Construction And Redox Responsiveness Of Spontaneous Vesicles And Microemulsions Based On Sodium Dodecylselanylpropyl Sulfate

Spontaneous vesicles formed by anionic and cationic surfactants have played an important role in application prospects such as drug loading and transporting;the thermodynamically stable microemulsions（MEs）have been widely used in various fields including enhanced oil recovery,soft template for nanoparticle synthesis and others.If spontaneous vesicles and MEs are constructed by a stimuli-responsive surfactant with response to external environmental stimuli,it may cause that spontaneous vesicles and MEs with stimuli-responsive to environmental stimuli being obtained;the stimuli that have been reported mainly contains temperature,pH,light,electricity,magnetism,CO₂/N₂ and redox and so on.Therefore,the surfactant aggregates self-assembled by the stimuli-responsive surfactant should also have a corresponding response under the action of stimuli;this not only enriches the variety of surfactant types,but also greatly expands the potential applications of surfactants.In order to construct spontaneous vesicles and MEs formed by surfactant with redox response,a selenium-containing anionic surfactant,sodium dodecylselanylpropyl sulfate（SDSePS）,was studied in this paper,which has a reversible response to redox.SDSePS/DTAB spontaneous vesicles were formed by SDSePS and cationic surfactant dodecyltrimethylammonium bromide（DTAB）;SDSePS-ME stabilized with SDSePS as the main surfactant while n-butanol as the co-surfactant were obtained.Since the SDSePS can be converted into SDSePS-Ox after oxidized,and then the SDSePS-Ox can be reduced to SDSePS（SDSePS-Re）again,causing SDSePS/DTAB spontaneous vesicles and SDSePS-ME also have corresponding redox response behavior.In the scope of the experiment,the main research results and conclusions are summarized as follows:（1）Construction and redox responsiveness of SDSePS/DTAB spontaneous vesiclesWhen the total concentration was fixed at 5 mmol/L,the SDSePS/DTAB spontaneous vesicle was formed in the molar ratios of n_SDSePS:n_DTAB=1:9⁷:3;with the increase of n_SDSePS:n_DTAB,the light blue opalescence of SDSePS/DTAB spontaneous vesicles increased first and then weakened were observed,and the light blue opalescence reached the strongest at n_SDSePS:n_DTAB=5:5;the dynamic light scattering（DLS）results showed that the average radius（R_V,nm）of SDSePS/DTAB spontaneous vesicles changed in V-shape with the increase of n_SDSePS:n_DTAB and reached the minimum at n_SDSePS:n_DTAB=5:5;the SDSePS/DTAB spontaneous vesicles(n_SDSePS:n_DTAB=3:7,the R_V was about 50 nm)was with the best tolerance to Na₂SO₄;the nuclear magnetic resonance spectroscopy（¹H NMR）,nuclear magnetic resonance selenium spectrum(⁷⁷Se NMR),electrospray ionization mass spectrometry（ESI-MS）and cryo-transmission electron microscopy（Cryo-TEM）were used to prove that the divalent selenide group（-Se-）in the SDSePS molecule was oxidized to tetravalent selenium sulfoxide（-Se=O）under the action of oxidant H₂O₂,SDSePS/DTAB spontaneous vesicles were disintegrated into SDSePS-Ox/DTAB globular micelles,and then under the action of reducing agent Na₂SO₃,-Se=O was reduced to-Se-,SDSePS-Re/DTAB spontaneous vesicles were regenerated;under the alternating action of H₂O₂ and Na₂SO₃,the SDSePS/DTAB spontaneous vesicles can switch the reversible cycle over 10 times at least between the two states of micelles and vesicles,and the R_V of the SDSePS-Re/DTAB vesicles remained in the range of115¹30 nm;it was detected by fluorescence spectrophotometer that the cationic dye Rhodamine B（RhB）can be embedded to the SDSePS/DTAB spontaneous vesicles to a certain extent,which can slow the release of RhB to some extent.（2）Construction and redox responsiveness of SDSePS-MEBoth SDSePS and SDSePS-Ox can be used as the main surfactants to form stable microemulsions with n-butanol（co-surfactant）,n-heptane（oil phase）and water,however,since the surface activity of SDSePS-Ox was lower than SDSePS,therefore,the ratio of the pseudo-ternary phase diagram area of the reduced-state ME（SDSePS-ME）to the entire triangular phase diagram area was about 49.12%,which was larger than that of the oxidized-state ME（SDSePS-Ox-ME,36.94%）while the ratio of the overlapping area of the two phase diagrams to the entire triangular phase diagram area was about 35.82%;both the two MEs can be divided into oil-in-water（O/W）type,bicontinuous（B.C.）type and water-in-oil（W/O）type by conductivity measurement and dilution method,the reversible conversion between these three types of SDSePS-ME and SDSePS-Ox-ME were achieved by oxidation with H₂O₂ followed by reduction with N₂H₄·H₂O;since the solvent water and by-product water brought in during the redox process will accumulate in the oxidized-state and the reduced-state ME,the average radius(R_ME,nm)of the O/W type SDSePS-ME increased continuously with the increase of the number of redox cycles and the number of cycles was very limited while the R_ME of O/W type SDSePS-Ox-ME increased first with the increase of oxidation number and the R_ME did not change after F_W was greater than 71.6%;the oil-soluble dye Nile Red（NR）probe was monitored by a fluorescence spectrophotometer with46.3±0.7%of the O/W type SDSePS-ME oxidized and released together with the oil phase.