**Acknowledgements**

*Environmental Issues and Sustainable Development*

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**Figure 4.**

located outside the cavity. The IR spectrum study has explained the role of the NO3 gas in the red-shifted of the O-H bonds in comparison with the other gases. The MEP results is clearly explained the charge distribution reactivity. The NCI-RDG analysis clearly shows the strong interactions of the gas NO3 and NO2 with the endo-cavity

*NCI-RDG plots of the electron density and its reduced gradient of the inclusion complexes for CX[4]-gas (CX[4]-CO2(a), CX[4]-N2(b), CX[4]-NO2(c) and CX[4]-NO3(d)). The iso-surfaces were constructed with* 

*RGD = 0.5a.u and the colors scaling from −0.01 to −0.01 a.u.*

The authors acknowledge financial support from the Tunisian's Ministry of high education and scientific research. In this work, we were granted access to the HPC resources of the FLMSN, 'Fédération Lyonnaise de Modélisation et Sciences Numériques', partner of EQUIPEX EQUIP@MESO and to the 'Centre de calcul CCIN2P3' at Villeurbanne, France.
