Oxide Ligands Research Articles

Supramolecular Polymers and Chiral Phosphine Oxides by Oxidation of Gold(I) Complexes

The chiral diphosphine ligand R,R-cyclo-C6H10-trans-1,2-{NHC(=O)C6H4-2-PPh2}2, 1, forms complexes with gold(I) of formula [Au(1)]Cl, 2, and [(ClAu)2(µ-1)], 3, in which the diphosphine acts as a trans-chelate and bridging ligand, respectively. Oxidation of these gold(I) complexes leads to dissociation and oxidation of the diphosphine ligand to form the corresponding diphosphine dioxide R,R-cyclo-C6H10-1,2-{NHC(=O)C6H4-2-P(=O)Ph2}2, which has been crystallized in its protonated form and as complexes with Na+ and Fe2+, with [AuBr2]− or [AuBr4]− anions. Some of these compounds form supramolecular polymers by intermolecular hydrogen bonding.

Contribution of Ligand Oxidation Products to High Durability of Copper Films Prepared from Low‐Sintering‐Temperature Copper Ink on Polymer Substrates

In electronic printing, ensuring high durability of sintered copper films on flexible substrates to obtain environmental stability and mechanical flexibility has become the most important task from a practical standpoint. In the study reported here, the authors develop solution synthesis of 2‐amino‐2‐ethyl‐1,3‐propanediol (AEP)‐protected copper nanoparticles (AEP–Cu NPs) with sizes of 3–8 nm in ethylene glycol, where the Cu NPs are stabilized via the metallacyclic coordination stability of the AEP ligands. The sintered Cu film exhibits a resistivity of 50 μΩ cm−1 after heating at 150 °C under a nitrogen atmosphere. Most importantly, the resulting Cu films on the polyethylene terephthalate (PET) substrates show excellent durability in terms of bending and adhesion without requiring any additives like nanotubes and nanowires. Furthermore, the authors successfully demonstrated the high environmental stability of the resulting Cu film even after it is exposed to harsh environmental conditions (RH 80%, 60 °C) for 1 month. The environmental durability is further improved by utilizing a composite ink of AEP–Cu NPs with copper microflakes. It is experimentally proven that oxidation products from AEP ligands originating in the sintering process contributed to the high durability of sintered copper films on flexible substrates.

Prediction of Extremely Strong Antiferromagnetic Superexchange in Silver(II) Fluorides: Challenging the Oxocuprates(II).

Strong magnetic coupling between the spins of unpaired electrons is an essential ingredient of many fascinating physical phenomena. Here we report calculations using the hybrid HSE06 functional of magnetic superexchange constants, J, for a series of low-dimensional CuII and AgII binary and ternary systems with fluoride and oxide ligands. The calculations correctly reproduce the sign and size of the magnetic superexchange constants for prototypical antiferromagnetic (AFM) 1D (J1D ) and 2D (J2D ) systems, while overestimating the absolute values of J by about 11 %. We find that [AgF][BF4 ], a quasi-1D system with linear infinite [AgII F+ ] chains, is predicted to exhibit an unprecedented strong AFM superexchange via one atom (F), with J1D about -300 meV. Compression of [AgF][BF4 ] to 10 GPa should lead to a further increase in AFM interactions with J1D reaching -360 meV at 10 GPa.

Outer-Sphere Reactivity Shift of Secondary Phosphine Oxide-Based Nickel Complexes: From Ethylene Hydrophosphinylation to Oligomerization.

A new dimension for secondary phosphine oxide (SPOs) ligands is described in this article. Demonstrated on original π-allylic nickel structures, these self-assembled complexes trigger catalytic hydrophosphinylation reactions. Addition of a Lewis acid B(C6 F5 )3 switches the reactivity towards migratory insertion and thus ethylene oligomerization through an unprecedented outer-sphere interaction with the coordinated SPO ligand. NMR experiments and X-ray analyses allowed for the observation of the formation of zwitterionic active species as well as their degradation pathway.

Determination of flunixin by sensitized terbium fluorescence in the presence of surfactant micelles

The effect of surfactant micelles and the second ligand on the efficiency of energy transfer in the Tb3+–flunixin complex was studied. The fluorescence intensity of the Tb3+–flunixin complex was shown to 100-fold increase in the presence of Tween 80 micelles and the second trioctylphosphine oxide ligand. A procedure for the fluorimetric determination of flunixin in the Flunex drug product (NITA-FARM, Saratov, Russia) was developed. The linearity range of the calibration curve was from 1 × 10–7 to 1 × 10–4 M, r 2 = 0.991, and the limit of detection was 4 × 10–8 M (3σ).

Lactoferrin modified graphene oxide iron oxide nanocomposite for glioma-targeted drug delivery

Targeting delivery of drugs in a specific manner represents a potential powerful technology in gliomas. Herein, we prepared a multifunctional targeted delivery system based on graphene oxide (GO) that contains a molecular bio-targeting ligand and superparamagnetic iron oxide nanoparticles on the surface of GO for magnetic targeting. Superparamagnetic Fe3O4 nanoparticles was loaded on the surface of GO via chemical precipitation method to form GO@Fe3O4 nanocomposites. Lactoferrin (Lf), an iron-transporting serum glycoprotein that binds to receptors overexpressed at the surface of glioma cells and vascular endothelial cell of the blood brain barrier, was chosen as the targeted ligand to construct the targeted delivery system Lf@GO@Fe3O4 through EDC/NHS chemistry. With the confirmation of TEM, DLS and VSM, the resulting Lf@GO@Fe3O4 had a size distribution of 200–1000nm and exhibited a superparamagnetic behavior. The nano delivery system had a high loading capacity and exhibited a pH-dependent release behavior. Compared with free DOX and DOX@GO@Fe3O4, Lf@GO@Fe3O4@DOX displayed greater intracellular delivery efficiency and stronger cytotoxicity against C6 glioma cells. The results demonstrated the potential utility of Lf conjugated GO@Fe3O4 nanocomposites for therapeutic application in the treatment of gliomas.

Encapsulation of TOPO stabilized NaYF4:Er3+,Yb3+ nanoparticles in biocompatible nanocarriers: Synthesis, optical properties and colloidal stability

The emulsification process leading to up-converting NaYF4:Er3+,Yb3+ NPs encapsulation, was performed using a modified water/oil/water double emulsion evaporation method, where poly(lactic-co-glycolic acid) was used as biocompatible polymer. Span 80 and Cremophor A25 were applied as non-ionic surfactants and dichloromethane as oily phase. The use of trioctylphosphine oxide ligands for the synthesis of up-converting NaYF4:Er3+,Yb3+ NPs allowed to obtain spherical particles with sizes below 10nm, what further facilitated the efficient encapsulation process. Those newly designed nanosystems were subjected to analysis of their morphology, colloidal stability and optical properties by: dynamic light scattering, ζ-potential, atomic force microscopy, transmission electron microscopy and measuring the up-conversion emission spectra of free and loaded NaYF4:Er3+,Yb3+ NPs. The encapsulated NaYF4:Er3+,Yb3+ NPs showed increased colloidal stability for a long period of 60 days of storage in different conditions. Simultaneously, the encapsulation process did not significantly influenced their optical properties and strong visible emission could be observed upon nearinfrared excitation.

Post‐Synthetic Modification of Mesoporous Zinc‐Adeninate Framework with Tris(2,2′‐bipyridine) Ruthenium(II) Complex and its Electrochemiluminescence

Herein we report a redox‐active metal‐organic framework (MOF) via post‐synthetic cation exchange with tris(2,2′‐biprydine) ruthenium(II) complex (Ru(bpy)32+). A porous anionic zinc‐adeninate framework (bMOF‐100) is spacious enough to easily entrap 2.43 of Ru(bpy)32+ cations within the mesopore. The encapsulation supported the framework structure preventing any distortion from a rapid solvent evaporation under SEM observation. Ru(bpy)32+@bMOF‐100 was then immobilized on the surface of glassy carbon electrode, and its electrocatalytic and electrochemiluminescent (ECL) properties were investigated in aqueous and organic solution. Especially, Ru(bpy)32+@bMOF‐100 showed the excellent electrochemical properties of Ru(bpy)32+, but gradual decomposition of the MOF structure was observed under electrochemical measurements because of the sluggish oxidation of adeninate ligand.

Dynamic Magnetic and Optical Insight into a High Performance Pentagonal Bipyramidal DyIII Single-Ion Magnet.

The pentagonal bipyramidal single-ion magnets (SIMs) are among the most attractive prototypes of high-performance single-molecule magnets (SMMs). Here, a fluorescence-active phosphine oxide ligand CyPh2 PO (=cyclohexyl(diphenyl)phosphine oxide) was introduced into [Dy(CyPh2 PO)2 (H2 O)5 ]Br3 ⋅2 (CyPh2 PO)⋅EtOH⋅3 H2 O, and combined dynamic magnetic measurement, optical characterization, ab initio calculation, and magneto-optical correlation of this high-performance pseudo-D5h DyIII SIM with large Ueff (508(2) K) and high magnetic hysteresis temperature (19 K) were performed. This work provides a deeper insight into the rational design of promising molecular magnets.

Crystallography as Forensic Tool for Understanding Electrolyte Degradation in Dye–sensitized Solar Cells

AbstractThe precipitation of solid compounds from model electrolytes for liquid dye‐sensitized solar cells has a story to tell regarding decomposition processes to be expected in such systems. Of course, the crystal lattice energy for a specific crystalline compounds plays a role in what compound that will eventually precipitate, but the compounds nevertheless serve as indicators for what type of processes that take place in the solar cell electrolytes upon ageing. From the compounds isolated in this study we learn that both ligand exchange processes, double‐salt precipitation and oxidation are degradation processes that should not be overlooked when formulating efficient and stable electrolytes for this type of electrochemical system.

Iridium versus Iridium: Nanocluster and Monometallic Catalysts Carrying the Same Ligand Behave Differently.

A specific secondary phosphine oxide (SPO) ligand (tert-butyl(phenyl)phosphine oxide) was employed to generate two iridium catalysts, an Ir-SPO complex and IrNPs (iridium nanoparticles) ligated with SPO ligands, which were compared mutually and with several supported iridium catalysts with the aim to establish the differences in their catalytic properties. The Ir-SPO-based catalysts showed totally different activities and selectivities in the hydrogenation of various substituted aldehydes, in which H2 is likely cleaved by a metal-ligand cooperation, that is, the SPO ligand and a neighboring metal centre operate in tandem to activate the hydrogen molecule. In addition, the supported IrNPs behave very differently from both Ir-SPO catalysts. This study exemplifies perfectly the advantages and disadvantages related to the use of the main types of catalysts, and thus the dissimilarities between them.

Roles of phenol groups and auxiliary ligand of copper(ii) complexes with tetradentate ligands in the aerobic oxidation of benzyl alcohol.

Herein, six copper(ii) complexes with multidentate ligands, [Cu(HL1)(OAc)(HOAc)] (1), [Cu(HL2)(OAc)] (2), [Cu(HL3)(OAc)] (3), [CuL4(OAc)] (4), [Cu(HL2)Cl] (5), and [Cu(HL3)Cl] (6) {H2L1 = [bis(3-tert-butyl-2-hydroxybenzyl)](2-pyridylmethyl)amine, H2L2 = [(3-tert-butyl-2-hydoxybenzyl)(3-trifluoromethyl-2-hydroxybenzyl) (2-pyridylmethyl)]amine, H2L3 = [bis(3-trifluoromethyl-2-hydroxybenzyl)] (2-pyridylmethyl)amine, and HL4 = [bis(2-pyridylmethyl)] (3-tert-butyl-2-hydroxybenzyl)amine}, are reported. The complexes were characterized by UV-vis spectroscopy, high-resolution mass spectrometry, X-ray single-crystal diffraction analysis and electrochemistry. These copper(ii) complexes have been investigated as catalysts for the aerobic oxidation of benzyl alcohol to benzaldehyde mediated by TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxyl) radical in water at ambient temperature. Mechanistic investigations have revealed that the phenolate/phenol is involved in the intramolecular proton transfer with a bound substrate in catalysis. Hence, the presence of the trifluoromethyl group on the phenol ring significantly affects the catalysis process since the substituent affects the acidity of phenol, and subsequently, the intramolecular proton transfer from the bound substrate. During catalysis, the dissociation of the auxiliary ligand (Cl- or OAc-) occurred in the SN1 pathway, and it is necessary for the substrate to bind. To complete the catalytic cycle, the cleaved auxiliary ligand rebinds to the metal center to regenerate the catalyst.

Influence of Graphene Oxide Supports on Solution-Phase Catalysis of Thiolate-Protected Palladium Nanoparticles in Water.

The influence of graphene oxide supports and thiolate surface ligands on the catalytic activity of colloidal Pd nanoparticles for alkyne hydrogenation in water is investigated. The studies show that unsupported, water-soluble thiolate-capped Pd nanoparticle catalysts favor the semi-hydrogenation over full-hydrogenation of dimethyl acetylene dicarboxylate (DMAD) under the atmospheric pressure and at room temperature. Pd nanoparticles supported on graphene oxide exhibit a similar activity for the hydrogenation of DMAD, but they show an improved long-term colloidal stability in aqueous solution after multiple catalytic cycles. After the heat treatment of Pd nanoparticles supported on graphene oxide at 300 °C, these heated hybrids exhibit an enhanced catalytic activity towards the full-hydrogenation. Overall, the studies suggest some influences of graphene oxide supports on the stability and thiolate surface ligands on the activity and selectivity of Pd nanoparticle catalysts.

Characterization of secondary phosphine oxide ligands on the surface of iridium nanoparticles.

The synthesis of iridium nanoparticles (IrNPs) ligated by various secondary phosphine oxides (SPOs) is described. This highly reproducible and simple method via H2 reduction produces well dispersed, small nanoparticles (NPs), which were characterized by the state-of-the-art techniques, such as TEM, HRTEM, WAXS and ATR FT-IR spectroscopy. In particular, multinuclear solid state MAS-NMR spectroscopy with and without cross polarization (CP) enabled us to investigate the different binding modes adopted by the ligand at the nanoparticle surface, suggesting the presence of three possible types of coordination: as a purely anionic ligand Ir-P(O)R2, as a neutral acid R2P-O-H and as a monoanionic bidentate H-bonded dimer R2P-O-HO[double bond, length as m-dash]PR2. Specifically, the higher basicity of the dicyclohexyl system leads to the formation of IrNPs in which the bidentate binding mode is most abundant. Such cyclohexyl groups are bent towards the edges, as is suggested by the study of 13CO coordination on the NP surface. This study also showed that the number of surface sites on faces available for bridging CO molecules is higher than the number of sites for terminal CO species on edges and apices, which is unexpected taking into account the small size of the nanoparticles. In addition, the IrNPs present a high chemoselectivity in the hydrogenation of cinnamaldehyde to the unsaturated alcohol.

Two cadmium coordination polymers based on tris(p-carboxyphenyl) phosphane oxide with highly selective sensing of nitrobenzene derivatives and Hg2+ cations

Based on the tris(p-carboxyphenyl)phosphane oxide ligand, two Cd(ii) CPs were obtained which could highly sense nitrobenzene derivatives and Hg2+ cations.

Electron Paramagnetic Resonance as a Tool for Studying the Mechanisms of Paramagnetic Anticancer Metallodrugs

Electron paramagnetic resonance spectroscopy (EPR) is an invaluable method for characterizing ligand environments and oxidation states of paramagnetic metal complexes. In this review we describe applications of this technique to understanding the often complicated mechanisms of metal‐based anticancer compounds. EPR has been instrumental in unravelling this in many instances, providing insight into conformations upon dissolution, aqueous ligand exchange, pH effects, and redox processes. EPR studies have also characterized the protein and DNA interactions of metal‐based chemotherapeutics, enabling discrimination of different binding modes. EPR can also be used to probe the behaviour of metallodrugs with whole cells, revealing interactions with cellular components and redox stability. Together, these studies provide important information on aspects of anticancer activity and demonstrate the scope and potential of EPR to contribute to the ongoing development of metal‐based anticancer complexes.

Redox and Photophysical Behaviour of Complexes of NpO2+ Ions with Carbomyl methyl phosphine oxide in 1-Hexyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide Ionic Liquid

Room temperature ionic liquids (RTIL) have attracted considerable attention due to their many remarkable properties useful for technological applications not only involving formation of metal ion complexes but also as electrolyte. For understanding the role of ionic liquid in such applications requires the experimental and theoretical studies on the metal ion complexes. Therefore, an electrochemical, theoretical and luminescence studies have been carried out in the present work to correlate redox behavior, complexation, and photophysical characteristics NpO2+ complexes with carbomyl methyl phosphine oxide (CMPO) ligand in ionic liquid, which is important for the actinide partitioning. The electrochemical behavior of NpO2+extracted by CMPO in 1-Hexyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide (HmimNTf2) (IL) was studied at glassy carbon (GC) electrode. The redox reaction of NpO2+ to NpO22+and vice versa in HmimNTf2 is quasi-reversible and controlled by diffusion as well as charge transfer kinetics. The cyclic voltammograms obtained in ionic liquid were much broader with reduced cathodic and anodic peak current densities (jpc and jpa) as compared to the one obtained with aqueous solution. The transport properties and kinetics of Np(V) were deduced from electrochemical calculations. The complexation behaviour of CMPO with Np(V) in aqueous solution as well as in HmimNTf2 was studied using density function theory (DFT). Based on these calculations NpO2+forms [Np(CMPO)2(NO3)2]1− type of complex in aqueous solution whereas [Np(CMPO)2(NO3)2]1−.(IL)2complex in IL. Oxidation state of neptunium was further confirmed using Time resolved fluorescence spectroscopy (TRFS) and UV–vis absorption spectroscopy. Moreover TRFS data depicted the stabilization of Np as NpO2+ in both aqueous as well as in RTIL phases. The emission spectroscopic measurement also pin pointed the fact that emission peaks of Np-CMPO complex in RTIL is blue shifted with respect to aqueous solution, which is attributed to the change in equatorial bonding/coordination of the NpO2+in the basal plane. From Photoluminescence (PL) spectroscopy and its kinetics; it was also observed that emission intensity and average lifetime are more in case of Np-CMPO complex in RTIL as compared to aqueous phase because of presence of relatively higher concentration OH group in aqueous phase which are known to be fluorescence quencher. This is a rare study where electrochemical measurements established the redox behavior, DFT calculations confirms the complexation behavior and TRFS brings out the interesting optical features of NpO2+in aqueous and ionic liquid media.

234 - Investigation into the Oxidation of CuATSM as a Mechanism for Copper Release

Copper delivery to superoxide dismutase (SOD) by copper transport agent CuATSM (diacetyl-bis(N4-methylthiosemi-carbazone) copper(II)) is protective in mouse models of amyotrophic lateral sclerosis (ALS). CuATSM is a neutral, hydrophobic compound, able to cross into the CNS without facilitated transport. Reduction of CuII has frequently been proposed as the mechanism of copper release from the ATSM ligand. However, with a reduction potential of -0.46V, CuII reduction will be difficult to accomplish in a cellular environment. In contrast to reduction, oxidation of the ATSM ligand could serve as a mechanism of copper release in a biological system. We investigated the oxidation of CuATSM ligand in an assay utilizing 10-9M horseradish peroxidase (HRP), 2-10 µM hydrogen peroxide, and 10 to 100 µM 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) as a competitive substrate to test for inhibition by CuATSM. Surprisingly, low micromolar concentrations of CuATSM accelerated the oxidation of ABTS by HRP. Our kinetic results suggest that CuATSM was efficiently oxidized by HRP and the CuATSM radical cation in turn oxidized ABTS, We conclude that oxidative reactions involving CuATSM are likely to occur in vivo and need to be further investigated as clinical trials are now underway in treating human ALS patients. This work is supported by funding from the DoD Congressionally Directed Medical Research Program (AL140108) and by Ice Bucket donations made to the ALSA (Research Award ALSA 320).

5,6‐ and 6,6‐Membered Palladium(II) Pincer Complexes Based on Functionalized Carboxamides with Ancillary Sulfur and Nitrogen Donors

New multidentate ligands have been synthesized by the condensation of 2‐(methylsulfanyl)benzoyl chloride with a range of amines bearing ancillary N or S donors. In reactions with PdCl2(NCPh)2, the ligands smoothly underwent direct cyclopalladation to give pincer complexes with 5,6‐ or 6,6‐membered fused metallocycles. The oxidation of the sulfide ligands with H2O2 afforded the corresponding sulfoxide derivatives, which readily formed analogous pincer complexes with the PdII ions. The realization of κ3‐S,N,X coordination (X = N or S) was confirmed by multinuclear NMR and IR spectroscopic data and, in some cases, X‐ray crystallography. An unusual dynamic behavior of the 6,6‐membered S,N,S complex with an organophosphorus ligand was additionally studied by the ROESY technique. All of the palladocycles obtained were tested as precatalysts for the Suzuki cross‐coupling of aryl bromides with arylboronic acids, which allowed us to evaluate the main structure–activity relationships.

Titanium(IV) complexes bearing the (CpC)− ligand

CpCH is a chiral cyclopentadienide-type ligand consisting of a CpH core with two annulated dibenzocycloheptatriene wings. Due to the presence of the seven-membered rings, the wings are bent making CpCH a novel, intrinsically chiral CpH derivative. Starting from ClTi(OiPr)3 and (CpC)-, obtained by deprotonation of CpCH with BuLi, the titanium (IV) half-sandwich complex (CpC)Ti(OiPr)3 was obtained. Further treatment of (CpC)Ti(OiPr)3 with an excess of Me3SiI gave the iodo derivative (CpC)Ti(OiPr)I2 in good yields. Both complexes could structurally be characterized by means of single crystal X-ray crystallography. Direct conversion of (CpC)- with TiCl4 resulted in oxidation of the anionic ligand and thus formation of the CC bridged dimer (CpC)2.