ENDOR study of CH₂COOH radicals in γ-irradiated single crystals of glycine

Abstract

The CH~COOH radicals in ~,-irradiated glycine have been observed in two spectroscopically inequivalent forms by the ENDOR method. The first form (A) was induced by warming ~,-irradiated crystals at 77 K up to 120-140 K, the second one (A')--up to 140-300 K.The proton and nitrogen couplings are given for these two forms. The transition from A to A' form was observed at 140-160 K. This transition is discussed in terms of a double-minimum potential curve for the hydrogen bond protons.The second-order effects are reduced to indirect nuclear-nuclear interaction terms giving rise to the splitting of ENDOR lines. The general expression for this interaction has been obtained. The indirect nuclearnuclear interaction of two ~-protons of CHzCOOH radicals is examined. The relative signs of proton hyperfine couplings were determined by comparison with experimental data.

EPR and ENDOR Studies of Single Crystals of α-Glycine X-ray Irradiated at 295 K

“…Radical II. As shown in Figure , two new ENDOR lines ( #12 and #13 ) were observed at 100 K, at positions coincident with those determined for the two α-protons of radical II by Teslenko et al Figure shows EIE from these ENDOR lines with the external magnetic field along 〈 b 〉. The EIE appear as a triplet resonance, as expected for radical II at this orientation .…”

“…As shown in Figure , two new ENDOR lines ( #12 and #13 ) were observed at 100 K, at positions coincident with those determined for the two α-protons of radical II by Teslenko et al Figure shows EIE from these ENDOR lines with the external magnetic field along 〈 b 〉. The EIE appear as a triplet resonance, as expected for radical II at this orientation . The two lines denoted #12 ‘ and #12 ‘‘ are due to two slightly different conformations of radical II (similarly, line #13 is also broadened, at other orientations split, for the same reason).…”

“…This is followed by deamination yielding the ĊH 2 COOH radical (A2) 6 which has been suggested to deprotonated (A2‘). A major part of the A2 or A2‘ radicals transform by H-abstraction from a neighboring molecule 34 into the N CHCOO - product, radical I, above 200 K, but a fraction of the ĊH 2 COO(H) species remain stable at room temperature and has been analyzed by various authors. , …”

New Radical Detected by HF-EPR, ENDOR, and Pulsed EPR in a Room Temperature Irradiated Single Crystal of Glycine

“…The hyperfine coupling tensors of radical A have been determined from the room temperature EPR spectra of a glycine crystal irradiated at 77 K, since in this case radical A is the more stable radical at room temperature . The hyperfine coupling tensors of the two protons of radical B have been determined by an ENDOR study at low temperature . At room temperature the two protons are equivalent, since the methylene is rotating fastly …”

“…1 The hyperfine coupling tensors of the two protons of radical B have been determined by an ENDOR study at low temperature. 5 At room temperature the two protons are equivalent, since the methylene is rotating fastly. 1 A third type of radical usually formed in irradiated aminoacids is produced by decarboxylation of the primary anion radical.…”