Phototautomerism of Isocytosine in a Water Medium: Theoretical and Experimental Study

Photo-induced Dissociation of the N1–H Bond in the Imino Tautomers of Isocytosine in Water Medium

“…Recently we proposed a mechanism explaining the oxo -hydroxy phototautomerism of isocytosine in water surroundings. [25] Our experiment gave information for the presence of these tautomers in water surroundings which is in accord with other observations. [26][27][28][29] To explain the phototransformations of some pyrimidine derivatives Sobolewski has proposed so-called PIDA (photo-induced dissociation-association) mechanism.…”

“…For tautomer D (oxo amino) the 1 ππ * excited state has energy of 4.68 eV in the gas phase which is in accord with other investigations. [25,32] In water surroundings it increases slightly the energy as for cytosine according to the investigations of Improta et al [42] The 1 ππ * excited states can be directly populated by excitation of the ground states of tautomers. The dark 1 nπ * excited states of the tautomers A, B, and C have higher energies than the 1 ππ * excited states.…”

“…Tautomer D has been proven to be available in water solution of isocytosine. [25] A B C D Figure 1. Optimized ground-state equilibrium geometries of the tautomers of isocytosine in water surroundings.…”

Ultrafast excited state dynamics of isocytosine unveiled by femtosecond broadband time‐resolved spectroscopy combined with density functional theoretical study

“…6 The molecule has attracted attention due to its various properties, and the photo-induced excited state dynamics of isocytosine have been investigated both theoretically [7][8][9][10] and experimentally. [11][12][13][14] Previous studies have demonstrated that isocytosine can exist in different tautomeric forms depending on the environmental conditions, as shown in Scheme 1. For example, in the crystal phase, it exists in the keto form, with nearly equal percentages of two keto tautomers.…”

“…Recent research has shown that isocytosine is one of the building blocks for Hachimoji DNAs and RNAs, a genetic system that may support life in the cosmos 6 . The molecule has attracted attention due to its various properties, and the photo‐induced excited state dynamics of isocytosine have been investigated both theoretically 7–10 and experimentally 11–14 . Previous studies have demonstrated that isocytosine can exist in different tautomeric forms depending on the environmental conditions, as shown in Scheme 1.…”