UV Blocking by Mg–Zn–Al Layered Double Hydroxides for the Protection of Asphalt Road Surfaces

Mg_aZn_bAl_c–CO₃ layered double hydroxides (LDHs) with varying magnesium/zinc ratios have been synthesized by a method involving separate nucleation and aging steps. The resulting LDHs were analyzed by powder X-ray diffraction, laser particle size analysis, scanning electron microscopy, and diffuse reflectance UV spectroscopy. The results show that the UV blocking properties of Mg_aZn_bAl_c–CO₃–LDHs depend on both the proportion of zinc and the particle size distribution. The UV absorbing properties of Mg_aZn_bAl_c–CO₃–LDHs increase with the content of zinc, which can be ascribed to the decrease in the band gap energy, as has been observed experimentally and confirmed by density functional theory calculations. The UV screening properties of Zn₄Al₂–CO₃–LDHs were found to increase with increasing particle size, which can be explained by Mie scattering theory. Moreover, in accelerated UV light irradiation aging tests, LDH-modified asphalt samples showed excellent resistance to UV aging, with the efficacy of the LDH increasing with increasing zinc content

Selective Hydrogenation of Cinnamaldehyde over Co-Based Intermetallic Compounds Derived from Layered Double Hydroxides

Selective hydrogenation of unsaturated carbonyl compounds plays a key role in the production of fine chemicals and pharmaceutical agents. In this work, two kinds of intermetallic compounds (IMCs: CoIn3 and CoGa3) were prepared via structural topotactic transformation from layered double hydroxide (LDH) precursors, which exhibited surprisingly high catalytic activity and selectivity toward hydrogenation reaction of α,β-unsaturated aldehydes (CO vs CC). Notably, the CoGa3 catalyst shows a hydrogenation selectivity of 96% from cinnamaldehyde (CAL) to cinnamyl alcohol (COL), significantly higher than CoIn3 (80%) and monometallic Co catalyst (42%). A combination study including XANES, XPS, and CO-IR spectra verifies electron transfer from Ga (or In) to Co, leading to the formation of CoGa (or CoIn) coordination. FT-IR measurements and DFT calculation studies substantiate that the electropositive element (Ga or In) in IMCs serves as an active site and facilitates the adsorption of polarized CO, while CC adsorption on the Co site is extremely depressed, which is responsible for the markedly enhanced selectivity toward hydrogenation of CO. This work reveals the key role of functional group adsorption in determining the hydrogenation selectivity of α,β-unsaturated aldehydes, which gives an in-depth understanding on the structure–property correlation and reaction mechanism

Additional file 1 of Efficient bioproduction of 5-aminolevulinic acid, a promising biostimulant and nutrient, from renewable bioresources by engineered Corynebacterium glutamicum

Additional file 1: Figure S1. Plasmid pRpA1P4 used for hemA and ppc overexpression in strain CA1P4. Figure S2. By-product lactate and acetate of fed-batch fermentations using different carbon sources. Table S1. Primers used in this study. Table S2. RBSs used in this study

Conformational Switch of the 250s Loop Enables the Efficient Transglycosylation in GH Family 77

Amylomaltases (AMs) play important roles in glycogen and maltose metabolism. However, the molecular mechanism is elusive. Here, we investigated the conformational dynamics of the 250s loop and catalytic mechanism of Thermus aquaticus TaAM using path-metadynamics and QM/MM MD simulations. The results demonstrate that the transition of the 250s loop from an open to closed conformation promotes polysaccharide sliding, leading to the ideal positioning of the acid/base. Furthermore, the conformational dynamics can also modulate the selectivity of hydrolysis and transglycosylation. The closed conformation of the 250s loop enables the tight packing of the active site for transglycosylation, reducing the energy penalty and efficiently preventing the penetration of water into the active site. Conversely, the partially closed conformation for hydrolysis results in a loosely packed active site, destabilizing the transition state. These computational findings guide mutation experiments and enable the identification of mutants with an improved disproportionation/hydrolysis ratio. The present mechanism is in line with experimental data, highlighting the critical role of conformational dynamics in regulating the catalytic reactivity of GHs

Conformational Switch of the 250s Loop Enables the Efficient Transglycosylation in GH Family 77

Amylomaltases (AMs) play important roles in glycogen and maltose metabolism. However, the molecular mechanism is elusive. Here, we investigated the conformational dynamics of the 250s loop and catalytic mechanism of Thermus aquaticus TaAM using path-metadynamics and QM/MM MD simulations. The results demonstrate that the transition of the 250s loop from an open to closed conformation promotes polysaccharide sliding, leading to the ideal positioning of the acid/base. Furthermore, the conformational dynamics can also modulate the selectivity of hydrolysis and transglycosylation. The closed conformation of the 250s loop enables the tight packing of the active site for transglycosylation, reducing the energy penalty and efficiently preventing the penetration of water into the active site. Conversely, the partially closed conformation for hydrolysis results in a loosely packed active site, destabilizing the transition state. These computational findings guide mutation experiments and enable the identification of mutants with an improved disproportionation/hydrolysis ratio. The present mechanism is in line with experimental data, highlighting the critical role of conformational dynamics in regulating the catalytic reactivity of GHs

Conformational Switch of the 250s Loop Enables the Efficient Transglycosylation in GH Family 77

Amylomaltases (AMs) play important roles in glycogen and maltose metabolism. However, the molecular mechanism is elusive. Here, we investigated the conformational dynamics of the 250s loop and catalytic mechanism of Thermus aquaticus TaAM using path-metadynamics and QM/MM MD simulations. The results demonstrate that the transition of the 250s loop from an open to closed conformation promotes polysaccharide sliding, leading to the ideal positioning of the acid/base. Furthermore, the conformational dynamics can also modulate the selectivity of hydrolysis and transglycosylation. The closed conformation of the 250s loop enables the tight packing of the active site for transglycosylation, reducing the energy penalty and efficiently preventing the penetration of water into the active site. Conversely, the partially closed conformation for hydrolysis results in a loosely packed active site, destabilizing the transition state. These computational findings guide mutation experiments and enable the identification of mutants with an improved disproportionation/hydrolysis ratio. The present mechanism is in line with experimental data, highlighting the critical role of conformational dynamics in regulating the catalytic reactivity of GHs

Conformational Switch of the 250s Loop Enables the Efficient Transglycosylation in GH Family 77

Amylomaltases (AMs) play important roles in glycogen and maltose metabolism. However, the molecular mechanism is elusive. Here, we investigated the conformational dynamics of the 250s loop and catalytic mechanism of Thermus aquaticus TaAM using path-metadynamics and QM/MM MD simulations. The results demonstrate that the transition of the 250s loop from an open to closed conformation promotes polysaccharide sliding, leading to the ideal positioning of the acid/base. Furthermore, the conformational dynamics can also modulate the selectivity of hydrolysis and transglycosylation. The closed conformation of the 250s loop enables the tight packing of the active site for transglycosylation, reducing the energy penalty and efficiently preventing the penetration of water into the active site. Conversely, the partially closed conformation for hydrolysis results in a loosely packed active site, destabilizing the transition state. These computational findings guide mutation experiments and enable the identification of mutants with an improved disproportionation/hydrolysis ratio. The present mechanism is in line with experimental data, highlighting the critical role of conformational dynamics in regulating the catalytic reactivity of GHs

Insights into Interfacial Synergistic Catalysis over Ni@TiO_2–<i>x</i> Catalyst toward Water–Gas Shift Reaction

The mechanism on interfacial synergistic catalysis for supported metal catalysts has long been explored and investigated in several important heterogeneous catalytic processes (e.g., water–gas shift (WGS) reaction). The modulation of metal–support interactions imposes a substantial influence on activity and selectivity of catalytic reaction, as a result of the geometric/electronic structure of interfacial sites. Although great efforts have validated the key role of interfacial sites in WGS over metal catalysts supported on reducible oxides, direct evidence at the atomic level is lacking and the mechanism of interfacial synergistic catalysis is still ambiguous. Herein, Ni nanoparticles supported on TiO_2–<i>x</i> (denoted as Ni@TiO_2–<i>x</i>) were fabricated via a structure topotactic transformation of NiTi-layered double hydroxide (NiTi-LDHs) precursor, which showed excellent catalytic performance for WGS reaction. <i>In situ</i> microscopy was carried out to reveal the partially encapsulated structure of Ni@TiO_2–<i>x</i> catalyst. A combination study including <i>in situ</i> and <i>operando</i> EXAFS, <i>in situ</i> DRIFTS spectra combined with TPSR measurements substantiates a new redox mechanism based on interfacial synergistic catalysis. Notably, interfacial Ni species (electron-enriched Ni^δ− site) participates in the dissociation of H₂O molecule to generate H₂, accompanied by the oxidation of Ni^δ−–O_<i>v</i>–Ti³⁺ (O_<i>v</i>: oxygen vacancy) to Ni^δ+–O–Ti⁴⁺ structure. Density functional theory calculations further verify that the interfacial sites of Ni@TiO_2–<i>x</i> catalyst serve as the optimal active site with the lowest activation energy barrier (∼0.35 eV) for water dissociation. This work provides a fundamental understanding on interfacial synergistic catalysis toward WGS reaction, which is constructive for the rational design and fabrication of high activity heterogeneous catalysts