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Magnetic Resonance in Chemistry: MRC

Simone Di Micco, Clelia Giannini, Andrea Previtali, Elena Lucenti, Giuseppe Bifulco
Solid state organic compounds, endowed with enhanced emission, have been gaining great attention in the scientific community for their potential application in different areas, such as lighting technologies or bioimaging. In this field, mono- and di-bromo derivatives of triimidazo[1,2-a:1',2'-c:1",2"-e][1,3,5] triazine have been proposed as new organic molecules presenting a very rich and complex photophysical behavior. Their structures were investigated by standard 1D and 2D NMR experiments, but the correct structural assignment of all proton and carbon resonances was made difficult since the lack of crucial and diagnostic long-range correlations between quaternary carbon and proton signals...
November 13, 2018: Magnetic Resonance in Chemistry: MRC
Shelly Gordon, Mario Wibowo, Qian Wang, Jeff Holst, Rohan A Davis
Four new dihydro-β-agarofurans, denhaminols K-N (4-7), along with three known secondary metabolites, denhaminols A-C (1-3) were obtained from the large-scale isolation studies of the leaves of the Australian endemic rainforest plant, Denhamia celastroides. The structures of the previously undescribed compounds were determined by detailed 1D and 2D NMR, MS, UV and IR data analysis. All compounds were found to inhibit the activity of leucine transport in the human prostate cancer cell line LNCaP with IC50 values ranging from 5...
October 22, 2018: Magnetic Resonance in Chemistry: MRC
Sam Smet, Pieter Verlooy, Fadila Saïdi, Francis Taulelle, Johan A Martens, Charlotte Martineau-Corcos
The 1 H-29 Si multiple-contact CP (MC-CP) MAS NMR experiment is evaluated for the class of silicate-siloxane copolymers called Posisils, i.e. polyoligosiloxysilicones. It proves a reasonably good solution to tackle the challenge of recording quantitative 29 Si NMR data in experimental time much reduced compared to single pulse acquisition. In a second time, we report 29 Si-29 Si MC-CP double-quantum single-quantum (MC-CP-DQ-SQ) NMR experiment, which provides information about the through-space proximities between all silicon species despite the high degree of heterogeneity of this material...
October 16, 2018: Magnetic Resonance in Chemistry: MRC
Deepak Kumar, Samanwita Pal
In this report, our main focus is to introduce a set of one-dimensional (1D) NMR methods based on chemical shift, relaxation, and magnetization transfer, namely, NOE and chemical exchange involving selective pulse excitation to study the solution dynamics of drug in free and encapsulated state within polymeric microsphere. In this regard 5-fluorouracil (5-FU) loaded poly lactic-co-glycolic acid (PLGA) microspheres are prepared as model system via standard water-in-oil-in-water emulsification method. One-dimensional 1 H and 19 F nuclear magnetic resonance (NMR) spectra of 5-FU in presence of PLGA microspheres presented a significant change in linewidth and relaxation rates compared with free 5-FU confirming encapsulation...
October 10, 2018: Magnetic Resonance in Chemistry: MRC
Yulia B Monakhova, Bernd W K Diehl
Nuclear magnetic resonance spectrometry (NMR) finds numerous applications in pharmacy, cosmetic and food control as well as in developing tools for "big data" analysis. However, there remains a need for automated tools to assess instrument system suitability in real time for each particular routine sample. An automated procedure has been introduced to monitor a number of characteristics (resolution, symmetry, half width) in real time after the measurement of two samples distributed by the vendor (0...
October 2, 2018: Magnetic Resonance in Chemistry: MRC
Łukasz Szeleszczuk, Monika Zielińska-Pisklak, Dariusz Maciej Pisklak
No abstract text is available yet for this article.
September 26, 2018: Magnetic Resonance in Chemistry: MRC
Mateusz Urbańczyk, Alexandra Shchukina, Dariusz Gołowicz, Krzysztof Kazimierczuk
NMR spectroscopy, used routinely for structure elucidation, has also become a widely applied tool for process and reaction monitoring. However, the most informative of NMR methods-correlation experiments-are often useless in this kind of applications. The traditional sampling of a multidimensional FID is usually time-consuming, and thus, the reaction-monitoring toolbox was practically limited to 1D experiments (with rare exceptions, e.g., single-scan or fast-sampling experiments). Recently, the technique of time-resolved non-uniform sampling (TR-NUS) has been proposed, which allows to use standard multidimensional pulse sequences preserving the temporal resolution close to that achievable in 1D experiments...
September 25, 2018: Magnetic Resonance in Chemistry: MRC
Robert P Young, Corbin R Lewis, Chen Yang, Luther Wang, James K Harper, Leonard J Mueller
The representation of NMR tensors as surfaces on three-dimensional molecular models is an information-rich presentation that highlights the geometric relationship between the tensor principal components and the underlying molecular and electronic structure. Here we describe a new computational tool, TensorView, for depicting NMR tensors on the molecular framework. This package makes use of the graphical interface and built-in molecular display functionality present within the Mathematica programming environment and is robust for displaying tensor properties from a broad range of commercial and user-specific computational chemistry packages...
September 19, 2018: Magnetic Resonance in Chemistry: MRC
Miri Zilka, Jonathan R Yates, Steven P Brown
This paper presents an NMR crystallography study of three polymorphs of furosemide. Experimental magic-angle spinning (MAS) solid-state NMR spectra are reported for form I of furosemide, and these are assigned using density-functional theory (DFT)-based gauge-including projector augmented wave (GIPAW) calculations. Focusing on the three known polymorphs, we examine the changes to the NMR parameters due to crystal packing effects. We use a recently developed formalism to visualise which regions are responsible for the chemical shielding of particular sites and hence understand the variation in NMR parameters between the three polymorphs...
August 23, 2018: Magnetic Resonance in Chemistry: MRC
Benjamin Görling, Wolfgang Bermel, Stefan Bräse, Burkhard Luy
Similar to J-resolved spectroscopy, also, heteronuclear multiple bond correlation (HMBC), heteronuclear single bond correlation (HSBC), and heteronuclear multiple quantum coherence (HMQC) types of correlation experiments result in homonuclear tilted multiplet patterns. On the example of the high-resolution heteronuclear single bond correlation (HR-HSBC) pulse sequence, it is shown how the tilt angle can be varied within a wide range of positive and negative values. Projection along the tilt angles in all cases results in homonuclear decoupling...
October 2018: Magnetic Resonance in Chemistry: MRC
Laura Castañar
No abstract text is available yet for this article.
October 2018: Magnetic Resonance in Chemistry: MRC
Julian Ilgen, Lukas Kaltschnee, Christina M Thiele
Band selective techniques offer the highest sensitivity of all pure shift approaches and thus are the best choice for decoupling well-separated 1 H-frequency regions, such as the amide- or the α-proton region of α-peptides. They are inept to fully decouple the amide- and the α-proton region simultaneously, though. Herein, we present a new homonuclear decoupling technique, which extends the capabilities of band selective decoupling using the perfect echo principle. This modification allows a complete backbone decoupling (amide- and α-protons) in peptides and opens band selective homonuclear decoupling to substances with two mutually coupled protons in the spectral range of interest...
October 2018: Magnetic Resonance in Chemistry: MRC
Josep Saurí, Wolfgang Bermel, Teodor Parella, R Thomas Williamson, Gary E Martin
1,n-ADEQUATE is a powerful NMR technique for elucidating the structure of proton-deficient small molecules that can help establish the carbon skeleton of a given molecule by providing long-range three-bond 13 C─13 C correlations. Care must be taken when using the experiment to identify the simultaneous presence of one-bond 13 C─13 C correlations that are not filtered out, unlike the HMBC experiment that has a low-pass J-filter to filter 1 JCH responses out. Dual-optimized, inverted 1 JCC 1,n-ADEQUATE is an improved variant of the experiment that affords broadband inversion of direct responses, obviating the need to take additional steps to identify these correlations...
October 2018: Magnetic Resonance in Chemistry: MRC
Juan A Aguilar, Raquel Belda, Benjamin R Gaunt, Alan M Kenwright, Ilya Kuprov
Recent developments in data sampling and processing techniques have made it possible to acquire 2-dimensional NMR spectra of small molecules at digital resolutions in both dimensions approaching the intrinsic limitations of the equipment and sample on a realistic timescale. These developments offer the possibility of enormously increased effective resolution (peak dispersion) and the ability to effectively study samples where peak overlap was previously a limiting factor. Examples of such spectra have been produced for a number of 2-dimensional techniques including TOCSY and HSQC...
October 2018: Magnetic Resonance in Chemistry: MRC
Veera Mohana Rao Kakita, Kanaka Mahalakshmi Jerripothula, Sahithya Phani Babu Vemulapalli, Jagadeesh Bharatam
JHH scalar couplings carry rich structural information and their measurements are fundamental in the 1 H NMR based elucidation of small and medium molecules, which, however, are hampered in the presence of large J-coupling network. Further, enhanced spectral resolution is often essential for precise determination of a specific set of 1 H-1 H J-couplings among the complex J-multiplets. In the light of the recent advancements in homodecoupling pure shift strategies, here, we report absorption mode, band-selective refocused pure shift spin-echo method, which helps in determining 1 H-1 H J-couplings from crowded spectral regions...
October 2018: Magnetic Resonance in Chemistry: MRC
Nilamoni Nath, Priyakshi Bordoloi, Bhaskar Barman, Bikash Baishya, Sachin R Chaudhari
Enantiodiscrimination and their quantification using nuclear magnetic resonance (NMR) spectroscopy has always been a subject of great interest. Proton is the nucleus of choice for enantiodiscrimination due to its high sensitivity and ubiquitous presence in nature. Despite its advantages, enantiodiscrimination suffers from extensive signal splitting by the proton-proton scalar couplings, which give complex multiplets that spread over a frequency range of some tens of hertz. These multiplets often overlap, further complicating interpretation of the spectra and quantifications...
October 2018: Magnetic Resonance in Chemistry: MRC
Juan A Aguilar, Alan M Kenwright
Historically, the resolution of multidimensional nuclear magnetic resonance (NMR) has been orders of magnitude lower than the intrinsic resolution that NMR spectrometers are capable of producing. The slowness of Nyquist sampling as well as the existence of signals as multiplets instead of singlets have been two of the main reasons for this underperformance. Fortunately, two compressive techniques have appeared that can overcome these limitations. Compressive sensing, also known as compressed sampling (CS), avoids the first limitation by exploiting the compressibility of typical NMR spectra, thus allowing sampling at sub-Nyquist rates, and pure shift techniques eliminate the second issue "compressing" multiplets into singlets...
October 2018: Magnetic Resonance in Chemistry: MRC
Peter Kiraly, Mathias Nilsson, Gareth A Morris
Pure shift NMR spectroscopy has become an efficient tool for improving resolution in proton NMR spectra by removing the effect of homonuclear couplings. The introduction of real-time acquisition methods has allowed the main drawback of pure shift NMR, the long experiment times needed, to be circumvented. Real-time methods use periodic application of J-refocusing pulse sequence elements, acquiring a single free induction decay, in contrast to previous methods that construct a pure shift interferogram by concatenating excerpts from multiple free induction decays...
October 2018: Magnetic Resonance in Chemistry: MRC
Kathrin Buchberger, Martin Walenta, Klaus Zangger
The measurement of small homonuclear coupling constants is often prevented by either their small size and/or overlap with other signal splittings. Here, we present a real-time method to extract such couplings without interference from other splittings, with a resolution that is beyond conventional NMR spectra. In this real-time J-upscaled SERF experiment, homonuclear coupling is removed by slice-selective pure shift NMR, whereas scalar coupling to only one selected signal is reintroduced by selective refocusing...
October 2018: Magnetic Resonance in Chemistry: MRC
Veera Mohana Rao Kakita, Jagadeesh Bharatam
The present manuscript reports development and applications of real-time homonuclear broadband decoupled pure shift version of in-phase zero-quantum filtered COSY (PS-IPZF-COSY) and clean in-phase COSY (PS-CLIP-COSY) pulse schemes. In contrast to the conventional COSY schemes, these pure shift versions provide enhanced spectral resolution and simplify the chemical shift correlation analysis of scalar coupled spins in complex organic molecules, which are exemplified for erythromycin A, estradiol, and a mixture of estradiol and testosterone...
October 2018: Magnetic Resonance in Chemistry: MRC
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