Reports of optical activity for assemblies of achiral entities in the absence of templates were greeted at first with skepticism. However, now that these findings have been confirmed, considerable attention has been focused on this phenomenon. The possibility that what is being observed in these systems is a spontaneous mirror-symmetry breaking has led to speculation about the relationship of these processes to those responsible for the ubiquitous homochirality in our universe. Achiral chromophores, especially porphyrins, have been of some considerable importance for such symmetry-breaking studies due to their rich spectral properties and their ability (under appropriate conditions) to self-assemble into chiral supramolecular structures. In particular, meso-tetrakis4-sulfonatophenyl (TPPS) and aryl-substituted porphyrins have been widely used as starting materials. TPPS J-aggregates, obtained in aqueous solution in the absence of any added chiral templating agent, show an unpredictable chirality, resulting in controversial proposals for their basis. Recently, we demonstrated the fundamental role of kinetic parameters in the expression and transmission of chirality in this supramolecular system. Whatever the source of the chiral bias promoting such symmetry breaking, the rate of the aggregation process leading to the formation of J-aggregates strongly affects the size of these nanoassemblies and the chiral induction. With the aim to resolve some of the confounding issues still open in literature related to the TPPS J-aggregate optical activity, here we report on detailed kinetic investigation on selfassembly processes induced by different inorganic achiral acid in the absence of an added chiral template and in presence of various chiral acids opportunely selected to have variability in terms of structure and strength. The results obtained have allowed to gain important information in the field of supramolecular architectures, highlighting the importance of the role of experimental parameters such as concentration and/or mixing order of the reagents. We anticipate that, depending on the overall rate of the process, a distinctive kinetic difference, together with a difference variance in the extent of the chiral transfer, is evident for the various acids and strictly connected with medium properties.

CHIRALITY IN PORPHYRIN AGGREGATES

ROMEO, Andrea;MONSU' SCOLARO, Luigi;Zagami, Roberto;
2015-01-01

Abstract

Reports of optical activity for assemblies of achiral entities in the absence of templates were greeted at first with skepticism. However, now that these findings have been confirmed, considerable attention has been focused on this phenomenon. The possibility that what is being observed in these systems is a spontaneous mirror-symmetry breaking has led to speculation about the relationship of these processes to those responsible for the ubiquitous homochirality in our universe. Achiral chromophores, especially porphyrins, have been of some considerable importance for such symmetry-breaking studies due to their rich spectral properties and their ability (under appropriate conditions) to self-assemble into chiral supramolecular structures. In particular, meso-tetrakis4-sulfonatophenyl (TPPS) and aryl-substituted porphyrins have been widely used as starting materials. TPPS J-aggregates, obtained in aqueous solution in the absence of any added chiral templating agent, show an unpredictable chirality, resulting in controversial proposals for their basis. Recently, we demonstrated the fundamental role of kinetic parameters in the expression and transmission of chirality in this supramolecular system. Whatever the source of the chiral bias promoting such symmetry breaking, the rate of the aggregation process leading to the formation of J-aggregates strongly affects the size of these nanoassemblies and the chiral induction. With the aim to resolve some of the confounding issues still open in literature related to the TPPS J-aggregate optical activity, here we report on detailed kinetic investigation on selfassembly processes induced by different inorganic achiral acid in the absence of an added chiral template and in presence of various chiral acids opportunely selected to have variability in terms of structure and strength. The results obtained have allowed to gain important information in the field of supramolecular architectures, highlighting the importance of the role of experimental parameters such as concentration and/or mixing order of the reagents. We anticipate that, depending on the overall rate of the process, a distinctive kinetic difference, together with a difference variance in the extent of the chiral transfer, is evident for the various acids and strictly connected with medium properties.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11570/3110608
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