Electrostatic loading and photoredox-based release of molecular cargo from oligoviologen-crosslinked microparticles

Although on-demand cargo release has been demonstrated in a wide range of microparticle platforms, many existing methods lack specific loading interactions and/or undergo permanent damage to the microparticle to release the cargo. Here, we report a novel method for electrostatically loading negatively charged molecular cargo in oligoviologen-crosslinked microparticles, wherein the cargo can be released upon activation by visible light. A water-in-oil (W/O) emulsion polymerization method was used to fabricate narrowly dispersed microparticles crosslinked by a dicationic viologen-based dimer and a poly(ethylene glycol) diacrylate. A zinc-tetraphenyl porphyrin photocatalyst was also polymerized into the microparticle and used to photochemically reduce the viologen subunits to their monoradical cations through a visible-light-mediated photoredox mechanism with triethanolamine (TEOA) as a sacrificial reductant. The microparticles were characterized by microscopy methods revealing uniform, spherical microparticles 481 ± 20.9 nm in diameter. Negatively charged molecular cargo (methyl orange, MO) was electrostatically loaded into the microparticles through counteranion metathesis. Upon irradiation with blue (450 nm) light, the photo-reduced viologen crosslinker subunits lose positive charges, resulting in release of the anionic MO cargo. Controlled release of the dye, as tracked by absorption spectroscopy, was observed over time, yielding release of up to 40% of the cargo in 2d and 60% in 5d in single dynamic dialysis experiment. However, full release of cargo was achieved upon transferring the microparticles to a fresh TEOA solution after the initial 5d period.

Chemical composition and colloidal properties of dissolved organic matter in Norway spruce forest stands of different ages

<p>     Dissolved organic matter (DOM) is the most mobile and actively cycling fraction of soil carbon and acts as a carrier of nutrients and contaminants. It is consumed by microbes, photodegraded, or adsorbed in soils and sediments on its way to the ocean. Despite intensive research in the last two decades, the formation and fate of DOM in soils and its response to changes in land use and climate are poorly understood [1-3]. The changes in temperature and chemical composition of soils affect substantially the rates of microbial decomposition. It has previously been observed that afforestation had a positive effect on carbon stocks approximately 3 decades after land-use change [4]. The aim of this study was to identify the role of afforestation on the chemical composition and colloidal nature of DOM. We compared water extractable DOM from an organic horizon in three differently aged (35-, 61-, 90-years-old) Norway spruce stands growing in the same Tönnersjöheden area located at Simlångsdalen, south-west Sweden . Arable fields that were adjacent to each of these three forests served as control DOM samples and represented the soil material before afforestation. Chemical composition of DOM was inferred from <sup>13</sup>C solid-state nuclear magnetic resonance (NMR), high-resolution <sup>1</sup>H NMR, infrared spectroscopy (DRIFT) and elemental analysis measurements. Colloidal properties of DOM were investigated using small-angle X-ray and dynamic light scattering methods together with electrophoretic mobility measurements. The dialysis experiment was additionally performed in order to investigate the high molecular fraction of DOM.</p><p>     Elemental analysis revealed an increase in the ratio between total organic C and total N with forest age and no differences between three field DOM extracts. <sup>1</sup>H and <sup>13</sup>C NMR results showed that both field and forest DOM extracts were dominated by carbohydrates and also contained carboxylic and aliphatic compounds. The aromatic structures were not detected using NMR. However, some features of aromatics and phenolics were detected in IR spectra, especially in forest cold DOM. Scattering data showed that field and forest DOM contained locally stable colloidal aggregates of ca. 100 nm in radius. The structures of these aggregates are consistent with a combination of globular and cluster-like colloids. Field DOM contained slightly higher fraction of clusters than forest DOM. According to the dialysis experiment the half of DOM was presented in high molecular weight fraction (> 12-14 kDa). Overall, our data suggest that DOM extracted from forest and field organic soils had similar chemical and colloidal properties. The relative composition was dictated more by temperature at which DOM was extracted.</p><ol><li>J. Lehmann, M. Kleber, Nature. <strong>528</strong>, 60–68 (2015).</li> <li>M. W. I. Schmidt et al., Nature. <strong>478</strong> (2011), pp. 49–56.</li> <li>K. Kalbitz, S. Solinger, J.-H. Park, B. Michalzik, E. Matzner, Soil Sci. <strong>165</strong>, 277–304 (2000).</li> <li>T. G. Bárcena et al., Glob. Chang. Biol. <strong>20</strong>, 2393–2405 (2014).</li> </ol>

The evaluation of initial rates in the presence of background noise

A three-parameter model was used to test a curvilinear regression for its gamma-intercept. It was applied in the kinetic analysis of a model reaction and of real experiments. The model reaction consisted of a dialysis experiment with increasing amounts of background added at t0. In the presence of this background, initial rates of solute exchange were determined precisely enough to be in agreement with Fick's law of diffusion. The biological experiments were concerned with the saturation kinetics of the acid-soluble radioactivity of cells exposed to 3H-labelled amino acids. Two models of regression were applied, facilitated and physical diffusion, both consistent with the assumption of a substantial amount of background. This background was assumed to be caused by adsorption of 3H-labelled amino acids to cell-surface proteins. Without further consideration it caused a systematic overestimation of the initial rates.

A new dialysis-ion exchange technique for determining the forms of trace metals in water

A new separation technique is described which should aid attempts to determine the physicochemical forms of trace metals in aquatic systems. The technique involves combined dialysis and ion exchange, and permits the dialysis experiment to be completed in times very much shorter than normal. Experiments reported in this paper indicated that an optimum time of 5 h was necessary for complete dialysis of all dialysable species from natural water samples. The method has been tested for Cd, Cu, Pb, Zn and Fe in synthetic solutions prepared from distilled-deionized water. In all cases it was apparent that, within the precision of the technique, almost 100% of the added trace metals was dialysed in the 5-h time period. The results give in- formation on the concentration of ionic species present in the water. Three natural river water samples were also dialysed, and the results compared with total and filterable (< 0.4 �m) trace metal concentrations obtained for the same samples.

The state of binding of intracellular K+ in Halobacterium cutirubrum

Intracellular K+ in lysed freeze-thawed cell pastes of the extreme halophile, H. cutirubrum, diffused readily against a concentration gradient during equilibrium dialysis, whereas the intracellular Mg2+ was not readily diffusible. The K+ activity in the lysed cell pastes, determined directly by K+ ion-specific electrode, was comparable to the total K-content of the cells, as determined by atomic absorption. This finding and the results of the dialysis experiment suggest that the intracellular K+ in H. cutirubrum is not bound.