Effect of reaction conditions on size and morphology of ultrasonically prepared Ni(OH)(2) powders.

Modern electrochemical devices require the morphological control of the active material. In this paper the synthesis of nickel hydroxide, as common active compound of such devices, is presented. The influence of ultrasound in the synthesis of nickel hydroxide from aqueous ammonia complexes is studied showing that ultrasound allows the fabrication of flower-like particles with sizes ranging in between 0.7 and 1.0µm in contrast with the 6-8µm particles obtained in the absence of ultrasound. The influence of gas flow, temperature of the process and surfactants in the ultrasonically prepared powders is discussed in term of shape, size and agglomeration of the particles. Adjusting the experimental condition, spherical or platelet-like particles are obtained with sizes ranging from 1.3µm to 200nm.

Upper bound for neutron emission from sonoluminescing bubbles in deuterated acetone.

An experimental search for nuclear fusion inside imploding bubbles of degassed deuterated acetone at 0 degrees C driven by a 15 atm sound field and seeded with a neutron generator reveals an upper bound that is a factor of 10 000 less than the signal reported by Taleyarkhan et al. The strength of our upper bound is limited by the weakness of sonoluminescence, which we ascribe to the relatively high vapor pressure of acetone.

Sonochemical preparation of supported hydrodesulfurization catalysts.

Sonochemical preparation of Co and Ni promoted MoS(2) supported on alumina was achieved by high-intensity ultrasonic irradiation of isodurene solutions containing molybdenum carbonyl, dicobalt octacarbonyl, elemental sulfur, and Al(2)O(3) or Ni-Al(2)O(3) under Ar flow. The sonochemically prepared catalysts were characterized by elemental analysis, XPS, SEM, TEM, and XEDS, and hydrodesulfurization (HDS) activity evaluated for thiophene and dibenzothiophene substrates. The TEM studies on the sonochemically prepared catalysts indicate the formation of layered hexagonal MoS(2) (lattice fringes approximately 6.2 A) on the alumina support. The sonochemically prepared Co-Mo-S/Al(2)O(3), Ni-Mo-S/Al(2)O(3), and Co-Ni-Mo-S/Al(2)O(3) are extremely active catalysts for the HDS of thiophene and dibenzothiophene, with activities severalfold those of comparable commercial catalysts under identical conditions. The layered structure of MoS(2) remained intact after 120 h of HDS, and the catalyst is reusable.

Molecular emission from single-bubble sonoluminescence.

Ultrasound can drive a single gas bubble in water into violent oscillation; as the bubble is compressed periodically, extremely short flashes of light (about 100 ps) are generated with clock-like regularity. This process, known as single-bubble sonoluminescence, gives rise to featureless continuum emission in water (from 200 to 800 nm, with increasing intensity into the ultraviolet). In contrast, the emission of light from clouds of cavitating bubbles at higher acoustic pressures (multi-bubble sonoluminescence) is dominated by atomic and molecular excited-state emission at much lower temperatures. These observations have spurred intense effort to uncover the origin of sonoluminescence and to generalize the conditions necessary for its creation. Here we report a series of polar aprotic liquids that generate very strong single-bubble sonoluminescence, during which emission from molecular excited states is observed. Previously, single-bubble sonoluminescence from liquids other than water has proved extremely elusive. Our results give direct proof of the existence of chemical reactions and the formation of molecular excited states during single-bubble cavitation, and provide a spectroscopic link between single- and multi-bubble sonoluminescence.

Effect of noble gases on sonoluminescence temperatures during multibubble cavitation.

Sonoluminescence spectra were collected from Cr(CO)6 solutions in octanol and dodecane saturated with various noble gases. The emission from excited-state metal atoms serves as an internal thermometer of cavitation. The intensity and temperature of sonoluminescence increases from He to Xe. The intensity of the underlying continuum, however, grows faster with increasing temperature than the line emission. Dissociation of solvent molecules within the bubble consumes a significant fraction of the energy generated by the collapsing bubble, which can limit the final temperature inside the bubble.

A colorimetric sensor array for odour visualization.

Array-based vapour-sensing devices are used to detect and differentiate between chemically diverse analytes. These systems--based on cross-responsive sensor elements--aim to mimic the mammalian olfactory system by producing composite responses unique to each odorant. Previous work has concentrated on a variety of non-specific chemical interactions to detect non-coordinating organic vapours. But the most odiferous, toxic compounds often bind readily to metal ions. Here we report a simple optical chemical sensing method that utilizes the colour change induced in an array of metalloporphyrin dyes upon ligand binding while minimizing the need for extensive signal transduction hardware. The chemoselective response of a library of immobilized vapour-sensing metalloporphyrin dyes permits the visual identification of a wide range of ligating (alcohols, amines, ethers, phosphines, phosphites, thioethers and thiols) and even weakly ligating (arenes, halocarbons and ketones) vapours. Water vapour does not affect the performance of the device, which shows a good linear response to single analytes, and interpretable responses to analyte mixtures. Unique colour fingerprints can be obtained at analyte concentrations below 2 parts per million, and responses to below 100 parts per billion have been observed. We expect that this type of sensing array will be of practical importance for general-purpose vapour dosimeters and analyte-specific detectors (for insecticides, drugs or neurotoxins, for example).

Near-field scanning optical microscopy of zinc-porphyrin crystals.

Using a near-field scanning optical microscope (NSOM), crystals of zinc-porphyrin network materials are characterized with respect to morphology and fluorescence. Needle-shaped crystals are observed. While the topography is flat, the fluorescence intensity profile in the width direction is approximately triangular. A numerical calculation shows that differences between the topographic and optical images cannot be due to an artifact. In some needle-shaped crystals, the fluorescence emission is strongly peaked at one or both ends, possibly indicating a polar crystal structure.

Ultrasound-enhanced reactivity of calcium in the reduction of aromatic hydrocarbons

Reductions of aromatic hydrocarbons by calcium in ethylenediamine-n-alkylamine mixture were investigated under ultrasonic conditions. Using an ultrasonic probe, with naphthalene as test molecule, it has been demonstrated that under ultrasonic action the reactions proceed faster (x10) and require a lower metal quantity (0.5) than the reactions conducted with an efficient mechanical stirrer. In addition, at ambient temperature and depending on the specific alcohol addition, selective naphthalene reduction can be performed using ultrasound. 1,2-Dihydronaphthalene (88% yield) results from the reaction in the presence of 2-propanol, and 1,4,5,8-tetrahydronaphthalene (88% yield) is obtained with tert-butanol. Investigation of the metal surface points out the characteristics of the calcium ultrasonic activation. The procedure was efficiently tested with several aromatic hydrocarbons.

Reduced oxy intermediate observed in D251N cytochrome P450cam.

Cytochrome P450s are ubiquitous heme proteins responsible for various oxidative metabolic processes. The overall rate-determining step in the catalytic cycle of native cytochrome P450cam is the reduction of the dioxygen complex, which has made detection of catalytic intermediates after this reduction impossible. However, for the site-specific mutant D251N cytochrome P450cam (which affects proton transfer near the catalytic center), the overall rate-determining step occurs after the reduction of oxy-P450. As a consequence, we have observed in the UV-visible spectrum during catalytic turnover a new intermediate that is one electron reduced from oxy-P450 with an intact dioxygen bond.

Sonochemically produced fluorocarbon microspheres: a new class of magnetic resonance imaging agent.

With the intent of increasing the signal-to-noise ratio (SNR) of fluorine magnetic resonance imaging and enabling new applications, we have developed a novel class of agents based on protein encapsulation of fluorocarbons. Microspheres formed by high-intensity ultrasound have a gaussian size distribution with an average diameter of 2.5 microns. As with conventional emulsions, these microspheres target the reticuloendothelial system. However, our sonochemically produced microspheres, because of a high encapsulation efficiency, show increases in the SNR of up to 300% compared to commercially available emulsions. We also demonstrate an increase in the circulation lifetime of the microspheres with the bloodstream by more than 30-fold with a chemical modification of the outer surface of the microsphere. Finally, by encapsulating mixtures of fluorocarbons that undergo solid/liquid phase transitions, we can map temperature in the reticuloendothelial system, with signal changes of approximately 20-fold over a 5 degrees C range.

The measurement of temperature with electron paramagnetic resonance spectroscopy.

An electron paramagnetic resonance (EPR) technique, potentially suitable for in vivo temperature measurements, has been developed based on the temperature response of nitroxide stable free radicals. The response has been substantially enhanced by encapsulating the nitroxide in a medium of a fatty acid mixture inside a proteinaceous microsphere. The mixture underwent a phase transition in the temperature range required by the application. The phase change dramatically altered the shape of the EPR spectrum, providing a highly temperature sensitive signal. Using the nitroxide dissolved in a cholesterol and a long-chain fatty acid ester, we developed a mixture which provides a peakheight ratio change from 3.32 to 2.11, with a standard deviation of 0.04, for a temperature change typical in biological and medical applications, from 38 to 48 degrees C. This translated to an average temperature resolution of 0.2 degree C for our experimental system. The average diameter of the nitroxide mixture-filled microspheres was approximately 2 microns. Therefore, they are compatible with in vivo studies where the microspheres could be injected into the microvasculature having a minimum vessel diameter of the order of 8 microns. This temperature measuring method has various potential clinical applications, especially in monitoring and optimizing the treatment of cancer with hyperthermia. However, several problems regarding temperature and spatial resolution need to be resolved before this technique can be successfully used to monitor temperatures in vivo.

In-vivo NMR thermometry with liposomes containing 59Co complexes.

The ability to make localized temperature measurements in tissue during hyperthermia treatment of cancer is an essential factor in optimizing its efficacy. To this end we have developed and evaluated the complex tris(ethylenediamine) cobalt(III) trichloride as a temperature sensor by determining the temperature dependence of it 59Co nuclear magnetic resonance chemical shift. Encapsulating this complex within liposomes targets the agent to the reticuloendothelial system. Temperature changes of the order of 0.1 degrees C have been measured in vivo on rats, and the half-life of the complex within the body determined by plasma emission spectroscopy.

In vivo measurement of oxygen concentration using sonochemically synthesized microspheres.

Proteinaceous microspheres filled with nitroxides dissolved in an organic liquid have been synthesized for the first time using high intensity ultrasound; these were used to measure oxygen concentrations in living biological systems. The microspheres have an average size of 2.5 microns, and the proteinaceous shell is permeable to oxygen. Encapsulation of the nitroxides into the microsphere greatly increased the sensitivity of the electron paramagnetic resonance signal line width to oxygen because of the higher solubility of oxygen in organic solvents. The encapsulation also protected the nitroxide from bioreduction. No decrease in intensity of the electron paramagnetic resonance signal was observed during 70 min after intravenous injection of the microspheres into a mouse. Measurement of the changes in oxygen concentration in vivo by means of restriction of blood flow, anesthesia, and change of oxygen content in the respired gas were made using these microspheres.

Air-filled proteinaceous microbubbles: synthesis of an echo-contrast agent.

Air-filled microbubbles are in clinical use as echo-contrast agents for sonographic applications. The synthesis of aqueous suspensions of air-filled proteinaceous microbubbles involves the ultrasonic irradiation of aqueous protein solutions in the presence of O2. Yields and size distributions of human and bovine serum albumin microbubbles have been determined as a function of various experimental parameters. The chemical nature of these microbubbles and the origin of their remarkably long lifetimes have been explored. The microbubbles are held together primarily by interprotein cross-linking of cysteine residues. The principal cross-linking agent is superoxide created by the extremely high temperatures produced during acoustic cavitation.

The temperature of cavitation.

Ultrasonic irradiation of liquids causes acoustic cavitation: the formation, growth, and implosive collapse of bubbles. Bubble collapse during cavitation generates transient hot spots responsible for high-energy chemistry and emission of light. Determination of the temperatures reached in a cavitating bubble has remained a difficult experimental problem. As a spectroscopic probe of the cavitation event, sonoluminescence provides a solution. Sonoluminescence spectra from silicone oil were reported and analyzed. The observed emission came from excited state C(2) (Swan band transitions, d(3)IIg-a(3)II(micro)), which has been modeled with synthetic spectra as a function of rotational and vibrational temperatures. From comparison of synthetic to observed spectra, the effective cavitation temperature was found to be 5075 +/- 156 K.

On the origin of sonoluminescence and sonochemistry.

Recent experimental results on the origins of sonoluminescence and sonochemistry are reviewed and the conclusion reached that most observed effects originate from thermal processes associated with a localized hot-spot created by acoustic cavitation. Sonoluminescence is definitively due to chemiluminescence from species produced thermally during cavitational collapse and is not attributable to electric microdischarge. Homogenous sonochemistry follows the behaviour expected for high temperature thermal reactions. Ultrasonic irradiation of liquids containing solid powders dramatically increases their chemical reactivity and improves chemical yields for a wide range of synthetically useful heterogenous reactions. Shock waves generated from the cavitational hot-spot cause high velocity interparticle collisions in such slurries. Brittle solids are shock fragmented, which increases surface area. This increase in reactive surface provides for substantial increases in chemical reactivity. For malleable metal powders, these collisions are sufficiently violent to remove surface oxide coatings and to induce local melting at the site of impact for most metals.

Interparticle collisions driven by ultrasound.

Ultrasound has become an important synthetic tool in liquid-solid chemical reactions, but the origins of the observed enhancements remained unknown. The effects of high-intensity ultrasound on solid-liquid slurries were examined. Turbulent flow and shock waves produced by acoustic cavitation were found to drive metal particles together at sufficiently high velocities to induce melting upon collision. A series of transition-metal powders were used to probe the maximum temperatures and speeds reached during such interparticle collisions. Metal particles that were irradiated in hydrocarbon liquids with ultrasound underwent collisions at roughly half the speed of sound and generated localized effective temperatures between 2600 degrees C and 3400 degrees C at the point of impact for particles with an average diameter of approximately 10 microns.

Sonochemistry.

Ultrasound causes high-energy chemistry. It does so through the process of acoustic cavitation: the formation, growth and implosive collapse of bubbles in a liquid. During cavitational collapse, intense heating of the bubbles occurs. These localized hot spots have temperatures of roughly 5000 degrees C, pressures of about 500 atmospheres, and lifetimes of a few microseconds. Shock waves from cavitation in liquid-solid slurries produce high-velocity interparticle collisions, the impact of which is sufficient to melt most metals. Applications to chemical reactions exist in both homogeneous liquids and in liquid-solid systems. Of special synthetic use is the ability of ultrasound to create clean, highly reactive surfaces on metals. Ultrasound has also found important uses for initiation or enhancement of catalytic reactions, in both homogeneous and heterogeneous cases.