************第４０回尾張コンプレックスセミナー*************

Title　：　Photochemistry of nucleic acid bases and base pairs

Speaker ：　Shohei Yamazaki

Affiliation：Division of Chemistry, Graduate School of Science, 
             Hokkaido University

Date　：　Wed. Jan. 26th, 1:30 pm (Almost one hour)

Place　：　Seminar Room (4F), 
            Graduate School of Information Science

Abstract：
The understanding of the mechanisms of photochemical 
processes in the nucleic acid bases and base pairs where the 
two base molecules are hydrogen bonded to each other is an 
essential prerequisite for clarifying the photostability and 
photodamage of DNA and RNA. The nucleic acid bases strongly 
absorb UV light, but the quantum yields of photochemical 
reaction products are very low. Theoretically, the photostability 
is rationalized by ultrafast nonradiative decay of the excited 
state of the bases via conical intersections between potential-
energy surfaces. For nucleic acid base pairs, the excited-state 
double proton transfer along the hydrogen bonds may generate 
rare tautomers of the bases, and thus it is considered as a 
possible cause of the photodamage of DNA. The first topic of 
this talk is the mechanism of the photostability of nucleic acid 
bases, studied by means of ab initio calculations of the excited-
state potential-energy profiles. The second topic is the excited-
state double proton transfer in 7-azaindole dimer, which has been 
studied as a model of DNA base pairs for several decades. We 
have investigated the mechanism of this reaction by accurate 
quantum chemical calculations using the CASPT2 method as well 
as the long-range corrected TDDFT method.

***********************************************************