Density function theory is used to study the H2S adsorption on the surface of pristine, Al-, P- and Al&P- doped (4, 4) armchair and (8, 0) zigzag BNNTs. All considered different models for H2S adsorption on the exterior and interior surface of nanotube are optimized by using B3LYP/6-31G (d, P) level of theory. The adsorption energy values (Eads) of the B-I, B-II,C-I, D-I, D-II, F-I, F-II and H-II models are negative, while the Eads values for the A-III, B-III, C-III, D-III, E-III, F-III, G-III and H-III models are positive. On the other hand, Al, P and Al&P doped in all models increase significantly the adsorption energy of H2S on the surface of BNNTs, and so the selectivity of nanotube for adsorbing and making a sensor of H2S increase significantly from original state. The positive values of the charge transfer parameters (ΔN) and more values of the electronic chemical potentials of H2S gas for all studied models demonstrate that H2S gas in this system has a donor electron effect on the nanotube. The MEP results display that a low charge transfer occurs from H2S gas toward nanotube, resulting in a weak ionic bonding in the BNNTs’ surface. 相似文献
In Parts I & II of this Series, we illustrated the process research studies on a new, trendsetting indirect syngas conversion process, the direct, one-step LPDMEtm process, which is now a shining example of “dual catalysis” or “cooperative/adaptive” catalysis and also of thermodynamic/kinetic coupling in series-parallel reactions.
In this part III, we take a look at several processes on the research and pilot scale that employ methanol and DME as chemical feedstocks for further conversion to value-added chemicals. A most rational and cogent argument for the use of DME as a feedstock is that the unit production cost of DME from the direct, one-step DME processes, most notably the LPDMEtm process, can be lower than methanol (from LPMeOHtm), on a methanol-equivalent basis. DME also has inherently more benign physical and chemical properties, contains 1 less mole of water, and results in a substantially similar product distribution, as methanol, for the methanol-to-gasoline (MTG) and methanol-to-olefins (MTO) process. DME can also be converted to several other important chemicals; some of these include dimethoxymethane, dimethoxyethane, methylal, formaldehyde, acetic acid, methyl acetate, and polyoxymethylene ethers. In this report, we offer a critical assessment of the current status of these processes and a projected path to commercialization. Considering the trendsetting and impactful nature of DME as a chemical entity and as a chemical feedstock, along with its “free” cost, we are of the opinion that the future of DME, and of its chemical conversions, as so-called “DME economy”, is very bright. 相似文献
ABSTRACT In this study, hydrogen sulfide interaction with pristine, B-, N-, and B&N atom-doped beryllium oxide nanotube (BeONTs) is investigated by the density functional theory (DFT) method. At the first step, we considered different configuration models for the adsorption of H2S on the surface of nanotube and then we selected 12 stable models for this study. The structures of all selected models are optimized and the quantum properties, thermodynamic parameters, natural bond orbitals (NBO), reduced density gradient (RDG), molecular electrostatic potential (MEP), and atom in molecule (AIM) parameters are calculated at the cam–B3LYP level of theory with 6–31G (d) base set. The obtained Eads for the exterior surface of nanotube is exothermic and is in the range –3.15 to –28.34?Kcal mol–1, and that for the interior surface is endothermic and is in the range 19.17 to 27.17?kcal mol–1. The gap energy for pure, B-doped, N-doped, and B&N-doped BeONTs is 10.11, 10.03 (α spin), 10.13 (α spin), and 9.35?eV, respectively. The results of thermodynamic parameters, such as ΔG and ΔH values for the adsorption of H2S, on the surface of B-doped BeONTs are more negative than other models and favorable in thermodynamic approach. The NBO, MEP, NMR, and HOMO–LUMO results confirm that the electron charge transfer occurs from H2S molecule toward BeONTs, as a result the bonding type of H2S?…?BeONTs is weak ionic. 相似文献
A 43,481 bp fragment from the left arm of chromosome XIV of Saccharomyces cerevisiae was sequenced. A gene for tRNAphe and 23 non-overlapping open reading frames (ORFs) were identified, seven of which correspond to known yeast genes: MFA2, MEP2, CAP/SRV2, NAM9, FKB1/FPR1/RBP1, MOM22 and CPT1. One ORF may correspond to the yet unindentified yeast adenosine deaminase gene. Among the 15 other ORFs, four exhibit known signatures, which include a protein tyrosine phosphatase, a cytoskeleton-associated protein and two ATP-binding proteins, four have similarities with putative proteins of yeast or proteins from other organisms and seven exibit no significant similarity with amino acid sequences described in data banks. One ORF is identical to yeast expressed sequence tags (EST) and therefore corresponds to an expressed gene. Six ORFs present similarities to human dbESTs, thus identifying motifs conserved during evolution. Nine ORFs are putative transmembrane proteins. In addition, one overlapping and three antisense ORFs, which are not likely to be functional, were detected. The sequence has been deposited in the EMBL data bank under Accession Number Z46843. 相似文献
IspH, also called LytB, a protein involved in the biosynthesis of isoprenoids through the methylerythritol phosphate pathway, is an attractive target for the development of new antimicrobial drugs. Here, we report crystal structures of Escherichia coli IspH in complex with the two most potent inhibitors: (E)-4-mercapto-3-methylbut-2-en-1-yl diphosphate (TMBPP) and (E)-4-amino-3-methylbut-2-en-1-yl diphosphate (AMBPP) at 1.95 and 1.7 Å resolution, respectively. The structure of the E. coli IspH:TMBPP complex exhibited two conformers of the inhibitor. This unexpected feature was exploited to design and evolve new antimicrobial candidates in silico. 相似文献