RESEARCH

6. Tetrapyrrolic Macrocycles and Phenols for Sensing Applications

The combination of calix[4]pyrrole macrocycle with electronically conjugated meso-substituents leads to a highly chromogenic molecule which not only responds to a variety of guests by undergoing a colour change but also can be synthetically modified to include other functionalities including porphyrins or fullerenes. These compounds can be used to detect anions, solvents (including water), acidity or basicity, and even enantiomeric excesses of many chiral compounds.

Sensing of Enantiomeric Excess

Recently we have discovered a novel method of determining enantiomeric excesses (ee) of chiral compounds using a saddle-shaped oxidized porphyrin macrocycle (which we refer to as OxP). A simple proton nuclear magnatice resonance protocol has been developed enabling ee of a great variety of chiral compounds including pharmaceuticals, natural products and synthetic intermediates.

Split resonances in the proton NMR spectrum of OxP can be used to determine enantiomeric excesses of chiral compounds. The mechanism involves concepts of protic tautomerism and morphological transformations of the tetrapyrrole macrocycle.
Split resonances in the proton NMR spectrum of OxP can be used to determine enantiomeric excesses of chiral compounds. The mechanism involves concepts of protic tautomerism and morphological transformations of the tetrapyrrole macrocycle.
Due to having similar molecular morphologies to OxP, tetraphenylporphyrin dication can also be used to detect enantiomeric excesses albeit in a more limited number of chiral analyte compounds.

Also recently, we have found that enantiomeric excess can be evaluated using NMR spectroscopy without the formation of diastereomeric species in solution. An extensive mechanistic investigation was also made.

DFT and molecular dynamics calculations were carried out to confirm the mechanism of enantiomeric excess detection in achiral OxP tetrapyrrole macrocycles.
DFT and molecular dynamics calculations were carried out to confirm the mechanism of enantiomeric excess detection in achiral OxP tetrapyrrole macrocycles.

Other Aspects of Sensing using Tetrapyrroles

The same saddle-shaped OxP as above can also be used to detect anions, solvents, water and can even be used to estimate acidity in non-polar solvents.

The chemical structure of OxP, its colour variation and the colour coordinates according to the 1934 Commission Internaionale de I’Eclairege (CIE) coordinate diagram.
The chemical structure of OxP, its colour variation and the colour coordinates according to the 1934 Commission Internaionale de I’Eclairege (CIE) coordinate diagram.

Sensing of Deleterious Metal Cations

In the wake of the Fukushima disaster it has become imperative that simple methods for detecting deleterious materials following nuclear reactor breaches are developed. In this context, we have developed a fluorogenic sensing system for detection of caesium cations contained in particulates, which are contaminants of ground soils. Caesium is not a common element in the Earth’s crust but its prevalence may increase in the locality of reactor breaches. Mapping of radiocaesium contaminated land will assist local clean-up operations.

Green fluorescence selective for the presence of caesium makes permits facile detection of Cs particulates at the micrometer level using simple reagents and a fluorescence lamp.
Green fluorescence selective for the presence of caesium makes permits facile detection of Cs particulates at the micrometer level using simple reagents and a fluorescence lamp.
Related publications