Neutral molecules sensing

Few chemical sensing mechanisms (other than bulk quenching) have been described for neutral molecules nevertheless, many small analytes of interest are uncharged glucose, for example. Of course, most carbohydrates are neither fluorescent nor are they fluorescence quenchers novel signal transduction mechanisms are required. 

The term molecules is used in the general sense to denote any molecular species atom, ion, neutral molecule or radical. 

A second type of metathesis reaction involves metals multiply bonded to nonmetals (equation 68). In one sense, this corresponds to a special case of dinuclear reductive elimination of neutral molecules in which multiply bonded species are involved. This reaction can occur in both directions. Multiply bonded metal-metal complexes can be cleaved by multiply bonded main group species. 

Not all "neutral" molecules are neutral, in the sense that they usually have some polarity and an end or section that is more hydrophobic or hydrophilic than the rest of the molecule. Other "neutral" molecules in a mixture may be slightly different and advantage is taken of this. If a low concentration of a surfactant, such as sodium dodecyl sulfonate (one end hydrophobic, one end hydrophilic) is added to the system, these surfactant molecules at first stay separated. As their concentration increases, the hydrophobic ends tend to associate and they form small clusters called micelles, which have a hydrophilic outside (net negative charge) and a hydrophobic inside. 

Ion—molecule reactions, in which we are interested here, are binary collisions of ions (positive or negative) with neutral molecules resulting in chemical reactions, in which at least one chemical bond is ruptured or one new chemical bond is formed. This is the definition of ion—molecule reactions in a narrow but rather conventional sense. Some of the possible types of such reactions are... 

In a wider sense, ion—molecule reactions include, in addition to the above, all kinds of physical collisions of ions and neutral molecules such as... 

In contrast to the recognition of cations or anions, the eiectrochemical sensing of neutral molecules by redox-active receptors is less common. A number of supramo-... 

The gas-phase reactivity of selected ionic species with borazine and borazine-derived ions with selected neutral molecules has been studied by FT-ICR and ab initio calculations. Evidence for an electrophilic substitution on the borazine ring was found in the alkylation by gaseous Me2F+, Me2CH+, and MesC that led to neutral substitution products, as a result of an N-alkylation. Further studies on the protonation, all lation, and nitration of neutral borazine have been compared with the corresponding reactions of benzene, and it was shown that the cyclic B3N3H5+ reacts similarly to the phenylium cation CeHs. In this sense, borazine shows a remarkable similarity to benzene. 

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