Investigating H2 Sorption in a Fluorinated Metal-Organic Framework with Small Pores Through Molecular Simulation and Inelastic Neutron Scattering.

Simulations of H2 sorption were performed in a metal-organic framework (MOF) consisting of Zn(2+) ions coordinated to 1,2,4-triazole and tetrafluoroterephthalate ligands (denoted [Zn(trz)(tftph)] in this work). The simulated H2 sorption isotherms reported in this work are consistent with the experimental data for the state points considered. The experimental H2 isosteric heat of adsorption (Qst) values for this MOF are approximately 8.0 kJ mol(-1) for the considered loading range, which is in the proximity of those determined from simulation. The experimental inelastic neutron scattering (INS) spectra for H2 in [Zn(trz)(tftph)] reveal at least two peaks that occur at low energies, which corresponds to high barriers to rotation for the respective sites. The most favorable sorption site in the MOF was identified from the simulations as sorption in the vicinity of a metal-coordinated H2O molecule, an exposed fluorine atom, and a carboxylate oxygen atom in a confined region in the framework. Secondary sorption was observed between the fluorine atoms of adjacent tetrafluoroterephthalate ligands. The H2 molecule at the primary sorption site in [Zn(trz)(tftph)] exhibits a rotational barrier that exceeds that for most neutral MOFs with open-metal sites according to an empirical phenomenological model, and this was further validated by calculating the rotational potential energy surface for H2 at this site.

Anomalous dynamics of water at the octopeptide lanreotide surface.

This work reports the study of water dynamics close to the cyclic octapeptide lanreotide from atomistic simulations of hydrated lanreotide, a cyclic octapeptide. Calculation of the hydrogen bonds between water molecules allows mapping of the hydrophilic regions of lanreotide. Whereas a super-diffusivity of the interfacial water molecules is established, a slowdown in rotational dynamics is observed, involving a decoupling between both processes. Acceleration in translation dynamics is connected to the hopping process between hydrophilic zones. Microscopically, this is correlated with the weakness of the interfacial hydrogen bonding network due to a hydrophobic interface at the origin of the interfacial sliding of water molecules. Heterogeneous rotational dynamics of water molecules close the lanreotide surface is evidenced and connected to heterogeneous hydration.

Force-Field Simulations of a Hydrated Lanreotide-Based Derivative: Hydration, Dynamics, and Numerical Evidence of Self-Assembly in Dimers.

Recently, self-organization of the cyclic octapeptide lanreotide and lanreotide-based derivatives in a nanotube to from a dimer structure has been experimentally evidenced. While the nature of the interactions between both monomers has been strongly investigated no molecular details of the hydration of the monomer and the formation of the dimer have been provided. Using molecular dynamics simulations, this work focuses on the structure, hydration, and dynamics of water and an analog of lanreotide. To do so, several models of monomers based on different schemes of partial charges and electrostatic interaction calculations are considered. By comparison with the experiments, we show that the model based on the combination of the AMBER force-field, CHELPG charge calculation, Ewald sum is the most relevant. Additionally, by mapping the interfacial hydration of the lanreotide monomer we evidence a heterogeneous surface in terms of hydrophilicity involving heterogeneous hydration. Furthermore, we show a slowdown in the translational dynamics of water molecules located close to the lanreotide surface. We also provide the molecular details of the self-assembly in the dimer in terms of structure, hydration, and energy.