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.     

Measurement of the change in partial molar volume during electrode reaction by gravity electrode—II. Examination of the accuracy of the measurement

The reliability of the measurement of the change in partial molar volume between product and reactant ions measured by gravity electrode (GE) was examined by the thermodynamic measurement of pycnometer (PM). Since the PM method requires an experimental equation of the apparent molar volume to calculate the partial molar volumes of the individual ions, the most suitable experimental equation must be first determined. As a test reaction for the experiment, oxidation of ferrocyanide (FERO) ion to ferricyanide (FERI) ion was adopted. After fitting several experimental equations to the data of the apparent molar volumes by the PM method, the calculated changes in the partial molar volume were compared with the data of the GM method. Then, it is concluded that the polynomial with a degree of 3 of the logarithm of the molality of the FERO ion suggests the most suitable equation. As a result, the reliability of the GE method was also experimentally validated.     

Synthesis and reaction of alpha-dithiolactone

Treatment of di-tert-butylthioketene S-oxide (5 a) with Lawesson reagent at room temperature resulted in the formation of 3,3-di-tert-butylthiirane-2-thione (4 a) in high yield. The oxidation of 4 a with mCPBA (mCPBA=m-chloroperbenzioc acid) gave 3,3-di-tert-butylthiirane-2-thione S-oxide (6) almost quantitatively. The reactions of 4 a with dimethyl acetylenedicarboxylate (DMAD) and benzyne afforded dimethyl 2-(2,2,4,4-tetramethylpentan-3-ylidene)-1,3-dithiole-4,5-dicarboxylate (13) and 2-(2,2,4,4-tetramethylpentan-3-ylidene)benzo[d][1,3]dithiole (15), respectively, in high yields, suggesting that 4 a is an excellent 1,3-dipole. The reaction of 4 a with ethylenebis(triphenylphosphine)platinum (16) gave dithiolato-platinum complex (22) in high yield. The structure of 22 was determined by X-ray crystallographic analysis.     

One-electron reduction of kinetically stabilized dipnictenes: synthesis of dipnictene anion radicals

The redox behavior of kinetically stabilized dipnictenes, BbtE=EBbt [E = P, Sb, Bi; Bbt = 2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl], was systematically disclosed using cyclic voltammetry and theoretical calculations. It was found that they showed reversible one-electron redox couples in the reduction region. The anion radical species of the Bbt-substituted diphosphene and distibene were successfully synthesized by the reduction of the corresponding neutral dipnictenes (BbtP=PBbt and BbtSb=SbBbt). Their structures were reasonably characterized by ESR, UV-vis, and Raman spectroscopy, and the distibene anion radical was structurally characterized by X-ray crystallographic analysis.     

Synthesis and properties of a new kinetically stabilized digermyne: new insights for a germanium analogue of an alkyne

The reduction of an overcrowded (E)-1,2-dibromodigermene, Bbt(Br)Ge=Ge(Br)Bbt (2) [Bbt = 2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl], with KC8 afforded a stable digermyne, BbtGe[triple bond]GeBbt (1). The Ge[triple bond]Ge triple-bond characters of 1 were revealed by the X-ray crystallographic analysis and spectroscopic studies (UV/vis and Raman spectra) together with theoretical calculations. The Ge[triple bond]Ge bond lengths of the two nonidentical molecules of 1 observed in the unit cell were shorter than that of the previously reported digermyne, Ar'Ge[triple bond]GeAr' (Ar' = 2,6-Dip2C6H3, Dip = 2,6-diisopropylphenyl).     

Structure-property correlation of CdSe clusters using experimental results and first-principles DFT calculations

Structures and properties of CdSe quantum dots (clusters) up to a diameter of approximately 2 nm were investigated by combining experimental absorption, photoluminescence (PL), and X-ray diffraction (XRD) spectroscopies as well as ab initio DFT calculations. These CdSe clusters were nucleated and grown from solutions containing respective cadmium and selenium precursors following the hot-injection technique that allows one to obtain size-controlled CdSe clusters having PL efficiency up to 0.5. The DFT calculations were performed at the B3LYP/Lanl2dz level and followed by time-dependent TDDFT calculations to estimate n energy singlet transitions. On the basis of the results of these experimental and theoretical studies, an approach to determine whether the proposed cluster with a mean diameter of approximately 2 nm is more physically reasonable is discussed. It was shown that the minimum nucleus of a CdSe cluster consists of (CdSe)(3) with a six-membered ring and planar structure. No PL is observed for this structure. The formation of the next stable cluster depends on whether hexadecylamine (HDA) was used for the growth of the CdSe clusters. In the absence of HDA, the second cluster was found to be (CdSe)(6) characterized by a broad PL spectrum, while in the presence of HDA, it was found to be (CdSe)(n) (where n > or = 14) with a sharp PL spectrum.     

DNA-based gels for oral delivery of probiotic bacteria

A single-stranded DNA, readily extracted from industrial discarded salmon milt, was used to prepare hydrogels and complex gels by cross-linking with gelatin and kappa-carrageenan, for the oral delivery of probiotic bacteria. The complex gels showed a higher protective capability over the hydrogels for approximately one log scale. However, the hydrogels were more stable during storage at 4 degrees C. The Lactobacillus and Lactococcus due to protection of the hydrogels could better tolerate to acid than the Bifidobacterium. Furthermore, food-graded hydrogels were prepared and optimized to a similar protective capability for future applications.     

Study of water properties in nanospace

Here we report an anomalous behavior of water, especially its viscosity and hydrodynamic flow, in a nanometer-confined space. As a typical model of a nanometer-confined space, the nanopillar chip, which was developed for DNA size-based separation was used, and single-particle tracking (SPT) technique was applied to investigate water viscosity and hydrodynamic flow in the nanopillar chip. The diffusion coefficients of nanospheres were almost one-third of the theoretical value derived from the Stokes-Einstein equation. This result gave indirect proof that water viscosity in a nanometer-confined space is higher than in a bulk solution. In order to improve resolution and throughput of the nanopillar chip for DNA separation, these potential factors affecting performance should be seriously considered.