Preparation of a H3PW12O40 Deposited Chitosan Coated Iron Oxide Magnetic Core-Shell Nanocomposite for Friedel-Crafts Acylation.

A novel H3PW12O40 deposited chitosan coated iron oxide magnetic core-shell nanocomposite (Fe3O4@CS@HPW) was prepared via a facile approach. Fe3O4 nanoparticles were first coated with crosslinking-agent-free chitosan, and then H3PW12O40 was loaded onto the surface of chitosan as an outer shell. The resultant nanocomposite was well characterized by Brunauer-Emmett-Teller surface area analysis (BET), inductively coupled plasma analysis (ICP), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and elemental mappings. Fe3O4@CS@HPW showed better catalytic performance than its counterpart with a chitosan-crosslinked shell in the Friedel-Crafts acylation of anisole to 4-methoxyacetophenone under solvent-free conditions, and can be easily separated by an external magnetic field and recycled effectively.

Biomass-Derived N-doped Carbon Materials with Silica-Supported Ultrasmall ZnO Nanoparticles: Robust Catalysts for the Green Synthesis of Benzimidazoles.

Ultrasmall ZnO nanoparticles anchored on N-doped carbon materials with a silica support (ZnO/SiO2 -NC) were fabricated from chitosan and metal ions by using a one-pot self-assembly strategy and were successfully applied to the synthesis of 2-arylbenzimidazoles under mild conditions. These catalysts showed excellent stability and could be used six times without any loss of conversion and selectivity. The use of silica gel and the biomass chitosan as a source of hydrophilic N-doped carbon materials facilitated the uniform dispersion of the ZnO nanoparticles in methanol and therefore the contact of these nanoparticles with reactants, thus contributing to a high catalytic performance. TEM analysis showed that the ZnO nanoparticles were around 2.55 nm in diameter and uniformly distributed on the support surface. The binding behavior of ZnO and N-doped carbon materials affected the catalytic activity. Interestingly, temperature-programmed NH3 desorption indicated that the interactions between ZnO and N-doped carbon materials might induce the presence of more acidic sites in these catalysts, thus resulting in enhanced activity and hence promoting this transformation.

Application of solubility parameters in 1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol organogel in binary organic mixtures.

The gelation behavior of 1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (DMDBS) in binary solvents has been systematically investigated. DMDBS is soluble in DMSO and insoluble in toluene (apolar) or 1-propanol (polar). When DMSO is added to a poor solvent at a certain volume fraction, DMDBS forms an organogel in the mixed solvent. With increasing DMSO content, the minimum gelation concentration increases and the gel-to-sol transition temperature decreases in both systems. However, compared with those in toluene-DMSO mixtures, the gelation ability and thermal stability are better in 1-propanol-DMSO mixtures. Scanning electron microscopy images reveal that the gelators aggregate to form three-dimensional networks. X-ray diffraction shows that the gel has a lamellar structure, which is different from the structure of the precipitate. Fourier transform infrared results reveal H-bonding is the main driving force for self-aggregation and indicate that stronger H-bonding interactions exist between gelators in 1-propanol-DMSO mixtures in contrast with toluene-DMSO mixtures. Attempts have been taken to correlate solvent parameters to gelation behavior in binary solvents. A Teas plot exhibits distinctly different solvent zones in the studied mixed solvents. The polar parameter (δp) indicates a narrow favorable domain for gel formation in the range of 1.64-7.99 MPa(1/2) for some apolar solvent-DMSO mixtures. The hydrogen-bonding parameter (δh) predicts that gelation occurs for values of 14.00-16.50 MPa(1/2) for some polar solvent-DMSO mixtures. The result may have potential applications in predicting the gelation behavior of 1,3:2,4-di-O-benzylidene-d-sorbitol derivatives in mixed solvents.

Plant-generated artificial small RNAs mediated aphid resistance.

BACKGROUND: RNA silencing is an important mechanism for regulation of endogenous gene expression and defense against genomic intruders in plants. This natural defense system was adopted to generate virus-resistant plants even before the mechanism of RNA silencing was unveiled. With the clarification of that mechanism, transgenic antiviral plants were developed that expressed artificial virus-specific hairpin RNAs (hpRNAs) or microRNAs (amiRNAs) in host plants. Previous works also showed that plant-mediated RNA silencing technology could be a practical method for constructing insect-resistant plants by expressing hpRNAs targeting essential genes of insects. METHODOLOGY/PRINCIPAL FINDINGS: In this study, we chose aphid Myzus persicae of order Hemiptera as a target insect. To screen for aphid genes vulnerable to attack by plant-mediated RNA silencing to establish plant aphid resistance, we selected nine genes of M. persicae as silencing targets, and constructed their hpRNA-expressing vectors. For the acetylcholinesterase 2 coding gene (MpAChE2), two amiRNA-expressing vectors were also constructed. The vectors were transformed into tobacco plants (Nicotiana tabacum cv. Xanti). Insect challenge assays showed that most of the transgenic plants gained aphid resistance, among which those expressing hpRNAs targeting V-type proton ATPase subunit E-like (V-ATPaseE) or tubulin folding cofactor D (TBCD) genes displayed stronger aphicidal activity. The transgenic plants expressing amiRNAs targeting two different sites in the MpAChE2 gene exhibited better aphid resistance than the plants expressing MpAChE2-specific hpRNA. CONCLUSIONS/SIGNIFICANCE: Our results indicated that plant-mediated insect-RNA silencing might be an effective way to develop plants resistant to insects with piercing-sucking mouthparts, and both the selection of vulnerable target genes and the biogenetic type of the small RNAs were crucial for the effectiveness of aphid control. The expression of insect-specific amiRNA is a promising and preferable approach to engineer plants resistant to aphids and, possibly, to other plant-infesting insects.

Application of solubility parameters in a D-sorbitol-based organogel in binary organic mixtures.

The gelation behaviour of a low molecular weight gelator 2,4-(3,4-dichlorobenzylidene)-D-sorbitol (DCBS) in a binary solvent system has been studied. DCBS was soluble in pure ethanol and insoluble in pure methylcyclohexane. However, DCBS formed opaque gels in ethanol-methylcyclohexane mixtures when the methylcyclohexane content varied from 50% to 80%. Within this range, an increase in the amount of methylcyclohexane reduced the gelation time and also caused the minimum gelation concentration to decrease. Scanning electron microscopy showed that the three-dimensional network structures of the xerogels became denser (from tape-like structures to uniform fibres) when the methylcyclohexane content increased from 40% to 80%. The precipitates that formed in 90% and 100% methylcyclohexane had rod-like structures. X-ray diffraction of the xerogels showed that in the gel state, the DCBS gelator had lamellar packing, which was different from the structure of the precipitate. Fourier transform infrared spectroscopy of the xerogels showed that H-bonding was a driving force for the self-aggregation of the DCBS and it was enhanced as the methylcyclohexane content increased. To estimate the gelator-solvent interactions, the Flory-Huggins parameter was calculated for the DCBS gelator in the binary mixed solvent systems. Based on the values of the Flory-Huggins parameter, the gelation behaviours could be grouped into four domains (solution, partial gel, gel and precipitation). This is a simple method to predict the gelation behaviour of DCBS in some mixed solvents.

Effects of salt on the gelation mechanism of a D-sorbitol-based hydrogelator.

The effect of salt on the gelatinization of 2,4-(3,4-dichlorobenzylidene)-D-sorbitol (DCBS), a novel low-molecular-weight gelator, was studied. DCBS showed pronounced hydrogelation and the electron micrographs indicated that the hydrogels consists of globular aggregates. Addition of NaCl to the aqueous medium accelerated the gelation process and also caused the gel's morphology to change from globular to long fibers. In addition, the thermal properties of the hydrogels were improved with the addition of NaCl. UV-vis and fluorescence emission spectra showed that extensive aggregation of the phenyl rings was responsible for the gelation. The presence of NaCl induced a red shift in the emission peaks of DCBS and a decrease of the pyrene polarity index I1/I3 in the gels, which indicated that there was more π-π stacking in the hydrogels with NaCl than in the gels without NaCl. Variable-temperature (1)H NMR spectra further demonstrated that the π-π interactions were enhanced by NaCl. FTIR studies showed that hydrogen bonding was also a contributing factor in the gelation process. Wide-angle X-ray diffraction (WXRD) showed that the hydrogels had a layered structure which did not change with the addition of NaCl. Density functional theory (DFT) calculations indicated the possible molecular packing of the gelator in the nanofibers.