Asymmetric Diels–Alder cycloadditions of d-erythrose 1,3-butadienes to achiral t-butyl 2H-azirine 3-carboxylate

Two d-erythrose 1,3-butadienes were reacted with electrophilic achiral t-butyl 2H-azirine 3-carboxylate giving cycloadducts with good yields and moderate selectivity. The isomers could be separated to give the major (R)-isomers at C-2 in approximately 50% yield in both cases. Alternatively LACASA-DA methodology was applied to one of the reactions leading to homochiral (R)- and (S)-products by changing the chiral nature of an extra chiral BINOL inductor used.     

CoII Cryptates Convert CO2 into CO and CH4 under Visible Light

Three Co^II octaazacryptates, with different substituents on the aromatic rings (Br, NO₂, CCH), were synthesised and characterised. These and the already published non-substituted cryptate catalysed CO₂ photoreduction to CO and CH₄ under blue visible light at room temperature. Although CO was observed after short irradiation times and a large range of catalyst concentrations, CH₄ was only observed after longer irradiation periods, such as 30 h, but with a small catalyst concentration (25 nm ). Experiments with ¹³C labelled CO₂ showed that CO is formed and reacts further when the reaction time is long. The CCH catalyst is deactivated faster than the others and the more efficient catalyst for CH₄ production is the one with Br. This reactivity trend was explained by an energy decomposition analysis based on DFT calculations.     

Synthesis,Characterization and Evaluation of the Antibacterial and Antitumor Activity of HalogenatedSalen Copper (II) Complexes derived from Camphoric Acid

Platinum metal complexes are the most common chemotherapeutics currently used in cancer treatment. However, the frequent adverse effects, as well as acquired resistance by tumor cells, urge the development of effective alternatives. In the recent past, copper complexes with Schiff base ligands have emerged as good alternatives, showing interesting results. Accordingly, and in continuation of previous studies in this area, three new camphoric acid-derived halogenated salen ligands and their corresponding Cu (II) complexes were synthesized and their antitumor activity was evaluated in order to determine the influence of the type and number of halogens present (Br, Cl). The in vitro cytotoxic activity was screened against colorectal WiDr and LS1034 and against breast MCF-7 and HCC1806 cancer cell lines. The results proved the halogenated complexes to be very efficient, the tetrachlorinated Cu (II) complex being the most promising, presenting IC₅₀ of 0.63–1.09 μM for the cell lines studied. The complex also shows selectivity to colorectal cancer cells compared to non-tumor colon cells. It is worth highlighting that the tetrachlorinated Cu (II) complex, our most efficient complex, shows a significantly more powerful antitumor effect than the reference drugs currently used in conventional chemotherapy. The halogenated salen and corresponding complexes were also screened for their antimicrobial activity against four bacterial species-Staphylococcus aureus, Enterococcus faecalis, Escherichia coli and Pseudomonas aeruginosa-and four fungal species-Candida albicans, Candida glabrata, Aspergillus fumigatus and Alternaria alternata. The compounds were found to exhibit moderate to strong antibacterial activity against the bacterial strains studied. NMR studies and theoretical calculations provided some insight into the structure of the ligands and copper complexes. Considering the results presented herein, our work validates the potential use of copper-based chemotherapeutics as alternatives for cancer treatment.     

Orbispaces as differentiable stratified spaces

We present some features of the smooth structure and of the canonical stratification on the orbit space of a proper Lie groupoid. One of the main features is that of Morita invariance of these structures—it allows us to talk about the canonical structure of differentiable stratified space on the orbispace (an object analogous to a separated stack in algebraic geometry) presented by the proper Lie groupoid. The canonical smooth structure on an orbispace is studied mainly via Spallek’s framework of differentiable spaces, and two alternative frameworks are then presented. For the canonical stratification on an orbispace, we extend the similar theory coming from proper Lie group actions. We make no claim to originality. The goal of these notes is simply to give a complementary exposition to those available and to clarify some subtle points where the literature can sometimes be confusing, even in the classical case of proper Lie group actions.     

Microextraction techniques for the determination of volatile and semivolatile organic compounds from plants: A review

Vegetables and fruits are necessary for human health, and traditional Chinese medicine that uses plant materials can cure diseases. Thus, understanding the composition of plant matrix has gained increased attention in recent years. Since plant matrix is very complex, the extraction, separation and quantitation of these chemicals are challenging.     

Characterizing pairwise contact patterns in human contact networks

We use a counting process representation of the pairwise contact process to analyze pairwise contact patterns. Studying two real-world traces, we find that the pairwise contact patterns have three characteristics. First, human contact patterns are influenced by daily and weekly cycles of activity. Second short time intervals with intensive contact event (bursts) are separated by long periods with few contact events. Third, the pairwise contact process exhibits long range dependence. We introduce a Markov modulated Poisson process (MMPP) as a flexible model for pairwise contact process exhibiting both regular structure and irregular bursts of activity. Using standard statistical techniques, we demonstrate that the proposed model is consistent with the empirical data. Our work has significant implication for mobility modeling and performance analysis in human contact networks.