Impact of 2.45 GHz Microwave Irradiation on the Fruit Fly, Drosophila melanogaster.

The physiological and behavioral influences of 2.45 GHz microwaves on Drosophila melanogaster were examined. Standing waves transitioned into heat energy effectively when passing through the insect body. On the contrary, travelling waves did not transit into heat energy in the insect body. This indicated that there was no concern regarding the thermal effects of microwave irradiation for levels of daily usage. However, we detected genotoxicity and behavioral alterations associated with travelling wave irradiation, which can be attributed to the non-thermal effects of the waves. Electron spin resonance (ESR) revealed that fruit flies possessed paramagnetic substances in the body such as Fe3+, Cu2+, Mn2+, and organic radicals. The temperature dependent intensities of these paramagnetic substances indicated that females possessed more of the components susceptible to electromagnetic waves than males, and the behavioral tests supported the differences between the sexes.

Directly Microwave-Accelerated Cleavage of C-C and C-O Bonds of Lignin by Copper Oxide and H2 O2.

Model erythro, phenolic, and nonphenolic lignin ß-O-4 dimer compounds are treated with copper oxide and H2 O2 at the electronic field maximum position of a single-mode 2.45 GHz microwave system equipped with a cavity resonator. The products obtained through microwave heating and oil-bath heating with the same reaction vessel and temperature profile are quantitatively compared. Dimer degradation is found to proceed through consecutive elementary reactions. The phenolic dimer is dehydroxylated and this is followed by the spontaneous cleavage of Cα -Cß and C-O-C bonds to produce guaiacol, vanillin, and vanillic acid. The reaction of the nonphenolic dimer produces veratric acid, veratraldehyde, and guaiacol. Microwave irradiation accelerates cleavage of the side chain and the oxidation of vanillin to vanillic acid. However, no acceleration of veratraldehyde oxidation to veratric acid or aromatic ring cleavage to produce dicarboxylic acids is observed. The selective acceleration of elementary reactions during the degradation of model lignin compounds indicates that microwaves interact with reaction intermediates that are sensitive to electromagnetic waves.

Physical assessments of termites (Termitidae) under 2.45 GHz microwave irradiation.

Demands for chemical-free treatments for controlling insect pests are increasing worldwide. One such treatment is microwave heating; however, two critical issues arise when using microwaves as a heat source: intensive labor and excessive energy-consumption. Optimization is thus required to reduce energy consumption while effectively killing insects. Currently, the lethal effect of microwaves on insects is considered to be due to the temperature of the irradiated materials. This study examines how the conditions of irradiation, such as resonance or traveling mode, changed the conversion of electromagnetic energy into heat when 2.45 GHz microwaves penetrated the body of the termite, C. formosanus. Our results indicated that it is possible to heat and kill termites with microwaves under resonance condition. Termites were however found to be very tolerant to microwave irradiation as the permittivity of the insect was low compared with other reported insects and plants. Electron spin resonance revealed that termites contained several paramagnetic substances in their bodies, such as Fe3+, Cu2+, Mn2+, and organic radicals. Interestingly, irradiation with traveling microwaves hardly produced heat, but increased the organic radicals in termite bodies indicating non-thermal effects of microwaves.

Proton-Enhanced Dielectric Properties of Polyoxometalates in Water under Radio-Frequency Electromagnetic Waves.

Electromagnetic waves, such as microwaves, have been used to enhance various chemical reactions over polyoxometalates. The dielectric properties of catalysts are among the relevant parameters facilitating catalytic reactions under electromagnetic radiation. This study describes the dielectric properties of polyoxometalate catalysts in aqueous and organic solutions to understand the mechanism of interactions between polyoxometalates and electromagnetic waves. Specific loss factors of polyoxometalates were observed at lower frequencies (<1 GHz) by the ionic conduction of the polyoxometalate solution. The evolution of ionic conduction depended strongly on cations rather than anions. Proton-type polyoxometalates exhibited significantly higher loss factors than other cations did. The activation energy for ionic conduction in protonated silicotungstic acid (H4SiW12O40) was significantly low in water (7.6⁻14.1 kJ/mol); therefore, the high loss factor of protonated polyoxometalates in water was attributed to the proton relay mechanism (i.e., Grotthuss mechanism). The results suggested that the proton relay mechanism at the radio-frequency band is critical for generating selective interactions of polyoxometalates with applied electromagnetic fields.

Effect of Aspect Ratio on the Permittivity of Graphite Fiber in Microwave Heating.

Microwave (MW) heating has received attention as a new heating source for various industrial processes. Some materials are expected to be a more effective absorber of MW, and graphite is observed as a possible candidate for high-temperature application. We investigated the dependence of the aspect ratio of graphite fibers on both their heating behavior and permittivity under a 2.45 GHz MW electric field. In these experiments, both loss tangent and MW heating behavior indicated that the MW absorption of conductive fibers increases with their aspect ratio. The MW absorption was found to be well accounted for by the application of a spheroidal model for a single fiber. The absorption of graphite fibers decreases with increasing aspect ratio when the long axis of the ellipsoid is perpendicular to the electric field, whereas it increases with the aspect ratio when the long axis is parallel to the electric field. The analytical model indicated that MW heating of the conductive fibers is expected to depend on both the shape and arrangement of the fibers in the electric field.

Effects of Normothermic Conditioned Microwave Irradiation on Cultured Cells Using an Irradiation System with Semiconductor Oscillator and Thermo-regulatory Applicator.

We investigated the effects of microwave irradiation under normothermic conditions on cultured cells. For this study, we developed an irradiation system constituted with semiconductor microwave oscillator (2.45 GHz) and thermos-regulatory applicator, which could irradiate microwaves at varied output powers to maintain the temperature of cultured cells at 37 °C. Seven out of eight types of cultured cells were killed by microwave irradiation, where four were not affected by thermal treatment at 42.5 °C. Since the dielectric properties such as ε', ε" and tanδ showed similar values at 2.45 GHz among cell types and media, the degree of microwave energy absorbed by cells might be almost the same among cell types. Thus, the vulnerability of cells to microwave irradiation might be different among cell types. In HL-60 cells, which were the most sensitive to microwave irradiation, the viability decreased as irradiation time and irradiation output increased; accordingly, the decrease in viability was correlated to an increase in total joule. However, when a high or low amount of joules per minute was supplied, the correlation between cellular viability and total joules became relatively weak. It is hypothesized that kinds of cancer cells are efficiently killed by respective specific output of microwave under normothermic cellular conditions.

Microwave-assisted hydrothermal extraction of sulfated polysaccharides from Ulva spp. and Monostroma latissimum.

Microwave-assisted hydrothermal extraction was applied for production of sulfated polysaccharides from Ulva spp. and Monostroma latissimum. The maximum ulvan yields attained 40.4±3.2% (Ulva meridionalis) and 36.5±3.1% (Ulva ohnoi) within 4min of come-up time and 10min of extraction time at 160°C, respectively. The rhamnan sulfate yield from M. latissimum further attained 53.1±7.2% at 140°C. The sulfated polysaccharides were easily recovered from the extract by simple ethanol precipitation. In addition, molecular weights and viscosity of the extracted polysaccharides could be controlled by varying the extraction temperature. Dielectric measurement revealed that ionic conduction was the important parameter that affect the microwave susceptibility of algae-water mixture. The sulfated polysaccharides extracts are expected as potential feedstock for medical and food applications.

Effects of ionic conduction on hydrothermal hydrolysis of corn starch and crystalline cellulose induced by microwave irradiation.

This study investigated the effects of ionic conduction of electrolytes under microwave field to facilitate hydrothermal hydrolysis of corn starch and crystalline cellulose (Avicel), typical model biomass substrates. Addition of 0.1M NaCl was effective to improve reducing sugar yield by 1.61-fold at unit energy (kJ) level. Although Avicel cellulose was highly recalcitrant to hydrothermal hydrolysis, addition of 0.1M MgCl2 improved reducing sugar yield by 6.94-fold at unit energy (kJ). Dielectric measurement of the mixture of corn starch/water/electrolyte revealed that ionic conduction of electrolytes were strongly involved in facilitating hydrothermal hydrolysis of polysaccharides.

Effects of acidic functional groups on dielectric properties of sodium alginates and carrageenans in water.

This study investigated the dielectric properties of sodium alginates and carrageenans in water at frequencies between 100 MHz and 20 GHz in regard to water-hydrocolloid interactions via acidic functional groups. Both sodium alginates and carrageenans showed conduction loss at lower frequencies and dielectric loss at higher frequencies. Reduction and desulfation of sodium alginates and carrageenans, which decreased the numbers of acidic functional groups, decreased their conduction loss. In addition, H(+)-form carrageenans showed the highest ionic conduction. Correlational analysis of dielectric properties and related physical parameters showed that the loss tangent (tanδ) of the hydrocolloid solution was determined by the conductivity of the aqueous solution. Especially at pH below 2, strong H(+) conduction was associated with high tanδ probably due to the Grotthuss mechanism. The molecular dynamics of free water and H(+), viscosity conditions were also suggested to be associated with dielectric property of water-hydrocolloid system.

Functional group dependent dielectric properties of sulfated hydrocolloids extracted from green macroalgal biomass.

Dielectric properties of aqueous solutions of sulfated hydrocolloids (ulvan and rhamnan sulfate) extracted from green macroalgal biomass were studied in a frequency range of 100 MHz-10 GHz. Counterion exchange of native hydrocolloids (mixture of Na(+), Mg(2+) and Ca(2+)) to H(+)-form showed significant increase in loss factor due to ionic conduction. On the other hand, desulfations decreased their loss factors. The results suggested that ionic conduction of H(+) has significant contribution to loss factors. Additionally, H(+)-form hydrocolloids showed significant improvement in hydration, which might also affect the dielectric property of the solution by reducing the amount of free water. The viscosity, however, did not show apparent relevance with the dielectric property.

Microwave-assisted hydrolysis of polysaccharides over polyoxometalate clusters.

Polyoxometalate (POM) clusters were utilized as recyclable acid catalysts and microwave-absorbing agents for the microwave-assisted hydrolysis of corn starch and crystalline cellulose. Phosphotungstic (PW) and silicotungstic (SiW) acids showed high hydrolyzing activity, while phosphomolybdic acid (PMo) showed lower glucose stability. The PW catalyst could be recycled by ether extraction at least 4 times without changing its catalytic activity. The addition of PW could reduce the energy demand required for running the hydrolysis by 17-23%. The dielectric property of the aqueous PW solution was important for increasing the microwave-absorption capability of the reaction system and reducing the energy consumption.