Post-synthetic derivatisation of a porous material produces a functionalized material that binds the metal complex V(O)acac2, in contrast to the unfunctionalized precursor, which is inactive for complex binding.

We investigate the possibility of using the protease thermolysin to drive the synthesis and gelation of ionic-complementary peptides from nongelling precursors. In this system, short peptide fragments are continuously interconverted to form a dynamic peptide library, which eventually favors synthesis of peptides that are thermodynamically stabilized by molecular self-assembly. Thermolysin was added at a fixed concentration (0.3 mg mL(-1)) to solutions (0-300 mg mL(-1)) of the short tetrapeptide FEFK. Initially, the protease partially hydrolyzed the tetrapeptide into dipeptides in all samples. Subsequently, longer peptide sequences were found to form through reverse-hydrolysis. The stability of the different sequences was found to be dependent on their self-assembling properties. The sequences that self-assembled into antiparallel beta-sheet rich fibers became the stable products for the reverse hydrolysis reaction, while the others formed were unstable and disappeared with increasing incubation time. Ultimately, the main product of the system was octapeptide, which suggests that it represents the thermodynamically favored product of this dynamic library. Its concentration dictated the gelation behavior of the sample, and gels with moduli up to 25 kPa where obtained depending on the initial concentration of tetrapeptide.

We have recently shown that thermolysine, a protease enzyme obtained from Bacillus thermoproteolyticus rokko , can be used to trigger the gelation of FEFK (F, phenylalanine; E, glutamic acid; K, lysine) tetrapeptides through reverse hydrolysis and formation of longer peptide sequences, mainly octapeptides, that self-assemble readily. In this article we investigate the effect of enzyme concentration on the morphology and properties of enzymatically triggered peptide hydrogels using HPLC, FTIR, real-time SAXS, TEM, and shear rheology. We have shown that the enzyme concentration, Cenz, does not affect the final composition of the samples. Instead, this is dictated by the initial tetrapeptide concentration, C0, suggesting the existence of a chemical equilibrium. We went on to show that Cenz does not affect the self-assembly of these peptides at a molecular level either nor the structure of the fibrillar network formed at the nanometer scale. Interestingly, the mechanical properties were found to be affected by Cenz, where the shear moduli of the hydrogels were found to increase with increasing Cenz. These results suggest that morphological differences between the hydrogels at the microscale are at the origin of their difference in mechanical properties. In this paper, we propose a morphological model in which denser network regions are found around the enzymes, resulting in the creation of heterogeneous networks. These were confirmed by TEM measurements. The existence of these denser network regions will result in the reinforcement of the hydrogels, thus, explaining the high shear moduli obtained increasing Cenz.

We have investigated the possibility of using enzymatically triggered peptide hydrogels for the encapsulation and culture of cells. Based on recent work done on the enzymatically triggered gelation of FEFK (F, phenylalanine; E, glutamic acid; K, lysine) using thermolysin, a protease enzyme from Bacillus Thermoproteolyticus Rokko, we have investigated the possibility of using this gelation triggering mechanism to encapsulate cells within a 3D hydrogel matrix. First, the properties of enzymatically triggered hydrogels prepared in phosphate buffer solution were investigated and compared with the properties of hydrogels prepared in HPLC grade water from our previous work. We showed that the use of phosphate buffer solution allowed the production of hydrogels with very high shear moduli (>1 MPa). The gelation kinetics was also investigated, and the mechanical properties of the system were shown to closely follow the synthesis of the octapeptide by the enzyme through reverse hydrolysis. In a second phase, we developed, on the basis of information acquired, a facile protocol for the encapsulation of cells and plating of the hydrogel. Human dermal fibroblasts were then used to exemplify the use of these materials. FEFEFKFK octapeptide hydrogels prepared under the same conditions and with the same mechanical properties were used as a control. We showed that no significant differences were observed between the two systems and that after a decrease in cell number on day 1, cells start to proliferate. After 5 days of culture, the cells can be seen to start to adopt a stretched morphology typical of fibroblasts. The results clearly show that the protocol developed minimises the potential detrimental effect that thermolysin can have on the cells and that these enzymatically triggered hydrogels can be used for the 3D encapsulation and culture of cells.

The cyclotriphosphazene P(3)N(3)Cl(6) reacts with six equivalents of DMAP (4-(dimethylamino)pyridine) in superheated chloroform to form crystals of composition [P(3)N(3)(DMAP)(6)]Cl(6).19CHCl(3) comprising [P(3)N(3)(DMAP)(6)](6+) ions, which host five chloride ions in basket-type cavities on either side of the ring and at equatorial positions via tetradentate ortho-H-donor arrangements.