Dönüs Tuncel

Rotaxanes can exhibit stimuli-responsive behavior by allowing positional fluctuations of their rota groups in response to physiochemical conditions such as the changes in solution pH. However, ionic strength of the solution also affects the molecular conformation by altering the charge state of the entire molecule, coupling the stimuli-responsiveness of rotaxanes with their conformation. A molecular-scale investigation on a model system can allow the decoupling and identification of various effects and can greatly benefit applications of such molecular switches. By using atomistic molecular dynamics simulations, we study equilibrium and kinetics properties of various charge states of the [5]rotaxane, which is a supramolecular moiety with four rotaxanes bonded to a porphyrin core. We model various physiochemical charge states, each of which can be realized at various solution pH levels as well as several exotic charge distributions. By analyzing molecular configurations, hydrogen bonding, and energetics of single molecules in salt-free water and its polyrotaxanated network at the interface of water and chloroform, we demonstrate that charge-neutral and negatively charged molecules often tend to collapse in a way that they can expose their porphyrin core. Contrarily, positively charged moieties tend to take more extended molecular configurations blocking the core. Further, sudden changes in the charge states emulating the pH alterations in solution conditions lead to rapid, sub-10 ns level, changes in the molecular conformation of [5]rotaxane via shuttling motion of CB6 rings along axles. Finally, simulations of 2D [5]rotaxane network structures support our previous findings on a few nanometer-thick film formation at oil-water interfaces. Overall, our results suggest that rotaxane-based structures can exhibit a rich spectrum of molecular configurations and kinetics depending on the ionic strength of the solution.

In this study, sulfur‐enriched microporous organic polymer (MOP) was prepared using one‐pot Shiff‐base type polycondensation reaction of thiophendicarboxaldehyde with melamine. With 195.731 m² g⁻¹ surface area and 0.047 cm³ g⁻¹ pore volume, the as‐synthesized MOP has a cotton‐like morphology and a micropore‐dominated pore size distribution. After loading MOP with nickel as a co‐catalyst, we demonstrated that the obtained framework could be used as an efficient and robust electrocatalyst for hydrogen evolution reaction (HER) in an alkaline medium with the optimum composite (Ni₂@MOP) exhibiting a low onset potential of −66 mV. Furthermore, the optimum electrocatalyst showed good stability, delivering 91% faradaic efficiency (FE) after a 3.5 h chronoamperometry experiment.

We report here the synthesis and characterization of a water dispersible conjugated polymer nanoparticle‐based photosensitizer and its application in the antibacterial and anticancer phototherapies. Nanoparticles (CPPN) were synthesized in one‐pot by nanoprecipitation method, in which a hydrophobic azide functionalized, red‐emitting thiophene‐benzothiodiazole based conjugated polymer (CP‐AZ) was cross‐linked with a hydrophilic, propargylamine functionalized porphyrin (TPP‐4AL) through cucurbit[6]uril (CB6) catalyzed azide‐alkyne cycloaddition (CB6‐AAC) reaction. CPPN demonstrated high stability in aqueous medium for more than a month without any visible aggregation and appeared to be a good photosensitizer with high light‐triggered reactive oxygen species (ROS) generation ability. Consequently, CPPN displayed photo‐induced biocidal activity against Gram‐negative (Escherichia coli, E. coli) and Gram‐positive (Bacillus subtilis, B. subtilis and Staphylococcus aureus, S. aureus) bacteria. When bacteria suspension was incubated with CPPN (20 μg ml⁻¹) and irradiated with white light (22 mW cm⁻²) for 10 min, more than 3.5‐log reduction in colony‐forming units (CFUs) was recorded for the three model bacteria. CPPN demonstrated minimal dark cytotoxicity against the bacteria. Moreover, the cytotoxicity of CPPN on mammalian cell was studied using MCF‐7 breast cancer cell line. The results demonstrated that CPPN is non‐toxic to mammalian cells in the dark even at a high concentration of 112.5 μg ml⁻¹ and this feature makes CPPN an ideal photosensitizer.

Under the simultaneous use of pressure-driven flow and DC electric field, migration of particles inside microfluidic channels exhibits intricate focusing dynamics. Available experimental and analytical studies fall short in giving a thorough explanation to particle equilibrium states. Also, the understanding is so far limited to the results based on Newtonian and neutral viscoelastic carrier fluids. Hence, a holistic approach is taken in this study to elaborate the interplay of governing electrophoretic and slip-induced/elastic/shear gradient lift forces. First, we carried out experimental studies on particle migration in Newtonian, neutral viscoelastic, and polyelectrolyte viscoelastic media to provide a comprehensive understanding of particle migration. The experiments with the viscoelastic media led to contradictory results with the existing explanations. Then, we introduced the Electro-Viscoelastic Migration (EVM) theory to give a unifying explanation to particle migration in Newtonian and viscoelastic solutions. Confocal imaging with fluorescent-labeled polymer solutions was used to explore the underlying migration behavior. A surprising outcome of our results is the formation of cross-sectionally non-uniform viscoelasticity that may have unique applications in microfluidic particle focusing.