Nanoscale MOFs in nanomedicine applications: from drug delivery to therapeutic agents

Metal-organic frameworks (MOFs) hold great promise for widespread applications in biomedicine and nanomedicine. MOFs are one of the most fascinating nanocarriers for drug delivery, benefiting from their high porosity and facile modification. Furthermore, the tailored components of MOFs can be therapeutic agents for various treatments, including drugs as organic ligands of MOFs, active metal as central metal ions of MOFs, and their combinations as carrier-free MOF-based nanodrug. In this review, the advances in delivery systems and applications as therapeutic agents for nanoscale MOF-based materials are summarized. The challenges of MOFs in clinical translation and the future directions in the field of MOFs therapy are also discussed. We hope that more researchers will focus their attention on advancing and translating MOF-based nanodrugs into pre-clinical and clinical applications.

Double helices of dissymmetrical α,α'-disubstituted tripyrrins

Dissymmetrical α,α'-disubstituted tripyrrins have been prepared using a modified synthetic protocol. Tripyrrin 2a bearing 3,5-bis(trifluoromethyl)phenyl and 4-methoxyphenyl moieties showed an anti-type dimer arrangement in the solid state. In contrast, syn-type dimers were observed for tripyrrin 2b bearing 3,5-bis(trifluoromethyl)phenyl and 3,5-di-t-butylphenyl moieties. In addition, proton-exchange NH tautomerization was observed in 2b.

Metal Coordination Effects on the Photophysics of Dipyrrinato Photosensitizers

Within this work, we review the metal coordination effect on the photophysics of metal dipyrrinato complexes. Dipyrrinato complexes are promising candidates in the search for alternative transition metal photosensitizers for application in photodynamic therapy (PDT). These complexes can be activated by irradiation with light of a specific wavelength, after which, cytotoxic reactive oxygen species (ROS) are generated. The metal coordination allows for the use of the heavy atom effect, which can enhance the triplet generation necessary for generation of ROS. Additionally, the flexibility of these complexes for metal ions, substitutions and ligands allows the possibility to tune their photophysical properties. A general overview of the mechanism of photodynamic therapy and the properties of the triplet photosensitizers is given, followed by further details of dipyrrinato complexes described in the literature that show relevance as photosensitizers for PDT. In particular, the photophysical properties of Re(I), Ru(II), Rh(III), Ir(III), Zn(II), Pd(II), Pt(II), Ni(II), Cu(II), Ga(III), In(III) and Al(III) dipyrrinato complexes are discussed. The potential for future development in the field of (dipyrrinato)metal complexes is addressed, and several new research topics are suggested throughout this work. We propose that significant advances could be made for heteroleptic bis(dipyrrinato)zinc(II) and homoleptic bis(dipyrrinato)palladium(II) complexes and their application as photosensitizers for PDT.

Metal-Organic Frameworks for NOx Adsorption and Their Applications in Separation, Sensing, Catalysis, and Biology

Nitrogen oxide (NO_x ) is a family of poisonous and highly reactive gases formed when fuel is burned at high temperatures during anthropogenic behavior. It is a strong oxidizing agent that significantly contributes to the ozone and smog in the atmosphere. Thus, NO_x removal is important for the ecological environment upon which the civilization depends. In recent decades, metal-organic frameworks (MOFs) have been regarded as ideal candidates to address these issues because they form a reticular structure between proper inorganic and organic constituents with ultrahigh porosity and high internal surface area. These characteristics render them chemically adaptable for NO_x adsorption, separation, sensing, and catalysis. In additional, MOFs enable potential nitric oxide (NO) delivery for the signaling of molecular NO in the human body. Herein, the different advantages of MOFs for coping with current environmental burdens and improving the habitable environment of humans on the basis of NO_x adsorption are reviewed.

Synthesis, Structure, and Properties of Helical Bis-Cu(II) Complex of Linear Hexapyrrolic Ligand

The chemistry of metal helical complexes has attracted wide interest not only because of their resemblance with DNA structure but also due to their unique photophysical and chiroptical properties. Linear hexapyrrolic ligand 1 has been designed and synthesized using 3-pyrrolyl BODIPY as a key precursor. The reactivity of the appended pyrrole group of 3-pyrrolyl BODIPY was taken as an advantage to synthesize bis(3-pyrrolyl BODIPY) by treating 3-pyrrolyl BODIPY with 10 equiv of acetone in CHCl₃ under acid-catalyzed conditions and afforded bis(3-pyrrolyl BODIPY) 2 in 20% yield. Bis(3-pyrrolyl BODIPY) 2, in which two 3-pyrrolyl BODIPY units were connected via sp³ meso carbon, was very stable, and its identity was confirmed by HR-MS, NMR, and X-ray crystallographic analysis. The X-ray structure revealed that the 3-pyrrolyl BODIPY moieties in bis(3-pyrrolyl BODIPY) 2 remained almost planar and arranged at an angle of 98.4° with each other, leading to a V-shaped conformation. In the next step, bis(3-pyrrolyl BODIPY) 2 was treated with AlCl₃ in acetonitrile/methanol at reflux to afford hexapyrrolic ligand 1. Hexapyrrolic ligand 1 was treated with CuCl₂ in acetonitrile at room temp for 1 h followed by crystallization to afford helical bis-Cu(II) complex 1-Cu. Bis-Cu(II) complex 1-Cu was characterized and studied by HR-MS, X-ray crystallography, ESR, absorption, and DFT/TD-DFT techniques. The X-ray structure revealed that the bis-Cu(II) complex was a double-stranded bimetallic helicate and each Cu(II) ion was coordinated to four nitrogen atoms of two dipyrrin units from two hexapyrrolic ligands in a distorted tetrahedral geometry. The crystal packing diagram showed that the bis-Cu(II) complex formed as a racemic mixture containing both M and P isomers which was unable to isolate. The ESR spectrum of bis-Cu(II) complex 1-Cu indicated the presence of two noninteracting Cu(II) ions in slightly different coordination environments. DFT and TD-DFT studies were in agreement with the experimental observations of bis(3-pyrrolyl BODIPY) 2 complex and bis-Cu(II) complex 1-Cu.

Synthesis, computational and optical studies of tetraphenylethene-linked Pd(ii)dipyrrinato complexes

A series of Pd(ii)dipyrrinato complexes are synthesized and characterized. Their DFT and aggregation studies and photo-catalytic applications are reported.

Luminescent Iridium(III) Dipyrrinato Complexes: Synthesis, X-ray Structures, DFT and Photocytotoxicity Studies of Glycosylated Derivatives

A series of luminescent Ir(III) dipyrrinato complexes were synthesized having various aromatic chromophores on the C-5 position of dipyrrin ligand. The presence of different chromophores on the Ir(III) dipyrrinato complexes...

Bending for Better: Flexible Organic Single Crystals with Controllable Curvature and Curvature-Related Conductivity for Customized Electronic Devices

Electronic microdevices of self-bending coronene crystals are developed to reveal an unexplored link between mechanical deformation and crystal function. First, a facile approach towards length/width/curvature-controllable micro-crystals through bottom-up solution crystallization was proposed for high processability and stability. The bending crystal devices show a significant increase beyond seven orders of magnitude in conductivity than the straight ones, providing the first example of deformation-induced function enhancement in crystal materials. Besides, double effects caused by bending, including the change of π electron level as well as the enhancement of carrier mobility, were determined, respectively by the X-ray photoelectric spectroscopy and X-ray crystallography to coexist, contributing to the conductivity improvement. Our findings will promote future creation of flexible organic crystal systems with deformation-enhanced functional features towards customized smart devices.

Dipyrrinato-Iridium(III) Complexes for Application in Photodynamic Therapy and Antimicrobial Photodynamic Inactivation

The generation of bio-targetable photosensitizers is of utmost importance to the emerging field of photodynamic therapy and antimicrobial (photo-)therapy. A synthetic strategy is presented in which chelating dipyrrin moieties are used to enhance the known photoactivity of iridium(III) metal complexes. Formed complexes can thus be functionalized in a facile manner with a range of targeting groups at their chemically active reaction sites. Dipyrrins with N- and O-substituents afforded (dipy)iridium(III) complexes via complexation with the respective Cp*-iridium(III) and ppy-iridium(III) precursors (dipy=dipyrrinato, Cp*=pentamethyl-η5 -cyclopentadienyl, ppy=2-phenylpyridyl). Similarly, electron-deficient [IrIII (dipy)(ppy)2 ] complexes could be used for post-functionalization, forming alkenyl, alkynyl and glyco-appended iridium(III) complexes. The phototoxic activity of these complexes has been assessed in cellular and bacterial assays with and without light; the [IrIII (Cl)(Cp*)(dipy)] complexes and the glyco-substituted iridium(III) complexes showing particular promise as photomedicine candidates. Representative crystal structures of the complexes are also presented.

Dipyrrin based metal complexes: reactivity and catalysis

Sometimes named half-porphyrins, bis-pyrrolic dipyrrin ligands endow their metal complexes with unique properties such as the potential to functionalize the heterocyclic backbone or the meso position and the ability to catalyze interesting chemical transformations. Thus, strategies towards the derivatization of or at the meso group and the use of dipyrrin metal complexes for the formation of a broad range of polypyrrolic derivatives such as 2,2'-bis-dipyrrins, nor-/hetero-corroles and porphynoids have been elaborated. Furthermore, the chelating ability of dipyrrins and the possibility of modifying their steric and electronic characteristics by functionalization can be exploited for the development of numerous complexes featuring appealing properties. Hence, C-H activation/amination, polymerization or oxidation reactions can be catalyzed by dipyrrin metal complexes and classical reagents such as Grignard species, Rh-based or Suzuki-Miyaura catalysts have been revisited by incorporation of dipyrrins in the coordination sphere of the metal cations. This contribution aims to review and illustrate all these aspects, highlighting the potential of these complexes for the design and synthesis of valuable organic compounds and metallo-organic architectures.

Gleaned snapshots on the road to coordination polymers: heterometallic architectures based on Cu(I) metallaclips and 2,2'-bis-dipyrrin metalloligands

The assembly of binuclear Cu(i) metallaclips with 2,2'-bis-dipyrrin based metalloligands gives rise to a diversity of architectures featuring a recurring π-stacked compact tetranuclear metallacycle but differing in their nuclearity and dimensionality depending on the nature of the capping ligands and metal cations.

Heterometallic coordination polymers based on homo- and heteroleptic Au(iii) dithiolene complexes

Two novel hetero- and homoleptic Au(iii) dithiolene complexes have been designed, synthesized, characterized and employed for the elaboration of heterometallic coordination networks.

A large anisotropic plasticity of L-leucinium hydrogen maleate preserved at cryogenic temperatures

L-Leucinium hydrogen maleate crystals are very plastic at ambient conditions. Here it is shown that this plasticity is preserved at least down to 77 K. The structural changes in the temperature range 293-100 K were followed in order to rationalize the large anisotropic plasticity in this compound. To the best of our knowledge, this is the first reported example of an organic compound remaining so plastic at cryogenic conditions.

Comprehensive Theoretical Study of Interactions between Ag+ and Polycyclic Aromatic Hydrocarbons

The first comprehensive and systematic theoretical exploration of the bonding nature and energetics of the interactions between Ag(I) cation and a wide set of π-ligands was accomplished. This set ranges from simple ethylene and aromatic benzene to planar and curved polyaromatic molecules and to closed-cage C₆₀ -fullerene. Simultaneous application of two energy decomposition schemes based on different ideas, namely, NBO-NEDA and EDA-NOCV, allowed shedding light on the nature of the bonding and its energetics. Importantly, our results unambiguously indicate that reliable results can be obtained only if using more than one theoretical approach. All methods clearly revealed the importance and even domination of the ionic contribution of the bonding in all adducts, except for those of C₆₀ -fullerene, in which the covalent component was found to be the largest. Subsequent decomposition of the orbital term onto components showed that it consists of two major parts: (i) ligand-to-metal (π(C=C)→s(Ag), L→M) and (ii) metal-to-ligand (M→L) terms, with significant domination of the former. Interestingly, while the L→M component is essentially the same for all systems considered, the nature of the M→L one depends on the coordination site of the polycyclic aromatic hydrocarbons (PAH). In most of adducts, the M→L can be described as d_xy (Ag)→π^* (C=C) donation, whereas for systems [Ag-spoke-C₁₂ H₈ ]⁺ and [Ag-spoke-C₂₀ H₁₀ ]⁺ it corresponds to the d_z ² (Ag)→π^* (C=C) type of interaction. As a result, the coordination mode in such complexes is switched from η² -type to η¹ . Thus, the nature of the bonding, its energetics and even coordination mode in adducts of unsaturated hydrocarbons with late transition metal cations should be considered as a function of many components, which primarily includes the topology and aromaticity of the (poly)aromatic molecules.

Pre-organization of clefts for Ag-π interactions in Zn(ii) bisdipyrrin helicates for the construction of heterometallic networks

Coordination of 2,2'-bisdipyrrin based ligands to Zn(ii) cations leads to the formation of binuclear helicates with pre-organized pyrrolic strands as well as peripheral aromatic moieties for Ag-π interactions, thus affording crystalline heterometallic networks upon further interactions with Ag(i) salts without the assistance of additional heteroatom-based coordinating units.

Symmetrical and dissymmetrical 2,2′-bis-dipyrrin ligands and Zn(ii) binuclear helicates

A series of amide functionalized symmetrical and dissymmetrical 2,2′-bis-dipyrrin ligands has been prepared and characterized and their assembly with Zn(ii) towards the formation of binuclear helicates has been investigated.

Spacer length dependent architectural diversity in bis-dipyrrin copper(ii) complexes

A series of copper(ii) complexes (1-9 and 3') derived from bis-dipyrrin ligands (L1-L9 and L3') with diverse spacer lengths [-(CH₂)_n-] have been described. Structural diversities in these complexes have been explicitly established by spectral and structural studies on these and a closely related nickel(ii) complex (3''). All the ligands and complexes have been thoroughly characterized by spectroscopic studies (ESI-MS, IR, ¹H, ¹³C NMR, UV/vis) and structures of 2, 3', 3'', 6, 8 and 9 were determined by X-ray single crystal analyses. It has been unambiguously established that ligands with n ≤ 6 gave heteroleptic binuclear (1-5), while those with n ≥ 7 yielded homoleptic mononuclear (6-9) bis-dipyrrinato complexes. Spectral and structural studies revealed distorted square planar (1-5) and distorted tetrahedral geometries (6-9) about the copper(ii) centre in these complexes which has further been evidenced by EPR and electrochemical studies. Structural differences based on the odd and even number of methylene spacers in these complexes have been supported by DFT studies. A line between the syn- and anti-conformations of the complexes has been drawn on the basis of a limiting spacer length.

Solvent and anion effects on the organization of a luminescent [2 + 2] BODIPY/Ag(i) metallamacrocycle in the crystalline state

The assembly of a novel BODIPY bearing peripheral vinyl–benzonitrile groups with AgX salts (X⁻ = AsF₆⁻, BF₄⁻, ClO₄⁻) leads to the recurrent formation of a [2 + 2] [Ag₂(BODIPY)₂]²⁺ type metallamacrocycle featuring emission in the crystalline state.

Half-sandwich iridiumIII complexes with pyrazole-substituted heterocyclic frameworks and their biological applications

Enhancement in the biological function, i.e., DNA binding, molecular docking, antiproliferative activity and DNA cleavage, of metal complexes as compared to free ligands is observed.

The first example of cofacial bis(dipyrrins)

Two series of cofacial bis(dipyrrins) were prepared and their photophysical properties as well as their bimolecular fluorescence quenching with C₆₀ were investigated.

Heteroleptic arene Ru(ii) dipyrrinato complexes: DNA, protein binding and anti-cancer activity against the ACHN cancer cell line

The in vitro cytotoxicities of heteroleptic Ru(ii) complexes were studied in ACHN cell lines by MTT assay, DNA cleavage, (AO/EtBr) and FACS analysis.

Postcomplexation synthetic routes to dipyrrin complexes

The postcomplexation reactivity of 5-thiomethyldipyrrin complexes provides a synthetic route to hitherto inaccessible dipyrrin complexes.

Molecular tectonics: heterometallic (Ir,Cu) grid-type coordination networks based on cyclometallated Ir(III) chiral metallatectons

A chiral-at-metal Ir(III) organometallic metallatecton was synthesised as a racemic mixture and as enantiopure complexes and combined with Cu(II) to afford a heterobimetallic (Ir,Cu) grid-type 2D coordination network.

On Zn(II) 2,2'-bisdipyrrin circular helicates

Coordination of two 2,2'-bisdipyrrin ligands, bearing methyl ester or methylthioether peripheral groups, with Zn(II) cations leads not only to the formation of the expected linear helicates but also concomitantly to novel tri- and tetra-nuclear circular species that have been isolated and fully characterized in solution and by X-ray diffraction.

Assembly, disassembly, and reassembly: conversion of homometallic coordination networks into mixed metal-organic frameworks

A strategy for the conversion of homometallic coordination networks into mixed metal-organic frameworks (MM'MOFs) is proposed. Ni(II) complexes of dipyrrin (dpm) ligands bearing peripheral pyridyl or imidazolyl units have been shown to self-assemble into coordination polymers with the metal cation in an octahedral environment coordinated to two bis-pyrrolic chelates and two neutral monodentate coordinating units such as pyridyl or imidazolyl moieties. Taking advantage of the chelate effect, the two monodentate units may be replaced by a diimine ligand leading to the disassembly of the networks by the formation of discrete soluble complexes. The latter can be employed as metallatectons for the construction of heterometallic architectures upon reaction with a secondary metal salt. This approach was applied using either 1,10-phenanthroline (phen) or 2,2'-bipyrimidine (bpm) as chelates leading to a series of mono- and binuclear metallatectons of the (phen)Ni(dpm)2 and (bpm)[Ni(dpm)2]2 type. Subsequent assembly with CdCl2 afforded either interpenetrated 2D grid-type architectures or 3D MM'MOFs.

Heteroleptic bis(dipyrrinato)copper(ii) and nickel(ii) complexes

Heteroleptic bis(dipyrrinato)copper(ii) and nickel(ii) complexes are synthesized for the first time, and their structural, photochemical, and electrochemical properties are disclosed.

Rigid yet flexible heteroleptic Co(iii) dipyrrin complexes for the construction of heterometallic 1- and 2-D coordination polymers

Acetylacetonate Co(iii)–dipyrrin complexes form flexible metallatectons displaying diverse shapes when combined with CdX₂salts.