Hydrolysis kinetics of the sulfonylurea herbicide Sulfosulfuron

The kinetics of hydrolytic degradation of Sulfosulfuron was investigated to predict the fate of the herbicide in an aqueous environment. The study revealed that the hydrolytic degradation of Sulfosulfuron followed first-order kinetics. The degradation of the herbicide was dependent on pH and temperature. Hydrolysis rate was faster in acidic condition (t _1/2 = 9.24 d at pH 4.0) than alkaline environment (t _1/2 = 14.14 d at pH 9.2). Several fold increase in the degradation rate was found when temperature was increased from 10 ± 1°C (t _1/2 = 518 h) to 50 ± 1°C (t _1/2 = 10 h). Activation energy (E _a) was also calculated as 63.87 KJ mol^?1, which is required for the hydrolytic degradation of the molecule. Both media pH and temperature effects were coupled together and derived a complex equation to estimate the overall effect of these two abiotic factors. The major degradation mechanism of the compound was the breaking of the sulfonylurea bridge yielding corresponding sulfonamide and aminopyrimidine. The possible significance of the results to persistence of the herbicide in the field condition is discussed.     

Absorption and emission of light in red emissive carbon nanodots

The structure–function relationship, especially the origin of absorption and emission of light in carbon nanodots (CNDs), has baffled scientists. The multilevel complexity arises due to the large number of by-products synthesized during the bottom-up approach. By performing systematic purification and characterization, we reveal the presence of a molecular fluorophore, quinoxalino[2,3-b]phenazine-2,3-diamine (QXPDA), in a large amount (∼80% of the total mass) in red emissive CNDs synthesized from o-phenylenediamine (OPDA), which is one of the well-known precursor molecules used for CND synthesis. The recorded NMR and mass spectra tentatively confirm the structure of QXPDA. The close resemblance of the experimental vibronic progression and the mirror symmetry of the absorption and emission spectra with the theoretically simulated spectra confirm an extended conjugated structure of QXPDA. Interestingly, QXPDA dictates the complete emission characteristics of the CNDs; in particular, it showed a striking similarity of its excitation independent emission spectra with that of the original synthesized red emissive CND solution. On the other hand, the CND like structure with a typical size of ∼4 nm was observed under a transmission electron microscope for a blue emissive species, which showed both excitation dependent and independent emission spectra. Interestingly, Raman spectroscopic data showed the similarity between QXPDA and the dot structure thus suggesting the formation of the QXPDA aggregated core structure in CNDs. We further demonstrated the parallelism in trends of absorption and emission of light from a few other red emissive CNDs, which were synthesized using different experimental conditions.

Herein we unveil the presence of a molecular fluorophore quinoxalino[2,3-b]phenazine-2,3-diamine (QXPDA) in a colossal amount in red emissive CNDs synthesized from o-phenylenediamine, a well-known precursor molecule used for CND synthesis.     

Synthesis of biologically active phenoxy derivatives of substituted benzothiazole organophosphates

The reaction of S‐(phenyl benzothiazolyl‐2)phosphorodichloridothioate/phosphorodichloridodithioate with 2 mol of phenol/4‐chlorophenol/4‐nitrophenol in the presence of stoichiometric amounts of triethylamine in dry THF/CH₂Cl₂ has afforded a series of the corresponding organophosphate phenoxy derivatives ( 1a , 1b , 2a , 2b , and 3a , 3b ). Plausible structures have been proposed on the basis of elemental analysis, IR, ¹H NMR, ³¹P NMR, and mass spectral studies. The antibacterial activity of these organophosphate phenoxy derivatives has been evaluated against pathogenic bacteria Staphylococcus aureus (+ve) and Escherichia coli (−ve). The antifungal activity of these organophosphate phenoxy derivatives has been evaluated against pathogenic fungi Aspergillus niger and Fusarium oxysporium. The results indicate that organophosphate phenoxy derivatives are found more active than the parent compounds. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:84–88, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20582     

Domain wall conductivity in La-doped BiFeO3

The transport physics of domain wall conductivity in La-doped bismuth ferrite (BiFeO3) has been probed using variable temperature conducting atomic force microscopy and piezoresponse force microscopy in samples with arrays of domain walls in the as-grown state. Nanoscale current measurements are investigated as a function of bias and temperature and are shown to be consistent with distinct electronic properties at the domain walls leading to changes in the observed local conductivity. Our observation is well described within a band picture of the observed electronic conduction. Finally, we demonstrate an additional degree of control of the wall conductivity through chemical doping with oxygen vacancies, thus influencing the local conductive state.     

Centers of generalized quantum groups

This paper treats the generalized quantum group $U=U(\chi ,\pi )$ with a bi-homomorphism χ for which the corresponding generalized root system is a finite set. We establish a Harish-Chandra type theorem describing the (skew) centers of U.     

Use of radiation sources with mercury isotopes for real-time highly sensitive and selective benzene determination in air and natural gas by differential absorption spectrometry with the direct Zeeman effect

A new analytical portable system is proposed for the direct determination of benzene vapor in the ambient air and natural gas, using differential absorption spectrometry with the direct Zeeman effect and innovative radiation sources: capillary mercury lamps with different isotopic compositions (¹⁹⁶Hg, ¹⁹⁸Hg, ²⁰²Hg, ²⁰⁴Hg, and natural isotopic mixture). Resonance emission of mercury at a wavelength of 254 nm is used as probing radiation. The differential cross section of benzene absorption in dependence on wavelength is determined by scanning of magnetic field. It is found that the sensitivity of benzene detection is enhanced three times using lamp with the mercury isotope ²⁰⁴Hg in comparison with lamp, filled with the natural isotopic mixture. It is experimentally demonstrated that, when benzene content is measured at the Occupational Exposure Limit (3.2 mg/m³ for benzene) level, the interference from SO₂, NO₂, O₃, H₂S and toluene can be neglected if concentration of these gases does not exceed corresponding Occupational Exposure Limits. To exclude the mercury effect, filters that absorb mercury and let benzene pass in the gas duct are proposed. Basing on the results of our study, a portable spectrometer is designed with a multipath cell of 960 cm total path length and detection limit 0.5 mg/m³ at 1 s averaging and 0.1 mg/m³ at 30 s averaging. The applications of the designed spectrometer to measuring the benzene concentration in the atmospheric air from a moving vehicle and in natural gas are exemplified.     

A bond orbital model investigation of the surface electronic energy structure of Si(111)

Intrinsic surface states for the Si(111) surface are investigated using the Bond Orbital Model. The semi-infinite crystal is simulated by gradually increasing the number of layers until the convergence is achieved. Total density of states are presented for unrelaxed, relaxed and the hydrogen chemisorbed Si(111) surfaces. The effect of the (2 × 1) reconstruction on the dangling bond surface state is also investigated. The results are in excellent agreement with photoemission experiments.     

Band structure of polyacetylene, (CH)x

The one-electron energy bands and densities of states of polyacetylene in both cis- and trans-conformations have been investigated. The principal issue addressed is whether the itinerant picture alone is sufficient to explain the experimental properties of this material. We conclude that the one-electron model provides an excellent zeroth-order explanation of current observations of optical and transport effects in both pure and doped forms of this unusual polymer.