Synthesis,characterization and catalytic activity in Suzuki–Miyaura coupling of palladacycle complexes with n‐butyl‐substituted N‐heterocyclic carbene ligands

A series of monomeric palladacycle complexes bearing n‐butyl‐substituted N‐heterocyclic carbenes, namely [Pd(NHC)X(dmba)] (dmba: dimethylbenzylamine and [Pd(NHC)X(ppy)]; NHC: 1‐n‐butyl‐3‐substituted benzylimidazol‐2‐ylidene; ppy: 2‐phenylpyridine), were prepared either by transmetallation from the corresponding silver carbene complexes or by the reaction of the corresponding acetate‐bridged palladacycle dimer with N‐heterocyclic carbene ligands in high yields. The palladium(II) complexes were characterized using elemental analyses, APCI‐MS, ¹H NMR and ¹³C NMR spectroscopies. These complexes are efficient in the Suzuki–Miyaura coupling reaction between phenylboronic acid and aryl bromides.     

Synthesis,characterization and anticancer activity of new palladacycles derived from chiral α‐diimines

Optically pure α‐diimines quantitatively obtained in solvent‐free conditions starting from 2,3‐butanedione and (S)‐(?)‐1‐phenylethylamine and (S)‐(?)‐1‐(4‐methylphenyl)ethylamine, respectively, yielded the new chiral mono‐Pd complexes 2a–b, which have been partly characterized by IR, ¹H‐ and ¹³C‐NMR spectroscopies along with MS‐FAB⁺ spectrometry. The crystal and molecular structure for palladacycle 2a has been fully confirmed by single‐crystal X‐ray studies. Studies in vitro of 2a–b have displayed growth inhibition against different classes of cancer: leukemia (K‐562 CML), colon cancer (HCT‐15), breast cancer (MCF‐7), central nervous system (U‐251 Glio) and prostate cancer (PC‐3) cell lines. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and Characterization of a Novel Thermo‐Sensitive Copolymer of N‐Isopropylacrylamide and Dibenzo‐18‐crown‐6‐diacrylamide

Summary: A series of novel, thermo‐sensitive copolymers with different molar ratios of N‐isopropylacrylamide (NIPAM) and hydrophobic cis‐dibenzo‐18‐crown‐6‐diacrylamide (cis‐DBCAm) were prepared via free‐radical copolymerization. cis‐DBCAm with polymerizable end groups was successfully synthesized by reacting the corresponding amino crown ether with acryloyl chloride. The copolymers were characterized by FT‐IR and elemental analysis, and the thermo‐sensitivities of the copolymers were evaluated by measuring their lower critical solution temperatures (LCSTs) in the absence or presence of various metal ions. The results indicated that incorporation of cis‐DBCAm lowered LCSTs, and that the LCSTs of the copolymers decreased with the increase in cis‐DBCAm content in the copolymers. When the cavities of the crown ether units captured either K⁺ or Cs⁺ ions, the LCST of the respective copolymer–metal ion complex was further decreased, whereas the capture of Na⁺ or Li⁺ ions did not have a significant influence on the LCSTs of the copolymers.

Incorporation of cis‐DBCAm into PNIPAM resulted in a lower LCST. The LCST was decreased more when the cavities of the crown ether units captured K⁺ ions.     

Site‐Selective δ‐C(sp3)−H Alkylation of Amino Acids and Peptides with Maleimides via a Six‐Membered Palladacycle

The site‐selective functionalization of unactivated C(sp³)?H bonds remains one of the greatest challenges in organic synthesis. Herein, we report on the site‐selective δ‐C(sp³)?H alkylation of amino acids and peptides with maleimides via a kinetically less favored six‐membered palladacycle in the presence of more accessible γ‐C(sp³)?H bonds. Experimental studies revealed that C?H bond cleavage occurs reversibly and preferentially at γ‐methyl over δ‐methyl C?H bonds while the subsequent alkylation proceeds exclusively at the six‐membered palladacycle that is generated by δ‐C?H activation. The selectivity can be explained by the Curtin–Hammett principle. The exceptional compatibility of this alkylation with various oligopeptides renders this procedure valuable for late‐stage peptide modifications. Notably, this process is also the first palladium(II)‐catalyzed Michael‐type alkylation reaction that proceeds through C(sp³)?H activation.     

A Novel Water‐Soluble Fluorescence Probe with Wash‐Free Cellular Imaging Capacity Based on AIE Characteristics

A potential real‐time imaging water‐soluble fluorescent polymer ( P3 ) is facilely prepared via one‐pot method. For P3 , tetraphenylethene unit serves as the fluorescent unit, poly(acryloyl ethylene diamine) (a kind of polyelectrolyte) with specific degree of polymerization acts as water‐soluble part. ¹H‐NMR, gel permeation chromatography (GPC), UV‐vis spectroscopy, photoluminescence (PL), and confocal laser scanning microscopy are undertaken to characterize the structure and property of P3 . The results of wash‐free cellular imaging show that the signal‐to‐noise ratio is high as the concentration of P3 is 50 μg mL⁻¹. In addition, the pH‐responsive and Cd²⁺‐responsive are also investigated in this paper. The results coming from pH‐responsive show that P3 solution displays significant fluorescence under near neutral. And the result from the cellular imaging shows that intracellular fluorescence intensity enhances with the augment of concentration of Cd²⁺, which reveals that P3 can give a hint to resolve the dilemma of traditional fluorescent dyes used as living cellular fluorescent probe.

     

Room temperature suzuki cross‐coupling polymerizations of aryl dihalides and aryldiboronic acid/acid esters with t‐Bu3P‐coordinated 2‐phenylaniline‐based palladacycle complex as the precatalyst

Room temperature Suzuki cross‐coupling polymerization of aryl dibromides/diiodides with aryldiboronic acids/acid esters with t‐Bu₃P‐coordinated 2‐phenylaniline‐based palladacycle complex, [2′‐(amino‐kN)[1,1′‐biphenyl]‐2‐yl‐kC]chloro(tri‐t‐butylphosphine)palladium, as a general precatalyst is described. Such room temperature Suzuki cross‐coupling polymerization is achieved by employing six equivalents or more of the base and affords polymers within an hour, with the yields and the molecular weights in general comparable to or higher than reported results that required higher reaction temperature and/or longer polymerization time. Our study provides a general catalyst system for the room temperature Suzuki cross‐coupling polymerization of aryl dibromides/diiodides with aryldiboronic acids/acid esters and paves the road for the investigation of employing other monodentate ligand‐coordinated palladacycle complexes including other electron‐rich monophosphine‐coordinated ones for room temperature cross‐coupling polymerizations. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1606–1611     

Free‐Standing,Single‐Bilayer‐Thick Polymeric Nanosheets via Spatially Confined Polymerization

Polymeric nanosheets organized by molecular building blocks bearing specifically oriented reactive groups provide abundant and versatile strategies for tailoring structure and chemical functionality periodically over extended length scales that complement graphene. Here we report the bulk synthesis of free‐standing polymeric nanosheets via spatially confined polymerization from an elaborate 2D supramolecular system composed of two liquid‐crystalline lamellar bilayer membranes of a self‐assembled nonionic surfactant—dodecylglyceryl itaconate (DGI)—sandwiched by a water layer. By employing a covalent polymerization on the lamellar bilayer membranes, single‐bilayer‐thick (4.2 nm), and large area (greater than 100 μm²) polymeric nanosheets of bilayer membranes are achieved. The polymeric nanosheets could serve as a well‐defined 2D platform for post‐functionalization for producing advanced hybrid materials by introducing the reactions on the hydroxyl groups at the head of DGI on the outer surfaces.

     

Preparation of Well‐Defined Poly[(ethylene oxide)‐block‐(sodium 2‐acrylamido‐2‐methyl‐1‐propane sulfonate)] Diblock Copolymers by Water‐Based Atom Transfer Radical Polymerization

Summary: Well‐defined poly[(ethylene oxide)‐block‐(sodium 2‐acrylamido‐2‐methyl‐1‐propane sulfonate)] diblock copolymers [P(EO_m‐b‐AMPS_n)], have been obtained by water‐based ATRP using α‐methoxy‐ω‐(2‐methylbromoisobutyrate) poly(ethylene oxide)s (MeO‐P[EO]_m‐BrⁱB with m ranging from 12 to 113) and CuBr · 2Bpy (Bpy for 2,2′‐bipyridyl) as macroinitiator and catalytic complex, respectively. Compared to direct polymerization in water, it has been demonstrated that the water/methanol (3:1, v/v) mixture is better suited for predicting the final number‐average molar mass from the initial monomer‐to‐macroinitiator molar ratio and achieving a quite narrow polydispersity, even at high monomer conversion ( ≈ 1.4 at 80% conversion). The effect of temperature, solvent mixture composition and addition of NaCl salt on the polymerization rate and extent of control over the copolymer molecular parameters have been highlighted as well.

     

Paper‐Based Electronic Tongue

We present a low cost paper‐based electronic tongue capable of discriminating forged water samples. System comprises of 4 paper‐based potentiometric sensors (sensitive to Cl^?, Na⁺/K⁺, Ca²⁺/Mg²⁺, ) and a traditional Ag/AgCl reference electrode. Different electrode materials and methods of insulation were tested with best results obtained for pencil graphite and lamination. The presented electronic tongue was able to distinguish tap and lake water from mineral water samples (PCA – Principal Component Analysis and KNN ? K‐nearest neighbour). In total 14 different water samples were used in this study. Sensors presented good signal repeatability, selectivity and reasonable sensitivity.     

Complexation‐Induced Supramolecular Assembly Drives Metal‐Ion Extraction

Combining experiment with theory reveals the role of self‐assembly and complexation in metal‐ion transfer through the water–oil interface. The coordinating metal salt Eu(NO₃)₃ was extracted from water into oil by a lipophilic neutral amphiphile. Molecular dynamics simulations were coupled to experimental spectroscopic and X‐ray scattering techniques to investigate how local coordination interactions between the metal ion and ligands in the organic phase combine with long‐range interactions to produce spontaneous changes in the solvent microstructure. Extraction of the Eu³⁺–3(NO₃^?) ion pairs involves incorporation of the “hard” metal complex into the core of “soft” aggregates. This seeds the formation of reverse micelles that draw the water and “free” amphiphile into nanoscale hydrophilic domains. The reverse micelles interact through attractive van der Waals interactions and coalesce into rod‐shaped polynuclear Eu^III‐containing aggregates with metal centers bridged by nitrate. These preorganized hydrophilic domains, containing high densities of O‐donor ligands and anions, provide improved Eu^III solvation environments that help drive interfacial transfer, as is reflected by the increasing Eu^III partitioning ratios (oil/aqueous) despite the organic phase approaching saturation. For the first time, this multiscale approach links metal‐ion coordination with nanoscale structure to reveal the free‐energy balance that drives the phase transfer of neutral metal salts.     

One‐Pot Glovebox‐Free Synthesis,Characterization, and Self‐Assembly of Novel Amphiphilic Poly(Sarcosine‐b‐Caprolactone) Diblock Copolymers

Novel amphiphilic polypeptoid‐polyester diblock copolymers based on poly(sarcosine) (PSar) and poly(ε‐caprolactone) (PCL) are synthesized by a one‐pot glovebox‐free approach. In this method, sarcosine N‐carboxy anhydride (Sar‐NCA) is firstly polymerized in the presence of benzylamine under N₂ flow, then the resulting poly(sarcosine) is used in situ as the macro­initiator for the ring‐opening polymerization (ROP) of ε‐caprolactone using tin(II) octanoate as a catalyst. The degree of poly­merization of each block is controlled by various feed ratios of monomer/initiator. The diblock copolymers with controlled molecular weight and narrow molecular weight distributions (Đ_M < 1.2) are characterized by ¹H NMR, ¹³C NMR, and size‐exclusion chromatography. The self‐assembly behavior of PSar‐b‐PCL in water is investigated by dynamic light scattering (DLS) and transmission electron microscopy. DLS results reveal that the diblock copolymers associate into nanoparticles with average hydrodynamic diameters (D_H) around 100 nm in water, which may be used as drug delivery carriers.

     

Surfactant‐Free Emulsion‐Based Preparation of Redox‐Responsive Nanogels

A surfactant‐free emulsion‐based approach is developed for preparation of nanogels. A water‐in‐oil emulsion is generated feasibly from a mixture of water and a solution of disulfide‐containing hyperbranched PEGylated poly(amido amine)s, poly(BAC2‐AMPD1)‐PEG, in chloroform. The water droplets in the emulsion are stabilized and filled with poly(BAC2‐AMPD1)‐PEG, and the crosslinked poly(amido amine)s nanogels are formed via the intermolecular disulfide exchange reaction. FITC‐dextran is loaded within the nanogels by dissolving the compound in water before emulsification. Transmission electron microscopy and dynamic light scattering are applied to characterize the emulsion and the nanogels. The effects of the homogenization rate and the ratio of water/polymer are investigated. Redox‐induced degradation and FITC‐dextran release profile of the nanogels are monitored, and the results show efficient loading and redox‐responsive release of FITC‐dextran. This is a promising approach for the preparation of nanogels for drug delivery, especially for neutral charged carbohydrate‐based drugs.

     

Solid‐State Synthesis and Characterization of 2‐Thioxo‐4‐Imidazolidinone Derivatives

A new and efficient two‐step solid‐state synthesis method is described for 2‐thioxo‐4‐imidazolidinone from aryl isothiocyanate and free amino acid. This method requires only simple equipment and is easy to perform. The products reported were characterized on the basis of IR, MS, ¹H NMR, ¹³C NMR and elemental analysis.     

Selective Detection of Ascorbic Acid Using Octacyanomolybdate‐Doped‐Glutaraldehyde‐Cross‐Linked Poly‐L‐Lysine Film Modified Glassy Carbon Electrode

The present work describes oxidation of ascorbic acid (AA) at octacyanomolybdate‐doped‐glutaraldehyde‐cross‐linked poly‐L ‐lysine (PLL‐GA‐Mo(CN) film modified glassy carbon electrode in 0.1 M H₂SO₄. The modified electrode has been successfully prepared by means of electrostatically trapping Mo(CN) mediator in the cationic film of glutaraldehyde‐cross‐linked poly‐L ‐lysine. The dependence of peak current of modified electrode in pure supporting indicates that the charge transfer in the film was a mixed process at low scan rates (5 to 200 mV s^?1), and kinetically restrained at higher scan rates (200 to 1000 mV s^?1). Cyclic voltammetry and rotating disk electrode (RDE) techniques are used to investigate the electrocatalytic oxidation of ascorbic acid and compared with its oxidation at bare and undoped PLL‐GA film coated electrodes. The rate constant of catalytic reaction k obtained from RDE analysis was found to be 9.5×10⁵ cm³ mol^?1 s^?1. The analytical determination of ascorbic acid has been carried out using RDE technique over the physiological interest of ascorbic acid concentrations with a sensitivity of 75 μA mM^?1. Amperometric estimation of AA in stirred solution shows a sensitivity of 15 μA mM^?1 over the linear concentration range between 50 and 1200 μM. Interestingly, PLL‐GA‐Mo(CN) modified electrode facilitated the oxidation of ascorbic acid but not responded to other electroactive biomolecules such as dopamine, uric acid, NADH, glucose. This unique feature of PLL‐GA‐Mo(CN) modified electrode allowed for the development of a highly selective method for the determination of ascorbic acid in the presence of interferents.     

Competitive Molecular‐/Ion‐Recognition Responsive Characteristics of Poly(N‐isopropylacrylamide‐co‐benzo‐12‐crown‐4‐acrylamide) Copolymers with Benzo‐12‐crown‐4 as Both Guest and Host Units

Novel dual molecular‐ and ion‐recognition responsive poly(N‐isopropylacrylamide‐co‐benzo‐12‐crown‐4‐acrylamide) (PNB₁₂C₄) linear copolymers with benzo‐12‐crown‐4 (B12C4) as both guest and host units are prepared. The copolymers exhibit highly selective sensitivities toward γ‐cyclodextrin (γ‐CD) and Na⁺. The presence of γ‐CD induces the lower critical solution temperature (LCST) of PNB₁₂C₄ copolymer to shift to a higher value due to the formation of 1:1 γ‐CD/B12C4 host‐guest inclusion complexes, while Na⁺ causes a negative shift in LCST due to the formation of 2:1 “sandwich” B12C4/Na⁺ host‐guest complexes. Regardless of the complexation order, when γ‐CD and Na⁺ coexist with PNB₁₂C₄, competitive complexation actions of B12C4 as both guest and host units toward γ‐CD and Na⁺ finally form equilibrium 2:2:1 γ‐CD/B12C4/Na⁺ composite complexes, and the final LCST values of PNB₁₂C₄ copolymer reach almost the same level. The results provide valuable guidance for designing and applying PNB₁₂C₄‐based smart materials in various applications.

     

Magnetic Nanoparticle Supported Ionic Liquid Assisted Green Synthesis of Pyrazolopyranopyrimidines and 1,6‐diamino‐2‐oxo‐1,2,3,4‐tetrahydropyridine‐3,5‐ dicarbonitriles

A simple and eco‐friendly green protocol was used for synthesis of pyrazolopyranopyrimidines via four‐component reaction of hydrazine hydrate, ethyl acetoacetate, barbituric acid or dimethyl barbituric acid, and aromatic aldehydes under thermal and solvent‐free conditions in the presence of magnetic nanoparticle supported silica bonded n‐propyl‐4‐aza‐1‐azoniabicyclo[2.2.2]octane chloride (MNPs@DABCO⁺Cl^?) as an efficient, recyclable heterogeneous catalyst. MNPs@DABCO⁺Cl^? also catalyzed the synthesis of 1,6‐diamino‐2‐oxo‐1,2,3,4‐tetrahydropyridine‐3,5‐dicarbonitrile derivatives by four‐component reaction of hydrazine hydrate, malononitrile, ethyl cyanoacetate and ketones under thermal and solvent‐free conditions at 80 °C. These methods are practical and offer many advantages, such as high yields, short reaction times, and simple work‐up.     

Synthesis,Characterization and X‐ray Crystal Structure of a Chromium(III) Complex Obtained from a Proton‐Transfer Compound Containing 1,10‐Phenanthroline‐2,9‐dicarboxylic Acid and 2,6‐Pyridinediamine

The novel 1,10‐phenanthroline‐2,9‐dicarboxylate containing Chromium(III) complex, (pydaH)[Cr(phendc)₂] · 5H₂O, was synthesized using proton‐transfer compound LH₂, (pydaH₂)²⁺(phendc)^2?, (pyda: 2,6‐pyridinediamine; phendcH₂: 1,10‐phenanthroline‐2,9‐dicarboxylic acid) and thoroughly characterized by elemental analysis, IR spectroscopy, X‐ray crystallography and cyclic voltammetry. The complex crystallizes in the monoclinic space group P2₁/n with four formula units in the unit cell. The unit cell dimensions are: a = 13.962(3) Å, b = 14.529(3) Å, c = 16.381(3) Å and β = 106.691(4)°. In this complex, 1,10‐phenanthroline‐2,9‐dicarboxylate acts as a tridentate ligand and the lattice is composed of anionic hexacoordinated complex, [Cr(phendc)₂]^?, 2,6‐pyridiniumdiamine counter ion, (pydaH)⁺, and five lattice water molecules. Crystallographic characterization revealed that the resulting supramolecular structure is strongly stabilized by complicated network of hydrogen bonds between the crystallization water molecules, counter ion and both coordinated and uncoordinated carboxylate groups. There is no relevant π‐π interaction for this anionic complex between pyda or phendc moieties. The electrochemical studies indicated over potential for both the cathodic and anodic peaks of the complex with respect to the free Cr³⁺ ion, as a consequence of the energy requirement for rearrangement of the ligand at electrode surface.     

Uncharged Water‐Soluble Metal‐Bis‐Porphyrins Like Molecular Tweezers for Amino Acids

Some new water‐soluble bis‐porphyrins, constituted of two porphyrin units spaced by means of aliphatic bridges of different lengths, were synthesized and characterized by MALDI‐TOF mass spectrometry, ¹H NMR and UV‐vis spectroscopy. The hydrosolubility of these uncharged compounds was guaranteed from the presence of six long PEG chains bound on the peripheral positions of the two porphyrins. Cobalt and zinc derivatives were also prepared. In the case of Co‐bis‐porphyrin, the appearance of induced circular dichroism (ICD) signals in water solution confirmed the formation of stable complexes with some amino acids, in which the bis‐porphyrin behaves like molecular tweezers.

     

A Deeper Insight into the Postpolymerization Modification of Polypenta Fluorophenyl Methacrylates to Poly(N‐(2‐Hydroxypropyl) Methacrylamide)

This work provides a detailed insight into the synthesis of N‐(2‐hydroxypropyl)methacrylamide (HPMA) polymers employing the activated ester approach. In this approach, polypenta fluorophenyl methacrylate (PFPMA)‐activated ester polymers are synthesized by the reversible addition–fragmentation chain transfer (RAFT) polymerization and transferred into HPMA‐based systems by the use of 2‐hydroxypropylamine. To prove quantitative conversion in the absence of side reactions, special attention is devoted to investigate different reaction conditions by different analytical methods (¹H, ¹⁹F, inverse‐gated ¹³C NMR, and zeta potential measurements). Furthermore the influence of common solvent impurities, such as water, is investigated. Besides differences in polymer tacticity, the poly(N‐(2‐hydroxypropyl) methacrylamide) (PHPMA) synthesized under water‐free conditions display the same properties like the conventional synthesized control‐PHPMA. However, 3% water content in the dimethylsulfoxide are already sufficient to yield PHPMA polymers with a negative zeta potential of –15.8 mV indication the presence of carboxylic groups due to partial hydrolysis of the activated ester.

     

Low‐Temperature Synthesis of Thermoresponsive Diblock Copolymer Nano‐Objects via Aqueous Photoinitiated Polymerization‐Induced Self‐Assembly (Photo‐PISA) using Thermoresponsive Macro‐RAFT Agents

Photoinitiated reversible addition‐fragmentation chain transfer (RAFT) dispersion polymerization of 2‐hydroxypropyl methacrylate is conducted in water at low temperature using thermoresponsive copolymers of 2‐(2‐methoxyethoxy) ethyl methacrylate and oligo(ethylene glycol) methacrylate (M_n = 475 g mol⁻¹) as the macro‐RAFT agent. Kinetic studies confirm that quantitative monomer conversion is achieved within 15 min of visible‐light irradiation (405 nm, 0.5 mW cm⁻²), and good control is maintained during the polymerization. The polymerization can be temporally controlled by a simple “ON/OFF” switch of the light source. Finally, thermoresponsive diblock copolymer nano‐objects with a diverse set of complex morphologies (spheres, worms, and vesicles) are prepared using this particular formulation.