Figure 4: Ultraviolet-Vis absorption with ECD and fluorescence spectra of X-FLFL-TPP.
(a) Fmoc-FLFL-TPP dissolved in dichloromethane (magenta traces with silent ECD spectrum in the Soret region) and after injection into n-heptane (blue traces). (b) Experimental (blue traces) versus calculated spectra (green traces) for self-assembled Fmoc-FLFL-TPP in n-heptane. An arbitrary scaling was performed at the maximum of the largest negative Cotton effect. (c) Boc-FLFL-TPP on changing the solvent composition as indicated in the inset. Half of the solution volume was removed from the cuvette and the corresponding amount of n-heptane was added. The Soret band of the green trace after addition of the first aliquot of 20 μl dichloromethane is slightly truncated due to saturation of the detector. The cartoons symbolize different self-assemblies of TPP (discs) via triple hydrogen bonding of the FF-dipeptide moieties (blue forms) protected by Fmoc or Boc groups (green spheres). (d) Fmoc-FLFL-ZnTPP after injection in n-heptane (green trace). In the chiral dimer, we presumed that due to the Fmoc protecting group there is no coordination to the Zn atom (grey disk). The magenta trace was obtained from Fmoc-FLFL-ZnTPP (1.85 mg dissolved in 400 μl dry dichloromethane) admixed (4/1, v/v) with Fmoc-FLFL-TPP (2.57 mg dissolved in 500 μl dry dichloromethane). A volume of 1.5 μl of this mixture was injected into n-heptane. Dilution with aliquots of dry dichloromethane gradually leads to a silent ECD (blue trace, after a twofold dilution). (e) Absorption of Fmoc-FLFL-ZnTPP after injection in n-heptane (green trace, lower panel) and after addition of dichloromethane (upper panel). The corresponding fluorescence spectra were obtained after excitation at 417 nm (blue traces) or at 440 nm (red trace). (f) Absorption of Fmoc-FLFL-TPP after injection in n-heptane (magenta trace, lower panel) and after addition of dichloromethane (upper panel). The corresponding fluorescence spectra were obtained after excitation at 417 nm (blue traces) or at 440 nm (red trace). The red fluorescence traces were vertically scaled by multiplying with factors of 7 and 85, which reflect the amount of quenching in the nonpolar solvent.
