Kinetics Studies on Isomerization and Unimolecular Decay Processes of the Criegee Intermediate, Methacrolein (MACR) Oxide

Alkenes are one of the major components of hydrocarbons in our atmosphere. One of the most common alkenes in our atmosphere is isoprene (2-methyl – 1,3 – butadiene). Currently, it is known that isoprene ozonolysis can lead to the production of Criegee intermediates CH2OO, methacrolein (MACR) oxide, and methyl vinyl ketone (MVK) oxide. In part, we were interested in studying one specific Criegee intermediate, MACR oxide. The competition between the isomerization reactions and the unimolecular reactions became the focus of our study. Rate constants for the relevant reactions were calculated by implementing RRKM theory and using Master Equation modeling to create a scheme for the system. The overall results show that the most favorable reaction of MACR oxide is the isomerization between the cis and trans conformations. Because the transition states between these conformations are relatively low compared to the other transition states in the reaction, the conversions are observed to happen much faster than the others. The next fastest reaction that takes place is the unimolecular decay reactions to the dioxiranes and the dioxole. The decay reactions involved barriers that were higher than the cis⇌trans conversion but still lower than the barrier between the anti⇌syn conversion. With dioxole being our most stable state, our main interest was if different conformers of MACR oxide will decay to this structure in an atmospherically relevant time frame. It was found that substantial fraction (80%) of MACR oxide cannot decompose to dioxole in the relevant time frame as the barrier for the conversion between anti and syn is too high. We saw that there was almost no anti⇌syn conversion in any of our calculations

Neural Transcription Factors: from Embryos to Neural Stem Cells

The early steps of neural development in the vertebrate embryo are regulated by sets of transcription factors that control the induction of proliferative, pluripotent neural precursors, the expansion of neural plate stem cells, and their transition to differentiating neural progenitors. These early events are critical for producing a pool of multipotent cells capable of giving rise to the multitude of neurons and glia that form the central nervous system. In this review we summarize findings from gain- and loss-of-function studies in embryos that detail the gene regulatory network responsible for these early events. We discuss whether this information is likely to be similar in mammalian embryonic and induced pluripotent stem cells that are cultured according to protocols designed to produce neurons. The similarities and differences between the embryo and stem cells may provide important guidance to stem cell protocols designed to create immature neural cells for therapeutic uses