Volume 95, Issue 10

Cesium lead bromide perovskite (CsPbBr 3 ) nanocrystals have raised impressive interest as efficient and stable optoelectronic materials. Size and morphology play important roles in the final performances of these materials and advanced characterization studies are needed to elucidate structural and surface properties. In this work, CsPbBr 3 cubic nanocrystals were obtained by colloidal synthesis and characterized by multinuclear Solid State NMR (SSNMR), complemented by X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and optical spectroscopy. The multinuclear NMR approach allowed the different components of the nanocubes to be separately observed. In particular, the surface ligands and their interactions with the nanocubes surface were investigated by 1 H and 13 C NMR experiments, while the structural investigation of the perovskite nanocubes was addressed by exploiting 207 Pb and 133 Cs spectral properties in comparison with bulk CsPbBr 3 . Static 207 Pb NMR spectra indicated a possible contribution of chemical shift anisotropy from the 207 Pb nuclei of the outer layer. The 133 Cs NMR spectra showed signals with different chemical shifts for cesium atoms in at least three regions of the nanocubes, from the inner core to the surface, which were interpreted in terms of cubic layers with different distances from the surface using a simple geometrical model. This interpretation was also supported by 133 Cs longitudinal relaxation time measurements.

Crystalline materials and crystallization processes play an important role in several fields of science, such as pharmaceuticals, material science, pigments, optoelectronics, catalysis and energy storage. Understanding and defining the right conditions of crystallization is therefore crucial. Among the several factors influencing the crystallization of a given compound, the choice of the solvent system is perhaps one of the most important. The nature of solvent–solute interactions can indeed have a role in promoting specific molecular assemblies, therefore affecting crystallisation rates of a crystal and often resulting in the nucleation of different polymorphs and solvates. Here we investigated the role of a binary mixture of solvent (water/acetone) in the crystallisation of a simple salt of 4-aminopyridinium chloride. Previous results on this compound showed that when crystallised from water it forms a simple hydrate structure, while in the presence of acetone, it undergoes a liquid-liquid phase separation, followed by the crystallisation of a complex structure belonging to the Frank–Kasper (FK) phases, a particular family of topologically close-packed structures never observed in small and rigid molecules. To broaden the understanding of how such a simple molecule may crystallise as an FK phase, we carried out the crystallization of the complex phase by antisolvent diffusion (in a mixture of water/acetone) and that of the monohydrate phase in water, monitoring the liquid precursors by liquid-state NMR. In particular, we applied 1 H, 13 C, 14 N, 17 O, and 35/37 Cl NMR as a function of the concentration of 4APH + Cl − until the moment when precipitation of the crystalline phases occurred. Variations of chemical shifts, T 1 relaxation times of 13 C signals, and full-width at half-maximum of the signals of quadrupolar nuclei were also measured. The spatial proximity between the different species in the solution was investigated by NOE experiments. In order to support these results, we also performed Molecular Dynamics simulations, investigating the potential solute/solvents interactions. The results strongly suggest that acetone, instead of behaving as an anti-solvent, interacts directly with the solute, preventing the formation of the simple monohydrate structure and, at the same time, promoting specific molecular aggregations.

Nuclear Magnetic Resonance is one of the most versatile structural biology tools. Its unique capacities remain unchallenged by the advances in other techniques, experimental, like cryo-electron microscopy, or computational, such as AlphaFold. In this perspective article we present the role played by various NMR techniques in the study of c-Src, a non-receptor protein tyrosine kinase that contains globular and intrinsically disordered domains. We show (i) how NMR helped chemical biology to discover the regulatory role of the Unique domain, (ii) its role in the characterization of the fuzzy intramolecular complex connecting the disordered region with the globular core through the SH3 domain, (iii) the identification of salt bridges connecting the main post-translational sites of the Unique domain with neighbor basic residues, and, (iv) the characterization of breathing motions and the independent dynamics of the two lobes of the kinase domain.

We have investigated an approach for obtaining 1 H NMR spectra of different alcohols on a large-bore (27 cm diameter), B 0  = 0.05 T ( f 0  = 2 MHz) portable MRI scanner. We used a Carr–Purcell–Meiboom–Gill (CPMG) sequence to acquire multiecho data from solutions of different alcohols, focusing on ethanol, a molecule of relevance to many applications in the food and beverage industry. Our results show that the Fourier transformed J-spectra at different echo spacings fit well with simulations of the evolution of the echo train signal with excellent signal to noise ratio (SNR) for concentrations of ∼10 % within a few minutes. Spectra were also obtained from intact bottles of whiskey and wine. Finally, we show that different alcohols with similar chemical structures can be differentiated using this approach.

Solid-state NMR methods incorporating dynamics-based spectral editing have a remarkable versatility for resolving and separately characterizing co-existing solid and liquid phases or domains in biologically and technically relevant organic materials. While 13 C spectra acquired under magic-angle spinning and 1 H decoupling provide atomic resolution, the signal intensities obtained with the CP and INEPT polarization transfer techniques give qualitative information about dynamics. This mini-review covers the basics of translational and rotational motion of atoms and molecules in organic materials, theoretical aspects of the relations between C–H bond reorientation and CP and INEPT signal intensities, and applications of the methods to a broad range of heterogeneous materials comprising hydrated assemblies of surfactants, lipids, proteins, and/or carbohydrates.

An NMR/MRI methodology is developed for the study of flows in miniaturized systems handling volumes of fluid in the microliter range. Specific MRI devices are implemented, including radiofrequency coils with millimetric dimensions whose size and geometry correspond to the studied systems. We follow a low-cost development procedure of home-made milli-RF coils, including their dimensioning, the simulation of the produced electromagnetic field, their fabrication and their integration in experimental devices. In each of the two cases presented the filling factor is optimized and the sensitivity of the measurement is greatly improved over standard commercial instrumentations by a factor up to 17. Two applications are then discussed: the characterization of the hydrodynamics in an anchor shaped micromixer and the monitoring of the development of a biofilm at the pore scale.

The International Union of Pure and Applied Chemistry has a long tradition of supporting the compilation of chemical data and their evaluation through direct projects, nomenclature and terminology work, and partnerships with international scientific bodies, government agencies, and other organizations. The IUPAC Interdivisional Subcommittee on Critical Evaluation of Data has been established to provide guidance on issues related to the evaluation of chemical data. In this first report, we define the general principles of the evaluation of scientific data and describe best practices and approaches to data evaluation in chemistry.

To bolster the series of Brief Guides released by International Union of Pure and Applied Chemistry (IUPAC), here we introduce the first Brief Guide to Polymer Characterization. This article provides a concise overview of characterization methods for teachers, students, non-specialists, and newcomers to polymer science as well as being a useful manual for researchers and technicians. Unlike pure low molar mass chemical substances, polymers are not composed of identical molecules. The macromolecules which comprise a single polymer sample vary from one another, primarily in terms of size and shape, but often also in the arrangement or positioning of atoms within macromolecules (e.g., chain branching, isomerism, etc.). Polymer properties are often drastically different from those of other substances and their characterization relies on specialist equipment and/or common equipment used in a specialized way (e.g., particular sample preparation or data analysis). This Brief Guide focuses uniquely on the structural characterization (i.e., analyzing the molecular and multi-molecular aspects) of polymers. The complex nature of the structural variables possible in macromolecular materials often presents a challenge with regard to the detailed structural characterization of polymers. This Brief Guide provides a useful starting point to direct the reader to the most commonly used and useful techniques to characterize these structural variables.