Observation of a distinct transition in the mode of interconversion of ring pucker conformers in non-crystalline d-ribose-2'-d from 2H NMR spin-alignment |
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Authors: | LiWang Andy C McCready David E Drobny Gary P Reid Brian R Kennedy Michael A |
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Institution: | (1) Department of Biochemistry & Biophysics, Texas A&M University, 2128 TAMU, College Station, TX, 77843-2128, U.S.A.;(2) Interfacial and Nano Science Facility, Pacific Northwest National Laboratory, EMSL 2569, K8-98, Richland, WA, 99352, U.S.A;(3) Department of Chemistry, University of Washington, Seattle, WA, 98195-1700, U.S.A;(4) Macromolecular Structure & Dynamics, Biological Sciences Laboratory, Pacific Northwest National Laboratory, EMSL 2569, K8-98, Richland, WA, 99352, U.S.A. |
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Abstract: | Internal motions of d-ribose selectively 2H-labeled at the 2 position were measured using solid state 2H NMR experiments. A sample of d-ribose-2
-d was prepared in a hydrated, non-crystalline state to eliminate effects of crystal-packing. Between temperatures of –74 and –60°C the C2–H2 bond was observed to undergo two kinds of motions which were similar to those of C2–H2/H2 found previously in crystalline deoxythymidine (Hiyama et al. (1989) J. Am. Chem. Soc., 111, 8609–8613): (1) Nanosecond motion of small angular displacement with an apparent activation energy of 3.6 ± 0.7 kcal mol–1, and (2) millisecond to microsecond motion of large amplitude with an apparent activation energy 4 kcal mol–1. At –74°C, the slow, large-amplitude motion was best characterized as a two-site jump with a correlation time on the millisecond time scale, whereas at –60°C it was diffusive on the microsecond time scale. The slow, large-amplitude motions of the C2–H2 bond are most likely from interconversions between C2-endo and C3-endo by way of the O4-endo conformation, whereas the fast, small-amplitude motions are probably librations of the C2–H2 bond within the C2-endo and C3-endo potential energy minima. |
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Keywords: | Arrhenius deuterium internal motions ribose solid state NMR spin alignment X-ray diffraction |
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