Ultrasound‐assisted swelling of bacterial cellulose

Bacterial cellulose (BC) was obtained by static cultivation using commercial BC gel from scoby. BC membranes (oven dried and freeze‐dried) were swelled with 8% NaOH, in the absence and in the presence of ultrasound (US), for 30, 60, and 90 min. The influence of swelling conditions on both physico‐chemical properties and molecules entrapment was evaluated. Considering the highest levels of entrapment, an optimum swelling procedure was established: 8% NaOH for 30 min at room temperature in the presence of US. Native and PEGylated laccase from Myceliophthora thermophila was immobilized on BC membranes and a different catalytic behaviour was observed after immobilization. Native laccase presented activity values similar to published reports (5–7 U/gBC) after immobilization whereas PEGylated enzymes showed much lower activity (1–2 U/gBC). BC swelled membranes are presented herein as a potential support for the preparation of immobilized enzymes for industrial applications, like phenolics polymerization.     

Structure of a cellulose I–ethylenediamine complex

The structure of a crystalline cellulose I–ethylenediamine complex has been determined by x-ray diffraction methods as part of an investigation of cellulose–solvent interaction. The complex studied is that formed when native ramie fibers are swollen in ethylenediamine and then vacuum-dried. The unit cell is monoclinic with dimensions a = 12.87 Å, b = 9.52 Å, c = 10.35 Å, and γ = 118.8°, and it contains disaccharide segments of two chains, with one ethylenediamine per glucose residue. The refined model contains parallel cellulose chains that are linked by hydrogen-bonded ethylenediamine molecules. The chains along the b-axis are packed in register, leading to stacks of chains analogous to those in chitin. All the hydroxyl groups are satisfactorily hydrogen-bonded and each ethylenediamine forms four donor and two acceptor hydrogen bonds. From this work it can be seen that the interaction of cellulose I with ethylenediamine involves scission of the intermolecular hydrogen bonds followed by disruption of the stacks of quarter-staggered chains.     

Carbohydrate derived‐pseudo‐lignin can retard cellulose biological conversion

Dilute acid as well as water only (hydrothermal) pretreatments often lead to a significant hemicellulose loss to soluble furans and insoluble degradation products, collectively termed as chars and/or pseudo‐lignin. In order to understand the factors contributing to reducing sugar yields from pretreated biomass and the possible influence of hemicellulose derived pseudo‐lignin on cellulose conversion at the moderate to low enzyme loadings necessary for favorable economics, dilute acid pretreatment of Avicel cellulose alone and mixed with beechwood xylan or xylose was performed at various severities. Following pretreatment, the solids were enzymatically hydrolyzed and characterized for chemical composition and physical properties by NMR, FT‐IR, and SEM imaging. It was found that hemicelluloses (xylan) derived‐pseudo‐lignin was formed at even moderate severities and that these insoluble degradation products can significantly retard cellulose hydrolysis. Furthermore, although low severity (CSF ～ 1.94) dilute acid pretreatment of a xylan–Avicel mixture hydrolyzed most of the xylan (98%) and produced negligible amounts of pseudo‐lignin, enzymatic conversion of cellulose dropped significantly (>25%) compared to cellulose pretreated alone at the same conditions. The drop in cellulose conversion was higher than realized for cellulase inhibition by xylooligomers reported previously. Plausible mechanisms are discussed to explain the observed reductions in cellulose conversions. Biotechnol. Bioeng. 2013; 110: 737–753. © 2012 Wiley Periodicals, Inc.     

White biotechnology for cellulose manufacturing—The HoLiR concept

A variety of approaches are available for generation of bacteria‐produced nanocellulose (BNC) in different forms. BNC production under static cultivation conditions usually results in fleeces or foils, characterized by a homogeneous, three‐dimensional network of nanofibers and a uniform surface. However, under static cultivation conditions in batch vessels, the widths and the lengths of the BNC sheets cultured are determined by the dimensions of the culture vessel. In this contribution, a novel, efficient process for a (semi‐)continuous cultivation of planar BNC fleeces and foils with a freely selectable length and an adjustable height is presented. By means of comprehensive investigations, the comparability of the BNC harvested to that gained from static cultivation under batch conditions is demonstrated. A first estimation of the production costs further shows that this type of processing allows for significant cost reductions compared to static cultivation of BNC in Erlenmeyer flasks. Biotechnol. Bioeng. 2010. 105: 740–747. © 2009 Wiley Periodicals, Inc.     

A novel thermotropic liquid crystalline – Benzoylated bacterial cellulose

Using the esterification of bacterial cellulose (BC), we have synthesized Benzoylated bacterial cellulose (BBC). The molecular structure of the BBC was characterized by means of Fourier transform infrared (FT-IR) spectroscopy, ¹H and ¹³C nuclear magnetic resonance (NMR). The BBC is found to display thermotropic liquid crystalline feature determined with differential scanning calorimetry (DSC), polarized optical microscope (POM) and wide-angle X-ray diffraction (WAXD). Here, we demonstrate that it is possible to obtain the BBC with degree of substitution (DS) from 0.88 to 2.46 by applying the different molar ratio of benzoyl chloride to the anhydrous glucose unit (AGU). The glass transition temperatures (T_g) of the liquid crystalline phases lie between 281.2 and 281.8 °C and the isotropic melt transition temperatures (T_i) vary from 341.6 to 362.8 °C, depending on the DS.     

Blue emitting ZnO nanostructures grown through cellulose bio‐templates

This paper presents a green and cost‐effective recipe for the synthesis of blue‐emitting ZnO nanoparticles (NPs) using cellulose bio‐templates. Azadirachta indica (neem) leaf extract prepared in different solvents were used as biological templates to produce nanostructures of wurtzite ZnO with a particle size ~12–36 nm. A cellulose‐driven capping mechanism is used to describe the morphology of ZnO NPs. The scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD), Fourier transform infra‐red (FTIR) and photoluminescence (PL) studies showed that solvents affect the growth process and the capping mechanism of bio‐template severely. Structural changes in ZnO NPs were evident with variation in pH, dielectric constants (DC) and boiling points (BP) of solvents. Furthermore, an energy band model is proposed to explain the origin of the blue emission in the as‐obtained ZnO NPs. PL excitation studies and the theoretical enthalpy values of individual defects were used to establish the association between the interstitial‐zinc‐related defect levels and the blue emission. Copyright © 2015 John Wiley & Sons, Ltd.     

Ultrasound mediated enzymatic hydrolysis of cellulose and carboxymethyl cellulose

A recombinant Trichoderma reesei cellulase was used for the ultrasound‐mediated hydrolysis of soluble carboxymethyl cellulose (CMC) and insoluble cellulose of various particle sizes. The hydrolysis was carried out at low intensity sonication (2.4–11.8 W cm^?2 sonication power at the tip of the sonotrode) using 10, 20, and 40% duty cycles. [A duty cycle of 10%, for example, was obtained by sonicating for 1 s followed by a rest period (no sonication) of 9 s.] The reaction pH and temperature were always 4.8 and 50°C, respectively. In all cases, sonication enhanced the rate of hydrolysis relative to nonsonicated controls. The hydrolysis of CMC was characterized by Michaelis‐Menten kinetics. The Michaelis‐Menten parameter of the maximum reaction rate V_max was enhanced by sonication relative to controls, but the value of the saturation constant K_m was reduced. The optimal sonication conditions were found to be a 10% duty cycle and a power intensity of 11.8 W cm^?2. Under these conditions, the maximum rate of hydrolysis of soluble CMC was nearly double relative to control. In the hydrolysis of cellulose, an increasing particle size reduced the rate of hydrolysis. At any fixed particle size, sonication at a 10% duty cycle and 11.8 W cm^?2 power intensity improved the rate of hydrolysis relative to control. Under the above mentioned optimal sonication conditions, the enzyme lost about 20% of its initial activity in 20 min. Sonication was useful in accelerating the enzyme catalyzed saccharification of cellulose. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:1448–1457, 2013     

Influence of precipitation seasonality on piñon pine cellulose δD values

The influence of seasonal to interannual climate variations on cellulose hydrogen isotopic composition (δD) was assessed by analysing tree rings and needles of piñon pine (Pinus edulis and P. monophylla). Sites spanned a gradient of decreasing summer precipitation, from New Mexico to Arizona to Nevada. Tree rings were divided into earlywood, latewood and whole‐year increments, and annual cohorts of needles were collected. The study period (1989–96) included two La Niña events (1989, 1996) and a prolonged El Niño event (1991–95). Winter and spring moisture conditions were strongly related to October–March Southern Oscillation Index (SOI) in New Mexico and Arizona, with above‐average precipitation occurring in El Niño years. Wood δD values at these sites were correlated with winter and spring moisture conditions. Needle δD values were correlated with summer moisture conditions in New Mexico and with winter moisture and SOI in Arizona. Low cellulose δD values observed from 1991 to 1993 in both wood and needles occurred during wet El Niño years, whereas high δD values in needles were present during the dry, La Niña years of 1989 and 1996. North‐eastern Nevada does not receive precipitation anomalies related to ENSO, and thus cellulose δD values did not reflect the ENSO pattern observed at the other sites. Cellulose δD values were strongly, inversely correlated with relative humidity variations at all sites, as predicted by a mechanistic model. Contrary to predictions from the same model and observations from more mesic areas, time series of cellulose δD values were not directly correlated with interannual or seasonal variations in precipitation δD values or temperature at any of the sites. On a regional basis, however, mean δD values in needles and wood were correlated with mean annual temperature and δD values of precipitation. This suggests that temporal averaging may bias relationships between biological systems and climate.     

Detrimental effect of cellulose oxidation on cellulose hydrolysis by cellulase

To effectively convert complex and recalcitrant biomass carbohydrates to simple platform sugars useful for fuel and chemicals production, mechanical or chemical pre-treatments are often required to make the carbohydrates more accessible for enzymatic hydrolysis. Due to their harsh conditions, some pre-treatments might negatively affect enzymatic hydrolysis because of events such as cellulose oxidation. To study how oxidative modification may impact cellulose's reactivity toward hydrolysis by cellulases, we prepared three cellulose substrates by cupric ion and hypochlorite oxidations, and subjected the derived celluloses to hydrolysis by various cellobiohydrolases from glycoside hydrolase families 6 and 7, and one cellulolytic Hypocrea jecorina extracellular enzyme mixture. We observed a profound decrease of enzymatic hydrolysis on the oxidized celluloses. The effect was attributed to the interference, from oxidized functional groups in cellulose, on its binding/activation in the active pocket/tunnel of cellobiohydrolases. Potential implication of the observed effect from cellulose oxidation on pre-treatment optimization and cellulase improvement was discussed.     

A structural study of fluorinated cellulose: crystallization of fluorinated cellulose by conversion treatments used for cellulose

A deoxyfluorocellulose derivative, with regioselective substitution mostly at the C-6 carbon atoms, has been studied by an X-ray diffraction method. The results showed that the crystallinity of the fluorinated cellulose is low but can be enhanced by a specific conversion treatment. The hydrothermally treated sample displayed a spectrum similar to that of cellulose IV.     

Enhancement of enzymatic saccharification of cellulose by cellulose dissolution pretreatments

Attempts were made to enhance cellulose saccharification by cellulase using cellulose dissolution as a pretreatment step. Four cellulose dissolution agents, NaOH/Urea solution, N-methylmorpholine-N-oxide (NMMO), ionic liquid (1-butyl-3-methylimidazolium chloride; [BMIM]Cl) and 85% phosphoric acid were employed to dissolve cotton cellulose. In comparison with conventional cellulose pretreatment processes, the dissolution pretreatments were operated under a milder condition with temperature <130 °C and ambient pressure. The dissolved cellulose was easily regenerated in water. The regenerated celluloses exhibited a significant improvement (about 2.7- to 4.6-fold enhancement) on saccharification rate during 1st h reaction. After 72 h, the saccharification yield ranged from 87% to 96% for the regenerated celluloses while only around 23% could be achieved for the untreated cellulose. Even with high crystallinity, cellulose regenerated from phosphoric acid dissolution achieved the highest saccharification rates and yield probably due to its highest specific surface area and lowest degree of polymerization (DP).     

Polymorphism of cellulose I family: reinvestigation of cellulose IVI

Polymorphs of cellulose I, III(I), and IV(I) have been investigated by X-ray diffraction, FT-IR, and solid-state (13)C NMR spectroscopy. Highly crystalline cellulose III(I) samples were prepared by treating cellulose samples in supercritical ammonia at 140 degrees C for 1 h, and conventional cellulose III(I) samples were prepared by liquid ammonia treatment. The cellulose IV(I) sample of highest crystallinity was that prepared from Cladophora cellulose III(I) in supercritical ammonia, followed by the sample treated in glycerol at 260 degrees C for 0.5 h, whereas the lowest crystallinity was observed in ramie cellulose prepared by conventional liquid ammonia treatment followed by glycerol annealing. In general, the perfection of cellulose IV(I) depends on the crystallinity of the original material: either of the starting cellulose I or of the cellulose III(I) after ammonia treatment. The product thus obtained was analogous to cellulose I(beta), which is what it should be called rather than cellulose IV(I). If the existence of the polymorph cellulose IV(I) is not accepted, the observations on which it has been based may be explained by the fact that the structure termed cellulose IV(I) is cellulose I(beta) which contains lateral disorder.     

Pyrolysis of cellulose

Pyrolysis of cellulose under vacuum and atmospheric pressure gave a tar containing various amounts of 1,6-anhydro-β-D-glucopyranose, 1,6-anhydro-β-D-glucofuranose, α- and β-D-glucose, 3-deoxy-D-erythro-hexosulose, oligo- and polysaccharides, and some dehydration products. The polysaccharide fraction had no reducing end-group, was randomly linked, contained some furanoid rings, and was very similar to the polysaccharide condensation-product of 1,6-anhydro-β-D-glucose. These results are consistent with a series of inter- and intra-molecular transglycosylation and dehydration and rehydration reactions.