Lars Andersen Bratholm edited Similarly_Delta_sigma_i__D__.tex  almost 9 years ago

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Similarly, $\Delta\sigma^i_{D^\circ H_A}$ is computed as the change in chemical shielding of the corresponding atom in the donor molecule Acetyl-L-alanine methyl amide due to the $H_A$ proton hydrogen bonding to an acceptor NMA, methanol, or acetate molecule (Figure 2).  $\Delta\sigma^i_{A^\circ H_A}$ is the change in chemical shielding of an atom in an acceptor NMA due to the carbonyl oxygen hydrogen bonding to a donor Acetyl-L-alanine methyl amide molecule.  $\Delta \sigma^i_{D\circ H_A}$ is the effect of hydrogen bonding to the HA and O(C) atoms of residue i on the chemical shielding of the backbone atoms and CB and has two contributions   $$\Delta \sigma^i_{HB}=\Delta\sigma^i_{1^\circ H\alpha B}(r_{\mathrm{H\alpha O}},\theta_{\mathrm{H\alpha}},\rho_{\mathrm{H\alpha}})+\Delta\sigma^i_{2^\circ H\alpha B}(r_{\mathrm{OH\alpha}},\theta_{\mathrm{O}},\rho_{\mathrm{O}})$$  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 3). 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. $\Delta\sigma^i_{1^\circ H\alpha B}$ is computed for Cā€™, HA and CA using the O of residue $i$, while for H(N) and N, it is computed using the O(C) atom of the preceding ($i-1$) residue. $\Delta\sigma^i_{2^\circ H\alpha B}$ is the change in chemical shielding of Ala atoms in (except HB) in Ac-A-NMe due to the HA hydrogen bonding to the oxygen atom of a NMA, methanol, or acetate molecule (Figure 3). $\Delta\sigma^i_{2^\circ H\alpha B}$ is the change in 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 3a). For $\Delta\sigma^i_{2^\circ H\alpha B}$ CA is defined at the methyl C bonded to Cā€™ in the H accepting NMA molecule and HA is taken as the average of the H chemical shielding values for that methyl group. The range of bond lengths and angles considered is described in Section 3.3.