Synthesis And Properties Of Alkylselenyl-propyl Anionic And Zwitterionic Surfactants

In recent years,controlling the properties of surfactants by some external stimulus has attracted considerable attention from scientists.To date,the switching of properties in surfactants by a physical or chemical stimulus,such as temperature,light,magnetic field,pH,redox and so on,have been extensively reported.Selenium-containing surfactants are considered as one new kind of redox-responsive surfactants,having fast and sensitive response.Four kinds of surfactant based on alkylselenyl-propyl were designed and synthesized.Usually,selenium-containing surfactants reported have mainly been limited to those containing benzylselanylalkyl or phenylselanylalkyl,in which the selenium atom is located at the end of the hydrophobic tail,far from the hydrophilic headgroup.However,the position of selenium atom of surfactants based on alkylselenyl-propyl was close to hydrophilic headgroup,which separated from headgroup by three CH₂ units.The main results and conclusions are summarized as following:?1?Synthesis and characterization of alkylselenyl-propyl anionic and zwitterionic surfactantsFour kinds of surfactant were synthesized through the nucleophilic reaction of organic selenium reagent.The final products were sodium 3-dodecylselen-1-propanesulfonate(C₁₂SeAS),sodium 3-dodecylselen-1-propanesulfonate(C₁₂SeSS),sodium 3-tetradecylselenium-1-propane-sulfonate(C₁₄SeSS)and 3-tetradecylselen-1-propanesulfobetaine(C₁₄SeSB),respectively.Their structures were comfired through ¹H NMR,⁷⁷Se NMR,ESI-MS.?2?Redox-responsive properties of alkylselenyl-propyl anionic and zwitterionic surfactantsThose surfactants can be oxidized with adding H₂O₂ and their structures of oxidized states were characterized through ¹H NMR,⁷⁷Se NMR and ESI-MS.The selenide was turned into selenone,when selenium-containing surfactants were oxidized with equimolar H₂O₂.In fact,this change of molecular structure can be recovered by adding reducing agents,such as N₂H₄·H₂O,Na₂SO₃ or Vc.Before oxidation,these surfactants present high Krafft temperature?T_K?and micellization could not occur spontaneously at 4?.The poor ability reducing surface tension and foaming was presented in addition to C₁₂SeAS.C₁₂SeAS can decrease the value of surface tension more than 20mN·m^-1 due to its better solubility at 25?.After oxidation,the oxidized states have low T_K.The resulted solution of oxidization is transparent even if temperature is lowered to 0?,revealing the oxidized state is more water-soluble than its initial state.The ability of decreasing surface tension and foaming is also better than their initial states obviously at any temperature.Alkylselenyl-propyl anionic and zwitterionic surfactants act as stimuli-responsive switch type surfactants.Their switching cycle is reflected in the cycle of T_K.Therefore,the T_K of surfactants could be reversibly tuned,which is triggered by the redox chemistry of selenium.Bovine serum albumin?BSA?recovery can be achieved through regulation of T_K.?3?Study on the dual stimulus-responsive worm-like micelles in C₁₂SeAS-BTA systemThe combination of 120 mmol·L^-1 C₁₂SeAS and N,N-dimethylbenzyl tertiary amine?BTA?in a 3:2 ratio enables the formation of a highly viscoelastic gel with a zero shear viscosity of up to 10⁵mPa·s or more.The rheological tests and cryo-transmission electron microscopy confirmed that the highly viscoelastic gel is a worm-like micelle with three-dimensional network structure formed by self-assembly of C₁₂SeAS and protonated BTA.The redox response of selenium and the CO₂-N₂response of the tertiary amine group make this worm-like micelle system have a dual stimulus response.When C₁₂SeAS is not oxidized,CO₂/N₂ is alternately introduced to allow the system to switch between a highly viscoelastic gel and a low viscoelastic water-like solution;with the presence of CO₂,0.4 equivalent H₂O₂/N₂H₄·H₂O can also transform the system.The amount of H₂O₂ and N₂H₄·H₂O only accounts for 0.15%and 0.22%of the system quality.