Synthesis of Succinic Gemini Surfactants and the Effect of Stereochemistry on Their Monolayer Behaviors

In this work, succinic gemini surfactants, dl - and meso -2,3-bis(alkyl)succinic acids (alkyl: C 6 H 13 –C 13 H 27 ), were successfully synthesized by oxidative coupling of enolates of fatty acid tert -butyl esters with copper(II) bromide followed by treatment with CF 3 COOH. Focusing on the influence of stereochemistry ( dl - and meso -) of succinic geminis, their monolayer behaviors at the air–water interface were explored using surface pressure–area ( Π – A ) isotherms, the compression modulus of monolayers ( ε s ), and Brewster angle microscope (BAM) analysis. meso -2,3-Bis(undecyl)succinic acid showed a unique isotherm where the surface pressure drastically decreased at A = ~0.56 nm 2 ( Π = 21.9 mN m −1 ) regardless of compression rates and subphase temperatures, while dl -isomer showed the common isotherm of gas → liquid-expanded → liquid-condensed phase transitions. BAM analysis on meso -2,3-bis(undecyl)succinic acid films at the air–water interface showed that small islands of aggregates appear just after the maximum pressure ( A = ~0.56 nm 2 ), and on further compression needle-shaped assemblies appear that can grow in size. It was reasonably concluded that hydrophobic interactions can operate more effectively in meso -isomers than in dl -isomers, and that meso -molecules can “jump up” to cause a transition from monolayer to bilayer. This is the first finding of the “jumping-up” phenomenon of gemini surfactants having meso -stereochemistry.