conformational variation of GT5 at various stages of hydration as a function of its torsional angles is shown in Figure 8 . The strength of H-bond (X Z H . . . Y) can be predicted using the H-bond distance (H . . . Y) and the corresponding angles (‹X Z H . . . Y). The H-bond lengths and angles involving the prominent intermolecular H-bonds formed in the hydrated GT n . . . 4W n ¼ 1–5 and GT5 . . . 11W complexes are listed in Table 5 . In the hydrated GT n . . . 4W n ¼ 1–5 complexes, the lengths of O Z H . . . O, N Z H . . . O and C Z H . . . O H-bonds vary from 1.538 to 2.251 A ˚ , from 1.923 to 2.276 A ˚ and from 2.238 to 2.51 A ˚ , respectively. In GT5 . . . 11W complexes, these distances vary between 1.804 and 2.132 A ˚ , between 1.716 and 1.912 A ˚ and between 2.319 and 2.532 A ˚ , respectively. Figure 9 shows that H-bond length of the prominent H-bonding interactions observed in the hydrated GT complexes. Here, the homonuclear inter- actions were found to be marginally stronger than the heteronuclear interactions. The O Z H and N Z H bonds were found to be elongated from their corresponding monomers up to 0.033 and 0.008 A ˚ , respectively. This is due to the well-known fact that during the H-bond formation, the proton-donating bond is elongated. This lengthening was observed to be greater for stronger H- bonds. On the contrary, the C Z H . . . O bonds were contracted up to 0.005 A ˚ . The H . . . Y distances in the solvated complexes were observed to fluctuate from 2.548 to 3.233 A ˚ . It is well known that the H-bond angle for strong H-bonds ranges from 170 8 to 180 8 .  For stronger H-bonds, the angle was found to be closer to 180 8 . In this investigation, the O Z H . . . O, C Z H . . . O and N Z H . . . O intermolecular angles fluctuate from 129.94 8 to 169.72 8 , from 115.5 8 to 146.5 8 and from 132.84 8 to 169.68 8 , respectively. In the hydrated GT complexes, only one O Z H . . . N interaction (O34 Z H36 . . . N5) exists in the hydrated complexes (GT5 . . . 4W) with angle closer to 180 8 (173.75 8 ), implying that the H-bond is strong (1.796 A ˚ ). In GT5 . . . 11W complexes, these angles vary from 139.4 8 to 169.62 8 , from 135.74 8 to 144.55 8 and from Table 4. Relative energy D E (in kcal/mol), BSSE corrected interaction energy E int (in kcal/mol) and dipole moment m m (in D) for the hydrated GT n . . . 4W n ¼ 1–5 and GT5 . . . 11W complexes calculated at the MP2/6-311G ** //B3LYP/6-311G ** and B3LYP/6-311G ** levels of theory. D E – E int m m Complex MP2 B3LYP MP2 B3LYP MP2 B3LYP GT1 . . . 4W 0.63 2.51 40.41 44.05 7.749 6.715 GT2 . . . 4W 9.41 10.60 35.96 39.60 7.557 6.833 GT3 . . . 4W 15.77 10.79 34.64 37.46 5.009 4.323 GT4 . . . 4W 6.27 8.16 37.40 41.10 9.910 9.071 GT5 . . . 4W 0.00 0.00 46.12 51.39 3.529 3.471 GT5 . . . 11W – – 116.78 124.62 4.521 4.182 Molecular Simulation 951 Downloaded by [Thammasat University Libraries] at 03:39 08 October 2014
150.99 8 to 162.3 8 , respectively. In GT5 . . . 11W complex, only one O Z H . . . N interaction between O Z H (W) and nitrogen atom belongs to the third glycine fragment with intermolecular H-bond angle 156.56 8 with comparatively higher H-bond length (2.051 A ˚ ) than the O Z H . . . N interaction, taking place in GT5 . . . 4W with the nitrogen atom (N5) of the first glycine fragment (1.796 A ˚ ).
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