On-line concentration sample stacking coupled with water-in-oil microemulsion electrokinetic chromatography

This study describes for the first time, the ability of a normal stacking mode (NSM) on-line concentration step coupled with water-in-oil (W/O) microemulsion electrokinetic chromatography (MEEKC), using six common penicillin antibiotics (oxacillin, penicillin V, penicillin G, nafcillin, ampicillin, and amoxicillin) as test analytes. Optimization of penicillin separation in the conventional W/O MEEKC system demonstrated that change in the type and concentration of the oil phase (1-butanol) and column temperature had a pronounced effect on the separation. With the subsequent development of the NSM coupled with W/O MEEKC, improved separation and detection sensitivities were observed when an organic solvent plug (1-propanol; 1.04 cm) was placed between the W/O microemulsion and the sample solutions. This could be attributed to the solution viscosity difference between the aqueous sample zone and the organic solvent plug causing the penicillin to be stacked in this 1-propanol plug. The optimal NSM W/O MEEKC provided about 12-fold increase in detection sensitivity compared with conventional sample injection (50 mbar, 3 s). Finally, this proposed method was successfully applied in the analyses of several food samples (porcine organs) spiked with penicillin.     

Prediction of thermal hazard of liquid organic peroxides by non-isothermal and isothermal kinetic model of DSC tests

Liquid organic peroxides (LOPs) have been widely used as initiators of polymerization, hardening, or cross-linking agents. We evaluated a beneficial kinetic model to acquire accurate thermokinetic parameters to help preventing runaway reactions, fires or explosions in the process environment. Differential scanning calorimetry was used to assess the kinetic parameters, such as kinetic model, reaction order, heat of reaction (??H _d), activation energy (E _a), frequency factor (lnk ₀), etc. The non-isothermal and isothermal kinetic models were compared to determine the validity of the kinetic model, and then applied to the thermal hazard assessment of commercial package contaminated with LOPs. Simulations of a 0.5-L Dewar vessel and 25-kg commercial package were performed. We focused on the thermal stability of different liquid system properties for LOPs. From the results, the optimal conditions were determined for avoiding violent heat effects that can cause a runaway reaction in storage, transportation, and manufacturing.     

Expanded substrate scope and catalyst optimization for the catalytic kinetic resolution of N-heterocycles

The scope, reactivity, and selectivity of the chiral hydroxamic acid-catalyzed kinetic resolution of chiral amines are improved by a new catalyst structure and a more environmentally friendly reaction protocol. In addition to increasing selectivity across all substrates, these conditions make possible the resolution of N-heterocycles containing lactams or other basic functional groups that can inhibit the catalyst.     

Selective encapsulation of volatile and reactive methyl iodide

A simple organic molecular container can selectively encapsulate the volatile and highly reactive MeI through hydrogen-bonding interactions in solution. The remarkable encapsulation of MeI without self-methylation of the container appears to be determined by the complementary binding sites and the rigidity of the hydrogen-bonding array constrained by the molecular framework.     

Copper-catalyzed domino coupling reaction: an efficient method to synthesize oxindoles

An efficient and novel procedure for a copper catalyzed domino coupling reaction has been developed, which afforded various oxindoles in good to excellent yields with tolerance of various substituents. In addition, this method could be applied to synthesize horsfiline and coerulescine in few steps with high total yields.     

Structural tuning intra- versus inter-molecular proton transfer reaction in the excited state

A series of 2-pyridyl-pyrazole derivatives 1-4 possessing five-membered ring hydrogen bonding configuration are synthesized, the structural flexibility of which is strategically tuned to be in the order of 1 > 2 > 3 > 4. This system then serves as an ideal chemical model to investigate the correlation between excited-state intramolecular proton transfer (ESIPT) reaction and molecular skeleton motion associated with hydrogen bonds. The resulting luminescence data reveal that the rate of ESIPT decreases upon increasing the structural constraint. At sufficiently low concentration where negligible dimerization is observed, ESIPT takes place in 1 and 2 but is prohibited in 3 and 4, for which high geometry constraint is imposed. The results imply that certain structural bending motions associated with hydrogen bonding angle/distance play a key role in ESIPT. This trend is also well supported by the DFT computational approach, in which the barrier associated with ESIPT is in the order of 1 < 2 < 3 < 4. Upon increasing the concentration in cyclohexane, except for 2, the rest of the title compounds undergo ground-state dimerization, from which the double proton transfer takes place in the excited state, resulting in a relatively blue shifted dimeric tautomer emission (cf. the monomer tautomer emission). The lack of dimerization in 2 is rationalized by substantial energy required to adjust the angle of hydrogen bond via twisting the propylene bridge prior to dimerization.     

Chemical Dealloying Mechanism of Bimetallic Pt–Co Nanoparticles and Enhancement of Catalytic Activity toward Oxygen Reduction

The chemical dealloying mechanism of bimetallic Pt–Co nanoparticles (NPs) and enhancement of their electrocatalytic activity towards the oxygen reduction reaction (ORR) have been investigated on a fundamental level by the combination of X‐ray absorption spectroscopy (XAS) and aberration‐corrected scanning transmission electron microscopy (STEM). Structural parameters, such as coordination numbers, alloy extent, and the unfilled d states of Pt atoms, are derived from the XAS spectra, together with the compositional variation analyzed by line‐scanning energy‐dispersive X‐ray spectroscopy (EDX) on an atomic scale, to gain new insights into the dealloying process of bimetallic Pt–Co NPs. The XAS results on acid‐treated Pt–Co/C NPs reveal that the Co–Co bonding in the bimetallic NPs dissolves first and the remaining morphology gradually transforms to a Pt‐skin structure. From cyclic voltammetry and mass activity measurements, Pt–Co alloy NPs with a Pt‐skin structure significantly enhance the catalytic performance towards the ORR. Further, it is observed that such an imperfect Pt‐skin surface feature will collapse due to the penetration of electrolyte into layers underneath and cause further dissolution of Co and the loss of Pt. The electrocatalytic activity decreases accordingly, if the dealloying process lasts for 4 h. The findings not only demonstrate the importance of appropriate treatment of bimetallic catalysts, but also can be referred to other Pt bimetallic alloys with transition metals.     

Ultra-performance liquid chromatography/tandem mass spectrometric determination of testosterone and its metabolites in in vitro samples

This paper describes the development and partial validation of a fast, sensitive and specific ultra-performance liquid chromatography/tandem mass spectrometric (UPLC/MS/MS) method for the determination of testosterone (T) and its four metabolites, 6beta-OH-T, 16alpha-OH-T, 16beta-OH-T and 2alpha-OH-T, in in vitro samples. The analytical method involves direct dilution of samples with acetonitrile containing an internal standard, followed by separation of testosterone and the four metabolites on an Acquity UPLCtrade mark C(18) column and detected by selected reaction monitoring (SRM) in positive ionization mode using turbo ionspray ionization. The parent compound and its metabolites investigated were well separated (Rs >1.5) with a run time of 4 min under a gradient condition. The method was partially validated. The linear concentration range was 0.01 to 5 microM for all the compounds of interest. Inter-assay mean bias and relative standard deviation (RSD) were in the range of -12% to 8% and 4.1% to 8.5%, respectively. Intra-assay mean bias and RSD were in the range of -8.0% to 5.2% and 3.4% to 9.6%, respectively. The lower limit of quantitation for this assay was 0.01 microM. The differences in LC/MS performance were investigated by conducting a comparison of UPLC with another method previously optimized for HPLC-based separation and quantification of testosterone and its metabolites.     

Extensive spectral tuning of the proton transfer emission from 550 to 675 nm via a rational derivatization of 10-hydroxybenzo[h]quinoline

Via a systematic derivatization of the excited-state intramolecular proton-transfer system, 10-hydroxybenzo[h] quinoline, the proton-transfer emission can be extensively tuned from 550 nm (1) to 675 nm (6), in which amplified spontaneous emission was readily observed for , generating a new family of proton transfer laser dyes.