The reaction kinetics between like-charged compounds in water is extremely slow due to Coulomb repulsions. Here, we demonstrate that by screening these interactions and, in consequence, increasing the local concentration of reactants, we boost the reactions by many orders of magnitude. The reaction between negatively charged Coenzyme A molecules accelerates ~5 million-fold using cationic micelles. That is ~104 faster kinetics than in 0.5 M NaCl, although the salt is ~106 more concentrated. Rate enhancements are not limited to micelles, as evidenced by significant catalytic effects (104–105-fold) of other highly charged species such as oligomers and polymers. We generalize the observed phenomenon by analogously speeding up a non-covalent complex formation—DNA hybridization. A theoretical analysis shows that the acceleration is correlated to the catalysts’ surface charge density in both experimental systems and enables predicting and controlling reaction rates of like-charged compounds with counter-charged species.

Most experimental procedures applied in modern biology involve cargo delivering into cells. One of the ways to cargo introduction is osmotic-mediated intracellular vesicle swelling. However, its widespread use was hindered due to cargo size (<10 nm) and cell-type-related restrictions. We addressed the issue of the composition of colloidal loading solution to enhance the efficiency of cellular delivery. We examined the effectiveness of colloidal loading solutions of varied compositions, including various types and sizes of polymers building osmotic pressure. We used confocal imaging coupled with fluorescence correlation spectroscopy to evaluate the introduction of polymers, proteins, nanoparticles, and DNA plasmids (cargos of sizes 1–175 nm) to cells representing eight cell lines: cancer, normal, epithelial, and mesenchymal ones. We found that cellular delivery effectiveness strongly correlates with the size and concentration of osmotic pressure building polymers and not with the high value of the osmotic pressure itself. We show that polymer solutions at the entangled regime of concentrations enhance the delivery of large biomacromolecules even of size 200 nm (DNA plasmids) into cells, including MDA-MB-231 cells – so far resistant to the osmotic procedure. We show that the colloid loading medium based on entangled polymer chains is a versatile cargo delivery tool for molecular biology.

Biocompatible polyacrylamide gel and core–shell nanoparticles (NPs) were synthesized using a one-step electrochemically initiated gelation. Constant-potential electrochemical decomposing of ammonium persulfate initiated the copolymerization of N-isopropyl acrylamide, methacrylic acid, and N,N′-methylenebisacrylamide monomers. This decomposing potential and monomers’ concentrations were optimized to prepare gel NPs and thin gel film-grafted core–shell NPs. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) imaging confirmed the gel NP formation. The lyophilized gel NPs and core–shell NPs were applied to support the three-dimensional (3D) cell culture. In all, core–shell NPs provided superior support for complex 3D tissue structures.

Nitrophenols (NPs) are hazardous pollutants found in various environmental matrices, including ambient fine particulate matter (PM2.5), agricultural residues, rainwater, wildfires, and industrial wastes. This study showed for the first time the effect of three pure nitrophenols and their mixture on human lung cells to provide basic understanding of the NP influence on cell elements and processes. We identified NPs in ambient PM2.5 and secondary organic aerosol (SOA) particles generated from the photooxidation of monocyclic aromatic hydrocarbons in the U.S. EPA smog chamber. We assessed the toxicity of identified NPs and their equimolar mixture in normal bronchial epithelial (BEAS-2B) and alveolar epithelial cancer (A549) lung cell lines. The inhibitory concentration-50 (IC50) values were highest and lowest in BEAS-2B cells treated with 2-nitrophenol (2NP) and 4-nitrophenol (4NP), respectively, at 24 h of exposure. The lactate dehydrogenase (LDH) assay showed that 4NP, the most abundant NP we identified in PM2.5, was the most cytotoxic NP examined in both cell lines. The annexin-V/fluorescein isothiocyanate (FITC) analysis showed that the populations of late apoptotic/necrotic BEAS-2B and A549 cells exposed to 3NP, 4NP, and NP equimolar mixture increased between 24 and 48 h. Cellular reactive oxygen species (ROS) buildup led to cellular death post exposure to 3NP, 4NP and the NP mixtures, while 2NP induced the lowest ROS buildup. An increased mitochondrial ROS signal following NP exposure occurred only in BEAS-2B cells. The tetramethylrhodamine, methyl ester, perchlorate (TMRM) assay showed that exposed cells exhibited collapse of the mitochondrial membrane potential. TMRM signals decreased significantly only in BEAS-2B cells, and most strongly with 4NP exposures. Our results suggest that acute atmospheric exposures to NPs may be toxic at high concentrations, but not at ambient PM2.5 concentrations. Further chronic studies with NP and NP-containing PM2.5 are warranted to assess their contribution to lung pathologies.

We investigate the thermal relaxation of an ideal gas from a nonequilibrium stationary state. The gas is enclosed between two walls, which initially have different temperatures. After making one of the walls adiabatic, the system returns to equilibrium. We notice two distinct modes of heat transport and associated timescales: one connected with a traveling heat front and the other with internal energy diffusion. At the heat front, which moves at the speed of sound, pressure, temperature, and density change abruptly, leaving lower values behind. This is unlike a shock wave, a sound wave, or a thermal wave. The front moves multiple times between the walls and is the dominant heat transport mode until surpassed by diffusion. We found that it can constitute an order 1 factor in shaping the dynamics of the outflow of internal energy. We found that cooling such a system is quicker than heating, and that hotter bodies cool down quicker than colder ones. The latter is known as the Mpemba effect.

We study the relaxation dynamics of a binary liquid mixture near a light-absorbing Janus particle after switching on and off illumination using experiments and theoretical models. The dynamics is controlled by the temperature gradient formed around the heated particle. Our results show that the relaxation is asymmetric: The approach to a nonequilibrium steady state is much slower than the return to thermal equilibrium. Approaching a nonequilibrium steady state after a sudden temperature change is a two-step process that overshoots the response of spatial variance of the concentration field. The initial growth of concentration fluctuations after switching on illumination follows a power law in agreement with the hydrodynamic and purely diffusive model. The energy outflow from the system after switching off illumination is well described by a stretched exponential function of time with characteristic time proportional to the ratio of the energy stored in the steady state to the total energy flux in this state.

The equilibrium constant (K) of biochemical complex formation in aqueous buffers with high concentration (>20 wt %) of nonionic compounds can vary by orders of magnitude in comparison with the K in a pure buffer. The precise molecular mechanisms of these profound changes are not known. Herein, we show up to a 1000-fold decrease of the K value of DNA hybridization (at nM concentration) in standard molecular crowder systems such as PEG, dextrans, Ficoll, and glycerol. The effect responsible for the decrease of K is the complexation of positively charged ions from a buffer by nonionic polymers/small molecules. We determined the average equilibrium constant for the complexation of ions per monomer (∼0.49 M–1). We retrieve K’s original value for a pure buffer if we properly increase the ionic strength of the buffer crowded by the polymers, compensating for the loss of complexed ions.

We analyze a compressible Poiseuille flow of ideal gas in a plane channel. We provide the form of internal energy U for a nonequilibrium stationary state that includes viscous dissipation and pressure work. We demonstrate that U depends strongly on the ratio Δ p / p 0 , where Δ p is the pressure difference between inlet and outlet and p 0 is the outlet’s pressure. In addition, U depends on two other variables: the channel aspect ratio and the parameter equivalent to Reynolds number. The stored internal energy, Δ U = U − U 0 , is small compared to the internal energy U 0 of the equilibrium state for a moderate range of values of Δ p / p 0 . However, Δ U can become large for big Δ p or close to vacuum conditions at the outlet ( p 0 ≈ 0 Pa ).