Search

Lignin nanoparticles containing saccharides from fishery wastes were prepared as sustainable biofillers for advanced materials. Organosolv lignin and Kraft lignin were used as polyphenol components in association with chitosan and chitooligosaccharides. The chemophysical and biological activities of lignin/saccharide nanoparticles, such as UV-shielding, antioxidant, and antimicrobial activities, were found to be dependent on both molecular weight and deacetylation degree of saccharides, with the best performance being obtained in the presence of low-molecular-weight and highly deacetylated chitooligosaccharides. In addition, chitooligosaccharides showed a synergistic antioxidant effect with lignins, associated with antimicrobial activity against Escherichia coli(Gram-negative) and Staphylococcus aureus(Gram-positive).

Spectroscopical characterization of melanins is a prior requirement for the efficient tailoring of their radical scavenging, ultraviolet–visible radiation absorption, metal chelation, and natural pigment properties. Electron paramagnetic resonance (EPR), exploiting the common persistent paramagnetism of melanins, represents the elective standard for the structural and dynamical characterization of their constituting radical species. Although melanins are mainly investigated using X-band (9.5 GHz) continuous wave (CW)-EPR, an integration with the application of Q-band (34 GHz) in CW and pulse EPR for the discrimination of melanin pigments of different compositions is presented here. The longitudinal relaxation times measured highlight faster relaxation rates for cysteinyldopa melanin, compared to those of the most common dopa melanin pigment, suggesting pulse EPR spin–lattice relaxation time measurements as a complementary tool for characterization of pigments of interest for biomimetic materials engineering.

The interaction between cytochrome c(Cyt c) and cardiolipin (CL) plays a vital role in the early stages of apoptosis. The binding of CL to Cyt cinduces a considerable increase in its peroxidase activity that has been attributed to the partial unfolding of the protein, dissociation of the Met80 axial ligand, and formation of non-native conformers. Although the interaction between Cyt cand CL has been extensively studied, there is still no consensus regarding the conformational rearrangements of Cyt cthat follow the protein–lipid interaction. To rationalize the different results and gain better insight into the Cyt c–CL interaction, we have studied the formation of the CL complex of the horse heart wild-type protein and selected mutants in which residues considered to play a key role in the interaction with CL (His26, His33, Lys72, Lys73, and Lys79) have been mutated. The analysis was conducted at both room temperature and low temperatures via ultraviolet–visible absorption, resonance Raman, and electron paramagnetic resonance spectroscopies. The trigger and the sequence of CL-induced structural variations are discussed in terms of disruption of the His26–Pro44 hydrogen bond. We unequivocally identify the sixth ligand in the partially unfolded, non-native low-spin state that Cyt ccan adopt following the protein–lipid interaction, as a His ligation, ruling out the previously proposed involvement of a Lys residue or an OH–ion.

Antimicrobial peptides (AMPs) are an important component of innate immunity and have generated considerable interest as a potential new class of antibiotic. The biological activity of AMPs is strongly influenced by peptide-membrane interactions; however, for many of these peptides the molecular details of how they disrupt and/or translocate across target membranes are not known. CM15 is a linear, synthetic hybrid AMP composed of the first seven residues of the cecropin A and residues 2–9 of the bee venom peptide mellitin. Previous studies have shown that upon membrane binding CM15 folds into an α-helix with its helical axis aligned parallel to the bilayer surface and have implicated the formation of 2.2–3.8nm pores in its bactericidal activity. Here we report site-directed spin labeling electron paramagnetic resonance studies examining the behavior of CM15 analogs labeled with a methanethiosulfonate spin label (MTSL) and a brominated MTSL as a function of increasing peptide concentration and utilize phospholipid-analog spin labels to assess the effects of CM15 binding and accumulation on the physical properties of membrane lipids. We find that as the concentration of membrane-bound CM15 is increased the N-terminal domain of the peptide becomes more deeply immersed in the lipid bilayer. Only minimal changes are observed in the rotational dynamics of membrane lipids, and changes in lipid dynamics are confined primarily to near the membrane surface. However, the accumulation of membrane-bound CM15 dramatically increases accessibility of lipid-analog spin labels to the polar relaxation agent, nickel (II) ethylenediaminediacetate, suggesting an increased permeability of the membrane to polar solutes. These results are discussed in relation to the molecular mechanism of membrane disruption by CM15.

Human prion protein (hPrP) fragments encompassing the 91–120 region, namely hPrP92–100 (SP1), hPrP106–113 (SP2), hPrP91–120 (LP1), and hPrP91–114 (LP2), were considered for delineation of the CuII‐binding site(s). NMR and EPR spectroscopy results obtained from LP1 or LP2 were compared with those obtained from SP1 and SP2. The coexistence of two binding sites, one centered at His96 and the other at His111, was evidenced and ratified by ESI mass spectrometry at low and high metal:peptide ratios. While room‐temperature NMR spectroscopy data were consistent with the binding site centered on His111 being approximately fourfold stronger than that centered on His96, low‐temperature EPR spectroscopy results yielded evidence for the opposite trend. This disagreement, which has also occurred in the literature, was clarified by temperature‐dependent molecular dynamics runs that demonstrated Met112 approaching the metal at room temperature, a process that is expected to stabilize the His111‐centered binding site through hydrophobic shielding of the metal coordination sphere.

Three copperii complexes containing β-cyclodextrin βCD derivatives as ligands mono-6-methylamino-6-deoxy-βCD dithiocarbamate CDTC, mono-6-histamino-6-deoxy-βCD CDHM and mono-6-Nα-arginyl-6-deoxy-βCD CDARG have been studied by electron paramagnetic resonance. The spectra have been recorded at X- and S-bands and different temperatures and simulated to obtain the best set of magnetic parameters. In particular, the 300 K spectra are typical of the slow motion regime, as expected considering the high molecular weight of the ligands. Some structural characteristics of the complexes are proposed on the basis of dynamic and covalency parameters obtained from simulation.

Three copper(ii) complexes containing β-cyclodextrin (βCD) derivatives as ligands [mono-6-methylamino-6-deoxy-βCD dithiocarbamate (CDTC), mono-6-histamino-6-deoxy-βCD (CDHM) and mono-6-N_α-arginyl-6-deoxy-βCD (CDARG)] have been studied by electron paramagnetic resonance. The spectra have been recorded at X- and S-bands and different temperatures and simulated to obtain the best set of magnetic parameters. In particular, the 300 K spectra are typical of the slow motion regime, as expected considering the high molecular weight of the ligands. Some structural characteristics of the complexes are proposed on the basis of dynamic and covalency parameters obtained from simulation.

No Abstract

No Abstract

A series of X-band electron paramagnetic resonance (EPR) spectra were obtained in the temperature range 120–280 K at 10 K intervals for the bis(acetylacetonate) complexes of copper(II) and oxovanadium(IV) cations in dimethylformamide. The magnetic parameters and molecular rotational correlation time determined from simulations of the spectra revealed an unexpected temperature dependence of the isotropic hyperfine coupling constant (Aiso). A small, but non-negligible, abrupt increase in Aiso is observed for both complexes at a temperature (215 K) corresponding to the change in molecular motional state from the rigid limit to slow motion. The change is approximately the same for both the Cu(II) and vanadyl complexes (ca 2 × 10⁻⁴ cm⁻¹). No temperature dependence is observed in the isotropic g-factor for either complex within the experimental error. It is proposed that the data can be explained in terms of a change in the degree of distortion at the metal site coincident with the change in motional state and induced by a solvent (dimethylformamide) phase transition. Calculation of the bonding parameters shows that the in-plane π-bonding is more covalent in the vanadyl complex. Comparison with data from the literature reveals the importance of the solvent in determining the type of temperature dependence displayed by the magnetic parameters. Copyright © 1999 John Wiley & Sons, Ltd.

The reaction of heme proteins and H2O2 is thought to proceed via two-electron oxidation, resulting in the formation of ferryl heme (Fe^IV&dbond;O), and a protein radical. The ferryl-radical form of heme proteins would then catalyze the oxidation of molecules. Incubation of heme proteins with H2O2 in the presence of methyl-nitrosopropane (MNP) resulted in the detection of electron paramagnetic resonance (EPR) spectra characteristic of a highly immobilized nitroxide. Lineshapes of the EPR spectra were consistent with a slow tumbling molecule as it is evident from the broadening of the high field lines. This is consistent with the high molecular mass of the radical adduct. The goal of this work is, using a computer program based on the stochastic Liouville equation, to simulate directly these slow-motional EPR spectra and obtain information on magnetic and dynamic parameters of the complexes. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 73: 249–254, 1999