In-situ synchrotron X-ray imaging of ultrasound (US)-generated bubbles: Influence of US frequency on microbubble cavitation for membrane fouling remediation

Gaining an in-depth understanding of the characteristics and dynamics of ultrasound (US)--generated bubbles is crucial to effectively remediate membrane fouling. The goal of present study is to conduct in-situ visualization of US-generated microbubbles in water to examine the influence of US frequency on the dynamics of microbubbles. This study utilized synchrotron in-line phase contrast imaging (In-line PCI) available at the biomedical imaging and therapy (BMIT) beamlines at the Canadian Light Source (CLS) to enhance the contrast of liquid/air interfaces at different US frequencies of 20, 28 and 40 KHz at 60 Watts. A high-speed camera was used to capture 2,000 frames per second of the bubble cavitation generated in water under the ultrasound influence. Key parameters at the polychromatic beamlines were optimized to maximize the phase contrast of gas/liquid of the microbubbles with a minimum size of 5.5 µm. ImageJ software was used to analyze the bubble characteristics and their behavior under the US exposure including the microbubble number, size, and fraction of the total area occupied by the bubbles at each US frequency. Furthermore, the bubble characteristics over the US exposure time and at different distances from the transducer were studied. The qualitative and quantitative data analyses showed that the microbubble number or size did not change over time; however, it was observed that most bubbles were created at the middle of the frames and close to the US field. The number of bubbles created under the US exposure increased with the frequency from 20 kHz to 40 kHz (about 4.6 times). However, larger bubbles were generated at 20 kHz such that the average bubble radius at 20 kHz was about 6.8 times of that at 40 kHz. Microbubble movement/traveling through water was monitored, and it was observed that the bubble velocity increased as the frequency was increased from 20 kHz to 40 kHz. The small bubbles moved faster, and the majority of them traveled upward towards the US transducer location. The growth pattern (a correlation between the mean growth ratio and the exposure time) of bubbles at 20 kHz and 60 W was obtained by tracking the oscillation of 22 representative microbubbles over the 700 ms of imaging. The mean growth ratio model was also obtained.     

Proteomic response and molecular regulatory mechanisms of Bacillus cereus spores under ultrasound treatment

This study was aimed at providing new insights on the proteomic response of bacterial spores to ultrasound. Data-independent-acquisition method was used to quantify the proteome change of Bacillus cereus spores after ultrasound treatment (200 W). This study revealed that 2485 proteins were extracted from Bacillus cereus spores, most of them were related to metabolism. After ultrasound treatment, the expression of 340 proteins were significantly changed (the fold change ≥ 2 and p < 0.05), of which 207 proteins were significantly down-regulated. KEGG pathway analysis showed that differentially expressed proteins mainly distributed in metabolism pathway, cell process pathway and genetic information processing pathway after ultrasound treatment. Furthermore, this study analyzed the differentially expressed proteins in significant enrichment pathways. In particular, the expression of key proteins in the phosphorylation reaction of spores was significantly decreased after ultrasound treatment. Thus, ATP synthesis rate decreased and the phosphorylation reaction inhibited. Also, the decrease of the expression of key proteins related to the tricarboxylic acid cycle led to the decrease of nutrients metabolism of spores. Ultrasound treatment induced the down-regulation of fatty acid synthetase expression and promoted fatty acid metabolism at the same time. The content of fatty acids decreased in spores consequently.     

Effect mechanism of ultrasound pretreatment on fibrillation Kinetics,physicochemical properties and structure characteristics of soy protein isolate nanofibrils

Self-assembly of soy proteins into nanofibrils is gradually considered as an effective method to improve their technical and functional properties. Ultrasound is a non-thermal, non-toxic and environmentally friendly technology that can modulate the formation of protein nanofibrils through controlled structural modification. In this research, the effect of ultrasound pretreatment on soy protein isolate nanofibrils (SPIN) was evaluated by fibrillation kinetics, physicochemical properties and structure characteristics. The results showed that the optimum ultrasound condition (20% amplitude, 15 min, 5 s on-time and 5 s off-time) could increase the formation rate of SPIN by 38.66%. Ultrasound reduced the average particle size of SPIN from 191.90 ± 5.40 nm to 151.83 ± 3.27 nm. Ultrasound could increase the surface hydrophobicity to 1547.67 in the initial stage of nanofibrils formation, and extend the duration of surface hydrophobicity increased, indicating ultrasound could expose more binding sites, creating more beneficial conditions for nanofibrils formation. Ultrasound could change the secondary and tertiary structure of SPIN. The reduction of α-helix content of ultrasound-pretreated soy protein isolate nanofibrils (USPIN) was 12.1% (versus 5.3% for SPIN) and the increase of β-sheet content was 5.9% (versus 3.5% for SPIN) during fibrillation. Ultrasound could accelerate the formation of SPIN by promoting the unfolding of SPI, exposure of hydrophobic groups and formation of β-sheets. Microscopic images revealed that USPIN generated a curlier and looser shape. And ultrasound reduced the zeta potential, free sulfhydryl groups content and viscosity of SPIN. SDS-PAGE results showed that ultrasound could promote the conversion of SPI into low molecular weight peptides, providing building blocks for the nanofibrils formation. The results indicated that ultrasound pretreatment could be a promising technology to accelerate SPIN formation and promote its application in food industry, but further research is needed for the improvement of the functional properties of SPIN.     

Ultrasound-assisted one-pot three-component synthesis of new isoxazolines bearing sulfonamides and their evaluation against hematological malignancies

In the present study, following a one-pot two-step protocol, we have synthesized novel sulfonamides-isoxazolines hybrids (3a-r) via a highly regioselective 1,3-dipolar cycloaddition. The present methodology capitalized on trichloroisocyanuric acid (TCCA) as a safe and ecological oxidant and chlorinating agent for the in-situ conversion of aldehydes to nitrile oxides in the presence of hydroxylamine hydrochloride, under ultrasound activation. These nitrile oxides could be engaged in 1,3-dipolar cycloaddition reactions with various alkene to afford the targeted sulfonamides-isoxazolines hybrids (3a-r). The latter were assessed for their antineoplastic activity against model leukemia cell lines (Chronic Myeloid Leukemia, K562 and Promyelocytic Leukemia, HL-60).     

Combining ultrasound,vacuum and/or ethanol as pretreatments to the convective drying of celery slices

This work studied three emerging approaches to improve the convective drying (50 °C, 0.8 m/s) of celery. Celery slices of 2 mm thick were pretreated for 5 min using ultrasound (32 W/L, 40 kHz), vacuum (75 kPa vacuum pressure) and ethanol (99.8% v/v, as drying accelerator) applied individually or in combination. To evaluate individual effects of ultrasound and vacuum, the treatments were also performed with distilled water or air medium, respectively. Moreover, the cavitational level was characterized in each condition. Drying kinetics was evaluated tending into account the drying time required by each treatment and the Page’s model parameters. In addition, microstructural effects and shrinkage were evaluated. As results, ethanol combined with ultrasound significantly improved drying kinetics reducing drying time by around 38%. However, vacuum pretreatment did not affect drying kinetics even in combination with ethanol and/or ultrasound. Microstructural evaluation did not evidence cell disruption, suggesting changes in intercellular spaces, pores and/or cell wall permeability. The use of ethanol and vacuum showed a greater effect on shrinkage after pretreatment and after drying, respectively. In conclusion, at the studied conditions, the drying acceleration by vacuum and ultrasound is lower compared to the effect produced using ethanol.     

Effect of ultrasound on the properties of rice bran protein and its chlorogenic acid complex

Ultrasound technology was used to treat rice bran protein (RBP), and the structural and functional properties of ultrasonically treated RBP (URBP) and its chlorogenic acid (CA) complex were studied. When ultrasonic power of 200 W was applied for 10 min, the maximum emission peak λ_max of the URBP-CA complex in the fluorescence spectrum was red-shifted by 3.6 nm compared to that of the untreated complex. The atomic force microscope (AFM) analysis indicated that the surface roughness of the complex was minimized (3.89 nm) at the ultrasonic power of 200 W and treatment time of 10 min. Under these conditions, the surface hydrophobicity (H₀) was 1730, the contents of the α-helix and β-sheet in the complex were 2.97% and 6.17% lower than those in the untreated sample, respectively, the particle size decreased from 106 nm to 18.2 nm, and the absolute value of the zeta-potential increased by 11.0 mV. Therefore, ultrasonic treatment and the addition of CA changed the structural and functional properties of RBP. Moreover, when ultrasonic power of 200 W was applied for 10 min, the solubility, emulsifying activity index (EAI), and emulsion stability index (ESI) were 68%, 126 m²/g, and 37 min, respectively.     

Production of tung oil epoxy resin using low frequency high power ultrasound

Epoxy resins made from vegetable oils are an alternative to synthesize epoxy resins from renewable sources. Tung oil is rich in α -eleostearic fatty acid, which contains three double bonds producing epoxy resins with up to three epoxy groups per fatty acid. This work studied the production of tung oil epoxy resin using hydrogen peroxide as an oxidizing agent and acetic and formic acid as percarboxylic acid precursors, applying low frequency high power ultrasound. This study evaluated the effects of ultrasound power density, hydrogen peroxide concentration, acetic acid concentration, and formic acid concentration on the yield into epoxy resin, selectivity, and by-products formation. Application of ultrasound was carried out using a 19 kHz probe ultrasound (horn ultrasound) with a 1.3 cm diameter titanium probe, 500 W nominal power, 2940 W L⁻¹ maximum effective power density applied to the reaction mixture. Ultrasound technology yielded up to 85% of epoxy resin in 3 h of reaction. The use of formic acid resulted in a slightly lower oil conversion than acetic acid but with a much higher selectivity towards epoxidized tung oil. However, using acetic acid resulted in the production of high-value by-products, such as 2-heptenal and 2,4-nonadienal. The ultrasound-assisted epoxidation showed to be particularly efficient when applied to oils containing conjugated double-bonds.     

Structural and physicochemical characterization of modified starch from arrowhead tuber (Sagittaria sagittifolia L.) using tri-frequency power ultrasound

Sagittaria sagittifolia L. is a well-known plant, belongs to the Alismataceae family. Sonication can improve the functional properties of starch; hence, the aim of this study was to develop ultrasonically modified arrowhead starch (UMAS) using a sophisticated and eco-friendly tri-frequency power ultrasound (20/40/60 kHz) method at 300, 600, and 900 W for 15 and 30 min. Significant (p < 0.05) increases in swelling power, solubility, and water and oil holding capacities were achieved. FTIR spectroscopy corroborated the ordered, amorphous, and hydrated crystals of the sonicated samples. Increases in sonication frequency and power led to significant (p < 0.05) increases in onset gelatinization temperatures. Scanning electron microscopic analysis of sonicated samples showed superficial cracks and roughness on starch granules appeared in a sonication power-dependent manner compared with that of untreated sample. Overall, the ultrasonically-treated samples showed improved physicochemical properties, which could be useful for industrial applications.     

Unsupported gold nanocones as sonocatalytic agents with enhanced catalytic properties

Gold catalysts have attracted attention for enabling sustainable chemical processes under ambient conditions. This reactivity is attributed to the small size of the catalysts (<5 nm); however, their size also creates difficulty when removing from product streams and often require rare-metal additives to enhance reaction rate kinetics, thereby limiting the environmental benefits of these catalysts. Comparatively, submicron gold catalysts are easier to separate but are much less reactive under ambient conditions. In this study, we synthesized submicron gas-stabilising gold nanocones (gs-AuNCs) that are acoustically responsive to afford greater reaction rates than other conventional gold catalysts. We explore the catalytic performance of acoustically responsive gs-AuNCs exposed to focussed ultrasound at 5.0 MPa peak negative pressure and 1.1 MHz center frequency. Cavitation nucleated from gs-AuNCs significantly increased the sonocatalytic degradation of water pollutants without the need for co-catalysts. The ability to amplify catalysis with ultrasound by tailoring the morphology of the catalyst to control cavitation opens new paths for future designs of sonocatalysts that may enable a sustainable chemical approach needed for a broad range of industrial processes.