Trimethylammonium cation

Nucleophiles can also act as acids and bases, and this behavior substantially alters their nucleophilicity. At pH 5, trimethylamine exists mainly as its conjugate acid, trimethylammonium cation. First draw a Lewis structure, and then examine the electrostatic potential for trimethylammonium ion. On the basis of the map, which is the better nucleophile, the cation or the corresponding neutral amine At pH 12, phenol exists mainly as its conjugate base, phenoxide anion. First draw a Lewis structure (or series of Lewis structures), and then examine the electrostatic potential map for phenoxide anion. Which is the better nucleophile, phenoxide or phenol ... 

Fig. 9.6 Three-component model used for basal spacing simulations, consisting of two layers of MMT with K+ cations (stick model), four molecules of trimethylammonium cation (A) or dimethylstearylammoniumcation (B) (stickand ball model), and one molecule of maleated PP (PP-MA) (ball model). Reprinted from [24], 2006, Elsevier Science.

Reynes, 0., Moutet, J. C., Pecaut, J., Royal, G., Saint-Aman, E., (Ferrocenylmethyl)trimethylammonium cation a very simple probe for the electrochemical sensing of dihydrogen phosphate and ATP anions. New J. Chem. 2002, 26, 9-12. 

A possibly serious defect in the design of compounds such as the piperidinium (222), the morpholinium (223), the tropines (226) and (227), and the decahydroquinoliniums (228) is that these molecules do not bear the trimethylammonium cation characteristic of acetylcholine, but rather the quaternary head is a part of a ring system. It was indicated previously that incorporation of the nitrogen atom of acetylcholine itself into a ring is detrimental to cholinergic activity and potency. 

In the case of trimethylammonium cations, products are obtained as solid except for the bistriflimide salts. In contrast, pyridinium and methylimidazolium salts usually have low melting points. In all, physical properties can easily be modulated by modifying the cation, the anion and the linker length [20],... 

Groups that are not pi acceptors stabilize an adjacent anion less effectively, and their CH3 ewg pAfaS are not yet available. Very electronegative groups, such as trimethylammonium cation, " N(CH3)3, and trifluoromethyl, CF3, can withdraw electron... 

Over the years there have been a number of mechanistic proposals for substrate oxidation by TMADH. An early proposal considered a carbanion mechanism in which an active site base deprotonates a substrate methyl group to form a substrate carbanion [69] reduction of the flavin was then achieved by the formation of a carbanion-flavin N5 adduct, with subsequent formation of the product imine and dihydroflavin. A number of active site residues were identified as potential bases in such a reaction mechanism. Directed mutagenesis and stopped-flow kinetic studies, however, have been used to systematically eliminate the participation of these residues in a carbanion-type mechanism [76-79], thus indicating that a proton abstraction mechanism initiated by an active site residue does not occur in TMADH. Early proposals also invoked the trimethylammonium cation as the reactive species in the enzyme-substrate complex, owing to the high (9.81) of free... 

Figure 18.8 Examples of some successful water-soluble ligands. Amphos = (2-diphenyl-phosphinoethyl)-trimethylammonium cation TPP = triphenylphosphine MS, DS, TS = mono-, di-, and trisubstituted DPPAA = diphenylphosphinoacetic acid (adapted from Cornils and Wiebus, 1995).

Table 12.3 The specificity of bis-trimethylammonium cations, of different chain-lengths, for two important acetylcholine receptors. (Potencies are relative 1.0 is maximal for each site)...

The crystal structure of X is isomorphous to crystals II and III. Since the occupancy factor of the acridine molecule is 0.5, there is one acridine molecule, on average, in the two unit cells along the c-axis. Although there is no hydrogen bond between acridine and the bromide anion, the intermolecular distances suggest the presence of a weak C-H... Br contact. The hydrophilic ribbon comprises the bromide anion and trimethylammonium cation, and the hydrophobic ribbon comprises the alkyl group and acridine. The ribbons are packed alternately to define a planar sheet parallel to the ac-plane. The crystal structures of XI and XII are isostructural to X, with the same pattern of occupancy of the heteroaromatic rings. 

The above aggregation forms a layer structure, which is schematically shown in Figure 4.17. One side of the layer is hydrophilic composed of the trimethylammonium cation and the bromide anion. In some cases the solvent water molecules are included. The other side of the layer is hydrophobic, being composed of the alkyl groups of the surfactant molecules and the aromatic molecules if the alkyl chain is short. 

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