Humidity‐Responsive ON/OFF Switching of Gas Inclusion by Using Cooperative Opening/Closing of Heterogeneous Crystalline Cavities in a Peptide Ni II Macrocycle

• Published in: Chemistry : a European journal 2018-01, Vol.24 (4), p.793-797
• Main Authors: Miyake, Ryosuke, Kuwata, Chika, Ueno, Manami, Yamada, Teppei
• Format: Article
• Language: English
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201704809

Humidity‐responsive ON/OFF switching of CO 2 inclusion, associated with cooperative structural changes of heterogeneous cavities in crystalline peptide Ni II macrocycles, 1 ⋅NO 3 , is demonstrated. The structural transformation between an “open form” and a “closed form” was caused by reversible water uptake into one of the cavities. The adsorption behavior of CO 2 was studied with and without water vapor, combined with gas‐composition analysis by using gas chromatography. The studies revealed that the open form of 1 ⋅NO 3 adsorbs CO 2 gas up to 34 g mol −1 , whereas the closed form adsorbs only a negligible amount of CO 2 gas. Also, structural studies (X‐ray and IR spectroscopies) and investigation of water‐content dependence of CO 2 adsorption revealed that the switching of gas inclusion occurred abruptly over a narrow range of water‐vapor pressure and was caused by the cooperative opening of vacant space to give the open form due to the structural transformation by water uptake.