English

• Unregulated emissions and special incidents (e. g. explosion) of chemistry industry were often accompanied by the spillage of some toxic organic solvents from chemical plants, and then leading to the spill of a large amount of these toxic organic liquids into the local river, which would threaten the fresh water ecology and pollute the local sources of drinking water^[1-6]. To deal with the difficulty, various simple and efficient treatments of similar spill cases have been developed. In the present, the possible methods for the treatment of such water pollutants are related to applying adsorbents, chemical dispersants, microbials and so on^[7-11]. However, these methods have some limitations in real life.

  Phase-selective gelators (PSGs) that prefer to gelate one solvent rather than the other in a biphasic mixture have been actively studied in sewage treatment. Since Bhattacharya group reported their novel findings in this area in 2001, more and more results concerning phase-selective molecular systems based on carbohydrates, organic salts, cholesteryl derivatives, calixarene derivatives, and amino acids/dipeptides, have also been reported in recent years^[12-25]. However, most of the results in the literatures were depended on the heating cooling process for the realization of phase-selective gels, which limited their uses in practice.

  In order to promote the application of gels in practice, new approaches to prepare gels at room temperature were explored, for example mechanical shaking, ultrasonic treatment, addition of pre-dissolved gelators in a co-solvent and so on^[26-29]. Powder gelators that can gel oil in the powder form are most promising in practice. However, at the present time, powder gelators being able to solidify oils within minutes at room temperature still remain unknown.

  To this end, we synthesized a series of dipeptide gelators (Scheme 1) in our work as powder phase-selective gelators for oils from their two-phase mixtures with water. Moreover, the gels selected could also be used for the absorption of toxic dyes from the polluted water.

  Scheme 1

  

  Scheme 1.  (A) Target dipeptide compounds and (B) synthetic route

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  1.   Experimental

  N-(9-fluorenylmethoxycarbonyl)-L-alanine (Fmoc-Ala-OH), N-(9-fluorenylmethoxycarbonyl)-L-valine (Fmoc-Val-OH), N-(9-fluorenylmethoxycarbonyl)-L-leucine (Fmoc-Leu-OH), N-(9-fluorenylmethoxycarbonyl)-L-isoleucine (Fmoc-Ile-OH), N-(9-fluorenylmethoxycarbonyl)-L-phenylalanine (Fmoc-Phe-OH) and n-hexylamine were obtained from Shanghai Titan Technology Co., Ltd. All organic solvents of analytical grade for synthesis were obtained commercially and were used without further purification. ¹H and ¹³C nuclear magnetic resonance (NMR) spectra were recorded using a Bruker Avance HD400 spectrometer with tetramethylsilane as an internal standard. Mass spectra (MS) were measured using a SHIMADZU LCMS-8030. Ultraviolet-visible(UV-Vis) spectroscopy were measured using a UV-2401PC.

  1.1   Synthesis

  1.1.1   Preparation of Fmoc-R-C6 (1)

  Fmoc-R-OH (1.0 mmol), n-hexylamine (1.0 mmol) and (benzotriazollyloxy)tris(dimethylamino)phosphonium hexafluophosphate (BOP) (486 mg, 1.1 mmol) were dissolved in CH₂Cl₂/N, N-dimethylformamide (DMF) (20 mL/10 mL) to which N, N-diisopropylethylamine (DIEA) (0.39 mL, 2.2 mmol) was added. The reaction mixture was stirred for 20 h at room temperature. The solvent was removed in vacuo and the crude product was dissolved in CH₂Cl₂ (50 mL), washed with water (50 mL×2) and dried over Na₂SO₄ to give the crude product, which was subjected to column purification (V(MeOH):V(CH₂Cl₂)=1:25) to yield the pure product 1 as a white solid.

  1.1.2   Preparation of NH₂-R-C6 (2)

  To a solution of compound 1 (4 mmol) in CHCl₃ (20 mL) was added piperidine (2.0 mL), and the reaction was stirred at room temperature for 12 h. Then the solvent was removed in vacuo and the crude product was purified by flash column chromatography (V(MeOH):V(CH₂Cl₂)=1:20) to afford the target compound 2 as a pale yellow solid.

  1.1.3   Preparation of Fmoc-R-R-C6 (3)

  Fmoc-R-OH (1.0 mmol), 2 (1.0 mmol) and BOP (486 mg, 1.1 mmol) were dissolved in CH₂Cl₂/DMF (20 mL/10 mL) to which DIEA (0.39 mL, 2.2 mmol) was added. The reaction mixture was stirred for 20 h at room temperature. The solvent was removed in vacuo and the crude product was dissolved in CH₂Cl₂ (50 mL), washed with water (50 mL×2) and dried over Na₂SO₄ to give the crude product, which was subjected to column purification (V(MeOH):V(CH₂Cl₂)=1:25) to yield the pure product 3 as a white solid.

  3a a white solid in 95% yield. ¹H NMR(400 MHz, CDCl₃), δ:7.76(d, J=7.5 Hz, 2H), 7.58(d, J=7.5 Hz, 2H), 7.40(t, J=7.5 Hz, 2H), 7.30(t, J=7.5 Hz, 2H), 6.91(d, J=7.7 Hz, 1H), 6.42(t, J=5.7 Hz, 1H), 5.60(d, J=7.0 Hz, 1H), 4.46(t, J=7.2 Hz, 1H), 4.40(d, J=7.6 Hz, 2H), 4.28(t, J=7.0 Hz, 1H), 4.20(d, J=7.0 Hz, 1H), 3.24~3.16(m, 2H), 1.51~1.34(m, 8H), 1.31~1.17(m, 6H), 0.85(t, J=6.2 Hz, 3H); ¹³C NMR(100 MHz, CDCl₃), δ:172.26, 171.82, 156.17, 143.73, 141.32, 127.81, 127.12, 125.04, 120.05, 67.12, 55.08, 50.85, 49.02, 47.10, 43.15, 39.69, 36.80, 36.76, 31.43, 29.35, 26.52, 22.55, 18.76, 18.35, 14.03;MS-ESI:calculated for [M+Na]⁺(C₂₇H₃₅O₄N₃Na):m/z 488.25, found:m/z 488.18.

  3b a white solid in 97% yield. ¹H NMR(400 MHz, CDCl₃), δ:7.77(d, J=7.6 Hz, 2H), 7.58(d, J=7.5 Hz, 2H), 7.40(t, J=7.4 Hz, 2H), 7.32(t, J=4.6 Hz, 2H), 6.47(d, J=8.8 Hz, 1H), 5.92(s, 1H), 5.36(d, J=9.1 Hz, 1H), 4.50~4.34(m, 2H), 4.26~4.14(m, 2H), 4.02(t, J=7.2 Hz, 1H), 3.33~3.15(m, 2H), 2.19~2.09(m, 2H), 1.52~1.43(m, 2H), 1.32~1.20(m, 6H), 0.98~0.81(m, 15H). Because of poor solubility, ¹³C NMR(100 MHz, DMSO-d₆), δ:172.29, 171.80, 156.19, 143.73, 143.77, 141.35, 127.83, 127.14, 125.09, 125.06, 120.05, 67.11, 55.08, 50.80, 49.12, 47.11, 43.16, 39.67, 36.81, 36.77, 31.45, 29.36, 26.53, 22.55, 18.77, 18.35, 14.13;MS-ESI:calculated for [M+Na]⁺ (C₃₁H₄₃O₄N₃Na):m/z 544.32, found:m/z 544.23.

  3c a white solid in 95% yield. ¹H NMR(400 MHz, CDCl₃), δ:7.75(d, J=7.5 Hz, 2H), 7.56(d, J=7.5 Hz, 2H), 7.39(t, J=7.5 Hz, 2H), 7.33~7.26(m, 2H), 6.98(d, J=8.4 Hz, 1H), 6.50(s, 1H), 5.56(d, J=8.1 Hz, 1H), 4.48~4.34(m, 3H), 4.30~4.16(m, 2H), 3.29~3.09(m, 2H), 1.74~1.39(m, 6H), 1.32~1.20(m, 8H), 0.98~0.80(m, 15H); ¹³C NMR(100 MHz, CDCl₃), δ:172.54, 171.78, 156.35, 143.83, 143.78, 141.31, 127.78, 127.10, 125.07, 125.03, 120.03, 67.09, 53.62, 51.89, 47.20, 41.51, 40.83, 39.69, 31.81, 29.38, 29.33, 26.88, 24.73, 22.97, 22.77, 22.66, 21.96, 14.13;MS-ESI:calculated for [M+Na]⁺(C₃₃H₄₇O₄N₃Na):m/z 572.35, found:m/z 572.25.

  3d a white solid in 96% yield. ¹H NMR(400 MHz, CDCl₃), δ:7.76(d, J=7.5 Hz, 2H), 7.61~7.53(m, 2H), 7.39(t, J=7.3 Hz, 2H), 7.34~7.27(m, 2H), 6.73~6.61(m, 1H), 6.14(s, 1H), 5.53(d, J=7.3 Hz, 1H), 4.47~4.31(m, 2H), 4.28~4.16(m, 2H), 4.12~4.04(m, 1H), 3.33~3.12(m, 2H), 1.97~1.83(m, 2H), 1.48(d, J=5.1 Hz, 4H), 1.32~1.22(m, 6H), 1.16~1.02(m, 2H), 0.97~0.82(m, 15H); ¹³C NMR(100 MHz, CDCl₃), δ:171.39, 170.63, 156.46, 143.85, 143.72, 141.31, 127.75, 127.09, 125.09, 125.04, 120.02, 67.11, 59.88, 58.02, 47.14, 39.59, 37.53, 36.69, 31.80, 29.47, 29.22, 26.90, 24.91, 22.65, 15.53, 14.12;MS-ESI:calculated for [M+Na]⁺(C₃₃H₄₇O₄N₃Na):m/z 572.35, found:m/z 572.23.

  3e a white solid in 96% yield. ¹H NMR(400 MHz, CDCl₃), δ:7.76(d, J=7.5 Hz, 2H), 7.50(t, J=7.7 Hz, 2H), 7.40(t, J=7.3 Hz, 2H), 7.33~7.05(m, 12H), 6.59(d, J=7.1 Hz, 1H), 5.74(s, 1H), 5.32(d, J=6.0 Hz, 1H), 4.61~4.51(m, 1H), 4.46~4.34(m, 2H), 4.26~4.17(m, 1H), 4.13(t, J=6.8 Hz, 1H), 3.19~2.86(m, 6H), 1.31~1.10(m, 8H), 0.90~0.83(m, 3H); ¹³C NMR(100 MHz, CDCl₃), δ:170.61, 169.90, 156.15, 156.10, 143.67, 141.33, 136.50, 136.06, 129.27, 128.84, 128.66, 127.84, 127.26, 127.14, 127.04, 125.08, 125.00, 120.07, 67.20, 56.25, 54.51, 47.05, 39.63, 38.27, 31.82, 29.25, 29.20, 26.82, 22.67, 14.14;MS-ESI:calculated for [M+Na]⁺(C₃₉H₄₃O₄N₃Na):m/z 640.32, found:m/z 640.21.

  1.2   Gelation Test

  The gelation abilities of the dipeptide compounds were estimated by mixing a small amount of the gelator (10 mg) with 0.2 mL of a pure liquid in a screw-capped glass vial, heating until the solids were dissolved completely, and then cooling to room temperature. And the gels were confirmed by turning the vial upside-down at room temperature and ensuring that the gels stay where they are after repeated thermo-reversible tests.

  1.3   Minimum Gelation Concentration (MGC) Test

  The MGCs of the dipeptide gelators were determined using a dilution method. Firstly, 10 mg of each gelator was added to 0.2 mL of a known organic solvent in a screw-capped glass vial. Then the formed gel system was progressively diluted with a small amount of the tested solvent and the heating-cooling process was repeated until the gel was not achieved. The last concentration at which the gel state remained was recorded as the MGC value with mg/mL as the unit. This process was repeated more than three times for each measurement and the average values were reported to be the MGC value.

  1.4   Procedure for Phase Selective Gelation (PSG)

  Generally, a weighted amount of each dipeptide gelator in dry powder form was added to a biphasic mixture of an organic solvent (0.5 mL) and water (2.0 mL) via simple shaking at gelator loading of 50 mg/mL at room temperature. Selective gelation of the organic phase was achieved upon resting the sample at room temperature.

  1.5   Test for Dye Adsorption

  The removal capacities of dyes from their aqueous solutions were estimated using UV-Vis is spectroscopy. And the final concentrations of the dyes in their aqueous solutions were calculated according to the Beer-Lambert law (A=αlρ, A is the absorbance of the dye at a certain absorption wavelength in aqueous solution, α is the extinction coefficient where the unit is L/(mg·cm), l is the path length of the incident light with the unit cm, ρ is the concentration of the dye in solution with the unit mg/L). Here, crystal violet and rhodamine B were selected to be examined and the maximum absorption wavelengths in their aqueous solutions monitored were 585 and 555 nm, respectively. And the final concentrations of the dyes in their aqueous solutions could be obtained by the Beer-Lambert equation, which finally determined the removal efficiency (RE) of each dye by the equation as follows:RE=(ρ₁-ρ₀)/ρ₀, in which ρ₀ (mg/L) represents the initial concentration of the dye in its aqueous solution; ρ₁(mg/L) is the final mass concentration of the dye in the presence of an dsorbing agent.

  2.   Results and Discussion

  2.1   Gelation Capability of the Target Compounds

  The gelation abilities of these dipeptide compounds were estimated by the heating-cooling method and determined using a sealed-vial inversion test, and the experiment results were summarized in Table 1. As observed, target dipeptide compounds can gelate aromatic solvents with the minimum gelation concentration values (MGCs) ranging from 0.2~19.8 mg/mL. Moreover, the heating-cooling cycles could be repeated more than 30 times in the gelation solvents, showing that these gels are completely thermo-reversible. The gels formed are stable for at least one month at room temperature.

  Table 1

  

  Table 1.  Gelation abilities of target dipeptide compounds^a and minimum gelation concentration (MGC) of the resulting gels of gelators in organic liquids

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  Solvent	0.1×MGC/(mg·mL-1)
  	3a	3b	3c	3d	3e
  Benzene	1.52	1.60	1.52	0.52	1.55
  Toluene	0.55	0.69	0.51	0.31	0.76
  Xylenes	0.53	0.72	0.78	0.19	1.31
  Nitrobenzene	1.98	1.20	A	0.38	1.95
  Benzyl alcohol	Ab	A	A	0.88	A
  Petrol	0.094	0.061	0.060	0.023	0.046
  Diesel	0.099	0.056	0.056	0.020	0.042
  a.The mixture of 10 mg of each gelator and 0.2 mL of a known liquid was heated until the gelator was dissolved completely, and then cooled to room temperature to form gel; b.A=Non-gel state at gelator loading of 50 mg/mL. All gels formed at room temperature are stable at least for one month.

  The gelation abilities in dry powder form of selected dipeptide compounds were further estimated via shaking and resting at gelator loading of 50 mg/mL at room temperature and determined using a sealed-vial inversion test (Fig. 1A), and the experiment results were summarized in Table 2. Among the dipeptides tested, compound 3c showed pretty good gelation abilities in dry powder form via simple shaking and resting at gelator loading of 50 mg/mL and the gelling times of compound 3c in benzene, toluene, xylenes and petrol were within 5 min and the corresponding gels were shown in Fig. 2.

  Figure 1

  

  Figure 1.  (A) Reversible sol-to-gel transitions of 3c-xylenes gel stimulated by heating at its MGC and (B) 3c-xylenes gel stimulated by shaking at 50 mg/mL loading of gelator

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  Table 2

  

  Table 2.  Gelation abilities and gelling times of room-temperature oil gelation by target dipeptide compounds in dry powder form via simple shaking and resting at 50 mg/mL loading of gelator within 1 h

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  Solvent	Gelling time/min
  	3a	3b	3c	3d	3e
  Benzene	Aa	8	5	A	A
  Toluene	A	A	5	A	A
  Xylenes	A	A	4	A	A
  Nitrobenzene	A	A	—	A	A
  Benzyl alcohol	—b	—	—	A	—
  Petrol	A	A	3	4	A
  Diesel	A	A	A	A	A
  a.A=Non-gel state; b.Gelation abilities in dry powder form were not determined because of their MGCs above 50 mg/mL. All gels formed at room temperature are stable at least for one month.

  Figure 2

  

  Figure 2.  Photographs of the gels formed in benzene (A), toluene (B), xylenes (C) and petrol (D) with compound 3c as the gelator in dry powder form by shaking and resting at 50 mg/mL loading of gelator

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  2.2   Phase-Selective Gelation of Organic Solvents in Their Water Mixtures

  The feasibility of actualizing methods is the key for the practical application of a PSG in the treatment of a spillage event. Direct power strategy is the most ideal but very difficult to achieve. However, luckily several dipeptides selected, especially compound 3c in our study showed pretty good gelation abilities in dry powder form via simple shaking. For example, the compound 3c in dry powder form was directly added into a xylenes/water (0.5 mL/2.0 mL) mixture in a glass vial, and then simple shaking was carried out to cause dissolution of compound 3c in xylenes. The resulting feculent mixture was rested at room temperature, giving rise to a gel-like chunk within 1 min (Fig. 3A). The gel-phase could be easily separated by filtration (Fig. 3B) and subsequently distilled to recover the xylenes phase and the gelator could be achieved by recrystallization (Fig. 3C). The recovered gelator was reused in a new cycle with a fresh xylenes/water mixture. And in the same way, the 3c-benzene gel, 3c-toluene gel and 3c-petorl gel were achieved using compound 3c in dry powder form at gelator loading of 50 mg/mL in two-phase mixtures with water (0.5 mL/2.0 mL) within 1 min. In addition, compound 3c with the concentration 50 mg/mL in benzene/toluene/xylenes/petrol in dry powder form was directly added to oil/water mixture (0.5 mL/2.0 mL) in a glass vial, and then the mixture was violently shook and then rested at room temperature, giving rise to a strong gel. And the resulting gel could seal the water in the glass vial and support its own weight plus the weight of water when the glass vial was inverted (Fig. 4A-4D). These findings, as shown in Fig. 4, indicated that the phase-selectively formed gel possess relatively high mechanical strength, which is beneficial to the real-life applications of the gelator in the treatment of water pollution.

  Figure 3

  

  Figure 3.  (A) Specific gelation of the xylenes phase using 3c dry powder as a PSG in a two-phase mixture of xylenes and water (0.5 mL/2.0 mL). (B) 3c-Xylenes gel and clear water separated via filtration from formed gel-water mixture. (C) Recovery of xylenes from the 3c-xylenes gel via distillation and purification of the restored gelator by recrystallization

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  Figure 4

  

  Figure 4.  Inverted vials of gels formed phase-selectively in a two-phase mixture of organic phase and water (0.5 mL/2.0 mL): (A) 3c-benzene gel (50 mg/mL of compound 3c in 0.5 mL of benzene), (B) 3c-toluene gel (50 mg/mL of compound 3c in 0.5 mL of toluene), (C) 3c-xylenes gel (50 mg/mL of compound 3c in 0.5 mL of xylenes), (D) 3c-petrol gel (50 mg/mL of compound 3c in 0.5 mL of petrol)

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  2.3   Dye Adsorption

  With the rapid development of our society, the industrial and daily discharge of water-soluble toxic dyes to groundwater is also a serious environmental and economic problem, so the study of such the sewage treatments has also been a focus of attention in recent years. In this study, compound 3d as a selected adsorbing agent was found to be able to effectively remove toxic dyes such as crystal violet and rhodamine B from their aqueous solutions. And the abilities of compound 3d to remove these dyes were determined using UV-Vis spectroscopy. Taking the high toxicity of aniline, nitrobenzene or other aromatic solvents into account, benzyl alcohol, as a relatively safe solvent, was employed as the gelation solvent in this work. Efficient removal behaviors for crystal violet, and rhodamine B were described in Fig. 5, and the dye-adsorbed gels could be separated from the clean aqueous phase by simple filtration. Furthermore the removal abilities of 2.0 mg/mL of 3d benzyl alcohol for crystal violet and rhodamine B from their highly concentrated solutions could reach 99% and 98%, respectively, and the adsorption time to reach equilibrium were 2 and 8 hours, respectively (Fig. 6A and 6B). These findings manifest that compound 3d is an excellent sewage treatment agent for these toxic dyes.

  Figure 5

  

  Figure 5.  Photographs of (A) crystal violet (250.0 mg/L) aqueous solution (2 mL), (B) crystal violet aqueous solution+3d-benzyl alcohol gel (20 mg/mL of compund 3d in 0.2 mL of benzyl alcohol), (C) crystal violet-adsorbed gel; (D) rhodamine B (500.0 mg/L) aqueous solution (2 mL), (E) rhodamine B aqueous solution+3d-benzyl alcohol gel (20 mg/mL of compound 3d in 0.2 mL of benzyl alcohol), (F) rhodamine B-adsorbed gel

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  Figure 6

  

  Figure 6.  Concentration changes of the dye solutions with compound 3d gel as the adsorbing agent (20 mg/mL of compound 3d in 0.2 mL of benzyl alcohol) recorded at 585 nm for crystal violet (250.0 mg/L, 2 mL) with an efficiency of 99% (A), at 555 nm for rhodamine B (500.0 mg/L, 2 mL) with an efficiency of 98% (B)

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  3.   Conclusions

  In summary, a series of dipeptide gelators has been synthesized with pretty high yields. These dipeptide gelators are able to gel a wide range of aromatic solvents, and some of them are effective phase-selective gelators for the biphasic mixture with oils/water, which have the advantages of being harmless to the environment, an easily implementable method through simple shaking and easy recycling of the gelators and oils by simple distillation and recrystallization. Especially, the use of dipeptide gelators in dry powder form can contribute to the real-life application of compound 3c for the removal of benzene, toluene, xylenes and petrol from their biphasic mixtures with water in water purification. In addition, the gelator 3d can be used to effectively remove crystal violet and rhodamine B from their highly concentrated solutions with desirable high removal efficiencies even to reach 99% in the gel form. The impressive results in this work led us to believing that these dipeptide gelators will be promising sewage treatment agents in the future.

  
  
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  Scheme 1  (A) Target dipeptide compounds and (B) synthetic route

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  Figure 1  (A) Reversible sol-to-gel transitions of 3c-xylenes gel stimulated by heating at its MGC and (B) 3c-xylenes gel stimulated by shaking at 50 mg/mL loading of gelator

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  Figure 2  Photographs of the gels formed in benzene (A), toluene (B), xylenes (C) and petrol (D) with compound 3c as the gelator in dry powder form by shaking and resting at 50 mg/mL loading of gelator

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  Figure 3  (A) Specific gelation of the xylenes phase using 3c dry powder as a PSG in a two-phase mixture of xylenes and water (0.5 mL/2.0 mL). (B) 3c-Xylenes gel and clear water separated via filtration from formed gel-water mixture. (C) Recovery of xylenes from the 3c-xylenes gel via distillation and purification of the restored gelator by recrystallization

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  Figure 4  Inverted vials of gels formed phase-selectively in a two-phase mixture of organic phase and water (0.5 mL/2.0 mL): (A) 3c-benzene gel (50 mg/mL of compound 3c in 0.5 mL of benzene), (B) 3c-toluene gel (50 mg/mL of compound 3c in 0.5 mL of toluene), (C) 3c-xylenes gel (50 mg/mL of compound 3c in 0.5 mL of xylenes), (D) 3c-petrol gel (50 mg/mL of compound 3c in 0.5 mL of petrol)

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  Figure 5  Photographs of (A) crystal violet (250.0 mg/L) aqueous solution (2 mL), (B) crystal violet aqueous solution+3d-benzyl alcohol gel (20 mg/mL of compund 3d in 0.2 mL of benzyl alcohol), (C) crystal violet-adsorbed gel; (D) rhodamine B (500.0 mg/L) aqueous solution (2 mL), (E) rhodamine B aqueous solution+3d-benzyl alcohol gel (20 mg/mL of compound 3d in 0.2 mL of benzyl alcohol), (F) rhodamine B-adsorbed gel

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  Figure 6  Concentration changes of the dye solutions with compound 3d gel as the adsorbing agent (20 mg/mL of compound 3d in 0.2 mL of benzyl alcohol) recorded at 585 nm for crystal violet (250.0 mg/L, 2 mL) with an efficiency of 99% (A), at 555 nm for rhodamine B (500.0 mg/L, 2 mL) with an efficiency of 98% (B)

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  Table 1.  Gelation abilities of target dipeptide compounds^a and minimum gelation concentration (MGC) of the resulting gels of gelators in organic liquids

  Solvent	0.1×MGC/(mg·mL-1)
  	3a	3b	3c	3d	3e
  Benzene	1.52	1.60	1.52	0.52	1.55
  Toluene	0.55	0.69	0.51	0.31	0.76
  Xylenes	0.53	0.72	0.78	0.19	1.31
  Nitrobenzene	1.98	1.20	A	0.38	1.95
  Benzyl alcohol	Ab	A	A	0.88	A
  Petrol	0.094	0.061	0.060	0.023	0.046
  Diesel	0.099	0.056	0.056	0.020	0.042
  a.The mixture of 10 mg of each gelator and 0.2 mL of a known liquid was heated until the gelator was dissolved completely, and then cooled to room temperature to form gel; b.A=Non-gel state at gelator loading of 50 mg/mL. All gels formed at room temperature are stable at least for one month.

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  Table 2.  Gelation abilities and gelling times of room-temperature oil gelation by target dipeptide compounds in dry powder form via simple shaking and resting at 50 mg/mL loading of gelator within 1 h

  Solvent	Gelling time/min
  	3a	3b	3c	3d	3e
  Benzene	Aa	8	5	A	A
  Toluene	A	A	5	A	A
  Xylenes	A	A	4	A	A
  Nitrobenzene	A	A	—	A	A
  Benzyl alcohol	—b	—	—	A	—
  Petrol	A	A	3	4	A
  Diesel	A	A	A	A	A
  a.A=Non-gel state; b.Gelation abilities in dry powder form were not determined because of their MGCs above 50 mg/mL. All gels formed at room temperature are stable at least for one month.

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