William R. Potter

Characteristics of trapped electrons and electron traps in single crystals

Two additional carbohydrates are reported whose crystal structures trap electrons intermolecularly in single crystals x irradiated at low temperature, namely sucrose and rhamnose. Five carbohydrate and polyhydroxy compounds are now known which exhibit this phenomenon. The following characteristics of the phenomenon were investigated: (1) the hyperfine couplings of the electron with protons of the polarized hydroxy groups forming the trap; (2) the distances between these protons and the trapped electron; (3) the spin density of the electron at the protons and (4) the relative stabilities of the electron trapped in various crystal structures.

Trapped electrons in irradiated single crystals of polyhydroxy compounds

The intermolecular trapping of electrons has been observed in single crystals of dulcitol and L(+) arabinose x‐irradiated at 4.2 °K. Attribution of a major component of the ESR absorption to trapped electrons is based upon the character of the hyperfine pattern, which arises from multiple anisotropic hyperfine interactions with exchangeable protons, and on the g value of the absorption, which is always less than the free spin value. The removal of the trapped electron absorption upon irradiation with visible light has also been demonstrated. In these experiments all of the electrons are trapped in identical sites. This circumstance provides some important advantages in the study of the factors affecting the stabilization of charge in an environment of polarizable molecules.

The reduction of nucleotides by ionizing radiation: Uridine 5′ phosphate and cytidine 3′ phosphate

Anions formed by the addition of an electron to the uracil base were observed in single crystals of the barium salt of uridine 5′ phosphate x‐irradiated at 4.2 °K. The hyperfine coupling tensor for the C6–H proton was deduced from ENDOR measurements; the principal values are −59.12, −32.92, and −16.24 MHz. Similar measurements were made on single crystals of cytidine 3′ phosphate. The principal values for the C6–H proton hyperfine coupling in the anion formed on the cytosine base are −59.26, −33.98, and −14.68 MHz.

Radiation effects in x‐irradiated hydroxy compounds

Radiation effects are compared in single crystals of xylitol, sorbitol, and dulcitol x‐irradiated at 4.2 °K. In xylitol and dulcitol, but not in sorbitol, a primary oxidation product is identified as an alkoxy radical. ENDOR measurements detected three proton hyperfine couplings associated with the alkoxy ESR absorption, one of which is attributed to a proton three bond lengths removed from the seat of unpaired spin density. Intermolecular trapping of electrons is observed in all three crystals. ENDOR measurements were made of the hyperfine couplings between the trapped electron and the hydroxy protons forming the trap.

Effects of Ionizing Radiation on Potassium Hydrogen Malonate

Electron spin resonance spectroscopy was used to observe the primary effects of x rays on a single crystal of KOOC–CH2–COOH irradiated at 4.2°K. Three effects were observed: (1) Anions are formed by the addition of an electron to the oxygen of the carbonyl group; (2) a unique paramagnetic center results from the loss of a hydrogen atom shared between two molecules; (3) pairs of radicals are created by the removal of a hydrogen atom from the CH2 groups of each of two adjacent molecules. In order to explain the hyperfine pattern associated with the radical pair absorption it is necessary to develop the theory of “forbidden” transitions for the triplet state.

ENDOR characterization of the free radical in irradiated thymidine

The stable free radical produced by ionizing radiation in the nucleoside thymidine has been studied by ENDOR spectroscopy. The radical is formed by addition of hydrogen to the C6 carbon atom of the thymine ring. The hyperfine couplings of the CH2 protons and the methyl group rotational splitting constant are deduced from ENDOR measurements at 4.2°K.

Radical ion saturation in some sulfur compounds x-irradiated at 4.2 degrees K.

Single crystals of dimethylthiourea and dibenzoyldisulfide were exposed to ionizing radiation at 4.2°K. At this temperature positive and negative free radical ions are stable and can be identified ...