Competitive ionization of tetraphenylporphyrin in a laser-generated metal ion plasma

The ionization of tetraphenylporphyrin (TPP) in a laser-desorbed metal ion plasma is examined by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Competitive reaction pathways observed to generate abundant molecular ion species include electron detachment, cation attachment, charge exchange, metallation, and transmetallation in the positive ion mode and electron capture, metallation, and transmetallation in the negative ion mode. In general, cation attachment reactions dominate positive ion spectra below the laser irradiance threshold for plasma ignition, although the metallation product from [TPP]⁺ reaction with the metal atom, M, is observed. Negative ion products are not observed in the FT-ICR spectrum when a plasma is not formed. Under plasma ignition conditions, positive ion spectra include [TPP]⁺ formed by charge exchange with M⁺, which is also present in the spectrum. Negative ion spectra are dominated by [TPP]^?; which is formed by attachment to thermal electrons generated in the plasma. Metallation reactions involving TPP and the metal substrate are examined. Positive ion metallation products are observed both in the absence of a plasma through reaction of [TPP]⁺ with M and by a second pathway under plasma ignition conditions through reaction of TPP with M⁺. In negative ion mode, metallation is only observed under plasma ignition conditions through reaction of [TPP]^? with M. Observation of metallated products is found to be consistent with formation of stable metal oxidation states in the metallated porphyrin.     

A new thermoelectric material: CsBi4Te6

The highly anisotropic material CsBi(4)Te(6) was prepared by the reaction of Cs/Bi(2)Te(3) around 600 degrees C. The compound crystallizes in the monoclinic space group C2/m with a = 51.9205(8) A, b = 4.4025(1) A, c = 14.5118(3) A, beta = 101.480(1) degrees, V = 3250.75(11) A(3), and Z = 8. The final R values are R(1) = 0.0585 and wR(2) = 0.1127 for all data. The compound has a 2-D structure composed of NaCl-type [Bi(4)Te(6)] anionic layers and Cs(+) ions residing between the layers. The [Bi(4)Te(6)] layers are interconnected by Bi-Bi bonds at a distance of 3.2383(10) A. This material is a narrow gap semiconductor. Optimization studies on the thermoelectric properties with a variety of doping agents show that the electrical properties of CsBi(4)Te(6) can be tuned to yield an optimized thermoelectric material which is promising for low-temperature applications. SbI(3) doping resulted in p-type behavior and a maximum power factor of 51.5 microW/cm.K(2) at 184 K and the corresponding ZT of 0.82 at 225 K. The highest power factor of 59.8 microW/cm.K(2) at 151 K was obtained from 0.06% Sb-doped material. We report here the synthesis, physicochemical properties, doping characteristics, charge-transport properties, and thermal conductivity. Also presented are studies on n-type CsBi(4)Te(6) and comparisons to those of p-type.     

The impact of polystyrene resins in solid-phase organic synthesis

Summary A major objective of the DIVERSOMER^® technology is to provide pure and characterized compounds for biological testing in order to prevent false negatives in our libraries. On several occasions, analysis of the final products by¹H-NMR and MS, has revealed by-products from the polystyrene solid support. Subsequently, three alternative methods were studied to remove polystyrene by-products; (i) prewashing of the resin prior to execution of the synthesis; (ii) pretreatment of the resin with the cleavage conditions consistent with the solid-phase synthesis reaction scheme; and (iii) parallel purification.