Influence of receptor flexibility on intramolecular H-bonding interactions

New Polyporphyrin Arrays with Controlled Fluorescence Obtained by Diaxial Sn(IV)-Porphyrin Phenolates Chelation with Cu2+ Cation

New coordination oligomers and polymers of Sn(IV)-tetra(4-sulfonatophenyl)porphyrin have been constructed by the chelation reaction of its diaxialphenolates with Cu2+. The structure and properties of the synthesized polyporphyrin arrays were investigated by 1H Nuclear Magnetic Resonance (1H NMR), Infra Red (IR), Ultra Violet - Visible (UV-Vis) and fluorescence spectroscopy, mass spectrometry, Powder X-Rays Diffraction (PXRD), Electron Paramagnetic Resonance (EPR), thermal gravimetric, elemental analysis, and quantum chemical calculations. The results show that the diaxial coordination of bidentate organic ligands (L-tyrazine and diaminohydroquinone) leads to the quenching of the tetrapyrrole chromophore fluorescence, while the chelation of the porphyrinate diaxial complexes with Cu2+ is accompanied by an increase in the fluorescence in the organo-inorganic hybrid polymers formed. The obtained results are of particular interest to those involved in creating new 'chemo-responsive' (i.e., selectively interacting with other chemical species as receptors, sensors, or photocatalysts) materials, the optoelectronic properties of which can be controlled by varying the number and connection type of monomeric fragments in the polyporphyrin arrays.

New Polyporphyrin Arrays with Controlled Fluorescence Obtained by Diaxial Sn(IV)-Porphyrin Phenolates Chelation with Cu2+ Cation

New coordination oligomers and polymers of Sn(IV)-tetra(4-sulfonatophenyl)porphyrin have been constructed by the chelation reaction of its diaxialphenolates with Cu2+. The structure and properties of the synthesized polyporphyrin arrays were investigated by 1H Nuclear Magnetic Resonance (1H NMR), Infra Red (IR), Ultra Violet - Visible (UV-Vis) and fluorescence spectroscopy, mass spectrometry, Powder X-Rays Diffraction (PXRD), Electron Paramagnetic Resonance (EPR), thermal gravimetric, elemental analysis, and quantum chemical calculations. The results show that the diaxial coordination of bidentate organic ligands (L-tyrazine and diaminohydroquinone) leads to the quenching of the tetrapyrrole chromophore fluorescence, while the chelation of the porphyrinate diaxial complexes with Cu2+ is accompanied by an increase in the fluorescence in the organo-inorganic hybrid polymers formed. The obtained results are of particular interest to those involved in creating new ‘chemo-responsive’ (i.e., selectively interacting with other chemical species as receptors, sensors, or photocatalysts) materials, the optoelectronic properties of which can be controlled by varying the number and connection type of monomeric fragments in the polyporphyrin arrays.

Elucidating Atropisomerism in Nonplanar Porphyrins with Tunable Supramolecular Complexes

Atropisomerism is a fundamental feature of substituted biaryls resulting from rotation around the biaryl axis. Different stereoisomers are formed due to restricted rotation about the single bond, a situation often found in substituted porphyrins. Previously NMR determination of porphyrin atropisomers proved difficult, if not almost impossible to accomplish, due to low resolution or unresolvable resonance signals that predominantly overlapped. Here, we shed some light on this fundamental issue found in porphyrinoid stereochemistry. Using benzenesulfonic acid (BSA) for host‐guest interactions and performing 1D, 2D NMR spectroscopic analyses, we were able to characterize all four rotamers of the nonplanar 5,10,15,20‐tetrakis(2‐aminophenyl)‐2,3,7,8,12,13,17,18‐octaethylporphyirin as restricted H‐bonding complexes. Additionally, X‐ray structural analysis was used to investigate aspects of the weak host–guest interactions. A detailed assignment of the chemical signals suggests charge‐assisted complexation as a key to unravel the atropisomeric enigma. From a method development perspective, symmetry operations unique to porphyrin atropisomers offer an essential handle to accurately identify the rotamers using NMR techniques only.

Understanding coordination equilibria in solution and gel-phase [2]rotaxanes

An active-metal template approach has been use to synthesise solution and surface bound addressable [2]rotaxanes giving unique insights into thermodynamic equilibria in interlocked structures.

Enhanced Chelate Cooperativity in Polar Solvents

High-throughput UV-vis titrations in combination with chemical double-mutant cycles (DMCs) have been used to study the competition of a polar solvent for formation of intramolecular H-bonds. Twenty-four different zinc porphyrin-pyridine complexes were investigated in mixtures of toluene and phenol. DMCs were used to determine effective molarities (EM) for the formation of intramolecular phenol-amide H-bonds as a function of solvent composition. The values of EM increase by an order of magnitude with increasing concentrations of the more polar solvent, phenol. Phenol solvates the amide groups on the ligands strongly, increasing the steric bulk and destabilizing the complexes. These adverse steric interactions are removed when intramolecular H-bonds are formed and therefore provide an increased driving force for formation of cooperative interactions. The result is that the effects of competitive interactions with polar solvents that reduce binding affinity are attenuated to a significant extent by a corresponding increase in EM in multivalent complexes.

Assessing cooperativity in supramolecular systems

In this tutorial review, different aspects of cooperativity in supramolecular chemistry and their thermodynamic analysis are discussed.