Neutral molecules, incorporation into

Monolayers of the cavitand 8a have been successfully used for the detection of small neutral organic molecules. Therefore, gold electrodes of a quartz microbalance oscillator were covered with monolayers of 8a and this device was exposed to ppm concentrations of perchloroethylene and other small organic molecules (chloroform, trichloroethylene, and toluene) in synthetic air. Fast, reversible, and relatively large shifts in the fundamental oscillation frequency are observed with remarkable selectivity (> 7-25) for perchloroethylene. In contrast, monolayers of didecyl sulfide exhibit almost no detectable signal. These results indicate that perchloroethylene molecules incorporate into the molecular cavities of the cavitand monolayers. Further studies of these supramolecular assemblies with surface recognition sites are in progress. 

Protonation, if forced upon pyrrole, is found to take place not on nitrogen but on the a-carbon atom (19). This occurs because incorporation of the nitrogen atom s lone pair of electrons into the aromatic 6jre system leaves the N atom positively polarised protons tend to be repelled by it, and are thus taken up by the adjacent a-carbon atom. The basicity situation rather resembles that already encountered with aniline (p. 70) in that the cation (19) is destabilised with respect to the neutral molecule (18a). The effect is much more pronounced with pyrrole, however, for to function as a base it has to lose all aromatic character, and consequent stabilisation this is reflected in its related pKa (-0-27) compared with aniline s of 4-62, i.e. pyrrole is a very weak base indeed. It can in fact function as an acid, albeit a very weak one, in that the H atom of the NH group may be removed by strong bases, e.g. eNH2 the resultant anion (20) then retains the aromatic character of pyrrole, unlike the cation (19) ... 

The unit cell volume, and with it the T, can also be increased by incorporation of a neutral molecule such as ammonia into the lattice by leaving the fcc-structure and oxidation state of the metal intact (Table 2.4). If the cubic lattice is disordered by this incorporation, a decrease rather than an increase of is observed [113,122, 123]. 

Neutral. A bis(ethylenediamine) structure has been incorporated into the surfactant molecule -Ci6H33C(H)[CON(H)(CH2)2NH2]2 in older to incorporate metal ions in an LB film structure via coordination instead of ionic complexation as occurs for anionic/cationic amphiphiles (14). Also, films of n-octadecylacetoacetate containing Cu2+ have been prepared, and exposure to H2S has resulted in the formation of a copper sulfide (39). Ditetradecyl-A-[4- [6-(A, N, W -trimethyl-ethylenediamino)-hexyl]oxy]benzoyl]-L-glutamate (DTG), which also contains the ethylenediamine unit, was used to make self-assembled films containing Cd2+ (40). 

The pore diameter of zeolite beta is 7 A, larger than those of silicalite-1 and silicalite-2 (5.5 A). Titanium incorporated into zeolite beta reacts with molecules whose dimensions are too big to diffuse in the pores and be oxidized by TS-1 or TS-2. The drawback is that zeolite beta must contain Al3+ to crystallize, and this imparts strong protonic acidity to the solid, with the consequence that secondary acid-catalyzed reactions also take place. However, the acidic properties can be neutralized in several ways and highly selective oxidations can be carried out on Ti-beta (Section V.C.3.b). 

The cholesterol activity on lipid bilayers has been subjected to extensive studies. As described above, cholesterol belongs to the class of neutral (non-polar) lipids and can be characterized as an amphiphilic molecule having a hydroxyl group at the C-3 position and a non-polar region. Frequently, cholesterol is incorporated into lipid membranes and studies concerning the influence on the phase transition between gel and liquid crystalline phases of the lipid bilayers hav been published [26, 27]. 

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