Bioavailability, bioaccumulation and tolerance of chromium: consequences in the food chain of freshwater ecosystems

Many abiotic and biotic factors can influence the partitioning equilibrium of heavy metals, thus influencing metal impact on aquatic environments. Unicellular algal species release soluble organic substances able to complex metals. In our laboratory a Cr-tolerant strain was selected and isolated from a wild type strain of Scenedesmus acutus. The exudates released by the two strains counteracted the growth inhibition caused by Cr(VI) and the exudates of the Cr-tolerant strain were more effective. On the contrary, the exudates did not reduce chromium toxicity to the cladoceran Daphnia magna. The reduction of chromium effect on algae seems the consequence of an algae-specific interaction among Cr(VI), exudates and algal cells. Chromium uptake resulted to be energy-dependent since bioaccumulation rate in subdued light condition was lower than at high light intensity. The effect of Cr(VI) on algae changed depending on metabolism of the cells and in particular it seemed to be related to the bioaccumulation rate. Tolerance in the selected strain could not be ascribed to a lower uptake of chromium. The difference in sensitivity to chromium between the two strains was exploited to evaluate if tolerance acquired by algae could have consequences for Daphnia. After treatment with Cr(VI), the two strains of S. acutus were used as food source for D. magna. The results indicate that chromium is accumulated by algae in a form not available for daphnids and that Cr tolerance acquired by the algae can be of some advantage to the consumer organism.     

Enantioselective straightforward access to benzo[b]thiophene analogs of Azatoxin

Horner-Wadsworth Emmons olefination followed by asymmetric hydrogenation allowed the first synthetic access to the chiral thiotryptophan with good enantiomeric excess. Oxazolidinone formation followed by a Pictet–Spengler condensation provided the benzothiophenic analog of Azatoxin.     

Hydrostannylation of phosphaalkenes [1]

Hydrostannylation reactions of the phosphaalkenes 9,11, and 21 with the triorganotin hydrides 1 proceed by different routes. Whereas the trior-ganotin hydrides 1a,b undergo regioselective 1,2-addition to the P/C double bond of the P-aminophosphaalkene 9 to furnish the 2-stannylphosphanes 17a,b, the 1,2-addition products to the P-halophosphaalkenes 11 and 21 can only be postulated as the reactive intermediates 20 and 23, respectively. The reactions of 11 with 1a,b proceed with cleavage of the triorganotin halide via the diphosphene 15 to furnish the cyclophosphanes 18 and 19. On the other hand, the hydrostannylation reactions of the phosphaalkene 21 are not selective, and the 1,3-diphosphetane 22 is isolated as one of the reaction products. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:453–460, 1998     

Cyclometalated Iridium(III) Complexes Containing Semicarbazone Ligands: Synthesis,Characterization, Photophysical and Biological Studies

The synthesis, crystal structure, photophysical properties, and biological activity of the novel bis‐cyclometalated complexes [Ir(ptpy)₂(vnsc)] ( 2 ) and [Ir(ptpy)₂(acsc)] ( 3 ) [ptpy = 2‐(p‐tolyl)pyridinato, vnsc = vanillin semicarbazone, acsc = acetone semicarbazone] are described. The new compounds were prepared by the reaction of [{Ir(μ‐Cl)(ptpy)₂}₂] ( 1 ) with the corresponding semicarbazone ligands under basic conditions. The molecular structure of compound 3 was confirmed by a single‐crystal X‐ray diffraction study. The complex crystallized from chloroform as a mono‐ solvate in the orthorhombic space group Pcab with eight molecules in the unit cell.     

Influence of chain structure on crystal polymorphism of poly(lactic acid). Part 1: effect of optical purity of the monomer

The influence of chain structure on crystal polymorphism of poly(lactic acid) (PLA) with high l-lactic acid content (97.8–100 %) is detailed in this contribution. Upon usual processing conditions of PLA, only α and α′ crystals grow, which makes these two polymorphs of major interest for research. The two crystal modifications have similar chain packing, which complicates their quantitative analysis by diffraction methods. The two crystal modifications are instead easily identified by analysis of the crystallization kinetics, which varies not only with temperature, but also with crystal polymorphism. The dependence of the rate of ordering on temperature shows two distinct maxima around 105–110 and 120–125 °C, which are related to growth of α′ and α crystals, respectively. Addition of d-lactic acid co-units leads to a decrease of the overall crystallization rate of PLA, as well as of the rate of spherulite growth (G) of both the crystal modifications. The relative crystallization rates of α and α′ forms are highly affected by stereoregularity, especially in the PLA grades that have a high crystallization rate. A high d-lactic acid content results not only in an overall slower crystal growth, but also in a varied temperature range where each of the two crystal modifications prevail, with a shift to lower temperatures of both the maxima of the G vs. temperature plots, indicating that inclusion of d-lactic acid units in the PLA chain affects crystallization rate of both α and α′ crystal modifications.     

Chemistry of Lipid A: At the Heart of Innate Immunity

In many Gram‐negative bacteria, lipopolysaccharide (LPS) and its lipid A moiety are pivotal for bacterial survival. Depending on its structure, lipid A carries the toxic properties of the LPS and acts as a potent elicitor of the host innate immune system via the Toll‐like receptor 4/myeloid differentiation factor 2 (TLR4/MD‐2) receptor complex. It often causes a wide variety of biological effects ranging from a remarkable enhancement of the resistance to the infection to an uncontrolled and massive immune response resulting in sepsis and septic shock. Since the bioactivity of lipid A is strongly influenced by its primary structure, a broad range of chemical syntheses of lipid A derivatives have made an enormous contribution to the characterization of lipid A bioactivity, providing novel pharmacological targets for the development of new biomedical therapies. Here, we describe and discuss the chemical aspects regarding lipid A and its role in innate immunity, from the (bio)synthesis, isolation and characterization to the molecular recognition at the atomic level.     

Application of comprehensive two-dimensional gas chromatography mass spectrometry and different types of data analysis for the investigation of cigarette particulate matter

In tobacco research, the comparison of different tobacco blends as well as the puff-dependent behaviour of cigarettes is a matter of particular interest. For the investigation of smoke characteristics, GC x GC offers different ways for data analysis, namely, compound target analysis, automated peak-based compound classification and comprehensive pixel-based data analysis. This study will show the application as well as the pros and cons of these types of data analysis for very complex matrices like cigarette particulate matter. In addition, new aspects about the recently discovered puff-dependent behaviour of compounds in cigarette smoke will be presented. Automated peak-based compound classification including mass spectrometric pattern recognition is used for the classification of tobacco particulate matter samples and the puff-dependent investigation of different compound classes. This compound group specific analysis is further reinforced by applying an even more comprehensive pixel-based analysis. This kind of analysis is used to generate fingerprints of different types of cigarettes. The combination of fast feature reduction methods like analysis of variance (ANOVA) and t-test with multivariate feature transformation methods like partial least squares discriminate analysis (PLSDA) for feature selection provides a powerful tool for a detailed inspection of different types of cigarettes.