Dithiadiazolium salts as initiators for the cationic ring-opening polymerization of tetrahydrofuran

Mono-, bis- and tris-(1,3,2,4-dithiadiazolium) salts [R-(CNSNS ⁺)_n]_n+[AsF^-₆]_n (R = aryl, n = 1, 2, 3) were found to initiate the cationic ring-opening polymerization of tetrahydrofuran (THF) at room temperature to give clear gels from which the pure polymer was precipitated. 1,3,2,4-Dithiadiazolium cations associated with the hard [AsF₆]^- anion thus constitute a new class of cationic polymerization initiators. The poly(THF) formed by initiation with 1,3,2,4-dithiadiazolium cation was characterized by gel permeation chromatography, infrared spectrophotometry, and ¹³C-NMR spectroscopy. Number-average molecular weights of 198 700 g mol^-1 (polydispersity 1.96) and 190 000 g mol^-1 (polydispersity 1.61) were obtained using [PhCNSNS ] [AsF₆] and [C₆H₃-1,3,5-(CNSNS )₃][AsF₆]₃, respectively, as initiators. The use of multifunctional dithiadiazolium salts as initiators suggests that they may be useful in the preparation of starburst and dendritic polymers. © 1992 John Wiley & Sons, Inc.     

Transfer of near-infrared monochromator calibrations for tobacco constituents to tilting-filter instruments

Near-infrared calibrations for water, reducing sugar, glycerin, propylene glycol, nicotine, and menthol in tobacco blends were first obtained with a monochromator instrument. Transfer of calibrations to a tilting-filter instrument for factory trials is shown to be facilitated greatly by the computer-assisted scheme MTRAN. By means of this software, calibration equations were established for a Neotec 51A instrument that is sufficiently rugged for factory use. The predictive capabilities of the transferred calibrations are similar to those of the research monochromator.     

Bench Scale Studies of the Soil Aeration Process for Bioremediation of Petroleum Hydrocarbons

An alternative to traditional hydrocarbon bioremediation is to pump air through unsaturated soils to create aerobic conditions and induce biodegradation. This study examines the effects of moisture and nutrient augmentation on biodegradation of petroleum hydrocarbons in aerated soils. Findings indicate that forced aeration, coupled with additions of nutrients and moisture, stimulate hydrocarbon-degrading microorganisms and present a feasible approach to bioremediation management.     

Electrospray mass spectrometry of methanol and water solutions suppression of electric discharge with SF6 gas

An equation by D. P. H. Smith predicts the capillary voltage required for the onset of electrospray (ES). For different solvents the voltage increases with the square root of the surface tension. Water requires a potential that is 1.8 times higher than that for methanol. This is verified experimentally. The higher potential required for water leads to ES in the presence of corona electric discharge. For low total ES plus corona currents, the electrosprayed analyte ion intensity is not adversely affected by the presence of discharge. At high total currents, there is a large decrease of analyte sensitivity. The sensitivity decrease is probably due to adverse space charge effect at high currents. The discharge can be suppressed by adding sulfur hexafluoride to the ambient gas. Both sensitivity and signal stability are improved. However, the sensitivity still remains lower by a factor of ≈ 4 relative to that observed with methanol. This is attributed to lower efficiency of gas-phase ion formation from charged water, relative to methanol, droplets.     

Acid–base sensor based on sol–gel encapsulation of bromothymol blue in silica: application for milk spoilage detection

Journal of Sol-Gel Science and Technology - In this work, silica capsules containing bromothymol blue (BTB) were synthesized by a modified Stöber sol–gel method. These silica capsules...     

Are there reliable DFT approaches for 13C NMR chemical shift predictions of fullerene C60 derivatives?

The relationships between experimental and theoretical ¹³C NMR chemical shifts of a pristine fullerene C₆₀, monoadducts from [2 + n] cycloaddition (n = 1–3), and one [2 + 1] bis‐adduct are systematically analyzed for the first time by using diverse quantum‐chemical levels of theory. These levels involved B3LYP, B3PW91, B97‐2, mPW1PW91, PBE1PBE, and X3LYP hybrid functionals combined with 3‐21G, 6‐31G, 6‐31G(d), 6‐31G(d,p), 6‐31G(d,2p), LanL2DZ, and SDDAll basis sets. X3LYP/6‐31G approach is determined to have the lowest deviations from the ¹³C NMR experimental data compared to the other methods for all the fullerene compounds (mean absolute error value is 0.856 ppm and root mean squared error value is 1.197 ppm). The highest deviations are characteristic for α (sp² C2/C5/C8/C10) and β (sp² C6/C7/C11/C12) carbon atoms relative to a functionalization site and for those (sp³ C1/C9) directly attached with a side fragment in the [2 + n] monoadducts (n = 1–3). A probable reason of such deviation is that the approaches do not take into account a contribution of paramagnetic ring currents to ¹³C NMR chemical shifts. The results will be useful in design of novel fullerene derivatives and in performing unambiguous ¹³C NMR chemical shift assignments with modern quantum chemistry calculations.