Amphoteric surfactants containing α-hydroxy ester group and an amino acid residue

A series of amphoteric surfactants containing α -hydroxy ester group and an amino acid residue were prepared with the addition of epoxy derivatives (which were prepared from epoxidation of alkyl methacrylate) to different types of amino acids (glycine, alanine, valine, isoleucine, phenylalanine, tyrosine, serine, threonine, aspartic and anthranilic acid).The structures of the prepared compounds were confirmed by infrared spectra, proton magnetic resonance spectra, Mass spectra and elementary analysis. Surface tension, Kraft point, foaming power, critical micelle concentration emulsion and Ca ++ stabilities were determined. Antimicrobial activity and biodegradability were also screened.


INTRODUCTION
As a part of our program (Eissa., 2002;Eissa et al. 1996;Eissa. 1995;Eissa et al. 2003;Amin et al., 2004;El-Dougdoug et al., 2001) on the synthesis and characterization of different types of surface active agents, the author attempts to synthesize a novel group of amphoteric surfactants based on amino acid residue.Amino acids are not only solution was shaken and heated for 2 hr, then allowed to stand overnight at room temperature.
Water was then added and the separated solid was crystalized using a suitable solvent to give (2a-c).

General procedure of the reaction of epoxy fatty ester with amino acids
Triethylamine (1 mmole) dissolved in an aqueous ethanol solution (65 wt % ethanol) was added to amino acid (1 mmole) to protect (as a salt) the carboxyl group of the amino acid.The mixture was stirred at room temperature for 20 min.Subsequently, epoxy fatty ester 2 (1 mmole) was added using a dropper, and the mixture was stirred at 50 °C for 8hr or at 60 °C for one night.Then the triethylamine and ethanol were evaporated.The residue obtained was washed with water and petroleum ether, then dried under vacuum and crystalized using a suitable solvent to obtain (3a-c to 11a-c).

Kraft point
The prepared amphoteric surfactants were measured as the temperature where 1 % dispersion becomes clear under gradual heating (Wiel et al., 1963).

Wetting time
Wetting time was determined by immersing a sample of cotton fabric in a 1.0 wt % aqueous solution of surfactants ( Masuyama et al., 1987).

Foaming power
Foaming power was measured according to (Somaya et al., 1998).In this procedure a 25 ml solution (1.0 wt %) was shaken vigorously for 10 seconds in a 100 ml glass stopper, graduated cylinder, at 25 °C.the solution was allowed to stand.The foam height and foaming stability were measured.

Emulsification stability
Emulsification stability was tested using 10 ml of a 20 m mol.aqueous solution of surfactant and 5 ml of toluene at 40 °C.The emulsifying property was determined as the time its took for an aqueous volume separating from the emulsion layer to reach 9 ml counting from the moment of the cession shaking (El-Sawy et al., 1991).

Critical micelle concentration
(CMC) values for the prepared surfactants were determined by the electrical conductivity method (Takeshi., 1970).

Ca ++ stability
Calcium stability of compounds was determined as described according to (Bristiline et al., 1980).

Biodegradability test
Biodegradability Die-away test in river water of the prepared surfactants (1.0 wt %) was determined by the surface tension method (Eter et al., 1974) using Du Nouy Tensiometer (Kruss type 8451).Samples taken daily or even more frequently were filtered through Wattmann filter paper number (1) before measuring the surface tension.Surface tension measurements were made periodically each day, on each sample during the degradation test.Biodegradation percent (D) for each sample was calculated using the equation, D = [(γ t -γ o )/(γ btγ o )] x 100 where γ t = surface tension at time t, γ o = surface tension at zero time, γ bt = surface tension of blank experiment at time t (without samples).

Antimicrobial activity
The antimicrobial activities of the surfactants were evaluated by the agar dilution method (El-Sukkary et al., 1987).Three kinds of Gram-positive bacterial strains, Stophylococcus Aureus; Bacillus Subtiles and Sarcina Lutea, three kinds of Gramnegative bacteria strains, Escherichia Coli, Salmonella Trphi and Pseudomonas Aeruginosa and six kinds of fungal strains, Candida Albicans, Saccharomyces Cerevisiae, Alternaria Humicala, Fusazium Oxysporum, Aspergillus Flavus and Microsporium Gypseum were used for the testes.Nutrient agar and Sabouraud dextrose agar were used for bacteria and fungi, respectively.In the screening test for antimicrobial activity, 0.4 % stock solutions were prepared by dissolving 40 mg of the test compound in 10 ml of distilled water or ethanol.The stock solutions were diluted in an orderly manner by successive piping of the solution in water containing nutrient agar or sabouraud dextrose agar to obtain 400, 200, 100, 50, 25, 10, 5, 2.5 and 1 ppm concentrations of the compound.After sterilization of the agar, the solutions were poured into sterile Petri dishes, allowed to harden, and were then individually inoculated with one drop of each suspension, each containing a separate test microorganism.The inoculated dishes were then inoculated at 37 °C for two days with bacteria strains and 25 °C for five days with fungal strains, and examined for the presence or absence of growth.Antimicrobial activities are represented in terms of minimum inhibitory concentrations (MIC).

RESULTS AND DISCUSSION
A number of amphoteric surfactants was synthesized by the reaction of alkyl ester epoxides and amino acids (glycine, alanine, valine, isoleucine, phenylalanine, tyrosine, serine, threonine, aspartic and anthranilic acid).This group can be prepared from readily accessible starting materials without expensive reagents or special equipment.In general, the synthetic procedures gave relatively high yields in two simple synthetic steps.

Surface active properties
The surface properties (surface and interfacial tension, Kraft point, wetting power, foaming properties, emulsifying power and critical micelle 324 GRASAS Y ACEITES, 57 (3), JULIO-SEPTIEMBRE, 319-327, 2006,  Error of measurements was: Surface and interfacial tensions = ± 0.1 dynes/cm.Kraft point = ± 1 °C Foam height = ± 2 mm Wetting time = ± 1 sec Emulsion stability = ± 1 min concentration) of well purified compounds were investigated in distilled water.These surfactants show relatively high surface activity and a comparative study between the structure and the result was made.

Surface and interfacial tension
The measurements of the individual compounds are listed in (Table 3).The results indicated that, a linear relationship was observed between surface and interfacial tension and alkyl chain length (as the number of carbon atoms in the alkyl chain increases the surface and interfacial tension increases).

Kraft point
The Kraft point of a surfactant molecule is the temperature at which 1% dispersion solution becomes clear under gradual heating.The Kraft points of all synthesized amphoteric surfactants are also summarized in (Table 3).Although the Kraft points increase in the order C 18 > C 12 > C 8 no remarkable difference among three homologues was observed.However, as the molecular weight of an amino acid increases the Kraft point increases.

Wetting power
The wetting time of the tested amphoteric surface active agents was determined by calculating the sinking time in seconds of a grey cotton cloth in the surfactant solution.The synthesized surfactants showed good performance for wetting power (shorter sinking time).Compounds (8a, 9a-c, 10a-c and 11a) recorded excellent wetting power which makes them useful for extensive applications in the textile industry.

Foaming power
The foaming properties of all the synthesized surfactants were measured by the Ross and Miles method (Ross et al., 1941).Amphoteric surfactants showed good foam production as well as better foam stability above the (CMC).On the other hand, amphoteric surfactants containing an aromatic ring such as (7a-c, 8a-c and 12a-c) showed poor foaming properties.Extremely low foaming can probably be ascribed to the low solubility (low hydrophilicity) of the compounds in water.Table 3 shows the foam production and foam stability of all the synthesized amphoteric surfactants.

Emulsifying power
Emulsification is one of the most important properties of surfactants.In many textile processes such as scouring and dyeing, it is necessary to introduce surfactants into a bath to remove oily impurities from the fibers.On the other hand, amphoteric surfactants with good emulsion stability have been used in such fields as shampoos and cosmetics, emulsion paints and in the textile industry.The emulsification power is determined and listed in (Table 3).The results reflect the fact that as the alkyl chain length increases the emulsifying power increases.

Ca ++ -Stability
The calcium ion stability results of amphoteric surfactants are shown in ( decreased with the increase in the molecular weight of the hydrophobic part of the surfactant under the conditions of constant temperature.

Critical micelle concentration (CMC)
The critical micelle concentration values of the prepared amphoteric surfactants were determined using the electrical conductivity method.The results showed that as the hydrophobic part increases the CMC values decrease, this means that aliphatic compounds exhibit larger intermolecular hydrophilic interactions, making it easier for them to form aggregates in water than those which contain an aromatic ring.Also, the results of CMC measurements reflect the fact that as the length of alkyl chain increases the CMC decreases.

Biodegradability
The biodegradability of the tested compounds after one week was determined and listed in (Table 4).Each experiment was repeated three times, and the results are reported as averages of three values.For example, compound (9a) was 100% degraded in 6 days and 81% degraded in 4 days which makes it an excellent biodegradable surface active agent.