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Aebischer K, Ernst M. INEPT and CP transfer efficiencies of dynamic systems in MAS solid-state NMR. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2024; 359:107617. [PMID: 38244331 DOI: 10.1016/j.jmr.2024.107617] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/13/2023] [Revised: 01/09/2024] [Accepted: 01/10/2024] [Indexed: 01/22/2024]
Abstract
Hartmann-Hahn cross polarization and INEPT polarization transfer are the most popular sequences to increase the polarization of low-γ nuclei in magic-angle spinning solid-state NMR. It is well known that the two methods preferentially lead to polarization transfer in different parts of molecules. Cross polarization works best in rigid segments of the molecule while INEPT-based polarization transfer is efficient in highly mobile segments where (nearly) isotropic motion averages out the dipolar couplings. However, there have only been few attempts to define the time scales of motion that are compatible with cross polarization or INEPT transfer in a more quantitative way. We have used simple isotropic jump models in combination with simulations based on the stochastic Liouville equation to elucidate the time scales of motion that allow either cross polarization or INEPT-based polarization transfer. We investigate which motional time scales interfere with one or both polarization-transfer schemes. We have modeled isolated I-S two-spin systems, strongly-coupled I2S three-spin systems and more loosely coupled I-I-S three-spin systems as well as I3S groups. Such fragments can be used as models for typical environments in fully deuterated and back-exchanged molecules (I-S), for fully protonated molecules (I2S and I3S) or situations in between (I-I-S).
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Affiliation(s)
- Kathrin Aebischer
- Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 2, Zürich, 8093, Switzerland
| | - Matthias Ernst
- Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 2, Zürich, 8093, Switzerland.
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2
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Dwivedi N, Siddiqui MA, Srivastava S, Sinha N. 1 H- 13 C cross-polarization kinetics to probe hydration-dependent organic components of bone extracellular matrix. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2023; 61:397-406. [PMID: 36946081 DOI: 10.1002/mrc.5347] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2022] [Revised: 02/17/2023] [Accepted: 03/19/2023] [Indexed: 06/09/2023]
Abstract
Bone is a living tissue made up of organic proteins, inorganic minerals, and water. The organic component of bone (mainly made up of Type-I collagen) provides flexibility and tensile strength. Solid-state nuclear magnetic resonance (ssNMR) is one of the few techniques that can provide atomic-level structural insights of such biomaterials in their native state. In the present article, we employed the variable contact time cross-polarization (1 H-13 C CP) kinetics experiments to study the hydration-dependent atomic-level structural changes in the bone extracellular matrix (ECM). The natural abundant 13 C CP intensity of the bone ECM is measured by varying CP contact time and best fitted to the nonclassical kinetic model. Different relaxation parameters were measured by the best-fit equation corresponding to the different hydration conditions of the bone ECM. The associated changes in the measured parameters due to varying levels of hydration observed at different sites of collagen protein have provided its structural arrangements and interaction with water molecules in bone ECM. Overall, the present study reveals a better understanding of the kinetics of the organic part inside the bone ECM that will help in comprehending the disease-associated pathways.
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Affiliation(s)
- Navneet Dwivedi
- Centre of Biomedical Research, SGPGIMS Campus, Raebareli Road, Lucknow, 226014, India
- Department of Physics, Integral University, Lucknow, 226026, India
| | - Mohd Adnan Siddiqui
- Centre of Biomedical Research, SGPGIMS Campus, Raebareli Road, Lucknow, 226014, India
| | - Seema Srivastava
- Department of Physics, Integral University, Lucknow, 226026, India
| | - Neeraj Sinha
- Centre of Biomedical Research, SGPGIMS Campus, Raebareli Road, Lucknow, 226014, India
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Freitas JCC, Ejaz M, Toci AT, Romão W, Khimyak YZ. Solid-state NMR spectroscopy of roasted and ground coffee samples: Evidences for phase heterogeneity and prospects of applications in food screening. Food Chem 2023; 409:135317. [PMID: 36586269 DOI: 10.1016/j.foodchem.2022.135317] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2022] [Revised: 12/16/2022] [Accepted: 12/22/2022] [Indexed: 12/25/2022]
Abstract
The advancement in the use of spectroscopic techniques to investigate coffee samples is of high interest especially considering the widespread problems with coffee adulteration and counterfeiting. In this work, the use of solid-state nuclear magnetic resonance (NMR) is investigated as a means to probe the various chemically-distinct phases existent in roasted coffee samples and to detect the occurrence of counterfeiting or adulterations in coffee blends. Routine solid-state 1H and 13C NMR spectra allowed the distinction between different coffee types (Arabica/Robusta) and the evaluation of the presence of these components in coffee blends. On the other hand, the use of more specialized solid-state NMR experiments revealed the existence of phases with different molecular mobilities (e.g., associated with lipids or carbohydrates). The results illustrate the usefulness of solid-state NMR spectroscopy to examine molecular mobilities and interactions and to aid in the quality control of coffee-related products.
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Affiliation(s)
- Jair C C Freitas
- Laboratory of Carbon and Ceramic Materials, Department of Physics, Federal University of Espírito Santo (UFES), Av. Fernando Ferrari, 514, Vitória, Espírito Santo 29075-910, Brazil; School of Pharmacy, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, United Kingdom.
| | - Maryam Ejaz
- School of Pharmacy, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, United Kingdom
| | - Aline T Toci
- Environmental and Food Interdisciplinary Studies Laboratory (LEIMAA), Latin American Institute of Life and Nature Science, Federal University for Latin American Integration (UNILA), Foz do Iguaçu, Paraná 85867-970, Brazil
| | - Wanderson Romão
- Laboratory of Petroleomics and Forensics, Federal University of Espírito Santo (UFES), Av. Fernando Ferrari, 514, Vitória, Espírito Santo 29075-910, Brazil; Federal Institute of Espírito Santo (IFES), Av. Ministro Salgado Filho, Vila Velha, Espírito Santo 29106-010, Brazil
| | - Yaroslav Z Khimyak
- School of Pharmacy, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, United Kingdom.
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Influence of Interpenetrating Chains on Rigid Domain Dimensions in Siloxane-Based Block-Copolymers. Polymers (Basel) 2022; 14:polym14194048. [PMID: 36235995 PMCID: PMC9572696 DOI: 10.3390/polym14194048] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2022] [Revised: 09/20/2022] [Accepted: 09/23/2022] [Indexed: 11/18/2022] Open
Abstract
1H spin-diffusion solid-state NMR was utilized to elucidate the domain size in multiblock-copolymers (BCPs) poly-(block poly(dimethylsiloxane)-block ladder-like poly(phenylsiloxane)) and poly-(block poly((3,3′,3″-trifluoropropyl-methyl)siloxane)-block ladder-like poly(phenylsiloxane). It was found that these BCPs form worm-like morphology with rigid cylinders dispersed in amorphous matrix. By using the combination of solid-state NMR techniques such as 13C CP/MAS, 13C direct-polarization MAS and 2D 1H EXSY, it was shown that the main factor which governs the diameter value of these rigid domains is the presence of interpenetrating segments of soft blocks. The presence of such interpenetrating chains leads to an increase of rigid domain diameter.
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Widaningrum, Flanagan BM, Williams BA, Sonni F, Chen P, Mikkelsen D, Gidley MJ. In vitro fermentation profiles of undigested fractions from legume and nut particles are affected by particle cohesion and entrapped macronutrients. Food Funct 2022; 13:5075-5088. [PMID: 35411900 DOI: 10.1039/d2fo00250g] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Insoluble undigested food residues are the predominant dietary form of 'fibre' from food plants, with the potential for fermentation by microbial species resident within the large intestine. Here we present results on in vitro fermentation of undigested fractions of legumes (chickpea flour, lentil flour, mung bean flour), and nuts (peanut, almond, macadamia) using a pooled faecal inoculum from pigs fed a nut- and legume-free diet. All substrates were pre-digested in vitro. Nuts were also separated into two particle sizes (PS), cell cluster (CC = 710-1000 μm) and fine (F = 250-500 μm), to test the effect of PS. All substrates tested were fermented for 48 hours, and measured according to gas production, with lentil (within legume flours) being the highest gas producer, and peanut being the highest gas producer within nuts. Undigested fractions from Nuts_F had significantly higher gas production than those from Nuts_CC, consistent with differences in surface area between the two PS. Relative short chain fatty acid concentrations between samples as metabolite end-products were consistent with relative gas production. Analysis of unfermented residues after different fermentation times, showed that cellular integrity was a major factor controlling fermentation rates and that entrapped protein/starch (legumes) and lipid (nuts) all contributed to the fermentation outcomes.
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Affiliation(s)
- Widaningrum
- Centre for Nutrition and Food Sciences (CNAFS), Queensland Alliance for Agriculture and Food Innovation (QAAFI), The University of Queensland, St. Lucia, QLD 4072, Australia. .,Indonesian Center for Agricultural Postharvest Research and Development (ICAPRD), Bogor, Indonesia
| | - Bernadine M Flanagan
- Centre for Nutrition and Food Sciences (CNAFS), Queensland Alliance for Agriculture and Food Innovation (QAAFI), The University of Queensland, St. Lucia, QLD 4072, Australia.
| | - Barbara A Williams
- Centre for Nutrition and Food Sciences (CNAFS), Queensland Alliance for Agriculture and Food Innovation (QAAFI), The University of Queensland, St. Lucia, QLD 4072, Australia.
| | - Francesca Sonni
- Centre for Nutrition and Food Sciences (CNAFS), Queensland Alliance for Agriculture and Food Innovation (QAAFI), The University of Queensland, St. Lucia, QLD 4072, Australia.
| | - Pengfei Chen
- Centre for Nutrition and Food Sciences (CNAFS), Queensland Alliance for Agriculture and Food Innovation (QAAFI), The University of Queensland, St. Lucia, QLD 4072, Australia.
| | - Deirdre Mikkelsen
- Centre for Nutrition and Food Sciences (CNAFS), Queensland Alliance for Agriculture and Food Innovation (QAAFI), The University of Queensland, St. Lucia, QLD 4072, Australia. .,School of Agriculture and Food Sciences, The University of Queensland, St. Lucia, QLD 4072, Australia
| | - Michael J Gidley
- Centre for Nutrition and Food Sciences (CNAFS), Queensland Alliance for Agriculture and Food Innovation (QAAFI), The University of Queensland, St. Lucia, QLD 4072, Australia.
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Linear/Ladder-Like Polysiloxane Block Copolymers with Methyl-, Trifluoropropyl- and Phenyl- Siloxane Units for Surface Modification. Polymers (Basel) 2021; 13:polym13132063. [PMID: 34201838 PMCID: PMC8271457 DOI: 10.3390/polym13132063] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2021] [Revised: 06/20/2021] [Accepted: 06/21/2021] [Indexed: 11/17/2022] Open
Abstract
Multiblock copolymers containing linear polydimethylsiloxane or polymethyltrifluoropropylsiloxane and ladder-like polyphenylsiloxane were synthesized in a one-step pathway. The functional homopolymer blocks and final multiblock copolymers were characterized using solution and solid-state multinuclear 1H, 13C, 19F, and 29Si NMR spectroscopy. It was shown that the ladder-like block contains silanol units, which influence the adhesion properties of multiblock copolymers and morphology of their casted films. The adhesion to metals and mechanical properties of multiblock copolymers were tested. The SEM study of casted films of multiblock copolymers shows the variety of formed morphologies, including long-strip-like or globular.
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Interplay of Structural Factors in Formation of Microphase-Separated or Microphase-Mixed Structures of Polyurethanes Revealed by Solid-State NMR and Dielectric Spectroscopy. Polymers (Basel) 2021; 13:polym13121967. [PMID: 34198643 PMCID: PMC8232235 DOI: 10.3390/polym13121967] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2021] [Revised: 06/10/2021] [Accepted: 06/10/2021] [Indexed: 11/16/2022] Open
Abstract
A set of aromatic-oxyaliphatic polyurethanes (PUs) with different mass fractions of components also containing fluorinated fragments was synthesized and studied using various solid-state NMR techniques and dielectric spectroscopy. In contrast to the common model suggested by Cooper and Tobolsky in 1966, the rigid domains of microphase separated PUs are formed, not only by units containing urethane bonds, but also by oxyethylene fragments that form a common rigid phase. The urethane bonds and oxyethylene fragments are incorporated into both rigid and soft phases. Good agreement with the Cooper and Tobolsky model is observed only when solubility parameters are significantly different for the hard and soft segments, such as hydrocarbon aromatics and perfluoroaliphatic blocks.
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9
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Marques CS, Carvalho SG, Bertoli LD, Villanova JCO, Pinheiro PF, dos Santos DCM, Yoshida MI, de Freitas JCC, Cipriano DF, Bernardes PC. β-Cyclodextrin inclusion complexes with essential oils: Obtention, characterization, antimicrobial activity and potential application for food preservative sachets. Food Res Int 2019; 119:499-509. [DOI: 10.1016/j.foodres.2019.01.016] [Citation(s) in RCA: 52] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2018] [Revised: 12/17/2018] [Accepted: 01/07/2019] [Indexed: 02/07/2023]
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Duan P, Schmidt-Rohr K. Composite-pulse and partially dipolar dephased multiCP for improved quantitative solid-state 13C NMR. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2017; 285:68-78. [PMID: 29121512 DOI: 10.1016/j.jmr.2017.10.010] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/02/2017] [Revised: 10/22/2017] [Accepted: 10/24/2017] [Indexed: 05/22/2023]
Abstract
Improved multiple cross polarization (multiCP) pulse sequences for quickly acquiring quantitative 13C NMR spectra of organic solids are presented. Loss of 13C magnetization due to imperfect read-out and storage pulses in multiCP has been identified as a significant mechanism limiting polarization enhancement for 13C sites with weak couplings to 1H. This problem can be greatly reduced by composite 90° pulses with non-orthogonal phases that flip the magnetization onto the spin-lock field and back to the longitudinal direction for the 1H repolarization period; the observed loss is <3% for over ±10 kHz resonance offset and up to 20% flip-angle error. This composite-pulse multiCP (ComPmultiCP) sequence consistently provides performance superior to that of conventional multiCP, without any trade-off. The longer total CP time enabled by the composite pulses allows for a wider amplitude ramp during CP, which decreases the sensitivity to Hartmann-Hahn mismatch by a factor of two, with a <7% root-mean-square deviation within a 1-dB range for Boc-alanine. In samples with very short T1ρ, under-polarization of non-protonated carbons can be compensated by slight dipolar dephasing of CHn signals resulting from relatively weak decoupling during the Hahn spin echo period before detection. Quantitative spectra have been obtained by ComPmultiCP for low-crystallinity branched polyethylene at 4.5 kHz MAS, and in combination with partial dipolar dephasing for soil organic matter at 14 kHz MAS.
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Affiliation(s)
- Pu Duan
- Department of Chemistry, Brandeis University, Waltham, MA 02453, USA
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11
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Cui J, Li J, Peng X, Fu R. Transient NOE enhancement in solid-state MAS NMR of mobile systems. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2017; 284:73-79. [PMID: 28961480 DOI: 10.1016/j.jmr.2017.09.011] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2017] [Revised: 09/13/2017] [Accepted: 09/16/2017] [Indexed: 06/07/2023]
Abstract
It has been known that the heteronuclear cross-relaxation affects the dilute S spin magnetization along the longitudinal direction, causing an overshoot phenomenon for those mobile systems in spin-lattice relaxation rate measurements. Here, we analyze the Solomon equations for an I-S system and derive the transient cross relaxation effect as to when an overshoot phenomenon would take place and what the maximum enhancement could be at the time of the overshoot. In order to utilize such a transient nuclear Overhauser effect (NOE), we first time apply it to dynamic solid samples by inverting the 1H magnetization prior to the excitation of the S spin. It is found that the overshoot depends on the ratio of the I and S spin-lattice relaxation rates, i.e. RSS/RII. When RSS/RII≫1, the maximum enhancement factor for transient NOE could be larger than that obtained in steady-state NOE experiments. Furthermore, transient NOE appears to be more efficient in terms of sensitivity enhancement of dilute spins in solid-state NMR of mobile systems than the traditional cross polarization scheme whose efficiency is greatly compromised by molecular mobility. A sample of natural abundance l-isoleucine amino acid, in which the spin-lattice relaxation rates for the four methyl carbons are different, has been used to demonstrate sensitivity enhancement factors under various experimental schemes.
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Affiliation(s)
- Jiangyu Cui
- CAS Key Laboratory of Microscale Magnetic Resonance and Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China
| | - Jun Li
- Beijing Computational Science Research Center, Beijing 100193, China
| | - Xinhua Peng
- CAS Key Laboratory of Microscale Magnetic Resonance and Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China; Synergetic Innovation Center for Quantum Effects and Applications, Hunan Normal University, Changsha 410081, China; Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China.
| | - Riqiang Fu
- National High Magnet Field Lab, 1800 East Paul Dirac Drive, Tallahassee, FL 32310, USA.
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Yuan Y, Shu J, Kolman K, Kiersnowski A, Bubeck C, Zhang J, Hansen MR. Multiple Chain Packing and Phase Composition in Regioregular Poly(3-butylthiophene) Films. Macromolecules 2016. [DOI: 10.1021/acs.macromol.6b01828] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- Yuan Yuan
- Key Laboratory of Rubber-Plastics, Ministry of Education/Shandong Provincial Key Laboratory of Rubber-plastics, Qingdao University of Science & Technology, Qingdao 266042, China
- Max Planck Institute
for Polymer Research, Ackermannweg
10, 55128 Mainz, Germany
| | - Jie Shu
- Max Planck Institute
for Polymer Research, Ackermannweg
10, 55128 Mainz, Germany
- Analysis and Testing Center, Suzhou University, Renai Road 199, 215123 Suzhou, China
| | - Krzysztof Kolman
- Faculty of Chemistry, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland
- Division of Applied Chemistry, Department of Chemistry and Chemical
Engineering, Chalmers University of Technology, SE 412 96 Gothenburg, Sweden
| | - Adam Kiersnowski
- Max Planck Institute
for Polymer Research, Ackermannweg
10, 55128 Mainz, Germany
- Faculty of Chemistry, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland
| | - Christoph Bubeck
- Max Planck Institute
for Polymer Research, Ackermannweg
10, 55128 Mainz, Germany
| | - Jianming Zhang
- Key Laboratory of Rubber-Plastics, Ministry of Education/Shandong Provincial Key Laboratory of Rubber-plastics, Qingdao University of Science & Technology, Qingdao 266042, China
- Max Planck Institute
for Polymer Research, Ackermannweg
10, 55128 Mainz, Germany
| | - Michael Ryan Hansen
- Max Planck Institute
for Polymer Research, Ackermannweg
10, 55128 Mainz, Germany
- Institute of Physical Chemistry, Westfälische Wilhelms-Universität Münster, Münster, Germany
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Zhang R, Mroue KH, Ramamoorthy A. Hybridizing cross-polarization with NOE or refocused-INEPT enhances the sensitivity of MAS NMR spectroscopy. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2016; 266:59-66. [PMID: 27040936 PMCID: PMC4851575 DOI: 10.1016/j.jmr.2016.03.006] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2016] [Revised: 03/13/2016] [Accepted: 03/24/2016] [Indexed: 05/05/2023]
Abstract
Heteronuclear cross polarization (CP) has been commonly used to enhance the sensitivity of dilute low-γ nuclei in almost all solid-state NMR experiments. However, CP relies on heteronuclear dipolar couplings, and therefore the magnetization transfer efficiency becomes inefficient when the dipolar couplings are weak, as is often the case for mobile components in solids. Here, we demonstrate methods that combine CP with heteronuclear Overhauser effect (referred to as CP-NOE) or with refocused-INEPT (referred to as CP-RINEPT) to overcome the efficiency limitation of CP and enhance the signal-to-noise ratio (S/N) for mobile components. Our experimental results reveal that, compared to the conventional CP, significant S/N ratio enhancement can be achieved for resonances originating from mobile components, whereas the resonance signals associated with rigid groups are not significantly affected due to their long spin-lattice relaxation times. In fact, the S/N enhancement factor is also dependent on the temperature, CP contact time as well as on the system under investigation. Furthermore, we also demonstrate that CP-RINEPT experiment can be successfully employed to independently detect mobile and rigid signals in a single experiment without affecting the data collection time. However, the resolution of CP spectrum obtained from the CP-RINEPT experiment could be slightly compromised by the mandatory use of continuous wave (CW) decoupling during the acquisition of signals from rigid components. In addition, CP-RINEPT experiment can be used for spectral editing utilizing the difference in dynamics of different regions of a molecule and/or different components present in the sample, and could also be useful for the assignment of resonances from mobile components in poorly resolved spectra. Therefore, we believe that the proposed approaches are beneficial for the structural characterization of multiphase and heterogeneous systems, and could be used as a building block in multidimensional solid-state NMR experiments.
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Affiliation(s)
- Rongchun Zhang
- Biophysics and Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055, USA
| | - Kamal H Mroue
- Biophysics and Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055, USA
| | - Ayyalusamy Ramamoorthy
- Biophysics and Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055, USA.
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Johnson RL, Anderson JM, Shanks BH, Fang X, Hong M, Schmidt-Rohr K. Spectrally edited 2D 13C-13C NMR spectra without diagonal ridge for characterizing 13C-enriched low-temperature carbon materials. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2013; 234:112-124. [PMID: 23871898 DOI: 10.1016/j.jmr.2013.06.006] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2013] [Revised: 06/04/2013] [Accepted: 06/07/2013] [Indexed: 06/02/2023]
Abstract
Two robust combinations of spectral editing techniques with 2D (13)C-(13)C NMR have been developed for characterizing the aromatic components of (13)C-enriched low-temperature carbon materials. One method (exchange with protonated and nonprotonated spectral editing, EXPANSE) selects cross peaks of protonated and nearby nonprotonated carbons, while the other technique, dipolar-dephased double-quantum/single-quantum (DQ/SQ) NMR, selects signals of bonded nonprotonated carbons. Both spectra are free of a diagonal ridge, which has many advantages: Cross peaks on the diagonal or of small intensity can be detected, and residual spinning sidebands or truncation artifacts associated with the diagonal ridge are avoided. In the DQ/SQ experiment, dipolar dephasing of the double-quantum coherence removes protonated-carbon signals; this approach also eliminates the need for high-power proton decoupling. The initial magnetization is generated with minimal fluctuation by combining direct polarization, cross polarization, and equilibration by (13)C spin diffusion. The dipolar dephased DQ/SQ spectrum shows signals from all linkages between aromatic rings, including a distinctive peak from polycondensed aromatics. In EXPANSE NMR, signals of protonated carbons are selected in the first spectral dimension by short cross polarization combined with dipolar dephasing difference. This removes ambiguities of peak assignment to overlapping signals of nonprotonated and protonated aromatic carbons, e.g. near 125 ppm. Spin diffusion is enhanced by dipolar-assisted rotational resonance. Before detection, C-H dipolar dephasing by gated decoupling is applied, which selects signals of nonprotonated carbons. Thus, only cross peaks due to magnetization originating from protonated C and ending on nearby nonprotonated C are retained. Combined with the chemical shifts deduced from the cross-peak position, this double spectral editing defines the bonding environment of aromatic, COO, and C=O carbons, which is particularly useful for identifying furan and arene rings. The C=O carbons, whose chemical shifts vary strongly (between 212 and 165 ppm) and systematically depend on their two bonding partners, show particularly informative cross peaks, given that one bonding partner is defined by the other frequency coordinate of the cross peak. The new techniques and the information content of the resulting spectra are validated on sulfuric-acid treated low-temperature carbon materials and on products of the Maillard reaction. The crucial need for spectral editing for correct peak assignment is demonstrated in an example.
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Affiliation(s)
- Robert L Johnson
- Department of Chemistry, Iowa State University, Ames, IA 50011, United States
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16
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Separation and composition distribution determination of triblock copolymers by thermal field-flow fractionation. Anal Bioanal Chem 2013; 405:9033-40. [DOI: 10.1007/s00216-013-7282-6] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2013] [Revised: 07/29/2013] [Accepted: 07/29/2013] [Indexed: 11/26/2022]
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17
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Zhao H, Shu J, Chen Q, Zhang S. Quantitative structural characterization of POSS and octavinyl-POSS nanocomposites by solid state NMR. SOLID STATE NUCLEAR MAGNETIC RESONANCE 2012; 43-44:56-61. [PMID: 22503875 DOI: 10.1016/j.ssnmr.2012.02.005] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2011] [Revised: 12/24/2011] [Accepted: 02/15/2012] [Indexed: 05/31/2023]
Abstract
The ratio between two different (29)Si atoms in chloromethylphenyl isobutyl Polyhedral Oligomeric Silsesquioxane (POSS) was determined based on the quantitative cross polarization (QCP) (Shu et al., Chem. Phys. Lett. 462 (2008) 125) in solid-state NMR. For a (29)Si/(1)H spin system, cross polarization and depolarization together with the reciprocity relation were performed with optimized experimental conditions. It saves considerable experimental time compared to the (29)Si direct polarization experiment. The same method was further applied to octavinyl-POSS nanocomposites containing perfluoropolyether (PFPE) for deriving directly and accurately the average numbers of reacted vinyl groups, which may not be obtained by combining FTIR and solution (1)H NMR. In principle, the aforementioned method proves to be valuable in quantitative characterization of silicon related structures in bulk materials.
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Affiliation(s)
- Huipeng Zhao
- Shanghai Key Laboratory of Magnetic Resonance, Department of Physics, East China Normal University, Shanghai 200062, China
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Shu W, Zhang S. Relaxation compensated and intensity recovered dynamics of cross polarization in the frame of reciprocity relation. Chem Phys Lett 2011. [DOI: 10.1016/j.cplett.2011.06.037] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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