HRMAS (high-resolution magic angle spinning) nuclear magnetic resonance (NMR) spectroscopy of low-density polyethylene (LDPE) affords 1H and 13C NMR spectra with superior resolution. For acquiring HRMAS NMR spectra, the polymer is first swollen with representative organic solvents. Then, the samples are measured with a conventional solid-state NMR spectrometer in the wideline mode or at the low spinning speed of 2 kHz. Anisotropic interactions like CSA (chemical shift anisotropy) and dipolar interactions are reduced due to the additional mobility of the polymer chains in the presence of the solvent within the polymer network. The combined effect of this mobility and MAS leads to signals with substantially reduced halfwidths as compared to classic MAS of the dry polymer. With HRMAS, all signals of the polymer become visible, and the spectra can be used for a quick and easy assessment of the polymer swelling behavior in diverse solvents. Being able to characterize polymers on the molecular level, and identifying the solvents that penetrate the polymer network best, enables the study of post-synthesis modifications of the polymers. It is demonstrated by paramagnetic HRMAS that the metallocene nickelocene (Cp2Ni) penetrates the LDPE network along with the solvent and is homogeneously dispersed in the polymer. SEM images prove that the structure of the polymer is not altered by the presence of a solvent and Cp2Ni. The impact of the paramagnetic Cp2Ni on the 1H signal halfwidth and T1 time of LDPE is studied. HRMAS allows a quick assessment of metal complexes regarding their ability to penetrate the LDPE network and therefore supports future studies of catalytic polymer degradation.
{"title":"HRMAS NMR for Studying Solvent-Induced Mobility of Polymer Chains and Metallocene Migration Into Low-Density Polyethylene (LDPE).","authors":"John C Hoefler, Maxwell R Kimball, Janet Blümel","doi":"10.1002/mrc.5484","DOIUrl":"https://doi.org/10.1002/mrc.5484","url":null,"abstract":"<p><p>HRMAS (high-resolution magic angle spinning) nuclear magnetic resonance (NMR) spectroscopy of low-density polyethylene (LDPE) affords <sup>1</sup>H and <sup>13</sup>C NMR spectra with superior resolution. For acquiring HRMAS NMR spectra, the polymer is first swollen with representative organic solvents. Then, the samples are measured with a conventional solid-state NMR spectrometer in the wideline mode or at the low spinning speed of 2 kHz. Anisotropic interactions like CSA (chemical shift anisotropy) and dipolar interactions are reduced due to the additional mobility of the polymer chains in the presence of the solvent within the polymer network. The combined effect of this mobility and MAS leads to signals with substantially reduced halfwidths as compared to classic MAS of the dry polymer. With HRMAS, all signals of the polymer become visible, and the spectra can be used for a quick and easy assessment of the polymer swelling behavior in diverse solvents. Being able to characterize polymers on the molecular level, and identifying the solvents that penetrate the polymer network best, enables the study of post-synthesis modifications of the polymers. It is demonstrated by paramagnetic HRMAS that the metallocene nickelocene (Cp<sub>2</sub>Ni) penetrates the LDPE network along with the solvent and is homogeneously dispersed in the polymer. SEM images prove that the structure of the polymer is not altered by the presence of a solvent and Cp<sub>2</sub>Ni. The impact of the paramagnetic Cp<sub>2</sub>Ni on the <sup>1</sup>H signal halfwidth and T<sub>1</sub> time of LDPE is studied. HRMAS allows a quick assessment of metal complexes regarding their ability to penetrate the LDPE network and therefore supports future studies of catalytic polymer degradation.</p>","PeriodicalId":18142,"journal":{"name":"Magnetic Resonance in Chemistry","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2024-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142591104","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jiachen Liu, Qingjiang Xu, Xin Wang, Ronghua Pan, Lizhong Zheng, Yonghong Zhang, Xiaoya Shang, Nan Wang
One new monacolin analog, monacolin V (1), together with two new monacolin-like natural products, 6-hydroxyl monacolin P (2) and 3-keto monacolin S (3), were isolated from the ethyl acetate portion of red yeast rice ethanol extract. Their structures were identified by HRESIMS and NMR experiments, and the complete assignments of 1H and 13C NMR data for three compounds were obtained by the aid of HSQC, HMBC, 1H-1H COSY, and NOESY data. This is the first time that the NMR data of compounds 2 and 3 have been fully assigned.
{"title":"Structural Elucidation and Complete NMR Spectral Assignments of Monascus Monacolin Analogs.","authors":"Jiachen Liu, Qingjiang Xu, Xin Wang, Ronghua Pan, Lizhong Zheng, Yonghong Zhang, Xiaoya Shang, Nan Wang","doi":"10.1002/mrc.5489","DOIUrl":"https://doi.org/10.1002/mrc.5489","url":null,"abstract":"<p><p>One new monacolin analog, monacolin V (1), together with two new monacolin-like natural products, 6-hydroxyl monacolin P (2) and 3-keto monacolin S (3), were isolated from the ethyl acetate portion of red yeast rice ethanol extract. Their structures were identified by HRESIMS and NMR experiments, and the complete assignments of <sup>1</sup>H and <sup>13</sup>C NMR data for three compounds were obtained by the aid of HSQC, HMBC, <sup>1</sup>H-<sup>1</sup>H COSY, and NOESY data. This is the first time that the NMR data of compounds 2 and 3 have been fully assigned.</p>","PeriodicalId":18142,"journal":{"name":"Magnetic Resonance in Chemistry","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2024-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142583169","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Franciane G Dos Santos, Daiane S Carvalho, Fernando Hallwass, Armando Navarro-Vázquez
A chemically cross-linked version of polystyrene is presented here that allows the preparation of reversibly mechanically compressible gels as NMR weakly aligning media. The gels can be successfully swollen in aromatic solvents such as toluene-d8 and pyridine-d5, as well as in CDCl3, and provided accurate measurements of 1DCH RDCs and 13C-RCSAs.
{"title":"Reversibly Compressible Cross-Linked Polystyrene Gels, Compatible With Toluene-d<sub>8</sub> and Pyridine-d<sub>5</sub>, for Measurement of Residual Dipolar Couplings and Residual Chemical Shift Anisotropies.","authors":"Franciane G Dos Santos, Daiane S Carvalho, Fernando Hallwass, Armando Navarro-Vázquez","doi":"10.1002/mrc.5494","DOIUrl":"https://doi.org/10.1002/mrc.5494","url":null,"abstract":"<p><p>A chemically cross-linked version of polystyrene is presented here that allows the preparation of reversibly mechanically compressible gels as NMR weakly aligning media. The gels can be successfully swollen in aromatic solvents such as toluene-d<sub>8</sub> and pyridine-d<sub>5</sub>, as well as in CDCl<sub>3</sub>, and provided accurate measurements of <sup>1</sup>D<sub>CH</sub> RDCs and <sup>13</sup>C-RCSAs.</p>","PeriodicalId":18142,"journal":{"name":"Magnetic Resonance in Chemistry","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2024-11-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142576370","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Carlos Cobas, José Antonio García-Pulido, Paula Mora, Giovanni Selva, Stan Sykora
In this work, we introduce a novel NMR apodization function designed to enhance spectral resolution while maintaining compatibility with qNMR standards. This function is based on a modified Savitzky-Golay filter, adapted for time-domain application. It effectively suppresses the negative components typically associated with derivative spectra, while also ensuring the preservation of quantitative integrity in NMR analyses.
{"title":"A New qNMR Compliant Savitzky-Golay Apodization Function for Resolution Enhancement.","authors":"Carlos Cobas, José Antonio García-Pulido, Paula Mora, Giovanni Selva, Stan Sykora","doi":"10.1002/mrc.5492","DOIUrl":"https://doi.org/10.1002/mrc.5492","url":null,"abstract":"<p><p>In this work, we introduce a novel NMR apodization function designed to enhance spectral resolution while maintaining compatibility with qNMR standards. This function is based on a modified Savitzky-Golay filter, adapted for time-domain application. It effectively suppresses the negative components typically associated with derivative spectra, while also ensuring the preservation of quantitative integrity in NMR analyses.</p>","PeriodicalId":18142,"journal":{"name":"Magnetic Resonance in Chemistry","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2024-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142568528","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Marie Bernardi, Rodrigo de Oliveira Silva, Quoc Lam Vuong, Dimitrios Sakellariou, Yves Gossuin
The removal of heavy metal ions from wastewater often necessitates the use of ion exchange resins. Current methods for assessing ion exchange efficiency are indirect and destructive. Some heavy metal ions, such as Cu2+ and Ni2+, are paramagnetic and influence the NMR relaxation times of water protons. NMR relaxometry can therefore be utilized to track the removal of these ions by ion exchange resins. In this study, we use relaxometry to monitor in situ the loading with Ni2+ and Cu2+ of Amberlite IR120 and Dowex Marathon MSC resins, with the resin column inserted into a low-field NMR device. The multiexponential transverse relaxation curves were fitted using a biexponential model. Before and during the loading of the resin, the water with the slowest relaxation corresponds to treated water (free of Ni2+ or Cu2+) flowing between the resin beads. After saturation, the slowest fraction corresponds to the untreated solution (containing Ni2+ or Cu2+) flowing between the resin beads saturated with paramagnetic ions. The evolution with time of the transverse relaxation rate and the amplitude of the slowly relaxing water fraction shows a clear transition, occurring later at the bottom of the resin bed compared with the middle and top. This is interpreted as an indication of the saturation of the studied zone with paramagnetic ions, confirmed by the quantification of Ni2+ or Cu2+ in the effluent using AES spectroscopy. This proof-of-concept study demonstrates that NMR relaxometry can be used in situ to monitor the loading of a resin bed with paramagnetic ions.
{"title":"NMR Relaxometry to Monitor In Situ the Loading of Amberlite IR120 and Dowex Marathon MSC Resins With Ni<sup>2+</sup> and Cu<sup>2+</sup> During a Column Experiment.","authors":"Marie Bernardi, Rodrigo de Oliveira Silva, Quoc Lam Vuong, Dimitrios Sakellariou, Yves Gossuin","doi":"10.1002/mrc.5490","DOIUrl":"https://doi.org/10.1002/mrc.5490","url":null,"abstract":"<p><p>The removal of heavy metal ions from wastewater often necessitates the use of ion exchange resins. Current methods for assessing ion exchange efficiency are indirect and destructive. Some heavy metal ions, such as Cu<sup>2+</sup> and Ni<sup>2+</sup>, are paramagnetic and influence the NMR relaxation times of water protons. NMR relaxometry can therefore be utilized to track the removal of these ions by ion exchange resins. In this study, we use relaxometry to monitor in situ the loading with Ni<sup>2+</sup> and Cu<sup>2+</sup> of Amberlite IR120 and Dowex Marathon MSC resins, with the resin column inserted into a low-field NMR device. The multiexponential transverse relaxation curves were fitted using a biexponential model. Before and during the loading of the resin, the water with the slowest relaxation corresponds to treated water (free of Ni<sup>2+</sup> or Cu<sup>2+</sup>) flowing between the resin beads. After saturation, the slowest fraction corresponds to the untreated solution (containing Ni<sup>2+</sup> or Cu<sup>2+</sup>) flowing between the resin beads saturated with paramagnetic ions. The evolution with time of the transverse relaxation rate and the amplitude of the slowly relaxing water fraction shows a clear transition, occurring later at the bottom of the resin bed compared with the middle and top. This is interpreted as an indication of the saturation of the studied zone with paramagnetic ions, confirmed by the quantification of Ni<sup>2+</sup> or Cu<sup>2+</sup> in the effluent using AES spectroscopy. This proof-of-concept study demonstrates that NMR relaxometry can be used in situ to monitor the loading of a resin bed with paramagnetic ions.</p>","PeriodicalId":18142,"journal":{"name":"Magnetic Resonance in Chemistry","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2024-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142546278","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Milagros Amichetti, Bruno A Franco, María Marta Zanardi, Ariel M Sarotti
The application of quantum-based NMR methods for the structural elucidation of natural and unnatural products has grown significantly. However, accurately calculating the conformational landscape of flexible molecules with intricate intramolecular hydrogen bonding (IHB) networks continues to be a major challenge. In this work, we thoroughly studied the effect of entropic contributions (trough Gibbs free energies calculations) in the DP4+ performance. Our results show that to solve biased systems with strong IHB interactions requires computing the Boltzmann contributions using Gibbs free energies computed with at least triple-ξ basis set and SMD solvation model. In response to this finding, we have updated our DP4+App, a user-friendly Python applet that automates the entire process of calculating DP4+ probabilities. In the new version, the program allows for calculating of conformational contributions at any selected theory level, using either SCF or Gibbs free energies.
{"title":"To Gibbs or Not to Gibbs Effect of Entropic Contribution in the NMR Calculations of Flexible and Polar Molecules-Updating the DP4+App.","authors":"Milagros Amichetti, Bruno A Franco, María Marta Zanardi, Ariel M Sarotti","doi":"10.1002/mrc.5491","DOIUrl":"https://doi.org/10.1002/mrc.5491","url":null,"abstract":"<p><p>The application of quantum-based NMR methods for the structural elucidation of natural and unnatural products has grown significantly. However, accurately calculating the conformational landscape of flexible molecules with intricate intramolecular hydrogen bonding (IHB) networks continues to be a major challenge. In this work, we thoroughly studied the effect of entropic contributions (trough Gibbs free energies calculations) in the DP4+ performance. Our results show that to solve biased systems with strong IHB interactions requires computing the Boltzmann contributions using Gibbs free energies computed with at least triple-ξ basis set and SMD solvation model. In response to this finding, we have updated our DP4+App, a user-friendly Python applet that automates the entire process of calculating DP4+ probabilities. In the new version, the program allows for calculating of conformational contributions at any selected theory level, using either SCF or Gibbs free energies.</p>","PeriodicalId":18142,"journal":{"name":"Magnetic Resonance in Chemistry","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2024-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142546279","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Dillip K Senapati, Jayasubba Reddy Yarava, K V Ramanathan, S Raghothama
Glutathione (GSH) and its oxidized dimer (GSSG) play an important role in living systems as an antioxidant, balancing the presence of reactive oxygen species (ROS). The central thiol (-S-S-) bond in GSSG can undergo free rotation, providing multiple conformations with respect to the S-S bridge. The six titratable sites of GSSG, which are influenced by pH variations, affect these conformations in solution, whereas in solids, additionally crystal packing effects come into play. In view of differing reports about the structure of GSSG in literature, we have here conducted an extensive reexamination of its conformations using NMR, and contrasting results have been obtained for solution and solid state. In solution, the existence of more than one antiparallel orientation of the monomer unit with different hydrogen bonding schemes has been indicated by NOE and amide temperature coefficient results. On the other hand, in the solid-state, a 1H-1H double-quantum (DQ) to 13C single-quantum (SQ) correlation study has confirmed a parallel orientation, consistent with the reported X-ray crystal structure. Experimentally assigned solid-state NMR resonances have been validated using GIPAW calculations incorporated in the Quantum ESPRESSO package.
{"title":"Deciphering the Conformations of Glutathione Oxidized Peptide: A Comparative NMR Study in Solution and Solid-State Environments.","authors":"Dillip K Senapati, Jayasubba Reddy Yarava, K V Ramanathan, S Raghothama","doi":"10.1002/mrc.5486","DOIUrl":"https://doi.org/10.1002/mrc.5486","url":null,"abstract":"<p><p>Glutathione (GSH) and its oxidized dimer (GSSG) play an important role in living systems as an antioxidant, balancing the presence of reactive oxygen species (ROS). The central thiol (-S-S-) bond in GSSG can undergo free rotation, providing multiple conformations with respect to the S-S bridge. The six titratable sites of GSSG, which are influenced by pH variations, affect these conformations in solution, whereas in solids, additionally crystal packing effects come into play. In view of differing reports about the structure of GSSG in literature, we have here conducted an extensive reexamination of its conformations using NMR, and contrasting results have been obtained for solution and solid state. In solution, the existence of more than one antiparallel orientation of the monomer unit with different hydrogen bonding schemes has been indicated by NOE and amide temperature coefficient results. On the other hand, in the solid-state, a <sup>1</sup>H-<sup>1</sup>H double-quantum (DQ) to <sup>13</sup>C single-quantum (SQ) correlation study has confirmed a parallel orientation, consistent with the reported X-ray crystal structure. Experimentally assigned solid-state NMR resonances have been validated using GIPAW calculations incorporated in the Quantum ESPRESSO package.</p>","PeriodicalId":18142,"journal":{"name":"Magnetic Resonance in Chemistry","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2024-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142469117","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Malak Dia, Jonathan Farjon, Clotilde Raveleau, André Simpson, Pierre-Emmanuel Peyneau, Béatrice Béchet, Denis Courtier-Murias
The interaction between humic acid (HA) and engineered nanoparticles (NPs) is critical in environmental sciences, especially for understanding the behavior of NPs in natural waters. This study employs 1H 2D Multi-Exponential Transverse Relaxation (METR) NMR spectroscopy to examine the molecular-level interactions between Pahokee Peat humic acid (HA) and carboxyl-functionalized iron oxide nanoparticles (NPCOs). First, 1H 2D METR NMR spectroscopy allowed not only the identification of HA in terms of its chemical composition but also the separation of molecules with the same chemical shift values but different rates of molecular tumbling. Then, using solutions with varying NPCO concentrations (0, 10, 40, and 100 μM), we observed significant changes in the T2 relaxation times of HA components, indicating interactions between HA and NPCO. Analysis showed the biggest effect on two chemical shift regions, corresponding to lipids and carbohydrates, revealing that smaller molecules within these regions exhibit the most significant changes in T2 values upon the addition of NPCO. This suggests that these molecules are the initial sites of interaction, with the entire HA system being affected at higher NPCO concentrations. These findings highlight the utility of METR NMR spectroscopy in studying complex environmental mixtures and provide insights into the behavior of HA and NPs, essential for understanding the fate of NPs in the environment.
腐植酸(HA)与工程纳米粒子(NPs)之间的相互作用在环境科学中至关重要,特别是对于了解天然水体中 NPs 的行为。本研究采用 1H 2D 多指数横向弛豫(METR)核磁共振波谱来研究帕霍基泥炭腐植酸(HA)与羧基功能化氧化铁纳米粒子(NPCOs)之间的分子级相互作用。首先,通过 1H 2D METR NMR 光谱不仅可以识别 HA 的化学成分,还可以分离出化学位移值相同但分子翻滚速率不同的分子。然后,使用不同浓度的 NPCO 溶液(0、10、40 和 100 μM),我们观察到 HA 成分的 T2 弛豫时间发生了显著变化,这表明 HA 与 NPCO 之间存在相互作用。分析表明,与脂质和碳水化合物相对应的两个化学位移区域受到的影响最大,这表明在添加 NPCO 后,这些区域中的小分子在 T2 值上表现出最显著的变化。这表明这些分子是相互作用的初始位点,当 NPCO 浓度较高时,整个 HA 系统都会受到影响。这些发现凸显了 METR NMR 光谱在研究复杂环境混合物方面的实用性,并提供了有关 HA 和 NPs 行为的见解,这对了解 NPs 在环境中的归宿至关重要。
{"title":"Understanding the Interactions of Nanoparticles and Dissolved Organic Matter at the Molecular Level by <sup>1</sup>H 2D Multi-Exponential Transverse Relaxation NMR Spectroscopy.","authors":"Malak Dia, Jonathan Farjon, Clotilde Raveleau, André Simpson, Pierre-Emmanuel Peyneau, Béatrice Béchet, Denis Courtier-Murias","doi":"10.1002/mrc.5487","DOIUrl":"https://doi.org/10.1002/mrc.5487","url":null,"abstract":"<p><p>The interaction between humic acid (HA) and engineered nanoparticles (NPs) is critical in environmental sciences, especially for understanding the behavior of NPs in natural waters. This study employs <sup>1</sup>H 2D Multi-Exponential Transverse Relaxation (METR) NMR spectroscopy to examine the molecular-level interactions between Pahokee Peat humic acid (HA) and carboxyl-functionalized iron oxide nanoparticles (NPCOs). First, <sup>1</sup>H 2D METR NMR spectroscopy allowed not only the identification of HA in terms of its chemical composition but also the separation of molecules with the same chemical shift values but different rates of molecular tumbling. Then, using solutions with varying NPCO concentrations (0, 10, 40, and 100 μM), we observed significant changes in the T<sub>2</sub> relaxation times of HA components, indicating interactions between HA and NPCO. Analysis showed the biggest effect on two chemical shift regions, corresponding to lipids and carbohydrates, revealing that smaller molecules within these regions exhibit the most significant changes in T<sub>2</sub> values upon the addition of NPCO. This suggests that these molecules are the initial sites of interaction, with the entire HA system being affected at higher NPCO concentrations. These findings highlight the utility of METR NMR spectroscopy in studying complex environmental mixtures and provide insights into the behavior of HA and NPs, essential for understanding the fate of NPs in the environment.</p>","PeriodicalId":18142,"journal":{"name":"Magnetic Resonance in Chemistry","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2024-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142469121","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Emily F Griffiths, Jay A Dixon, Andrew J M Caffyn, Stuart K Langley, Beatriz Maciá, Vittorio Caprio, Ryan E Mewis
Brønsted acids, such as phosphoric acids derived from chiral 1,1'-bi-2-naphthol (BINOL), are important catalysts in the formation of carbon-carbon and carbon-heteroatom bonds, for example. The catalytic activity of these Brønsted acids is strongly linked to their acidity, and as such, the evaluation of compounds to determine pKa values provides insight into their catalytic activity. Herein, a 19F{1H} NMR methodology is detailed to determine the pKa of a fluorinated binaphthyl-derived phosphinic acid, rac-1, in acetonitrile and in the presence of a fluorinated sulfonamide reference compound (2-4). The approach was tested initially using 2 and 3, with the ΔpKa (0.08) in strong agreement with previously reported values (6.6 for 2 and 6.68/6.73 for 3). Sigmoidal curves of normalised chemical shift change (Δδ) against equivalents of the base phosphazene P1-tBu added overlapped for 2 and 3, but in the case of rac-1 and either 2, 3 or 4, there was significant separation. A variety of different approaches for determining the ΔpKa were compared. Values of pKa determined when the normalised Δδ was 90% were optimal for 2 and 3, whereas a normalised Δδ of 75% was optimal for 4, resulting in the pKa of rac-1 being determined to be 8.47-8.71.
{"title":"Determination of the pK<sub>a</sub> Value of a Brønsted Acid by <sup>19</sup>F NMR Spectroscopy.","authors":"Emily F Griffiths, Jay A Dixon, Andrew J M Caffyn, Stuart K Langley, Beatriz Maciá, Vittorio Caprio, Ryan E Mewis","doi":"10.1002/mrc.5485","DOIUrl":"https://doi.org/10.1002/mrc.5485","url":null,"abstract":"<p><p>Brønsted acids, such as phosphoric acids derived from chiral 1,1'-bi-2-naphthol (BINOL), are important catalysts in the formation of carbon-carbon and carbon-heteroatom bonds, for example. The catalytic activity of these Brønsted acids is strongly linked to their acidity, and as such, the evaluation of compounds to determine pK<sub>a</sub> values provides insight into their catalytic activity. Herein, a <sup>19</sup>F{<sup>1</sup>H} NMR methodology is detailed to determine the pK<sub>a</sub> of a fluorinated binaphthyl-derived phosphinic acid, rac-1, in acetonitrile and in the presence of a fluorinated sulfonamide reference compound (2-4). The approach was tested initially using 2 and 3, with the ΔpK<sub>a</sub> (0.08) in strong agreement with previously reported values (6.6 for 2 and 6.68/6.73 for 3). Sigmoidal curves of normalised chemical shift change (Δδ) against equivalents of the base phosphazene P<sub>1</sub>-<sup>t</sup>Bu added overlapped for 2 and 3, but in the case of rac-1 and either 2, 3 or 4, there was significant separation. A variety of different approaches for determining the ΔpK<sub>a</sub> were compared. Values of pK<sub>a</sub> determined when the normalised Δδ was 90% were optimal for 2 and 3, whereas a normalised Δδ of 75% was optimal for 4, resulting in the pK<sub>a</sub> of rac-1 being determined to be 8.47-8.71.</p>","PeriodicalId":18142,"journal":{"name":"Magnetic Resonance in Chemistry","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2024-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142469118","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Andreas H Franz, Kendall S Bromley, Ei T Aung, Stephen Q L Do, Hana M Rosenblatt, Amelia J Watson
The quantitative solution conformations of 2-(hydroxymethyl)-tetrahydropyran, α-methyl-d-mannopyranoside, and 6-[α-d-mannopyranosyl]-d-mannopyranose (mannobiose) are described. Parametrized Karplus equations for redundant spin pairs across the terminal ω-torsion and the glycosidic ω-torsion for mannobiose are developed, including ω/θ-hypersurfaces for the terminal hydroxymethylene group. Experimental NMR data, algorithmic spectral simulation (clustered Hamiltonian method), molecular dynamics (MD) simulations (GLYCAM06), energy minimizations by DFT, and adjusted torsion angle populations weighted over the Karplus-type equations are used. We demonstrate that spectral simulation is a powerful tool in the refinement of initial J values obtained from static GAIO DFT calculations. We also show that only as few as one of multiple redundant torsions can be diagnostic for conformational analysis of the disaccharide.
{"title":"NMR Coupling Constants, Karplus Equations, and Adjusted MD Statistics: Detecting Diagnostic Torsion Angles for the Solution Geometry of 6-[α-d-Mannopyranosyl]-d-Mannopyranose (Mannobiose).","authors":"Andreas H Franz, Kendall S Bromley, Ei T Aung, Stephen Q L Do, Hana M Rosenblatt, Amelia J Watson","doi":"10.1002/mrc.5483","DOIUrl":"https://doi.org/10.1002/mrc.5483","url":null,"abstract":"<p><p>The quantitative solution conformations of 2-(hydroxymethyl)-tetrahydropyran, α-methyl-d-mannopyranoside, and 6-[α-d-mannopyranosyl]-d-mannopyranose (mannobiose) are described. Parametrized Karplus equations for redundant spin pairs across the terminal ω-torsion and the glycosidic ω-torsion for mannobiose are developed, including ω/θ-hypersurfaces for the terminal hydroxymethylene group. Experimental NMR data, algorithmic spectral simulation (clustered Hamiltonian method), molecular dynamics (MD) simulations (GLYCAM06), energy minimizations by DFT, and adjusted torsion angle populations weighted over the Karplus-type equations are used. We demonstrate that spectral simulation is a powerful tool in the refinement of initial J values obtained from static GAIO DFT calculations. We also show that only as few as one of multiple redundant torsions can be diagnostic for conformational analysis of the disaccharide.</p>","PeriodicalId":18142,"journal":{"name":"Magnetic Resonance in Chemistry","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2024-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142469119","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}