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Magnetic Resonance in Chemistry: MRC

Roberto Gil
No abstract text is available yet for this article.
July 12, 2017: Magnetic Resonance in Chemistry: MRC
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
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
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
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
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 NMR 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
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
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
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
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 NMR spectra of alcoholic beverages on cryoprobe instruments was developed and applied to acquire NMR spectra of Scotch Whisky. The method uses three 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. Based on the well-established 1D 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
Ilhem Zebiri, Audrey Gratia, Jean Marc Nuzillard, Mohamed Haddad, Billy Cabanillas, Dominique Harakat, Laurence Voutquenne-Nazabadioko
No abstract text is available yet for this article.
May 30, 2017: Magnetic Resonance in Chemistry: MRC
Joshua B Hayton, Gary D Grant, Anthony R Carroll
No abstract text is available yet for this article.
May 30, 2017: Magnetic Resonance in Chemistry: MRC
Jacob Powell, Domenic Valenti, Harley Bobnar, Erika Drain, Blaine Elliott, Sydney Frank, Tyler McCullough, Sean Moore, Andrew Kettring, Robbie Iuliucci, James K Harper
This study explores the feasibility of using a combination of experimental and theoretical 1-bond (13) C─(13) C scalar couplings ((1) JCC ) to establish structure in organic compounds, including unknowns. Historically, (n) JCC and (n) JCH studies have emphasized 2 and 3-bond couplings, yet (1) JCC couplings exhibit significantly larger variations. Moreover, recent improvements in experimental measurement and data processing methods have made (1) JCC data more available. Herein, an approach is evaluated in which a collection of theoretical structures is created from a partial nuclear magnetic resonance structural characterization...
May 30, 2017: Magnetic Resonance in Chemistry: MRC
Dmitry O Samultsev, Yury Yu Rusakov, Leonid B Krivdin
Long-range β- and γ-relativistic effects of halogens in (15) N NMR chemical shifts of 20 halogenated azines (pyridines, pyrimidines, pyrazines and 1,3,5-triazines) are shown to be unessential for fluoro- chloro- and bromo-derivatives (1-2 ppm in average). However, for iodocontaining compounds, β- and γ-relativistic effects are important contributors to the accuracy of the (15) N calculation. Taking into account long-range relativistic effects slightly improves the agreement of calculation with experiment...
May 30, 2017: Magnetic Resonance in Chemistry: MRC
Gualberto Bottini, Guillermo Moyna
The relative strengths of aromatic and aliphatic C-H⋅⋅⋅X hydrogen bonds in imidazolium ionic liquids were investigated through measurement of H/D isotope effects on the (19) F nuclear shielding of deuterated isotopologues of 1-n-butyl-3-methylimidazolium hexafluorophosphate and tetrafluoroborate ([C4 mim]PF6 and [C4 mim]BF4 ). Δ(19) F(H,D) values ranging from 9.7 to 49.7 ppb were observed for [C4 mim]PF6 isotopologues, while for the [C4 mim]BF4 series these went from 26.2 to 83.8 ppb. Our findings indicate that the interactions between the fluorinated anions and protons on the C-1' and C-1" position of the N-alkyl sidechains are comparable to, and in some cases stronger than, those involving protons on the aromatic ring, underscoring the role that these weak interionic forces have on the local ordering of imidazolium salts in the liquid state...
May 29, 2017: Magnetic Resonance in Chemistry: MRC
Li-Na Wu, Shao-Yi Wu, Li-Juan Zhang, Xu-Sheng Liu, Li Peng
The copper electron paramagnetic resonance (EPR) gyromagnetic factors are theoretically studied for three novel Cu(2+) coordination polymers [Cu(XL)(NO3 )2 ]n (1), {[Cu(XL)(4,4'-bpy)(NO3 )2 ]•CH3 CN}n (1a) and {[Cu(XL)3 ](NO3 )2 •3.5H2 O}n (2) with bi-triazole ligand (XL)=N,N'-bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxdiimide bi(1,2,4-triazole) from the high order perturbation calculations of the g factors for a rhombically elongated octahedral 3d(9) group. The order (1 ≤ 1a < 2) of gz can be illustrated by the dominant second-order perturbation term roughly proportional to the square of the covalency factor N...
May 25, 2017: Magnetic Resonance in Chemistry: MRC
Jean-Marc Nuzillard, Bertrand Plainchont
Automatic structure elucidation of small molecules by means of the "logic for structure elucidation" (LSD) software is introduced in the context of the automatic exploitation of chemical shift correlation data and with minimal input from chemical shift values. The first step in solving a structural problem by means of LSD is the extraction of pertinent data from the 1D and 2D spectra. This operation requires the labeling of the resonances and of their correlations; its reliability highly depends on the quality of the spectra...
May 24, 2017: Magnetic Resonance in Chemistry: MRC
Akhnef A Fatykhov, Elvira A Sedova, Aleksander Е Egorov, Sergey N Salazkin, Vladimir A Kraikin
All (1) H and (13) C NMR signals of the four poly(phenylenephthalides): polydiphenylenephthalide (P(DPh)-1), polyterphenylenephthalide (P(TPh)-2) and two sequentially ordered polymers with different ratios of alternating diphenylenephthalide and terphenylenephthalide units (P(DTPh)-3, P(DDTPh)-4) were assigned unequivocally with two-dimensional NMR techniques ((1) H-(1) H COSY and NOESY; (1) H-(13) C HSQC and HMBC). There are four types of polyphenylene fragments: not symmetrical end, symmetrical inner, symmetrical pre-end, and formally symmetric pre-end...
May 18, 2017: Magnetic Resonance in Chemistry: MRC
Dongsoo Koh, Yearam Jung, Seunghyun Ahn, Kenneth Hun Mok, Soon Young Shin, Yoongho Lim
No abstract text is available yet for this article.
May 15, 2017: Magnetic Resonance in Chemistry: MRC
Sumit Kumar Panja, Satyen Saha
Existence of microheterogeinity of imidazolium and piperidinium cation based ILs containing PF6 and NTf2 anions havebeen investigated by 1D and 2D NMR spectroscopy. 2D NMR (especially NOESY and HOESY) has been employed for studying the interactions present between cation and anion as well as the intermolecular interaction among cations. HOESY spectrum shows that fluorine of anion ( PF6- and NTf2-) significantly interacts with proton of the cations. Combined results of HOESY and NOESY for imidazolium IL indicate that the PF6- and imidazolium cation are distributed in organized manner, resulting a heterogeneous environment in liquid state...
May 15, 2017: Magnetic Resonance in Chemistry: MRC
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