Surface-active betaines

Fig. 8 General structiu e of a betaine ester. In a surface active betaine ester the R group makes up the hydrophobic tail...

Most work on surface active betaine esters have been performed on substances made from saturated long-chain alcohols [20,27-30,32-34], These compounds can be prepared by the simple two-step synthesis route shown in Fig. 9. 

For a surface active betaine ester the rate of alkaline hydrolysis shows significant concentration dependence. Due to a locally elevated concentration of hydroxyl ions at the cationic micellar surface, i.e., a locally increased pH in the micellar pseudophase, the reaction rate can be substantially higher when the substance is present at a concentration above the critical micelle concentration compared to the rate observed for a unimeric surfactant or a non-surface active betaine ester under the same conditions. This behavior, which is illustrated in Fig. 10, is an example of micellar catalysis. The decrease in reaction rate observed at higher concentrations for the C12-C18 1 compounds is a consequence of competition between the reactive hydroxyl ions and the inert surfactant counterions at the micellar surface. This effect is in line with the essential features of the pseudophase ion-exchange model of micellar catalysis [29,31]. 

Fig. 10 Concentration dependence of the pseudo first-order rate constants in a 100 mM phosphate buffer at pH 7.5 and 37 °C for a niunber of surface active betaine esters with hydrophobic tails of different sizes. For comparison, the rate constant for a non-siuface active compound (ethyl betainate) is included, (o) Oleyl betainate, ( ) tetradecyl be-tainate, ( ) dodecyl betainate, ( ) decyl betainate, (0) ethyl betainate. All compounds have chloride counterions...

Another interesting system containing a surface active betaine ester is the dilute aqueous mixture of dodecyl betainate and hydrophobically modified hydroxyethylcellulose (HM-HEC) that has been studied by Karlberg et al. [33]. It is well known that the viscosity of mixtures of HM polymers and surfactants is strongly dependent on the concentration of the amphiphile. By preparing a mixture of a surface active betaine ester and HM-HEC in a solution buffered at a pH where the surfactant is hydrolyzed, it is possible to make a gel with a time-dependent viscosity. 

Since surface active betaine esters can be degraded under mild conditions and the hydrolysis products, i.e., the amino acid betaine and a long-chain alcohol can be expected to be less toxic than the intact surfactant, these am-phiphiles are interesting candidates for use in applications where surfactant toxicity is an issue. Surface active betaine esters have been evaluated as temporary bactericides [34] and have been studied as potential candidates for use as pharmaceutical excipients (pharmaceutical helper molecules) [30]. 

Betaine-type surfactants do not show anionic character in alkaline solutions or reduced water solubility close to the isoelectric point as other amphoterics do. These surface-active betaines generally exhibit excellent solubility in water and compatibility with anionics over a wide pH range. So, the betaines are often specified as zwitter-ionic surfactants. 

Surface-active betaines can be synthesized also by quatemisation of long-chain tertiary amines with acrylic acid or P-propiolactone and from partially acylated dibasic amino acids and alkyl halides. 

Taking into account the unsurpassed mildness of all these surfactants, promising sphere of their application is "no-more-tears" child shampoos and products for intimate hygiene. In various combinations phosphobetaines and phosphatobetaines are patented in a range of personal care products by Johnson Johnson [44, 45, 111]. Zwitter-ionic 3-amidopropyldimethylammonio-l-propane-3-sulphonate derived from cholic acid (ChAPS) has been used as selective membrane protein solubiliser in the biochemical practice. All surface-active betaines are compared favourably with quaternary ammonium compounds in respect to their moderate toxicity, low mucous membrane irritation and better biodegradation. 

Figure 17.20. Structures of two surface-active betaine esters (R and X are the same as those in Figure 17.17)...

The kinetics of hydrolysis of a series of surface-active betaine esters was studied both below and above the CMC of the surfactants [11]. Figure 7 shows the compounds used in the study and the synthesis route employed in the preparation. The rate constant for the hydrolysis reaction as a function of... 

Weissen, H.J. Porta, N. Eur. Patent Appl. EP 638639 A1 950215, 1995. Lundberg, D. Holmberg, K. Synthesis and hydrolysis of surface-active betaine esters. J. Surf. Det. submitted. 

The synthesis and surface-active properties of higher hydroxyalkanediphos-phonates are discussed in Ref. 67. Phosphorus-containing betaines as hydrolytically stable surfactants, free from alkali salt impurities, were prepared by a reaction of amidoamines and equimolar amounts of phosphonate esters with 1.5-2 eq of formaldehyde at 60-140°C in a polar solvent [72]. 

Maleic acid mono[2-(4-alkylpiperazinyl)ethyI esters] (CnPIP) also are amphoteric surfactants and the ionic form depends on the pH, [44, 45]. Four ionic forms are known, of which the most surface active one is similar to the betain, with two oppositely charged atoms bF and 0 . At pH = 6.2 approximately 99.6% of all CnPIP molecules in solution exist in the betain form, while each of the other two forms, containing one ionised atom (either N or O ) is represented by 0.2% [45]. The experimental and theoretical surface tension isotherms of C PIP solutions at pH = 6.2 and 24"C are presented in Fig. 3.21. The theoretical curves calculated from the Frumkin and reorientation models are essentially the same with similar deviations, and therefore neither model could be preferred. The dependencies of the main parameters on n for the two models are shown in Figs. 3.22 - 3.24. 

Undecylenic amidopropyl betaine combines the antimicrobial activity of the undecylenic moiety with surface-active properties. Since this betaine acts as a mild active, selectively against Malassezia furfur, it is an interesting raw material for the formulation of antidandruff shampoos (22). 

Amine oxides are similar to betaines because of the protonation at acid pH they behave as cationic surfactants. At alkaUne pH, amine oxides behave as nonionic. Amine oxides are good foaming agents and also act as foam booster and foam stabilizers for anionic surfactants. With anionics, amine oxides can form a complex that has better surface activity than either the anionic or the amine oxide. 

The threat of accidental misuse of quaternary ammonium compounds coupled with potential harmful effects to sensitive species of fish and invertebrates has prompted some concern. Industry has responded with an effort to replace the questionable compounds with those of a more environmentally friendly nature. Newer classes of quaternaries, eg, esters (206) and betaine esters (207), have been developed. These materials are more readily biodegraded. The mechanisms of antimicrobial activity and hydrolysis of these compounds have been studied (207). AppHcations as surface disinfectants, antimicrobials, and in vitro microbiocidals have also been reported. Examples of ester-type quaternaries are shown in Figure 1. 

Theoretical calculations on the cycloaddition reactions of a range of 1,3-dipoles to ethene in the gas phase have been carried out (85) with optimization of the structures of these precursor complexes and the transition states for the reactions at the B3LYP/6-31G level. Calculated vibration frequencies for the orientation complexes revealed that they are true minima on the potential energy surface. The dipole-alkene bond lengths in the complexes were found to be about twice that in the final products and binding was relatively weak with energies <2 kcal mol . Calculations on the cycloaddition reactions of nitrilium and diazonium betaines to ethene indicate that the former have smaller activation energies and are more exothermic. 

The best activity was observed for PCMEDDAC dissolved in n-hexane. Initial waxy crude oil behaves hke a viscoplastic fluid. Doped by PCMEDDAC, waxy oil approaches a Newtonian liquid, and the shear stress decreases considerably due to the modification of the paraffin crystals by the hydropho-bized macromolecules, hi oily environments, PCMEDDAC forms micelles consisting of a hydrophihc core (made of the betaine groups) and a hydrophobic corona (made of the dodecyl groups). The PPD mechanism of PCMEDDAC with respect to waxy crude oil suggests the adsorption of definite fractions of paraffin molecules on the surface of micelles and further retardation of agglomeration. 

In this report, we examine the effects of millimolar to molar levels of Cl" and of other anions on the electron transport activity of isolated PS2 particles. At a concentration approx, above 0.1 M) anions inactivate PS2 via chaotropic interactions that require neutralization of the negative particle charge by binding metal cations. Betaine is shown to protect the PS2 particles against anion-induced inactivation and removal of extrinsic proteins. Protection Is visualized to be due to a surface layer of betaine zwitterions, preferentially oriented with the positive end groups facing the particle surface. This dipole layer shields the PS2 particles against bulk phase anions both sterically and electrostatically-... 

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