School of Chemistry - Research Publications

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    Incorporating whey protein aggregates produced with heat and ultrasound treatment into rennet gels and model non-fat cheese systems
    Gamlath, CJ ; Leong, TSH ; Ashokkumar, M ; Martin, GJO (Elsevier, 2020-12-01)
    Native whey proteins (WP) are expulsed from cheese coagulation during syneresis. Although incorporating denatured WP aggregates into cheese gels has been previously proposed to improve the overall cheese yield, the effects of WP aggregate properties on gelation kinetics and protein retention are not yet fully understood. In this study, heat and power ultrasound were used to produce denatured whey protein aggregates with a wide range of sizes. The effects of size and hydrophobicity differences in WP aggregates produced by heat and heat coupled with ultrasound were investigated in relation to the kinetics of rennet gelation and protein retention in model non-fat cheddar cheeses. Rheological measurements showed that sufficiently large, denatured WP aggregates could avoid impairment of rennet gelation caused by native WP, irrespective of changes in the soluble calcium concentration or the surface hydrophobicity of the aggregates. WP aggregates formed by the combined heat and ultrasound treatment were more hydrophobic than the larger heat-treated aggregates and were better retained in the cheese. However, inclusion of sufficiently large aggregates in cheese milk conferred an openness to the cheese microstructure and showed promise in improving the otherwise rigid non-fat cheese.
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    A double co-sensitization strategy using heteroleptic transition metal ferrocenyl dithiocarbamate phenanthrolene-dione for enhancing the performance of N719-based DSSCs
    Singh, A ; Srivastava, D ; Gosavi, SW ; Chauhan, R ; Ashokkumar, M ; Albalwi, AN ; Muddassir, M ; Kumar, A (ROYAL SOC CHEMISTRY, 2022-09-28)
    Three new heteroleptic dithiocarbamate complexes with formula [M(Phen-dione)(Fcdtc)]PF6 (where M = Ni(ii) Ni-Fc, Cu(ii) Cu-Fc) and [Co(Phen-dione)(Fcdtc)2]PF6 (Co-Fc) (Fcdtc = N-ethanol-N-methylferrocene dithiocarbamate and Phen-dione = 1,10-phenanthroline-5,6-dione; PF6 - = hexafluorophosphate) were synthesized and characterized using microanalysis, FTIR, electronic absorption spectroscopy and mass spectrometry. The solution state electronic absorption spectroscopy for all three complexes displayed a band at ∼430 nm corresponding to the ferrocene unit and another low-intensity band in the visible region arising because of the d-d transitions. These newly synthesized complexes were used as co-sensitizers for the state-of-the-art di-tetrabutylammonium cis-bis(isothiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylato)ruthenium(ii) (N719) dye in dye-sensitized solar cells (DSSCs). Among the three co-sensitizers/co-adsorbent-based DSSC set-ups, the assembly fabricated using Co-Fc/N719 displayed good photovoltaic performance with 5.31% efficiency (η) while a new triple component strategy inculcating N719, Co-Fc and Cu-Fc dyes offered the best photovoltaic performance with 6.05% efficiency (η) with incident photon to current conversion efficiency (IPCE) of 63%. This indicated an upliftment of the DSSC performance by ∼38% in comparison to the set-up constructed by employing only N719 dye (η = 4.39%) under similar experimental conditions.
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    Chemoenzymatic surface decoration of Nisin-shelled nanoemulsions: Novel targeted drug-nanocarriers for cancer applications
    Hashad, RA ; Singla, R ; Bhangu, SK ; Jap, E ; Zhu, H ; Peleg, AY ; Blakeway, L ; Hagemeyer, CE ; Cavalieri, F ; Ashokkumar, M ; Alt, K (ELSEVIER, 2022-11)
    Nisin, a peptide used as a natural food preservative, is employed in this work for the development of a novel nanocarrier system. Stable and uniform nisin-shelled nanoemulsions (NSNE) with a diameter of 100 ± 20 nm were successfully prepared using 20 kHz flow-through ultrasonication technique. The NSNE showed limited toxicity, high bactericidal activity and high drug loading capacity (EE 65 % w/w). In addition, the nisin shell was exploited for the site-specific attachment of a recombinantly produced cancer targeting ligand (αHER2LPETG IgG). Employing a unique two phases (bio-click) approach which involved both Sortase A mediated Azide Bioconjugation (SMAB) and Strain Promoted Azide Alkyne Cycloaddition (SPAAC) reactions, targeted NSNE (NSNEDOX-αHER2 IgG) were successfully assembled and loaded with the chemotherapeutic drug Doxorubicin (DOX). Finally, NSNEDOX-αHER2 IgG showed cancer-specific binding and augmented cytotoxicity to HER2 expressing tumour cells.
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    Impacts of sonication and high hydrostatic pressure on the structural and physicochemical properties of quinoa protein isolate dispersions at acidic, neutral and alkaline pHs
    Luo, L ; Yang, Z ; Wang, H ; Ashokkumar, M ; Hemar, Y (ELSEVIER, 2022-12)
    Herein, 1 wt% quinoa protein isolate (QPI) was exposed to sonication using a 20 kHz ultrasonicator equipped with a 6 mm horn (14.4 W, 10 mL, up to 15 min) or high hydrostatic pressure (HHP, up to 600 MPa, 15 min) treatments at pH 5, pH 7, and pH 9. The changes to physicochemical properties were probed by SDS-PAGE, FTIR, free sulfhydryl group (SH), surface hydrophobicity (H0), particle size and solubility. As revealed by SDS-PAGE, substantial amounts of 11S globulin participated in the formations of aggregates via SS bond under HHP, particularly at pH 7 and pH 9. However, protein profiles of QPI were not significantly affected by the sonication. Free SH groups and surface hydrophobicity were increased after the sonication treatment indicating protein unfolding and exposure of the embedded SH and/or hydrophobic groups. An opposite trend was observed in HHP treated samples, implying aggregation and reassociation of structures under HHP. HHP and sonication treatments induced a decrease in ordered secondary structures (random coil and β-turn) accompanied with an increase in disordered secondary structures (α-helix and β-sheet) as probed by FTIR. Finally, the sonication treatment induced a significant improvement in the solubility (up to ∼3 folds at pH 7 and ∼2.6 folds at pH 9) and a reduction in particle sizes (up to ∼3 folds at pH 7 and ∼4.4 folds at pH 9). However, HHP treatment (600 MPa) only slightly increased the solubility (∼1.6 folds at pH 7 and ∼1.2 folds at pH 9) and decreased the particle size (∼1.3 folds at pH 7 and ∼1.2 folds at pH 9). This study provides a direct comparison of the impacts of sonication and HHP treatment on QPI, which will enable to choose the appropriate processing methods to achieve tailored properties of QPI.
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    Nanoarchitectonics of Congo red dye to biocompatible fluorescent carbon dots for highly sensitive Fe3+ and ferritin detection
    Kathiravan, A ; Thulasi, S ; Smith, TA ; Ashokkumar, M ; Jhonsi, MA (ROYAL SOC CHEMISTRY, 2022-12-20)
    In this work, we have meticulously tuned the carcinogenic Congo red dye to environmentally benign fluorescent carbon dots (CDs) by adopting a typical hydrothermal method without any additives. The as-synthesized CDs were extremely water soluble, exhibited an excitation wavelength independent emission with a high fluorescence quantum yield (46%) and were biocompatible. The microscopy results revealed that the CDs were quasi-spherical with a particle diameter of ∼5 nm. The structure and functional groups of the CDs were comprehensively investigated using Fourier-transform infrared, X-ray photoelectron and Raman spectroscopy analyses. These studies show that the CDs were intrinsically functionalized with -OH, N-H and CO groups. In the sensing experiments, the CDs selectively responded to Fe3+ ions over other analytes with a detection limit of 12 nM. The time-resolved fluorescence quenching measurements were used to decipher the sensing mechanism. For the onsite 'equipment-free' detection of iron, we have developed a CD adsorbed paper-based analytical tool. Furthermore, the selective nature of CDs was highly beneficial for detecting Fe3+ in non-heme metalloprotein (ferritin) and real water samples. Thus, the CDs produced from the Congo red dye could be a prospective asset to the bio-imaging and biosensing research fields.
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    Turbulence-dependent reversible liquid-gel transition of micellar casein-stabilised emulsions
    Li, W ; Wu, Y ; Martin, GJO ; Ashokkumar, M (ELSEVIER SCI LTD, 2022-10)
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    Protein fortification of model cheese matrices using whey protein-enriched double emulsions
    Gamlath, CJ ; Lo, KY ; Leong, TSH ; Ashokkumar, M ; Martin, GJO (Elsevier, 2023-02)
    Whey proteins represent 20% of the protein content of milk and are an underutilised by-product of cheese manufacturing. This study was aimed at encapsulating whey proteins in the fat content of cheese using double emulsions. A two-stage power ultrasound (20 kHz) emulsification process was used to produce double emulsions with an internal aqueous phase enriched with high concentrations of whey proteins contained within droplets of sunflower oil. Primary water-in-oil (W1/O) nanoemulsions were successfully formed at an applied ultrasonic power of 1.35 W/mL, using 20% w/w and 30% w/w whey protein concentrate (WPC) solutions in the internal phase. The inner water droplets were stabilised by a combination of food grade lipophilic emulsifiers included in the sunflower oil at minimum concentrations of 1% w/w lecithin and 3% w/w PGPR. The secondary oil emulsions were formed by emulsifying the primary W1/O emulsions in 5% w/w WPC solutions, with the whey proteins serving as the emulsifying agent. The encapsulation loading rate of whey proteins within the double emulsion droplets was investigated in relation to ultrasound parameters and formulation loading rates. A very high encapsulation loading rate of ∼45 gwhey protein/Ldouble emulsion was achieved using 0.81 W/mL of ultrasound, with oil droplets of comparable diameter to native milk fat globules (∼10 μm). These double emulsions were successfully incorporated into renneted and cooked curd systems to enable the retention of whey protein in cheese matrices. This study demonstrates the potential of ultrasound emulsification to form whey protein-enriched double emulsions with minimum food-grade emulsifiers to fortify the protein content of cheese and other food products.
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    Ultrasonics in polymer science: applications and challenges
    Kumar, ARSS ; Padmakumar, A ; Kalita, U ; Samanta, S ; Baral, A ; Singha, NK ; Ashokkumar, M ; Qiao, GG (PERGAMON-ELSEVIER SCIENCE LTD, 2023-07)
    Ultrasonic waves in a liquid media generate both chemical and mechanistic effects that are actively used to perform chemical reactions, polymer synthesis, nanoparticle synthesis, colloids, food processing and so on. The application of sonochemistry in polymer science has been an interesting topic of research in the recent years. Ultrasonication acts as an external stimulus to initiate free radical polymerization (FRP) by the homolysis of the solvent, thereby generating radicals. The recent utilization of high frequency ultrasound (>100 KHz) for polymer synthesis has evoked new interest in the use of sonochemistry in the field of polymer chemistry, especially in chain growth polymerization reactions including reversible-deactivation radical polymerization (RDRP) techniques and novel applications. This review presents the principles of sonochemisty and the fundamental aspects governing the cavitation process and the radical generation process. A historical overview of the development of ultrasound-assisted polymerization with a focus on chain-growth polymerizations operating under pseudo-“living” conditions including nitroxide-mediated polymerization (NMP), atom transfer radical polymerization (ATRP) and reversible addition–fragmentation chain transfer (RAFT) polymerization is provided. The utilization of ultrasound in polymer applications such as hydrogels, biomedical nanostructures, drug delivery, nanocomposite synthesis is also discussed. Unlike conventional FRP, ultrasound-initiated polymerization does not involve any external toxic chemical initiators, adds temporal control to the polymerization process, offers excellent control over the molecular weight and the microstructure of the final polymers, etc. The ultrasound assisted polymerization is a novel, clean and green technology, which can be investigated further by coupling with thermo-, mechano- or photochemical stimuli or flow chemistry. It has the potential to be scaled up into an industrial process.
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    High chain-end fidelity in sono-RAFT polymerization
    Padmakumar, AK ; Kumar, ARSS ; Allison-Logan, S ; Ashokkumar, M ; Singha, NK ; Qiao, GG (Royal Society of Chemistry, 2022-10-15)
    The chain-end fidelity of polymers synthesized via the sono-RAFT technique in an aqueous medium was investigated by performing chain extension studies and preparation of multi-block copolymers. Sono-RAFT polymerization of N,N-dimethylacrylamide (DMA), 2-hydroxyethyl acrylate (HEA) and N-acryloyl morpholine (NAM) exhibited higher conversion values, low dispersity and excellent chain-end fidelity. MALDI-TOF analysis indicated that the fraction of dead chains observed was almost negligible indicating high livingness of the polymer end groups. The sono-RAFT technique was compared to the photo-iniferter method by performing chain extension experiments. Polymers prepared via sono-RAFT were identical to those prepared via the photo-iniferter RAFT method in terms of livingness, and the polymer reached very high conversion within a fraction of the time compared to the latter method. An icosapenta block copolymer (25 blocks) was synthesized at room temperature within 46 h. The resulting block copolymer displayed a controlled molecular weight and a final dispersity of 1.39.