Electronic Structure Determines Geometry: Bond Length Alternating in Cyclo[2n]carbons.

Structure determines the properties. However, whether electronic structure determines geometry or geometry determines electronic structure seems a philosophical question in a chicken and egg situation, which remains unclear. In this work, by applying density functional theory (DFT) and DMRG(4n,4n)-CASSCF methods, theoretical investigation suggested that the dual antiaromaticity in cyclo[2n]carbons with even n should be attributed to the electron correlation effect, instead of decreased geometric symmetry, which actually exists in all cyclo[2n]carbon molecules and does not point out the essence. Such dual antiaromaticity can be conceptualized as electron correlation-stabilized dual antiaromaticity. Results also showed that DFT is reliable for cyclocarbons larger than C14, but we should be careful when applying it to smaller ones. DFT failed to give the correct structure of C6 compared with density matrix renormalization group results.

Enantioselective Ni-Catalyzed 1,2-Borylalkynylation of Unactivated Alkenes.

Enantioselective three-component difunctionalization of alkenes with boron reagents represents an attractive strategy for assembling three-dimensional chiral organoboron compounds. However, regio- and enantiocontrol comprise the pivot challenges in these transformations, which predominantly require the use of activated conjugated alkenes. Herein, by utilizing various carbonyl directing groups, including amides, sulfinamides, ketones, and esters, we succeed in realizing a nickel-catalyzed 1,2-borylalkynylation of unactivated alkenes to enable the simultaneous incorporation of a boron entity and an sp-fragment across the double bond. The products contain boryl, alkynyl, and carbonyl functional groups with orthogonal synthetic reactivities, offering three handles for further derivatization to access valuable intermediates. The utility of this ligand-enabled asymmetric protocol has been highlighted through the late-stage decoration of drug-relevant molecules.

Effect of Modified Cow Dung Fibers on Strength and Autogenous Shrinkage of Alkali-Activated Slag Mortar.

Alkali-activated slag (AAS) presents a promising alternative to ordinary Portland cement due to its cost effectiveness, environmental friendliness, and satisfactory durability characteristics. In this paper, cow dung waste was recycled as a renewable natural cellulose fiber, modified with alkali, and then added to AAS mortar. The physico-chemical characteristics of raw and modified cow dung fibers were determined through Fourier transform infrared (FTIR), X-ray diffraction (XRD), and Scanning electron microscope (SEM). Investigations were conducted on the dispersion of cow dung fibers in the AAS matrix, as well as the flowability, strength, and autogenous shrinkage of AAS mortar with varying cow dung fiber contents. The results indicated that modified fiber has higher crystallinity and surface roughness. The ultrasonic method showed superior effectiveness compared to pre-mixing and after-mixing methods. Compared with raw cow dung fibers, modified fibers led to an increase of 11.3% and 36.3% of the 28 d flexural strength and compressive strength of the AAS mortar, respectively. The modified cow dung fibers had a more significant inhibition on autogenous shrinkage, and the addition of 2 wt% cow dung fibers reduced the 7 d autogenous shrinkage of the AAS paste by 52.8% due to the "internal curing effect." This study provides an alternative value-added recycling option for cow dung fibers as a potential environmentally friendly and sustainable reinforcing raw material for cementitious materials, which can be used to develop low autogenous shrinkage green composites.

Nickel/Photoredox Dual-Catalyzed Regiodivergent Aminoalkylation of Unactivated Alkyl Halides.

A mild and regiodivergent aminoalkylation of unactivated alkyl halides is disclosed via a dual photoredox/nickel catalysis. Bipyridyl-type ligands without an ortho-substituent control the site-selective coupling at the original position, while ortho-disubstituted ligands tune the site-selectivity at a remote, unprefunctionalized position. Mechanistic studies combined with DFT calculations give insight into the mechanism and the origins of the ligand-controlled regioselectivity. Notably, this redox-neutral, regiodivergent alkyl-alkyl coupling features mild conditions, broad substrate scope for both alkyl coupling partners, and excellent site-selectivity and offers a straightforward way for α-alkylation of tertiary amines to synthesize structurally diverse alkylamines and value-added amino acid derivatives.

Unraveling the Pivotal Roles of Various Metal Ion Centers in the Catalysis of Quercetin 2,4-Dioxygenases.

Quercetin 2,4-dioxygenase (QueD) with various transition metal ion co-factors shows great differences, but the internal reasons have not been illustrated in detail. In order to explore the effects of metal ion centers on the catalytic reactivity of QueD, we calculated and compared the minimum energy crossing point (MECP) of dioxygen from the relatively stable triplet state to the active singlet state under different conditions by using the DFT method. It was found that the metal ions play a more important role in the activation of dioxygen compared with the substrate and the protein environment. Simultaneously, the catalytic reactions of the bacterial QueDs containing six different transition metal ions were studied by the QM/MM approach, and we finally obtained the reactivity sequence of metal ions, Ni2+ > Co2+ > Zn2+ > Mn2+ > Fe2+ > Cu2+, which is basically consistent with the previous experimental results. Our calculation results indicate that metal ions act as Lewis acids in the reaction to stabilize the substrate anion and the subsequent superoxo and peroxo species in the reaction, and promote the proton coupled electron transfer (PCET) process. Furthermore, the coordination tendencies of transition metal ion centers also have important effects on the catalytic cycle. These findings have general implications on metalloenzymes, which can expand our understanding on how various metal ions play their key role in modulating catalytic reactivity.

NOx degradation ability of S-g-C3N4/MgAl-CLDH nanocomposite and its potential application in cement-based materials.

In this study a new photocatalytic nanocomposite, S-g-C3N4/MgAl-CLDH, was synthesized and implemented into cement mortar by internal mixing or coating. The photocatalytic NOx degradation efficiency of the S-g-C3N4/MgAl-CLDH and photocatalytic mortar was investigated. The NOx degradation efficiency and photoluminescence spectra of S-g-C3N4/MgAl-CLDH after being immersed in the simulated concrete pore solution were evaluated to assess its chemical stability. The results show that compared with S-g-C3N4, the S-g-C3N4/MgAl-CLDH exhibits a narrower bandgap (2.45 eV), a lower photogenerated electron-hole pair recombination rate and a higher specific surface area (36.86 m2 g-1). After 21 min of visible light irradiation, the NOx degradation rate of S-g-C3N4/MgAl-CLDH achieves 100% as compared to merely 81.5% of S-g-C3N4. After being submerged in simulated concrete pore solution, the S-g-C3N4/MgAl-CLDH exhibits only a slight decrease of 5% in degradation rate after 12 min of irradiation, confirming a good compatibility and stability in cement-based materials. The NOx degradation ability of the internally mixed mortar is enhanced with an increase in the dosage of S-g-C3N4/MgAl-CLDH. For coated mortar, in contrast, a decline in NOx degradation rate is observed after 5 layers of coating owing to the lower porosity of mortar after excessive coating.

S-Scheme 2D/2D Heterojunction of ZnTiO3 Nanosheets/Bi2WO6 Nanosheets with Enhanced Photoelectrocatalytic Activity for Phenol Wastewater under Visible Light.

The pollution of phenol wastewater is becoming worse. In this paper, a 2D/2D nanosheet-like ZnTiO3/Bi2WO6 S-Scheme heterojunction was synthesized for the first time through a two-step calcination method and a hydrothermal method. In order to improve the separation efficiency of photogenerated carriers, the S-Scheme heterojunction charge-transfer path was designed and constructed, the photoelectrocatalytic effect of the applied electric field was utilized, and the photoelectric coupling catalytic degradation performance was greatly enhanced. When the applied voltage was +0.5 V, the ZnTiO3/Bi2WO6 molar ratio of 1.5:1 had highest degradation rate under visible light: the degradation rate was 93%, and the kinetic rate was 3.6 times higher than that of pure Bi2WO6. Moreover, the stability of the composite photoelectrocatalyst was excellent: the photoelectrocatalytic degradation rate of the photoelectrocatalyst remained above 90% after five cycles. In addition, through electrochemical analysis, XRD, XPS, TEM, radical trapping experiments, and valence band spectroscopy, we found that the S-scheme heterojunction was constructed between the two semiconductors, which effectively retained the redox ability of the two semiconductors. This provides new insights for the construction of a two-component direct S-scheme heterojunction as well as a feasible new solution for the treatment of phenol wastewater pollution.

A theoretical study of the ligand-controlled palladium-catalysed regiodivergent synthesis of dibenzosilepin derivatives.

Palladium-catalysed ligand-controlled 1,n-palladium migration of silicon-tethering substrates provides a regiodivergent synthesis strategy for constructing silicon-bridged π-conjugated compounds possessing a 6,6-fused or a 5,7-fused scaffold. Density functional theory (DFT) calculations were carried out to elucidate the detailed mechanism of this 1,n-palladium migration involving syn- or anti-carbopalladation. The computational results suggest that alkyne insertion is the regioselectivity-determining step. Upon catalysis without the BINAP ligand, the 1,2-insertion of an alkyne into the Pd-aryl bond leads to the formation of 6,6-fused benzophenanthrosiline, which is more favorable than the 2,1-insertion of alkyne by 4.2 kcal mol-1. The selective formation of 5,7-fused benzofluorenosilepins via the 2,1-alkyne insertion is facilitated by the BINAP ligand. The 1,2-alkyne insertion with the BINAP ligand is disfavoured due to the steric repulsion between the phenyl group of the substrate and the naphthalene group of the BINAP ligand. The 2,1-alkyne insertion with the BINAP ligand orients the ligand away from the phenyl group of the substrate, which can avoid steric repulsion.

Theoretical investigations on the interactions of glucokinase regulatory protein with fructose phosphates.

Glucokinase (GK) plays a critical role in maintaining glucose homeostasis in the human liver and pancreas. In the liver, the activity of GK is modulated by the glucokinase regulatory protein (GKRP) which functions as a competitive inhibitor of glucose to bind to GK. Moreover, the inhibitory intensity of GKRP-GK is suppressed by fructose 1-phosphate (F1P), and reinforced by fructose 6-phosphate (F6P). Here, we employed a series of computational techniques to explore the interactions of fructose phosphates with GKRP. Calculation results reveal that F1P and F6P can bind to the same active site of GKRP with different binding modes, and electrostatic interaction provides a major driving force for the ligand binding. The presence of fructose phosphate severely influences the motions of protein and the conformational space, and the structural change of sugar phosphate influences its interactions with GKRP, leading to a large conformational rearrangement of loop2 in the SIS2 domain. In particular, the binding of F6P to GKRP facilitates the protruding loop2 contacting with GK to form the stable GK-GKRP complex. The conserved residues 179-184 of GKRP play a major role in the binding of phosphate group and maintaining the stability of GKRP. These results may provide deep insight into the regulatory mechanism of GKRP to the activity of GK.