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Acta Cryst. (2014). A70, C215
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Previously, we reported the crystal structure of DNA d(CGCGXATTCGCG), which revealed that X (O6-carboxymethyl-G) at the 5th position forms a Watson-Crick (WC) type pair with T (Fig. 1a) similar to the canonical A:T pair [1]. In order to investigate the versatility of X in the base-pair formation, another DNA d(CGCXAATTTGCG) containing X at the 4th position has been X-ray analyzed using four different crystals. In the four crystals, the T bases are always largely wobbled into the major groove side to form a hydrogen bond between N3 of T and the carboxyl group of X. In addition, a water molecule bridges between the two bases through two hydrogen bonds to stabilize the pair formation (Fig.1b). This high-wobble (hW) pair is quite different from the previously reported one [1]. Now we succeeded to reveal the two types of pairing modes of X:T pair, WC type and hW type. Since the four crystals were obtained in different conditions, the large displacement of T cannot be ascribed to the interactions with solvent cations. Another possibility is Hoechst33258 used for crystallization. But, as the crystals were obtained in both the presence and the absence of Hoechst33258, this is not the case. The remaining possibility would be the location of the modified base, because the sequence of the used DNA contains an AATT tract at the center and two CGCG tracts at the both ends. The AATT tract is well known to be more flexible (ω*≍ -160) than CGCG tract (ω*≍ -8.70). We found that the WC type X:T pairing requires a large ω angle (-180) between the bases. When X is located at the 5th position (in the AATT tract), the WC type is allowed to occur, while at the 4th position (in the CGCG tract) the WC type is difficult to occur. Here it could be concluded that X form a pair with T in the mode of WC if it is in the flexible tract, while in the mode of hW if it is in the rigid tract, because T base is out of the base stacking. * propeller twist angle between the two bases.

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Acta Cryst. (2014). A70, C1556
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LixMn2O4 is attracting much interest as a positive electrode material for Li-ion rechargeable batteries. Redox orbitals of LixMn2O4 under the charge or discharge process are not fully understood yet. Some band calculations have pointed out that intercalated Li 2s electrons occupy Mn sites or down-spin Mn 3d bands [1,2]. On the other hand molecular orbital calculation has reported the Li 2s electrons occupy O sites [3]. To clarify the redox orbital is important to understand the electrochemical reaction in the electrodes. In this study we have investigated the redox orbitals in LixMn2O4 by X-ray Compton scattering. Compton profiles were measured at BL08W of SPring-8, Japan. The energy of incident X-rays were 115keV and the scattering angle was 165 degrees. Energy spectra of Compton scattered X-rays were measured using a two-dimensional position sensitive detector. The measurements were performed under room temperature and vacuum conditions. Samples are polycrystalline of LixMn2O4 (x=0.5, 1.1, 1.2, 1.8 and 2.0). In order to clarify the redox orbitals of LixMn2O4, we obtained difference Compton profiles which represent the incremental electronic states on Li intercalation. Comparing the results with KKR-CPA and DFT calculations, we found that the O 2p bands play an important role for the redox process in LixMn2O4 with 0
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