Acoustic cavitation produced by microsecond pulses of ultrasound: a discussion of some selected results.

Because of its extensive utilization in clinical practice, and because the subjects examined are often fragile and sensitive to trauma, the safety of diagnostic ultrasound has always been of concern. Of the various mechanisms through which ultrasound could act in a manner deleterious to a patient, acoustic cavitation, should it occur, appears to possess significant potential for biological damage. This paper reviews several recent reports of progress by our two groups and demonstrates the conditions under which cavitation has been observed by microsecond pulses of ultrasound. Although these results give no indications that diagnostic ultrasound may pose a true risk to a patient, they do indicate that in vivo cavitation may occur under certain conditions.     

Application of 30-MHz acoustic scattering to the study of human red blood cells

A technique for simultaneously measuring the scattering amplitude of individual particles at two angles is applied to human red blood cells. Using a Rayleigh scattering model, the density and compressibility of the cells may be determined given a priori knowledge of their volume. A calibration method relying on measurements of the bulk properties of particle suspensions is described. Red cell properties in hypotonic and hypertonic hosts are compared with a homogeneous mixture model, and a linear relation between hemoglobin content and scattering amplitude at a 90 deg scattering angle is established.     

Thresholds for cavitation produced in water by pulsed ultrasound

The threshold for transient cavitation produced in water by pulsed ultrasound was measured as a function of pulse duration and pulse repetition frequency at both 0.98 and 2.30 MHz. The cavitation events were detected with a passive acoustic technique which relies upon the scattering of the irradiation field by the bubble clouds associated with the events. The results indicate that the threshold is independent of pulse duration and acoustic frequency for pulses longer than approximately 10 acoustic cycles. The threshold increases for shorter pulses. The cavitation events are likely to be associated with bubble clouds rather than single bubbles.     

Evidence of Sulfur Non-Innocence in [CoII(dithiacyclam)]2+-Mediated Catalytic Oxygen Reduction Reactions

In many metalloenzymes, sulfur-containing ligands participate in catalytic processes, mainly via the involvement in electron transfer reactions. In a biomimetic approach, we now demonstrate the implication of S-ligation in cobalt mediated oxygen reduction reactions (ORR). A comparative study between the catalytic ORR capabilities of the four-nitrogen bound [Co(cyclam)]²⁺ ( 1 ; cyclam=1,5,8,11-tetraaza-cyclotetradecane) and the S-containing analog [Co(S₂N₂-cyclam)]²⁺ ( 2 ; S₂N₂-cyclam=1,8-dithia-5,11-diaza-cyclotetradecane) reveals improved catalytic performance once the chalcogen is introduced in the Co coordination sphere. Trapping and characterization of the intermediates formed upon dioxygen activation at the Co^II centers in 1 and 2 point to the involvement of sulfur in the O₂ reduction process as the key for the improved catalytic ORR capabilities of 2 .     

Time course of expiratory propofol after bolus injection as measured by ion molecule reaction mass spectrometry

Propofol in exhaled breath can be detected and monitored in real time by ion molecule reaction mass spectrometry (IMR-MS). In addition, propofol concentration in exhaled breath is tightly correlated with propofol concentration in plasma. Therefore, real-time monitoring of expiratory propofol could be useful for titrating intravenous anesthesia, but only if concentration changes in plasma can be determined in exhaled breath without significant delay. To evaluate the utility of IMR-MS during non-steady-state conditions, we measured the time course of both expiratory propofol concentration and the processed electroencephalography (EEG) as a surrogate outcome for propofol effect after an IV bolus induction of propofol. Twenty-one patients scheduled for routine surgery were observed after a bolus of 2.5 mg kg⁻¹ propofol for induction of anesthesia. Expiratory propofol was measured using IMR-MS and the cerebral propofol effect was estimated using the bispectral index (BIS). Primary endpoints were time to detection of expiratory propofol and time to onset of propofol’s effect on BIS, and the secondary endpoint was time to peak effect (highest expiratory propofol or lowest BIS). Expiratory propofol and changes in BIS were first detected at 43 ± 21 and 49 ± 11 s after bolus injection, respectively (P = 0.29). Peak propofol concentrations (9.2 ± 2.4 parts-per-billion) and lowest BIS values (23 ± 4) were reached after 208 ± 57 and 219 ± 62 s, respectively (P = 0.57). Expiratory propofol concentrations measured by IMR-MS have similar times to detection and peak concentrations compared with propofol effect as measured by the processed EEG (BIS). This suggests that expiratory propofol concentrations may be useful for titrating intravenous anesthesia.     

{1,1′‐(Dimethylsilylene)bis[methanechalcogenolato]}diiron Complexes [2Fe2E(Si)] (E=S,Se, Te) – [FeFe] Hydrogenase Models

(Bis‐selenolato) and (bis‐tellurolato)diiron complexes [2Fe2E(Si)] were prepared and compared with the known (bis‐thiolato)diiron complex A to assess their ability to produce hydrogen from protons. Treatment of [Fe₃(CO)₁₂] with 4,4‐dimethyl‐1,2,4‐diselenasilolane ( 1 ) in boiling toluene afforded hexacarbonyl{μ‐{[1,1′‐(dimethylsilylene)bis[methaneselenolato‐κSe : κSe]](2 ?)}}diiron(Fe? Fe) ( 2 ). The analog bis‐tellurolato complex hexacarbonyl{μ‐{[1,1′‐(dimethylsilylene)bis[methanetellurolato‐κTe : κTe]](2 ?)}}diiron(Fe? Fe) ( 3 ) was obtained by treatment of [Fe₃(CO)₁₂] with dimethylbis(tellurocyanatomethyl)dimethylsilane, which was prepared in situ. All compounds were characterized by NMR, IR spectroscopy, mass spectrometry, elemental analysis and single‐crystal X‐ray analysis. The electrocatalytic properties of the [2Fe2X(Si)] (X=S, Se, Te) model complexes A, 1 , and 2 towards hydrogen formation were evaluated.