Catecholate Ligands Research Articles

Structural and magnetic properties of semiquinonate based Al(iii) and Ga(iii) complexes.

The reaction of anhydrous MCl3 (M = Al(iii) or Ga(iii)) with one-electron-reduced 3,5-di-tert-butyl-1,2-ortho-benzoquinone (using metallic sodium) led us to isolate two distinct metal complexes of Al(iii) and Ga(iii), which were structurally and magnetically characterized. Complex 1 crystallized in the monoclinic P21/n space group, whereas 2 crystallized in the triclinic P1[combining macron] space group. Interestingly, whereas the Al(iii) derivative was obtained as a dimer with the molecular formula [Al2(μ-HL-)2(L˙-)4] (1) (where L˙- is a semiquinonate radical and HL- is a monoanionic catecholate ligand), the Ga(iii) derivative crystallized as [Ga(L˙-)3] (2), which is a polymorph of a previously reported complex. The presence of both catecholate and/or semiquinonate ligands in 1 and 2 was confirmed by single-crystal X-ray diffraction, mass spectrometry, and NMR and infrared spectroscopy techniques. The crystalline phase purity of the complexes was confirmed by powder X-ray diffraction (PXRD). Measurements of direct-current magnetic susceptibility, which were performed on a polycrystalline samples, revealed that in both complexes the semiquinonate radical anions are coupled ferromagnetically via the diamagnetic metal ion. The magnetism data of both complexes were modelled using the Heisenberg-Van Vleck-Dirac (HDVV) Hamiltonian, and the extracted parameters are consistent with the literature reports. The details of the electronic structures of the ground states of 1 and 2 were further investigated via X-band (ca. 9 GHz) electron paramagnetic resonance (EPR). The EPR spectrum of 2 could be reproduced by considering a quartet ground state with zero-field splitting and hyperfine coupling, whereas attempts to simulate all the EPR spectral features observed in a frozen solution of 1 by assuming it was a pure phase failed. A correct simulation required the simultaneous inclusion of contributions from a quartet and a triplet state. This evidently suggests that the dimeric complex of 1 is in equilibrium with a monomeric [Al(L˙-)3] complex in solution.

A Family of Titanium Complexes with Catechol Ligands: Structural Investigation and Catalytic Application

Four new titanium catecholate complexes – [Ti2(Cat)2(CatH)2(OCH3)2(CH3OH)2] (1; Cat = C6H4O22–), [Ti2(4tBuCat)4(CH3OH)2]·2CH3OH (2·2CH3OH; 4tBuCat = [4‐t‐C4H9‐C6H3O2]2–), [Ti(Cat)2(dmf)2] (3; dmf = N,N‐dimethylformamide), and [Na(dme)Ti(Cat)3]2[Na(dme)CH3OH]2 (4; dme = 1,2‐dimethoxyethane) – have been obtained by treatment of Ti(OCH3)4 with catechols in methanol and structurally characterized. Complex 3 is the first example of a neutral mononuclear titanium catecholate containing more than one catechol molecule per titanium atom. Complexes 1 and 2 are neutral dimers in the solid state, each with a catechol/Ti ratio equal to 2 and featuring one of the catechol ligands bridging two titanium centres in a singly bridging chelate µ2‐(O,O′,O′) mode. The other catechol molecule is either a terminal bidentate chelating ligand (complex 2) or a Ti monodentate ligand (complex 1). Complex 4 is a heterometallic aryloxide complex with a tetrameric [{Na(dme)Ti(Cat)3)2]2– (Ti2Na2) core as an anionic moiety and Na ions, solvated by methanol and dme ligands – [{Na(dme)(CH3OH)}2]2+ – as a cationic counterpart. Each Ti centre in 4 is octahedrally coordinated by three catechol ligands, demonstrating three distinct types of bridging modality. It was shown that 1–4 effectively catalyze the selective homogeneous hydrogenation of acetylene to ethylene. Various kinetic relationships were determined and analyzed, enabling a reaction pathway for this catalytic reaction to be proposed.

Tin(IV) and Antimony(V) Complexes Bearing Catecholate Ligands Connected to Ferrocene – Syntheses, Molecular Structures, and Electrochemical Properties

The ferrocenyl‐containing 3,5‐di‐tert‐butylcatechol Fc‐L‐CatH2 (2) was synthesized by the condensation of the precursor 6‐(hydrazonomethyl)‐3,5‐di‐tert‐butylcatechol 6‐(H2N–N=CH)CatH2 (1) with ferrocenecarboxaldehyde (L = –CH=N–N=CH–, Cat = 3,5‐di‐tert‐butylcatecholate, Fc = ferrocene). The exchange reaction between catechol 2 and Ph3SbBr2 in the presence of a base (Et3N) in toluene leads to the formation of the triphenylantimony(V) catecholate (Fc‐L‐Cat)SbPh3 (3) as the main product and the ionic bromotriphenylantimony(V) catecholate (Fc‐LH‐Cat)SbPh3Br (4) containing a hydraziniumylidene cation (LH = –CH=NH+–N=CH–) as the byproduct. The change of toluene to tetrahydrofuran (THF) results in the formation of 4 as the main product in nearly quantitative yield. The exchange reactions of catechol 2 with Ph2SnCl2 and SnCl4 give anionic catecholate complexes bridged with hydraziniumylidene cations even in the presence of excess base. Complexes (Fc‐LH‐Cat)SnPh2Cl (5), (Fc‐LH‐Cat)2SnPh2 (6), and (Fc‐LH‐Cat)2SnCl2 (7) were synthesized. The compounds obtained were characterized by IR spectroscopy, 1H and 13C NMR spectroscopy, elemental analysis, and cyclic voltammetry. The molecular structures of crystals of 5–7 were determined by X‐ray diffraction analysis. The formation of catecholates 4–7 with hydraziniumylidene cations is caused by intramolecular hydrogen bonding between the hydroxy and imine groups, which leads to proton transfer from the oxygen atom to the nitrogen atom of the hydrazine linker.

Hot Hole Hopping in a Polyoxotitanate Cluster Terminated with Catechol Electron Donors

Fast hole hopping in Ti17cat4, a 1 nm diameter molecular polyoxotitanate cluster bearing four catechol ligands (Ti17(μ4-O)4(μ3-O)16(μ2-O)4(cat)4(OPri)16), was investigated by ultrafast spectroscopy and quantum dynamics simulations. The catechol moieties coupled to the TiO2 core of the cluster give rise to a charge-transfer band, the excitation of which promotes an electron from the highest occupied molecular orbital of the ligand to the inorganic core, resulting in the formation of {cat+•,Ti3+}, a vibrationally hot polaronic exciton. Dynamic depolarization measurements indicate that within less than 100 fs the Franck–Condon polaronic state formed at the interface evolves into a fully charge-separated state and the injected electron delocalizes over the quasi conduction band of the cluster. The positive charge (hole) resulting from the injection does not remain static either. The initial hole hopping between the catechol sites occurs with the rate of ∼5 × 1011 s–1 or more and competes with the intramolecul...

Back Cover: Quantitative Determination and Comparison of the Surface Binding of Phosphonic Acid, Carboxylic Acid, and Catechol Ligands on TiO2 Nanoparticles (Chem. Eur. J. 38/2016)

Back Cover: Quantitative Determination and Comparison of the Surface Binding of Phosphonic Acid, Carboxylic Acid, and Catechol Ligands on TiO₂ Nanoparticles (Chem. Eur. J. 38/2016)

Quantitative Determination and Comparison of the Surface Binding of Phosphonic Acid, Carboxylic Acid, and Catechol Ligands on TiO2 Nanoparticles.

The adsorption, desorption, co-adsorption, and exchange behavior of phosphonic acid, carboxylic acid, and catechol derivatives on the surface of titanium oxide (anatase) nanoparticles are investigated. Thermogravimetric analysis provides a facile and fast-track quantitative determination of the wet-chemical monolayer adsorption constants and grafting densities of ten adsorbates, all under neutral pH conditions. This characterization protocol allows straightforward quantification of the relevant thermodynamic data of ligand adsorption and a comparison of ligand adsorption strengths. The reported procedure is proposed as a universal tool and it should be applicable to many other colloidal metal oxide materials. Moreover, the determined values for the adsorption constants and the monolayer grafting densities provide a toolbox for the assessment of the adsorbates' behavior in desorption, exchange, and co-adsorption equilibria. This versatile evaluation procedure will help to identify optimal monolayer-surface combinations and to evaluate critical parameters, such as monolayer robustness, ligand exchange rates, or targeted mixed assembly of functionalities.

A Post-Functionalizable Iso-Polyoxotitanate Cage Cluster.

During solvothermal alcoholysis of a mixture of TiI4 and Ti(O(i)Pr)4, a {I@Ti22} cage cluster encapsulating an OH and iodide guests is crystallized. The {I@Ti22} host-guest cluster surface is postfunctionalizable with catecholate and carboxylate ligands. The synthetic details, structural characterization, spectroscopic properties of the obtained cages clusters are provided. The present study provides candidates for modeling ligand exchange and electron-hole transfer at the titanate nanoparticle surface, and meanwhile offers new opportunities for understanding the TiO2 nanocrystalline formation in solvothermal processes.

Cycloaurated gold(III) complexes derived from the functionalised catecholate ligands alizarin and 3,4-dihydroxybenzaldehyde

Reactions of the cycloaurated gold(III) dichloride complexes [AuCl2(anp)] (anp = 2-anilinopyridyl), [AuCl2(bp)] (bp = 2-benzylpyridyl) and [AuCl2(tolpy)] (tolpy = 2-(p-tolyl)pyridyl) with alizarin (H2az) and Me3N base in refluxing methanol gave the complexes [Au(az)L] (L = anp, bp or tolpy). Additionally, the reaction of [AuCl2(tolpy)] with 3,4-dihydroxybenzaldehyde (H2dhb) and Me3N gave the complex [Au(dhb)(tolpy)]. These complexes contain the ligands coordinated as functionalised catecholate groups, allowing introduction of new functionalities into this class of complex. The complexes are poorly soluble in most organic solvents but were successfully characterised by ESI MS, IR and NMR spectroscopies. A detailed 1H and 13C NMR study on [Au(dhb)(tolpy)] shows that it exists as two isomers with regard to the position of the aldehyde group compared to the cycloaurated ring system; DFT calculations were carried out in order to provide some insight on the spectroscopic assignment of the two isomers.

Perfluoroalkylation of Square-Planar Transition Metal Complexes: A Strategy To Assemble Them into Solid State Materials with a π–π Stacked Lamellar Structure

Formation of π–π stacked lamellar structure is important for high performance organic semiconductor materials. We previously demonstrated that perfluoroalkylation of aromatics and heteroaromatics was one of the strategies to design organic crystalline materials with π–π stacked lamellar structures while improving air stability as a result of the strong electron withdrawing ability of perfluoroalkyl substituents. Square-planar transition metal complexes with large π-conjugated ligands are also an important category of semiconductor materials. We have perfluoroalkylated square-planar transition metal complexes, leading to the formation of a π–π stacked lamellar crystal packing motif in the solid state. Here we report six crystal structures of Pd and Pt complexes with bis-perfluorobutylated catechol ligand as one of the two ligands that bonds to the metal centers. This structural design possesses similar molecular topology when compared to perfluoroalkylated aromatics and heteroaromatics we have reported pre...

Valence tautomerism induced nucleophilic ipso substitution in a coordinated tetrabromocatecholate ligand and diverse catalytic activity mimicking the function of phenoxazinone synthase

Two new manganese(III) complexes, [pyH][Mn(Br4Cat)2(py)] (1) and [Mn(Br4Cat)(Br3pyCat)(py)2] (2), where py is pyridine, Br4CatH2 is tetrabromocatechol and Br3pyCatH2 is 3,5,6-tribromo-4-pyridiniumcatechol, derived from redox ‘noninnocent’ bromo-substituted catecholate ligands are reported. Both complexes were characterized by various spectroscopic techniques in addition to the single crystal X-ray crystallography, and the electrochemical behavior of these complexes was investigated by cyclic voltammetry. Variable temperature UV–vis spectral studies for complex 1 reveal an unprecedented observation in which a dramatic increase of the ligand-to-metal charge transfer band at 592nm associated with concomitant change in color of the solution from olive-green to dark-green is noticed with increase in temperature. This unprecedented spectral feature is consistent with the formation of a new species 2 in which valence tautomerism induced aromatic nucleophilic substitution of a tetrabromocatecholate ligand by pyridine is observed. DFT calculations have been used to rationalize this unexpected result. To the best of our knowledge, the nucleophilic aromatic substitution of tetrabromosemiquinone by pyridine to generate this pyridinium-containing catecholate ligand is the first example of valence tautomerism induced nucleophilic ipso substitution by a nitrogen containing ligand. Although the electrochemical behavior of both complexes is similar, the probable role of a positive charge on the ligand backbone has been discussed in order to justify the significantly higher catalytic activity of complex 2 over complex 1.

“Single-” and “multi-core” FePt nanoparticles: from controlled synthesis via zwitterionic and silica bio-functionalization to MRI applications

The value of the magnetization has a strong influence on the performance of nanoparticles that act as the contrast agent material for MRI. In this article, we describe processing routes for the synthesis of FePt nanoparticles of different sizes, which, as a result, exhibit different magnetization values. “Single-core” FePt nanoparticles of different sizes (3–15 nm) were prepared via one-step or two-step synthesis, with the latter exhibiting twice the magnetization (m (1.5T) = 14.5 emu/g) of the nanoparticles formed via the one-step synthesis (m (1.5T) 20 nm) leads to an increase in the magnetization m (1.5T) from 8 to 19.5 emu/g, without exceeding the superparamagnetic limit. Stable water suspensions were prepared using two different approaches: (a) functionalization with a biocompatible, zwitterionic, catechol ligand, which was used on the FePt nanoparticles for the first time, and (b) coating with SiO2 shells of various thicknesses. These FePt-based nanostructures, the catechol- and SiO2-coated “single-core” and “multi-core” FePt nanoparticles, were investigated in terms of the relaxation rates. The higher r 2 values obtained for the “multi-core” FePt nanoparticles compared to that for the “single-core” ones indicate the superiority of the “multi-core” FePt nanoparticles as T 2 contrast agents. Furthermore, it was shown that the SiO2 coating reduces the r 1 and r 2 relaxation values for both the “single-core” and “multi-core” FePt nanoparticles. The high r 2/r 1 ratios obtained in our study put FePt nanoparticles near the top of the list of candidate materials for use in MRI.

Click Synthesis of Hydrophilic Maltose-Functionalized Iron Oxide Magnetic Nanoparticles Based on Dopamine Anchors for Highly Selective Enrichment of Glycopeptides.

The development of methods to isolate and enrich low-abundance glycopeptides from biological samples is crucial to glycoproteomics. Herein, we present an easy and one-step surface modification strategy to prepare hydrophilic maltose functionalized Fe3O4 nanoparticles (NPs). First, based on the chelation of the catechol ligand with iron atoms, azido-terminated dopamine (DA) derivative was assembled on the surface of magnetic Fe3O4 nanoparticles by sonication. Second, the hydrophilic maltose-functionalized Fe3O4 (Fe3O4-DA-Maltose) NPs were obtained via copper(I)-catalyzed azide-alkyne cycloaddition (click chemistry). The morphology, structure, and composition of Fe3O4-DA-Maltose NPs were investigated by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), X-ray photoelectron spectrometer (XPS), and vibrating sample magnetometer (VSM). Meanwhile, hydrophilicity of the obtained NPs was evaluated by water contact angle measurement. The hydrophilic Fe3O4-DA-Maltose NPs were applied in isolation and enrichment of glycopeptides from horseradish peroxidase (HRP), immunoglobulin (IgG) digests. The MALDI-TOF mass spectrometric analysis indicated that the novel NPs exhibited high detection sensitivity in enrichment from HRP digests at concentration as low as 0.05 ng μL(-1), a large binding capacity up to 43 mg g(-1), and good recovery for glycopeptides enrichment (85-110%). Moreover, the Fe3O4-DA-Maltose NPs were applied to enrich glycopeptides from human renal mesangial cells (HRMC) for identification of N-glycosylation sites. Finally, we identified 115 different N-linked glycopeptides, representing 93 gene products and 124 glycosylation sites in HRMC.

Coordination Chemistry of Microbial Iron Transport.

ConspectusThis Account focuses on the coordination chemistry of the microbial iron chelators called siderophores. The initial research (early 1970s) focused on simple analogs of siderophores, which included hydroxamate, catecholate, or hydroxycarboxylate ligands. The subsequent work increasingly focused on the transport of siderophores and their microbial iron transport. Since these are pseudo-octahedral complexes often composed of bidentate ligands, there is chirality at the metal center that in principle is independent of the ligand chirality. It has been shown in many cases that chiral recognition of the complex occurs. Many techniques have been used to elucidate the iron uptake processes in both Gram-positive (single membrane) and Gram-negative (double membrane) bacteria. These have included the use of radioactive labels (of ligand, metal, or both), kinetically inert metal complexes, and Mössbauer spectroscopy. In general, siderophore recognition and transport involves receptors that recognize the metal chelate portion of the iron–siderophore complex. A second, to date less commonly found, mechanism called the siderophore shuttle involves the receptor binding an apo-siderophore.Since one of the primary ways that microbes compete with each other for iron stores is the strength of their competing siderophore complexes, it became important early on to characterize the solution thermodynamics of these species. Since the acidity of siderophores varies significantly, just the stability constant does not give a direct measure of the relative competitive strength of binding. For this reason, the pM value is compared. The pM, like pH, is a measure of the negative log of the free metal ion concentration, typically calculated at pH 7.4, and standard total concentrations of metal and ligand. The characterization of the electronic structure of ferric siderophores has done much to help explain the high stability of these complexes.A new chapter in siderophore science has emerged with the characterization of what are now called siderocalins. Initially found as a protein of the human innate immune system, these proteins bind both ferric and apo-siderophores to inactivate the siderophore transport system and hence deny iron to an invading pathogenic microbe. Siderocalins also can play a role in iron transport of the host, particularly in the early stages of fetal development. Finally, it is speculated that the molecular targets of siderocalins in different species differ based on the siderophore structures of the most important bacterial pathogens of those species.

Synthesis and nanostructure of [Mo(C6H4O2)3]·2(C4H8N2O) and the synthesis from 1,2-PDA to (C4H8N2O)

Continuing our work on the synthesis of MoO2L2 and MoO3LALB that show excellent anti-cancer activities in vitro, the MoL3 have been synthesized by the solvothermal reaction of Na2MoO4 with catechols and 1,2-DPA in the mixed solvent of MeCN/MeOH. X-ray diffraction revealed that Mo in chiral octahedral geometry coordinate with three catechol ligands formed three five-membered rings, and the [Mo(C6H4O2)3] are linked by hydrogen bonds Mo(OC6H4)O…H–N(C4H8O)N–H…O(C6H4O)Mo through the by-product (C4H8N2O) that are formed by one 1,2-DPA with one CO2 on the catalysis of Mo-complex. Also, we have disassembled bulk crystal into nano-aggregates, and under TEM mono-lamella morphology of nanostructures was observed, which agrees well with the previous conclusion that the morphologies of the nano-aggregates are associated with the quantum motifs in their crystal lattices. [Mo(C6H4O2)3] have also been characterized by UV–vis spectra, cyclic voltammogram and thermogravimetric analysis.

Synthesis of Catecholate Ligands with Phosphonate Anchoring Groups.

New catecholate ligands containing protected phosphonate anchoring groups in the 4-position of the catecholate ring were synthesized. The catechol 4-diethoxyphosphorylbenzene-1,2-diol, ((Et)phoscat)H2, was prepared in three steps from pyrocatechol; whereas, the catechol 4-(diethoxyphosphorylmethyl)benzene-1,2-diol, ((Et)Bnphoscat)H2, containing a methylene spacer between the catecholate ring and phosphonate anchor, was prepared from protocatechuic acid in six linear steps. Both catechol derivatives were further elaborated to their trimethylsilyl-protected counterparts to facilitate their binding to nanocrystalline metal oxides. Electronic spectroscopy and cyclic voltammetry were used to probe the electronic properties of the phosphonate-functionalized catecholates in charge-transfer complexes of the general formula (catecholate)Pd(pdi) (pdi = N,N'-bis(mesityl)phenanthrene-9,10-diimine). These studies show that attachment of the phosphonate anchor directly to the 4-position of the ((Et)phoscat)(2-) ligand significantly perturbs the donor ability of the catecholate ligand; however, incorporation of a single methylene spacer group in ((Et)Bnphoscat)(2-) helps to isolate catecholate from the electron-withdrawing phosphonate group.

Catecholato complexes of cobalt and nickel with 1,4-disubstituted-1,4-diazabutadiens-1,3 and 1,2-bis(diphenylphosphino)ethane

Divalent cobalt and nickel form four-coordinate complexes with sterically hindered 3,6-di-tert-butylcatecholato dianion (3,6-DBCat) and neutral bidentate 1,4-disubstituted-1,4-diazabutadiens-1,3 (DAB). Structural study of (1,4-di-tert-butyl-1,4-diazabutadiene-1,3)(3,6-di-tert-butyl-catecolato)nickel and (1,4-bis-(2,6-di-iso-propylphenyl)-2,3-dimethyl-1,4-diazabutadiene-1,3)(3,6-di-tert-butyl-catecolato)cobalt indicates square-planar environment of metals. Chemical one-electron oxidation of nickel complexes proceeds through catecholate ligand and leads to o-semiquinonato adducts. EPR spectral parameters indicate preservation of square-planar configuration after oxidation. Complexes (DAB)M(Cat) (M = Ni, Co) undergo neutral ligand substitution reactions. A number of four-coordinated square-planar mono-catecholato complexes of cobalt and nickel of general formula (L)M(3,6-DBCat) were synthesized and characterized (L= N,N’-disubstituted 1,4-diazabutadienes-1,3 (DAB), dipyridine, bis(diphenylphosphino)ethane; M=Co, Ni; 3,6-DBCat =3,6-di-tert-butyl-catecholato dianion).

New avenues for ligand-mediated processes--expanding metal reactivity by the use of redox-active catechol, o-aminophenol and o-phenylenediamine ligands.

Redox-active ligands have evolved from being considered spectroscopic curiosities - creating ambiguity about formal oxidation states in metal complexes - to versatile and useful tools to expand on the reactivity of (transition) metals or to even go beyond what is generally perceived possible. This review focusses on metal complexes containing either catechol, o-aminophenol or o-phenylenediamine type ligands. These ligands have opened up a new area of chemistry for metals across the periodic table. The portfolio of ligand-based reactivity invoked by these redox-active entities will be discussed. This ranges from facilitating oxidative additions upon d(0) metals or cross coupling reactions with cobalt(iii) without metal oxidation state changes - by functioning as an electron reservoir - to intramolecular ligand-to-substrate single-electron transfer to create a reactive substrate-centered radical on a Pd(ii) platform. Although the current state-of-art research primarily consists of stoichiometric and exploratory reactions, several notable reports of catalysis facilitated by the redox-activity of the ligand will also be discussed. In conclusion, redox-active ligands containing catechol, o-aminophenol or o-phenylenediamine moieties show great potential to be exploited as reversible electron reservoirs, donating or accepting electrons to activate substrates and metal centers and to enable new reactivity with both early and late transition as well as main group metals.

Photoswitchable stable charge-distributed states in a new cobalt complex exhibiting photo-induced valence tautomerism.

We report the synthesis and magnetic and photomagnetic behaviour of a novel valence tautomeric cobalt complex, [Co(3,5-dbbq)2(μ-bpym)] (1) (3,5-dbbq = 3,5-di-tert-butyl-1,2-benzoquinone and μ-bpym = 2,2'-bipyrimidine). The synthesis is performed by reacting Co2(CO)8 and μ-bpym in the presence of the ligand 3,5-dbbq in a mixed solvent under inert atmosphere. The magnetic behavior clearly shows the presence of electron transfer from the catecholate ligand to the cobalt center, producing valence tautomers of [Co(II)(SQ)2] with a transition temperature (T1/2) of 215 K. Photomagnetic studies, performed via both SQUID magnetometry and X-band electron paramagnetic resonance, show the clear presence of photoinduced valence tautomerism, at temperatures considerably higher than previous systems. A metastable charge distribution is observed, strengthening previous investigations on the character of mixed valence ligands. Entropy-driven valence tautomeric interconversion is observed, and drives the transition to the most stable charge distribution. The complex has the ability to coordinate and can be used as a photoswitchable building block, with the photomagnetic characterisation evidencing a metastable state lifetime of the photo-induced valence tautomeric process of ca. 2.9 × 10(4) s below 20 K. The observed yields are higher than ones in similar systems, showing that tiny changes in the molecular structures may have a huge impact.

2-(Phenylazo)pyridineplatinum(II) catecholates showing photocytotoxicity, nuclear uptake, and glutathione-triggered ligand release.

Platinum(II) complexes [Pt(pap)(an-cat)] (1) and [Pt(pap)(py-cat)] (2) with 2-(phenylazo)pyridine (pap), 4-[2-[(anthracen-9-ylmethylene)amino]ethyl]benzene-1,2-diol (H2an-cat), and 4-[2-[(pyren-1-ylmethylene)amino]ethyl]benzene-1,2-diol (H2py-cat) were prepared, and their photoinduced cytotoxicity was studied. The complexes were found to release catecholate ligand in the presence of excess glutathione (GSH), resulting in cellular toxicity in the cancer cells. The catecholate complex [Pt(pap)(cat)] (3) was prepared and used as a control. Complex 3, which is structurally characterized by X-ray crystallography, has platinum(II) in a distorted square-planar geometry. The complexes are redox-active, showing responses near 0.6 and 1.0 V versus SCE in N,N-dimethylformamide/0.1 M tetrabutylammonium perchlorate corresponding to a two-step catechol oxidation process and at -0.3 and -1.3 V for reduction of the pap ligand. Complex 1 showed remarkable light-induced cytotoxicity in HaCaT (human skin keratinocytes) and MCF-7 (human breast cancer) cells, giving IC50 value of ∼5 μM in visible light of 400-700 nm and >40 μM in the dark. The 2',7'-dichlorofluorescein diacetate (DCFDA) assay showed the generation of reactive oxygen species (ROS), which seems to trigger apoptosis, as is evident from the annexin V-fluorescein isothiocyanate (FITC)/propidium iodide (PI) assay. The fluorescence microscopic images showed significant nuclear localization of the complexes and free ligands. A mechanistic study revealed possible reduction of the coordinated azo bond of pap by cellular GSH, releasing the catecholate ligand and resulting in remarkable photochemotherapeutic action of the complexes.

Catechol versus bisphosphonate ligand exchange at the surface of iron oxide nanoparticles: towards multi-functionalization

We report an investigation of the ligand exchange at the surface of iron oxide nanoparticles in water. For this purpose we compared two strong chelating agents on the iron oxide surface containing catechol and bisphosphonate moieties. Interactions between the coating agents (catechol/bisphosphonate) and the nanoparticle’s surface were studied by FTIR and DFT calculations. Ligand exchange experiments were performed using sonication and the exchange yield was characterized by FTIR and EDX. This methodology allowed introducing bisphosphonates with various functionalities (alkyne or biotin) permitting multi-functionalization.