Take your Positions and Shine: Effects of Positioning Aggregation-Induced Emission Luminophores within Sequence-Defined Macromolecules

Abstract

A luminophore with aggregation-induced emission (AIE) is employed for the conjugation onto supramolecular ligands to allow for detection of ligand binding. Supramolecular ligands are based on the combination of sequence-defined oligo(amidoamine) scaffolds and guanidiniocarbonyl-pyrrole (GCP) as binding motif. We hypothesize that AIE properties are strongly affected by positioning of the luminophore within the ligand scaffold. Therefore, we systematically investigate the effects placing the AIE luminophore at different positions within the overall construct, for example, in the main or side chain of the olig(amidoamine). Indeed, we can show that the position within the ligand structure strongly affects AIE, both for the ligand itself as well as when applying the ligand for the detection of different biological and synthetic polyanions.

Keywords: aggregation induced emission; biosensors; sequence-defined oligomers; solid phase polymer; supramolecular synthesis.

Scheme 1

Synthesis of AIE‐ and GCP‐functionalized oligomers 1–5 using solid phase polymer synthesis. Reaction conditions: 1) 5 equiv. building block, 5 equiv. PyBOP, 10 equiv. DIPEA in DMF, 90 min/2) 25 v % piperidine in DMF, 20 min, 3) 10 equiv. CATE, 10 equiv. PyBOP, 20 equiv. DIPEA in DMF, 48 h, 4) 5 equiv. Isopropylamine, 5 equiv. PyBOP, 10 equiv. DIPEA in DMF, 90 min/ Ac2O, 20 min (acetylation of N‐terminus), 5) 4 M HCl in dioxane, 20 min (on‐resin cleavage of Boc), 6) 5 equiv. (Boc)GCP‐COOH, 5 equiv. PyBOP, 10 equiv. DIPEA in DMF, 90 min (double coupling), 7) TentaGel® S RAM: 5 % triisopropylsilane, 95 % TFA, 90 min.

Figure 1

A) Starting fluorescence spectra of O1‐5 (9.74 μM; 9.71 μM; 9.75 μM; 9.77 μM; 9.77 μM) in 10 mM HEPES buffer at pH=7.4, (Triplicates, λ_ex=380 nm). B) Starting fluorescence maxima at 450 nm of O1‐5 in 10 mM HEPES buffer at pH=7.4 and 6.5 (Triplicates, λ_ex=380 nm).

Figure 2

Change in fluorescence emission of O1‐5 (9.74 μM; 9,71 μM; 9.75 μM; 9.77 μM; 9.77 μM) in the presence of different anionic molecules, aggregates and materials measured in 10 mM HEPES buffer at pH=7.4, (Triplicates, λ_ex=380 nm, λ_em=450 nm, E=Final Emission, E₀=Start; BSA, Con A, Heparin, PAA, PBS, Trypsin and 14‐3‐3 ζ 10 μM; Esterase and Micro gel (NIPAM‐co‐MAA Copolymer) 2 and 5 %, RNA 100 μg/ml and SDS 10 mM) and O4 (6.5) (10 mM HEPES buffer at pH=6.5) PAA, Micro gel (NIPAM‐co‐MAA Copolymer) 2 and 5 %. Samples that showed turbidity are marked with *.

Figure 3

A) Fluorescence spectra of O4 (9.77 μM) pure (black) and in the presence of MG 2 % 100 μg/ml, MG 5 % 100 μg/ml and PAA 10 μM (triplicates, λ_ex=380 n, λ_em=450 nm). Samples that showed turbidity are marked with *. Comparison of fluorescence emission of B) O4 and C) O5 (both 9.77 μM) with and without anionic binders. Reflection effects on the glass surface were removed using GIMP 2.10 software.

Figure 4

Change in fluorescence emission of O4 (9.77 μM) in the presence of PAA A) 1–10 μM and B) 0.01–1 μM; both assays in 10 mM HEPES buffer at pH=7.4, (triplicates, λ_ex=380 nm, λ_em=450 nm, E=Final Emission, E₀=Start). In concentration series B, turbidity was observed for all samples.

Figure 5

Atomic force microscope images of O1‐5 (100 μM in Millipore water). Further AFM, SEM images and their analysis see the Supporting Information.