Metal Coordination Research Articles

Voltammetric Investigations of Low-Coordinate Manganese As an Electrocatalyst for Organic Coupling and Functionalization

Earth-abundant, first row, low coordinate transition metal complexes are considered promising candidates for the electrocatalysis of many organic reactions. The use of transition metal catalysts is no stranger to the field of synthetic organic chemistry; however, many of the existing catalysts require the use of rare and expensive metals such as platinum, palladium, ruthenium, and iridium. In this study, we seek to identify and understand the mechanism by which an Mn(I) complex may act as an electrocatalyst for simple organic coupling and C-H functionalization reactions, beginning with the radicalization of benzyl bromide and benzyl chloride as representative organic halide substrates. The careful design and evaluation of this manganese complex has the potential to offer an effective non-toxic 3d metal electrocatalyst, provided that common transition metal behaviors, such as disproportionation or carbon-metal bond formation, are avoided. Initial characterization of the complex by cyclic voltammetry (CV) demonstrates general reversibility of the catalyst, while additions of benzyl halide exhibit the execution of the electron transfer and catalytic step. Electrochemical simulations run in parallel with CV experiments provide supplementary guidance into the relationship between the substrate and catalyst. Additional studies conducted using bulk electrolysis, mass spectrometry, nuclear magnetic resonance, and density functional theory (DFT) calculation will help to further characterize the mechanism and supporting details. Elucidation of the catalytic mechanism will allow us to use this electrocatalyst in a series of synthetic organic conditions and aid in our advancement toward sustainable organometallic catalysis.

Two new coordination polymers: crystal structures and photodegradation of the organic dye RhB

The solvothermal assemblies of a silicon-centered tetrahedral ligand as a principal building block, an N-donor ancillary ligand, and the corresponding metal salts yield two new transition metal coordination polymers (CPs), [Zn3(OH)(H2O)3L(ttb)]·3H2O (1) and [Co3(OH)(H2O)2L(ttb)(DMF)2]·2H2O (2) [H4L = 4,4',4'',4'''-silanetetrayltetrabenzoic acid, ttp = 1-(tetrazo-5-yl)-4-(triazo-1-yl)benzene, DMF = N,N-dimethylformamide]. Photocatalytic test results indicate that 1 and 2 can serve as excellent photocatalysts for Rhodamine B (RhB) degradation.

Carboxylate-Based Metal-Organic Framework and Coordination Polymer Glasses: Progress and Perspectives.

ConspectusCoordination polymers (CPs) and metal-organic frameworks (MOFs) represent versatile materials with diverse structural and functional properties, making them appealing for various applications. However, their conventional forms, which are typically synthesized as powders or crystals, pose challenges due to limited processability and mechanical fragility. Recently, CP/MOF glasses have emerged as promising alternatives, offering enhanced processability while retaining some of the unique characteristics shown in the mother crystalline materials. Despite the prevalence of carboxylate ligands in CP/MOF synthesis, the development of carboxylate-based CP/MOF glasses has been limited compared to that of zeolitic-imidazole framework (ZIF)-based glasses. This is attributed to the strong metal-ligand bonds and low thermal stability of carboxylic acids, which hinder their melting in CP/MOF structures. Nonetheless, recent advancements have led to a surge in methods for synthesizing carboxylate-based CP/MOF glasses. So far, desolvation and melt-quenching have been introduced for achieving glass structures from CP/MOF precursors.The first melt-quenched MOF glass was reported in 2015 with ZIFs. However, we informally observed the melting of the MOF during thermal decomposition research of aliphatic carboxylate-based MOFs as a sacrificial template dating back to 2013. In that study, aliphatic ligands, instead of aromatic carboxylate, were employed due to their high lability, lower thermal stability, and high degree of freedom, which facilitated pyrolysis. The results were published with a focus on synthesizing hierarchically porous MgO via the pyrolysis of an aliphatic ligand-based Mg-MOF in an inert environment. A decade later, it was revisited and studied as the first melt-quenched carboxylate-based MOF glass, converted from a crystalline MOF through the liquid phase before decomposition during the heating process.This Account aims to introduce six studies, including the aforementioned example, on the synthesis of CP/MOF glasses from carboxylate-based CPs/MOFs that have been published so far. To overcome the challenges with aromatic carboxylates in CP/MOF glass formation, the metal coordination sphere should be altered and the degree of freedom in the ligands should be increased. Based on these approaches, the strategies for vitrification of carboxylate-based CPs/MOFs can be divided into two categories: desolvation and melt-quenching. Desolvation can be preceded by vapor perturbation such as hydration. Carboxylate-based CP/MOF glasses possess the potential to expand into a broader range of applications beyond those of existing CP/MOF glasses. Alongside the diversity offered by carboxylic acid ligands, these materials mirror the extensive range of applications previously explored in the existing carboxylate-based CP/MOF crystals. Moreover, their high processability, inherent to glass materials, enables their applications in various industrial fields. This versatility may extend to previously unexplored areas of utilization such as a novel class of bioactive glass.

Coordination-Driven Nanomedicine Mitigates One-Lung Ventilation-Induced Lung Injury via Radicals Scavenging and Cell Pyroptosis Inhibition.

One-lung ventilation (OLV) during thoracic surgery often leads to post-operative complications, yet effective pharmacological interventions are lacking. This study reports a baicalin-based metal-coordination nanomedicine with disulfiram (DSF) co-loading to address one-lung ventilation-induced lung injury and reperfusion injury (OLV-LIRI). Baicalin, known for its robust antioxidant properties, suffers from poor water solubility and stability. Leveraging nanotechnology, baicalin's coordination is systematically explored with seven common metal ions, designing iron/copper-mediated binary coordination nanoparticles to overcome these limitations. The self-assembled nanoparticles, primarily formed through metal coordination and π-π stacking forces, encapsulated DSF, ensuring high colloidal stability in diverse physiological matrices. Upon a single-dose administration via endotracheal intubation, the nanoparticles efficiently accumulate in lung tissues and swiftly penetrate the pulmonary mucosa. Intracellularly, baicalin exhibits free radical scavenging activity to suppress inflammation. Concurrently, the release of Cu2+ and DSF enables the in situ generation of CuET, a potent inhibitor of cell pyroptosis. Harnessing these multifaceted mechanisms, the nanoparticles alleviate lung injury symptoms without notable toxic side effects, suggesting a promising preventive strategy for OLV-LIRI.

The enzymatic oxygen sensor cysteamine dioxygenase binds its protein substrates through their N-termini

The non-heme iron-dependent dioxygenase 2-aminoethanethiol (aka cysteamine) dioxygenase (ADO) has recently been identified as an enzymatic oxygen sensor that coordinates cellular changes to hypoxia by regulating the stability of proteins bearing an N-terminal cysteine (Nt-cys) through the N-degron pathway. It catalyzes O2-dependent Nt-cys sulfinylation, which promotes proteasomal degradation of the target. Only a few ADO substrates have been verified, including regulators of G-protein signaling (RGS) 4 and 5, and the proinflammatory cytokine interleukin-32, all of which exhibit cell and/or tissue specific expression patterns. ADO, in contrast, is ubiquitously expressed, suggesting it can regulate the stability of additional Nt-cys proteins in an O2-dependent manner. However, the role of individual chemical groups, active site metal, amino acid composition, and globular structure on protein substrate association remains elusive. To help identify new targets and examine the underlying biochemistry of the system, we conducted a series of biophysical experiments to investigate the binding requirements of established ADO substrates RGS5 and interleukin-32. We demonstrate, using surface plasmon response and enzyme assays, that a free, unmodified Nt-thiol and Nt-amine are vital for substrate engagement through active site metal coordination, with residues next to Nt-cys moderately impacting association and catalytic efficiency. Additionally, we show, through 1H-15N heteronuclear single quantum coherence nuclear magnetic resonance titrations, that the globular portion of RGS5 has limited impact on ADO association, with interactions restricted to the N-terminus. This work establishes key features involved in ADO substrate binding, which will help identify new protein targets and, subsequently, elucidate its role in hypoxic adaptation.

Flexible Metal-Organic Frameworks: From Local Structural Design to Functional Realization.

ConspectusFlexible metal-organic frameworks (MOFs), also known as soft porous crystals, exhibit dynamic behaviors in response to external physical and chemical stimuli such as light, heat, electric or magnetic field, or the presence of particular matters, on the premise of maintaining their crystalline state. The reversible structural transformation of flexible MOFs, a unique characteristic seldomly found in other types of known solid-state materials, affords them distinct properties in the realms of molecule separation, optoelectronic devices, chemical sensing, information storage, biomedicine applications, and so on. The mechanisms underlying their dynamic behaviors can be comprehensively investigated at the molecular level by means of in situ single-crystal or powder X-ray diffraction as well as other in situ spectroscopic techniques due to the high regularity of these crystalline materials during stimuli-responsive phase transitions. Through the introduction of specific stimuli-responsive groups/moieties into the well-defined and ordered molecular arrays, targeted applications can be achieved, and the performance of flexible MOFs can also be further improved via rational structural design.In this Account, we summarize our progress on the design, synthesis, and applications of flexible MOFs over the past few years. First, we highlight the construction principle of flexible MOFs, emphasizing the pivotal role of local structural design. Using an F-modified ligand, a flexible MOF with remarkable structural transformations can be obtained; the regulation of the metal coordination environment and interpenetrating frameworks is also crucial for achieving flexible MOFs. We also propose a strong correlation strategy based on the supramolecular interactions between the guest molecules and the framework, which realizes the temperature-responsive dynamic spatial "open-closed" regulation. Mechanisms of the dynamic behaviors investigated by the in situ techniques were also presented for the obtained materials. Second, some representative specific applications of the newly developed dynamic coordination systems were reviewed. The gas molecule responsive flexible MOFs show efficient short-chain alkane separation properties with discriminatory sorption behavior toward similar gaseous substrates. Smart sensing of temperature, pressure, and volatile organic compounds was achieved by several novel flexible fluorescent MOFs, with optimization potential through state-of-the-art chemical design. Furthermore, multiferroic materials with multiple bistable states and high working temperatures were also obtained based on flexible MOFs.Finally, we provide a discussion of the challenges of flexible MOFs in future research, including precise and efficient synthesis, in-depth structure-property relationship investigation, performance optimization, and industrialization. We hope that this Account will stimulate further research interest in developing next-generation smart materials based on flexible MOFs for applications in challenging chemical separation, extreme environmental sensing, massive information storage, and beyond.

Ultrarobust, Self-Healing Poly(urethane-urea) Elastomer with Superior Tensile Strength and Intrinsic Flame Retardancy Enabled by Coordination Cross-Linking.

Poly(urethane-urea) elastomers (PUUEs) have gained significant attention recently due to their growing demand in electronic skin, wearable electronic devices, and aerospace applications. The practical implementation of these elastomers necessitates many exceptional properties to ensure robust and safe utilization. However, achieving an optimal balance between high mechanical strength, good self-healing at moderate temperatures, and efficient flame retardancy for poly(urethane-urea) elastomers remains a formidable challenge. In this study, we incorporated metal coordination bonds and flame-retarding phosphinate groups into the design of poly(urethane-urea) simultaneously, resulting in a high-strength, self-healing, and flame-retardant elastomer, termed PNPU-2%Zn. Additional supramolecular cross-links and plasticizing effects of phosphinate-endowed PUUEs with relatively remarkable tensile strength (20.9 MPa), high elastic modulus (10.8 MPa), and exceptional self-healing efficiency (above 97%). Besides, PNPU-2%Zn possessed self-extinguishing characteristics with a limiting oxygen index (LOI) of 26.5%. Such an elastomer with superior properties can resist both mechanical fracture and fire hazards, providing insights into the development of robust and high-performance components for applications in wearable electronic devices.

Review of Hydrogen Sulfide Based on Its Activity Mechanism and Fluorescence Sensing

The significance of hydrogen sulfide (H2S) in biological research is covered in detail in this work. H2S is a crucial gas-signaling molecule that is involved in a wide range of illnesses and biological processes. Whether H2S has a beneficial therapeutic effect or negative pathological toxicity in an organism depends on changes in its concentration. A novel approach to treatment is the regulation of H2S production by medications or other measures. Furthermore, H2S is a useful marker for disease assessment because of its dual nature and sensitivity. We can better understand the onset and progression of disease by developing probes to track changes in H2S concentration based on the nucleophilicity, reducing properties, and metal coordination properties of H2S. This will aid in diagnosis and treatment. These results demonstrate the enormous potential of H2S in the detection and management of disease. Future studies should concentrate on clarifying the relationship between diseases and the mechanism of action of H2S in organisms. Ultimately, this work opens new possibilities for disease diagnosis and treatment while highlighting the significance of H2S in biological research. Future clinical practice and medical advancements will benefit greatly from our thorough understanding of the mechanism of action and therapeutic applications of H2S.

Cinquefoil Knot Possessing Dynamic and Tunable Metal Coordination.

While the majority of knots are made from the metal-template approach, the use of entangled, constrained knotted loops to modulate the coordination of the metal ions remains inadequately elucidated. Here, we report on the coordination chemistry of a 140-atom-long cinquefoil knotted strand comprising five tridentate and five bidentate chelating vacancies. The knotted loop is prepared through the self-assembly of asymmetric "3 + 2" dentate ligands with copper(II) ions that favor five-coordination geometry. The formation of the copper(II) pentameric helicate is confirmed by X-ray crystallography, while the corresponding copper(II) knot is characterized by XPS and LR-/HR ESI-MS. Upon removal of the original template, the knotted ligand facilitates zinc(II) ions, which typically form four- or six-coordination geometries, resulting in the formation of an otherwise inaccessible zinc(II) metallic knot with coordinatively unsaturated metal centers. The coordination numbers and geometries of the zinc(II) cations are undoubtedly determined by X-ray crystallography. Despite the kinetically labile nature and high reversibility of the zinc(II) complex preventing the detection of 5-to-6 coordination equilibrium in solution, the effects on metal-ion coordination induced by knotting hold promise for fine-tuning the coordination of metal complexes.

Proton Transfer Kinetics in Histidine Side Chains Determined by pH-Dependent Multi-Nuclear NMR Relaxation.

Histidine is a key amino-acid residue in proteins with unique properties engendered by its imidazole side chain that can exist in three different states: two different neutral tautomeric forms and a protonated, positively charged one with a pKa value close to physiological pH. Commonly, two or all three states coexist and interchange rapidly, enabling histidine to act as both donor and acceptor of hydrogen bonds, coordinate metal ions, and engage in acid/base catalysis. Understanding the exchange dynamics among the three states is critical for assessing histidine's mechanistic role in catalysis, where the rate of proton exchange and interconversion among tautomers might be rate limiting for turnover. Here, we determine the exchange kinetics of histidine residues with pKa values representative of the accessible range from 5 to 9 by measuring pH-dependent 15N, 13C, and 1H transverse relaxation rate constants for 5 nuclei in each imidazole. Proton exchange between the imidazole and the solvent is mediated by hydronium ions at acidic and neutral pH, whereas hydroxide mediated exchange becomes the dominant mechanism at basic pH. Proton transfer is very fast and reaches the diffusion limit for pKa values near neutral pH. We identify a direct pathway between the two tautomeric forms, likely mediated by a bridging water molecule or, in the case of high pH, hydroxide ion. For histidines with pKa 7, we determine all rate constants (lifetimes) involving protonation over the entire pH range. Our approach should enable critical insights into enzymatic acid/base catalyzed reactions involving histidines in proteins.

Electrocatalytic CO2 conversion on boron nitride nanotubes by metal single-atom engineering

Atomically dispersed single metal on defective boron nitride nanotubes (BNNTs) show promising potential for CO2 electrocatalytic reduction reaction (CO2ERR). Using density functional theory calculations, we explore the CO2ERR mechanism on single-atom catalysts (SACs) supported on BNNTs as well as assess their electrocatalytic performance of these catalysts. Boron or nitrogen vacancies in BNNTs are doped with palladium, platinum, or rhodium atoms to form three-coordinated metal centers, denoted as M@BNNT-V (M = Pt, Rh, Pd; V = B vacancy or N vacancy). Pt@BNNT with boron vacancies (Pt@BNNT-Bvac) demonstrates a tendency to facilitate multi-electron reduction processes leading to the formation of complex molecules such as CH2O, CH3OH, and CH4 with a limiting potential (UL) of −0.36 V. Conversely, Rh@BNNT-Bvac and Pd@BNWNT-Bvac show significantly lower limiting potentials of −0.06 V and −0.12 V, respectively, for the reduction to formic acid (HCOOH), with Rh@BNNT-Bvac exhibiting enhanced activity and selectivity. Additionally, the deep reduction to other hydrocarbons or oxygenates, which typically requires potentials of −0.72 V and −0.60 V, appears less likely on both Rh and Pd doped BNNT-Bvac, further delineating the nuanced performance differences induced by metal type and coordination environment within the BNNT structure.

Functionalizing Thiosemicarbazones for Covalent Conjugation.

Thiosemicarbazones (TSCs) with their modular character (thiosemicarbazides + carbonyl compound) allow broad variation of up to four substituents on the main R1R2C=N(1)-NH-C(S)-N(4)R3R4 core and are thus interesting tools for the formation of conjugates or the functionalization of nanoparticles (NPs). In this work, di-2-pyridyl ketone was introduced for the coordination of metals and 9-anthraldehyde for luminescence as R1 and R2 to TSCs. R3 and R4 substituents were varied for the formation of conjugates. Amino acids were introduced at the N4 position to produce [R1R2TSC-spacer-amino acid] conjugates. Further, functions such as phosphonic acid (R-P(O)(OH)2), D-glucose, o-hydroquinone, OH, and thiol (SH) were introduced at the N4 position producing [R1R2TSC-spacer-anchor group] conjugates for direct NP anchoring. Phenyl, cyclohexyl, benzyl, ethyl and methyl were used as spacer units. Both phenyl phosphonic acid TSC derivatives were bound on TiO2 NPs as a first example of direct NP anchoring. [R1R2TSC-spacer-end group] conjugates including OH, S-Bn (Bn = benzyl), NH-Boc (Boc = tert-butyloxycarbonyl), COOtBu, C≡CH, or N3 end groups were synthesized for potential covalent binding to functional molecules or functionalized NPs through amide, ester, or triazole functions. The synthesis of the thiosemicarbazides H2NNH-C(S)-NR3R4 starting from amines, including amino acids, SCCl2 or CS2, and hydrazine and their condensation with dipyridyl ketone and anthraldehyde led to 34 new TSC derivatives. They were synthesized in up to six steps with overall yields ranging from 10 to 85% and were characterized by a combination of nuclear magnetic resonance spectroscopy and mass spectrometry. UV-vis absorption and photoluminescence spectroscopy allowed us to easily trace the dipyridyl imine and anthracene chromophores.

Synthesis, structural, biological applications, DFT, molecular docking studies on Fe(III), Co(II), and Ni(II) complexes incorporating 2‐(pyridin‐2‐yl)phenol and 1H‐benzimidazole‐2‐carboxylic acid

This study provides a detailed investigation into the synthesis, characterization, and biological activities of the coordination compounds FePPHBZC, CoPPHBZC, and NiPPHBZC. These compounds were synthesized with high yields by reacting chloride salts of Iron, Cobalt, or Nickel with 2‐(pyridin‐2‐yl)phenol (PPH) and 1H‐benzimidazole‐2‐carboxylic acid (BZC) in a 1:1:1 ratio. Various techniques including spectroscopic (IR, UV–vis, mass spectra), elemental analysis, conductivity, magnetic, and thermal analyses confirmed the formation and structure of these coordination compounds. Density functional theory (DFT) calculations were used to study their electronic structure, stability, and reactivity. 3D modeling revealed hexacoordinated geometries for Fe and Co complexes and a tetrahedral coordination for the Ni complex. Analysis of the highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), and other reactivity parameters indicated changes in reactivity upon metal coordination. Molecular Electrostatic Potential (MEP) diagrams identified electron‐rich areas prone to nucleophilic attack, important for protein interactions during docking studies. Biological evaluations demonstrated that metal–ligand complexes exhibit enhanced antimicrobial, antioxidant, and anti‐inflammatory activities compared to individual ligands, with larger inhibition zones and higher inhibitory activity. Molecular docking studies showed strong interactions between metal–ligand complexes and target proteins, suggesting potential therapeutic applications. Among them, FePPHBZC exhibited the strongest interactions, followed by CoPPHBZC and NiPPHBZC, characterized by hydrogen bonding, ionic interactions, and other non‐covalent interactions, contributing to their enhanced stability and binding affinity.

Capturing Mercury-197m/g for Auger Electron Therapy and Cancer Theranostic with Sulfur-Containing Cyclen-Based Macrocycles.

The interest in mercury radioisotopes, 197mHg (t1/2 = 23.8 h) and 197gHg (t1/2 = 64.14 h), has recently been reignited by the dual diagnostic and therapeutic nature of their nuclear decays. These isotopes emit γ-rays suitable for single photon emission computed tomography imaging and Auger electrons which can be exploited for treating small and metastatic tumors. However, the clinical utilization of 197m/gHg radionuclides is obstructed by the lack of chelators capable of securely binding them to tumor-seeking vectors. This work aims to address this challenge by investigating a series of chemically tailored macrocyclic platforms with sulfur-containing side arms, namely, 1,4,7,10-tetrakis[2-(methylsulfanyl)ethyl]-1,4,7,10-tetraazacyclododecane (DO4S), 1,4,7-tris[2-(methylsulfanyl)ethyl]-1,4,7,10-tetraazacyclododecane (DO3S), and 1,7-bis[2-(methylsulfanyl)ethyl]-1,4,7,10-tetraazacyclododecane-4,10-diacetic acid (DO2A2S). 1,4,7,10-Tetrazacyclododecane-1,4,7,10-tetracetic acid (DOTA), the widest explored chelator in nuclear medicine, and the nonfunctionalized backbone 1,4,7,10-tetrazacyclododecane (cyclen) were considered as well to shed light on the role of the sulfanyl arms in the metal coordination. To this purpose, a comprehensive experimental and theoretical study encompassing aqueous coordination chemistry investigations through potentiometry, nuclear magnetic resonance (NMR) spectroscopy, X-ray crystallography, and density functional theory (DFT) calculations, as well as concentration- and temperature-dependent [197m/gHg]Hg2+ radiolabeling and in vitro stability assays in human serum was conducted. The obtained results reveal that the investigated chelators rapidly complex Hg2+ in aqueous media, forming extremely thermodynamically stable 1:1 metal-to-ligand complexes with superior stabilities compared to those of DOTA or cyclen. These complexes exhibited 6- to 8-fold coordination environments, with donors statically bound to the metal center, as evidenced by the presence of 1H-199Hg spin-spin coupling via NMR. A similar octacoordinated environment was also found for DOTA in both solution and solid state, but in this case, multiple slowly exchanging conformers were detected at ambient temperature. The sulfur-rich ligands quantitatively incorporate cyclotron-produced [197m/gHg]Hg2+ under relatively mild reaction conditions (pH = 7 and T = 50 °C), with the resulting radioactive complexes exhibiting decent stability in human serum (up to 75% after 24 h). By developing viable chelators and understanding the impact of structural modifications, our research addresses the scarcity of suitable chelating agents for 197m/gHg, offering promise for its future in vivo application as a theranostic Auger-emitter radiometal.

Strain-Releasing Ring-Opening Diphosphinations for the Synthesis of Diphosphine Ligands with Cyclic Backbones.

Diphosphine ligands based on cyclobutane, bicyclo[3.1.1]heptane, and bicyclo[4.1.1]octane were synthesized from the corresponding highly strained, small, cyclic organic molecules, i.e., bicyclo[1.1.0]butane, [3.1.1]propellane, and [4.1.1]propellane, employing a ring-opening diphosphination. Under photocatalytic conditions, the three-component reaction of a diarylphosphine oxide, one of the aforementioned strained molecules, and a diarylchlorophosphine results in the smooth formation of the corresponding diphosphines in high yield. The obtained diphosphines can be expected to find applications in functional molecules due to their unique structural characteristics, which likely impart specific properties on their associated metal complexes and coordination polymers (e.g., a zigzag-type structure). The feasibility of the initial radical addition can be estimated using density-functional-theory calculations using the artificial force induced reaction (AFIR) method. This study focuses on the importance of integrating experimental and computational methods for the design and synthesis of new diphosphination reactions that involve strained, small, cyclic organic molecules.

Polymeric pH-Responsive Metal-Supramolecular Nanoparticles for Synergistic Chemo-Photothermal Therapy.

Stimuli-responsive drug delivery carriers, particularly those exhibiting pH sensitivity, have attracted significant scholarly interest due to their promising potential in anticancer therapeutic applications. This phenomenon can primarily be ascribed to the inherently acidic nature of tumor microenvironments. However, pH-responsive carriers frequently require the incorporation of functional groups or materials sensitive to pH changes. Given the pH-sensitive characteristics of metal coordination with natural small-molecule drugs, organometallic supramolecules present a facile and effective strategy for integrating pH-responsive behavior into these systems. Meanwhile, utilizing the natural compound luteolin in conjunction with iron ions (Fe3+) through the advanced engineering technique of flash nanoprecipitation (FNP) results in the synthesis of stable, highly loaded nanoparticles (NPs) exhibiting a supramolecular photothermal effect. Our experimental findings substantiate that the photothermal effect persists over time, even after the pH-responsive release phase has ended. Consequently, these polymeric pH-responsive metallic supramolecular nanoparticles integrate chemotherapy and photothermal therapy, creating a synergistic approach to cancer treatment. This bifunctional platform, which exhibits both pH-responsive and photothermal properties, presents a highly promising avenue for biomedical applications, particularly in the area of tumor therapies. Its dual function offers a potentially efficacious approach to tumor treatment.

Preparation and Properties of Multiple Dynamic Crosslinked Poly(siloxane‐urethane)

AbstractSelf‐healing poly(siloxane‐urethane) materials have garnered significant interest among researchers, owing to their superior resistance to high and low temperatures, solvents, corrosion, and biocompatibility. Nevertheless, most existing self‐healing poly(siloxane‐urethane) materials face challenges, including limited repair conditions and the challenge of balancing mechanical properties with repair efficiency. In this research, we introduced hydrogen bonds, metal coordination bonds, π–π bonds, and reversible ring structures into the poly(siloxane‐urethane) system through molecular chain structure design, successfully developing a multi‐dynamic cross‐linked poly(siloxane‐urethane) (PU‐Si), a development rarely reported in prior studies. This study examines the impact of varying amounts of hydroxyl‐terminated polydimethylsiloxane (PDMS‐OH) on the properties of PU‐Si. The results indicate that PU‐Si, regardless of the amount of PDMS‐OH added, can self‐healing under conditions of heating at 60 °C, and exposure to ultraviolet and infrared radiation. Specifically, when the PDMS‐OH addition reaches 1.0 g, the material exhibits superior mechanical properties and self‐healing efficiency, achieving a mechanical strength of 9.68 MPa and a self‐healing efficiency of 86.6 %. This material shows significant application potential in areas such as electronic skins, flexible sensors, and brain‐computer interfaces.

Investigation of physical, thermal and morphological properties of CuCl2 modified polyurethane sponges

There are many types of polyurethane sponge (PUS), depending on properties such as hardness, flexibility and surface texture. The fact that it can be produced in any shape and size has given it very wide range of applications. Surface modification is one of the most commonly used methods to improve the performance of PUS. Here, inspired by metal coordination polymers, a simpler and faster method for surface modification of PUS with metal ions compared to bulk modification was proposed. In the case of copper, which is often used for PUS modification, the change in the basic properties sought in different applications as a function of the concentration of the modifier was investigated. Samples prepared by immersing sponges in solutions of copper chloride salt were subjected to physical, thermal and morphological analyses. Due to the modification, the coordination bonds between CuCl2 and polyurethane were revealed by XPS and FTIR. SEM and EDS studies of the PUS revealed both closed and open cells. DSC and TGA analysis showed that the obtained product had better thermal stability than the unmodified product. When the PUS was modified with 0.5 Cu, the water contact angle increased from 101.32° to 135.01° and hydrophobic properties were imparted to all pore surfaces, and the desired properties such as porosity, density could be adjusted. Furthermore, it is envisaged that the surface, mechanical and thermal properties will make it suitable for use in a range of practical applications such as medical and environmental.

Protonation of histidine rings using quantum-mechanical methods.

Histidine can be protonated on either or both of the two N atoms of the imidazole moiety. Each of the three possible forms occurs as a result of the stereochemical environment of the histidine side chain. In an atomic model, comparing the possible protonation states in situ, looking at possible hydrogen bonding and metal coordination, it is possible to predict which is most likely to be correct. A more direct method is described that uses quantum-mechanical methods to calculate, also in situ, the minimum geometry and energy for comparison, and therefore to more accurately identify the most likely protonation state.

Multisite Amino‐Allylidene Ligands from Thermal CO Elimination in Diiron Complexes and Catalytic Activity in Hydroboration Reactions

AbstractThe new diiron(I) complexes [Fe2Cp2(μ‐CO){μ‐k3C,kN‐C(R1)C(R2)C(CN)NMe(R)}], 3 a–o (R=alkyl or 4‐C6H4OMe; R1=alkyl, aryl, ferrocenyl (Fc), thiophenyl, CO2Me or SiMe3; R2=H, Me or CO2Me) were synthesized in moderate to high yields from the thermal decarbonylation of the bis‐carbonyl precursors 2 a–o, and were structurally characterized by IR and NMR spectroscopy, and single crystal X‐ray diffraction in four cases. Electrochemical behavior of one complex was also investigated. Complexes 3 a–o comprise a highly functionalized, multisite amino‐(cyano)allylidene ligand, including metal coordination of a tertiary amine group. Selected complexes displayed negligible to moderate catalytic activity in CO2/propylene oxide coupling, working under ambient conditions. Additionally, they were investigated as catalysts for the conversion of benzaldehyde to the corresponding borate ester 6 a, using pinacolborane (HBpin) as the borylating agent. Most complexes achieved good conversions at room temperature with 1 % catalyst loading, and data highlight the significant influence of the multisite ligand substituents on the catalytic performance. Notably, complex 3 m (featuring R=4‐methoxyphenyl, R1=Fc, R2=H) displayed the highest activity and effectively catalyzed the hydroboration of various aldehydes and ketones. A plausible mechanistic cycle involves metal coordination of the carbonyl substrate, its activation being possibly facilitated by intramolecular interactions.