Protein-Mediated Efficient Synergistic “Antenna Effect” in a Ternary System in D₂O Medium

Abstract

A ternary system consisting of a protein, catechin (either + or – epimer), and Tb­(III) in suitable aqueous buffer medium at physiological pH (= 6.8) has been shown to exhibit highly efficient “antenna effect”. Steady state and time-resolved emission studies of each component in the binary complexes (protein with Tb­(III) and (+)- or (−)-catechin with Tb­(III)) and the ternary systems along with the molecular docking studies reveal that the efficient sensitization could be ascribed to the effective shielding of microenvironment of Tb­(III) from O–H oscillator and increased Tb–C (+/−) interaction in the ternary systems in aqueous medium. The ternary system exhibits protein-mediated efficient antenna effect in D₂O medium due to synergistic ET from both the lowest ππ* triplet state of Trp residue in protein and that of catechin apart from protection of the Tb­(III) environment from matrix vibration. The simple system consisting of (+)- or (−)-catechin and Tb­(III) in D₂O buffer at pH 6.8 has been prescribed to be a useful biosensor