In-situ analysis of polyelectrolyte complexes by flow cytometry

Abstract

Polyelectrolyte complexes (PECs) from common papermaking additives were prepared at different cation/anion ratios, resulting in colloidal light scattering particles. The polycations were cationic starches and polyDADMACs, while the polyanions were different carboxymethyl celluloses. The PECs were studied by turbidity measurements, as well as by flow cytometry (FCM). Turbidity maxima were detected close to the theoretical neutralization point of the polycation and polyanion. The turbidity response of the PEC mixtures varied with polyelectrolyte charge density. The PECs were in most cases quite stable over 24 h, but certain combinations resulted in unstable particles over time. Flow cytometry of PECs revealed clear populations of hydrophilic particles. The light scattering properties of PECs in side direction (SSC) and forward direction (FSC) were recorded for the different PEC combinations. The determined FSC and SSC offered information about very different PEC properties, and a new term was suggested for better understanding the mechanisms behind PEC formation; FSC/SSC. It was suggested that the determined FSC/SSC values were connected to the structural density of different particles. The premise was tested by analyses of solid, dense particles as well as swollen, soft particles. In addition to this, the hydrophobicity of PECs was determined by FCM. It was seen that the PECs were quite hydrophilic overall and that the measured hydrophobicities were lowest around the theoretical point of neutralization. Finally, the behavior of a coagulating PEC mixture as a function of contact time was studied with FCM.

Structure and cytotoxicity of zinc (II) and cobalt (II) complexes based on 1,3,5‐tris(1‐imidazolyl) benzene

“…Apoptosis is the programmed cell death that controls the development and homeostasis of multicellular organisms by elimination of aged, damaged or mutated cells, and which has been shown to be the key cellular event responsible for the anti‐cancer activity of metal anti‐cancer drugs . To determine whether the observed cell death induced by the three complexes was due to apoptosis, the interaction of HeLa cells with the complexes was investigated using an Annexin V‐FITC/PI assay.…”

Analysis of cellulose nanocrystals (CNCs) with flow cytometry

“…The shapes of the CNC populations were slightly different depending on the raw material used, which indicated that the choice of raw material influenced the resulting CNCs. Previously, FCM measurements of polyelectrolyte complexes (PECs) highlighted that the FSC and SSC offers quite different information about particles in suspension (Strand et al 2018). It was theorized that the SSC gives information about the amount of dense and light scattering surfaces in a particle, while the FSC offers information about the transparency of a particle, as well as the complexity of its external or internal texture.…”

“…Sodium carboxymethyl cellulose, M w 250, degree of substitution 0.9, was obtained from Acros Organics. Polyelectrolyte complexes (PECs) were prepared from the cationic starch and CMCs at a polycation to polyanion ratio of 5.5:1 according to a previously published procedure (Strand et al 2018). The lipophilic extractives from thermomechanical pulp from Norway spruce were extracted with hexane.…”

“…Filtered distilled water was used as sheath fluid in the analyses. Nile red (Tamro, Vantaa, Finland) was used as a fluorescent dye to stain the particles prior to FCM analysis, as in previously published studies (Vähäsalo et al 2003;Vähäsalo and Holmbom 2005;Strand et al 2013Strand et al , 2018. Nile red is an environment-sensitive fluorophore that exhibits a blue-shift proportional to the hydrophobicity of its environment (Greenspan and Fowler 1985).…”

“…Furthermore, FCM can be used to measure the fluorescence of particles at different wavelengths, which is very useful when combined with addition of selective dyes to the samples. In the field of pulping and papermaking, FCM has so far been used to analyze colloidal wood pitch, bacteria, coated broke, precipitated oxalate, various filler particles, and polyelectrolyte complexes (Vähäsalo et al 2003;Lindberg et al 2004;Vähäsalo and Holmbom 2005;Strand et al 2013;Häärä et al 2014;Strand et al 2018). With FCM techniques, it is possible to analyze particles in suspension directly without complicated pre-treatments.…”