Nanoparticles coated with poly(octadecyl acrylate) (POA) pour-point depressants are investigated, and the effect of the amount of coating material is investigated and compared with the effect of the coating material without nanomaterial. Pour point depressing performance is demonstrated using a model waxy oil system in order to isolate material performance. The present study focus on the effect of how the amount of coverage of the nanoparticles affects the performance of the nanoparticles. In order to access this information, the adsorption of the poly(octadecyl acrylate) (POA) on silica (the material of the nanoparticles) was determined using a quartz crystal microbalance with dissipation monitoring (QCM-D). Adsorption was performed from two different solvents, toluene and dodecane, because the nanoparticles were been prepared from toluene while the model system used is dodecane-based. Using the QCM-D data, it was possible to prepare nanoparticles with different amounts of poly(octadecyl acrylate), as defined by amount of the silica covered, and investigate the effect of the coating material coverage on the performance of the nanoparticles in the model waxy oil system. The nanoparticle performance was estimated with rheology to determine differences in the strength of the wax gel formed, with differential scanning calorimetry (DSC) to assess the wax appearance temperature and any differences in crystallization, and visual observation of the formed wax with polarized microscopy. Rheological measurements showed that nanoparticles with low POA coverage had almost no effect on the strength of the formed wax gel, while nanoparticles with full coverage of POA significantly lowered the wax gel strength. Nanoparticles with more than full coverage of POA further lowered the strength of the formed wax gel. DSC showed that the wax appearance temperature is lowered by the nanoparticles, and that there is little or no effect when using nanoparticles with more POA than 100% coverage. DSC also showed that the presence of the nanoparticles changes the nature of the wax crystallization, most likely by introducing multiple nucleation centers, causing a sharp peak in crystallization (in contrast to the more broad crystallization of neat wax). Polarized microscopy showed that, in the presence of the nanoparticles, large particles were formed, compared to the added silica. There was also a reduced amount of birefringence, indicating a possible change in wax morphology. This change in wax morphology may hinder efficient formation of a volume spanning gel network, explaining the efficiency of the nanoparticles. By flushing water over a silica surface with adsorbed POA in a QCM-D, it was shown that the POA does not detach from the silica, even when exposed to large amounts of water. This opens up the possibility to recover the nanoparticles with the covering POA after usage, providing possible ecological benefits. The research conducted here shows that it is possible to further optimize the effect of coated nanoparticles on wax gels...
Alginate is a linear polysaccharide from brown algae consisting of 1,4-linked β-d-mannuronic acid (M) and α-l-guluronic acid (G) arranged in M, G, and mixed MG blocks. Alginate was assumed to be indigestible in humans, but bacteria isolated from fecal samples can utilize alginate. Moreover, genomes of some human gut microbiome–associated bacteria encode putative alginate-degrading enzymes. Here, we genome-mined a polysaccharide lyase family 6 alginate lyase from the gut bacterium Bacteroides cellulosilyticus (BcelPL6). The structure of recombinant BcelPL6 was solved by X-ray crystallography to 1.3 Å resolution, revealing a single-domain, monomeric parallel β-helix containing a 10-step asparagine ladder characteristic of alginate-converting parallel β-helix enzymes. Substitutions of the conserved catalytic site residues Lys-249, Arg-270, and His-271 resulted in activity loss. However, imidazole restored the activity of BcelPL6-H271N to 2.5% that of the native enzyme. Molecular docking oriented tetra-mannuronic acid for syn attack correlated with M specificity. Using biochemical analyses, we found that BcelPL6 initially releases unsaturated oligosaccharides of a degree of polymerization of 2–7 from alginate and polyM, which were further degraded to di- and trisaccharides. Unlike other PL6 members, BcelPL6 had low activity on polyMG and none on polyG. Surprisingly, polyG increased BcelPL6 activity on alginate 7-fold. LC–electrospray ionization–MS quantification of products and lack of activity on NaBH4-reduced octa-mannuronic acid indicated that BcelPL6 is an endolyase that further degrades the oligosaccharide products with an intact reducing end. We anticipate that our results advance predictions of the specificity and mode of action of PL6 enzymes.
Reducing end activation of poly-and oligosaccharides by bifunctional dioxyamines and dihydrazides enables aniline-free and cyanoborohydride-free conjugation to aldehyde-containing molecules, particles and surfaces without compromising the chain structure. Chitosans are due to their polycationic character, biodegradability, and bioactivity important candidates for conjugation. Here, we present a kinetic and structural study of the conjugation of a dioxyamine and a dihydrazide to enzymatically produced chitooligosaccharides ranging from N,N'-diacetylchitobiose to a decamer, all having N-acetyl D-glucosamine at the reducing end. Conjugation of the dioxyamine resulted in mixtures of (E)-and (Z)-oximes and β-Npyranoside, whereas the dihydrazide yielded cyclic N-glycosides. Reaction kinetics was essentially independent of DP. Stable secondary amines were in both cases obtained by reduction with α-picoline borane, but higher temperatures were needed to obtain acceptable reduction rate. Comparison to dextran oligomers shows that the nature of the reducing end strongly influences the kinetics of both the conjugation and reduction.
Renewable resources can provide a range of different polysaccharide blocks that can be used to prepare new types of stimuli-responsive polysaccharide-based block copolymers. Alginates are natural polysaccharides widely used as...
Engineered block polysaccharides is a relatively new class of biomacromolecules consisting of chemical assembly of separate block structures at the chain termini. In contrast to conventional, laterally substituted polysaccharide derivatives, the block arrangement allows for much higher preservation of inherent chain properties such as biodegradability and stimuli-responsive self-assembly, while at the same time inducing new macromolecular properties. Abundant, carbon neutral, and even recalcitrant biomass is an excellent source of blocks, opening for numerous new uses of biomass for a wide range of novel biomaterials. Among a limited range of methodologies available for block conjugation, bifunctional linkers allowing for oxyamine and hydrazide 'click' reactions have recently proven useful additions to the repertoire. This article focuses the chemistry and kinetics of these reactions. It also presents some new data with the aim to provide useful protocols and methods for general use towards new block polysaccharides.
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