Search

Metastable binding sites (MBS) have been observed in a multitude of molecular dynamics simulations and can be considered low affinity allosteric binding sites (ABS) that function as stepping stones as the ligand moves toward the orthosteric binding site (OBS). Herein, we show that MBS can be utilized as ABS in ligand design, resulting in ligands with improved binding kinetics. Four homobivalent bitopic ligands ( 1 - 4 ) were designed by molecular docking of ( S )-alprenolol (( S )-ALP) in the cocrystal structure of the β 2 adrenergic receptor (β 2 AR) bound to the antagonist ALP. Ligand 4 displayed a potency and affinity similar to ( S )-ALP, but with a >4-fold increase in residence time. The proposed binding mode was confirmed by X-ray crystallography of ligand 4 in complex with the β 2 AR. This ligand design principle can find applications beyond the β 2 AR and G protein-coupled receptors (GPCRs) as a general approach for improving the pharmacological profile of orthosteric ligands by targeting the OBS and an MBS simultaneously.

Synergistic control of nitrogen oxides (NO x ) and nitrogen-containing volatile organic compounds (NVOCs) from industrial furnaces is necessary. Generally, the elimination of n -butylamine ( n -B), a typical pollutant of NVOCs, requires a catalyst with sufficient redox ability. This process induces the production of nitrogen-containing byproducts (NO, NO 2 , N 2 O), leading to lower N 2 selectivity of NH 3 selective catalytic reduction of NO x (NH 3 -SCR). Here, synergistic catalytic removal of NO x and n -B via spatially separated cooperative sites was originally demonstrated. Specifically, titania nanotubes supported CuO x -CeO 2 (CuCe-TiO 2 NTs) catalysts with spatially separated cooperative sites were creatively developed, which showed a broader active temperature window from 180 to 340 °C, with over 90% NO x conversion, 85% n -B conversion, and 90% N 2 selectivity. A synergistic effect of the Cu and Ce sites was found. The catalytic oxidation of n -B mainly occurred at the Cu sites inside the tube, which ensured the regular occurrence of the NH 3 -SCR reaction on the outer Ce sites under the matching temperature window. In addition, the n -B oxidation would produce abundant intermediate NH 2 *, which could act as an extra reductant to promote NH 3 -SCR. Meanwhile, NH 3 -SCR could simultaneously remove the possible NO x byproducts of n -B decomposition. This novel strategy of constructing cooperative sites provides a distinct pathway for promoting the synergistic removal of n -B and NO x .

NO x and CH 3 SH as two typical air pollutants widely coexist in various energy and industrial processes; hence, it is urgent to develop highly efficient catalysts to synergistically eliminate NO x and CH 3 SH. However, the catalytic system for synergistically eliminating NO x and CH 3 SH is seldom investigated to date. Meanwhile, the deactivation effects of CH 3 SH on catalysts and the formation mechanism of toxic byproducts emitted from the synergistic catalytic elimination reaction are still vague. Herein, selective synergistic catalytic elimination (SSCE) of NO x and CH 3 SH via engineering deep oxidation sites over Cu-modified Nb-Fe composite oxides supported on TiO 2 catalyst against toxic CO and HCN byproducts formation has been originally demonstrated. Various spectroscopic and microscopic characterizations demonstrate that the sufficient chemisorbed oxygen species induced by the persistent electron transfer from Nb-Fe composite oxides to copper oxides can deeply oxidize HCOOH to CO 2 for avoiding highly toxic byproducts formation. This work is of significance in designing superior catalysts employed in more complex working conditions and sheds light on the progress in the SSCE of NO x and sulfur-containing volatile organic compounds.

Catalyst deactivation caused by alkali metal poisoning has long been a key bottleneck in the application of selective catalytic reduction of NO x with NH 3 (NH 3 -SCR), limiting the service life of the catalyst and increasing the cost of environmental protection. Despite great efforts, continuous accumulation of alkali metal deposition makes the resistance capacity of 2 wt % K 2 O difficult to enhance via merely loading acid sites on the surface, resulting in rapid deactivation and frequent replacement of the NH 3 -SCR catalyst. To further improve the resistance of alkali metals, encapsulating alkali metals into the bulk phase could be a promising strategy. The bottleneck of 2 wt % K 2 O tolerance has been solved by virtue of ultrahigh potassium storage capacity in the amorphous FePO 4 bulk phase. Amorphous FePO 4 as a support of the NH 3 -SCR catalyst exhibited a self-adaptive alkali-tolerance mechanism, where potassium ions spontaneously migrated into the bulk phase of amorphous FePO 4 and were anchored by PO 4 3- with the generation of Fe 2 O 3 at the NH 3 -SCR reaction temperature. This ingenious potassium storage mechanism could boost the K 2 O resistance capacity to 6 wt % while maintaining approximately 81% NO x conversion. Besides, amorphous FePO 4 also exhibited excellent resistance to individual and coexistence of alkali (K 2 O and Na 2 O), alkali earth (CaO), and heavy metals (PbO and CdO), providing long durability for CePO 4 /FePO 4 catalysts in flue gas with multipollutants. The cheap and accessible amorphous FePO 4 paves the way for the development and implementation of poisoning-resistant NO x abatement.

Using adenine and metal ions to form secondary building units (SBUs), further connected by a highly symmetrical multicarboxylic linker to construct an amino-modified porous framework with high porosity, is an effective strategy. By regulating the deprotonation and hydrolysis capacity of the synthesized solvent, it is possible to obtain different charged frameworks. In this work, two stable anionic/neutral MOFs, (Et 2 NH 2 )[Zn 3 (TCPE)(adenine) 2 CH 3 COO]·DEF·3H 2 O ( 1 ) and [Zn 3.5 (adenine)(TCPE) 1.5 (DMA)(H 2 O) 0.5 ]·2DMA·2H 2 O ( 2 ), have been synthesized based on zinc-adeninate building units and symmetric tetrakis(4-carboxyphenyl)ethylene (H 4 TCPE) in N , N -diethylformamide (DEF) and N , N -dimethylacetamide (DMA) reaction systems, respectively. 1 is an anionic framework based on 1D rod zinc-adeninate SBU, containing 1D rectangular (14.3 × 6.3 Å 2 ) and square (14.3 × 14.3 Å 2 ) channels. While 2 is a neutral framework built from isolated zinc-adeninate SBU, it contains hexagonal cages with a dimension of 5.5 Å in the structure. Both of them have high porosity (61.6% for 1 and 46.3% for 2 ) and high stability in a wide range of pH. 1 and 2 show high C 2 H 2 adsorption capacity at 298 K (48.1 and 70.1 cm 3 g -1 , respectively) and selective capacity for C 2 H 2 /CO 2 mixtures, which was confirmed by the breakthrough experiments. Furthermore, the interaction between the frameworks and gas molecules has also been explained by theoretical calculation. This work provides a good example of the design and regulation of porous structures for adsorption and separation functions.

Mn-based catalysts are promising for selective catalytic reduction (SCR) of NO x with NH 3 at low temperatures due to their excellent redox capacity. However, the N 2 selectivity of Mn-based catalysts is an urgent problem for practical application owing to excessive oxidizability. To solve this issue, we report a Mn-based catalyst using amorphous ZrTiO x as the support (Mn/ZrTi-A) with both excellent low-temperature NO x conversion and N 2 selectivity. It is found that the amorphous structure of ZrTiO x modulates the metal-support interaction for anchoring the highly dispersed active MnO x species and constructs a uniquely bridged Mn 3+ bonded with the support through oxygen linked to Ti 4+ and Zr 4+ , respectively, which regulates the optimal oxidizability of the MnO x species. As a result, Mn/ZrTi-A is not conducive to the formation of ammonium nitrate that readily decomposes to N 2 O, thus further increasing N 2 selectivity. This work investigates the role of an amorphous support in promoting the N 2 selectivity of a manganese-based catalyst and sheds light on the design of efficient low-temperature deNO x catalysts.

Selective catalytic reduction (SCR) of NO x from the flue gas is still a grand challenge due to the easy deactivation of catalysts. The copoisoning mechanisms and multipoisoning-resistant strategies for SCR catalysts in the coexistence of heavy metals and phosphorus are barely explored. Herein, we unexpectedly found unique compensation effects of heavy metals and phosphorus copoisoning over NO x reduction catalysts and the introduction of heavy metals results in a dramatic recovery of NO x reduction activity for the P-poisoned CeO 2 /TiO 2 catalysts. P preferentially combines with Ce as a phosphate species to reduce the redox capacity and inhibit NO adsorption. Heavy metals preferentially reduced the Brønsted acid sites of the catalyst and inhibited NH 3 adsorption. It has been demonstrated that heavy metal phosphate species generated over the copoisoned catalyst, which boosted the activation of NH 3 and NO, subsequently bringing about more active nitrate species to relieve the severe impact by phosphorus and maintain the NO x reduction over CeO 2 /TiO 2 catalysts. The heavy metals and P copoisoned catalysts also possessed more acidic sites, redox sites, and surface adsorbed oxygen species, which thus contributed to the highly efficient NO x reduction. This work elaborates the unique compensation effects of heavy metals and phosphorus copoisoning over CeO 2 /TiO 2 catalysts for NO x reduction and provides a perspective for further designing multipoisoning-resistant CeO 2 -based catalysts to efficiently control NO x emissions in stationary sources.

SO 2 -resistant selective catalytic reduction (SCR) of NO x remains a grand challenge for eliminating NO x generated from stationary combustion processes. Herein, SO 2 -resistant NO x reduction has been boosted by modulating electronic interaction of short-range Fe-O coordination over Fe 2 O 3 /TiO 2 catalysts. We report a remarkable SO 2 -tolerant Fe 2 O 3 /TiO 2 catalyst using sulfur-doped TiO 2 as the support. Via an array of spectroscopic and microscopic characterizations and DFT theoretical calculations, the active form of the dopant is demonstrated as SO 4 2- residing at subsurface TiO 6 locations. Sulfur doping exerts strong electronic perturbation to TiO 2 , causing a net charge transfer from Fe 2 O 3 to TiO 2 via increased short-range Fe-O coordination. This electronic effect simultaneously weakens charge transfer from Fe 2 O 3 to SO 2 and enhances that from NO/NH 3 to Fe 2 O 3 , resulting in a remarkable "killing two birds with one stone" scenario, that is, improving NO/NH 3 adsorption that benefits SCR reaction and inhibiting SO 2 poisoning that benefits catalyst long-term stability.

The catalyst deactivation caused by the coexistence of alkali and heavy metals remains an obstacle for selective catalytic reduction of NO x with NH 3 . Moreover, the copoisoning mechanism of alkali and heavy metals is still unclear. Herein, the copoisoning mechanism of K and Cd was revealed from the adsorption and variation of reaction intermediates at a molecular level through time-resolved in situ spectroscopy combined with theoretical calculations. The alkali metal K mainly decreased the adsorption of NH 3 on Lewis acid sites and altered the reaction more depending on the formation of the NH 4 NO 3 intermediate, which is highly related to NO x adsorption and activation. However, Cd further inhibited the generation of active nitrate intermediates and thus decreased the NO x abatement about 60% on potassium-poisoned CeTiO x catalysts. Physically mixing with acid additives for CeTiO x catalysts could significantly liberate the active Lewis acid sites from the occupation of alkali metals and relieve the high dependence on NO x adsorption and activation, thus recovering the NO x removal rate to the initial state. This work revealed the copoisoning mechanism of K and Cd on Ce-based de-NO x catalysts and developed a facile anti-poisoning strategy, which paves a way for the development of durable catalysts among alkali and heavy metal copoisoning resistant catalytic reduction of NO x .

Selective catalytic reduction (SCR) of NO x over V 2 O 5 -based oxide catalysts has been widely used, but it is still a challenge to efficiently reduce NO x at low temperatures under SO 2 and H 2 O co-existence. Herein, SO 2 - and H 2 O-tolerant catalytic reduction of NO x at a low temperature has been originally demonstrated via engineering polymeric VO x species by CeO 2 . The polymeric VO x species were tactfully engineered on Ce-V 2 O 5 composite active sites via the surface occupation effect of Ce, and the obtained catalysts exhibited remarkable low-temperature activity and strong SO 2 and H 2 O tolerance at 250 °C. The strong interaction between Ce and V species induced the electron transfer from V to Ce and tuned the SCR reaction via the E-R pathway between the NH 4 + /NH 3 species and gaseous NO. In the presence of SO 2 and H 2 O, the polymeric VO x species had not been hardly influenced, while the formation of sulfate species on Ce sites not only promoted the adsorption of NH 4 + species and the reaction between gaseous NO and NH 4 + but also facilitated the decomposition of ammonium bisulfate through weakening the strong bond between HSO 4 - and NH 4 + . This work provided a new strategy for SO 2 - and H 2 O-tolerant catalytic reduction of NO x at a low temperature.

The β 2 -adrenergic receptor (β 2 AR) is a G-protein-coupled receptor (GPCR) that responds to the hormone adrenaline and is an important drug target in the context of respiratory diseases, including asthma. β 2 AR function can be regulated by post-translational modifications such as phosphorylation and ubiquitination at the C-terminus, but access to the full-length β 2 AR with well-defined and homogeneous modification patterns critical for biochemical and biophysical studies remains challenging. Here, we report a practical synthesis of differentially modified, full-length β 2 AR based on a combined native chemical ligation (NCL) and sortase ligation strategy. An array of homogeneous samples of full-length β 2 ARs with distinct modification patterns, including a full-length β 2 AR bearing both monoubiquitination and octaphosphorylation modifications, were successfully prepared for the first time. Using these homogeneously modified full-length β 2 AR receptors, we found that different phosphorylation patterns mediate different interactions with β-arrestin1 as reflected in different agonist binding affinities. Our experiments also indicated that ubiquitination can further modulate interactions between β 2 AR and β-arrestin1. Access to full-length β 2 AR with well-defined and homogeneous modification patterns at the C-terminus opens a door to further in-depth mechanistic studies into the structure and dynamics of β 2 AR complexes with downstream transducer proteins, including G proteins, arrestins, and GPCR kinases.

Releasing the poisoning effect of alkali metals over catalysts is still an intractable issue for selective catalytic reduction (SCR) of NO x with ammonia. The presence of K in fly ash always dramatically suppressed catalytic activity by impairing acidity and redox properties, leading to severe reduction of lifetime for SCR catalysts. Herein, alkali-resistant NO x reduction over TiO 2 -supported Fe 2 (SO 4 ) 3 catalysts was originally demonstrated via naturally coupling active and poisoning sites. Notably, TiO 2 -supported Fe 2 (SO 4 ) 3 catalysts expressed admirable NO x conversion and K resistance within a quite broad temperature window of 200-500 °C. The catalysts with more conserved sulfate species revealed that sulfate groups preferred to migrate from the bulk phase to surface, thus effectively binding with K poisons to release the damage on iron active sites. Because of protection effects of migrated sulfates and closely coupling effects with Fe active sites, NH 3 and NO adsorption amounts and rates were well maintained. In this way, Fe metal sites and sulfate species closely coupled together on a self-preserved TiO 2 -supported Fe 2 (SO 4 ) 3 catalyst played essential roles as highly active sites and unique poisoning sites. This work paves a new way to design SCR catalysts with superior alkali resistance that are more reliable in practical deNO x application.

Energetic metal-organic frameworks (EMOFs) are very promising as heat-resistant explosives, affording both thermal stability and energy properties. In this work, the self-assembly of high-energy nitrogen-rich linkers with nontoxic alkali-metal lithium/sodium leads to four new solvent-free EMOFs. Because of unparalleled decomposition temperature ( T dec = 403 °C) and heats of detonation (3.475 kcal·g -1 ), a 3D Li(I)-EMOF can be considered to be a superheat-resistant explosive candidate.

It is challenging for selective catalytic reduction (SCR) of NO x by NH 3 due to the coexistence of heavy metal and SO 2 in the flue gas. A thorough probe into deactivation mechanisms is imperative but still lacking. This study unravels unexpected offset effects of Cd and SO 2 deactivation over CeO 2 -WO 3 /TiO 2 catalysts, potential candidates for commercial SCR catalysts. Cd- and SO 2 -copoisoned catalysts demonstrated higher activity for NO x reduction than a Cd-poisoned catalyst but lower than that for an SO 2 -poisoned catalyst. In comparison to SO 2 , Cd had more severe effects on acidic and redox properties, distinctly decreasing the SCR activity. After sulfation of Cd-poisoned catalysts, SO 4 2- preferentially bonded with the surface CdO and released CeO 2 active sites poisoned by CdO, thus reserving the highly active CeO 2 -WO 3 sites and maintaining a high activity. The sulfation of Cd-poisoned catalysts also provided more strong acidic sites, and the synergistic effects between the formed cerium sulfate and CeO 2 contributed to the high-temperature SCR performance. This work sheds light on the deactivation mechanism of heavy metals and SO 2 over CeO 2 -WO 3 /TiO 2 catalysts and provides an innovative pathway for inventing high-performance SCR catalysts, which have great resistance to heavy metals and SO 2 simultaneously. This will be favorable to academic and practical applications in the future.