Time-dependent DFT studies of metal core-electron excitations in Mn complexes

Time-dependent density functional theory (TDDFT) has been applied to study core excitations from 1s and 2p Mn orbitals in a series of manganese complexes with oxygen and nitrogen donor ligands. The effect of basis set and functional on the excitation energy was evaluated in detail for one complex, Mn(acac)2 x (H2O)2. The results obtained for a range of compounds, namely, [Mn(Im)6]Cl2, Mn(CH3COO)2 x 4 H2O, Mn(acac)3, Mn(SALADHP)2 and [Mn(SALPN)O]2, show good consistency with the data from X-ray absorption spectroscopy (XAS), confirming the relation between the Mn K-edge energy and the oxidation state of the Mn atom. The energies predicted for 2p core excitations show a dependence on the metal oxidation state very similar to that determined experimentally by 1s2p resonant inelastic X-ray scattering (RIXS) studies for Mn(acac)2 x (H2O)2, Mn(acac)3, and Mn(sal)2(bipy). The reliability of the K-edge energies obtained in the present study indicates that TDDFT can be used in determining the oxidation states of Mn atoms in different computational models of the manganese cluster of photosystem II (PSII).     

Laser induced breakdown spectroscopy on metallic alloys: Solving inhomogeneous optically thick plasmas

In this work, laser-induced breakdown spectroscopy (LIBS) has been applied to the characterization of a plasma generated on a ternary Co–Cr–Mo alloy commonly used on hip prosthesis in air at atmospheric pressure. A method to achieve analytical results without employing any reference sample was implemented within a two-region plasma picture of a hot dense core surrounded by a colder periphery, where both self-absorption and inhomogeneity effects were taken into account. High resolution spectra of three strong Co I–II lines from different regions of the plasma plume were recorded and the analysis was carried out by means of a least-squares calibration-free algorithm. In this approach, theoretical spectra were matched to the experimental line profiles. Thus, the plasma parameters (temperature, atom, ion and electron densities) and the line widths were obtained, demonstrating the feasibility of the method to characterize the physical state of a laser-induced plasma.     

Highly phosphorylated core oligosaccharide structures from cold-adapted Psychromonas arctica

Many cold habitats contain plenty of microorganisms that represent the most abundant cold-adapted life forms on earth. These organisms have developed a wide range of adaptations that involve the cell wall of the microorganism. In particular, bacteria enhance the synthesis of unsaturated fatty acids of membrane lipids to maintain the membrane fluidity, but very little is known about the adaptational changes in the structure of the lipopolysaccharides (LPSs), the main constituent of the outer leaflet of the outer membrane of Gram-negative bacteria. The aim of this study was to investigate the chemical structure of these LPSs for insight into the temperature-adaptation mechanism. For this objective, the cold-adapted Psychromonas arctica bacterium, which lives in the arctic sea-water near Spitzbergen (Svalbard islands, Arctic) was cultivated at 4 degrees C. The lipooligosaccharides (LOSs) were isolated and analysed by means of chemical analysis and electrospray ionisation high-resolution Fourier transform mass spectrometry. The LOS was then degraded either by mild hydrazinolysis (O-deacylation) or with hot 4 M KOH (N-deacylation). Both products were investigated in detail by using 1H and 13C NMR spectroscopy and mass spectrometry. The core consists of a mixture of species that differ because of the presence of nonstoichiometric D-fructose and/or D-galacturonic acid units.     

In vitro evaluation of cytotoxic and mutagenic activity of avarol

The cytotoxicity of avarol, a main secondary metabolite of the Mediterranean sponge Dysidea avara, was in vitro screened by MTT assay against four human tumour cell lines. The colon HT-29 tumour cells practically showed to be the only sensitive ones towards this organic compound. No toxicity was found against the fetal lung fibroblast MRC-5 cells at the concentrations tested. In comparison with doxorubicin, used as a positive control, avarol actually exhibited at least 588-fold less toxicity towards normal MRC-5 cells. Finally, comet assay indicated that DNA fragmentation was almost fivefold higher upon the treatment with doxorubicin, compared to avarol. The obtained results have actually confirmed that avarol scaffold may contribute to development of new cytostatics inspired by nature.     

In vitro avarol does affect the growth of Candida sp.

This work extends in vitro screening of antimicrobial activity of avarol, the marine natural product firstly isolated from the Mediterranean sponge Dysidea avara. Its anticandidial activity was evaluated by microdilution method against eight Candida strains, two ATCC and six clinical ones. At a different extent this compound was proven to be active against all the strains tested (MIC 0.8–6.0 μg/mL and MFC 1.6–12.0 μg/mL, respectively). According to the best of our knowledge, this is the first report on avarol activity towards any yeast strain which may be of relevance for Alzheimer’s disease. Indeed, avarol derivatives showing moderate AChE activity should be screened for anticandidial activity both in vitro and in vivo.     

Fluoropolymer based on a polyaspartamide containing 1,2,4-oxadiazole units: a potential artificial oxygen (O2) carrier

In this preliminary work we have prepared a fluorinated polymer capable of solubilizing an appreciable amount of O(2) and, at the same time, maintaining a higher water solubility than perfluoroalkanes investigated as injectable O(2) carriers. In particular, we describe the synthesis and characterization of a new macromolecular conjugate obtained by derivatization of alpha,beta-poly(N-2-hydroxyethyl)-DL-aspartamide (PHEA) with 5-pentafluorophenyl-3-perfluoroheptyl-1,2,4-oxadiazole, called PHEA-F. This new water soluble fluoropolymer was prepared in high yield using a simple procedure. It was characterized by FT-IR and UV-vis spectrophotometry, (19)F-NMR and SEC measurements. O(2) solubility studies on PHEA-F aqueous solutions were carried out at 25 degrees C and 37 degrees C at atmospheric pressure and showed that PHEA-F conjugate, despite its low degree of derivatization in fluorine containing groups (2.60 mol-%), is capable of dissolving 13-15% more O(2) than non-fluorinated PHEA. Moreover, O(2) release in simulated physiological conditions is faster for PHEA-F than for PHEA. The biocompatibility of this conjugate has been evaluated by performing an in vitro viability assay on human chronic myelogenous leukaemia cells (K-562) chosen as a model cell line and in vitro haemolysis experiments on human RBCs. All these properties suggest the potential use of PHEA-F as an artificial O(2) carrier.     

Identification of phosphoproteins and determination of phosphorylation sites by zirconium dioxide enrichment and SELDI-MS/MS

Reversible protein phosphorylation mediated by protein kinases and phosphatases is the most studied post-translational modification. Efficient characterization of phosphoproteomes is hampered by (1) low stoechiometry, (2) the dynamic nature of the phosphorylation process and (3) the difficulties of mass spectrometry to identify phosphoproteins from complex mixtures and to determine their sites of phosphorylation. Combination of the phosphopeptide enrichment method with MALDI-TOFMS, or alternatively, with HPLC-ESI-MS/MS and MS(3) analysis was shown to be a step forward for the successful application of MS in the study of protein phosphorylation. In our study we used phosphopeptide enrichment performed in a simple single-tube experiment using zirconium dioxide (ZrO(2)). A simple protein mixture containing precipitated bovine milk caseins was enzymatically digested and the mixture of tryptic fragments was analysed before and after enrichment using nanoflow HPLC-ESI-MS/MS and surface-enhanced laser desorption/ionization (SELDI)-MS/MS on QqTOF instruments to compare the efficiency of the two methods in the determination of phosphorylation sites. Both approaches confirm the high selectivity obtained by the use of batch-wise, ZrO(2)-based protocol using di-ammonium phosphate as the eluting buffer. More phosphorylation sites (five for beta-casein and three for alpha(S1)-casein) were characterized by SELDI-MS/MS than by nanoflow HPLC-ESI-MS/MS. Therefore, ZrO(2)-based phosphopeptide enrichment combined with SELDI-MS/MS is an attractive alternative to previously reported approaches for the study of protein phosphorylation in mixtures of low complexity with the advance of fast in situ peptide purification. The method was limited to successful analysis of high-abundance proteins. Only one phosphorylation site was determined for the minor casein component alpha(S2)-casein by ESI-MS/MS and none for kappa-casein. Therefore an improvement in enrichment efficiency, especially for successful phosphoproteomic applications, is needed.