The paper was published in International Journal of Molecular Sciences.
The presented study employed density functional theory (DFT) simulations to comprehensively investigate the adsorption behavior of riboflavin (Rf) on both defect-free and vacancy-containing hexagonal boron nitride systems. The findings reveal that the Rf molecule undergoes physical adsorption on the surface of the carrier, exhibiting minimal alteration in its chemical structure.
The most stable configuration observed involves the parallel alignment of the riboflavin molecule with the h-BN surface, forming π-π stacking interactions. This is corroborated by the adsorption energies obtained at various positions of the drug molecule. The molecular orbitals of riboflavin's isosurfaces provides a comprehensive understanding of the binding nature between riboflavin and h-BN based on the HOMO and LUMO location on the isoalloxazine site.
Remarkably, the presence of nitrogen vacancies significantly impacts the binding characteristics, as the carriers interact with the vacant riboflavin orbitals. Consequently, riboflavin transforms into an electron acceptor in the BN(Nv)@Rf system, attracting electron density by approximately 0.5 e-. This behavior starkly contrasts with the interactions observed in defect-free h-BN and h-BN with boron vacancies (BN(Bv)), see the Figure.
Distribution of spatial charge density difference in (a) BN@Rf, (b) BN(Bv)@Rf and (c) BN(Nv)@Rf structures and corresponding freestanding parts, side and top view. The loss and gain of charge are denoted by blue and yellow clouds, respectively. The boron, nitrogen, carbon, oxygen, and hydrogen atoms are marked by green, blue, black, red and cyan colors, respectively
These results validate the potential of h-BN as a promising carrier for riboflavin molecules, as the π-π bond formed between the drug and the carrier exhibits substantial strength, providing a solid foundation for drug delivery systems. However, it is crucial to exercise control over the structural perfection of h-BN, as the presence of vacancies can induce charging on riboflavin.
In summary, our study provides valuable insights into the stability and interactions of vitamin B2 with hexagonal boron nitride. The comprehensive understanding gained regarding their binding characteristics and the influence of defects enhances our ability to design and optimize drug delivery systems based on h-BN.