Pulsed Sonochemistry

Very few papers are devoted to the study of the chemical effects of pulsed ultrasound in the low-frequency range. The present work consists of a systematic experimental study of the effects of pulsed ultrasound in the 20 kHz range using an immersed titanium horn. The light scattered by the bubble cloud, the acoustic pressure, and the sonochemical activity were measured. The sonochemical activity was studied by measuring the light emitted by a fast chemiluminescent reaction (oxidation of luminol). The chemiluminescence behavior observed at 20 kHz was compared with the behavior observed at 1.7 MHz. The chemiluminescence takes time to install when sonication starts and, at 20 kHz, the luminescence intensity decreases monoexponentially when sonication stops. Interestingly, at 1.7 MHz, the luminescence intensity decreases biexponentially with an important fast component. The interpretation of these various behaviors requires that the acoustical characteristics of the ultrasound generator and of the vessel, and also the properties of the bubble field, be considered.info:eu-repo/semantics/publishe

Characterization of the affinity of calix[6]tris-ureas receptors for ion pairs and triads

info:eu-repo/semantics/nonPublishe

129Xe and 1H NMR Study of the Reversible Trapping of Xenon by Cryptophane-A in Organic Solution

The interaction of xenon with cryptophane-A in 1,1,2,2-tetrachloroethane-d2 is investigated by 129Xe and 1H NMR spectroscopy. Xenon is reversibly trapped into the cavity of this host to form a 1 to 1 host−guest complex with an apparent association constant K of the order of at least 3 × 103 M-1 at 278 K. The exchange between the free and bound xenon is slow on the 129Xe NMR time scale, and the bound xenon resonance is shifted by approximately 160 ppm to lower frequencies with respect to the free xenon resonance. The xenon complex is at least 4 and 20 times more stable, respectively, than the corresponding chloroform and methane complexes under the same conditions. The stability of this xenon complex appears to be much greater than that of the previously described xenon complex of α-cyclodextrin in water. This is probably due to the combination of three favorable effects: (i) good size matching between the guest and the cryptophane cavity in its most relaxed conformation, resulting in the optimization of the London forces between the highly polarizable guest and the electron rich aromatic rings of the host (enthalpic stabilization); (ii) no rotational or vibrational entropy loss of the monatomic guest in the cryptophane cavity; and (iii) no (or little) entropy loss due to reduction of the conformational freedom of the host. Analysis of the line widths of the signals corresponding to the free and bound xenon as a function of the relative xenon/cryptophane ratio suggests that the incoming xenon atom must displace the departing one to enter the cryptophane cavity, and that the empty cryptophane is not involved in the complexation equilibrium.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Xe NMR to probe hydrophobic cavities

info:eu-repo/semantics/nonPublishe

Topsentins, new toxic bis-indole alkaloids from the marine sponge Topsentia genitrix

Three new bis-indole alkaloids, topsentin-A (1), -B 1 (2), and -B2 (3) have been isolated from the Mediterranean sponge Topsentia genitrix and their structure determined by spectroscopic methods. These compounds are weakly toxic for fish and for dissociated cells of the freshwater sponge Ephydatiafluviatilis and thus might be partially responsible for the chemical defense of the sponge.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

1st Snow Data Assimilation Workshop in the framework of COST HarmoSnow ESSEM 1404

The 1st Snow Data Assimilation Workshop, organized under the COST Action ESSEM 1404 HarmoSnow, took place in Offenbach, Germany, on 8–9 March 2017. Of particular relevance for the workshop were thematic sessions on i) data assimilation methods and the use of snow observations, ii) snow observations and evaluation, iii) snow observations and physical snow models, and iv) snow observations and hydrological models. This report summarizes the scientific contributions presented at the workshop. The discussions mainly focused on methods for combining satellite observations with conventional in-situ snow measurements and modeling results, as well as on errors in the spatial and temporal representation of snow measurements for data assimilation in NWP and hydrological models. It has been shown that the assimilation of in-situ and satellite-based snow observations improves the quality of the snow analysis and forecast. However, in order to achieve this positive impact, a thorough quality control of the observational data is necessary, in particular because of the automation of the ground-based networks