Unusual ph-dependent Surface Adsorption and Aggregation Behavior of a series of Asymmetric Gemini Amino-acid Surfactants

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1 Electronic Supplementary Material (ESI) for Soft Matter. This journal is The Royal Society of Chemistry 2015 Supplementary Information for: Unusual ph-dependent Surface Adsorption and Aggregation Behavior of a series of Asymmetric Gemini Amino-acid Surfactants Jing Lv 1, Weihong Qiao* 1 1 State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian, , P. R. China Contents 1. Synthesis 1.1 Single substituted N-alkyl-ethylenediamine 1.2 N,N -dialkyl-ethylenediamine (m)-2-(n) 1.3 N,N -dialkyl-n,n -diacetate ethylenediamine : Ace(m)-2-Ace(n) 2. Acidic Titration Curves of Ace(m)-2-Ace(n) 3. Aqueous Ace(m)-2-Ace(n) Solution Appearance 4. The results of surface tension and fluorescence measurements 5. Fluorescence intensity of Ace(m)-2-Ace(n) at different ph 6. Dynamic Light Scattering Results of Ace(m)-2-Ace(n) 7. ph-regulated Reversibility

2 1. Synthesis 1.1 Single substituted N-alkyl-ethylenediamine The N,N -dialkyl-ethylenediamine was synthesized in two steps. Before introducing the other alkyl chain to the ethylenediamine spacer group, single substituted N-decylethylenediamine and N-dodecyl-ethylenediamine were synthesized referring to the procedure reported previously. 1 In diethyl ether, the single substituted N-alkylethylenediamine was well dissolved while the dialkyl substitution was recrystallized as white solid. So diethyl ether was used as the recrystallization solvent to remove the dialkyl substitution and purify the single substituted N-alkyl-ethylenediamine during the post-processing. The yield was 70% for N-decyl-ethylenediamine and 80% for N- dodecyl-ethylenediamine. The mass spectrum results are shown in Fig. S1. Fig. S1 Mass spectrum of single substituted N-alkyl-ethylenediamine 1.2 N,N -dialkyl-ethylenediamine (m)-2-(n) N,N -dialkyl-ethylenediamine ((m)-2-(n) for short) was synthesized by bromoalkane reacting directly with N-alkyl-ethylenediamine in the molar ration of 1:1. Bromooctane, bromododecane, bromotetradecane or bromohexadecane was added

3 dropwise to the N-alkyl-ethylenediamine/propanol system in motor stirring. The mixture was refluxed at 373 K for 18 h. After removing the propanol by rotary evaporating, the residual was poured into aqueous NaOH solution (ph 12) and was stirred for 3h. Then the solution was heated under stirring. Used diethylether to extract and immediately separated the upper organics. As the diethylether solution was cooled down to room temperature, white solid was precipitated. After filtration and subsequent drying in a vacuum drying oven, the obtained crude intermediates were further purified using 300 mesh silicones and chloroform-methanol eluent (6:1 by volume). The purified intermediates were verified by mass spectrum and 1 H NMR (in Fig. S2). The yield average for the intermediates with different alkyl chain lengths was 24%. 1.3 N,N -dialkyl-n,n -diacetate ethylenediamine : Ace(m)-2-Ace(n) Aqueous sodium 2-bromoacetate solution was added drop wise to a ethanol solution of (m)-2-(n), ensuring the molecular ratio to be 2.00:1. The mixture was stirred at approximately 80 ºC. During the reaction, sodium hydroxide solution was used to adjust the system ph at near 9. After the system ph hardly changed, kept reflux for another 10 h. After cooling down to room temperature, concentrated hydrochloric acid was added slowly to adjust ph from alkaline to highly acid (ph 2) and then stratification appeared. The upper organic layer was taken out and evaporated. The residual after evaporation was dissolved in sodium hydroxide solution, and a transparent aqueous solution was obtained. Adding concentrated hydrochloric acid induced the precipitation of white solid. After filtration, the solid was washed by

4 deionized water until reaching neutrality. This dissolving-precipitating-washing procedure was repeated for twice. The final product was white solid which was then dried in a drying oven. The yield was approximately 50% and the overall yield was about 9%. The relevant characterization information was displayed in Figures S3 and 4, including Accurate-Mass TOF LC/MS, 1 H NMR and 13 C NMR.

5 Fig. S2 Mass spectrum and 1 H NMR (CDCl 3, 400MHz) of N,N -dialkylethylenediamine ((m)-2-(n)).

6 Fig. S3 Accurate-Mass TOF LC/MS of N,N -dialkyl-n,n -diacetate ethylenediamine Ace(m)-2-Ace(n).

7 Fig. S4 1 H NMR and 13 C NMR (CD 3 OD, 400MHz) of N,N -dialkyl-n,n -diacetate ethylenediamine Ace(m)-2-Ace(n).

8 2. Acidic Titration Curves of Ace(m)-2-Ace(n) Fig. S5 Acidic titration curves of Ace(m)-2-Ace(n) The original aqueous Ace(m)-2-Ace(n) solution was dissolved in excess of aqueous NaOH. The added H + preferentially neutralized with the excess OH - in the solution. That means the excess NaOH was gradually becoming NaCl with the adding of HCl in the first stage of acidic titration. When the ph equals to the first equivalence point (pk a1 ), all the excess OH - was exactly neutralized by H + and the excess NaOH was completely neutralized into NaCl. The conductivity capacity of Cl - is weaker than that of OH -, both in the electric mobility and limiting molar conductivity [electric mobility (298K): u Cl -= m 2 s-1 V-1, u OH -= m 2 s-1 V-1 ; limiting molar conductivity (298K): κ Cl -=7.635 ms m 2 /mol, κ OH -=19.91 ms m 2 /mol]. So the conductivity curve exhibited a minimum near to the first equivalence point. In the second stage of acidic titration (between pk a1 and pk a2 ), the added H + gradually combined with the tertiary nitrogen atoms and added Cl - increased the conductivity of the solution. In the third stage of acidic titration (after pk a2 ), the protonation

9 combination between H + and the tertiary nitrogen atoms was completed and the added H + and Cl - made the conductivity rapidly increase. 3. Aqueous Ace(m)-2-Ace(n) Solution Appearance Fig.S6 Photograph of Ace(m)-2-Ace(n) series at the concentration 10-3 mol/l, from left to right the ph values are 11.50, 8.50, 7,50, 6.50, 5.00, and 4.00, respectively.

10 4. The results of surface tension and fluorescence measurements Fig.S7 Six curves about surface tension versus log concentration and three curves about I 1 /I 3 versus surfactant concentration of aqueous Ace(m)-2-Ace(n) solution at different ph conditions

11 5. Fluorescence intensity of Ace(m)-2-Ace(n) at different ph Fig. S8 Fluorescence intensity of Ace(m)-2-Ace(n) at different ph

12 6. Dynamic Light Scattering Results of Ace(m)-2-Ace(n) Table S1 DLS measurement results of Ace(m)-2-Ace(n) at the concentration between cmc s and cmc f. Concentration Z-Average Peak Counter ph PDI rate mol/l d.nm size/nm intensity kcps Standard deviation nm Ace(8)-2-Ace(10) % % / / / / / / / / / 16.9 / Ace(10)-2-Ace(12) % % % % / / / / 10.5 / Ace(8)-2-Ace(12) % % % % % Ace(10)-2-Ace(14) % % % % / / / / Ace(12)-2-Ace(14) % % % % / / / / 23.4 / Ace(10)-2-Ace(16) % / / / / 40.1 /

13 Table S2. DLS measurement results of Ace(m)-2-Ace(n) at 10-3M Z-Average Peak ph PDI d.nm size/nm intensity Counter rate kcps Standard deviation nm Ace(8)-2-Ace(10) % % / / / / 68.6 / / / / / 87.6 / Ace(10)-2-Ace(12) % % % / / / / 27.3 / Ace(8)-2-Ace(12) % % % % % % Ace(10)-2-Ace(14) % % % % % / / / / 48.6 / Ace(12)-2-Ace(14) % % % % % % 4.15 Ace(10)-2-Ace(16) % % % % % 5.20

14 Fig. S9. DLS measurement results of Ace(m)-2-Ace(n) at 10-3 M

15 7. ph-regulated Reversibility Fig. S10 The transmittance of Ace(m)-2-Ace(n) solution as a function of time of treatment with HCl followed by NaOH solution Reference: 1 X. Lu, Z. Zhang, and Y. Liang, Langmuir 1997, 13,

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