High dispersion dendritic fibrous morphology nanospheres for electrochemical CO2 reduction to C2H4.

The electrochemical CO2 reduction to specific multi-carbon product on copper-based catalysts is subjected to low activity and poor selectivity. Herein, catalyst structure, morphology, and chemical component are systematically studied for bolstering the activity and selectivity of as-prepared catalyzers in this study. Dendritic fibrous nano-silica spheres favor the loading of active species and the transport of reactant from the central radial channel. Cu/DFNS with high dispersion active sites are fabricated through urea-assisted precipitation way. The coexistence of Cu(I)/Cu(II) induces a close combination of Cu active sites and CO2 on the Cu/DFNS interface, promoting the CO2 activation and CC coupling. The Cu-O-Si interface (Cu phyllosilicate) can improve CO2 and CO attachment. Cu/DFNS show the utmost Faradaic efficiency of C2H4 with a value of 53.04% at -1.2 V vs. RHE. And more importantly, in-situ ATR-SEIRAS reveals that the CC coupling is boosted for effectively producing C2H4 as a consequence of the existence of *COL, *COOH, and *COH intermediates. The mechanism reaction path of Cu/DFNS is inferred to be *CO2 â†’ *COOH â†’ *CO â†’ *CO*COH â†’ C2H4. Our findings will be helpful to gain insight into the links between morphology, texture, chemical component of catalyzers, and electrochemical reduction of CO2, providing valuable guidance in the design of more efficient catalysts.

Structure Property-CO2 Capture Performance Relations of Amine-Functionalized Porous Silica Composite Adsorbents.

In order to investigate the influence of support structure properties on CO2 capture performances of solid amine adsorbents, a novel three-dimensional disordered porous silica (3dd) with hierarchical pore networks was developed and then compared to other three materials as adsorbent support, namely, hierarchical porous silica (HPS), MCM-41, and SBA-15. They were all functionalized with tetraethylenepentaamine (TEPA) to prepare CO2 adsorbents. The adsorbents' ability to capture CO2 was examined on a fixed-bed reactor. When these supports had 60 wt% TEPA loading, the amounts of CO2 captured followed the order 3dd > HPS > SBA-15 > MCM-41 at 75 °C; the adsorption capacities were 5.09, 4.9, 4.58, and 2.49 mmol/g, respectively. The results indicate that a larger pore volume can promote the dispersion of amine species to expose more active sites for CO2 capture. The larger pore size can decrease the CO2 diffusion resistance. High surface area is not an important factor in determining capture performance. In addition, compared with conventional single-size mesopores, the hierarchical pore networks can disperse the TEPA species in different levels of the channel to limit undesired loss/aggregation of impregnated TEPA species. Thus, the 3dd support exhibits the best stability and highest regeneration conversion compared to the other three supports. This work demonstrates that the rational design of adsorbent support systems can effectively relieve the trade-off between amine loading and diffusion resistance. One method to surmount this trade-off is to utilize an adsorbent platform with hierarchical pore networks. Thus, this work may provide a feasible strategy for the design of CO2 solid amine adsorbents with high capture amount and amine utilization efficiency.

Structural insights into the assembly of the 30S ribosomal subunit in vivo: functional role of S5 and location of the 17S rRNA precursor sequence.

The in vivo assembly of ribosomal subunits is a highly complex process, with a tight coordination between protein assembly and rRNA maturation events, such as folding and processing of rRNA precursors, as well as modifications of selected bases. In the cell, a large number of factors are required to ensure the efficiency and fidelity of subunit production. Here we characterize the immature 30S subunits accumulated in a factor-null Escherichia coli strain (∆rsgA∆rbfA). The immature 30S subunits isolated with varying salt concentrations in the buffer system show interesting differences on both protein composition and structure. Specifically, intermediates derived under the two contrasting salt conditions (high and low) likely reflect two distinctive assembly stages, the relatively early and late stages of the 3' domain assembly, respectively. Detailed structural analysis demonstrates a mechanistic coupling between the maturation of the 5' end of the 17S rRNA and the assembly of the 30S head domain, and attributes a unique role of S5 in coordinating these two events. Furthermore, our structural results likely reveal the location of the unprocessed terminal sequences of the 17S rRNA, and suggest that the maturation events of the 17S rRNA could be employed as quality control mechanisms on subunit production and protein translation.

Structural basis for the function of a small GTPase RsgA on the 30S ribosomal subunit maturation revealed by cryoelectron microscopy.

The bacterial RsgA, a circularly permutated GTPase, whose GTPase activity is dependent on the 30S ribosomal subunit, is a late-stage ribosome biogenesis factor involved in the 30S subunit maturation. The role of RsgA is to release another 30S biogenesis factor, RbfA, from the mature 30S subunit in a GTP-dependent manner. Using cryoelectron microscopy, we have determined the structure of the 30S subunit bound with RsgA in the presence of GMPPNP at subnanometer resolution. In the structure, RsgA binds to the central part of the 30S subunit, close to the decoding center, in a position that is incompatible with multiple biogenesis factors, all three translation initiation factors, as well as A-, P-site tRNAs and the 50S subunit. Further structural analysis not only provides a structural model for the RsgA-dependent release of RbfA from the nascent 30S subunit, but also indicates RsgA's role in the ribosomal protein assembly, to promote some tertiary binding protein incorporation. Moreover, together with available biochemical and genetic data, our results suggest that RsgA might be a general checkpoint protein in the late stage of the 30S subunit biogenesis, whose function is not only to release biogenesis factors (e.g., RbfA) from the nascent 30S subunit, but also to block the association of initiation factors to the premature 30S subunit.