Calcium oxide is a promising sorbent for the capture of carbon dioxide. In this work, CaO sorbents were prepared using different precursors, including Ca(NO 3 ) 2 ‚4H 2 O, CaO, Ca(OH) 2 , CaCO 3 , and Ca(CH 3 COO) 2 ‚ H 2 O. Of these, the sorbent prepared from calcium acetate (CaAc 2 -CaO) resulted in the best uptake characteristics for CO 2 . This sorbent had a higher BET surface area and larger pore volume than the other sorbents. According to SEM images, this sorbent exhibits a "fluffy" structure, which probably contributes to its high surface area and large pore volume. This sorbent also showed almost 100% carbonation, at temperatures between 550 and 800 °C. Moreover, the carbonation progressed dominantly during an initial short period. Under numerous carbonation/decarbonation cycles, the CaAc 2 -CaO sorbent demonstrated the best reversibility, even in the presence of 10 vol % water vapor. During a 27-cycle operation, the sorbent maintained fairly high conversion of 62 mol % at 700 °C. Pore size distribution measurements indicate that the pore volume decreased as the experimental cycles continued. Silica was doped on the CaAc 2 -CaO sorbent in various weight percentages, but the resultant sorbents did not exhibit better performance under cyclic operation than those without Si dopant.

The present study deals with the design and development of novel calcium-oxide-based refractory sorbents synthesized by flame spray pyrolysis (FSP) for carbon dioxide capture. The FSP-derived sorbents inherently exhibit very large CO 2 uptake capacity in the present investigation. Sorbents derived from conventional wet chemistry, possessing identical composition, were synthesized and evaluated. A wide range of refractory dopants (Si, Ti, Cr, Co, Zr, and Ce) were employed, aiming at developing sorbents with good mechanical strength. Among all of the doped CaO sorbents, Zr-doped CaO was found to exhibit the best CO 2 -capture performance under identical conditions of operation. To study the effect of Zr in depth and find out the optimal concentration of Zr needed in the CaO matrix, a series of Zr-incorporated CaO sorbents were synthesized by varying the relative composition of Zr in the CaO base matrix. The present studies suggest that Zr/Ca in the 3:10 atomic ratio results in the formation of the most robust nanosorbent for multicyclic operation. This sorbent retained, unchanged, its ability to capture CO 2 during extended cycles. It also demonstrated excellent stability under operating in the presence of water vapor (10 vol %). The present paper represents two novel developments in the field of CO 2 capture, first, the superiority of FSP process and, second, the role of ZrO 2 dopant in improving the durability and robustness of the CaO-based sorbent.

Processed dsRNAs can act directly to mediate RNAi, with the antisense strand determining mRNA target specificity. The involvement of 21-23 nt RNAs is supported by the kinetics of the processing reaction and the observed size dependence. RNAi depends on a limiting factor, possibly the nuclease that generates the 21-23 mer species. The active moiety appears to contain both sense and antisense RNA strands.

A series of CaO-based sorbents were synthesized from various organometallic precursors, namely, calcium propionate, calcium acetate, calcium acetylacetonate, calcium oxalate, and calcium 2-ethylhexanoate, by a simple calcination technique. In general, the five organometallic precursors (OMPs) exhibit a three-step weight loss regime in their respective thermogravimetic (TG) profiles. The first weight loss occurs because of dehydration in the temperature range of 50−200 °C. The second one results from decomposition leading to the formation of calcium carbonate in the temperature range of 450−550 °C. The calcium carbonate so formed then undergoes decarboxylation at higher temperatures of 710−750 °C and results in the formation of calcium oxide. Among the various precursors evaluated, CaO-sorbents obtained from calcium propionate and calcium acetate precursors were found to exhibit the highest CO2 capture capacity. The observed results were correlated with the intrinsic properties of the precursors by means of various techniques like thermogravimetric analysis (TGA), pore-size distribution (PSD), and differential scanning calorimetry (DSC). It was found that these two sorbents possessed higher surface area and larger pore volume compared to other sorbents prepared in this work. Thermal decomposition of these two OMPs resulted in the maximum evolution of heat, which could eventually lead to the generation of larger macropores, thus explaining the resultant CO2-uptake capacity we observed. Interestingly, the CO2 capture capacity of the sorbents was found to be directly proportional to the porosity per unit surface area. In summary, we were successful in correlating the intrinsic properties of an OMP to the eventual CO2 capture capacity of the sorbent. From the present investigation, it seems that the amount of heat evolved during the course of decomposition plays a direct role in the resultant porosity and thereby regulates the eventual CO2 capture capacity.

There is an urgent need to understand sorbent tolerance for capturing carbon dioxide (CO2) in the presence of sulfur dioxide (SO2). Sulfur oxide is emitted together with CO2 from various combustion systems and can cause severe air pollution. In this study, the behavior of different dopants on the performance of calcium oxide (CaO) sorbent for capturing CO2 in the presence of SO2 was investigated. Three main sets of experiments were carried out to study carbonation and sulfation both separately and simultaneously using a thermogravimetric analyzer (TGA). The results show that SO2 reduced the capability of the sorbents for capturing CO2 because of the competition between carbonation and sulfation reactions. Formation of calcium carbonate (CaCO3) and calcium sulfate (CaSO4) took place upon carbonation and sulfation, respectively. Our TGA and X-ray photoelectron spectroscopy (XPS) results indicate that the carbonation is totally reversible, while this is not the case with the sulfation. The permanent residual weight gained by the sorbents during the course of sulfation is attributed to the irreversible formation of sulfate species, which is confirmed by both the TGA and XPS results. The Ce promoted CaO sorbent exhibits the best performance for CO2 capture and is the most SO2 tolerant sorbent. On the other hand, the Mn doped dopant has the strongest affinity for SO2.

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For Drosophila melanogaster flies, sexual fate is determined by the X chromosome number. The basic helix-loop-helix protein product of the X-linked sisterlessB (sisB or scute) gene is a key indicator of the X dose and functions to activate the switch gene Sex-lethal (Sxl) in female (XX), but not in male (XY), embryos. Zygotically expressed sisB and maternal daughterless (da) proteins are known to form heterodimers that bind E-box sites and activate transcription. We examined SISB-Da binding at Sxl by using footprinting and gel mobility shift assays and found that SISB-Da binds numerous clustered sites in the establishment promoter Sxl Pe . Surprisingly, most SISB-Da sites at Sxl Pe differ from the canonical CANNTG E-box motif. These noncanonical sites have 6-bp CA(G/C)CCG and 7-bp CA(G/C)CTTG cores and exhibit a range of binding affinities. We show that the noncanonical sites can mediate SISB-Da-activated transcription in cell culture. P-element transformation experiments show that these noncanonical sites are essential for Sxl Pe activity in embryos. Together with previous deletion analysis, the data suggest that the number, affinity, and position of SISB-Da sites may all be important for the operation of the Sxl Pe switch. Comparisons with other dose-sensitive promoters suggest that threshold responses to diverse biological signals have common molecular mechanisms, with important variations tailored to suit particular functional requirements.Cell fate determinations often depend on the ability to recognize and respond to subtle differences in the concentrations of regulatory proteins. The quantitative nature of the problem is particularly clear in Drosophila melanogaster sex determination, for which a twofold difference in the collective concentration of four X-linked gene products ultimately signals sexual fate. Central to the sex determination mechanism are several proteins of the basic helix-loop-helix (bHLH) family. bHLH proteins play important roles in a variety of cellular process, including cell proliferation, blood and muscle development, and neurogenesis (37, 39). These proteins share a bipartite DNA binding and dimerization motif, which consists of a basic ␣-helix that mediates sequence-specific binding to the consensus E-box sequence CANNTG, and two amphipathic ␣-helices, which are separated by a loop of variable length, controlling protein dimerization. Although DNA binding by homodimers is not uncommon, most bHLH proteins appear to function as heterodimers. Based on their evolutionary, structural, and DNA-binding characteristics, most bHLH proteins can be grouped into two classes (1, 2). Class A bHLH proteins, including the MyoD family, E12/E47, and the achaete-scuterelated proteins, favor E-box sites containing a central GC pair (CAGCTG), while class B proteins, including Myc, Max, and the Hairy-related proteins, prefer E boxes with a central CG pair (CACGTG) (5,6,16,40).In Drosophila, the class A bHLH protein encoded by the X-linked sisterlessB gene (sisB, also called scute or T4) participates i...

In Drosophila, XX embryos are fated to develop as females, and XY embryos as males, because the diplo-X dose of four X-linked signal element genes, XSEs, activates the Sex-lethal establishment promoter, SxlPe, whereas the haplo-X XSE dose leaves SxlPe off. The threshold response of SxlPe to XSE concentrations depends in part on the bHLH repressor, Deadpan, present in equal amounts in XX and XY embryos. We identified canonical and non-canonical DNA-binding sites for Dpn at SxlPe and found that cis-acting mutations in the Dpn-binding sites caused stronger and earlier Sxl expression than did deletion of dpn implicating other bHLH repressors in Sxl regulation. Maternal Hey encodes one such bHLH regulator but the E(spl) locus does not. Elimination of the maternal corepressor Groucho also caused strong ectopic Sxl expression in XY, and premature Sxl activation in XX embryos, but Sxl was still expressed differently in the sexes. Our findings suggest that Groucho and associated maternal and zygotic bHLH repressors define the threshold XSE concentrations needed to activate SxlPe and that they participate directly in sex signal amplification. We present a model in which the XSE signal is amplified by a feedback mechanism that interferes with Gro-mediated repression in XX, but not XY embryos.