Direct observation of ion evaporation from a triply charged nanodroplet

Triply charged, highly solvated metal ions of the form [Ln(H(2)O)(n)](3+) can be generated using a commercial mass spectrometer, and CID studies on these highly charged metal-solvent clusters allow for the direct observation of a process best described as ion evaporation.     

Experimental quantification of cavitation yield revisited: focus on high frequency ultrasound reactors

Acoustic cavitation plays an important role in enhancing the reaction rate of chemical processes in sonochemical systems. However, quantification of cavitation intensity in sonochemical systems is generally limited to low frequency systems. In this study, an empirical determination of cavitation yield in high frequency ultrasound systems was performed by measuring the amount of iodine liberated from the oxidation of potassium iodide (KI) solution at 1.7 and 2.4 MHz. Experiments for determining cavitation were carried out at various solute (KI) concentrations under constant temperature, obtained by direct cooling of the solution and variable temperature conditions, in the absence of external cooling. Cavitation yield measurements, reported in this work, extend previously reported results and lend credence to the two step reaction pathway in high frequency systems. Additionally, the concentration of KI and temperature affect the cavitation yield of a system such that the iodine production is proportional to both conditions. It is proposed that direct cooling of sonicated KI solution may be advantageous for optimization of cavitation intensity in high frequency sonochemical reactors.     

A threatened beluga (Delphinapterus leucas) population in the traffic lane: vessel-generated noise characteristics of the Saguenay-St. Lawrence Marine Park, Canada

The threatened resident beluga population of the St. Lawrence Estuary shares the Saguenay-St. Lawrence Marine Park with significant anthropogenic noise sources, including marine commercial traffic and a well-established, vessel-based whale-watching industry. Frequency-dependent (FD) weighting was used to approximate beluga hearing sensitivity to determine how noise exposure varied in time and space at six sites of high beluga summer residency. The relative contribution of each source to acoustic habitat degradation was estimated by measuring noise levels throughout the summer and noise signatures of typical vessel classes with respect to traffic volume and sound propagation characteristics. Rigid-hulled inflatable boats were the dominant noise source with respect to estimated beluga hearing sensitivity in the studied habitats due to their high occurrence and proximity, high correlation with site-specific FD-weighted sound levels, and the dominance of mid-frequencies (0.3-23 kHz) in their noise signatures. Median C-weighted sound pressure level (SPL(RMS)) had a range of 19 dB re 1 μPa between the noisiest and quietest sites. Broadband SPL(RMS) exceeded 120 dB re 1 μPa 8-32% of the time depending on the site. Impacts of these noise levels on St. Lawrence beluga will depend on exposure recurrence and individual responsiveness.     

Insights into the post-translational methylation of arginine from studies of guanidinium-water nanodroplets

Highly solvated methylated guanidinium ions ([Me nGuan(H2O)m](+); n=0-4 and 6; m=1->50), which model the various post-translationally methylated states of arginine, were generated in the electrospray ionization (ESI) source of an unmodified commercial tandem mass spectrometer. The dehydration processes of highly solvated [Me nGuan(H2O)21](+) ions were monitored by using energy-dependent ESI MS. These data, together with supporting calculations, provide a detailed picture of the interplay of methylation and hydration, and both the calculations and the experimental evidence suggest a specific structural basis for the observed effects. The ramifications for biochemical binding events that are controlled by the post-translational methylation of arginine to give dimethylarginines are discussed.