Ultrasonic Characterisation of W/O Microemulsions - Structure, Phase Diagrams, State of Water in Nano-Droplets, Encapsulated Proteins, Enzymes

Ultrasonic Monitoring of Biocatalysis in Solutions and Complex Dispersions

“…For illustrative purposes, the negative value of concentration increment of ultrasonic velocity of decomposition of hydrogen peroxide, Red squares: a G n of glucose oligomers in the aqueous droplets of IPM microemulsion system (water (24% kg/kg), oil (isopropilmiristate (IPM), 38% kg/kg), cosurfactant (n-propanol, 19% kg/kg), surfactant (E200, 19% kg/kg)) at concentration 0.025 kg per kg of the aqueous phase (overall concentration 0.06 kg/kg), calculated according to Equation (6) from ultrasonic velocities at 8 MHz (no significant frequency dependence detected within the analyzed frequency range 3 to 8 MHz). Details of preparation of the microemulsion were described earlier [29][30][31]. n = 1-glucose, n = 2-maltose, n = 3-maltotriose, n = 4-maltotetrose, n = 5-maltopentose, n = 7-maltoheptaose, and average n = 7.55-maltodextrin (provided by manufacturer and confirmed with bicinchoninic acid (BCA) assay [32,33]).…”

“…According to Equations, for dispersions of solid particles of micron and submicron size, the dependence of the scattering contributions α scatt measured at ultrasonic frequencies on the size of the particle has a 'bell' shape profile. The 'bell' has two, normally unresolved, maxima at the particle sizes close to (comparable with) the wavelength of the shear wave in the continuous medium and with the wavelength of the thermal wave in the particle and in the continuous medium (examples of the profiles are given in references [29,31,41]). The scattering contribution to ultrasonic velocity produces an increase of velocity with size following the S-shape profile with plateaus at small and large sizes and the transition sizes around the maxima of ultrasonic attenuation.…”

“…Therefore, successful encapsulation of enzymes and of the components of reactions involves identification of the parts of the w/o microemulsion phase diagrams where nanodroplets contain the required for the hydration of enzyme and substrate/product amount of free water. HR-US titration analysis allows for identification of these parts of microemulsion phase diagrams [31]. Ultrasonic pseudo-ternary (concentration scale, % kg/kg) phase diagram of water/isopropyl myristate (IPM)/epikuron 200 (E200) and n-propanol (1:1) at 25 °C.…”

“…In addition to this, the ultrasonic titration profiles demonstrate a range of transitions below the blue line, which allows distinguishing different 'sub phases', Ia, Ib, II and III. The nature of these 'sub phases' is related to the state of water and surfactant, including hydration water in the dispersed phase, hydration water in swollen reverse micelles and water in aqueous nano-size droplets surrounded by surfactant, realized in 'sub phase' III [31]. According to Figure 10 the sub-phase III shall provide a reasonable hydration level for hydrophilic enzymes, substrates and products (see more discussions in [29][30][31]69]).…”

“…The nature of these 'sub phases' is related to the state of water and surfactant, including hydration water in the dispersed phase, hydration water in swollen reverse micelles and water in aqueous nano-size droplets surrounded by surfactant, realized in 'sub phase' III [31]. According to Figure 10 the sub-phase III shall provide a reasonable hydration level for hydrophilic enzymes, substrates and products (see more discussions in [29][30][31]69]). Figure 11 compares the real-time ultrasonic profiles of hydrolysis of maltodextrin catalyzed by α-amylase from Bacillus sp.…”