Lysine-Based Silicone Surfactants

Abstract

Highly efficient silicone surfactants are typically based on polyether hydrophiles. As part of a program to increase the natural content of silicones, we describe the synthesis of silicone surfactants with amino acid hydrophiles (cysteine, arginine, and lysine). The compounds were prepared using a radial thiol–ene reaction with vinylsilicones for cysteine derivatives and a catalyst-free aza-Michael reaction with arginine and lysine. Short chain surfactants with silicone monomer:hydrophile ratios of 5:1 or less (e.g., telechelic silicones of lysine-linker-(Me2OSi)n-linker-lysine n = 10) were ineffective at stabilizing emulsions of silicone oil (D4): water. However, excellent surfactants were realized as the chain length (n) increased to 25 or 50, stabilizing water-in-oil emulsions with high water content (80% or 90%). The surfactants, especially the longer chain compounds, were stable against pH except <4 or >9 and survived freeze/thaw cycles. These surfactants contain 12–25% natural materials, improving their sustainability compared to those containing synthetic hydrophiles.

Protecting group-free introduction of amino acids to polymers through the aza-Michael reaction

“…The few reported examples of amino acid-modified silicone synthesis required protecting groups, as in the Diels-Alder reaction with phenylalanine-modified maleimides, 28 or radical catalysts for the thiol-ene reaction of cysteine with vinylsilicones; 6 an inefficient aza-Michael reaction of lysine with acrylates was also described. 6 The self-catalyzing ChAAIL readily reacted with either silicone acrylates that possessed a beta hydroxy group (Di9_OH)…”

“…Amino acids, the building blocks of proteins, are attracting attention in many fields of research including pharmaceuticals, 1 biocatalysis, [2][3][4][5] sustainable surfactants, 6,7 as well as functional/sustainable polymers and materials. [8][9][10][11][12][13][14] They are attractive because of their innate biocompatibility and biodegradability as natural materials, 8,11,15 zwitterionic nature and versatility as multifunctional molecules.…”

“…[8][9][10][11][12][13][14] Some interesting examples of properties of selected materials include anti-biofouling and stimuli-responsive behavior, 13 biomedical materials, 10,17 drug delivery systems, 12,18 and smart materials. 6,7 The rich functionality of amino acids is a double-edged sword. The nature and density of the functional groups makes it difficult to perform controlled reactions without resorting to protecting groups, which goes against Green Chemistry principle 8.…”

Biodegradable, crosslinked silicone-gelatin hydrogels

“…There is some concern that polyethers may have biological activity. 31,32 Natural amino acid/peptides hydrophiles 33,34 could be advantageous based on expected biodegradation at end of life. More detailed studies of structure property relationships for surface active silicones based on amino acids is warranted.…”

Functional silicone oils and elastomers: new routes lead to new properties

“…5G). 43 Thus, the thiol–ene reaction provides a protection free way to introduce thiol-containing natural materials in synthetic silicone polymers .…”