Despite the simple molecular structure of quercetin, the exact conformation of the hydroxyl groups and the induced hydrogen bonding network in its anhydrous form could not be determined if starting from crystal structure models provided by X-ray powder diffraction (XRPD) alone. If instead a multi-technique approach that combines XRPD data analysis with information from ¹³C and ¹H solid-state Nuclear Magnetic Resonance (ss-NMR) and molecular modeling is employed the ambiguities could be largely reduced. A conformational analysis was performed on the isolated molecule at the molecular mechanics (MM) level of theory, whereas quantum chemical computations of the full crystal were employed for geometry optimization and chemical shift calculation based on the Gauge Including Projector Augmented-Wave (GIPAW) method. ¹³C and ultra-fast MAS (60 kHz) ¹H ss-NMR data were used at 11.75 T to assess the reliability of the derived structure solutions, and to obtain important insights into the relationship between the hydrogen bonding network and the induced supra-molecular architectures/crystal packing patterns. A direct comparison with the data recorded on quercetin dihydrate, of which single-crystal X-ray structure is known, proved useful for increasing the confidence level in the derived conclusions. Also, an ultra-fast MAS ¹H double-quantum (DQ) excitation scheme is employed, which has the advantage of providing better resolution at long DQ excitation times compared with conventional multiple-pulse homonuclear decoupling: this may be relevant for further methodological development in NMR crystallography, especially when dealing with the effects of increased lattice disorder.

Manganese doped crystalline copper oxide (CuO:Mn) and undoped CuO were prepared at room temperature by the hydrothermal method. The complete physico-chemical characterization of the materials was performed using X-ray diffraction (XRD), transmission/scanning electron microscopy (TEM/SEM), and X-ray photoelectron spectroscopy (XPS). Furthermore, their analytical applicability was tested in electrochemical experiments for a dopamine assay. According to the morphological investigation, the materials had a flat structure with nearly straight edges. The XRD analysis proved the formation of the CuO phase with good crystallinity, while the Mn doping was determined by XPS to be around 1 at.%. Under optimized conditions, at pH 5.0, the CuO:Mn modified electrode (CuO:Mn/SPE) showed a high signal for dopamine oxidation, with a linear response in the 0.1–1 µM and 1–100 µM ranges and a low limit of detection of 30.3 nM. Five times higher sensitivity for manganese doped copper oxide in comparison with the undoped sample was achieved. The applicability of the developed CuO:Mn/SPE electrode was also tested in a commercially available pharmaceutical drug with good results, suggesting that the developed sensor has promising biomedical application potential.

Hydrogen atoms play a crucial role in the aggregation of organic (bio)molecules through diverse number of noncovalent interactions that they mediate, such as electrostatic in proton transfer systems, hydrogen bonding, and CH–π interactions, to mention only the most prominent. To identify and adequately describe such low-energy interactions, increasingly sensitive methods have been developed over time, among which quantum chemical computations have witnessed impressive advances in recent years. For reaching the present state-of-the-art, computations had to rely on a pool of relevant experimental data, needed at least for validation, if not also for other purposes. In the case of molecular crystals, the best illustration for the synergy between computations and experiment is given by the so-called NMR crystallography approach. Originally designed to increase the confidence level in crystal structure determination of organic compounds from powders, NMR crystallography is able now to offer also a wealth of information regarding the noncovalent interactions that drive molecules to pack in a given crystalline pattern or another. This is particularly true for the noncovalent interactions which depend on the exact location of labile hydrogen atoms in the system: in such cases, NMR crystallography represents a valuable characterization tool, in some cases complementing even the standard single-crystal X-ray diffraction technique. A concise introduction in the field is made in this mini-review, which is aimed at providing a comprehensive picture with respect to the current accuracy level reached by NMR crystallography in the characterization of hydrogen-mediated noncovalent interactions in organic solids. Different types of practical applications are illustrated with the example of molecular crystals studied by our research group, but references to other representative developments reported in the literature are also made. By summarizing the major concepts and methodological progresses, the present work is also intended to be a guide to the practical potential of this relatively recent analytical tool for the scientists working in areas where crystal engineering represents the main approach for rational design of novel materials.

Androsta-1,4-dien-17β-ol-3-one, also known as boldenone, is an anabolic-androgenic steroid derived from testosterone. The crystal structures of boldenone base, boldenone acetate, boldenone propionate, boldenone cypionate and a boldenone acetate polymorph obtained by high throughput screening were investigated. Hirshfeld surfaces and fingerprint plots breakdown revealed that the molecular packing in the crystals are driven by dominant H⋯H intermolecular contacts, followed by O⋯H/H⋯O contacts and to a lesser degree C⋯H/H⋯C contacts. The steroid skeleton rings, for all the reported compounds, adopt the following conformation: planar in A, chair in B and C, whereas C(13) envelope conformations are found for the five-membered D rings. The total lattice energies were calculated as a sum of four terms (Coulombic, polarization, dispersion, repulsion).