Polymerization of the through-pores in HPLC columns for enhanced SEM based assessment of packing order

Recent developments in chip-based column technology, whereby plate heights corresponding to the domain size can be obtained,[1] suggest that it might also be possible to improve the lower minimal plate height limit in packed column HPLC (h≈2dp), down to lower values if feasible improved packing procedures can be developed. In order to allow enhanced understanding of the order in packed HPLC columns, in this work a methodology for immobilizing silica particles is developed based on the polymerization of a monomer and a cross-linker in the interstitial pores of HPLC columns. Subsequent mechanical cutting allows scanning electron microscopy (SEM) based imaging of cross sections of the packed bed over the entire length of the column. In this way the packing efficiency of in-house packed and commercial HPLC columns comprising the same packing material can be compared. The methodology is developed for native silica used in e.g. hydrophilic interaction liquid chromatography and the information obtained is cross-referenced with external porosity measurements obtained via inversed size exclusion approach

Exploration of the selectivity and retention behavior of alternative polyacrylamides in temperature responsive liquid chromatography

Temperature responsive liquid chromatography (TRLC) allows for separation of organic solutes in purely aqueous mobile phases whereby retention is controlled through temperature. The vast majority of the work has thus far been performed on poly[N-isopropylacrylamide] (PNIPAAm)-based columns, while the performance of other temperature responsive polymers has rarely been compared under identical conditions. Therefore, in this work, two novel TRLC phases based on poly[N-n-propylacrylamide] (PNNPAAm) and poly[N,N-diethylacrylamide] (PDEAAm) are reported and compared to the state of the art PNIPAAm based column. Optimal comparison is thereby obtained by the use of controlled radical polymerizations, identical molecular weights, and by maximizing carbon loads on the silica supporting material. Analysis of identical test mixtures of homologue series and pharmaceutical samples revealed that PNNPAAm performs in a similar way as PNIPAAm while offering enhanced retention and a shift of the useable temperature range toward lower temperatures. PDEAAm offers a range of novel possibilities as it depicts a different selectivity, allowing for enhanced resolution in TRLC in, for example, coupled column systems. Reduced plate heights of 3 could be obtained on the homemade columns, offering the promise for reasonable column efficiencies in TRLC despite the use of bulky polymers as stationary phases in HPLC

Oxidation of monoterpenes catalysed by a water-soluble Mn(III) PEG-porphyrin in a biphasic medium

It is well established that the transformation of abundant and cheap natural products, such as terpenoids, can produce other more valuable compounds. Thymoquinone, which has a commercial value significantly higher than that of its precursors, can be obtained by oxidation of carvacrol and thymol. In this work, a new water-soluble Mn-III PEG-porphyrin is reported as catalyst in a water/hexane (1:1) biphasic medium for the oxidation of carvacrol and thymol into thymoquinone. The reactions were performed using tert-butyl hydroperoxide as oxidant in the presence of ammonium acetate as co-catalyst, reaching 94 and 78% of conversion after 5 h of reaction for thymol and carvacrol, respectively. Experiments with oregano essential oil as substrate revealed selective transformation of thymol and carvacrol into thymoquinone. The main advantage of this biphasic system based on a water-soluble catalyst and on substrates and products soluble in hexane, is the straightforward isolation, recovery and recycling of the catalyst by simple phase separation. Recycling studies of the Mn-III PEG-porphyrin using thymol as substrate showed high conversion values throughout four catalytic cycles

Reversible covalent locking of a supramolecular hydrogel via UV-controlled anthracene dimerization

Supramolecular hydrogels gained significant attention as shear-thinning, self-healing materials. However, the introduction of non-covalent crosslinks inherently decreases the strength and stability of the hydrogel. In this work, we developed a novel supramolecular hydrogel that undergoes a reversible transformation to the corresponding covalently crosslinked hydrogel upon UV-irradiation. The supramolecular hydrogel was developed based on the ternary host-guest interaction of two anthracene moieties and one large macrocyclic host. Anthracene functionalized poly(N-acryloylmorpholine)s were synthesized by post-polymerization modification of a copolymer consisting of N-acryloylmorpholine and an activated ester comonomer, whereby two different polymers were prepared having either neutral anthracene side-chains or carrying a positive charge next to the anthracene to enhance the interaction with the host. The binding affinity of the anthracene side chains with and without an additional cationic charge were studied with two macrocyclic hosts, namely cucurbit[8]uril and gamma-cyclodextrin (gamma-CD) by UV-Vis titration revealing a markedly stronger binding in the presence of the cationic charge due to additional ion-dipole one of the macrocyclic hosts, cucurbit[8]uril. Subsequently, the effect of the binding affinity on the hydrogelation was investigated, indicating that the stronger binding affinity facilitated the hydrogel formation at lower concentration. Finally, the reversible transformation of the supramolecular hydrogel to a chemical hydrogel by anthracene dimerization was studied by the UV irradiation of the hydrogel at 365 nm for covalent crosslinking or at 254 nm for decrosslinking. It could be demonstrated that the dynamic nature of the hydrogel, that is responsible for the shear-thinning behavior, was indeed lost upon UV-irradiation indicative of the formation of a covalently crosslinked hydrogel. The capabilities of the formed supramolecular hydrogel that is easily processable and able to reversibly convert to a chemical hydrogel, provides potential applications in applying mechanically robust covalently crosslinked hydrogels in complex shapes and difficult to reach locations making use of the dynamic nature of the supramolecular crosslinks

Through-pore polymerization in polar high-performance liquid chromatography columns allowing scanning electron microscopy based imaging of the packing order

To allow an enhanced understanding of the order in packed HPLC columns, in this work a methodology for immobilizing native polar silica particles is developed based on the polymerization of a methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDMA) as a cross-linker in the interstitial pores of HPLC columns. Subsequent mechanical cutting then allows scanning electron microscopy (SEM) based imagery of cross-sections of the packed bed. In this way, the packing efficiency of home-made and commercial HPLC columns with 4.6 mm inner diameter and 150 mm length comprising the same packing material of 5 mu m silica particles are compared. The methodology is developed for native silica used in e.g. hydrophilic interaction liquid chromatography (HILIC) and in normal phase LC. In order to confirm the feasibility of the developed methodology, the conventional methods for the evaluation of column, efficiency and porosity, are also employed. The obtained porosity information is compared and showed the same trend with the external porosity measurements obtained via inverse size exclusion approach, illustrating its potential application to study the micro-heterogeneity of packed HPLC columns and to guide the optimization of the packing process of HPLC columns. (C) 2020 Elsevier B.V. All rights reserved

Effect of host-guest complexation on the thermoresponsive behavior of poly(oligo ethylene glycol acrylate)s functionalized with dialkoxynapththalene guest side chains

The combination of thermoresponsive polymers with supramolecular host-guest interactions enables accurate tuning of the phase transition temperature, while also providing additional response mechanisms based on host-guest complexation. Most studies focused on a single thermoresponsive polymer to demonstrate the effect of host-guest complexation on the responsive behavior. In this work, the effect of the polymer structure on the host-guest complexation and thermoresponsive behavior is reported. Therefore, different poly(oligoethylene glycol acrylate)s, namely, poly(2-hydroxyethylacrylate) (PHEA), poly(methoxy diethylene glycol acrylate), poly(methoxy triethylene glycol acrylate), and poly(methoxy tetraethylene glycol acrylate), are synthesized functionalized with 1,5-dialkoxynaphthalene guest molecules in the side chain. Their complexation with the cyclobis(paraquat-p-phenylene) tetrachloride host is studied to understand the effect of polymer structure on the supramolecular association and the polymer phase transition, revealing that the oligoethylene glycol side chains lead to weaker host-guest complexation and also have a smaller increase in the cloud point temperature compared to PHEA

A supramolecular miktoarm star polymer based on porphyrin metal complexation in water

A novel supramolecular miktoarm star polymer was successfully constructed in water from a pyridine end-decorated polymer (Py-PmDEGA) and a metalloporphyrin based star polymer (ZnTPP-(PEG)(4)) via metal-ligand coordination. The Py-PmDEGA moiety was prepared via a combination of reversible addition-fragmentation chain transfer polymerization (RAFT) and subsequent aminolysis and Michael addition reactions to introduce the pyridine end-group. The ZnTPP(PEG)(4) star-polymer was synthesized by the reaction between tetrakis(p-hydroxyphenyl) porphyrin and toluenesulfonyl-PEG, followed by insertion of a zinc ion into the porphyrin core. The formation of a well-defined supramolecular AB(4)-type miktoarm star polymer was unambiguously demonstrated via UV-Vis spectroscopic titration, isothermal titration calorimetry (ITC) and diffusion ordered NMR spectroscopy (DOSY)

Supramolecular Competitive Host–Guest Interaction Induced Reversible Macromolecular Metamorphosis

In this work, a rational strategy of competitive host-guest complexation between dioxynaphthalene (Naph) and tetrathiafulvalene (TTF) subunits as guests and cyclophane cyclobis(paraquat-p-phenylene) (CBPQT(4+)) module as host is exploited to modify the macromolecular architecture, so-called supramolecular metamorphosis, in aqueous media. The architectures of the polymers can be reversibly transformed from a linear diblock copolymer AB to a linear AC block copolymer or from a linear block copolymer to a comb copolymer by redox switching. Interestingly, as TTF- and Naph-based complexes feature different characteristic colors, it offers a great opportunity to directly observe nanoscaled macromolecular metamorphosis of materials with the naked eye

Oxidation of Monoterpenes Catalysed by a Water-Soluble Mn-III PEG-Porphyrin in a Biphasic Medium

© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim It is well established that the transformation of abundant and cheap natural products, such as terpenoids, can produce other more valuable compounds. Thymoquinone, which has a commercial value significantly higher than that of its precursors, can be obtained by oxidation of carvacrol and thymol. In this work, a new water-soluble Mn III PEG-porphyrin is reported as catalyst in a water/hexane (1:1) biphasic medium for the oxidation of carvacrol and thymol into thymoquinone. The reactions were performed using tert-butyl hydroperoxide as oxidant in the presence of ammonium acetate as co-catalyst, reaching 94 and 78 % of conversion after 5 h of reaction for thymol and carvacrol, respectively. Experiments with oregano essential oil as substrate revealed selective transformation of thymol and carvacrol into thymoquinone. The main advantage of this biphasic system based on a water-soluble catalyst and on substrates and products soluble in hexane, is the straightforward isolation, recovery and recycling of the catalyst by simple phase separation. Recycling studies of the Mn III PEG-porphyrin using thymol as substrate showed high conversion values throughout four catalytic cycles.status: publishe