University of North Florida
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Stuart Chalk, Ph.D.
Department of Chemistry
University of North Florida
Phone: 1-904-620-1938
Fax: 1-904-620-3535
Email: schalk@unf.edu
Website: @unf

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Spectroscopy

Citations 4

"Flow Analysis Of UV-irradiated Chemicals By Chemiluminescence And Electron Spin Resonance Spectroscopy"
Anal. Chim. Acta 1992 Volume 261, Issue 1-2 Pages 39-43

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Sumiko Suzuki, Hiroyuki Nakazawa* and Masahiko Fujita, Shin-ya Ono, Masao Suzuki and Shouji Takitani, Masaru Sonoda and Yoshikatsu Sakagishi

Abstract: Imipramine (I) was used as model compound for evaluating the effect of UV irradiation on chemical compounds. The flow injection system (shown diagrammatically) incorporated a simple injector, a 4-m coil of PTFE tubing (0.3 mm i.d.) in which the sample stream (I injected into acetonitrile) was exposed to 254-nm radiation, a T-piece by which a spin trapping substance (e.g., methylnitrosopropane) was optionally introduced, a 2-m mixing coil, and chemiluminescence (CL), fluorescence (350-nm excitation, 450-nm emission) and UV detectors in series, as well as an ESR spectrometer as modified for LC experiments (Makino and Hatano, Chem. Lett., 1979, 119) connected after the CL detector. Changes induced in I by irradiation were detectable only by CL and ESR, and CL was closely related to radical-forming reactions. A novel method for detecting changes in chemicals, especially radical formation after UV irradiation, was developed using imipramine as a marker of light-sensitive materials. The system consisted of a pump, an injection port for the sample, an online UV irradiation. device and detectors for chemiluminescence and ESR. Most chemicals that were chemiluminescence positive after UV irradiation. in this flow system were found to show spectra of free radicals by ESR spectroscopy. These results suggested that the proposed online system may be useful for the rapid and simple determination of the stability and light-induced degradation of chemicals.
Imipramine Dual detection Photochemistry UV reactor

"Ascorbyl Free-radical As A Reliable Indicator Of Free-radical-mediated Myocardial Ischemic And Postischemic Injury - A Real-time Continuous-Flow ESR Study"
Eur. J. Biochem. 1990 Volume 193, Issue 3 Pages 845-854

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S Pietri, M Culcasi, L Stella and PJ Cozzone

Abstract: The real-time kinetics of the release of ascorbyl free radicals in the coronary perfusate from isolated rat hearts submitted to an ischemia/reperfusion sequence has been achieved by continuous-flow ESR using high-speed acquisition techniques. Enhanced ESR detection of ascorbyl free radicals was obtained by addition of dimethyl sulfoxide (Me2SO), a strong cation chelator and oxidizing agent. A continuous- flow device allowed a direct monitoring of the ascorbyl free radical and/or ascorbate leakage in coronary perfusate by observation of the ascorbyl radical doublet (aH = 0.188 mT and g = 2.0054). 1. The results showed that ascorbyl free radical release occurred mainly during sequences of low-flow ischemia (90 min) coupled or not with 30 min of zero-flow ischemia followed by reperfusion (60 min). The kinetic profiles of ascorbyl-free-radical detection confirm in quantitative terms the expected correlation between the duration of the ischemic insult and the magnitude of ascorbate extracellular release upon reperfusion. There is indication that ascorbyl free radical depletion could be secondary to oxygen-derived-free-radical-induced cellular damage. 2. The amount of residual ascorbic acid was quantitated on myocardial tissue at the end of reperfusion using Me2SO as extracting solvent. Intense oxidation of ascorbate and chemical stabilization of the resulting free radical species provided by Me2SO allowed ESR measurement of a marked tissue ascorbate depletion related to the duration of ischemia. 3. Perfusion of superoxide dismutase during low- flow ischemia and the first 10 min of reperfusion greatly inhibited both extracellular release and endogenous ascorbate depletion. These results suggest that the ascorbate redox system constitutes a major protective mechanism against free-radical-induced myocardial injury. 4. The proposed direct ESR detection of ascorbyl free radicals in the coronary perfusates or in tissue extracts does not require extensive chemical preparation and conditioning of effluent or tissue samples. It provides an interesting straightforward alternative to the evaluation of detrimental free radical processes affecting the myocardium during ischemia and reperfusion.

"Transient Free Radicals In Iron/oxygen Reconstitution Of Mutant Protein R2 Y122F. Possible Participants In Electron Transfer Chains In Ribonucleotide Reductase"
J. Biol. Chem. 1995 Volume 270, Issue 21 Pages 12361-12372

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Margareta Sahlin, Gunter Lassmann, Stephan Potsch, Britt-Marie Sjoberg, and Astrid Graslund

Abstract: Ferrous iron/oxygen reconstitution of the mutant R2 apoprotein Y122F leads to formation of a diferric center similar to that of the wild- type R2 protein of Escherichia coli ribonucleotide reductase. This reconstitution reaction requires two extra electrons, supplied or transferred by the protein matrix of R2. We observed several transient free radical species using stopped-flow and freeze quench EPR and stopped-flow UV-visible spectroscopy. Three of the radicals occur in the time window 0.1-2 s, i.e. concomitant with formation of the diferric site. They include a strongly iron-coupled radical (singlet EPR signal) observed only at < or = 77 K, a singlet EPR signal observed only at room temperature, and a radical at Tyr-356 (light absorption at 410 nm), an invariant residue proposed to be part of an electron transfer chain in catalysis. Three additional transient radicals species are observed in the time window 6 s to 20 min. Two of these are conclusively identified, by specific deuteration, as tryptophan radicals. Comparing side chain geometry and distance to the iron center with EPR characteristics of the radicals, we propose certain Trp residues in R2 as likely to harbor these transient radicals.
Stopped-flow Kinetic

"Flow System For Continuous ESR Measurement Of Propagating Free-radical Concentrations During Semicontinuous Emulsion Polymerization"
Macromolecules 1992 Volume 25, Issue 17 Pages 4448-4449

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Willie Lau and David G. Westmoreland

Abstract: A closed-loop flow system was developed and used to study semicontinuous emulsion polymn. reactions by ESR . Latex was continuously circulated during a polymn. from a custom reactor through the ESR cavity equipped with a customized flat cell and then back to the reactor. The utility of this system was illustrated by following the propagating free radical concentration. in a semicontinuous emulsion polymn. of Me methacrylate at 50°C. The experimental results showed that the average number of free radicals per particle increased during the reaction due to a steady accumulation of free radicals as the particle size increased, which indicated the presence of 'trapped' radicals. The relatively small increase in radical concentrations. based on polymer volume suggested that a radical required a min. polymer volume to remain unterminated.
Methylmethacrylate Closed loop Heated reaction Process monitoring Latex