Embedded Files
T. Parella
Fast 2D Solution-State NMR, RSC Book, Chapter 1, 1-41 (2023). DOI
The Role of Pulsed-field Gradients in Modern NMR Pulse Sequence Design
Pulsed-field gradients (PFGs) play an important role in the development and understanding of modern NMR methods. With the ultimate goal of constructing robust pulse sequences that create high-quality NMR spectra with minimum set-up, PFGs are utilized to achieve an exclusive selection of a specific coherence transfer pathway as well as to purge all kinds of undesired magnetization. PFGs reduce the number of needed phase cycle steps to a bare minimum, allowing for accelerated NMR data acquisition in shorter spectrometer times. The potential and diversity of several PFG-based NMR elements are presented, as well as instances of their implementation in time-efficient NMR solutions. Practical aspects such as NMR data collection needs and the attainment of pure in-phase absorption lineshapes are discussed for the most useful NMR experiments.
T. Parella
Magn. Reson. Chem., 57, 13-29 (2019). DOI
Towards perfect NMR: Spin‐echo versus perfect‐echo building blocks
The concept of “perfect NMR” includes the design of robust pulse sequences that allow an investigator to obtain undistorted pure in‐phase signals, with pure absorption lineshapes that are free of phase anomalies derived from undesired J modulations. Here, alternative NMR building blocks to the spin‐echo that are based on a general double SE module, known as a perfect‐echo, are reviewed. Several implementations to minimize/remove unwanted dispersive contributions in homonuclear and heteronuclear NMR experiments are described and illustrated with some examples of broad interest for small molecules
T. Parella
Chemistry, Molecular Sciences and Chemical Engineering; Encyclopedia of Analytical Science, 3rd Edition, 386-396 (2019). DOI
NMR Spectroscopy, Applications, Small Molecule Structuring Strategies
Nuclear magnetic resonance (NMR) spectroscopy is a powerful tool for the efficient elucidation and validation of constitution, conformation and configuration of small and medium-sized molecules in solution. A basic description of fundamental NMR experiments regarding chemical structure is provided. Although spectral NMR data analysis and interpretation are performed manually, the combination of computer-assisted structure elucidation (CASE) expert systems and density functional theory (DFT) calculations are increasingly used for structure verification. The important role of anisotropic NMR parameters (residual dipolar couplings (RDCs) and residual chemical shift anisotropy (RCSA)) determined in weakly aligned media is also discussed for the automated determination of the relative configuration in complex molecular systems having multiple chiral centers. Finally, some modern NMR concepts incorporated in current pulse sequence developments are briefly described.
T. Parella
Magn. Reson. Chem., 56, 230-250 (2018). DOI
Current developments in homonuclear and heteronuclear J‐resolved NMR experiments
Two‐dimensional J‐resolved (Jres) NMR experiments offer a simple, user‐friendly spectral representation where the information of coupling constants and chemical shifts are separated into two orthogonal frequency axis. Since its initial proposal 40 years ago, Jres has been the focus of considerable interest both in improving the basic pulse sequence and in its successful application to a wide range of studies. Here, the latest developments in the design of novel Jres pulse schemes are reviewed, mainly focusing on obtaining pure absorption lineshapes, minimizing strong coupling artifacts, and also optimizing sensitivity and experimental measurements. A discussion of several Jres versions for the accurate measurement of a different number of homonuclear (JHH) and heteronuclear (JCH) coupling constants is presented, accompanied by some illustrative examples.
T. Parella
Modern NMR Approaches to the Structure Elucidation of Natural Products : Volume 2: Data Acquisition and Applications to Compound Classes, 199-250 (2017). DOI
Chapter 6: Current Pulse Sequence Developments in Small-molecule Nuclear Magnetic Resonance Spectroscopy
The current developments in the design and the application of modern nuclear magnetic resonance (NMR) pulse sequences in small molecules are overviewed. The concepts of fast NMR, pure-shift NMR, perfect NMR and ultra-long-range correlation NMR are described and illustrated with examples.
L. Castañar and T. Parella
Magn. Reson. Chem., 53, 399-426 (2015). DOI
Broadband 1H homodecoupled NMR experiments: Recent developments, methods and applications
This review aims at presenting the most recent advances in pure shift NMR spectroscopy, with a particular emphasis to the Zangger-Sterk experiment. A detailed discussion about the most relevant practical aspects in terms of pulse sequence design, selectivity, sensitivity, spectral resolution and performance is provided. Finally, the implementation of the different reported strategies into traditional 1D and 2D NMR experiments is described while several practical applications are also reviewed.
L. Castañar and T. Parella
Annual Reports on NMR Spectroscopy, 84, 163-232 (2015). DOI
Recent Advances in Small Molecule NMR: Improved HSQC and HSQMBC Experiments
A general description of the latest developments in HSQC and HSQMBC experiments designed for small molecules at the natural isotopic abundance is reported. A discussion is made on the details introduced into novel NMR pulse sequences with special emphasis on modern concepts such as fast NMR or pure-shift NMR and also on robust techniques affording pure in-phase multiplet patterns, which are amenable for a simpler and a more accurate analysis. The suitability of some of these methods for the quantitative measurement of one-bond and long-range proton–carbon coupling values in molecules in isotropic and weakly aligned anisotropic conditions is also reviewed.
Long-Range Proton-Carbon Coupling Constants: NMR Methods and applications
A general review of novel NMR methods to measure heteronuclear long-range proton–carbon coupling constants (nJCH; n > 1) in small molecules is made. NMR experiments are classified in terms of NMR pulse scheme and cross-peak nature. A discussion about simplicity, general applicability and accuracy for each particular NMR experiment is presented and exemplified. Important aspects such as the sign determination and measurement of very small coupling values involving protonated and non-protonated carbons as well as the complementarity between different experiments are also discussed. Finally, a compilation of applications in structural and conformational analysis of different types of molecules since 2000 is surveyed.
Time-Shared NMR Experiments
Details on the implementation of the simultaneous evolution of multiple frequencies into the same time period of a NMR pulse sequence are introduced. Timeshared (TS) versions of the most useful inverse 2D NMR experiments (TS-HMBC, TS-HSQC, TS-HSQC-TOCSY, and TS-HSQMBC) are presented and illustrated for simultaneous acquisition of 1H/13C and 1H/15N NMR spectra. The major benefits associated to the parallel acquisition of multiple spectra from a single NMR experiment are spectrometer time savings and the achievement of multiple and complementary information with improved sensitivity gains per time unit.
Multidimensional NMR Methods for the Measurement of Long-Range Proton-Carbon Coupling Constants at Natural Abundance
Details on the implementation of the simultaneous evolution of multiple frequencies into the same time period of a NMR pulse sequence are introduced. Timeshared (TS) versions of the most useful inverse 2D NMR experiments (TS-HMBC, TS-HSQC, TS-HSQC-TOCSY, and TS-HSQMBC) are presented and illustrated for simultaneous acquisition of 1H/13C and 1H/15N NMR spectra. The major benefits associated to the parallel acquisition of multiple spectra from a single NMR experiment are spectrometer time savings and the achievement of multiple and complementary information with improved sensitivity gains per time unit.
P. Nolis and T. Parella
Current Analytical Chemistry, 3, 47-68 (2007). DOI
Solution-State NMR Experiments based on heteronuclear cross-polarization
Heteronuclear coherence transfer in liquid-state NMR applications has been traditionally performed using pulse-interrupted delay schemes such as INEPT-type pulse trains. So far, the alternative use of heteronuclear crosspolarization (HCP) has only been limited to a few cases involving exclusively in-phase to in-phase transfers. In this revision work a theoretical description on the effect and the characteristic anisotropic features of HCP is introduced in terms of product operator formalism. A very intuitive and simple graphical black-box approach based on a pictorial nonclassical vector representation that only consider the available input/output magnetization is also presented to understand the general transformations that are undergoing under such rather complex HCP processes. The appropriate manipulation of magnetization components during the HCP block offers novel concepts in pulse sequence design. In this way, new liquid- state multidimensional NMR methods incorporating HCP-driven processes have recently been developed and successfully applied for both small-to-medium-sized molecules and large labeled bio-molecules, as will be discussed in this review.
T. Parella
Magn. Reson. Chem, 36, 467 (1998). DOI
Pulsed Field gradients : a new tool for routine NMR
A complete review of 1D and 2D gradient-based NMR experiments published since 1990 is provided. The ease of implementation and the excellent and reproducible results obtained from such experiments offer a powerful tool for the study of molecular structures and dynamics. Thus, when sufficient sample concentration is available, ultra-clean spectra are obtained in very short acquisition times, making the experiments suitable for automated data acquisition. For these reasons, the concept of routine NMR work for chemists has been dramatically changed in the last few years and, with the correct choice of the experiments to be performed, a large number of chemical questions can be resolved in considerably reduced times. However, sensitivity and resolution are dependent on where the PFGs are incorporated into the pulse sequences and, therefore, these two important factors need to be considered in highly demanding applications. Illustrative examples of the most interesting applications to typical organic compounds are given.
Google Sites
Report abuse