Study on Formation Kinetics and Mechanism of Barium-Calcium Phosphoaluminate Mineral

Barium-calcium phosphoaluminate ((C,B)8A6P) mineral was synthesized by introducing Ba2+ into the lattice of calcium phosphoaluminate (C8A6P) mineral and it owned the better hydration activity than C8A6P. In this study, the formation kinetics and mechanism of (C,B)8A6P mineral was firstly systematically explored. The experimental results indicated that calcination temperature had a significant effect on the formation of (C,B)8A6P mineral. The conversion rate of (C,B)8A6P mineral was less than 0.5 and reaction rate was less than 9.4 × 10-7 with the holding time of 8 h at 1500-1530 °C. Nevertheless, the conversion rate and reaction rate reached 0.8 and 9.4 × 10-7, respectively, with the holding time of only 2 h when the calcination temperature ranged from 1540 °C to 1560 °C. In addition, the Jander equation was feasible for the formation of (C,B)8A6P with activation energy of 1310 kJ ∙ mol-1 at 1500-1530 °C, while the Ginstling equation was feasible for use with activation energy of 324 kJ ∙ mol-1 when the calcination temperature ranged from 1540 to 1560 °C.

m7G cap-eIF4E interaction stimulates polysome formation by enhancing first-round initiation kinetics

Translation in eukaryotic cells occurs predominantly through a 7-methylguanosine (m7G) cap-dependent mechanism. m7G cap interactions with eukaryotic initiation factor 4E (eIF4E) facilitates 43S recruitment to the mRNA 5' end and enhances the translation efficiency of mRNA. However, it remains poorly understood how m7G cap-eIF4E interactions affect polysome formation kinetics. Here, we examine the role of the m7G cap in polysome formation by utilizing a single-molecule approach to track individual ribosomes during active translation. Translation was monitored in wheat germ extract with capped and uncapped synthetic mRNAs and in HeLa extract with purified human eIF4E titration. The presence of the m7G cap and the supplementation of eIF4E to eIF4E-deficient extract enhanced the kinetics of the first initiation event of polysomes. Subsequent to the first initiation event, efficient polysome-forming initiation events occurred independent of mRNA m7G capping status and eIF4E concentration. Our results indicate that m7G cap-eIF4E interactions in wheat germ and HeLa extracts promote polysome formation by enhancing first-round initiation kinetics. The dynamics of individual translation events on polysomal mRNAs suggest that first-round initiation events activate mRNAs for efficient subsequent rounds of polysome-forming initiation.

Global simulations of monoterpene-derived peroxy radical fates and the distributions of highly oxygenated organic molecules (HOM) and accretion products

We evaluate monoterpene-derived peroxy radical (MT-RO2) unimolecular autoxidation and self and cross reactions with other RO2 in the GEOS-Chem global chemical transport model. Formation of associated highly oxygenated organic molecule (HOM) and accretion products are tracked in competition with other bimolecular reactions. Autoxidation is the dominant fate up to 6–8 km for first-generation MT-RO2 which can undergo unimolecular H-shifts. Reaction with NO can be a more common fate for H-shift rate constants < 0.1 s−1 or at altitudes higher than 8 km due to the imposed Arrhenius temperature dependence of unimolecular H-shifts. For MT-derived HOM-RO2, generated by multi-step autoxidation of first-generation MT-RO2, reaction with other RO2 is predicted to be the major fate throughout most of the boreal and tropical forested regions, while reaction with NO dominates in temperate and subtropical forests of the Northern Hemisphere. The newly added reactions result in ~4 % global average decrease of HO2 and RO2 mainly due to faster self-/cross-reactions of MT-RO2, but the impact upon HO2/OH/NOx abundances is only important in the planetary boundary layer (PBL) over portions of tropical forests. Within the bounds of formation kinetics and HOM photochemical lifetime constraints from laboratory studies, predicted HOM concentrations in MT-rich regions and seasons reach 10 % or even exceed total organic aerosol as predicted by the standard GEOS-Chem model. Comparisons to observations reveal large uncertainties remain for key reaction parameters and processes, especially the photochemical lifetime of HOM and associated accretion products. Using the highest reported yields and H-shift rate constants of MT-RO2 that undergo autoxidation, HOM concentrations tend to exceed the limited set of observations. Similarly, we infer that RO2 cross reactions rate constants near the gas-kinetic limit with accretion product branching greater than ~0.25 are inconsistent with total organic aerosol unless there is rapid decomposition of accretion products, the accretion products have saturation vapor concentrations > > 1 μg m−3, or modeled MT emission rates are overestimated. This work suggests further observations and laboratory studies related to MT-RO2 derived HOM and gas-phase accretion product formation kinetics, and especially their atmospheric fate, such as gas-particle partitioning, multi-phase chemistry, and net SOA formation, are needed.