Fig. 10. Hirshfeld surfaces “dnorm ”,
“Shape index ” and “Curvedness ” of Chloroquine
molecule.
The normalized contact distance (dnorm ) of the
Chloroquin compound makes it possible to graphically illustrate the
relative positioning of the neighboring atoms belonging to the molecule
interacting together. This analysis type displays a surface with a color
scheme (red, blue, white), where the red spots highlight the shortest
intermolecular contacts which are attributed to C-H···N interactions.
The blue areas indicate the most language intermolecular contacts in the
structure and the white regions represent the contacts around the van
der Waals separation. The latter corresponds respectively to the H···H,
C···H and H···Cl interactions [81-84]. Concerning the two maps (3D)
Shape index and Curvedness, indeed the two blue and red triangles
located at the level of Chloroquin phenyl on the Shape index cartography
and the large flat region delimited by a blue outline observed on the
Curvedness graph suggest the presence of C-H… π interactions
[83]. The percentages of the different contacts as well as the
fingerprint plots of the main contacts existing in the chloroquin
structure are illustrated respectively in Figs. 11 and 12. The
hydrogen-hydrogen contacts (H … H) (Fig. 12a) occupy almost half of
the entire Hirshfeld surface (44.6%) with a high concentration in the
central region where de =di = 1.1Å. C… H / H… C (Fig. 12b)
and H… Cl / Cl… H (Fig. 12c) contacts comprise
respectively 29.8% and 10.2% of the entire Hirshfeld surface and
represented by two symmetrical wings with de +di ~ 3 Å and 3.2 Å, the large
percentage (29.8%) confirms the presence of the C-H… π
interactions already mentioned in the three-dimensional graphs (Shape
index and Curvedness). The nitrogen-hydrogen contacts (N… H /
H… N) show on its 2D graph the presence of two narrow and
symmetrical pointed points centered around a sumde + di ~
2.2 Å, these contacts are responsible for the hydrogen bonds C-H…
N. Based on the van der Waals rays of involved atoms in contacts (H:
1.09 Å, C: 1.70 Å, N: 1.55 Å, Cl: 1.75) Å and the de and
di distances we carried out a comparative study to find
out the nature of contacts, close or distant, this study is summarized
in Table 7. We note from this table that only N… H / H… N
contacts are considered close with a sum di +de less than the sum of van der Waals rays of
involved atoms.
Table 7 Nature of main contacts existing in chloroquine
molecule.