Crystal Structure of Cl-Deficient Analogue of Taseqite from Odikhincha Massif

An eudialyte group mineral, found in pegmatites of the Odikhincha massif (the northern part of the Siberian platform), has been investigated using X-ray diffraction, IR spectroscopy, and Raman spectroscopy. The mineral is characterized by a high strontium content and a low chlorine content. It has a trigonal unit cell with the following parameters: a = 14.2700(6) Å and c = 30.057(1) Å; V = 5300.6(1) ų; sp. gr. R3m. The structure has been refined to R = 0.047 in the anisotropic approximation of atomic displacements using 1697F > 4σ(F). The idealized formula (Z = 3) was found to be Na₁₂Sr₂Ca₆Fe ₃ ²⁺ Zr₃NbSi₂₅O₇₂(OH,O)₄Cl(Н₂О)_0.2. The chemical composition and structure of this mineral are close to those of taseqite; however, it differs from the holotype sample by a low chlorine content and peculiarities of cation distribution over basic structure sites. A comparative analysis of strontium-rich eudialytes has revealed their important crystallochemical feature: selective concentration of strontium in the N4 site. Thus, taseqite, along with heterophyllosilicates, may play a role of strontium concentrator in agpaitic pegmatites.     

Rapid and cost-effective LC–MS/MS method for determination of hydroxycitric acid in plasma: Application in the determination of pharmacokinetics in commercial Garcinia preparations

Garcinia cambogia is one of the most commonly used anti-obesity dietary supplements, and hydroxycitric acid (HCA) is a major constituent in the commercial preparations of Garcinia. High doses of HCA are often consumed without much awareness of its pharmacokinetic and toxicokinetic parameters, and therefore, a complete understanding of its effects is lacking. The first step in understanding these parameters is the availability of a reliable bioanalytical method. Here, we present the first report on a UPLC–MS/MS method for analysis of HCA in rat plasma after a simplified and cost-effective protein precipitation. Chromatographic separation of the analytes in the supernatant was achieved using hydrophilic interaction liquid chromatography, where mass parameters were optimized and a rapid 5-min quantitative assay was developed. The method was highly sensitive, accurate, precise and linear in the concentration range of 10.5–5000 ng/mL (validated according to the United States Food and Drug Administration guidelines). Further, the method was successfully used to describe the pharmacokinetic profile of HCA in rat plasma after the administration of pure HCA and commercial Garcinia preparations.     

Analyses of reaction rate data for the simple hydrolysis of acetic anhydride in the acetonitrile/water and acetone/water cosolvent systems using recently developed thermodynamic rate equations

This article presents reaction rate data for the simple hydrolysis of acetic anhydride in the acetonitrile/water and acetone/water cosolvent systems and regression analyses using recently developed thermodynamic rate equations that contain electrostatic and solvent-solute terms. The isomole fraction plots for these reaction systems are linear, and previous theoretical work has shown that the electrostatic term is negligible for such systems. On the other hand, the reaction rates are dependent upon the cosolvent mole fraction, indicating that the solvent-solute term, which is modeled empirically, is significant. The results of the analyses provide the foundation for a paradigm shift away from the emphasis on electrostatic effects to more tenable explanations of kinetic behavior in solvent systems.     

The pyrolysis of propane

The pyrolysis of propane plays an important role in determining the combustion properties of natural gas mixtures and offers insight into the cracking patterns of larger fuels. This work investigates propane pyrolysis behind reflected shock waves with a multiwavelength laser-absorption speciation technique. Nine laser wavelengths, sensitive to key pyrolysis species, were used to measure absorbance time histories during the decomposition of 2% propane in argon between 1022 and 1467 K, 3.7-4.3 atm. Absorbance models were developed at each diagnostic wavelength to interrogate common initial conditions, and time histories of all major species are reported at 1250, 1290, 1330, 1370, and 1410 K. Nearly complete carbon recovery observed at lower temperatures enabled the inference of hydrogen formation from atomic conservation, while decaying carbon recovery at high temperatures suggests the formation of allene and 1-butene. The results show systematically faster pyrolysis than predicted by kinetic modeling and motivate further study into the kinetics of propane pyrolysis.     

In vivo comprehensive multiphase NMR

Traditionally, due to different hardware requirements, nuclear magnetic resonance (NMR) has developed as two separate fields: one dealing with solids, and one with solutions. Comprehensive multiphase (CMP) NMR combines all electronics and hardware (magic angle spinning [MAS], gradients, high power Radio Frequency (RF) handling, lock, susceptibility matching) into a universal probe that permits a comprehensive study of all phases (i.e., liquid, gel-like, semisolid, and solid), in intact samples. When applied in vivo, it provides unique insight into the wide array of bonds in a living system from the most mobile liquids (blood, fluids) through gels (muscle, tissues) to the most rigid (exoskeleton, shell). In this tutorial, the practical aspects of in vivo CMP NMR are discussed including: handling the organisms, rotor preparation, sample spinning, water suppression, editing experiments, and finishes with a brief look at the potential of other heteronuclei (²H, ¹⁵N, ¹⁹F, ³¹P) for in vivo research. The tutorial is aimed as a general resource for researchers interested in developing and applying MAS-based approaches to living organisms. Although the focus here is CMP NMR, many of the approaches can be adapted (or directly applied) using conventional high-resolution magic angle spinning, and in some cases, even standard solid-state NMR probes.     

NMR spectral analysis of strongly second-order 6-, 8-, 9- and 10- spin-systems (1H─19F, 19F─19F,and 13C─19F) in perfluorotoluyl- and tetrafluoro-pyridyl-aromatics using the lineshape method ANATOLIA

A simple to use nuclear magnetic resonance analysis method has been tested on complex ¹H, ¹⁹F, and ¹³C multiplets. This open-source line-shape analysis method analysis of total lineshape (ANATOLIA)¹ provides some significant advantages over traditional assign-iterate methods of NMR spectral analysis by avoiding false minima and progressing optimisation to the global minimum. The target molecules are 1-perfluorotol-4-yl-2-perfluorotol-4-yl-oxymethyl-1H-benzimidazole (molecule-I) and 1-tetrafluoropyrid-4-yl-2-tetrafluoropyrid-4-yl-thio-1H-benzimidazole (molecule-II) which were produced as part of a family of fluorinated drug scaffolds prepared for anticancer and antiparasitic screening. Spectra display significant second-order effects with ¹H Δδ = 3.68 and 4.67 Hz for the aromatic hydrogen “triplets”, with ¹⁹F ⁴J_AA', ⁴J_BB', ⁴J_XX', and ⁴J_YY' coupling constants range from +4.8 to −14.0 Hz and for ¹³C-isotopomers ¹⁹F Δδ of up to 111.56 Hz. A spin-system of six coupling nuclei (H_aH_bH_cH_d F_YF_Y') was analysed in 12 s, a spin-system of nine coupling fluorine nuclei (AA'BB'CCC-YY') was analysed within 2 min, and 10 coupling nuclei (XX'YY'ZZZ-BB'-H_d) was optimised in 6 min using a laptop computer. ANATOLIA was also robust enough to be able to yield accurate spectral values from inaccurate input values. In both compounds, a fluorine–fluorine coupling constant was identified between the two fluoro-aromatic rings (F_BB' and F_YY') of +4.05 and +4.67 Hz and attributed to a through-space interaction. Ab initio structure optimisations and coupling constant calculations provided useful input data for spectral analysis. A modern ¹⁹F nuclear magnetic resonance spectrum of perfluorotoluene (octafluorotoluene) and analysis from 1975 was used as a test data set to assess ANATOLIA.     

Identifying aspirin polymorphs from combined DFT-based crystal structure prediction and solid-state NMR

A combined experimental and computational approach was used to distinguish between different polymorphs of the pharmaceutical drug aspirin. This method involves the use of ab initio random structure searching (AIRSS), a density functional theory (DFT)-based crystal structure prediction method for the high-accuracy prediction of polymorphic structures, with DFT calculations of nuclear magnetic resonance (NMR) parameters and solid-state NMR experiments at natural abundance. AIRSS was used to predict the crystal structures of form-I and form-II of aspirin. The root-mean-square deviation between experimental and calculated ¹H chemical shifts was used to identify form-I as the polymorph present in the experimental sample, the selection being successful despite the large similarities between the molecular environments in the crystals of the two polymorphs.     

Measurement of the hydrodynamic radii of PEE-G dendrons by diffusion spectroscopy on a benchtop NMR spectrometer

Benchtop nuclear magnetic resonance (NMR) spectroscopy is a useful tool for the rapid determination of the self-diffusion coefficient and the hydrodynamic radius of dendrons. The self-diffusion coefficients of the first four generations of poly ethoxy ethyl glycinamide (PEE-G) dendrons are measured by diffusion-ordered spectroscopy (DOSY) on a benchtop NMR equipped with diffusion gradient coils. The hydrodynamic radii of the dendrons are calculated via the Stokes–Einstein equation. The effects of solvent and pH are determined with the hydrodynamic radius increasing with generation and decreasing upon neutralization of an acidic solution. These measurements provide valuable information for biological and pharmaceutical applications of dendrons.     

5-amino-2-methylpyridinium hydrogen fumarate: An XRD and NMR crystallography analysis

Single-crystal X-ray diffraction structures of the 5-amino-2-methylpyridinium hydrogen fumarate salt have been solved at 150 and 300 K (CCDC 1952142 and 1952143). A base–acid–base–acid ring is formed through pyridinium-carboxylate and amine-carboxylate hydrogen bonds that hold together chains formed from hydrogen-bonded hydrogen fumarate ions. ¹H and ¹³C chemical shifts as well as ¹⁴N shifts that additionally depend on the quadrupolar interaction are determined by experimental magic angle spinning (MAS) solid-state nuclear magnetic resonance (NMR) and gauge-including projector-augmented wave (GIPAW) calculation. Two-dimensional homonuclear ¹H-¹H double-quantum (DQ) MAS and heteronuclear ¹H-¹³C and ¹⁴N-¹H spectra are presented. Only small differences of up to 0.1 and 0.6 ppm for ¹H and ¹³C are observed between GIPAW calculations starting with the two structures solved at 150 and 300 K (after geometry optimisation of atomic positions, but not unit cell parameters). A comparison of GIPAW-calculated ¹H chemical shifts for isolated molecules and the full crystal structures is indicative of hydrogen bonding strength.