University of Rennes

About: University of Rennes is a education organization based out in Rennes, France. It is known for research contribution in the topics: Population & Crystal structure. The organization has 18404 authors who have published 40374 publications receiving 995327 citations.

Exploring Electronic versus Steric Effects in Stereoselective Ring‐Opening Polymerization of Lactide and β‐Butyrolactone with Amino‐alkoxy‐bis(phenolate)–Yttrium Complexes

Abstract: A series of methoxy-amino-bis(phenol)s (ONOO(R(1),R(2)))H(2) possessing on the phenol rings R(1) ortho substituents with variable steric and electronic properties (R(1)=CMe(2)Ph, 1; CMe(2)tBu, 3; CMe(2)(4-CF(3)C(6)H(4)), 5; CPh(3), 9; Cl, 10) has been synthesized and further reacted with [Y{N(SiHMe(2))(2)}(3)](THF)(2) to give cleanly the corresponding yttrium compounds [Y(ONOO(R(1),R(2))){N(SiHMe(2))(2)}(thf)(n)] (Y-x); the solid-state structures of Y-3 and Y-10 have been determined. These amido complexes have been used as initiators for the ring-opening polymerization (ROP) of rac-lactide (LA) and rac-β-butyrolactone (BBL) to provide heterotactically enriched poly(lactic acid)s (PLAs) and syndiotactically enriched poly(3-hydroxybutyrate)s (PHBs), respectively, by means of a chain-end control mechanism. Most of these polymerizations proceeded in a controlled fashion, giving polymers with narrow polydispersities and experimental molecular weights in good agreement with calculated values. The nature of the R(1) ortho substituents has a profound impact on the rates and, more spectacularly, on the stereocontrol of the polymerizations. The heterotactic stereocontrol in the ROP of rac-LA appears to be governed essentially by steric considerations; the larger the substituent, the higher the heterotacticity: R(1)=Cl (P(r)=0.56)≪CMe(3) (P(r)=0.80)≪CMe(2)Ph (P(r)=0.90)

Post-collisional Neogene magmatism of the Mediterranean Maghreb margin: a consequence of slab breakoff

Abstract: A 1 200 km-long linear magmatic belt extends along the Mediterranean coast of the Maghreb from Eastern Tunisia to Morocco. This belt is mainly composed of Langhian calc-alkaline metaluminous to peraluminous granitoids and associated andesites/dacites in Central and Eastern Algeria. In Tunisia and Oranie/Western Morocco, calc-alkaline activity started later (during the Serravallian) and was followed by the emplacement of alkali basalts and basanites since the Tortonian to the Pliocene and, in some places, the Pleistocene. Available data on the tectonic setting, petrology, age and geochemistry of this belt show that most of its striking features, e.g. (1) very low magma production rate, subduction-related geochemical imprint, extensive crustal contamination for the calc-alkaline magmatism and (2) progressive magmatic change from calc-alkaline to alkaline, are consistent with magma generation during a slab breakoff process as proposed by Carminati et al. in 1998. The magmatism associated with this breakoff started in Central Eastern Algeria at 16 Ma, then propagated eastwards and westwards. The upward flow of asthenospheric enriched plume-type mantle through the tear in the downgoing slab first triggered melting of the overlying lithospheric mantle which had been metasomatised during a previous subduction period. Heat supply from this uprising asthenosphere may have warmed up the continental crust and made its involvement in assimilation processes easier. As the asthenosphere ascended through the ‘window’ in the slab, partial melting occurred at the uprising boundary between asthenosphere and lithosphere, generating basalts with transitional characteristics between those of calc-alkaline and alkaline basalts. As the asthenospheric upwelling proceeded, partial melting then occurred in the sole asthenospheric mantle, producing alkali basalts.

Overview of Disinfection By-products and Associated Health Effects.

Abstract: The presence of chemical compounds formed as disinfection by-products (DBPs) is widespread in developed countries, and virtually whole populations are exposed to these chemicals through ingestion, inhalation, or dermal absorption from drinking water and swimming pools. Epidemiological evidence has shown a consistent association between long-term exposure to trihalomethanes and the risk of bladder cancer, although the causal nature of the association is not conclusive. Evidence concerning other cancer sites is insufficient or mixed. Numerous studies have evaluated reproductive implications, including sperm quality, time to pregnancy, menstrual cycle, and pregnancy outcomes such as fetal loss, fetal growth, preterm delivery, and congenital malformation. The body of evidence suggests only minor effects from high exposure during pregnancy on fetal growth indices such as small for gestational age (SGA) at birth. Populations highly exposed to swimming pools such as pool workers and professional swimmers show a higher prevalence of respiratory symptoms and asthma, respectively, although the direction of the association, and thus causality, is not clear among professional swimmers. The risk of asthma, wheezing, eczema, and other respiratory outcomes among children attending swimming pools has been the object of extensive research. Early studies suggested a positive association, while subsequent larger studies found no correlations or showed a protective association. Future research should develop methods to evaluate the effects of the DBP mixture and the interaction with personal characteristics (e.g., genetics, lifestyle), clarify the association between swimming pools and respiratory health, evaluate the occurrence of DBPs in low- and middle-income countries, and evaluate outcomes suggested by animal studies that have not been considered in epidemiological investigations.