Cationic with Delocalized Charge

If the smaller monomer, capable of forming the cation with least charge delocalization, is indicated as monomer 1 and monomer 2 is characterized in an opposite manner, then the ratio r2/r, decreases during the transition into a more polar solvent. 

Weissig V, Lizano C, Ganellin CR, Torchilin VP. DNA binding cationic bola-somes with delocalized charge center a structure-activity relationship study. STP Pharma Sci 2001 11 91-96. 

Weissig V, Torchhin VP. Cationic bolasomes with delocalized charge centers as mitochondria-specihc DNA delivery systems. Adv Drug Deliv Rev 2001 49(1-2) 127-149. 

The first protonation of uracil in trifluoroacetic acid was found by nmr spectroscopy to occur at the oxygen atom in the 4-position, giving a cation with extensive charge delocalization [139], and the second protonation in fluorosulphuric acid occurs at the oxygen in position 2, giving cation [140], in which the two charges are delocalized over the whole molecule (Wagner and von Philipsbom,... 

Cationic dyes with delocalized charge are classified with the methine dyes (see Section 2.6). They may be viewed as vinylogous amidinium salts 3 [1] ... 

In the case of anthracene, which forms large anions with delocalized charge, the ion-pairing effect is related to the size of the solvated cation the interaction increases as the solvated cation becomes smaller. 

An interesting example of intracellular targeting of liposomes was described recently, when liposomes containing in their membrane composition mitochonriotropic amphiphilic cation with delocalized positive charge were shown to specifically target mitochondria in inact cells (153). The liposomes were deemed mitochondriotropic due to inclusion of lipidic analogues of triphenylphosphonium cations, which facilitates the efficient subcellular delivery of proapototic ceramide to mitochondria of mammalian cells and improves its activity in vitro and in vivo (154). 

An interesting example of intracellular targeting of liposomes was described recently, when liposomes containing in their membrane composition mitochonriotropic amphiphilic cation with delocalized positive charge were shown to specifically target mitochondria in inact cells. ... 

Acyl cations are relatively weak electrophiles. This is easily understood, because their structure is of a predominantly linear carboxon-ium ion nature, with the neighboring oxygen atom delocalizing charge and limiting their carbocationic nature. 

Figure 9).18 DFT studies, however, indicate that the tertiary a,a-dimethylcyclobutylmethyl cation is a minimum on the potential surface, with substantial charge delocalization into the neighboring cyclobutyl ring (vide infra). 

For mesitylene and durene, the kinetics have been followed by specular reflectance spectroscopy [159]. The results indicated that mesitylene produces a fairly stable radical cation that dimerizes. That of durene, however, is less stable and loses a proton to form a benzyl radical, which subsequently leads to a diphenylmethane. The stability of the radical cation increases with increasing charge delocalization, blocking of... 

It is into the LUMO, the energetically most accessible unfilled molecular orbital, that any further electrons will go. Hence, it may be thought of as demarking the location of positive charge in a molecule. The LUMO in planar benzyl cation is delocalized away from the formal cation center and onto the ortho and para ring carbons, in accord with classical resonance structures. On the other hand, the LUMO in perpendicular benzyl cation remains primarily localized on the benzy lie carbon. Resonance theory suggests that delocalization of the positive charge leads to stabilization. Thus, planar benzyl cation is more stable than perpendicular benzyl cation. 

Thomas (63JMC456) has shown that the antiacetylcholinesterase activity of aromatic cations increases with the number of rings for the sequence (V-methylpyridinium iodide, quinolizinium bromide, benzo[6]quinolizinium bromide. He reasons that the flat ring structure coupled with delocalization of the positive charge is favorable to coulombic interaction with the anionic center of the enzyme. Lower activity was shown with the only tetracyclic cation tested, naphtho[2,l-6]quinolizinium ion. 

---