School of Chemistry - Research Publications
Now showing items 1-12 of 418
Ultrasonic pretreatment of food waste to accelerate enzymatic hydrolysis for glucose production
(ELSEVIER SCIENCE BV, 2019-05-01)
Recovering valuable materials from food waste by applying the concept of a bio-refinery is attracting considerable interest. To this effect, we investigated the possibility of enhancing the enzymatic hydrolysis of food waste using ultrasonic technology. The effect of pre-treating blended food waste with high-intensity ultrasound (20 kHz) on subsequent hydrolysis by glucoamylase was investigated as a function of sonication time and temperature. Particle sizing by laser diffraction, and imaging via scanning electronic microscopy showed that ultrasonic pre-treatment could reduce the particle size of the blended food waste significantly, resulting in a better interaction with the enzyme. As a consequence, the glucose yield of enzymatic hydrolysis was ∼10% higher for food waste pre-sonicated using the most intensive ultrasonication conditions studied (5 min sonication at a power of 0.8 W/mL at 20 °C) than for the untreated control. In addition, the time required to achieve high yields of glucose could be more than halved using ultrasonic pre-treatment. This could enable the hydrolysis reactor size or the enzyme usage to be reduced by more than 50%. Therefore, an ultrasound-assisted bioconversion process from food waste into a value-added product has been demonstrated.
Emulsifying properties of ruptured microalgae cells: Barriers to lipid extraction or promising biosurfactants?
(ELSEVIER SCIENCE BV, 2018-10-01)
A systematic investigation of the emulsifying properties of ruptured algae cells was performed for the first time. The slurry of ruptured algae cells was separated into different biomass fractions, namely the cell debris, the delipidated debris, the serum, and the lipid. The interfacial interactions of these biomass fractions with a nonpolar solvent (e.g. hexane or hexadecane) were characterized using pendant drop tensiometry and interfacial shear rheology. The stability of the different emulsions (formed by the different biomass fractions) was tested using analytical centrifugation. The extracted lipid was an excellent surfactant that reduced the interfacial tension, however, it was not effective at stabilizing the emulsions. The protein-rich serum produced a strong interfacial film that stabilized the emulsions against coalescence during centrifugation. The cell debris stabilized the emulsions to a lesser extent by adsorbing to the droplet surface, presumably via interactions with hydrophobic extracellular polymeric substances (EPS). However, neither the serum nor the cell debris were very effective surfactants, and required the presence of the lipid fraction to produce small emulsion droplets. When present together, the components exhibited competitive interfacial adsorption, which influenced emulsion stability. In particular, the interruption of the protein film by the presence of lipid or cell debris reduced the stability of the emulsions. This study provides a new mechanistic understanding of emulsification during wet lipid extraction from microalgae that will be useful for determining strategies to improve solvent recovery. The results also suggest potential for developing effective bioemulsifiers or biosurfactants from fractionated microalgae biomass for commercial application.
Screening of Isochrysis Strains and Utilization of a Two-Stage Outdoor Cultivation Strategy for Algal Biomass and Lipid Production
(HUMANA PRESS INC, 2018-08-01)
Isochrysis is a genus of marine algae without cell wall and capable of accumulating lipids. In this study, the lipid production potential of Isochrysis was assessed by comparing 15 Isochrysis strains with respect to their growth rate, lipid production, and fatty acid profiles. Three best strains were selected (lipid productivity, 103.0~121.7 mg L−1 day−1) and their lipid-producing capacities were further examined under different controlled parameters, e.g., growth phase, medium nutrient, and light intensity in laboratory cultures. Furthermore, the three Isochrysis strains were monitored in outdoor panel photobioreactors with various initial cell densities and optical paths, and the strain CS177 demonstrated the superior potential for outdoor cultivation. A two-stage semi-continuous strategy for CS177 was subsequently developed, where high productivities of biomass (1.1 g L−1 day−1) and lipid (0.35 g L−1 day−1) were achieved. This is a comprehensive study to evaluate the lipid-producing capability of Isochrysis strains under both indoor and outdoor conditions. Results of the present work lay a solid foundation for the physiological and biochemical responses of Isochrysis to various conditions, shedding light on the future utilization of this cell wall-lacking marine alga for biofuel production.
Introductory text to sonochemistry
Sonochemistry is a multi-disciplinary and an emerging research field that has potential applications in many areas that include chemistry, physics, biology, materials, food science, engineering, and medicine. The primary focus of this article is to provide a basic, textbook-type introduction highlighting the fundamental aspects and selected applications of sonochemistry. The purpose of this article is not to provide a full literature review, but to give the readers a birds’ eye view of the basics of acoustic cavitation and selected examples of applied sonochemistry. Extensive review articles and book chapters are available that provide in-depth analysis of the current literature in various topics.
A model for the effect of bulk liquid viscosity on cavitation bubble dynamics
(ROYAL SOC CHEMISTRY, 2017-08-21)
A new model of single cavitation bubble dynamics has been developed to include the effect of bulk liquid viscosity in addition to the effects of evaporation/condensation of water vapor, thermal conduction and the compressibility of a liquid. In this study, the liquid viscosity is divided into two parts: viscosity at the bubble interface (μ′) and viscosity of the bulk liquid (μ). A set of numerical calculations with and without μ has been completed under different viscosities (0.001–0.014 Pa s) to quantitatively analyze the effect of μ on single cavitation bubble dynamics. The results show that the effect can be negligible for small viscosities, but it should be taken into account for relatively high viscosities.
Biodiesel synthesis assisted by ultrasonication using engineered thermo-stable Proteus vulgaris lipase
(ELSEVIER SCI LTD, 2017-11-15)
Nature has evolved and designed enzymes to perform an exquisite array of tasks, but in the pursuit of biotechnological interests, these enzymes must often be improved, altered, or even completely redesigned. In the present work, production of biodiesel was carried out using Neem oil and methanol catalysed by “engineered” Proteus vulgaris lipase (PVL). Two major issues have been addressed in this study in order to improve the efficiency of biodiesel synthesis by enzyme catalysis. The thermal stability of PVL was increased by introduction of a disulfide bond in G181 and T238 by mutation to cysteines. The transesterification reaction was carried out using sonication under different ultrasonic experimental conditions using a 20 kHz horn. The results showed that the application of ultrasound, using 20 kHz horn with 1 cm tip diameter, decreased the reaction time from 22–24 h to 30 min at an applied power of 40 W and methanol to oil molar ratio of 5:1. Temperature raised due to sonication had no effect on engineered PVL (PVLC181-238) activity. A comparative study of wild type (WT-PVL) and engineered PVLC181-238 for different temperature has been performed and results showed that introduction of a single disulfide in PVL significantly stabilized it, increasing the half-inactivation temperature (IT1/2) from 37 °C for the WT-PVL to 50 °C for the PVLC181-238 engineered one. In biodiesel synthesis also after immobilization on (Polysulfone) PS beads, PVLC181-238 showed better performance compared to WT-PVL.
The effect of high-intensity ultrasound on cell disruption and lipid extraction from high-solids viscous slurries of Nannochloropsis sp biomass
(ELSEVIER SCIENCE BV, 2018-11-01)
The effect of ultrasonication on the cell rupture of marine microalgae Nannochloropsis sp. was studied as a function of the slurry solids concentration and treatment time. The concentrated viscous wet-biomass (~12 to 25% solids concentration) was subjected to ultrasonication (20 kHz) at 3.8 W/mL for up to 5 min. Compared to extraction without cell rupture, sonication led to a significant increase in lipid yield from ~11% to about 70% within 5 min of sonication. The extraction yield was found to decrease with increased solids concentration, with a large decrease between 20% to 25% solids. This is attributed to the increase in viscosity and decrease in speed of sound with increase in solids. The ultrasound attenuation coefficient increased 320-fold as the solids increased from 20 to 25%. Such a large attenuation of ultrasound places a limit of 20% solids to be used for cell rupture by ultrasound. The specific energy requirements per unit mass of extracted lipid were lowest at 20% solids. At lower concentrations energy was wasted heating water, at higher concentrations the lipid yields were reduced due to ultrasound attenuation.
Effect of Bulk Viscosity and Emulsion Droplet Size on the Separation Efficiency of Model Mineral Oil-in-Water (O/W) Emulsions under Ultrasonic Standing Wave Fields: A Theoretical and Experimental Investigation
(American Chemical Society (ACS), 2020-04-22)
Ultrasound standing waves can be used to separate emulsions. So far, they have been applied to oil-in-water emulsions with low continuous phase viscosity. This technique has the potential to be used for novel applications such as separating lipids from algal biomass; however, this requires the methodology to be optimized to process viscous emulsions. We have addressed this issue by studying the effects of bulk phase viscosity (1–23 mPa·s), emulsion droplet size (4.5–20 μm), power (10–54 W/L), and frequency (1 and 2 MHz) of ultrasound on the separation efficiency of model mineral oil-in-water–glycerol-mixture emulsions. For the small droplet size (4.5 μm) emulsion in water, the maximum separation achieved increased from 36 to 79% when ultrasound power increased from 10 to 54 W/L. However, for the large droplet size (11 μm) emulsion, the maximum separation was greater than 95% and was independent of ultrasound power. The maximum separation efficiency for small droplet size (4.5–6 μm) emulsions decreased from 80 to 14% when the viscosity increased from 1 to 23 mPa·s. However, for the large droplet size (11–20 μm) emulsion, the maximum separation efficiency decreased from 98 to 62% when the viscosity of the bulk phase was increased from 1 to 23 mPa·s. The experimental results were then interpreted using analytical and numerical simulations by calculating the time required for the emulsion droplets to migrate to the nearest pressure antinodal plane under the influence of ultrasound standing waves. Further experiments showed that increasing the ultrasound frequency from 1 to 2 MHz increased the maximum separation from 36 to 86% for fine emulsions and water as the continuous phase.
Sound-driven dissipative self-assembly of aromatic biomolecules into functional nanoparticles
(Royal Society of Chemistry, 2020-03-01)
Dissipative self-assembly processes were recently exploited to assemble synthetic materials into supramolecular structures. In most cases, chemical fuel or light driven self-assembly of synthetic molecules was reported. Herein, experimental and computational approaches were used to unveil the role of acoustic cavitation in the formation of supramolecular nanoaggregates by dissipative self-assembly. Acoustic cavitation bubbles were employed as an energy source and a transient interface to fuel and refuel the dissipative self-assembly of simple aromatic biomolecules into uniform nanoparticles. Molecular dynamics simulations were applied to predict the formation of metastable aggregates and the dynamic exchange of the interacting molecules in the nanoaggregates. The intracellular trafficking and dissipative dissolution of the nanoparticles were tracked by microscopy imaging.
Electronic spectrum and photodissociation chemistry of the linear methyl propargyl cation H2C4H3+
(AMER INST PHYSICS, 2017-01-28)
The electronic spectrum of the methyl propargyl cation (2-butyn-1-yl cation, H2C4H3+) is measured over the 230-270 nm range by photodissociating the bare cation and its Ar and N2 tagged complexes in a tandem mass spectrometer. The observed A'1←A'1 band system has an origin at 37 753 cm-1 for H2C4H3+, 37738 cm-1 for H2C4H3+-Ar, and 37 658 cm-1 for H2C4H3+-N2. The methyl propargyl cation photodissociates to produce either C2H3++C2H2 (protonated acetylene + acetylene) or H2C4H++H2 (protonated diacetylene + dihydrogen). Photodissociation spectra of H2C4H3+, H2C4H3+-Ar, and H2C4H3+-N2 exhibit similar vibronic structure, with a strong progression of spacing 630 cm-1 corresponding to excitation of the C-C stretch mode. Interpretation of the spectra is aided by ground and excited state calculations using time dependent density functional theory at the ωB97X-D/aug-cc-pVDZ level of theory. Ab initio calculations and master equation simulations were used to interpret the dissociation of H2C4H3+ on the ground state manifold. These calculations support the experimentally observed product branching ratios in which acetylene elimination dominates and also suggests that channel switching occurs at higher energies to favor H2 elimination.
In-situ X-ray diffraction snapshotting: Determination of the kinetics of a photodimerization within a single crystal
(NATURE PUBLISHING GROUP, 2014-10-29)
In a single-crystal-to-single-crystal (SCSC) transformation, a preformed three-dimensional coordination polymer,[Ni3(oba)2(bpe)2(SO4)(H2O)4]· H2O (H2oba = 4,4'-oxydibenzoic acid; bpe = (E)-1,2-di(pyridin-4-yl)ethane) (1), was shown to undergo a [2+2] cycloaddition reaction upon exposure to UV irradiation. The kinetics of this reaction were followed by taking "snapshots" of the solid state transformation using in situ single crystal X-ray crystallography; a first order process was indicated. The reaction rate was influenced by many factors such as the separation of the sample from the UV light source, the heat produced by the UV irradiation, the light flux of the UV lamp used, the size of the single-crystal and the powder samples. The investigation of the kinetics was complemented by (1)H NMR studies. The results clearly demonstrate that in situ single-crystal X-ray diffraction is able to provide useful insights into the gradual formation of the photoproducts and the reaction processes. The work also offers a clear indication that it is possible to use the technique to study the kinetics of other photocycloaddition reactions and SCSC processes in general.
Site-Specific Glycation and Chemo-enzymatic Antibody Sortagging for the Retargeting of rAAV6 to Inflamed Endothelium
(CELL PRESS, 2019-09-13)
Gene therapy holds great potential for conditions such as cardiovascular disease, including atherosclerosis and also vascular cancers, yet available vectors such as the adeno-associated virus (rAAV) transduce the vasculature poorly. To enable retargeting, a single-chain antibody (scFv) that binds to the vascular cell-adhesion molecule (VCAM-1) overexpressed at areas of endothelial inflammation was site specifically and covalently conjugated to the exterior of rAAV6. To achieve conjugation, the scFv was functionalized with an orthogonal click chemistry group. This conjugation utilized site-specific sortase A methodology, thus preserving scFv binding capacity to VCAM-1. The AAV6 was separately functionalized with 4-azidophenyl glyoxal (APGO) via covalent adducts to arginine residues in the capsid's heparin co-receptor binding region. APGO functionalization removed native tropism, greatly reducing rAAV6-GFP transduction into all cells tested, and the effect was similar to the inhibition seen in the presence of heparin. Utilizing the incorporated functionalizations, the scFv was then covalently conjugated to the exterior of rAAV6 via strain-promoted azide-alkyne cycloaddition (SPAAC). With both the removal of native heparin tropism and the addition of VCAM-1 targeting, rAAV6 transduction of endothelial cells was greatly enhanced compared to control cells. Thus, this novel and modular targeting system could have further application in re-directing AAV6 toward inflamed endothelium for therapeutic use.