Pressure and temperature dependence of enantioselective excited-state quenching of chiral Tb(III) and Eu(III) tris(pyridine-2,6-dicarboxylate) chelates by various C-type ferricytochromes.

The research study investigates the impact of temperature and pressure on the quenching of luminescence in certain compounds when influenced by proteins derived from various animal and bacterial sources. Major attention is given to variations in activation volumes and energies, and how these are affected by the origin of the chelates and proteins

Overview of the Research

• This study examines the relationship between temperature, pressure, and the quenching of luminescence (emitted light) in chelates – compounds that occur when a central metallic ion is bonded to a molecule. Specific chelates studied include Tb(DPA)3(3-) and Eu(DPA)3(3-).
• The chelates are influenced by proteins derived from horse, cow, tuna, and bacterial mitochondria. Also, the luminescence quenching characteristics of these proteins differ depending on their source.

Investigation Methods and Findings

• The researchers measured the activation volumes and energies (delta V# and Ea) between the pressure range of 0-3 kbar and the temperature range of 15-40 degrees C.
• Findings reveal that for the lambda enantiomers of the chelates, delta V# and Ea remained nearly constant across all proteins: 0.4 < or = delta V# < or = 1.1 cm3/mol and 0 < or = Ea < or = 2 kJ/mol.
• However, for the delta enantiomer – whose luminescence is quenched faster – the activation parameters varied significantly depending on the protein’s origin and chelate type.

Differences in Quenching Characteristics

• Values for delta V# for the delta enantiomer ranged from +4.9 +/- 0.5 (Eu/horse) to +0.5 +/- 0.5 cm3/mol (Tb/tuna), while Ea varied from +8 +/- 1 (Tb/cow) to -1 +/- 1 kj/mol (Tb/tuna).
• The extent of enantioselectivity in quenching was nearly identical in proteins from horse, cow, chicken, and pigeon, but notably higher than in tuna.
• The researchers attributed the unique quenching characteristics of the tuna protein to variations in the exposed heme edge’s amino acid content, specifically Ile9–>Thr, Thr28–>Val and/or Phe46–>Tyr.
• Other variations in this region, such as Thr47–>Ser and Ala15–>Ser, did not impact the degree of enantioselectivity in quenching (Eq).