Photoinduced Water Oxidation in Chitosan Nanostructures Containing Covalently Linked RuII Chromophores and Encapsulated Iridium Oxide Nanoparticles

The luminophore Ru(bpy)₂(dcbpy)²⁺ (bpy=2,2’-bipyridine; dcbpy=4,4’-dicarboxy-2,2’-bipyridine) is covalently linked to a chitosan polymer; crosslinking by tripolyphosphate produced Ru-decorated chitosan fibers (NS-RuCh), with a 20 : 1 ratio between chitosan repeating units and Ru^II chromophores. The properties of the Ru^II compound are unperturbed by the chitosan structure, with NS-RuCh exhibiting the typical metal-to-ligand charge-transfer (MLCT) absorption and emission bands of Ru^II complexes. When crosslinks are made in the presence of IrO₂ nanoparticles, such species are encapsulated within the nanofibers, thus generating the IrO₂⊂NS-RuCh system, in which both Ru^II photosensitizers and IrO₂ water oxidation catalysts are within the nanofiber structures. NS-RuCh and IrO₂⊂NS-RuCh have been characterized by dynamic light scattering, scanning electronic microscopy, and energy-dispersive X-ray analysis, which indicated a 2 : 1 ratio between Ru^II chromophores and IrO₂ species. Photochemical water oxidation has been investigated by using IrO₂⊂NS-RuCh as the chromophore/catalyst assembly and persulfate anions as the sacrificial species: photochemical water oxidation yields O₂ with a quantum yield (Φ) of 0.21, definitely higher than the Φ obtained with a similar solution containing separated Ru(bpy)₃²⁺ and IrO₂ nanoparticles (0.05) or with respect to that obtained when using NS-RuCh and “free” IrO₂ nanoparticles (0.10). A fast hole-scavenging process (rate constant, 7×10⁴ s⁻¹) involving the oxidized photosensitizer and the IrO₂ catalyst within the IrO₂⊂NS-RuCh system is behind the improved photochemical quantum yield of IrO₂⊂NS-RuCh.     

Poly‐l‐Lactic Acid Nanofiber–Polyamidoamine Hydrogel Composites: Preparation,Properties, and Preliminary Evaluation as Scaffolds for Human Pluripotent Stem Cell Culturing

Electrospun poly‐l ‐lactic acid (PLLA) nanofiber mats carrying surface amine groups, previously introduced by nitrogen atmospheric pressure nonequilibrium plasma, are embedded into aqueous solutions of oligomeric acrylamide‐end capped AGMA1, a biocompatible polyamidoamine with arg‐gly‐asp (RGD)‐reminiscent repeating units. The resultant mixture is finally cured giving PLLA‐AGMA1 hydrogel composites that absorb large amounts of water and, in the swollen state, are translucent, soft, and pliable, yet as strong as the parent PLLA mat. They do not split apart from each other when swollen in water and remain highly flexible and resistant, since the hydrogel portion is covalently grafted onto the PLLA nanofibers via the addition reaction of the surface amine groups to a part of the terminal acrylic double bonds of AGMA1 oligomers. Preliminary tested as scaffolds, the composites prove capable of maintaining short‐term undifferentiated cultures of human pluripotent stem cells in feeder‐free conditions.

     

Nonlinear effects on edge wave development

The effect of nonlinearity on the evolution of free edge waves is investigated by solving numerically the nonlinear shallow water equations. The numerical scheme is the two-dimensional WAF method, originally developed by Toro [Riemann Solvers and Numerical Methods for Fluid Dynamics, Springer, 1997]. First, a simple beach geometry [J. Fluid Mech. 381 (1999) 271] is considered and the numerical results are validated against available analytical solutions for small amplitude edge waves. Then, results are obtained for edge waves of larger amplitude. Nonlinear effects are found to be relevant even for moderate values of the nonlinearity parameter a which is the ratio between the wave amplitude and the water depth. In particular a resonance phenomenon has been observed which causes a modulation in time of the ultra-harmonic components of the wavefield. Larger values of a lead to a complex time evolution.     

Effect of dissolved carbon dioxide on accumulation of organic acids in liquid hot water pretreated biomass hydrolyzates

Liquid hot water pretreatment has been proposed as a possible means of improving rates of enzymatic hydrolysis of biomass while maintaining low levels of inhibitory compounds. Supplementation of liquid hot water pretreatment with dissolved carbon dioxide, yielding carbonic acid, has been shown to improve hydrolysis of some biomass substrates compared with the use of water alone. Previous studies on the application of carbonic acid to biomass pretreatment have noted a higher pH of hydrolyzates treated with carbonic acid as compared with the samples prepared with water alone. This study has applied recently developed analytical methods to quantify the concentration of organic acids in liquid hot water pretreated hydrolyzates, prepared with and without the addition of carbonic acid. It was observed that the addition of carbon dioxide to liquid hot water pretreatment significantly changed the accumulated concentrations of most measured compounds. However, the measured differences in product concentrations resulting from addition of carbonic acid did not account for the measured differences in hydrolyzate pH.     

Ultrastructural localization of Trypanosoma cruzi lysosomes by aryl sulphatase cytochemistry

Lysosomes of trypanosomatid protozoa are poorly known. In this work we have cytochemically detected the lysosomal enzyme aryl sulphatase in the trypanosomatids Trypanosoma cruzi and Crithidia fasciculata, by using p-nitrocatecholsulphate as substrate. Positive reaction was located exclusively inside membrane-bound cytoplasmic vesicles distributed throughout the cell body. Electron-dense reaction was either dispersed homogeneously through the vesicular matrix or located at the vesicle periphery, apposed to the membrane, with fine granular deposits occasionally found at the vesicular matrix. Trypomastigote and epimastigote forms of T. cruzi lacked electron-dense deposits at the plasma membrane, thus indicating that aryl sulphatase was not secreted to the environment. Furthermore, no positive reaction was detected in epimastigote reservosomes, which are organelles considered as pre-lysosomal compartments. Thus, our data show that reservosomes and lysosomes are organelles that can be distinguished by the cytochemical localization of aryl sulphatase in T. cruzi epimastigotes and trypomastigotes. Positive reaction in cytoplasmic vesicles of C. fasciculata choanomastigotes confirmed the specificity of the reaction for lysosomes in other trypanosomatid species.     

Absorption spectra, photophysical properties, and redox behavior of ruthenium(II) polypyridine complexes containing accessory dipyrromethene-BF2 chromophores

The six multichromophoric species 1-6, containing the potentially luminescent Ru(II) polypyridine subunits and 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene fluorophores (dipyrromethene-BF(2) dyes, herein after called bodipy), have been prepared and their absorption spectra, luminescence properties (both at room temperature in fluid solution and at 77 K in rigid matrix), and redox properties have been investigated (for the structuralformulas of all the compounds, see Figure 1). For comparison purposes, also the same properties of the bodipy-based free ligands have been examined. Three of the multichromophoric species (1-3) are based on the Ru(bpy)(3)-type metal subunit, whereas 4-6 are based on the Ru(terpy)(2)-type metal subunit. Transient absorption spectroscopy at room temperature of all the compounds has also been performed. The absorption spectra of all the metal complexes show features that can be assigned to the Ru(II) polypyridine subunits and to the bodipy centers. In particular, the lowest energy spin-allowed pi-pi* transition of the bodipy groups dominates the visible region, peaking at about 530 nm. All the new complexes exhibit a rich redox behavior, with reversible processes attributed to specific sites, indicating a small perturbation of each redox center and therefore highlighting the supramolecular nature of the multichromophoric assemblies. Despite the good luminescence properties of the separated components, 1-6 do not exhibit any luminescence at room temperature; however, transient absorption spectroscopy evidences that for all of them a long-lived (microsecond time scale) excited state is formed, which is identified as the bodipy-based triplet state. Pump-probe transient absorption spectroscopy suggests that such a triplet state is formed from the promptly prepared bodipy-based (1)pi-pi* state in most cases by the intervention of a charge-separated level. At 77 K, all the complexes except complex 1 exhibit the bodipy-based fluorescence, although with a slightly shortened lifetime compared to the corresponding free ligand(s), and 4-6 also exhibit a phosphorescence assigned to the bodipy subunits. Phosphorescence of bodipy species had never been reported in the literature to the best of our knowledge: in the present cases we propose that it is an effective decay process thanks to the presence of the ruthenium heavy atom and of the closely lying (3)MLCT state of the Ru(terpy)(2)-type subunits.     

Different cell death pathways induced by drugs in Trypanosoma cruzi: an ultrastructural study

Electron microscopy has proven to be a reliable and essential tool to determine morphological alterations and target organelles in the investigation of new drugs for Chagas disease. In this review, we focused on evaluating different agents that induce death of Trypanosoma cruzi, i.e. lysophospholipids analogues, naphthoquinones and derivatives, cytoskeletal inhibitors and natural products. Apoptosis-like presents as morphological characteristics DNA fragmentation, membrane blebbing and apoptotic body formation. Autophagy involves autophagosome formation, with the appearance of membranes surrounding organelles and cytosolic structures. Necrosis causes the loss of osmotic balance, an increase of cytoplasmic vacuolization and plasma membrane disruption. Mitochondrion appears as a central checkpoint in both apoptosis and necrosis. Our evidences of ultrastructural changes to T. cruzi treated with the different classes of compounds point to dramatic mitochondrial alterations and similar autophagic phenotypes. Lysophospholipid analogues interfere in the lipid biosynthesis in epimastigotes, altering the amount of both phospholipids and sterols, and consequently the physical properties of the membrane. Naphthoquinone derivatives led to a strong DNA fragmentation in trypomastigotes and to the release of cysteine proteases from reservosomes to cytosol in epimastigotes, starting a proteolytic process which results in parasite death. The susceptibility of reservosomes was also observed in parasites treated with propolis, suggesting impairment of lipid metabolism, compromising membrane fluidity and leading to lysis. The cytoskeletal agents blocked mitosis of epimastigotes, arresting cell cycle and impairing the parasite proliferation. The variety of drug stimuli converge to the same pathway of death suggests an intense cross-talking between the three types of PCD in the protozoa.     

A study on synergistic effects and protonation of a selected calixarene based picolinamide ligand used in the An/Ln separation

A series of liquid-liquid extraction tests was performed on the ligand hexakis(3-N-picoline-amidepropyloxy)calix[6]arene (PAR4). First, a screening campaign was carried out, in order to select the best organic solvent to be coupled to the aforementioned calixarene ligand. 2-Nitrophenyl hexyl ether (NPHE) was chosen to this purpose, and it was used in all the subsequent experiments, because of its excellent properties from both the viewpoints of calixarene solubility and ligand extracting capabilities. In solvent extraction tests, ²⁴¹Am was used as representative of minor actinides, while ¹⁵²Eu was employed to simulate lanthanides. Distribution coefficients and separation factors were obtained via γ-spectrometry. In addition, the synergism between the ligand and the lipophilic dicarbollide anion Cesium commo-3,3-cobalta-Bis(8,9,12 tribromo-1,2 dicarbacloso-Dodecarborane)ate(1-) (Br-Cosan) was investigated. Experimental results indicate that at pH ≥2 a strong synergistic effect between the calixarene ligand and Br-Cosan takes place. At higher acidity, on the other hand, the ligand protonation dramatically affects the efficiency and selectivity of the system.