Electron- and energy-transfer properties of hydrophilic carotenoids.

The antioxidant activities-expressed as the electron-donating properties-of five hydrophilic carotenoids (carotenoid surfactants) and three related hydrophobic carotenoids were investigated by flash photolysis. The electron-transfer rates of the carotenoids to the triplet state of the sensitizer 2-nitronaphthalene and the energy transfer rates of triplet 2-nitronaphthalene to the carotenoids were determined. The results demonstrate that the electron-donating effects of the hydrophilic and hydrophobic carotenoids were comparable when evaluated in acetonitrile.

Hydrophilic carotenoid amphiphiles: methods of synthesis and biological applications.

Carotenoid bioactivity, namely the quenching of reactive oxygen species (ROS) and other excited-state oxidants, suggests significant clinical potential for these natural products. However, a thorough therapeutic evaluation of the carotenoids has been hampered by limited water-solubility and/or water-dispersibility ("hydrophilicity") as well as poor bioavailability. Hydrophilic carotenoid derivatives have been designed and prepared for parenteral administration.

Hydrophilic carotenoids: surface properties and aqueous aggregation of a rigid, long-chain, highly unsaturated dianionic bolaamphiphile with a carotenoid spacer.

The water dispersibility of astaxanthin was greatly enhanced by converting it to a disodium disuccinate salt. This carotenoid salt behaved as a bolaamphiphile in water; dynamic light scattering (DLS) revealed the formation of stable aggregates with an average hydrodynamic radius close to 1 microm. Larger aggregates were observed in solutions of increased osmolarity.

Optically active oligomer units in aggregates of a highly unsaturated, optically inactive carotenoid phospholipid.

Enantiomers of glycerophospholipids show low or no optical activity. Accordingly, optical activity was not observed with the R enantiomer of a highly unsaturated carotenoyl lysophospholipid in solution. In spite of this, strong Cotton effects are detected in water.

Hydrophilic carotenoids: surface properties and aggregation behavior of a highly unsaturated carotenoid lysophospholipid.

The water dispersibility of a hydrophobic carotenoid has been greatly enhanced by using it as the acyl part in the synthesis of a highly unsaturated lysophospholipid. Dynamic light scattering has revealed the formation of stable aggregates with an average hydrodynamic radius of a few nanometers, and absorption spectra show that the aggregates can withstand the addition of ethanol or acetonitrile until the volume fraction of water falls below 70 and 62%, respectively. The properties of the carotenoid phospholipids have been characterized by determining surface tension, critical micelle concentration, surface concentration, molecular area, free energy of adsorption and micellation, adsorption-micellar energy relationship, and equilibrium constants.

Direct superoxide anion scavenging by a highly water-dispersible carotenoid phospholipid evaluated by electron paramagnetic resonance (EPR) spectroscopy.

Synthetic carotenoid analogs, with increased utility for biological applications, are sparingly reported in the literature. Synthetic modification, which may increase the water solubility and/or water dispersibility of lipophilic carotenoids, allows their use in aqueous environments as potent antioxidants against potentially deleterious reactive oxygen species (ROS) that can be generated in vivo. Superoxide anion, produced by activated human neutrophils, can be a source of additional harmful ROS and nonradical species such as singlet oxygen in vivo.

Structural elucidation by 1D and 2D NMR of three isomers of a carotenoid lysophosphocholine and its synthetic precursors.

A carotenoic acid was used to obtain a long-chain unsaturated lysophosphocholine. The carotenoid lysophosphocholine was synthesized by two methods. The first method resulted in mixtures of regioisomers for each step in the synthetic route.