Broadband dielectric spectroscopy of glucose aqueous solution: Analysis of the hydration state and the hydrogen bond network.

Recent studies of saccharides' peculiar anti-freezing and anti-dehydration properties point to a close association with their strong hydration capability and destructuring effect on the hydrogen bond (HB) network of bulk water. The underlying mechanisms are, however, not well understood. In this respect, examination of the complex dielectric constants of saccharide aqueous solutions, especially over a broadband frequency region, should provide interesting insights into these properties, since the dielectric responses reflect corresponding dynamics over the time scales measured. In order to do this, the complex dielectric constants of glucose solutions between 0.5 GHz and 12 THz (from the microwave to the far-infrared region) were measured. We then performed analysis procedures on this broadband spectrum by decomposing it into four Debye and two Lorentz functions, with particular attention being paid to the β relaxation (glucose tumbling), δ relaxation (rotational polarization of the hydrated water), slow relaxation (reorientation of the HB network water), fast relaxation (rotation of the non-HB water), and intermolecular stretching vibration (hindered translation of water). On the basis of this analysis, we revealed that the hydrated water surrounding the glucose molecules exhibits a mono-modal relaxational dispersion with 2-3 times slower relaxation times than unperturbed bulk water and with a hydration number of around 20. Furthermore, other species of water with distorted tetrahedral HB water structures, as well as increases in the relative proportion of non-HB water molecules which have a faster relaxation time and are not a part of the surrounding bulk water HB network, was found in the vicinity of the glucose molecules. These clearly point to the HB destructuring effect of saccharide solutes in aqueous solution. The results, as a whole, provide a detailed picture of glucose-water and water-water interactions in the vicinity of the glucose molecules at various time scales from sub-picosecond to hundreds of picoseconds

Static and dynamic evaluations of acoustic positioning system using TDMA and FDMA for robots operating in a greenhouse

Acoustic positioning system has great potential to be applied in a greenhouse due to its centimeter-level accuracy, low cost, and ability of extensive greenhouse coverage. Spread Spectrum Sound-based local positioning system (SSSLPS) was proposed to be a navigation tool for multiple agricultural robots by the authors' research team. However, to increase the system capacity for positioning multiple robots in a greenhouse, the near-far problem caused by the interference between speakers needs to be overcome. The use of different access methods, Time Division Multiple Access (TDMA) or Frequency Division Multiple Access (FDMA), is essential in the SSSLPS system for solving the near-far problem. The static positioning in a greenhouse was first evaluated by setting different parameters to determine the optimal signal setting for a dynamic experiment. From that, the moving robot tests were added with a motion capture system and tested the performance of TDMA and FDMA. The results demonstrated that TDMA can be used in a stationary sound-based positioning system with 12.2 mm accuracy, but it has a time delay problem in dynamic positioning. A simulation was designed to mimic the position error increases with different moving speeds. Although FDMA has the sound damping problem in high-frequency regions creating a peak detection issue, it achieved a higher accuracy with an average position error of 62.1 mm compared to 180.3 mm of TDMA. This study shows that the TDMA method is suitable for static measurements, while the FDMA method is suitable for measuring dynamic objects and controlling mobile robots

Increase in the Intracellular Bulk Water Content in the Early Phase of Cell Death of Keratinocytes, Corneoptosis, as Revealed by 65 GHz Near-Field CMOS Dielectric Sensor

While bulk water and hydration water coexist in cells to support the expression of biological macromolecules, how the dynamics of water molecules, which have long been only a minor role in molecular biology research, relate to changes in cellular states such as cell death has hardly been explored so far due to the lack of evaluation techniques. In this study, we developed a high-precision measurement system that can discriminate bulk water content changes of ±0.02% (0.2 mg/cm3) with single-cell-level spatial resolution based on a near-field CMOS dielectric sensor operating at 65 GHz. We applied this system to evaluate the temporal changes in the bulk water content during the cell death process of keratinocytes, called corneoptosis, using isolated SG1 (first layer of stratum granulosum) cells in vitro. A significant irreversible increase in the bulk water content was observed approximately 1 h before membrane disruption during corneoptosis, which starts with cytoplasmic high Ca2+ signal. These findings suggest that the calcium flux may have a role in triggering the increase in the bulk water content in SG1 cells. Thus, our near-field CMOS dielectric sensor provides a valuable tool to dissect the involvement of water molecules in the various events that occur in the cell

Coexistence of Kosmotropic and Chaotropic Impacts of Urea on Water As Revealed by Terahertz Spectroscopy

Whether urea can serve as a kosmotrope or chaotrope has long been a topic of debate. In this study, broad-band THz spectroscopy (0.2–12 THz) of aqueous solutions of urea was used to characterize the hydration state and the hydrogen bond structure of water around urea. Three low-frequency vibration modes of urea were found around 2, 4, and above 12 THz. After eliminating the contribution of these modes, the “urea-vibration-free” complex dielectric constant was decomposed into the relaxation modes of bulk water and the oscillation modes of water. When hydration water is defined to be reorientationally retarded relative to bulk, our analysis revealed that the hydration number is 1.9 independent of urea concentrations up to 5 M, and this number is in close agreement with that of water constrained by strong acceptor hydrogen bonds of urea oxygen. Regarding the hydrogen bond structure, it was found that the tetrahedral-like water structure is mostly preserved (though the hydrogen bond lifetime is significantly shortened) but the population of non-hydrogen-bonded water molecules fragmented from the network is markedly increased, presumably due to urea’s NH₂ inversion. These experimental results point to the coexistence of apparently two contradictory aspects of urea: dynamical retardation (the kosmotropic aspect) by the −CO group and slight structural disturbance (the chaotropic aspect) by the −NH₂ group