Quantum mechanics

Catalysis

Boronic acid

Vicinal

Phenylboronic acid

Turn (biochemistry)

Biochemistry

Diol

Stereochemistry

Combinatorial chemistry

Physics

Organic chemistry

Amine gas treating

Fluorescence

Chemistry

Nature Chemistry

ortho-Aminomethylphenylboronic acids are used in receptors for carbohydrates and various other compounds containing vicinal diols. The presence of the o-aminomethyl group enhances the affinity towards diols at neutral pH, and the manner in which this group plays this role has been a topic of debate. Further, the aminomethyl group is believed to be involved in the turn-on of the emission properties of appended fluorophores upon diol binding. In this treatise, a uniform picture emerges for the role of this group: it primarily acts as an electron-withdrawing group that lowers the pKa of the neighbouring boronic acid thereby facilitating diol binding at neutral pH. The amine appears to play no role in the modulation of the fluorescence of appended fluorophores in the protic-solvent-inserted form of the boronic acid/boronate ester. Instead, fluorescence turn-on can be consistently tied to vibrational-coupled excited-state relaxation (a loose-bolt effect). Overall, this Review unifies and discusses the existing data as of 2019 whilst also highlighting why o-aminomethyl groups are so widely used, and the role they play in carbohydrate sensing using phenylboronic acids. ortho-Aminomethylphenylboronic acids are routinely used in sensors for carbohydrates, but the function of the o-aminomethyl group in enhancing binding affinity and modulating the emission of appended fluorophores has been the matter of some debate. This Review presents a unified picture of the structural features, mechanisms of sugar complexation and photophysics of these kinds of sensors.

The mechanisms of boronate ester formation and fluorescent turn-on in ortho-aminomethylphenylboronic acids