School of Chemistry - Research Publications

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    Sonosynthesis of nanobiotics with antimicrobial and antioxidant properties.
    Zhu, H ; Wen, Q ; Bhangu, SK ; Ashokkumar, M ; Cavalieri, F (Elsevier BV, 2022-05)
    Transforming small-molecule antibiotics into carrier-free nanoantibiotics represents an opportunity for developing new multifunctional therapeutic agents. In this study, we demonstrate that acoustic cavitation produced by high-frequency ultrasound transforms the antibiotic doxycycline into carrier-free nanobiotics. Upon sonication for 1 h at 10-15 W cm-3, doxycycline molecules underwent hydroxylation and dimerization processes to ultimately self-assemble into nanoparticles of ∼100-200 nm in size. Micrometer sized particles can be also obtained by increasing the acoustic power to 20 W cm-3. The nanodrugs exhibited antioxidant properties, along with antimicrobial activity against both Gram-positive (S. aureus) and Gram-negative (E. coli) bacterial strains. Our results highlight the feasibility of the ultrasound-based approach for engineering drug molecules into a nanosized formulation with controlled and multiple bio-functionalities.
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    Lysozyme microspheres incorporated with anisotropic gold nanorods for ultrasound activated drug delivery.
    Bhargawa, B ; Sharma, V ; Ganesh, M-R ; Cavalieri, F ; Ashokkumar, M ; Neppolian, B ; Sundaramurthy, A (Elsevier BV, 2022-05)
    We report on the fabrication of lysozyme microspheres (LyMs) incorporated with gold nanorods (NRs) as a distinctive approach for the encapsulation and release of an anticancer drug, 5-Fluorouracil (5-FU). LyMs with an average size of 4.0 ± 1.0 µm were prepared by a sonochemical method and characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier-transform infrared spectroscopy (FTIR). The LyMs were examined using hydrophobic (nile red) as well as hydrophilic (trypan blue) dyes under confocal laser scanning microscopy (CLSM) to obtain information about the preferential distribution of fluorescent molecules. Notably, the fluorescent molecules were accumulated in the inner lining of LyMs as the core was occupied with air. The encapsulation efficiency of 5-FU for LyMs-NR was found to be ∼64%. The drug release from control LyMs as well as LyMs incorporated with NRs was investigated under the influence of ultrasound (US) at 200 kHz. The total release for control LyMs and LyMs incorporated with gold NRs was found to be ∼70 and 95% after 1 h, respectively. The density difference caused by NR incorporation on the shell played a key role in rupturing the LyMs-NR under US irradiation. Furthermore, 5-FU loaded LyMs-NR exhibited excellent anti-cancer activity against the THP-1 cell line (∼90% cell death) when irradiated with US of 200 kHz. The enhanced anti-cancer activity of LyMs-NR was caused by the transfer of released 5-FU molecules from bulk to the interior of the cell via temporary pores formed on the surface of cancer cells, i.e., sonoporation. Thus, LyMs-NR demonstrated here has a high potential for use as carriers in the field of drug delivery, bio-imaging and therapy.
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    Ultrasonic microencapsulation of oil-soluble vitamins by hen egg white and green tea for fortification of food
    Zhu, H ; Mettu, S ; Cavalieri, F ; Ashokkumar, M (ELSEVIER SCI LTD, 2021-03-10)
    We report the microencapsulation of oil soluble vitamins (A, D and E) using a one pot ultrasonic process and raw egg white proteins as a shell material. Green tea catechin/iron complex coating method was further developed to impart UV filtering property to the microcapsules in order to protect the encapsulated nutrients from photodegradation. The microcapsules showed antibacterial properties and long shelf-life. The encapsulated vitamins were protected from degradation upon heating, UV irradiation, simulated storage/transit and cooking processes. The in-vitro digestion study showed that functional vitamin D can be potentially released in the gastrointestinal tract improving vitamin D availability by more than 2-fold compared to the free vitamin. The vitamin D microcapsules were highly stable and maintained their microstructures once incorporated into staple food products. The low-cost egg white shell encapsulated vitamins can improve the nutritional value of staple food products to combat maternal and child malnutrition.
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    Ultrasound-induced protein restructuring and ordered aggregation to form amyloid crystals
    Pathak, R ; Bhangu, SK ; Martin, GJO ; Separovic, F ; Ashokkumar, M (SPRINGER, 2022-05-16)
    Amyloid crystals, a form of ordered protein aggregates documented relatively recently, have not been studied as extensively as amyloid fibres. This study investigates the formation of amyloid crystals with low frequency ultrasound (20 kHz) using β-lactoglobulin, as a model protein for amyloid synthesis. Acoustic cavitation generates localised zones of intense shear, with extreme heat and pressure that could potentially drive the formation of amyloid structures at ambient bulk fluid temperatures (20 ± 1 °C). Thioflavin T fluorescence and electron microscopy showed that low-frequency ultrasound at 20 W/cm3 input power induced β-stacking to produce amyloid crystals in the mesoscopic size range, with a mean length of approximately 22 µm. FTIR spectroscopy indicated a shift towards increased intermolecular antiparallel β-sheet content. An increase in sonication time (0-60 min) and input power (4-24 W/cm3) increased the mean crystal length, but this increase was not linearly proportional to sonication time and input power due to the delayed onset of crystal growth. We propose that acoustic cavitation causes protein unfolding and aggregation and imparts energy to aggregates to cross the torsion barrier, to achieve their lowest energy state as amyloid crystals. The study contributes to a further understanding of protein chemistry relating to the energy landscape of folding and aggregation. Ultrasound presents opportunities for practical applications of amyloid structures, presenting a more adaptable and scalable approach for synthesis.
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    A correlation between cavitation bubble temperature, sonoluminescence and interfacial chemistry - A minireview.
    Yusof, NSM ; Anandan, S ; Sivashanmugam, P ; Flores, EMM ; Ashokkumar, M (Elsevier BV, 2022-04)
    Ultrasound induced cavitation (acoustic cavitation) process is found useful in various applications. Scientists from various disciplines have been exploring the fundamental aspects of acoustic cavitation processes over several decades. It is well documented that extreme localised temperature and pressure conditions are generated when a cavitation bubble collapses. Several experimental techniques have also been developed to estimate cavitation bubble temperatures. Depending upon specific experimental conditions, light emission from cavitation bubbles is observed, referred to as sonoluminescence. Sonoluminescence studies have been used to develop a fundamental understanding of cavitation processes in single and multibubble systems. This minireview aims to provide some highlights on the development of basic understandings of acoustic cavitation processes using cavitation bubble temperature, sonoluminescence and interfacial chemistry over the past 2-3 decades.
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    Ultrasound-aided synthesis of gold-loaded boron-doped graphene quantum dots interface towards simultaneous electrochemical determination of guanine and adenine biomolecules.
    Kaimal, R ; Mansukhlal, PN ; Aljafari, B ; Anandan, S ; Ashokkumar, M (Elsevier BV, 2022-02)
    To acquire substantial electrochemical signals of guanine-GUA and adenine-ADE present in deoxyribonucleic acid-DNA, it is critical to investigate innovative electrode materials and their interfaces. In this study, gold-loaded boron-doped graphene quantum dots (Au@B-GQDs) interface was prepared via ultrasound-aided reduction method for monitoring GUA and ADE electrochemically. Transmission electron microscopy-TEM, Ultraviolet-Visible spectroscopy-UV-Vis, Raman spectroscopy, X-ray photoelectron spectroscopy-XPS, cyclic voltammetry-CV, and differential pulse voltammetry-DPV were used to examine the microstructure of the fabricated interfaceand demonstrate its electrochemical characteristics. The sensor was constructed by depositing the as-prepared Au@B-GQDs as a thin layer on a glassy carbon-GC electrode by the drop-casting method and carried out the electrochemical studies. The resulting sensor exhibited a good response with a wide linear range (GUA = 0.5-20 μM, ADE = 0.1-20 μM), a low detection limit-LOD (GUA = 1.71 μM, ADE = 1.84 μM), excellent sensitivity (GUA = 0.0820 µAµM-1, ADE = 0.1561 µAµM-1) and selectivity with common interferents results from biological matrixes. Furthermore, it seems to have prominentselectivity, reproducibility, repeatability, and long-lastingstability. The results demonstrate that the fabricated Au@B-GQDs/GC electrode is a simple and effective sensing platform for detecting GUA and ADE in neutral media at low potential as it exhibited prominent synergistic impact and outstanding electrocatalytic activity corresponding to individual AuNPs and B-GQDs modified electrodes.
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    Transforming the Chemical Structure and Bio-Nano Activity of Doxorubicin by Ultrasound for Selective Killing of Cancer Cells
    Bhangu, SK ; Fernandes, S ; Beretta, GL ; Tinelli, S ; Cassani, M ; Radziwon, A ; Wojnilowicz, M ; Sarpaki, S ; Pilatis, I ; Zaffaroni, N ; Forte, G ; Caruso, F ; Ashokkumar, M ; Cavalieri, F (WILEY-V C H VERLAG GMBH, 2022-02-18)
    Reconfiguring the structure and selectivity of existing chemotherapeutics represents an opportunity for developing novel tumor-selective drugs. Here, as a proof-of-concept, the use of high-frequency sound waves is demonstrated to transform the nonselective anthracycline doxorubicin into a tumor selective drug molecule. The transformed drug self-aggregates in water to form ≈200 nm nanodrugs without requiring organic solvents, chemical agents, or surfactants. The nanodrugs preferentially interact with lipid rafts in the mitochondria of cancer cells. The mitochondrial localization of the nanodrugs plays a key role in inducing reactive oxygen species mediated selective death of breast cancer, colorectal carcinoma, ovarian carcinoma, and drug-resistant cell lines. Only marginal cytotoxicity (80-100% cell viability) toward fibroblasts and cardiomyocytes is observed, even after administration of high doses of the nanodrug (25-40 µg mL-1 ). Penetration, cytotoxicity, and selectivity of the nanodrugs in tumor-mimicking tissues are validated by using a 3D coculture of cancer and healthy cells and 3D cell-collagen constructs in a perfusion bioreactor. The nanodrugs exhibit tropism for lung and limited accumulation in the liver and spleen, as suggested by in vivo biodistribution studies. The results highlight the potential of this approach to transform the structure and bioactivity of anticancer drugs and antibiotics bearing sono-active moieties.
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    Sono-Fenton Chemistry Converts Phenol and Phenyl Derivatives into Polyphenols for Engineering Surface Coatings
    Mei, H ; Gao, Z ; Zhao, K ; Li, M ; Ashokkumar, M ; Song, A ; Cui, J ; Caruso, F ; Hao, J (WILEY-V C H VERLAG GMBH, 2021-08-25)
    We report a sono-Fenton strategy to mediate the supramolecular assembly of metal-phenolic networks (MPNs) as substrate-independent coatings using phenol and phenyl derivatives as building blocks. The assembly process is initiated from the generation of hydroxyl radicals (. OH) using high-frequency ultrasound (412 kHz), while the metal ions synergistically participate in the production of additional . OH for hydroxylation/phenolation of phenol and phenyl derivatives via the Fenton reaction and also coordinate with the phenolic compounds for film formation. The coating strategy is applicable to various phenol and phenyl derivatives and different metal ions including FeII , FeIII , CuII , and CoII . In addition, the sono-Fenton strategy allows real-time control over the assembly process by turning the high-frequency ultrasound on or off. The properties of the building blocks are maintained in the formed films. This work provides an environmentally friendly and controllable method to expand the application of phenolic coatings for surface engineering.
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    Turbulence-induced formation of emulsion gels
    Li, W ; Martin, GJO ; Ashokkumar, M (ELSEVIER, 2021-12-01)
    Emulsion gels have a wide range of applications. We report on a facile and versatile method to produce stable emulsion gels with tunable rheological properties. Gel formation is triggered by subjecting a mixture containing aqueous colloidal particle (CP) suspensions and water-immiscible liquids to intense turbulence, generated by low frequency (20 kHz) ultrasound or high-pressure homogenization. Through systematic investigations, requisite gel formation criteria are established with respect to both formulation and processing, including ratio/type of liquid pairs, CP properties, and turbulence conditions. Based on the emulsion microstructure and rheological properties, inter-droplet bridging and CP void-filling are proposed as universal stabilization mechanisms. These mechanisms are further linked to droplet-size scaling and sphere close-packing theory, distinctive from existing gel-conferring models. The study thereby provides the foundation for advancing the production of emulsion gels that can be tailored to a wide range of current and emerging applications in the formulation and processing of food, cosmetics or pharmaceutical gels, and in material science.
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    Formation by high power ultrasound of aggregated emulsions stabilised with milk protein concentrate (MPC70).
    Zhang, R ; Luo, L ; Yang, Z ; Ashokkumar, M ; Hemar, Y (Elsevier BV, 2021-12-03)
    In this work, oil-in-water emulsions stabilised by milk protein concentrate (MPC70) were investigated. The MPC70 concentration was kept constant at 5% (close to the protein content found in skim milk) and the oil volume fraction was varied from 20 to 65%. Sonication was performed at 20 kHz and at a constant power of 14.4 W for a total emulsion volume of 10 mL. Under certain oil concentration (≥35%) and sonication times (≥3s) the emulsion aggregated and formed high-viscosity pseudo plastic materials. However, the viscosity behaviour of the emulsion made with 35% oil reverted to that of a liquid if sonicated for longer times (≥15 s). Confocal laser scanning microscopy showed clearly that the oil droplets are aggregated under the sonication conditions and oil concentrations indicated above. An attempt to explain this behaviour through a simple model based on the bridging of oil droplets by the MPC70 particles and, taking into account the oil droplet and MPC70 particle sizes as well as the oil volume fraction, was made. The model fails to describe in details the aggregation behaviour of these emulsions, likely due to the inhomogeneous protein layer, where both free caseins and casein micelles are adsorbed, and to the packing of the oil droplets at concentrations ≤55%. Nonetheless, this work demonstrates the potential of ultrasound processing for the formation of dairy emulsions with tailored textures.