Abstract
Flexible linkers such as uridine or 2′-deoxyuridine pre-organize bis-porphyrins in a face-to-face conformation, thus forming stable sandwich complexes with a bidentate base such as 1,4-diazabicyclo[2.2.2]octane (DABCO). Increased stability can be even greater when a dinucleotide linker is used. Such pre-organization increases the association constant by one to two orders of magnitude when compared to the association constant of DABCO with a reference porphyrin. Comparison with rigid tweezers shows a better efficiency of nucleosidic dimers. Thus, the choice of rigid spacers is not the only way to pre-organize bis-porphyrins, and well-chosen nucleosidic linkers offer an interesting option for the synthesis of such devices.
Highlights
Chemistry “beyond the molecule” is expressed in nature by a number of relatively weak noncovalent interactions [1,2]
As a module in the construction of supramolecular assemblies, porphyrins and metalloporphyrins can be exploited in two different ways: porphyrins can behave as donor building blocks insofar as they comprise meso-substituents, such as pyridyl groups, which can act as ligands that can suitably coordinate to metal cations, while metalloporphyrins can act as acceptor building blocks as soon as the metal atom inside the porphyrin core has at least one axial site available for coordination
We reported a few years ago the binding studies of three bis-porphyrinic tweezers bearing nucleosidic linkers (Figure 1) [41]
Summary
Chemistry “beyond the molecule” is expressed in nature by a number of relatively weak noncovalent interactions [1,2]. The coordination bond formed by metalloporphyrins has been explored in understanding how metal–ligand interactions are directing the formation of supramolecular porphyrin arrays. In this respect, a vast array of supramolecular systems has been prepared, such as cyclic oligomers [7,15,27,28], linear oligomers [29,30,31] and polymers [32,33,34], Molecules 2017, 22, 1112; doi:10.3390/molecules22071112 www.mdpi.com/journal/molecules squares [8,38].
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