Complexation Research Articles

Characteristics and Treatment of Effluent from a Ceramic Fiber Products Manufacturing Factory

Abstract: Wastewater generated from Ceramic Fiber industry poses serious environmental pollution due to its high chemical load and complex composition. This study investigates the wastewater generated from the production of various ceramic fiber products, such as ceramic fiber paper, board, and vacuum formed shapes. As ceramic fiber products provide excellent thermal insulation and are helpful in energy savings, growth of this industry in future is obvious. Though ceramic fiber production uses water in a considerable amount, comprehensive wastewater treatment is a necessity to reduce environmental footprint of this industry. The primary objective of this study was to analyze and characterize wastewater parameters such as Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), and Total Dissolved Solids (TDS). In this study, the chemical treatment utilizes poly aluminum chloride as a coagulant and poly electrolyte as a flocculant. Chemical treatment yields BOD and COD removal by 70.12% and 73.9% respectively. Further, the aerobic biological treatment provides a reduction of BOD by 77.1% and COD by 63.21%. An advanced oxidation process, ozonation trial was also employed for the evaluation of further reduction of pollutants to bring them within regulatory limits. The ozonation trail yields BOD and COD reduction by 75.2% and 55.8% respectively.

Review article the significance applications Schiff rules: Systematic review of the literature

The number of Shaf rules is one of the most important bridge bonds used in coordination chemistry. It has been used in the preparation of a large number of transition elements in particular and in the preparation of complexes with metal ions in general due to its coordination strength and also its ability to form complexes with different bases and different uses., and they are organic compounds containing the azomethine group (C=N-R R2). For the first time in the year (1864), I was the first to discover the process of condensing aliphatic ,aromatic ketones or aldehydes with primary aromatic amines or aliphatic, where the carbonyl group and primary amines are condensed so that the monoalkyl amine or monoaryl amine is added to the atom carbon of the carbonyl group belonging to the middle aldehyde or ketone. Later, the absence of the water molecule of the intermediate compound (N-substituted imine) which represents the base of the final shef result And why are there so many names, including amines, as well as when it is derived from a ketone, it is called ketamine, and when it is derived from an aldehyde, it is called an aldehyde. This biological activity of Scheff's rules also plays important roles in environmental chemistry, analytical chemistry, and industrial chemistry and is considered as a catalyst in photochemical reactions

Transition metal complexes: next-generation photosensitizers for combating Gram-positive bacteria.

The rise of antibiotic-resistant Gram-positive bacterial infections poses a significant threat to public health, necessitating the exploration of alternative therapeutic strategies. A photosensitizer (PS) can convert energy from absorbed photon into reactive oxygen species (ROS) for damaging bacteria. This photoinactivation action bypassing conventional antibiotic mechanism is less prone to resistance development, making antibacterial photodynamic therapy (aPDT) highly efficient in combating Gram-positive bacteria. Photodynamic transition metal complexes leveraging the unique properties of metals to enhance the aPDT activity are the next-generation PS. This review provides an overview of metal-based PS for combating Gram-positive bacteria. Based on the structures, these metal-PS could be mainly classified as metal-tetrapyrrole derivatives, ruthenium complexes, iridium complexes, and zinc complexes. PS based on complexes of other transition metals such as silver, cobalt, and rhenium are also presented. Finally, we summarize the advantages and shortcomings of these metal- PS, conclude some critical aspects impacting their aPDT performances and give a perspective on their future development.

NH2-MIL-125(Ti) and its functional nanomaterials - a versatile platform in the photocatalytic arena.

Titanium (Ti)-based MOFs are promising materials known for their porosity, stability, diverse valence states, and a lower conduction band (CB) than Zr-MOFs. These features support stable ligand-to-metal charge transfer (LMCT) transitions under photoirradiation, enhancing photocatalytic performance. However, Ti-MOF structures remain a challenge owing to the highly volatile and hydrophilic nature of ionic Ti precursors. The discovery of MIL-125 marked a breakthrough in Ti-cluster coordination chemistry. Combining it with NH2 chromophores to form NH2-MIL-125 enhanced its structural design and extended its activity into the visible light region. This review delves into the high-performance photocatalytic properties of NH2-MIL-125, focusing on its applications in H2O2 and H2 production, CO2 and N2 reduction, drug and dye degradation, photocatalytic sensors, and organic transformation reactions. The discussion considers the influence of the Ti precursor, coordination environment, synthesis process, and charge transfer mechanisms. Numerous strategic methods have been discussed to improve the performance of NH2-MIL-125 by incorporating linker modification, metal node modification, encapsulation of active species, and post-modification for enhancing light absorption ability, promoting charge separation, and improving photocatalytic efficiency. Moreover, future perspectives include methods to investigate how the efficiency of NH2-MIL-125-based materials can be planned in promoting research by highlighting their versatility and potential impacts in the area of photocatalysis.

The Lanthanide Contraction: What is an Abnormal and Why?

The lanthanide contraction is a widely known phenomenon in which the ionic radii of the Ln3+ ions decrease across the series from La3+ to Lu3+. As a result, the distance d(Ln-Y), where Y is a ligand donor atom, decreases across the series. As shown previously, the decrease normally has a linear dependence on the number of 4f Ln3+ electrons, n, and the net change, Δ', is between 0.15 and 0.20 Å. However, previous reports have shown that Δ' can be much larger than normal, and it is shown here that Δ' can be much smaller than normal. The present study seeks to determine the source and a possible explanation of these anomalies. A definitive conclusion is that the large Δ' is due to large d(Ln-Y) for the early lanthanides. The small Δ' can result from chelate constraints and intramolecular H-bonding. As an outgrowth of this search, it is shown that consistent radii for donor atoms, r(Y), can be obtained if the system satisfies certain conditions. Finally, the impact of the results on the normal and inverse trans influences is discussed.

Vanillin Derived Hydrazone Ligands and Their Transition Metal Complexes: Synthesis, Characterization, Biological Activity and Molecular Docking Studies

Vanillin Derived Hydrazone Ligands and Their Transition Metal Complexes: Synthesis, Characterization, Biological Activity and Molecular Docking Studies

Electronic structures and EDA-NOCV and absorption spectra analysis of Schiff base and pyridine derivatives mixed ligands in transition metal complexes

Electronic structures and EDA-NOCV and absorption spectra analysis of Schiff base and pyridine derivatives mixed ligands in transition metal complexes

Data‐Driven Analysis of Ni‐Catalyzed Semihydrogenations of Alkynes

The semihydrogenation of alkynes to alkenes has historically been an essential technique in organic chemistry. In this context, researchers often employ transition metal complexes to achieve this conversion. Given the pronounced polarization of results, often yielding either very high or very low values, it remains challenging to discern the factors influencing reactivity and selectivity in many cases. In this work, we combine different sub‐disciplines of digital chemistry with experimental outcomes to rationalize the results of a model Ni‐catalyzed semihydrogenation that leads to E‐alkenes. First, we analyze the main factors behind successful reactions using a machine learning classification model. The descriptors are computed directly from the SMILES strings of the reacting alkynes using an automated protocol that relies on structural features, molecular mechanics, and semi‐empirical techniques. This workflow requires minimal human intervention and provides a fast yet useful approach. Next, we couple the same descriptors with activation barriers calculated with density functional theory, generating a regression model that explains reactivity based on the properties of the alkyne substrates. Overall, this study demonstrates the potential of using a combination of digital chemistry techniques to uncover reaction trends in Ni‐catalyzed semihydrogenations of alkynes, an area where human intuition proves limited in application.

2-Guanidinobenzimidazole as Ligand in Supramolecular, Coordination and Organometallic Chemistry

Abstract: The benzimidazole core (BI) plays a central role in biologically active molecules. The BI nucleus is widely used as a building block to generate a variety of bioactive heterocyclic compounds to be used as antihelmintics, antiprotozoal, antimalarials, anti-inflammatories, antivirals, antimicrobials, antiparasitics, and antimycobacterials. A versatile BI derivative is the 2-guanidinobenzimidazole (2GBI), which, together with its derivatives, is a very interesting poly-functional planar molecule having a delocalised 10 π electrons system conjugated with the guanidine group. The 2GBI molecule has five nitrogen atoms containing five labile N–H bonds, which interact with the out-ward-facing channel entrance, forming a labile complex with the biological receptor sites. In this work, 2GBI and their derivatives were analyzed as ligands to form host–guest, coordination and organometallic complexes. Synthesis methodology, metal geometries, hydrogen bonding (HB) interactions, and the biological activities of the complexes were discussed.

Versatile applications of cobalt and copper complexes of biopolymeric Schiff base ligands derived from chitosan.

In the present study, biopolymeric Schiff base (SB) ligands were synthesized from chitosan and isatin. Consequently, their earth abundant transition metal complexes of cobalt and copper were synthesized. All compounds were extensively characterized using FTIR and UV spectroscopy, thermo-gravimetric (TG) analysis, X-ray powder diffraction (XRD) and FESEM (field emission scanning electron microscopy). The impetus of this study was to explore different applications of the same transition metal complexes, thereby converting them to broad spectrum antimicrobial drugs and to useful chemical catalysts. Thus, these cobalt and copper complexes were applied as anti-bacterial and anti-fungal agents and in reductive degradation of common pollutants. Specifically, chitosan, and all synthesized compounds were investigated against fungal species, namely, Candida and Aspergillus, and bacterial species, like Pseudomonas syringae, Escherichia coli, Staphylococcus aureus and Staphylococcus epidermis. All compounds demonstrated promising antimicrobial activity. Chitosan-modified compounds demonstrated a high antifungal activity against Candida albicans and possessed superior antibacterial action than free chitosan. Additionally, catalytic ability in reductive degradation of common dyes, methylene blue (MEB), Congo red (CR) and methyl orange (MO), was investigated. These dyes were conveniently degraded in presence of metal complexes, whereas neither chitosan nor the Schiff base ligand derived from it could carry out similar reaction.

Enhancing Activation Energy Predictions under Data Constraints Using Graph Neural Networks.

Accurately predicting activation energies is crucial for understanding chemical reactions and modeling complex reaction systems. However, the high computational cost of quantum chemistry methods often limits the feasibility of large-scale studies, leading to a scarcity of high-quality activation energy data. In this work, we explore and compare three innovative approaches (transfer learning, delta learning, and feature engineering) to enhance the accuracy of activation energy predictions using graph neural networks, specifically focusing on methods that incorporate low-cost, low-level computational data. Using the Chemprop model, we systematically evaluated how these methods leverage data from semiempirical quantum mechanics (SQM) calculations to improve predictions. Delta learning, which adjusts low-level SQM activation energies to align with high-level CCSD(T)-F12a targets, emerged as the most effective method, achieving high accuracy with substantially reduced data requirements. Notably, delta learning trained with just 20-30% of high-level data matched or exceeded the performance of other methods trained with full data sets, making it advantageous in data-scarce scenarios. However, its reliance on transition state searches imposes significant computational demands during model application. Transfer learning, which pretrains models on large data sets of low-level data, provided mixed results, particularly when there was a mismatch in the reaction distributions between the training and target data sets. Feature engineering, which involves adding computed molecular properties as input features, showed modest gains, particularly in thermodynamic properties. Our study highlights the trade-offs between accuracy and computational demand in selecting the best approach for enhancing activation energy predictions. These insights provide valuable guidelines for researchers aiming to apply machine learning in chemical reaction engineering, helping to balance accuracy with resource constraints.

CaXML: Chemistry-informed machine learning explains mutual changes between protein conformations and calcium ions in calcium-binding proteins using structural and topological features.

Proteins' flexibility is a feature in communicating changes in cell signaling instigated by binding with secondary messengers, such as calcium ions, associated with the coordination of muscle contraction, neurotransmitter release, and gene expression. When binding with the disordered parts of a protein, calcium ions must balance their charge states with the shape of calcium-binding proteins and their versatile pool of partners depending on the circumstances they transmit. Accurately determining the ionic charges of those ions is essential for understanding their role in such processes. However, it is unclear whether the limited experimental data available can be effectively used to train models to accurately predict the charges of calcium-binding protein variants. Here, we developed a chemistry-informed, machine-learning algorithm that implements a game theoretic approach to explain the output of a machine-learning model without the prerequisite of an excessively large database for high-performance prediction of atomic charges. We used the ab initio electronic structure data representing calcium ions and the structures of the disordered segments of calcium-binding peptides with surrounding water molecules to train several explainable models. Network theory was used to extract the topological features of atomic interactions in the structurally complex data dictated by the coordination chemistry of a calcium ion, a potent indicator of its charge state in protein. Our design created a computational tool of CaXML, which provided a framework of explainable machine learning model to annotate ionic charges of calcium ions in calcium-binding proteins in response to the chemical changes in an environment. Our framework will provide new insights into protein design for engineering functionality based on the limited size of scientific data in a genome space.

Increased sensitivity in electron–nuclear double resonance spectroscopy with chirped radiofrequency pulses

Abstract. Electron–nuclear double resonance (ENDOR) spectroscopy is an EPR technique to detect the nuclear frequency spectra of hyperfine coupled nuclei close to paramagnetic centers, which have interactions that are not resolved in continuous wave EPR spectra and may be fast relaxing on the timescale of NMR. For the common case of non-crystalline solids, such as powders or frozen solutions of transition metal complexes, the anisotropy of the hyperfine and nuclear quadrupole interactions renders ENDOR lines often several megahertz (MHz) broad, thus diminishing intensity. With commonly used ENDOR pulse sequences, only a small fraction of the NMR/ENDOR line is excited with a typical radiofrequency (RF) pulse length of several tens of microseconds (µs), and this limits the sensitivity in conventional ENDOR experiments. In this work, we show the benefit of chirped RF excitation in frequency-domain ENDOR as a simple yet effective way to significantly improve sensitivity. We demonstrate on a frozen solution of Cu(II)-tetraphenylporphyrin that the intensity of broad copper and nitrogen ENDOR lines increases up to 9-fold compared to single-frequency RF excitation, thus making the detection of metal ENDOR spectra more feasible. The tunable bandwidth of the chirp RF pulses allows the operator to optimize for sensitivity and choose a tradeoff with resolution, opening up options previously inaccessible in ENDOR spectroscopy. Also, chirp pulses help to reduce RF amplifier overtones, since lower RF powers suffice to achieve intensities matching conventional ENDOR. In 2D triple resonance experiments (TRIPLE), the signal increase exceeds 10 times for some lines, thus making chirped 2D TRIPLE experiments feasible even for broad peaks in manageable acquisition times.

Reversible Piezochromism of Platinum(II) and Palladium(II) Dimers in Molecular Single Crystals.

Transition metal complexes are well-known for their efficient light emission and are promising for applications ranging from bioimaging to light-emitting diodes. In solution, interactions between the metal centers of two complexes become possible and drastically change the photophysical properties. For real-world devices, solid-state materials consisting of these molecules are preferable. Recently, the ligand-controlled aggregation of platinum(II) and palladium(II) complexes into molecular single crystals and the controlled formation of metal-metal contacts have been demonstrated. Here, we show how the metal-metal distance can be tuned in a controlled way by exerting pressure on the molecular crystal. Using optical spectroscopy inside a diamond anvil cell, we find strong and reversible piezochromism up to 18 GPa. Using time-dependent density functional theory, we attribute the wavelength shift to a reduction in the metal-metal distance and enhanced π orbital overlap in the dimers.

Environmental Catalysis for NOx Reduction by Manipulating the Dynamic Coordination Environment of Active Sites.

Nowadays, it is challenging to achieve SO2-tolerant environmental catalysis for NOx reduction because of the thermodynamically favorable transformation of reactive sites to inactive sulfate species in the presence of SO2. Herein, we achieve enhanced low-temperature SO2-tolerant NOx reduction by manipulating the dynamic coordination environment of active sites. Engineered by coordination chemistry, SiO2-CeO2 composite oxides with a short-range ordered Ce-O-Si structure were elaborately constructed on a TiO2 support. A dynamic coordination environment of active sites is demonstrated from a Ce-O-Si local structure to a low-coordinated Ce-SO42- species in the presence of SO2. The low-coordinated Ce-SO42- species as new active sites maintain a high NO removal efficiency by preserving the good adsorption and activation capacity of NO and NH3 reactants. This work proposes a new notion to improve the SO2 resistance of catalysts by regulating the coordination environment of sulfated active sites, which is of significance for SO2-tolerant environmental catalysis in practical applications.

Hypoxia-activated dissociation of heteroleptic cobalt(III) complexes with functionalized 2,2'-bipyridines and a model anticancer drug esculetin.

A low oxygen level in solid tumors is behind the modern concept of selective chemotherapy by hypoxia-activated prodrugs, such as heteroleptic complexes of transition metals (cobalt(III), iron(III) or platinum(IV)) with bi- or tetradentate ligands and an anticancer drug molecule as a co-ligand. A series of new cobalt(III) complexes [Co(LR)2(esc)]ClO4 with esculetin (6,7-dihydroxycoumarin) and 2,2'-bipyridines (2,2'-bipy) functionalized by different substituents R were probed in the hypoxia-activated delivery of this model anticancer drug. Their combined study by cyclic voltammetry and in situ NMR spectroscopy allowed identifying linear correlations of the electrochemical reduction potentials and the rate of the hypoxia-activated dissociation of [Co(LR)2(esc)]ClO4 with the Hammett constants of the substituents in 2,2'-bipy ligands. The latter, therefore, should be decorated with the most electron-withdrawing groups (unless they preclude the formation of a heteroleptic complex) to promote the drug release and increase the anticancer activity towards, e.g., human epidermoid carcinoma A431.These correlations can be transferred to other types of bi- or tetradentate ligands, thereby paving the way towards the molecular design of cobalt complexes as prodrugs for hypoxia-activated anticancer drug delivery with high therapeutic efficiency.

Microbe-assisted phytoremediation for sustainable management of heavy metal in wastewater - A green approach to escalate the remediation of heavy metals.

Water pollution from Heavy metal (HM) contamination poses a critical threat to environmental sustainability and public health. Industrial activities have increased the presence of HMs in wastewater, necessitating effective remediation strategies. Conventional methods like chemical precipitation, ion exchange, adsorption, and membrane filtration are widely used but possess various limitations. These include high costs, environmental impacts, and the potential for generating secondary pollutants, highlighting the need for sustainable alternatives. Phytoremediation, enhanced by microbial interactions, offers an eco-friendly solution to this issue. The unique physiological and biochemical traits of plants, combined with microbial metabolic capabilities, enable efficient uptake and detoxification of HMs. Microbial enzymes play a crucial role in these processes by breaking down complex compounds, enhancing HM bioavailability, and facilitating their conversion into less toxic forms. Synergistic interactions between root-associated microbes and plants further improves metal absorption and stabilization, boosting phytoremediation efficiency. However, challenges remain, including the limited bioavailability of contaminants and plant resilience in highly polluted environments. Recent advancements focus on improving microbial-assisted phytoremediation through mechanisms like bioavailability facilitation, phytoextraction, and phytostabilization. Genetic engineering facilitates the altering of genes that control plant immune responses and growth which improves the ability of plants to interact beneficially with microbes to thrive in HM rich environments while efficiently cleaning contaminated wastewater. This review examines these strategies and highlights future research directions to enhance wastewater remediation using phytoremediation technologies.

Hydrogen Tunneling and Conformational Motions in Nonadiabatic Proton-Coupled Electron Transfer between Interfacial Tyrosines in Ribonucleotide Reductase.

Ribonucleotide reductase (RNR) is essential for DNA synthesis and repair in all living organisms. The mechanism of E. coli RNR requires long-range radical transport through a proton-coupled electron transfer (PCET) pathway spanning two different protein subunits. Herein, the direct PCET reaction between the interfacial tyrosine residues, Y356 and Y731, is investigated with a vibronically nonadiabatic theory that treats the transferring proton and all electrons quantum mechanically. The input quantities to the PCET rate constant expression are computed with a combination of density functional theory and molecular dynamics simulations. The calculations highlight the importance of hydrogen tunneling in this PCET reaction. Compression of the distance between the proton donor and acceptor oxygen atoms of the interfacial tyrosine residues is essential to facilitate hydrogen tunneling by increasing the overlap between the reactant and product proton vibrational wave functions. This compression occurs by thermal conformational fluctuations of these interfacial tyrosine residues. N733 and R411 are identified as key residues that can hydrogen bond to Y731 and Y356, respectively, and thereby compete with the hydrogen-bonding interaction between Y731 and Y356 required for direct PCET. Understanding the roles of hydrogen tunneling and conformational motions in this interfacial PCET reaction, as well as identifying other residues that may impact the kinetics, is important for targeted protein engineering efforts to modulate RNR activity.

Investigating Benzoic Acid Derivatives as Potential Atomic Layer Deposition Inhibitors Using Nanoscale Infrared Spectroscopy

Area-selective atomic layer deposition (AS-ALD) is a technique utilized for the fabrication of patterned thin films in the semiconductor industry due to its capability to produce uniform and conformal structures with control over thickness at the atomic scale level. In AS-ALD, surfaces are functionalized such that only specific locations exhibit ALD growth, thus leading to spatial selectivity. Self-assembled monolayers (SAMs) are commonly used as ALD inhibiting agents for AS-ALD. However, the choice of organic molecules as viable options for AS-ALD remains limited and the precise effects of ALD nucleation and exposure to ALD conditions on the structure of SAMs is yet to be fully understood. In this work, we investigate the potential of small molecule carboxylates as ALD inhibitors, namely benzoic acid and two of its derivatives, 4-trifluoromethyl benzoic acid (TBA), and 3,5-Bis (trifluoromethyl)benzoic acid (BTBA) and demonstrate that monolayers of all three molecules are viable options for applications in ALD blocking. We find that the fluorinated SAMs are better ALD inhibitors; however, this property arises not from the hydrophobicity but the coordination chemistry of the SAM. Using nanoscale infrared spectroscopy, we probe the buried monolayer interface to demonstrate that the distribution of carboxylate coordination states and their evolution is correlated with ALD growth, highlighting the importance of the interfacial chemistry in optimizing and assessing ALD inhibitors.

Thorium(IV) and Uranium(IV) Complexes with 2,6-Dipicolinoylbis(N,N-diethylthiourea) Ligands

The reaction of thorium nitrate hydrate with 2,6-dipicolinoylbis(N,N-diethylthiourea), H2Lpic, results in the hydrolysis of the organic ligand and the formation of [Th(2,6-dipicolinolate)2(H2O)4] (1). Hydrolysis can be avoided by the use of [ThCl4(DME)2] (DME = 1,2-dimethoxyethane) as the starting material and the exclusion of water. The product, [Th(Lpic)3]2− (2), crystallizes as diammonium salt in form of yellow crystals in moderate yields. The thorium ion in the complex is nine-coordinate by the central O,N,O donor atoms of three deprotonated {Lpic}2− ligands. The sulfur atoms of the ligands do not bind to the actinide ion, but establish hydrogen bonds to the ammonium counter ions. A similar coordination sphere is also observed in the uranium(IV) complex [UAu2(Lpic)3}] (3), which was obtained from a reaction between H2Lpic, [U2I6(1,4-dioxane)3] and [AuCl(tht)] (tht = tetrahydrothiophene) in the presence of triethylamine. Charge compensation is established by the linear coordination of two Au+ ions between each two sulfur atoms of the ligands. The products have been studied by X-ray diffraction and IR spectroscopy. The actinide ions in both {Lpic}2− complexes have coordination number nine, but establish slightly different coordination spheres.