Computational Insights into Nitro-BBTP: Crystal Packing, Electronic Structure, Molecular Reactivity, and Predicted C5aR1 Recognition

The experimentally determined crystal structure of 13-nitrobenzo[a][1,4]benzothiazino [3,2-c]phenoxazine (Nitro-BBTP) was investigated using Hirshfeld surface analysis, density functional theory (DFT), natural bond orbital (NBO) analysis, molecular electrostatic potential mapping, local reactivity descriptors, molecular docking, and in silico ADMET prediction. H···H contacts dominate the crystal surface (31.1%), followed by O···H (18.1%) and C···C (12.0%) contacts. The HOMO–LUMO gap decreases from 2.249 eV in the gas phase to 2.168 eV in acetonitrile, while MEP, Fukui-function, and NBO analyses reveal differentiated reactive regions and extensive π-electron delocalization. Docking against C5aR1 produced a best-pose score of −10.1 kcal mol−1; this is interpreted as a computational prediction, not an experimental binding affinity. SwissADME and ProTox-3.0 predictions indicate high gastrointestinal absorption, limited aqueous solubility, and potential toxicity alerts, including predicted mutagenicity. Overall, the study connects crystal packing and molecular electronic properties with exploratory predictions of receptor recognition and ADMET characteristics.