Properties of an in vitro selected Pb2+ cleavage motif

The addition of Pb 2+ to a small RNA molecule consisting of an asymmetric internal loop of six nucleotides results in site-specific cleavage followed by hydrolysis of the 2′,3′-cyclic phosphate intermediate [Pan, T., & Uhlenbeck, O. C. (1992) Nature 358, 560-563]. Here we show that the reaction is highly specific for Pb 2+ and the cleavage rate increases exponentially with pH from 5.5 to 7.0, both in the presence and in the absence of Mg 2+. This suggests that the reaction mechanism involves Pb 2+ hydroxide acting as a base. Several sequence variants of the RNA are found to be equally active in both steps of the reaction, suggesting that they fold into a similar structure.

Replacement of RNA hairpins by in vitro selected tetranucleotides

An in vitro selection method based on the autolytic cleavage of yeast tRNAPhe by Pb2+ was applied to obtain tRNA derivatives with the anticodon hairpin replaced by four single-stranded nucleotides. Based on the rates of the site-specific cleavage by Pb2+ and the presence of a specific UV-induced crosslink, certain tetranucieotide sequences allow proper folding of the rest of the tRNA molecule, wheras others do not. One such successful tetramer sequence was also used to replace the acceptor stem of yeast tRNAPhe and the anticodon hairpin of E.coli tRNAPhe without disrupting folding. These experiments suggest that certain tetramers may be able to replace structurally non essential hairpins in any RNA.

MoO3 nanoparticles dispersed uniformly in carbon matrix : a high capacity composite anode for Li-ion batteries

A MoO₃-carbon nanocomposite was synthesized from a mixture of MoO₃ and graphite by a controlled ball milling procedure. The as-prepared product consists of nanosized MoO₃ particles (2-180 nm) homogeneously distributed in carbon matrix. The nanocomposite acts as a high capacity anode material for lithium-ion batteries and exhibits good cyclic behavior. Its initial capacity exceeds the theoretical capacity of 745 mA h g^-1 in a mixture of MoO₃ and graphite (1:1 by weight), and the stable capacity of 700 mA h g^-1 (94% of the theoretical capacity) is still retained after 120 cycles. The electrode performance is linked with the unique nanoarchitecture of the composite and is compared with the performance of MoO₃-based anode materials reported in the literature previously (nanoparticles, ball milled powders, and carbon-coated nanobelts). The high value of capacity and good cyclic stability of MoO₃-carbon nanocomposite are attractive in respect to those of the reported MoO₃ electrodes.

Ilmenite FeTiO3 nanoflowers and their pseudocapacitance

Pronounced and stable pseudocapacitance has been found in flowerlike FeTiO3 nanostructures that were synthesized from ball-milled ilmenite (natural mineral) under mild hydrothermal conditions. Each nanoflower is composed of many thin petals with a thickness of 5–20 nm and a width of 100–200 nm. The formation of these flowerlike nanostructures is attributed to a dissolution–precipitation mechanism involving an intermediate sodium-containing phase. Electrochemical properties of the obtained FeTiO3 nanostructures are evaluated in aqueous electrolytes. The capacitance of 122 ± 14.5 F/g is measured in 1 M KOH aqueous electrolyte at the current rate of 500 mA/g, and 50 ± 6 F/g is retained at 5 A/g. The material has good long-term cycling stability. According to our data, FeTiO3 nanostructures show functionality as an electrode material for supercapacitors.

Secure localization with attack detection in wireless sensor networks

Rapid technological advances have enabled the development of low-cost sensor networks for various monitoring tasks, where it is important to estimate the positions of a number of regular sensor nodes whose locations cannot be known apriori. We address the problem of localizing the regular nodes with range-based location references obtained from certain anchor nodes referred to as beacons, particularly in an adverse environment where some of the beacons may be compromised. We propose an innovative modular solution featuring two lightweight modules that are for dedicated functionalities, respectively, but can also be closely integrated. First, we harness simple geometric triangular rules and an efficient voting technique to enable the attack detection module, which identifies and filters out malicious location references. We then develop a secure localization module that computes and clusters certain reference points, and the position of the concerned regular node is estimated with the centroid of the most valuable reference points identified. Extensive simulations show that our attack detection module can detect compromised beacons effectively, and the secure localization module can subsequently provide a dependable localization service in terms of bounded estimation error. The integrated system turns out to be tolerant of malicious attacks even in highly challenging scenarios.

Regulation of human pregnane X receptor and its target gene cytochrome P450 3A4 by Chinese herbal compounds and a molecular docking study

1. The pregnane X receptor (PXR) plays a critical role in the regulation of human cytochrome P450 3A4 (CYP3A4) gene. In this study, we investigated the effect of an array of compounds isolated from Chinese herbal medicines on the activity of PXR using a luciferase reporter gene assay in transiently transfected HepG2 and Huh7 cells and on the expression of PXR and CYP3A4 in LS174T cells. Furthermore, molecular docking was performed to investigate the binding modes of herbal compounds with PXR.

2. Praeruptorin A and C, salvianolic acid B, sodium danshensu, protocatechuic aldehyde, cryptotanshinone, emodin, morin, and tanshinone IIA significantly transactivated the CYP3A4 reporter gene construct in either HepG2 or Huh7 cells. The PXR mRNA expression in LS174T cells was significantly induced by physcion, protocatechuic aldehyde, salvianolic acid B, and sodium danshensu. However, epifriedelanol, morin, praeruptorin D, mulberroside A, tanshinone I, and tanshinone IIA significantly down-regulated the expression of PXR mRNA in LS174T cells.

3. All the herbal compounds tested can be readily docked into the ligand-binding cavity of PXR mainly through hydrogen bond and aromatic interactions with Ser247, Gln285, His407, and Arg401.

4. These findings suggest that herbal medicines can significantly regulate PXR and CYP3A4 and this has important implication in herb–drug interactions.

Two-dimensional correlation localized surface plasmon resonance spectroscopy for analysis of the interaction between metal nanoparticles and bovine serum albumin

Time-resolved extinction spectra assisted with two-dimensional correlation spectroscopy (2DCOS) analysis and principal component analysis (PCA) were employed to investigate the interaction between bovine serum albumin (BSA) and metal nanoparticles (NPs). A series of localized surface plasmon resonance (LSPR) spectra of metal NPs were measured just after a small amount of BSA was added into metal colloids. Through 2DCOS analysis, remarkable changes in the intensities of the LSPR were observed. The interaction process was totally divided into three periods according to the PCA. Transmission electron microscopy, dynamic light scattering, and ζ-potential measurements were also employed to characterize the interaction between BSA and metal NPs. The addition of BSA brings silver NPs to aggregate through the electrostatic interaction between them, but it has less effect on gold NPs. In a gold and silver mixed system, gold NPs can affect the interaction of silver NPs and BSA, leading it to weaken. The combination of 2DCOS analysis and LSPR spectroscopy is powerful for exploring the LSPR spectra of the metal NP involved systems. This combined technique holds great potential in LSPR sensing through analysis of slight, slim spectral changes of metal colloids