Physical Chemistry Commons^™

An Experiment In Electron Paramagnetic Resonance Spectroscopy For Undergraduate Labs In Physical Chemistry Or Physical Biochemistry, Evan A. Old, Matthew C. Rehak, Jefferson C. Thompson, Herbert J. Sipe Jr.

TeachEPR Submissions

We report a biochemically based EPR experiment for undergraduate laboratories that will serve as instruction for learning EPR sample preparation, spectral observation, and spectral analysis. There is a current lack of EPR instructional experiments that present complex spectra in which computational analysis may be required. The biochemical oxidation system of horse radish peroxidase (HRP) activated by H₂O₂ acts on 2,6-di-t-butyl-4-hydroxyanisole (DTBHA) to form phenoxyl radicals. This experiment produces moderately complex spectra of moderately long-lived radicals using relatively small amounts of readily available reactants. Spectrum analysis and simulation is accomplished using software freely available on-line. If desired, EPR …

Characterization Of L-Band Resonators And Relaxation Times Of Soₓ- Radicals At X-Band, Georgina Naa Odey Amassah

Electronic Theses and Dissertations

Electron Paramagnetic Resonance (EPR) analysis requires resonators optimized for specific experimental challenges. Volume resonators enclose samples, while surface coil resonators allow imaging of larger subjects. For in vivo studies, L-band frequencies are commonly used because they offer a good balance between signal-to-noise ratio (S/N) and the ability to penetrate tissue. Rapid Scan (RS) EPR at L-band frequencies was chosen for my studies of resonators because of this balance but presents a challenge for sensitivity.

The spatial position dependence of signal intensity was evaluated for selected paramagnetic samples using 10 mm and 30 mm surface coils. The 10 mm coil, with …

Epr Imaging Workshop: From Theory And Practice To Applications, Arthur H. Heiss, Ralph T. Weber, Sandra S. Eaton, Gareth R. Eaton

TeachEPR Submissions

Methods of imaging and insights from imaging are described. Practical aspects of sample type and dimensions are described.

Workshop presented at the 27th International EPR Symposium, sponsored by Bruker BioSpin EPR Division and the University of Denver, in Denver, Colorado on August 1, 2004.

Workshop On The Epr Of Aqueous Samples, Gareth R. Eaton

TeachEPR Submissions

The problem with water and other materials that absorb microwave energy are described. Dielectric properties are described as a function of frequency.

Workshop presented at the 25th International EPR Symposium on July 28, 2002.

Special Purpose Epr Resonators, Gareth R. Eaton

TeachEPR Submissions

Many types of EPR resonators are described.

Special applications that use various resonators are mentioned.

Lab Practical: Cw Basics, Gareth R. Eaton

TeachEPR Submissions

1. How do you position the sample in the resonator?
2. How do you select the center field for a spectrum?
3. How do you select the modulation amplitude?
4. How do you select the microwave power?

Lab Practical: Transition Metals: Epr Of A Vanadyl Complex, Gareth R. Eaton

TeachEPR Submissions

1. What information can you obtain from a spectrum of one orientation of a single crystal that is wide enough to encompass all of the vanadium hyperfine lines?

2. How does the spectrum change when you rotate the crystal? Look at both the position of the center of the spectrum and the hyperfine splitting.

Lab Practical: Pulse Epr, Gareth R. Eaton

TeachEPR Submissions

1. How do you over-couple the resonator for a pulse experiment?
2. How do you find a 2-pulse echo?
3. How do you select the microwave attenuation?

How To Measure Q, Gareth R. Eaton

TeachEPR Submissions

•Frequency bandwidth
–Using spectrometer frequency sweep
–Using a network analyzer

•Ring down following a pulse

Lab Practical: Nitroxides, Gareth R. Eaton

TeachEPR Submissions

1. How do you fill a capillary tube with an aqueous solution? How are capillaries positioned in the resonator?
2. How does the spectrum of a nitroxide change when the viscosity of a solution is increased?
3. How do you determine the concentration of the radical in the solution?

How To Measure B1, Gareth R. Eaton

TeachEPR Submissions

• CW Methods
• Pulsed EPR Methods

Lab Practical: Rapid Scan Epr, Gareth R. Eaton

TeachEPR Submissions

• To develop an understanding of the rapid scan experiment relative to other EPR methods.
• To observe the effects of scan rate on samples with differing T₂ relaxation times.

Motion Of Nitroxide Radicals, Gareth R. Eaton

TeachEPR Submissions

A brief outline is presented of how motion of a nitroxide radical can be estimated from the continuous wave (CW) EPR line shape.

Types Of Epr Resonators, Gareth R. Eaton

TeachEPR Submissions

Fundamental properties of resonators are described with photographs of a variety of actual EPR resonators.

Distances Between Spins, Gareth R. Eaton

TeachEPR Submissions

• Distance measurement by measuring T₁ and T_2.
• Relation to DEER and CW simulation and half-field intensity.
• Dipolar and exchange interactions.
• The dynamic NMR spectral collapse picture.

Epr Workshop: Lab Practicals Summary, Gareth R. Eaton

TeachEPR Submissions

• Basics – nitroxide and trityl
• Nitroxides
• Metals - vanadyl
• Pulse
• Rapid scan

Workshop On Quantitative Epr, Dave Barr, Sandra S. Eaton, Gareth R. Eaton, Ralph T. Weber, Patrick Carl, Peter Höfer, Richard W. Quine, George A. Rinard, Colin Mailer

TeachEPR Submissions

Presentations on quantitative EPR at the workshop that preceded the writing of our text, Quantitative EPR.

Presented at the 31^st Annual EPR Symposium in Breckenridge, Colorado on July 27, 2008.

Vanadium Line Shapes, Gareth R. Eaton

TeachEPR Submissions

VO²⁺ complexed with water, acetylacetonate, and/or other ligands yields a well-resolved 8-line spectrum (I = 7/2 for V) in solution. Powder spectra show that the hyperfine couplings are anisotropic.

Introduction To Epr, Gareth R. Eaton

TeachEPR Submissions

A very brief introduction to the scope of EPR at the beginning of a workshop in 2019.

Anisotropy Of Nitroxide Radicals, Gareth R. Eaton

TeachEPR Submissions

The special utility of nitroxide radicals for probing orientation and motion depends on the anisotropy of g-values and hyperfine values, especially the ¹⁴N hyperfine.

Copper Line Shapes, Gareth R. Eaton

TeachEPR Submissions

The spectrum of Cu²⁺ has 4 lines, since I = 3/2. Cu has two major isotopes, ⁶³Cu (69.2%) and ⁶⁵Cu (30.8%). The magnetic moment of ⁶⁵Cu is 7% larger than that for ⁶³Cu, so the hyperfine coupling is 7% larger. If the lines are narrow enough, one can observe superposition of spectra due to complexes of the two isotopes.

Concentration Effects On Nitroxides, Gareth R. Eaton

TeachEPR Submissions

We need to distinguish line broadening due to restricted motion from line broadening due to concentration of the same or other paramagnetic species. For example, if you increase the concentration of nitroxyl to get better S/N, the lines will broaden due to collisions with other nitroxyl molecules.

Workshop On Rapid Scan Epr, Gareth R. Eaton, Arthur H. Heiss, Deborah Gale Mitchell, Joshua R. Biller, Richard W. Quine, George A. Rinard, Mark Tseitlin, Sandra S. Eaton

TeachEPR Submissions

An introduction to the method of rapid scan EPR is given with emphasis on the design of rapid scan coils, selection of scan parameters, and the reasons that the method improves signal to noise per unit time.

Workshop On Selecting An Epr Resonator, Gareth R. Eaton

TeachEPR Submissions

Guidance is presented to help select a resonator to optimize a measurement. Different resonator types are described with information about resonator Q and microwave power efficiency.

Workshop presented at the 28th International EPR Symposium on July 31, 2005.

Dinitroxides In Rapid Scan Electron Paramagnetic Resonance Imaging, Lukas B. Woodcock

Electronic Theses and Dissertations

Local tissue physiology is an important parameter in understanding disease behavior. Rapid Scan (RS) electron paramagnetic resonance (EPR) offers a unique, non-invasive tool for investigation of these so-called microenvironments through EPR Imaging (EPRI). Research into advancement of EPRI falls into many categories. Not least among those are advances in instrumentation and methodology. Presented here are updates to a benchtop EPRI instrument operating at 1 GHz targeted at pre-clinical EPRI applications. Newly developed methods for reducing RS-EPR background through inversion of the magnetic field are also demonstrated. EPR applications are limited in native biological systems due to the miniscule concentration of …

Inhibitors Of Alpha-Synuclein Aggregation, Jemil Ahmed

Electronic Theses and Dissertations

Alpha-Synuclein (αS) – a neuronal, disordered, presynaptic protein – aggregates into amyloid fibrils and accumulates in the substantia nigra pars compacta of Parkinson's Disease (PD) patients. The aggregation and accumulation of αS amyloid fibrils leads to death of dopaminergic neurons; a hallmark of PD. Although it’s not clear why αS aggregates, prior studies have found that intrastriatal injection of fibril alone is sufficient to cause PD pathology in mouse and non-human primates models. These observations implicate αS as a therapeutic target against PD.

Unfortunately, there are three caveats when attempting to target αS. First, αS is a neuronal protein expressed …

Epr Relaxation Of Modified Triphenylmethyl And Nitroxide Radicals, Whylder Moore

Electronic Theses and Dissertations

Trityl and nitroxide radicals are widely used as probes in chemical and biochemical systems. Understanding of factors that impact the electron spin relaxation for these radicals is important for selection of probes and experimental operating conditions. It has been previously reported that ¹³C isotope enrichment of the central carbon of the trityl yields a highly sensitive micro viscosity probe. It was important to characterize the impact of this substitution on the relaxation processes in fluid solution and immobilized samples.

Electron spin relaxation times for perdeuterated Finland trityl 99% enriched in ¹³C at the central carbon (¹³C …

Instrument And Application Development In Saturation Recovery And Rapid Scan Electron Paramagnetic Resonance, Joseph E. Mcpeak

Electronic Theses and Dissertations

Enhanced signal sensitivity by the use of Rapid Scan (RS) electron paramagnetic resonance (EPR), a technique that allows for much faster magnetic field scans than traditional field-swept techniques, has facilitated improved data acquisition for many types of samples. For example, irradiated fingernails for radiation dosimetry have been studied using RS-EPR, which resulted in substantial decreases in detection limits. Samarium-mediated reduction mechanisms in organic synthesis have been investigated by RS-EPR providing evidence for a radical intermediate. Spectra of organic radicals exhibiting both narrow lines and closely spaced hyperfine interactions have been recorded via RS-EPR. Well-resolved spectra can be recorded at a …

Nitroxide Radicals For Low Frequency Electron Paramagnetic Resonance Imaging (Epri), Joshua R. Biller

Electronic Theses and Dissertations

Optimization of nitroxides as probes for EPR imaging requires detailed understanding of spectral properties such as spin lattice relaxation times, spin packet linewidths, and nuclear hyperfine splitting. Initial measurements of relaxation times for six low molecular weight nitroxides at X-band stimulated further measurement at frequencies between 250 MHz and 34 GHz. The impact of tumbling was studied with perdeuterated 2,2,6,6-tetramethyl-4-piperidinyl-1-oxyl (PDT) in five solvents with viscosities resulting in tumbling correlation times, τ_R, between 4 and 50 ps. A set of three ¹⁴N/¹⁵N pairs of nitroxides in water was selected such that τ_R varied between …

Probing Structure For Photophysical Properties Through Synthesis Of Novel Nucleosides, Brittney Jean Rodgers

Electronic Theses and Dissertations

A brief history of nucleosides and their photophysics provides the background information for the discussion of synthesis, photophysics and incorporation of fluorescent nucleotide analogs during enzymatic DNA synthesis. Through the use of nucleoside starting material, it is possible to synthesize a number of modified nucleotides for use as fluorescent probes in biochemical research. Synthetic endeavors into the synthesis of these and related molecules from nucleobase starting materials are also presented. The synthesis of these molecules involved re-development of the synthetic routes to broaden substrate scope by overcoming the changed reactivity resulting from the presence of additional functionality.

While many highly …