Low-Molecular-Weight Organo- and Hydrogelators Based on Cyclo(l‑Lys‑l‑Glu)

Four cyclo­(l-Lys-l-Glu) derivatives (<b>3</b>–<b>6</b>) were synthesized from the coupling reaction of protecting l-lysine with l-glutamic acid followed by the cyclization, deprotection, and protection reactions. They can efficiently gelate a wide variety of organic solvents or water. Interestingly, a spontaneous chemical reaction proceeded in the organogel obtained from <b>3</b> in acetone exhibiting not only visual color alteration but also increasing mechanical strength with the progress of time due to the formation of Schiff base. Moreover, <b>6</b> bearing a carboxylic acid and Fmoc group displayed a robust hydrogelation capability in PBS solution. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) revealed the characteristic gelation morphologies of 3D fibrous network structures in the resulting organo- and hydrogels. FT-IR and fluorescence analyses indicated that the hydrogen bonding and π–π stacking play as major driving forces for the self-assembly of these cyclic dipeptides as low-molecular-weight gelators. X-ray diffraction (XRD) measurements and computer modeling provided information on the molecular packing model in the hydrogelation state of <b>6</b>. A spontaneous chemical reaction proceeded in the organogel obtained from <b>3</b> in acetone exhibiting visual color alteration and increasing mechanical strength. <b>6</b> bearing an optimized balance of hydrophilicity to lipophilicity gave rise to a hydrogel in PBS with MGC at 1 mg/mL

Preparation and Evaluation of Core–Shell Nanofibers Electrospun from PEU and PCL Blends via a Single-Nozzle Spinneret

The core–shell structured nanofibers are routinely fabricated by coaxial solution and single-nozzle emulsion electrospinning of two polymers. Herein, the core–shell structured polymeric nanofibers were electrospun from mixed solutions of poly­(ether urethane) (PEU) with poly­(ε-caprolactone) (PCL) or other biodegradable aliphatic polyesters via a single-nozzle spinneret. For comparison, the mixed solutions electrospinning of poly­(carbonate urethane) (PCU) with these polyesters including PCL was also conducted. The morphologies and hierarchical structures of the as-spun nanofibers were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), in vitro lipase degradation, differential scanning calorimeter (DSC), and Fourier-transform infrared (FTIR) analyses. It was shown that the blends of PEU with PCL or other biodegradable aliphatic polyesters were solely electrospun into the core–shell structured nanofibers with PEU as a shell and PCL or other biodegradable aliphatic polyesters as a core. The thickness of core/shell layers from 833/606 to 193.3/54.2 μm was adjustable by varying the feeding mass ratio from 1:3 to 3:1 of PEU to PCL or other biodegradable aliphatic polyesters. In DSC analysis, the Tonset of PEU@PCL core–shell fiber was 1.31 °C higher than that of the PCL fiber, while Tm was approximate. Furthermore, changing the electrospinning solvents of PEU with PCL or other biodegradable aliphatic polyesters retained the formation of core–shell nanofibers. In contrast, the blends of PCU with these polyesters tended to form co-continuous structured nanofibers. The effects of the physicochemical properties of mixed solutions on the charged liquid droplets, whipped jets, and morphology of the electrospun nanofibers were also inspected. The creation of core–shell nanofibers from the blends of PEU with PCL or other biodegradable aliphatic polyesters was most likely due to the interaction between the inherent thermodynamic phase separation of the polymers and their external stretching kinetic phase separation during electrospinning