A NMR method to enhance the sensitivity and resolution in band-selective long-range
heteronuclear correlation spectra is proposed. The excellent in-phase nature of the
selHSQMBC experiment allows that homonuclear and/or heteronuclear decoupling can
be achieved in the detected dimension of a 2D multiple-bond correlation map, obtaining
simplified cross-peaks without their characteristic fine J multiplet structure. The
experimental result is a resolution improvement while the highest sensitivity is also
achieved. Specifically, it is shown that the 1H-homodecoupled band-selective (HOBS)
HSQMBC experiment represents a new way to measure heteronuclear coupling
constants from the simplified in-phase doublets generated along the detected dimension.
The utility of 13C NMR spectroscopy for the differentiation of enantiomers using chiral solvating agents (CSA) is stated. Three examples involving the enantiodifferentiation of a drug, a metabolite and a reactant in aqueous and organic solutions have been chosen to show it. The intrinsic high dispersion of 13C nucleus as well as the singlet nature of the signals in standard experiments makes 13C NMR experiments a powerful alternative and/or complement to 1H NMR experiments; specially, when studying pure compounds with complex proton spectra or mixtures of compounds, as in chiral metabonomics, where severe overlapping exists in proton spectrum. To evaluate and compare the quality of the enantioresolution of a NMR signal we introduce the enantiodifferentiation quotient, E, that considers the complexity of 1H multiplets (and in general the width) of the original signal. It has been observed that the error in the measurement of the enantiomeric molar ratio can be related to the E value. The sensitivity and experimental time of a wide range of chiral analyte concentrations was also assessed.
A NMR pulse scheme that provides full sensitivity in homodecouped band-selective NMR experiments is proposed. The easy implementation of this HOBS scheme as a general building block into a great variety of multidimensional NMR experiments leads to pure-shift spectra with enhanced resolution and with the maximum attainable sensitivity.
A novel strategy to enhance the experimental sensitivity in spatially encoded NMR experiments has been developed. The use of a multiple-frequency modulated pulse applied simultaneously to an encoding gradient can afford a substantial sensitivity gain with respect to single-slice selected experiments.
In his poster “HSQMBC-TOCSY Experiment: A complementary tool for structure elucidation“ Josep discussed the merits of several versions of the HSQMBC-TOCSY experiment applied to the structural elucidation of small molecules in solution, and compared the information obtained with that provided by the conventional HMBC and HSQC-TOCSY experiments, in particular with regard to the accurate measurement of the magnitude of heteronuclear coupling constants.
Josep has been working as a Ph.D. candidate at the SeRMN under the direction of Dr. Teodor Parella since Sept 2010, when he enrolled in the Chemistry Department doctoral program at Universitat Autònoma de Barcelona with a fellowship from MICINN. He is currently in his fourth year and expects to defend his thesis on 2014. You can read about his work on this blog.
Two complementary 1D NMR approaches for the fast and easy determination of the magnitude and the sign of heteronuclear J(XH) coupling constants are proposed: The Up&Down technique relies on the direct analysis of anti-phase multiplets whereas the Left&Right technique is based on the relative displacement between separate IPAP components.
Next week several SeRMN members will present our research work at the SMASH NMR Conference 2013 that will take place in Santiago de Compostela (Spain) from 22nd to 25th September. Find below a summary of our contributions.
Josep Saurípresents a Poster entitled “HSQMBC-TOCSY Experiment: A complementary tool for structure elucidation“. Several versions of a HSQMBC-TOCSY experiment for the success application on structural elucidation of small molecules in solution are presented. We evaluate the possibility to obtain TOCSY information for a non-protonated carbon and we also extend this feature to other heteronuclei, such as 19F or 77Se. We compare experimental data obtained from the conventional HMBC and HSQC-TOCSY experiments with respect to this complementary HSQMBC-TOCSY experiment. Additionally, 1H-selective versions will be also proposed for the accurate measurement of the magnitude of heteronuclear coupling constants, with special emphasis on the determination of the positive/negative sign of these couplings on non-protonated centers. We also evaluate the implementation of multiplicity-edited information, where CH/CH3 cross peaks can be clearly distinguished from CH2/C correlations thanks to their opposite up/down relative phase.
Laura Castañar presents a Poster entitled “Simultaneous milti-slice excitation in spatial encoded NMR experiments”. In this work a novel strategy to enhance the experimental sensitivity in spatially encoded NMR experiments is presented. We explore the sensitivity benefits of applying a multiple-frequency modulated pulse to excite simultaneously different slices in a single NMR experiment. Our proposal is based on the careful setting of multiple offsets to avoid the excitation of mutually J-coupled protons into the same slice which would produce distorted multiplets due to JHH evolution. The experimental set-up protocol to fulfill the sampled frequency requirement is simple and the results can be inmediately adapted to a wide range of applications, for instance, to obtain broadband homodecoupled 1H-MNR spectra.
Albert Gargallo presents a Poster entitled “Metabolomic responses of Quercus ilex seedlings to wounding simulating herbivory“. Plants defense themselves against herbivore attack at several levels, being one of them the synthesis of inducible chemical defenses. The study of plant metabolic changes and processes related with herbivore attack has been mostly limited to the identification of single compounds or families of metabolites. We think that an ecometabonomic approach would provide a wider view of the phenomena, since that approach considers the metabolome of the plant, i.e. the total number of metabolites, and their shifts in response to an environmental change or, as in our case, in response to a plant-herbivore interaction. We have studied the metabolic changes of plant leaves after a wounding treatment simulating herbivore attack in the Mediterranean sclerophyllous tree Quercus ilex by a NMR-based metabolomic study. There is no much reported work regarding the response to wounding in trees by metabolomics. We aimed to discern whether mechanical wound injury in leaves changes its metabolome; for that we have chosen the widespread Mediterranean tree, Quercus ilex L. (holm oak), one of the most abundant species in Mediterranean forests.
Location: SeRMN, Facultats de Ciències i Biociències, C2/-135
Speaker: Laura Castañar, SeRMN PhD Student & Teaching Assistant, Dept. of Chemistry.
Simultaneous multi-slice excitation in spatially encoded NMR experiments
A novel strategy to enhance the experimental sensitivity in spatially encoded NMRexperiments is presented. The use of a multiple-frequency modulated pulse applied simultaneously to an encoding gradient can afford a substantial sensitivity gain with respect to single-slice selected experiments. The z-dependent position of each individual proton resonance allows the choice of a determined number of complementary k offsets that allows parallel data collection for a specific proton in multiple parts of the NMR tube whereas other mutually J-coupled protons are not excited into the same slice. The experimental set-up protocol to fulfill the sampled frequency requirement is simple and the results can be inmediately adapted to a wide range of applications.
The determination of enantiomeric purity of drugs and/or endogenous molecules is crucial since its chirality could determine its pharmacological or biological behavior . Many analytical techniques are available to determine the enantiomeric excess (ee) such as, circular dichroism, capillary electrophoresis, chromatographic techniques with chiral stationary phases, etc.; having each of them drawbacks and advantages . Nuclear magnetic resonance (NMR) using a chiral solvating agent (CSA) as chiral auxiliary is an easy, fast and very powerful analytical tool that allows the measurement of ee by simple signal integration . Continue reading →
The Spanish Ministry of Economy and Competitiveness (MINECO) has open the call for FPI-funded PhD thesis. At the time, applications are welcome for an FPI (Formación de Personal Investigador)-funded PhD thesis (4 years) associated to the project “NUEVOS MÉTODOS EN RESONANCIA MAGNÉTICA NUCLEAR (IV)” (Novel methodologies in Nuclear Magnetic Resonance (IV) – ref: CTQ2012-32436) at the SeRMN in the Universitat Autònoma of Barcelona (UAB). FPI fellowships are granted by the Spanish Ministry of Economy and Competitiveness.
The call for applications begins August 26th, 2013, and the deadline for submission of applications is September 10th, 2013 at 15:00. All information relating to the call for applications can be found the at Minister’s web page or contact to email@example.com for further details or questions.