The crystalline structure of hydroquinone clathrates has been studied using molecular dynamics. A flexible non-polarizable all-atom molecular model, based on the original Optimized Potentials for Liquid Simulations force field with recalculated point electric charges, has been used to describe the hydroquinone molecule, and the crystalline solid structure of the α native phase has been analyzed. Then, the β clathrates have been studied, considering CO and CH as guest molecules, and also the empty clathrate structure. In all cases, the lattice parameters obtained through molecular simulation show excellent agreement with reported experimental values, showing that the molecular model selected is able to reproduce both the native crystalline phase and also the clathrate structures. In addition, the process of clathrate guest molecule release upon heating has been characterized, and the simulations show a good correspondence with the very recent experimental trends observed for both guest molecules analyzed.

Using molecular simulation techniques, we investigate the storage capabilities of H 2 gas by the clathrate of hydroquinone (HQ). Quantum mechanics calculations have been used to assess structure and interactions at the atomic scale and molecular dynamics to model the HQ clathrate at successive equilibriums during the processes of capture and release of H 2 , as well as the diffusion of H 2 inside the clathrate structure. The thermodynamic conditions of the simulations performed try to reproduce closely the corresponding experimental procedures, with results that are in good agreement with literature observed trends. The results obtained contribute to depict a more complete and better substantiated image of the mechanisms involved in stability and in the processes of capture and release of H 2 by the HQ clathrate.

Organic clathrates, particularly those formed by hydroquinone (HQ) and gas mixtures, have been far less studied than other inclusion compounds, such as gas hydrates. In this study, experiments and molecular dynamics simulations were performed on mixed (CO 2 + CH 4)−HQ clathrates. Single crystals were synthesized using gas mixtures with different compositions, ranging from pure CO 2 to pure CH 4. The crystal structure, the guest occupancy in the clathrates, and the variation of the crystal lattice parameters according to clathrate composition were obtained by X-ray diffraction measurements. In addition, molecular dynamics simulations were performed on the same systems, with state-of-the-art molecular models and force fields. The experimental results obtained and the molecular dynamics simulation estimations were in good agreement. The clathration selectivity was also calculated on the basis of experimental results, and the composition of the solid phase was correlated with the composition of the gas phase at equilibrium. These new insights into these structures will be useful from both a fundamental and a practical point of view, particularly for further developing innovative gas separation techniques using HQ clathrates.

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Previous studies focused on understanding the role of physical drivers on phytoplankton bloom formation mainly used indirect estimates of turbulent mixing. Here we use weekly observations of microstructure turbulence, dissolved inorganic nutrients, chlorophyll a concentration and primary production carried out in the Ría de Vigo (NW Iberian upwelling system) between March 2017 and May 2018 to investigate the relationship between turbulent mixing and phytoplankton growth at different temporal scales. In order to interpret our results, we used the theoretical framework described by the Critical Turbulent Hypothesis (CTH). According to this conceptual model if turbulence is low enough, the depth of the layer where mixing is active can be shallower than the mixed-layer depth, and phytoplankton may receive enough light to bloom. Our results showed that the coupling between turbulent mixing and phytoplankton growth in this system occurs at seasonal, but also at shorter time scales. In agreement with the CTH, higher phytoplankton growth rates were observed when mixing was low during spring-summer transitional and upwelling periods, whereas low values were described during periods of high mixing (fall-winter transitional and downwelling). However, low mixing conditions were not enough to ensure phytoplankton growth, as low phytoplankton growth was also found under these circumstances. Wavelet spectral analysis revealed that turbulent mixing and phytoplankton growth were also related at shorter time scales. The higher coherence between both variables was found in spring-summer at the ~16–30 d period and in fall-winter at the ~16–90 d period. These results suggest that mixing could act as a control factor on phytoplankton growth over the seasonal cycle, and could be also involved in the formation of occasional short-lived phytoplankton blooms.