@article{oai:repo.qst.go.jp:00048303,
 author = {Morishita, Kosuke and Murayama, Shuhei and Araki, Takeru and Aoki, Ichio and Karasawa, Satoru and 村山 周平 and 青木 伊知男},
 issue = {18},
 journal = {J. Org. Chem.},
 month = {Aug},
 note = {For development of the metal-free MRI contrast agents, we prepared the supra-molecular organic radical, TEMPO-UBD, carrying TEMPO radical, as well as the urea, alkyl group, and phenyl ring, which demonstrate self-assembly behaviors using noncovalent bonds in an aqueous solution. In addition, TEMPO-UBD has the tertiary amine and the oligoethyleneglycol chains (OEGs) for the function of pH and thermal responsiveness. By DLS and TEM imaging, the resulting self-assembly was seen to form the spherical nano-particles 10 – 150 nm in size. On heating, interestingly, the nano-particles showed a lower critical solution temperature (LCST) behavior having two-step variation. This double-LCST behavior is the first such example among the supra-molecules. To evaluate of the ability as MRI contrast agents, the values of proton (1H) longitudinal relaxivity (r1) were determined using MRI apparatus. In conditions below and above CAC at pH 7.0, the distinguishable r1 values were estimated to be 0.17 and 0.21 mM(-1)s(1), indicating the suppression of fast tumbling motion of TEMPO moiety in a nano-particle. Furthermore, r1 values became larger in the order of pH 7.0 > 9.0 > 5.0. Those thermal and pH dependencies indicated the possibility of metal-fee MRI functional contrast agents in the future.},
 pages = {8351--8362},
 title = {Thermal- and pH-Dependent Size Variable Radical Nanoparticles and Its Water Proton Relaxivity for Metal-free MRI Functional Contrast Agents},
 volume = {81},
 year = {2016}
}