Chiroptical detection of self‐aggregating fluorescent rhodamine conjugates: Mistakes and prospects

• Published in: Journal of peptide science 2022-12, Vol.28 (12), p.e3442-n/a
• Main Author: Zsila, Ferenc
• Format: Article
• Language: English
• Subjects: aggregation; Circular dichroism; Conjugates; Conjugation; Dichroism; Dyes; exciton coupling; Excitons; Fluorescence; fluorophore labelling; Peptides; Rhodamine; rhodamine B; Spectroscopy; Thyroid; thyroid hormones
• ISSN: 1075-2617; 1099-1387
• DOI: 10.1002/psc.3442

Fluorescent conjugation can be considered as the chromophoric derivatization of the target, and as such, it may provide additional structure‐related information available by using circular dichroism (CD) spectroscopy. In this essay, peculiar CD spectroscopic data reported earlier for thyroid hormone–rhodamine conjugates have been re‐evaluated. Contrary to the original proposal on the intramolecular folding of the labelled hormone, the bisignate motif observed in the CD spectrum is a clear evidence of dye–dye intermolecular chiral exciton coupling, indicating supramolecular self‐association of the conjugates. This anomalous solution behaviour undermines the credibility of experimental results reported with such conjugates still being used in the laboratory practice. The extension of routine far‐ultraviolet (UV) CD spectroscopic scans of chiral fluorophore conjugates into the near‐UV and visible spectral region is strongly recommended. Peculiar CD spectroscopic data reported earlier for thyroid hormone–rhodamine conjugates are re‐evaluated. In contrast to the original interpretation, the bisignate motif observed in the CD spectrum proves dye–dye intermolecular chiral exciton coupling, indicating supramolecular self‐association of the conjugates, which weakens the credibility of experimental results reported with such conjugates still being used in the laboratory practice.