The origin of the splitting of 13C and 15N NMR signals of 3(5)-phenyl-5(3)-methylpyrazolium chloride and bromide in the solid state: Quantum Espresso calculations

NMR crystallography of molecular organics

Developments of NMR methodology to characterise the structures of molecular organic structures are reviewed, concentrating on the previous decade of research in which density functional theory-based calculations of NMR parameters in periodic solids have become widespread. With a focus on demonstrating the new structural insights provided, it is shown how "NMR crystallography" has been used in a spectrum of applications from resolving ambiguities in diffraction-derived structures (such as hydrogen atom positioning) to deriving complete structures in the absence of diffraction data. As well as comprehensively reviewing applications, the different aspects of the experimental and computational techniques used in NMR crystallography are surveyed. NMR crystallography is seen to be a rapidly maturing subject area that is increasingly appreciated by the wider crystallographic community.

Investigation of the molecular structure of 4-(3-methyl-3-phenylcyclobutyl)-2-[2-(3-methylbenzylidene)hydrazinyl]thiazole in the gas and solid phases

In this study, the title Shiff base, C₂₂H₂₃N₃S, was synthesized and examined by ¹H and ¹³C NMR spectroscopy and X-ray analysis techniques. The crystal structure is stabilized by classical intermolecular N-H...N hydrogen bonding. The crystal packing is additionally stabilized by C-H...π interactions. It has been observed that the compound can exist in two different tautomeric forms, and experimental and theoretical studies were carried out on these tautomeric structures. For this purpose, the gas phase of the compound was optimized by density functional theory (DFT) using the B3LYP/6-311G(d) method, which allowed for the structural parameters (bond angles, bond lengths and dihedral angles), as well as the frontier molecular orbitals (FMO), to be examined. In addition, stable structures of the two tautomers in the solid phase were obtained using Quantum ESPRESSO under periodic boundary conditions (PBC).

Environmental metabolomics with data science for investigating ecosystem homeostasis

A natural ecosystem can be viewed as the interconnections between complex metabolic reactions and environments. Humans, a part of these ecosystems, and their activities strongly affect the environments. To account for human effects within ecosystems, understanding what benefits humans receive by facilitating the maintenance of environmental homeostasis is important. This review describes recent applications of several NMR approaches to the evaluation of environmental homeostasis by metabolic profiling and data science. The basic NMR strategy used to evaluate homeostasis using big data collection is similar to that used in human health studies. Sophisticated metabolomic approaches (metabolic profiling) are widely reported in the literature. Further challenges include the analysis of complex macromolecular structures, and of the compositions and interactions of plant biomass, soil humic substances, and aqueous particulate organic matter. To support the study of these topics, we also discuss sample preparation techniques and solid-state NMR approaches. Because NMR approaches can produce a number of data with high reproducibility and inter-institution compatibility, further analysis of such data using machine learning approaches is often worthwhile. We also describe methods for data pretreatment in solid-state NMR and for environmental feature extraction from heterogeneously-measured spectroscopic data by machine learning approaches.

A theoretical and experimental study of the NMR spectra of 4,5,6,7-tetrafluorobenzazoles with special stress on PCM calculations of chemical shifts

The chemical shifts and several (19)F-(19)F, (13)C-(19) F and (1)H-(19)F spin-spin coupling constants (SSCSs) of eight 4,5,6,7-tetraflurobenzazoles (three benzimidazoles, three benzimidazolinones and two indazoles) have been determined. The chemical shifts were discussed using gauge including atomic orbital-density functional theory calculations taking into account solvent effects (polarizable continuum model) and, for the solid state, hydrogen bonds (clusters up to three molecules).