Cationic nitrogens

The sufficient selectivity to a principal component is the most important condition determining the possibility of ion-selective electrodes (ISEs) practical appliances. In this work, the relationship between the potentiometric selectivity of alkylammonium-selective electrodes and factors such as the nature of plasticizer, ion-exchanger and substitution degree of cationic nitrogen atoms of the principal and foreign ions, is discussed. 

Laboratory observations have shown that a combination of thiosulfate with cationic nitrogenous inhibitors has a significant effect on improving their performance [1432]. 

Methyl groups a or y to the cationic nitrogen are active towards condensation as illustrated (Scheme 120) by the reaction of 2,4-dimethyl-l-azaquinoIizinium ion with p-dimethyl-aminobenzaldehyde (72UKZ262). 

Note the use of azonia to denote the cationic nitrogen in the ring, whereas az.a is used for neutral nitrogen (see Section 15-11 A). 

A new direction in the chemistry of hypervalent silicon compounds has recently been developed by Tacke and coworkers the chemistry of zwitterionic organosilicates28-31. In these compounds the silicon is formally negative, with a cationic nitrogen attached to it by an alkyl chain. One of the groups of products of this general class is the pentacoordinate zwitterionic fluorosilicates31. 

Cordes and co-workers 191 found that the alkaline hydrolysis of p-nitrophenyl hexanoate is subject to catalysis by polyvinylpyridine-based polysoaps. For example, k bs is increased from 0.1 mm to 1.4 mm in the presence of 5 x 10 7 M 38% polysoap (23) (the same material used in the Strauss work). With 5 x 10-7 M polymer having a 15 % dodecyl content, the rate is increased only 3 times above background. The simplest rationale for the kinetics invokes both hydrophobic and electrostatic forces. Thus, dodecyl chains on the polymer hydrophobically bind p-nitrophenyl hexanoate to the polymer surface. Since the polymer possesses a high density of cationic nitrogens, hydroxide ions also accumulate at the polymer surface where they catalyze the hydrolysis of bound ester. Addition of nitrate ion to the aqueous reaction... 

A. The DADMe modification also provides a favorable charge localization to place the cation at the l -position. The pKa of l -pyrrolidine nitrogen in DADMe system is 8.575 and provides the cationic nitrogen to ion pair with phosphate in the active site of phosphorylases. The N4 nitrogen of Immucillin-H has a pKa of 6.972 and is cationic in the active site, however the Cl -C9 distance is only... 

Other reactions, such as Friede 1C "rafts acylations, require Lewis adds and these too react at nitrogen. Pyridine is a good ligand for metals such as Al(IIT) or Sn(IV) and, once again, the complex with its cationic nitrogen is completely unreactive towards electrophiles. 

The upper oxygen is closer to the cationic nitrogen N3-r of the leucine, and so the cationic N3-r probe may experience an unfavorable electrostatic repulsion when it is dose to the leudne nitrogen s cationic charge. 

Substantial shifts were observed in the spectra of Af-ethylquinolinium iodide, N-methylnicotinium iodide (72) and [3-(dunethylamino)propyl]trimethyl ammonium iodide with [Eu(fod)4]. In the case of 72, the relative magnitude of the shifts indicated that the cationic nitrogen was the site of association with [Eu(fod)4]" rather than the tertiary nitrogen coordinating directly with the Eu(III) °. ... 

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