A series of neutral N-(substituted-benzamido)-N'-phenylthioureas (substituent = p-OC(2)H(5), p-CH(3), m-CH(3), H, p-Cl, p-Br, m-Cl, and p-NO(2)) were designed as anion receptors, in which the thiourea binding site was attached to the benzamido moiety via an N-N bond. The absorption spectra of these N-benzamidothioureas in acetonitrile peaked at ca. 270 nm were found to show unprecedented red shifts by 7 373 to 14 325 cm(-1) in the presence of anions such as AcO(-), F(-), and H(2)PO(4)(-). Under the same conditions, the classic neutral thiourea receptors, N-(substituted-phenyl)-N'-phenylthioureas, showed absorption spectral shifts in most cases of less than 800 cm(-1) with one exception of 6501 cm(-1). Control experiments, effects of protic solvent, and (1)H NMR titration confirmed the formation of hydrogen-bonding complexes between the new N-benzamidothiourea receptors and anions. The binding constants with AcO(-), for example, are at 10(5)-10(7) mol(-1) L order of magnitude, which are 13 to 590 times those of the corresponding classic N-phenylthioureas in the same solvent. It was found that, whereas the absorption of the N-benzamidothiourea receptors showed essentially no dependence on the substituent, the substantially red-shifted new absorption band of the N-benzamidothiourea-anion binding complex was sensitively subject to the substituent. A linear relationship was found between the absorption energies of the N-benzamidothiourea-acetate binding complexes and the Hammett constants of the substituents with a negative slope of -0.34 eV. This led to the assignment that the substantially red-shifted absorption band was the ground-state intramolecular charge-transfer absorption with the substituent locating in the electron acceptor moiety. It was concluded that anion binding to the thiourea moiety of the N-benzamidothiourea receptors switched on their ground-state charge transfer. An anion-binding induced structural change was suggested to occur around the N-N bond in N-benzamidothioureas, which resulted in a substantially increased electron donating ability of the electron donor in the receptor molecules. As a consequence, the ground-state charge transfer takes place in the N-benzamidothiourea-anion binding complexes, leading to unprecedented red shifts in the absorption spectra and substantially enhanced anion binding affinities than those of the corresponding N-phenylthiourea receptors. N-Benzamido-N'-phenylthioureas represent a new generation of neutral thiourea-based anion receptors that show substantially improved anion binding performance important for anion sensing and recognition. 相似文献
The transport characteristics of high temperature superconductor current and Josephson current is inves-tigated in the framework of the modified time-dependent Ginzburg-Landau model and the Lawrence-Doniach model.We evaluated the vortex equation and found that the signs of the high temperature superconductor current and theJosephson current can reverse. Some explicit expressions for different cases are derived, which accord with experimentaldata. 相似文献
p-Toluenesulfonylamide was immobilized on silica gel and on nm-sized silicium dioxide (SiO2). Their adsorption efficiency toward metal ions was investigated by the batch equilibrium technique. Although silica gel
and nm-SiO2 have the same composition (silicon and oxygen), the difference in their sizes and surface structures results in distinct
chemical activity and selectivity. At pH 4, the adsorption capacity of modified silica gel adsorbent was found to be 4.9,
5.0, 33.2, and 12.6 mg g−1 for Cr(III), Cu(II), Pb(II) and Zn(II), respectively. However, the adsorption capacity of nm-SiO2 adsorbent toward Cr(III) was 26.7 mg g−1 under ultrasonic dispersing. The potential application of p-toluenesulfonylamide-modified silica gel for simultaneous preconcentration of trace chromium, copper, lead and zinc from
two standard reference materials and two food samples was performed with satisfactory results.
Correspondence: Xijun Chang, Department of Chemistry, Lanzhou University, Lanzhou 730000, P.R. China 相似文献
Organosilicon compounds are important reagents and synthetic intermediates that play a key role in the construction of new materials and complex products. Here we show a highly diastereoselective rhodium-catalyzed cycloisomerization of 1,6-dienes, in which the use of (EtO)3SiH accelerates the intramolecular cyclization reaction to afford a novel spiro-fused succinimide and pyrazolone derivatives in moderate to excellent yields as a single diastereoisomer. The proposed mechanism involves an active Rh−H species from the hydrosilane that is the H-donor in this spiro-type cycloisomerization reaction. 相似文献
A label-free, rapid response colorimetric aptasensor for sensitive detection of chloramphenicol (CAP) was proposed, which was based on the strategy of ssDNA-modified gold nanoparticle (AuNP) aggregation assisted by lanthanum (La3+) ions. The AuNPs generated a color change that could be monitored in the red, green, and blue and analyzed by the smartphone imaging app. La3+, as a trigger agent, strongly combined with the phosphate groups of the surface of ssDNA-AuNPs probe, which helps create AuNP aggregation and the color change of AuNPs from red to blue. On the contrary, when mixing with CAP, the aptamer (Apt) bound to CAP to form a rigid structure of the Apt-CAP complex, and La3+ attached to the phosphate groups of the complex, which prevented the aptamer from binding to the surface of the AuNPs. As a result, the color of the AuNPs changed to violet-red. Finally, UV-vis absorption spectroscopy and the smartphone imaging app were employed to determine CAP with a lower detection limit of 7.65 nM and 5.88 nM, respectively. The proposed strategy featuring high selectivity and strong anti-interference ability for detection of CAP in practical samples was achieved. It is worth mentioning that the simple and portable colorimetric aptasensor will be used for facilitating on-site detection of food samples.
We consider a Ginzburg-Landau modified model of layered high-temperature superconductor under pressure. We have theoretically studied the relation between the pressure and the temperature of layered high-temperature superconductor. If the pressure is not a constant, we have a relation of quadratic equation between the pressure and the temperature of layered high-temperature superconductor. In a special case, we find the critical temperature decreases with further increasing pressure. In another special case, the critical temperature increases with furtherincreasing pressure. 相似文献