Key physicochemical properties of nanomaterials in view of their toxicity: an exploratory systematic investigation for the example of carbon-based nanomaterial

Currently, a noncomprehensive understanding of the physicochemical properties of carbon-based nanomaterial (CBNs), which may affect toxic effects, is still observable. In this study, an exploratory systematic investigation into the key physicochemical properties of multiwall carbon nanotube (MWCNT), single-wall carbon nanotube (SWCNT), and C₆₀-fullerene on their ecotoxicity has been undertaken. We undertook an extensive survey of the literature pertaining to the ecotoxicity of organism representative of the trophic level of algae, crustaceans, and fish. Based on this, a set of data reporting both the physicochemical properties of carbon-based nanomaterial and the observed toxic effect has been established. The relationship between physicochemical properties and observed toxic effect was investigated based on various statistical approaches. Specifically, analysis of variance by one-way ANOVA was used to assess the effect of categorical properties (use of a dispersant or treatments in the test medium, type of carbon-based nanomaterial, i.e., SWCNT, MWCNT, C₆₀-fullerene, functionalization), while multiple regression analysis was used to assess the effect of quantitative properties (i.e., diameter length of nanotubes, secondary size) on the toxicity values. The here described investigations revealed significant relationships among the physicochemical properties and observed toxic effects. The research was mainly affected by the low availability of data and also by the low variability of the studies collected. Overall, our results demonstrate that the here proposed and applied approach could have a major role in identifying the physicochemical properties of relevance for the toxicity of nanomaterial. However, the future success of the approach would require that the ENMs and the experimental conditions used in the toxicity studies are fully characterized.     

Monitoring the Evolution of Asynchrony between Mean Arterial Pressure and Mean Cerebral Blood Flow via Cross-Entropy Methods

Cerebrovascular control is carried out by multiple nonlinear mechanisms imposing a certain degree of coupling between mean arterial pressure (MAP) and mean cerebral blood flow (MCBF). We explored the ability of two nonlinear tools in the information domain, namely cross-approximate entropy (CApEn) and cross-sample entropy (CSampEn), to assess the degree of asynchrony between the spontaneous fluctuations of MAP and MCBF. CApEn and CSampEn were computed as a function of the translation time. The analysis was carried out in 23 subjects undergoing recordings at rest in supine position (REST) and during active standing (STAND), before and after surgical aortic valve replacement (SAVR). We found that at REST the degree of asynchrony raised, and the rate of increase in asynchrony with the translation time decreased after SAVR. These results are likely the consequence of the limited variability of MAP observed after surgery at REST, more than the consequence of a modified cerebrovascular control, given that the observed differences disappeared during STAND. CApEn and CSampEn can be utilized fruitfully in the context of the evaluation of cerebrovascular control via the noninvasive acquisition of the spontaneous MAP and MCBF variability.     

Cationic Zinc Organyls as Precatalysts for Hydroamination Reactions

The cationic zinc triple‐decker complex [Zn₂Cp*₃]⁺[BAr^F₄]^? (BAr^F₄=B(3,5‐(CF₃)₂C₆H₃)₄) exhibits catalytic activity in intra‐ and intermolecular hydroamination reactions in the absence of a cocatalyst. These hydroaminations presumably proceed through the activation of the C?C multiple bond of the alkene or alkyne by a highly electrophilic zinc species, which is formed upon elimination of the Cp* ligands. The reaction of [Zn₂Cp*₃]⁺[BAr^F₄]^? with phenylacetylene gives the hydrocarbonation product (Cp*)(Ph)CCH₂, which might be formed via a similar reaction pathway. Additionally, several other structurally well‐defined cationic zinc organyls have been examined as precatalysts for intermolecular hydroamination reactions without the addition of a cocatalyst. These studies reveal that the highest activity is achieved in the absence of any donor ligands. The neutral complex [ZnCp^2S₂] (Cp^2S=C₅Me₄(CH₂)₂SMe) shows a remarkably high catalytic activity in the presence of a Brønsted acid.     

Efficient microwave combinatorial parallel and nonparallel synthesis of N-alkylated glycine methyl esters as peptide building blocks

An easy and convenient microwave-assisted synthesis of N-alkylated glycine methyl esters is described. Parallel and nonparallel combinatorial methods are described and compared. The described reactions are reductive alkylations of several aldehydes and glycine methyl ester in the presence of NaBH3CN. Good yields and short reaction times are the main aspects of these procedures.     

Synthesis of substituted naphthalenes from alpha-tetralones generated by a xanthate radical addition-cyclisation sequence

A simple, highly efficient and cheap synthesis of substituted naphthalenes is reported. These aromatic compounds can be easily prepared in acidic or basic conditions from [small alpha]-tetralones, obtained by a xanthate-mediated addition-cyclisation sequence.     

Hierarchical self-assembly in molecularly ordered phenylene-bridged mesoporous organosilica nanofilaments.

Herein we report on the mechanism of formation of a hybrid phenylene-bridged hexagonally ordered mesoporous organosilica with crystal-like walls (CW-Ph-HMM). Electron microscopy and X-Ray diffraction studies indicate that the formation of CW-Ph-HMM involves the surfactant-mediated hydrothermal transformation of an amorphous organosilica precursor and that the final product is hierarchically ordered. Significantly, the material is in the form of submicrometre-thick sheets that consist of co-aligned aggregates of needle-like particles (up to 500 nm in length and 50 nm in width). The results suggest that preferential growth along the channel direction of the hexagonally ordered mesostructure is coupled with the propagation of molecular periodicity in the pore walls. Together, these factors give rise to the growth of highly anisotropic primary nanofilaments that become co-aligned to produce micrometer-thick sheets consisting of a periodic array of mesoscopic channels oriented perpendicular to the surface of the flake-like particles.     

Synthesis of Dendritic Metalloporphyrins with Distal H‐Bond Donors as Model Systems for Hemoglobin

We report the synthesis of the first‐ (G1) and second‐generation (G2) dendritic Fe^II porphyrins 1?Fe – 4?Fe (G1) and 6?Fe (G2) bearing distal H‐bond donors ideally positioned for stabilization of Fe^II? O₂ adducts by H‐bonding (Fig. 1). A first approach towards the construction of these novel biomimetic systems failed unexpectedly: the Suzuki cross‐coupling between appropriately functionalized Zn^II porphyrins and ortho‐ethynylated aryl derivatives, serving as anchors for the distal H‐bond donor moieties, was unsuccessful (Schemes 1, 3, and 5), presumably due to steric hindrance resulting from unfavorable coordination of the ethynyl residue to the Pd species in the catalytic cycle (Scheme 6). The target molecules were finally prepared by a route in which the ortho‐ethynylated meso‐aryl ring is introduced during porphyrin construction in a mixed condensation involving the two dipyrrylmethanes 33 and 34 , and aldehyde 36 (Schemes 7 and 8). Following attachment of the dendrons (Scheme 11), the distal H‐bond donors were introduced by Sonogashira cross‐coupling (Scheme 12), and subsequent metallation afforded the dendritic Fe^II porphyrins 1?Fe – 6?Fe . ¹H‐NMR Spectroscopy proved the location of the H‐bond donor moiety atop the porphyrin surface, and X‐ray crystal‐structure analysis of model system 45 (Fig. 2) revealed that this moiety would not sterically interfere with gas binding. With 1,2‐dimethyl‐1H‐imidazole (DiMeIm) as ligand, the dendritic Fe^II porphyrins formed five‐coordinate high‐spin complexes (Figs. 3 and 4) and addition of CO led reversibly to the corresponding stable six‐coordinate gas complexes (Fig. 6). Oxygenation, however, did not result in defined Fe^II? O₂ complexes as rapid decomposition to Fe^III species took place immediately, even in the case of the G2 dendrimer 6?Fe (DiMeIm) (Fig. 7). In contrast, stable gas adducts are formed between dendritic Co^II porphyrins and O₂ in the presence of DiMeIm as axial ligand, as revealed by electron paramagnetic resonance (EPR). The possible stabilization of these complexes through H‐bonding involving the distal ligand is currently under investigation in multidimensional and multifrequency pulse EPR experiments.     

Vitamin B12: How the Problem of Its Biosynthesis Was Solved

Vitamin B₁₂ is an essential vitamin for human health, and lack of it leads to pernicious anemia. This biological activity has attracted intense interest for some time; in addition, the complex architecture of the B₁₂ molecule has fascinated chemists and biochemists since its discovery as the first natural organocobalt complex and the establishment of its structure by X-ray analysis. The organic ligand surrounding the cobalt displays many stereogenic centers along its periphery carrying reactive functional groups. This complexity led vitamin B₁₂ to be rightly regarded as an extreme challenge to the synthetic chemist. Yet microorganisms achieve this synthesis in vivo with complete control of regio- and stereochemistry. How do they do it? This review tells the full remarkable story. Success in unraveling this biosynthetic puzzle resulted from a collaborative effort by biologists and chemists using the full range of methods available from their disciplines–from genetics at one end of the spectrum to synthesis and NMR spectroscopy at the other. This work can act as a guide for future research on the biosynthesis of yet more complex natural substances.