Microwave-assisted headspace solid-phase microextraction for the rapid determination of organophosphate esters in aqueous samples by gas chromatography-mass spectrometry

The rapid and solvent-free determination of organophosphate esters (OPEs) in aqueous samples via one-step microwave-assisted headspace solid-phase microextraction (MA-HS-SPME) followed by gas chromatography-mass spectrometry (GC-MS) analysis is described. Tri-n-butyl phosphate (TnBP) and tris-(2-ethylhexyl) phosphate (TEHP) were selected as model compounds for the method of development and validation. The effects of various extraction parameters for the quantitative extraction of these analytes by MA-HS-SPME were systematically investigated and optimized. The analytes, in a 20 mL water sample (in a 40 mL sample bottle containing 2 g of NaCl, pH 3.0), were efficiently extracted by a polydimethylsiloxane-divinylbenzene (PDMS-DVB) fiber placed in the headspace when the system was microwave irradiated at 140 W for 5 min. The limits of quantification (LOQs) for TnBP and TEHP were 0.5 and 4 ng/L, respectively. Using the standard addition method, MA-HS-SPME coupled with GC-MS was utilized to determine selected OPEs in surface water and wastewater treatment plants (WWTP) influent/effluent samples. Preliminary results show that TnBP was commonly detected OPEs in these aqueous samples, the correlation coefficients (r²) of the standard addition curves were greater than 0.9822, indicating that the developed method appears to be a good alternative technique for analyzing OPEs in aqueous samples.     

Production of l-lactic acid byRhizopus oryzae in a bubble column fermenter

Two distinctive forms of growth (mycelial filamentous and mycelial pellets) ofRhizopus oryzae were obtained by manipulating the initial pH of the medium with the controlled addition of CaCO₃ in a bubble fermenter. In the presence of CaCO₃, diffused filamentous growth was obtained when the initial pH of the substrate was 5.5. In the absence of CaCO3, mycelial pellet growth was obtained when the initial pH was 2.0. The fermentation study indicated that the mycelial growth has a shorter lag period before the onset of acid formation. Both physical forms of growth ofRhizopus exhibited a high yield of L-lactic acid in the bubble fermenter when the initial glucose concentration exceeded 70 g/L. A final lactic acid concentration of 62 g/L was produced by the filamentous form ofRhizopus from 78 g/L glucose after 27 h. This showed a weight yield of 80% of glucose consumed, with an average specific productivity of 1.46 g/h/g. Similarly, the pellet form ofRhizopus produced a final lactic acid concentration of 66 g/L from 76 g/L glucose after 43 h, with a weight yield of 86% and an average specific productivity of 1.53 g/h/g.     

Unbinding of the streptavidin-biotin complex by atomic force microscopy: a hybrid simulation study

A hybrid molecular simulation technique, which combines molecular dynamics and continuum mechanics, was used to study the single-molecule unbinding force of a streptavidin-biotin complex. The hybrid method enables atomistic simulations of unbinding events at the millisecond time scale of atomic force microscopy (AFM) experiments. The logarithmic relationship between the unbinding force of the streptavidin-biotin complex and the loading rate (the product of cantilever spring constant and pulling velocity) in AFM experiments was confirmed by hybrid simulations. The unbinding forces, cantilever and tip positions, locations of energy barriers, and unbinding pathway were analyzed. Hybrid simulation results from this work not only interpret unbinding AFM experiments but also provide detailed molecular information not available in AFM experiments.     

Interfacial Speciation Determines Interfacial Chemistry: X-ray-Induced Lithium Fluoride Formation from Water-in-salt Electrolytes on Solid Surfaces

Super-concentrated “water-in-salt” electrolytes recently spurred resurgent interest for high energy density aqueous lithium-ion batteries. Thermodynamic stabilization at high concentrations and kinetic barriers towards interfacial water electrolysis significantly expand the electrochemical stability window, facilitating high voltage aqueous cells. Herein we investigated LiTFSI/H₂O electrolyte interfacial decomposition pathways in the “water-in-salt” and “salt-in-water” regimes using synchrotron X-rays, which produce electrons at the solid/electrolyte interface to mimic reductive environments, and simultaneously probe the structure of surface films using X-ray diffraction. We observed the surface-reduction of TFSI⁻ at super-concentration, leading to lithium fluoride interphase formation, while precipitation of the lithium hydroxide was not observed. The mechanism behind this photoelectron-induced reduction was revealed to be concentration-dependent interfacial chemistry that only occurs among closely contact ion-pairs, which constitutes the rationale behind the “water-in-salt” concept.     

Morphologies of multicompartment micelles formed by triblock copolymers

Multicompartment micelles are desirable for advanced applications such as drug delivery. Recently, core-shell-corona (CSC) and segmented-worm (SW) micelles formed by ABC triblock terpolymers with three mutually immiscible blocks are observed in experiments. We have performed dissipative particle dynamics simulations to study the effects of molecular architecture, block length, and solution concentration on the morphologies of ABC triblock terpolymers. The formation of CSC and SW micelles for linear and miktoarm star ABC terpolymers is confirmed in this work. In addition, we predict that different multicompartment micellar morphologies (e.g., incomplete skin-layered micelles and segmented worms) can be formed by linear copolymer with different arrangements of the three blocks.     

Paper-based enzyme-free immunoassay for rapid detection and subtyping of influenza A H1N1 and H3N2 viruses

Development of rapid screening in the ambulatory environment is the most pressing needs for the control of spread of infectious disease. Despite there are many methods to detect the immunoassay results, quantitative measurement in rapid disease screening is still a great challenge for point-of-care applications. In this work, based on the internal structural protein, i.e., nucleoprotein (NP), and outer surface glycoproteins, i.e., H1 and H3, of the influenza viruses, specific and sensitive immunoassay on paper-based platform was evaluated and confirmed. Detection and subtyping of influenza A H1N1 and H3N2 viruses found in people were demonstrated by colorimetric paper-based sandwich immunoassay. Concentration-dependent response to influenza viruses was shown and the detection limits could achieve 2.7 × 10³ pfu/assay for H1 detection and 2.7 × 10⁴ pfu/assay for H3 detection, which are within the clinical relevant level. Moreover, detection of influenza virus from infected cell lysate and clinical samples was demonstrated to further confirm the reliability of the paper-based immunoassay. The use of paper for the development of diagnostic devices has the advantages of lightweight, ease-of-use, and low cost and paper-based immunoassay is appropriate to apply for rapid screening in point-of-care applications.     

Electroosmotic Flow through an Annulus

The electro-osmosis through an annulus is investigated. The electric potential and flow velocity profile are obtained by solving the linearized Poisson-Boltzmann equation and the Stokes equation. Both the thin and thick double layer limits are analyzed. Under the condition of thin double layer, the electro-osmotic mobility can be described by the Helmholtz-Smoluchowski equation with a geometry-dependent correction factor. There exist net flows even for zero area-averaged surface charge density due to the curvature differences between the inner and outer walls. The flow direction is determined by the sign of the charge on the inner cylinder. We also found that under certain circumstances the flow direction in an annulus is opposite to that in a capillary with the same sign of the net charge. Copyright 2000 Academic Press.     

Formal Syntheses of (±)‐Methylenomycins A and B

The syntheses of methyl ester of (±)‐desepoxy‐4,5‐didehydromethylenomycin A ( 4 ) and 2,3‐dimethyl‐5‐methoxycarbonyl‐2‐cyclopentenone ( 5 ) were accomplished from a common starting material, 2,3‐dimethyl‐4‐methoxyphenol (8), in only four and two steps in 35% and 53% overall yields, respectively. Photochemical rearrangements of masked p‐benzoquinones in methanol are the key steps.     

Coproduction of ethanol and glycerol

Ethanol and glycerol are both metabolic products of yeasts. There are occasions when coproduction of both is considered desirable in industrial operations. In this article, we describe the potential of integrating the two processes. A LORRE Y8 yeast culture isolated from molasses is capable of efficient glycerol production from glucose, and a yeast Culture 1400 is an excellent producer of ethanol. By controlling the process conditions, the ratio of ethanol and glycerol production can be varied.