Copper(II) ions interactions in the systems with triamines and ATP. Potentiometric and spectroscopic studies.

The mode of interaction and thermodynamic stability of complexes formed in binary and ternary Cu(II)/ATP/triamines systems were studied using potentiometric and spectroscopic (NMR, EPR, UV-Vis) methods. It was found that in binary metal-free systems ATP/HxPA species are formed (PA: Spd=spermidine or 3,3-tri=1,7-diamino-4-azaheptane) where the phosphate groups from nucleotides are preferred negative centers and protonated amine groups of amines are positive centers of reaction. In the ternary systems Cu/ATP/Hx(PA) as well as Cu/(ATP)(PA) species are formed. The type of the formed Cu(II) complexes depends on pH of the solution. For a low pH value the complexation appears between Cu(II) and ATP molecules via oxygen atoms of phosphate groups. For a very high pH value, where ATP is hydrolyzed, the Cu(II) ions are bound to the nitrogen atoms of polyamine molecules. We did not detect any direct coordination of the N7 nitrogen atom of adenosine to Cu(II) ions. It means that the CuN7 interaction is an indirect type and can be due to noncovalent interplay including water molecule. EPR studies were performed at glassy state (77K) after a fast freezing both for binary and ternary systems. The glassy state EPR spectra do not reflect species identified in titration studies indicating significant effect of rapid temperature decrease on equilibrium of Cu(II) complexes. We propose the molecular structure of all the studied complexes at the glassy state deduced from EPR and optical spectroscopy results.

Resonance local phonon mode and electron spin-lattice relaxation of formate-type free radicals studied by electron spin echo in Cd(HCOO)2·2H2O crystal.

The results of X-band electron spin resonance (ESR) and electron spin echo (ESE) measurements for free radicals generated in Cd(HCOO)2·2H2O single crystal are presented. From ESR spectra analysis the radicals were identified as CO2(-) after x-ray irradiation and as HOCO after γ-ray irradiation. The room temperature g-factors are: g|| = 1.9969 and g⊥ = 2.0024 for CO2(-) and g1 = 2.0087, g2 = 2.0029 and g3 = 1.9960 for HOCO. Axial g-tensor symmetry for CO2(-) is due to fast reorientation of the radical molecule around the g||-axis. Assignment of HOCO is confirmed by hyperfine splitting (Amax = 0.4 mT) from a single distant proton. Spin lattice relaxation rate was determined from ESE measurements in temperature range 4-250 K. Both radicals relax via local resonance mode lying within acoustic phonon branch. The existing theories of electron spin-lattice relaxation via local resonance mode are critically reviewed and compared with experimental data. A new approximation is proposed giving local mode energy hω(R) = 56 cm(-1) for CO2(-) and hω(R) = 44 cm(-1) for the HOCO-radical.

ESR lineshape and 1H spin-lattice relaxation dispersion in propylene glycol solutions of nitroxide radicals--joint analysis.

Electron Spin Resonance (ESR) spectroscopy and Nuclear Magnetic Relaxation Dispersion (NMRD) experiments are reported for propylene glycol solutions of the nitroxide radical: 4-oxo-TEMPO-d16 containing (15)N and (14)N isotopes. The NMRD experiments refer to (1)H spin-lattice relaxation measurements in a broad frequency range (10 kHz-20 MHz). A joint analysis of the ESR and NMRD data is performed. The ESR lineshapes give access to the nitrogen hyperfine tensor components and the rotational correlation time of the paramagnetic molecule. The NMRD data are interpreted in terms of the theory of paramagnetic relaxation enhancement in solutions of nitroxide radicals, recently presented by Kruk et al. [J. Chem. Phys. 138, 124506 (2013)]. The theory includes the effect of the electron spin relaxation on the (1)H relaxation of the solvent. The (1)H relaxation is caused by dipole-dipole interactions between the electron spin of the radical and the proton spins of the solvent molecules. These interactions are modulated by three dynamic processes: relative translational dynamics of the involved molecules, molecular rotation, and electron spin relaxation. The sensitivity to rotation originates from the non-central positions of the interacting spin in the molecules. The electronic relaxation is assumed to stem from the electron spin-nitrogen spin hyperfine coupling, modulated by rotation of the radical molecule. For the interpretation of the NMRD data, we use the nitrogen hyperfine coupling tensor obtained from ESR and fit the other relevant parameters. The consistency of the unified analysis of ESR and NMRD, evaluated by the agreement between the rotational correlation times obtained from ESR and NMRD, respectively, and the agreement of the translation diffusion coefficients with literature values obtained for pure propylene glycol, is demonstrated to be satisfactory.

Suppression of Raman electron spin relaxation of radicals in crystals. Comparison of Cu2+ and free radical relaxation in triglycine sulfate and Tutton salt single crystals.

Electron spin-lattice relaxation was measured by the electron spin echo method in a broad temperature range above 4.2 K for Cu(2+) ions and free radicals produced by ionizing radiation in triglycine sulfate (TGS) and Tutton salt (NH4)(2)Zn(SO4)2 ⋅ 6H2O crystals. Localization of the paramagnetic centres in the crystal unit cells was determined from continuous wave electron paramagnetic resonance spectra. Various spin relaxation processes and mechanisms are outlined. Cu(2+) ions relax fast via two-phonon Raman processes in both crystals involving the whole phonon spectrum of the host lattice. This relaxation is slightly slower for TGS where Cu(2+) ions are in the interstitial position. The ordinary Raman processes do not contribute to the radical relaxation which relaxes via the local phonon mode. The local mode lies within the acoustic phonon band for radicals in TGS but within the optical phonon range in (NH4)(2)Zn(SO4)2 ⋅ 6H2O. In the latter the cross-relaxation was considered. A lack of phonons around the radical molecules suggested a local crystal amorphisation produced by x- or γ-rays.

Dynamical properties and instability of local fluorite BaF(2) structure around doped Mn(2+) ions-EPR and electron spin echo studies.

The electron paramagnetic resonance (EPR) and electron spin echo (ESE) were measured at the X-band for Mn(2+) in a BaF(2) crystal in the temperature range 4.2-300 K. In addition to the cubic symmetry centre, two other lower concentration tetragonal centres were identified. Temperature variations and computer simulation of the EPR spectrum confirm that the cubic symmetry of the MnF(8) centre is deformed to two T(d) tetrahedra of different dimensions at around 45 K. Electron spin relaxation was measured in the temperature range 4.2-35 K, where the ESE signal was detectable. For higher temperature the Mn(2+) dynamics produces homogeneously broadened EPR lines. At the lowest temperatures the spin-lattice relaxation is governed by ordinary phonon processes with 1/T(1)∼T(5). The efficiency of these processes rapidly decreases and at about 11 K a local mode of energy 17 cm(-1) becomes the relaxation mechanism. Phase relaxation observed as ESE signal dephasing indicates that after the local deformation jumps (tunnelling with frequency 4 × 10(8) s(-1)) between the two tetrahedral configurations appear, with the energy barrier being the local mode energy. This motion is directly visible as a resonance-type enhancement of the ESE dephasing rate 1/T(M) around 11 K. Only the cubic centre displays the above dynamics.

Molecular structure and dynamics of off-center Cu(2+) ions and strongly coupled Cu(2+)-Cu(2+) pairs in BaF(2) crystals: electron paramagnetic resonance and electron spin relaxation studies.

X-band and Q-band electron paramagnetic resonance (EPR) spectra of Cu(2+) in BaF(2) crystal were recorded in the temperature range of 4.2-200 K. Spin-Hamiltonian parameters of single Cu(2+) complexes and of Cu(2+)-Cu(2+) pairs were derived and discussed. A special attention was paid to the dimeric species. Their molecular ground state configuration was found as having antiferromagnetic intradimer coupling with the singlet-triplet splitting J=-35 cm(-1). The zero-field splitting being D=0.0365 cm(-1) at 4.2 K increases with temperature as an effect of thermal population of excited dimer configurations. Electron spin echo (ESE) method was used for measurements of electron spin lattice and phase relaxation. The spin-lattice relaxation data show that except for coupling to the host lattice phonons the Cu(2+) ions are involved in local mode motions with energy of 82 cm(-1). Phase relaxation (ESE dephasing) of single Cu(2+) ions is due to spin diffusion at low temperatures. This relaxation is hampered for temperatures higher than 30 K due to the triplet state population of neighboring Cu(2+)-Cu(2+) dimers, which disturb dipolar coupling between Cu(2+) ions. For higher temperatures the relaxation is dominated by Raman T(1) processes. Fourier transform ESE spectrum displays dipolar Cu-F splitting which allowed determination of the off-center shift of Cu(2+) as delta(s)=0.132 nm. The dynamical effects observed in EPR spectra and in electron spin relaxation both for single Cu(2+) ions and Cu(2+)-Cu(2+) pairs are discussed as due to jumps between six off-center positions in the crystal unit cell and jumps between various dimer configurations.

Electron spin echo of Cu(2+) in the triglycine sulfate crystal family (TGS, TGSe, TGFB): electron spin-lattice relaxation, Debye temperature and spin-phonon coupling.

The electron spin-lattice relaxation of Cu(2+) has been studied by the electron spin echo technique in the temperature range 4.2-115 K in triglycine sulfate (TGS) family crystals. Assuming that the relaxation is due to Raman relaxation processes the Debye temperature Θ(D) was determined as 190 K for TGS, 168 K for triglycine selenate (TGSe) and 179 K for triglycine fluoroberyllate (TGFB). We also calculated the Θ(D) values from the sound velocities derived from available elastic constants. The elastic Debye temperatures were found as 348 K for TGS, 288 K for TGSe and 372 K for TGFB. The results shown good agreement with specific heat data for TGS. The elastic Θ(D) are considerably larger than those determined from the Raman spin-lattice relaxation. The possible reasons for this discrepancy are discussed. We propose to use a modified expression describing two-phonon Raman relaxation with a single variable only (Θ(D)) after elimination of the sound velocity. Moreover, we show that the relaxation data can be fitted using the elastic Debye temperature value as a constant with an additional relaxation process contributing at low temperatures. This mechanism can be related to a local mode of the Cu(2+) defect in the host lattice. Electron paramagnetic resonance g-factors and hyperfine splitting were analysed in terms of the molecular orbital theory and the d-orbital energies and covalency factors of the Cu(gly)(2) complexes were found. Using the structural data and calculated orbital energies the spin-phonon coupling matrix element of the second-order Raman process was calculated as 553 cm(-1) for TGS, 742 cm(-1) for TGSe and 569 cm(-1) for TGFB.

Water and lipid relations in beech (Fagus sylvatica L.) seeds and its effect on storage behaviour.

Beech (Fagus sylvatica L.) seeds indicate intermediate storage behaviour. Properties of water in seed tissues were studied to understand their requirements during storage conditions. Water sorption isotherms showed that at the same relative humidity (RH) the water content is significantly higher in embryo axes than cotyledons. This tendency maintains also after recalculating the water content for zero amount of lipids in tissues. Differential thermal analysis (DTA) indicated water crystallization exotherms in the embryo axes at moisture content (MC) higher than 29% and 16% in the cotyledons. In order to examine the occurrence of glassy state in the cytoplasm of beech embryos as a function of water content, isolated embryo axes were examined using electron spin resonance (ESR) of nitroxide TEMPO probe located inside axes cells. TEMPO molecules undergo fast reorientations with correlation time varied from 2 x 10(-9) s at 180 K to 2 x 10(-11) s at 315 K. Although the TEMPO molecules label mainly the lipid bilayers of cell membranes, they are sensitive to the dynamics and phase transformation of the cytoplasmic cell interior. The label motion is clearly affected by a transition between liquid and glassy state of the cytoplasm. The glass transition temperature (T(g)) raises from 253 to 293 K when water content decreases from 18% to 8%. Far from T(g) the motion is described by Arrhenius equation with very small activation energy E(a) in the liquid state and is relatively small in the glassy state where E(a)=1.5 kJ/mol for 28% H(2)O and E(a)=4.7 kJ/mol for 8% H(2)O or less. The optimal storage conditions of beech seeds are proposed in the range from 255 K for 15% H(2)O to 280 K for 9% H(2)O.

Dephasing relaxation of the electron spin echo of the vibronic Cu(H(2)O)(6) complexes in Tutton salt crystals at low temperatures.

Two-pulse electron spin echo (ESE) measurements of the phase relaxation (phase memory time T(M)) were performed in a series of Tutton salt crystals M(I)(2)M(II)(SO(4))(2).6X(2)O (M(I)=NH(4), K, Cs; M(II)=Zn, Mg; X=H, D) weakly doped with Cu(2+) ions (c approximately equal to 10(18) ions/cm(3)) in temperature range 4-60 K where ESE signals were detectable. The ESE decay was strongly modulated with proton (or deuteron) frequencies and described by the decay function V(2tau)=V(0)exp(-btau-mtau(2)) with the mtau(2) term being temperature independent and negligible above 20 K. Various mechanisms leading to the tau- or tau(2)-type ESE decay are reviewed. The m and b coefficients for nuclear spectral diffusion (NSD), electron spectral diffusion (SD), and instantaneous diffusion (ID) were calculated in terms of existing theories and the resulting rigid lattice T(0)(M) times were found to be close one to another within the crystal family with average values: 17.5 micros (NSD protons), 200 micros (NSD deuterons), 8 micros (SD), and 5 micros (ID). The ID dominates but the calculated effective T(M)(0) is longer than the experimental T(M)(0)=2 micros. This is due to a nonuniform distribution of the Cu(2+) ions with a various degree of the disorder in the studied crystals. The acceleration of the dephasing rate 1/T(M) with temperature is due to the mechanisms producing exp(-btau) decay. They are reviewed and two of them were found to be operative in Tutton salt crystals: (a) Excitations to the vibronic levels of energy Delta leading to the temperature dependence 1/T(M)=B exp(-Delta/kT), with the vibronic levels produced by strong Jahn-Teller effect, and (b) spin-lattice relaxation processes being effective above 50 K. Based on the Delta values being on the order of 100 cm(-1), the scheme of vibronic levels in the Tutton salts is presented, and the independence of the Delta on temperature proves that the adiabatic potential surface shape of Jahn-Teller active Cu(H(2)O)(6) complexes is not affected by temperature below 65 K.

Electron spin relaxation in pseudo-Jahn-Teller low-symmetry Cu(II) complexes in diaqua(L-aspartate)Zn(II).H(2)O crystals.

Low-temperature (4-55 K) pulsed EPR measurements were performed with the magnetic field directed along the z-axis of the g-factor of the low-symmetry octahedral complex [(63)Cu(L-aspartate)(2)(H2O)2] undergoing dynamic Jahn-Teller effect in diaqua(L-aspartate)Zn(II) hydrate single crystals. Spin-lattice relaxation time T(1) and phase memory time T(M) were determined by the electron spin echo (ESE) method. The relaxation rate 1/T(1) increases strongly over 5 decades in the temperature range 4-55 K. Various processes and mechanisms of T(1)-relaxation are discussed, and it is shown that the relaxation is governed mainly by Raman relaxation processes with the Debye temperature Theta(D)=204 K, with a detectable contribution from disorder in the doped Cu(2+) ions system below 12 K. An analytical approximation of the transport integral I(8) is given in temperature range T=0.025-10Theta(D) and applied for computer fitting procedures. Since the Jahn-Teller distorted configurations differ strongly in energy (delta(12)=240 cm(-1)), there is no influence of the classical vibronic dynamics mechanism on T(1). Dephasing of the ESE (phase relaxation) is governed by instantaneous diffusion and spectral diffusion below 20 K with resulting rigid lattice value 1/T(0)(M)=1.88 MHz. Above this temperature the relaxation rate 1/T(M) increases upon heating due to two mechanisms. The first is the phonon-controlled excitation to the first excited vibronic level of energy Delta=243 cm(-1), with subsequent tunneling to the neighbor potential well. This vibronic-type dynamics also produces a temperature-dependent broadening of lines in the ESEEM spectra. The second mechanism is produced by the spin-lattice relaxation. The increase in T(M) is described in terms of the spin packets forming inhomogeneously broadened EPR lines.

Flexibility of CuCl4-tetrahedra in bis[cinchoninium tetrachlorocuprate(II)]trihydrate single crystals. X-ray diffraction and EPR studies.

Crystal structure of bis[cinchoninium tetrachlorocuprate(II)] trihydrate, [(C19H24N2O)CuCl4]2-3H2O, has been determined by X-ray diffraction at 100 K and reexamined at 293 K. The compound crystallizes in orthorhombic system with a P2(1)2(1)2(1) space group and unit cell parameters a = 15.3031(14), b = 36.415(3), and c = 7.8341(5) A at 100 K, and Z = 4. The asymmetric unit consists of two (CuCl4)(2-) tetrahedral anions linked by hydrogen bonds to two doubly protonated cinchonine molecules and three water molecules. The tetrahedra are strongly flattened, to approximately D(2d) symmetry, with different deformation for two inequivalent (CuCl4)(2-) -ions in the asymmetric unit. The deformation of (CuCl4)(2-) and cinchoninium cations varies with temperature due to a rearrangement of the bifurcated hydrogen bond network. This is a continuous process observed as a monotonic variation of the EPR spectral parameters and the unit cell dimensions. EPR spectra show that very weak exchange coupling J(12) = 0.0030 cm(-1) operates between Cu(2+) ions within asymmetric units, corresponding to the general formula of the compound, as well as between equivalent Cu(2+) sites of different molecules, whereas the coupling is negligible between inequivalent sites. The intermolecular J(12) coupling is temperature-independent indicating that the whole asymmetric unit behaves as a magnetic unit (pseudodimer) in the whole temperature range.

Molecular changes in erythrocyte membranes induced by nitroimidazoles and radiation.

A damage of erythrocyte membranes by gamma-irradiation in the presence of nitroimidazole derivatives was shown by the demonstration of their effect on lipid peroxidation and SDS-PAGE protein pattern (1000 Gy) as well as on electron spin resonance (ESR) spectra of maleimide spin-labels attached to the membrane (for doses < or = 300 Gy). Erythrocyte membranes were labeled with two maleimide labels MAL-6 and MAL-M-3-PROXYL under strictly controlled and reproducible conditions with incubation at physiological temperature of 37 degrees C. The labels were bound to SH groups on the protein surface (weakly immobilized W-sites) as well as to internal SH-groups (strongly immobilized S-sites). The amplitude ratio W/S of the ESR signals was used for a monitoring of an influence of nitroimidazole drugs and gamma-irradiation. The influence appeared, even for the lowest doses, only when nitroimidazole drug was attached to the membrane. It was due to a destruction of spin-label paramagnetic centre both at W and S-sites and was related to the recombination processes during radiolysis connected with nitroimidazoles. It indicated a radiosensitivity of the nitroimidazoles. However, the persistent degradation of the membranes by the oxidative stress appeared above the threshold dose of 300 Gy determined from transformation of the W-sites into S-sites in ESR spectra. For the higher dose (1000 Gy) a fragmentation of the band 3 proteins was clearly seen as well as a partial damage of higher molecular-weight proteins with a simultaneous formation of much higher molecular-weight polymers.

Anisotropic Exchange Effects in Temperature and Pressure Dependences of EPR Zero-Field Splitting in [(C(6)H(5))(3)(n-propyl)P](2)Cu(2)Cl(6).

X-band single-crystal and powder EPR data were collected in the temperature range 4.2-300 K and under hydrostatic pressure up to 500 MPa for [(C(6)H(5))(3)(n-propyl)P](2)Cu(2)Cl(6) (C(42)H(44)P(2)Cu(2)Cl(6)). The crystal and molecular structure have been determined from X-ray diffraction. The compound crystallizes in the monoclinic space group P2(1)/n (Z = 2) and have unit cell dimensions of a = 9.556(5) Å, b= 17.113(3) Å, c = 13.523(7) Å, and beta = 96.10(4) degrees. The structure consists of two controsymmetric Cu(2)Cl(6)(2)(-) dimers well separated by complex anions. EPR spectra are typical for the triplet S = 1 state of Cu(2)Cl(6)(2)(-) dimer with parameters g(x)() = 2.114(8), g(y)() = 2.095(8), g(z)() = 2.300(8), and D(x)() = 0.025(1) cm(-)(1), D(y)() = 0.057(1) cm(-)(1), and D(z)() = -0.082(1) cm(-)(1) at room temperature. The D tensor is dominated by a contribution from anisotropic exchange but the dipole-dipole Cu-Cu coupling is not much less. The anisotropic exchange integrals were estimated to be as follows: J(xy,x)()()2(-)(y)()()2(an) = -45 cm(-)(1), J(xy,xy)()(an) = +17 cm(-)(1), J(xy,yz)()(an) = +62 cm(-)(1). The D tensor components are strongly temperature dependent and linearly increase on cooling with an anomalous nonlinear behavior below 100 K. The D values increase linearly with pressure, but the effect is much smaller than the temperature effect. This suggests that the D vs T dependence is dynamical in origin. EPR data, a possible mechanism, and contributions to the observed dependences are discussed and compared to EPR results for similar compounds.