Zwitterions, effect

Byme N, Hewlett PC, MacFarlane DR et al (2005) The zwitterion effect in ionic liquids towards practical rechargeable lithium-metal batteries. Adv Mater 17 2497-2505... 

Figure 15.2-2 Ionization reactions of glycine (ignoring the zwitterion effect).

Gan LM, Chow PY, Liu Z, Hana M, Quek CH. The zwitterion effect in proton exchange membranes as synthesised by polymerisation of bicontinuous microemulsions. Chem Commun 2005 2005(35) 4459 461. 

Tiyapiboonchaiya C, Pringle JM, Sun J et al (2004) The zwitterion effect in high-conductivity polyelectrolytes materials. Nat Mater 3 29-32... 

As a multidimensional PES for the reaction from quantum chemical calculations is not available at present, one does not know the reason for the surprismg barrier effect in excited tran.s-stilbene. One could suspect diat tran.s-stilbene possesses already a significant amount of zwitterionic character in the confomiation at the barrier top, implying a fairly Tate barrier along the reaction path towards the twisted perpendicular structure. On the other hand, it could also be possible that die effective barrier changes with viscosity as a result of a multidimensional barrier crossing process along a curved reaction path. 

When the nitrogen atom is substituted by a nitrophenacyl group, OH attack gives the betainic zwitterion (Scheme 13). which is soluble in organic solvents (32). The stability of the C-betainic or ylid structure has been explained as an effect of resonance of the negative charge in the molecule (33, 34). 

However, as can also be seen in Fig. 11, primary and secondary amines do not perform very effectively as primers, compared to tertiary amines, even though they also contain long alkyl chains. It has been demonstrated that, instead of directly initiating ECA polymerization, primary and secondary amines first form aminocyanopropionate esters, 12, because proton transfer occurs after formation of the initial zwitterionic species, as shown in Eq. 7 [8,9]. 

The reactions of enamines as 1,3-dipolarophiles provide the most extensive examples of applications to heterocyclic syntheses. Thus the addition of aryl azides to a large number of cyclic (596-598) and acyclic (599-602) enamines has led to aminotriazolines which could be converted to triazoles with acid. Particular attention has been given to the direction of azide addition (601,603). While the observed products suggest a transition state in which the development of charges gives greater directional control than steric factors, kinetic data and solvent effects (604-606) speak against zwitterionic intermediates and support the usual 1,3-dipolar addition mechanism. 

The relations 4- > 2-position in rate and 4- < 2-position in will apparently apply to reactions with anions, but the reverse relation is observed in piperidination, presumably due to 2-substitution being favored by hydrogen bonding in the zwitterionic transition state (cf. 47, 59, and 277) or by solvent-assisted proton removal from the intermediate complex (235). Substitutions of polychloroquino-lines (in which there is a combined effect of azine-nitrogen and unequal mutual activation of the chlorine substituents) also show 4- > 2-position in reactivity contrary statements are documented by these same references. Examples are cited below of the relation 2- > 4-position when a protonated substrate or a cyclic transition state is involved. 

The mixture was stirred at ice bath temperature for 2 hours, 1 ml of methanol was added and the mixture was filtered to remove insoluble impurities. Two milliliters of water were added to the filtrate and the pH was adjusted momentarily to pH 1.5, to effect removal of theenamine block, and then to pH 4.5 with triethylamine. After stirring for an additional hour at ice bath temperature the reaction product,7-(D-0 -phenylglycylamido)-3-chloro-3-cephem-4-carboxylic acid (zwitterion) precipitated from the reaction mixture as a crystalline solid. 

The formation of a single complex species rather than the stepwise production of such species will clearly simplify complexometric titrations and facilitate the detection of end points. Schwarzenbach2 realised that the acetate ion is able to form acetato complexes of low stability with nearly all polyvalent cations, and that if this property could be reinforced by the chelate effect, then much stronger complexes would be formed by most metal cations. He found that the aminopolycarboxylic acids are excellent complexing agents the most important of these is 1,2-diaminoethanetetra-aceticacid (ethylenediaminetetra-acetic acid). The formula (I) is preferred to (II), since it has been shown from measurements of the dissociation constants that two hydrogen atoms are probably held in the form of zwitterions. The values of pK are respectively pK, = 2.0, pK2 = 2.7,... 

More pronounced solvent effects have been observed in special cases where substrates or products possess ionic character. Ito and Matsuda76 found a 35-fold reduction in the rate of addition of the arenethiyl radical 18 to cx-methylstyrene when the solvent was changed from dimelhylsulfoxide to cyclohexane. Rates for addition of other arenethiyl radicals do not show such a marked solvent dependence. The different behavior was attributed to the radical 18 existing partly in a zwitterionic quinonoid form (Scheme 1,7).77... 

The development of monoalkyl phosphate as a low skin irritating anionic surfactant is accented in a review with 30 references on monoalkyl phosphate salts, including surface-active properties, cutaneous effects, and applications to paste and liquid-type skin cleansers, and also phosphorylation reactions from the viewpoint of industrial production [26]. Amine salts of acrylate ester polymers, which are physiologically acceptable and useful as surfactants, are prepared by transesterification of alkyl acrylate polymers with 4-morpholinethanol or the alkanolamines and fatty alcohols or alkoxylated alkylphenols, and neutralizing with carboxylic or phosphoric acid. The polymer salt was used as an emulsifying agent for oils and waxes [70]. Preparation of pharmaceutical liposomes with surfactants derived from phosphoric acid is described in [279]. Lipid bilayer vesicles comprise an anionic or zwitterionic surfactant which when dispersed in H20 at a temperature above the phase transition temperature is in a micellar phase and a second lipid which is a single-chain fatty acid, fatty acid ester, or fatty alcohol which is in an emulsion phase, and cholesterol or a derivative. 

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