Visible-light photocatalysis, particularly in its application to organic synthesis, has experienced a big renaissance in the past decade. The rational design of new photocatalysts with designed and improved photocatalytic properties, that at the same time circumvents the necessity of using scarce and toxic transition metals, will predictably play a key role in photocatalysis in the next few years. Although free-base porphyrins were identified some years ago as a promising, easily accessible and easily tunable class of organic photoredox catalysts, a systematic study on the effect of the electronic nature and of the position of the substituents on both the ground-state and the excited-state redox potentials of these compounds is still lacking. We have prepared a set of known functionalized derivatives of meso-tetraphenyl porphyrin containing different substituents either in one of the meso-positions or at a beta-pyrrole carbon and we have determined their ground- and (singlet) excited-state redox potentials. This survey has led us to conclude that the introduction of a carbonyl group at the beta-pyrrolic position strongly increases the facility of the monoelectronic reduction of the porphyrin both in the ground state and in the singlet excited state. We have also prepared a second set of four previously unknown benzoyl derivatives of meso-tetraphenylporphyrin, and we have confirmed the validity of our conclusions.

As a consequence of a three-stage synthesis from terephthalic aldehyde, a series of 3,3 '- (1,4-phenylene) perchlorates including methyl, hydrogen, acetyl, bromio, methoxy and nitro groups (R = Br, H, Me). The matching formazans were reacted with formalin in dioxane in the presence of perchloric acid to produce tetrazin ium salts. Formazans were synthesized by reacting terephthalic aldehyde phenylhydrazone with ar ene diazonium tosylates in a DMF/pyridine combination. The use of ar ene diazonium tosylates greatly simplified the separation and purification of formazans. The p henylhydrazone was produced in aqueous dioxane using the usual approach from terephthalic aldehyde and phenylhydrazine/hydrochloric acid. Individual f ormazans and tetrazinium perchlorates were isolated and characterized by elemental analysis, IR, NMR, UV spectroscopy. The electrochemical reduction of tetrazinium perchlorates was investigated using cyclic voltammetry (CV). Thus, all salts in the cathode region have two one-electron reduction peaks, which are connected to the sequential production of a radical cation and a biradical. It was discovered that donor substituents (R: OMe, Me) in the aromatic ring at position 1 accelerate tetrazinium cation reduction, whereas acceptor substituents (R: NO₂, COMe,) inhibit this process. On this premise, it was proposed that in the presence of donor substituents in the aromatic ring at position 1, the matching bis-verdazyl radicals should be easily generated. As a result, 3,3'- (1,4-phenylene) perchlorates are possible antecedents of symmetric biradical systems based on verdazyl radicals.

The objective of this study was to synthesize 9-/13-position substituted berberine derivatives and evaluated their cytotoxic and photocytotoxic effects against three human cancer cell lines. Among all the synthesized compounds, 9-O-dodecyl- (5e), 13-dodecyl- (6e) and 13-O-dodecyl-berberine (7e) exhibited stronger growth inhibition against three human cancer cell lines, (HepG2, HT-29 and BFTC905), in compare with structurally related berberine (1). These three compounds also showed the photocytotoxicity in human cancer cells in a concentration-dependent and light dose-dependent manner. Through flow cytometry analysis, we found out a lipophilic group at 9-/13-position of berberine may have facilitated its penetration into test cell and hence enhanced its photocytotoxicity on human liver cancer cell HepG2. Further, in cell cycle analysis, 5e, 6e and 7e induced HepG2 cells to arrest at S phase and caused apoptosis upon irradiation. In addition, photodynamic treatment of berberine (1) and its derivatives 5e, 6e and 7e again showed a significant photocytotoxic effects on HepG2 cells, induced remarkable cell apoptosis, greatly increased intracellular ROS level and the loss of mitochondrial membrane potential. These results over and again confirmed that berberine derivatives 5e, 6e and 7e greatly enhanced photocytotoxicity. Taking together, the test data led us to conclude that berberine derivatives with a dodecyl group at 9-/13-position could be great candidates for the anti-liver cancer medicines developments.

Abstract: Agarose is known to form a homogeneous thermoreversible gel in aqueous medium over a critical polymer concentration. The solid-liquid phase transitions are thermoreversible but depend on the molecular structure of the agarose sample tested. Then, in a first step, the structure was characterised by 1H and 13C NMR in D2O and in DMSO which is a solvent of agarose whatever the temperature. A low yield in methyl substituent on the D-galactose unit was determined. Then, evolution of the 1H NMR spectrum was followed as a function of temperature in increasing and decreasing temperature process from 25 to 80°C. A large thermal hysteresis is obtained and discussed. It helps to interpret rheological behaviour. In fact, NMR signals are related to proton relaxation and especially to proton involved in H-bonds between water and -OH agarose for tightly bound water and agarose/agarose in chain packing. In a second step, water was exchanged against ethanol which is a non solvent of agarose. A stable gel was demonstrated and characterised by rheology to be compared with aqueous behaviour. Bound water playing the role of plasticizer is probably removed and the gel is much stronger (and brittle) in ethanol with a larger thermal stability. It is the first time that such gel is characterised without phase transition when passing from a good-solvent to a non-solvent. This extends the domains of application of agarose.