The structural changes in crystalline cellulose and effects on enzymatic digestibility

The enzymatic hydrolysis of cellulose I achieves almost complete digestion when sufficient enzyme loading as much as 20 mg/g-substrate is applied. However, the yield of digestion reaches the limit when the enzyme dosage is decreased to 2 mg/g-substrate. Therefore, we have performed three pretreatments such as mercerization, dissolution into phosphoric acid and EDA treatment. Transformation into cellulose II hydrate by mercerization and dissolution into phosphoric acid were not sufficient because substrate changed to highly crystalline structure during saccharification. On the other hand, in the case of crystalline conversion of cellulose I to III_I by EDA, almost perfect digestion was achieved even in enzyme loading as small as 0.5 mg/g-substrate, furthermore, hydrolyzed residue was typical cellulose I. The structural analysis of substrate after saccharification provides an insight into relationships between cellulose crystalline property and cellulase toward better enzymatic digestion.     

Enzymatic hydrolysis of cellulose hydrates

We prepared two cellulose hydrates, Na-cellulose IV and cellulose II hydrate, along with their respective anhydrous forms, cellulose II and II′, from microcrystalline cellulose. X-ray diffractometry analysis showed that the structure of the hydrophobic stacking sheet was conserved in the samples, but the distance between the sheets was in the order: cellulose II hydrate > Na-cellulose IV > cellulose II and II′. The hydrates exhibited an expanded structure compared with the anhydrous form from the incorporation of hydrate water, and cellulose II hydrate contained more hydrate water than Na-cellulose IV. Enzymatic hydrolysis of the samples was carried out at 37 °C using solutions comprising a mixture of cellulase and β-glucosidase. The hydrates were hydrolyzed more efficiently than the anhydrous forms, and cellulose II hydrate showed a more efficient hydrolysis than Na-cellulose IV. This result also agrees well with the enzymatic adsorption properties of each sample, where the samples that adsorbed the greater amount of enzyme showed a higher degradability. The results obtained in this study provide useful knowledge on controlling the biodegradability of cellulose by converting its structure.     

Enzymatic hydrolysis of different allomorphic forms of microcrystalline cellulose

This paper investigates the enzymatic hydrolysis of three main allomorphic forms of microcrystalline cellulose using different cellulases, from Trichoderma reesei and from Aspergillus niger, respectively. It was demonstrated that both the morphological and crystalline structures are important parameters that have a great influence on the course of the hydrolysis process. The efficiency of the enzymatic hydrolysis of cellulosic substrates was estimated by the amounts of reducing sugar and by the yield of the reaction. Changes in the average particle sizes of the cellulose allomorphs were determined during enzymatic hydrolysis. The accumulation of soluble sugar within the supernatant was used as a measure of the biodegradation process’s efficiency, and was established by HPLC-SEC analysis. Any modifications in the supramolecular structure of the cellulosic residues resulting from the enzymatic hydrolysis were determined by X-ray diffraction. The action of each cellulase was demonstrated by a reduction in the crystalline index and the crystallite dimensions of the corresponding allomorphic forms. The crystalline structure of allomorphic forms I and II did not suffer significant modifications, while cellulose III recorded a partial return to the crystalline structure of cellulose I. The microstructures of cellulose allomorph residues were presented using optical microscopy and scanning electron microscopy.     

To understand the superior hydrolytic activity after polymorphic conversion from cellulose I to II from the adsorption behaviors of enzymes

The role of the cellulose ultrastructure on the relationship between cellulase binding and activity is not clear yet. In this article, a quartz crystal microbalance with dissipation (QCM-D) was employed to monitor the interactions between a given cellulase and the cellulose substrates with varied polymorphs of pure cellulose I and II and the intermediate state (I/II). Initially, cellulose nanocrystals (CNCs) with polymorphs of cellulose I, I/II and II were prepared and spin-coated on QCM sensors. The cellulose substrates’ crystallinity degree was examined by XRD, and morphology was detected by AFM. Then, a commercial cellulase from Trichoderma reesei was used to test the adsorption and hydrolysis of cellulose substrates with polymorphs of I, I/II and II, respectively. The results revealed that in the enzyme adsorption and desorption process at a temperature of 15 °C, CNC-II had the lowest adsorption capacity with a total adsorption mass of 179 ng cm^?2 but the highest reversible binding ratio of 33.7%; for comparison, the values were 235 ng cm^?2 versus 25.6% and 207 ng cm^?2 versus 26.9% for CNC-I and -I/II, respectively. And the conformation of adlayers on CNC-I, -I/II and -II derived from the QCM data became softer and softer in turn. On the other hand, CNC-II exhibited the best enzymatic hydrolytic ability among three substrates when enzymatic hydrolysis experiments were conducted at 45 °C. The results indicated that polymorphic conversion from I to II changes the affinity between the enzyme and cellulose surface; CNC-II has the lowest affinity to the enzyme, but the softer conformation of the adsorbed enzyme layer, and the more reversible adsorption may facilitate its hydrolytic activity. This article gives a perspective from the adsorption dynamics and conformation of the adsorbed enzyme layer, helping to understand the superior hydrolytic activity of cellulose with polymorph II. Thus, there is a potential of polymorphic conversion in the reduction of enzyme dosage and cost in the enzymatic hydrolysis process.     

Mercerized cellulose biocomposites: a study of influence of mercerization on cellulose supramolecular structure, water retention value and tensile properties

In this study the effect of the mercerization degree on the water retention value (WRV) and tensile properties of compression molded sulphite dissolving pulp was evaluated. The pulp was treated with 9, 10, or 11 % aqueous NaOH solution for 1 h before compression molding. To study the time dependence of mercerization the pulp was treated with 12 wt% aqueous NaOH for 1, 6 or 48 h. The cellulose I and II contents of the biocomposites were determined by solid state cross polarization/magic angle spinning carbon 13 nuclear magnetic resonance (CP/MAS ¹³C NMR) spectroscopy. By spectral fitting of the C6 and C1 region the cellulose I and II content, respectively, could be determined. Mercerization decreased the total crystallinity (sum of cellulose I and cellulose II content) and it was not possible to convert all cellulose I to cellulose II in the NaOH range investigated. Neither increased the conversion significantly with 12 wt% NaOH at longer treatment times. The slowdown of the cellulose I conversion was suggested as being the result from the formation of cellulose II as a consequence of coalescence of anti-parallel surfaces of neighboring fibrils (Blackwell et al. in Tappi 61:71–72, 1978; Revol and Goring in J Appl Polym Sci 26:1275–1282, 1981; Okano and Sarko in J Appl Polym Sci 30:325–332, 1985). Compression molding of the partially mercerized dissolving pulps yielded biocomposites with tensile properties that could be correlated to the decrease in cellulose I content in the pulps. Mercerization introduces cellulose II and disordered cellulose and lowered the total crystallinity reflected as higher water sensitivity (higher WRV values) and poorer stiffness of the mercerized biocomposites.     

Bioethanol from cellulose with supercritical water treatment followed by enzymatic hydrolysis

The water-soluble portion and precipitates obtained by supercritical (SC) water treatment of microcrystalline cellulose (Avicel) were enzymatically hydrolyzed. Glucose could be produced easily from both substrates, compared with the Avicel. Therefore, SC water treatment was found to be effective for enhancing the productivity of glucose from cellulose by the enzymatic hydrolysis. It is also found that alkaline treatment or wood charcoal treatment reduced inhibitory effects by various decomposed compounds of cellulose on the enzymatic hydrolysis to achieve higher glucose yields. Furthermore, glucose obtained by SC water treatment followed by the enzymatic hydrolysis of cellulose could be converted to ethanol by fermentation without any inhibition.     

Mercerization of primary wall cellulose and its implication for the conversion of cellulose I→cellulose II

The mercerization of homogenized primary wall cellulose extracted fromsugar beet pulp was investigated by transmission electron microscopy (TEM),X-ray diffraction together with ¹³C CP-MAS NMR, and FT-IR spectroscopy.For samples resulting from acid extraction, mercerization began at 9% NaOH, whereasfor samples purified by alkaline treatment, the mercerization started at 10%NaOH. The change in morphology when going from cellulose I to cellulose II wasspectacular, as all the microfibrillar cellulose morphology disappeared duringthe treatment. This change in morphology was very drastic as soon as the NaOHconcentrations were increased beyond 8 and 9% for the acid and alkalinepreparedsamples, respectively. On the other hand, the conversion was found to be moreprogressive in terms of increasing NaOH concentration when the transformationwas analyzed by X-ray diffraction or spectroscopy. Our observations of themercerization of isolated cellulose microfibrils are consistent with theconceptof cellulose microfibrils made of parallel chains in cellulose I and crystalsofcellulose II consisting of antiparallel chains.     

Cellulose nanocrystals obtained from microcrystalline cellulose by p-toluene sulfonic acid hydrolysis,NaOH and ethylenediamine treatment

Cellulose nanocrystals (CNCs) were first isolated from microcrystalline cellulose (MCC) by p-toluene sulfonic acid (p-TsOH) hydrolysis. Cellulose II nanocrystal (CNC II) and cellulose III nanocrystal (CNC III) were then formed by swelling the obtained cellulose I nanocrystal (CNC I) in concentrated sodium hydroxide solutions and ethylenediamine (EDA) respectively. The properties of CNC I, CNC II and CNC III were subjected to comprehensive characterization by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The results indicated that CNC I, CNC II and CNC III obtained in this research had high crystallinity index and good thermal stability. The degradation temperatures of the resulted CNC I, CNC II and CNC III were 300 °C, 275 °C and 242 °C, respectively. No ester bonds were found in the resulting CNCs. CNCs prepared in this research also had large aspect ratio and high negative zeta potential.

     

Cascade Enzymatic Hydrolysis Coupling with Ultra ne Grinding Pretreatment for Sugarcane Bagasse Sacchari cation

The biorefinery process for sugarcane bagasse saccharification generally requires significant accessibility of cellulose. We reported a novel method of cascade cellulase enzymatic hydrolysis coupling with ultrafine grinding pretreatment for sugarcane bagasse saccharification. Three enzymatic hydrolysis modes including single cellulase enzymatic hydrolysis, mixed cellulase enzymatic hydrolysis, and cascade cellulase enzymatic hydrolysis were compared. The changes on the functional group and surface morphology of bagasse during cascade cellulase enzymatic hydrolysis were also examined by FT-IR and SEM respectively. The results showed that cascade enzymatic hydrolysis was the most efficient way to enhance the sugarcane bagasse sacchari cation. More than 65% of reducing sugar yield with 90.1% of glucose selectivity was achieved at 50 oC, pH=4.8 for 72 h (1200 r/min) with cellulase I of 7.5 FPU/g substrate and cellulase II of 5 FPU/g substrate.     

Assessment of endoglucanase activity by analyzing the degree of cellulose polymerization and high-throughput analysis by near-infrared spectroscopy

We developed a novel and practical assessment technique for endoglucanase (EG) activity by measuring the degree of polymerization (DP) of cellulose from Eucalyptus globulus. This evaluation method demonstrated that EG II from Trichoderma reesei had higher endoglucanase activity than EG I, which has not been detected in conventional experiments using carboxymethyl cellulose as a model substrate. In addition, a high-throughput protocol for DP measurement was developed by using near-infrared spectroscopy combined with a multivariate analysis. Interpreting the regression coefficient, a reciprocal correlation was observed between the relative crystallinity of the cellulosic residue after enzymatic hydrolysis and the DP.     

Amperometric glucose biosensor based on a gold nanorods/cellulose acetate composite film as immobilization matrix

We report on the utilization of gold nanorods to create a highly responsive glucose biosensor. The feasibility of an amperometric glucose biosensor based on immobilization of glucose oxidase (GOx) in gold nanorod is investigated. GOx is simply mixed with gold nanorods and cross-linked with a cellulose acetate (CA) medium by glutaraldehyde. The adsorption of GOx on the gold nanorods is confirmed by X-ray photoelectron spectroscopy (XPS) measurements. Circular dichroism (CD) and UV-spectrum results show that the activity of GOx was preserved after conjugating with gold nanorods. The current response of modified electrode is 10 times higher than that of without gold nanorods. Under optimal conditions, the biosensor shows high sensitivity (8.4 μA cm⁻² mM⁻¹), low detection limit (2 × 10⁻⁵ M), good storage stability and high affinity to glucose (). A linear calibration plot is obtained in the wide concentration range from 3 × 10⁻⁵ to 2.2 × 10⁻³ M.     

Conversions between ordered and disordered cellulose. Effects of mechanical treatment followed by cyclic wetting and drying

An investigation into the effects of mechanical treatment and hydration on the order of cellulose substrates (microcrystalline cellulose and Cladophora cellulose) was performed by the use of ball milling followed by cyclic wetting and drying. The results, monitored by¹³C-CP/MAS NMR-spectroscopy, were evaluated by calculation of the crystallinity indices and principal component analysis of the NMR data acquired. The results showed that a large part of the disorder induced by the mechanical treatment of cellulose by ball milling is reversible and reordering upon hydration leads to the cellulose I form initially present. The C4 signals corresponding to the reversibly disordered cellulose chains are observed in the amorphous region between 79 and 86 ppm in the¹³C-CP/MAS NMR-spectra together with signals from cellulose chains on the surface of ordered regions. The peak cluster which contains the C2, C3 and C5 ring carbons can be divided into two specific spectral regions; one between 74 and 77 ppm largely originates from ring carbons within disordered cellulose structures, and one between 70 and 74 ppm contains larger contributions from ordered cellulose. The behaviour of the celluloses upon milling is in accordance with a concept of ordered cellulose fibrils containing amorphous cellulose mainly as surface layers and induced reversible lattice distortions.     

Influence of cellulose polymorphs on the polypropylene crystallization

Results of the hitherto research work on alkalisation of lignocellulosic materials have been much divergent. In view of the above, the subject of this study is mercerization of cellulose from pine wood. This choice of the subject permitted observation of transformation of cellulose I to cellulose II with no participation of other components of lignocellulosic materials. According to X-ray results, during mercerization the isolated cellulose was easily (completely) transformed into cellulose II variety, while the pine wood was converted more slowly to cellulose II polymorphs. Therefore, it could be concluded that the presence of lignin and hemicelluloses in wood prevented the transformation from cellulose I to II. The main objective of this research was to establish the effect of cellulose varieties on the nucleation ability of different fillers by using differential scanning calorimetry (DSC) and polarizing microscopy. The nucleating effect of the fillers occurs only in the presence of cellulose I variety. In contrast, the presence of cellulose II variety seems to practically eliminate the nucleating effect of the fillers. Moreover, nucleation of the mercerized wood (mixture of cellulose I and II) can be also observed, but this effect is not strong. It should be emphasised that as yet no correlation has been reported between the quantitative composition of cellulose polymorphic forms (appearing not only in wood, but in cellulose isolated from wood as well) and the nucleation ability of lignocellulosic fillers.     

Cellulose loading and water sorption value as important parameters for the enzymatic hydrolysis of cellulose

The enzymatic hydrolysis of cotton raw cellulose (RC) samples, sieved RC samples through meshes <100 (CS1), 100–200 (C12), 200–400 (C24), mercerized RC samples (M-C), freeze-dried RC (RC-FD) samples, microcrystalline cellulose Avicel, bacterial cellulose (BC), raw sisal pulp and mercerized sisal pulp (S-M) was performed at cellulose-to-cellulase mass ratios of 1,000:1, 699:1, 400:1, 100:1 and 10:1. The index of crystallinity and water sorption values were quantified for all samples. The morphological features were analyzed by means of scanning electron microscopy (SEM). For cellulose-to-cellulase mass ratio of 100:1 and 10:1, the maximum hydrolysis extents of cellulose samples after 24 h reaction could not be correlated with their physical characteristics. However, hydrolyses of samples with large water sorption values were faster than those with lower water sorption values. The hydrolysis efficiency decreased when the cellulose-to-cellulase mass ratio was greater than 400:1; under this condition a remarkable dependence of the hydrolysis yield on the type of cellulosic sample was observed. The water sorption ability could be directly correlated with the hydrolysis extent, except for RC-FD and BC samples, which presented the lowest values. In the former, freeze-drying has led to pore collapse, with concomitant reduction of the amount of adsorbed water. For the latter sample, the densely packed structure made the water sorption slower than in all other samples. Despite of this fact, the presence of nanofibrils on the surface of BC (as detected by SEM) improved the enzyme adsorption, indicating that analysis by complementary techniques should be performed in order to predict the enzymatic hydrolysis efficiency.     

Structure and properties of composites of highly crystalline cellulose with polypropylene: Effects of polypropylene molecular weight

Composite of highly crystalline fibrous cellulose (CE) and polypropylene (PP) of different molecular weights () was prepared via melting-mixing, maleic anhydride grafted polypropylene (MAPP) was used as a compatibilizer. And the effects of molecular weight of PP on the properties of the composites were investigated. Through the studying of mechanical properties, dynamic mechanical properties, melting and crystallization behaviors, thermo-oxidative properties, water absorption behaviors, and the morphology of the composites, it was found that PP with higher molecular weight revealed stronger interfacial interaction with cellulose in the composites. Compared with the lower molecular weight, the composites derived from higher molecular weight of PP exhibited stronger tensile strength at the same cellulose content.     

Synthesis and characterization of microcrystalline cellulose produced from bacterial cellulose

In this study, microcrystalline cellulose (MCC) was prepared from the acid hydrolysis of bacterial cellulose (BC) produced in culture medium of static Acetobacter xylinum. The MCC-BC produced an average particle size between 70 and 90 μm and a degree of polymerization (DP) of 250. The characterization of samples was performed by thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy (SEM). The MCC shows a lower thermal stability than the pristine cellulose, which was expected due to the decrease in the DP during the hydrolysis process. In addition, from X-ray diffractograms, we observed a change in the crystalline structure. The images of SEM for the BC and MCC show clear differences with modifications of BC fiber structure and production of particles with characteristics similar to commercial MCC.     

Auger recombination dynamics in clusters

Electronic relaxation dynamics following interband excitation from the 6s to the 6p band in mass selected clusters are measured through femtosecond time-resolved photoelectron imaging (TRPEI). This interband transition is pumped at 4.65 eV and probed at 1.55 eV. Auger decay of occurs on a timescale of 490 ± 100 fs, and a similar time constant is seen for the transient excited state population created by the pump pulse. These time constants are an order of magnitude faster than those seen in previous experiments in which the lone p-electron in was excited within the p-band. The results presented here imply that substantial relaxation of either electrons in the p-band or the hole in the s-band takes place prior to Auger emission, with electron–electron scattering playing a key role in the fast observed dynamics.     

Spectroscopy of Ru(II) polypyridyl complexes used as intercalators in DNA: Towards a theoretical study of the light switch effect

The absorption spectroscopy of [Ru(phen)₂dppz]²⁺ and [Ru(tap)₂dppz]²⁺ (phen = 1,10-phenanthroline, tap = 1,4,5,8-tetraazaphenanthrene; dppz = dipyridophenazine) complexes used as molecular light switches by intercalation in DNA has been analysed by means of Time-Dependent Density Functional Theory (TD-DFT). The electronic ground state structures have been optimized at the DFT (B3LYP) level of theory. The absorption spectra are characterized by a high density of excited states between 500 nm and 250 nm. The absorption spectroscopy of [Ru (phen)₂dppz]²⁺ in vacuum is characterized by metal-to-ligand-charge-transfer (MLCT) transitions corresponding to charge transfer from Ru(II) either to the phen ligands or to the dppz ligand with a strong MLCT () absorption at 411 nm. In contrast, the main feature of the lowest part of the vacuum theoretical spectrum of [Ru(tap)₂dppz]²⁺ between 522 nm and 400 nm is the presence of various excited states such as MLCT (), ligand-to-ligand-charge-transfer LLCT () or intra-ligand IL () states. When taking into account solvent corrections within the polarizable continuum model (PCM) approach (H₂O, CH₃CN) the absorption spectrum of [Ru(tap)₂dppz]²⁺ is dominated by a strong absorption at 388 nm (CH₃CN) or 390 nm (H₂O) assigned to a ¹IL () corresponding to a charge transfer from the outside end of the dppz ligand to the site of coordination to Ru(II). These differences in the absorption spectra of the two Ru(II) complexes have dramatic effects on the mechanism of deactivation of these molecules after irradiation at about 400 nm. In particular, the electronic deficiency at the outside end of the dppz ligand created by absorption to the ¹IL state will favour electron transfer from the guanine to the Ru(II) complex when it is intercalated in DNA.     

Crystal structure of cobalt molybdate hydrate CoMoO4·nH2O

We have determined the crystal structure of the title compound, which has a triclinic cell with cell parameters of , , , α=76.617°, β=84.188°, γ=74.510° and space group . The crystal structure suggests the chemical formula CoMoO₄·3/4H₂O. The structure consists of MoO₄ tetrahedra and CoO₆ octahedra, confirming the earlier X-ray absorption near-edge spectroscopic (XANES) investigation on the hydrate. The comparison of the crystal structures of the hydrate and the α-,β-, and hp-phases shows that the hydrate exhibits metal cation coordinations similar to those of the β-phase, but had arrangements of CoO₆ and MoO_n polyhedra similar to those of the hp-phase.