Self-solvating bases

The potassium complex of mono-aza-18-crown-6 (80) is a self-solvating base potentially useful for performing clean E2 eliminations from alkyl halides in non-polar solvents,whilst avoiding the loss of reactivity and changes in product distribution sometimes observed in such media due to base-cation association. 

In 1977, Gokel and Garcia prepared 1 in the hope that it could be treated with KH to form the self-solvating and overall neutral base system, 2. 

Another structural motif, the zwitterion, is potentially present in molecules that contain both acidic and basic functional groups, a situation present in many biomolecules [81-90].However,zwitterions are intrinsically not stable (for common acids and bases) and require a large amount of stabilization by (self-) solvation and Coulomb interaction with other charges. Zwitterions and non-zwit-terions of flexible molecules sometimes assume sufficiently different geometries that the ion mobility technique can be used to distinguish between the two forms. The best examples reported to date are the sodiated oligoglycines that were found not to be zwitterions [91]. 

A further feature of PEG-based copolyesters is that since the copolymers comprised self-solvating molecules, their conversion to a hydrogel about a drug provides a uniform distribution of the therapeutic agent and thus a more predictable release profile. This is in contrast to conventional systems in which the presence of leachable solvents leads to complex physical events that can alter the kinetics of the system. ... 

As noted above, the use of a continuum solvent model [58-61] is one of the most appealing ways to describe solvation in a readily tractable form, and one we will consider further below. We note here that for spherical geometries (spherical solutes) with uniform solvent density, the description is simply given by the Bom equation. In general, for uniform dielectrics and nonspherical solute geometries, the underlying Poisson equation can be solved numerically[58, 59]. Generalization to the case of an arbitrary nonuniform density which is found self-consistently based on the bulk equations of electrostriction has been carried out more recently[60, 61]. 

In this paper we have developed the main features of a Self-Consistent Reaction Field Model of solvation based on the use of generalized reaction field factors which enable us to relate the perturbation caused by the solvent on the solute to the multipole moments of the solute. 

An alternative to the use of a dipolar aprotic solvent is to use a nonpolar medium and a cation solvating additive. The use of beta-diamines to solvate and enhance the reactivity of organolithium compounds is well known and documented [15]. Polyethylene glycol derived bases were known to be self-solvating as early as 1963 [16]. 

As mentioned above, the PCM is based on representing the electric polarization of the dielectric medium surrounding the solute by a polarization charge density at the solute/solvent boundary. This solvent polarization charge polarizes the solute, and the solute and solvent polarizations are obtained self-consistently by numerical solution of the Poisson equation with boundary conditions on the solute-solvent interface. The free energy of solvation is obtained from the interaction between the polarized solute charge distribution and the self-... 

Possible measures that are expected to improve the potentiometric selectivity are (1) use of hosts that form stronger complexes, (2) modification of the host to avoid ionophore self-association, and (3) an improved choice of the membrane solvent to avoid strong solvation of the hosts in the membrane. Evidence for the importance of (2) and (3) has been obtained from C NMR spectra of 12. While the properties of 1 1 host-guest complexes are very often of primary interest in supramolecular chemistry, the above results show that use of receptors for sensing purposes must be based on a receptor design that goes beyond this viewpoint. 

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