Vibrational Spectra and Experimental Assignments of Thymine and Nine of Its Isotopomers

Abstract

FT-IR and FT-Raman spectra of polycrystalline natural abundance thymine, nine of its isotopic derivatives, and 2-thiothymine (5-methyl-2-thiouracil) are reported from 50 to 3500 cm-1. The isotopic derivatives are thymine-6-13 C, thymine-α-13 C, thymine-15 N 2, thymine-α,α,α,6-d 4, and their respective N-deuterated compounds. The vibrational spectra are assigned using the frequency shifts upon isotopic substitution and are compared to previous assignments, both experimental and ab initio based. Extensive mixing of the vibrations in the region below 1750 cm-1 complicates the vibrational assignments in this region. However, many of the exocyclic stretching and bending vibrations are assigned with confidence, and many of the couplings can be ascertained with these thymine derivatives. The spectra of the isotopic derivatives described here resolve many of the controversial assignments in the literature and correct some previously misassigned vibrational bands. This represents the most complete experimental vibrational study of thymine to date and provides a useful experimental basis for future theoretical calculations.

Time-resolved infrared spectroscopy of the lowest triplet state of thymine and thymidine

“…Normal mode analysis reveals that the carbonyl stretches are strongly coupled to the N-H (or -D) bends, but basically decoupled from all other motions, as previously reported [24,38]. The C2=O motion is strongly coupled to both the N1-H and N3-H bends in the case of thymine, while for thymidine the C2=O bend is coupled to the N3-H bend and (to a lesser extent owing to the increased mass) the in-plane bend of the N1-C glycosidic bond.…”

“…Thymine-d 2 was prepared after the method of Zhang et al [24] by dissolving several milligrams of thymine in excess D 2 O. The D 2 O was then removed on a vacuum line, and the sample was dissolved in acetonitrile-d 3 .…”

2,4-Dihydroxy and O2 Protonated Tautomers of dThd and Thd Coexist in the Gas Phase: Methylation Alters Protonation Preferences versus dUrd and Urd

“…Another intriguing characteristic of thymine is its ability to undergo keto-enol tautomerization, which may alter its base pairing properties, form mispairs, and eventually lead to point mutations and molecular based diseases [5]. The tautomeric behavior of thymine has been examined both experimentally and theoretically [6][7][8][9]. These studies suggest that the canonical diketo-tautomer of neutral thymine predominates, whereas upon protonation, keto-enol tautomerization takes place rapidly, and the minor 2,4-dihydroxy tautomer is predominant in the population with the O4 protonated canonical tautomer also present in low abundance.…”

“…The photochemical properties and the tautomeric behavior of thymine have motivated a great deal of experimental and theoretical studies during the past two decades [6][7][8][9][12][13][14]. However, much less attention has been paid to the thymine nucleosides, thymidine (dThd) and its ribonucleoside counterpart, 5-methyluridine (Thd).…”

Probing Noncovalent Interactions in Biomolecular Crystals with Terahertz Spectroscopy

“…[2,21] They have been obtained with THz time-domain [2] and FTIR spectroscopy. [21] To obtain experimental THz spectra for dimethyluracil we use the same experimental techniques. We use a standard time-domain THz spectrometer with photoconductive dipole antennas to cover the frequency range between 100 GHz to 2 THz.…”