74 FORMULATING FOR MILDNESS


Amino acid-based surfactants: more than just ‘natural’!


n Dr Alexander T Wagner - Zschimmer & Schwarz, Germany


Amino acids are key components of the human metabolism: Glutamate (Fig 1a), for instance, is the most important substance in the brain to transport information from one nerve cell to another. It is a neurotransmitter. Additionally, amino acids can be linked together in different combinations to create shorter (peptides) and longer (proteins) chains. Both fulfil a variety of different vital functions in the human body: Collagen, for instance, is the most frequently occurring protein in the human body. It is composed of three intertwined chains (triple helix) to lend structure to connective tissue. Simply for spatial arrangement reasons in this protein the smallest amino acid, glycine (Fig 1b), is the main component. The water solubility of amino acids also


makes them an attractive choice for the hydrophilic part of surfactants. When an amino acid is linked with a triglyceride- derived fatty acid (e. g. from coconut oil), surfactants (N-acyl derivatives, “amino acid surfactants“, Fig 2a) exclusively based on natural components are created. When the amino acid is produced via a fermentation process starting from glucose or its derivatives, the surfactants even are completely composed of renewable raw materials (e. g. cocoyl glutamate). Those


a O O


R* N


b O O-


Figure 2: a) Surfactants based on N-lauroyl amino acids (amino acid surfactants), R: Amino acid specific rest, R*: H for glutamates and glycinates, CH3


for sarcosinates b) Soap (laurate) PERSONAL CARE ASIA PACIFIC R O- O H3


N +


O- O a b


Figure 1: Examples for natural amino acids in aqueous solutions (pH 7): a)Glutamate, b)Glycine, c) Sarcosine


surfactants are an ideal choice for natural cosmetic applications. Contrary to expectations, the


development of amino acid surfactants is not a result of the current trend towards ‘green’ surfactants. The first examples were patented in the 1930s.1


Already at that time


one candidate, a derivative of sarcosine (Figs 1c, 2a), was introduced to the market. The original idea behind this development was to create surfactants alternative to soaps (Fig 2b) to overcome their drawbacks (precipitation in pH-neutral aqueous


solutions, sensitivity to water hardness).2 The ‘trick’ is to insert a suitable spacer between the hydrophobic part and the carboxylate group (Fig 2). By the way, in the 1930s also another solution was found: To introduce a sulfo-group and to “block” or replace the carboxylic group of fatty acids (e. g. acyl isethionates2


and fatty alcohol


sulfates).3 The attractiveness of amino acid


surfactants for cosmetic applications is additionally based on two other aspects: At first, they are proven mild and well foaming surfactants. Secondly, they are excellent biodegradable. The linkage between the hydrophobic and the hydrophilic part of the surfactant is an amide bond (Fig 2a). This type of bondage is frequently ‘used’ by nature (e.g. in peptides and proteins) and can therefore easily be cleaved by nature´s enzymes.


Acyl sarcosinates and acyl glycinates: unequal siblings The difference between sarcosine and glycine is: In sarcosine one hydrogen atom at the nitrogen atom is replaced by a methyl group (Figs 1b,1c). The seemingly small difference has an immense impact on the physical properties of the corresponding N-acyl derivatives. This can directly be traced back to the capability of acyl glycinates to create hydrogen bonds


November 2020 c O- O H3


N +


O- O H2


N +


O-


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