• Proceedings of the Korean Magnetic Resonance Society Conference
• /
• 2002.01a
• /
• pp.30-30
• /
• 2002

• Biophysical Society Newsletter
• /
• v.7 no.2
• /
• pp.10-18
• /
• 2001

• Journal of the Korean Magnetics Society
• /
• v.20 no.3
• /
• pp.120-128
• /
• 2010

Electron spin resonance (ESR) is one of an experimental choice for studying magnetic materials that have one or more unpaired electrons. ESR spectroscopy finds its wide applications in branches of science encompassing physics, chemistry, biology, medicine and quantum computation. In this brief review we introduce a basic principle of ESR and describe how to extract information on g-factor, spin and orbital states from the ESR spectral parameters. Finally, several examples are discussed with an intention to have a practical feeling of what ESR can do in magnetism.

• Journal of the Korean Magnetic Resonance Society
• /
• v.3 no.2
• /
• pp.109-126
• /
• 1999

The location of Cu(II) exchanged into measoporous aluminosilicate MCM-41(AlMCM-41) material and its interaction with various adsorbate molecules were investigated by electron spin resonance and electron spin echo modulation spectroscopies. Cu(II) is fully coordinated to adsorbates in a wide open mesopore of AlMCM-41 for the formation of favorable complexes. It was found that in the fresh hydrated material, Cu(II) is octahedrally coordinated to six water molecules as evidenced by an isotropic room temperature ESR signal. This species is located in a cylindrical MCM-41 channel and rotates rapidly at room temperature. Evacuation at room temperature removes some of these water molecules, leaving the Cu(II) coordinated to less water molecules and anchored to oxygens in an MCM-41 channel wall. Dehydration at 450$^{\circ}C$ produces one Cu(II) species located on the internal wall of a channel, which is easily accessible to adsorbates. Adsorption of adsorbate molecules such as water, methanol, ammonia, pyridine, aniline, acetonitrile, benzene, and ethylene on a dehydrated Cu-AlMCM-41 material causes changes in the ESR spectrum of Cu(II), indicating the complex formation with these adsorbates. Cu(II) forms a complex with six molecules of methanol as evidenced by an isotropic room temperature ESR signal and ESEM analysis like upon water adsorption. Cu(II) also forms a square planar complex containing four molecules of N-containing adsorbates such as ammonia, pyridine and aniline based on resolved nitrogen superhyperfine interaction and their ESR parameters. However, Cu(II) forms a complex with six-molecules of acetonitrile based on ESR parameters. Only one molecule of benzene or ethylene is coordinated to Cu(II).

• Journal of Marine Bioscience and Biotechnology
• /
• v.1 no.4
• /
• pp.252-259
• /
• 2006

Extracts which were prepared by four different extractions - 80% methanol extracts (ME) at high ($70^{\circ}C$) and a room temperature ($20^{\circ}C$), respectively and aqueous extracts (AE) at both temperatures with the residue after the methanol extracts - of 10 green, 19 brown and 25 red seaweeds collected in Jeju Island coast were examined for their DPPH free radical scavenging activity using a ESR (electron spin resonance) spectroscopy. A variety of the extracts showed positive scavenging effect against DPPH free radical (except the green seaweeds). Among the extracts, the brown seaweed extracts exhibited the highest scavenging activity. Especially, Sargassum spp. of the brown seaweeds have remarkable scavenging activities - both methanolic and aqueous at the both temperatures ($20^{\circ}C$ and $70^{\circ}C$). On the other hand, ME showed better scavenging activity than AE in the red seaweed extracts. These results indicate that autogenous seaweeds in Jeju will be potential natural antioxidants for functional food compounds.

• Journal of the Korean Magnetic Resonance Society
• /
• v.9 no.2
• /
• pp.138-154
• /
• 2005

Vanadium-incorporated aluminophosphate molecular sieve $VO^{2+}-SAPO-5$ was studied by electron spin resonance (ESR) and electron spin echo modulation (ESEM) spectroscopies to determine the vanadium structure and interaction with various adsorbate molecules. It was found that the main species at low concentration of vanadium is a monomeric vanadium units in square pyramidal or distorted octahedral coordination, both in oxidation state (IV) for the calcined hydrated material and in oxidation state (V) for the calcined material. After calcinations in $O_2$ and exposure to moisture, only species A is observed with reduced intensities. It is suggested as a $VO(H_2O)_3^{2+}$ complex coordinated to two framework oxygen bonded aluminum. When calcined, hydrated $VO^{2+}-}SAPO-5$ is dehydrated at elevated temperature, a species loses its water ligands and transforms to $VO^{2+}$ ions coordinated to two framework oxygens (species B). Species B reduces its intensity, significantly after treatment with $O_2\;at\;600^{\circ}C$ for 5 h, thus suggesting oxidation of $V^{4+}\;to\;V^{5+}$. When dehydrated $VO^{2+}-SAPO-5$ contacts with $D_2O$ at room temperature, the EPR signal of species A is observed. Thus species assumed as a $VO^{2+}(O_f)_2(D_2O)_3$, by considering two framework oxygens. Adsorption of deuterated ethanol, propanol on dehydrated $VO^{2+}_{-}SAPO-5$ result in another new vanadium species E and F, respectively, which are identified as a $VO^{2+}-(CH_3CH_2OD)_3,\;VO^{2+}-(CH_3CH_2CH_2OD)_2$ complex. When deuterated benzene is adsorbed on dehydrated $VO^{2+}-SAPO-5$, another new vanadium species G, identified as a $VO^{2+}-(C_6D_6)$ is observed. Possible coordination geometries of these various complexes are discussed.

• Journal of Magnetics
• /
• v.2 no.4
• /
• pp.123-125
• /
• 1997

We have studied a series of I2-doped poly [2-buthoxy-5-methoxy-1, 4-phenylenevinylene] (PBMPV) conducting polymers by means of electron paramagnetic resonance (EPR) measurements. In this work, the EPR linewidth and spin density were obtained from the EPR intensity and studied as a function of the degree of doping.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.02a
• /
• pp.16-17
• /
• 2010

Molecular spintronics has attracted attentions, which combines molecular electronics with the spin degree of freedom in electron transport. Among various molecules as candidates of the molecular spintronics, single molecule magnet (SMM) is one of the most promising material. SMM molecules show a ferromagnetic behavior even as a single molecule and hold the spin information even after the magnetic field is turned off. Here in this report, we show the spin behavior of SMM molecules adsorbed on the Au surface by combining the observation of Kondo peak in the STS and ESR-STM measurement. Kondo resonance state is formed near the Fermi level when degenerated spin state interacts with conduction electrons. ESR-STM detects the Larmor frequency of the spin in the presence of a magnet field. The sample include $MPc_2$ and $M_2Pc_3$ molecules ($M\;=\;Tb^{3+}$, $Dy^{3+}$, and $Y^{3+}$ Pc=phthalocyanine) whose critical temperature as a ferromagnet reaches 40 K. A clear Kondo peak was observed which is originated from an unpaired electron in the ligand of the molecule, which is the first demonstration of the Kondo peak originated from electron observed in the STS measurement. We also observed corresponding peaks in ESR-STM spectra. [1] In addition we found that the Kondo peak intensity shows a clear variation with the conformational change of the molecule; namely the azimuthal rotational angle of the Pc planes. This indicates that the Kondo resonance is correlated with the molecule electronic state. We examined this phenomena by using STM manipulation technique, where pulse bias application can rotate the relative azimuthal angle of the Pc planes. The result indicates that an application of ~1V pulse to the bias voltage can rotate the Pc plane and the Kondo peaks shows a clear variation in intensity by the molecule's conformational change.

• Journal of the Korean Magnetic Resonance Society
• /
• v.1 no.2
• /
• pp.126-140
• /
• 1997

Mesoporous MCM-41 gallosilicate material was synthesized through shifting through shifting gallosilicate polymer equilibrium towards a MCM-41 phase by addition of acid. The location of Cu(II) exchanged into MCM-41 and its interaction with various adsorbate molecules were investigated by electron spin responance and electron spin echo modulation spectroscopies. It was found that in the fresh hydrated material, Cu(II) is octahedrally coordinated to six water molecules. This species is located in a cylindrical channel and rotates rapidly at room temperature. Evacuation at room temperature removes three of these water molecules, leaving the Cu (II) coordinated to three water molecules and anchored to oxygens in the channel wall. Dehydration at 45$0^{\circ}C$ produces one Cu (II) species located in the inner surface of a channel as evidenced by broadening of its ESR lines by oxygen. Adsorption of polar molecules such as water, methanol and ammonia on dehydrated CuNa-MCM-41 gallosilicate material causes changes in the ESR spectrum of Cu (II), indicating the complex formation with these adsorbates. Cu (II) forms a complex with six molecules of methanol as evidenced by an isotropic room temperature ESR signal and ESEM data like upon water adsorption. Cu(II) also forms a complex containing four molecules of ammonia based on resolved nitrogen superhyperfine interaction.

• Journal of the Korean Ceramic Society
• /
• v.40 no.11
• /
• pp.1102-1105
• /
• 2003

The fiber drawing process induced defects in silica fiber have been investigated. This study has focused on the Oxygen Deficient Centers (ODCs) and E' centers induced by the fiberization process in low-OH silica fibers. To investigate those defects induced by the fiberization process, the optical absorption spectrum and Electron Spin Resonance (ESR) have both been employed. The concentration of Oxygen Deficient Centers (ODCs) and E' centers are increased by the fiber drawing process. The population of defects in the neck-down region has also been investigated. The most significant generation of defects during fiber drawing process has been shown to occur in this region of silica preform. The population of defects is higher on the edge region than in the center of neck-down region.