Σάββατο, 22 Ιουνίου 2019

Applied Magnetic Resonance

Multi-frequency Dynamic Weighted Functional Connectivity Networks for Schizophrenia Diagnosis


Frequency-specific functional connectivity (FC) networks based on resting-state functional magnetic resonance imaging (rs-fMRI) have been successfully applied to the analysis and diagnosis of various mental illnesses, such as schizophrenia. However, most of the existing frequency-specific FC studies just focus on investigating the static temporal properties of FC networks, ignoring the important dynamic characteristics and spatial properties of FC networks. To address these issues, we proposed novel dynamic weighted FC networks to investigate the interactions among distributed brain regions. To take full advantage of the dynamic characteristics of the networks, temporal, spatial and spatio-temporal variabilities of dynamic networks were extracted as the classification features. To validate the effectiveness of our proposed method, we performed experiments on subjects with baseline rs-fMRI data from SchizConnect database. Experimental results demonstrated that the proposed method outperforms the state-of-the-art approaches in schizophrenia identification. In addition, we found most of the discriminative features distributed in frontal and subcortical area, which coincide with the pathological regions of cognitive progressing in schizophrenia patients.

Substituent Influences on the NMR Signal Amplification of Ir Complexes with Heterocyclic Carbene Ligands


A number of Ir–N-heterocyclic carbene (Ir–NHC) complexes with asymmetric N-heterocyclic carbene (NHC) ligands have been prepared and examined for signal amplification by reversible exchange (SABRE). Pyridine was chosen as model compound for hyperpolarization experiments. This substrate was examined in a solvent mixture using several Ir–NHC complexes, which differ in their NHC ligands. The SABRE polarization was created at 6 mT and the 1H nuclear magnetic resonance signals were detected at 7 T. We show that asymmetric NHC ligands, because of their favorable chemistry, can adapt the SABRE active complexes to different chemical scenarios.

A Simple, Accurate Method to Determine the Effective Value of the Magnetic Induction of the Microwave Field from the Continuous Saturation of EPR Spectra of Fremy's Salt Solutions. Representative values of $$T_{1}$$ T 1


A simple protocol to measure the effective value of the circularly polarized magnetic induction of the microwave field is proposed and demonstrated employing continuous-wave saturation of a standard sample of Fremy's salt measured under specified conditions. The fact that the doubly integrated intensity of first-derivative spectra is invariant with respect to the line shape is used to take into account the non-Lorentzian line shape to study the peak-to-peak intensity or the line width. Corrections for the use of line- rather than point-samples are developed.

EPR and Mössbauer Characteristics of Aqueous Solutions of 57 Fe-Dinitrosyl Iron Complexes with Glutathione and Hydroxyl Ligands


Our electron paramagnetic resonance (EPR) studies have demonstrated that at 293 K and 77 K, the spin–lattice relaxation time, T1, of paramagnetic mononuclear dinitrosyl iron complexes (M-DNICs) with glutathione and hydroxyl ligands containing isotopes 57Fe and 56Fe notably exceeds the halflife of the Mössbauer transition, i.e., the lifetime of the 57Fe nucleus in the first excited state (10−7 s). The Mössbauer spectra of M-DNIC with hydroxyl ligands, binuclear DNIC with glutathione (B-DNIC) and sodium dithionite-treated solution of B-DNIC with glutathione did not display the presence of the magnetic hyperfine structure (MHFS) characteristic of M-DNIC with glutathione. The Mössbauer spectra of all these DNICs were characterized by quadrupole splitting. The results of a comprehensive comparative analysis of MHFS of M-DNIC with glutathione and that in DMF reduced sodium nitroprusside suggest that M-DNIC with glutathione have a low-spin (S = ½) d7 electronic configuration with the predominant localization of the unpaired electron on the d z 2 orbital of iron. This conclusion is fully consistent with the results of our previous studies of M-DNIC using the EPR method.

ESEEM Reveals Bound Substrate Histidine in the ABC Transporter HisQMP 2


Localization of substrates in membrane proteins is an important but challenging task. In this paper, we show that deuterium electron spin echo envelope modulation spectroscopy (2H ESEEM) combined with site-directed spin labeling is a powerful tool to localize the substrate, histidine-d5, in the ABC transporter HisQMP2. Based on a homology model and spin label rotamer analyses, we calculated 2H ESEEM spectra for eight possible labeling positions close to the putative substrate-binding site. Experimental 2H ESEEM spectra were determined with spin labels bound either at position 169 of HisM, for which a detectable 2H ESEEM signal was calculated, or with a spin label bound at position 54 of HisQ as a negative control. The agreement between the calculated and experimental ESEEM spectra provides strong evidence for the histidine located in a binding site primarily liganded by residues of HisM as proposed by the homology model.

Characterization of the Distribution of Spin–Lattice Relaxation Rates of Lipid Spin Labels in Fiber Cell Plasma Membranes of Eye Lenses with a Stretched Exponential Function


The stretched exponential function (SEF) was used to analyze and interpret saturation recovery (SR) electron paramagnetic resonance (EPR) data obtained from spin-labeled porcine eye-lens membranes. This function has two fitting parameters: the characteristic spin–lattice relaxation rate (T1str−1) and the stretching parameter (β), which ranges between zero and one. When β =1, the function is a single exponential. It is assumed that the SEF arises from a distribution of single exponential functions, each described by a T1 value. Because T 1 −1 s are determined primarily by the rotational diffusion of spin labels, they are a measure of membrane fluidity. Since βdescribes the distribution of T 1 −1 s, it can be interpreted as a measure of membrane heterogeneity. The SEF was used to analyze SR data obtained from intact cortical and nuclear fiber cell plasma membranes extracted from the eye lenses of 2-year-old animals and spin labeled with phospholipid and cholesterol analogs. The lipid environment sensed by these probe molecules was found to be less fluid and more heterogeneous in nuclear membranes than in cortical membranes. Parameters T 1str −1 and β were also used for a multivariate K-means cluster analysis of stretched exponential data. This analysis indicates that SEF data can be assigned accurately to clusters in nuclear or cortical membranes. In future work, the SEF will be applied to analyze data from human eye lenses of donors with differing health histories.

Design and Simulation of a Helmholtz Coil for Magnetic Resonance Imaging and Spectroscopy Experiments with a 3T MR Clinical Scanner


Magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) are non-invasive techniques for tissue characterization. MRI/MRS in small phantoms with a clinical magnetic resonance scanner requires the design and development of dedicated radiofrequency coils. This paper describes the simulation, design, and application of a 1H transmit/receive Helmholtz coil, suitable for MRI/MRS studies in small phantoms with a clinical 3T scanner. Coil inductance and resistance were analytically calculated by taking into account the conductors cross geometry while magnetic field and sample-induced resistance were calculated with magnetostatic approaches. Finally, the coil sensitivity was measured with the perturbing sphere method. Successively, a coil prototype was built and tested on the workbench and by acquisition of MRI and MRS data. Results show that such coil could provide a low cost and easy to build device for MRI/MRS experiments with a clinical scanner in small specimens.

The In Situ Study of the Fe 3 O 4 /DMSO Ferrofluid Synthesis


Electron spin resonance in situ was applied to study the initial stages of ferrofluid formation in combination with the X-ray diffraction, high-resolution transmission electron microscopy and Fourier transform infrared spectroscopy studies data. The ultrafine (d = 4 nm) magnetite in dimethylsulfoxide ferrofluid with a narrow size nanoparticles distribution was obtained in a single step at room temperature by admixing butylene oxide to a solution of iron (II) and (III) chlorides in dimethylsulfoxide. It has been shown that at the first step of the ferrofluid synthesis antiferromagnetically ordered iron containing phase is formed, which can be correlated with iron hydroxides.

Towards a Model-Based Field-Frequency Lock for Fast-Field Cycling NMR


Fast-field cycling nuclear magnetic resonance (FFC NMR) relaxometry allows to investigate molecular dynamics of complex materials. FFC relaxometry experiments require the magnetic field to reach different values in few milliseconds and field oscillations to stay within few ppms during signal acquisition. Such specifications require the introduction of a novel field-frequency lock (FFL) system. In fact, control schemes based only on current feedback may not guarantee field stability, while standard FFLs are designed to handle very slow field fluctuations, such as thermal derives, and may be ineffective in rejecting faster ones. The aim of this work is then to propose a methodology for the synthesis of a regulator that guarantees rejection of field fluctuations and short settling time. Experimental trials are performed for both model validation and evaluation of the closed-loop performances. Relaxometry experiments are performed to verify the improvement obtained with the new FFL. The results highlight the reliability of the model and the effectiveness of the overall approach.

Persistence of Nitroxide Radicals in Solution


Data on long-term persistence of nitroxide radicals typically are focused on solid samples. Less information is available for nitroxides in fluid solution. Sealed deoxygenated solutions of a doxyl nitroxide in tetrahydrofuran and a piperidinyl nitroxide in toluene in 4 mm EPR tubes were kept in a laboratory environment at ambient temperature and without protection from light. After more than 40 years, the concentrations of the solutions had decreased by about factors of 12 and 6, respectively. The longevity in solution probably depends strongly on the purity of the solvent, but these results indicate remarkable persistence.

Alexandros Sfakianakis
Anapafseos 5 . Agios Nikolaos

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