Electron Paramagnetic Resonance Study of Organic Radicals in Some Herbal Plants

In this work we show the impact of the roasting process on the properties of organic radicals in some herbal products added to cereal coffee. The EPR study shows the presence of radicals in dried herbal products, both natural and roasted. Changes in the relative intensity of the EPR signal and in the g-factor for unroasted and roasted plant material can be observed. This indicates to the recombination processes of radicals. Roasting process increases the number of radicals. The analysis of EPR spectra show that they consist of two Gaussian lines which indicate that there are at least two different kinds of radicals. The values of g-factor about 2 may be derived from a number of very different radicals. For this reason the identification of such radicals is not strictly possible

Spin Transition Diagram of (2Me-5Et-PyH)[Fe(Th-5Cl-Sa)2\text{}_{2}] Studied by EPR

The high-spin↔ low-spin transition in (2Me-5Et-PyH)[Fe(Th-5Cl-Sa)$\text{}_{2}$] was studied by EPR under hydrostatic pressure in the temperature range of 80-310 K. Two modifications of the low-spin complexes: low-pressure (LS-1) and high-pressure (LS-2) ones were revealed. The low-spin complexes are associated in domains. Under atmospheric pressure LS-1 appears or disappears at 220 K. The hydrostatic pressure shifts the transition to high temperatures. Above 410 MPa the abrupt changes of the g-factor and width Δ B of the EPR line are observed. The pressure-induced transition LS-1 ↔ LS-2 is almost independent of T up to 275 K where under pressure 420 MPa a triple point is observed. When the pressure has been decreased the reverse transition from LS-2 to LS-1 or to high spin phase (at T>260 K) occurs with a large hysteresis about 95 MPa

Intramolecular and Lattice Dynamics in V 6-n

Multi-nuclear mixed-valence clusters V$\text{}_{4}^{IV}$V$\text{}_{2}^{V}$O$\text{}_{7}$(OCH$\text{}_{3}$)$\text{}_{12}$ were studied by X-band EPR in the temperature range 4.2-300 K. An isotropic exchange interactions between four V$\text{}^{IV}$ ions with individual spin S$\text{}_{i}$=1/2 determine the energy levels structure of the compound with the total spin states S=0, 1, and 2, which are doubled and split due to the extra electron transfer. The spin-Hamiltonian approach was used for the analysis of the temperature dependences of the EPR spectra parameters and the cluster dynamics. Two types of the electron transfer are assumed: the single jump transfer leading to the splitting of the total spin states by intervals comparable in magnitude with the exchange parameter J≈100-150 cm$\text{}^{-1}$ and the double jump one resulting in dynamics. The dependence of the transition ratesν$\text{}_{tr}$ on the energy of the total spin states was observed. In particular, in the range 300-220 K theν$\text{}_{tr}$ ≈0.7×10$\text{}^{10}$ cm$\text{}^{-1}$ and below 180 K the ν$\text{}_{tr}$≈1×10$\text{}^{10}$ cm$\text{}^{-1}$ was estimated. The g-factors of the spin states were shown to depend on the values of the intermediate spins. A phase transition in the T-range 210-180 K leading to the change in the initial V$\text{}^{IV}$ ions localization was discovered

Intramolecular and Lattice Dynamics in V6−nIV\text{}_{6-n}^{IV}VnV\text{}_{n}\text{}^{V} O7\text{}_{7}(OCH3\text{}_{3})12\text{}_{12} Crystal

Multi-nuclear mixed-valence clusters V$\text{}_{4}^{IV}$V$\text{}_{2}^{V}$O$\text{}_{7}$(OCH$\text{}_{3}$)$\text{}_{12}$ were studied by X-band EPR in the temperature range 4.2-300 K. An isotropic exchange interactions between four V$\text{}^{IV}$ ions with individual spin S$\text{}_{i}$=1/2 determine the energy levels structure of the compound with the total spin states S=0, 1, and 2, which are doubled and split due to the extra electron transfer. The spin-Hamiltonian approach was used for the analysis of the temperature dependences of the EPR spectra parameters and the cluster dynamics. Two types of the electron transfer are assumed: the single jump transfer leading to the splitting of the total spin states by intervals comparable in magnitude with the exchange parameter J≈100-150 cm$\text{}^{-1}$ and the double jump one resulting in dynamics. The dependence of the transition ratesν$\text{}_{tr}$ on the energy of the total spin states was observed. In particular, in the range 300-220 K theν$\text{}_{tr}$ ≈0.7×10$\text{}^{10}$ cm$\text{}^{-1}$ and below 180 K the ν$\text{}_{tr}$≈1×10$\text{}^{10}$ cm$\text{}^{-1}$ was estimated. The g-factors of the spin states were shown to depend on the values of the intermediate spins. A phase transition in the T-range 210-180 K leading to the change in the initial V$\text{}^{IV}$ ions localization was discovered

EPR Discovery of a New Pressure-Induced Low-Spin Phase in (2Me-5Et-PyH)[Fe(Th-5Cl-Sa) 2

Electron paramagnetic resonance studies of the high-spin (HS) ↔ low-spin (LS) transition in 2-methyl-5-ethyl-pyridine-5-chloro-salicylalt hiosemicarbazonatoferrate(III) performed under hydrostatic pressure up to 500 MPa in a temperature range of 80-310 K have revealed two modifications of the low spin complexes: low-pressure (LS1) and high-pressure (LS2) ones. Under atmospheric pressure LS1 appears on cooling and disappears on heating at 220 K. The hydrostatic pressure shifts the transition to higher temperatures. Below 275 K an increase in pressure to 410 MPa results in abrupt changes in the g-factor and widthΔ B of the EPR line indicating a transition to a new phase. The pressure-induced transition LS1 ↔ LS2 is almost independent of T up to 275 K, where at a pressure of 420 MPa a triple point is observed. The LS1↔ LS2 and HS↔ LS2 (at T>260 K) transitions occur with a large hysteresis of about 95 MPa. The process of the spin transition has been shown to begin with the formation of domains of LS complexes in the matrix of HS ones. The response of the domains to external factors has been studied

The Origin of EPR Signals in SrCuO2\text{}_{2} Ceramics

The origin and thermal evolution of the EPR signals in SrCuO$\text{}_{2}$ ceramics are studied. It has been shown that the EPR signals observed in this ceramic material are due to contamination with other phases. The axial signal is due to SrCu(OH)$\text{}_{4}$·H$\text{}_{2}$O, which is a product of water reactions with SrCuO$\text{}_{2}$

EPR Study of Water Induced Decomposition of the SrCuO2\text{}_{2} and Sr2\text{}_{2}CuO3\text{}_{3} Ceramics Surface. The Role of Carbon Dioxide

Processes of SrCuO$\text{}_{2}$ and Sr$\text{}_{2}$CuO$\text{}_{3}$ ceramics decomposition induced by contact with water and carbon dioxide were studied by EPR. The dominant signals in the spectra were found to originate from Sr$\text{}_{2}$Cu(OH)$\text{}_{6}$ (for Sr$\text{}_{2}$CuO$\text{}_{3}$) and SrCu(OH)$\text{}_{4}$·H$\text{}_{2}$O (for SrCuO$\text{}_{2}$) compounds. The thermally induced conversion of SrCu(OH)$\text{}_{4}$·H$\text{}_{2}$O into Sr$\text{}_{2}$Cu(OH)$\text{}_{6}$ was analysed, and its product CuO was found to exist in the nanocrystalline form. The presence of CO$\text{}_{2}$, reacting with Sr(OH)$\text{}_{2}$, was shown to modify the decomposition process leading to the appearance of SrCu(OH)$\text{}_{4}$·H$\text{}_{2}$O, some hydroxycarbonates and Cu(OH)$\text{}_{2}$ on the surface of ceramics studied. At temperatures higher than 300ºC CuO reacts back with Sr(OH)$\text{}_{2}$. For the samples being in contact with atmospheric moisture this compound, deposited on a surface of SrCuO$\text{}_{2}$, decomposes to Sr$\text{}_{2}$Cu(OH)$\text{}_{6}$. The presence of the antiferromagnetic compounds Cu(OH)$\text{}_{2}$, CuO, and Cu$\text{}_{2}$[(OH)$\text{}_{2}$CO$\text{}_{3}$] in the samples can influence the results of magnetic measurements of the studied ceramics