Simultaneous Application of Mixotrophic Culture and Magnetic Fields as a Strategy to Improve Spirulina sp. LEB 18 Phycocyanin Synthesis.

Spirulina is a filamentous microalga which is considered a promising alternative source of essential nutrients and active biomolecules. High production cost and the space required to install a photobioreactor are two of the greatest challenges in the industrial application of microalga-based products. Thus, this study aimed to improve Spirulina sp. LEB 18 biomass and phycocyanin content by combining the application of mixotrophic culture and magnetic fields (MF). Zarrouk medium was modified with 1 and 3 g/L liquid molasses and the application of 30 mT for 1·h/d was investigated. Mixotrophic culture with 1 g/L molasses showed the highest biomass concentration (1.62 g/L), carbohydrate content (25.6%), and lipid contents (8.7%) after 15 days. Although the combination of 30 mT and 1 g/L liquid molasses decreased biomass production (1.44 g/L), there was increase in protein yield (76.9%) and protein productivity (73.8 mg/L·d). The proposed method increased phycocyanin production by 145% and its purity from 0.584 in the control culture to 0.627. Data described by this study show that the combination of mixotrophic culture and MF application is a promising alternative to increase microalga protein and phycocyanin production.

Proton transfer in fluorescent secondary amines: synthesis, photophysics, theoretical calculation and preparation of photoactive phosphatidylcholine-based liposomes.

In this article, new fluorescent lipophilic based benzazoles were synthesized from the reaction between photoactive formyl derivatives and aliphatic amines followed by NaBH4 reduction with good yields. The photophysics of the benzazoles was investigated experimentally and theoretically. These compounds present absorption maxima in the UV region (∼339 nm) and fluorescence emission maxima in the cyan to green region with a large Stokes shift (∼175 nm) due to a proton transfer process in the excited state. Two fluorophores were successfully used as a proof of concept to produce stable photoactive liposomes prepared from phosphatidylcholine (PC) and were characterized by zeta potential, small angle X-ray scattering (SAXS), FTIR and UV-Vis experiments (turbidity). The scattering data indicate that the presence of compounds 20 and 23 reduces the overall surface charge of the PC vesicles, possibly due to the partial neutralization of phosphatidic acid and/or phosphatidylinositol phosphate by the amine groups, and they also modify the structural features of the assemblies, leading, in particular, to a reduction in the thickness of the hydrophobic inner segment (tt) of the liposomes. DFT and TD-DFT calculations were performed with the ωB97XD functional. Geometric analyses show that the 2-(2'-hydroxyphenyl)benzazolic planar portion allows an effective ππ* electronic transition. Additionally, the calculations indicate a small energy barrier to proton transfer. The results of the absorption and emission maxima show a slight solvent influence on the wavelengths.

Influence of melatonin on the order of phosphatidylcholine-based membranes.

The effect of melatonin was evaluated on three phosphatidylcholine-based membrane models. Changes in liposome dynamics were monitored by fluorescence, following the response of the probe merocyanine-540, as well as by differential scanning calorimetry (DSC). Langmuir monolayers were investigated using molecular area measurements, as well as by Brewster angle microscopy (BAM). Mica-supported bilayers were observed via atomic force microscopy (AFM). Fluorescence results demonstrating that melatonin increases the affinity between MC-540 and lipid molecules possibly because of an increase in the membrane fluidity in liposomes. DSC analyses showed that melatonin promoted a reduction in enthalpy in the lipid nonpolar chains. Melatonin also promoted an increase in the molecular area of Langmuir monolayers, as well as a decrease in membrane thickness. Consequently, melatonin appeared to induce re-ordering effects in liposome and Langmuir monolayers. AFM images of bilayers immobilized on mica suggested that melatonin induced a gel state predominance or a delay in the main phase transition. At experimental conditions, melatonin interacted actively with all membranes models tested and induced changes in their physico-chemical properties. The data presented here may contribute to the understanding of melatonin physiologic properties, as well as the development of therapeutic advanced systems, such as drug delivery systems and biosensors.

Self-assembled dithiothreitol on Au surfaces for biological applications: phospholipid bilayer formation.

Self-assembly of dithiothreitol (DTT) on Au(111) from solution deposition has been studied by X-ray photoelectron spectroscopy and electrochemical data. DTT molecules self-assemble on Au(111) in a lying-down configuration irrespective of the concentration and temperature. XPS and electrochemical data indicate a DTT surface coverage of theta approximately 0.16 with two S-head-Au covalent bonds per DTT molecule. The DTT monolayer turns the Au surface hydrophilic enough to allow the formation of fluid dimyristoylphosphatidylcholine (DMPC) bilayer domains by vesicle fusion as revealed by in situ atomic force imaging. Methylene blue (MB) and flavin adenine dinucleotide (FAD) have been used as probes to study molecule transport across the bilayer.

Melatonin protects against pro-oxidant enzymes and reduces lipid peroxidation in distinct membranes induced by the hydroxyl and ascorbyl radicals and by peroxynitrite.

We have investigated the action of melatonin against lipid peroxidation in membranes including brain homogenates (BH), brain and liver microsomes (MIC), and phosphatidylcholine (PC) liposomes, as well as its effect on the activity of pro-oxidant enzymes such as constitutive neuronal nitric oxide synthase (cnNOS), xanthine oxidase (XO) and myeloperoxidase (MPO). The liposomes were reconstituted by a dialysis method, lipid peroxidation was monitored using the thiobarbituric reactive substances (TBARS) method and enzyme activities were measured spectrophotometrically. The ascorbyl and hydroxyl free radicals were generated by the reaction of ascorbic acid + FeSO4 and H2O2 + FeCl2, respectively, and peroxynitrite using a mixture of NaNO2 in an alkaline medium. Melatonin protected against lipid peroxidation induced by distinct reactive oxygen species (ROS) in all membranes tested although with different potency, in the following order BH < MIC < PC. The K0.5 for enzyme inhibition by melatonin was determined for nNOS (2.0 +/- 0.1 mm), for XO (0.8 +/- 0.1 mm) and for MPO (0.063 +/- 0.003 mm), the latter one with high affinity. Melatonin showed a weak effect as a nitrogen monoxide (NO) scavenger in the presence of sodium nitroprusside (NO donor) and low reactivity with 1,1-diphenyl-2-picryl hydrazyl (DPPH). These results demonstrate the antioxidant action of melatonin, principally that related to the activity of pro-oxidant enzymes such as XO and MPO.