Comparison of different types of outlet frits in slurry‐packed capillary columns

Fused‐silica capillary columns for high‐performance liquid chromatography with 320 and 250 μm inner diameter were prepared by slurry packing with 5 and 3 μm Nucleosil C₁₈ stationary phase. Different types of mechanical and monolithic outlet frits were used and their influence on the resulting column performance was evaluated. Columns with quartz wool exhibited symmetrical peaks and low theoretical plate height, and the preparation time was short. The performance of monolithic frits varied based on type of monolith, length of the frit, and silanization procedure. The best frit performed similarly to the quartz wool ones, but the preparation took several hours. Their main advantage lies in the possibility of on‐column detection, because the detection window can be burnt immediately behind the frit.     

Molecular Dynamics in 1- and 2-D Confinement as Studied for the Case of Poly(Cis-1,4-Isoprene)

Broadband Dielectric Spectroscopy (BDS) is used to probe the molecular dynamics of Type A polymer, poly(cis-1,4-isoprene), when confined in the 1-dimensional (1D) exploring space of thin layers and the 2-dimensional (2D) constraining geometry of unidirectional anodic aluminum oxide (AAO) nanopores. For both cases, it was observed that the structural relaxation remains bulk-like in its mean relaxation rate, although the distribution of its relaxation times is broadened in 2D confinement. Furthermore, the fluctuation of the end-to-end vector is interrupted, with the 1D case being relatively less pronounced. By this clear-cut comparison, it is demonstrated that the effects of confinement on molecular dynamics depend, inter alia, on the dimensionality of the restricting space.     

Preparation and evaluation of monolithic poly(N-vinylcarbazole-co-1,4-divinylbenzene) capillary columns for the separation of small molecules

Short-term polymerization or the so-called low-conversion polymerization was applied for the preparation of N-vinylcarbazole (NVC) and 1,4-divinylbenzene (DVB) monolithic capillary columns. The synthesis was carried out by thermally initiated free radical copolymerization under the influence of inert micro- (toluene) and macroporogen (1-decanol) and α,α′-azoisobutyronitrile (AIBN) as radical initiator. The morphological and porous properties were studied by scanning electron microscopy (SEM), nitrogen adsorption, and mercury intrusion porosimetry (MIP). The copolymerization process was studied by monomer conversion measurements. This approach led to increased porosity and specific surface area. A specific surface area above 400 m²/g of the monolith and a distinct bimodal pore size distribution were obtained. The chromatographic performance was determined in terms of theoretical plate heights and number of theoretical plates. The lowest plate height value was found to be 3.9 μm (corresponding to ≈256,000 plates per meter) applying methylparaben utilizing an 80 mm?×?0.2 mm i.d. monolithic capillary. The developed NVC/DVB monolithic supports showed high separation efficiency towards small molecules, which was exemplified applying reversed-phase (RP) separation of alkylbenzenes, beta-blockers, flavanoids, parabens, and phenones. The loading capacity was analyzed for isocratic separation of seven alkylbenzenes and was found to be up to 77 ng total mass of alkylbenzenes. Furthermore, a long-term stability test of 1,000 consecutive runs was performed and resulted in a maximum variance of 0.97, 0.85, and 0.16 % RSD for resolution, peak width at half height, and retention times, respectively. The material was proven to have a high permeability of 1.11E?14 m², applying water as a mobile phase.     

Quantitative characterization by asymmetrical flow field-flow fractionation of IgG thermal aggregation with and without polymer protective agents

Complexes formed between poly(acrylates) and polyclonal immunoglobulin G (IgG) in its native conformation and after heat stress were characterized using asymmetric flow field-flow fractionation (AF4) coupled with on-line UV-Vis spectroscopy and multi-angle light-scattering detection (MALS). Mixtures of IgG and poly(acrylates) of increasing structural complexity, sodium poly(acrylate) (PAA), a sodium poly(acrylate) bearing at random 3 mol % n-octadecyl groups, and a random copolymer of sodium acrylate (35 mol %), N-n-octylacrylamide (25 mol %) and N-isopropylacrylamide (40 mol %), were fractionated in a sodium phosphate buffer (0.02 M, pH 6.8) in the presence, or not, of 0.1 M NaCl. The AF4 protocol developed allowed the fractionation of solutions containing free poly(acrylates), native IgG monomer and dimer, poly(acrylates)/IgG complexes made up of one IgG molecule and a few polymer chains, and/or larger poly(acrylates)/IgG aggregates. The molar mass and recovery of the soluble analytes were obtained for mixed solutions of poly(acrylates) and native IgG and for the same solutions incubated at 65 °C for 10 min. From the combined AF4 results, we concluded that in solutions of low ionic strength, the presence of PAA increased the recovery ratio of IgG after thermal stress because of the formation of electrostatically-driven PAA/IgG complexes, but PAA had no protective effect in the presence of 0.1 M NaCl. Poly(acrylates) bearing hydrophobic groups significantly increased IgG recovery after stress, independently of NaCl concentration, because of the synergistic effect of hydrophobic and electrostatic interactions. The AF4 results corroborate conclusions drawn from a previous study combining four analytical techniques. This study demonstrates that AF4 is an efficient tool for the analysis of protein formulations subjected to stress, an important achievement given the anticipated important role of proteins in near-future human therapies. ?      

Copper(I)‐Catalyzed Regioselective Addition of Nucleophilic Silicon Across Terminal and Internal Carbon–Carbon Triple Bonds

The copper(I) alkoxide‐catalyzed release of a silicon‐based cuprate reagent from a silicon–boron pronucleophile is applied to the addition across carbon–carbon triple bonds. Commercially available CuBr?Me₂S was found to be a general precatalyst that secures high regiocontrol for both aryl‐ and alkyl‐substituted terminal as well as internal alkynes. The solvent greatly influences the regioisomeric ratio, favoring the linear regioisomer with terminal acceptors. This facile protocol even allows for the transformation of internal acceptors with remarkable levels of regio‐ and diastereocontrol.     

ABC Triblock Copolymer Micelles: Spherical Versus Worm‐Like Micelles Depending on the Preparation Method

Well‐defined ABC triblock copolymers based on two hydrophilic blocks, A and C, and a hydrophobic block B are synthesized and their self‐assembly behavior is investigated. Interestingly, at the same solvent, concentration, pH, and temperature, different shape micelles are observed, spherical and worm‐like micelles, depending on the preparation method. Specifically, spherical micelles are observed with bulk rehydration while both spherical and worm‐like micelles are observed with film rehydration.

     

Self‐Regulation in Flow‐Induced Structure Formation of Polypropylene

Flow‐induced structure formation is investigated with in situ wide‐angle X‐ray diffraction with high acquisition rate (30 Hz) using isotactic polypropylene in a piston‐driven slit flow with high wall shear rates (up to ≈900 s⁻¹). We focus on crystallization within the shear layers that form in the high shear rate regions near the walls. Remarkably, the kinetics of the crystallization process show no dependence on either flow rate or flow time; the crystallization progresses identically regardless. Stronger or longer flows only increase the thickness of the layers. A conceptual model is proposed to explain the phenomenon. Above a certain threshold, the number of shish‐kebabs formed affects the rheology such that further structure formation is halted. The critical amount is reached already within 0.1 s under the current flow conditions. The change in rheology is hypothesized to be a consequence of the “hairy” nature of shish. Our results have large implications for process modelling, since they suggest that for injection molding type flows, crystallization kinetics can be considered independent of deformation history.