Two new 14-membered cyclopeptide alkaloids from Zizyphus xylopyra

The phytochemical investigation of the bark of Zizyphus xylopyra resulted in the isolation of two new 14-membered ring cyclopeptide alkaloids, xylopyrine-G and xylopyrine H. Their structures have been established by chemical and spectral evidences.     

Solution-phase detection of dual microRNA biomarkers in serum

A strategy for the simultaneous detection of multiple microRNA (miRNA) targets was developed utilizing fluorophore/quencher-labeled oligonucleotide probe sets. Two miRNA targets (miR-155 and miR-103), whose misregulation has afforded them status as putative biomarkers in certain types of cancer, were detected using our assay design. In the absence of target, the complementary fluorophore-probe and quencher-probe hybridize, resulting in a fluorescence resonance energy transfer-based quenching of the fluorescence signal. In the presence of unlabeled target, however, the antisense quencher-probe can hybridize with the target, resulting in increased fluorescence intensity as the quencher-probe is sequestered beyond the Förster radius of the fluorescent-probe. The assay design was tested in multiple matrices of buffer, cellular extract, and serum; and detection limits were found to be matrix-dependent, ranging from 0.34 to 8.89 pmol (3.4–59.3 nM) for miR-155 and 2.90–11.8 pmol (19.3–79.0 nM) for miR-103. Single, double, and triple nucleotide selectivity was also tested. Additionally, miR-155 concentrations were assessed in serum samples obtained directly from breast cancer patients without the need for RNA extraction. This assay is quantitative, possesses a low detection limit, can be applied in multiple complex matrices, and can obtain single-nucleotide selectivity. This method can be employed for the multiplex detection of solution-phase DNA or RNA targets and, more specifically, for the direct detection of serum miRNA biomarkers.     

An overview of commonly used semiconductor nanoparticles in photocatalysis

The depletion of non-renewable resources and rise in global warming has caused great concern to humankind. With a view to use renewable source of energy and to eliminate hazardous chemical compounds from air, soil, and water, photocatalysis utilizing solar energy is becoming a rapidly expanding technology. Semiconductor nanoparticles have the ability to undergo photoinduced electron transfer to an adsorbed particle governed by the band energy positions of the semiconductor and the redox potential of the adsorbate. A brief overview of metal oxides and sulphides that can act as sensitizers for light-induced redox processes due to their electronic structure is presented here.     

Preconcentration method on modified silica fiber for chromium speciation

A new method involving pre-concentration on modified silica fiber is described for the speciation of chromium(III) [Cr(III)] and chromium(VI) [Cr(VI)] in aqueous media. This method is based on the different chelating behavior of Cr(III) and Cr(VI) with morpholine-4-carbodithioate (MDTC). Both complexes are extracted on silica fiber modified by sol-gel technology by using 3-aminopropyltriethoxysilane (APS) as a precursor. All extracted samples are directly injected into an high-performance liquid chromatography injector for the simultaneous determination of Cr(III) and Cr(VI). Cr(VI) forms two different complexes, and Cr(III) forms a single complex with MDTC. Therefore, the concentration of Cr(VI) is determined directly from the peak area obtained at 5.4 min; whereas, the assay of Cr(III) is based on subtracting the peak area of Cr(VI) from the total peak area obtained at 4.3 min. Under the optimized conditions, the limits of detection for Cr(III) and Cr(VI) are found to be 0.7 ng/mL and 0.2 ng/mL, respectively.     

An analytic algorithm for time fractional nonlinear reaction–diffusion equation based on a new iterative method

A new analytic algorithm for highly nonlinear time fractional reaction–diffusion equations is proposed in this paper. The proposed method is an amalgamation of variational iteration method (VIM), Adomian decomposition method (ADM) and further refined by introducing a new correction functional. This new correction functional is obtained from the standard correction functional of VIM by introducing an auxiliary parameter γ and an auxiliary function H(x) in it. Further, a sequence G_n(x, t), with suitably chosen support, is also introduced in the new correction functional. The algorithm is easy to implement and only four to six iterations are sufficient for fairly accurate solutions. The algorithm is tested on Fitzhugh – Nagumo and generalized Fisher equations with nonlinearity ranging from 2 to 5.     

Extensional rheology of a shear-thickening cornstarch and water suspension

A filament-stretching rheometer is used to measure the extensional viscosity of a shear-thickening suspension of cornstarch in water. The experiments are performed at a concentration of 55 wt.%. The shear rheology of these suspensions demonstrates a strong shear-thickening behavior. The extensional rheology of the suspensions demonstrates a Newtonian response at low extension rates. At moderate strain rates, the fluid strain hardens. The speed of the strain hardening and the extensional viscosity achieved increase quickly with increasing extension rate. Above a critical extension rate, the extensional viscosity goes through a maximum and the fluid filaments fail through a brittle fracture at a constant tensile stress. The glassy response of the suspension is likely the result of jamming of particles or clusters of particles at these high extension rates. This same mechanism is responsible for the shear thickening of these suspensions. In capillary breakup extensional rheometry, measurement of these suspensions demonstrates a divergence in the extensional viscosity as the fluid stops draining after a modest strain is accumulated.     

A theoretical perspective on the accuracy of rotational resonance (R 2)-based distance measurements in solid-state NMR

The application of solid-state NMR methodology for bio-molecular structure determination requires the measurement of constraints in the form of ¹³C–¹³C and ¹³C–¹⁵N distances, torsion angles and, in some cases, correlation of the anisotropic interactions. Since the availability of structurally important constraints in the solid state is limited due to lack of sufficient spectral resolution, the accuracy of the measured constraints become vital in studies relating the three-dimensional structure of proteins to its biological functions. Consequently, the theoretical methods employed to quantify the experimental data become important. To accentuate this aspect, we re-examine analytical two-spin models currently employed in the estimation of ¹³C–¹³C distances based on the rotational resonance (R ²) phenomenon. Although the error bars for the estimated distances tend to be in the range 0.5–1.0 Å, R ² experiments are routinely employed in a variety of systems ranging from simple peptides to more complex amyloidogenic proteins. In this article we address this aspect by highlighting the systematic errors introduced by analytical models employing phenomenological damping terms to describe multi-spin effects. Specifically, the spin dynamics in R ² experiments is described using Floquet theory employing two different operator formalisms. The systematic errors introduced by the phenomenological damping terms and their limitations are elucidated in two analytical models and analysed by comparing the results with rigorous numerical simulations.     

Organoboranes—34 : General synthesis of chiral boronic and borinic esters via asymmetric hydroboration-displacement. carbenoidation of chiral borinic esters to acyclic ketones of high enantiomeric purities

Asymmetric hydroboration of appropriate alkenes with diisopinocampheylborane (Ipc₂BH) or monoisopinocampheylborane (IpcBH₂) produces intermediates that readily eliminate α-pinene on treat- ment with acetaldehyde, providing a direct, convenient route to chiral boronic esters of high enantiomeric purities. Mixed chiral trialkylboranes, readily prepared by stepwise hydroboration of appropriate alkenes with IpcBH₂, eliminate α-pinene on treatment with acetaldehyde under very mild conditions. The procedure makes readily available chiral borinic esters of high enantiomeric purities. The synthetic utility of chiral borinic esters is demonstrated by converting them into acyclic ketones including an alarm pheromone of the ant Monica mutica.     

Estimation of a parameter of Morgenstern type bivariate exponential distribution by ranked set sampling

Ranked set sampling is applicable whenever ranking of a set of sampling units can be done easily by a judgement method or based on the measurement of an auxiliary variable on the units selected. In this work, we consider ranked set sampling, in which ranking of units are done based on measurements made on an easily and exactly measurable auxiliary variable X which is correlated with the study variable Y. We then estimate the mean of the study variate Y by the BLUE based on the measurements made on the units of the ranked set sampling regarding the study variable Y, when (X ,Y) follows a Morgenstern type bivariate exponential distribution. We then consider unbalanced multistage ranked set sampling and estimate the mean of the study variate Y by the BLUE based on the observations made on the units of multistage ranked set sample regarding the study variable Y. Efficiency comparison is also made on all estimators considered in this work.     

A note on mixed summation-integral-type operators

Very recently Deo, in the paper “Simultaneous approximation by Lupas operators with weighted function of Szasz operators” [J. Inequal. Pure Appl. Math., 5, No. 4 (2004)] claimed to introduce the integral modifications of Lupas operators. These operators were first introduced in 1993 by Gupta and Srivastava. They estimated the simultaneous approximation for these operators and called them Baskakov-Szasz operators. There are several misprints in the paper by Deo. This motivated us to perform subsequent investigations in this direction. We extend the study and estimate a saturation result in simultaneous approximation for the linear combinations of these summation-integral-type operators. Published in Ukrains’kyi Matematychnyi Zhurnal, Vol. 59, No. 8, pp. 1135–1139, August, 2007.