Synthesis Of Some Amide Compounds And Their Stimuli-responsiveness

Stimuli-responsive materials can alter their properties in response to changes inthe environment or an external stimulus. Currently, a lot of stimuli are utilized tocontrol properties including electrical potential, light, pH, temperature, chemicals, andmechanical forces. We know that amide bond is widespread in nature as the backboneof peptides and proteins. Amide group is a good hydrogen bond donor and accepter,and significant delocalisation of the lone pair of electrons on the nitrogen atom givesthe group a partial double bond character, which make it a good choice for preparationof stimuli-responsive materials. In this paper, we designed and synthesized severalamide compounds, and investigated their stimuli-responsiveness. Some creativeresults are described in the following paragraphs.(1) We have designed and synthesized a dithiooctanoic acid derivative bearingN,N-disubstituted amide groups, DL-N-(6,8-dithiooctanoyl)-L-prolinol (1a), and usedit to fabricate self-assembled monolayers (SAMs) on gold surface, resulting in asolvent-responsive surface SAM-1a. The film showed reversible changes inwettability, which was indicated by surface contact angle switching between40°and59°upon alternating treatments with ethanol and cyclohexane. NMR experimentalresults of a model molecule, N-pentanoyl-L-prolinol (1b), suggests that thesolvent-responsive wettability of the SAMs could be related with the changes in therelative populations of two stereoisomers of amide. Then, we synthesized aN-monosubstituted amide, N-hydroxyethyl-6,8-dithiooctanamide (2a), and aN,N-disubstituted amide, N-hydroxyethyl-N-methyl-6,8-dithiooctanamide (2b), andused them to fabricated SAM-2a and SAM-2b, respectively. Comparison of theirsolvent-responsiveness confirmed that N,N-disubstitution was essential to obtain a stimuli-responsive surface. Further, we synthesized N,N-disubstituted dithiooctanoicacid derivatives with different alkyl chain lengths, and the SAMs fabricated fromthem performed different response ranges of the contact angle.(2) According to the structure of thermo-responsive amide polymers, wedesigned and synthesized three amide-based thermo-responsive molecules,N-propylpropionamide (nPPAm), N-sec-butylpropionamide (sBPAm) andN-butyl-N-methylpropionamide (MBPAm). Their aqueous solutions undergo phaseseparation when the ambient temperature exceeds their cloud points. We draw theirphase diagrams of amide/water systems, in which the lower critical solutiontemperature (LCST) of nPPAm and MBPAm were indicated as19.7°C and33.9°C,respectively. By introducing chiral groups, several chiral amide molecules, withthermo-responsive character, were obtained, including (S)-N-sec-butyl-N-methylpropionamide (M(S)sBPAm), N-pentanoyl-L-prolinol ((S)PPAm), N-pentanoyl-(S)-proline methyl ester (B(S)PME), N-((R)-1-hydroxypropyl)pentanamide((R)HMPPtAm), and N-((R)-1-(methoxymethyl)propyl)butyramide ((R)MMPBAm).Their phase diagrams were drawn, and the LCSTs of M(S)sBPAm,(S)PPAm andB(S)PME were49.7°C,62.4°C and75.7°C, respectively.(3) We designed and synthesized a number of oligo(N-methylglycine))-bearingamphiphilic molecules, N-dodecyl-N-methyl-2-(N-methyl-2-(N-methylacetamido)acetamido)acetamide (C12A3), N-tetradecyl-N-methyl-2-(N-methyl-2-(N-methyl-acetamido)acetamido)acetamide (C14A3), N-hexadecyl-N-methyl-2-(N-methyl-2-(N-methylacetamido)acetamido)acetamide (C16A3), N-octadecyl-N-methyl-2-(N-methyl-2-(N-methylacetamido)acetamido)acetamide(C18A3). C12A3and C14A3canself-assemble into micelle in water, with critical micelle concentration (CMC) of0.15mM and0.01mM, respectively. When environment temperature rises to someextent, the micellar solution becomes turbid, which is characterized by UV-visspectrometer. The LCSTs for C12A3and C14A3are79.5°C and61.2°C, respectively.We studied the application of thermo-responsive micelles of C12A3in cloud pointextraction. After adding Nile Red as pollutants, the micelle solution separated into two phases at the temperature above the cloud point. It can be seen clearly that the Nilered is enriched into the micelle-rich phase, which is also confirmed by a decrease offluorescence intensity for micelle-lean phase and a significant increase offluorescence intensity for micelle-rich phase. C16A3and C18A3can formthermo-responsive hydrogel, which have dual temperature-response, and a reversiblesol-gel-emulsion transition can be achieved. At the concentration of50mM, the geltemperature (Tgel) and cloud point (TCP) for C16A3was22.6°C and51.0°C,respectively; and the Tgeland TCPfor C18A3were38.0°C and39.9°C.