Red Wine Inspired Chromophores as Photodynamic Therapy Sensitizers.

Hydroxypyranoflavylium (HPF) cations are synthetic analogs possessing the same basic chromophore as the pyranoanthocyanins that form during the maturation of red wine. HPF cations absorb strongly in the visible spectral region, and most are fluorescent, triplet-sensitize singlet oxygen formation in solution and are strong photooxidants, properties that are desirable in a sensitizer for photodynamic therapy (PDT). The results of this study demonstrate that several simple HPF dyes can indeed function as PDT sensitizers. Of the eight HPF cations investigated in this work, four were phototoxic to a human cervical adenocarcinoma cell line (HeLa) at the 1-10 µmol dm-3 level, while only one of the eight compounds showed noticeable cytotoxicity in the dark. Neither a Type I nor a Type II mechanism can adequately rationalize the differences in phototoxicity of the compounds. Colocalization experiments with the most phototoxic compound demonstrated the affinity of the dye for both the mitochondria and lysosomes of HeLa cells. The fact that relatively modest structural differences, e.g., the exchange of an electron-donating substituent for an electron-withdrawing substituent, can cause profound differences in the phototoxicity, together with the relatively facile synthesis of substituted HPF cations, makes them interesting candidates for further evaluation as PDT sensitizers.

Hybrid Pigments from Anthocyanin Analogues and Synthetic Clay Minerals.

Flavylium cations are synthetic analogues of anthocyanins, the natural plant pigments that are responsible for the majority of the red, blue, and purple colors of flowers, fruits, and leaves. Unlike anthocyanins, the properties and reactivity of flavylium cations can be manipulated by the nature and position of substituents on the flavylium cation chromophore. Currently, the most promising strategies for stabilizing the color of anthocyanins and flavylium cations appear to be to intercalate and/or adsorb them on solid surfaces and/or in confined spaces. We report here that hybrid pigments with improved thermal stability, fluorescence, and attractive colors are produced by the cation-exchange-mediated adsorption of flavylium cations (FL) on two synthetic clays, the mica-montmorillonite SYn-1, and the laponite SYnL-1. Compared to the FL/SYn-1 hybrid pigments, the FL/SYnL-1 pigments exhibited improved thermal stability as judged by color retention, better preferential adsorption of the cationic form of FL1 at neutral to mildly basic pH (pH 7-8), and lower susceptibility to color changes at pH 10. Although both clays adsorb the cationic form on their external surfaces, SYnL-1 gave more evidence of adsorption in the interlayer regions of the clay. This interlayer adsorption appears to be the contributing factor to the better properties of the FL/SYnL-1 hybrid pigments, pointing to this clay to be a promising inorganic matrix for the development of brightly colored, thermally more stable hybrid pigments based on cationic analogues of natural plant pigments.

Highly fluorescent hybrid pigments from anthocyanin- and red wine pyranoanthocyanin-analogs adsorbed on sepiolite clay.

Flavylium cations serve as models for the chemical and photochemical reactivity of anthocyanins, the natural plant pigment responsible for many of the red, blue and purple colors of fruits and flowers. Likewise, pyranoflavylium cations serve as models of the fundamental chromophoric moiety of pyranoanthocyanins, molecules that can form from reactions of grape anthocyanins in red wines during their maturation. In the present work, hybrid pigments are prepared by the adsorption of a series of five synthetic flavylium cations (FL) and five synthetic pyranoflavylium cations (PFL) on sepiolite clay (SEP). The FL are smaller in size than the PFL, but both can in principle fit into the tunnels and/or external grooves (with dimensions of 3.7 × 10.6 Å) of SEP. Measurements of the fluorescence quantum yields of the adsorbed dyes indicate that they are at least as fluorescent as in acidic acetonitrile solution, and in a few cases substantially more fluorescent. The observation of biexponential fluorescence decays is consistent with emission from dye molecules adsorbed at two distinct sites, presumably tunnels and grooves. These hybrid materials also have improved properties in terms of stability of the color in contact with pH 10 aqueous solution and resistance to thermal degradation of the dye. SEP thus appears to be a promising substrate for the development of highly fluorescent flavylium or pyranoflavylium cation-derived hybrid pigments with improved color and thermal stability.

The electronic transitions of analogs of red wine pyranoanthocyanin pigments.

There is increasing interest in using natural colorants like anthocyanins in cosmetics, food and pharmaceuticals as replacements for synthetic colorants. During the maturation of red wines, the anthocyanin pigments contained in grapes are transformed via reaction with copigments and metabolic products into pyranoanthocyanins, responsible in part for the final color of the wine. In order to understand structural effects on the absorption spectra of pyranoanthocyanins, the calculated excited state energies and spectroscopic states of a series of substitued pyranoflavylium cation analogs of pyranoanthocyanins have been compared to experimental spectroscopic data for these compounds. The vertical excitation energies, calculated by using the ADC(2) approach, gave excellent agreement with the experimental UV-Vis spectra and the nature of the lowest excited state correlates with the observed photophysical behavior in solution. The present results thus provide a basis for the design of new pyranoflavylium chromophores with the desired colors and photophysics, as well as for understanding the analogous properties of natural pyranoanthocyanin pigments in red wine.

Typical Monoterpenes as Insecticides and Repellents against Stored Grain Pests.

Five monoterpenes naturally occurring in essential oils were tested for their insecticidal and repellent activities against the bruchid beetle Callosobruchus maculatus and the maize weevil Sitophilus zeamais. The monoterpenes were highly efficient as inducers of mortality or repellency against both insect species. They were more efficient in their fumigant activity against C. maculatus than against S. zeamais, while this profile of action was inverted when considering the repellent activities. Eugenol was one the most effective fumigants against both insects and one the most effective repellent against C. maculatus, while citronellal and geranial were one the most effective repellents against S. zeamais. Functional and positional isomerism of the monoterpenes pairs appears to exert little or no influence on theirs effects, especially in case of repellency. The validation of the insecticidal/repellent efficacy of isolated monoterpenes may permit a more advantageous, rapid, economic and optimized approach to the identification of promising oils for commercial formulations when combined with ethnobotanical strategies.

L-Methionine inhibits growth of human pancreatic cancer cells.

We have previously shown that L-methionine inhibits proliferation of breast, prostate, and colon cancer cells. This study extends these findings to BXPC-3 (mutated p53) and HPAC (wild-type p53) pancreatic cancer cells and explores the reversibility of these effects. Cells were exposed to L-methionine (5 mg/ml) for 7 days or for 3 days, followed by 4 days of culture without L-methionine (recovery). Cell proliferation, apoptosis, and cell cycle effects were assessed by flow cytometry after staining for Ki-67 or annexin V/propidium iodide. Cell proliferation was reduced by 31-35% after 7 days of methionine exposure; the effect persisted in BXPC-3 and HPAC cells after 4 days of recovery. Methionine increased apoptosis by 40-75% in HPAC cells, but not in BXPC-3 cells. Continuous exposure to methionine caused accumulation of BXPC-3 cells in the S phase and HPAC cells in both the G0/G1 and S phases; however, after 4 days of recovery, these effects disappeared. In conclusion, L-methionine inhibits proliferation and interferes with the cell cycle of BXPC-3 and HPAC pancreatic cancer cells; the effects on apoptosis remarkably persisted after methionine withdrawal. Apoptosis was induced only in BXPC-3 cells. Some of the differences in the effects of methionine between cell lines may be related to disparate p53 status. These findings warrant further studies on the potential therapeutic benefit of L-methionine against pancreatic cancer.