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Applications of NMR Spectroscopy to Problem Solving for Inorganic, Organometallic, and Organic Compounds

A special issue of Molecules (ISSN 1420-3049).

Deadline for manuscript submissions: 30 September 2024 | Viewed by 4799

Special Issue Editor

Dr. Paride Papadia

E-Mail Website
Guest Editor
Dipartimento di Scienze e Tecnologie Biologiche e Ambientali, Università del Salento, Via Monteroni, 73100 Lecce, Italy
Interests: NMR spectroscopy; platinum compounds; metals and metalloids in the environment; metabolomics; platinum drugs delivery

Special Issue Information

Dear Colleagues,

Since the first paradigm-changing 1H NMR spectrum of ethanol published in 1951, NMR spectroscopy has rightfully become a contender for the title of best method for the structural determination of molecules in condensed matter.

Every further advancement, such as bidimensional and multidimensional spectroscopy, high field cryomagnets, pulsed field gradients, solid state cross polarization experiments, improvements in computer technology related both to speed and to software development, and variable temperature experiments, has expanded the scope of application of NMR spectroscopy as a mature structure determination method and simultaneously allowed researchers to probe the dynamic nature of the molecules.

The goal of this Special Issue is to provide, in the form of both original papers and reviews, an overview of practical strategies to solve structural, dynamic, kinetic, and mixture analysis problems in inorganic, organometallic, and organic chemistry via the creative and synergic application of multiple tools provided by the full NMR toolbox.

Dr. Paride Papadia
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • NMR spectroscopy
  • metabolomics
  • structure determination
  • biomolecular NMR
  • solid state NMR
  • conformational analysis
  • molecular diffusion
  • low field NMR spectroscopy

Published Papers (5 papers)

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Research

14 pages, 3297 KiB  
Article
Diffusion Nuclear Magnetic Resonance Measurements on Cationic Gold (I) Complexes in Catalytic Conditions: Counterion and Solvent Effects
by Filippo Campagnolo, Eleonora Aneggi, Walter Baratta, Talha Munir and Daniele Zuccaccia
Molecules 2024, 29(13), 3018; https://doi.org/10.3390/molecules29133018 - 26 Jun 2024
Viewed by 707
Abstract
The amount of free ions, ion pairs, and higher aggregate of the possible species present in a solution during the gold(I)-catalyzed alkoxylation of unsaturated hydrocarbon, i.e., ISIP (inner sphere ion pair) [(NHC)AuX] and OSIP (outer sphere ion pairs) [(NHC)Au(TME)X] [NHC 1,3-bis(2,6-di-isopropylphenyl)-imidazol-2-ylidene; TME = [...] Read more.
The amount of free ions, ion pairs, and higher aggregate of the possible species present in a solution during the gold(I)-catalyzed alkoxylation of unsaturated hydrocarbon, i.e., ISIP (inner sphere ion pair) [(NHC)AuX] and OSIP (outer sphere ion pairs) [(NHC)Au(TME)X] [NHC 1,3-bis(2,6-di-isopropylphenyl)-imidazol-2-ylidene; TME = tetramethylethylene (2,3-bis methyl-butene); X− = Cl−, BF4−, OTf−; and OTs− BArF4− (ArF = 3,5-(CF3)2C6H3)], has been determined. The 1H and 19F DOSY NMR measurements conducted in catalytic conditions indicate that the dissociation degree (α) of the equilibrium ion pair/free ions {[(NHC)Au(TME)X] [(NHC)Au(TME)]+ + X−} depends on the nature of the counterion (X−) when chloroform is the catalytic solvent: while the compounds containing OTs− and OTf− as the counterion gave a low α (which means a high number of ion pairs) of 0.13 and 0.24, respectively, the compounds containing BF4− and BArF4− showed higher α values of 0.36 and 0.32, respectively. These results experimentally confirm previous deductions based on catalytic and theoretical data: the lower the α value, the greater the catalytic activity because the anion that can activate methanol during a nucleophilic attack, although the lower propensity to activate methanol of BF4− and BArF4−, as suggested by the DFT calculations, cannot be completely overlooked. As for the effect of the solvent, α increases as the dielectric constant increases, as expected, and in particular, green solvents with high dielectric constants show a very high α (0.90, 0.84, 0.80, and 0.70 for propylene carbonate, γ-valerolactone, acetone, and methanol, respectively), thus confirming that the moderately high activity of NHC-Au-OTf in these solvents is due to the specific effect of polar functionalities (O-H, C=O, O-R) in activating methanol. Finally, the DOSY measurements conducted in p-Cymene show the formation of quadrupole species: under these conditions, the anion can better exercise its ‘template’ and ‘activating’ roles, giving the highest TOF. Full article
(This article belongs to the Special Issue Applications of NMR Spectroscopy to Problem Solving for Inorganic, Organometallic, and Organic Compounds)
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13 pages, 3473 KiB  
Article
75As Nuclear Magnetic Resonance Spectroscopic Investigation of the Thioarsenate Speciation in Strongly Alkaline Sulfidic Leaching Solutions
by Erica Brendler, Karsten Meiner, Jörg Wagler, Alexandra Thiere, Alexandros Charitos and Michael Stelter
Molecules 2024, 29(12), 2848; https://doi.org/10.3390/molecules29122848 - 14 Jun 2024
Viewed by 401
Abstract
Copper ores and concentrates thereof feature an increasingly notable content of impurities such as arsenic and other hazardous elements. As an alternative to the state-of-the-art partial roasting process, arsenic could be removed by the alkaline sulfide leaching of the copper concentrates. In order [...] Read more.
Copper ores and concentrates thereof feature an increasingly notable content of impurities such as arsenic and other hazardous elements. As an alternative to the state-of-the-art partial roasting process, arsenic could be removed by the alkaline sulfide leaching of the copper concentrates. In order to optimize and understand the processes, knowledge of the speciation and oxidation states is essential. In addition to methods such as UV/Vis spectroscopy, chromatography and ICP/MS methods, 75As NMR spectroscopy may be useful for the differentiation and quantification of the various species. Although arsenate(V) has been characterized by 75As NMR some time ago, to our knowledge, there are no data on tetrathioarsenate(V) AsS43− and the mixed oxygen/sulfur substituted mono-, di- and trithioarsenates(V) AsOxS4−x3−, x = 3, 2, 1, respectively. Therefore, we investigated several model solutions and samples from Cu-As leaching with 75As NMR. The strongly alkaline conditions of the leaching solution proved to be very advantageous for that purpose. Both the tetrathioarsenate(V) and the mixed species AsOxS4−x3− (x = 1–3) could be characterized and provide valuable data for the quantification of the material flows in the leaching process. Full article
(This article belongs to the Special Issue Applications of NMR Spectroscopy to Problem Solving for Inorganic, Organometallic, and Organic Compounds)
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17 pages, 3608 KiB  
Article
Isohexide-Based Tunable Chiral Platforms as Amide- and Thiourea-Chiral Solvating Agents for the NMR Enantiodiscrimination of Derivatized Amino Acids
by Federica Cefalì, Anna Iuliano, Federica Balzano, Gloria Uccello Barretta, Valerio Zullo and Carlo Baldassari
Molecules 2024, 29(6), 1307; https://doi.org/10.3390/molecules29061307 - 15 Mar 2024
Cited by 1 | Viewed by 840
Abstract
New arylamide- and arylthiourea-based chiral solvating agents (CSAs) were synthesized starting from commercially available isomannide and isosorbide. The two natural isohexides were transformed into the three amino derivatives, having isomannide, isosorbide, and isoidide stereochemistry, then the amino groups were derivatized with 3,5-dimethoxybenzoyl chloride [...] Read more.
New arylamide- and arylthiourea-based chiral solvating agents (CSAs) were synthesized starting from commercially available isomannide and isosorbide. The two natural isohexides were transformed into the three amino derivatives, having isomannide, isosorbide, and isoidide stereochemistry, then the amino groups were derivatized with 3,5-dimethoxybenzoyl chloride or 3,5-bis(trifluoromethyl)phenyl isothiocyanate to obtain the CSAs. Bis-thiourea derivative containing the 3,5-bis(trifluoromethyl)phenyl moiety with exo–exo stereochemistry was remarkably efficient in the differentiation of NMR signals (NH and acetyl) of enantiomers of N-acetyl (N-Ac) amino acids in the presence of 1,4-diazabicyclo[2,2,2]octane (DABCO). Nonequivalences in the ranges of 0.104–0.343 ppm and 0.042–0.107 ppm for NH and acetyl groups, respectively, allowed for very accurate enantiomeric excess determination, and a reliable correlation was found between the relative positions of signals of enantiomers and their absolute configuration. Therefore, a complete stereochemical characterization could be performed. Dipolar interactions detected in the ternary mixture CSA/N-Ac-valine/DABCO led to the identification of a different interaction model for the two enantiomers, involving the formation of a one-to-one substrate/CSA complex for (S)-N-Ac-valine and a one-to-two complex for (R)-N-Ac-valine, as suggested by the complexation stoichiometry. Full article
(This article belongs to the Special Issue Applications of NMR Spectroscopy to Problem Solving for Inorganic, Organometallic, and Organic Compounds)
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14 pages, 1835 KiB  
Article
Multitasking Pharmacophores Support Cabotegravir-Based Long-Acting HIV Pre-Exposure Prophylaxis (PrEP)
by Zheng Wan, Man Shi, Yanqing Gong, Massimo Lucci, Jinjin Li, Jiahai Zhou, Xiao-Liang Yang, Moreno Lelli, Xiao He and Jiafei Mao
Molecules 2024, 29(2), 376; https://doi.org/10.3390/molecules29020376 - 11 Jan 2024
Viewed by 1196
Abstract
Cabotegravir is an integrase strand transfer inhibitor (INSTI) for HIV treatment and prevention. Cabotegravir-based long-acting pre-exposure prophylaxis (PrEP) presents an emerging paradigm for infectious disease control. In this scheme, a combination of a high efficacy and low solubility of anti-infection drugs permits the [...] Read more.
Cabotegravir is an integrase strand transfer inhibitor (INSTI) for HIV treatment and prevention. Cabotegravir-based long-acting pre-exposure prophylaxis (PrEP) presents an emerging paradigm for infectious disease control. In this scheme, a combination of a high efficacy and low solubility of anti-infection drugs permits the establishment of a pharmaceutical firewall in HIV-vulnerable groups over a long period. Although the structure-activity-relationship (SAR) of cabotegravir as an INSTI is known, the structural determinants of its low solubility have not been identified. In this work, we have integrated multiple experimental and computational methods, namely X-ray diffraction, solid-state NMR (SSNMR) spectroscopy, solution NMR spectroscopy, automated fragmentation (AF)-QM/MM and density functional theory (DFT) calculations, to address this question. The molecular organization of cabotegravir in crystal lattice has been determined. The combination of very-fast magic-angle-sample-spinning (VF MAS) SSNMR and solution NMR, as supported by AF-QM/MM and DFT calculations, permits the identification of structural factors that contribute to the low aqueous solubility of cabotegravir. Our study reveals the multitasking nature of pharmacophores in cabotegravir, which controls the drug solubility and, meanwhile, the biological activity. By unraveling these function-defining molecular features, our work could inspire further development of long-acting HIV PrEP drugs. Full article
(This article belongs to the Special Issue Applications of NMR Spectroscopy to Problem Solving for Inorganic, Organometallic, and Organic Compounds)
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17 pages, 4683 KiB  
Article
NMR-Verified Dearomatization of 5,7-Substituted Pyrazolo[1,5-a]pyrimidines
by Daria Novikova, Ammar Al Mustafa, Tatyana Grigoreva, Svetlana Vorona, Stanislav Selivanov and Vyacheslav Tribulovich
Molecules 2023, 28(18), 6584; https://doi.org/10.3390/molecules28186584 - 12 Sep 2023
Cited by 1 | Viewed by 1138
Abstract
Tetrahydropyrazolo[1,5-a]pyrimidine (THPP) is an attractive scaffold for designing biologically active compounds. The most obvious way to obtain such compounds is to reduce pyrazolopyrimidines with complex hydrides, because the pyrimidine ring is reduced in the preference over the pyrazole ring. The presence of substituents [...] Read more.
Tetrahydropyrazolo[1,5-a]pyrimidine (THPP) is an attractive scaffold for designing biologically active compounds. The most obvious way to obtain such compounds is to reduce pyrazolopyrimidines with complex hydrides, because the pyrimidine ring is reduced in the preference over the pyrazole ring. The presence of substituents at positions five and seven of pyrazolo[1,5-a]pyrimidines complicates the set of reaction products but makes it more attractive for medicinal chemistry because four possible stereoisomers can be formed during reduction. However, the formation of only syn-isomers has been described in the literature. This article is the first report on the formation of anti-configured isomers along with syn-isomers in the reduction of model 5,7-dimethylpyrazolo[1,5-a]pyrimidine, which was confirmed by NMR. The bicyclic core in the syn-configuration was shown to be conformationally stable, which was used to estimate the long-range interproton distances using NOESY data. At the same time, long-range dipole–dipole interactions corresponding to a distance between protons of more than 6 Å were first registered and quantified. In turn, the bicyclic core in the trans-configuration represents a conformationally labile system. For these structures, an analysis of conformations observed in solutions was carried out. Our results indicate the significant potential of trans-configured tetrahydropyrazolo[1,5-a]pyrimidines for the development of active small molecules. While possessing structural lability due to the low energy of the conformational transition, they have the ability to adjust to the active site of the desired target. Full article
(This article belongs to the Special Issue Applications of NMR Spectroscopy to Problem Solving for Inorganic, Organometallic, and Organic Compounds)
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