line with multi-angle laser light scattering (MALLS). The intermolecular associations were observed for DEAE-Pullulan and Y-Cx-DEAE-Pullulan in 0.1 M LiNO 3.

A new NMR method for directly monitoring and quantifying the dissolution kinetics of starch in DMSO

The kinetics of dissolution of starch is needed for (i) understanding digestive processes; (ii) providing data that could correlate with higher levels of starch structure; (iii) improving techniques for starch characterization in solution. A novel method is presented here to directly monitor these dissolution kinetics by time-resolved 1H solution-state nuclear magnetic resonance (NMR); studies were carried out in deuterated dimethyl sulfoxide (DMSO- d 6). By assuming pseudo-first-order kinetics with respect to starch concentration, the data for various starch samples yield values of the apparent rate coefficients for the rate of appearance of completely dissolved anhydroglucose units, results which have not been obtained hitherto. The presence of a limited amount of water in DMSO had a drastic effect on dissolution kinetics (slowing it down at high temperatures), indicating multiple pathways for the dissolution mechanism. Dynamic light scattering (DLS) appears to be more limited than the NMR method to monitor the kinetics of dissolution. The newly developed NMR method can be extended to other solvents and polysaccharides.

Starch Functionalized by Chloroacetate Groups: Coupling of Bioactive Salicylic Acid

AbstractStarch partially functionalized with chloroacetate groups was obtained by reaction of starch with chloroacetyl chloride using the N,N‐dimethylacetamide/5%lithium chloride system as solvent and pyridine as catalyst. The coupling of salicylic acid to starch functionalized with chloroacetate groups was carried out by reaction with the sodium salt of salicylic acid. The structures of chloroacetylated starch and starch‐salicylic acid adducts were determined by means of FTIR, 1H‐NMR and 13C‐NMR spectra. The degree of substitution per anhydroglucose unit (AGU) of chloroacetylated starch was calculated from the chloride content and ranged from 0.52 to 2.34, depending on the ratio of chloroacetyl chloride to starch. The hydrolysis of starch‐salicylic acid adducts in a heterogeneous phase showed that the release of sodium salicylate from tablets is dependent on the hydrophilic character of the adduct and on the pH value of the medium.