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Jan Jensen edited Delta_sigma_i__H_alpha__.tex
almost 9 years ago
Commit id: b5915de75e47a0702eb7940431001ab5f8258b52
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$\Delta \sigma^i_{H\alpha B}$ is the effect of hydrogen bonding to the H$\alpha$ and amide O atoms of residue $i$ on the chemical shielding of the backbone atoms and C$\beta$ and has two contributions
$$\Delta \begin{equation}
\label{eqn:sigmahab}
\Delta \sigma^i_{H\alpha B}=\Delta\sigma^i_{1^\circ H\alpha B}(r_{\mathrm{H\alpha O}},\theta_{\mathrm{H\alpha}},\rho_{\mathrm{H\alpha}})+\Delta\sigma^i_{2^\circ H\alpha B}(r_{\mathrm{OH\alpha}},\theta_{\mathrm{O}},\rho_{\mathrm{O}})$$
Here $r_{\mathrm{H\alpha O}}$ refers to the OH HB distance involving the HA and $\theta_{\mathrm{H\alpha}}$ and $\rho_{\mathrm{H\alpha}}$ are the corresponding angles (Figure \ref{fig:HAB}). Similarly, $r_{\mathrm{OH\alpha}}$ refers to the OH HB distance involving the amide O and $\theta_{\mathrm{O}}$ and $\rho_{\mathrm{O}}$ are the corresponding angles. \end{equation}
$\Delta\sigma^i_{1^\circ
H\alpha B}$ is computed for Cā, H$\alpha$ and C$\alpha$ using the amide O of residue $i$, while for the amide H
and N it \alphaB}$ is computed using the
amide O atom of the preceding ($i-1$) residue. $\Delta\sigma^i_{2^\circ H\alpha B}$ is structural models shown in Figure \ref{fig:HAB} as the change in chemical shielding of
Ala the backbone and C$\beta$ atoms in
(except H$\beta$) in Ac-A-NMe
due to relative that of the
H$\alpha$ hydrogen bonding to free monomer computed at the
oxygen atom OPBE/6-31G(d,p)//PM6 level of
theory for a
NMA, methanol, or acetate molecule (Figure \ref{fig:HAB}). variety of orientations (see subsection \ref{subsec:HBscan} for more information) while the internal monomer geometries are kept fixed.
$\Delta\sigma^i_{2^\circ
H\alpha B}$ HB}$ is
computed as the change in
the chemical shielding of
an atom in NMA due to the carbonyl oxygen hydrogen bonding to the HA atom in Ac-A-NMe. These value are taken from the same NMA ā Ac-NMe calculations used to compute (Figure \ref{fig:HAB}a). For $\Delta\sigma^i_{2^\circ H\alpha B}$ C$\alpha$ is defined at the
methyl C bonded to top amide
C group in
the H-accepting NMA molecule and Figure \ref{fig:HAB}a. For H$\alpha$
the chemical shielding is taken as the average of the
H chemical shielding values for that three hydrogen atom on the methyl
group. The range group of
bond lengths the acetamide. Note in this case that the amide nitrogen and
angles considered is described hydrogen formally belong to residue $i+1$ and that $r_\mathrm{HO}$, $\theta$, and $\rho$ are defined relative to the carbonyl oxygen of residue $i$ rather than the amide proton as for $\Delta\sigma^i_{1^\circ HB}$. $r_\mathrm{H\alpha O}$, $\theta$, and $\rho$ are therefore labeled $r_\mathrm{OH\alpha}$, $\theta_{\mathrm{O}}$, and $\rho_{\mathrm{O}}$ in
Section \ref{subsec:HBscan}. Eq \ref{eqn:sigmahab}.
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