QENS and NMR Study of Water Dynamics in SBA-15 with a Low Water Content

In this study, motions performed by water molecules adsorbed on the silica surface of SBA-15 material with 6.1% of water content (15% of pore filling) were investigated using NMR and Quasielastic Neutron Scattering (QENS) techniques. The results show no sign of translational diffusion of water, but two types of stochastic localized motions were identified, and both described using a model of proton jumps between two sites. For both motions, the characteristic jump distances and correlation times, as well as activation energies, have been extracted and found to differ significantly. On this basis, the faster motion was ascribed to jumps of water molecules between neighboring positions (<i>d</i> = 2.5 Å, τ = 4 ps at 300 K, and <i>E</i>_a = 5.2 ± 0.2 kJ/mol from NMR data, and 5.6 ± 1.1 kJ/mol from QENS), while the slower one exhibits a temperature dependent jump distance and was ascribed to jumps of water molecules between more spatially separated positions (<i>d</i> = 2.9–4.3 Å, τ = 25 ps at 300 K, and <i>E</i>_a = 16.1 ± 0.3 kJ/mol from NMR, and 17.3 ± 0.3 kJ/mol from QENS data)

Computationally Assisted (Solid-State Density Functional Theory) Structural (X-ray) and Vibrational Spectroscopy (FT-IR, FT-RS, TDs-THz) Characterization of the Cardiovascular Drug Lacidipine

The structural properties of a second-generation dihydropyridine calcium antagonist, lacidipine, were explored by combining low-temperature X-ray diffraction with optical vibrational spectroscopy and periodic density functional theory (PBC DFT) calculations. Crystallographic analysis cannot discriminate between two possible molecular symmetries in crystals made of pure lacipidine: the space group <i>Ama</i>2, where the lacipidine molecule lies on mirror symmetry, or a <i>Cc</i> space group with distorted lacipidine molecules. Intermolecular interactions analysis reveals an infinite net of moderate-strength N–H···O hydrogen-bonds, which link the molecular units toward the crystallographic <i>b</i>-axis. Weak interactions were identified, revealing their role in stabilization of the crystal structure. The vibrational dynamics of lacidipine was thoroughly explored by combining infrared and Raman spectroscopy in the middle- and low-wavenumber range. The given interpretation was fully supported by state-of-the-art solid-state density functional theory calculations (plane-wave DFT), giving deep insight into the vibrational response and providing a complex assignment of spectral features. The vibrational analysis was extended onto the lattice-phonon range by employing time-domain terahertz spectroscopy. Analysis of the anisotropic displacement parameters suggests noticeable dynamics of the terminal (<i>tert</i>-butoxycarbonyl)­vinyl moiety. The terahertz study provides direct experimental evidence of “crankshaft” type motions in the terminal chain. By combining low-wavenumber vibrational spectroscopy with the first-principles calculations, we were able to prove that the quoted thermodynamically stable phase corresponds to the monoclinic <i>Cc</i> space group