Water-Soluble Poly(γ-propargyl-l-glutamate) Containing Pendant Sulfonate Ions and Terminal Fluorophore: Aggregation-Enhanced Emission and Secondary Structure

Abstract

Tetraphenylthiophene (TP) with aggregation-enhanced emission (AEE) property was used as terminal fluorophore of the water-soluble poly(γ-propargyl-l-glutamate) (PPLG)-based polymers of TP-iPPLGs to probe the relationship between the secondary structure (α-helix) of polypeptides and the AEE-related emission behavior. Intermolecular aggregation of the terminal TP unit in TP-iPPLG is sterically blocked by the large α-helical PPLG chains, leading to the weak AEE-related fluorescence in water. In contrast, the intermolecular approach between the terminal TP units of TP-iPPLG is accessible if TP was connected by peptide chin in random coil structure. Therefore, the helix-to-coil transition induced in the alkaline aqueous solution successfully enhances the emission intensity of the TP-iPPLG solution. The pH-induced conformation change in relationship to the AEE-related emission behavior is therefore evaluated in this study.

An Amphiphilic Pyridinoyl-hydrazone Probe for Colorimetric and Fluorescence pH Sensing

“…The fluorescence quantum yield (Φ) of PHABr was measured in solution at pH = 10.0 by relative methods using quinine sulfate QS as standard (0.546 in H 2 SO 4 1.00 N, excited at 365 nm) according to [24,50,51]. The value Φ = 2.40% is comparable to that reported for similar amphiphilic pH sensing systems [43,52] and also for intracellular pH sensing molecules [53]. The weak solution emission efficiency is typical of AIE (aggregation-induced emission) active molecules [24,54,55], and is due to the free molecular rotation, which activates a nonradiative decay.…”

“…The charged amino group has been incorporated in the side chain of the fluorophore to achieve excellent water solubility. At the same time, solubility in the organic phase is sufficiently preserved [42,43].…”

A Highly Water-Soluble Fluorescent and Colorimetric pH Probe

“…The fluorescence quantum yield was measured in water for the deprotonated form D at pH = 11.0 by relative methods using quinine sulfate (QS) as standard (0.546 in H2SO4 1 N, excited at 365 nm) according to [32][33][34]. The value of 6.20% is comparable to that reported for water-soluble pH probes [35,36]. In more concentrated solutions, the emission increases become perceptible to the naked eye (see Section 2.3).…”

Controlling Molecular Aggregation-Induced Emission by Controlled Polymerization

“…Consequently, the specific polymer conformation has significant impact on the final photophysical properties, including both emission intensity and wavelength ( Figure 4 A), as also indicated in follow-up studies [ 73 ]. This feature can be used to detect variations in the aggregate structure, for example, as a probe for the detection of bovine serum albumin (BSA) [ 74 ].…”