Design and synthesis of a 4-aminoquinoline-based molecular tweezer that recognizes protoporphyrin IX and iron(iii) protoporphyrin IX and its application as a supramolecular photosensitizer

A 4-aminoquinoline-based molecular tweezer was developed as a synthetic receptor for protoporphyrin IX and iron(iii) protoporphyrin IX, and applied as a supramolecular photosensitizer.

Compound 11: A mixture of 10 (0.200 g, 0.459 mmol) and hydrazine monohydrate (0.206 g, 4.12 mmol) in ethanol (30 mL) was refluxed for 18 h under an Ar atmosphere and then the cooled to room temperature.
After removing the solvent, CHCl3 (30 mL) was added. The organic layer was washed with 5M NaOH solution (20 mL). The aqueous layer was extracted with CHCl3 (30 mL x 2). The combined organic layers were dried over Na2SO4 and then evaporated under reduced pressure to give 11 as a yellow gum    excitation at 402 nm; band width (ex. 5 nm, em. 5 nm); response 0.1 sec; sensitivity: medium; wavelength scan speed: 500 nm/min. On the basis of the resulting data, the binding constants were calculated using S10 a global curve fitting method using the Bindfit program. [S2] Binding constants were reported as the mean±standard deviation of three independent experiments.

Calculation study:
Minimization of the PPIX·1 complex was carried out by molecular mechanics calculation by Discovery studio 2017R2 (Biovia). The force filed used in the minimization was CHARMM force field with solvation mode (Algorithm: Adopted Basis Newton-Raphson (NR), max steps: 50000, RMS gradient: 0.01, solvation model: explicit periodic boundary, cell shape: truncated octahedron, add counter ion: sodium chloride).
After incubating the sample solution, UV-Vis and fluorescence emission spectra were measured.

Fluorescence imaging of HCT-116 cells:
DMEM used in this study contains 1% penicillin/streptomycin (Gibco) and 0.1% kanamycin (Sigma). The cells on the glass bottom petri dish were washed with fresh FBS free DMEM (high glucose, HEPES, no phenol red) (Gibco, 21063-029). After 300 L of sample solutions of PPIX alone, PPIX+1, and blank were added to each compartment of the glass bottom petri dish, the cells were incubated for 1 h at 37 °C S12 under a 5% CO2 atmosphere. After incubation, the medium was removed and the cells were washed twice with cold PBS (phosphate buffered saline) (Wako, 166-23555). Finally, 0.30 mL of cold PBS was added, and the cells were then observed on fluorescence microscopy (BZ-X710; Keyence, Osaka, Japan) using TRITC filter (Ex. 545±13 nm, Em. 605±35 nm).

Fluorescence emission spectra of cell suspension of HCT-116 cells:
The           Tetramethylsilane in CCl4 was used as external reference. Structure of 1 is described as tetra-protonated form.
Peak assignments of aliphatic protons of 1 were conducted according to the reference. [S4] Small up-field shifts (