Terahertz dichroism of MBBA liquid crystal on rubbed substrate

Terahertz (THz) dichroism of a nematic liquid N-(p-methoxybenzylidene)-p-butylaniline (MBBA) was measured using a GaP Raman THz spectrometer. MBBA on a rubbed plastic substrate generates a band at around 4.0 THz: its liquid crystal phase shows strong dichroism, which well corresponds to that of the IR absorption caused by π(CH) of MBBA molecule reported in the literature. Based on inferences drawn from the present THz and the published IR dichroic results, the 4.0 THz band probably stems from lateral intermolecular or intramolecular interactions of MBBA molecules aligned to the rubbing direction. The results clearly demonstrate that THz spectroscopy is powerful for discussing of phase transition and dichroism of liquid crystals.     

Strong and selective binding of amiloride to an abasic site in RNA duplexes: thermodynamic characterization and microRNA detection

Firmly tied: The binding affinity of amiloride for an abasic (AP) site-containing RNA duplex is two orders of magnitude superior to the affinity of the corresponding AP site-containing DNA duplex. The observed high binding affinity for the RNA duplex arises from a favorable enthalpy gain. The binding-induced fluorescence response of amiloride is applicable to microRNA detection.     

Bioactive Properties of Chitin/Chitosan—Calcium Phosphate Composite Materials

Calcium phosphate coating over phosphorylated derivatives of chitin/chitosan material was produced by a process based on phosphorylation, Ca(OH)₂ treatment and SBF (simulated body fluid solution) immersion. Chitin/chitosan phosphorylated using urea and H₃PO₄ and then soaked in saturated Ca(OH)₂ solution at ambient temperature, which lead to the formation of thin coatings formed by partial hydrolysis of the PO₄ functionalities, were found to stimulate the growth of a calcium phosphate coating on their surfaces after soaking in 1.5 × SBF solution for as little as one day. The Ca(OH)₂ treatment facilitates the formation of a calcium phosphate precursor over the phosphorylated chitin/chitosan, which in turn encourages the growth of a calcium deficient apatite coating over the surface upon immersion in SBF solution. The bio-compatibility of calcium phosphate compound—chitin/chitosan composite materials was evaluated by cell culture test using L-929 cells. The initial anchoring ratio and the adhesive strength of L-929 cells for composites was higher than that for the polystyrene disk (LUX, control). The results of in-vitro evaluation suggested that the calcium phosphate—chitin/chitosan composite materials were suitable for cell carrier materials.     

In situ SERS spectroscopy of Ag-modified pyrolytic graphite in organic electrolytes

Surface enhanced Raman scattering (SERS) has been applied to study the lithium intercalation/deintercalation process at the interface of a pyrolytic graphite electrode with propylene and ethylene carbonate containing organic solutions. We have focused on the lattice vibration of the most outer graphite surface layer simultaneously with cyclic voltammetric measurements. In situ Raman spectroscopy performed in this way allowed us to determine the La value that describes the size of graphitic microcrystallites along the a-axis. It was found that the La value decreases when the electrode is polarized to potentials between 0.02 and 1.0 V. This phenomenon can be correlated with the intercalation of lithium ions into the graphene structure. According to the spectral change, the size of the graphitic microcrystallites shows reversible behavior with potential cycling at the surface of the electrode. Electronic Publication     

Development of terahertz electromagnetic wave generation based on nanometer films with atomic accuracy

The terahertz region is between the optical wave and the so-called microwaves; it had not been studied until 1963, when Nishizawa started the development of a THz wave generation based on the character of lattice or molecular vibrations. In 1979, Raman laser oscillation was realized using GaP, and in 1983, the oscillation of lattice vibration (12 THz) was achieved by mixing with the original wave. Recently, many kinds of oscillators have been developed: LiNbO₃ and others for parametric oscillations, TUNNETT diode, so-called Ballistic SIT, etc. These frequencies can induce lattice or molecular vibrations, observable through reflection or transmission. Therefore, terahertz technology is useful for detection of toxins, including bacteria and viruses. It can be applied for investigation of structural changes in molecules, including those caused by disease or medical treatment. At the same time, it can heat up selectively a specified structure of a polymer and, hence, may be used for thermal treatment, or to enhance the reaction with a specific structure, suppressing side effects.     

Quantitative measurement of 125I with NaI(Tl) scintillation survey meter

This paper describes a NaI(Tl) scintillation survey meter which can quantify 125I on a contaminated surface in situ. This survey meter has four inherent windows; 20-45 keV the singles photopeak region, 45-80 keV the sum photopeak region, 20-80 keV the total photopeak region, and 80 keV-. The activity was calculated based on the sum peak method. The calculated activity of a point source agreed with the standardized source activity within an uncertainty of about 10% both up to the distance of 3 cm from the detector surface along the axis of the detector and on the detector surface. The activity of a simulated plate source also agreed with the source activity within the same uncertainty.     

FREQUENCY-TUNABLE TERAHERTZ-WAVE GENERATION FROM GaP USING Cr:FORSTERITE LASERS

We have constructed THz spectrometers using the widely frequency-tunable THz-wave generated from GaP crystal pumped at 1.2 μm region using two Cr:forsterite lasers and compared with that pumped at 1 μm region using a YAG laser and an optical parametric oscillator (OPO). The systems have sufficient resolution for observation of solids and liquids at room temperature. We have measured terahertz absorption spectra of all twenty kinds of amino acids which form proteins.     

Achievement of ring inversion of myo-inositol derivatives due to silyloxy/silyloxy repulsion enhanced by the trans-substituents on both sides

The introduction of quite bulky trialkyl or diarylalkylsilyl groups into vicinal trans-hydroxy groups induced a conformational flip of certain multifunctionalized cyclohexane rings from the usual chair form possessing more equatorial substituents (equatorial-rich chair form) into another chair-form that has more axial substituents (axial-rich chair form). This realization was experimentally revealed by the conformational study of the synthetic myo-inositol derivatives possessing two tert-butyldimethylsilyl (TBS), two triisopropylsilyl (TIPS), or two tert-butyldiphenylsilyl (TBDPS) groups on an adjacent trans-diol. Among them, the cyclohexane rings of the 4,5-bis-O-TIPS-myo-inositol, 4,5-bis-O-TBDPS-myo-inositol, and 1,2,3,6-tetra-O-benzyl-4,5-bis-O-TBDPS-myo-inositol were in the axial-rich chair form. Comparison of the ring conformations also revealed that the order of the repulsion was OTBDPS/OTBDPS>OTIPS/OTIPS>OTBS/OTBS, and the silyloxy/silyloxy repulsion was enhanced when the two silyloxy groups were placed in the center of the contiguous four equatorial substituents.     

Isolation and structural determination of spilacleosides A and B having a novel 1,3-dioxolan-4-one ring

As the first natural product incorporating 1,3-dioxolan-4-one in spiro structure, spilacleosides A and B were isolated from Ruscus aculeatus, and the absolute structures determined.