- Thermally controlled wettability of a nanoporous membrane grafted with catechol-tethered poly(N-isopropylacrylamide)
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A nanoporous membrane is coated with catechol-tethered poly(N- isopropylacrylamide). The thermosensitive variation of surface wettability determines the hindered diffusivity of dextran (40 kDa) through the nanopores.
- Kim, Jee Seon,Kim, Taek Gyung,Kong, Won Ho,Park, Tae Gwan,Nam, Yoon Sung
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- RAFT of sulfobetaine for modifying poly(glycidyl methacrylate) microspheres to reduce nonspecific protein adsorption
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The minimization of nonspecific protein adsorption is a crucial step in the development of bioseparation processes, immunoassays, and affinity diagnostics. Among the numerous biomaterials, polyzwitterions are known to effectively suppress protein and cell adhesion. This article describes the formation of monodisperse polymer microspheres coated with polysulfobetaine with the aim to limit nonspecific adsorption of bovine serum albumin (BSA) as a model protein. In this process, 2-μm poly(glycidyl methacrylate) (PGMA) microspheres were prepared by dispersion polymerization. To render the microspheres hydrophilic and biocompatible, [3-(methacryloylamino)propyl]dimethyl(3-sulfopropyl)ammonium hydroxide (MPDSAH) was grafted from the surface by reversible addition-fragmentation chain transfer (RAFT) polymerization. Elemental analysis of the modified microspheres revealed up to 20 wt % of poly{[3-(methacryloylamino)propyl]dimethyl(3-sulfopropyl)ammonimum hydroxide} (PMPDSAH). The microspheres were characterized in terms of particle size, morphology, and zeta potential. The amount of BSA nonspecifically adsorbed on the PMPDSAH-modified microspheres decreased to half of that captured on the unmodified PGMA microspheres.
- Koubková, Jana,MacKová, Hana,Proks, Vladimír,Trchová, Miroslava,Brus, Ji?í,Horák, Daniel
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- Synthesis and characterization of well-defined optically active methacrylic diblock copolymers
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A new, simple, and cost-effective approach toward the development of well-defined optically active diblock copolymers based on methacrylate monomers is described for the first time. Starting from the low-cost optically active (S)-(-)-2-methyl-1-butanol, a new optically active methacrylic monomer, namely, (S)-(+)-2-methyl-1-butyl methacrylate [(S)-(+)-MBuMA], was synthesized. Reversible addition fragmentation chain transfer polymerization was then used for preparing well-defined poly[(S)-(+)-MBuMA] homopolymers and water-soluble diblock copolymers based on [(S)-(+)-MBuMA] and the hydrophilic and ionizable monomer 2-(dimethyl amino)ethyl methacrylate (DMAEMA). The respective homopolymers and diblock copolymers were characterized in terms of their molecular weights, polydispersity indices, and compositions by size exclusion chromatography and 1H NMR spectroscopy. Polarimetry measurements were used to determine the specific optical rotations of these systems. The structural and compositional characteristics of micellar nanostructures possessing an optically active core generated by p((S)-(+)-MBuMA)-b-p(DMAEMA) chains characterized by predetermined molecular characteristics may be easily tuned to match biological constructs. Consequently, the aggregation behavior of the p[(S)-(+)-MBuMA]-b-p[DMAEMA] diblock copolymers was investigated in aqueous media by means of dynamic light scattering and atomic force microscopy, which revealed the formation of micelles in neutral and acidified aqueous solutions.
- Achilleos, Mariliz,Kafouris, Demetris,Holder, Simon J.,Krasia-Christoforou, Theodora
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- End-linked poly[2-(dimethylamino)ethyl methacrylate]-poly(methacrylic acid) polyampholyte conetworks: Synthesis by sequential RAFT polymerization and swelling and SANS characterization
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Four well-defined end-linked triblock polyampholyte conetworks composed of positively ionizable 2-(dimethylamino)ethyl methacrylate (DMAEMA) repeating units and negatively ionizable methacrylic acid (MAA) repeating units were synthesized using one-pot, sequential reversible addition-fragmentation chain transfer (RAFT) polymerization, by employing 1,4-bis[2-(thiobenzoylthio)prop-2- yl]benzene (1,4-BTBTPB) as the chain transfer agent, and ethylene glycol dimethacrylate (EGDMA) as the cross-linker. From the four end-linked conetworks, three were based on ABA triblock polyampholytes with polyDMAEMA midblocks with a constant degree of polymerization (DP) and polyMAA end-blocks of different DPs. The fourth end-linked polyampholytic conetwork was based on an equimolar BAB triblock polyampholyte with a polyMAA midblock. Furthermore, two polyampholyte networks were also prepared: one based on an end-linked equimolar statistical polyampholyte, and one with a randomly cross-linked, rather than an end-linked, architecture. Finally, the two homopolymer networks based on the DMAEMA and the MAA monomers were also synthesized. The MAA units were introduced in the (co)networks via the polymerization of 2-tetrahydropyranyl methacrylate (THPMA) followed by its acid hydrolysis after (co)network formation. The linear precursors to the (co)networks were found to have molecular weights and compositions close to the expected values, whereas the extractables from the (co)networks were determined to be lower than 30%. In water, the degrees of swelling (DS) of all the polyampholyte (co)networks presented a characteristic minimum at intermediate pH values, around the (co)network isoelectric point (pI), while they increased at acidic and basic pHs. The pI values of the ampholytic (co)networks were estimated as the midpoints of the regions of reduced swelling and ranged between 5.3 and 6.8, decreasing with the increase of the MAA content in the (co)networks. Finally, small-angle neutron scattering (SANS) studies of the polyampholyte (co)networks swollen in D2O provided SANS profiles without any peaks but broad shoulders whose location was consistent with the spacing of the cross-linking cores.
- Pafiti, Kyriaki S.,Philippou, Zelina,Loizou, Elena,Porcar, Lionel,Patrickios, Costas S.
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- Thermal decomposition of cumyl dithiobenzoate
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Thermal decomposition of cumyl dithiobenzoate (CDB), a reagent widely used in controlled polymerization of various monomers, was investigated. CDB was synthesized by flash chromatography followed by recrystallization and obtained as large purple crystals. A close analysis of the MS spectra revealed the presence of isopropylbenzene and cumyl thiobenzoate. Results show that the polymeric dithioesters, which are more stable than CDB, are formed after the initiation period, accounting for the fact that CDB-mediated RAFT polymerization of styrene works well at high temperature.
- Liu, Yang,He, Junpo,Xu, Jiangtao,Fan, Deqin,Tang, Wei,Yang, Yuliang
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- Synthesis and characterization of a naphthalimide-dye end-labeled copolymer by reversible addition-fragmentation chain transfer (RAFT) polymerization
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We describe the synthesis of an end-functionalized copolymer of N-(2-hydroxypropyl)methacrylamide (HPMA) and N-hydroxysuccinimide methacrylate (NMS) by reversible addition-fragmentation chain transfer (RAFT) polymerization. To control the polymer composition, the faster reacting monomer (NMS) was added slowly to the reaction mixture beginning 30 min after initating the polymerization (ca. 16% HPMA conversion). One RAFT agent, based on azocyanopentanoic acid, introduced a-COOH group to the chain at one end. Use of a different RAFT agent containing a 4-amino-1,8-naphthalimide dye introduced a UV-vis absorbing and fluorescent group at this chain end. The polymers obtained had molecular weights of 30000 and 20000, respectively, and contained about 30 mol% NMS active ester groups.
- Li, Binxin,Majonis, Daniel,Liu, Peng,Winnik, Mitchell A.
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- Intracellular nitric oxide delivery from stable NO-polymeric nanoparticle carriers
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The encapsulation of S-nitrosoglutathione into polymeric nanoparticles substantially improves NO stability in aqueous media without affecting the efficacy of intracellular delivery. The combination of nano-NO delivery and chemotherapy has been found to enhance antitumour activity of chemotherapeutics, as demonstrated using preliminary in vitro experiments with neuroblastoma cells.
- Duong, Hien T. T.,Kamarudin, Zulkamal M.,Erlich, Rafael B.,Li, Yang,Jones, Mathew W.,Kavallaris, Maria,Boyer, Cyrille,Davis, Thomas P.
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- Defect-free nanoporous thin films from ABC triblock copolymers
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The self-assembly of triblock copolymers of poly(ethylene oxide-b-methyl methacrylate-b-styrene) (PEO-b-PMMA-b-PS), where PS is the major component and PMMA and PEO are minor components, provides a robust route to highly ordered, nanoporous arrays with cylindrical pores of 10-15 nm that show promise in block copolymer lithography. These ABC triblock copolymers were synthesized by controlled living radical polymerization, and after solvent annealing, thin films showing defect-free cylindrical microdomains were obtained. The key to the successful generation of highly regular, porous thin films is the use of PMMA as a photodegradable mid-block which leads to nanoporous structures with an unprecedented degree of lateral order. The power of using a triblock copolymer when compared to a traditional diblock copolymer is evidenced by the ability to exploit and combine the advantages of two separate diblock copolymer systems, the high degree of lateral ordering inherent in PS-b-PEO diblocks plus the facile degradability of PS-b-PMMA diblock copolymer systems, while negating the corresponding disadvantages, poor degradability in PS-b-PEO systems and no long-range order for PS-b-PMMA diblocks.
- Bang, Joona,Kim, Seung Hyun,Drockenmuller, Eric,Misner, Matthew J.,Russell, Thomas P.,Hawker, Craig J.
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- RAFT polymer end-group modification and chain coupling/conjugation Via disulfide bonds
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End-group modification of polymers prepared by reversible additionfragmentation chain transfer (RAFT) polymerization was accomplished by the conversion of trithiocarbonate or dithioester end-groups into a pyridyl disulfide (PDS) functionality. Several different polymers, such as poly(methyl methacrylate), polystyrene, poly(oligoethylene glycol-acrylate), poly(hydroxypropylacrylamide), and poly(N-isopropylacrylamide) were prepared by RAFT polymerization, and subjected to aminolysis in the presence of 2,2′-dithiodipyridine to yield thiol-terminated polymers with yields in the range 6590% dependent on the polymer structure. Furthermore, this PDS end-group was utilized to generate higher-order architectures, such as diblock copolymers with high yields and selectively. In addition, the PDS end-groups were used for the bioconjugation of different biomolecules, such as oligonucleotides, carbohydrates, and peptides. The successful modification of well-defined polymers was confirmed by a combination of UV-vis, NMR spectroscopy, and gel permeation chromatography.
- Boyer, Cyrille,Liu, Jingquan,Bulmus, Volga,Davis, Thomas P.
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- Sequence-defined polypeptide-polymer conjugates utilizing reversible addition fragmentation transfer radical polymerization
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Straightforward solid-phase-supported synthesis routes were presented to obtain novel oligopeptide-based reversible addition fragmentation transfer (RAFT) agents. These approaches include the coupling of a functional RAFT agent to a resin-bound peptide and the functionality switch of an oligopeptide ATRP macroinitiator into an oligopeptide transfer agent. The solid-phase-supported methods allowed easy purification of the transfer agents, making difficult column purification steps unnecessary. Well-defined conjugates comprising sequence-defined peptides and synthetic polymers could be accessed by applying RAFT polymerization techniques in combination with the peptide macrotransfer agents. Polymerization reactions of n-butyl acrylate were performed in solution, yielding peptide-polymer conjugates with controllable molecular weight and low polydispersities of around 1.1. The peptide-polymer conjugates were characterized using 1H NMR spectroscopy and size exclusion chromatography (SEC), while the incorporation of the oligopeptide into the synthetic polymer and the preservation of the chirality were shown by circular dichroism (CD) spectroscopy.
- Ten Cate, Mattijs G.J.,Rettig, Hartmut,Bernhardt, Kaj,Borner, Hans G.
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- First RAFT polymerization of captodative 2-acetamidoacrylic acid (AAA) monomer: An experimental and theoretical study
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A capto-dative monomer, 2-acetamidoacrylic acid (AAA), was homopolymerized through RAFT polymerization method using 2-(2-cyanopropanyl dithiobenzoate) (CPDB) as a chain transfer agent and AIBN free radical initiator in DMF at 70 C. DFT calculations were performed in the selection of the CTA for this unique monomer as well as to elucidate the influence of cd-stabilized growing radical on the kinetic parameters in comparison to methacrylic acid (MAA) and N-(prop-1-en-2-yl)acetamide (NPAA), which represent the captive and dative groups of AAA, respectively. Keq for these three monomers is in the order of AAA β > k-add for NPAA and MAA, for AAA k-add is about four orders of magnitude larger than kβ. This is the major disadvantage in the RAFT process of AAA using CPDB. Yet, poly(AAA) could be achieved with PDI as low as 1.49. Molecular weight of the polymer can be tuned by the monomer/AIBN ratio. First block copolymers of AAA with MAA and MMA using poly(AAA) as a macro-CTA were also synthesized, indicating the presence of active chain ends.
- Dedeo?lu, Burcu,U?ur, Ilke,De?irmenci, Isa,Aviyente, Viktorya,Bar?in, Bilin?,?ayli, G?khan,Acar, Havva Yagci
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- Dithiocarboxylic Acids: An Old Theme Revisited and Augmented by New Preparative, Spectroscopic and Structural Facts
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The unstable dithiocarboxylic acids dithioacetic acid, 2-methyl-dithiopropionic acid, 2,2-dimethyl-dithiopropionic acid and dithiobenzoic acid were synthesized and characterized by NMR spectroscopy and GC/MS. The stable dithiocarboxylic acids 2,4,6-trimethyl benzoic acid, 2,4,6-tri-iso-propylbenzoic acid and 2,6-dimesityl benzoic acid were synthesized, isolated and characterized by spectroscopic methods and in parts by mass spectrometry and X-ray crystallography. The new data were used to re-evaluate literature data on the synthesis, spectroscopy and structural data of dithiocarboxylic acids as a fundamental class of organic compounds in general.
- Grote, Johanna,Friedrich, Felix,Berthold, Katarína,Hericks, Loreen,Neumann, Beate,Stammler, Hans-Georg,Mitzel, Norbert W.
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- Simplification of the synthesis of the reversible addition-fragmentation chain transfer agent 2-(2-cyanopropyl)-dithiobenzoate
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The general literature procedure for the preparation of the reversible addition-fragmentation chain transfer (RAFT) agent 2-(2-cyanopropyl)- dithiobenzoate (CPDB) was modified by omitting the recrystallisation of the intermediate di(thiobenzoyl)disulphide. The yield of the CPDB in the simplified synthesis was increased four times compared to the standard one. The behaviour of the CPDB obtained by the modified procedure and by the standard one in the polymerisation of methyl methacrylate was investigated. The CPDB synthesized by the simplified procedure showed itself to be a good RAFT agent, giving excellent control over the polymerisation of methyl methacrylate and it behaved in the same manner as the CPDB prepared by the literature method. The obtained poly(methyl methacrylate) had a narrow molecular weight distibution (PD = 1.1).
- Milovanovic, Milos B.,Avramovic, Milena,Katsikas, Lynne,Popovic, Ivanka G.
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- EPR measurement of fragmentation kinetics in dithiobenzoate-mediated RAFT polymerization
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The kinetics of reversible addition-fragmentation chain transfer (RAFT) polymerization of butyl acrylate with ethyl S-thiobenzoyl-2-thiopropionate (ETTP) as the RAFT agent has been studied. The concentrations of propagating (P?) and intermediate radicals (INT?) were measured via highly time-resolved EPR spectroscopy after initiation by a laser single pulse. Predici simulation of experimental data results in rate coefficients for -40 °C of kad = (1.4 ± 0.4) × 106 L mol-1 s-1, kβ = (4.7 ± 1.5) s-1, and ktcross = 0.25 × kt, where kt is the rate coefficient for termination of two P? species. Fast fragmentation of the intermediate radical is thus observed at this low temperature. Measuring the ratio of INT ? to P? concentrations during stationary polymerization at -40 and 70 °C yields Keq = k ad/kβ values of (2.3 ± 0.6) × 10 5 and 75 ± 15 L mol-1, respectively, which correspond to an apparent activation energy difference, EA(k ad/kβ), of -49.5 kJ mol-1.
- Meiser, Wibke,Barth, Johannes,Buback, Michael,Kattner, Hendrik,Vana, Philipp
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- Reaction of cyclic tetrathiophosphates with carboxylic acids as a means to generate dithioesters and control radical polymerization by RAFT
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Radical control: Controlled free-radical polymerization of styrene and methyl (meth)acrylate is achieved by using Davy reagents or P4S10 in conjunction with benzoic acid, which leads to in situ formation of dithioesters that act as chain-transfer agents and thus control the reaction. In the case of P4S10/PhCOOH, d[thiobenzoic acid is the key intermediate in this process (see scheme).
- Dureault, Alex,Gnanou, Yves,Taton, Daniel,Destarac, Mathias,Leising, Frederic
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- Well-defined diblock copolymers possessing fluorescent and metal chelating functionalities as novel macromolecular sensors for amines and metal ions
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The amino- and metal-ion sensing capability of a novel type of well-defined block copolymers based on 9-anthrylmethyl methacrylate (AnMMA; hydrophobic, fluorescent) and 2-(acetoacetoxy)ethyl methacrylate (AEMA; hydrophobic, metal chelating) has been investigated in organic media. AEMAx-b-AnMMA y diblock copolymers were prepared for the first time using reversible addition-fragmentation chain transfer (RAFT) polymerization. All polymers were characterized in terms of molecular weights, polydispersity indices and compositions by size exclusion chromatography and 1H NMR spectroscopy, respectively. The glass transition (Tg) temperatures of the AEMAx and AnMMAx homopolymers and the AEMA x-b-AnMMAy diblock copolymers were determined using differential scanning calorimetry. These systems were evaluated toward their ability to act as effective dual chemosensors (i.e., amino- and metal-ion sensors) in an organic solvent (chloroform). More precisely, the fluorescence intensity of both the AnMMAx homopolymers and the AnMMA x-b-AEMAy diblock copolymers in solution exhibited a significant decrease in the presence of triethylamine. Moreover, the presence of iron (III) cations were also found to significantly affect the fluorescence signal of the anthracene moieties when those were combined in a block copolymer structure with the AEMA units, due to complex formation occurring between the β-ketoester groups of the AEMAx segment and the cations.
- Demetriou, Maria,Krasia-Christoforou, Theodora
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- Monodisperse, micron-sized reactive low molar mass polymer microspheres by two-stage living radical dispersion polymerization of styrene
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Living/controlled radical dispersion polymerization of styrene was carried out in ethanol and in ethanol-water mixtures in the presence of perfluorohexyl iodide (C6F13I, 2-5 wt % based on styrene) as a degenerative chain transfer (DCT) agent or 1-cyano-1-methylpropyl dithiobenzoate (CMPDB, 0.5 and 1.0 mol % based on styrene) as a reversible addition-fragmentation chain transfer (RAFT) agent. These reagents disrupt the nucleation stage of particle formation when present at the start of the reaction. If their addition is delayed until the nucleation stage is complete, the reaction acquires the characteristics of a living/controlled radical polymerization: Mn increases linearly with the monomer conversion, and the molar mass distribution is much narrower (minimal Mw/M n: 1.2) than polystyrene prepared without C6F 13I or CMPDB. For reactions in ethanol, at low molar mass, the particles formed have a broad size distribution as a consequence of the solubility of the polymer at the reaction temperature, followed by precipitation upon cooling. When the reactions were run in a more polar medium (95 wt % aqueous ethanol), the polymer molecules precipitated as they were formed and were absorbed by the existing particles in the solution. The particles formed had an average diameter in the range 1-3 μm with a very narrow size distribution (CV 1%). The polymer chains in these particles are reactive and chain-extendible.
- Song, Jing-She,Winnik, Mitchell A.
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- Synthesis of biodegradable hydrogel nanoparticles for bioapplications using inverse miniemulsion RAFT polymerization
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We report the synthesis of biodegradable hydrogel nanoparticles using a RAFT inverse miniemulsion cross-linking polymerization process with 2-(dimethylamino)ethyl methacrylate (DMAEMA) as monomer. The experimental conditions were optimized to yield a colloidally stable miniemulsion polymerization, which required protonation of DMAEMA using aqueous hydrogen chloride to ensure minimal partitioning to the continuous phase (cyclohexane). The nanoparticles were cross-linked using a disulfide cross-linker, thereby enabling subsequent degradation of the polymer network to its constituent primary chains by exposure to a reductive environment. The molecular weight distributions of the constituent primary chains were consistent with satisfactory control/livingness during the polymerization. These biodegradable hydrogel nanoparticles may have potential application as nanocarriers for encapsulation and controlled release of siRNA.
- Oliveira, Marco Antonio M.,Boyer, Cyrille,Nele, Marcio,Pinto, Jose Carlos,Zetterlund, Per B.,Davis, Thomas P.
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- Imparting nanoparticle function with size-controlled amphiphilic polymers
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Herein we report our method of water solubilization and subsequent functionalization of a variety of nanoparticle systems with amphiphilic polymers containing build-in "chemical handles". We have used these polymers, which have narrow polydispersity indices, to impart water solubility and chemical sensitivity toward targeted species (here: pH). These material systems have high chemical conjugation efficiencies in aqueous conditions which may be used to create a variety of chemical and biological multifunctional materials. Copyright
- Chen, Yingchuan,Thakar, Rahul,Snee, Preston T.
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- PH-responsive polymeric carrier encapsulated magnetic nanoparticles for cancer targeted imaging and delivery
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Multifunctional drug delivery systems with favorable compatibility, high selectivity and efficiency are appropriate candidates for future medical applications. For this purpose, a multifunctional nanocomposite that enables selective magnetic resonance imaging and anticancer therapy by encapsulating hydrophobic superparamagnetic nanoparticles and chemotherapeutic agent doxorubicin with a novel biodegradable pH-activated polymeric carrier was synthesized. The as-synthesized amphiphilic polymer has excellent biocompatibility and pH-responsivity. The obtained nanocomposites selectively release the encapsulated drug and magnetic nanoparticles in mildly acidic endosomal/lysosomal compartments due to the degradation of the pH-responsive bonds, resulting in a change of imaging signal and cancer therapy. Furthermore, when compared with the nanocomposites without a targeting moiety, as studied from over-expression of the folic acid receptor tumor cell culturing, the conjugates with folic acid showed a significantly more potent targeting capability.
- Chen, Dongyun,Xia, Xuewei,Gu, Hongwei,Xu, Qingfeng,Ge, Jianfeng,Li, Yonggang,Li, Najun,Lu, Jianmei
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- Carbohydrate-based amphiphilic diblock copolymers with pyridine for the sensitive detection of protein binding
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Glycopolymers are useful macromolecules for presenting carbohydrates in multivalent form. Here, amphiphilic block copolymers consisting of hydrophilic lactose and hydrophobic pyridine were synthesized via reversible addition-fragmentation chain transfer polymerization (RAFT). RAFT polymerization of 2-O-methacryloyloxyethyl-(-D-lactoseheptaacetate) (2-O-MALac) was performed using cumyl dithiobenzoate (CDB) as the chain transfer agent to give well-defined glycopolymers. The livingness of the process was further demonstrated by successfully chain-extending one of obtained glycopolymers with 4-pyridyl methyl methacrylate affording narrow dispersed diblocks. With the obtained block copolymers, a glycosurface was generated on the gold surface of quartz crystal microbalance (QCM) through self-assembled strategy by the use of gold affinitive pyridine functional group. Furthermore, the resulting glycosurface was used to detect the binding of lactose specific lectin, ricinus communis agglutinin (RCA120) without non-specific protein adsorption.
- Otsuka, Hidenori,Hagiwara, Toshiya,Yamamoto, Sayuri
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- Ultra-fast microwave enhanced reversible addition-fragmentation chain transfer (RAFT) polymerization: Monomers to polymers in minutes
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Microwave mediated RAFT polymerization leads to ultra-fast polymerizations, whilst keeping excellent control over molecular weights and molecular weight distributions; this is the first example of such a dramatic effect of microwaves on living radical polymerization kinetics, and it shows the potential for chemists to produce very well controlled polymers in a matter of minutes. The Royal Society of Chemistry.
- Brown, Steven L.,Rayner, Christopher M.,Graham, Susan,Cooper, Andrew,Rannard, Steven,Perrier, Sebastien
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- Strain-Promoted 1,3-Dithiolium-4-olates–Alkyne Cycloaddition
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Reported here is the reactivity of mesoionic 1,3-dithiolium-4-olates towards strained alkynes, leading to thiophene cycloaddition products. In the process, the potential of these dipoles towards orthogonal reaction with azides, allowing efficient double ligation reactions, was discovered. A versatile process to access benzo[c]thiophenes, in an unprecedented divergent fashion, was developed and provides a new entry to unconventional polyaromatic thiophenes.
- Kumar, Ramar Arun,Pattanayak, Manas R.,Yen-Pon, Expédite,Eliyan, Jijy,Porte, Karine,Bernard, Sabrina,Riomet, Margaux,Thuéry, Pierre,Audisio, Davide,Taran, Frédéric
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supporting information
p. 14544 - 14548
(2019/09/17)
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- Formation of Group 11 Bismuth Sulfide Nanoparticles Using Bismuth Dithioates under Mild Conditions
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The formation of mixed-metal sulfides with the general structure AgBiS2 and Cu3BiS2 by a simple two-step process utilizing bismuth dithiocarboxylates as Bi and S precursors is described. A sonochemical reaction of Bi2O3 with six different aryl dithioic acids: dithiobenzoic acid (BDT-H), 4-methoxydithiobenzoic acid (4-MBDT-H), 3-methyldithiobenzoic acid (3-MBDT-H), 2-mesitylenedithioic acid (2-MDT-H), 4-fluorodithiobenzoic acid (4-FBDT-H), and 2-thiophenedithioic acid (2-TDT-H) resulted in the corresponding complexes: [Bi(BDT)3] 1, [Bi(4-MBDT)3] 2, [{Bi(3-MBDT)3}2?C7H8] (32?C7H8), [Bi(2-MDT)3] 4, [Bi(4-FBDT)3] 5 and [Bi(2-TDT)3] 6. Microwave irradiation of these bismuth(III)aryldithioate complexes with AgNO3 or CuCl under mild reaction conditions (140 °C) resulted in the respective mixed-metal sulfides. Attempt to synthesize AuBiS2 using similar reaction protocols were unsuccessful, resulting only in the formation of elemental Au0, S8 and BiOCl.
- Senevirathna, Dimuthu C.,Werrett, Melissa V.,Pai, Narendra,Blair, Victoria L.,Spiccia, Leone,Andrews, Philip C.
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supporting information
p. 8171 - 8175
(2017/06/23)
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- Pt nanoparticles stabilized by thermosensitive polymer as effective and recyclable catalysts for the asymmetric hydrogenation of ethyl pyruvate
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Thermosensitive and thiol-terminated poly(N-isopropylacrylamide)s (PNIPAM-SHs) were synthesized and used to stabilize Pt nanoparticles. After chiral modification with cinchonidine, these nanocatalysts were firstly applied in the asymmetric hydrogenation of ethyl pyruvate. The influences of reaction solvent, chiral modifier concentration, hydrogen pressure, mean molecular weight and amount of polymer on the catalytic performance were investigated. These colloidal Pt catalysts exhibited remarkably high catalytic activity and enantioselectivity. Especially, high turnover frequencies up to 17:820 h-1 were achieved, which is the best result for this reaction with regard to the colloidal Pt catalysts. The high catalytic activity was associated with the high hydrophobicity of isopropyl groups in polymer moieties in the catalyst. Moreover, recycling experiments showed that the thermosensitivity of PNIPAM-SH made these colloidal Pt catalysts easier to recover and reuse. Excellent stability and reusability were presented over these catalysts, and no obvious decrease in catalytic activity and enantioselectivity was observed for eleven runs.
- Yu, Wenjun,Lou, Lan-Lan,Yu, Kai,Li, Shanshan,Shi, Yang,Liu, Shuangxi
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p. 52500 - 52508
(2016/06/13)
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- Mechanisms and rates of proton transfer to coordinated carboxydithioates: Studies on [Ni(S2CR){PhP(CH2CH2PPh2)2}]+ (R = Me, Et, Bun or Ph)
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The complexes [Ni(S2CR)(triphos)]BPh4 (R = Me, Et, Bun or Ph; triphos = PhP{CH2CH2PPh2}2) have been prepared and characterised. X-ray crystallography (for R = Et, Ph, C6H4Me-4, C6H4OMe-4 and C6H4Cl-4) shows that the geometry of the five-coordinate nickel in the cation is best described as distorted trigonal bipyramidal, containing a bidentate carboxydithioate ligand with the two sulfur atoms spanning axial and equatorial sites, the other axial site being occupied by the central phosphorus of triphos. The reactions of [Ni(S2CR)(triphos)]+ with mixtures of HCl and Cl- in MeCN to form equilibrium solutions containing [Ni(SH(S)CR)(triphos)]2+ have been studied using stopped-flow spectrophotometry. The kinetics show that proton transfer is slower than the diffusion-controlled limit and involves at least two coupled equilibria. The first step involves the rapid association between [Ni(S2CR)(triphos)]+ and HCl to form the hydrogen-bonded precursor, {[Ni(S2CR)(triphos)]+...HCl} (KR1) and this is followed by the intramolecular proton transfer (kR2) to produce [Ni(SH(S)CR)(triphos)]2+. In the reaction of [Ni(S2CMe)(triphos)]+ the rate law is consistent with the carboxydithioate ligand undergoing chelate ring-opening after protonation. It seems likely that chelate ring-opening occurs for all [Ni(S2CR)(triphos)]+, but only with [Ni(S2CMe)(triphos)]+ is the protonation step sufficiently fast that chelate ring-opening is rate-limiting. With all other systems, proton transfer is rate-limiting. DFT calculations indicate that protonation can occur at either sulfur atom, but only protonation at the equatorial sulfur results in chelate ring-opening. The ways in which protonation of either sulfur atom complicates the analyses and interpretation of the kinetics are discussed. This journal is
- Alwaaly, Ahmed,Clegg, William,Henderson, Richard A.,Probert, Michael R.,Waddell, Paul G.
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p. 3307 - 3317
(2015/03/05)
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- Synthesis and biological evaluation of 5′-phenyl-3′H-spiro- [indoline-3,2′-[1,3,4]oxadiazol]-2-one analogs
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A series of 5′-phenyl-3′H-spiro[indoline-3,2′-[1,3,4] thiadiazol]-2-one analogs were synthesized and their Bcl-2 protein inhibitory activities were studied. The lead compound was originally identified using a fluorescence polarization-based competitive binding assay. Among the 10 compounds investigated, 1k showed good binding affinities to Bcl-xL and Mcl-1, with inhibition constants of 8.9 μmol/L and 3.4 μmol/L, respectively. While compound 1c achieved tight binding affinities to Bcl-xL (Ki = 0.16 μmol/L), has the potential to be a new lead compound.
- Liu, Hua-Quan,Wang, De-Cai,Wu, Fei,Tang, Wei,Ouyang, Ping-Kai
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p. 929 - 933
(2013/09/24)
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- Hybrid assemblies based on a gadolinium-containing polyoxometalate and a cationic polymer with spermine side chains for enhanced mri contrast agents
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Supramolecular assembly: Spherical and stable hybrid assemblies based on a cationic polymer with spermine side chains and an anionic Gd3+- containing polyoxometalate cluster (GdW) are prepared by electrostatic interaction (see figure). The T1-weighted MRI performance of GdW is enhanced about three times in the assemblies; meanwhile, the assemblies show good biocompatibility, which enables them to be promising candidates for MRI contrast agents. Copyright
- Chai, Wenqiang,Wang, Shan,Zhao, Hang,Liu, Guifeng,Fischer, Karl,Li, Haolong,Wu, Lixin,Schmidt, Manfred
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supporting information
p. 13317 - 13321
(2013/10/08)
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- Dependence of thermal stability on molecular structure of RAFT/MADIX agents: A kinetic and mechanistic study
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The thermal decomposition of different classes of RAFT/MADIX agents, namely dithioesters, trithiocarbonates, xanthates, and dithiocarbamates, were investigated through heating in solution. It was found that the decomposition behavior is complicated interplay of the effects of stabilizing Z-group and leaving R-group. The mechanism of the decomposition is mainly through three pathways, i.e., β-elimination, α-elimination, and homolysis of dithiocarbamate (particularly for universal RAFT agent). The most important pathway is the β-elimination of thiocarbonylthio compounds possessing β-hydrogen, leading to the formation unsaturated species. For the leaving group containing solely α-hydrogen, such as benzyl, α-elimination takes place, resulting in the formation of (E)-stilbene through a carbene intermediate. Homolysis occurs specifically in the case of a universal RAFT agent, in which a thiocarbonyl radical and an alkylthio radical are generated, finally forming thiolactone through a radical process. The stabilities of the RAFT/MADIX agents are investigated by measuring the apparent kinetics and activation energy of the thermal decomposition reactions. Both Z-group and R-group influence the stability of the agents through electronic and steric effects. Lone pair electron donating heteroatoms of Z-group show a remarkable stabilizing effect while electron withdrawing substituents, either in Z- or R-group, tends to destabilize the agent. In addition, bulkier or more β-hydrogens result in faster decomposition rate or lower decomposition temperature. Thus, the stability of the RAFT/MAIDX agents decreases in the order where R is (with identical Z = phenyl) -CH2Ph (5) > -PS (PS-RAFT 15) > -C(Me)HPh (2) > -C(Me)2C(=O)OC2H5 (7) > -C(Me)2Ph(1) > -PMMA (PMMA-RAFT 16) > -C(Me) 2CN (6). For those possessing identical leaving group such as 1-phenylethyl, the stability decreases in the order of O-ethyl (11) > -N(CH2CH3)2 (13) > -SCH(CH3)Ph (8) > -Ph (2) > -CH2Ph (4) > -PhNO2 (3). These results consort with the chain transfer acitivities measured by the CSIRO group and agree well with the ab initio theoretical results by Coote. In addition, the difference between thermal stabilities of the universal RAFT agents at neutral and protonated states has also been demonstrated.
- Zhou, Yanwu,He, Junpo,Li, Changxi,Hong, Linxiang,Yang, Yuliang
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experimental part
p. 8446 - 8457
(2012/03/12)
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- Microwave-induced electrostatic etching: Generation of highly reactive magnesium for application in Grignard reagent formation
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A detailed study regarding the influence of microwave irradiation on the formation of a series of Grignard reagents in terms of rates and selectivities has revealed that these heterogeneous reactions may display a beneficial microwave effect. The interaction between microwaves and magnesium turnings generates violent electrostatic discharges. These discharges on magnesium lead to melting of the magnesium surface, thus generating highly active magnesium particles. As compared to conventional operation the microwave-induced discharges on the magnesium surface lead to considerably shorter initiation times for the insertion of magnesium in selected substrates (i.e. halothiophenes, halopyridines, octyl halides, and halobenzenes). Thermographic imaging and surface characterization by scanning electron microscopy showed that neither selective heating nor a "specific" microwave effect was causing the reduction in initiation times. This novel and straightforward initiation method eliminates the use of toxic and environmentally adverse initiators. Thus, this initiation method limits the formation of by-products. We clearly demonstrated that microwave irradiation enables fast Grignard reagent formation. Therefore, microwave technology is promising for process intensification of Grignard based coupling reactions.
- Van De Kruijs, Bastiaan H. P.,Dressen, Mark H. C. L.,Meuldijk, Jan,Vekemans, Jef A. J. M.,Hulshof, Lumbertus A.
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experimental part
p. 1688 - 1694
(2010/07/04)
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- Process for the preparation of graft copolymers by Reversible Addition Fragmentation Chain Transfer (RAFT) and Ring Opening Polymerisation (ROP)
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A combined RAFT/ROP process for the preparation of a graft co-polymer having a backbone built-up from repeating units derived by polymerization of free-radically polymerizable monomers comprising vinylic monomers, and polyester side chains grafted to said backbone derived by ring-opening polymerisation of cyclic ester compounds; said process comprising reacting a mixture of (a) one or more vinylic monomers, optionally in combination with other monomers susceptible to free-radical polymerization, wherein at least one of said vinylic monomers comprises a (free) hydroxyl group; (b) a thiocarbonylthio compound as chain transfer agent; (c) one or more cyclic esters, which is/are susceptible to a ring-opening polymerization; and (d) a compound effective for initiating the ring-opening polymerization of the one or more cyclic esters; and reacting said mixture in an inert solvent at a temperature of more than 90°C under exclusion of oxygen to form the graft copolymer.
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