We prepared dual-cavity basket 1 to carry six (S)-alanine residues at the entrance of its two juxtaposed cavities (289 angstrom(3)). With the assistance of H-1 NMR spectroscopy and calorimetry, we found that 1 could trap a single molecule of 4 (K-1 = 1.45 +/- 0.40 X 10(4) M-1, ITC), akin in size (241 angstrom(3)) and polar characteristics to nerve agent VX (289 angstrom(3)). The results of density functional theory calculations (DFT, M06-2X/6-31G*) and experiments (H-1 NMR spectroscopy) suggest that the negative homotropic allosterism arises from the guest forming C-H center dot center dot center dot pi contacts with all three of the aromatic walls of the occupied basket's cavity. In response, the other cavity increases its size and turns rigid to prevent the formation of the ternary complex. A smaller guest 6 (180 angstrom(3)), akin in size and polar characteristics to soman (186 angstrom(3)), was also found to bind to dual-cavity 1, although giving both binary [1 subset of 6] and ternary [1 subset of 6(2)] complexes (K-1 = 7910 and K-2 = 2374 M-1, H-1 NMR spectroscopy). In this case, the computational and experimental CH NMR spectroscopy) results suggest that only two aromatic walls of the occupied basket's cavity form C-H center dot center dot center dot pi contacts with the guest to render the singly occupied host flexible enough to undergo additional structural changes necessary for receiving another guest molecule. The structural adaptivity of dual-cavity baskets of type 1 is unique and important for designing multivalent hosts capable of effectively sequestering targeted guests in an allosteric manner to give stable supramolecular polymers.