Macrocyclic Complexes Research Articles

Synthesis, spectroscopic characterization, density functional theory, molecular docking studies, antioxidant and antimicrobial potential of novel Schiff base macrocyclic complexes of bivalent manganese

The threat of antibiotic resistance to public health is becoming a major cause of mortality on a worldwide scale. It has stimulated the interest of researchers in the development of novel antibiotics. Therefore, a new series of Schiff base macrocyclic ligands (N8MacL1‐N8MacL3) and their bivalent manganese complexes were synthesized and analyzed for biological activities. Characterization of the synthesized macrocyclic compounds was done by various spectroscopic techniques like elemental analysis, infrared (IR), proton nuclear magnetic resonance (NMR), 13C NMR, ultraviolet–visible, mass, electron paramagnetic resonance (EPR), and powder X‐ray diffraction (PXRD). Based on spectral studies, an octahedral environment has been proposed around the manganese metal center in the synthesized macrocyclic complexes. Density functional theory (DFT) calculations were used to evaluate the stability and the electronic properties of the synthesized macrocyclic ligands and their Mn (II) complexes. The structures of the synthesized compounds were optimized by using the def2‐SVP basis set at B3LYP level. The synthesized compounds were evaluated against gram‐positive bacterial strains (Staphylococcus aureus and Bacillus cereus), gram‐negative bacterial strains (Escherichia coli and Xanthomonas campestris), and fungal strains (Candida albicans and Fusarium oxysporum) for their antimicrobial activity by agar well diffusion method. Among all of the newly synthesized compounds, the macrocyclic complex [Mn(N8MacL3)Cl2] exhibited high antimicrobial activity against all bacterial and fungal strains except S. aureus. The virtual screening of synthesized Schiff base ligand [L], macrocyclic ligands (N8MacL1‐N8MacL3), and their Mn (II) complex [Mn(N8MacL1)Cl2‐Mn(N8MacL3)Cl2] are performed against the receptors, which were used for in vitro antimicrobial testing, to identify the most plausible drug–ligand interactions. The scavenging activity of DPPH radicals was utilized to study the antioxidant activity of the synthesized compounds. The macrocyclic metal complex [Mn(N8MacL3)Cl2] exhibited excellent antioxidant activity.

Extraordinary Control of Photosensitized Singlet Oxygen Generation by Acyclic Cucurbituril-like Containers

Supramolecular control of singlet oxygen generation is incredibly valuable for several fields with broad applications and thus still challenging. However, macrocyclic inclusion complexes inherently restrict the interaction of photosensitizers with surrounding oxygen in the media. To circumvent this issue, we turned our attention in this work to acyclic cucurbituril-like containers and uncover their properties as supramolecular hosts for photosensitizers with extraordinary control of their photophysics, including singlet oxygen generation. Thermodynamic and photophysical studies were carried out showing that these acyclic containers compare very favorably to benchmark macrocycles such as cucurbiturils and cyclodextrins in terms of their binding affinities and supramolecular control of singlet oxygen generation. Acyclic container with terminal naphthalene walls offers a similar cavity to cucurbit[7]uril and the same carbonyl-lined portals for a tight binding of phenothiazinium dye methylene blue and stabilizing its singlet and triplet excited states. Thus, generation of singlet oxygen for this container is higher than for other macrocycles and even higher than the free photosensitizer. While the acyclic container with smaller terminal benzene walls, stacks over the dye through sulfur-π and π-π interactions deactivating the singlet and triplet excited states, thus showing the lowest generation of singlet oxygen out of all of the studied systems. Due to the great water solubility and biocompatibility of these systems, they possess great potential for novel applications in photocatalysis, synthesis, and biomedical fields, among others.

Optical and Antimicrobial Activity of Nanostructured Mn(II) and Cu(II) Macrocyclic Complexes Derived from Aspartic Acid

Optical and Antimicrobial Activity of Nanostructured Mn(II) and Cu(II) Macrocyclic Complexes Derived from Aspartic Acid

Trends in the Electronic Structure and Chemical Bonding of a Series of Porphyrinoid-Uranyl Complexes.

In this paper, we have explored the relativistic density functional theory study on a series of deprotonated porphyrinoid (Ln) complexes of uranyl to investigate the geometrical structures and chemical bonding. The ligands bound with uranyl in the 1:1 complexes [UO2(Ln)]x (n = 4, 5, 6; x = 0, -1, -2), showing more thermodynamic stability for "in-cavity" structures of L5 and L6 than that of the "side-on" structure of L4 and an increase in stability with the increase of negative charges, L2- < L3- < L4-. Among the six ligands, the cyclo[6]pyrrole presents the best selectivity toward uranyl. Based on chemical bonding analyses, the U-NL bond in the in-cavity complexes adopts a typical dative NL → U bond with mainly ionic bonding and significant covalency, which comes from the significant orbital interaction of U 5fϕ6dδ7s hybrid AOs and NL 2p-based MOs. This work provides a systematic understanding of the coordination chemistry in uranyl pyrrole-containing macrocycle complexes and the nature of chemical bonding in such systems, which may provide inspirations for the future design of synthetic targets that could be relevant to actinide separations or in the remediation of spent nuclear fuel.

DFT Method Used for Prediction of Molecular and Electronic Structures of Mn(VI) Macrocyclic Complexes with Porhyrazine/Phthalocyanine and Two Oxo Ligands.

By using the data of the DFT quantum chemical calculation in the OPBE/TZVP and B3PW91/TZVP levels, the possibility of the existence of a manganese(VI) heteroligand complex containing porphyrazine or its tetra[benzo] derivative (phthalocyanine) and two oxygen (O2-) ligands, which is still unknown for this element, is shown. The parameters of the molecular structure, multiplicity of the ground state, NBO analysis data and standard thermodynamic parameters (enthalpy ΔH0f, entropy S0f and Gibbs's energy ΔG0f of formation) of each of these metal macrocyclic compounds are presented. Additionally, it is noted that, based on the totality of structural data obtained by the above versions of the DFT method, the existence of a similar complex of manganese with di[benzo] derivative of porhyrazine and two oxygen (O2-) ligands seems doubtful.

Anti-corrosive agents based benzil-thiocarbohydrazone macrocyclic ligand-derived Cu (II) and Zn (II) chelates: template synthesis and physically admixing with epoxy coating

PurposeThis paper aims to focus on the synthesis of the macrocyclic complexes (Cu and Zn) and their applications as anticorrosive materials in epoxy paint formulation for surface coating application.Design/methodology/approachA selected macrocyclic Cu(II) and Zn(II) complexes were prepared via template synthesis and characterized using Fourier transform infrared, thermal gravimetric analysis, scanning electron microscope, flexibility, hardness and adhesion of coating films prepared using epoxy paint.FindingsThe corrosion resistance of the epoxy-painted films was improved due to the incorporation of the Zn and Cu complexes into the formulation.Originality/valueIt was found that the metal complex-based formulation with Cu(II) and Zn(II) had outperformed the sample blank.

Development of Macrocyclic Mn(II)−Bispyridine Complexes as pH‐Responsive Magnetic Resonance Imaging Contrast Agents

AbstractIn this study, macrocyclic complexes of Mn (II) with pH‐responsive relaxivities were developed. The ligands were based on the rigid MPi platform, which was composed of a triazacyclononane (TACN) macrocycle and two picolyl pendant arms. An aryl sulfonamide moiety introduced in the skeleton of MPi endowed the final Mn complex (Mn−MPA) with pH‐sensitive relaxivities. Mn−MPA showed a ∼3‐fold increase in longitudinal relaxivity associated with the protonation and decoordination of the sulfonamide group in an acidic environment. We found that it was feasible to tune the pH window of the complexes by choosing proper substituents on the aromatic ring or modifying on the picolyl pendants. Considering the good kinetic inertness, rapid and efficient response to pH stimuli, and easy modulation characteristics, Mn−MPAs can be considered ideal candidates for use as acidic microenvironment‐specific MRI contrast agents.

Carboxyl substituted Bambus[6]uril as a novel macrocyclic receptor for cyanide anion: A DFT study

Using density functional theory calculations, the most probable conformation of CN– based carboxyl substituted bambus[6]uril complex was investigated. The molecular complex shows the C3 symmetry in which the cyanide anion resides in the cavity of the macrocyclic complex. The parent macrocycle reduces the diameter of its inner cavity to adjust the anionic specie. Furthermore, we report the AIM and NCI analysis to interpret various non-covalent interactions between the CN– and carboxyl-substituted BU[6] macrocycle. The results of NCI analysis show certain types of noncovalent interactions between the receptor and anion, which are responsible for the stability of the complex. Four N….…H-type interactions between the anion and hydrogen atoms of the methine group in the macrocycle exhibit H-bonds, which are analyzed by QTAIM. The interaction energy of the optimized complex was –81.25 kcal/mol.

General Synthesis of a Diatomic Catalyst Library via a Macrocyclic Precursor-Mediated Approach.

Heterogeneous catalysts containing diatomic sites are often hypothesized to have distinctive reactivity due to synergistic effects, but there are limited approaches that enable the convenient production of diatomic catalysts (DACs) with diverse metal combinations. Here, we present a general synthetic strategy for constructing a DAC library across a wide spectrum of homonuclear (Fe2, Co2, Ni2, Cu2, Mn2, and Pd2) and heteronuclear (Fe-Cu, Fe-Ni, Cu-Mn, and Cu-Co) bimetal centers. This strategy is based on an encapsulation-pyrolysis approach, wherein a porous material-encapsulated macrocyclic complex mediates the structure of DACs by preserving the main body of the molecular framework during pyrolysis. We take the oxygen reduction reaction (ORR) as an example to show that this DAC library can provide great opportunities for electrocatalyst development by unlocking an unconventional reaction pathway. Among all investigated sites, Fe-Cu diatomic sites possess exceptional high durability for ORR because the Fe-Cu pairs can steer elementary steps in the catalytic cycle and suppress the troublesome Fenton-like reactions.

X-ray Absorption Spectroscopy Studies of a Molecular CO2-Reduction Catalyst Deposited on Graphitic Carbon Nitride

Metal–ligand complexes have been extensively explored as well-defined molecular catalysts in small molecule activation reactions such as carbon dioxide (CO2) reduction. Many hybrid photocatalysts have been prepared by coupling such complexes with photoactive surfaces for use in solar CO2 reduction. In this work, we employ X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies, density functional theory (DFT) and computational XANES modeling to interrogate the structure of a hybrid photocatalyst consisting of a macrocyclic cobalt complex deposited on graphitic carbon nitride (C3N4). Results show that the cobalt complex binds on C3N4 through surface OH or NH2 groups. By refining the local geometry and binding sites of this well-defined molecular cobalt complex on C3N4, we established an important benchmark for modeling a large class of molecular catalysts that can be adapted to in situ/operando studies and further enhanced by applying chemometrics-based approaches and machine learning methods of XANES data analysis.

Electrochemical, Antimicrobial, and Theoretical Investigations of Synthetic tetra-aza/penta-aza-Macrocyclic Complexes

The tailoring of the coordination environment around a central metal ion by changing ligands in macrocyclic complexes is one of the key approaches to monitoring their functions in various applications. Herein, two macrocyclic complexes of Co(II) transition metal ion, tetra-aza and penta-aza, were synthesized using a condensation reaction between different diamine and dicarboxylic precursors. The prepared complexes were analyzed using various characterization techniques. Further, the electrochemical behavior of both the tetra-aza and penta-aza complexes was investigated using cyclic voltammetry. The Co(II)-penta-aza-complex exhibited a quasi-reversible redox couple for Co(III)/Co(II) transition in the more anodic region as compared to Co(II)-tetra-aza-complex. According to theoretical calculations, the fifth N-coordination transferred a high electron density in the eg-orbital of Co-atom of penta-aza-complex, resulting in an anodic shift in the Co(III)/Co(II) redox potential when compared to the Co(II)-tetra-aza-complex. Furthermore, both complexes were tested for antimicrobial activity against P. aeruginosa, E. coli, S. aureus, and B. subtilis, with the results indicating that Co(II)-penta-aza-complex had higher antimicrobial activity against these bacteria than Co(II)-tetra-aza-complex. This study offers new insight into tailoring the electrochemical and biological features of macrocyclic complexes by tuning the coordination environment around the central metal ion.

Macrocyclic pseudo crown-ether- manganese (II) complex coated on nanomagnetic LDH- catalyzed Biginelli annulation reactions

A single-site macrocyclic pseudo crown ether-manganese complex was generated from the complexation of a new tetradentate ligand brought from a synthetic procedure with manganese (II) halide precursor in an electron-transfer process. The prepared [γ-Fe2O3@LDH/PCE-Mn(II)] acts as an efficient heterogeneous Mn-based catalyst – exhibiting efficient catalytic activity in the synthesis of the functionalized chromeno-pyrimidines via a Biginelli-like annulation process. Moreover, Biginelli reaction of a variety of aryl aldehydes and carbamide/thiocarbamide with a β-ketoester moiety was achieved in ethanol at 60 °C with 65–92% yield in 10–40 min. This catalytic process can be initiated using the Mn(II)-catalyzed in situ generation of an imine intermediate. Subsequently, the addition of a β-ketoester moiety – followed by the ring-closure reaction and removal of a water molecule – forms a library of new chromeno-pyrimidine-2,5-diones/thione products with a broad substrate scope.

Front Cover: Kinetically‐Locked Metallomacrocycle for Host‐Guest Chemistry with Bulky Anions (Eur. J. Inorg. Chem. 4/2023)

The Front Cover shows host-guest chemistry of the kinetically locked macrocyclic metal complex prepared in two steps, Co(II)-assisted self-assembly to form the discrete macrocycle and subsequent oxidation of the metal centers to fix the coordination bonds. Since the macrocycle has a robust and large cavity surrounded by 9,10-diphenylanthracence units as p panels and cationic charges on the metal centers, a bulky guest molecule, NaBPh4, was accommodated in it efficiently with multiple interaction. The cover was designed by Dr. Issey Takahashi (ITbM, Nagoya University). More information can be found in the Research Article by K. Tanaka and co-workers.

Acoplanarity, Aromaticity, Chirality, and Helical Twisting Power of Chlorin e6 13(N)-Methylamide-15,17-dimethyl Ester Complexes: Effect of a Metal

The experimental and theoretical study of the influence of metal complexing on geometry, aromaticity, chirality, and the ability to twist the nematic phase by complexes based on modified natural chlorin e6 was carried out. The geometry optimization of the chlorin e6 13(N)-methylamide-15,17-dimethyl ester (MADMECl) and its Zn, Cu, and Ni complexes by DFT (CAM-B3LYP/6–31 G(d,p) functional) method was performed. Based on these calculations, the acoplanarity degree of the macrocyclic ligand and the distortion energy of its dianion were estimated, which allowed the arrangement of the MADMECl complexes in the series Ni &gt; Cu &gt; Zn. Aromaticity was evaluated using the NICS criterion (nuclear independent chemical shift). An increase in the degree of aromaticity of the macrocycle upon complex formation was established. At the same time, the aromaticity of the inner conjugation contour corresponds to the same series as the acoplanarity, while the outer π-delocalization is characterized by the reverse sequence. An experimental evaluation of the electron circular dichroism of the Soret and the Q-bands, as well as the g-factor of dissymmetry, was carried out. The growth of these parameters with an increase in the degree of acoplanarity and aromaticity of the internal conjugation contour was determined. The induction of helical phases in mixtures of nematic liquid crystals (LCs) based on cyanobiphenyls and MADMECl macrocyclic metal complexes was studied by polarization microscopy, and the clearance temperatures and helix pitch of the mesophases were measured. A strong effect of the metal on the phase transition temperature and helical twisting power was established.

Synthesis, Characterization, Biological Activity and Molecular Docking Studies of Phthalic Acid based Macrocyclic Transition Metal Complexes

A novel series of macrocyclic complexes of [M(L)Cl2] (M = Co(II), Ni(II) and Cu(II), L = macrocyclic ligand) were synthesized by template condensation method using 3,4-diaminotoluene and phthalic acid in the presence of divalent transition metal ions e.g., Co(II), Ni(II) and Cu(II) in their chloride form. These synthesized metal complexes were fully characterized by spectroscopic techniques, namely UV-Visible, IR, ESR and ESI-MS. Their thermal behaviour was determined by TGA and DTA. Further these macrocyclic complexes were screened for antimicrobial activity against bacterial species (Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa and Escherichia coli) and fungi (Aspergillus niger and Candida albicans) and then compared against standard drug streptomycin and itraconazole, respectively. In addition to these the antioxidant activity of the macrocyclic complexes were also investigated through scavenging effect on the DPPH radicals. Finally, the biological potency of synthesized compounds was evaluated using Auto Dock Vina. All the synthesized macrocyclic complexes were found to be potent against bacterial and fungal species, which suggest their potential application as antibacterial and antifungal agents.

Stepwise formation of a chemodynamic therapy agent of {Cu8} macrocyclic complex recognized by iodide ions.

An atomically precise Cu(I) macrocyclic complex Cu8I was developed for chemodynamic therapy (CDT) research. The {Cu8} macrocyclic skeleton gradually forms with the selective recognition of iodide ions, and the monitoring of intermediate fragments during Cu8I formation using time-dependent electrospray ionization mass spectrometry indicates the following possible formation process: [Cu1] → [Cu2] → [Cu3] → [Cu4] → [Cu5I] → [Cu6I] → [Cu7I] → [Cu8I] when recognized by iodide ions. Furthermore, the Cu(I)-mediated Fenton-like reaction in Cu8I catalyzes the production of toxic ˙OH from H2O2, which results in efficient tumor suppression.

Templating metallocycles with a macrocycle: synthesis, structures and magnetic studies of {Cr11M2} complexes.

Addition of 1,4,8,11-tetrazacyclotetradecane (cyclam) to a reaction that produces octametallic rings when simpler amines are used, produces {Cr11M2} "pretzels" (M = ZnII or CuII) where the cyclam coordinates to the MII ion which then sits at the centre of a twelve-metal macrocycle. Magnetic studies were fitted using the finite-temperature Lanczos method (FTLM), and the results demonstrate that exchange interactions are transferable from previous exchange-coupled CrIII rings.

Kinetics of ligand exchange in solution: a quantitative mass spectrometry approach.

Complex speciation and exchange kinetics of labile ligands are critical parameters for understanding the reactivity of metal complexes in solution. We present a novel approach to determine ligand exchange parameters based on electrospray ionization mass spectrometry (ESI-MS). The introduction of isotopically labelled ligands to a solution of metal host and unlabelled ligands allows the quantitative investigation of the solution-phase equilibria. Furthermore, ion mobility separation can target individual isomers, such as ligands bound at specific sites. As a proof of concept, we investigate the solution equilibria of labile pyridine ligands coordinated in the cavity of macrocyclic porphyrin cage complexes bearing diamagnetic or paramagnetic metal centres. The effects of solvent, porphyrin coordination sphere, transition metal, and counterion on ligand dissociation are discussed. Rate constants and activation parameters for ligand dissociation in the solution can be derived from our ESI-MS approach, thereby providing mechanistic insights that are not easily obtained from traditional solution-phase techniques.

Cationic tetranuclear macrocyclic CaCo3 complexes as highly active catalysts for alternating copolymerization of propylene oxide and carbon dioxide.

We found that a cationic hetero tetranuclear complex including a calcium and three cobalts exhibited high catalytic activity toward alternating copolymerization of propylene oxide (PO) and carbon dioxide (CO2). The tertiary anilinium salt [PhNMe2H][B(C6F5)4] was the best additive to generate the cationic species while maintaining polymer selectivity and carbonate linkage, even under 1.0 MPa CO2. Density functional theory calculations clarified that the reaction pathway mediated by the cationic complex is more favorable than that mediated by the neutral complex by 1.0 kcal mol-1. We further found that the flexible ligand exchange between Ca and Co ions is important for the alternating copolymerization to proceed smoothly.

Highly selective and discriminative detection of small alcohols based on a dual-emission macrocyclic samarium complex.

Lower alcohols (C1-C7) have a close relationship with our lives and some of them are harmful to our body's health. For example, liquor mixed with a tiny amount of methanol is harmful to our health. Much of this study is about identifying one or two low-level alcohols. How to detect low-level alcohol and high-throughput and distinguish between analogues of alcohol remains a tremendous challenge. In this study, a new large ring Schiff base Sm(III) complex (Sm-2r) is synthesized with a double emission matrix using the template method. Its dynamic imine bond (CN) and organic ligands (H2L2r) with molecular rotor properties can respond to changes in viscosity and polarity in external environments. The PCA method is used to turn the data matrix into a fingerprint spectrum to distinguish different alcohols (C1-C7). Sm-2r enables the quantization of cyclopropyl and glycerol. Linear ranges of cyclopropanol and glycerol are 0-9.0% and 0-3.0% (v/v), respectively. In addition, Sm-2r has an excellent ability to distinguish the mixtures of n-PrOH and i-PrOH, C5H9OH and C6H11OH, n-PeOH and n-HeOH, 1,3-PDO and 1,2-PDO, MeOH and EtOH, 1,2-EG and 1,2-PDO at different volume ratios. We have provided a way to distinguish alcohol species based on their molecular polarity and viscosity.