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Stimuli-Responsive Langmuir Films Composed of Nanoparticles Decorated with Poly(N-isopropyl acrylamide) (PNIPAM) at the Air/Water Interface

(American Chemical Society, 2023-05-31) Zbonikowski, Rafał; Iwan, Michalina; Paczesny, Jan; Instytut Chemii Fizycznej Polskiej Akademii Nauk

The nanotechnology shift from static toward stimuli-responsive systems is gaining momentum. We study adaptive and responsive Langmuir films at the air/water interface to facilitate the creation of two-dimensional (2D) complex systems. We verify the possibility of controlling the assembly of relatively large entities, i.e., nanoparticles with diameter around 90 nm, by inducing conformational changes within an about 5 nm poly(N-isopropylacrylamide)(PNIPAM) capping layer. The system performs reversible switching between uniform and nonuniform states. The densely packed and uniform state is observed at a higher temperature, i.e., opposite to most phase transitions, where more ordered phases appear at lower temperatures. The induced nanoparticles’ conformational changes result in different properties of the interfacial monolayer, including various types of aggregation. The analysis of surface pressure at different temperatures and upon temperature changes, surface potential measurements, surface rheology experiments, Brewster angle microscopy (BAM), and scanning electron microscopy (SEM) observations are accompanied by calculations to discuss the principles of the nanoparticles’ self-assembly. Those findings provide guidelines for designing other adaptive 2D systems, such as programable membranes or optical interfacial devices.

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Droplet microfluidics for high-throughput analysis of antibiotic susceptibility in bacterial cells and populations

(American Chemical Society, 2022-02-04) Postek, Witold; Garstecki, Piotr; Instytut Chemii Fizycznej Polskiej Akademii Nauk

Antibiotic-resistant bacteria are an increasing concern both in everyday life and specialized environments such as healthcare. As the rate of antibiotic-resistant infections rises, so do complications to health and the risk of disability and death. Urgent action is required regarding the discovery of new antibiotics and rapid diagnosis of the resistance profile of an infectious pathogen as well as a better understanding of population and single-cell distribution of the resistance level. High-throughput screening is the major affordance of droplet microfluidics. Droplet screens can be exploited both to look for combinations of drugs that could stop an infection of multidrug-resistant bacteria and to search for the source of resistance via directed-evolution experiments or the analysis of various responses to a drug by genetically identical bacteria. In droplet techniques that have been used in this way for over a decade, aqueous droplets containing antibiotics and bacteria are manipulated both within and outside of the microfluidic devices. The diagnostics problem was approached by producing a series of microfluidic systems with integrated dilution modules for automated preparation of antibiotic concentration gradients, achieving the speed that allowed for high-throughput combinatorial assays. We developed a method for automated emulsification of a series of samples that facilitated measuring the resistance levels of thousands of individual cells encapsulated in droplets and quantifying the inoculum effect, the dependence of resistance level on bacterial cell count. Screening of single cells encapsulated in droplets with varying antibiotic contents has revealed a distribution of resistance levels within populations of clonally identical cells. To be able to screen bacteria from clinical samples, a study of fluorescent dyes in droplets determined that a derivative of a popular viability marker is more suitable for droplet assays. We have developed a detection system that analyzes the growth or death state of bacteria with antibiotics for thousands of droplets per second by measuring the scattering of light hitting the droplets without labeling the cells or droplets. The droplet-based microchemostats enabled long-term evolution of resistance experiments, which will be integrated with high-throughput single-cell assays to better understand the mechanism of resistance acquisition and loss. These techniques underlie automated combinatorial screens of antibiotic resistance in single cells from clinical samples. We hope that this Account will inspire new droplet-based research on the antibiotic susceptibility of bacteria.

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Carboxylated Pillar[6]arene Emulates Pillar[5]arene in the Host–Guest Crystal Complexes and Shows Conformational Flexibility in the Solution/Gas Phase

(American Chemical Society, 2022-12-08) Butkiewicz, Helena; Kosiorek, Sandra; Sashuk, Volodymyr; Zimnicka, Magdalena; Danylyuk, Oksana; Instytut Chemii Fizycznej Polskiej Akademii Nauk; Instytut Chemii Organicznej Polskiej Akademii Nauk

Despite the thriving interest in the aqueous complexation properties of carboxylated pillar[6]arene, its solid state supramolecular chemistry has remained a mystery. Here, overcoming challenging crystallogenesis, we report the first crystallographic authentication of carboxylated pillar[6]arene in the form of two host−guest inclusion complexes with methyl viologen and pentamidine. The key to the successful crystallization of carboxylated pillar[6]arene is the mixed ionization state of its 12 carboxylic substituents. The deprotonation of several but not all substituents enables intermolecular hydrogen bonding and, as a result, “gluing” and crystallization of pillar[6]arene complexes with the aid of carboxylic-carboxylate, carboxylic-carboxylic, and amidinium-carboxylate supramolecular synthons. Single crystal X-ray diffraction analysis revealed that upon guest inclusion pillar[6]arene adopts a quasi-pentagonal shape rather than the expected hexagonal shape. The squeezed quasi-pentagonal conformation of the six-membered macrocycle is stabilized by two intramolecular hydrogen bonds between pillar[6]arene substituents. Moreover, the distinctive deviation of the macrocycle from hexagonal shape stays operative in the solution/gas phase as concluded from ion mobility mass spectrometry (IM-MS) studies and theoretical calculations. These results provide the first insight into how to gain control over the conformation of flexible pillar[6]arene with a view of solid state design of more advanced supramolecular host−guest structures.

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