A nonradioactive method for detecting phosphates and polyphosphates separated by PAGE

Nonradioactive polyphosphate (poly(P); (PO(3) (-))(n)) species resolved by PAGE can be detected by hydrolytic degradation of the polyphosphates into orthophosphates (P(i)) with a 5 M HCl solution saturated with NaCl, followed by staining the P(i) degradation products in a 1 M HCl solution of 0.25% w/v methyl green and 1% w/v ammonium molybdate. This method detects down to 0.5 nmol of phosphate as P(i), linear poly(P) (condensed phosphate), pyrophosphate (P(2)O(7) (4) (-)), or cyclic trimetaphosphate ion (P(3)O(9))(3) (-) species. This method improves the current method of staining linear poly(P) longer than four phosphate units with Toludine blue-O after PAGE. This study also shows that Stains-All can visualize resolved linear poly(P) shorter than those visualized by Toluidine blue-O. It is hoped that this sequential hydrolytic degradation and phosphate visualization method for detecting ortho-, linear, and cyclic poly(P) species will be a useful tool, as poly(P) are being discovered in a wide variety of biological systems, and their biochemical roles are still largely unknown.     

Calibration transfer strategy to compensate for instrumental drift in portable quadrupole mass spectrometers

We report the use of a calibration transfer strategy to correct for drift in the quantitative sensitivity of a portable quadrupole mass spectrometer (QMS) aimed at process monitoring applications. Gas mixtures of CH₄/Ar/C₂H₆/CO₂ were studied with calibration phase measurements made of the pure gases for a univariate analysis and of 40 multi-component mixtures for a multivariate approach. To evaluate calibrations, test set spectra of a CH₄/Ar/C₂H₆/CO₂ gas mixture were recorded bi-weekly over a period of 12 months. As part of the strategy a standard of pure argon was measured during both calibration and test phases so that correction factors could be calculated for each measurement day. It was shown that in the absence of a calibration transfer strategy quantifications of test set spectra could be inaccurate by more than an order of magnitude over 12 months. Furthermore, due to the effects of drift in the sensitivity over the 6 days required to record the training set in the calibration phase it was found that the multivariate analysis quantified test spectra less accurately than the univariate analysis. However, by applying the calibration transfer strategy across all measurements (both calibration and test phases) it was shown that the errors in prediction using the multivariate analysis previously seen after 2 weeks were not observed until approximately 12 months later.     

Ion implant-induced change in polyimide films monitored by variable energy positron annihilation spectroscopy

6FDA-pMDA polyimide membranes were implanted with 140 keV N⁺ ions to fluences between 2 × 10¹⁴ and 5 × 10¹⁵ cm⁻². Variable energy positron annihilation spectra were taken and spectral features compared to previously reported changes in gas permeability and permselectivity of these membranes as a function of ion fluence. Positron data corroborate the explanation of these changes in terms of molecular damage caused by the implant: for fluences up to about 1 × 10¹⁵ cm⁻², the concentration of irradiation-induced defects merely increases with implant fluence; while fluences exceeding this threshold value create a second type of positron annihilation site, thereby marking a distinct change in the structure of the polymer, which is responsible for the vast improvement of gas permselectivity data found at the same threshold fluence. PACS codes: 78.70.Bj—positron annihilation; 61.82.Pv—polymers, organic compounds; 61.72.Ww—doping and impurity implantation. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2413–2421, 1998     

Oxygen initiated combustion: Thermochemistry and kinetics of unsaturated hydrocarbons

The thermochemistry and kinetics of the initiation reactions involved in the oxidation of unsaturated fuels are explored. The thermochemistry of intermediate radicals, diradicals, and molecular species involved are estimated using group additivity with some assistance from bond additivity. Kinetic parameters are estimated with the techniques of thermochemical kinetics. In the case of acetylene, estimated rate constants are in excellent agreement with experimental results on the induction period and flame speed. It is shown that the route initiated by O₂ addition to an unsaturated carbon atom to produce a 1,4 diradical is faster than any other path available to form radicals capable of propagating a chain. The 1,4 diradicals so produced can generally cyclize to form a dioxetane which exothermically opens to a dialdehyde which is the ultimate radical source. Below 1000 K unsaturates will always initiate oxidation faster than saturated fuels. © 1996 John Wiley & Sons, Inc.     

Dynamic visualization of membrane-inserted fraction of pHluorin-tagged channels using repetitive acidification technique

Background  

Changes in neuronal excitability, synaptic efficacy and generally in cell signaling often result from insertion of key molecules into plasma membrane (PM). Many of the techniques used for monitoring PM insertion lack either spatial or temporal resolution.     

tert‐Butyl 5‐methoxy‐3‐pentyl­indole‐1‐carboxyl­ate

The molecule of the title compound, C₁₉H₂₇NO₃, is essentially planar, with all non‐H atoms within 0.2 Å of the nine‐membered indole plane, except for the three tert‐butyl C atoms. The C₅ pentyl chain is in an extended conformation, with three torsion angles of 179.95 (13), 179.65 (13) and −178.95 (15)° (the latter two angles include the C atoms of the C₅ chain only). Three intramolecular C—H⋯Ozdbnd;C contacts are present (C⋯O < 3.05 Å and C—H⋯O > 115°), and an intermolecular C—H⋯Ozdbnd;C contact and π–π stacking complete the intermolecular interactions.     

Analysis of the optical and geometrical isomer distributions in selected propylene glycol acetals

For the first time, relative distributions of optical and geometrical isomers in selected propylene glycol acetals are determined. Resolution of the four acetal isomers possible through the reaction of racemic propylene glycol (PG) with selected aldehydes is demonstrated. The four isomers are ascribed to the presence of syn and anti geometrical isomers for each optically active PG acetal enantiomer. Thus, the (+) and well as (-) enantiomer are found to have a pair of syn and anti geometrical isomers. The ratio of the (+) and (-) isomers in the product remains at an approximate 50:50 ratio, as expected. However, somewhat unexpectedly, the syn/anti geometrical isomer ratio systematically varies with the nature of the substituent comprising the side chain of the aldehyde. Mechanisms involving electronic and minimal steric effects are advanced as possible reasons for the change in the syn/anti PG acetal ratios.     

Perchlorate in water via US Environmental Protection Agency Method 331 Determination of method uncertainties, lowest concentration minimum reporting levels, and Hubaux-Vos detection limits in reagent water and simulated drinking water

US Environmental Protection Agency (EPA) Method 331 determines perchlorate in drinking water using non-suppressed ion chromatography with tandem mass spectrometry. This study reports the results of calibration and recovery studies in reagent water, as well as of a recovery study in simulated drinking water (i.e., total dissolved solids are 500 mg/mL each of chloride, sulfate, and bicarbonate). The perchlorate concentrations in the study ranged from 0.05 to 64 ng/mL. At 95% confidence, the Hubaux-Vos detection limit (H-V DL) was 0.04 ng/mL for the calibration study and the simulated-drinking-water recovery study, and 0.03 ng/mL for the reagent-water recovery study. The lowest concentration minimum reporting level was 0.03 ng/mL for reagent water and 0.0 7 ng/mL for simulated drinking water, again at 95% confidence.