Kinetic modeling of carbon dioxide valorization with epoxides

The reaction between carbon dioxide and epoxides using a non-metallic catalytic system can produce cyclic carbonates with excellent yields. The activation of the chemical system can occur in two ways: activation of epoxide or activation of carbon dioxide at the first step. A kinetic investigation of epichlorohydrin carbonate synthesis from epichlorohydrin and carbon dioxide was performed. The mass transfer, the kinetic of reaction and the activation of the chemical system was included in the analysis. A kinetic model was developed based on the reaction mechanism and the mass transfer phenomena. The quasi steady state assumption was considered on intermediate species and its results were compared with the detailed model. The optimization of the kinetic parameters estimated was performed by using a genetic algorithm in the model, the results obtained were in agreement with the experimental data. Please click Additional Files below to see the full abstract

Adverse effects of endocrine disruptors on the foetal testis development: focus on the phthalates.

There are great concerns about the increasing incidence of abnormalities in male reproductive function. Human sperm counts have markedly dropped and the rate of testicular cancer has clearly augmented over the past four decades. Moreover, the prevalence rates of cryptorchidism and hypospadias are also probably increasing. It has been hypothesized that all these adverse trends in male reproduction result from abnormalities in the development of the testis during foetal and neonatal life. Furthermore, many recent epidemiological, clinical and experimental data suggest that these male reproductive disorders could be due to the effects of xenobiotics termed endocrine disruptors, which are becoming more and more concentrated and prevalent in our environment. Among these endocrine disruptors, we chose to focus this review on the phthalates for different reasons: 1) they are widespread in the environment; 2) their concentrations in many human biological fluids have been measured; 3) the experimental data using rodent models suggesting a reprotoxicity are numerous and are the most convincing; 4) their deleterious effects on the in vivo and in vitro development and function of the rat foetal testis have been largely studied; 5) some epidemiological data in humans suggest a reprotoxic effect at environmental concentrations at least during neonatal life. However, the direct effects of phthalates on human foetal testis have never been explored. Thus, as we did for the rat in the 1990s, we recently developed and validated an organ culture system which allows maintenance of the development of the different cell types of human foetal testis. In this system, addition of 10-4 M MEHP (mono-2-ethylhexyl phthalate), the most produced phthalate, had no effect on basal or LH-stimulated production of testosterone, but it reduced the number of germ cells by increasing their apoptosis, without modification of their proliferation. This is the first experimental demonstration that phthalates alter the development of the foetal testis in humans. Using our organotypic culture system, we and others are currently investigating the effect of MEHP in the mouse and the rat, and it will be interesting to compare the results between these species to analyse the relevance of toxicological tests based on rodent models

Concerns about the widespread use of rodent models for human risk assessments of endocrine disruptors.

International audienceFetal testis is a major target of endocrine disruptors (EDs). During the last 20 years, we have developed an organotypic culture system that maintains the function of the different fetal testis cell types and have used this approach as a toxicological test to evaluate the effects of various compounds on gametogenesis and steroidogenesis in rat, mouse and human testes. We named this test rat, mouse and human fetal testis assay. With this approach, we compared the effects of six potential EDs ((mono-(2-ethylhexyl) phthalate (MEHP), cadmium, depleted uranium, diethylstilboestrol (DES), bisphenol A (BPA) and metformin) and one signalling molecule (retinoic acid (RA)) on the function of rat, mouse and human fetal testis at a comparable developmental stage. We found that the response is similar in humans and rodents for only one third of our analyses. For instance, RA and MEHP have similar negative effects on gametogenesis in the three species. For another third of our analyses, the threshold efficient concentrations that disturb gametogenesis and/or steroidogenesis differ as a function of the species. For instance, BPA and metformin have similar negative effects on steroidogenesis in human and rodents, but at different threshold doses. For the last third of our analyses, the qualitative response is species specific. For instance, MEHP and DES affect steroidogenesis in rodents, but not in human fetal testis. These species differences raise concerns about the extrapolation of data obtained in rodents to human health risk assessment and highlight the need of rigorous comparisons of the effects in human and rodent models, when assessing ED risk

Recent advances in organocatalysis by means of chiral cooperative ion-pairing

International audienc

Nouveau modele du NADH en serie pyrrolo 2,3-b pyridine, plus stables, plus reactif, a domaine d'activite elargie, permettant d'obtenir l'un ou l'autre des enantiomeres

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 82379 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Nouveaux développements en organocatalyse par paires d'ions coopératifs

National audienc

Nouveaux développements en organocatalyse par paires d'ions coopératifs

National audienc

Recent advances in organocatalysis by means of chiral cooperative ion-pairing

National audienc

Chimie de l'équipe Hétérocycles au laboratoire COBRA

National audienc

Recent advances in organocatalysis by means of chiral cooperative ion-pairing

International audienc