TY - JOUR
T1 - Modeling β-scission reactions of peptide backbone alkoxy radicals
T2 - Backbone C-C bond fission
AU - Wood, Geoffrey P.F.
AU - Rauk, Arvi
AU - Radom, Leo
PY - 2005
Y1 - 2005
N2 - To model the C-C β-scission reactions of backbone peptide alkoxy radicals, enthalpies and barriers for the fragmentation of four substituted alkoxy radicals have been calculated with a variety of ab initio molecular orbital theory and density functional theory procedures. The high-level methods examined include CBS-QB3, variants of the G3 family, and W1. Simpler methods include HF, MP2, QCISD, B3-LYP, BMK, and MPW1K with a range of basis sets. We find that good accuracy can be achieved with the G3(MP2)//B3-LYP and G3X(MP2)-RAD methods. Lower-cost methods producing reasonable results are single-point energy calculations with UB3-LYP/6-311+G(3df,2p), RB3-LYP/6-311+G(3df,2p), UBMK/6-311+G(3df,2p), and RBMK/6-311+G(3df,2p) on geometries optimized with UB3-LYP/6-31G(d) or UBMK/6-31G(d). Heats of formation at 0 K for the alkoxy radicals and their fragmentation products were also calculated. We predict ΔfH0 values for the alkoxy radicals of-71.4 (·OCH2- CH=O),-102.5 (·OCH(CH 3)CH=O),-176.6 (·OCH(CH3)C(NH2)=O), and-264.6 (·OC(CH3)-(NHCH=O)CH=O) kJ mol-1. For the fragmentation products NH2C(·)=O and CH(=O)NHC-(CH 3)=O, we predict ΔfH0 values of-5.9 kJ mol-1 and-352.8 kJ mol-1.
AB - To model the C-C β-scission reactions of backbone peptide alkoxy radicals, enthalpies and barriers for the fragmentation of four substituted alkoxy radicals have been calculated with a variety of ab initio molecular orbital theory and density functional theory procedures. The high-level methods examined include CBS-QB3, variants of the G3 family, and W1. Simpler methods include HF, MP2, QCISD, B3-LYP, BMK, and MPW1K with a range of basis sets. We find that good accuracy can be achieved with the G3(MP2)//B3-LYP and G3X(MP2)-RAD methods. Lower-cost methods producing reasonable results are single-point energy calculations with UB3-LYP/6-311+G(3df,2p), RB3-LYP/6-311+G(3df,2p), UBMK/6-311+G(3df,2p), and RBMK/6-311+G(3df,2p) on geometries optimized with UB3-LYP/6-31G(d) or UBMK/6-31G(d). Heats of formation at 0 K for the alkoxy radicals and their fragmentation products were also calculated. We predict ΔfH0 values for the alkoxy radicals of-71.4 (·OCH2- CH=O),-102.5 (·OCH(CH 3)CH=O),-176.6 (·OCH(CH3)C(NH2)=O), and-264.6 (·OC(CH3)-(NHCH=O)CH=O) kJ mol-1. For the fragmentation products NH2C(·)=O and CH(=O)NHC-(CH 3)=O, we predict ΔfH0 values of-5.9 kJ mol-1 and-352.8 kJ mol-1.
UR - http://www.scopus.com/inward/record.url?scp=33748576150&partnerID=8YFLogxK
U2 - 10.1021/ct050133g
DO - 10.1021/ct050133g
M3 - Article
SN - 1549-9618
VL - 1
SP - 889
EP - 899
JO - Journal of Chemical Theory and Computation
JF - Journal of Chemical Theory and Computation
IS - 5
ER -