On the origin of the ferromagnetism in Zn0.8Mn0.2O having a higher Curie temperature than Zn0.8Co0.2O

Zn_0.8Co_0.2O and Zn_0.8Mn_0.2O films were deposited on substrates by a sol–gel technique. X-ray diffraction, field-emission scanning electron microscopy, photoluminescence, and ferromagnetism measurements were used to characterize these dilute magnetic semiconductors. It is shown that the ferromagnetic properties might be related to the formation of acceptor-like defects in the Zn_0.8Co_0.2O and Zn_0.8Mn_0.2O films. It is found that ferromagnetic Zn_0.8Mn_0.2O has a higher Curie temperature than Zn_0.8Co_0.2O. In addition, the higher ratio of grain-boundary area to grain volume of Zn_0.8Mn_0.2O than Zn_0.8Co_0.2O indicates that grain boundaries and related acceptors are the intrinsic origin for ferromagnetism.     

Application of Cryptand/Polystyrene Drift-Type Phase Transfer Catalysts for Reduction of Ketones

A drift-type phase transfer catalyst, cryptand-22, adsorbed on poly(styrene/diviny benzene)-sulfonic resin was prepared and applied to catalyze the reduction of ketones, e.g., acetophenone, benzophenone and benzaldehyde with NaBH₄ as a reducing agent. Before the reaction, cryptand-22 was adsorbed on the sulfonic resin with ion-pairing, resin-SO₃^{? +}NH-cryptand-22. The ion-pairs can be destroyed by adjusting the basicity of the reaction solution with NaOH and the cryptand can be released from the resin into the reaction solution as a homogeneous catalyst during the reaction period. After the reaction, the cryptand catalyst can be readsorbed on the resin by adjusting the acidity of the solution with HCl and can be readily recovered by filtration like a heterogeneous catalyst. The draft-type cryptand catalyst exhibited better catalytic ability than some common crown ethers, e.g., 15-crown-5, benzo-15-crown-5, 12-crown-4 and dibenzo-18-crown-6 for the reduction of acetophenone with NaBH₄. Effects of solvents, pH of solutions, concentration of the catalyst, reducing agents and resin property on the reduction of ketones were investigated and discussed. The reaction mechanism of the cryptand catalyzed reduction was also studied.     

Separation of crystal violet dyes and its application to pen ink analysis using CZE and MEKC methods

A crystal violet (CV) standard was irradiated under a Hg-Cd lamp for different exposure times to obtain various N-demethylation products. CZE effectively separated the photodegradation products based on molecular weight differences. In contrast, micellar EKC (MEKC), using SDS as the surfactant, was ineffective because the binding constants of the demethylation products and SDS were too close for separation. Nevertheless, MEKC analysis of ink has applications in forensic science because MEKC separated neutral components in the inks. Thus, MEKC can be used to obtain an ink "fingerprint" since each ink is unique depending on the location and time it was made. In contrast, CZE is useful for dating inks because CV is the primary ink dye and it photodegrades slowly.     

Phase‐separated,conducting composites from polyaniline and benzobisthiazole rigid‐rod polymer

As an alternative method for processing polyaniline (PANI) from its conducting (protonated) state, vacuum casting of PANI from a methanesulfonic acid (MSA) solution provided films with electrical conductivity values of about 130–150 S/cm. In addition, we similarly prepared blended films of PANI · MSA and poly(p‐phenylene benzobisthiazole) (PBZT). This process eliminated the need for a subsequent protonation step and had the additional advantage that the conjugated PBZT may provide alternative conducting pathways. Conductivity values of the composite films ranged from 100 pS/cm to 124 S/cm, and the films displayed critical concentration behavior with a PANI threshold concentration of 2.75% and a critical exponent of 4. Transmission electron micrographs displayed phase‐separated regions with PANI forming a continuous network at high concentrations. Thermogravimetric analysis results demonstrated the thermal and thermooxidative stability advantage of the blends due to the PBZT component. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2539–2548, 2001     

Molecular dynamics simulations of fluid methane properties using ab initio intermolecular interaction potentials

Intermolecular interaction energy data for the methane dimer have been calculated at a spectroscopic accuracy and employed to construct an ab initio potential energy surface (PES) for molecular dynamics (MD) simulations of fluid methane properties. The full potential curves of the methane dimer at 12 symmetric conformations were calculated by the supermolecule counterpoise‐corrected second‐order Møller‐Plesset (MP2) perturbation theory. Single‐point coupled cluster with single and double and perturbative triple excitations [CCSD(T)] calculations were also carried out to calibrate the MP2 potentials. We employed Pople's medium size basis sets [up to 6‐311++G(3df, 3pd)] and Dunning's correlation consistent basis sets (cc‐pVXZ and aug‐cc‐pVXZ, X = D, T, Q). For each conformer, the intermolecular carbon–carbon separation was sampled in a step 0.1 Å for a range of 3–9 Å, resulting in a total of 732 configuration points calculated. The MP2 binding curves display significant anisotropy with respect to the relative orientations of the dimer. The potential curves at the complete basis set (CBS) limit were estimated using well‐established analytical extrapolation schemes. A 4‐site potential model with sites located at the hydrogen atoms was used to fit the ab initio potential data. This model stems from a hydrogen–hydrogen repulsion mechanism to explain the stability of the dimer structure. MD simulations using the ab initio PES show quantitative agreements on both the atom‐wise radial distribution functions and the self‐diffusion coefficients over a wide range of experimental conditions. © 2008 Wiley Periodicals, Inc. J Comput Chem 2009     

Difference in Conversions Between Dimethyl Sulfide and Methanethiol in a Cold Plasma Environment

This study compared the conversion of two malodorous substances, dimethyl sulfide (CH₃SCH₃, DMS) and methanethiol (CH₃SH) in a cold plasma reactor. The DMS and CH₃SH were successfully destroyed at room temperature. DMS decomposed less than CH₃SH at the same conditions. In oxygen-free condition, CS₂ and hydrocarbons were the major products, while SO₂ and CO_x were main compounds in oxygen-rich environments. The DMS/Ar plasma yielded more hydrocarbons and less CS₂ than that of CH₃SH/Ar plasma. In the CH₃SH/O₂/Ar plasma, rapid formation of SO and CO resulted in the yields much more amounts of SO₂ and CO₂ than those in the DMS/O₂/Ar plasma; and remained only a trace of total hydrocarbons, CH₂O, CH₃OH, CS₂, and OCS. The major differences between the reaction mechanisms of DMS and CH₃SH were also proposed and discussed.     

Polymer Coated Piezoelectric Quartz Crystal Protein Bio‐Sensors

A polymer coated piezoelectric crystal detection system with a home‐made computer interface for signal acquisition and data processing was prepared as a liquid chromatographic detector for various proteins. Various polymers, e.g., polyvinyl aldehhyde (polyacrolein) (PVA), polyacrylamide/glutaldehyde (PAA/GA) and bio‐gel A, were used as coating materials on quartz crystals for adsorption of various protein molecules, e.g., catalase (CA), hemoglobin (Hb), α‐chymotrypsin (Ch), albumin (Ab). The frequency responses of the polyacrlein coated piezoelectric detector for various proteins were in the order: catalase> hemoglobin> α‐chymotrypsin > albumin. In contrast, the order of the frequency responses of bio‐gel A and polyacrylamide/glutaldehyde coated piezoelectric crystals for these proteins were: hemoglobin> catalase > α‐chymotrypsin ≥ albumin and hemoglobin > albumin > catalase. The polyacrolein coated piezoelectric crystal protein detector exhibited a good linear frequency response with a high sensitivity of about 2.5×10³ Hz/(mg/mL) for catalase. In addition, bio‐gel A and polyacrylamide/glutaraldehyde coated crystals were sensitive to hemoglobin with sensitivities of about 4.5×10³ Hz/(mg/mL) and 3.0×10³ Hz/(mg/mL), respectively. Study of the interference of various organic molecules, e.g., alcohols, amines, ketones and carboxylic acids, in the detection of proteins with theses polymer coated crystals was also made. The polyacrolein coated crystal for proteins under went less interference from various organic molecules than bio‐gel A or polyacrylamide/glutaraldehyde coated crystals. Effects of coating load, concentration of proteins and flow rate of liquid chromatographic eluent were also investigated and discussed.     

Effects of phenolic compounds on gelation behavior of gelatin gels

The effects of phenolic additives on the gelation behavior of gelatin gels were investigated using thermomechanical analysis (TMA) for study of gel‐melting temperature, dynamic mechanical analysis (DMA) for study of gel‐storage modulus and gel‐aging stability, viscometry for study of gelation time, and texture analyzer for study of gel strength and gel melting. Thermodynamically, the addition of 1,3‐benzenediol, 1,4‐benzenediol or 1,3,5‐benzenetriol favored the gelation process of gelatin solutions (increases in T_m and aging stability) due to the introduction of extra physical crosslinks among gelatin chains through hydrogen bonding, while the addition of 1,2‐benzenediol had a negative effect (decreases in T_m and aging stability) possibly due to intra‐hydrogen bonding of the additive molecule itself. All the phenolic compounds had little effect on gel moduli. Kinetically, the introduction of 1,2‐benzenediol or 1,4‐benzenediol slowed the gelation process, while introduction of catechin, a polyphenol, accelerated the first stage of the gelation process. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 224–231, 2001     

Synthesis of aminomethyl and amino analogs of 5-benzylacyclouridine and 5-benzyloxybenzylacyclouridine

Amino analogs of BAU (5-benzylacyclouridine) and BBAU (5-benzyloxybenzylacyclouridine) and their 2′-hydroxymethyl derivatives were synthesized for evaluation as inhibitors of uridine phosphorylase and hence potential cancer chemotherapeutic agents. Both aminomethyl analogs were found to be potent inhibitors of this enzyme and good potentiators of the anti-tumor action of FUdR.     

Optically clear simulataneous interpenetrating polymer networks based on poly(ethylene glycol) diacrylate and epoxy. II. Kinetic study

Simultaneous interpenetrating polymer networks (SINs) based on diglycidyl ether of bis-phenol A (DGEBA) and poly(ethylene glycol) diacrylate (PEGDA) in weight ratios of 100/0, 50/50, and 0/100 were blended and cured simultaneously by using benzoyl peroxide (BPO) and m-xylenediamine (MXDA) as curing agents. A kinetic study during SIN formation was carried out at 45, 55, 63, and 70°C. Concentration changes for both the epoxide and C?C bond were monitored with FTIR. A rate expression for DGEBA cure kinetics was established with a model reaction of phenyl glycidyl ether (PGE) and benzylamine. Experimental results revealed that lower rate constants and higher activation energy for the SIN were found, compared with those for the constituent DGEBA and PEGDA network formation. A model of network interlock was proposed to account for this phenomenon. During simultaneous cure of DGEBA and PEGDA, the interlock (mutual entanglement) between DGEBA and PEGDA networks provided a sterically hindered environment, which subsequently increased the activation energy and reduced cure rates for both DGEBA and PEGDA. © 1993 John Wiley & Sons, Inc.