Single crystals of DPPH grown from diethyl ether and carbon disulfide solutions - Crystal structures, IR, EPR and magnetization studies

Single crystals of the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) obtained from diethyl ether (ether) and carbon disulfide (CS2) were characterized by the X-ray diffraction, IR, EPR and SQUID magnetization techniques. The X-ray structural analysis and IR spectra showed that the DPPH form crystallized from ether (DPPH1) is solvent free, whereas that one obtained from CS2 (DPPH2) is a solvate of the composition 4DPPH.CS2. Principal values of the g-tensor were estimated by the X-band EPR spectroscopy at room and low (10 K) temperatures. Magnetization studies revealed the presence of antiferromagnetically coupled dimers in both types of crystals. However, the way of dimerization as well as the strength of exchange couplings are different in the two DPPH samples, which is in accord with their crystal structures. The obtained results improved parameters accuracy and enabled better understanding of properties of DPPH as a standard sample in the EPR spectrometry

Study of the local field distribution on a single-molecule magnet-by a single paramagnetic crystal; a DPPH crystal on the surface of an Mn12-acetate crystal

The local magnetic field distribution on the subsurface of a single-molecule magnet crystal, SMM, above blocking temperature (T >> Tb) detected for a very short time interval (~ 10-10 s), has been investigated. Electron Paramagnetic Resonance (EPR) spectroscopy using a local paramagnetic probe was employed as a simple alternative detection method. An SMM crystal of [Mn12O12(CH3COO)16(H2O)4].2CH3COOH.4H2O (Mn12-acetate) and a crystal of 2,2- diphenyl-1-picrylhydrazyl (DPPH) as the paramagnetic probe were chosen for this study. The EPR spectra of DPPH deposited on Mn12-acetate show additional broadening and shifting in the magnetic field in comparison to the spectra of the DPPH in the absence of the SMM crystal. The additional broadening of the DPPH linewidth was considered in terms of the two dominant electron spin interactions (dipolar and exchange) and the local magnetic field distribution on the crystal surface. The temperature dependence of the linewidth of the Gaussian distribution of local fields at the SMM surface was extrapolated for the low temperature interval (70-5 K)

Application of EPR spectroscopy in preservation of foodstuff with ionizing radiation 1. part - accurate detection of irradiation dose by EPR/alanine dosimetry

Paramagnetski centri u L-alaninu ozračenom - zračenjem pokazuju izuzetnu stabilnost u vremenu, a njihova koncentracija proporcionalna je dozi ionizacijskog zračenja za veliki raspon doza (0.5-105 Gy). Ove karakteristike čine osnovu na kojoj se zasniva dozimetrija uz pomoć elektronske paramagnetske rezonancije (EPR/Alaninska dozimetrija). U ovom radu dan je osvrt na primjenu EPR/Alaninske dozimetrije.Stability of paramagnetic centers in -irradiated L-alanine at room temperature and its linear dependence of concentration in the wide range of irradiation dose (0.5-105 Gy) are the most important properties of EPR/alanine dosimeter. In this paper, a review is presented about the use of EPR/alanine dosimetry

Application of epr spectroscopy in preservation of foodstuff with ionizing radiation Part 2. Testing of prescribed dose in foodstuff of animal origin preserved with ionising radiation

Primjena ionizacijskog zračenja u konzerviranju namirnica na svjetskom tržištu, zakonska regulativa vezana uz upotrebu tehnologije zračenja i zahtjev potrošača za jasnom deklaracijom ozračenih namirnica naglasila je potrebu razvoja analitičkih metoda za detekciju namirnica konzerviranih na takav način. Jedna od najpreciznijih metoda za identifikaciju ozračenih namirnica je metoda elektronske paramagnetske rezonancije (EPR). EPR spektroskopija je fizikalna metoda koja promatra nesparene elektrone, posebno slobodne radikale uzrokovane primjenom zračenja. Može se upotrijebiti kao identifikacijski test ako su radikali stabilni tijekom komercijalnog roka upotrebe ozračene namirnice, čije su komponente u čvrstom i suhom stanju, gdje je reaktivnost radikala međusobno i s vodom mala. Primjenjuje se na kostima u mesu i ribi, voću i povrću, te proizvodima takvih namirnica (čaj, začini i sl.), te namirnicama iz mora itd. U ovom radu opisana je primjena EPR spektroskopije u provjeri ispravnosti doze u raznim namirnicama animalnog porijekla konzerviranih ionizacijskim zračenjem.Application of ionising radiation in the preservation of foodstuffs on the world food market, irradiation treatment regulations and demands of consumers for clear declaration of irradiated foodstuffs have emphasised the need for the development of analytical methods for the detection of foodstuffs preserved by ionising radiation. One of the most accurate methods for the identification of irradiated foodstuffs is EPR spectroscopy. EPR spectroscopy is a physical method for detecting unpaired electrons, especially free radicals induced by ionising radiation. EPR can be used as identification test if the radicals are stable over the maximum commercial shelf life of irradiated food with solid and dry components, and where the rigid structure of the matrix inhibits radicals reacting with each other or with food components present in the its wet portion. EPR can be applied to meat and fish bones, fruit and vegetables and the relative products (tea, seasonings, etc.), seafood, etc. This paper describes the use of EPR spectroscopy for assessing the dose level in various foodstuffs of animal origin preserved with ionising radiation

Magnetic anisotropy of spin tetramer system SeCuO3_3 studied by torque magnetometry and ESR spectroscopy

We present an experimental study of macroscopic and microscopic magnetic anisotropy of a spin tetramer system SeCuO$_3$ using torque magnetometry and ESR spectroscopy. Large rotation of macroscopic magnetic axes with temperature observed from torque magnetometry agrees reasonably well with the rotation of the $\textbf{g}$ tensor above $T \gtrsim 50$~K. Below 50~K, the $\textbf{g}$ tensor is temperature independent, while macroscopic magnetic axes continue to rotate. Additionally, the susceptibility anisotropy has a temperature dependence which cannot be reconciled with the isotropic Heisenberg model of interactions between spins. ESR linewidth analysis shows that anisotropic exchange interaction must be present in SeCuO$_3$. These findings strongly support the presence of anisotropic exchange interactions in the Hamiltonian of the studied system. Below $T_N=8$~K, the system enters a long - range antiferromagnetically ordered state with easy axis along the $^*$ direction. Small but significant rotation of magnetic axes is also observed in the antiferromagnetically ordered state suggesting strong spin-lattice coupling in this system.Comment: 14 pages, 13 figure

Electron spin-lattice relaxation in solid ethanol: the effect of nitroxyl radical hydrogen bonding and matrix disorder

The electron spin-lattice relaxation of TEMPO and TEMPONE was measured at temperatures between 5 and 80 K in crystalline and glassy ethanol using X-band electron paramagnetic resonance spectroscopy. The experimental data at the lowest temperatures studied were explained in terms of electron-nuclear dipolar interaction between the paramagnetic center and the localized excitations, whereas at higher temperatures low-frequency vibrational modes from the host matrix and Raman processes should be considered. The strong impact of hydrogen bonding between the dopant molecule and ethanol host on the spin relaxation was observed in ethanol glass whereas in crystalline ethanol both paramagnetic guest molecules behaved similarly.Comment: 13 pages, 2 figures, 32 reference

Low temperature electron-spin relaxation in the crystalline and glassy states of solid ethanol

X-band electron paramagnetic resonance (EPR) spectroscopy was used to study the spectral properties of a nitroxide spin probe in ethanol glass and crystalline ethanol, at 5 - 11.5 K. The different anisotropy of molecular packing in the two host matrices was evidenced by different rigid limit values for maximal hyperfine splitting in the signal of the spin probe. The significantly shorter phase memory time, , for the spin probe dissolved in crystalline ethanol, as compared to ethanol glass, was discussed in terms of contribution from spectral diffusion. The effect of low-frequency dynamics was manifested in the temperature dependence of and in the difference between the data measured at different spectral positions. This phenomenon was addressed within the framework of the slow-motional isotropic diffusion model [S. Lee, and S. Z. Tang, Phys. Rev. B 31, 1308 (1985)] predicting the spin probe dynamics within the millisecond range, at very low temperatures. The shorter spin-lattice relaxation time of the spin probe in ethanol glass was interpreted in terms of enhanced energy exchange between the spin system and the lattice in the glass matrix due to boson peak excitations.Comment: 16 pages, 4 figures, 36 reference