Zinc versus Magnesium: Orthogonal Catalyst Reactivity in Selective Polymerizations of Epoxides, Bio-derived Anhydrides and Carbon Dioxide.
Ontology highlight
ABSTRACT:
SUBMITTER: Saini PK
PROVIDER: S-EPMC5434931 | biostudies-literature |
REPOSITORIES: biostudies-literature
Similar Datasets
Project description:The optimization of an organoaluminum catalytic system for the copolymerization of epoxides and anhydrides is presented. For this purpose, the influence of different variables in the process, such as catalysts, cocatalyst, solvent, or substrates, has been analyzed. Kinetic studies, a proposal for the catalytic mechanism, and full characterization of the copolymers obtained are also discussed. Finally, a new copolymer, poly(limonene succinate), obtained by the optimized catalytic system is reported.
| S-EPMC6643587 | biostudies-literature
Project description:The alternating copolymerization of epoxides with cyclic anhydrides (CAs) is a highly diverse synthetic method for polyesters as the polymers' architectures and properties can be easily controlled depending on the combination of two monomers. Thus, a variety of catalyst designs has been reported to prepare the desired copolymers efficiently. We herein report dinuclear cobalt-salen complexes with a benzene ring as a linker and their activities in copolymerization reactions. The dinuclear cobalt complexes showed a higher catalytic activity for the copolymerization of propylene oxide with phthalic anhydride than the corresponding mononuclear cobalt-salen complex and achieved one of the highest turnover frequencies ever reported. A variety of epoxides and CAs were also found to be copolymerized successfully by the dinuclear cobalt complex with a high catalytic activity.
| S-EPMC6244378 | biostudies-literature
Project description:Polymer chemical recycling to monomers (CRM) could help improve polymer sustainability, but its implementation requires much better understanding of depolymerization catalysis, ensuring high rates and selectivity. Here, a heterodinuclear [Mg(II)Co(II)] catalyst is applied for CRM of aliphatic polycarbonates, including poly(cyclohexene carbonate) (PCHC), to epoxides and carbon dioxide using solid-state conditions, in contrast with many other CRM strategies that rely on high dilution. The depolymerizations are performed in the solid state giving very high activity and selectivity (PCHC, TOF = 25700 h-1, CHO selectivity >99 %, 0.02 mol %, 140 °C). Reactions may also be performed in air without impacting on the rate or selectivity of epoxide formation. The depolymerization can be performed on a 2 g scale to isolate the epoxides in up to 95 % yield with >99 % selectivity. In addition, the catalyst can be re-used four times without compromising its productivity or selectivity.
| S-EPMC9562274 | biostudies-literature
Project description:Two novel polyesterurethane materials, PEU1 and PEU2, were synthesized via nontoxic and isocyanate-free route by simple conversion of two epoxides 1,2-epoxy-3-phenoxy propane (2) and styrene epoxide (3) utilizing CO2. Epoxides 2 and 3 were converted to the respective cyclic carbonates 4 and 5 by a new set of cobalt-based catalyst 1a in the presence of 10 bar of CO2 and 80 °C temperature without using cocatalyst tetrabutylammonium bromide (TBAB). The mechanistic pathway of the catalysis reaction for the cycloaddition of epoxides with CO2 to generate the cyclic carbonates was investigated by several spectroscopic techniques and utilizing analogous zinc-based 1D coordination polymer 1b, which does not act as an efficient catalyst in the absence of TBAB. Cyclic carbonates 4 and 5 were converted to the respective polyesterurethanes PEU1 and PEU2 sequentially by first synthesizing the ring-opened diols 6 and 7 reacting with ethylenediamine and subsequently annealing the respective diols 6 and 7 at 120 °C in the presence of terepthalyl chloride and triethylamine. The polyesterurethanes PEU1 and PEU2 were characterized by multinuclear NMR and FTIR. PEU1 was also characterized by MALDI-TOF mass spectrometry. The thermal studies of PEU1 and PEU2 showed the stability up to 200-270 °C. The number-average and weight-average molecular weights were determined for PEU1 and PEU2 by GPC analysis. The weight-average molecular weight for PEU1 was found to be 5948 with a polydispersity of 1.1, and PEU2 showed the weight-average molecular weight as 4224 with a polydispersity of 1.06.
| S-EPMC6714527 | biostudies-literature
Project description:We report the synthesis of bioinspired liposomal thrombomodulin (TM) conjugates by chemoselective and site-specific liposomal conjugation of recombinant TM at C-terminus. TM is an endothelial cell membrane protein that acts as a major cofactor in the protein C anticoagulant pathway. To closely mimic membrane protein structural features of TM, we proposed membrane-mimetic re-expression of recombinant TM onto liposome. A recombinant TM containing the EGF-like 456 domains and an azidohomoalanine at C-terminus was expressed in E. coli. Conjugation of the recombinant TM onto liposome via Staudinger ligation and copper-free click chemistry were investigated as an optimal platform for exploring membrane protein TM's activity, respectively. The bioinspired liposomal TM conjugates were confirmed with Western blotting and protein C activation activity. The recombinant TM-liposome conjugates showed a 2-fold higher k(cat)/K(m) value for protein C activation than that of the recombinant TM alone, which indicated that the lipid membrane has a beneficiary effect on the recombinant TM's activity. The reported liposomal protein conjugate approach provides a rational design strategy for both studying membrane protein TM's functions and generating a membrane protein TM-based anticoagulant agent.
| S-EPMC3630279 | biostudies-literature
Project description:The preparation of stereochemistry- and sequence-defined polymers, in which different monomer units are arranged in an ordered fashion just like biopolymers, is of great interest and has been a long-standing goal for chemists due to the expectation of unique macroscopic properties. Here, we describe the enantioselective terpolymerization of racemic terminal epoxides, meso-epoxides, and anhydrides mediated by the privileged chiral dinuclear Al(III) catalyst system, to afford optically active polyester terpolymers with either gradient or random distribution as determined by the epoxides employed during their preparation. The enantioselective terpolymerization of racemic tert-butyl glycidyl ether (rac-TBGE) and cyclopentene oxide with phthalic anhydride (PA) or naphthyl anhydride (NA) gives novel gradient polyesters, in which the crystallization behavior varies continuously along the main chain, due to the decrement of one ester component and the increment of the other occurring sequentially from one chain end to the other. In contrast, the enantioselective terpolymerization of rac-TBGE and meso-epoxide (cyclohexene oxide, 3,4-epoxytetrahydrofuran, or 1,4-dihydronaphthalene oxide) with an anhydride (PA or NA) provided chiral statistical terpolyesters with the random distribution of two kinds of ester units, resulting in a material possessing a mixed glass transition temperature. The present study therefore provides a convenient route to chiral polyesters bearing a range of physical and degradability properties.
| S-EPMC7355046 | biostudies-literature
Project description:A β-diiminato-zinc-N(SiMe3)2 complex (1) was synthesised and fully characterised, including an X-ray diffraction study. The activity of catalyst 1 towards the coupling reaction of CO2 and various epoxides, including propylene oxide (PO), cyclohexene oxide (CHO), styrene oxide (SO), limonene oxide (LO), octene oxide (OO) and epichlorohydrin (ECH), was investigated. Terpolymerisation of CO2, PO and LO, as well as CO2, CHO and PO, was successfully realised, resulting in polymers with adjustable glass transition temperatures and transparencies. Reaction conditions such as temperature, pressure and catalyst concentration were varied to find the optimal reaction values, especially regarding LO/CO2. In situ IR experiments hinted that at 60 °C and a critical LO concentration, polymerisation and depolymerisation are in an equilibrium (ceiling effect). Pressurising catalyst 1 with carbon dioxide resulted in a dimeric catalyst (2) with a OSiMe3 group as a new initiator. Homopolymerisation of different epoxides was carried out in order to explain the reactivity concerning copolymerisation reaction of CO2 and epoxides.
| S-EPMC5444112 | biostudies-literature
Project description:Responsive nanogel systems are interesting for the drug delivery of bioactive molecules due to their high stability in aqueous media. The development of nanogels that are able to respond to biochemical cues and compatible with the encapsulation and the release of large and sensitive payloads remains challenging. Here, multistimuli-responsive nanogels were synthesized using a bio-orthogonal and reversible reaction and were designed for the selective release of encapsulated cargos in a spatiotemporally controlled manner. The nanogels were composed of a functionalized polysaccharide cross-linked with pH-responsive hydrazone linkages. The effect of the pH value of the environment on the nanogels was fully reversible, leading to a reversible control of the release of the payloads and a "stop-and-go" release profile. In addition to the pH-sensitive nature of the hydrazone network, the dextran backbone can be degraded through enzymatic cleavage. Furthermore, the cross-linkers were designed to be responsive to oxidoreductive cues. Disulfide groups, responsive to reducing environments, and thioketal groups, responsive to oxidative environments, were integrated into the nanogel network. The release of model payloads was investigated in response to changes in the pH value of the environment or to the presence of reducing or oxidizing agents.
| S-EPMC8278386 | biostudies-literature
Project description:Poly(ester-alt-ethers) can combine beneficial ether linkage flexibility and polarity with ester linkage hydrolysability, furnishing fully degradable polymers. Despite their promising properties, this class of polymers remains underexplored, in part due to difficulties in polymer synthesis. Here, a catalyzed copolymerization using commercially available monomers, butylene oxide (BO)/oxetane (OX), tetrahydrofuran (THF), and phthalic anhydride (PA), accesses a series of well-defined poly(ester-alt-ethers). A Zr(IV) catalyst is reported that yields polymer repeat units comprising a ring-opened PA (A), followed by two ring-opened cyclic ethers (B/C) (-ABB- or -ABC-). It operates with high polymerization control, good rate, and successfully enchains epoxides, oxetane, and/or tetrahydrofurans, providing a straightforward means to moderate the distance between ester linkages. Kinetic analysis of PA/BO copolymerization, with/without THF, reveals an overall second-order rate law: first order in both catalyst and butylene oxide concentrations but zero order in phthalic anhydride and, where it is present, zero order in THF. Poly(ester-alt-ethers) have lower glass-transition temperatures (-16 °C < Tg < 12 °C) than the analogous alternating polyesters, consistent with the greater backbone flexibility. They also show faster ester hydrolysis rates compared with the analogous AB polymers. The Zr(IV) catalyst furnishes poly(ester-alt-ethers) from a range of commercially available epoxides and anhydride; it presents a straightforward method to moderate degradable polymers' properties.
| S-EPMC9084548 | biostudies-literature
Project description:A method was developed for the hydroboration of alkenyl-containing organotrifluoroborates to generate dibora intermediates. The reactivity differences between organotrifluoroborates and trialkylboranes facilitated the cross-coupling of the borane moiety of these intermediates in a highly chemoselective fashion with aryl halides, leaving the trifluoroborate intact for subsequent transformation. A one-pot hydroboration/two-directional cross-coupling sequence was also demonstrated, providing the fully elaborated products in good yields. These conditions were also amenable in the cross-coupling of trialkylboranes to halo-containing organotrifluoroborates. The stability of the trifluoroborate moiety to these conditions allows simple and efficient strategies for complex molecule construction.
| S-EPMC2645949 | biostudies-literature