We report magnetic birefringence measurements up to high fields (17.5 T) of dilute aqueous suspensions of rod-like cellulose nanocrystals with well characterized distributions of lengths, widths and ...thicknesses. We compare these data with three models, one with colinear (1), one with perpendicular cylindrically symmetric tensors for diamagnetic susceptibility and refractive index (2) and one with biaxial diamagnetic anisotropy (3). We find that taking into account polydispersities of length, width, and thickness is essential for accurate fitting and that model 1 is the most appropriate, presumably because of the twisting of the suspended nanocrystal along their long axis. The best-fitted susceptibility anisotropy was Δχ z(xy) = χ zz –(χ xx +χ yy )/2 = −2.44 × 10–6 when considering only the crystalline core of nanocrystals and, more appropriately, Δχ z(xy) = −0.95 × 10–6 when including crystalline core and skin. The latter value is slightly higher than Δχ z(xy) = −0.68(5) × 10–6 deduced from estimations using Pascal’s additivity law. The specific birefringence of the nanocrystals in water was found to be δn 0 = +0.120(2), which is well accounted for by the intrinsic birefringence of crystalline cellulose (δn 0 intr = n ∥–n ⊥ = +0.0744) and the birefringence arising from the slender shape of nanocrystals.
The cyanobacterium Anabaena sp. strain PCC 7120 exhibits dehydration tolerance. The regulation of gene expression in response to dehydration is crucial for the acquisition of dehydration tolerance, ...but the molecular mechanisms underlying dehydration responses remain unknown. In this study, the functions of the response regulator OrrA in the regulation of salt and dehydration responses were investigated. Disruption of orrA abolished or diminished the induction of hundreds of genes in response to salt stress and dehydration. Thus, OrrA is a principal regulator of both stress responses. In particular, OrrA plays a crucial role in dehydration tolerance because an orrA disruptant completely lost the ability to regrow after dehydration. Moreover, in the OrrA regulon, avaKa encoding a protein of unknown function was revealed to be indispensable for dehydration tolerance. OrrA and AvaK are conserved among the terrestrial cyanobacteria, suggesting their conserved functions in dehydration tolerance in cyanobacteria.
Highly porous and strong cellulose aerogels were prepared by gelation of cellulose from aqueous alkali hydroxide/urea solution, followed by drying with supercritical CO2. Their morphology, pore ...structure, and physical properties were characterized by scanning and transmission electron microscopy, X‐ray diffraction, nitrogen adsorption measurements, UV/Vis spectrometry, and tensile tests. The cellulose hydrogel was composed of interconnected fibrils of about 20 nm wide. By using supercritical CO2 drying, the network structure in the hydrogel was well preserved in the aerogel. The results are preliminary but demonstrate the ability of this method to give cellulose aerogels of large surface areas (400–500 m2 g−1) which may be useful as adsorbents, heat/sound insulators, filters, catalyst supports, or carbon aerogel precursors.
No lightweight when it comes to strength: Highly porous and strong cellulose hydrogels are obtained by dissolution of cellulose in aqueous alkali–urea solution followed by regeneration from various solvents. Drying the hydrogels gives rise to cellulose aerogels (see photo, right) which may be useful, for example, as catalyst supports.
A new catalytic oxidation using 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO) and NaClO is applied to hardwood cellulose in water at 60 °C and pH 6.8 with NaClO2 used as a primary oxidant. The ...oxidized celluloses with carboxylate content of approximately 0.8 mmol/g were convertible to highly crystalline and individual fibrils 5 nm in width and at least 2 μm in length by disintegration in water. The oxidized celluloses had no aldehyde groups, and high degrees of polymerization of more than 900. Solid-state 13C NMR and X-ray analyses revealed that the C6 carboxylate groups formed are selectively present on the crystalline fibril surfaces at high densities. Films prepared from the dispersions were transparent and flexible, and exhibited a high tensile strength of 312 MPa even at a low density of 1.47 g/cm3.
Diverse chemical modifications fine-tune the function and metabolism of tRNA. Although tRNA modification is universal in all kingdoms of life, profiles of modifications, their functions, and ...physiological roles have not been elucidated in most organisms including the human pathogen,
(
), the causative agent of tuberculosis. To identify physiologically important modifications, we surveyed the tRNA of
, using tRNA sequencing (tRNA-seq) and genome-mining. Homology searches identified 23 candidate tRNA modifying enzymes that are predicted to create 16 tRNA modifications across all tRNA species. Reverse transcription-derived error signatures in tRNA-seq predicted the sites and presence of nine modifications. Several chemical treatments prior to tRNA-seq expanded the number of predictable modifications. Deletion of
genes encoding two modifying enzymes, TruB and MnmA, eliminated their respective tRNA modifications, validating the presence of modified sites in tRNA species. Furthermore, the absence of
attenuated
growth in macrophages, suggesting that MnmA-dependent tRNA uridine sulfation contributes to
intracellular growth. Our results lay the foundation for unveiling the roles of tRNA modifications in
pathogenesis and developing new therapeutics against tuberculosis.
We demonstrated that a unique polysaccharide with extremely high molecular weight can be easily obtained via a low-cost, mild reaction in a water medium from sucrose, a photosynthetic product. ...α-1,3/1,6-Glucosyltransferase L (GtfL) from Streptococcus salivarius produced water-insoluble α-d-glucan from sucrose at 37 °C. Gel permeation chromatography revealed the molecular weight was extremely high; the weight-average molecular weight values were more than 1,000,000 irrespective of the substrate concentration. The Smith degradation of neat glucan and NMR spectroscopic analyses of the acetyl derivative revealed a structure similar to that of a comb-type graft copolymer, α-d-(1 → 3)-graft-(1 → 6)-glucan. The anhydroglucose units (AGUs) in the main-chain backbone are linked by (1 → 3)-glycosidic bonds, whereas a side chain consisting of four AGUs via (1 → 6)-glycosidic bonds alternately extends from C6 of the main chain.
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•In vitro synthesis of an α-d-glucan with α-1,3/1,6-glucosyltransferase L from S. salivarius.•Easily obtainable glucan with extremely high molecular weight under a mild condition.•Comb-like structure composed of (1 → 3)-linked main chain and (1 → 6)-linked side chains
The physiological roles of free Zn2+ have attracted great attention. To clarify those roles, there has been a need for ratiometric fluorescent Zn2+ probes for practical use. We report the rational ...design and synthesis of a series of ratiometric fluorescent Zn2+ probes. The structures of the probes are based on the 7-hydroxycoumarin structure. We focused on the relationship between the electron-donating ability of the 7-hydroxy group and the excitation spectra of 7-hydroxycoumarins, and exploited that relationship in the design of the ratiometric probes; as a result, most of the synthesized probes showed ratiometric Zn2+-sensing properties. Then, we designed and synthesized ratiometric Zn2+ probes that can be excited with visible light, by choosing adequate substituents on coumarin dyes. Since one of the probes could permeate living cell membranes, we introduced the probe to living RAW264 cells and observed the intracellular Zn2+ concentration via ratiometric fluorescence microscopy. As a result, the ratio value of the probe changed quickly in response to intracellular Zn2+ concentration.
•Biodegradable polyesters were selected to produce microbeads as alternatives to conventional microbeads.•Manufactured polyester microbeads have comparable compression strengths to those of commonly ...used microbeads.•PBSA and P(3HB) microbeads have good biodegradability under marine conditions.
The conventional microbeads in cosmetics and personal care products comprise non-biodegradable plastics, which pollute the marine environment. In the present study, we used a simple melt-homogenizing method to manufacture microbeads from four biodegradable polyesters, i.e., poly(butylene succinate) (PBS), poly(butylene succinate adipate) (PBSA), poly(lactic acid) (PLA), and poly(R)-3-hydroxybutyrate (P(3HB)). We then determined the morphology, compression properties, and biodegradability of each polyester. The microbeads ranged in size from 25 to 200 μm, were almost spherical, and had smooth surfaces, as verified by scanning electron microscopy (SEM). The single microbeads were subjected to compression tests because their mechanical properties are correlated to their sensory performance. The compression strengths of the four plastic microbeads, which were comparable to those of commonly used microbeads such as polyethylene and polypropylene, were widely distributed. In particular, the PBSA and P(3HB) microbeads were readily biodegradable, as evaluated by enzymatic degradation and sea water degradation tests, indicating their potential as alternatives to conventional microbeads.
Nitroxy radical catalyzed oxidation with hypochlorite/bromide (TEMPO-mediated oxidation) was performed on a cellulose hydrogel prepared using LiOH/urea solvent. TEMPO oxidation successfully ...introduced carboxyl groups onto the surface of the cellulose hydrogel with retention of the gel structure and its nanoporous property. The equilibrium measurement of Cu2+ adsorption showed favorable interaction with Cu2+ and high maximum adsorption capacity. In addition, over 98% of the adsorbed Cu2+ was recovered using acid treatment, and the subsequent washing allowed the TEMPO-oxidized gels to be used repeatedly. Furthermore, the TEMPO-oxidized cellulose hydrogel showed high adsorption capacity for other toxic metal ions such as Zn2+, Fe3+, Cd2+, and Cs+.
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