Highlights d Neural stem cell transition from quiescence to activation requires Sox5 and Sox6 d Loss of Sox5 or Sox6 decreases adult neurogenesis in the dentate gyrus d Transcription of neural stem cell activator Ascl1 is modulated by Sox5 and Sox6 d Environmental enrichment boosts stem cell activation, which is hampered by Sox5 loss

The addition of water molecules to unsaturated substrates is a highly desirable process. Additions to alkynes are very common, whereas additions to allenes and specially alkenes are rather scarce. One of the main aims here is to perform a comparative analysis of their reaction mechanisms for the process catalyzed by Au(I); another objective is to analyze why alkenes are much less reactive than their alkyne or allene counterparts. With this purpose the reaction mechanism for the addition of water to terminal and internal alkynes, alkenes, and allenes catalyzed by an [Au(NHC)] + complex (NHC = N-heterocyclic carbene) is analyzed by means of DFT calculations. The general catalytic cycle for the three kinds of substrates can be described by three main steps: (i) reactant π coordination to the Au(I) complex, (ii) water nucleophilic addition, and (iii) protodeauration, with subtle differences among the reactants. A comparative analysis, from the evolution of the centroids of localized molecular orbitals (CLMO), of the electronic rearrangements taking place in the protodeauration step reveals different mechanisms for these three substrates, both regarding the electron pair that accepts the proton and the fate of the Au−C bond pair. For alkenes calculations show that nucleophilic addition is highly demanding but affordable, whereas protodeauration is in any case energetically prohibitive. The main reason is not the intrinsic barrier of the protodeauration step, just a few kcal mol −1 higher than that of alkynes, but the high energy of the water-added intermediate. This issue is not related to the strength of the Au(I)−CC bond but to that of the C−O bond.

The reaction mechanism for the hydration of internal and terminal allenes catalyzed by [Au(NHC)] + is analyzed by means of DFT calculations. Several reaction pathways for generating the two possible regioisomers were evaluated. Direct addition on coordinated allenes or to an intermediate with a σ-allylic cation structure as suggested for the Au(I)-catalyzed hydroamination of allenes were considered. The isomerization between both regioisomeric products catalyzed by the same Au(I) catalyst was also investigated as suggested for hydroalkoxylation of allenes. The regioselectivity of the reaction predicted by computation agrees with experiment for both terminal and internal allenes. The presence of alkyl or aryl substituents introduces differences in the reaction mechanism for the hydration process.Special Issue: In Honor of the Career of Ernesto Carmona