Pore-size dependent THz absorption of nano-confined water.

We performed a THz absorption spectroscopy study on liquid water confined in mesoporous silica materials, MCM-41-S-18 and MCM-41-S-21, of two different pore sizes at room temperatures. We found that stronger confinement with a smaller pore size causes reduced THz absorption, indicating reduced water mobility due to confinement. Combined with recent theoretical studies showing that the microscopic structure of water inside the nanopores can be separated into a core water region and an interfacial water region, our spectroscopy analysis further reveals a bulk-water-like THz absorption behavior in the core water region and a solid-like THz absorption behavior in the interfacial water region.

Evaluation of the hydration state of saccharides using terahertz time-domain attenuated total reflection spectroscopy.

Despite intensive studies regarding the hydration state, experimental investigations have not fully explained the global hydration state. Terahertz (THz) spectroscopy is an emerging technology that has the potential to evaluate global hydration. This is because THz waves are very sensitive to picosecond water dynamics and, as such, effectively measures the state of water that is weakly bound to solute molecules by observing slowed down water dynamics. THz time-domain attenuated total reflection (THz TD-ATR) spectroscopy allowed to determine the complex refractive index of saccharide solutions and to experimentally characterize the global hydration state. Our result indicates the global hydration state is closely related to the number of hydrophilic groups and steric configuration of hydroxyl groups in saccharide molecules. This new tool to investigate the global hydration state will provide new knowledge about water dynamics around solutes that couldn't have been elucidated with the conventional techniques.

Applying terahertz technology for nondestructive detection of crack initiation in a film-coated layer on a swelling tablet.

Here, we describe a nondestructive approach using terahertz wave to detect crack initiation in a film-coated layer on a drug tablet. During scale-up and scale-down of the film coating process, differences in film density and gaps between the film-coated layer and the uncoated tablet were generated due to differences in film coating process parameters, such as the tablet-filling rate in the coating machine, spray pressure, and gas-liquid ratio etc. Tablets using the PEO/PEG formulation were employed as uncoated tablets. We found that heat and humidity caused tablets to swell, thereby breaking the film-coated layer. Using our novel approach with terahertz wave nondestructively detect film surface density (FSD) and interface density differences (IDDs) between the film-coated layer and an uncoated tablet. We also found that a reduced FSD and IDD between the film-coated layer and uncoated tablet increased the risk of crack initiation in the film-coated layer, thereby enabling us to nondestructively predict initiation of cracks in the film-coated layer. Using this method, crack initiation can be nondestructively assessed in swelling tablets after the film coating process without conducting accelerated stability tests, and film coating process parameters during scale-up and scale-down studies can be appropriately established.

Highly accurate Michelson type wavelength meter that uses a rubidium stabilized 1560 nm diode laser as a wavelength reference.

We investigated the accuracy limitation of a wavelength meter installed in a vacuum chamber to enable us to develop a highly accurate meter based on a Michelson interferometer in 1550 nm optical communication bands. We found that an error of parts per million order could not be avoided using famous wavelength compensation equations. Chromatic dispersion of the refractive index in air can almost be disregarded when a 1560 nm wavelength produced by a rubidium (Rb) stabilized distributed feedback (DFB) diode laser is used as a reference wavelength. We describe a novel dual-wavelength self-calibration scheme that maintains high accuracy of the wavelength meter. The method uses the fundamental and second-harmonic wavelengths of an Rb-stabilized DFB diode laser. Consequently, a highly accurate Michelson type wavelength meter with an absolute accuracy of 5 x 10(-8) (10 MHz, 0.08 pm) over a wide wavelength range including optical communication bands was achieved without the need for a vacuum chamber.