Krzysztof Tadyszak

Electronic structure and dynamics of low symmetry Cu2+ complexes in kainite-type crystal KZnClSO4·3H2O: EPR and ESE studies

EPR measurements at X-band were performed in the temperature range 4.2-300 K with angular dependence measurements at 77 K for Cu(2+) in KZnClSO(4).3H(2)O. Rigid lattice spin-Hamiltonian parameters are: g(z) = 2.4247, g(y) = 2.0331, g(x) = 2.1535, A(z) = -103 x 10(-4) cm(-1), 63 x 10(-4) cm(-1), and -31 x 10(-4) cm(-1). The parameters were analyzed using MO-theory with the d(x(2)-y(2)) ground state containing admixture of the d(z(2))-state in the rhombic symmetry D(2h). The analysis consistently explained unusual g-factor sequence and relatively small hyperfine splitting anisotropy as the consequence of the mixing and spin density delocalization via excited orbital states. We assigned that Cu(2+) ions substituting host Zn(2+) prefer one of the four structurally different zinc sites where they are coordinated by four water molecules and two SO(4) groups in an distorted octahedron elongated along SO(4)-Cu-SO(4) direction. The distortion is due to the Jahn-Teller effect which is static at low temperatures but becomes dynamic above 20 K with jumps of the Cu(2+) complex between two lowest potential wells. The jumps produce continuous g-factor and hyperfine splitting averaging when temperature increases. This process is discussed in terms of two motional averaging theories: classical theory based on generalized Bloch equations and Silver-Getz model. Their limitations are discussed. Importance of the difference in the g-factors of the averaged line is explained and a new expression for calculation of jump frequency from the line shift is proposed. The jumps are described as phonon induced tunneling via excited vibrational level of energy 76 (+/-6) cm(-1). This process is not effective enough at low temperatures and Boltzmann population of the two lowest energy potential wells is reached above 110 K. From electron spin-lattice relaxation measurements by electron spin echo methods the Debye temperature was determined as Theta(D) = 172 K. Fourier Transform of strongly modulated spin echo decay gives pseudo-ENDOR spectrum with peaks from (1)H and (35)Cl nuclei. From splitting of the peaks into doublets we determined the distance to the modulating nuclei and confirmed the position of the site where Cu(2+) ion is located.

Electron Paramagnetic Resonance Imaging and Spectroscopy of Polydopamine Radicals

A thorough investigation of biomimetic polydopamine (PDA) by Electron Paramagnetic Resonance (EPR) is shown. In addition, temperature dependent spectroscopic EPR data are presented in the range 3.8-300 K. Small discrepancies in magnetic susceptibility behavior are observed between previously reported melanin samples. These variations were attributed to thermally acitivated processes. More importantly, EPR spatial-spatial 2D imaging of polydopamine radicals on a phantom is presented for the first time. In consequence, a new possible application of polydopamine as EPR imagining marker is addressed.

Synthesis, structure, EPR studies and up-conversion luminescence of ZnO:Er3+–Yb3+@Gd2O3 nanostructures

ZnO:Er3+–Yb3+@Gd2O3 nanostructures were obtained by “wet” chemistry methods – the sol–gel technique for the preparation of ZnO and ZnO:Er3+–Yb3+ nanoparticles (NPs), and the seed deposition method for obtaining Gd2O3. The crystal structure, morphology, phase and elemental composition, resonant microwave absorption of rare earth ions, point defects in the ZnO:Er3+–Yb3+@Gd2O3 crystal structure and up-conversion luminescence were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) spectroscopy, and optical spectroscopy. The crystallization temperature (600 °C) of the Gd2O3 phase on the ZnO surface was found. As-obtained ZnO:Er3+–Yb3+ NPs (with size ∼7 nm) are highly crystalline and monodispersed. ZnO:Er3+–Yb3+ NPs annealing at 900 °C leads to the formation of highly polydispersed ZnO:Er3+–Yb3+ NPs, covered by a Gd2O3 shell. The process of the incorporation of the rare earth ions into the ZnO structure, as well as the effect of Gd2O3 content on the morphology and visible up-conversion (UC) luminescence in ZnO:Er3+–Yb3+ matrices were studied.

Size effects in the conduction electron spin resonance of anthracite and higher anthraxolite.

Electron paramagnetic resonance spectroscopy of conduction electrons, i.e. Conduction Electron Spin Resonance (CESR), is a powerful tool for studies of carbon samples. Conductive samples cause additional effects in CESR spectra that influence the shape and intensity of the signals. In cases where conduction electrons play a dominant role, whilst the influence of localized paramagnetic centres is small or negligible, the effects because of the spins on conduction electrons will dominate the spectra. It has been shown that for some ratios of the bulk sample sizes (d) to the skin depth (δ), which depend on the electrical conductivity, additional size effects become visible in the line asymmetry parameter A/|B|, which is the ratio of the maximum to the absolute, minimum value of the resonance signal. To study these effects the electrical direct current–conductivity and CESR measurements are carried out for two amorphous bulk coal samples of anthracite and a higher anthraxolite. The observed effects are described and discussed in terms of the Dyson theory. Copyright

Electron magnetic resonance data on high-spin Mn(III; S = 2) ions in porphyrinic and salen complexes modeled by microscopic spin Hamiltonian approach

The spin Hamiltonian (SH) parameters experimentally determined by EMR (EPR) may be corroborated or otherwise using various theoretical modeling approaches. To this end semiempirical modeling is carried out for high-spin (S=2) manganese (III) 3d4 ions in complex of tetraphenylporphyrinato manganese (III) chloride (MnTPPCl). This modeling utilizes the microscopic spin Hamiltonians (MSH) approach developed for the 3d4 and 3d6 ions with spin S=2 at orthorhombic and tetragonal symmetry sites in crystals, which exhibit an orbital singlet ground state. Calculations of the zero-field splitting (ZFS) parameters and the Zeeman electronic (Ze) factors (g||=gz, g⊥=gx=gy) are carried out for wide ranges of values of the microscopic parameters using the MSH/VBA package. This enables to examine the dependence of the theoretically determined ZFS parameters bkq (in the Stevens notation) and the Zeeman factors gi on the spin-orbit (λ), spin-spin (ρ) coupling constant, and the ligand-field energy levels (Δi) within the 5D multiplet. The results are presented in suitable tables and graphs. The values of λ, ρ, and Δi best describing Mn(III) ions in MnTPPCl are determined by matching the theoretical second-rank ZFSP b20(D) parameter and the experimental one. The fourth-rank ZFS parameters (b40, b44) and the ρ (spin-spin)-related contributions, which have been omitted in previous studies, are considered for the first time here and are found important. Semiempirical modeling results are compared with those obtained recently by the density functional theory (DFT) and/or ab initio methods.

Two-dimensional EPR imaging with the rapid scan and rotated magnetic field gradient

A new method for fast 2D Electron Paramagnetic Resonance Imaging (EPRI) is presented. To reduce the time of projections acquisition we propose to combine rapid scan of Zeeman magnetic field using high frequency sinusoidal modulation with simultaneously applied magnetic field gradient, whose orientation is changed at low frequency. The correctness of the method is confirmed by studies carried out on a phantom consisting of two LiPc samples. The images from the acquired data are reconstructed using iterative algorithms. The proposed method allows to reduce the image acquisition time up to 10 ms for 2D EPRI, and to detect the sinogram with infinitesimal angular step between projections.

Overmodulation of projections as signal-to-noise enhancement method in EPR imaging.

A study concerning the image quality in electron paramagnetic resonance imaging in two‐dimensional spatial experiments is presented. The aim of the measurements was to improve the signal‐to‐noise ratio (SNR) of the projections and the reconstructed image by applying modulation amplitude higher than the radical electron paramagnetic resonance linewidth. Data were gathered by applying four constant modulation amplitudes, where one was below 1/3 (Amod = 0.04 mT) of the radical linewidth (ΔBpp = 0.14 mT). Three other modulation amplitude values were used in this experiment, leading to undermodulated (Amod < 1/3 ΔBpp), partially overmodulated (Amod ~ 1/3 ΔBpp) and fully overmodulated (Amod > > 1/3 ΔBpp) projections. The advantages of an applied overmodulation condition were demonstrated in the study performed on a phantom containing four shapes of 1.25 mM water solution of 2, 2, 6, 6‐tetramethyl‐1‐piperidinyloxyl. It was shown that even when the overmodulated reference spectrum was used in the deconvolution procedure, as well as the projection itself, the phantom shapes reconstructed as images directly correspond to those obtained in undermodulation conditions. It was shown that the best SNR of the reconstructed images is expected for the modulation amplitude close to 1/3 of the projection linewidth, which is defined as the distance from the first maximum to the last minimum of the gradient‐broadened spectrum. For higher modulation amplitude, the SNR of the reconstructed image is decreased, even if the SNR of the measured projection is increased. Copyright

Polymerization of 1-Naphthylamine by DC discharge

Thin polymer films from 1-naphthylamine have been obtained for the first time by polymerization at the cathode and anode in DC discharge. The morphology of the films synthesized at the cathode was examined by SEM and AFM. The elemental composition, chemical structure, and thermal stability of the polymer have been studied by pyrolysis chromatography, IR and UV spectroscopy, and thermogravimetry, respectively. The surface contact properties of the films and their thickness have been determined with a microinterferometer. Polymer was also investigated by ESR method.

Preparation and characterization of partially reduced graphene oxide aerogels doped with transition metal ions

This work presents the preparation and characterization of pristine and transition metal doped partially reduced graphene oxide aerogels. The step-by-step preparation of aerogels from graphene oxide with an assistance of VCl3, CrCl3, FeCl2·4H2O, CoCl2, NiCl2 and CuCl2 chlorides as reducing agents is shown and explained. The influence of reducing agents on the structural and magnetic properties of prepared aerogels is investigated. The use of electron paramagnetic resonance in purification during synthesis of GO and characterization afterwards is shown. It was found that VCl3 was the strongest reducing agent leading to the formation of the most dense reduced graphene oxide aerogel, whereas vanadium is visible in EPR spectrum in form of V4+ complex as a VO2+ groups.

EPR Oximetry Sensor—Developing a TAM Derivative for In Vivo Studies

Oxygenation is one of the most important physiological parameters of biological systems. Low oxygen concentration (hypoxia) is associated with various pathophysiological processes in different organs. Hypoxia is of special importance in tumor therapy, causing poor response to treatment. Triaryl methyl (TAM) derivative radicals are commonly used in electron paramagnetic resonance (EPR) as sensors for quantitative spatial tissue oxygen mapping. They are also known as magnetic resonance imaging (MRI) contrast agents and fluorescence imaging compounds. We report the properties of the TAM radical tris(2,3,5,6-tetrachloro-4-carboxy-phenyl)methyl, (PTMTC), a potential multimodal (EPR/fluorescence) marker. PTMTC was spectrally analyzed using EPR and characterized by estimation of its sensitivity to the oxygen in liquid environment suitable for intravenous injection (1 mM PBS, pH = 7.4). Further, fluorescent emission of the radical was measured using the same solvent and its quantum yield was estimated. An in vitro cytotoxicity examination was conducted in two cancer cell lines, HT-29 (colorectal adenocarcinoma) and FaDu (squamous cell carcinoma) and followed by uptake studies. The stability of the radical in different solutions (PBS pH = 7.4, cell media used for HT-29 and FaDu cells culturing and cytotoxicity procedure, full rat blood and blood plasma) was determined. Finally, a primary toxicity test of PTMTC was carried out in mice. Results of spectral studies confirmed the multimodal properties of PTMTC. PTMTC was demonstrated to be not absorbed by cancer cells and did not interfere with luciferin-luciferase based assays. Also in vitro and in vivo tests showed that it was non-toxic and can be freely administrated till doses of 250 mg/kg BW via both i.v. and i.p. injections. This work illustrated that PTMTC is a perfect candidate for multimodal (EPR/fluorescence) contrast agent in preclinical studies.