Time-resolved EPR investigation on the photoreactions of vitamin K with antioxidant vitamins in micelle systems

The photochemical reactions of vitamin K (VK) with antioxidant vitamins (vitamin E (VE) and vitamin C (VC)) in aqueous hexadecyltrimethylammonium chloride (CTAC), sodium dodecyl sulfate (SDS), and Triton X-100 micelle systems, and in an aerosol OT (AOT) reversed micelle system were investigated by a time-resolved EPR (TR-EPR). The photolysis of VK with VE in the aqueous micelle solutions gave the TR-EPR spectra having strong intensity and net emissive polarization, suggesting that the excited triplet state of VK (³VK^*) was rapidly quenched by VE coexisting inside the micelle. On the other hand, the photolysis of VK with VC in the aqueous SDS and CTAC micelle systems gave the spectra having weak intensity, showing that the reaction between ³VK^* and VC was inefficient in these micelle systems, probably because ³VK^* scarcely diffused out from the micelle. The photolysis of VK with VC in the AOT reversed micelle solution gave the spin-correlated radical pair CIDEP spectrum. The result suggests that the long-lived radical pair was generated from the reaction between ³VK^* and VC in the water/oil interface region of the AOT micelle, although one of the reactants dissolved in the oil phase and another did in the separated water phase.     

Magnetic resonance in systems with equivalent spin-1/2 nuclides. Part 1

Electron paramagnetic resonance (EPR) spectra of S=1/2 systems XL(n) with n equivalent nuclei having spin I=1/2 have been simulated for microwave frequencies in the L-, X-, and W-bands. It has been shown that for n>2 nuclei, the EPR spectra have a more complicated form than anticipated from the usual oversimplified analysis, which predicts n+1 lines with intensity ratios given by the coefficients of the binomial expansion. For the XL(n) system with n=3, the EPR spectra in fact consist of six lines. The exact solution of the spin-hamiltonian for this case has been obtained, which gives four levels in zero magnetic field. For n>2 systems, the degeneracy of the energy levels cannot be completely removed by the Zeeman electronic and nuclear interactions. For n>4, certain spin states cannot occur, consistent with the (generalized) Pauli exclusion principle. Discussion of the underlying theory, invoking exchange degeneracy and the appropriate permutation group theory, is included in some detail. Analogous considerations hold for NMR spectroscopy of non-radicals.     

ESR and NMR studies of poly (amidoamine) dendrimers with ionic surfactants in different media

The electron paramagnetic resonance (EPR) study has been carried out for the micellar solutions of various ionic surfactant solutions as well as various generations of aqueous dendrimer both in their respective presence as well as their absence at 25°C and in different media. From these measurements, the rotation correlation time (τ_B) have been calculated for all the ionic surfactant + PAMAM + water system. A variation in the τ_Bvalue remains mostly constant for the dodecyltrimethyammonium bromide (DTAB) and tetradecyltrimethylammonium bromide (TTAB) + PAMAM + water ternary mixtures. The τ_Bvalue shows an increase with the increase in the amount of PAMAM for SDS in basic medium and for 12-2-12 in acidic medium. It has been concluded from these results that SDS undergo complexation with all generations of PAMAM in basic medium and 12-2-12 in acidic medium and produce stronger hydrophobic environment. The nuclear magnetic resonance study (NMR) allowed us to evaluate the spin–spin relaxation (T₁) times of SDS in the presence of all generations of PAMAM. The T₁ values for all the tail protons of SDS showed a slight decrease with the increase in the constant amount of PAMAM suggesting the adsorption of PAMAM molecules on the micelle surface.     

Resonant-Optical Detection of Nuclear Magnetization in the Si/CaF<Subscript>2</Subscript> Nanostructure

We have considered theoretically the characteristic features of optical detection of nuclear magnetization in the Si/CaF₂ structure under the conditions of EPR and NMR by measuring luminescence polarization. We show that application of EPR makes it possible to detect weak nuclear fields, but the time of spin relaxation of electrons imposes its constraint. The application of NMR is limited by nuclear fields of no less than 15–20 Gs. The possibility of using optical NMR for direct measurement of the nuclear field from changes in the luminescence polarization spectrum is shown. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 5, pp. 644–649, September–October, 2005.     

Ab initio EPR study of S and Se defects in alkali halides

Calculations using density functional theory are performed to study the electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) properties of S and Se impurities in alkali halide lattices. Cluster in vacuo models are used to describe the defect and the lattice surroundings. The trivacancy defect model proposed in the literature is able to reproduce both the experimental principal values and directions of the g tensor for S and Se defects doped in alkali halides. The alternative monovacancy model gives rise to important discrepancies with experiment and can be discarded. For the KCl lattice, the hyperfine tensors of the S and Se molecular ions also agree well with the available experimental data, giving further evidence to the trivacancy model. In addition, for NaCl:S and KCl:S computational results for the ²³Na and ³⁵Cl superhyperfine and quadrupole tensors are compared with experimental ENDOR parameters. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Mesogenic behaviour of isomeric bent-core 6-oxoverdazyls: 1,3-vrs 1,5-substitution pattern

Two series of isomeric bent-core derivatives of 6-oxoverdazyl, with alkyl and partially fluorinated alkyl chains, were investigated by thermo-optical, powder X-ray diffraction and electron paramagnetic resonance methods in the pure state and binary mixtures. The results revealed that the substitution position of the arms at the verdazyl ring (1,5 vs. 1,3) strongly affects mesogenic behaviour. Steric (torsion and bending angles) and dipolar factors in both isomers are considered.     

EPR spectra of (L-aspartate)di(2-pyridyl)aminezinc(II) hydrate substitutionally copper(II) doped complex

The [(L-aspartate)di(2-pyridyl)aminezinc(II)]hydrate doped with traces of copper was prepared. Electron paramagnetic resonance spectra of the polycrystalline sample were recorded at room temperature by using the X-band of the EPR spectrometer. The observedg factors for the complex areg _‖=2.258 andg _⊥=2.066. TheA _‖ value is 165.10⁻⁴ cm⁻¹. The crystal and molecular structure of the complex are also reported. The complex crystallizes in the monoclinic system; space groupP2₁ witha=7.2053(11),b=10.447(2),c=10.812(2) Å, β=108.489(14)° andZ=2. The structure can be described in the crystal lattice as polymeric chains.     

晶体(NH_4)_2C_4H_4O_6∶VO~(2 )的EPR参量及局域结构的研究

采用叠加模型和双旋-轨耦合参量模型,建立了结构参数与EPR参量之间的定量关系;较好地解释了[VO(H2O)5]2 络离子的局域结构和EPR参量;研究结果发现,(NH4)2C4H4O6:VO2 晶体中络离子[VO(H2O)5]2 的键长为R//≈0.130nm,R⊥≈0.195nm;在(NH4)2C4H4O6:VO2 晶体中,局域结构沿C4轴方向呈压缩的八面体结构;所得EPR参量的理论计算与实验测量数据符合很好。     

EPR spectra of (L-aspartate)di(2-pyridyl)aminezinc(II) hydrate substitutionally copper(II) doped complex

The [(L-aspartate)di(2-pyridyl)aminezinc(II)]hydrate doped with traces of copper was prepared. Electron paramagnetic resonance spectra of the polycrystalline sample were recorded at room temperature by using the X-band of the EPR spectrometer. The observedg factors for the complex areg _‖=2.258 andg _⊥=2.066. TheA _‖ value is 165.10⁻⁴ cm⁻¹. The crystal and molecular structure of the complex are also reported. The complex crystallizes in the monoclinic system; space groupP2₁ witha=7.2053(11),b=10.447(2),c=10.812(2) Å, β=108.489(14)° andZ=2. The structure can be described in the crystal lattice as polymeric chains.