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Slippage of a Porphyrin Macrocycle over Threads of Varying Bulkiness: Implications for the Mechanism of Threading Polymers through a Macrocyclic Ring
Author(s) -
Deutman Alexander B. C.,
Varghese Shaji,
Moalin Mohamed,
Elemans Johannes A. A. W.,
Rowan Alan E.,
Nolte Roeland J. M.
Publication year - 2015
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201403740
Subject(s) - slippage , threading (protein sequence) , porphyrin , ring (chemistry) , mechanism (biology) , chemistry , polymer chemistry , materials science , photochemistry , composite material , organic chemistry , physics , biochemistry , quantum mechanics , protein structure
Threading of a polymer through a macrocyclic ring may occur directly, that is, by finding the end of the polymer chain, or by a process in which the polymer chain first folds and then threads through the macrocyclic ring in a hairpin‐like conformation. We present kinetic and thermodynamic studies on the threading of a macrocyclic porphyrin receptor ( H 2 1 ) onto molecular threads that are blocked on one side and are open on the other side. The open side is modified by groups that vary in ease of folding and in bulkiness. Additionally, the threads contain a viologen binding site for the macrocyclic receptor, which is located close to the blocking group. The rates of threading of H 2 1 were measured under various conditions, by recording as a function of time the quenching of the fluorescence of the porphyrin, which occurs when receptor H 2 1 reaches the viologen binding site. The kinetic data suggest that threading is impossible if the receptor encounters an open side that is sterically encumbered in a similar way as a folded polymer chain. This indicates that threading of polymers through macrocyclic compounds through a folded chain mechanism is unlikely.