Applications of NMR Spectroscopy

Cyanobacteria are ubiquitous in nature as they efficiently tolerate various

extreme climatic conditions for survival, such as increasing effects of solar radiation,

salinity, temperature, etc. Cyanobacteria are important sources of secondary

metabolites, which enable them to withstand these harsh environmental conditions.

Small-molecular-weight secondary compounds are primarily implied in the defense

mechanisms in case of biotic and abiotic stresses. Various beneficiary secondary

compounds are extracted from cyanobacteria, such as UV-screening pigments

(mycosporine-like amino acids, scytonemin, carotenoids, etc.), phytohormones,

cyanotoxins and antioxidants. Bioactivity-directed isolation techniques are used to

identify these molecules from complicated matrices in pharmacognosy (discovery of

biologically active compounds from natural sources). NMR spectroscopy has appeared

as a specific major analytical technique applied in metabolomics. The easy sample

preparation, the expertise to evaluate metabolite quantity, the notable investigational

reliability, and the innately non-destructive quality of NMR spectroscopy have made it

the first-line option for significant scientific metabolic analyses. Unlike some mass

spectrometry methods, NMR is not discriminatory, depending on the metabolites'

precursors or their ionization potential. Screening of metabolites needs maximum

sensitivity, and it is a process with a broad scope. In this chapter, we have discussed the

usage of NMR spectroscopy in the identification of photoprotective compounds and its

advantages and disadvantages for metabolomic studies. We have also explored several

new NMR techniques that have recently become available in order to fortify its

advantages and overcome its inherent limitations in metabolomics applications. 

Nuclear magnetic resonance (NMR) spectroscopy is one of the most

important spectroscopic methods for lignin characterization, playing a key role in its

structural elucidation and the choice of its suitable application. This chapter intends to

cover a wide range of matters regarding the NMR utilization in the lignin field from the

biorefinery up to lignin valorization through different chemical modifications in order

to produce high-added-value products with potential technological applications. The

chapter is divided into four main sections, in which the first and second ones will

provide a review of the main structural properties, NMR experiments used for lignin

characterization, and the recent advances of this technique. The third section is

composed of topics about biorefinery with a focus on microwave-assisted organosolv

delignification (MWAOD) and how the main pulping parameters affect the lignin

structure, besides the use of NMR as a quality control tool for MWAOD up-scaling.

Finally, the fourth section discusses NMR as a tool for determining structure-property

relationship by performing some chemical modifications in lignin structure aiming its

valorization, such as glycidylation, microwave-assisted phosphorylation, microwaveassisted

selective acetylation, and the performance of lignins from different pulping

processes as antioxidant compounds and the influence of their structure on it.

Therefore, this chapter contributes to the development of the lignin field by reviewing

the recent advances provided by NMR spectroscopy.

Objective: The objective of this chapter is to highlight the current developments in NMR spectroscopy for chiral recognition of pharmaceuticals reported during the past five years.

Introduction: NMR spectroscopy is an effective technique to contextualize structural characteristics and chirality discrimination of various compounds. During the past few decades, extensive studies have been carried out on chirality recognition (CR) of organic compounds, including pharmaceuticals. The assessment of enantiomeric drugs and related methods have become a customary assignment in most NMR labs, enabling the identification of molecular connectivity as well as the development of conceptual frameworks.

Background: Various NMR active nuclei (1H, 13C, 19F, & 31P, etc.) can be used to strengthen the CR abilities of NMR spectroscopy. NMR active nuclei are isochronic in the optically inactive environment and thus unable to exhibit CR. However, certain nuclei are anisochronic in a chiral atmosphere making CR feasible. CR capabilities of NMR are dependent on the application of chiral discriminating agents such as chiral derivatizing agents (CDAs), chiral lanthanide shift reagents (CLSRs), and chiral solvating agents (CSAs) that essentially contain a chiral auxiliary. CDAs tend to bind covalently with a functional group of the analytes, whereas CSAs bind vis non-covalent associations, like dipoledipole

and ion-pair, etc. However, CLSRs, like CSAs, do not bind covalently with the enantiomers of analytes. However, CLSRs, like CSAs, do not bind covalently with the enantiomers of analytes rather they comprise a paramagnetic center that can bring chemical shift difference of diastereotopic nuclei.

Method: Herein, the recent developments in methods based on NMR spectroscopy for CR of certain chiral drugs using various chiral discriminating agents are discussed.

Application: The methods described herein can be an assessment tool to provide details of molecular geometry and the construction of spatial relationships of chiral molecules.

Metabolomics is defined as a matrix of studies on the methodologies and

analytical technologies related to data analysis in microorganisms, plants, and animals.

In humans, about 50–200 metabolites have been identified, improving our

understanding of the metabolome and genomics. A broad range of fields commonly

apply metabolomics studies, including those related to the effects of drugs, cellular

function, and drug discovery, as well as to the search for biomarkers of diseases. It is

possible to divide a well-designed metabolomics study into phases, including ethical

approval, sample collection and preparation, sample analysis (Liquid or Gas

Chromatography Coupled to Mass Spectrometry - LC-MS/GC-MS, High or Ultrahigh

Performance Liquide Chromatography - HPLC/UPLC, or Nuclear Magnetic Resonance

- NMR), identification/quantification of metabolites, statistical analysis, and

biochemical interpretation. In studies involving biological samples, the use of NMR

has increased, in comparison with GC-MS and LC-MS, because NMR presents

advantages, including the fact that it is nondestructive to samples, no chromatographic

separation is needed, and there is a possibility of determining unknown metabolites. In

addition to discussing NMR-based metabolomics studies involving biological samples

from humans, in this chapter, we discuss essential aspects in early stages, including

sample preparation in phosphate buffer, utilization of internal standards, the importance

of water suppression, and the use of 1D and 2D NMR spectroscopies for identification

of metabolites.