The local molecular environment is a critical factor which should be taken into account when measuring single-molecule electrical properties in condensed media or in the design of future molecular electronic or single molecule sensing devices. Supramolecular interactions can be used to control the local environment in molecular assemblies and have been used to create microenvironments, for instance, for chemical reactions. Here, we use supramolecular interactions to create microenvironments which influence the electrical conductance of single molecule wires. Cucurbit[8]uril (CB[8]) with a large hydrophobic cavity was used to host the viologen (bipyridinium) molecular wires forming a 1:1 supramolecular complex. Significant increases in the viologen wire single molecule conductances are observed when it is threaded into CB[8] due to large changes of the molecular microenvironment. The results were interpreted within the framework of a Marcus-type model for electron transfer as arising from a reduction in outer-sphere reorganization energy when the viologen is confined within the hydrophobic CB[8] cavity.

BackgroundRNA 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 findingsIn 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/SignificanceOur 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.

A two-component gel of melamine (M) and 2-ethylhexylphosphoric acid mono-2-ethylhexyl ester (P) in binary solvent mixtures has been investigated. PM formed opaque gels at a certain water volume fraction in methanol-water mixtures. The minimum gelation concentration (MGC) decreased with increasing the water content, whereas the gel-to-sol transition temperature (T gel ) increased firstly and had a decline at 60% water content. Scanning electron microscopy (SEM) images revealed that the gel fibers formed macroscopic aggregates when an appropriate amount of water was added. When the water content was increased from 25% to 50%, the network in the mixed-solvents became more "uniform" and "denser" and when the water content was increased to 60%, fibers packed more closely together and formed a sheet-like structure. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy patterns (FTIR) of xerogels showed that the gelator had a similar packing mode in the gel state, which was different from the precipitation state. The solvent viscosity had a good correlation with SEM images and gel-to-sol temperature. Hansen solubility parameters and Flory-Huggins parameters were calculated to estimate the gelator-solvent interaction. The results indicated that gelation occurred when the gelator-solvent interaction was neither too strong nor too weak, otherwise solution or precipitate was obtained.