39 research outputs found
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 SeCuO studied by torque magnetometry and ESR spectroscopy
We present an experimental study of macroscopic and microscopic magnetic
anisotropy of a spin tetramer system SeCuO 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 tensor above ~K. Below 50~K, the
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. These findings strongly
support the presence of anisotropic exchange interactions in the Hamiltonian of
the studied system. Below ~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