Asymmetric Kinetic Resolution Polymerization of Racemic Lactide Mediated by Axial-Chiral Thiourea/Phosphazene Binary Organocatalyst.

Asymmetric kinetic resolution polymerization (AKRP) provides an ideal way to obtain highly isotactic polylactide (PLA) with superior thermal-mechanical properties from racemic lactide (rac-LA). However, the development of a new catalytic system with concurrent high activity and selectivity at ambient temperature remains a great callenge. Here, a series of simple and effective binary organocatalytic pairs containing axial-chiral thioureas and commercially available phosphazene bases were designed. These chiral binary organocatalytic pairs allow for both high polymerization activity and moderate enantioselectivity for AKRP of rac-LA at room temperature, yielding semi-crystalline and metal-free stereoblock PLA with a melting temperature as high as 186 °C. The highest kinetic resolution coefficient (krel) of 8.5 at 47 % conversion was obtained, and D-LA was preferentially polymerized via kinetic resolution with a maximum selectivity factor (kD/kL) of 18.1, indicating that an enantiomorphic site control mechanism (ESC) was involved.

Tripeptide linked dispiro cyclotriphosphazene conjugates: Synthesis, molecular docking analysis of compounds binding within cancer cell line receptors and in vitro cytotoxic and genotoxic activities.

The novel dioxybiphenyl bridged-cyclotriphosphazenes (DPP) bearing tripeptide were synthesized and investigated for their molecular docking analysis, visualizing their binding profiles within various cancer cell line receptors and in vitro cytotoxic and genotoxic properties. The dipeptide compound (Tyr-Phe) was treated with various amino acids to obtain the tripeptide compounds (Tyr-Phe-Gly, Tyr-Phe-Ala, Tyr-Phe-Val, Tyr-Phe-Phe, and Tyr-Phe-Leu). These synthesized tripeptides were subsequently treated with DPP to obtain novel phosphazene compounds bearing tripeptide structures. As a result, the synthesis of target molecules with phosphazene compound in the center and biphenyl and tripeptide groups in the side arms was obtained for the first time in this study. Examining the cytotoxic studies in vitro of our newly synthesized compounds demonstrated the anticancer properties against four selected human cancer cell lines, including breast (MCF-7), ovarian (A2780), prostate (PC-3), and colon (Caco-2) cancer cells. The Comet Assay analysis determined that the cell death mechanism of most of the compounds with cytotoxic activity stemmed from the DNA damage mechanism. Among the compounds, the DPP-Tyr-Phe-Phe compound seems to have the best anticancer activity against the subjected cell lines (Except for A2780) with IC50 values equal to 20.18, 72.14, 12.21, and 5.17 µM against breast, ovarian, prostate, and colon cancer cell lines, respectively. For this reason, the molecular docking analysis was conducted for the DTPP compound to visualize its binding geometry and profile within the target enzyme's binding site associated with the specific cancer cell line. The analysis revealed that the DTPP derivative exhibited an optimal binding conformation and characteristics within the target enzyme's binding site, aligning well with the experimental data. Based on the data, these compounds are believed to be strong candidate molecules for both pharmaceutical and clinical applications.

Molecular-Cling-Effect of Fluoroethylene Carbonate Characterized via Ethoxy(pentafluoro)cyclotriphosphazene on SiOx/C Anode Materials - A New Perspective for Formerly Sub-Sufficient SEI Forming Additive Compounds.

Effective electrolyte compositions are of primary importance in raising the performance of lithium-ion batteries (LIBs). Recently, fluorinated cyclic phosphazenes in combination with fluoroethylene carbonate (FEC) have been introduced as promising electrolyte additives, which can decompose to form an effective dense, uniform, and thin protective layer on the surface of electrodes. Although the basic electrochemical aspects of cyclic fluorinated phosphazenes combined with FEC were introduced, it is still unclear how these two compounds interact constructively during operation. This study investigates the complementary effect of FEC and ethoxy(pentafluoro)cyclotriphosphazene (EtPFPN) in aprotic organic electrolyte in LiNi0.5 Co0.2 Mn0.3 O ∥ SiOx /C full cells. The formation mechanism of lithium ethyl methyl carbonate (LEMC)-EtPFPN interphasial intermediate products and the reaction mechanism of lithium alkoxide with EtPFPN are proposed and supported by Density Functional Theory calculations. A novel property of FEC is also discussed here, called molecular-cling-effect (MCE). To the best knowledge, the MCE has not been reported in the literature, although FEC belongs to one of the most investigated electrolyte additives. The beneficial MCE of FEC toward the sub-sufficient solid-electrolyte interphase forming additive compound EtPFPN is investigated via gas chromatography-mass spectrometry, gas chromatography high resolution-accurate mass spectrometry, in situ shell-isolated nanoparticle-enhanced Raman spectroscopy, and scanning electron microscopy.

The first peptide derivatives of dioxybiphenyl-bridged spiro cyclotriphosphazenes: In vitro cytotoxicity activities and DNA damage studies.

In this study, we aimed to synthesize new peptide-substituted cyclotriphosphazenes from a series of tyrosine-based peptides and dioxyphenyl-substituted spirocyclotriphosphazenes, and to evaluate their in vitro cytotoxicity and genotoxicity activities. Genotoxicity studies were conducted to understand whether the cytotoxic compounds cause cell death through DNA damage. The structures of the novel series of phosphazenes were characterized by FT-IR, elemental analysis, MS, 1D (31P, 1H, and 13C-APT NMR), and 2D (HETCOR) NMR spectroscopic techniques. In vitro cytotoxic activities were carried out against human breast (MCF-7), ovarian (A2780), prostate (PC-3), colon (Caco-2) cancer cell lines and human normal epithelial cell line (MCF-10A) at different concentrations by using an MTT assay. The compounds showed considerable reductions in cell viability against all human cancer cell lines. Especially, the compounds exhibited notable effects in A2780 cell lines (p < 0.05). The IC50 values of the compounds in the A2780 cell line were calculated to be 1.914 µM for TG, 20.21 µM for TV, 20.45 µM for TA, 4.643 µM for TP, 5.615 µM for BTG, 1.047 µM for BTV, 27.02 µM for BTA, 0.7734 µM for BTP, 21.5 µM for DTG, 1.65 µM for DTV, 2.89 µM for DTA and 4.599 µM for DTP. DNA damage studies of the compounds were conducted by the comet assay method using tail length, tail density, olive tail moment, head length, and head density parameters, and the results showed that the cell death occurred through DNA damage mechanism. In a nutshell, these compounds show promising cytotoxic effects and can be considered powerful candidate molecules for pharmaceutical applications.

Hexakis-2-(ß-carboxyethenylphenoxy)cyclotriphosphazene: Synthesis, Properties, Modeling Structure.

Condensation of hexakis-2-(formylphenoxy)cyclotriphosphazene with malonic acid yielded hexakis-2-(ß-carboxyethenylphenoxy)cyclotriphosphazene (2-CEPP), whose structure was confirmed by 31P, 1H, 13C NMR spectroscopy and MALDI-TOF mass spectrometry. A quantum-chemical calculation for the 2-CEPP molecule using the ab initio methods in the 6-311G** basis set and the DFT-PBE0/6-311g** method was performed with geometry optimization of all parameters by the standard gradient method. The acid strength of 2-CEPP was theoretically estimated. Using the small-angle X-ray scattering method, it was found that 2-CEPP is an amorphous substance, which, when heated, can transform into a crystalline state. However, when heated at 370 °C, 2-CEPP undergoes decarboxylation and polymerization to form an insoluble heat-resistant product. The occurrence of decarboxylation and polymerization reactions in the formed styrene fragments was confirmed by thermal (differential-scanning calorimetry) and spectral (solid-state 13C NMR spectroscopy) analysis.

A Phosphine-Amine-Linked Covalent Organic Framework with Staggered Stacking Structure for Lithium-Ion Conduction.

In-plane ionic conduction over two-dimensional (2D) materials is desirable for flexible electronics. Exfoliating 2D covalent organic frameworks (COFs) towards a few layers is highly anticipated, whereas most examples remain robust via π-stacking against the interlayered dislocation. Herein, we synthesize a phosphine-amine-linked 2D COF by a nucleophilic substitution reaction of phosphazene with amines. The synthesized COF is crystalline, and stacks in an AB-staggered fashion, wherein the AB dual layers are interlocked by embedding P-Cl bonds from one to another layer, and the non-interlocked layers are readily delaminated. Therefore, in situ post-quaternization over phosphazene can improve the ionization of backbones, accompanied by layered exfoliation. The ultrathin nanosheets can decouple lithium salts for fast solid-state ion transport, achieving a high conductivity and low activation energy. Our findings explore the P-N substitution reaction for COF crystallization and demonstrate that the staggered stacking 2D COFs are readily exfoliated for designing solid electrolytes.

A Facile Immobilization Strategy for Soluble Phosphazene to Actualize Stable and Safe Lithium-Sulfur Batteries.

Lithium-sulfur batteries (LSBs) have attracted extensive attention owing to their high energy density and abundant sulfur resources. However, LSBs are still restricted by the unsatisfactory electrochemical performance resulting from the shuttle effect of lithium polysulfide (LiPSs), and the potential fire hazard caused by inflammable ether electrolytes and polyolefin separators. Herein, a facile immobilization strategy for hexachlorocyclotriphosphazene (HCCP) is creatively applied to address the above issues simultaneously. Insoluble HCCP cross-linked microspheres (H-CMP) are firstly obtained at ambient temperature using tannic acid (TA) as a cross-linking agent and then a multifunctional separator coating is constructed based on H-CMP. The released phosphorus-related radicals from H-CMP in wide temperatures effectively prevent the combustion of electrolytes and separators, and hence improve the fire safety of the Li-S pouch cell. Furthermore, H-CMP availably chemisorbs LiPSs to interdict the shuttle effect, thereby dramatically improving the electrochemical performance of LSBs. The effectiveness of this strategy is also verified in high sulfur loading (6.38 mg cm-2 ), high temperature (50 °C), and Li-S pouch cells. More importantly, H-CMP exhibits sufficient stability for Li metal and suppression of Li dendrites. This facile immobilization strategy for multifunctional phosphazenes provides a competitive option for the large-scale fabrication of high-safety and high-performance LSBs.

Synthesis of 2,2-Disubstituted 2H-Chromenes through Carbon-Carbon Bond Formation Utilizing a [1,2]-Phospha-Brook Rearrangement under Brønsted Base Catalysis.

A new methodology for the synthesis of 2,2-disubstituted 2H-chromenes was developed by utilizing the [1,2]-phospha-Brook rearrangement under Brønsted base catalysis. Phosphazene P2-tBu efficiently catalyzed the addition reaction of 4H-chromen-4-ols containing a diethoxyphosphoryl group with α,ß-unsaturated ketones, which involved the catalytic generation of a carbanion through the [1,2]-phospha-Brook rearrangement and subsequent conjugate addition at the 2-position to afford adducts possessing an alkenylphosphate moiety in a highly diastereoselective manner. Further transformation of the adducts based on a nickel-catalyzed cross-coupling reaction with arylzinc reagents provided densely functionalized 2,2-disubstituted 2H-chromenes.

Block Copolymer Synthesis by a Sequential Addition Strategy from the Organocatalytic Group Transfer Polymerization of Methyl Methacrylate to the Ring-Opening Polymerization of Lactide.

Sequential block copolymerization involving comonomers belonging to different classes, e.g., a vinyl-type monomer and a heterocycle, is a challenging task in macromolecular chemistry, as corresponding propagating species do not interconvert easily from one to the other by crossover reactions. Here, it is first evidenced that 1-methoxy 2-methyl 1-trimethylsilyloxypropene (MTS), i.e., a silyl ketene acetal (SKA)-containing initiator, can be used in presence of the P4 -t-Bu phosphazene organic base to control the ring-opening polymerization (ROP) of racemic lactide (rac-LA). The elementary reaction, which rapidly transforms SKA groups into propagating alkoxides, can be leveraged to directly synthesize well-defined poly(methyl methacrylate)-b-polylactide block copolymers. This is achieved using P4 -t-Bu as the single organic catalyst and MTS as the initiator for the group transfer polymerization of methyl methacrylate, followed by the ROP of rac-LA. Both polymerization methods are implemented under selective and controlled/living conditions at room temperature in THF. This sequential addition strategy further expands the scope of organic catalysis of polymerizations for macromolecular engineering of block copolymers involving propagating species of disparate reactivity.

Phosphorus-Containing Superbases: Recent Progress in the Chemistry of Electron-Abundant Phosphines and Phosphazenes.

The renaissance of Brønsted superbases is primarily based on their pronounced capacity for a large variety of chemical transformations under mild reaction conditions. Four major set screws are available for the selective tuning of the basicity: the nature of the basic center (N, P, …), the degree of electron donation by substituents to the central atom, the possibility of charge delocalization, and the energy gain by hydrogen bonding. Within the past decades, a plethora of neutral electron-rich phosphine and phosphazene bases have appeared in the literature. Their outstanding properties and advantages over inorganic or charged bases have now made them indispensable as auxiliary bases in deprotonation processes. Herein, an update of the chemistry of basic phosphines and phosphazenes is given. In addition, due to widespread interest, their use in catalysis or as ligands in coordination chemistry is highlighted.

Non-Coordinated Phenolate Anions and Their Application in SF6 Activation.

The reaction of the strong monophosphazene base with the weakly acidic phenol leads to the formation of a phenol-phenolate anion with a moderately strong hydrogen bond. Application of the more powerful tetraphosphazene base (Schwesinger base) renders the isolation of the corresponding salt with a free phenolate anion possible. This compound represents the first species featuring the free phenolate anion [H5 C6 -O]- . The deprotonation of phenol derivatives with tetraphosphazene bases represents a great way for the clean preparation of salts featuring free phenolate anions and in addition allows the selective syntheses of hydrogen bonded phenol-phenolate salts. This work presents a phosphazenium phenolate salt with a redox potential of -0.72 V and its capability for the selective activation of the chemically inert greenhouse gas SF6 . The performed two-electron reduction of SF6 leads to phosphazenium pentafluorosulfanide ([SF5 ]- ) and fluoride salts.

The Influence of Weakly Coordinating Cations on the O-H⋠⋠⋠O- Hydrogen Bond of Silanol-Silanolate Anions.

The reaction of a saline phosphazenium hydroxide hydrate with siloxanes led to a novel kind of silanol-silanolate anions. The weakly coordinating behavior of the cation renders the formation of silanol-silanolate hydrogen bonds possible, which otherwise suffer from detrimental silanolate-oxygen cation interactions. We investigated the influence of various weakly coordinating cations on silanol-silanolate motifs, particularly with regard to different cation sizes. While large cations favor the formation of intramolecular hydrogen bonds resulting in cyclic structures, the less bulky tetramethyl ammonium cation encourages the formation of polyanionic silanol-silanolate chains in the solid state.

Stable Singlet Carbenes as Organic Superbases.

A simple experimental procedure for scaling carbene Brønsted basicity is described. The results highlight the strong basicity of pyrazol-4-ylidenes, a type of mesoionic carbene, also named cyclic-bentallenes (CBA). They are more basic (pKaH >42.7 in acetonitrile) than the popular proazaphosphatrane Verkade bases, and even the Schwesinger phosphazene superbase P4 (t Bu). The basicity of these compounds can readily be tuned, and they are accessible in multigram quantities. These results open new avenues for carbon centered superbases.

Synthesis and Reactivity of the First Isolated Hydrogen-Bridged Silanol-Silanolate Anions.

We report on the first examples of isolated silanol-silanolate anions, obtained by utilizing weakly coordinating phosphazenium counterions. The silanolate anions were synthesized from the recently published phosphazenium hydroxide hydrate salt with siloxanes. The silanol-silanolate anions are postulated intermediates in the hydroxide-mediated polymerization of aryl and alkyl siloxanes. The silanolate anions are strong nucleophiles because of the weakly coordinating character of the phosphazenium cation, which is perceptible in their activity in polysiloxane depolymerization.

Development of Chiral Organosuperbase Catalysts Consisting of Two Different Organobase Functionalities.

In the field of chiral Brønsted base catalysis, a new generation of chiral catalysts has been highly anticipated to overcome the intrinsic limitation of pronucleophiles that are applicable to the enantioselective reactions. Herein, we reveal conceptually new chiral Brønsted base catalysts consisting of two different organobase functionalities, one of which functions as an organosuperbase and the other as the substrate recognition site. Their prominent activity, which stems from the distinctive cooperative function by the two organobases in a single catalyst molecule, was demonstrated in the unprecedented enantioselective direct Mannich-type reaction of α-phenylthioacetate as a less acidic pronucleophile. The present achievement would provide a new guiding principle for the design and development of chiral Brønsted base catalysts and significantly broaden the utility of Brønsted base catalysis in asymmetric organic synthesis.

A Green Water-Soluble Cyclophosphazene as a Flame Retardant Finish for Textiles.

Poly- and cyclophosphazenes are excellent flame retardants but currently, are not used as textile finishing agents because water-soluble and permanent washing systems are missing. Here, we demonstrate for the first time, the successful usage of a water-soluble cyclotriphosphazene derivative for textile finishing for cotton, different cotton/polyester, and cotton/polyamide blend fabrics. A durable finish was achieved using a photoinduced grafting reaction. The flame retardant properties of the various fabrics were improved with a higher limiting oxygen index, a reduced heat release rate, and an exhibition of intumescent. Furthermore, the finished textiles passed several standardized flammability tests.

Generation and Applications of the Hydroxide Trihydrate Anion, [OH(OH2 )3 ]- , Stabilized by a Weakly Coordinating Cation.

The reaction of a strongly basic phosphazene (Schwesinger base) with water afforded the corresponding metastable hydroxide trihydrate [OH(OH2 )3 ]- salt. This is the first hydroxide solvate that is not in contact with a cation and furthermore one of rare known water-stabilized hydroxide anions. Thermolysis in vacuum results in the decomposition of the hydroxide salt and quantitative liberation of the free phosphazene base. This approach was used to synthesize the Schwesinger base from its hydrochloride salt after anion exchange in excellent yields of over 97 %. This deprotonation method can also be used for the phosphazene-base-catalyzed preparation of the Ruppert-Prakash reagent Me3 SiCF3 using fluoroform (HCF3 ) as the trifluoromethyl building block and sodium hydroxide as the formal deprotonation agent.

Phosphazene Bases as Organocatalysts for Ring-Opening Polymerization of Cyclic Esters.

Over the past several years, organocatalyzed polymerization reactions have attracted considerable attention, and these efforts have led to major advances. A large number of organic compounds have been proven active for the polymerization of a large variety of monomers. In particular, phosphazene bases (PBs) are a family of extremely strong, non-nucleophilic, and uncharged auxiliary bases, and have shown their remarkable potential as organocatalysts for the ring-opening polymerization (ROP) of cyclic monomers. By deprotonation of weak acids or in combination with lithium cation, PBs significantly enhance the nucleophilicity of the initiator/chain-end, thus allowing fast and usually controlled anionic polymerization. In this feature article, the recent advances in phosphazene-catalyzed ROP of cyclic esters are summarized. This review is divided into three sections, including general features, design and synthesis, and catalytic applications. It aims to provide a critical analysis of PB-mediated ROP systems and a useful guide for the further design of organocatalysts applied to polymer synthesis. An outlook is given at the end.

Construction of Vicinal Quaternary Stereogenic Centers by Enantioselective Direct Mannich-Type Reaction Using a Chiral Bis(guanidino)iminophosphorane Catalyst.

A novel asymmetric direct Mannich-type reaction of α-iminophenylacetate esters with thionolactones, bearing a substituent at the α-position, as a less acidic pronucleophile was developed. Using bis(guanidino)iminophosphorane as the chiral organosuperbase catalyst, the reaction afforded densely functionalized amino-acid derivatives having vicinal quaternary stereogenic centers, one of which is an all-carbon quaternary stereogenic center, in good yield with high diastereo- and enantioselectivities.

Wound Gel with Antimicrobial Effects Based on Polyvinyl Alcohol and Functional Aryloxycyclotriphosphazene.

A silver-containing gel based on polyvinyl alcohol and aryloxycyclotriphosphazene containing ß-carboxyethenylphenoxy and p-formylphenoxy groups has been developed. Phosphazene was synthesized via the Doebner reaction from hexakis[(4-formyl)phenoxy]cyclotriphosphazene and malonic acid and characterized by 1H, 13C, and 31P NMR spectroscopy and MALDI-TOF mass spectrometry. The study of the gel using scanning electron microscopy showed that the gel contains open pores and can absorb wound exudate. The maximum water absorption capacity of the gel was 272%, which was reached after 80 min of testing. The antimicrobial activity of the obtained silver-containing gel was evaluated using the diffusion method. The gel was found to inhibit the growth of the main microorganisms in contact with the skin: the bacteria S. aureus, P. aeruginosa, E. coli, B. subtilis, S. epidermidis, and C. stationis and the fungus C. albicans. The study of the wound-healing effect of the gel in vivo showed a decrease in the wound area of the rabbit hind limb by 91.43% (p < 0.05) on the 10th day of observation and a decrease in the content of C-reactive protein in the rabbit blood serum by 1.3 times (p < 0.05).