کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
10547205 964620 2005 14 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Protonated Adenine: Tautomers, Solvated Clusters, and Dissociation Mechanisms
موضوعات مرتبط
مهندسی و علوم پایه شیمی شیمی آنالیزی یا شیمی تجزیه
پیش نمایش صفحه اول مقاله
Protonated Adenine: Tautomers, Solvated Clusters, and Dissociation Mechanisms
چکیده انگلیسی
Ab initio and density functional theory calculations at the B3-MP2 and CCSD(T)/6-311 + G(3df,2p) levels of theory are reported that address the protonation of adenine in the gas phase, water clusters, and bulk aqueous solution. The calculations point to N-1-protonated adenine (1+) as the thermodynamically most stable cationic tautomer in the gas phase, water clusters, and bulk solution. This strongly indicates that electrospray ionization of adenine solutions produces tautomer 1+ with a specificity calculated as 97-90% in the 298-473 K temperature range. The mechanisms for elimination of hydrogen atoms and ammonia from 1+ have also been studied computationally. Ion 1+ is calculated to undergo fast migrations of protons among positions N-1, C-2, N-3, N-10, N-7, and C-8 that result in an exchange of five hydrogens before loss of a hydrogen atom forming adenine cation radical at 415 kJ mol−1 dissociation threshold energy. The elimination of ammonia is found to be substantially endothermic requiring 376-380 kJ mol−1 at the dissociation threshold and depending on the dissociation pathway. The overall dissociation is slowed by the involvement of ion-molecule complexes along the dissociation pathways. The competing isomerization of 1+ proceeds by a sequence of ring opening, internal rotations, imine flipping, ring closures, and proton migrations to effectively exchange the N-1 and N-10 atoms in 1+, so that either can be eliminated as ammonia. This mechanism explains the previous N-1/N-10 exchange upon collision-induced dissociation of protonated adenine.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Journal of the American Society for Mass Spectrometry - Volume 16, Issue 10, October 2005, Pages 1713-1726
نویسندگان
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