T1 Site Research Articles

Seeds Combining Pyrrolidine Control the Framework Al Distribution of FER Zeolite to Enhance Its Performance in the Skeletal Isomerization of n-Butene

FER zeolites have a unique framework structure and acid distribution, and are widely studied as a catalyst for reactions such as n-butene skeletal isomerization and dimethyl ether carbonylation. The Brönsted acid site (BAS) located in the 10-member ring (10-MR) of FER zeolites serves as the active site for the isomerization reaction of skeletal n-butene to produce isobutene. This study prepared five types of FER zeolites using different methods: using pyrrolidine (PY) alone as a template; using Na-form FER as seeds (SN) or H-form FER as seeds without organic structure directing agents (OSDAs); and combining the seeds of SN or SH with PY as OSDAs. The differences in the structure and acid distribution of the five zeolites were investigated, as well as their catalytic performance for the skeletal isomerization of n-butene. Experiments and characterization results showed that under hydrothermal synthesis conditions, the FER-PY+SH zeolites synthesized by using both H-form zeolites seeds and pyridine exhibited the highest aluminum concentrations at T1 and T3 sites, along with the greatest BAS located in the 10-MR. This unique composition contributed to the highest selectivity of isobutene. The FER-PY+SH catalyst was continuously used for 720 h at 350 °C, 0.1 MPa, and an n-butene mass space velocity of 2.0 h−1 for three cycles of 2160 h. During this period, the conversion of n-butene was over 39%, while the selectivity of isobutene exceeded 95%. The FER-PY+SH catalyst exhibited excellent stability and activity.

Al-Si Order and Chemical Composition Model across Scapolite Solid Solutions with Evidence from Rietveld Structure Refinements

Scapolite forms solid solutions between the end members marialite, Na4[Al3Si9O24]Cl = Me0, and meionite, Ca4[Al6Si6O24]CO3 = Me100. Al-Si order and chemical composition models are proposed for the scapolite solid solutions. These models predict the chemical composition, Al-Si order, and average <T–O> distances between Me0–Me100. These models are based on the observed order of clusters and on two solid solutions that meet at Me75 coupled with predicted chemical compositions and <T–O> distances. The [Na4·Cl]3+ and [NaCa3·CO3]5+ clusters are ordered between Me0–Me75, whereas the clusters [NaCa3·CO3]5+ and [Ca4·CO3]6+ are disordered from Me75–Me100. To confirm the structural model, the crystal structure of 27 scapolite samples between Me6–Me93 has been obtained using synchrotron high-resolution powder X-ray diffraction (HRPXRD) data and Rietveld structure refinements. The structure was refined in space group P42/n for all the samples. The <T–O> distances indicate that the T1 (=Si), T2 (=Al), and T3 (=Si) sites are completely ordered at Me37.5, where the 1:1 ratio of [Na4·Cl]3+:[NaCa3·CO3]5+ clusters are ordered and gives rise to antiphase domain boundaries (APBs) based on Cl-CO3 order instead of Al-Si order. The presence of APBs based on Cl-CO3 order and cluster order indicate that neither space group P42/n nor I4/m are correct for the structure of scapolite, but the lower symmetry space group P42/n is a good approximation for modeling the average structure of scapolite. The complete Al-Si order at Me37.5 changes in a regular and predictable manner toward the end members: Me0, Me75, and Me100. The observed unit cell and several structural parameters show a discontinuity at Me75, where the series is divided into two. There is no structural evidence to support any phase transition in the scapolite series. The T1 site contains only Si from Me0–Me37.5; from Me37.5–Me100, Al atoms enter the T1 site and the <T1–O> distance increases linearly to Me100.

Impact of surface-active ionic solutions on the structure and function of laccase from trametes versicolor: Insights from molecular dynamics simulations

Many protein-ionic liquid investigations have examined laccase interactions. Laccases are a class of poly-copper oxidoreductases that retain significant biotechnological relevance owing to their notable oxidative capabilities and their application in the elimination of synthetic dyes, phenolic compounds, insecticides, and various other substances. This study investigates the impact of surface active ionic liquids (SAILs), namely, decyltrimethylammonium bromide [N10111][Br] and 1-decyl-3-methylimidazolium chloride [C10mim][Cl] as cationic surfactant ionic liquids and cholinium decanoate [Chl][Dec], an anionic surfactant ionic liquid, on the structure and function of laccase from the fungus Trametes versicolor (TvL) by the molecular dynamics (MD) simulation method. In summary, this study showed that laccase solvent-accessible surface area increased in the ionic liquid [Chl][Dec] while it decreased in the other two ionic liquids. Interestingly, [Chl][Dec] ionic liquid components formed hydrogen bonds with laccase, while [N10111][Br] and [C10mim][Cl] components were unable to form hydrogen bonds with laccase. The quantity of hydrogen bonds formed between water molecules and the enzyme was also diminished in the presence of [Chl][Dec] in comparison to the other two ionic liquids. especially at a concentration of 250 mM. In 250 mM concentrations of [N10111][Br] and [C10mim][Cl], clusters of long-chain cations are likely to form near the copper T1 site. However, even at low [Chl][Dec] concentrations, long [Dec]- chains were observed to penetrate the enzyme near the copper T1 site, and at 250 mM [Chl][Dec], a large cluster of anions occupied the opening of the active site. The results of the analysis also show that the interaction between the [Dec]- anion and the enzyme is stronger than the interaction between [N10111]+ and [C10mim]+ with laccase; in addition, the [Dec]- anion, compared to [Br]- and [Cl]- has a much greater tendency to bind with the enzyme residues.

MOR-Type Titanosilicate with Specific Ti Location in Defective T3 Sites for Efficient Cyclohexanone Ammoximation

MOR-Type Titanosilicate with Specific Ti Location in Defective T3 Sites for Efficient Cyclohexanone Ammoximation

Solvent structure and dynamics over Brønsted acid MWW zeolite nanosheets

In the liquid phase of heterogeneous catalysis, solvent plays an important role and governs the kinetics and thermodynamics of a reaction. Although it is often difficult to quantify the role of the solvent, it becomes particularly challenging when a zeolite is used as the catalyst. This difficulty arises from the complex nature of the liquid/zeolite interface and the different solvation environments around catalytically active sites. Here, we use ab initio molecular dynamics simulations to probe the local solvation structure and dynamics of methanol and water over MWW zeolite nanosheets with varying Brønsted acidity. We find that the zeolite framework and the number and location of the acid sites in the zeolite influence the structure and dynamics of the solvent. In particular, methanol is more likely to be in the vicinity of the aluminum (Al3+) at the T4 site than at T1 due to easy accessibility. The methanol oxygen binds strongly to the Al at the T4 site, weakening the Al–O for the bridging acid site, which results in the formation of the silanol group, significantly reducing the acidity of the site. The behavior of methanol is in direct contrast to that of water, where protons can easily propagate from the zeolite to the solvent molecules regardless of the acid site location. Our work provides molecular-level insights into how solvent interacts with zeolite surfaces, leading to an improved understanding of the catalytic site in the MWW zeolite nanosheet.

A DFT study on Cu-ZSM-5 as a catalyst for NO decomposition: Possible activity of a Cu(I) pair located at the T3 tetrahedral sites

The decomposition of NO catalysed by Cu+ pairs coordinated at the Al-substituted T3 sites of the 10-membered rings of Cu-ZSM-5 was studied by means of DFT/ONIOM calculations. Three mechanisms for NO decomposition were defined on the active site, all based on the formation and further decomposition of an hyponitrite anion, which gives the N2O molecule and a [Cu‒O‒Cu]2+ bridge, where both copper ions are oxidized. N2O can react with the oxidized active site according to two different spin-allowed mechanisms which give immediately the products, N2 + O2. Otherwise, N2O reacts with a new reduced site according to a spin-forbidden mechanism which gives N2 and a second [Cu‒O‒Cu]2+ bridge. When the latter mechanism occurs, reduced sites are restored by further reaction of [Cu‒O‒Cu]2+ with NO and desorption of NO2, which is finally decomposed on a second [Cu‒O‒Cu]2+ site, giving O2 + NO. Turnover frequencies (TOFs) calculated by means of the Energetic Span model showed that one of the spin-allowed mechanisms should be relatively fast, whereas the spin-forbidden one is expected to be extremely slow. Computational results were discussed with reference to experimental data available in the literature.

Green emissive Tb(III) complexes based on photosensitizing antenna: Synthesis and optoelectronic analysis

Mononuclear octacoordinated ternary Tb(III) complexes involving 1,1,1-trifluoroacteylacetone (tfaa) as main ligand and monodentate or bidentate moieties as secondary ligand, were prepared. Tri-n-octyl phosphine oxide (TOPO) serves as a monodentate ligand with a single donor site (–O), while 1,10-phenanthroline and its derivatives function as bidentate ligands with –N as the donor atoms. The molecular stoichiometry and bonding environment about Tb(III) ion in synthesized samples were confirmed with the help of elemental analysis and the spectroscopic studies of FTIR and proton NMR, respectively. The octacoordinated arrangement around trivalent lanthanides was the outcome of their interactions occurs with oxygen donor sites in T1 and nitrogen sites in T2-T4. The optical investigation was concentrated on examining the absorption, excitation, emission and lifetime spectral data of the complexes. The dominating peak in Tb(III) complexes observed at around 545 nm is accountable for their green color. Thermogravimetric analysis demonstrates the stability of the complexes up to 150–250 °C. The synthesized complexes exhibit significant opto-electronic characteristics and large thermal stability, making them potentially suitable for lighting applications.

Controllable interlayer hydroxyl condensation of MWW zeolite and its alkylation performance of benzene with ethylene

MWW zeolite holds great promise in the petrochemical industry. However, achieving precise control over its dimension and interlayer hydroxyl condensation remains challenging when using a single, low-toxicity, readily available template. In this study, the rational and targeted hydrothermal synthesis of two-dimensional (2D) MCM-22(P) and three-dimensional (3D) MCM-49 using low-toxic piperidine is realized. The synergistic effect of the organic template and inorganic ions plays a crucial role in the precise synthesis of 2D and 3D MWW zeolite. In contrast to the traditional hexamethyleneimine template, piperidine introduces a distinct characteristic whereby disordered MWW layers coexist with the synthesized products. Specifically, the higher concentration of Na+ species directs more Al species to locate in the T1 site, promoting the condensation of interlayer hydroxyl and leading to the formation of 3D MWW zeolite. In contrast, a system with abundant PI can suppress the condensation of interlayer hydroxyl, resulting in the formation of 2D MWW zeolite. H-MCM-49 synthesized exhibits higher ethylene conversion and ethylbenzene selectivity than H-MCM-22 in the liquid alkylation of benzene and ethylene.

Theoretical calculation study on the reaction mechanism of methanol/dimethyl ether carbonylation catalyzed by the B/Al/Ga-MOR zeolites

The reaction mechanism of methanol/dimethyl ether (DME) carbonylation catalyzed by isomorphously substituted B-, Al-, and Ga-MOR zeolites (B/Al/Ga-MOR) was comparatively investigated by the density functional theory (DFT) calculations. The commonalities and differences between methanol and dimethyl ether as the reactant as well as among various MOR zeolites in the catalytic reaction pathways were disclosed, where one Si atom was substituted by B, Al or Ga at the 8-ring side pockets T3 sites or the 12-ring channels T4 sites of MOR. The results indicate that the insertion of CO into methoxy group to form acetyl groups follows the SN2 mechanism and is the rate-determining step in the carbonylation reactions. Under 473 K, either methanol or dimethyl ether is used as feedstock, the formed acetyl group prefers to interact with CH3O in methanol to form methyl acetate. The T3 sites show better carbonylation selectivity, whereas T4 sites display better trimethoxonium ions selectivity which favors the generation of aromatics and leads to the catalyst deactivation. Comparing with Al-MOR, the introduction of Ga and B at the T3 sites increases the free energy barriers of carbonylation, whereas the introduction of Ga and B in particular at the T4 sites can substantially increase the energy barriers of generating trimethyloxonium ions, which can effectively suppress the side reaction and improve the catalyst stability. This work contributes to the understanding of the catalytic roles of various acidic sites in different channels of the MOR zeolites and provides certain theoretical support for tailoring and designing efficient MOR zeolite catalysts for methanol/dimethyl ether carbonylation.

Craniocaudal spread and clinical translation for combined erector spinae plane block and retrolaminar block in soft embalmed cadavers: a randomised controlled equivalence study

BackgroundErector spinae plane (ESP) block spread can be unpredictable. We previously improved the spread of ESP injection by addition of retrolaminar (RL) injection. However, it is not clear whether spread at high thoracic levels is similar to spread at midthoracic levels. Our primary objective was to demonstrate that craniocaudal dye spread was equivalent after combined ESP and RL injection using a 19 G Tuohy needle at the third (T3) and sixth (T6) vertebrae in soft embalmed Thiel cadavers. MethodsWe randomised 20 combined ESP and RL injections to the T3 and T6 vertebral levels on both sides of 10 prone Thiel cadavers. A 3–8 MHz transducer was placed in the paramedian sagittal plane and a single anaesthetist injected 10 ml dye onto the transverse process, then 10 ml dye onto the laminae of T3 or T6. Cadavers were dissected 24 h later. ResultsMean (sd) craniocaudal spread of dye after combined ESP + RL injection at T3 and T6 vertebral levels was equivalent: 8.6 (1.8) vs 8.7 (2.3) levels, respectively; difference (90% confidence interval): –0.1 (–1.4 to 1.6), P=0.904. Dye extended uniformly, cranially and caudally, from the point of injection. A 3D prosection created from a Thiel cadaver confirmed that the dorsal ramus emerges from the costotransverse foramen deep to the intertransverse ligament within the retro-superior costotransverse ligament space. Combined ESP and RL block in six patients before mastectomy achieved extensive anterior, lateral, and posterior chest wall paraesthesia over four to six dermatomes. ConclusionsCombined ESP and RL injections showed equivalent and consistent spread at T3 and T6 injection sites. A pilot study confirmed translation to patients.

Synthesis and Structural Analysis of High-Silica ERI Zeolite with Spatially-Biased Al Distribution as a Promising NH3-SCR Catalyst.

Erionite (ERI) zeolite has recently attracted considerable attention for its application prospect in the selective catalytic reduction of NOx with NH3 (NH3-SCR), provided that the high-silica (Si/Al > 5.5) analog with improved hydrothermal stability can be facilely synthesized. In this work, ERI zeolites with different Si/Al ratios (4.6, 6.4, and 9.1) are synthesized through an ultrafast route, and in particular, a high-silica ERI zeolite with a Si/Al ratio of 9.1 is obtained by using faujasite (FAU) as a starting material. The solid-state 29Si MAS NMR spectroscopic study in combination with a computational simulation allows for figuring out the atomic configurations of the Al species in the three ERI zeolites. It is revealed that the ERI zeolite with the highest Si/Al ratio (ERI-9.1, where the number indicates the Si/Al ratio) exhibits a biased Al occupancy at T1 site, which is possibly due to the presence of a higher fraction of the residual potassium cations in the can cages. In contrast, the Al siting in ERI-4.6 and ERI-6.4 proves to be relatively random.

Understanding the role of aliovalent cation substitution on the li-ion diffusion mechanism in Li6+xP1-xSixS5Br argyrodites.

Due to their high ionic conductivity, lithium-ion conducting argyrodites show promise as solid electrolytes for solid-state batteries. Aliovalent substitution is an effective technique to enhance the transport properties of Li6PS5Br, where aliovalent Si substitution triples ionic conductivity. However, the origin of this experimentally observed increase is not fully understood. Our density functional theory (DFT) study reveals that Si4+ substitution increases Li diffusion by activating Li occupancy in the T4 sites. Redistribution of Li-ions within the lattice results in a more uniform distribution of Li around the T4 and neighboring T5 sites, flattening the energy landscape for diffusion. Since the T4 site is positioned in the intercage jump pathway, an increase in the intercage jump rate is found, which is directly related to the macroscopic diffusion and bulk conductivity. Analysis of neutron diffraction experiments confirms partial T4 site occupancy, in agreement with the computational findings. Understanding the aliovalent substitution effect on interstitials is crucial for improving solid electrolyte ionic conductivity and advancing solid-state battery performance.

Tools to Simulate Resonance Raman Spectra for in-Situ Studies of Electron Transport Mediators and Bioelectrocatalysts

Raman spectroscopy is widely applied as an in-situ probe of electrochemical processes. When the excitation light is resonant with an electronic transition, the detected signal can be enhanced by more than 1,000-fold. Resonance Raman (RR) spectroscopy has broad application in the study of common organic electron transport mediators (i.e., viologens, phenazines, photosynthetic pigments) and active sites of redox proteins (i.e., laccases, peroxidases, flavin-containing enzymes). To support investigations of bioelectrocatalytic membranes, we have been adapting RR spectroscopy to gain insights into the properties of immobilized redox mediators and biocatalyst active sites.1,2 Computational methods can be useful for guiding spectral interpretation. This poster reports on applications of recently advanced time-dependent density functional theory (TDDFT) codes that enable the simulation of RR spectra for small electron transport mediators (e.g., methyl viologen radical anion) and redox protein active site models (e.g., laccase T1 site mimics). The ORCA program suite3 was adapted. A series of Cu-centered compounds that model the T1 active site in laccases was studied along with the methyl viologen radical cation. The T1 site in laccases facilitates direct electron transport to an electrode and is a target for in-situ RR measurements. The reported work demonstrates careful selection of the functional (B3-LYP versus the long-range corrected hybrid exchange functional, ωB97X-D3) results in TDDFT-calculated electronic absorption and RR spectra that have features in excellent agreement with experiment. The results provide a foundation to build from in advancing models of small redox mediators and laccase catalytic active sites in support of sustainable technologies. Ozuguzel, U.; Aquino, A.J.A.; Nieman, R.; Minteer, S.D.; Korzeniewski, C. “Calculation of Resonance Raman Spectra and Excited State Properties for Blue Copper Protein Model Complexes” ACS Sustainable Chem. Eng. 2022, 10, 14614. Xu, J.; Koh, M.; Minteer, S. D.; Korzeniewski, C. “In Situ Confocal Raman Microscopy of Redox Polymer Films on Bulk Electrode Supports” ACS Measurement Science Au 2023 (DOI: 10.1021/acsmeasuresciau.2c00064). Neese, F.; Wennmohs, F.; Becker, U.; Riplinger, C. “ORCA Quantum Chemistry Program Package” J. Chem. Phys. 2020, 152, 224108.

Mass transfer during hydrothermal bleaching alteration of red beds in the Lanping Basin, SW China: Implications for regional Cu(–Co) and Pb-Zn mineralization

The Lanping Basin in SW China hosts many hydrothermal Cu(–Co) and Pb-Zn deposits. Widespread bleaching alterations of red beds in the basin record mass transfer during the hydrothermal fluid migration and may provide useful information about metal sources for the deposits. Based on fluid inclusion study, mineral and elemental mapping of thin sections, and whole-rock major and trace element analyses, this study investigates fluid properties and mass transfer during the hydrothermal bleaching alterations at T1 and T2 two places where Jurassic red siltstones have been bleached in association with sulfides-free hydrothermal quartz(-siderite) veins. Mineral compositions and fluid inclusion microthermometry indicate that both T1 and T2 fluids are CO2-free, weakly acidic to neutral, S-poor, hydrocarbon-bearing reduced fluids, but the former is higher than the latter in the homogenization temperatures (188 – 265 ℃ versus 136 – 184 ℃) and salinities (17 – 36 wt% NaCl eq. versus < 11 wt.%NaCl eq.). These reduced fluids caused the bleaching alterations due to the loss of Fe3+ (in terms of hematite) from the red siltstones. The T1 fluid is comparable to the vein-type Cu-Co and Pb-Zn ore fluids in the Baiyangping district. Enrichment of Cu-Co and depletion of Pb-Zn in the bleached rocks relative to the protolith at T1 suggest that the two pairs of elements are less possibly derived from the same source rocks. Red beds probably provided Pb and Zn, while other rock types, such as mafic volcanic rocks, were likely the sources of Cu and Co. As such, various degrees of contributions from different source rock types during the ore fluid migration may determine the variable (Cu-Co)/(Pb-Zn) ratios observed in the vein-type Cu-Co and Pb-Zn deposits. The T2 fluid is similar to the ore fluids of some vein-type Cu deposits along the western margin of the Lanping Basin. Considering that the T2 hydrothermal veins are free of sulfides and the fluid inclusions from the vein-type Cu deposits in this region either contain CO2 or do not contain CO2, the abundance of reduced sulfur rather than CO2 determines whether the reduced fluids in this area are capable of causing Cu mineralization. Different from T1, Mg and TFe2O3 were introduced into the bleached rocks at T2 site. This possibly resulted from interaction between the migration fluids and widespread mafic volcanic rocks in this region. Enrichment degree of Cu is apparently greater than those of Co, Zn, and Pb in the bleached rocks, which is consistent with the Cu-only mineralization for the vein-type Cu deposits in this area.

Ferrierite nanosheets with preferential Al locations as catalysts for carbonylation of dimethyl ether

Enriching Al atoms in T2 and T4 sites of FER zeolite is decisive for achieving high catalytic activity in the carbonylation reaction of dimethyl ether (DME). Regulating the spatial position of Al atoms in targeted framework sites remains to be a great challenge during the synthesis of FER zeolite. The FER nanosheets with preferential Al-sitting in T2 and T4 sites were successfully synthesized with the assistance of cetyltrimethylammonium bromide (CTAB). The effect of CTAB on the morphology and Al distribution has been investigated in detail. CTAB mostly adsorbed on external surface serving as growth inhibitors, which resulted in nanosheet morphology and changed the length ratio along the b-axis to c-axis of the crystals. A minor portion of CTAB located in the channels may favor the spatial Al location in T2 and T4 sites, indicated by the results from 27Al MAS NMR spectra. The FER nanosheets exhibited improved DME conversion, stability, space–time yield (STY), and lifetime compared to conventional FER in DME carbonylation reaction.

Laccase Engineering: Redox Potential Is Not the Only Activity-Determining Feature in the Metalloproteins.

Laccase, one of the metalloproteins, belongs to the multicopper oxidase family. It oxidizes a wide range of substrates and generates water as a sole by-product. The engineering of laccase is important to broaden their industrial and environmental applications. The general assumption is that the low redox potential of laccases is the principal obstacle, as evidenced by their low activity towards certain substrates. Therefore, the primary goal of engineering laccases is to improve their oxidation capability, thereby increasing their redox potential. Even though some of the determinants of laccase are known, it is still not entirely clear how to enhance its redox potential. However, the laccase active site has additional characteristics that regulate the enzymes' activity and specificity. These include the electrostatic and hydrophobic environment of the substrate binding pocket, the steric effect at the substrate binding site, and the orientation of the binding substrate with respect to the T1 site of the laccase. In this review, these features of the substrate binding site will be discussed to highlight their importance as a target for future laccase engineering.

Trametes versicolor laccase activity modulated by the interaction with gold nanoparticles

In this study, the impact of gold nanoparticles (AuNPs) on the structure and activity of laccase from Trametes versicolor (Lc) was described. Fluorescence experiments revealed that AuNPs efficiently quench Lc's tryptophan fluorescence by a static and dynamic process. By using differential scanning microcalorimetry and circular dichroism spectroscopy, it was determined how the concentration of nanoparticles and the composition of the medium affected the secondary structure of Lc. The data revealed that upon binding with AuNPs, conformational changes take place mainly in presence of high amounts of nanoparticles. The complex kinetic analysis unveiled the Lc activity enhancement at low concentrations of AuNPs as opposed to the concentrated regime, where it can be reduced by up to 55%. The Michaelis-Menten tests highlighted that the activity of the biocatalyst is closely related to the concentration of AuNPs, while the Selwyn analysis demonstrated that even in a concentrated regime of Lc it is not deactivated regardless of the amount of AuNPs added. The thermal parameters improved by twofold in the presence of low AuNPs concentration, whereas the activation energy increased with AuNPs content, implying that not all collisions are beneficial to the enzyme structure. The effect of AuNPs on the decomposition of a recalcitrant dye (naphthol green B, NG) by Lc was also evaluated, and the Michaelis-Menten model revealed that only the high AuNPs content influenced negatively the Lc activity. The isothermal titration calorimetry revealed that hydrogen bonds are the main intermolecular forces between Lc and AuNPs, while electrostatic interactions are responsible for NG adsorption to AuNPs. The results of the docking analysis show the binding of NG near the copper T1 site of Lc with hydrogen bonds, electrostatic and hydrophobic interactions. The findings of this work provide important knowledge for laccase-based bio-nanoconjugates and their use in the field of environmental remediation.

Correlation between Si-Al disorder and hydrogen-bonding distance variation in ussingite (Na2AlSi3O8OH) revealed by one- and two-dimensional multi-nuclear NMR and first-principles calculation

Abstract Ussingite (Na2AlSi3O8OH) is a mineral with a unique interrupted framework structure and strong hydrogen bonding. It contains 4-, 6-, and 8-membered tetrahedral rings resembling feldspars, but, unlike the latter, is partially depolymerized. There are four crystallographically distinct tetrahedral (T) sites, two of which (T1, T2) are Q4 [i.e., having 4 next nearest neighbor (NNN) T sites], and the other two (T3, T4) are Q3 (i.e., having 3 NNN T sites), each with NNN (in brackets) of T1(1T2, 1T3, 2T4), T2(1T1, 2T3, 1T4), T3(1T1, 2T2), and T4(2T1, 1T2). There is one unique OH site in the T4-O8-H···O2-T3 configuration, where O8 and O2 are nonbridging O atoms (NBO). In the ordered structure, T1 is fully occupied by Al, and the other three T sites by Si. Previous X-ray and neutron diffraction and 1H and 29Si NMR studies gave contradictory conclusions regarding Si-Al disorder. In this study, we were able to unambiguously clarify the issue via comprehensive one- and two-dimensional 1H, 29Si, 27Al, and 23Na NMR and first-principles calculation. It was revealed that there is ~3% Si-Al disorder that occurs between neighboring T1-(O)-T2 sites, such that the formation of Al-O-Al linkage and Al(Q3) are avoided. The disorder was found to result in the development of Si(Q3) sites with various NNN, including 3Al and 3Si, and neighboring OH sites having significantly shorter and longer hydrogen-bonding distances than in the ordered structure, with 1H chemical shifts near 15~16 ppm and 11 ppm, in addition to a main peak near 13.9 ppm. Good correlation was found between 1H chemical shift, hydrogen-bonding (O-H, H···O, and O···O) distances, and Si-O distances in the Si-O-H···O-Si linkage. This suggests that Si-Al disorder is correlated with variation in hydrogen-bonding distances via through-bond transmission of bond valence variations. This could be a universal phenomenon also applicable to other hydrous minerals. The revelation of preferential partition of Al in Q4 over Q3 sites to avoid the formation of Al-OH and Al-NBO provides insight into their behavior in other partially depolymerized hydrous aluminosilicate systems, such as glasses and melts.

Mechanistic Investigations into the Selective Reduction of Oxygen by a Multicopper Oxidase T3 Site-Inspired Dicopper Complex.

Understanding how multicopper oxidases (MCOs) reduce oxygen in the trinuclear copper cluster (TNC) is of great importance for development of catalysts for the oxygen reduction reaction (ORR). Herein, we report a mechanistic investigation into the ORR activity of the dinuclear copper complex [Cu2L(μ-OH)]3+ (L = 2,7-bis[bis(2-pyridylmethyl)aminomethyl]-1,8-naphthyridine). This complex is inspired by the dinuclear T3 site found in the MCO active site and confines the Cu centers in a rigid scaffold. We show that the electrochemical reduction of [Cu2L(μ-OH)]3+ follows a proton-coupled electron transfer pathway and requires a larger overpotential due to the presence of the Cu-OH-Cu motif. In addition, we provide evidence that metal-metal cooperativity takes place during catalysis that is facilitated by the constraints of the rigid ligand framework, by identification of key intermediates along the catalytic cycle of [Cu2L(μ-OH)]3+ . Electrochemical studies show that the mechanisms of the ORR and hydrogen peroxide reduction reaction found for [Cu2L(μ-OH)]3+ differ from the ones found for analogous mononuclear copper catalysts. In addition, the metal-metal cooperativity results in an improved selectivity for the four-electron ORR of more than 70% because reaction intermediates can be stabilized better between both copper centers. Overall, the mechanism of the [Cu2L(μ-OH)]3+ -catalyzed ORR in this work contributes to the understanding of how the cooperative function of multiple metals in close proximity can affect ORR activity and selectivity.

Amphibolite dissolution mechanism under chlorine-rich conditions during freeze-thaw cycles

The low-temperature weathering behavior of amphibolite is vital for revealing the cation source of groundwater and for understanding a wide range of geochemical evolution. This study aims to observe the macroscopic and microscopic characteristics of amphibolite dissolution under the freeze-thaw cycles (-25–25 °C) and chlorides (HCl, NaCl, KCl). The results show that Mg-hornblende was dissolved in chloride solutions of the same pH or concentration before albite. The change rule of the solution composition of freeze-thaw cycles is consistent with the results obtained from the dissolution experiment at room temperature. In addition, in an HCl solution of pH 1 and NaOH solutions of pH 11, 13, and 14, the dissolved amount of quartz in amphibolite can reach 11 wt %. KCl can powerfully dissolve quartz and efficiently dissolve Si in the silica-oxide tetrahedron (especially the T2 site) of Mg-hornblende. However, NaCl significantly dissolves cations in the Mg-hornblende octahedron. Analysis indicates that the leaching of Ca2+ and Mg2+ in proton-promoted dissolution strongly depended on the concentration of H+. At the same time, the release of Mg is closely related to Cl−. The results can help understand chemical element migration in the earth, especially providing a theoretical basis for groundwater cation in the Qaidam Basin.