The crystal structure of thymine

Abstract

the present molecule is too simple to distinguish the out-of-plane oxygen vibration from the rigid body libration of the whole molecule. Concluding remarksIn the present calculations, ordinary spherical scattering factors were used for the carbon and hydrogen atoms, and the effect of bond scattering factor (McWeeny, 1952) and the possibility of the charge transfer as a result of the hydrogen bond (Tsubomura, 1954) were completely neglected. In this respect, the present treatment is still too naive to discuss the distribution of valence electrons. Also, an R value of around 10% is sufficient to determine the atomic positions, but not enough to discuss the effect of bonding. This will be the limit of the ordinary photographic measurement of diffraction intensity.One aim of this paper, however, is to show that even at this level of accuracy the introduction of the aspherical atomic scattering factor can improve the results of structure analyses.In the present study, the changes in bond distances and angles were negligible. However, this result should not be considered to be general. If an atom is not centrosymmetric, the imaginary component in equation (10) will introduce the shift of the positional parameter, as discussed by Dawson (1964a).It can be seen from Table 6, that there still remains a small but systematic discrepancy of the Un component of the oxygen atom. This may be due to the effect of bonding.In order to clarify these points, accurate counter measurements at various temperatures are now being planned.

Local piezoresponse and polarization switching in nucleobase thymine microcrystals

“…Therefore, the observed piezoelectric contrast must be related to the variations of spontaneous polarization P (that can be switched by the external electric field if the material is ferroelectric) and dielectric permittivity, e. The presence of a notable piezoresponse contrast in thymine microcrystals thus proves the existence of spontaneous polarization without any dc bias field in apparent contradiction with early XRD data for pure anhydrate and monohydrate thymine phases. 37,38 Such a behavior (piezoelectricity in a nominally centrosymmetric material) has been previously demonstrated by PFM in SrTiO 3 ceramics 43 and at the interfaces. 44 OOP and IP PFM images (cf.…”

“…h00 is a predominant peak for thymine anhydrate and 0k0 is for thymine monohydrate. As it is known from the literature, the space group for both thymine anhydrate and monohydrate crystals 37,38 is centrosymmetric (P2 1 /c) in which piezoelectricity is not permitted. Therefore, no piezoelectric activity was found in large thymine anhydrate crystals by PFM measurements.…”

“…Theoretical analysis of the crystal structure of thymine based on XRD measurements was first performed by Ozeki et al 37 In this work, the authors established a simple twolayer stacking model of individual molecules of thymine anhydrate crystal viewed perpendicular to the plane (001), as well as similar molecular stacking for thymine monohydrate (Figs. 9 and 10).…”

“…This model is in a full agreement with the earlier reported data. 33,37 However, taking into account hydrogen atoms and their effect on the final structure, we could calculate the lengths of hydrogen bonds and dipole moments of the individual thymine molecules (D % 4.5 Debye, see Table I) for the entire crystal structure. We could determine the polarization of thymine (as well as other physical parameters) in various volume partitions and directions.…”

Potassium thyminate trihydrate, K(C5H5N2O2).3H2O

“…* Although the structures of thymine and thymine-p-benzoquinone have been determined (Ozeki, Sakabe & Tanaka, 1969;Sakurai & Okunuki, 1971) they are not particularly accurate and we have used the more accurate work of Gerdil (1961) Nevertheless, some electronic rearrangement has taken place, since the internal angle at deprotonated N(1)has decreased significantly (8.8o) compared to the corresponding angle in thymine, while the adjacent internal angles at C(2) and C(6) have increased (5.0o and 7.40 respectively). This change of the internal angles upon protonation has been noticed previously (Singh, 1965).…”