Water’s unique physicochemical properties arise from its dynamic hydrogen-bonding network, yet the precise molecular threshold at which these cooperative behaviors emerge remains a key question. This study employed nuclear magnetic resonance (NMR) spectroscopy and density functional theory (DFT) calculations to investigate the evolution of hydrogen bonding strength in small water clusters, ranging from dimers to pentamers. The observed exponential increase in NMR chemical shift up to the pentamer reflects growing hydrogen bond cooperativity, identifying the (H₂O)₅ cluster as a critical structural and energetic threshold. At this size, the network achieves sufficient connectivity to support key bulk-like phenomena such as proton transfer and dielectric relaxation. These conclusions were corroborated by complementary FT-IR and electrochemical impedance spectroscopy (EIS) measurements of bulk water. Our results position the water pentamer as the molecular onset of emergent solvent behavior, effectively bridging the divide between discrete clusters and the macroscopic properties of liquid water.

The present study investigated the ¹H Nuclear Magnetic Resonance (NMR) spectra of hydrogen-rich water (HRW) produced using the EVObooster device. The analyzed HRW has pH = 7.1 ± 0.11, oxidation–reduction potential (ORP) of (−450 ± 11) mV, and a dissolved hydrogen concentration of 1.2 ppm. The control sample was tap water filtered by patented technology. A 600 NMR spectrometer was used to measure NMR spectra. Isotropic 1H nuclear magnetic shielding constants of the most stable clusters (H₂O)_n with n from 3 to 28 have been calculated by employing the gauge-including-atomic-orbital (GIAO) method at the MPW1PW91/6-311+G(2d,p) density function level of theory (DFT). The HRW chemical shift is downfield (higher chemical shifts) due to increased hydrogen bonding. More extensive formations were formed in HRW than in control filtered tap water. The exchange of protons between water molecules is rapid in HRW, and the ¹H NMR spectra are in fast exchange mode. Therefore, we averaged the calculated chemical shifts of the investigated water clusters. As the size of the clusters increases, the number of hydrogen bonds increases, which leads to an increase in the chemical shift. The dependence is an exponential saturation that occurs at about N = 10. The modeled clusters in HRW are structurally stabilized, suggesting well-ordered hydrogen bonds. In the article, different processes are described for the transport of water molecules and clusters. These processes are with aquaporins, fusion pores, gap-junction channels, and WAT FOUR model. The exponential trend of saturation shows the dynamics of water molecules in clusters. In our research, the chemical shift of 4.257 ppm indicates stable water clusters of 4–5 water molecules. The pentagonal rings in dodecahedron cage H₃O⁺(H₂O)₂₀ allow for an optimal arrangement of hydrogen bonds that minimizes the potential energy.

This study explores the structural and chemical interactions between glacial water, ice I_h, and hydration clusters of divalent cations (Ca²⁺ and Mg²⁺). Ice I_h, with its hexagonal lattice and tetrahedral bonding network, is incompatible with the hydration shells of Ca²⁺ and Mg²⁺, which adopt octahedral geometries in aqueous solutions. During freezing, these hydration clusters become disordered, causing distortions in the ice structure. Slow freezing reduces these distortions, while rapid freezing traps ions in amorphous regions, preventing proper alignment of hydration clusters. Through advanced techniques such as chemical and isotopic analysis, computational modeling, and electrical impedance spectroscopy, this study examines ion exclusion mechanisms and water-clustering behaviors. The results show that both ions are largely excluded from the solid phase during freezing, with Mg²⁺ exhibiting stronger exclusion due to its smaller ionic radius and greater hydration energy. This study also highlights the role of sediments in modulating ion patterns in glacial ice. This work deepens our understanding of ion–ice interactions, offering insights for cryochemistry, hydrology, and environmental science. The integration of experimental and computational methods provides new perspectives on divalent cations’ role in modifying ice’s crystalline structure and explains isotopic variability in glacial waters.

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are pollutants of concern due to their long-term persistence in the environment and human health effects. Among them, perfluorooctane sulfonic acid (PFOS) is very ubiquitous and dangerous for health. Currently, the detection levels required by the legislation can be achieved only with expensive laboratory equipment. Hence, there is a need for portable, in-field, and possibly real-time detection. Optical and electrochemical transduction mechanisms are mainly used for the chemical sensors. Here, we report the first gravimetric detection of small-sized molecules like PFOS (MW 500) dissolved in water. A 100 MHz quartz crystal microbalance (QCM) measured at the third harmonic and an even more sensitive 434 MHz two-port surface acoustic wave (SAW) resonator with gold electrodes were used as transducers. The PFOS selective sensing layer was prepared from the metal organic framework (MOF) MIL-101(Cr). Its nano-sized thickness and structure were optimized using the discreet Langmuir–Blodgett (LB) film deposition method. This is the first time that LB multilayers from bulk MOFs have been prepared. The measured frequency downshifts of around 220 kHz per 1 µmol/L of PFOS, a SAW resonator-loaded Q_L-factor above 2000, and reaction times in the minutes’ range are highly promising for an in-field sensor reaching the water safety directives. Additionally, we use the micrometer-sized interdigitated electrodes of the SAW resonator to strongly enhance the electrochemical impedance spectroscopy (EIS) of the PFOS contamination. Thus, for the first time, we combine the ultra-sensitive gravimetry of small molecules in a water environment with electrical measurements on a single device. This combination provides additional sensor selectivity. Control tests against a bare resonator and two similar compounds prove the concept’s viability. All measurements were performed with pocket-sized tablet-powered devices, thus making the system highly portable and field-deployable. While here we focus on one of the emerging water contaminants, this concept with a different selective coating can be used for other new contaminants.

We suggest a new construction of spin-VCSEL with an embedded nematic liquid crystal (LC) in a second cavity. We design such a coupled-cavity LC-VCSEL and develop a procedure for calculating its LC-voltage dependent polarization resolved resonant longitudinal modes and their quantum-well confinement factors. Using these characteristics, we are able to slightly modify the spin-flip VCSEL model to include the voltage dependent birefringence and anisotropy. Then, we show that such an LC-VCSEL can reach small signal modulation response with a $3\mathrm{dB}$ cut off frequency of several hundreds of GHz.