Cucurbit[ n ]urils (CB[ n ]s) are among the most important supramolecular macrocycles owing to their remarkable host–guest recognition ability, rigid hydrophobic cavities, and highly polarized carbonyl portals, which collectively enable the encapsulation of a wide range of biologically relevant molecules. In the present study, a comprehensive computational investigation was performed to elucidate the structure-dependent binding behavior between cucurbit[7]uril (CB7) and a homologous series of N-acyl-L-homoserine lactones (AHLs), namely N-pentanoyl-L-homoserine lactone (C5), N-hexanoyl-L-homoserine lactone (C6), N-heptanoyl-L-homoserine lactone (C7), and N-octanoyl-L-homoserine lactone (C8). These quorum-sensing signaling molecules differ systematically in hydrophobic acyl-chain length, providing an excellent model for probing supramolecular recognition within the CB7 cavity. Molecular dynamics (MD) simulations combined with Molecular Mechanics/Generalized Born Surface Area (MM/GBSA) free-energy calculations were employed to investigate complex stability, binding energetics, conformational behavior, and intermolecular interactions. Center-of-mass radial distribution function (COM-RDF) analysis revealed a progressive sharpening and intensification of the host–guest distribution from C5 to C8, with the COM standard deviation decreasing from 0.96 Å for C5–CB7 to 0.48 Å for C8–CB7, indicating increasingly tight encapsulation of the longer acyl chains within the CB7 cavity. Energy decomposition analysis demonstrated that complex formation is predominantly governed by favorable van der Waals interactions arising from efficient hydrophobic packing of the alkyl chains inside the CB7 cavity, whereas electrostatic contributions remained comparatively modest. Furthermore, the unfavorable solvation penalty decreased substantially with increasing chain length, indicating improved shielding of hydrophobic surfaces from the aqueous environment upon encapsulation. Structural stability analysis from RMSD trajectories confirmed that the C8–CB7 complex achieved the most stable conformational state during the simulation period. The combined energetic and dynamic analyses establish a direct correlation between hydrophobic chain extension and supramolecular binding efficiency within CB7. These findings provide detailed molecular-level insight into the recognition mechanism of AHLs by cucurbiturils and highlight the potential of CB7-based supramolecular systems for the selective capture, sensing, and modulation of quorum-sensing molecules.
A simple pyrazole-based colorimetric chemosensor, 4(E)-1-(4-((2-(2,4-dinitrophenyl)hydrazinylidene)methyl)phenyl)-1H-pyrazole (PY-09), was developed for the selective detection of arsenate (AsO43−) and cyanide (CN−) ions through distinct optical responses. The free probe exhibited a yellow colour, which changed to magenta upon interaction with either AsO43− or CN−, enabling rapid naked-eye detection. UV–Vis absorption studies revealed a bathochromic shift from 403 nm to 507 nm for AsO43− and to 508 nm for CN−. The probe demonstrated high sensitivity, with detection limits of 0.99 μM for AsO43− and 0.29 μM for CN−. Job's plot analysis indicated binding stoichiometries of 1:1 for both AsO43− and CN−, while the corresponding association constants were determined to be 2.14 × 105 M−1 and 4.4 × 104 M−1, respectively. The sensing process was reversible upon the addition of trifluoroacetic acid (TFA). Furthermore, hydrogen peroxide was successfully employed as a masking agent to selectively eliminate cyanide interference, enabling the specific detection of arsenate ions. The practical applicability of PY-09 was validated through successful analysis of real water samples, demonstrating excellent recovery and reliability. These findings highlight PY-09 as a simple, sensitive, and cost-effective colorimetric chemosensor, demonstrating its potential for colorimetric arsenate detection in water samples.
