Chemistry Research Articles

Water‐Harvesting Metal–Organic Frameworks with Gigantic Al24Units and their Deconstruction into Molecular Clusters

AbstractIn contrast to the vast Al‐oxo molecular cluster chemistry, Al‐based building units for metal–organic framework (MOF) construction are limited in structural diversity and complexity. Synthesis of single crystalline MOFs based on this “hard” metal is further complicated by the poor reversibility of the Al‐organic coordination linkages. Here, a strategy to employ two kinds of linkages with distinct strength—strong Al‐carboxylate linkage and weak Cu‐pyrazol N linkage—gives FDM‐91 (FDM=Fudan Materials) with gigantic Al24‐based units. After replacing the weak moieties with organic linkers post‐synthetically, two new stable MOFs with exceptional water harvesting capacity (up to 0.53 g g−1) and outstanding cycling performance are developed. Linkage‐selective dissociation of FDM‐91 further leads to the isolation of the Al24molecular clusters. The versatile chemistry performed here to reinforce or deconstruct MOFs provides a new way to make important extended and discrete structures.

Mapping NGC 7027 in New Light: CO+ and HCO+ Emission Reveal Its Photon- and X-Ray-dominated Regions

The young and well-studied planetary nebula (PN) NGC 7027 harbors significant molecular gas that is irradiated by luminous, pointlike UV (central star) and diffuse (shocked nebular) X-ray emission. This nebula represents an excellent subject to investigate the molecular chemistry and physical conditions within photon- and X-ray-dominated regions (PDRs and XDRs). As yet, the exact formation routes of CO+ and HCO+ in PN environments remain uncertain. Here we present ∼2″ resolution maps of NGC 7027 in the irradiation tracers CO+ and HCO+ obtained with the IRAM NOEMA interferometer, along with SMA CO and HST 2.12 μm H2 data for context. The CO+ map constitutes the first interferometric map of this molecular ion in any PN. Comparison of CO+ and HCO+ maps reveals strikingly different emission morphologies, as well as a systematic spatial displacement between the two molecules; the regions of brightest HCO+, found along the central waist of the nebula, are radially offset by ∼1″ (∼900 au) outside the corresponding CO+ emission peaks. The CO+ emission furthermore precisely traces the inner boundaries of the nebula’s PDR (as delineated by near-IR H2 emission), suggesting that central star UV emission drives CO+ formation. The displacement of HCO+ radially outward with respect to CO+ is indicative that dust-penetrating soft X-rays are responsible for enhancing the HCO+ abundance in the surrounding molecular envelope, forming an XDR. These interferometric CO+ and HCO+ observations of NGC 7027 thus clearly establish the spatial distinction between the PDR and XDR formed (respectively) by intense UV and X-ray irradiation of molecular gas.

Novel Biosurfactants for Effective Inhibition of Gas Hydrate Agglomeration and Corrosion in Offshore Oil and Gas Pipelines

Gas hydrate and corrosion inhibitors are widely used to ensure a successful and economic hydrocarbon stream flow inside oil and gas pipelines. However, compatibility problems are observed during their co-injection into the flowlines as they have different molecular chemistry. Using anti-agglomerant hydrate inhibitors is an effective method to control the gas hydrate plugging risk in deep-water hydrocarbon flow lines or throughout drilling operations. Here, oleic acid was used to develop the first class of biosurfactants as anti-agglomerant and corrosion inhibitors using click chemistry for flow assurance applications. The results of high-pressure autoclave showed that both bio-based anti-agglomerants (BAAs) significantly inhibited gas hydrate agglomeration, and the value of torque remained constant during the hydrate formation process. The hydrate particles were effectively dispersed in liquid paraffin in the presence of 1 wt % of BAA1 or BAA2. In addition, molecular dynamic simulation revealed that the headgroup of BAA1 was adsorbed on the hydrate surface, and its alkyl chain dispersed the hydrate formed in the hydrocarbon phase as a slurry. According to electrochemical measurements, both BAAs were highly efficient inhibitors for the prevention of mild steel corrosion in saturated H2S and CO2-simulated oilfield water. BAA1 and BAA2 completely protected the steel in the corrosive medium by 99 and 98.8%, respectively, at 0.1 wt %. Moreover, the adsorption of BAA1 molecules on the steel surface was both physically and chemically in a direction that was almost parallel to the surface. Such adsorption provides the maximum surface coverage against corrosion. These findings suggest that oleic acid can be used as a potential starting material to develop eco-friendly inhibitors for flow assurance in oil and gas pipelines.

Angewandte Chemie: A Team Effort

<i>Angewandte Chemie</i>: A Team Effort

Electrocatalytic Reduction of Aldonic Acids to Aldoses on Gold Electrodes

Spent sulfite liquor, a side-stream from the pulp and paper industry, is an abundantly available carbon source for bio-based platform chemicals. The biotechnological valorization of side streams in biorefineries is hampered by the inability of many microorganisms to metabolize and deal with aldonic acids. Based on the principles of Green Chemistry, the electrochemical reduction of aldonic acids into the corresponding biomass sugars appears as a prospective process for the conversion of these acids into fermentable carbohydrates. In our paper, the investigation of electrochemical reduction of gluconic and xylonic acids into glucose and xylose, respectively, is presented. The proposed mechanism on a gold-coated silver electrode was determined via ReaxFF molecular dynamics simulations and quantum chemistry calculations. Model solutions with an aldonic acid concentration of 2.5 wt % were used for the experiments. Compared to a two-electrode compartment cell, the amounts of glucose and xylose produced in the undivided cell were more than 4 and 5.5 times higher, respectively. The electrode surface was analyzed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. Despite the relatively low conversion rate, our results show that electrochemical reduction of aldonic acids into their corresponding aldoses in model solutions is possible, which represents an important step toward side-stream valorization.

QC and MD Modelling for Predicting the Electrochemical Stability Window of Electrolytes: New Estimating Algorithm

The electrolyte is an important component of lithium-ion batteries, especially when it comes to cycling high-voltage cathode materials. In this paper, we propose an algorithm for estimating both the oxidising and reducing potential of electrolytes using molecular dynamics and quantum chemistry techniques. This algorithm can help to determine the composition and structure of the solvate complexes formed when a salt is dissolved in a mixture of solvents. To develop and confirm the efficiency of the algorithm, LiBF4 solutions in binary mixtures of ethylene carbonate (EC)/dimethyl carbonate (DMC) and sulfolane (SL)/dimethyl carbonate (DMC) were studied. The structure and composition of the complexes formed in these systems were determined according to molecular dynamics. Quantum chemical estimation of the thermodynamic and oxidative stability of solvate complexes made it possible to establish which complexes make the most significant contribution to the electrochemical stability of the electrolyte system. This method can also be used to determine the additive value of the oxidation and reduction potentials of the electrolyte, along with the contribution of each complex to the overall stability of the electrolyte. Theoretical calculations were confirmed experimentally in the course of studying electrolytes by step-by-step polarisation using inert electrodes. Thus, the main aim of the study is to demonstrate the possibility of using the developed algorithm to select the optimal composition and solvent ratio to achieve predicted redox stability.

Phosphorescent Metal Halide Nanoclusters for Tunable Photodynamic Therapy.

Photodynamic therapy (PDT) is currently limited by the inability of photosensitizers (PSs) to enter cancer cells and generate sufficient reactive oxygen species. Utilizing phosphorescent triplet states of novel PSs to generate singlet oxygen offers exciting possibilities for PDT. Here, we report phosphorescent octahedral molybdenum (Mo)-based nanoclusters (NC) with tunable toxicity for PDT of cancer cells without use of rare or toxic elements. Upon irradiation with blue light, these molecules are excited to their singlet state and then undergo intersystem crossing to their triplet state. These NCs display surprising tunability between their cellular cytotoxicity and phototoxicity by modulating the apical halide ligand with a series of short chain fatty acids from trifluoroacetate to heptafluorobutyrate. The NCs are effective in PDT against breast, skin, pancreas, and colon cancer cells as well as their highly metastatic derivatives, demonstrating the robustness of these NCs in treating a wide variety of aggressive cancer cells. Furthermore, these NCs are internalized by cancer cells, remain in the lysosome, and can be modulated by the apical ligand to produce singlet oxygen. Thus, (Mo)-based nanoclusters are an excellent platform for optimizing PSs. Our results highlight the profound impact of molecular nanocluster chemistry in PDT applications.

A chemical approach to the adhesion ability of cement-based mortars with metakaolin applied to solid substrates

Chemical interactions in cement-based materials affect important properties, such as mechanical performance. In this sense, a simple theoretical model based on the strength of hydrogen bonds and SiO2/(Ca(OH)2 stoichiometric ratio is employed to advance a chemical approach to the adhesion ability of mortars with metakaolin applied to solid substrates (concrete and roughcast/concrete). To evaluate the robustness of the theoretical model, the investigated mortars were prepared, and tests of XRD, SEM, stereoscopy, and adhesion resistance were performed. The results revealed that the model was useful in predicting aspects of the adhesion capacity of the mortars with metakaolin. In addition, the XRD and SEM results showed the presence of important phases in the microstructures of the investigated mortars, such as Portlandite and CSH. Further, the tests of adhesion strength agreed with the predicted by the simple theoretical model, in which: similar average values were obtained to reference, and the mortars prepared with the addition of metakaolin, that are higher than the corresponding adhesion strengths of the mortars prepared with cement replaced by metakaolin. The stereograms of the rupture interfaces revealed a non-homogeneous adhesion when the mortar is directly applied to the concrete substrate and a homogeneous adherence when the mortar is applied to roughcast/concrete substrate. Finally, from a molecular chemistry perspective, the role of the roughcast in the adherence mechanism is to facilitate the transfer of hydrogen bonds in the sense of the mortar to the concrete substrate.

CRYSTAL23: A Program for Computational Solid State Physics and Chemistry.

The Crystal program for quantum-mechanical simulations of materials has been bridging the realm of molecular quantum chemistry to the realm of solid state physics for many years, since its first public version released back in 1988. This peculiarity stems from the use of atom-centered basis functions within a linear combination of atomic orbitals (LCAO) approach and from the corresponding efficiency in the evaluation of the exact Fock exchange series. In particular, this has led to the implementation of a rich variety of hybrid density functional approximations since 1998. Nowadays, it is acknowledged by a broad community of solid state chemists and physicists that the inclusion of a fraction of Fock exchange in the exchange-correlation potential of the density functional theory is key to a better description of many properties of materials (electronic, magnetic, mechanical, spintronic, lattice-dynamical, etc.). Here, the main developments made to the program in the last five years (i.e., since the previous release, Crystal17) are presented and some of their most noteworthy applications reviewed.

Toward Quantitative Surface-Enhanced Raman Scattering with Plasmonic Nanoparticles: Multiscale View on Heterogeneities in Particle Morphology, Surface Modification, Interface, and Analytical Protocols.

Surface-enhanced Raman scattering (SERS) provides significantly enhanced Raman scattering signals from molecules adsorbed on plasmonic nanostructures, as well as the molecules' vibrational fingerprints. Plasmonic nanoparticle systems are particularly powerful for SERS substrates as they provide a wide range of structural features and plasmonic couplings to boost the enhancement, often up to >108-1010. Nevertheless, nanoparticle-based SERS is not widely utilized as a means for reliable quantitative measurement of molecules largely due to limited controllability, uniformity, and scalability of plasmonic nanoparticles, poor molecular modification chemistry, and a lack of widely used analytical protocols for SERS. Furthermore, multiscale issues with plasmonic nanoparticle systems that range from atomic and molecular scales to assembled nanostructure scale are difficult to simultaneously control, analyze, and address. In this perspective, we introduce and discuss the design principles and key issues in preparing SERS nanoparticle substrates and the recent studies on the uniform and controllable synthesis and newly emerging machine learning-based analysis of plasmonic nanoparticle systems for quantitative SERS. Specifically, the multiscale point of view with plasmonic nanoparticle systems toward quantitative SERS is provided throughout this perspective. Furthermore, issues with correctly estimating and comparing SERS enhancement factors are discussed, and newly emerging statistical and artificial intelligence approaches for analyzing complex SERS systems are introduced and scrutinized to address challenges that cannot be fully resolved through synthetic improvements.

MD and DFT computational simulations of Caffeoylquinic derivatives as a bio-corrosion inhibitor from quince extract with experimental investigation of corrosion protection on mild steel in 1M H2SO4

The inhibition performance of Quince Extract (Q.E.) at concentrations of 0–1200 ppm on the low carbon steel corrosion in the corrosive media of sulfuric acid (H2SO4) was evaluated by using conventional electrochemical methods (potentiodynamic polarization and impedance spectroscopy). Based on the results, Q.E. displays a mixed-type behavior as an inhibitor. The inhibition efficiency of Q.E. increased with its concentration in the acid solution .The highest performance was observed at the maximum tested concentration (1200 ppm). Using polarization and EIS results, the highest inhibition efficiency of Q.E. was estimated to be 94.5% and 90.7%, respectively. Structural units and functional groups of Q.E. were detected by Fourier transform infrared spectroscopy. This spectroscopy confirmed that the extract contains nitrogen atoms, oxygen atoms, and aromatic rings that are known to have corrosion inhibition effects. The morphology of the specimen's surface after exposure to H2SO4 with and without Q.E. was examined by SEM and AFM techniques. This examination showed substantially lower surface degradation in the low-carbon steel specimens exposed to the acid in the presence of Q.E. The Langmuir isotherm approach was utilized to explain the adsorption of Q.E. onto the low-carbon steel surface. The Gibbs free energy calculated based on this approach (-21.05 kJ-mol−1) confirmed that the Q.E. adsorption onto the steel surface is supposed to involve more physisorption. In addition to the results of molecular simulation and computational chemistry, such as molecular dynamics simulation (MD), density functional theory (DFT), and Monte Carlo for all Caffeoylquinic acid derivatives confirmed that amino acid of quince extracts in an acidic medium (1 M sulfuric acid) adsorbed on compact and energetic iron surfaces mainly surfaces with miller index (110), which are inclined to corrosion and electrochemical reactions, takes place spontaneously.

From carbon superbases to superacids

Florian Mulks studied chemistry at Heidelberg University, where he obtained his doctorate with Stephen Hashmi in 2014. He spent his postdoctoral time in a variety of chemical disciplines with Shirin Faraji (University of Groningen), Eva Hevia (University of Strathclyde and University of Bern), Mu-Hyun Baik (Institute for Basic Science and Korea Advanced Institute of Science & Technology), and Guy Bertrand (University of California, San Diego). In early 2022, he founded a research group funded by the Alexander von Humboldt Foundation and Fonds der Chemischen Industrie at RWTH Aachen University to investigate molecular carbon chemistry and steric measurements.

The SURFCAT Summer School 2022: The Science of Sustainable Fuels and Chemicals

The SURFCAT Summer School 2022: The Science of Sustainable Fuels and Chemicals

CanSAR: update to the cancer translational research and drug discovery knowledgebase.

canSAR (https://cansar.ai) is the largest public cancer drug discovery and translational research knowledgebase. Now hosted in its new home at MD AndersonCancer Center,canSAR integrates billions of experimental measurements from across molecular profiling, pharmacology, chemistry, structural and systems biology. Moreover, canSAR applies a unique suite of machine learning algorithms designed to inform drug discovery. Here, we describe the latest updates to the knowledgebase, including a focus on significant novel data. These include canSAR's ligandability assessment of AlphaFold; mapping of fragment-based screening data; and new chemical bioactivity data for novel targets. We also describe enhancements to the data and interface.

Cellulose Nanocrystals (CNCs) and Its Modified Form from Durian Rind as Dexamethasone Carrier.

In this study, CNCs were extracted from durian rind. Modification to CNCs with saponin was conducted at 50 °C for one h. CNCs and CNCs-saponin were employed as dexamethasone carriers. Modification to CNCs using saponin did not change the relative crystallinity of CNCs. CNCs' molecular structure and surface chemistry did not alter significantly after modification. Both nanoparticles have surface charges independently of pH. Dexamethasone-released kinetics were studied at two different pH (7.4 and 5.8). Higuchi, Ritger-Peppas, first-order kinetic and sigmoidal equations were used to represent the released kinetic data. The sigmoidal equation was found to be superior to other models. The CNCs and CNCs-saponin showed burst release at 30 min. The study indicated that cell viability decreased by 30% after modification with saponin.

Barts and The London School of Medicine and Dentistry

The Institute of Dentistry at Barts and The School of Medicine and Dentistry, Queen Mary University of London, has seen much change since 1857 when surgeon dentist, H. J. Barrett, was appointed to The London to oversee the extraction of teeth. However, the mission remains the same: provision of excellent patient care through our education and research to improve the oral health and general health of our local population, but also with global impact.The Institute of Dentistry is embedded in a fundamentally multidisciplinary environment of the wider university and this is reflected in our research activity. The available complementary skills in cell and molecular biology, microbiology, materials science, chemistry, biophysics, clinical science and population health allows us to undertake basic science research, patient- and population-based research and clinical biometric research.Our Centre for Teaching and Innovation is a catalyst for educational research, including that related to new technologies and the expansion of e-learning, to ultimately inform local practice and the experience of our students.

Matching textural properties of commercial meat and cheese products using zein as the viscoelastic agent and calcium hydroxide as the textural modifier in plant-based formulations

Plant-based proteins have the potential to replace animal proteins in food applications; however, they do not provide cohesive and viscoelastic properties to mimic such products. Matching textural properties is one of the biggest challenges in plant-based formulations. In this study, building upon our previous work, we developed a zein-pea protein-based formulation and adjusted the textural properties by varying the calcium hydroxide concentration to match the textural properties of commercial meat and cheese products. Weak frequency dependence and higher storage modulus compared to loss modulus suggested solid-like behavior in the dough-like blends, possessing a strong and elastic inner network that retained energy inside the structure rather than dissipating it. Imaging using scanning electron and confocal microscopies showed well-incorporated web-like networks of zein conferring the viscoelastic and cohesive structure. Infrared spectroscopy (FT-IR) showed that calcium hydroxide addition at various levels (1–7%) had no significant effect on the product's molecular and structural chemistry. A high amount of β-sheet structure was found in all formulations, resulting in good viscoelastic characteristics. Notably, textural properties (i.e., hardness, chewiness, gumminess) of the formulated ingredient blends could be matched to those of tested commercial products by changing the calcium hydroxide concentration (1%-tilapia fish, 3%-chicken nugget and mozzarella cheese, 5%-tuna fish and Colby cheese, 7%-burger patties). Practical outcomes are formulations of new plant-based analogues that match the textural properties of existing animal-based commercial products.

Unified representation of molecules and crystals for machine learning

Accurate simulations of atomistic systems from first principles are limited by computational cost. In high-throughput settings, machine learning can reduce these costs significantly by accurately interpolating between reference calculations. For this, kernel learning approaches crucially require a representation that accommodates arbitrary atomistic systems. We introduce a many-body tensor representation that is invariant to translations, rotations, and nuclear permutations of same elements, unique, differentiable, can represent molecules and crystals, and is fast to compute. Empirical evidence for competitive energy and force prediction errors is presented for changes in molecular structure, crystal chemistry, and molecular dynamics using kernel regression and symmetric gradient-domain machine learning as models. Applicability is demonstrated for phase diagrams of Pt-group/transition-metal binary systems.

Surface Protection of Quaternary Gold Alloys by Thiol Self-Assembled Monolayers.

This work deals with a physical and chemical surface characterization of quaternary 18K, 14K, and 9K gold alloys and pure polycrystalline gold substrates. Surface microstructure and composition are evaluated by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray fluorescence spectroscopy. Corrosion resistance of 18K gold alloys is explored by potentiodynamic polarization showing the influence of the manufacturing process on materials fabricated as plates and wires. The research is also in the framework of one of the most common strategies on the modification of metallic surface properties, i.e., the building of self-assembled monolayers (SAM) from organic thiols. The metal affinity of the head group to produce the coating of the substrate by covalent binding is approached by using thiol compounds with different molecular structures and functional group chemistries exposed to an electrolyte solution. Therefore, a comparative study on the surface protection of a quaternary 18K gold alloy and pure gold substrates by SAMs of 6-mercaptopurine (6MP), 1-decanethiol (DT), and 11-mercaptoundecanoic acid (MUA) has been carried out. Surface modification and SAM organization are followed by cyclic voltammetry (CV), and the behavior of the double layer of the electrode-electrolyte interface is evaluated by electrochemical impedance spectroscopy (EIS). The study of these materials allows us to extract fundamental knowledge for its potential application in improving the bioactive properties of different jewelry pieces based on 18K gold alloys.

On the Binding Mechanisms of Calcium Ions to Polycarboxylates: Effects of Molecular Weight, Side Chain, and Backbone Chemistry.

We experimentally determined the characteristics and Langmuir parameters of the binding of calcium ions to different polycarboxylates. By using potentiometric titrations and isothermal titration calorimetry, the effects of side chain chemistry, pH value, and chain length were systematically investigated using the linear polymers poly(aspartic acid), poly(glutamic acid), and poly(acrylic acid). We demonstrate that for polymers with high polymerization degrees, the binding process is governed by higher-order effects, such as the change of apparent pKa of carboxyl groups, and contributions arising from the whole polymer chain while the chemistry of the monomer unit constituting the polymer plays a subordinate role. In addition, primary binding sites need to be present in the polymer, thus rendering the abundance and sequential arrangement of protonated and deprotonated groups important. The detection of higher-order effects contradicts the assumptions posed by the Langmuir model of noninteracting binding sites and puts a question mark on whether ion binding to polycarboxylates can be described using solely a Langmuir binding model. No single uniform mechanism fits all investigated systems, and the whole polymer chain, including terminal groups, needs to be considered for the interpretation of binding data. Therefore, one needs to be careful when explaining ion binding to polymers solely based on studies on monomers or oligomers.