Yusuke Miyake

Hydrodynamic Interpretation on the Rotational Diffusion of Peroxylamine Disulfonate Solute Dissolved in Room Temperature Ionic Liquids As Studied by Electron Paramagnetic Resonance Spectroscopy

Rotational motion of a nitroxide radical, peroxylamine disulfonate (PADS), dissolved in room temperature ionic liquids (RTILs) was studied by analyzing electron paramagnetic resonance spectra of PADS in various RTILs. We determined physical properties of PADS such as the hyperfine coupling constant (A), the temperature dependence of anisotropic rotational correlation times (τ(∥) and τ(⊥)), and rotational anisotropy (N). We observed that the A values remain unchanged for various RTILs, which indicates negligible interaction between the N-O PADS group and the cation of RTIL. Large N values suggest strong interaction of the negative sulfonyl parts of PADS with the cations of RTILs. Most of the τ(∥), τ(⊥), and (τ(∥)τ(⊥))(1/2) values are within the range calculated on the basis of a hydrodynamic theory with stick and slip boundary conditions. It was deduced that this theory could not adequately explain the measured results in some RTILs with smaller BF(4) and PF(6) anions.

Use of silylmethoxy groups as inducers of efficient room temperature phosphorescence from precious-metal-free organic luminophores

We designed and characterized 1,4-diaroyl-2,5-bis(silylmethoxy)benzenes as precious-metal-free organic luminophores that efficiently phosphoresce at room temperature. The benzene derivatives in crystals emit green phosphorescence with quantum yields up to 0.45 under ambient conditions. The luminescence quantum yield increases with increasing number of intermolecular interactions in the crystal, such as hydrogen bonding and CH–π interactions. The luminescence lifetimes are inversely proportional to temperature over the −80 to 80 °C range, demonstrating the potential of the benzene derivatives as materials for temperature sensing. Poly(methyl methacrylate) films doped with these luminophores also exhibit intense green phosphorescence at room temperature under vacuum, while they emit very faint blue fluorescence under ambient conditions. Electron spin resonance spectroscopy of a UV-excited diphenylmethylsilyl-derivative in toluene at 77 K reveals a triplet diradical species, whose electronic distribution is similar to that of naphthalene, indicating that the triplet diradical is distributed over almost ten atoms.

In vivo tumour extracellular pH monitoring using electron paramagnetic resonance: the effect of X-ray irradiation

The in vivo quantification of extracellular pH (pHe) in tumours may provide a useful biomarker for tumour cell metabolism. In this study, we assessed the viability of continuous‐wave electron paramagnetic resonance (CW‐EPR) spectroscopy with a pH‐sensitive nitroxide for the measurement of extracellular tumour pH in a mouse model. CW‐EPR spectroscopy (750 MHz) of C3H HeJ mice hind leg squamous cell tumour was performed after intravenous tail vein injection of pH‐sensitive nitroxide (R‐SG, 2‐(4‐((2‐(4‐amino‐4‐carboxybutanamido)‐3‐(carboxymethylamino)‐3‐oxoproylthio)methyl)phenyl)‐4‐pyrrolidino‐2,5,5‐triethyl‐2,5‐dihydro‐1Н‐imidazol‐1‐oxyl) during stages of normal tumour growth and in response to a single 10‐Gy dose of X‐ray irradiation. An inverse relationship was observed between tumour volume and pHe value, whereby, during normal tumour growth, a constant reduction in pHe was observed. This relationship was disrupted by X‐ray irradiation and, from 2–3 days post‐exposure, a transitory increase in pHe was observed. In this study, we demonstrated the viability of CW‐EPR spectroscopy using R‐SG nitroxide to obtain high‐sensitivity pH measurements in a mouse tumour model with an accuracy of <0.1 pH units. In addition, the measured changes in pHe in response to X‐ray irradiation suggest that this may offer a useful method for the assessment of the physiological change in response to existing and novel cancer therapies. Copyright

Simultaneous Imaging of an Enantiomer Pair by Electron Paramagnetic Resonance Using Isotopic Nitrogen Labeling

This Article describes the simultaneous imaging of chiral nitroxyl radicals using electron paramagnetic resonance (EPR). Chiral nitroxyl radicals could be simultaneously visualized with the labeling of isotopic nitrogen. Chiral nitroxyl radicals, hydroxylmethyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl, were visualized using the method of simultaneous EPR imaging, which refers to the visualization of two kinds of molecules with unpaired electrons in a single image scan. EPR spectra of a racemic mixture of chiral nitroxyl radicals and those of the respective R and S configurations confirmed labeling by isotopic nitrogen. (1)H nuclear magnetic resonance (NMR) imaging and simultaneous imaging of solutions of chiral nitroxyl radicals were performed. The advantages and limitations of simultaneous imaging using EPR are also discussed. Simultaneous imaging with chiral-labeled nitroxyl radicals is a new application of EPR imaging and may be useful for biological studies involving biologically active chiral molecules.

Novel blood-brain barrier-permeable spin probe for in vivo electron paramagnetic resonance imaging.

A novel blood-brain barrier (BBB)-permeable compound 10 was discovered, wherein the nitroxide moiety was linked to a nicotine acetylcholine receptor ligand. It was applied as a probe for electron paramagnetic resonance (EPR) imaging of the mouse brain. The results demonstrated that the newly synthesized compound 10 exhibited BBB permeability. These findings provide an essential discovery for in vivo EPR imaging.

Artifact suppression in electron paramagnetic resonance imaging of (14)N- and (15)N-labeled nitroxyl radicals with asymmetric absorption spectra.

This article describes an improved method for suppressing image artifacts in the visualization of (14)N- and (15)N-labeled nitroxyl radicals in a single image scan using electron paramagnetic resonance (EPR). The purpose of this work was to solve the problem of asymmetric EPR absorption spectra in spectral processing. A hybrid function of Gaussian and Lorentzian lineshapes was used to perform spectral line-fitting to successfully separate the two kinds of nitroxyl radicals. This approach can process the asymmetric EPR absorption spectra of the nitroxyl radicals being measured, and can suppress image artifacts due to spectral asymmetry. With this improved visualization method and a 750-MHz continuous-wave EPR imager, a temporal change in the distributions of a two-phase paraffin oil and water/glycerin solution system was visualized using lipophilic and hydrophilic nitroxyl radicals, i.e., 2-(14-carboxytetradecyl)-2-ethyl-4,4-dimethyl-3-oxazolidinyloxy (16-DOXYL stearic acid) and 4-hydroxyl-2,2,6,6-tetramethylpiperidine-d17-1-(15)N-1-oxyl (TEMPOL-d17-(15)N). The results of the two-phase separation experiment verified that reasonable artifact suppression could be achieved by the present method that deals with asymmetric absorption spectra in the EPR imaging of (14)N- and (15)N-labeled nitroxyl radicals.