Biomedical subjects
Publications and source records attributed to Xu-Feng Lin.
A variety of substituted iminocoumarins are prepared in good to excellent yields via a copper-catalyzed multicomponenet reaction of sulfonyl azides, terminal alkynes, and salicylaldehydes or o-hydroxylacetophenones. The method is general, mild, versatile, and efficient. A plausible mechanism for the domino process is proposed.
[reaction: see text] A new triethylamine-catalyzed cascade reaction of aromatic aldehydes with propiolates has been developed. This serial multi-bond-forming process furnishes diverse polycyclic aromatic hydrocarbons, including naphthalenes, phenanthrenes, benzofurans, and 2,3,9,9a-tetrahydronaphtha[2,3-b]furans. The chemical outcome of the process depends on the reaction temperature and can be tailored selectively by an appropriate choice of experimental conditions.
This discussion focuses on our recent approaches at aiming to optimize surface-enhanced Raman scattering (SERS) activity for transition metals (group VIII B elements), by intentionally fabricating desired surface nanostructures or synthesizing nanoparticles. The SERS activity of transition metals critically depends on the surface morphology of electrodes and on size, shape and aggregation form of nanoparticles. A correct surface roughening procedure for transition-metal electrodes is indispensable for fabricating cauliflower-like nanostructures that show a higher SERS activity. Two more methods have been explored to synthesize nanoparticles, i.e., cubic nanoparticles and gold-core palladium-shell nanostructures, respectively. Their SERS activities are considerably higher than those of normal spherical mono-metallic nanoparticles. To explain these observations, a preliminary theoretical calculation, using the three-dimensional finite difference time domain (3D-FDTD) method, was performed to evaluate the local electromagnetic field on transition metal surfaces. The result is in good agreement with the experimental data.
[reaction: see text] A facile parallel synthesis of polysubstituted 2,6-dicyanoanilines via microwave-promoted three-component reaction of aldehydes, ketones, and propanedinitrile in solution and also on polymer support has been developed. The screening for optical properties identified two new compounds with high fluorescence quantum yields.
We report the first observation of surface-enhanced Raman scattering (SERS) excited with ultraviolet (UV) light from transition metal electrodes. Adsorbed pyridine and SCN- on rough rhodium (Rh) and ruthenium (Ru) electrodes, respectively, have been studied using 325 nm laser excitation. In contrast, the best enhancers in the visible and near infrared, silver and gold, do not produce UV-SERS. The experimental data of UV-SERS are in agreement with our preliminary theoretical calculation based on the electromagnetic enhancement mechanism. The enhancement factor is about 2 orders of magnitude for the Rh and Ru electrodes when they are excited at 325 nm.
Some points on how to improve the detection sensitivity of confocal Raman microscopy for the study of surface-enhanced Raman scattering (SERS) of transition-metal electrodes are discussed, including the careful design of the spectroelectrochemical cell, proper selection of the thickness of the solution layer, the binning of charge-coupled device (CCD) pixels, and appropriate setting of the notch filter. Various roughening methods for the Pt, Rh, Fe, Co, and Ni electrode surfaces have been introduced in order to obtain SERS-active surfaces. It has been shown that the appropriate roughening procedure and the optimizing performance of the confocal Raman microscope are the two most important factors to directly generate and observe SERS on net transition-metal electrodes.