Phosphine-Catalyzed Synthesis and Cytotoxic Evaluation of Michael Adducts of the Sesquiterpene Lactone Arglabin

A general method for chemo- and diastereoselective modification of anticancer natural product arglabin with nitrogen- and carbon-centered pronucleophiles under the influence of nucleophilic phosphine catalysts was developed. The locked s-cis-geometry of α-methylene-γ-butyrolactone moiety of arglabin favors for the additional stabilization of the zwitterionic intermediate by electrostatic interaction between phosphonium and enolate oxygen centers, leading to the unprecedentedly high efficiency of the phosphine-catalyzed Michael additions to this sesquiterpene lactone. Using n-Bu3P as the catalyst, pyrazole, phthalimide, 2-oxazolidinone, 4-quinazolinone, uracil, thymine, cytosine, and adenine adducts of arglabin were obtained. The n-Bu3P-catalyzed reaction of arglabin with active methylene compounds resulted in the predominant formation of bisadducts bearing a new quaternary carbon center. All synthesized Michael adducts and previously obtained phosphorylated arglabin derivatives were evaluated in vitro against eleven cancer and two normal cell lines, and the results were compared to those of natural arglabin and its dimethylamino hydrochloride salt currently used as anticancer drugs. 2-Oxazolidinone, uracil, diethyl malonate, dibenzyl phosphonate, and diethyl cyanomethylphosphonate derivatives of arglabin exhibited more potent antiproliferative activity towards several cancer cell lines and lower cytotoxicity towards normal cell lines in comparison to the reference compounds, indicating the feasibility of the developed methodology for the design of novel anticancer drugs with better therapeutic potential.

α-Umpolung/Michael Addition/Quaternization Tandem Reaction to provide α-Imido-β-phosphonium Propanoates with Broad Spectrum of Biological Activity

This paper has been supported by the Kazan Federal University Strategic Academic Leadership Program ('PRIORITY-2030'). HRMS data were obtained in the CSF-SAC FRC KSC RAS by support of the State Assignment of the Federal Research Center "Kazan Scientific Center", Russian Academy of Sciences. A.D.V, conducted studies of anticancer activity with financial support form the government assignment for FRC Kazan Scientific Center of RAS.

Linkage of the Dinuclear Gold(I) Complex Luminescence and Origin of Endocyclic Amino Group of Cyclic P2N2-Bridging Ligands

Gold(I) complexes of LAu2Cl2 composition based on P2N2 ligands, namely 1,5-diaza-3,7-diphosphacyclooctanes, containing ethylpyridyl substituents at the phosphorus atoms and sp2- or sp3-hybridized endocyclic nitrogen atoms were synthesized. The SCXRD analysis indicated the strong impact of the geometry of the nitrogen atom on the structure and conformational flexibility of the complexes. The N-aryl substituted ligand with the planar endocyclic nitrogen atom provides higher flexibility of the complex and an ability to bind the solvent molecules in the "host-guest" mode, whereas that kind of behavior is forbidden for the complex with an N-alkyl substituted ligand with a pyramidal nitrogen atom. The substituents at nitrogen atoms also control the origin of the emission, which is phosphorescence for the N-aryl substituted complex and fluorescence for the N-alkylaryl substituted complex. The phosphorescent gold(I) complex displays high cytotoxicity without selectivity toward the m-HeLa and normal cells, but the core-shell nanoparticles formed on the base of the complex demonstrate reduced cytotoxicity. The luminescence of the NPs allows tracking the complexes in the cell samples.

Stereoelectronic Effect in the Reaction of α-Methylene Lactones with Tertiary Phosphines and Its Application in Organocatalysis

The kinetic data indicate that the addition of tertiary phosphines to α-methylene lactones in acetic acid is strongly accelerated in comparison to the reactions of related open-chain esters. Six-membered α-methylene-δ-valerolactone exhibited a more pronounced rate increase than five-membered α-methylene-γ-butyrolactone. The use of α-methylene-γ-butyrolactam as a nitrogen analogue of α-methylene-γ-butyrolactone resulted in a total loss of the reaction acceleration. The observed reactivities were rationalized by DFT calculations at the RwB97XD/6-31+G(d,p) level of theory, showing that the intramolecular interaction between phosphonium and enolate oxygen centers provided by the locked s-cis-geometry of the heterocycles plays an important role in the stabilization of intermediate zwitterions. The reactivity is also controlled by the conformational flexibility of the heterocycle. The geometries of five-membered and, especially, six-membered lactone cycles are slightly changed upon the nucleophilic attack of phosphine, leading to the stabilizing stereoelectronic effect by the Ρ···Ο interaction. The addition of phosphine to α-methylene-γ-butyrolactam significantly distorts the initial geometry of the heterocycle, making the nucleophilic attack unfavorable. The application of the stereoelectronic effect to enhance the efficiency of the phosphine-catalyzed Michael and Pudovik reactions of α-methylene lactones was demonstrated.

Tuning Crystal Packing and Magnetic Properties in a Series of [Dy12] Metallocubanes Based on Azobenzene Derivatives of Salicylic Acid

A series of four new Dy₁₂ dodecanuclear clusters based on azobenzene derivative ligands of salicylic acid (L1-L4) has been synthesized and characterized in the crystalline phase using X-ray diffraction on single crystal and powder, IR spectroscopy, elemental analysis, and DSC-TGA methods. It was revealed that all obtained clusters exhibit the formation of the similar metallic cluster nodes, as vertex-sharing heterocubanes, obtained from four Dy³⁺ cations, three bridging hydroxyl groups, and O atoms from the salicylic ligands. The coordination geometry around the Dy(III) centers has been carefully analyzed. Whereas Dy₁₂-L1 and Dy₁₂-L2 with L1 and L2 containing Me and OMe groups in para positions of the phenyl rings, respectively, form similar porous 3D diamond-like molecular networks due to CH-π interactions, for Dy₁₂-L3 with L3 bearing NO₂-electron-withdrawing group, the generation of 2D molecular grids assembled by π-π staking is observed, and for Dy₁₂-L4 with L4 bearing phenyl substituent, 3D hexagonal channels have been generated. The complexes Dy₁₂-L1, Dy₁₂-L2, and Dy₁₂-L3 exhibit a zero-field slow magnetic relaxation effect. After UV irradiation of Dy₁₂-L1, a decrease of the magnetic anisotropy energy barrier displaying the possibility of control over magnetic properties by the external stimulus has been observed.

Cobalt(II) coordination to an N4-acenaphthene-based ligand and its sodium complex

A new bifunctional N₄-ligand was obtained via the condensation reaction of acenaphthenequinone and 2-picolylamine. A peculiarity of this synthesis is the formation of a new intramolecular C-C bond during the reaction. The structure and redox properties of the ligand were studied. The anion-radical form of the ligand was prepared via the chemical reduction of the latter with metallic sodium as well as in situ via its electrochemical reduction in a solution. The sodium salt prepared was structurally characterized using single-crystal X-ray diffraction (XRD). New cobalt complexes with the ligand in neutral and anion-radical forms were synthesized and further studied. As a result, three new homo- and heteroleptic cobalt(II) complexes were obtained, in which the cobalt atom demonstrates different modes of coordination with the ligand. Cobalt(II) complex CoL₂ with two monoanionic ligands was prepared by the electrochemical reduction of a related L₂CoBr₂ complex or by treating cobalt(II) bromide with the sodium salt. XRD was used to study the structures of all cobalt complexes prepared. Magnetic and electron paramagnetic resonance studies were performed: Co^II ion states with S = 3/2 and S = 1/2 were found for the complexes. A quantum-chemical study confirmed that the spin density is mainly located at the cobalt center.

Chemical and Electrochemical Reductions of Monoiminoacenaphthenes

Redox properties of monoiminoacenaphthenes (MIANs) were studied using various electrochemical techniques. The potential values obtained were used for calculating the electrochemical gap value and corresponding frontier orbital difference energy. The first-peak-potential reduction of the MIANs was performed. As a result of controlled potential electrolysis, two-electron one-proton addition products were obtained. Additionally, the MIANs were exposed to one-electron chemical reduction by sodium and NaBH₄. Structures of three new sodium complexes, three products of electrochemical reduction, and one product of the reduction by NaBH₄ were studied using single-crystal X-ray diffraction. The MIANs reduced electrochemically by NaBH₄ represent salts, in which the protonated MIAN skeleton acts as an anion and Bu₄N⁺ or Na⁺ as a cation. In the case of sodium complexes, the anion radicals of MIANs are coordinated with sodium cations into tetranuclear complexes. The photophysical and electrochemical properties of all reduced MIAN products, as well as neutral forms, were studied both experimentally and quantum-chemically.

Ferrocene-based P-chiral amidophosphinate: stereoselective synthesis and X-ray structural study

Racemic and enantiopure ferrocene-based P-chiral amidophosphinates have been simply and stereoselectively synthesized by ortho-lithiation of rac- or (R)-Ugi's amine and further reaction with amidochlorophenylphosphinate Cl-P(O)(Ph)NEt₂. This is the first example of an asymmetric reaction of ortho-lithiated Ugi's amine with tetracoordinated phosphorus(V) chlorides. The structures of rac- and (R)-Ugi's amine ferrocenyl(phenyl)phosphinic acid N,N-diethylamide have been extensively studied experimentally (NMR, X-ray analysis, electrochemistry). The CV first peak refers to the oxidation of the amine fragment, which is clearly seen when (R)-Ugi's amine ferrocenyl(phenyl)phosphinic acid N,N-diethylamide reacts with anhydrous acid. The addition of two equivalents of CF₃COOH leads to the protonation of nitrogen atoms, and a classical reversible wave of oxidation of Fe(II) to Fe(III) is observed.

Complexation of Oligo- and Polynucleotides with Methoxyphenyl-Functionalized Imidazolium Surfactants

Interaction between cationic surfactants and nucleic acids attracts much attention due to the possibility of using such systems for gene delivery. Herein, the lipoplexes based on cationic surfactants with imidazolium head group bearing methoxyphenyl fragment (MPI-n, n = 10, 12, 14, 16) and nucleic acids (oligonucleotide and plasmid DNA) were explored. The complex formation was confirmed by dynamic/electrophoretic light scattering, transmission electron microscopy, fluorescence spectroscopy, circular dichroism, and gel electrophoresis. The nanosized lipoplex formation (of about 100-200 nm), contributed by electrostatic, hydrophobic interactions, and intercalation mechanism, has been shown. Significant effects of the hydrocarbon tail length of surfactant and the type of nucleic acid on their interaction was revealed. The cytotoxic effect and transfection ability of lipoplexes studied were determined using M-HeLa, A549 cancer cell lines, and normal Chang liver cells. A selective reduced cytotoxic effect of the complexes on M-HeLa cancer cells was established, as well as a high ability of the systems to be transfected into cancer cells. MPI-n/DNA complexes showed a pronounced transfection activity equal to the commercial preparation Lipofectamine 3000. Thus, it has been shown that MPI-n surfactants are effective agents for nucleic acid condensation and can be considered as potential non-viral vectors for gene delivery.

Comparison of crystal structure and DFT calculations of triferrocenyl trithiophosphite’s conformance

A triferrocenyl trithiophosphite was studied by X-ray single-crystal diffraction. Triferrocenyl trithiophosphite has nine axes of internal rotation: three P–S bonds, three C–S bonds and three Fe–cyclopentadienyl axes. Rotation around the P–S bonds results in a totally asymmetric structure with three ferrocenylthio groups exhibiting different orientations towards the phosphorus lone electron pair (LEP). A comparison of DFT calculations and X-ray diffraction data is presented, herein we show which conformations are preferred for a given ligand.

Deep-Blue Emissive Copper(I) Complexes Based on P-Thiophenylethyl-Substituted Cyclic Bisphosphines Displaying Photoinduced Structural Transformations of the Excited States

A synthetic method for a primary 2-(thiophen-2'-yl)ethylphosphine was developed. The reaction of thiophenylethylphosphine with paraformaldehyde and primary arylamines leads to the formation of cyclic bisphosphines, namely, 1,5-di(aryl)-3,7-bis(thiophenylethyl)-1,5-diaza-3,7-diphosphacyclooctane (aryl = phenyl, p-tolyl). The obtained bisphosphines form cationic bis-P,P-chelate complexes with copper(I) tetrafluoroborate, which were structurally characterized by NMR spectroscopy, mass spectrometry, and elemental and XRD analyses. Surprisingly, the copper(I) complexes display a multiband emission in the solid state with maxima at 355-360, 425-430, and 480-490 nm and nanosecond lifetimes (1.2-1.4 ns) upon a 335 nm excitation. The excitation of the complexes at 360 nm at room temperature results in a deep-blue emission at 425-430 nm and a tail at 460-490 nm. A temperature decrease leads to an increased intensity of the emission band at 480 nm, while the luminescence lifetimes insignificantly increased up to 14 ns. Quantum chemical calculations explain the observed unusual luminescent behavior by the existence of "undistorted" and "flattened" singlet excited states of copper(I) complexes at room temperature and at 77 K, respectively.

Thermodynamic vs. Kinetic Control in Synthesis of O-Donor 2,5-Substituted Furan and 3,5-Substituted Pyrazole from Heteropropargyl Precursor

Elaboration of a convenient route towards donor-substituted pyrazoles from heteropropargyl precursors is challenging due to a number of thermodynamically favorable side reactions (e.g., acetylene-allene isomerization and Glaser homocoupling). In this work, Sonogashira cross-coupling conditions of 4-tert-butylphenyl propargyl ether with benzoyl chloride followed by tandem Michael addition/cyclocondensation with hydrazine into 3,5-disubstituted pyrazole (kinetic control), as well as cycloisomerization conditions of ketoacetylene intermediate into 2,5-disubstituted furan (thermodynamic control), were established through a variation of the catalyst loading, solvent polarity, excess of triethylamine, and time of reaction. During the optimization of process parameters, a number of by-products represented by a monophosphine binuclear complex (PPh₃PdI₂)₂ with two bridging iodine atoms and diyne were identified and isolated in the pure form. The quantum-chemical calculations and solution-state ¹H/¹³C NMR spectroscopy suggested that the 5(3)-(4-tert-butylphenyloxy)methoxy-3(5)-phenyl-1H-pyrazole exists in the tautomeric equilibrium in a polar methanol solvent and that individual tautomers could be characterized in case aprotic solvents employed. The pyrazole features a unique tetramer motif in the crystal phase formed by alternating 3(5)-phenyl-1H-pyrazole tautomers, which was stabilized by N-H···N bonds and stacking interactions of pyrazole rings, whereas pyrazole dimers were identified in the gas phase.

Synthesis, biological evaluation and structure-activity relationship of 2-(2-hydroxyaryl)alkenylphosphonium salts with potency as anti-MRSA agents

Here we report the synthesis, in vitro antimicrobial activity, preliminary toxicity and mechanism study of a new series of 2-(2-hydroxyaryl)alkenylphosphonium salts with the variation of phosphonium moiety obtained by a two-step synthetic method from phosphine oxides. The salts showed pronounced activity against Gram-positive bacteria, including MRSA strains, and some fungi. Mechanism of action against S. aureus was studied by CV test, TEM and proteomic assay. No cell wall integrity loss was observed while proteomic assay results suggested interference in different metabolic processes of S. aureus. For this series, lipophilicity was determined as a key factor for the inhibition of Gram-positive bacteria growth and S. aureus killing. Biological properties of methylated derivatives were notably different with manifested action against Gram-negative bacteria.

Design, Spectral Characteristics, Photostability, and Possibilities for Practical Application of BODIPY FL-Labeled Thioterpenoid

This paper presents the design and a comparative analysis of the structural and solvation factors on the spectral and biological properties of the BODIPY biomarker with a thioterpene fragment. Covalent binding of the thioterpene moiety to the butanoic acid residue of meso-substituted BODIPY was carried out to find out the membranotropic effect of conjugate to erythrocytes, and to assess the possibilities of its practical application in bioimaging. The molecular structure of the conjugate was confirmed via X-ray, UV/vis-, NMR-, and MS-spectra. It was found that dye demonstrates high photostability and high fluorescence quantum yield (to ~100%) at 514–519 nm. In addition, the marker was shown to effectively penetrate the erythrocytes membrane in the absence of erythrotoxicity. The conjugation of BODIPY with thioterpenoid is an excellent way to increase affinity dyes to biostructures, including blood components.

Effects of ms-aryl substitution on the structure and spectral properties of new CH(Ar)-bis(BODIPY) luminophores

In this article, we present synthesis, spectral characteristics, and results of DFT calculations of new CH(R)-bis(BODIPY) 1-3. They are characterized by the conformational mobility and sensitivity of fluorescence to polarity, proton-, electron donor ability and viscosity of the solvation environment. It is shown that fluorescence intensity of 1-3 increases in the homologous series of alcohols (ethanol, 1-propanol, 1-butanol, 1-octanol, 1-decanol) mainly due to decrease of medium acidic properties. The viscosity of the medium effects on the 1-3 fluorescence in a lesser degree. Compared to 1 and 2, the 3 is the most sensitive towards viscosity both in low-viscosity homologous alcohols and in high-viscosity ethanol-glycerol mixtures. In this regard, the sensitivity of fluorescence of CH(MeOPh)-bis(BODIPY) (compound 3) to the viscosity was studied in binary mixtures of polar DMF and low-polarity toluene with castor and vaseline oils, as well as to the macroviscosity of the solvate environment in mixtures of toluene with polystyrene. Prospects of the practical application of CH(R)-bis(BODIPY)s are proposed for the analysis of polarity, proton-donor properties and viscosity of the medium.

Porous nickel and cobalt hexanuclear ring-like clusters built from two different kind of calixarene ligands – new molecular traps for small volatile molecules

The formation and structural analysis of porous hexanuclear ring-like cluster complexes built from two different kind of calixarene ligands is presented, together with their stability and vapor solvent sorption properties.

Impact of flexible succinate connectors on the formation of tetrasulfonylcalix[4]arene based nano-sized polynuclear cages: structural diversity and induced chirality study

The formation of three types of supramolecular coordination cages is described. Tetrasulfonylcalixarene, combined with metallic salts (Ni, Co and Zn) and the flexible succinate ligand, led to cages. H bonded induced chirality was observed for both isomorphous cages.

Rational Design 2-Hydroxypropylphosphonium Salts as Cancer Cell Mitochondria-Targeted Vectors: Synthesis, Structure, and Biological Properties

It has been shown for a wide range of epoxy compounds that their interaction with triphenylphosphonium triflate occurs with a high chemoselectivity and leads to the formation of (2-hydroxypropyl)triphenylphosphonium triflates 3 substituted in the 3-position with an alkoxy, alkylcarboxyl group, or halogen, which were isolated in a high yield. Using the methodology for the disclosure of epichlorohydrin with alcohols in the presence of boron trifluoride etherate, followed by the substitution of iodine for chlorine and treatment with triphenylphosphine, 2-hydroxypropyltriphenylphosphonium iodides 4 were also obtained. The molecular and supramolecular structure of the obtained phosphonium salts was established, and their high antitumor activity was revealed in relation to duodenal adenocarcinoma. The formation of liposomal systems based on phosphonium salt 3 and L-α-phosphatidylcholine (PC) was employed for improving the bioavailability and reducing the toxicity. They were produced by the thin film rehydration method and exhibited cytotoxic properties. This rational design of phosphonium salts 3 and 4 has promising potential of new vectors for targeted delivery into mitochondria of tumor cells.

Composing NLO Chromophore as a Puzzle: Electrochemistry-based Approach to Design and Effectiveness

A series of D-π-A, D-π-D'-π-A, D-π-A'-π-A nonlinear optical chromophores with vinylene π-electron bridges or bridges with π-deficient/π-excessive heterocyclic moieties along with the corresponding precursors D-vinylene, D-π-D', D'-π-A, D-π-A' and A'-π-A are synthesized and studied both experimentally and computationally. The effect of the heterocycle in the π-electron bridge on the oxidation/reduction potentials and the energy gap (ΔE^el ) is investigated in detail. The properties of the D-π-A'(D')-π-A chromophores are shown to correlate with those of building blocks: the oxidation potential is determined by the D-vinylene, and the reduction potential is determined by A'(D')-π-A truncated compounds. The contribution of the acceptor to the oxidation potential of chromophores in comparison with those of the precursors was estimated and analyzed in terms of electronic communication between the end groups. A good correlation between the ΔE^el and the chromophores' first hyperpolarizability is revealed.

Design, Spectral Characteristics, and Possibilities for Practical Application of BODIPY FL-Labeled Monoterpenoid

This article describes the design and biological properties of a BODIPY FL-labeled monoterpenoid BF₂-meso-(4-((1″R)-6″,6″-dimethylbicyclo[3.1.1]hept-2″-ene-2″)yl-methoxycarbonylpropyl)-3,3',5,5'-tetramethyl-2,2'-dipyrromethene conjugate (BODIPYmyrt). The fluorophore was characterized using X-ray, NMR, MS, and UV/vis spectroscopy. The conjugate exhibits a high quantum yield (to ∼100%) in the region 515-518 nm. BODIPYmyrt effectively penetrates the membranes of the bacterial and fungal cells and therefore can be used to examine the features of a broad spectrum of Gram-positive and Gram-negative bacteria and pathogenic fungi as well. Moreover, BODIPYmyrt exhibits a moderate tropism to the subcellular structures in mammalian cells (e.g., mitochondria), thereby providing an attractive scaffold for fluorophores to examine these particular organelles.

Trialkyl(vinyl)phosphonium Chlorophenol Derivatives as Potent Mitochondrial Uncouplers and Antibacterial Agents

Trialkyl phosphonium derivatives of vinyl-substituted p-chlorophenol were synthesized here by a recently developed method of preparing quaternary phosphonium salts from phosphine oxides using Grignard reagents. All the derivatives with a number (n) of carbon atoms in phosphonium alkyl substituents varying from 4 to 7 showed pronounced uncoupling activity in isolated rat liver mitochondria at micromolar concentrations, with a tripentyl derivative being the most effective both in accelerating respiration and causing membrane potential collapse, as well as in provoking mitochondrial swelling in a potassium-acetate medium. Remarkably, the trialkyl phosphonium derivatives with n from 4 to 7 also proved to be rather potent antibacterial agents. Methylation of the chlorophenol hydroxyl group suppressed the effects of P₅₅₅ and P₄₄₄ on the respiration and membrane potential of mitochondria but not those of P₆₆₆, thereby suggesting a mechanistic difference in the mitochondrial uncoupling by these derivatives, which was predominantly protonophoric (carrier-like) in the case of P₅₅₅ and P₄₄₄ but detergent-like with P₆₆₆. The latter was confirmed by the carboxyfluorescein leakage assay on model liposomal membranes.

The formation of cage phosphoranes and their rearrangements in the reactions of substituted 2-(3-oxo-3-phenyl)ethoxybenzo[d]-1,3,2-dioxaphospholes with perfluorodiacetyl

The Kukhtin-Ramirez reaction of 2-(3-oxo-3-phenyl)ethoxy-benzo[d]-1,3,2-dioxaphospholes with perfluorodiacetyl was monitored by NMR methods. To our surprise the initial stage involved a kinetically controlled [4+4]-cycloaddition with the formation of a cage phosphorane containing a 2',5',8',9'-tetraoxa-2λ⁵-phosphaspiro[benzo[d][1,3,2]dioxaphosphole-2,1'-bicyclo[4.2.1]nonan]-3'-ene (compound 5) scaffold. Intermediate 5 then converts to spirophosphorane-4',5'-bis(trifluoromethyl)-2λ⁵-spiro[benzo[d] [1,3,2]dioxaphosphole-2-yl-2,2'-[1,3,2] dioxaphosphole (compound 4). Compound 4 further rearranges into a cage phosphorane derivative containing a [2,5]epoxybenzo[d][1,3,6,2]trioxaphosphocine] (compound 3) backbone.

Towards Universal Stimuli-Responsive Drug Delivery Systems: Pillar[5]arenes Synthesis and Self-Assembly into Nanocontainers with Tetrazole Polymers

In this work, we have proposed a novel universal stimulus-sensitive nanosized polymer system based on decasubstituted macrocyclic structures-pillar[5]arenes and tetrazole-containing polymers. Decasubstituted pillar[5]arenes containing a large, good leaving tosylate, and phthalimide groups were first synthesized and characterized. Pillar[5]arenes containing primary and tertiary amino groups, capable of interacting with tetrazole-containing polymers, were obtained with high yield by removing the tosylate and phthalimide protection. According to the fluorescence spectroscopy data, a dramatic fluorescence enhancement in the pillar[5]arene/fluorescein/polymer system was observed with decreasing pH from neutral (pH = 7) to acidic (pH = 5). This indicates the destruction of associates and the release of the dye at a pH close to 5. The presented results open a broad range of opportunities for the development of new universal stimulus-sensitive drug delivery systems containing macrocycles and nontoxic tetrazole-based polymers.

Assembly of Heterometallic AuICu2I2 Cores on the Scaffold of NPPN-Bridging Cyclic Bisphosphine

The row of metallocyclic dinuclear gold(I) complexes with cyclic diphosphines, namely, P-pyridylethyl-substituted 1,5-diaza-3,7-diphosphacyclooctanes, has been obtained. Further interaction of the dinuclear gold(I) complexes with copper(I) iodide gave the first examples of hexanuclear Au^I/Cu^I complexes containing two unusual trinuclear AuICu₂I₂ fragments. The structures of di- and hexanuclear complexes were confirmed by NMR spectroscopy, ESI mass spectrometry, elemental analysis, and single-crystal X-ray diffraction. All of the obtained complexes are moderate emitters in the solid state. Dinuclear gold(I) complexes displayed a greenish emission with the maxima in the emission spectra at ca. 550 nm. The obtained hexanuclear heterobimetallic Au^I/Cu^I complexes are triplet solid-state blue emitters with the maximum in the emission spectra at 463 and 484 nm. According to the TD-DFT calculations, the observed emission of all studied complexes had a triplet origin and was caused by the ³CC or ³(MLCT) T₁ → S₀ transitions for dinuclear and hexanuclear complexes, respectively.

Influence of the active TaN/ZrO x /Ni memristor layer oxygen content on forming and resistive switching behavior

The influence of oxygen content in active zirconium oxide layers on the electrophysical properties of TaN/ZrO x /Ni memristors is investigated. The [O]/[Zr] atomic ratio (x) in the oxide layers was varied in the range from 1.56 to 2.0 by changing the partial oxygen pressure during their deposition by ion-beam sputtering deposition. The ZrO x film compositions were analyzed using x-ray photoelectron spectroscopy and density functional theory simulations. The multiple resistive switching phenomenon in TaN/ZrO x /Ni memristors was found to occur in a certain range of x ≥ 1.78. With the x value decreasing in the oxide layers, the forming voltage of memristors decreased. Furthermore, at the lower edge of x values the switchable range, they no longer required forming. At the same time, as the x value decreased, the memory window (I ON/I OFF ratio) also decreased from 5 to 1 order of magnitude due to an increase in the memristor conductivity in the high resistance state. In order to identify the underlying conduction mechanism of TaN/ZrO x /Ni memristors, their current-voltage curves in low and high resistance states were analyzed in the temperature range from 250 to 400 K for the samples with x = 1.78 (forming-free) and 1.97 (which required forming). It was found that, for both samples, the conductivity in the low-resistance state is characterized by the trap-free space-charge-limited current (SCLC) model, whereas the conductivity in the high-resistance state is characterized by the trap-mediated SCLC model. The possible origins of structural defects involved in the memristor conductivity and resistive switching are discussed based on the obtained results.

Sterically Hindered Phosphonium Salts: Structure, Properties and Palladium Nanoparticle Stabilization

A new family of sterically hindered alkyl(tri-tert-butyl) phosphonium salts (n-CnH2n+1 with n = 2, 4, 6, 8, 10, 12, 14, 16, 18, 20) was synthesized and evaluated as stabilizers for the formation of palladium nanoparticles (PdNPs), and the prepared PdNPs, stabilized by a series of phosphonium salts, were applied as catalysts of the Suzuki cross-coupling reaction. All investigated phosphonium salts were found to be excellent stabilizers of metal nanoparticles of small catalytically active size with a narrow size distribution. In addition, palladium nanoparticles exhibited exceptional stability: the presence of phosphonium salts prevented agglomeration and precipitation during the catalytic reaction.

Triple-bridged helical binuclear copper(i) complexes: Head-to-head and head-to-tail isomerism and the solid-state luminescence

A family of helical dinuclear copper(i) pyridylphospholane complexes [Cu₂L₃X]X (X = BF₄^-, Cl^- and Br^-) was prepared. The family includes the first examples of this type of complex based on copper(i) chloride and copper(i) bromide. The two isomers typical of this class of compounds, namely head-to-head and head-to-tail complexes, were studied in solution by spectroscopic and optical methods, and in the solid state by X-ray diffraction. Furthermore, the solid-state luminescence of the complexes at different temperatures was studied, and the results were interpreted using quantum-chemical calculations. It was shown that the luminescence of the complexes is attributed to the ³(M + X)LCT transitions.

Synthesis of the first chiral polynuclear copper(i) complex based on (R)-1-(1-phenyl)ethyl-3-(O,O-diethylthiophosphoryl)thiourea and its characterization in the solid state and solution

The reaction of chiral N-thiophosphorylated thiourea with Cu(ii) acetate is accompanied by copper reduction and leads to the formation of a polynuclear complex with the core composed of six Cu(i) ions alternating with sulfur atoms.

Nuclearity control in calix[4]arene-based zinc(ii) coordination complexes

Three zinc-based coordination complexes were selectively generated in the crystalline phase using a new flexible molecular “tweezers” calix[4]arene derivative ligand decorated with two appended carboxylic moieties and benzyl spacers ((3-4H)).

Phosphine-catalyzed Michael additions to α-methylene-γ-butyrolactones

The highly efficient addition of phosphorus and carbon pronucleophiles to α-methylene-γ-butyrolactones (tulipalin A and arglabin) under n-Bu3P catalysis is reported. Kinetic experiments indicate that the unprecedentedly high reactivity of α-methylene-γ-butyrolactones results from the rigid s-cis geometry of the 1-oxa-1,3-butadiene moiety that favors generation of zwitterionic intermediate stabilized by interaction between the phosphonium center and adjacent carbonyl oxygen. The presented strategy offers an economical and practical method for functionalization of natural biologically active α-methylene-γ-butyrolactones with high levels of chemo- and stereoselectivity.

Structure of copper(II) complexes grown from ionic liquids - 1-ethyl-3-methyl-imidazolium acetate or chloride

Crystals of four new copper(II) complexes have been grown from copper(II) acetate/chloride-1-ethyl-3-methyl-imidazolium acetate/chloride-water systems and characterized by X-ray analysis. The first complex, bis-(1-ethyl-3-methyl-imidazolium) tetra-μ-acetato-bis[chloridocuprate(II)], [Emim]2[Cu2(C2H3O2)4Cl2] (1) (Emim is 1-ethyl-3-methyl-imidazolium, C6H11N2), contains [Cu2(C2H3O2)4Cl2]2- coordination anions with a paddle-wheel structure and ionic liquid cations. Two of the synthesized complexes are one-dimensional polymers, namely catena-poly[1-ethyl-3-methyl-imidazolium [[tetra-μ-acetato-dicuprate(II)]-μ-chlorido] monohydrate], {[Emim][Cu2(C2H3O2)4Cl]·H2O} n (2), and catena-poly[1-ethyl-3-methyl-imidazolium [[tetra-μ-acetato-dicuprate(II)]-μ-acetato]], {[Emim][Cu2(C2H3O2)5]} n (3). In these compounds, the Cu2(C2H3O2)4 units with a paddle-wheel structure are connected to each other through chloride (in 2) or acetate (in 3) anions to form parallel chains, between which cations of ionic liquid are situated. The last compound, bis-(1-ethyl-3-methyl-imidazolium) tetra-μ-acetato-bis[aquacopper(II)] tetra-μ-acetato-bis[acetatocuprate(II)] dihydrate, [Emim]2[Cu2(C2H3O2)4(H2O)2][Cu2(C2H3O2)6]·2H2O (4), contains two different binuclear coordination units (neutral and anionic), connected through hydrogen bonds between water mol-ecules and acetate ions.

Electronic structure of stoichiometric and oxygen-deficient ferroelectric Hf0.5Zr0.5O2

The electronic structure of oxygen-deficient Hf_0.5Zr_0.5O₂ in the non-centrosymmetric orthorhombic (ferroelectric) phase was investigated by means of x-ray photoelectron spectroscopy and first-principle density functional theory calculations. It was established that a peak in the photoelectron spectra observed at an energy above the valence band top of ferroelectric Hf_0.5Zr_0.5O₂ in ion-etched samples was due to oxygen vacancies. A method for evaluating the oxygen vacancies concentration in the material from the comparison of experimental and theoretical photoelectron spectra of the valence band is proposed. It is found that oxygen polyvacancies are not formed in ferroelectric Hf_0.5Zr_0.5O₂: an energy-favorable spatial arrangement of several oxygen vacancies in the crystal corresponds to the configuration formed by noninteracting vacancies distant from each other. The oxygen vacancies in five charged states were simulated. The electron levels in the bandgap caused by charged oxygen vacancies indicate that any type of oxygen vacancies in ferroelectric Hf_0.5Zr_0.5O₂ can capture both electrons and holes, i.e. can act as an amphoteric localization center for charge carriers.

A new surfactant–copper(ii) complex based on 1,4-diazabicyclo[2.2.2]octane amphiphile. Crystal structure determination, self-assembly and functional activity

A new complex [Cu(L)Br₃] (where LBr is 1-cetyl-4-aza-1-azoniabicyclo[2.2.2]octane bromide) has been synthesized and characterized.