Preliminary studies on unusual polymorphs of thymine: Structural comparison with other nucleobases

• Published in: Journal of molecular structure Vol. 1120; pp. 86 - 99
• Main Authors: Chennuru, Ramanaiah, Muthudoss, Prakash, Ramakrishnan, Srividya, Mohammad, Amjad Basha, Ravi Chandra Babu, R., Mahapatra, Sudarshan, Nayak, Susanta K.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.09.2016
• Subjects: Diffraction; Hydrogen; Molecular structure; Networks; Polymorphism; Thermal analysis; Thermal properties; Thymine; X-ray diffraction and nucleobase; X-rays; Thymine; Polymorphism; X-ray diffraction and nucleobase
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2016.05.014

Two polymorphs Form-R2 and Form-R4 of anhydrous thymine, one of the four nucleobases in the nucleic acid of DNA were obtained via sublimation crystallization and desolvation technique respectively. Form-R2 crystallizes in monoclinic C 2/c with a = 25.107(7) Å, b = 6.846(2) Å, c = 6.715(2) Å, β = 90.529(6)⁰ and V = 1154.1(5) Å3. The supramolecular assembly in Form-R2 is a sheet of hydrogen bonded network similar to that found in the crystal structures of other reported anhydrous form of thymine (Form-R1). Interestingly the thermal behavior is similar for these two forms with a minor difference in powder X-ray diffraction pattern. Further thymine Form-R2 closely matches with one of the predicted form of thymine using Polymorph module of Accelrys. Form-R4 is obtained by the dehydration of the mono hydrated form (Form-R3) and characterized by powder X-ray diffraction, FTIR spectroscopic techniques and thermal analysis. [Display omitted] •Two new polymorphic forms of anhydrous thymine.•Crystal obtained by sublimation technique.•Transformation among monohydrated thymine and anhydrous form.