Complexes of syn-(Me,Me)bimane with biorelevant metals: Crystal structures and metal-ion-induced fluorescence quenching

syn-Bimanes are used as fluorescent labeling agents for various biomolecules, such as proteins and amino acids, capitalizing on their strong fluorescence, low molecular weight, and low toxicity. We have recently shown that one of these heterobicyclic compounds, syn-(Me, Me)bimane, chelates Pd(II) through its two carbonyl oxygens.^[1] This was the first reported case of metal-bimane coordination, to the best of our knowledge. We have since expanded our investigation beyond Pd(II), to include the coordination chemistry of syn-(Me,Me)bimane with different alkali and alkaline earth metal cations, which are ubiquitous in biological systems. Our study revealed that this bimane coordinates mono- and divalent metal ions by several binding modes, all of which involve the carbonyl oxygen atoms of the bimane. Na⁺, Ca²⁺ and Mg²⁺, when coordinated with bimane, afford fluorescent and non-fluorescent complexes, some of which are polymeric. This coordination was found to be highly reversible in solution, yet exert a significant effect on bimane fluorescence. Na⁺ ions induce the quenching of bimane fluorescence, both in organic solvents and in water.^[2] This finding is highly relevant to the general use of bimane dyes in biological media, which normally contain metal cations like Na⁺nd indicates that fluorescence data generated with these fluorophores should be interpreted with caution. The syntheses of metal-bimane complexes, as well as their spectroscopic and crystallographic characterization, will be presented.

1. P. J. Das, Y. Diskin-Posner, M. Firer, M. Montag, F. Grynszpan, Dalton Trans. 2016, 45, 17123-17131.
2. A. Roy, P. J. Das, Y. Diskin-Posner, M. Firer, F. Grynszpan, M. Montag, New. J. Chem. 2018, 42, 15541-15545.