NOVELTY - A composition comprises: (i) a stable guest-host assembly containing a generally spheroidal host assembly formed of trimers of calixarene molecules in a hexagonal close-packed assembly of the trimers associated together predominantly by van der Waals forces (a) to provide at least one dilated channel having a void volume of 100 - 200 Angstrom 3; and (ii) a guest component encapsulated within the at least one dilated channel and retaining within the channel predominantly by (a).    USE - For operating a replenishable fuel cell and a replenishable canister for release and recovery of a volatile component in a constrained environment (claimed). In the storage of volatile fuels e.g. hydrogen and methane, fuel storage cells for vehicle powered by the combustion of hydrogen or methane; and in the operation of a replenishable canister for release and subsequent recovery of a volatile component in a constrained environment e.g. combustion suppressant such as space vehicles.    ADVANTAGE - The guest-host assembly is stable at least 150 (preferably at least 200)degreesC. The composition has a thermal stability (K) of 70 - 460degreesC (where K is T'-Tb, T' is the onset temperature of guest release in degreesC and Tb is the boiling point of the guest component in degreesC).    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) forming (M1) the guest-host assembly and releasing a guest component from the guest-host assembly, involving: either (a1) providing the spheroidal guest-host assembly; (a2) heating the assembly to a temperature in excess of 150degreesC, which is sufficient to destabilize the guest-host assembly and release the guest molecules; (a3) cooling the host assembly molecules and reassembling the molecules to form the generally spherical assembly formed of trimers of the calixarene molecules in the hexagonal close-packed assembly of the trimers associated together predominantly by (a) to provide the at least one dilated channel; and (a5) infusing the guest component in the dilated channel to provide the assembly in which the guest component is retained in the assembly predominantly by (a). The guest component is stable at least 150degreesC; or (b1) providing the spherical host assembly formed of trimers of calixarene molecules in the hexagonal close-packed assembly to provide at least one dilated channel having a void volume within the range of 100 - 200 Angstrom 3 (preferably 140 - 170); (b2) infusing the guest component into the dilated channel of the host assembly to provide a guest-host assembly in which the guest component is retained in the assembly predominantly by van der Waals forces; and (b3) heating the guest-host assembly to a temperature in excess of 150degreesC which is above the boiling point of the guest component and is sufficient to destabilize the guest-host assembly and release the molecules of the guest component; or (c1) providing the generally spherical host assembly formed of trimers of calixarene molecules in the hexagonal close-packed assembly of the trimers associated together predominantly by (a) to provide at least one dilated channel having a void volume of 80 - 180 Angstrom 3; (c2) infusing the guest component into the dilated channel to provide a guest-host assembly in which the guest component is retained in the assembly predominantly by (a) and is stable at a temperature of at least 200degreesC; (c3) heating the guest-host assembly to a temperature in excess of 200degreesC, which is sufficient to destabilize the guest-host assembly and release the molecules of the guest component; (c4) cooling the host assembly molecules and reassembling the molecules to form the generally spherical assembly formed of trimers of the calixarene molecules in the hexagonal close-packed assembly of the trimers associated together predominantly by van der Waals forces to provide at least one dilated channel having a void volume of 100 - 200 Angstrom 3; and (c5) infusing the guest component in the dilated channel of the host assembly to provide the guest-host assembly in which the guest component is retained in the assembly predominantly by (a) and is stable at least 200degreesC;    (2) operating a replenishable fuel cell involving (d1) providing a vessel containing a solid fuel cell structure having a lattice structure of molecular crystals having lattice voids and incorporating the calixarene molecules in the hexagonal close-packed assembly of trimers of the calixarene molecules associated together predominantly by (a) to provide the host assembly having interstitial voids capable of sustaining a guest component within the voids predominantly by (a) and is stable at a temperature substantially in excess of ambient temperature conditions; (d2) retaining a volatile fuel component which is normal gaseous at ambient temperature conditions within the interstitial voids of the lattice structure predominantly by (a) to provide the guest/host assembly of the lattice structure and the volatile fuel component; (d3) heating the fuel cell to heat the hexagonal close packed assembly to destabilize the guest/host assembly and disassembling the calixarene molecules to release the fuel component; (d3) supplying the released fuel component to an internal combustion engine; (d4) cooling the host assembly molecules to reassemble the molecules to form the hexagonal close-packed assembly of trimers to provide a fuel cell lattice structure. The lattice structure is stable at a temperature substantially in excess of ambient temperature; and (d5) infusing the volatile fuel component to the fuel cell lattice structure to reestablish the fuel cell in which the fuel component is retained as a guest in the assembly predominantly by (a); and    (3) operating (M3) a replenishable canister for release and recovery of a volatile component in a constrained environment.