TITLE: L-Leucine based supramolecular gelator 
AUTHORS: Raviraj Kusanur, Trilokchandran B, G Vijaya Kumar, M R Padmini, Sushma C, Namrata Patil, Rajalaxmi.S

[DESCRIPTION]


Gels are basically made up of polymers which, are either cross-linked or entangled in order to form a solid-like network. A new class of gels known as the supramolecular gels was formulated when small molecules self-assemble through various non-covalent interactions. These weak non-covalent interactions help in preventing the supramolecular gels from time-varying changes in their material properties. They self-assemble in order to form a micro-scale or nano-scale fibrillar network which, helps in immobilizing a large volume of solvents. This particular L-Leucine-based supramolecular gelator is composed of three main components that is, a hydrophobic tail, gluconic acid, and L-Leucine amino acid. It was tested for it's gelation properties using various solvents. Based on the observations made, we have concluded that liquid paraffin when used as a solvent for gelation had shown the best gelation properties by being stable and firm.




[STEPS]
SECTION: ESTERIFICATION
1. L-Leucine (C6H13NO2) 2.62g (0.02 mol) and Cetyl alcohol (C16H34O) 4.85g (0.02mol) were dissolved in toluene (75 ml). P-toluene sulphonic acid monohydrate (C7H8O3S.H2O) 7.60g (0.04mol) was added.

SECTION: ESTERIFICATION
2. The reaction mixture was refluxed at 95℃ for 10 hours.

SECTION: ESTERIFICATION
3. The progress of the reaction was monitored by TLC (15% ethyl acetate in Hexane).

SECTION: ESTERIFICATION
4. After completion of the reaction, toluene was removed using rotary evaporator and allowed to cool to room temperature.

SECTION: ESTERIFICATION
5. The residue obtained was dissolved in dichloromethane (75ml) and washed with 10% sodium carbonate solution (70ml, twice), water (50ml, twice) and brine solution (50 ml).

SECTION: ESTERIFICATION
6. The organic layer was dried over anhydrous magnesium sulphate. The dichloromethane was removed using rotary evaporator.

SECTION: ESTERIFICATION
7. The amino ester obtained was purified by converting the amino ester hydrochloride salt by dissolving in acetone 100ml and Conc. Hydrochloric acid 25ml.

SECTION: ESTERIFICATION
8. The solution was kept in refrigerator at 5℃ for 16 hours. The hydrochloride salt obtained was dissolved in DCM (75 ml) and washed with 10% sodium carbonate solution (50ml, twice), water (50ml, twice) and brine solution (50 ml). The organic layer was dried over anhydrous magnesium sulphate.

        


SECTION: COUPLING
9. The crude oily liquid obtained from first step (6.6g, 0.18 mmol) was dissolved in ethyl alcohol 75ml and Glucono delta lactone (C6H10O6) 3.6g (0.02mol) was added.

SECTION: COUPLING
10. The mixture was refluxed for 8 hours.

SECTION: COUPLING
11. The progress of the reaction was monitored by TLC.

SECTION: COUPLING
12. After completion of the reaction, ethyl alcohol was removed by using rotary evaporator.

SECTION: COUPLING
13. The crude compound was dissolved in THF and filtered hot.

SECTION: COUPLING
14. The THF was removed to get colourless powder.

SECTION: COUPLING
15. The powder obtained was further purified by recrystallisation in acetonitrile to get the colourless solid.


      

SECTION: GELATION
16. The dry gelator obtained after the process of recrystallization was weighed.The gelation properties were tested through the tube inversion test which, was done by dissolving the gelator using various solvents

SECTION: GELATION
17. The gelator was uniformly dissolved in liquid paraffin using a sonicator for 20 minutes at 60 ℃ which, which was very firm and stable even after 48 hours.


  
     Gelator Volume (mg)      Solvent (ml)       Inference        500       De-ionised water -1.5 ml       Gel was partially formed at 30° C         500      NaCl (20mM)  -1.5 ml       Solvent is not completely miscible with
  the gelator        500      Acetone-1.5 ml       Cracks are observed after the gel cools.        500       Toluene-1.5 ml       Gel is formed after cooling (5 minutes)
  when kept in oil bath at 90° C  and the
  gel remains stable even after 48 hours        500       Paraffin- 1 ml       Gel completely solidifies after 20
  minutes.  Its stable even after 48 hours.  There are no cracks        500      Ethanol-1.5 ml       Slight cracks were observed after 24
  hours.