Abstract
The NMR spin-spin coupling constants (SSCCs) across the H-bond in proteins are sensitive to the electronic structure of the H-bonded system, i.e., the N-H···O=C group in proteins. The spin-spin coupling mechanism across the H-bond involves a strong electric field effect, steric exchange interactions, and some weak covalent effects (transfer of electronic charge). The electric field effect is reflected by one-orbital contributions to the SSCC and can be tested with the help of probe charges. A negative charge opposite to the N-H bond leads to increased polarization of the N-H bond, a larger contact density at the N nucleus, and a stronger FC coupling mechanism for those SSCCs involving the N nucleus. Similarly, a positive charge opposite to the O=C bond, distorts the O density into the direction of the external charge and in this way decreases the spin density at the O nucleus. All SSCCs across the H-bond depend primarily on the electric field effect and two-orbital steric exchange interactions. The lone pair contributions to the Fermi contact ferm of 2h J(ON) (and to a lesser extent 3h J(CN)) provide a direct measure on possible covalent contributions in the form of charge-transfer interactions. According to calculated charge-transfer values and lone-pair contributions to SSCC 2h J(ON), the covalent contribution to the H-bond is rather small (less than 15% at 1.9 Å for a bending angle β(COH) of 120°). The zeroth-order density and the spin-spin coupling mechanism, which depends largely on the first-order spin density, both describe the H-bond as being electrostatic rather than covalent. The electric field effect largely determines the geometrical dependence of the SSCCs of a hydrogen-bonded system.
| Language | English |
|---|---|
| Pages | 1115-1129 |
| Number of pages | 15 |
| Journal | Journal of Physical Chemistry B |
| Volume | 108 |
| Issue number | 3 |
| Early online date | 24 Dec 2003 |
| DOIs | |
| Publication status | Published - 22 Jan 2004 |
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Keywords
- spin−spin coupling constants
- SSCCs
- H-bond
- proteins
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Analysis of the NMR spin-spin coupling mechanism across a H-bond : nature of the H-bond in proteins. / Tuttle, Tell; Gräfenstein, Jürgen; Wu, Anan; Kraka, Elfi; Cremer, Dieter.
In: Journal of Physical Chemistry B , Vol. 108, No. 3, 22.01.2004, p. 1115-1129.Research output: Contribution to journal › Article
TY - JOUR
T1 - Analysis of the NMR spin-spin coupling mechanism across a H-bond
T2 - Journal of Physical Chemistry B
AU - Tuttle, Tell
AU - Gräfenstein, Jürgen
AU - Wu, Anan
AU - Kraka, Elfi
AU - Cremer, Dieter
PY - 2004/1/22
Y1 - 2004/1/22
N2 - The NMR spin-spin coupling constants (SSCCs) across the H-bond in proteins are sensitive to the electronic structure of the H-bonded system, i.e., the N-H···O=C group in proteins. The spin-spin coupling mechanism across the H-bond involves a strong electric field effect, steric exchange interactions, and some weak covalent effects (transfer of electronic charge). The electric field effect is reflected by one-orbital contributions to the SSCC and can be tested with the help of probe charges. A negative charge opposite to the N-H bond leads to increased polarization of the N-H bond, a larger contact density at the N nucleus, and a stronger FC coupling mechanism for those SSCCs involving the N nucleus. Similarly, a positive charge opposite to the O=C bond, distorts the O density into the direction of the external charge and in this way decreases the spin density at the O nucleus. All SSCCs across the H-bond depend primarily on the electric field effect and two-orbital steric exchange interactions. The lone pair contributions to the Fermi contact ferm of 2h J(ON) (and to a lesser extent 3h J(CN)) provide a direct measure on possible covalent contributions in the form of charge-transfer interactions. According to calculated charge-transfer values and lone-pair contributions to SSCC 2h J(ON), the covalent contribution to the H-bond is rather small (less than 15% at 1.9 Å for a bending angle β(COH) of 120°). The zeroth-order density and the spin-spin coupling mechanism, which depends largely on the first-order spin density, both describe the H-bond as being electrostatic rather than covalent. The electric field effect largely determines the geometrical dependence of the SSCCs of a hydrogen-bonded system.
AB - The NMR spin-spin coupling constants (SSCCs) across the H-bond in proteins are sensitive to the electronic structure of the H-bonded system, i.e., the N-H···O=C group in proteins. The spin-spin coupling mechanism across the H-bond involves a strong electric field effect, steric exchange interactions, and some weak covalent effects (transfer of electronic charge). The electric field effect is reflected by one-orbital contributions to the SSCC and can be tested with the help of probe charges. A negative charge opposite to the N-H bond leads to increased polarization of the N-H bond, a larger contact density at the N nucleus, and a stronger FC coupling mechanism for those SSCCs involving the N nucleus. Similarly, a positive charge opposite to the O=C bond, distorts the O density into the direction of the external charge and in this way decreases the spin density at the O nucleus. All SSCCs across the H-bond depend primarily on the electric field effect and two-orbital steric exchange interactions. The lone pair contributions to the Fermi contact ferm of 2h J(ON) (and to a lesser extent 3h J(CN)) provide a direct measure on possible covalent contributions in the form of charge-transfer interactions. According to calculated charge-transfer values and lone-pair contributions to SSCC 2h J(ON), the covalent contribution to the H-bond is rather small (less than 15% at 1.9 Å for a bending angle β(COH) of 120°). The zeroth-order density and the spin-spin coupling mechanism, which depends largely on the first-order spin density, both describe the H-bond as being electrostatic rather than covalent. The electric field effect largely determines the geometrical dependence of the SSCCs of a hydrogen-bonded system.
KW - spin−spin coupling constants
KW - SSCCs
KW - H-bond
KW - proteins
UR - http://www.scopus.com/inward/record.url?scp=0742321701&partnerID=8YFLogxK
UR - https://pubs.acs.org/journal/jpcbfk
U2 - 10.1021/jp0363951
DO - 10.1021/jp0363951
M3 - Article
VL - 108
SP - 1115
EP - 1129
JO - Journal of Physical Chemistry B
JF - Journal of Physical Chemistry B
SN - 1520-6106
IS - 3
ER -