Reactive oxygen and nitrogen species (ROS/RNS) has been a double-edged sword in the pathogenesis of a number of human diseases. It can be an oxidant and cause oxidative stress leading to progression of tissue injury. It can also be a secondary messenger triggering protective responses so as to enable the conditioned tissue to endure further injurious insults. Due to its important role in biology, a reliable technique to measure the generation and distribution is needed. In vivo electron paramagnetic resonance (EPR) spectroscopy and imaging technique has emerged as an important tool for characterizing and mapping of free radicals in biological systems. The EPR spectral characteristics including line-width, intensity, and lifetime, as well as spatial distribution of the radicals can provide vital information to enable the measurement of localized tissue redox status and oxygenation in disease models and even humans. In this brief review, a number of in vivo applications of EPR spectroscopy and imaging are discussed, including redox and oximetry spectroscopy, spatial and spectral-spatial imaging of organs and tissues.

Many of EPR(electron paramagnetic resonance) experimental methods can be used in studies of antioxidation activities of natural products, such as spin trapping EPR, cryogenic EPR for modeled animals and spin labeling EPR et al. It is an elementary requirement for an antioxidant to scavenge oxygen free radicals in vitro, but evaluating method in vivo is more valuable when the antioxidant is applied to a biological system. Through the studies of more than 200 herbages and some TCM recipes, the EPR screening methods for natural products as antioxidants have been established and described in detail. With the above EPR methods, it is believed that antioxidation activities of natural products can be obtained at molecular, cell, and tissue levels, respectively.

The linear-hyperbranched block polyethylene (LHBPE) is a new class  of polymer with useful combinations of amorphous and crystalline segments. This LHBPE could be prepared  via ethylene polymerization catalyzed by α-diimine nickel complex/ansa-ethylene bis-(1-η⁵-indenyl)-zirconium dichloride/methylaluminoxane (MAO) in the presence of chain transfer agent. Herein, a ¹³C NMR study of the LHBPEs is presented. Short branches such as methyl, ethyl, propyl, butyl and amyl  were assigned and quantified.

In this review, we briefly summarized the historical development of spin trapping-EPR technology during the past 30 years in China, including the molecular design and synthesis of new spin traps and the applications of spintrapping experiments coupled with EPR detection in photochemistry, electrochemistry and biology. Based on the present status of spin trapping research, finally we discussed the prospects for the future development of spin trapping technique.

Electron spin resonance (ESR) is the most direct technique and an effective and unique way to detect free radicals in biological samples. This paper reviews the applications of ESR in biology and medicine. The topics reviewed include development of spin labeling and spin trapping, ESR imaging and applications of ESR in studies of cell membrane, protein structure, and diseases (i.e., heart diseases, Alzheimer's disease, Parkinson’s disease, stoke, radiation damage and plant diseases).

Nuclear magnetic resonance (NMR) spectroscopy is often valued for its ability to shed light on molecular structure, but its greatest potential in drug discovery probably lies in the information it can reveal about molecular interactions at atomic level. The NMR parameters of the atoms in a compound, such as chemical shift, diffusion coefficient and relaxation time, are highly sensitive to the chemical environment surrounding them. Measuring these parameters therefore can provide information on whether a small molecule binds to a target protein or nucleic acid,  and what are the interacting parts of the small molecule and the macromolecular target. The NMR approaches can be used to validate ligand binding and/or to identify potential ligands in the mixtures of compounds. In the last decade, the ability of NMR spectroscopy as a tool to monitor intermolecular interactions in drug discovery has been increasingly appreciated in both academia and industry. In this perspective, we highlight some major applications of NMR in drug discovery in this review article, with focus on hit screening.

A novel linear nitrone spin-trap, DSC-PBN (N-(4-(((2,5-dioxopyrrolidin-1-yloxy)carbonyloxy)methyl)benzylidene)-2-methylpropan-2-N-oxide), was designed and synthesized. Its structure was characterized by UV, MS and ¹H NMR techniques. ESR results showed that the compound could be used to trap various free radicals efficiently, and the ESR spectra of the trapped radicals were readily recognizable. DSC-PBN could easily form a covalent link to the N-terminal peptides (or proteins) via succinimide intermediates, thus showing high potential for biological applications.

A cell perfusion system for online NMR studies is reported. The system was used to measure ³¹P NMR signals of ATP in living breast cancer cells (MCF-7), with or without perfusion with cantharidin solution. The results- showed that online NMR on perfused cell culture is an effective way to identify active components from extracts of traditional Chinese medicine. The method can also be used to study the interactions between drugs and cancer cells.

A biradical TN3 was synthesized, which is composed of a fully substituted triphenylmethyl radical and a nitroxide. EPR spectrum of TN3 at room temperature  consists of an asymmetric quartet broad lines, suggesting its typical biradical structure. Using- ascorbate as a model compound, we proved that TN3 can be used to evaluate redox status and oxygen level simultaneously.

Space radiation, especially heavy-ion radiation, can cause the damages to DNA, cell death and incidence of some types of cancer. We studied the effects of heavy-ion radiation on cerebral metabolism in rats. To simulate the biological effects of space heavy ions radiation on the central nervous system (CNS), rats heads were exposed to ¹²C⁶⁺ particle beam. The ¹H NMR based metabonomics approach was used to analyze the changes in metabolic profiles of the frontal cortex of the rats exposed to radiation. The results revealed that heavy-ion radiation caused significant changes in the levels of some cerebral metabolites, including taurine, lactate, creatine, myo-inositol, phosphorylcholine and some key neurotransmitters (i.e., glutamate and 4-aminobutyric acid).  The results of further differential proteomics analysis showed that there were significant changes in the  neurotransmitter synthesis pathway and neurotransmitter receptor-mediated signaling pathways after heavy-ion radiation. The findings from this study provided useful information on the molecular mechanism of the effects of heavy-ion radiation on cerebral metabolism.

Measuring distances among the functional domains of a protein is essential for understanding the structurefunction relationship in the protein. Electron paramagnetic resonance (EPR) combined with site-directed spin labeling (SDSL) is an important approach for determining the distances among selected points in a protein. With this approach, Fourier deconvolution distance measurement (FDDM) was often used to calculate the distances. The FDDM method, however, may show poor performance under special experimental conditions, such that some crucial parameters need to be set up manually, resulting in increased susceptibility to subjective errors. To solve this problem, a new distance calculation method, spectrum simulation-Fourier deconvolution distance measurement (SS-FDDM), was developed in this study. The validity of the method was tested with an experimental model of frozen free radical solution. SS-FDDM was then compared to FDDM in terms of practicability, antinoise performance and susceptibility to field shifting. The results showed that, with SS-FDDM, calculation errors originated from spectrum center shift and high noise levels can be reduced substantially, thus giving more reliable results.

The ¹H NMR spectrum and UV spectrum of cantharidin isolated from the body fluid of Epicauta aptera Kaszab were obtained. Discrepancies were found between our spectral results and those reported in published references. The mechanisms that had potentially led to such discrepancies were discussed.

The inversion-recovery pulse sequence used for routine measurement of spinlattice relaxation time (T₁) was modified to measure T₁ of water under high magnetic field (14.1 T). A pair of bipolar pulsed field gradients were added to suppress the effects of radiation damping, which often occurs with concentrated sample such as water. With this method, the relaxivity of commercial magnetic resonance imaging (MRI) contrast agent Gd-DTPA in aqueous solution was measured and found to be similar to the value reported in the literature. The method was also used to evaluate the performance of a newlysynthesized MRI contrast agent compound TEMDP-EMFs.

Baicalein, a primary metabolite of baicalin, differs from its mother compound merely by the 7-substituent (i.e. it possesses a phenolic hydroxyl (7-OH) instead of a glucuronic acid). The present work is intended to compare, by means of steady-state optical absorption spectroscopy, cyclic voltammetry, ESR and quantum chemical calculation, their physicochemical properties, such as pKa, log10 partition coefficient, redox potential and dipole moment, as well as their capacities of scavenging ABTS^·+ (TEAC) and autoxidation of baicalein. Experimental results showed that the 7-OH group of baicalein was rather acidic (pK_a=5.4). In addition, baicalein showed a lower redox potential (0.32 V vs. NHE) and a 1.8-fold higher TEAC with reference to baicalin under physiological pH. Theoretical results showed that the difference in 7-substituent resulted in significantly different molecular structures, physicochemical properties and radical scavenging activities of the flavonoids in question, which are discussed in terms of their micro- and macro-molecular properties. It was concluded that the number of phenolic hydroxyls and the corresponding pKa values, as well as the molecular structures are all important for the antioxidative activity of flavonoids.