It undergoes photoinduced dimerization via a charge-transfer state. Since the discovery of thymine–thymine (TT) dimer, there has been intense research on the mechanism of this fundamental process [117, 118]. The typical quantum yield of dimerization in DNA is <1%.

Femtosecond time-resolved infrared spectroscopy is used to study the formation of cyclobutane dimers in the all-thymine oligonucleotide (dT) 18 by ultraviolet light at 272 nanometers. The appearance of marker bands in time-resolved spectra indicate that dimers are fully formed ∼1 picosecond after ultraviolet excitation.

Cyclobutane pyrimidine dimer (CPD) is a dimer which features a four-membered ring formed by the fusion of two double-bonded carbons from adjacent pyrimidines. CPDs disrupt the formation of the base pair during DNA replication , potentially leading to mutations .

The most common reaction is shown here: two thymine bases have formed a tight thymine dimer, with two bonds gluing the bases together. The upper image is from PDB entry 1n4e and the close-up picture at the bottom is from PDB entry 1ttd .

Thymidine Dimers are produced when adjacent thymidine residues are covalently linked by exposure to ultraviolet radiation. Covalent linkage may result in the dimer being replicated as a single base, which results in a frameshift mutation.

The most common covalently linked adjoining pyrimidines are T-T (thymine dimers), T-C (thymine-cytosine dimers) and C-C (cytosine-cytosine dimers). T-T dimers cause kinks in the DNA strand that prevent both replication and transcription of that part of the DNA.

The paper presents quantum yield results for the [2+2] and 6-4 photodimerization of TT steps in several DNA structures, including hairpins where the context dependence of the photodimerization yield is determined, and it develops a theoretical model that correctly describes the trends in dimerization yield with DNA structure.

The kinetics of thymine-thymine cyclobutane pyrimidine dimer (TT-CPD) formation was studied at 23 thymine-thymine base steps in two 247-base pair DNA sequences irradiated at 254 nm.

Oct 21, 2011 · In particular, photoinduced thymine-thymine (TT) dimer formation has been found to be a picosecond process. The most prevalent TT dimer is formed by a [2+2] addition of the C5–C6 double bonds of the dimerizing thymines.

Aug 1, 2013 · The kinetics of thymine-thymine cyclobutane pyrimidine dimer (TT-CPD) formation was studied at 23 thymine-thymine base steps in two 247-base pair DNA sequences irradiated at 254 nm.