7025-74-3

Usage

Chemical compound

A compound formed from the reaction of two molecules of thymine, a nucleobase found in DNA, when exposed to UV radiation.

Formation process

The dimerization process involves the formation of a cyclobutane ring between the two thymine molecules, resulting in a covalent bond between the carbon atoms at positions 5 and 6 of the pyrimidine ring.

DNA disruption

This type of dimer is known to cause mutations in DNA by disrupting the normal base pairing during DNA replication.

Genetic mutations

The disruption of normal base pairing can potentially lead to genetic mutations.

Health risk

Increasing the risk of skin cancer due to the DNA mutations caused by the 1,3-dimethylthymine cyclobutane dimer.

Photoproduct

The 1,3-dimethylthymine cyclobutane dimer is considered a photoproduct of DNA damage.

Research interest

It is an area of research interest in understanding the effects of UV radiation on genetic material.

Upstream product

• 4401-71-2 1,3-dimethylthymine 
• 65-71-4 thymin 

Relevant academic research and scientific papers

Model studies of DNA photorepair: Enthalpy of cleavage of a pyrimidine dimer measured by photothermal beam deflection calorimetry

The enzyme DNA photolyase mediates the repair of pyrimidine dimers. This repair step, a net retro [2+2] reaction, proceeds through either the cation or anion radical of the pyrimidine dimer. In order to understand how electron transfer makes the repair process possible, its energetics have been examined by photothermal beam deflection calorimetry, fluorescence quenching and quantum yield studies. The enthalpy for the cleavage reaction of cis-syn 1,3-dimethylthymine dimer itself was found to be -19 kcal/mol. In addition, from the redox potentials, the enthalpies for the cleavage reactions of the dimer cation radical and the anion radical were determined to he -19 kcal/mol and -28 kcal/mol, respectively.

Dissociative electron transfer to and from pyrimidine cyclobutane dimers: an electrochemical study.

Cyclic voltammetry was used to study the reduction and oxidation behaviour of several pyrimidine cyclobutane dimers mimicking UV induced lesion in DNA strands in polar solvents (N,N-dimethylformamide and acetonitrile). Both electron injection and removal to and from the dimers, respectively, lead to their cleavage and reformation of the monomeric base. The influence of stereochemistry and substitution pattern at the cyclobutane motif on the reactivity has been studied. It appears that the repair process always proceeds in a sequential fashion with initial formation of a dimer ion radical intermediate, which then undergoes ring opening by homolytic cleavage of the two C-C bonds. Standard redox potentials for the formation of both radical anion and radical cation state of the dimers were determined. Quantum calculations on simplified model compounds reveal the reason for the finding that the exergonic homolytic cleavages of the carbon-carbon bonds are endowed with sizeable activation barriers. The consequences of these mechanistic studies on the natural enzymatic repair by photolyase enzyme are discussed. Copyright 2004 The Royal Society of Chemistry

Photoinduced electron transfer to pyrimidines and 5,6-dihydropyrimidine derivatives: Reduction potentials determined by fluorescence quenching kinetics

The dynamics of flourescence quenching of excited state electron donor sensitizers by various pyrimidine and 5,6-dihydropyrimidine substrates was examined. For all of the substrates studied the rate constant of fluorescence quenching (kq) increases as the excited state oxidation potential (Eox*) becomes more negative. The dependence of kq on Eox* in each case is well described by the Rehm-Weller relationship. Fits of the data to this relationship allow for the estimation of the reduction potentials of the substrates (Ered). The pyrimidines 1,3-dimethylthymine, 1,3-dimethyluracil, and 1,3,6-trimethyluracil give Ered values (in CH3CN) ranging from -2.06 (vs SCE) to -2.14 V. Their dihydro derivatives, 1,3-dimethyl-5,6-dihydrothymine, 1,3-dimethyl-5,6-dihydrouracil, and 1,3,6-trimethyl-5,6-dihydrouracil gave Ered values ranging from -1.90 to -2.07 V. The higher Ered values for the dihydropyrimidines compared with their unsaturated derivatives is attributed to aromatic stabilization in the pyrimidines, which is not present in the dihydro derivatives. In addition, the Ered for both the trans-syn and cis-syn diastereomers of the dimethylthymine cyclobutane dimer was examined using the same method. The trans-syn dimer gives an Ered of -1.73 V and the cis-syn dimer gives an Ered of -2.20 V. This remarkable difference is attributed to a stereoelectronic effect. The cis-syn dimer anion radical suffers from an unfavorable charge-dipole interaction between the added electron and the O4 carbonyl group in the remaining pyrimidine ring. In contrast, the trans-syn dimer anion radical shows mainly a stabilizing inductive electron-withdrawing effect of the remaining O4 carbonyl group. Solvent effects on Ered were also examined. It is shown that the protic solvent, CH3OH, significantly stabilizes the anion radicals, raising Ered by ca. 400 mV over the value in CH3CN.

HIGHLY STEREOSELECTIVE PHOTODIMERIZATION OF 1,3-DIMETHYLTHYMINE IN LIQUID CRYSTALLINE MEDIA

Ordered media such as cholesteric and smectic solvents greatly enhance the stereoselectivity and the rate in photodimerization of 1,3-dimethylthymine, in contrast to the isotropic phase reactions leading to a poor product-selectivity.