Shunsuke Kazama

Spectral simulation study of the positional exchange of a spin probe in an aerosol OT reversed micelle

Abstract The ESR spectra of a spin probe, 2,2,6,6-tetramethyl-4-piperidone N -oxide, in degassed Aerosol OT reversed micelle in heptane solution were examined using computer simulation on the sample in which the molar ratio of water to surfactant was 31. For such largely water-containing micelles, each line of the hyperfine structure split into a doublet at low temperatures as a result of the spin probe locating in the water pool and in the shell formed by the surfactant molecules. From the simulation of the high-field line, the exchange rates between these positions and the fractions in each were obtained as a function of temperature. A two phase model of the water pool was proposed in order to fit the calculated to the observed spectra.

ESR Imaging on a Solid-tumor-bearing Mouse Using Spin-labeled Dextran

Imaging of a tumor with ESR was tried using two different types of spin probes, a low molecular weight spin probe, CPROXYL, and a polymer spin probe, TEMPO-DX. Spin probes were administered to a mouse bearing a solid tumor that was a transplanted Ehrlich’s ascites carcinoma in the back, using two methods, conventional intraperitoneal injection and continuous intravenous injection with a micro-feeder. First, the accumulation of the probe was examined by X-band ESR. CPROXYL, which was administered to a mouse intraperitoneally, was exclusively retained in urine, showing that it was rapidly excreted into the bladder, while TEMPO-DX was absorbed from the peritoneal cavity with difficulty to the vessel. Using continuous intravenous injection, CPROXYL was also rapidly excreted, but it was confirmed that TEMPO-DX concentrated in tumor tissue because it has a long half-life in vivo. In addition, measurement of ESR imaging was done to measure the distribution of spin probes with continuous intravenous injection. The strongest spot of CPROXYL was observed on ESR images, showing the accumulation at the bladder, while the spot of TEMPO-DX was observed in the solid tumor of the back of the mouse. These results suggest that TEMPO-DX could stay much longer than a low molecular weight spin probe in vivo and concentrate at the tumor. TEMPO-DX may be useful for developing specific ESR imaging agents for tumor.

Sulfated N-Myristoyl Chitosan as a Surface Modifier of Liposomes

Sulfated N-myristoyl chitosan (S-M-chitosan), which is strongly electrolytic and water soluble as well as partly hydrophobic due to long alkyl chains, was synthesized to be used as a liposome-surface modifier. The effects of the treatment with an aqueous S-M-chitosan solution on the stability of the liposome suspension prepared from hydrogenated egg yolk lecithin were examined on several points. A suspension of large liposomes prepared by the Bangham method was precipitated by standing for a day, but the precipitation was restrained when the sample was treated with S-M-chitosan solution. The turbidity of a small liposome suspension was changed greatly after the suspension was freeze-thawed, but the change was small in the treated sample. A similar result was obtained when the suspension was freeze-dried following the addition of water. These results come from the facts that the surface of the liposome was coated with S-M-chitosan and negatively charged as ascertained by the measurement of zeta potential and the electron microscopic observation. The repulsive force between charges was considered to be the origin of the stabilization. It was also shown from an ESR experiment that the treatment suppressed the elution rate of the material incorporated into the liposomes.