Beyond the Surface: A Methodological Exploration of Enzyme Impact along the Cellulose Fiber Cross-Section.

Despite the wide range of analytical tools available for the characterization of cellulose, the in-depth characterization of inhomogeneous, layered cellulose fiber structures remains a challenge. When treating fibers or spinning man-made fibers, the question always arises as to whether the changes in the fiber structure affect only the surface or the entire fiber. Here, we developed an analysis tool based on the sequential limited dissolution of cellulose fiber layers. The method can reveal potential differences in fiber properties along the cross-sectional profile of natural or man-made cellulose fibers. In this analytical approach, carbonyl groups are labeled with a carbonyl selective fluorescence label (CCOA), after which thin fiber layers are sequentially dissolved with the solvent system DMAc/LiCl (9% w/v) and analyzed with size exclusion chromatography coupled with light scattering and fluorescence detection. The analysis of these fractions allowed for the recording of the changes in the chemical structure across the layers, resulting in a detailed cross-sectional profile of the different functionalities and molecular weight distributions. The method was optimized and tested in practice with LPMO (lytic polysaccharide monooxygenase)-treated cotton fibers, where it revealed the depth of fiber modification by the enzyme.

A novel approach to analyze the impact of lytic polysaccharide monooxygenases (LPMOs) on cellulosic fibres.

Enzymatic treatment of cellulosic fibres is a green alternative to classical chemical modification. For many applications, mild procedures for cellulose alteration are sufficient, in which the fibre structure and, therefore, the mechanical performance of cellulosic fibres are preserved. Lytic polysaccharide monooxygenases (LPMOs) bear a great potential to become a green reagent for such targeted cellulose modifications. An obstacle for wide implementation of LPMOs in tailored cellulose chemistry is the lack of suitable techniques to precisely monitor the LPMO impact on the polymer. Soluble oxidized cello-oligomers can be quantified using chromatographic and mass-spectrometric techniques. A considerable portion of the oxidized sites, however, remain on the insoluble cellulose fibres, and their quantification is difficult. Here, we describe a method for the simultaneous quantification of oxidized sites on cellulose fibres and changes in their molar mass distribution after treatment with LPMOs. The method is based on quantitative, heterogeneous, carbonyl-selective labelling with a fluorescent label (CCOA) followed by cellulose dissolution and size-exclusion chromatography (SEC). Application of the method to reactions of seven different LPMOs with pure cellulose fibres revealed pronounced functional differences between the enzymes, showing that this CCOA/SEC/MALS method is a promising tool to better understand the catalytic action of LPMOs.

Viscoacoustic model for near-field ultrasonic levitation.

Ultrasonic near-field levitation allows for contactless support and transportation of an object over vibrating surface. We developed an accurate model predicting pressure distribution in the gap between the surface and levitating object. The formulation covers a wide range of the air flow regimes: from viscous squeezed flow dominating in small gap to acoustic wave propagation in larger gap. The paper explains derivation of the governing equations from the basic fluid dynamics. The nonreflective boundary conditions were developed to properly define air flow at the outlet. Comparing to direct computational fluid dynamics modeling our approach allows achieving good accuracy while keeping the computation cost low. Using the model we studied the levitation force as a function of gap distance. It was shown that there are three distinguished flow regimes: purely viscous, viscoacoustic, and acoustic. The regimes are defined by the balance of viscous and inertial forces. In the viscous regime the pressure in the gap is close to uniform while in the intermediate viscoacoustic and the acoustic regimes the pressure profile is wavy. The model was validated by a dedicated levitation experiment and compared to similar published results.