Effects of Substituents on the Properties of Metal-Free MRI Contrast Agents

Ryoma Shiraishi, Tomoyo Kaneko, Kazuteru Usui, Tatsuya Naganuma, Naoko Iizuka, Kosuke Morishita, Shigeki Kobayashi, Yasufumi Fuchi, Yuta Matsuoka, Go Hirai, Ken Ichi Yamada, Satoru Karasawa

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)


Materials possessing electron spin can shorten the T1 relaxation times in magnetic resonance imaging (MRI). For example, gadolinium (Gd) complexes with seven f-orbital electrons are widely used as contrast agents in clinical applications. However, Gd has severe potential side effects, and thus metal-free alternatives are needed. Toward this end, we synthesized seven NO radicals consisting of a dioxa-azaspiro[4.5]decane framework having various substituents, DAD-X (X = methyl, ethyl, n-propyl, c-propyl, vinyl, phenyl, and 2-pyridyl), that functioned as metal-free MRI contrast agents. The relationship between (i) water-proton relaxivity and log※P and (ii) reactivity for ascorbic acid and the spin density of the NO oxygen atom were established, which provided a basis for the rational design of practical metal-free contrast agents.

Original languageEnglish
Pages (from-to)20715-20723
Number of pages9
JournalACS Omega
Issue number24
Publication statusPublished - Dec 10 2019

All Science Journal Classification (ASJC) codes

  • General Chemistry
  • General Chemical Engineering


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