Ligand binding by butadiyne-linked porphyrin dimers, trimers and tetramers

Abstract

The binding of oligopyridyl ligands to butadiyne-linked zinc porphyrin dimers, trimers and tetramers has been investigated in detail using NMR and electronic spectroscopy. Pyridine binds to zinc porphyrin monomers in CH2C12 solution at 300 K with binding constants of ca. lo3 mo1-' dm3, while 4,4'-bipyridyl binds to the cyclic zinc porphyrin dimer with a binding constant of 1 x lo9 mol-' dm3, giving an effective molarity, or chelation factor, of 76 mol dmP3. The analogous linear dimer binds to this ligand 100 times less strongly, but adopts a similar conformation when bound. s-Tri(4-pyridy1)triazine has an affinity of ca. 10" mol-' dm3 for the cyclic zinc trimer, reflecting reasonably good host-guest complementarity. The affinity of 4,4'bipyridyl for the trimer is ca. lo5 mol-' dm3, implying two-point binding accompanied by host distortion and strain which reduce the binding constant; the trimer is therefore an elastic host, able to respond to the geometrical demands of rigid guests. The cyclic tetramer is a relatively flexible molecule, but its complexes with both bidentate and tetradentate ligands have more highly defined geometries. The cyclic dimer and t rimer have open pre-organised cavities, with no conformational barrier to ligand binding inside the cavity, whereas the cyclic tetramer can adopt many conformations in free solution.

Excellent Correlation between Drug Release and Portal Size in Metalla‐Cage Drug‐Delivery Systems

“…2,4,6-Tris(pyridine-4-yl)-1,3,5-triazine (tpt) [34] and [Ru 2 (p-iPrC 6 H 4 Me) 2 -A C H T U N G T R E N N U N G (OO\OO)Cl 2 ] (OO\OO = donq, [19] doaq [35] and dotq [24f] ) were prepared according to published methods. 1-(4,6-Dichloro-1,3,5-triazin-2-yl)pyrene, PdA C H T U N G T R E N N U N G (acac) 2 and all other reagents were commercially available (Sigma-Aldrich) and used as received.…”

Química de sistemas supramoleculares constituídos por porfirinas e complexos metálicos

“…Entretanto, para se utilizar essa estratégia é necessária a introdução de grupos coordenantes adequadamente distribuídos e orientados na estrutura da porfirina. Por exemplo, Fleischer e colaboradores 45 mostraram que os meso-(fenilpiridil)porfirinato zinco(II) podem se associar formando dímeros, trímeros ou mesmo Reconhecimento molecular por meio de ligações de hidrogênio na meso-tetra(4-hidroxifenil)porfirina e meso-tetra(4-carboxifenil)porfirina 85,86 , respectivamente, formando fitas e grades quadradas Por sua vez, Sanders e colaboradores 47 prepararam supermoléculas cíclicas e alicíclicas ligando 5,15-fenilporfirinas através de pontes acetileno-Pt-acetileno, butadiinos ou cadeias superiores, utilizando 4,4-bipiridina, tris-4-piridiltriazina e meso-tetra(4-piridil)porfirinas, H 2 (4-TPyP), como templatos. Numa série de artigos publicados em 1995, as vantagens desse método para a preparação de porfirinas supermoleculares mais complexas foram extensamente exploradas.…”

Adventures in molecular recognition. The ins and outs of templating

“…Using alkyne linkers between the porphyrins and oligopyridine templates to organize the building blocks, a variety of linear and cyclic oligomers have been prepared [4,5], and their binding properties studied [6].…”