Rheological Study of Physical Cross-Linked Quaternized Cellulose Hydrogels Induced by β-Glycerophosphate

As a weak base, β-glycerophosphate (β-GP) was used to spontaneously initiate gelation of quaternized cellulose (QC) solutions at body temperature. The QC/β-GP solutions are flowable below or at room temperature but gel rapidly under physiological conditions. In order to clarify the sol–gel transition process of the QC/β-GP systems, the complex was investigated by dynamic viscoelastic measurements. The shear storage modulus (<i>G′</i>) and loss modulus (<i>G</i>″) as a function of (1) concentration of β-GP (<i>c</i>_β‑GP), (2) concentration of QC (<i>c</i>_QC), (3) degree of substitution (DS; i.e., the average number of substituted hydroxyl groups in the anhydroglucose unit) of QC, (4) viscosity-average molecular weight (<i>M</i>_η) of QC, and (5) solvent medium were studied by the oscillatory rheology. The sol–gel transition temperature of QC/β-GP solutions decreased with an increase of <i>c</i>_QC and <i>c</i>_β‑GP, the <i>M</i>_η of QC, and a decrease of the DS of QC and pH of the solvent. The sol–gel transition temperature and time could be easily controlled by adjusting the concentrations of QC and β-GP, <i>M</i>_η and DS of QC, and the solvent medium. Gels formed after heating were irreversible; i.e., after cooling to lower temperature they could not be dissolved to become liquid again. The aggregation and entanglement of QC chains, electrostatic interaction, and hydrogen bonding between QC and β-GP were the main factors responsible for the irreversible sol–gel transition behavior of QC/β-GP systems

Systematic Analysis and Identification of Stress-Responsive Genes of the NAC Gene Family in <i>Brachypodium distachyon</i>

<div><p>Plant-specific NAC proteins are one of the largest families of transcription factors in plants, and members of this family have been characterized with roles in the regulation of diverse biological processes, including development and stress responses. In the present study, we identified 101 putative NAC domain-encoding genes (<i>BdNACs</i>) through systematic sequence analysis in <i>Brachypodium distachyon</i>, a new model plant of family Poaceae. BdNAC proteins were phylogenetically clustered into 13 groups, and each group possesses similar motif compositions. Phylogenetic analysis using known stress-related NACs from Arabidopsis and rice as query sequences identified 18 <i>BdNACs</i> as putative stress-responsive genes. <i>In silico</i> promoter analysis showed that almost all <i>BdNAC</i> genes contain putative stress-related cis-elements in their promoter regions. Expression profile of <i>BdNAC</i> genes in response to abiotic stresses and phytohormones was analyzed by quantitative real-time RT-PCR. Several putative stress-responsive <i>BdNAC</i> genes, including <i>BdNAC003</i> and <i>BdNAC044</i> which is ortholog of known stress-responsive rice gene <i>SNAC1</i> and <i>SNAC2</i>, respectively, were highly regulated by multiple abiotic stresses and stress-related phytohormone treatments. Taken together, our results presented here would be helpful in laying the foundation for understanding of the complex mechanisms of NAC mediated abiotic stress signaling transduction pathways in <i>B</i>. <i>distachyon</i>.</p></div

Greatly Accelerated Condensation of d‑Mannose Diacetonide with Aqueous Formaldehyde (Formalin)

Condensation of d-mannose diacetate with aqueous formaldehyde, a long known quaternary center-generating transformation, was reinvestigated to solve the hidden problem of incomplete conversion, a lasting challenge since 1979 despite many previous efforts. The mysterious cause for the retarded transformation was found to be generation of formic acid by a Cannizzaro reaction. By using additional amounts of base, the reaction time was shortened from 48 h to 100 min and the product was readily isolated in 81% yield

Phylogenetic analysis-based prediction of abiotic stress-related <i>BdNAC</i> genes.

<p>(A). Phylogenetic relationship of NAC proteins from <i>B</i>. <i>distachyon</i>, Arabidopsis and rice. The unroofed phylogenetic tree was constructed using the full-length of 332 NAC proteins from <i>B</i>. <i>distachyon</i>, Arabidopsis and rice by MEGA5. Only the tree topology was presented. The detailed unroofed phylogenetic tree was shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122027#pone.0122027.s006" target="_blank">S6 Fig</a>. (B-F). Clades enriched with stress-related NACs including NAC-n (B), NAC-b (C), NAC-c (D), NAC-j (E) and NAC-k (F). Group NAC-n contains most stress-related NACs (also named it as SNAC), and can be further divided into three subgroups (SNAC-I, SNAC-II and SNAC-III). NAC proteins from <i>B</i>. <i>distachyon</i>, Arabidopsis and rice were denoted by red circle, green triangle and blue diamond, respectively. Known stress-responsive <i>NAC</i> genes from Arabidopsis and rice were indicated in red. Putative stress-related <i>BdNAC</i> genes based on phylogenetic analysis were indicated in blue.</p

Expression profile of <i>BdNAC</i> genes in response to various abiotic stresses.

<p>(A). Hierarchical clustering of expression profile of <i>BdNAC</i> genes in response to drought (D), salinity (S), cold (C) and heat (H) stresses. Three-week-old seedlings were subjected to drought stress (growth without water supply), salt (200 mM NaCl), cold (4°C) and heat (42°C) stresses. Relative expression levels of the <i>BdNAC</i> genes were analyzed by quantitative real-time RT-PCR (qPCR), and log2-transformed fold-change values were used for creating the heatmap (original data were shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122027#pone.0122027.s007" target="_blank">S7 Fig</a>.). Venn diagram illustrated the distribution of the up-regulated (B) or down-regulated (C) <i>BdNAC</i> genes response to different abiotic stresses. The common subset of genes regulated by two or more stresses was marked by the overlapping circle.</p

Phylogenetic relationships, gene structure and motif compositions of <i>BdNAC</i> genes.

<p>(A). The unrooted phylogenetic tree was created in MEGA5 software with the neighbor-joining method with 1,000 bootstrap iterations based on 101 full-length amino acids of BdNAC TFs. Thirteen major phylogenetic groups designated as I to XIII were marked with different color backgrounds. (B). Exon/intron structures of <i>BdNAC</i> genes. Exons and introns were represented by green boxes and black lines, respectively. Sizes of exons and introns could be estimated using the scale at bottom. (C). Schematic representation of the conserved motifs in the BdNAC TFs elucidated by MEME. Each motif was represented by a colored box numbered at the bottom. The black lines represented the non conserved sequences. The length of protein could be estimated using the scale at the bottom. The details of individual motif were shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122027#pone.0122027.s005" target="_blank">S5 Fig</a>.</p

Chromosomal distribution of <i>NAC</i> genes in <i>B</i>. <i>distachyon</i>.

<p>Totally 101 <i>BdNAC</i> genes were mapped to the 5 chromosomal according to their positions in the <i>B</i>. <i>distachyon</i> genome. The chromosome number (Chr1–Chr5) was shown on the top of each chromosome. The number below indicated the number of <i>BdNAC</i> genes in each chromosome. Nine clusters of <i>BdNAC</i> genes were indicated in boxes. The scale bar indicated a chromosomal distance of 10.0 Mb.</p

Circle plot showing segmentally duplicated <i>BdNAC</i> genes on 5 <i>B</i>. <i>distachyon</i> chromosomes.

<p>Grey lines indicated collinear blocks in whole <i>B</i>. <i>distachyon</i> genome, and red lines indicated duplicated <i>BdNAC</i> gene pairs.</p

Biomimetic Hybridization of Kevlar into Silk Fibroin: Nanofibrous Strategy for Improved Mechanic Properties of Flexible Composites and Filtration Membranes

Silk, one of the strongest natural biopolymers, was hybridized with Kevlar, one of the strongest synthetic polymers, through a biomimetic nanofibrous strategy. Regenerated silk materials have outstanding properties in transparency, biocompatibility, biodegradability and sustainability, and promising applications as diverse as in pharmaceutics, electronics, photonic devices and membranes. To compete with super mechanic properties of their natural counterpart, regenerated silk materials have been hybridized with inorganic fillers such as graphene and carbon nanotubes, but frequently lose essential mechanic flexibility. Inspired by the nanofibrous strategy of natural biomaterials (<i>e.g.</i>, silk fibers, hemp and byssal threads of mussels) for fantastic mechanic properties, Kevlar was integrated in regenerated silk materials by combining nanometric fibrillation with proper hydrothermal treatments. The resultant hybrid films showed an ultimate stress and Young’s modulus two times as high as those of pure regenerated SF films. This is not only because of the reinforcing effect of Kevlar nanofibrils, but also because of the increasing content of silk β-sheets. When introducing Kevlar nanofibrils into the membranes of silk nanofibrils assembled by regenerated silk fibroin, the improved mechanic properties further enabled potential applications as pressure-driven nanofiltration membranes and flexible substrates of electronic devices

Novel Cellulose Polyampholyte–Gold Nanoparticle-Based Colorimetric Competition Assay for the Detection of Cysteine and Mercury(II)

We provide a highly sensitive and selective assay to detect cysteine (Cys) and Hg²⁺ in aqueous solutions using Au nanoparticles (NPs) stabilized by carboxylethyl quaternized cellulose (CEQC). This method is based on the thiophilicity of Hg²⁺ and Au NPs as well as the unique optical properties of CEQC-stabilized Au NPs. CEQC chains are good stabilizing agents for Au NPs even in a high-salt solution. The addition of Cys results in the aggregation of CEQC-stabilized Au NPs, which induces the visible color change and obvious redshift in UV–visible absorption spectra. On the other hand, Hg²⁺ is more apt to interact with thiols than Au NPs; thus, it can remove the Cys and trigger Au NP aggregate redispersion again. By taking advantage of this mechanism, a novel off–on colorimetric sensor has been established for Cys and Hg²⁺ detection. This new assay could selectively detect Cys and Hg²⁺ with the detection limits as low as 20 and 40 nM in aqueous solutions, respectively