Interaction of Heme Proteins with Anionic Polyfluorene: Insights into Physiological Effects, Folding Events, and Inhibition Activity

Because of the toxicity caused by the heme redox-active iron proteins, their elevated levels, localization, and accumulation in the brain, many forms of neurodegenerative diseases, such as Alzheimer’s disease, Parkinson’s disease, and Huntington’s disease, occur as a result of which the brain becomes vulnerable to oxidative stress, ultimately resulting in neuronal death. An anionic water-soluble conjugated polyfluorene derivative poly­(9,9-bis­(6-sulfate hexyl) fluorene-<i>alt</i>-1,4-phenylene) sodium salt (P1) that binds Fe³⁺ proteins with very high selectivity and sensitivity is reported here. The photophysical properties of P1 were modified by the interaction with ferric heme-containing proteins cytochrome <i>c</i> (C<i>c</i>), methemoglobin (MetHb), and hemin. P1 was found to be highly sensitive toward Fe³⁺ heme proteins as compared to nonmetalloproteins. We observed that the respective activities of ferric heme proteins were inhibited and proteins were unfolded, due to modification in their heme microenvironment in the presence of the polymer P1. The observations reported in this article provide the first example for the use of a water-soluble conjugated polymer in applications, such as (1) to detect small quantities of iron proteins in aqueous medium/physiological condition with the highest <i>K</i>_sv values of 2.27 × 10⁸ M^–1 for C<i>c</i>, 3.81 × 10⁷ M^–1 for MetHb, and 5.31 × 10⁷ M^–1 for hemin; (2) to study the physiological effects of heme metalloproteins; (3) to visualize the folding events in real time; and (4) the inhibition activity of metalloproteins can be selectively studied using a conjugated polymer based assay system rapidly without interference from nonmetalloproteins at biological pH. All this is achieved by generating optical events, taking advantage of the bright fluorescence of anionic polyfluorene P1 in this case, that can be observed and monitored by modification in the absorption and emission color in real time

Exploration of Energy Modulations in Novel RhB-TPE-Based Bichromophoric Materials via Interactions of Cu²⁺ Ion under Various Semiaqueous and Micellar Conditions

Novel bichromophoric materials <b>TR-A</b> and <b>TR-B</b> consisting of an entirely new combination of TPE and RhB units were developed to explore the optimum conditions of energy modulations via pH variation and Cu²⁺ interaction at various water contents of CH₃CN. Interestingly, <b>TR-A</b> and <b>TR-B</b>, at 60 and 70% water contents, respectively, favored the optimum Cu²⁺-mediated energy modulations from TPE to RhB and thus achieve the brightest orange emissions of free RhB with complete disappearance of aggregation-induced emission (AIE) from TPE. Furthermore, various micellar conditions of triton-X-100, SDS, and CTAB were employed to adjust energy modulations of <b>TR-A</b> and <b>TR-B</b> at high water contents (at 80 and 90%, respectively). The incorporation of RhB into triton-X-100 micellar cavities disrupted AIE from TPE; thus, none of the energy modulations from TPE to RhB occurred even in the presence of Cu²⁺ ion. Interestingly, the micellar conditions of anionic surfactant (SDS) favored the increased local concentration of Cu²⁺ ions in the vicinity of scavangable RhB and facilitated the generation of noncyclic free RhB in situ via bright-orange emissions

Novel Water-Soluble Cyclodextrin-Based Conjugated Polymer for Selective Host–Guest Interactions of Cationic Surfactant CTAB and Reverse FRET with Rhodamine B Tagged Adamantyl Guest

A new water-soluble π-conjugated main-chain polymer <b>P1</b> bearing a β-cyclodextrin (β-CD) pendant was designed and synthesized. The aggregation and disaggregation of <b>P1</b> generated faded yellow-greenish and bright-yellow emissions, respectively. The inclusion complexation capability of <b>P1</b> through β-CD pendant with a cationic surfactant cetyl­trimethyl­ammonium bromide (CTAB) guest and associative interactions of <b>P1</b> with Fe³⁺ through triazole spacers resulted in significantly enhanced and completely diminished emission profiles of <b>P1</b> in pure water, respectively. Interestingly, ADRhB as another rhodamine B (RhB) tagged adamantyl guest was transformed into ADRhB­(O), i.e., the open form of ADRhB, to generate RhB emission in the presence of Fe³⁺ ion selectively for the pendent host β-CD of <b>P1</b>, and the further interaction of ADRhB­(O)/Fe³⁺ with <b>P1</b> prevailed a completely quenched RhB emission via the inclusion complexation of adamantyl terminal of ADRhB­(O) in β-CD. Moreover, stronger interactions of CTAB with β-CD further generated RhB emission of ADRhB­(O) even in the presence of acceptor <b>P1</b>. Finally, a novel β-CD bearing water-soluble <b>P1</b> with selective and strong interactions of CTAB toward disaggregation events in pure water, and further electrostatic repulsion and utilization of RhB via RhB-tagged adamantyl guest ADRhB­(O) as a donor revealed the reverse-fluorescence resonance energy transfer (FRET) process of <b>P1</b>