Enzymatic hydrolysis of native cellulose nanofibrils and other cellulose model films: effect of surface structure

Model films of native cellulose nanofibrils, which contain both crystalline cellulose I and amorphous domains, were used to investigate the dynamics and activities of cellulase enzymes. The enzyme binding and degradation of nanofibril films were compared with those for other films of cellulose, namely, Langmuir-Schaefer and spin-coated regenerated cellulose, as well as cellulose nanocrystal cast films. Quartz crystal microbalance with dissipation (QCM-D) was used to monitor the changes in frequency and energy dissipation during incubation at varying enzyme concentrations and experimental temperatures. Structural and morphological changes of the cellulose films upon incubation with enzymes were evaluated by using atomic force microscopy. The QCM-D results revealed that the rate of enzymatic degradation of the nanofibril films was much faster compared to the other types of cellulosic films. Higher enzyme loads did not dramatically increase the already fast degradation rate. Real-time measurements of the coupled contributions of enzyme binding and hydrolytic reactions were fitted to an empirical model that closely described the cellulase activities. The hydrolytic potential of the cellulase mixture was found to be considerably affected by the nature of the substrates, especially their crystallinity and morphology. The implications of these observations are discussed in this report.     

Topochemical modification of cotton fibres with carboxymethyl cellulose

Adsorption of carboxymethyl cellulose (CMC) as a method to introduce charged (ionizable) groups onto cellulose cotton fibre surfaces was investigated. The method was based on application of a previously published method used for wood fibres. The amount of adsorbed ionizable groups was determined indirectly by analysis of CMC in solution by the phenol–sulphuric acid method and directly by conductometric titration of the fibres. Results from the two methods correlated well. The molecular weight and purity of the CMC had an influence on its adsorption onto cotton; high molecular weight CMC was preferentially adsorbed. The adsorbed charge correlated linearly with the amount of CMC adsorbed. The total charge of the cotton fibres could be increased by more than 50% by adsorption of CMC. It is expected that this modification procedure can be used in a wide spectrum of practical applications. Lidija Fras Zemljič and Karin Stana-Kleinschek are the members of the European Polysaccharide Network of Excellence (EPNOE).     

Avoiding Carbothermal Reduction: Distillation of Alkoxysilanes from Biogenic,Green, and Sustainable Sources

The direct depolymerization of SiO₂ to distillable alkoxysilanes has been explored repeatedly without success for 85 years as an alternative to carbothermal reduction (1900 °C) to Si_met, followed by treatment with ROH. We report herein the base‐catalyzed depolymerization of SiO₂ with diols to form distillable spirocyclic alkoxysilanes and Si(OEt)₄. Thus, 2‐methyl‐2,4‐pentanediol, 2,2,4‐trimethyl‐1,3‐pentanediol, or ethylene glycol (EGH₂) react with silica sources, such as rice hull ash, in the presence of NaOH (10 %) to form H₂O and distillable spirocyclic alkoxysilanes [bis(2‐methyl‐2,4‐pentanediolato) silicate, bis(2,2,4‐trimethyl‐1,3‐pentanediolato) silicate or Si(eg)₂ polymer with 5–98 % conversion, as governed by surface area/crystallinity. Si(eg)₂ or bis(2‐methyl‐2,4‐pentanediolato) silicate reacted with EtOH and catalytic acid to give Si(OEt)₄ in 60 % yield, thus providing inexpensive routes to high‐purity precipitated or fumed silica and compounds with single Si−C bonds.     

Cellulose nanocrystal submonolayers by spin coating

Dilute concentrations of cellulose nanocrystal solutions were spin coated onto different substrates to investigate the effect of the substrate on the nanocrystal submonolayers. Three substrates were probed: silica, titania, and amorphous cellulose. According to atomic force microscopy (AFM) images, anionic cellulose nanocrystals formed small aggregates on the anionic silica substrate, whereas a uniform two-dimensional distribution of nanocrystals was achieved on the cationic titania substrate. The uniform distribution of cellulose nanocrystal submonolayers on titania is an important factor when dimensional analysis of the nanocrystals is desired. Furthermore, the amount of nanocrystals deposited on titania was multifold in comparison to the amounts on silica, as revealed by AFM image analysis and X-ray photoelectron spectroscopy. Amorphous cellulose, the third substrate, resulted in a somewhat homogeneous distribution of the nanocrystal submonolayers, but the amounts were as low as those on the silica substrate. These differences in the cellulose nanocrystal deposition were attributed to electrostatic effects: anionic cellulose nanocrystals are adsorbed on cationic titania in addition to the normal spin coating deposition. The anionic silica surface, on the other hand, causes aggregation of the weakly anionic cellulose nanocrystals which are forced on the repulsive substrate by spin coating. The electrostatically driven adsorption also influences the film thickness of continuous ultrathin films of cellulose nanocrystals. The thicker films of charged nanocrystals on a substrate of opposite charge means that the film thickness is not independent of the substrate when spin coating cellulose nanocrystals in the ultrathin regime (<100 nm).     

Analysis of hydrogen peroxide and an organic hydroperoxide via the electrocatalytic Fenton reaction

A new concept for the electrochemical detection of hydrogen peroxide, and organic hydroperoxides is presented. One advantage of the significance of this technique is that it does not require chemical modification of the electrode or addition of enzymes. Direct electro-reduction of the peroxides was not observed on the carbon disk electrode as it is a kinetically slow process. Redox cycling of the iron complex is apparent as Fe^IIEDTA rapidly reduces the O-O bond of the peroxides (Fenton Reaction) upon its production by the kinetically facile electro-reduction of Fe^IIIEDTA. This provides an enhanced and steady-state reductive current as observed by cyclic voltammetry. These features are indicative of the electrocatalytic (EC′) mechanism. A calibration curve was constructed based on the chronoamperometric response at 32 s and a detection limit for H₂O₂ and t-butyl hydroperoxide was calculated to be 0.4 μM and 20 µM, respectively. This difference is attributable to the rate in which the iron(II) complex reduces the O-O bond, H₂O₂ (2.3 × 10⁵ M^− 1 s^− 1) being faster than for the organic peroxide (5.1 × 10⁴ M^− 1 s^− 1). The Fe^IIEDTA complex was observed to be unreactive toward dialkyl peroxides. This method may find use in the detection of peroxide-based explosives or in enzymatic assays as it is rapid, simple, inexpensive and should prove to be robust.     

An optimization approach for communal home meal delivery service: A case study

This paper is the first to discuss the communal home meal delivery problem. The problem can be modelled as a multiple travelling salesman problem with time windows, that is closely related to the well-studied vehicle routing problem with time windows. Experimental results are reported for a real-life case study from Central Finland over several alternative scenarios using the SPIDER commercial solver. The comparison with current practice reveals that a significant savings potential can be obtained using off-the-shelf optimization tools. As such, the potential for supporting real-life communal routing problems can be considered to be important for VRP practitioners.     

A powerful route minimization heuristic for the vehicle routing problem with time windows

We suggest an efficient route minimization heuristic for the vehicle routing problem with time windows. The heuristic is based on the ejection pool, powerful insertion and guided local search strategies. Experimental results on the Gehring and Homberger’s benchmarks demonstrate that our algorithm outperforms previous approaches and found 18 new best-known solutions.     

Electron ionization mass spectra of phosphorus-containing heterocycles. II. 1,2,3,4,4a,5,6,7,8,8a-decahydro-1,3,2-benzodiazaphosphinine 2-oxides

The electron ionization mass spectra of cis- and trans-fused 1,2,3,4,4a,5,6,7,8,8a-decahydro-1,3,2-benzodiazaphosphinine 2-oxides (1-17) were recorded, and the fragmentation pathways were established and compared with those of 1,4,4a,5,6,7,8,8a-octahydro-2H-3,1,2-benzoxazaphosphinine 2-oxides. In general, the mass spectral behaviors of the isomeric compounds were very similar and it was mostly impossible to differentiate them from each other on the basis of the relative abundances of their characteristic fragment ions. The compounds in which R(2) = Ph or OPh exhibited a series of common fragments, e.g. [R(2)H](+), R(2)PONHR(1(3)+), [M-C(3)H(7)](+) and [M-C(4)H(9)](+), the latter two ions being present in the spectra of only two of the derivatives with an N(CH(2)CH(2)Cl)(2) substituent on the P atom. When R(2) = Ph, numerous other alkyl radicals, alkenes and a cycloalkane were also ejected and these compounds also lost NH(2), NH(3), CH(3)N, CH(4)N or CH(3)NH(2). The compounds with an N(CH(2)CH(2)Cl)(2) substituent on the P atom most closely resembled their 3,1,2-O,N,P analogs in respect of the dominant role of this substituent.