Definitive Benchmark Study of Ring Current Effects on Amide Proton Chemical Shifts

TY - JOUR

T1 - Definitive Benchmark Study of Ring Current Effects on Amide Proton Chemical Shifts

AU - Christensen, Anders Steen

AU - Sauer, Stephan P. A.

AU - Jensen, Jan Halborg

PY - 2011/7/12

Y1 - 2011/7/12

N2 - The ring current effect on chemical shifts of amide protons (ΔδRC) is computed at the B3LYP/6-311++G(d,p)//B3LYP/aug- cc-pVTZ level of theory for 932 geometries of dimers of N-methylacetamide and aromatic amino acid side chains extracted from 21 different proteins. These ΔδRC values are scaled by 1.074, based on MP2/cc-pVQZ//B3LYP/aug-cc-pVTZ chemical shift calculations on four representative formamide/benzene dimers, and are judged to be accurate to within 0.1 ppm based on CCSD(T)/CBS//B3LYP/aug-cc-pVTZ calculations on formamide. The 932 scaled ΔδRC values are used to benchmark three empirical ring current models, including the Haigh-Mallion model used in the SPARTA, SHIFTX, and SHIFTS chemical shift prediction codes. Though the RMSDs for these three models are below 0.1 ppm, deviations up to 0.29 ppm are found, but these can be decreased to below 0.1 ppm by changing a single parameter. The simple point-dipole model is found to perform just as well as the more complicated Haigh-Mallion and Johnson-Bovey models.

AB - The ring current effect on chemical shifts of amide protons (ΔδRC) is computed at the B3LYP/6-311++G(d,p)//B3LYP/aug- cc-pVTZ level of theory for 932 geometries of dimers of N-methylacetamide and aromatic amino acid side chains extracted from 21 different proteins. These ΔδRC values are scaled by 1.074, based on MP2/cc-pVQZ//B3LYP/aug-cc-pVTZ chemical shift calculations on four representative formamide/benzene dimers, and are judged to be accurate to within 0.1 ppm based on CCSD(T)/CBS//B3LYP/aug-cc-pVTZ calculations on formamide. The 932 scaled ΔδRC values are used to benchmark three empirical ring current models, including the Haigh-Mallion model used in the SPARTA, SHIFTX, and SHIFTS chemical shift prediction codes. Though the RMSDs for these three models are below 0.1 ppm, deviations up to 0.29 ppm are found, but these can be decreased to below 0.1 ppm by changing a single parameter. The simple point-dipole model is found to perform just as well as the more complicated Haigh-Mallion and Johnson-Bovey models.

KW - Faculty of Science

KW - Quantum Chemistry

KW - NMR spectrocopy

KW - NMR; chemical shift

KW - ring current

U2 - 10.1021/ct2002607

DO - 10.1021/ct2002607

M3 - Journal article

C2 - 26606479

SN - 1549-9618

VL - 7

SP - 2078

JO - Journal of Chemical Theory and Computation

JF - Journal of Chemical Theory and Computation

IS - 7

ER -