Neutral molecule recognition

The binding and recognition of neutral molecules make use of electrostatic, donor-acceptor and especially of hydrogen bonding interactions [2.119-2.123]. Polar organic molecules such as malonodinitrile form weak complexes with crown ethers and related ligands [2.120]. 

Zehnacker A, Suhm MA (2008) Chirality recognition between neutral molecules in the gas phase. Angew Chem Int Ed 47 6970-6992... 

Not all separations can be accomplished with simple buffers. For example, chiral recognition and separation of neutral molecules always require additives. Even charged-molecule separations can often be improved via secondary equi-... 

The recognition that solutions of acid and bases (and also solutions of salts) contain ions rather than just neutral molecules is due to the Swedish chemist Svante Arrhenius (1859-1927), in 1887. Arrhenius pointed out that the electrical conductivity of these solutions could be understood as due to the motion of the ions through the solution between the electrodes. 

S. E. Matthews and P. D. Beer, Calixarene-based Anion Receptors, in Reference lb, p. 421. A. Arduini, A. Pochini, A. Secchi and F. Ugozzoli, Recognition of Neutral Molecules,in Reference lb, p. 457. 

The first practical application for cyclophanes was found in host-guest chemistry [4]. Molecular recognition of ions and neutral molecules in functionalized cavities of cyclophanes has been demonstrated for numerous examples. Here, special interest has been attracted by complexes in water since it can directly model molecular recognition events in biological systems. The development of suitable water soluble hosts with high binding selectivity is an active field of research [5] that has recently been reviewed [6]. 

The chiral molecular recognition of neutral molecules has become an important subject in the fields of analytical, biochemical and pharmaceutical technologies. 

Neutral molecules are also interesting as adsorbates, because they influence or participate in faradaic processes (2-, 6-8, 13, 16-19, 34). They can be detected and studied by the methods we have outlined above (see Problem 13.6). An interesting aspect of their behavior is that adsorption from aqueous solutions is often effective only at potentials relatively near the PZC. The usual rationale for this phenomenon rests on a recognition that adsorption of a neutral molecule requires the displacement of water molecules from the surface. When the interface is strongly polarized, the water is tightly bound and its displacement by a less dipolar substance is energetically unfavorable. Adsorption can take... 

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