Temperature-sensitive photoluminescence of CdSe quantum dot clusters

The formation of narrow size dispersed and nanometer size aggregates (clusters) of cadmium selenide (CdSe) quantum dots (QDs) and their temperature-sensitive photoluminescence (PL) spectral properties close to room temperature (298 K) are discussed. CdSe QDs formed stable clusters with an average diameter of approximately 27 nm in the absence of coordinating solvents. Using transmission electron microscopy (TEM) imaging, we identified the association of individual QDs with 2-5 nm diameters into clusters of uniform size. A suspension of these clusters in different solvents exhibited reversible PL intensity changes and PL spectral shifts which were correlated with temperature. Although the PL intensity of CdSe QDs encapsulated in host matrixes and the solid state showed a response to temperature under cryogenic conditions, the current work identified for the first time QD clusters showing temperature-sensitive PL intensity variations and spectral shifts at moderate temperatures above room temperature. Temperature-sensitive reversible PL changes of clusters are discussed with respect to reversible thermal trapping of electrons at inter-QD interfaces and dipole-dipole interactions in clusters. Reversible luminescence intensity variations and spectral shifts of QD clusters show the potential for developing sensors based on QD nanoscale assemblies.     

Quantum dot-conjugated hybridization probes for preliminary screening of siRNA sequences

In the present study, we describe the design and fabrication of quantum dot-conjugated hybridization probes and their application to the development of a comparatively simple and rapid procedure for the selection of highly effective small-interfering RNA (siRNA) sequences for RNA interference (RNAi) in mammalian cells, for example, siRNAs with high accessibility and affinity to the respective mRNA target. A single-stranded siRNA was conjugated with a quantum dot and used as a hybridization probe. The target mRNA was amplified in the presence of Cy5-labeled nucleotides, and Cy5-mRNA served as a hybridization sample. The formation of siRNA/mRNA duplexes during a comparatively short hybridization time (1 h) was used as a criterion for the selection of highly effective, target-specific siRNA sequences. The accessibility and affinity of the siRNA sequence for the target mRNA site were determined by fluorescence resonance energy transfer (FRET) between a quantum dot (donor) and a fluorescent dye molecule (Cy5, acceptor) localized at an appropriate distance from each other when hybridization occurred. The FRET signal was observed only when there was high accessibility between an antisense siRNA and a sense mRNA and did not appear in the case of mismatch siRNAs. Moreover, the amplitude of the FRET signal significantly correlated with the specific effect of siRNA on the expression of the target mRNA and protein, determined in native cells by RT-PCR and immunoblot analysis, respectively.     

A triple-injection method for microchip electrophoresis

We report here a novel triple injection method for microchip electrophoresis (micro-CE) that results in a higher intensity of DNA peaks. This new method includes a triple-repeated process of a combination of a sample loading voltage and a separation voltage in each interval, namely (loading time) + (separation time) + (loading time) + (separation time) + (loading time), prior to electrophoretic separation. All these injections were electrokinetically controlled by a software. Although the usual sample injection, which included the process of one 60 s electrokinetically application, was limited by the amount of sample, peaks of 40% higher intensity were obtained using the new method within half of the conventional injection time compared to the conventional method. Maximum peak intensity was successfully achieved with integration of the intensities of the triple-repeated peaks by adjusting the application period of the separation voltage. Repetition of the sample loading voltage for an adjusted period with a further adjusted period of separation voltage in each interval may be an effective method for injection of samples that results in peaks with higher intensity.     

The reducive amination of phthalaldehyde by tetracarbonylhydridoferrate : Synthesis of 2-arylisoindoles

Phthalaldehyde reacted with primary amines in the presence of tetracarbonylhydridoferrate under mild conditions to give 2-substituted isoindoles and/or isoindolines in good to excellent yields. Aliphatic amines gave selectively the isoindolines but aromatic amines had a great tendency to the isoindoles. 2-(2-Tolyl)-, 2-(4-tolyl)-, 2-(4-methoxyphenyl)-, 2-(3-chlorophenyl)-, 2-(4-chlorophenyl)- and 2-(3,4-dichlorophenyl)-isoindole were prepared by this method.     

Removal of proteins from natural rubber with urea

Removal of proteins from natural rubber was achieved by incubation of the rubber latex with urea in the presence of a surfactant to prevent the latex‐allergy caused with thin film products. Temperature, pH and time for the incubation were investigated to remove the proteins effectively, in which nitrogen content of the rubber was reduced to 0.02 from 0.38 wt% under the optimum condition. To remove further the proteins, deproteinization of natural rubber was made by incubation of the latex with proteolytic enzyme in the presence of a surfactant followed by incubation with urea. Amount of allergen decreased through the procedure to less than 0.7 μg/ml, which is a small amount of allergen compared to that for the commercial, deproteinized natural rubber. Copyright © 2004 John Wiley & Sons, Ltd.     

Triplet diphenylcarbenes protected by (trimethylsilyl)ethynyl groups

(2,4,6-Tribromophenyl)(4-tert-butyl-2,6-dimethylphenyl)diazomethane (1a) was shown to be stable enough to survive Sonogashira coupling reaction conditions at an elevated temperature and gave not only a para-monosubstituted product, (4-trimethylsilylethynyl-2,6-dibromophenyl)(4-tert-butyl-2,6-dimethylphenyl)diazomethane (1b), but also a disubstituted one, [2,4-bis(trimethylsilylethynyl)-6-bromophenyl](4-tert-butyl-2,6-dimethylphenyl)diazomethane (1c), and a trisubstituted product, [2,4,6-tris(trimethylsilylethynyl)phenyl](4-tert-butyl-2,6-dimethylphenyl)diazomethane (1d). Triplet diphenylcarbenes (DPCs) generated by photolysis of those ethynylated diphenyldiazomethanes were characterized by ESR and UV-vis spectroscopies at low temperature and laser flash photolysis techniques in solution at room temperature. Although ESR data indicated that ethynyl groups at the ortho positions are likely to stabilize triplet DPCs both sterically and electronically more effectively than o-bromine groups, kinetic studies suggested that the stability of triplet DPCs is not increased by o-ethynyl groups, as opposed to o-bromine groups. It is likely that triplet DPCs decay by interacting with the o-ethynyl groups.     

Quantum dots for single bio-molecule imaging.

The emerging nanomaterial, quantum dots or QDs, offers numerous potential applications in the biological area. As cell labeling probes, QDs become now an alternative of existing organic fluorescent dyes and fluorescent proteins. In this short review, we cover typical and successful applications of QDs as fluorescent probes in cell labeling and genomic diagnosis. As a future important application, biomolecular detection at a single molecule level utilizing QDs is also discussed.     

Electrophilic cyclization of N-alkenylamides using a chloramine-T/I2 system

A new protocol for the cyclization of N-alkenylamides using chloramine-T and iodine is described. When N-alkenylsulfonamides are treated with chloramine-T and iodine, three- to six-membered N-heterocycles are obtained with complete stereoselectivity. The method is compatible with the cyclization of the allylbenzamide or allylbenzthioamide to afford an oxazoline or thiazoline derivative, respectively. Mechanistic studies indicate that the chloramine-T/I₂ system functions as an effective iodonium species.     

Die potentiometrische Bestimmung des Kupfers als Ferrocyankupfer

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