Ildar Kh. Rizvanov

Experimental Evidence of Phosphine Oxide Generation in Solution and Trapping by Ruthenium Complexes

Phosphorus oxides, oxyacids, and their esters are important chemicals for industry. Apart from playing a role in most organisms in ruling their energy transformations, they find wide and diverse applications, such as fertilizers, pesticides, herbicides, lubricants, flame retardants, additives for special plastics and materials, and drugs for different diseases. Little attention has however been paid to lower-oxidation-state species, such as PO, HPO, and P2O, for which synthetic isolation procedures and even direct evidence of their existence are scarce. One of the most elusive species in this regard is phosphine oxide, H3PO (I ; Scheme 1). This molecule was first observed by reacting atomic oxygen with PH3 using a discharge–flow system equipped with molecularbeam sampling mass spectrometry. Alternatively, red-light photolysis of co-deposited PH3/O3 onto an argon matrix at 12–18 K was used to generate and trap I in a very diluted concentration together with its tautomer phosphinous acid H2P(OH) (II), which was identified by FTIR. [4] Finally, Ault and Kayser observed the formation of H3PO in argon matrices after photochemical irradiation of a mixture of VOCl3, CrO2Cl2, and PH3. [5] Both molecules have been studied by theoretical methods. Application of an adequate phosphorus basis set has recently shown that, in contrast with previous ab initio studies, I is more stable than II by only about 1 kcalmol 1 in the gas phase. In contrast, computational analysis in aqueous solution showed that upon solvation I is largely preferred by about 10 kcal mol 1 owing to stronger hydrogen bonding with the highly polar P!O bond. The possible involvement of H3PO in the oxidative polymerization of phosphine to give polyhydride phosphorus PxHy polymers has been also proposed. Herein we show that the previously unknown P I species H3PO (I) can be easily generated in solution by electrochemical methods, and we provide evidence of its solution stability, its characterization by conventional NMR spectroscopy, and its trapping as a ligand in the coordination sphere of hydrosoluble ruthenium complexes after tautomerization to II. The electrochemical generation of H3PO was performed in a single electrochemical cell with a lead cathode and a sacrificial zinc anode using P4 melted in a slightly acidic water/ ethanol solution (2:1 volume ratio, water acidified with HCl, 2m) at 60 8C (Supporting Information, Figures S1, S2). The overall electrochemical process may be divided in two parts. In the first step, the electrochemical generation of PH3 on the lead cathode takes place as previously described, 11] while in the second step, mild oxidation of PH3 to H3PO occurs at the anodic surface of the zinc electrode. In agreement with cyclic voltammetry experiments showing an irreversible oxidation wave, PH3 is electrochemically active in the anodic potential range + 0.80–1.25 V (vs. Ag/AgNO3, 0.01m in CHCN3) and can be therefore oxidized in acidic water/ethanol 2:1 solution to H3PO (Supporting Information, Figure S3). Scheme 2 shows the overall electrochemical process resulting in the cathodic reduction of P4 to PH3 and anodic oxidation of PH3 to H3PO (E = + 1.24 V vs. Ag/AgNO3, 0.01m in CHCN3). Different working conditions were investigated to optimize the production of H3PO. The best performance was Scheme 1. Phosphine oxide (I) and its tautomer, phosphinous acid (II).

Phosphonium ionic liquids based on bulky phosphines: synthesis, structure and properties

A series of new ionic liquids based on sterically hindered decyl(tri-tert-butyl)phosphonium (DTBP) or decyl(tricyclohexyl)phosphonium (DCHP) cations were prepared using quaternisation of tri-tert-butyl- or tricyclohexylphosphine with decylbromide and subsequent bromide exchange with the weakly-coordinating anions BF(4)(-), PF(6)(-), SO(3)CF(3)(-), N(SO(2)CF(3))(2)(-). The salts obtained melt below 100 degrees C and possess a broad electrochemical window. Density functional theory combined with X-ray crystallography, IR and Raman spectroscopy has been used to analyze the molecular and supramolecular structures of the compounds obtained and their possible influence on their physical properties.

Triphenylphosphonium Cations of the Diterpenoid Isosteviol: Synthesis and Antimitotic Activity in a Sea Urchin Embryo Model.

A series of novel triphenylphosphonium (TPP) cations of the diterpenoid isosteviol (1, 16-oxo-ent-beyeran-19-oic acid) have been synthesized and evaluated in an in vivo phenotypic sea urchin embryo assay for antimitotic activity. The TPP moiety was applied as a carrier to provide selective accumulation of a connected compound into mitochondria. When applied to fertilized eggs, the targeted isosteviol TPP conjugates induced mitotic arrest with the formation of aberrant multipolar mitotic spindles, whereas both isosteviol and the methyltriphenylphosphonium cation were inactive. The structure-activity relationship study revealed the essential role of the TPP group for the realization of the isosteviol effect, while the chemical structure and the length of the linker only slightly influenced the antimitotic potency. The results obtained using the sea urchin embryo model suggested that TPP conjugates of isosteviol induced mitotic spindle defects and mitotic arrest presumably by affecting mitochondrial DNA. Since targeting mitochondria is considered as an encouraging strategy for cancer therapy, TPP-isosteviol conjugates may represent promising candidates for further design as anticancer agents.

p-tert-Butyl thiacalix[4]arenes functionalized at the lower rim by amide, hydroxyl and ester groups as anion receptors

New p-tert-butyl thiacalix[4]arenes differently substituted at the lower rim with amide, hydroxyl and ester groups were synthesized. Binding properties of the compounds toward some tetrabutylammonium salts n-Bu(4)NX (X = F(-), Cl(-), Br(-), I(-), CH(3)CO(2)(-), H(2)PO(4)(-), NO(3)(-)) were studied by UV spectroscopy. It was found that the stoichiometry of the complexes, generally, is 1 : 1, and the association constants are in the range of 10(3)-10(5) M(-1). The p-tert-butyl thiacalix[4]arenes containing secondary amide groups trisubstituted at the lower rim bind the studied anions most effectively. Selective receptors for fluoride and dihydrogen phosphate salts of tetrabutylammonium were found.

Supramolecular assemblies of triblock copolymers with hexanuclear molybdenum clusters for sensing antibiotics in aqueous solutions via energy transfer

The work introduces the supramolecular assembly of triblock copolymers, namely (PEO)13(PPO)30(PEO)13 (L64), (PPO)14(PEO)24(PPO)14 (17R4), (PPO)8(PEO)22(PPO)8 (10R5) and (PEO)21(PPO)67(PEO)21 (P123) with novel cluster complexes [K(diglyme)(CH3CN)]2[Mo6I14] (1) and [K2(diglyme)(CH3CN)5][Mo6I14] (2) as a route to increase their water solubility. Dynamic light scattering and photophysical measurements reveal the decisive influence of the arrangement of PEO and PPO blocks and of their length on both colloidal and photophysical properties of these solutions. ES-MS data reveal [Mo6I14]2− clusters as the predominant form in aqueous solutions of L64 and P123. The steady state and time resolved luminescence data indicate concentration dependent sensitizing of the Mo-centered luminescence through the energy transfer from difloxacin to [Mo6I14]2− mediated by the ion-pairing. The impact of both arrangement and length of PEO and PPO blocks in the luminescent response of [Mo6I14]2− to difloxacin is discussed. The aqueous solutions of L64 at pH 4 provide the optimal conditions for the sensing of difloxacin through the cluster luminescence.

A facile synthetic route to convert Tb(III) complexes of novel tetra-1,3-diketone calix[4]resorcinarene into hydrophilic luminescent colloids

The work presents the synthesis of a novel calix[4]resorcinarene cavitand bearing four 1,3-diketone groups at the upper rim and its complex formation with Tb(III) ions in DMF and DMSO solutions. Electrospray ionization mass spectra, 1H NMR, UV-Vis and luminescence spectra indicate a long (three hours at least) equilibration time for the complex formation between the cavitand and Tb(III) in alkaline DMF and DMSO solutions. These results are explained by the restricted keto–enol conversion, resulting from the steric hindrance effect of the methylenedioxy-groups linking the benzene rings within the cavitand framework. A facile synthetic route to convert luminescent Tb(III) complexes of various stoichiometries into luminescent hydrophilic colloids is disclosed in this work. The route is based on the reprecipitation of the Tb(III) complexes from DMF to aqueous solutions with further polyelectrolyte deposition without prior separation of the luminescent complexes. The luminescent colloids exhibit high stability over time and in buffer systems, which is a prerequisite for their applicability in analysis and biolabeling.

Heteroditopic p-tert-butyl thiacalix[4]arenes for creating supramolecular self-assembles by cascade or commutative mechanisms

New p-tert-butylthiacalix[4]arenes functionalized with hydrazides of nicotinic, isonicotinic, 3-nitrobenzoic acids, 2-hydrazinopyridine, phenylhydrazine, benzotriazole groups at the lower rim in cone, partial cone and 1,3-alternate conformation have been synthesized. The mechanism of self-assembly of supramolecular nanosized particles based on functionalized p-tert-butylthiacalix[4]arenes with silver nitrate and or dicarboxylic acids (oxalic, malonic, succinic acid) has been determined by dynamic light scattering . For the first time, it has been shown that nanoscale particles based on p-tert-butylthiacalix[4]arenes, capable of recognizing metal cations and dicarboxylic acids can form cascade or commutative three-component supramolecular systems. Also for the first time, it has been shown that p-tert-butylthiacalix[4]arenes containing N-substituted hydrazide and heterocyclic fragments are coreceptors, capable of simultaneously binding silver (I) cations and dicarboxylic acids. The formation of cascade systems: “macrocycle-silver (I) nitrate-dicarboxylic acid” is a characteristic of p-tert-butyl thiacalix[4]arenes containing N-substituted hydrazide fragments.

MALDI-TOF MS and Morphology Studies of Thiacalixarene-Silsesquioxane Products of Oligo- and Polycondensation

For the first time condensed silsesquioxane derivatives of tetratrialkoxysilyl compounds have been characterized by MALDI-TOF mass spectrometry. Tetrasubstituted p-tert-butyl thiacalix[4]arene derivatives containing organosilicon fragments with variable stereochemistry were chosen as organosilicon compounds for polycondensation. Information obtained from mass spectra was used to deduce both the structures of oligomeric derivatives, as well as the structure of silsesquioxane framework. The morphology of formed polysilsesquioxanes was investigated by scanning and transmission electron microscopy.

Redox trends in cyclometalated palladium( ii ) complexes

A series of diverse binuclear and mononuclear cyclometalated palladium(ii) complexes of different structure was investigated by electrochemical techniques combined with density functional theory (DFT) calculations. The studies including cyclic and differential pulse voltammetry, X-ray structure analysis and quantum chemical calculations revealed a regularity of the complexes oxidation potential on the metal-metal distance in the complexes: the larger Pd-Pd distance, the higher oxidation potentials. The reduction potentials feature unusually high negative values while no correlation depending on the structure could be observed. These results are in a good agreement with the electron density distribution in the complexes. Additionally, ESR data obtained for the complexes upon oxidation is reported.

Nanoparticle-Delivered 2-PAM for Rat Brain Protection against Paraoxon Central Toxicity

Solid lipid nanoparticles (SLNs) are among the most promising nanocarriers to target the blood-brain barrier (BBB) for drug delivery to the central nervous system (CNS). Encapsulation of the acetylcholinesterase reactivator, pralidoxime chloride (2-PAM), in SLNs appears to be a suitable strategy for protection against poisoning by organophosphorus agents (OPs) and postexposure treatment. 2-PAM-loaded SLNs were developed for brain targeting and delivery via intravenous (iv) administration. 2-PAM-SLNs displayed a high 2-PAM encapsulation efficiency (∼90%) and loading capacity (maximum 30.8 ± 1%). Drug-loaded particles had a mean hydrodynamic diameter close to 100 nm and high negative zeta potential (-54 to -15 mV). These properties contribute to improve long-term stability of 2-PAM-SLNs when stored both at room temperature (22 °C) and at 4 °C, as well as to longer circulation time in the bloodstream compared to free 2-PAM. Paraoxon-poisoned rats (2 × LD50) were treated with 2-PAM-loaded SLNs at a dose of 2-PAM of 5 mg/kg. 2-PAM-SLNs reactivated 15% of brain AChE activity. Our results confirm the potential use of SLNs loaded with positively charged oximes as a medical countermeasure both for protection against OPs poisoning and for postexposure treatment.