187 research outputs found
Hydrolases in polymer chemistry:chemoenzymatic approaches to polymeric materials
No full textLipases show high activity in the polymerization of a range of monomers using ring-opening polymerization and polycondensation. The range of polymer structures from this enzymatic polymerization can be further increased by combination with chemical methods. This paper reviews the developments of the last 5-8 years in chemoenzymatic strategies towards polymeric materials. Special emphasis is on the synthesis of polymer architectures like block and graft copolymers and polymer networks. Moreover, the combination of chemical and enzymatic catalysis for the synthesis of unique chiral polymers is highlighted.</p
Hydrolases part I : enzyme mechanism, selectivity and control in the synthesis of well-defined polymers
No full textLipases are highly activity in the polymerization of a range of monomers. Both ring-opening polymerization of cyclic esters and polycondensation reactions of AA–BB and AB monomers have been investigated in great detail. This paper reviews the increased understanding in enzymatic strategies for the production of well-defined polymers. Major advantages of enzymatic catalysts are the relatively mild reaction conditions, and the often-observed excellent regio-, chemo-, and enantioselectivity that allow for the direct preparation of functional materials. However, as a result of the monomer activation mechanism, polymers of low polydispersity and low quantitative degree of endgroup functionality are difficult to attain. A wide variety of (co)polymers have been synthesized and explored in a variety of applications using lipase catalysts
Intramolecular hydrogen bonding in acylated 3,3'-diamino-2,2'-bipyridines : towards supramolecular chemistry in two dimensions
No full textPushing the limits of chiral amplification in supramolecular polymers
No full textN,N',N''-trialkylated-benzene-1,3,5-tricarboxamides (BTAs) self-assemble via strong, threefold αhelix type intermolecular hydrogen bonding into well-defined, helical, one dimensional columnar aggregates. The introduction of a stereogenic centre into the alkyl side chains of BTAs gives rise to strong Cotton effects in dilute apolar solutions indicating the preference for one helical conformation over the other. Here, we summarise our research on the influence of the position of the stereogenic centre on the aggregate stability and the degree of amplification of chirality in BTAs. In addition, we disclose our results on creating a preferred helical sense in BTAbased supramolecular polymers by introducing H/D isotope chirality into the alkyl side chains of BTAs at the a-position. We determine the relative stabilities of the leftand right-handed helical conformers formed by these deuterated molecules by performing a conformational analysis in different alkane solvents. Our findings show that the subtle difference between the stabilities of the two conformers leads to a cooperative self-assembly process, which is highly sensitive to the applied solvent
Supramolecular structures based on the intramolecular H-bonding in the 3,3'-di(acylamino)-2,2'-bipydridine unit
Full text linkDeracemisations under kinetic and thermodynamic control
Full text linkDeracemisation reactions occur when a racemic mixture is converted into a nonracemic mixture by increasing the quantity of one enantiomer at the expense of the other. This process can take place under thermodynamic control, but when combined with crystallisation processes kinetic factors also play a role. This review summarises the different approaches that have been taken to achieve efficient deracemisations. Starting from examples in which spontaneous symmetry breaking was found to occur, attrition enhanced deracemisation will be discussed in which solid-solution equilibria drive the deracemisation process. The combination of detailed experimental studies and mathematical models resulted in a profound understanding of this complex process, which is applicable to all congomerate forming compounds with a racemisable stereocenter. Then, we focus on deracemisations that occur under full thermodynamic control. Especially the combination of supramolecular interactions with a racemisation process gives interesting results, albeit that they are less predictable. The review will end with the possibilities supramolecular helical structures that show dynamic helicity can offer in conjunction with asymmetric catalysis. Herein, the helical preference induced by a minute amount of chiral compound is relayed to high enantiomeric excesses in a variety of reactions
"Soldier-Sergeant-Soldier" triblock copolymers : revealing the folded structure of single-chain polymeric nanoparticles
Full text link"Soldiers-Sergeant-Soldiers" experiments performed on single-chain polymeric nanoparticles (SCPNs) with an ABA-type triblock architecture carrying chiral and achiral benzene-1,3,5-tricarboxamides (BTAs) in different blocks reveal that the BTAs form segregated, multiple stacks in a single SCPN. © the Partner Organisations 2014
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