scholarly journals A Rudimentary X band CW-EPR Spectrometer Based on FPGA

2021 ◽  
Vol 17 (6) ◽  
pp. 829-837
Author(s):  
Wei Siang Eow ◽  
Yung Szen Yap
Keyword(s):  
Resonant Frequency ◽  
Coaxial Cable ◽  
Q Factor ◽  
Paramagnetic Resonance ◽  
Analog To Digital ◽  
X Band ◽  
Field Homogeneity ◽  
Field Programmable ◽  
Standard Value ◽  
Electron Paramagnetic

A rudimentary Electron Paramagnetic Resonance (EPR) spectrometer is design using a field programmable gate array (FPGA) equipped with two digital-to-analog (DAC) and two analog-to-digital (ADC) channels.  The single stage heterodyne setup operates at X band frequencies and is used to detect EPR signals from 2,2-diphenyl-1-picrylhydrazyl (DPPH) in a loop-gap resonator.  We design the loop gap resonator with 3 loops 2 gaps for high field homogeneity and moderate Q-factor. The resonator is coupled capacitively to the coaxial cable and is designed to have an unloaded resonant frequency of 8.856 GHz with a Q-factor of 646.0 when critically coupled. The loaded resonant frequency is reported to be 8.668 GHz with a Q-factor of 615.8. Using this setup, EPR signal is successfully detected at 311.4 mT and 8.688 GHz with an experimental g-factor of 1.99450.0012, which is very near to the standard value for DPPH.

scholarly journals Photoreactivity of Hair Melanin from Different Skin Phototypes—Contribution of Melanin Subunits to the Pigments Photoreactive Properties

2021 ◽  
Vol 22 (9) ◽  
pp. 4465
Author(s):  
Krystian Mokrzynski ◽  
Shosuke Ito ◽  
Kazumasa Wakamatsu ◽  
Theodore G. Camenish ◽  
Tadeusz Sarna ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Singlet Oxygen ◽  
Near Infrared ◽  
Paramagnetic Resonance ◽  
Time Resolved ◽  
W Band ◽  
Epr Oximetry ◽  
X Band ◽  
Hair Samples ◽  
Electron Paramagnetic

Photoreactivity of melanin has become a major focus of research due to the postulated involvement of the pigment in UVA-induced melanoma. However, most of the hitherto studies were carried out using synthetic melanin models. Thus, photoreactivity of natural melanins is yet to be systematically analyzed. Here, we examined the photoreactive properties of natural melanins isolated from hair samples obtained from donors of different skin phototypes (I, II, III, and V). X-band and W-band electron paramagnetic resonance (EPR) spectroscopy was used to examine the paramagnetic properties of the pigments. Alkaline hydrogen peroxide degradation and hydroiodic acid hydrolysis were used to determine the chemical composition of the melanins. EPR oximetry and spin trapping were used to examine the oxygen photoconsumption and photo-induced formation of superoxide anion, and time-resolved near infrared phosphorescence was employed to determine the singlet oxygen photogeneration by the melanins. The efficiency of superoxide and singlet oxygen photogeneration was related to the chemical composition of the studied melanins. Melanins from blond and chestnut hair (phototypes II and III) exhibited highest photoreactivity of all examined pigments. Moreover, melanins of these phototypes showed highest quantum efficiency of singlet oxygen photogeneration at 332 nm and 365 nm supporting the postulate of the pigment contribution in UVA-induced melanoma.

An X-band time domain electron paramagnetic resonance spectrometer

Pramana ◽  
1986 ◽  
Vol 27 (5) ◽  
pp. 661-677 ◽  
Author(s):  
Ranjan Das ◽  
Balu Venkataraman ◽  
Vinod R Bhagat ◽  
Ajit S Ghangrekar ◽  
Thomas Kuruvilla ◽  
...  
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Time Domain ◽  
Electron Paramagnetic Resonance Spectrometer ◽  
Paramagnetic Resonance ◽  
X Band ◽  
Electron Paramagnetic

X-band electron paramagnetic resonance of a quasi-bidimensional molecular composite [NH3(CH2)4NH3]CuCl4

1996 ◽  
Vol 97 (8) ◽  
pp. 669-674 ◽  
Author(s):  
Jean-Claude Bissey ◽  
René Berger ◽  
Pierre Béziade ◽  
Nguyen-Ba Chanh ◽  
Thierry Maris ◽  
...  
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Paramagnetic Resonance ◽  
Band Electron ◽  
X Band ◽  
Electron Paramagnetic

scholarly journals Intramolecular Mobility in Nitroxide Biradicals with Flexible Linkers

2020 ◽  
Vol 51 (9-10) ◽  
pp. 1031-1040
Author(s):  
Günter Grampp ◽  
Van Anh Tran ◽  
Petr V. Pantyukhov ◽  
Alexander I. Kokorin
Keyword(s):  
Thermodynamic Parameters ◽  
Spin Exchange ◽  
Thermodynamic Characteristics ◽  
Conformational Transitions ◽  
Polar Solvents ◽  
Paramagnetic Resonance ◽  
Solvent Viscosity ◽  
X Band ◽  
Intramolecular Mobility ◽  
Electron Paramagnetic

Abstract Intramolecular electron spin exchange has been studied by X-band electron paramagnetic resonance (EPR) spectroscopy in two long-chain flexible nitroxide biradicals existing in fluid solutions in three spectroscopy-different spatial conformations as a function of temperature, solvent viscosity and polarity. Certain thermodynamic parameters of the conformational transitions were calculated from the EPR spectra. The process of spin-exchange in these biradicals dissolved in five different alcohols was compared with that in the non-polar solvents (toluene) and aprotic (acetonitrile), as well as with two other biradicals studied earlier, and with thermodynamic characteristics of the solvents. A distinct correlation was found between macroscopic (solvent viscosity) characteristics of solvents and thermodynamic parameters of the intramolecular conformational transitions.

scholarly journals Comparison of Continuous Wave and Rapid Scan X-band Electron Paramagnetic Resonance of Irradiated Clipped Fingernails

2016 ◽  
Vol 172 (1-3) ◽  
pp. 133-138 ◽  
Author(s):  
Hanan Elajaili ◽  
Joseph McPeak ◽  
Alexander Romanyukha ◽  
Priyanka Aggarwal ◽  
Sandra S. Eaton ◽  
...  
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Continuous Wave ◽  
Paramagnetic Resonance ◽  
Band Electron ◽  
Rapid Scan ◽  
X Band ◽  
Electron Paramagnetic

Quantitative Electron Paramagnetic Resonance: The Importance of Matching the Q-Factor of Standards and Samples

2001 ◽  
Vol 55 (10) ◽  
pp. 1375-1381 ◽  
Author(s):  
Richard L. Blakley ◽  
Dwight D. Henry ◽  
Walter T. Morgan ◽  
William L. Clapp ◽  
Carr J. Smith ◽  
...  
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Free Radicals ◽  
Free Radical ◽  
Spin Trapping ◽  
Microwave Energy ◽  
Q Factor ◽  
Paramagnetic Resonance ◽  
Tert Butyl ◽  
Electron Paramagnetic ◽  
Stable Free Radicals

Electron paramagnetic resonance (EPR) quantification of free radicals from different samples facilitates comparison of free radical concentrations. Stable free radicals, such as 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), in a suitable solvent (e.g., benzene) can be used as a quantification standard. Free radicals found in samples can be shorter lived than radicals in prepared standards and require stabilizing spin-trapping agents such as N-tert-butyl-α-phenylnitrone (PBN) in an appropriate solvent (e.g., benzene). Analysis in our laboratory showed that free radicals from spin-trapped samples quantified against a standard of TEMPO in benzene displayed large differences among identical samples measured on either a Micro-Now 8300, Micro-Now 8400, or Bruker EMX EPR instrument. The Bruker instrument reported that the typical TEMPO in benzene standard had a Q-factor of ∼4400 while the Q-factor of our PBN-containing samples was ∼2500. (The Q-factor is inversely proportional to the amount of dissipated microwave energy in an EPR cavity.) By placing the TEMPO standard in a PBN/benzene solvent matrix we were able to match the Q-factor of our standards and samples, resulting in each of the three EPR instruments giving the same quantified free radical yields for the samples. This result points out the importance of matching the Q-factor between samples and standards for any quantitative EPR measurement.

Sign in / Sign up

Export Citation Format

Share Document