title: Photodissociation of S atom containing amino acid chromophores.
abstract: Photodissociation of 3-(methylthio)propylamine and cysteamine, the chromophores of S atom containing amino acid methionine and cysteine, respectively, was studied separately in a molecular beam at 193 nm using multimass ion imaging techniques. Four dissociation channels were observed for 3-(methylthio)propylamine, including (1) CH(3)SCH(2)CH(2)CH(2)NH(2)-->CH(3)SCH(2)CH(2)CH(2)NH+H, (2) CH(3)SCH(2)CH(2)CH(2)NH(2)-->CH(3)+SCH(2)CH(2)CH(2)NH(2), (3) CH(3)SCH(2)CH(2)CH(2)NH(2)-->CH(3)S+CH(2)CH(2)CH(2)NH(2), and (4) CH(3)SCH(2)CH(2)CH(2)NH(2)-->CH(3)SCH(2)+CH(2)CH(2)NH(2). Two dissociation channels were observed from cysteamine, including (5) HSCH(2)CH(2)NH(2)-->HS+CH(2)CH(2)NH(2) and (6) HSCH(2)CH(2)NH(2)-->HSCH(2)+CH(2)NH(2). The photofragment translational energy distributions suggest that reaction (1) and parts of the reactions (2), (3), (5) occur on the repulsive excited states. However, reaction (4), (6) occur only after the internal conversion to the electronic ground state. Since the dissociation from an excited state with a repulsive potential energy surface is very fast, it would not be quenched completely even in the condensed phase. Our results indicate that reactions following dissociation may play an important role in the UV photochemistry of S atom containing amino acid chromophores in the condensed phase. A comparison with the potential energy surface from ab initio calculations and branching ratios from RRKM calculations was made.
authors: Institute of Atomic and Molecular Sciences, Academia Sinica, P.O. Box 23-166, Taipei 10617, Taiwan.
authors: Ming-Fu
authors: MF
authors: Lin
authors: Yuri A
authors: YA
authors: Dyakov
authors: Yuan T
authors: YT
authors: Lee
authors: S H
authors: SH
authors: Lin
authors: Alexander M
authors: AM
authors: Mebel
authors: Chi-Kung
authors: CK
authors: Ni
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D002627:Chemistry, Physical / Q000379:methods*; D003545:Cysteine / Q000737:chemistry; D004583:Electrons; D006859:Hydrogen; D007477:Ions; D008715:Methionine / Q000737:chemistry; D008956:Models, Chemical; D008968:Molecular Conformation; D015394:Molecular Structure; D010777:Photochemistry / Q000379:methods*; D011437:Propylamines / Q000737:chemistry; D013455:Sulfur / Q000737:chemistry*; D014466:Ultraviolet Rays
chemical_list: D000596:Amino Acids; D007477:Ions; D011437:Propylamines; C055136:3-methylthiopropylamine; D013455:Sulfur; D006859:Hydrogen; D008715:Methionine; D003545:Cysteine