Direct Electrochemistry of Horseradish Peroxidase Immobilized in a Low Molecular Weight Gel

The ternary system of dodecylpyridinium bromide(DDPB)/acetone/H2O with appropriate composition can form a gel spontaneously and the gel is stable in hydrophobic ionic liquid 1-butyl-3-methylimidazolium hexafluorophos-phate([Bmim]PF_(6)).Based on the gelation phenomenon we observed,the low molecular weight gelator(LMWG)was first tried to immobilize horseradish peroxidase(HRP)on glassy carbon electrode(GCE).The scanning elec-tron microscope(SEM)images,the UV-Vis spectra and the bioactivity measurement indicate that the gel is suitable for the immobilization of HRP.The direct electrochemistry of the HRP-gel modified GCE(HRP-gel/GCE)in[Bmim]PF_(6)shows a pair of well-defined and quasi-reversible redox peaks with the heterogeneous electron transfer rate constant(ks)being 14.4 s^(−1),indicating that the direct electron transfer between HRP and GCE is fast.The HRP-gel/GCE is stable and reproducible.Also the electrode exhibits good electrocatalytic effect on the reduction of trichloroacetic acid(TCA),showing good promise in bioelectrocatalysis.

Designing the mechanical properties of peptide-based supramolecular hydrogels for biomedical applications

Hydrogels are a class of special materials that contain a large amount of water and behave like rubber.These materials have found broad applications in tissue engineering,cell culturing,regenerative medicine etc.Recently,the exploration of peptide-based supramolecular hydrogels has greatly expanded the repertoire of hydrogels suitable for biomedical applications.However,the mechanical properties of peptide-based hydrogels are intrinsically weak.Therefore,it is crucial to develop methods that can improve the mechanical stability of such peptide-based hydrogels.In this review,we explore the factors that determine or influence the mechanical stability of peptide-based hydrogels and summarize several key elements that may guide scientists to achieve mechanically improved hydrogels.In addition,we exemplified several methods that have been successfully developed to prepare hydrogels with enhanced mechanical stability.These mechanically strong peptide-based hydrogels may find broad applications as novel biomaterials.It is still challenging to engineer hydrogels in order to mimic the mechanical properties of biological tissues.More hydrogel materials with optimal mechanical properties suitable for various types of biological applications will be available in the near future.

Synthesis and Gelation Capability of Fmoc and Boc Mono-substituted Cyclo（L-Lys-L-Lys）s

Fmoc or Boc mono-substituted cyclo（L-Lys-L-Lys）s were synthesized via the reaction of lysine cyclic dipeptide with Fmoc N-hydroxysuccinimide este（Fmoc-OSu） and di-tert-butyl dicarbonate[（Boc）20], respectively. The resulted mono-substituted cyclo（L-Lys-L-Lys）s（2-4） by means of test tube inversion method served as organogelators enabled to form stable thermo-reversible organogels in alcoholic, substituted benzene and chlorinated solvents, with the minimum gelation concentration（MGC） in a range of 1%-4%（mass fraction）. The transmission electron microscopy（TEM） and scanning electron microscopy（SEM） observations reveal that these gelators self-assembled into 3D nanofiber, nanoribbon or nanotube network structures. The rheological measurement exhibited that the sto- rage modulus of gels is higher than the loss one, and the complex viscosity is reduced linearly with the increasing of scanning frequency. The fluorescence spectrum of compound 2 in 1,2-dichloroethane and benzene demonstrates that the emission peak of Fmoc at 320 nm has red-shifted and the intensity decreases gradually, while the intensity of the emission peak at 460 nm substantially enhances as a function of concentration, indicating the existence of π-π stacking interactions and the formation of J-type aggregates. Meanwhile, compound 4 self-assembled into nanotubes via the stacking of multiple bilayer membranes. Fmoc and Boc disubstituted cyclo（L-Lys-L-Lys）（3） holds the relatively lower MGC values, showing the stronger gelation ability in most selected organic solvents due to the presence of both Fmoc and Boc groups.