Massimo Corsi

Oxidation of hydroxylamines to nitrones catalyzed by (salen)Mn(III) complexes. Enantioselective synthesis of a protected cis-dihydroxypyrroline N-oxide with jacobsen catalyst

Oxidation of N,N-disubstituted hydroxylamines to nitrones catalyzed by the Jacobsen catalyst occurs cleanly in the presence of hydrogen peroxide, sodium hypochlorite or iodosylbenzene as the stoichiometric oxidant. Meso 3,4-cis-isopropylidenedioxy-1-hydroxypyrrolidine gave the corresponding protected 3,4-cis-dihydroxypyrroline N-oxide in an enantioenriched fashion for the first time (up to 36% e.e.).

Practical synthesis of N-alkyl-N-glycosylhydroxylamines, multitalented precursors of enantiomerically pure nitrones

Abstract A practical synthesis of N -benzyl- N -glycosylhydroxylamines 3 (R=CH 2 Ph) is reported. The ability of these compounds to act as versatile synthetic intermediates is demonstrated by their oxidation followed by cycloaddition to N -glycosyl isoxazolidines and by the novel direct cycloaddition as masked acyclic, highly functionalized chiral nitrones.

On the interaction between ultrasound and contrast agents during Doppler investigations

Knowledge of interaction mechanisms between ultrasound (US) and contrast agents (CA) suspended in blood is important for a correct interpretation of clinical investigation results. Experiments performed in different laboratories have shown that, as a consequence of primary radiation force, CA tend to move away from the US transducer. Accordingly, Doppler spectra produced by particles suspended in moving water turn out to be significantly altered from what is theoretically expected. The purpose of this paper is twofold. First, an original model describing the bubble dynamics as the outcome of the balance between US radiation force and fluid drag force is validated for the case in which bubbles are suspended in blood. The high fluid viscosity is shown to prevent significant bubble deviations from the unperturbed fluid streamlines so that, in large vessels, a residual spectral distortion may exist only at the highest intensity levels permitted by current regulations. Finally, the relative importance and differences between the effect of primary radiation force and streaming mechanisms that, in principle, could lead to similar effects, are discussed.

Different effects of microbubble destruction and translation in Doppler measurements

In flow measurements in which microbubbles are involved, the amplitude and phase of the received echo signal are noticeably influenced by the transmitted ultrasound intensity. Previous studies have shown that, when such intensity is progressively increased, the Doppler spectrum is accordingly distorted, i.e., it is asymmetrically broadened toward the negative frequency side. Such deformation has been attributed to radiation force, which pushes the microbubbles into the sound propagation direction, thus yielding additional phase delays in the received echoes. However, the possible contribution of microbubble destruction to this spectral deformation has not been considered yet. In this paper, this issue is investigated by analyzing the experimental spectra produced by two different types of microbubbles suspended in a moving fluid and insonified in pulsed wave (PW) mode at programmable pulse repetition frequency (PRF) and pressure. Conditions are created in which either the radiation force or the destruction mechanism is expected to be dominant. Effects produced by the two phenomena on the Doppler spectrum are shown to be different. When the PRF is low (2 kHz), so that, according to theoretical simulations, the radiation force effect is negligible, a 26 dB noise floor increase is observed for a 13 dB pressure increment. For a higher PRF (16 kHz), the same pressure increase not only affects the noise floor, but also causes the bubbles to deviate from their original streamlines, yielding a Doppler bandwidth increase by a factor of 5. It is concluded that asymmetrical spectral broadening is mainly due to radiation force, and microbubble destruction mainly results in an increased noise floor without affecting the spectral shape.

Decolorization of acid and basic dyes: understanding the metabolic degradation and cell-induced adsorption/precipitation by Escherichia coli

Escherichia coli strain DH5α was successfully employed in the decolorization of commercial anthraquinone and azo dyes, belonging to the general classes of acid or basic dyes. The bacteria showed an aptitude to survive at different pH values on any dye solution tested, and a rapid decolorization was obtained under aerobic conditions for the whole collection of dyes. A deep investigation about the mode of action of E. coli was carried out to demonstrate that dye decolorization mainly occurred via three different pathways, specifically bacterial induced precipitation, cell wall adsorption, and metabolism, whose weight was correlated with the chemical nature of the dye. In the case of basic azo dyes, an unexpected fast decolorization was observed after just 2-h postinoculation under aerobic conditions, suggesting that metabolism was the main mechanism involved in basic azo dye degradation, as unequivocally demonstrated by mass spectrometric analysis. The reductive cleavage of the azo group by E. coli on basic azo dyes was also further demonstrated by the inhibition of decolorization occurring when glucose was added to the dye solution. Moreover, no residual toxicity was found in the E. coli-treated basic azo dye solutions by performing Daphnia magna acute toxicity assays. The results of the present study demonstrated that E. coli can be simply exploited for its natural metabolic pathways, without applying any recombinant technology. The high versatility and adaptability of this bacterium could encourage its involvement in industrial bioremediation of textile and leather dyeing wastewaters.

Water recycle as a must: decolorization of textile wastewaters by plant-associated fungi

Textile dye effluents are among the most problematic pollutants because of their toxicity on several organisms and ecosystems. Low cost and ecocompatible bioremediation processes offer a promising alternative to the conventional and aspecific physico‐chemical procedures adopted so far. Here, microorganisms resident on three real textile dyeing effluent were isolated, characterized, and tested for their decolorizing performances. Although able to survive on these real textile‐dyeing wastewaters, they always showed a very low decolorizing activity. On the contrary, several plant‐associated fungi (Bjerkandera adusta, Funalia trogii, Irpex lacteus, Pleurotus ostreatus, Trametes hirsuta, Trichoderma viride, and Aspergillus nidulans) were also assayed and demonstrated to be able both to survive and to decolorize to various extents the three effluents, used as such in liquid cultures. The decolorizing potential of these fungi was demonstrated to be influenced by nutrient availability and pH. Best performances were constantly obtained using B. adusta and A. nidulans, relying on two strongly different mechanisms for their decolorizing activities: degradation for B. adusta and biosorption for A. nidulans. Acute toxicity tests using Daphnia magna showed a substantial reduction in toxicity of the three textile dyeing effluents when treated with B. adusta and A. nidulans, as suggested by mass spectrometric analysis as well.

N-GLYCOSYLHYDROXYLAMINES AS MASKED POLYHYDROXYLATED CHIRAL NITRONES IN CYCLOADDITION REACTIONS : AN ACCESS TO PYRROLIZIDINES

- N-glycosylhydroxylamines undergo 1,3-dipolar cycloadditions via their tautomeric open chain nitrones. Cycloadditions to maleic acid esters occur with high diastereoselectivity and the products can be converted into highly functionalized pyrrolizidines.

A Doppler Viewpoint on Microbubble Destruction

Several mechanisms are involved when ultrasound (US) fields of relatively high intensity hit microbubbles [1]. In particular, as reported in several papers, both bubble rupture [2] and bubble displacement from original position/trajectory [3] can take place.