ELECTRON PARAMAGNETIC RESONANCE STUDIES OF $gamma$-IRRADIATED POLYPEPTIDES

Journal Article · Tue May 01 04:00:00 EDT 1962 · Dissertation Abstr.

OSTI ID:4814987

Drew, R C

Electron paramagnetic resonance studies were made on a group of eighteen gamma -irradiated synthetic polypeptides. These compounds are composed of amino acid residues of a single amino acid, joined together through the formation of peptide bonds to create macromolecules of 18-150 residues, with a structure similar to the proteins and the nucleic acids. The polypeptides were studied in a powder form and include samples constructed from the L- and, when available, the DL- configurations of the following amino acids: glycine, sarcosine, alanine, valine, leucine, proline, hydroxyproline, phenylalanine, tyrosine, tryptophan, aspartic acid, glutamic acid, and lysine. The spin resonance pattern was observed for each substance under the following conditions: irradiated and observed in vacuum at 300 deg K, irradiated and observed in vacuum at 77 deg K, warming from 77 deg K to 300 deg K and returned to 77 deg K, and opened to air at 300 deg K. Tracings of the resonance curves obtained in the first 2 are included for all compounds as well as representative spectra illustrating the special effects noted in the others. To clarify the analysis of the spectra observed, the theory of electron paramagnetic resonance was developed, from a derviation of the basic resonance condition, h nu = g BETA H relating the frequency of the transition, nu u, to the gfactor and the magnetic field, H, through the more advanced aspects of configurational interaction and hyperconjugation. Application of the theory to the present case, that of free radicals formed by irradiation of biological material, is stressed. A standard X-band spectrometer system operating at 9.2 Kmcs was used to obtain all curves. This system employs a direct transmission cavity, operating in the TE/sub 012/ mode, with a bolometer and a phase-sensitive lock-in detection system. Sensitivity is such that a minimum of ~10/sub 15/ unpaired spins may be detected. Of the polypeptides investigated, only poly-glycine and poly-sarcosine give the doublet spectrum similar- to that found for a great number of proteins. Other samples gave characteristically different spin resonance patterns, many of which could be related to a particular free radical structure. These results confirm the postulate that the glycine-type residue is the site of unpaired spin density ior proteins which exhibit the typi-cal doublet spectrum. A pronounced oxygen effect'' was noted for all samples when opened to air at 300 deg K. The observed effects may be classified into three groups: samples which show complete quenching of the resonance within three minutes, those which have their characteristic patterns replaced by a singlet which then decays, and samples which have their resonance patterns unchanged but begin an accelerated decay when opened to air. This behavior is suggested to be the result of the formation of peroxide radicals, X-O-O-, which subsequently decay to form nonradical end products. The degree to which the molecular oxygen may diffuse to the spin sites and form the peroxide radicals and variations in their subsequent decay rates would then explain differences in the observed behavior. A probable correlation is proposed between the spatial configuration of the molecule and the oxygen effect' obtained.

• Research Organization: Duke Univ., Durham, N.C.
• NSA Number: NSA-16-022179
• OSTI ID: 4814987
• Journal Information: Dissertation Abstr., Journal Name: Dissertation Abstr. Vol. Vol: 22
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

AIR
ALANINE
AMINO ACIDS
ASPARTIC ACID
BOLOMETERS
CHEMISTRY
CONFIGURATION
DETECTION
DIAGRAMS
ELECTRON SPIN RESONANCE
ELECTRONS
FREE RADICALS
GAMMA RADIATION
GLUTAMIC ACID
GLYCINE
HYDROXIDES
HYDROXYPROLINE
IRRADIATION
ISOMERS
LEUCINE
LYSINE
MAGNETIC FIELDS
MAGNETIC RESONANCE
MOLECULES
NUCLEIC ACIDS
OXIDATION
OXIDES
OXYGEN
PEPTIDES
PEROXIDES
PHENYLALANINE
POLYMERS
POLYPEPTIDES
POWDERS
PROLINE
PROTEINS
RADIATION EFFECTS
SARCOSINE
SENSITIVITY
SPECTRA
SPECTROMETERS
SPIN
TEMPERATURE
THERMOMETERS
TRYPTOPHAN
TYROSINE
VACUUM
VALINE