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Magnetic Resonance in Chemistry: MRC

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https://www.readbyqxmd.com/read/28806857/structure-elucidation-total-assignment-of-the-1-h-and-13-c-chemical-shifts-and-absolute-configuration-by-nmr-techniques-of-dammarane-type-triterpenes-from-hippocratea-volubilis
#1
LETTER
María L Kennedy, Atteneri López-Arencibia, María Reyes-Batlle, Jacob Lorenzo-Morales, José E Piñero, Isabel L Bazzocchi, Ignacio A Jiménez
No abstract text is available yet for this article.
August 14, 2017: Magnetic Resonance in Chemistry: MRC
https://www.readbyqxmd.com/read/28783883/a-theoretical-and-nmr-lanthanide-induced-shift-lis-investigation-of-the-conformations-of-lactams
#2
Raymond J Abraham, Marco Filippi, Giovanni Petrillo, Paola Piaggio, Chiara Vladiskovic, Fernando Sancassan
Molecular mechanics (MM) with MMFF94 and MMX force-fields and ab initio (RHF/6-31G*,RHF/6-311G** and B3LYP/6-311G** ) calculations are used with LIS to investigate the conformations of N-methyl-2-pyrrolidone 1, N-methyl-2-piperidone 2, ε-caprolactam 3, γ-valerolactam (1,5-dimethyl-2-pyrrolidone) 4, 2-azetidinone 5, 4-methyl azetidinone 6, 4-phenyl azetidinone 7, and N-methyl-4-phenyl azetidinone 8. The Yb(fod)3 paramagnetic induced shifts of all the (1) H and (13) C nuclei are measured and the corresponding diamagnetic complexation shifts obtained by the addition of Lu(fod)3 ...
August 7, 2017: Magnetic Resonance in Chemistry: MRC
https://www.readbyqxmd.com/read/28778115/new-cyclic-2-3-sulfite-ester-derivatives-of-poststerone-discriminating-diastereomers-and-probing-spatial-proximities-by-nmr-and-dft-calculations
#3
LETTER
Attila Balázs, Attila Hunyadi, József Csábi, L M Viranga Tillekeratne, Ana Martins, Gábor Tóth
No abstract text is available yet for this article.
August 4, 2017: Magnetic Resonance in Chemistry: MRC
https://www.readbyqxmd.com/read/28762528/-19-f-nmr-isotropic-chemical-shift-for-efficient-screening-of-fluorinated-fragments-which-are-racemates-and-or-display-multiple-conformers
#4
Claudio Dalvit, Stefan Knapp
Fluorine ligand-based NMR spectroscopy is now an established method for performing binding screening against a macromolecular target. Typically, the transverse relaxation rate of the fluorine signals is monitored in the absence and presence of the target. However, useful structural information can sometimes be obtained from the analysis of the fluorine isotropic chemical shift. This is particularly relevant for molecule that are racemates and/or display multiple conformers. The large difference in fluorine isotropic chemical shift between free and bound state deriving mainly from the breaking and/or making of intramolecular and/or intermolecular hydrogen bonds allows the detection of very weak affinity ligands...
August 1, 2017: Magnetic Resonance in Chemistry: MRC
https://www.readbyqxmd.com/read/28755418/a-13-c-nmr-method-for-determining-secondary-nitroxide-substrate-associations
#5
Nicholas A Eddy, Michael S Martin, Pranjali Ichalkaranje, Martha D Morton
The major effects of nitroxides on substrates in proton spectra is well studied, while the effect on carbon spectra has received less attention. Present knowledge relies on chemical shift differences between diamagnetic and paramagnetic solutions of the substrates to propose interactions. Changes in scalar coupling constants (JCH ) would, however, provide better insight. Herein, we present a method of utilizing coupled (13) C NMR spectra where differences in (1) JCH coupling show alternate modes of association between nitroxides and test substrates...
July 28, 2017: Magnetic Resonance in Chemistry: MRC
https://www.readbyqxmd.com/read/28752526/dynamic-properties-of-imidazolium-orthoborate-ionic-liquids-mixed-with-polyethylene-glycol-studied-by-nmr-diffusometry-and-impedance-spectroscopy
#6
Andrei Filippov, Nail Azancheev, Amal Gibaydullin, Shubhankar Bhattacharyya, Oleg N Antzutkin, Faiz Ullah Shah
We used (1) H pulsed field gradient (PFG) NMR to study the self-diffusion of polyethylene glycol (PEG) with average molecular mass of 200 and ions in mixtures of PEG with imidazolium bis(mandelato)borate (BMB) and imidazolium bis(oxalato)borate (BOB) ionic liquids (ILs). The ionic liquid was mixed with PEG in the concentration range of 0-100 wt%. Within the temperature range of 295 to 353 K, the diffusion coefficient of BMB is slower than that of the imidazolium cation. The diffusion coefficients of PEG, as well as the imidazolium cation and BMB anions, differ under all experimental conditions tested...
July 27, 2017: Magnetic Resonance in Chemistry: MRC
https://www.readbyqxmd.com/read/28736823/distinct-alignment-of-benzene-derivatives-in-stretched-polystyrene-and-polybutylacrylate-gels-specific-polymer-solute-interactions
#7
T Niklas, C Steinmetzger, F Rüttger, D Stalke, M John
We have measured the alignment of a range of benzene derivatives in cross-linked polystyrene and poly(butyl acrylate) using a small number of residual dipolar couplings and simple geometric considerations. For apolar solutes in polystyrene and protic solutes in poly(butyl acrylate), the preferred molecular orientation does not coincide with the longest molecular axis (steric aligment). This behavior may be explained by specific π-π and hydrogen bonding interactions between solute and polymer, respectively, the latter being confirmed by molecular dynamics simulations...
July 23, 2017: Magnetic Resonance in Chemistry: MRC
https://www.readbyqxmd.com/read/28731512/fast-and-simultaneous-determination-of-1-h-1-h-and-1-h-19-f-scalar-couplings-in-complex-spin-systems-application-of-psyche-homonuclear-broadband-decoupling
#8
Veera Mohana Rao Kakita, Kavitha Rachineni, Ramakrishna V Hosur
The present manuscript focuses on fast and simultaneous determination of (1) H-(1) H and (1) H-(19) F scalar couplings in fluorinated complex steroid molecules. Incorporation of broadband PSYCHE homonuclear decoupling in the indirect dimension of zero-quantum filtered diagonal experiments (F1-PSYCHE-DIAG) suppresses (1) H-(1) H scalar couplings, however it retains (1) H-(19) F scalar couplings (along F1-dimension) for the (19) F coupled protons while preserving the pure-shift nature for (1) H resonances uncoupled to (19) F...
July 21, 2017: Magnetic Resonance in Chemistry: MRC
https://www.readbyqxmd.com/read/28730621/multiple-homonuclear-band-selective-decoupling-nmr-fast-and-unambiguous-determination-of-diastereomeric-excess
#9
Kavitha Rachineni, Veera Mohana Rao Kakita, Ramakrishna V Hosur
Discrimination and quantification of chiral stereoisomers have been studied by different analytical methods and NMR has emerged as a powerful one with the advancements in pure-shift NMR methods. In the present manuscript, an al-F1F2-MHOBS-DIAG NMR method for the quantification of diastereomeric excess ratio (dr) has been proposed and demonstrated, using Hesperidin and Naringin mixtures. This method enables simultaneous quantification of dr at multiple resonances, in a single experiment, and it takes only ~10 min to record...
July 20, 2017: Magnetic Resonance in Chemistry: MRC
https://www.readbyqxmd.com/read/28703432/the-mutual-effect-of-a-carbonyl-polar-bond-and-an-endocyclic-oxygen-on-the-1-jc-f-coupling-constant-of-fluorinated-six-membered-rings
#10
Josué M Silla, Matheus P Freitas
The (1) JC-F coupling constant can be useful to probe the conformational landscape of organofluorine compounds and the intramolecular interactions governing the stereochemistry of these compounds. Neighboring oxygen electron lone pairs and a carbonyl group relative to a C-F bond affect this coupling constant in an opposite way and, therefore, analysis of the interactions involving these entities simultaneously indicates which effect dominates (1) JC-F . Spin-spin coupling constant calculations for a series of fluorinated tetrahydropyrans, cyclohexanones and dihydropyran-3-ones indicated that an electrostatic/dipolar interaction between the C-F and C=O bonds is more important than the steric interaction between the C-F bond and the oxygen electron lone pairs...
July 13, 2017: Magnetic Resonance in Chemistry: MRC
https://www.readbyqxmd.com/read/28699648/mrc-s-proposal-to-change-the-submission-procedure-for-the-future-submission-of-assignment-papers
#11
EDITORIAL
Roberto Gil
No abstract text is available yet for this article.
July 12, 2017: Magnetic Resonance in Chemistry: MRC
https://www.readbyqxmd.com/read/28665001/nmr-spectroscopic-conformational-analysis-of-4-methylene-cyclohexyl-pivalate-the-effect-of-sp-2-hybridization
#12
Erich Kleinpeter, Matthias Heydenreich, Andreas Koch, Angela Krtitschka, Tobias Krüger, Torsten Linker
The conformational equilibrium of the axial/equatorial conformers of 4-methylene-cyclohexyl pivalate is studied by dynamic NMR spectroscopy in a methylene chloride/freon mixture. At 153 K the ring interconversion gets slow on the NMR time scale, the conformational equilibrium (-ΔG°) can be examined and the barrier to ring interconversion (ΔG(#) ) can be determined. The structural influence of sp(2) hybridization on both ΔG° and ΔG(#) of the cyclohexyl moiety can be quantified.
June 30, 2017: Magnetic Resonance in Chemistry: MRC
https://www.readbyqxmd.com/read/28644528/a-systematic-1-h-and-13-c-nmr-spectral-analysis-of-bicyclo-n-3-1-alkanone-systems-determination-of-the-relative-configuration-of-the-stereogenic-centres-and-conformation-of-the-six-membered-ring
#13
Giorgio Giorgi, Pilar López-Alvarado, J Carlos Menéndez
No abstract text is available yet for this article.
June 23, 2017: Magnetic Resonance in Chemistry: MRC
https://www.readbyqxmd.com/read/28600816/on-the-accuracy-factors-and-computational-cost-of-the-giao-dft-calculation-of-15-n-nmr-chemical-shifts-of-amides
#14
Dmitry O Samultsev, Valentin A Semenov, Leonid B Krivdin
The main factors affecting the accuracy and computational cost of GIAO-DFT calculation of (15) N NMR chemical shifts in the benchmark series of 16 amides are considered. Among those are the choice of the DFT functional and basis set, solvent effects, internal reference conversion factor and applicability of the locally dense basis set (LDBS) scheme. Solvent effects are treated within the polarizable continuum model scheme (PCM) as well as at supermolecular level with solvent molecules considered in explicit way...
June 9, 2017: Magnetic Resonance in Chemistry: MRC
https://www.readbyqxmd.com/read/28599057/dynamic-nuclear-polarization-studies-of-nitroxyl-spin-probes-in-agarose-gel-using-overhauser-enhanced-magnetic-resonance-imaging-omri
#15
V Meenakumari, Hideo Utsumi, Fuminori Hyodo, A Jawahar, A Milton Franklin Benial
Agarose is a tissue-equivalent material and its imaging characteristics similar to those of real tissues. Hence the dynamic nuclear polarization studies of carboxy-PROXYL in agarose gel were carried out. The DNP parameters such as spin lattice relaxation time, longitudinal relaxivity, leakage factor, saturation parameter and coupling parameter were estimated for 2 mM carboxy-PROXYL in PBS solution and water/agarose mixture (99:1). From these results, the spin probe concentration was optimized as 2 mM, and the reduction in enhancement was observed for carboxy-PROXYL in water/agarose mixture (99:1) compared with PBS solution...
June 9, 2017: Magnetic Resonance in Chemistry: MRC
https://www.readbyqxmd.com/read/28593642/assembly-and-performance-of-a-6-4%C3%A2-t-cryogen-free-dynamic-nuclear-polarization-system
#16
Andhika Kiswandhi, Peter Niedbalski, Christopher Parish, Qing Wang, Lloyd Lumata
We report on the assembly and performance evaluation of a 180-GHz/6.4 T dynamic nuclear polarization (DNP) system based on a cryogen-free superconducting magnet. The DNP system utilizes a variable-field superconducting magnet that can be ramped up to 9 T and equipped with cryocoolers that can cool the sample space with the DNP assembly down to 1.8 K via the Joule-Thomson effect. A homebuilt DNP probe insert with top-tuned nuclear magnetic resonance coil and microwave port was incorporated into the sample space in which the effective sample temperature is approximately 1...
June 7, 2017: Magnetic Resonance in Chemistry: MRC
https://www.readbyqxmd.com/read/28577309/-1-h-19-f-redor-filtered-nmr-spin-diffusion-measurements-of-domain-size-in-heterogeneous-polymers
#17
Eric G Sorte, Todd M Alam
Solid state NMR spectroscopy is inherently sensitive to chemical structure and composition, and thus makes an ideal method to probe the heterogeneity of multicomponent polymers. Specifically, NMR spin diffusion experiments can be used to extract reliable information about spatial domain sizes on multiple length scales, provided that magnetization selection of one domain can be achieved. In this paper, we demonstrate the preferential filtering of protons in fluorinated domains during NMR spin diffusion experiments using (1) H-(19) F heteronuclear dipolar dephasing based on rotational echo double resonance (REDOR) MAS NMR techniques...
June 2, 2017: Magnetic Resonance in Chemistry: MRC
https://www.readbyqxmd.com/read/28568740/dynamics-of-binary-mixtures-of-an-ionic-liquid-and-ethanol-by-nmr
#18
Amin Ordikhani-Seyedlar, João P de Almeida Martins, Pedro J Sebastião, Maria J Jardim Beira, Sigfried Stapf, Fabián Vaca Chávez, Carlos Mattea
A study of molecular dynamics of the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoro-methylsulphonyl) imide ([Emim][Tf2N]) in solution with deuterated ethanol, at different molar concentration and temperatures is presented. The study was performed using (1) H and (2) H nuclear magnetic relaxation and (2) H 1D spectroscopy. The temperature dependence of the spin-lattice relaxation time T1 of the cations allows the evaluation of the activation energies of the rotational degree of freedom of these molecules...
May 31, 2017: Magnetic Resonance in Chemistry: MRC
https://www.readbyqxmd.com/read/28561374/practical-guide-for-selection-of-1-h-qnmr-acquisition-and-processing-parameters-confirmed-by-automated-spectra-evaluation
#19
Yulia B Monakhova, Bernd W K Diehl
In our recent paper, a new technique for automated spectra integration and quality control of the acquired results in qNMR was developed and validated (Monakhova & Diehl, Magn. Res. Chem. 2017, doi: 10.1002/mrc.4591). The present study is focused on the influence of acquisition and postacquisition parameters on the developed automated routine in particular, and on the quantitative NMR (qNMR) results in general, which has not been undertaken previously in a systematic and automated manner. Results are presented for a number of model mixtures and authentic pharmaceutical products measured on 500- and 600-MHz NMR spectrometers...
May 31, 2017: Magnetic Resonance in Chemistry: MRC
https://www.readbyqxmd.com/read/28558164/advanced-solvent-signal-suppression-for-the-acquisition-of-1d-and-2d-nmr-spectra-of-scotch-whisky
#20
Will Kew, Nicholle G A Bell, Ian Goodall, Dušan Uhrín
A simple and robust solvent suppression technique that enables acquisition of high-quality 1D (1) H nuclear magnetic resonance (NMR) spectra of alcoholic beverages on cryoprobe instruments was developed and applied to acquire NMR spectra of Scotch Whisky. The method uses 3 channels to suppress signals of water and ethanol, including those of (13) C satellites of ethanol. It is executed in automation allowing high throughput investigations of alcoholic beverages. On the basis of the well-established 1D nuclear Overhauser spectroscopy (NOESY) solvent suppression technique, this method suppresses the solvent at the beginning of the pulse sequence, producing pure phase signals minimally affected by the relaxation...
May 30, 2017: Magnetic Resonance in Chemistry: MRC
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