Metal Complexes Research Articles

Hydrolysis of Nerve Agent Simulants Accelerated by Stimuli-Responsive Dinuclear Catalysts.

The ability to control the catalytic activity of enzymes in chemical transformations is essential for the design and development of artificial catalysts. Herein, we report the synthesis and characterization of functional ligands featuring two 1,4,7,10-tetraazacyclododecane units linked by an azobenzene group and their corresponding dinuclear Zn(II) complexes. We show that the configuration switching (E/Z) of the azobenzene spacer in the ligands and their dinuclear Zn(II) complexes is reversibly controlled by irradiation with UV and visible light. The Zn(II)-metal complexes are light-responsive catalysts for the hydrolytic cleavage of nerve agent simulants, i.e., p-nitrophenyl diphenyl phosphate and methyl paraoxon. The catalytic activity of the Z-isomers of the dinuclear Zn(II) complexes outperformed that of the E-counterparts. Moreover, combining the less active E-isomers with gold nanoparticles induced an enhancement in the hydrolysis rate of p-nitrophenyl diphenyl phosphate. Kinetic analysis has shown that the catalytic site appears to involve a single metal ion. We explain our results by considering the different desolvation effects occurring in the catalyst's configurations in the solution and the catalytic systems involving gold nanoparticles.

Enhanced Near-infrared Phosphorescent Emission Modulated by Clipping of Metallotweezers in Aqueous Media.

Near-infrared phosphorescent materials have received significant attention due to their potential applications in bioimaging and diagnostics. Although, many types of organic phosphors with near-infrared emission have been developed, the low phosphorescence efficiency in aqueous solution hampers their practical applications in biological systems. Hence, there is an urgent need to develop near-infrared phosphorescent materials with high emission efficiency in aqueous media. Metallotweezers, based on d8 transition metal complexes, emerge as the potential candidates for realizing this objective. Specifically, metallotweezers, featuring two positively charged platinum(II) terpyridine and neutral gold(III) diphenylpyridine pincers on diphenylpyridine spacer, have been designed and synthesized, respectively. The pre-organization effect, rendered by the rigid spacer, enables the resulting metallotweezers to complex with each other, resulting in the formation of clipping complex. The synergistic rigidifying and shielding effects of clipping structure results in enhanced phosphorescent emission intensity. Concurrently, due to phase segregation between the clipping units and the polyethylene glycol tail, the clipping complex undergoes self-assembly in aqueous solution, resulting in phosphorescent emission in the near-infrared region. Overall, non-covalent clipping of metallotweezers illustrated in this study presents a new and effective approach toward near-infrared phosphorescent materials.

Square-planar Tetranuclear Cluster-based Alkaline Earth Metal-organic Frameworks with Enhanced Proton Conductivity.

Alkaline earth (AE) metal complexes have garnered significant interest in various functional fields due to their nontoxicity, low density, and low cost. However, there is a lack of systematic investigation into the structural characteristics and physical properties of AE-metal-organic frameworks (MOFs). In this research, we synthesized isostructural MOFs consisting of AE4(μ4-Cl) clusters bridged by benzo-(1,2;3,4;5,6)-tris(thiophene-2'-carboxylic acid) (BTTC3-) ligands. The resulting structure forms a truncated octahedral cage denoted as [AE4(m4-Cl)]6(BTTC)8, which further linked to a porous three-dimensional framework. Among the investigated AE ions (Ca, Sr, and Ba), the Ca4-MOF demonstrated good chemical stability in water compared to Sr4-MOF and Ba4-MOF. The N2 adsorption and solid-state UV-vis-NIR absorption behaviors were evaluated for all AE4-MOFs, showing similar trends among the different metal ions. Additionally, the proton conduction study revealed that the Ca4-MOF exhibited ultra-high proton conductivity, reaching 3.52×10-2 S cm-1 at 343 K and 98 % RH. Notably, the introduction of LiCl via guest exchange resulted in an improved proton conduction of up to 6.36×10-2 S cm-1 under similar conditions in the modified LiCl@Ca4-MOF. The findings shed light on the regulation of physical properties and proton conductivity of AE-MOFs, providing valuable insights for their potential applications in various fields.

LigandDiff: de Novo Ligand Design for 3D Transition Metal Complexes with Diffusion Models.

Transition metal complexes are a class of compounds with varied and versatile properties, making them of great technological importance. Their applications cover a wide range of fields, either as metallodrugs in medicine or as materials, catalysts, batteries, solar cells, etc. The demand for the novel design of transition metal complexes with new properties remains of great interest. However, the traditional high-throughput screening approach is inherently expensive and laborious since it depends on human expertise. Here, we present LigandDiff, a generative model for the de novo design of novel transition metal complexes. Unlike the existing methods that simply extract and combine ligands with the metal to get new complexes, LigandDiff aims at designing configurationally novel ligands from scratch, which opens new pathways for the discovery of organometallic complexes. Moreover, it overcomes the limitations of current methods, where the diversity of new complexes highly relies on the diversity of available ligands, while LigandDiff can design numerous novel ligands without human intervention. Our results indicate that LigandDiff designs unique and novel ligands under different contexts, and these generated ligands are synthetically accessible. Moreover, LigandDiff shows good transferability by generating successful ligands for any transition metal complex.

Coinage Metal Complexes of a Sterically Encumbered Anionic Pyridylborate.

Sterically loaded, anionic pyridine has been synthesized and utilized successfully in the stabilization of a homoleptic series of coinage metal complexes. The treatment of [4-(Ph3B)-2,6-Trip2Py]K (Trip =2,4,6-iPr3C6H2) with CuBr(PPh3), AgCl(PPh3) or AuCl(PPh3) (Py = pyridine) afforded the corresponding [4-(Ph3B)-2,6-Trip2Py]M(PPh3) (M = Au, Ag, Cu) complexes, via salt metathesis, as isolable, crystalline solids. Notably, these reactions avoid the facile single electron transfer chemistry reported with the less bulky ligand systems. The X-ray structures revealed that they are two-coordinate metal adducts. The M-N and M-P bond distances are longest in the silver and shortest in the copper adduct among the three group 11 family members. Computational analysis revealed an interesting stability dependence on steric bulk of the anionic pyridine (i.e., pyridyl borate) ligand. A comparison of structures and bonding of [4-(Ph3B)-2,6-Trip2Py]Au(PPh3) to pyridine and m-terphenyl complexes, {[2,6-Trip2Py]Au(PPh3)}[SbF6] and [2,6-Trip2Ph]Au(PPh3) are also provided. The Au(I) isocyanide complex, [4-(Ph3B)-2,6-Trip2Py]Au(CNBut) has been stabilized using the same anionic pyridylborate illustrating that it can support other gold-ligand moieties as well.

Synthesis, characterization, and evaluation of the antimicrobial, cytotoxic properties of alkaline earth metal complexes containing the nucleobase guanine

Synthesis, characterization, and evaluation of the antimicrobial, cytotoxic properties of alkaline earth metal complexes containing the nucleobase guanine

Oxygen Vacancy-Laden Confinement Impact on Degradation of Metal Complexes.

Oxygen vacancies (Vo) have been recognized as the superior active site for PS-mediated environmental remediation; however, the formation and activation of Vo associated with the effects of chemical and spatial environments remain ambiguous. Herein, attributing to the low defect-formation energy of Vo in the presence of sulfonate groups, an in situ nucleating Vo-laden CuO nanosheet was deliberately fabricated inside the phase of a sulfonated mesoporous polystyrene substrate (Vo-CuO@SPM). The as-prepared nanocomposite demonstrated an excellent treatment efficiency toward metal complexes [Cu-EDTA as a case] with ignorable Cu(II) leaching, and it can be repeatedly employed for 25 recycles (not limited). Mechanistically, the electron transfer and the mass transport for PDS nonradical activation were proved to be substantially enhanced by the delocalized electrons and with the assistance of the microchannel environment. This work not only establishes insight into the formation of oxygen vacancies but also reveals the PS activation mechanism in the spatially confined sites.

Determination of Binding Constants for the Complexes Between Heavy Metal Ions and Cucurbit[n]uril

AbstractOne of the major concerns worldwide is the rapid increase in water pollution with hazardous heavy metals. The Cucurbit[n]uril (CB[n]) structure provides an inner hydrophobic cavity accessible through two electrostatically negative portals with polar carbonyl groups, allowing for charged ion–dipole interaction between cationic species with excellent binding affinities. In this work we selected CB[5], and CB[7] for the titrimetric and electrochemical evaluation of the heavy metal complexes formed with Copper(II), Cadmium(II) and Lead(II). The host–guest interaction was found by either attenuation of the redox peaks, the formation of a new peak, or the slight shift in the redox peaks of the heavy metal ions. Titration data were obtained for CB[n] with the heavy metal solutions to determine the molar coefficient of binding. The stoichiometry of the complexes was 1 : 1 by Job′s plot. We calculated the binding constants using the Benesi–Hildebrand method achieving relatively good binding constants (K) ranging from (1.80±0.14)×105–(4.98±0.13)×105 M−1. The results showed that the complexes of Cadmium(II) and Lead(II) with both CB[5] and CB[7] are highly stable in aqueous media. Copper(II) was able to bind to the smaller sized portal of CB[5], whereas with CB[7] the heavy metal ion could not form a favourable complex. This phenomenon suggests that the CB[5] is an ideal host at forming stable host–guest interactions than their larger homologue.

AcSac, SacSac, and SacNac, the Forgotten Sulfur‐Based Ligands and their Reactivity in the Formation of Main and Transition Metal Complexes

AcAc (β‐acetylacetonate) are among the first ligands ever, to be studied. They all form stable complexes with most metals. During the 1960s, their sulfur derivatives were introduced; AcSac (β‐thioketonate), SacSac (β‐dithioketonate) and SacNac (β‐thioketoiminate). These derivatives were conferred contrasting reactivity, stereochemical, magnetic and spectral properties to their formed complexes. Later, sulfur‐ligands were at their pinnacle in the early 1970s, but their fall into disuse was due to the lack of methodologies for obtaining them and the lack of synthetic tools for their structural modification. As an effort to promote the study and application of these sulfur‐ligands; this review will address its history, the properties they bring to the metal centers and their potential applications.

Characterization of Deformational Isomerization Potential and Interconversion Dynamics with Ultrafast X-ray Solution Scattering.

Dimeric complexes composed of d8 square planar metal centers and rigid bridging ligands provide model systems to understand the interplay between attractive dispersion forces and steric strain in order to assist the development of reliable methods to model metal dimer complexes more broadly. [Ir2 (dimen)4]2+ (dimen = para-diisocyanomenthane) presents a unique case study for such phenomena, as distortions of the optimal structure of a ligand with limited conformational flexibility counteract the attractive dispersive forces from the metal and ligand to yield a complex with two ground state deformational isomers. Here, we use ultrafast X-ray solution scattering (XSS) and optical transient absorption spectroscopy (OTAS) to reveal the nature of the equilibrium distribution and the exchange rate between the deformational isomers. The two ground state isomers have spectrally distinct electronic excitations that enable the selective excitation of one isomer or the other using a femtosecond duration pulse of visible light. We then track the dynamics of the nonequilibrium depletion of the electronic ground state population─often termed the ground state hole─with ultrafast XSS and OTAS, revealing a restoration of the ground state equilibrium in 2.3 ps. This combined experimental and theoretical study provides a critical test of various density functional approximations in the description of bridged d8-d8 metal complexes. The results show that density functional theory calculations can reproduce the primary experimental observations if dispersion interactions are added, and a hybrid functional, which includes exact exchange, is used.

Investigation of half-sandwich platinum group metal complexes featuring benzamide derived ligands and their diazido derivatives: Synthesis, molecular structures and biological studies

Benzamide derivative ligands L1 and L2 were synthesized and reactions of these ligands with metal dimers [Ru(p-cymene)Cl2]2 and [Cp*MCl2]2 (M = Rh/Ir) yielded a series of “piano-stool”-type neutral mononuclear metal-arene-benzamide complexes (1, 2, 3, 4, 5 and 6) of the general formula [(arene)M(κ1(N)L)Cl2] (where arene = p-cymene and Cp*, M = Ru, Rh and Ir and L = L1 and L2). Further treatment of the neutral complexes 1-6 with sodium azide in methanol resulted in the formation of diazido complexes 7, 8, 9 and 10. Crystallographic studies of the complexes 2, 5, 7 and 8 revealed the ligands coordinated to the metal centers through the nitrogen atom of thiazole/thiadiazole ring in a monodentate fashion. The complexes were characterized by NMR, FTIR, UV-Vis spectroscopy and ESI-mass spectrometry. All the ligands and metal complexes were screened for their antibacterial and antioxidant activities. Interestingly, it was observed that only the diazido complexes were active towards the Gram-positive Staphylococcus aureus bacterial strains, with activities more than the standard. Antioxidant study revealed that the compounds possess insignificant activities.

Ultra-high performance concrete with metal mine tailings and its properties: a review

Abstract Metal mine tailings (MMT) are a kind of industrial solid waste, with an increasing accumulation year by year, which has seriously damaged the ecological environment. Incorporating MMT in ultra-high performance concrete (UHPC) is an effective means to achieve green sustainable development, which can not only make wastes be resources and prevent pollution but also save raw material costs and reduce energy consumption. However, metal mine tailings contain complex and diverse metal oxides and other chemical substance and even contain certain radioactive elements and heavy metal ions. These factors can affect the corrosion resistance of UHPC, accelerate its aging and damage, and in addition may have serious impacts on the environment and human health. This paper summarizes the material properties of MMT and its application in UHPC; analyzes the effects of MMT as powder or fine aggregate on the workability, mechanical properties, durability, and leaching toxicity of UHPC; and elaborates the hydration products, interfacial transition zone, and pore structure of UHPC incorporating MMT (MMT-UHPC). Based on previous research results, the relationship between flowability, flexural strength, porosity, and compressive strength of MMT-UHPC is established.

Deciphering Charge Transfer Processes in Transition Metal Complexes from the Perspective of Ultrafast Electronic and Nuclear Motions.

Chemical transformations in charge transfer states result from the interplay between electronic dynamics and nuclear reorganization along excited-state trajectories. Here, we investigate the ultrafast structural dynamics following photoinduced electron transfer from the metal-metal-to-ligand charge transfer state of an electron donor, a Pt dimer complex, to a covalently linked electron acceptor group using ultrafast time-resolved wide-angle X-ray scattering and optical transient absorption spectroscopy methods to disentangle the interdependence of the excited-state electronic and nuclear dynamics. Following photoexcitation, Pt-Pt bond formation and contraction takes up to 1 ps, much slower than the corresponding process in analogous complexes without electron acceptor groups. Because the Pt-Pt distance change is slow with respect to excited-state electron transfer, it can affect the rate of electron transfer. These results have potential impacts on controlling electron transfer rates via structural alterations to the electron donor group, tuning the charge transfer driving force.

Anticancer potential of the S-heterocyclic ring containing drugs and its bioactivation to reactive metabolites.

Sulfur-containing heterocyclic derivatives have been disclosed for binding with a wide range of cancer-specific protein targets. Various interesting derivatives of sulfur-containing heterocyclics such as benzothiazole, thiazole, thiophene, thiazolidinedione, benzothiophene, and phenothiazine, etc have been shown to inhibit diverse signaling pathways implicated in cancer. Significant progress has also been made in molecular targeted therapy against specific enzymes such as kinase receptors due to potential binding interactions inside the ATP pocket. Sulfur-containing heterocyclic ring metal complexes i.e., benzothiazole, thiazole, thiophene, benzothiophene and phenothiazines are among the most promising active anticancer compounds. However, sulfur heteroaromatic rings, particularly thiophene, are of high structural alert due to their metabolism to reactive metabolites. The mere presence of a structural alert itself does not determine compound toxicity therefore, this review focuses on some specific findings that shed light on factors influencing the toxicity. In the current review, synthetic strategies of introducing the sulfur core ring in the synthesized derivatives are discussed with their structure-activity relationships to enhance our understanding of toxicity mechanisms and develop safer therapeutic options. The sulfur-containing marketed anticancer drugs included in this review direct the synthesis of novel compounds and willhelp in the development of potent, safer sulfur-based anticancer drugs in near future.

Preparation, Characterization, and Biological Assessment of Heterocyclic Schiff Base Metal Complexes

MIIMC, MMIIMC, and CMIIMC are biologically significant Schiff bases formed by the condensation of 3-amino-5-methyl isoxazole with formyl chromone. Substituted formyl chromones and metal chelates containing Cu(II), Ni(II), Co(II), and Zn(II) are prepared. These were studied utilising elemental analysis, FTIR, UV-VIS, 1H, 13C, mass spectra, magnetic susceptibility, conductance tests, and thermogravimetric techniques. The data revealed that the ligands display neutral, bidentate coordination through carbonyl oxygen and azomethine nitrogen. The antibacterial activity of the ligands and metal complexes is determined in vitro against bacteria and fungus using the paper disc method. Metal chelates have significantly higher MIC values against bacteria than ligands. The DNA binding properties of Cu(II) complexes were examined. MTT is used to determine the complexes' anticancer efficacy against HL60 tumour cells. The researchers discovered that the complexes prevented apparent morphological alterations. The inhibition ratio was hastened by increasing the dosage, and it had a strong positive association with the medicine dosage. Thermal analysis of complexes showed initial mass loss due to moisture and hydrated water molecules, followed by weight loss at 220oC due to coordinated water molecules, indicating metal oxide breakdown.

Augmented photocatalytic degradation of diclofenac by a novel TiO2-Chitosan-Bocalanine-Ni hybrid material under illumination of various light sources

TiO2-CBA-Ni composite (hydrothermally synthesized TiO2 nanoparticles loaded chitosan-bocalanine nickel complex) was successfully produced using solid and solution approaches, and the finished product was characterized using a variety of instrumentation techniques including UV–Visible, FT-IR, XRD, and SEM. Further, the efficient photocatalytic activity and recombination rates of the prepared TiO2-CBA-Ni composite were evaluated through photoluminescence (PL) spectra compared with pure TiO2. The photocatalytic degradation of diclofenac sodium (DCF) molecules was accomplished utilizing a TiO2-CBA-Ni composite with a pH range of 4.0 to 10.0 and varied light sources. Lower pH levels (pH = 4.0) reveal improved DCF degradation efficiency as compared to higher values (pH = 7.0 and 10.0) under any light source. More importantly, the TiO2-CBA-Ni composite degraded at a greater rate of 94.3 % in an identical reaction time (250 min) than other sources when exposed to visible light and at a lower pH (4.0). This effort has generated interest about the biopolymer grafted ligand metal complex functionalization over the photocatalyst and the effectiveness of the amalgamation, paving the way for a new path to eradicate the toxicity of pharmaceutical items from the ecosystem.

Distributed electrified heating for efficient hydrogen production

This study introduces a distributed electrified heating approach that is able to innovate chemical engineering involving endothermic reactions. It enables rapid and uniform heating of gaseous reactants, facilitating efficient conversion and high product selectivity at specific equilibrium. Demonstrated in catalyst-free CH4 pyrolysis, this approach achieves stable production of H2 (530 g h−1 L reactor−1) and carbon nanotube/fibers through 100% conversion of high-throughput CH4 at 1150 °C, surpassing the results obtained from many complex metal catalysts and high-temperature technologies. Additionally, in catalytic CH4 dry reforming, the distributed electrified heating using metallic monolith with unmodified Ni/MgO catalyst washcoat showcased excellent CH4 and CO2 conversion rates, and syngas production capacity. This innovative heating approach eliminates the need for elongated reactor tubes and external furnaces, promising an energy-concentrated and ultra-compact reactor design significantly smaller than traditional industrial systems, marking a significant advance towards more sustainable and efficient chemical engineering society.

Applications of Biodegradable Polymers in the Encapsulation of Anticancer Metal Complexes

AbstractMetal complexes have recently attracted a lot of attention, particularly as anticancer and antibacterial agents, owing to their versatile mechanisms and easily tunable characteristics. However, the application of such compounds in a medical context, especially in cancer treatment, has been hampered due to their limited solubility and stability in water and aqueous solutions, as well as a lack of selectivity. To address these limitations, several approaches have been developed to improve the targeted delivery of these compounds and their solubility. The first strategy involves the physical encapsulation of these metal complexes within carriers to facilitate controlled drug release. The second strategy involves covalently linking metal complexes to polymers, creating prodrugs that can be converted to active drugs at a more controllable rate. Despite the increasing variety of polymers available, the need to develop those able to be metabolized by the body, producing non‐toxic residues, remains crucial for effective treatment, particularly in the area of diseases such as cancer. In this perspective article, an overview of recent developments in the encapsulation of metal complexes using biodegradable polymers for cancer therapy is provided. It is specifically highlighting how the formed nanoparticles (NPs) enhance the selectivity and toxicity toward cancer cells compared to the parent metal complex, while simultaneously reducing the harmful side effects of traditional chemotherapies, opening the door for using them in combination therapies (PDT, PTT).

Comprehensive investigation on fabrication, spectral characterization and biological importance of Co(II) and Ni(II) heteroleptic complexes

Using the microwave irradiation approach, novel metallic complexes of Cobalt [Co(II)] and Nickel [Ni(II)] complexes of 2-aminothiazole (ATZ) and thiocyanate ligands [IUPAC Name: Di(2-aminothiazole) thiocyanato cobalt(II), Di(2-aminothiazole) thiocyanato nickel(II)] were created. The molecular formulas and the geometry of the complexes have been deduced by elemental analysis, molar conductance, magnetic moment, UV–visible, FT-IR, thermogravimetric analysis, cyclic voltammetry, and powder-XRD techniques. Molar conductance values indicate that the complexes are non-electrolyte (1:0) type. The complexes have octahedral structure is revealed by the magnetic moment and UV–visible spectra. The FT-IR spectra reveal that the 2-aminothiazole and thiocyanate ions are coordinated to the metal ion in a monodentate manner. The antibacterial capabilities of ligands and their Co(II) and Ni(II) compounds were studied against a restricted set of microorganisms utilizing the agar-well diffusion method and varying concentrations.When compared to free 2-aminothiazole ligand, the complexes exhibit possible activity against the fungus than bacteria. By assessing how well the complexes and ligands interact with the stable free radical DPPH, their ability to scavenge free radicals has been established. Comparing the complexes to the free ligand, the complexes exhibit greater antioxidant activity due to the fact that metal complexes are widely recognized for their capacity to accelerate medication action and boost therapeutic agent potency when they coordinate with a metal ion. The primary goal of this research is to develop multimodal medicinal drugs, which include studying the roles of 2-aminothiazole and its transition metal complexes.

Computational design of cooperatively acting molecular catalyst systems: carbene based tungsten- or molybdenum-catalysts with rhodium- or iridium-complexes for the ionic hydrogenation of N2 to NH3.

This density functional theory (DFT) study explores the efficacy of cooperative catalytic systems in enabling the ionic hydrogenation of N2 with H2, leading to NH3 formation. A set of N-heterocyclic carbene-based pincer tungsten/molybdenum metal complexes of the form [(PCP)M1(H)2] (M1 = W/Mo) were chosen to bind N2 at the respective metal centres. Simultaneously, cationic rhodium/iridium complexes of type [Cp*M2{2-(2-pyridyl)phenyl}(CH3CN)]+ (Cp* = C5(CH3)5 and M2 = Rh/Ir), are employed as cooperative coordination partners for heterolytic H2 splitting. The stepwise transfer of protons and hydrides to the bound N2 and intermediate NxHy units results in the formation of NH3. Interestingly, the calculated results reveal an encouraging low range of energy spans ranging from ∼30 to 42 kcal mol-1 depending on different combinations of ligands and metal complexes. The optimal combination of pincer ligand and metal center allowed for an energy span of unprecedented 29.7 kcal mol-1 demonstrating significant potential for molecular catalysts for the N2/H2 reaction system. While exploring obvious potential off-cycle reactions leading to catalyst deactivation, the computed results indicate that no increase in energy span would need to be expected.