Synthesis and solid state structure of Co(II) complexes of OPTA

Beyond transition block metals: exploring the reactivity of phosphine PTA and its oxide [PTA(O)] towards gallium(iii)

The water-soluble cage-like phosphine PTA (1,3,5-triaza-7-phosphaadamantane) and its phosphine oxide derivative [PTA(O)] (1,3,5-triaza-7-phosphaadamantane-7-oxide) were used to explore their reactivity towards two gallium(iii)-halide precursors, namely GaCl3 and GaI3, for the first time. By using various reaction conditions, a series of N-mono-protonated phosphine salts with [GaCl4]- or [I]- as counterions were obtained in all cases, while the formation of coordinated Ga-PTA and Ga-[PTA(O)] complexes was not observed. All compounds were characterized in solution using multinuclear NMR spectroscopy (1H, 13C{1H}, 31P{1H} and 71Ga) and in the solid state using FT-IR spectroscopy and X-ray crystal diffraction. The new Ga-phosphine salts resulted stable and highly soluble in aqueous solution at room temperature. Density functional theory (DFT) calculations were also performed to further rationalize the coordination features of PTA with Ga3+ metal ion, highlighting that the phosphorus-gallium bond is about twice weaker than the phosphorus-metal bond commonly established by PTA with transition metals such as gold. Furthermore, the mono-protonation of PTA (or [PTA(O)]) makes the formation of ionic gallium-PTA coordination complexes thermodynamically unstable, as confirmed experimentally by the formation of Ga-phosphine salts reported herein.

For Whom a Puddle Is the Sea? Adsorption of Organic Guests on Hydrated MCM-41 Silica

Thermal and hydration effects on the mobility of compact and branched organic molecules and a bulky pharmaceutical substance loaded in submonolayer amounts onto mesoporous silica have been elucidated using ¹H and ³¹P solid-state NMR. In all cases, the ambient hydration has a stronger effect than an increase in temperature to 370 K for water-free silica. The effect of hydration depends on the guest and ranges from complete solvation to a silica-water-guest sandwich structure to a silica-guest/silica-water pattern. The mobility of the guests under different conditions has been described. The specific structure of the MCM-41 surface allows one to study very slow surface diffusion, a diffusivity of about 10^-15-10^-16 m²/s. The data reported are relevant to any nonfunctionalized silica, while the method used is applicable to any phosphor-containing guest on any host.

Synthesis, Structural, and Cytotoxic Properties of New Water-Soluble Copper(II) Complexes based on 2,9-Dimethyl-1,10-Phenanthroline and Their One Derivative Containing 1,3,5-Triaza-7-Phosphaadamantane-7-Oxide

A series of water-soluble copper(II) complexes based on 2,9-dimethyl-1,10-phenanthroline (dmphen) and mixed-ligands, containing PTA=O (1,3,5-triaza-7-phosphaadamantane-7-oxide) have been synthesized and fully characterized. Two types of complexes have been obtained, monocationic [Cu(NO₃)(O-PTA=O)(dmphen)][PF₆] (1), [Cu(Cl)(dmphen)₂][PF₆] (2), and neutral [Cu(NO₃)₂(dmphen)] (3). The solid-state structures of all complexes have been determined by single-crystal X-ray diffraction. Magnetic studies for the complex 1–3 indicated a very weak antiferromagnetic interaction between copper(II) ions in crystal lattice. Complexes were successfully evaluated for their cytotoxic activities on the normal human dermal fibroblast (NHDF) cell line and the antitumor activity using the human lung carcinoma (A549), epithelioid cervix carcinoma (HeLa), colon (LoVo), and breast adenocarcinoma (MCF-7) cell lines. Complexes 1 and 3 revealed lower toxicity to NHDF than A549 and HeLa cells, meanwhile compound 2 appeared to be more toxic to NHDF cell line in comparison to all cancer lines. Additionally, interactions between the complexes and human apo-transferrin (apo-Tf) using fluorescence and circular dichroism (CD) spectroscopy were also investigated. All compounds interacted with apo-transferrin, causing same changes of the protein conformation. Electrostatic interactions dominate in the 1/2 – apo- Tf systems and hydrophobic and ionic interactions in the case of 3.

Unusual Water-Soluble Imino Phosphine Ligand: Enamine and Imine Derivatives of 1,3,5-Triaza-7-phosphaadamantane (PTA)

A series of water-soluble and air-stable E-enamine derivatives of 1,3,5-triaza-7-phosphaadamantane (PTA), PTA═C(R)NH₂, 1-4, are reported along with data on E-Z isomerization and tautomerization to the imine form (PTA-CR═NH). Reaction of 1,3,5-triaza-7-phosphaamantane-6-yl lithium, PTA-Li, with aromatic nitriles afforded E-enamine derivatives of PTA in good yield (49-91%). Phosphines 1-4 are stable toward water and air, and do not appear to isomerize or tautomerize, unless coordinated to a metal or oxidized. The corresponding oxides, O═PTA═C(R)NH₂ (5-8), were observed as ∼55/45 mixtures of E and Z isomers. Kinetic data on the E-Z isomerization is reported. Upon coordination of 1-4 to W(CO)₄(pip)₂, a κ¹- P enamine is formed, [W(CO)₄(pip)(κ¹- P-PTA═CRNH₂)]. Enamine-imine tautomerization of the metal bound phosphine was observed resulting in κ²- P, N imine complexes, [W(CO)₄(κ²- P, N-PTA-CR═NH)], 9-12. The crystal structures of the κ¹- P enamine 11a, κ²- P, N imine 9 and 12, phosphines 1 and 3, as well as phosphine oxide 8a were obtained. DFT calculations on the various isomers of the phosphines and phosphine oxides are also reported.

Water driven formation of channels: unusual solid-state structural transformation of a heterometallic polymer

We describe the synthesis of trans-{[(PTA)₂CpRu-μ-CN-RuCp(PTA)₂-μ-CoCl₃]}_n·(DMSO)_n, and its crystal-to-crystal transformation to its cis isomer, with channels where water is nanoconfined, upon addition of water to the crystallization medium.

Post-assembly guest oxidation in a metallo-supramolecular host and structural rearrangement to a coordination polymer

PTA hosted in a copper metallo-supramolecular triangle undergoes post-assembly oxidation to form PTAO in aerated solutions. The oxidation is triggered by selected co-solvents that also govern the formation of the final crystalline product leading to a discrete host-guest triangle {PTAO@[Cu(o-L)]3} or to a 1D coordination polymer {(PTAO)2@[Cu8][Cu2]}∞ containing a {Cu8} ring with a double hosting pocket.

Copper(I) targeting in the Alzheimer's disease context: a first example using the biocompatible PTA ligand

Copper(I) coordinating ligands in the Alzheimer's disease context have remained unexplored, despite the biological relevance of this redox state of the copper ion. Here, we show that the PTA ligand can remove copper from Aβ, prevent reactive oxygen species production and oligomer formation, two deleterious events in the disease's etiology.

Lithium cation enhances anion binding in a tripodal phosphine oxide-based ditopic receptor

A tripodal ditopic receptor presents H-bond donors and a phosphine oxide to potential guests. In the idealized binding conformation, an endohedral P=O functionality provides enhanced halide binding in the presence of lithium with the greatest ΔΔG° observed for bromide, while minimal changes in K(a) are observed in the presence of sodium.