Quantum dot FRET biosensors that respond to pH, to proteolytic or nucleolytic cleavage, to DNA synthesis, or to a multiplexing combination

Fluorescent acceptors have been immobilized on nanoparticulate quantum dots (QDs), which serve in turn as their FRET donors. The broad excitation and narrow emission bands of QDs mark them as having excellent potential as donors for FRET and, in principle, differently colored QDs could be excited simultaneously. The present work describes the preparation and operation of FRET-based QD bioprobes individually able to detect the actions of protease, deoxyribonuclease, DNA polymerase, or changes in pH. In addition, two such QD-mounted biosensors were excited at a single wavelength, and shown to operate simultaneously and independently of each other in the same sample solution, allowing multiplex detection of the action of a protease, trypsin, in the presence of deoxyribonuclease.     

Application of electrospray ionization tandem mass spectrometry for the rapid and sensitive determination of cobalt in urine

Recently, cobalt (Co) is reported to be taken as a supplement by athletes for improving anaerobic performance. For the diagnosis of abuse, the limit of detection (LOD) of Co in the analysis should be lower than the concentrations of Co in plasma and urine of normal persons. A simple, rapid and sensitive method has been developed for the determination of Co in urine. Co was complexed with diethyldithiocarbamate (DDC) and extracted with isoamyl alcohol in the presence of citric acid. The detection of Co was achieved by injecting a 1-μL aliquot of isoamyl alcohol containing Co-DDC complex directly into an electrospray ionization tandem mass spectrometric (ESI-MS-MS) instrument without chromatographic separation. The quantification was performed using selected reaction monitoring at m/z 291 of the product ion Co(C₄H₁₀NCS)₂⁺ which was produced by collision-induced dissociation from the precursor ion Co(DDC)₂⁺ at m/z 355. ESI-MS-MS data were obtained in less than 10 min with an LOD of 0.05 μg L⁻¹ and a linear calibration range of 0.1-100 μg L⁻¹ using 10 μL of urine. The procedure was validated with certified reference materials (SRM 2670a and SRM 1643e). This method is suitable for the analysis of Co in the laboratories already equipped with an ESI-MS-MS instrument.     

Rh-N-heterocyclic carbene (NHC) complex-catalyzed addition of phenylboronic acid to N-sulfonyl and N-phosphinoyl aldimines

Rh-N-heterocyclic carbene (NHC) complexes were generated in situ from imidazolium salts, [RhCl(cod)](2) and t-BuOK in dioxane. In the presence of a catalytic amount of Rh-NHC complexes, the addition reaction of phenylboronic acid to N-sulfonylarylimines and N-phosphinyolarylimines gave the corresponding amines in high yields.     

Control of aqueous droplets using magnetic and electrostatic forces

Basic control operations were successfully performed on an aqueous droplet using both magnetic and electrostatic forces. In our droplet-based microfluidics, magnetic beads were incorporated in an aqueous droplet as a force mediator. This report describes droplet anchoring and separation of the beads from the droplet using a combination of magnetic and electrostatic forces. When an aqueous droplet is placed in an oil-filled reservoir, the droplet sinks to the bottom, under which an electrode had been placed. The droplet was adsorbed (or anchored) to the bottom surface on the electrode when a DC voltage was applied to the electrode. The magnetic beads were removed with magnetic force after the droplet had been anchored. Surfactant addition into droplet solution was very effective for the elimination of electric charge, which resulted in the stable adsorption of a droplet to hydrophobic substrate under an applied voltage of DC 0.5-3 kV. In a sequential process, small volume of aqueous liquid was successfully transferred using both magnetic and electrostatic forces.     

Disorder in crystalline phases of chiral glass formers 5CB and 8OCB evidenced by the low temperature heat capacity

The heat capacity of two glass formers 5^*CB and 8^*OCB, each of which has two crystalline polymorphs (phases I and II) as well as a glass phase, was determined between 0.35 K and 20 K. The T-linear term of the heat capacity becomes significant below 1 K for both glasses. The glassy crystalline phase II of 5^*CB also shows such contribution, which is consistent with the existence of a residual entropy. Unexpectedly, however, the ‘stable’ phase II of 8^*OCB shows the similar contribution, indicating that this phase is disordered, whereas the glassy crystalline phase I shows no such contribution.     

Kinetic evidence for high reactivity of 3-nitrophenylboronic acid compared to its conjugate boronate ion in reactions with ethylene and propylene glycols

The rate constants for a boronate ion were determined for the first time using the reaction systems of 3-nitrophenylboronic acid (3-NO2PhB(OH)2) with ethylene glycol (EG) and propylene glycol (PG) in an alkaline solution: the rate constants (25 degrees C, I = 0.10 M) for the reactions of 3-NO2PhB(OH)3- are 1.2 M(-1) s(-1) (EG) and 1.5 M(-1) s(-1) (PG), which are at least 10(3) times smaller than those for the reactions of 3-NO 2PhB(OH)2 [1.0 x 10(4) M(-1) s(-1) (EG) and 5.8 x 10(3) M(-1) s(-1) (PG)].     

An ab initio study based on a finite nucleus model for isotope fractionation in the U(III)-U(IV) exchange reaction system

Isotope fractionation in the U(III)-U(IV) reaction system was investigated by a series of atomic relativistic ab initio calculations using the multiconfigurational Dirac-Coulomb Hartree-Fock method. To evaluate the nuclear volume effect on the fractionation, the Fermi statistical distribution function was adopted for nuclear charge density. The isotope fractionation coefficient epsilon resulting from the nuclear volume difference was evaluated from the total electronic energies of U3+ and U4+, based on the theoretical equation proposed by Bigeleisen [J. Am. Chem. Soc. 118, 3676 (1996)]. The calculated fractionation coefficient epsilon in the present work for the isotopic pair 235U and 238U at 293 K is 0.0031, which is quite close to the experimentally observed value of 0.0027. Discussion is extended to the nuclear volume effects on isotopic fractionations in the Pu(III)-Pu(IV) and Eu(II)-Eu(III) exchange systems.     

One-Step Synthesis of Cyclobutene-Annulated Fullerenes through a Cascade Reaction

The physicochemical properties of fullerene-based materials typically vary depending on the type and mode of addition of functional groups; therefore, developing fullerene derivatives with novel structures is imperative for further progress in materials science. In this study, we develop an efficient one-step strategy for synthesizing cyclobutene-annulated fullerene derivatives (cyclobutenofullerenes) and characterize their electronic properties. Despite the steric strain, cyclobutenofullerenes can be easily prepared via a one-step reaction of C₆₀ with a secondary propargylic phosphate. Structural analysis of the reaction intermediates suggests that the cascade reaction proceeds through a formal [2+2] cycloaddition of C₆₀ with an allene, caused by the 1,3-migration of the propargylic phosphate, followed by an additional 1,3-migration and the subsequent 1,2-elimination of the phosphodiester moiety.     

Local fields in Co and Mn Co-doped ZnO

The magnetic properties of ZnO co-doped with 5 at. % Co and 5 at. % Mn(Zn_0.90Co_0.05Mn_0.05O) synthesized by a solid-state reaction were investigated by means of ⁵⁷Co emission Mössbauer spectroscopy. The majority of the probe ions (80 %) residing in defect-free substitutional Zn sites take the oxidation state of ⁵⁷Fe ²⁺, and the others presumably form local defects taking the state of ⁵⁷Fe ³⁺ at room temperature. Both components show doublets, and RT ferromagnetism was thus absent in the sample. For the measurement at 10 K, spectral broadening was observed, implying a possible presence of a weak magnetic component.