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PubMed Journals Articles About "Tailored Silyl Ether Monomers Enable Backbone Degradable Polynorbornene" RSS

00:23 EST 12th December 2019 | BioPortfolio

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Showing "Tailored silyl ether monomers enable backbone degradable polynorbornene" PubMed Articles 1–25 of 3,400+

Controlled Living Cascade Polymerization To Make Fully Degradable Sugar-Based Polymers from d-Glucose and d-Galactose.

Monomers derived from glucose and galactose, which contain an endocyclic alkene (in the sugar ring) and a terminal alkyne, underwent a cascade polymerization to prepare new polymers with the ring-opened sugar incorporated into the polymer backbone. Polymerizations were well-controlled, as demonstrated by a linear increase in molecular weight with monomer-to-initiator ratio and generally narrow molecular weight dispersity values. The living nature of the polymerization was supported by the preparation of a b...


Gold-Catalyzed Silyl-Migrative Cyclization of Homopropargylic Alcohols Enabled by Bifunctional Biphenyl-2-ylphosphine and DFT Studies.

The development of novel ligands specifically tailored for homogeneous gold catalysis permits the development of new gold catalysis. In this work, we report that a remotely functionalized biphenyl-2-ylphosphine ligand enables gold-catalyzed cyclization of homopropargylic alcohols accompanied by an unusual silyl migration, which provides efficient access to 3-silyl-4,5-dihydrofurans. DFT studies of the mechanism of this novel transformation suggest the synergy between the steric bulk of the ligand and its pr...

NHC-Stabilized Silyl-Substituted Chlorosilylene.

The first N-heterocyclic carbene (NHC) stabilized silyl-substituted chlorosilylene () was isolated via selective dehydrochlorination by NHC from silyl-based Si(IV) precursor BuSiSiHCl. Compound can form an iron chlorosilylene complex () with an iron carbonyl dimer and undergoes chloride/hydride metathesis to yield a stable NHC-silylene hydride borane adduct (). Upon treatment with additional NHC, chlorosilylene was converted into silyl-substituted silyliumylidene ions ().


Modular Approach to Degradable Acetal Polymers Using Cascade Enyne Metathesis Polymerization.

A modular synthetic approach to degradable metathesis polymers is presented using acetal-containing enyne monomers. The monomers are prepared in a short and divergent synthetic sequence that features two points of modification to tune polymerization behavior and introduce molecular cargo. Steric and stereochemical elements are critical in the monomer design in order to provide rapid and living polymerizations capable of generating block polymers. The developed polyacetal materials readily undergo pH-depende...

Comparison of Rosetta flexible-backbone computational protein design methods on binding interactions.

Computational design of binding sites in proteins remains difficult, in part due to limitations in our current ability to sample backbone conformations that enable precise and accurate geometric positioning of side chains during sequence design. Here we present a benchmark framework for comparison between flexible-backbone design methods applied to binding interactions. We quantify the ability of different flexible backbone design methods in the widely used protein design software Rosetta to recapitulate ob...

Synthesis and quantitative analyses of acrylamide-grafted poly(lactide-co-glycidyl methacrylate) amphiphilic copolymers for environmental and biomedical applications.

Bio-degradable/bio-compatible poly(lactide-co-glycidyl methacrylate), P(LA-co-GMA), a copolymer has been synthesized. The material contains curable CC groups, which enable its self-curing and grafting reactions with other vinyl monomers. The copolymer was grafted with a pH-responsive polyacrylamide (PAAm), by UV-assisted reactions using acrylamide (AAm) and N,N'-methylene bisacrylamide monomers, and various photoinitiator systems. The original copolymer and its partially-cured counterpart were employed in t...

One-Pot Two-fold Unsymmetrical C-Si bond 2,6-Bifunctionalization of Arenes via Sequential 1,4-Csp2 to O-Silyl Migration.

Two-fold unsymmetrical C-Si bond bifunctionalization of 2,6-di(trimethylsilyl) benzyl alcohols has been achieved in one pot via sequential [1,4]-Csp2 to O-silyl migration. The hydroxyl group functions as an "on-off-on" switch to control two successive silyl migrations, and 4,7-dimethyl-o-phenanthroline ligand favors cleavage of the endo-cyclic C-Si bond. Diverse Csp3/Csp3 or Csp2/Csp3 electrophiles can be installed at the 2- and 6-positions. This approach was used to chemoselectively functionalize the three...

Polymeric Photoacids based on Naphthols - Design Criteria, Photostability, and Light-Mediated Release.

The implementation of photoswitches within polymers offers an exciting toolbox in the design of light-responsive materials as irradiation can be controlled both spatially and temporally. Herein, we introduce a range of water-soluble copolymers featuring naphthol-based chromophores as photoacids in the side chain. With that, the resulting materials experience a drastic increase in acidity upon stimulation with UV light and we systematically studied how structure and distance of the photoacid from the copolym...

Nickel-Catalyzed Synthesis of Silanes from Silyl Ketones.

An unprecedented nickel-catalyzed decarbonylative silylation via CO extrusion intramolecular recombination fragment coupling of unstrained and nondirecting group-assisted silyl ketones is described. The inexpensive and readily available catalyst performs under mild reaction conditions and enables the synthesis of structurally diverse arylsilanes, including heterocyclic and natural product derivatives.

An alternative approach for quantification of glyceraldehyde and dihydroxyacetone as trimethylsilyl derivatives by GC-FID.

A method for quantification of glyceraldehyde (GA), dihydroxyacetone (DHA) and glycerol (GLY) by gas chromatography coupled to a flame ionization detector (GC-FID) involving one-step derivatization into trimethylsilyl ethers is presented. In pyridine, DHA and GA showed predominant peaks assigned to dimeric structures and smaller peaks corresponding to the monomers. The later were identified by GC-MS as their completely derivatized molecules and were useful for construction of calibration curves with high li...

Copper-catalyzed regiodivergent 1,4- and 1,6-conjugate silyl addition to diendioates: access to functionalized allylsilanes.

A copper-catalyzed regioselective 1,4- and 1,6-conjugate addition of a silyl reagent to diendioates was established. Various 1,4- and 1,6-protosilylation products were obtained in good yields and with high regioselectivity via tuning the ligands used in the reactions. This protocol has provided a simple and efficient method for the synthesis of multisubstituted functionalized allylsilanes.

Biorefinery by-products and epoxy biorenewable monomers: a structural elucidation of humins and triglycidyl ether of phloroglucinol crosslinking.

TThe need for thermosets from renewable resources is permanently increasing in order to find eco-friendly alternatives to petroleum-derived materials. Products obtained from biomass have shown to play an important role in this challenge. Here we present the structural characterization of new bio-based thermosets made by humins, a by-product of lignocellulosic biorefinery, and glycidylated phloroglucinol coming from biomass phenolic fraction. By employing ATR-FTIR and NMR spectroscopies, we elucidated the co...

Functionalized and Degradable Polyphthalaldehyde Derivatives.

Polymers that depolymerize back to monomers can be repeatedly chemically recycled, thereby reducing their environmental impact. Polyphthalaldehyde is a metastable polymer that can rapidly and quantitatively depolymerize due to its low ceiling temperature. However, the effect of substitution on the physical and chemical properties of polyphthalaldehyde derivatives has not been systematically studied. Herein, we investigate the cationic polymerization of seven -phthalaldehyde derivatives and demonstrate that ...

Chemical synthesis of diglucosyl diacylglycerols utilizing glycosyl donors with stereodirecting cyclic silyl protective groups.

Chemical syntheses of the bacterial diglucosyl diacylglycerols 1-heptadecanoyl-2-pentadecanoyl-3-O-[6-O-(β-d-glucopyranosyl)-β-d-glucopyranosyl]-sn-glycerol and 1-(cis-13-octadecenoyl)-2-palmitoyl-3-O-[2-O-(α-d-glucopyranosyl)-α-d-glucopyranosyl]-sn-glycerol are described. The syntheses feature the stereoselective construction of glycosidic linkages in glycosylation reaction by utilizing glycosyl donors with stereodirecting cyclic silyl protective groups. The 1,1,3,3-tetraisopropyldisiloxane-1,3-diyl (T...

Recent Advances in Metal-Mediated Stereoselective Ring-Opening Polymerization of Functional Cyclic Esters towards Well-defined Poly(hydroxy acid)s.

Poly(hydroxy acid)s are a family of biocompatible and (bio)degradable polyesters with various outcomes in different domains of application. To date, poly(hydroxy acid)s are best prepared by ring-opening polymerization (ROP) of the corresponding cyclic esters. Using racemic chiral monomers featuring side-chain groups enables to access, providing a stereoselective catalyst/initiator system is implemented, stereoregular functional polymers, thereby improving their physico-chemical properties and ultimately wid...

A Silyl-Nickel Moiety as a Metal-Ligand Cooperative Site.

Nickel(II) complexes supported by a diphosphinosilyl ligand, [PhSi(2-PPrCH)] (PhSiP), reveal unusual metal-ligand cooperativity (MLC). While (PhSiP)Ni(NHMes) () was cleanly isolated at room temperature, a nickel triisopropylphenylamido species, (PhSiP)Ni(NHTrip) (), slowly transformed into a nickel(II) phenyl species, [(ArNH)SiP]Ni(Ph) (), where (ArNH)SiP = [(NHTrip)Si(2-PPrCH)]. The X-ray crystallographic data of exhibit a Si-N bond generated from Si-N coupling between the silyl moiety and amino group, al...

Enzymatically-degradable alginate hydrogels promote cell spreading and in vivo tissue infiltration.

Enzymatically-degradable materials recapitulate the dynamic and reciprocal interactions between cells and their native microenvironment by allowing cells to actively shape the degradation process. In order to engineer a synthetic 3D environment enabling cells to orchestrate the degradation of the surrounding material, norbornene-modified alginate was crosslinked with two different peptide crosslinkers susceptible to cleavage by matrix metalloproteinases using UV-initiated thiol-ene chemistry. Resulting hydr...

Asymmetric synthesis of biaryl atropisomers using an organocatalyst-mediated domino reaction as a key step.

A three-pot synthetic method that features the use of an organocatalyst as a key step was developed for the preparation of biaryl atropisomers. The first reaction is an asymmetric domino Michael-Henry reaction catalyzed by diphenylprolinol silyl ether to afford the substituted nitrocyclohexanecarbaldehyde with four chiral centers and one axial information with excellent enantioselectivity. Removal of the central chirality from the domino products afforded biaryl atropisomers having axial chirality with exce...

Antibacterial, Ester-Free Monomers: Polymerization Kinetics, Mechanical Properties, Biocompatibility and Anti-Biofilm Activity.

Quaternary ammonium (QA) methacrylate monomers have been extensively investigated and demonstrate excellent antibacterial properties. However, the presence of ester bonds makes them prone to degradation in the oral cavity. In this study, ester-free QA monomers based on meth-acrylamides were synthesized and screened for polymerization kinetics, mechanical properties and antibacterial effects.

Synthesis of 3,5-Disubstituted 1,2-Dioxolanes through the Use of Acetoxy Peroxyacetals.

The synthesis of acetoxyendoperoxyacetal derivatives allowed the formation of functionalized 3,5-disubstituted 1,2-dioxolanes through the formation of reactive peroxycarbenium species under Lewis acid mediation. The introduction of a neutral nucleophile such as allylsilane, silane, or silyl enol ether was accomplished with moderate to good yields. The two studied Lewis acids, TiCl and SnCl, gave contrasting results. The higher diastereoselectivity toward the trans diastereomer in experiments with TiCl as Le...

Diastereoselective Methylation at the Congested β-Position of a Butenolide Ring: Studies toward the Synthesis of -Prezizaane-Type Sesquiterpenes.

We established a method for installing a methyl group at the β-position of a butenolide ring. The methylated position is located at the congested ring juncture of a 5,6,5-tricyclic lactone, which is common to neurotrophic -prezizaane-type sesquiterpenes. The samarium(II)-mediated conjugate addition of the halomethylsilyl ethers tethered to the proximal hydroxy groups efficiently formed the desired C-C bond. Subsequent fluoride-free Tamao oxidation and Barton-McCombie deoxygenation converted the resultant c...

Interactions of aggregating peptides probed by IR-UV action spectroscopy.

Peptide aggregation, the self-assembly of peptides into structured beta-sheet fibril structures, is driven by a combination of intra- and intermolecular interactions. Here, the interplay between intramolecular and formed inter-sheet hydrogen bonds and the effect of dispersion interactions on the formation of neutral, isolated, peptide dimers is studied using infrared action spectroscopy. Therefore, four different homo- and heterogenous dimers resulting from three different alanine-based model peptides have ...

-Butyl Nitrite Mediated Synthesis of Fluorinated -Alkyloxime Ether Derivatives.

A -butyl nitrite (TBN)-mediated synthesis of fluorinated -alkyloxime ether derivatives with bromodifluoroalkyl reagents as the fluorine sources has been developed. A variety of halodifluorinated compounds were found compatible, delivering the desired products in moderate to excellent yields. This transformation features a simple operation, can be done in air, and found to involve radicals. This protocol represents a straightforward approach to access various fluorinated -alkyloxime ether derivatives.

Classification of RNA backbone conformations into rotamers using C' chemical shifts: exploring how far we can go.

The conformational space of the ribose-phosphate backbone is very complex as it is defined in terms of six torsional angles. To help delimit the RNA backbone conformational preferences, 46 rotamers have been defined in terms of these torsional angles. In the present work, we use the ribose experimental and theoretical C' chemical shifts data and machine learning methods to classify RNA backbone conformations into rotamers and families of rotamers. We show to what extent the experimental C' chemical shifts c...

Oxyallyl Cation Capture via Electrophilic Deborylation of Organoboronates: Access to ,'-Substituted Cyclic Ketones.

An umpolung strategy to synthesize ,'-substituted cyclic ketones through the nucleophilic addition of organoboronates to -hydroxyl silyl enol ethers is described. The reaction proceeds via the trapping of in situ generated oxyallyl cations via the electrophilic deborylation of C(sp) and C(sp) borates. This efficient and straightforward method provides direct access to -substituted silyl enol ethers in high yield with complete regioselectivity. Desilylation in a one-pot procedure provides the corresponding ,...


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