A First-Principles Investigation of the Encapsulation of Nucleic-Acid-Derived Aromatic Heterocycles in Boron Nitride Nanotubes.

This work investigates the encapsulation of five nucleic-acid-derived aromatic heterocycles (nucleobases)- adenine, cytosine, guanine, thymine, and uracil- inside boron nitride nanotubes (BNNTs) to understand the fundamental mechanisms governing host-guest interactions in confined nanoscale environments. Four BNNTs with different chiralities and diameters, namely the zigzag (11,0) and (12,0) nanotubes and the armchair (6,6) and (7,7) nanotubes, were studied using periodic density functional theory calculations. The results indicate that encapsulation is energetically favorable for all heterocycle-BNNT combinations considered. The confinement process induces measurable structural distortions in the smaller-diameter nanotubes and modifies the electronic properties of the host nanotubes through local charge redistribution arising from the proximity of electronegative atoms in the encapsulated molecules. Among the systems investigated, adenine exhibits the most favorable formation energy. Analysis of the electronic structure reveals a systematic reduction of the BNNT band gap upon encapsulation, with uracil producing the largest effect and guanine the smallest relative to the pristine nanotubes. Effectively, the process of encapsulation transforms the insulating BNNTs into wide-gap semiconductors while preserving the confined molecules. These findings demonstrate that molecular confinement inside BNNT cavities can significantly influence the structural stability and electronic properties of the host nanotubes. The study provides fundamental insight into confinement-driven interactions between aromatic heterocycles and boron nitride nanotubes and contributes to a deeper understanding of host-guest behavior in nanoscale tubular materials.