Peculiarities of Spin Exchange in Nitroxide Biradicals Containing Two para-Phenylene Groups in the Bridge. EPR Investigation and DFT Calculations

Abstract Two nitroxide biradicals of similar composition: R5-CC-Ph-Ph-CC-R5 (B3a) and R6-CC-Ph-Ph-CC-R6 (B3b), where Ph = p-C6H4, and R6 is 1-oxyl-2,2,6,6-tetramethyl piperidine-3,4-ene- , and R5 is 1-oxyl-2,2,5,5-tetramethylpyrroline-3,4-ene- nitroxide rings, have been studied by electron paramagnetic resonance (EPR) spectroscopy. Variations of the intramolecular electron spin exchange in the biradicals, dissolved in toluene, as a function of temperature were characterized by changes in the isotropic 14N hyperfine splitting (hfs) constant a, values of the exchange integral |J|, and compared with the data obtained by DFT calculations. Thermodynamic parameters of the conformational rearrangements were calculated. Geometries of nitroxide biradicals in PES local minima and transition states in the triplet state were calculated at UDFT/B3LYP level with split-valence basis set cc-PVTZ [43]. Probable differences in biradicals behavior are discussed

Spin Density Distribution in a Nitroxide Biradical Containing 13C-Enriched Acetylene Groups in the Bridge: DFT Calculations and EPR Investigation

Abstract A specially synthesized nitroxide biradical R6-13C:C-p-C6H4–C:13CR6,B3, where R6 = 1-oxyl-2,2,6,6-tetramethyl-1,2,3,6-tetrahydropyridine nitroxide, has been studied by electron paramagnetic resonance spectroscopy, and electron-nuclear double resonance (ENDOR). Spin density distribution and hyperfine splitting (hfs) constant on 13C atoms calculations for biradical B3 were carried out using B3LYP and PBE0 functionals and several different basis sets including N07 family and were compared with the experimental value of the hfs constant on 13C atoms, measured from ENDOR spectra of B3. The mechanism of the intramolecular electron spin exchange in B3 biradical is discussed

Novel Orientation-Sensitive Spin Probes for Graphene Oxide Membranes Study

Abstract: Spin probe EPR spectroscopy is currently the only method to quantitatively report on the orientational ordering of graphene oxide membranes. This technique is based on the analysis of EPR spectra of a membrane containing stable radicals sorbed on oxidized graphene planes. The efficiency of the method depends on the spin probe structure; therefore, it is important to find stable paramagnetic substances that are most sensitive to the alignment of graphene oxide membranes. In the present work, three novel stable nitroxide radicals containing aromatic fragments with two nitrogen atoms were tested as spin probes to study graphene oxide membranes. The spinHamiltonian parameters of the radicals in graphite oxide powder and orientational order parameters of the probes inside graphene oxide membrane were determined. The sensitivity of one of these radicals to membrane orientational ordering was found to be higher than for any of spin probes used previously. A likely reason for this higher sensitivity is the presence of heteroatoms which can facilitate interaction between paramagnetic molecules and oxygen-containing groups on the inner surface of the membrane. The new high-sensitivity spin probe may significantly increase the potential of EPR spectroscopy for studying the internal structure of graphene oxide membranes

EPR, the X-ray Structure and DFT calculations of the Nitroxide Biradical with One Acetylene Group in the bridge

Two short nitroxide biradicals of similar composition, R6'-R6' (B0) and R6'-(C≡C)-R6' (B1), where R6' is 1-oxyl-2,2,6,6-tetramethyl-3,4-ene-nitroxide ring, have been investigated by EPR spectroscopy and X-ray structural analysis. Quantum chemical calculations at UDFT/B3LYP/cc-pVDZ level were also performed and compared with the X-ray structural data. Zero field splitting parameters D for B0 and B1 were found to be equal 0.0048 cm-1 and 0.0022 cm-1 respectively in good agreement with quantum chemical prediction. Potential energy surface scans corresponding to pathways of the conformational rearrangements were calculated, rotation barriers for B0 and B1 were found to be 19.2 kJ/mol and 4.0 kJ/mol respectively, structural rigidity and probable differences in biradicals behavior are discussed. Calculations of spin density distribution in biradicals B0 and B1 were also carried out

Deeplearning4j: Distributed, open-source deep learning for Java and Scala on Hadoop and Spark

Deeplearning4j implements deep artificial neural networks on the JVM, with a Java API and C++ for computation. Deeplearning4j includes recurrent neural networks such as long short-term memory networks, as well as convolutional networks, restricted boltzmann machines, deep-belief networks, deep autoencoders and shallow neural networks such as word2vec. Deeplearning4j integrates with Hadoop and Spark, and is built to train neural networks in parallel on CPUs and GPUs