Supramolecular control of complexation-induced fluorescence change of water-soluble, beta-cyclodextrin-modified CdS quantum dots

The fluorescence of beta-cyclodextrin-modified CdS quantum dots can be reversibly tuned by introducing different substrates in aqueous media.     

Subfemtosecond pulse generation and multiplicative increase of pulse spacing in high-order stimulated Raman scattering

We demonstrate a technique for multiplicatively increasing the pulse spacing of subfemtosecond pulse trains generated by high-order stimulated Raman scattering, which uses pairs of off-resonant two-photon excitation of a molecular Raman mode to establish strong molecular modulation in the medium. Every laser pair has two single-mode laser beams tuned slightly off two-photon resonance, and the laser pairs have their corresponding carrier frequencies shifted from each other by one half, one third, or one fourth of the selected molecular Raman mode frequency. Theoretical analyses and calculations based on the fundamental vibrational transition of solid hydrogen show that the pulse spacing of the subfemtosecond pulse trains thus generated can readily be doubled, tripled, or even quadrupled.     

The shock formation distance in a bounded sound beam of finite amplitude

This paper investigates the shock formation distance in a bounded sound beam of finite amplitude by solving the Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation using frequency-domain numerical method. Simulation results reveal that, besides the nonlinearity and absorption, the diffraction is another important factor that affects the shock formation of a bounded sound beam. More detailed discussions of the shock formation in a bounded sound beam, such as the waveform of sound pressure and the spatial distribution of shock formation, are also presented and compared for different parameters.     

Characterizing individual scattering events by measuring the amplitude and phase of the electric field diffusing through a random medium

We describe observations of the amplitude and phase of an electric field diffusing through a three-dimensional random medium, using terahertz time-domain spectroscopy. These measurements are spatially resolved with a resolution smaller than the speckle spot size and temporally resolved with a resolution better than one optical cycle. By computing correlation functions between fields measured at different positions and with different temporal delays, it is possible to obtain information about individual scattering events experienced by the diffusing field. This represents a new method for characterizing a multiply scattered wave.     

Growth and morphologies of large-scale SnO2 nanowires, nanobelts and nanodendrites

Single-crystalline SnO₂ nanowires, nanobelts and nanodendrites were synthesized by a simple gas-reaction route on a large scale at 900 °C. They were characterized by means of X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and selected-area electron diffraction (SAED). FE-SEM images showed that the products consisted of nanowires, nanobelts and nanodendrites that represent a novel morphology reported for the first time. XRD, SAED and EDS indicated that they were single-crystalline tetragonal SnO₂. The influence of experimental conditions on the morphologies of the products is discussed. Received: 3 June 2002 / Accepted: 10 June 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: 86-10/82649531, E-mail: xlchen@aphy.iphy.ac.cn     

Facile optical resolution of tert-butanethiosulfinate by molecular complexation with (R)-BINOL and study of chiral discrimination of the diastereomeric complexes

An important synthon, tert-butanethiosulfinate (2), has been effectively resolved by forming molecular complexes with (R)-2,2'-dihydroxy-1,1'-binaphthyl (BINOL, 3) in high enantioselectivity (>99 % ee). The present procedure represents the first example of the resolution of thiosulfinate. The mechanism of chiral discrimination is discussed in terms of molecular recognition based on IR and Xray analyses of the diastereomeric complexes during the resolution. In the less-soluble complex, (R)-3 and (R)-2 self-assembled as a linear supramolecule; however, in the more-soluble complex, (R)-3 and (S)-2 formed a simple bimolecular complex by one stronger hydrogen bond. Hydrogen bonding is the major driving force for effective resolution.     

HAD: an automated database tool for analyzing screening hits in drug discovery

Collecting, organizing, and reviewing chemical information associated with screening hits are human time-consuming. The task depends highly on the individual, and human errors may result in missing leads or wasting resources. To overcome these hurdles, we have developed a decision support system, Hits Analysis Database (HAD). HAD is a software tool that automatically generates an ISIS database file containing compound structures, biological activities, calculated properties such as clogP, hazard fragment labels, structure classifications, etc. All data are processed by available software and packed into a single SD file. In addition to search capabilities, HAD provides an overview of structural classes and associated activity statistics. Chemical structures can be organized by maximum common substructure clustering. The ease of use and customized features make HAD a chief tool in lead selection processes.     

Chemistry of the Si-Si and Fe-Fe bonds in the cyclic structure (Me2SiSiMe2)[eta5-C5H4FeCO2]2. Selective cleavage of the Fe-Fe bond by I2 and unexpected properties of the iodide

The Si-Si bond in the title cyclic structure (1) exhibited unexpected stability toward I(2). Thus, the reaction of 1 with 1 equiv of I(2) in chloroform resulted in selective cleavage of the Fe-Fe bond to afford diiodide (Me(2)SiSiMe(2))[eta(5)-C(5)H(4)Fe(CO)(2)I](2) (2) with retention of the Si-Si bond. When excess (2-4 equiv) I(2) was used to react with 1 in either benzene or chloroform, iodonium-bridged diiron complex [(Me(2)SiSiMe(2))[eta(5)-C(5)H(4)Fe(CO)(2)](2)I(+)](I(5)(-)) (4) was obtained, in which the Si-Si bond was still retained. It is noteworthy that 4 contains a counteranion I(5)(-) rather than the expected I(3)(-), which is the first example for an iodonium-bridged diiron complex to combine a polyiodide anion larger than I(3)(-). UV irradiation of 2 did not affect the stability of the silicon-silicon bond and, in the presence of PR(3), resulted in CO substitution to give (Me(2)SiSiMe(2))[eta(5)-C(5)H(4)Fe(CO)(PR(3))I](2) (5, R = Ph; 6, R = OPh). The molecular structure of 2 was determined by the X-ray diffraction method. It is noteworthy that the structure of 2 does not take the expected anti conformation but adopts a gauche one. The length of the Si-Si bond of 2 [2.353(3) A] is about the same as that of 1 [2.346(4) A], which can be direct evidence to demonstrate that the Si-Si bond in the cyclic structure of 1 is not subject to significant ring strain. The molecular structure of 4 was also determined by the X-ray diffraction method. It is noted that the structure of 4 contains an abnormally large Fe-I(+)-Fe bond angle of 121.25(7) degrees. Of particular interest is the observation that the I(5)(-) anions of 4 are self-assembled into novel layered, two-dimensional networks with the (Me(2)SiSiMe(2))[eta(5)-C(5)H(4)Fe(CO)(2)](2)I(+) cations as the template.