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81.
Itsenko O Norberg D Rasmussen T Långström B Chatgilialoglu C 《Journal of the American Chemical Society》2007,129(29):9020-9031
Photoinitiated carbonylation of alkyl iodides with [11C]carbon monoxide (11C t1/2=20.4 min) is enhanced by ketones that have lowest-lying excited triplet state of npi* character. For example, adding 5 mol % of acetophenone increases radiochemical yields from 3 to 59% in brief 6-min long reactions. Similar or higher yields were achieved by adding di-tert-butyl peroxide. Since radicaloid npi* exited-state ketones and tert-butoxyl radicals have similar reactivity, the photosensitization proceeds most likely via a H-atom transfer mechanism rather than via energy transfer. We propose a mechanism that can account for the enhancement as well as for the formation of observed byproducts. The energy profile obtained by DFT calculations support the feasibility of the mechanism, and observed experimental differences in reactivity could be well rationalized by the calculated data. NBO calculations were performed to further analyze the obtained energetics. Various [carbonyl-11C]esters and some [carbonyl-11C]amides were synthesized in good radiochemical yields from primary and secondary alkyl iodides illustrating the utility of dialkyl peroxides to accelerate the carbonylations. These findings have potential in elaborating new synthetic protocols for the production of 11C-labeled tracers for positron emission tomography. 相似文献
82.
Sergey N. Fedosov Lars Berglund Torben E. Petersen 《Journal of organometallic chemistry》2007,692(6):1234-1242
Cobalamin (Cbl, vitamin B12) consists of two moieties: (i) the corrin ring with the central Co-ion in the oxidation states Co3+/2+/1+ and (ii) the nucleotide side chain. The lower position of the ring is typically occupied by the nucleotide base (Bzm), whereas the upper surface coordinates exchangeable ligands. We have found that amino-tetrazole can coordinate to H2O · Cbl (Co3+) with Kd = 10−5-10−6 M. A specific group (presumably tetrazole, TZ) can be easily created in CNBr-activated Sepharose by treatment with . The prepared matrix (STZ) contained ≈10 mM of the active groups, which bound H2O · corrinoids with Kd = 10−5-10−6 M. Stability of STZ-Cbl bonds gradually increased and reached Kd = 10−7 M over 10-20 h (20 °C, pH 6-7). This effect can be ascribed to partial displacement of Bzm and coordination of TZ to the lower position. The binding was most efficient at pH 4-7 and low ionic strength, yet, noticeable adsorption took place even at extreme conditions, pH 1-9 and I = 0-2 M. Reduced corrins (Co2+) also exhibited high affinity for STZ. The bound ligands could be eluted as H2O · Cbl (pH 0), HO · Cbl (pH 14) or diCN · Cbl (pH 9-12, CN−). The adsorbent is applicable for one-step purification of corrins from a crude extract; separation of aquo- and diaquo-forms; specific capturing of H2O · Cbl from a mixture containing organo-Cbls or protein-bound Cbl, analysis of peptide-Cbl dissociation kinetics, etc. 相似文献
83.
Improved wastewater disinfection by ultrasonic pre-treatment 总被引:1,自引:0,他引:1
The objective of our work is to evaluate the scientific and economic potential of US application as a pre-treatment step in combination with UV to optimise the disinfection process of wastewaters. Ultrasound application of 20 s at low density of 30 W/l changed the particle size distribution (PSD) of the samples, the mean particle diameter dropped from 70 to 11 microm. Generally it is assumed that bioparticles bigger than 50 microm are difficult to disinfect by UV. We observed that the relevant particle size range >50 microm in samples taken from the primary clarifier was reduced by at least three-quarters by low ultrasound doses. As expected, these changes in PSD notably effect the disinfection efficiency of UV. Whereas UV treatment of secondary clarifier's effluents alone led to a reduction of fecal coliforms by 2.5 log units, pre-treatment by sonication (only 5 s at densities of 50 and 310 W/l) clearly enhanced the disinfection efficiency: reductions of CFU (colony forming unit) concentration now ranged between 3.3 and 3.7 log units. We noticed an influence of the bacteria's morphology on the disinfection efficiency of the combined process (US plus UV). Gram-positive streptococci seem less vulnerable to ultrasound exposure than thinner-walled gram-negative bacteria like the entire group of coliforms. The application of an ultrasound step might be also useful in terms of cost-effectiveness. In our lab-scale tests 30 s of UV treatment alone were required to reduce the number of fecal coliforms by 3.7 log units. When applied in combination, 5 s of ultrasonic followed by only 5 s of UV irradiation had the same result and energy consumption was only 43%. 相似文献
84.
85.
86.
Robert Kun Sndor Tarjn Albert Oszk Torben Seemann Volker Zllmer Matthias Busse Imre Dkny 《Journal of solid state chemistry》2009,182(11):3076-3084
Nitrogen-doped TiO2 catalysts were prepared by a precipitation method. The samples were calcined at 400 °C for 4 h in air. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), low temperature N2-adsorption was used for structural characterization and UV-diffuse reflectance (UV-DR) was applied to investigate the optical properties of the as-prepared samples. It was found that microporous N-doped catalysts have solely anatase crystalline structure. Acidic treatment of the calcined samples was performed using sulfuric acid agitation. The crystalline structure remained unchanged due to surface treatment, while the porosity and the surface areas were decreased dramatically. Optical characterization of the doped catalysts showed that they could be excited by visible light photons in the 400–500 nm wavelength range (λg,1=390 nm, λg,2=510 nm). It was also established that surface treatment enhances the Vis-light absorption of the N-TiO2 powders. Finally the catalysts were tested in the photocatalytic degradation of phenol in aqueous suspensions. Two different light sources were used; one of them was a UV-rich high pressure Hg-lamp, while the other was a tubular visible light source. We found that using visible light illumination N-doped, acid treated TiO2 samples were more catalytically active than non-doped TiO2 catalysts. 相似文献
87.
Edit Pál Torben Seemann Volker Zöllmer Matthias Busse Imre Dékány 《Colloid and polymer science》2009,287(4):481-485
Zinc oxide/poly(acrylic acid) (ZnO/PAA) multilayered hybrid films with different layer thicknesses were prepared by radio
frequency magnetron sputtering. Zinc peroxide was used as precursor materials for the preparation of ZnO layers, since the
zinc peroxide decomposes to ZnO during the film deposition. The films have a high transmittance in the visible region and
exhibit visible photoluminescence emission. The band gap energy of the films—determined by the Tauc relationship—decreases
with increasing layer thickness (3.40–3.36 eV) due to the increasing crystalline size of the ZnO particles. The morphological
investigations showed that a real layered hybrid film structure formed. 相似文献
88.
We report on the direct observation of the transition from a compressible superfluid to an incompressible Mott insulator by recording the in-trap density distribution of a Bosonic quantum gas in an optical lattice. Using spatially selective microwave transitions and spin-changing collisions, we are able to locally modify the spin state of the trapped quantum gas and record the spatial distribution of lattice sites with different filling factors. As the system evolves from a superfluid to a Mott insulator, we observe the formation of a distinct shell structure, in good agreement with theory. 相似文献
89.
90.
Darden SK Pedersen SB Larsen ON Dabelsteen T 《The Journal of the Acoustical Society of America》2008,124(2):758-766
The acoustic environment of swift foxes Vulpes velox vocalizing close to the ground and the effect of propagation on individual identity information in vocalizations were quantified in a transmission experiment in prairie habitat. Sounds were propagated (0.45 m above the ground) at distances up to 400 m. Effects of transmission were measured on three sound types: synthesized sweeps with 1.3 kHz bandwidths spanning in the range of 0.3-8.0 kHz; single elements of swift fox barking sequences (frequency range of 0.3-4.0 kHz) and complete barking sequences. Synthesized sweeps spanning 0.3-1.6 and 1.2-2.5 kHz propagated the furthest and the latter sweeps exhibited the best transmission properties for long-range propagation. Swift fox barking sequence elements are centered toward the lower end of this frequency range. Nevertheless, measurable individual spectral characteristics of the barking sequence seem to persist to at least 400 m. Individual temporal features were very consistent to at least 400 m. The communication range of the barking sequences is likely to be farther than 400 m and it should be considered a long-ranging vocalization. However, relative to the large home ranges of swift foxes (up to 16 km(2) in the experimental area) the barking sequence probably functions at intermediate distances. 相似文献