Magali A. Rodrigues

Effect of cholesterol on the interaction of the amphibian antimicrobial peptide DD K with liposomes.

DD K is an antimicrobial peptide previously isolated from the skin of the amphibian Phyllomedusa distincta. The effect of cholesterol on synthetic DD K binding to egg lecithin liposomes was investigated by intrinsic fluorescence of tryptophan residue, measurements of kinetics of 5(6)-carboxyfluorescein (CF) leakage, dynamic light scattering and isothermal titration microcalorimetry. An 8 nm blue shift of tryptophan maximum emission fluorescence was observed when DD K was in the presence of lecithin liposomes compared to the value observed for liposomes containing 43 mol% cholesterol. The rate and the extent of CF release were also significantly reduced by the presence of cholesterol. Dynamic light scattering showed that lecithin liposome size increase from 115 to 140 nm when titrated with DD K but addition of cholesterol reduces the liposome size increments. Isothermal titration microcalorimetry studies showed that DD K binding both to liposomes containing cholesterol as to liposomes devoid of it is more entropically than enthalpically favored. Nevertheless, the peptide concentration necessary to furnish an adjustable titration curve is much higher for liposomes containing cholesterol at 43 mol% (2 mmol L(-1)) than in its absence (93 micromol L(-1)). Apparent binding constant values were 2160 and 10,000 L mol(-1), respectively. The whole data indicate that DD K binding to phosphatidylcholine liposomes is significantly affected by cholesterol, which contributes to explain the low hemolytic activity of the peptide.

Inclusion complexes of naphthalimide derivatives with cyclodextrins

Abstract Complex formation between naphthalimide derivatives (2,3- and 1,8-naphthalimides and their respective N -butyl derivatives) and α-, β- and γ-cyclodextrins (CDs) was studied by UV and fluorescence spectroscopy. All the naphthalimides studied from 1:1 inclusion complexes with β- and γ-CDs, and the corresponding binding constants were determined. For β-CD complexes, the data obtained suggest a relatively tight axial inclusion of 2,3-naphthalimides and an equatorial inclusion of 1,8-naphthalimides. In contrast, for the γ-CD complexes, the data indicate a loose fit of the naphthalimides within the cavity. A remarkable exception is 2,3- N -butylnaphthalimide, which forms an unusually tight inclusion complex with γ-CD. In this complex, the quenching of the naphthalimide fluorescence by bromide ion is fully prevented.

Stabilization of naphthalene-1,8:4,5-dicarboximide radicals in zirconium phosphonate solid materials and thin films

Solid zirconium phosphonate (ZP) materials were prepared by direct precipitation of N,N′-bis(2-phosphonoethyl)naphthalene-1,8:4,5-dicarboximide (NDI-BP) from aqueous solution by addition of a ZrOCl2 solution. Slow precipitation in the presence of HF gave crystalline NDI-BP/ZP materials with a layered structure, whereas rapid precipitation in the absence of HF gave mainly amorphous materials. When ZrOCl2 solutions were added to photolyzed NDI-BP solutions, radical-doped solid materials with intense EPR response were obtained. Multilayer thin films of NDI-BP/ZP were grown on gold substrates in a layer-by-layer fashion, by exposing the phosphonate-rich modified surface to solutions of ZrOCl2 and NDI-BP, alternately. Electrochemical reduction of 20-layer films resulted in the formation of stable NDI-BP radical anions and dianions.

Novel self-assembled films of zirconium phosphonate/1,4,5,8-naphthalenediimides

Abstract The construction and characterization of novel self-assembled thin films of zirconium phosphonate/1,4,5,8-naphthalenediimides is described. The films were grown on silica or quartz substrates by deposition of alternated layers of Zr +4 and N , N ′-di(2-phosphonoethyl)-1,4,5,8-naphthalenediimide (DPN). Films containing up to 16 layers were obtained. Film growth, followed by either absorption spectroscopy or ellipsometry, was linear with the number of layers, showing that equal amounts of material were deposited in each cycle. Atomic force microscopy (AFM) images showed, however, that the films were microscopically not homogeneous, but rather constituted of crystallites of DPN. When irradiated, the initially colorless films turned to a persistent pinky color reminiscent of that of DPN anion radical.

Photophysical and photochemical properties of porphyrin and naphthalene diimide modified silica-gel particles

Abstract Silica-gel particles modified with photoactive molecules have applications in several fields including photocatalysis, chromatography, combinatorial chemistry, and chemical sensors. By using phosphonate/sulfonate zirconium chemistry, silica-gel particles were functionalized with two photoactive molecules, N , N ′ -bis(2-phosphonoethyl)-1,4,5,8-naphthalene diimide (DPN) and meso -tetra(4-sulfonatophenyl)porphyrin sodium salt (TPPS4). The photophysical and photochemical properties of the bound chromophores were shown to differ from their solution properties. In the luminescence spectra of DPN bound to silica-gel particles (DPN–silica gel), a band centered at 500 nm, which was not observed in solution, appeared and it was assigned to the emission of DPN excimers. The ratio of monomer to excimer emission was shown to change with the solution pH. In TPPS4 modified silica, changes in the absorption and in the emission spectra were observed when compared with the emission of TPPS4 in solution. These changes were correlated with the presence of TPPS4 dimers in the silica surface. Alterations in the photochemical reaction routes of DPN and TPPS4 were also observed by laser flash photolysis experiments. We were able to demonstrate that there are two competing photochemical reactions, i.e., energy transfer between triplet species and oxygen and electron transfer between triplets and ground state chromophores. Due to the close proximity of the chromophores in the silica surface, electron transfer processes are favored as demonstrated by the increase in the photogeneration of reduced radical species of DPN ( Δ Abs max =480 nm) and of TPPS4 ( Δ Abs max =700 nm).

Antimicrobial properties of two novel peptides derived from Theobroma cacao osmotin.

The osmotin proteins of several plants display antifungal activity, which can play an important role in plant defense against diseases. Thus, this protein can be useful as a source for biotechnological strategies aiming to combat fungal diseases. In this work, we analyzed the antifungal activity of a cacao osmotin-like protein (TcOsm1) and of two osmotin-derived synthetic peptides with antimicrobial features, differing by five amino acids residues at the N-terminus. Antimicrobial tests showed that TcOsm1 expressed in Escherichia coli inhibits the growth of Moniliophthora perniciosa mycelium and Pichia pastoris X-33 in vitro. The TcOsm1-derived peptides, named Osm-pepA (H-RRLDRGGVWNLNVNPGTTGARVWARTK-NH2), located at R23-K49, and Osm-pepB (H-GGVWNLNVNPGTTGARVWARTK-NH2), located at G28-K49, inhibited growth of yeasts (Saccharomyces cerevisiae S288C and Pichia pastoris X-33) and spore germination of the phytopathogenic fungi Fusarium f. sp. glycines and Colletotrichum gossypi. Osm-pepA was more efficient than Osm-pepB for S. cerevisiae (MIC=40μM and MIC=127μM, respectively), as well as for P. pastoris (MIC=20μM and MIC=127μM, respectively). Furthermore, the peptides presented a biphasic performance, promoting S. cerevisiae growth in doses around 5μM and inhibiting it at higher doses. The structural model for these peptides showed that the five amino acids residues, RRLDR at Osm-pepA N-terminus, significantly affect the tertiary structure, indicating that this structure is important for the peptide antimicrobial potency. This is the first report of development of antimicrobial peptides from T. cacao. Taken together, the results indicate that the cacao osmotin and its derived peptides, herein studied, are good candidates for developing biotechnological tools aiming to control phytopathogenic fungi.

Synthesis and Properties of New Paramagnetic Hybrid Bayerite from Al(0)/Naphthalene Dianhydride Reaction

The reaction of Naphthalene 1,4,5,8-dianhydride (NTCDA) with elemental aluminum(0) powder is studied in an aqueous alcoholic KOH mixture to search for the NTCDA anion and dianion electron-adducts. After analyzing various reaction conditions it was found that the reaction yielded a greenish precipitate in 3:1 (v:v) ethanol:water mixture. This powder is composed mainly of aluminum trihydroxide crystallites of bayerite [α-Al(OH3)(s)] and the organic content is approximately 6%. This hybrid material proved to be paramagnetic even after exposure to air for one year and at temperatures up to 200 oC. Typical carbonylic bound to metal IR bands and reflectance UV-VIS spectra demonstrate the entrapment of NTCDA radical anion into the aluminum trihydroxide, hence rendering its green color and a paramagnetic behavior. Thus, besides the understanding of an aluminum reaction in suspension, the entrapment of an organic material (NTCDA) that stays stable as the corresponding radical can provide an interesting option for the synthesis of aluminum trihydroxide composites.