Physical guest-host effect

More quantitative information about host-guest proximity may be obtained by application of the nuclear overhauser effect (NOE). Very simply, the NOE involves the saturation of the spin of one nucleus by continuous irradiation, and monitoring the resulting intensity enhancements of the NMR resonances of adjacent atoms. The idea is that the irradiation of one nucleus causes it to become excited to a nonequilibrium distribution of spin states. Relaxation of this excited state situation occurs by dipole-dipole spin-lattice transfer of the excess energy, resulting in enhancement of the intensity of signals for nuclei physically close to the irradiated nucleus, irrespective of whether they are actually bonded. NOE intensity enhancements may be anywhere... 

The existence of the hydrophobic effect [14] in the formation of micelles, liposomes and other aggregates in water has been recognized and elaborately studied for several decades. Detergents, lipids and many derivatives made from them have been extensively studied and there are numerous reviews which document these in greater detail [15]. Synthetic bilayer membranes (BLMs) have been studied for the past three decades by using a variety of physical techniques [16]. Hydrophobic interaction has also been utilized for the design of hosts that bind guest molecules in water [17]. 

CyD ICs of diazirine 63 were prepared to determine the effect of supramolecular inclusion upon carbene 64. The a-CyD and /(-CyD ICs were analyzed using 111 NMR,14 including 2-D ROESY 15 ICD 17 and microanalysis. The integral structures of the CyD ICs were concluded to be 63 (a-CyD)2 and (63 / -CyD)2, based on their physical and chemical characteristics (vide infra). These stoichiometries denote that diazirine 63 is sandwiched between two a-CyD units, but that it forms a twofold 1 1 complex with /1-CyD.18 It has been demonstrated that a guest must have a substituent capable of hydrogen bonding, like —F or —OH,15,18 to effect an opposite inclusion orientation within CyD in the aqueous versus solid phase. Hence, it is likely that hydrophobic diazirine 63 adopted the same orientation within its CyD host during photolyses in both phases that were employed. 

EFFECTS OF CUCURBIT[n]URIL HOSTS ON GUEST PHYSICAL AND STRUCTURAL PROPERTIES... 

---