Abstract
The absolute configuration of chiral 2-aryl and 2-aryloxy propionic acids, which are among the most common chiral environmental pollutants, has been readily and reliably established by either electronic circular dichroism spectroscopy or optical rotation measurements employing suitably designed 4,4′-disubstituted biphenyl probes. In fact, the 4,4′-biphenyl substitution gives rise to a red shift of the diagnostic electronic circular dichroism signal of the biphenyl A band employed for the configuration assignment, removing its overlap with other interfering dichroic bands and allowing its clear sign identification. The largest A band red shift, and thus the most reliable results, are obtained by employing as a probe the 4,4′-dinitro substituted biphenylazepine 3c. The method was applied to the absolute configuration assignment of 2-arylpropionic acids ibuprofen (1a), naproxen (1b), ketoprofen (1c) and flurbiprofen (1d), as well as to the 2-aryloxypropionic acids 2-phenoxypropionic acid (2a) and 2-naphthoxypropionic acid (2b). This approach, allowing us to reveal the sample’s absolute configuration by simple optical rotation measurements, is potentially applicable to online analyses of both the enantiomeric composition and absolute configuration of these chiral pollutants.
Highlights
We envisaged that a possible solution could be obtained by employing, as chiroptical probes, suitably designed biphenyl azepines 4,40 -disubstituted with groups extending the electron conjugation which, as we have recently shown, give rise to a red shift of the A band absorption, avoiding the above spectral overlap problems [20]
We have shown that the use of suitably designed 4,4′-disubstituted biphenyl probes allows the detection and sensing, by either electronic circular dichroism (ECD) spectroscopy or optical rotation (OR)
We have shown that the use of suitably designed 4,40 -disubstituted biphenyl probes allows the detection and sensing, by either ECD spectroscopy or OR
Summary
This approach still presents some limitations and/or difficulties when dealing with highly flexible molecules, giving rise to low chiroptical responses In these cases, the so-called “chiroptical probes” offer a practical and reliable alternative which. Chemosensors 2021, 9, 154 of natural [15] and synthetic [16] compounds In these cases, the so-called “chiroptical probes” offer a practical and reliable alternative which is available to non-specialists in spectroscopy and computations, the advantagein that the configurational assignmentwith can be by is availablewith to non-specialists spectroscopy and computations, theobtained advantage a simple visual inspection of the spectrum. Large aryl chromophores on the chiral acid, absorbing in the 220–300 nm range and overlapping to the diagnostic 250 nm biphenyl A band, it is necessary to employ specifi of 13 cally designed 4,4′-substituted biphenyl probes
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