Excited-State Proton Transfer and Geminate Recombination in Hydrogels Based on Self-Assembled Peptide Nanotubes

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• 作者：Sun-Young Park ; Hyeok Jeong ; Hahkjoon Kim ; Jin Yong Lee ; Du-Jeon Jang
• 刊名：Journal of Physical Chemistry C
• 出版年：2011
• 出版时间：December 22, 2011
• 年：2011
• 卷：115
• 期：50
• 页码：24763-24770
• 全文大小：918K
• 年卷期：v.115,no.50(December 22, 2011)
• ISSN：1932-7455

文摘

The excited-state proton transfer (ESPT) of 7-hydroxyquinoline (7HQ) embedded in hydrogels based on self-assembled peptide nanotubes (PNTs) has been investigated with variation of peptides as well as protic hydrogen isotopes. In the inner cavities of PNT-based hydrogels, 7HQ prefers to exist as an anionic species rather than a normal species or a cationic species already in the ground state because the hydrogels are mildly basic. Upon excitation, ESPT takes place from a water molecule in a PNT hydrogel nanocavity to the imino group of the anionic species to produce a zwitterionic species, and its back reaction, that is, geminate recombination between the proton of the iminium group of the zwitterionic species and the deprotonated water molecule, also occurs because of the extremely viscous environment as well as the spatial constraint of semirigid PNT hydrogels. As a result, an excited-state prototropic equilibrium between the anionic and the zwitterionic species is established in PNT hydrogels. Water nanopools confined in smaller PNTs are denser than those in larger PNTs, so that 7HQ molecules in the smaller PNTs have more chances to form strong hydrogen bonds with water molecules. Consequently, both ESPT and geminate-recombination in the smaller PNTs are faster than the respective ones in the larger PNTs.