## 3 Results and Discussion
### In Silico Colorimetric Analysis of the Grape Seed Peptide-Mv3 glc Interaction
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline  & \multicolumn{4}{c}{**Quantum Chemical Calculations**} & \multicolumn{4}{c}{**Spectral**} & \multicolumn{4}{c}{**CIELAB Color Parameters**} \\  & **Dihedral** & **E Docking** & **Molecular** & **\(\lambda_{\text{max}}\)** & **A\({}_{520}\)** & **L\({}^{*}\)** & \(a^{*}\)** & \(b^{*}\)** & \(C^{*}_{ab}\) & \(h_{ab}\) \\  & **Angle (\(\circ\))** & (**kcal/mol**) & **Interaction** & & & & & & & & \\ \hline
1 & \(67.0^{\circ}\) & \(-4.1\) & \(\pi\)-\(\pi\)-\(\pi\)-alkyl & 492 & 0.36 & 79.4 & 20.0 & 7.3 & 21.3 & 20.2\({}^{\circ}\) \\
2 & \(-85.3^{\circ}\) & \(-4.1\) & hydrogen bond/\(\pi\)-alkyl & 424 & 0.08 & 94.4 & \(-2.5\) & 28.6 & 28.7 & 94.9\({}^{\circ}\) \\
3 & \(66.5^{\circ}\) & \(-4.1\) & \(\pi\)-\(\pi\)-\(\pi\)-alkyl & 542 & 0.32 & 77.1 & 10.4 & \(-5.2\) & 11.6 & 333.4\({}^{\circ}\) \\
4 & \(71.3^{\circ}\) & \(-4.0\) & hydrogen bond/\(\pi\)-alkyl & 476 & 0.29 & 82.5 & 14.2 & 12.3 & 18.8 & 40.9\({}^{\circ}\) \\
5 & \(66.5^{\circ}\) & \(-4.0\) & \(\pi\)-\(\pi\)-\(\pi\)-alkyl & 512 & 0.45 & 72.8 & 22.8 & \(-7.3\) & 23.9 & 342.2\({}^{\circ}\) \\
6 & \(58.0^{\circ}\) & \(-4.0\) & \(\pi\)-\(\pi\)-\(\pi\)-alkyl & 472 & 0.43 & 77.3 & 21.7 & 22.4 & 31.2 & 45.9\({}^{\circ}\) \\
7 & \(60.0^{\circ}\) & \(-4.0\) & hydrogen bond/\(\pi\)-alkyl & 484 & 0.54 & 74.4 & 30.8 & 16.4 & 34.9 & 28.1\({}^{\circ}\) \\
8 & \(-83.7^{\circ}\) & \(-4.0\) & \(\pi\)-\(\pi\)-\(\pi\)-alkyl & 428 & 0.08 & 93.4 & \(-1.0\) & 15.2 & 15.6 & 93.9\({}^{\circ}\) \\
9 & \(-85.1^{\circ}\) & \(-3.9\) & \(\pi\)-\(\pi\)-\(\pi\)-alkyl & 428 & 0.08 & 93.9 & \(-1.1\) & 16.2 & 16.2 & 93.9\({}^{\circ}\) \\ \hline \end{tabular}
\end{table} 
Table 3: Results obtained for the nine docking conformations: chemical interaction parameters (mv3 glc dihedral angle, binding energy, and type of intermolecular interaction), spectral parameters (\(\lambda_{\text{max}}\) and A\({}_{520}\) nm), and CIELAB color parameters. interaction with the peptide. In addition, the predicted color of conformations 2, 8, and 9 corresponded to very pale tonalities according to the predicted high values of lightness (\(L^{*}>90\)). In comparison, conformations 1, 3, 5, and 7 closely reproduced the wide range of tonalities based on their predicted \(h_{ab}\) values, distinctive of the flavylium cation in acid conditions. Figure S2 shows the absorption spectra calculated with the B3 LYP/6-31+G(d,p) theoretical level for the isolated mv3 glc molecule corresponding to these minimum-energy configurations. Notably, conformations 1 and 7 with predicted \(h_{ab}\) values of 20\({}^{\circ}\) and 28\({}^{\circ}\), respectively, reproduced red-orange tonalities, while conformations 3 and 5 with \(h_{ab}\) values of 333.4\({}^{\circ}\) and 342.2\({}^{\circ}\) accurately reproduced red-bluish tonalities. In all cases, the C\({}^{*}_{ab}\) values ranged from 11 to 35 units, suggesting vivid tonalities. Regarding the conformations that reproduced the red-bluish colorations properly (3 and 5), the docking results indicate that mv3 glc interacts with the grape seed peptide through \(\pi\)-\(\pi\) and \(\pi\)-alkyl interactions, which has been described in copigmentation interactions involving the flavylium cation form. Moreover, from a structural perspective, the dihedral angles of these conformations (3 and 5) corresponded to 66.5\({}^{\circ}\); therefore, this parameter could provide a structural reference of the flavylium cation's torsion caused by the malvidin-GSP interaction. Thus, B3 LYP combined with 6-31+G(d,p) has also been demonstrated to be effective in the prediction of spectroscopic and colorimetric features of anthocyanins related to interaction effects, offering a satisfactory balance between accuracy and computational efficiency. However, its performance has also limitations such as the systematic underestimation of \(\lambda_{\max}\), suggesting the importance of exploring additional approaches.