Application of EPR Spectroscopy to Examination of the Effect of Sterilization Process on Free Radicals in Different Herbs

How alanine catalyzes melanoidin formation and dehydration during synthesis from glucose

The chemical composition of melanoidins formed from glucose (Glc) and alanine (Ala) in different molar ratios was investigated using UV/Vis, FTIR, EPR spectroscopy and elemental analysis (EA). Melanoidin samples were prepared at varying molar ratios of Glc and Ala ranging from 10:1 to 1:10 (Glc:Ala). Reaction systems containing a higher molar ratio of Ala show higher melanoidin yields and higher UV/Vis absorbance. This indicates that an excess of Ala facilitates the formation of larger π-electron systems and catalyzes the melanoidin formation. EPR spectroscopy showed more radicals in Ala enriched samples. The EA data suggest that during the formation of melanoidin from Glc and Ala higher amounts of amino acid support dehydration of the reaction products. On the basis of our data, we postulate the structures of products and intermediates for the reaction at different Glc/Ala ratios. PCA of the FTIR spectra allows to separate different melanoidin samples formed at varying molar ratios indicating their different molecular compositions.

An X-band pulsed electron paramagnetic resonance spectrometer with time resolution improved by a field-programmable-gate-array based pulse generator

We report an X-band pulsed electron paramagnetic resonance (EPR) spectrometer using a Field-Programmable-Gate-Array (FPGA) based pulse generator. The microwave (MW) pulse length and pulse-pulse interval can be adjusted with 50 ps time resolution. A FPGA based pulse generator is utilized to achieve such time resolution. There are eight pulse channels integrated in the pulse generator. Each channel outputs rectangular pulses with 50 ps time resolution. The spectrometer includes a pulse forming unit, where four high-speed PIN diode switches are controlled by the pulse generator to generate MW pulses. A commercial digital storage oscilloscope is used to record the EPR signal. A customized software is developed to control the components of the spectrometer and to perform data processing task. The usefulness of high time resolution is demonstrated by the results of Rabi oscillation.

Effect of UV irradiation on Echinaceae purpureae interactions with free radicals examined by an X-band (9.3 GHz) EPR spectroscopy

The effect of UVA (315-400 nm) irradiation on Echinaceae purpureae interactions with free radicals was examined by the use of electron paramagnetic resonance (EPR) spectroscopy. The changes of antioxidant properties of E. purpureae with time of UV irradiation from 10 to 110 min (10 min steps) were determined. DPPH as the paramagnetic reference was used in this study. Changes of EPR signals of the reference after interactions with nonirradiated and UV-irradiated E. purpureae were detected. Interactions of the tested E. purpureae samples caused decrease of the EPR signal of DPPH as the result of its antioxidant properties. The decrease of the amplitude of EPR line of DPPH was lower for interactions with UV-irradiated E. purpureae. EPR examination confirmed antioxidant properties of E. purpureae. The weaker antioxidant properties of E. purpureae after UV irradiation were pointed out. E. purpureae should be storage in the dark. The tests bring to light usefulness of electron paramagnetic resonance with microwave frequency of 9.3 GHz (an X-band) in examination of storage conditions of pharmacological herbs.