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Zhao, Zhihong; Wang, Bin; Tan, Rui; Liu, Wenjing; Zhang, Minghui
doi: 10.1002/mrc.5247pmid: 34993993
In this study, the transverse relaxation time (T2) of activated carbon (AC) in different relative environment humidity was detected firstly by low‐field nuclear magnetic resonance (LFNMR). The pore size (diameter) of AC distributions was calculated by the relationship between T2 and surface relaxation rate (ρ), where ρ was obtained by the detection of nine porous materials with known pore size. The results showed that the pore size distributions of AC calculated by ρ < 0.19 nm/ms were in good agreement with that obtained by nitrogen adsorption method and proved that LFNMR as a new detection method was feasible for characterizing AC pore size distribution.
Martorano, Lucas H.; Brito, Jordana T.; Albuquerque, Ana Carolina F.; Ribeiro, Carlos Magno Rocha; Fiorot, Rodolfo Goetze; Carneiro, José Walkimar de Mesquita; Costa, Fabio Luiz Paranhos; Valverde, Alessandra L.; Santos Junior, Fernando Martins
doi: 10.1002/mrc.5230
Alkorta, Ibon; Benito, María Teresa; Elguero, José; Doyagüez, Elisa García; Patterson, Monika R.; Jimeno, María Luisa; Dias, H. V. Rasika; Reviriego, Felipe
doi: 10.1002/mrc.5242pmid: 34935188
A series of DOSY experiments have been carried out to determine the solution stoichiometry of silver(I) 3,5‐bis (trifluoromethyl)pyrazolate species. This compound exists as a trimer in the solid state (n = 3) but in solutions of chlorinated solvents, the DOSY data suggest the presence of a mixture of solvent stabilized monomer (n = 1) and dimer (n = 2) in equilibrium. Different approximations have been used including the Stokes–Einstein and the Stokes–Einstein–Gierer–Wirtz equations. Some methodological problems are discussed.
Rudszuck, Thomas; Schork, Nicolas; Nirschl, Hermann; Guthausen, Gisela
doi: 10.1002/mrc.5243pmid: 34961977
Lubricating greases were investigated by nuclear magnetic resonance/magnetic resonance imaging (NMR/MRI) to get insight into their structure and into their response to mechanical forces, which is related to bleeding and aging. The investigated greases are based on metallic soaps of fatty acids and oils, whereby LiOH is often used. These organic soaps act as thickeners and provide a network in which oils and their additives are embedded. Lubricating greases can thus be considered as a class of substances similar to oleogels or even hydrogels. Questions arise about translational mobility of guest molecules, mainly base oil, in these networks. Molecular structuring and interactions within the network of thickeners are of interest as they are related to macroscopic stability. Apart from NMR spectroscopy (1H‐, 7Li‐ and 31P‐NMR), spectrally resolved relaxation and diffusion measurements are used for characterization. In addition, magic angle spinning (MAS)‐NMR was combined with 1H‐MRI to investigate the impact of mechanical stress and swelling of lubricating greases.
Samultsev, Dmitry O.; Semenov, Valentin A.; Krivdin, Leonid B.
doi: 10.1002/mrc.5245pmid: 34978105
The nonrelativistic and four‐component fully relativistic calculations of 1H, 15N, 59Co, 103Rh, and 193Ir shielding constants of pentaammineaquacomplexes of cobalt(III), rhodium(III), and iridium(III) were carried out at the density functional theory (DFT) level of theory. The noticeable deshielding relativistic corrections were observed for nitrogen shielding constants (chemical shifts), whereas those corrections were found to be negligible for protons. For the transition metals cobalt, rhodium, and iridium, relativistic corrections to their nuclear magnetic resonance (NMR) shielding constants were found to be rather small for cobalt and rhodium (some 5–10%), whereas they are essentially larger for iridium (up to 70%).
Showing 1 to 7 of 7 Articles
Recently, structural elucidation of natural products has undergone a revolution. The combined use of different modern spectroscopic methods has allowed obtaining a complete structural assignment of natural products using small amounts of sample. However, despite the extraordinary ongoing advances in spectroscopy, the mischaracterization of natural products has been and remains a recurrent problem, especially when the substance presents several stereogenic centers. The misinterpretation of nuclear magnetic resonance (NMR) data has resulted in frequent reports addressing structural reassignment. In this context, a great effort has been devoted to developing quantum chemical calculations that simulate NMR parameters accurately, allowing to achieve a more precise spectral interpretation. In this work, we employed a protocol for theoretical calculations of 1H NMR chemical shifts and coupling constants using density functional theory (DFT), followed by the application of the DP4+ method to revisit the structure of Heliannuol L, a member of the Heliannuol class, isolated from Helianthus annuus. Our results indicate that the originally proposed structure of Heliannuol L needs a stereochemical reassignment, placing the hydroxyl bonded to C10 in the opposite side of the methyl and hydroxyl groups bonded to C7 and C8, respectively.