Carbohydrate-Aromatic Interactions: The Role of Curvature on XH•••π Interactions

The interaction between the fragment of carbon nanotube (CNT) and carbohydrates has been investigated using MP2 and M05-2X methods using various basis sets in gas phase. Three carbohydrates, viz., beta-D-glucose, beta-D-galactose, and beta-D-xylose with different degree of hydrophobic nature have been selected for this investigation. With a view to assess the effect of curvature on the interaction between the carbohydrates and CNT, calculations on intermolecular complexes comprising of coronene (COR) and carbohydrates have also been carried out in gas phase. Results obtained from electronic structure calculations combined with the Bader's electron density analysis reveal that CH center dot center dot center dot pi interaction is the predominant one in the stabilization of the carbohydrate-CNT and carbohydrate-COR complexes. Furthermore, the importance of OH center dot center dot center dot pi and lone pair center dot center dot center dot pi (lp center dot center dot center dot pi) interactions also evident from the results. The calculated BEs for the various carbohydrate-CNT and carbohydrate-COR complexes at M05-2X with dual basis set [aug-cc-pVTZ for carbohydrate + cc-PVTZ for both CNT and COR] vary from -2.52 to -5.14 and from -4.14 to -8.04 kcal/mol, respectively. The corresponding BEs obtained from MP2/6-311++G(d,p)//M05-2X/6-31+G(d,p) level of calculation range from -4.92 to -9.93 and from -6.75 to - 12.53 kcal/mol. Close scrutiny of the energetics of all the complexes elucidate that the electron correlation energy (dispersion energy) significantly contribute to the stability of these complexes. It is found from the analysis of geometrical parameters and BEs that the interplay of orientation of the X-H (X = C and O) bond to the pi-surface is crucial for the recognition and further stabilization. Molecular electrostatic potential (MESP) isosurfaces of curved and planar surfaces have clearly provided the difference between the pi-electron distributions. Evidences form the energy decomposition analysis elicit that the dispersive interaction plays a significant role in the overall stabilization of the complexes. And, it is possible to observe the delicate balance between the electrostatic interaction and the exchange-repulsion energy.