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Assessing the Mechanical Properties of a Molecular Spring

Authors

  • Emanuela Berni Dr.,

    1. Université Bordeaux 1 - ENITAB - CNRS UMR5248, Institut Européen, de Chimie et Biologie, 2 rue Robert Escarpit, 33607 Pessac, France, Fax: (+33) 540-002-215
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  • Brice Kauffmann Dr.,

    1. Université Bordeaux 1 - ENITAB - CNRS UMR5248, Institut Européen, de Chimie et Biologie, 2 rue Robert Escarpit, 33607 Pessac, France, Fax: (+33) 540-002-215
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  • Chunyan Bao Dr.,

    1. Université Bordeaux 1 - ENITAB - CNRS UMR5248, Institut Européen, de Chimie et Biologie, 2 rue Robert Escarpit, 33607 Pessac, France, Fax: (+33) 540-002-215
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  • Julien Lefeuvre,

    1. Université Bordeaux 1 - ENITAB - CNRS UMR5248, Institut Européen, de Chimie et Biologie, 2 rue Robert Escarpit, 33607 Pessac, France, Fax: (+33) 540-002-215
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  • Dario M. Bassani Dr.,

    1. Université Bordeaux 1 - CNRS UMR5255, Institut des Sciences Moléculaires, 351 cours de la Libération, 33405 Talence, France
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  • Ivan Huc Dr.

    1. Université Bordeaux 1 - ENITAB - CNRS UMR5248, Institut Européen, de Chimie et Biologie, 2 rue Robert Escarpit, 33607 Pessac, France, Fax: (+33) 540-002-215
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Abstract

We report on the dramatic effect of increasing helix diameter on the hybridization of oligopyridine-dicarboxamide strands into double helices. Upon replacing a single pyridine by a 1,8-diazaanthracene unit within an oligomeric strand, a 4.7 Å enlargement of the helix diameter occurs parallel to the long anthracene axis. This structure change results in a spectacular stabilization of the double helical hybrids derived from these strands (factors of over 107). Detailed investigations of the hybridization process using X-ray crystallography, NMR, fluorescence measurements and molecular mechanics calculations allowed us to assign the duplex stabilization to two enthalpic effects. First, the increase in diameter results in an augmented surface, involved in intermolecular π–π stacking. Second, the enlarged diameter leads to a lower tilt angle of the helical strand, with respect to the helix axis, which in turn results in smaller dihedral angles at the aryl–amide linkages and thus a considerably lowered enthalpic cost of the spring-like extension of the strands during the hybridization process. These results provide novel insights into how subtle tuning of molecular components may result in considerable and rationalizable changes in double helical supramolecular architectures.

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