Sequestration of Small Ions and Weak Acids and Bases by a Polyelectrolyte Complex Studied by Simulation and Experiment.

Mixing of oppositely charged polyelectrolytes can result in phase separation into a polymer-poor supernatant and a polymer-rich polyelectrolyte complex (PEC). We present a new coarse-grained model for the Grand-reaction method that enables us to determine the composition of the coexisting phases in a broad range of pH and salt concentrations. We validate the model by comparing it to recent simulations and experimental studies, as well as our own experiments on poly(acrylic acid)/poly(allylamine hydrochloride) complexes. The simulations using our model predict that monovalent ions partition approximately equally between both phases, whereas divalent ones accumulate in the PEC phase. On a semiquantitative level, these results agree with our own experiments, as well as with other experiments and simulations in the literature. In the sequel, we use the model to study the partitioning of a weak diprotic acid at various pH values of the supernatant. Our results show that the ionization of the acid is enhanced in the PEC phase, resulting in its preferential accumulation in this phase, which monotonically increases with the pH. Currently, this effect is still waiting to be confirmed experimentally. We explore how the model parameters (particle size, charge density, permittivity, and solvent quality) affect the measured partition coefficients, showing that fine-tuning of these parameters can make the agreement with the experiments almost quantitative. Nevertheless, our results show that charge regulation in multivalent solutes can potentially be exploited in engineering the partitioning of charged molecules in PEC-based systems at various pH values.

Biocatalytic membranes through aqueous phase separation.

HYPOTHESIS: Polymer membranes play a critical role in water treatment, chemical industry, and medicine. Unfortunately, the current standard for polymer membrane production requires unsustainable and harmful organic solvents. Aqueous phase separation (APS) has recently been proposed as a method to produce membranes in a more sustainable manner through induced polyelectrolyte complexation in aqueous solutions. EXPERIMENTS: We demonstrate that APS has another natural advantage that goes beyond sustainability: the easy incorporation of enzymes in the membrane structure. Biocatalytic membranes hold great promise in for example biorefinery, but the most common current post-production processes to immobilize enzymes on the membrane surface are complicated and expensive. FINDINGS: In this study we demonstrated the first biocatalytic membrane produced via APS. We demonstrate an easy procedure to incorporate lysozyme in polyelectrolyte complex membranes made via APS. Our functionalized membranes have the same structure, water permeability (in the range of high nanofiltration, low ultrafiltration), and retention as membranes without lysozyme. Lysozyme is antibacterial by catalysing the hydrolysis of specific peptidoglycan bonds in bacteria walls. We demonstrate that the functionalized membranes are also capable of catalysing this reaction. The membranes remain enzymatically active for a period of at least one week. This opens new routes to produce polymer membranes with added biological function.

Extraction of Lysozyme from Chicken Albumen Using Polyelectrolyte Complexes.

Cells use droplet-like membrane-less organelles (MLOs) to compartmentalize and selectively take-up molecules, such as proteins, from their internal environment. These membraneless organelles can be mimicked by polyelectrolyte complexes (PECs) consisting of oppositely charged polyelectrolytes. Previous research has demonstrated that protein uptake strongly depends on the PEC composition. This suggests that PECs can be used to selectively extract proteins from a multi-protein mixture. With this in mind, the partitioning of the protein lysozyme in four PEC systems consisting of different weak and strong polyelectrolyte combinations is investigated. All systems show similar trends in lysozyme partitioning as a function of the complex composition. The release of lysozyme from complexes at their optimal lysozyme uptake composition is investigated by increasing the salt concentration to 500 mm NaCl or lowering the pH from 7 to 4. Complexes of poly(allylamine hydrochloride) and poly(acrylic acid) have the best uptake and release properties. These are used for selective extraction of lysozyme from a hen-egg white protein matrix. The (back)-extracted lysozyme retains its enzymatic activity, showing the capability of PECs to function as extraction media for proteins.

Charge-Based Separation of Proteins Using Polyelectrolyte Complexes as Models for Membraneless Organelles.

Membraneless organelles are liquid compartments within cells with different solvent properties than the surrounding environment. This difference in solvent properties is thought to result in function-related selective partitioning of proteins. Proteins have also been shown to accumulate in polyelectrolyte complexes, but whether the uptake in these complexes is selective has not been ascertained yet. Here, we show the selective partitioning of two structurally similar but oppositely charged proteins into polyelectrolyte complexes. We demonstrate that these proteins can be separated from a mixture by altering the polyelectrolyte complex composition and released from the complex by lowering the pH. Combined, we demonstrate that polyelectrolyte complexes can separate proteins from a mixture based on protein charge. Besides providing deeper insight into the selective partitioning in membraneless organelles, potential applications for selective biomolecule partitioning in polyelectrolyte complexes include drug delivery or extraction processes.

Going door-to-door to reach men and young people with HIV testing services to achieve the 90-90-90 treatment targets.

Setting: Mulanje District, Malawi. Objective: To examine the effectiveness of door-to-door (DtD) testing in reaching young people and men in a remote, rural area with a high prevalence of human immunodeficiency virus (HIV) infection. Design: This was a retrospective analysis of data collected for a pilot DtD program. HIV testing services (HTS) visited targeted villages for 1-2 weeks. All current residents aged ⩾2 years not known to be HIV-positive were offered testing. Results: Ninety per cent (13 783/15 391) of individuals eligible for testing accepted. Forty-one per cent (n = 5693) of those tested were males and 56% (n = 7752) were aged <20 years. The overall proportion who tested positive was 4% (n = 524), with half as many males as females testing positive (OR 0.49, 95%CI 0.40-0.60, P < 0.001). There was a higher positive yield rate for those aged ⩾20 years (6% for men and 8% for women). Two thirds were first-time testers; males were half as likely as females to have been previously tested (OR 0.43, 95%CI 0.40-0.47, P < 0.001). Conclusion: DtD-HTS can be an effective way to reach populations in remote, rural high-prevalence areas where access to fixed facilities is inadequate. It has the potential to reach young people and men better than facility-based testing or other community strategies, and can identify young HIV-positive children who may have been missed by other methods.

Contexte: Le district de Mulanje, Malawi.Objectif: Examiner l'efficacité d'un test pour le virus de l'immunodéficience humaine (VIH) en porte à porte (DtD) pour atteindre les jeunes et les hommes dans une zone rurale isolée, à prévalence élevée du VIH.Schéma: Une analyse rétrospective des données recueillies lors d'un programme pilote DtD. Des services de test du VIH (HTS) ont été offerts pendant 1­2 semaines dans les villages ciblés. Tous les résidents actuels (âgés de ⩾2 ans) non connus comme VIH positifs ont été invités à bénéficier du test.Résultats: Il y avait 90% (13 783/15 391) des individus éligibles au test qui ont accepté. Parmi les patients testés, 41% (n = 5693) ont été des hommes et 56% (n = 7752) avaient <20 ans. Le pourcentage total de tests positifs a été de 4% (n = 524), avec deux fois moins d'hommes VIH-positifs (OR 0,49, IC95% 0,40­0,60 ; P < 0,001) et le rendement a été plus élevé pour les patients âgés de ⩾20 ans (6% pour les hommes et 8% pour les femmes). Pour les deux tiers des patients, il s'agissait du premier test, les hommes étant deux fois moins susceptibles d'avoir été testés auparavant (OR 0.43, IC95% 0,40­0,47 ; P < 0,001).Conclusion: Les services de test DtD peuvent être une manière efficace d'atteindre les populations dans les zones rurales isolées, avec une prévalence élevée de VIH, où l'accès aux structures fixes est insuffisant. Cette stratégie aura le potentiel d'atteindre les jeunes et les hommes mieux que les tests en structures de santé ou les stratégies communautaires, et peuvent identifier les jeunes enfants VIH-positifs qui peuvent avoir été manqués par les autres méthodes.

Marco de referencia: El distrito de Mulanje, en Malawi.Objetivo: Examinar la eficacia de la oferta de la prueba diagnóstica de puerta a puerta con el objeto de llegar a los jóvenes y los hombres en una zona rural remota donde existe una alta prevalencia de infección por el virus de la inmunodeficiencia humana (VIH).Método: Un análisis retrospectivo de los datos recogidos para un programa piloto de puerta a puerta. Se logró una cobertura completa de las aldeas destinatarias con servicios de diagnóstico del VIH durante 1 a 2 semanas. Se ofreció la prueba a todos los residentes actuales (⩾2 años de edad), con la excepción de quienes conocían su situación positiva frente al VIH.Resultados: El noventa por ciento de las personas que cumplían los requisitos aceptaron la prueba (13 783/15 391), de las personas en quienes se practicó, 41% eran de sexo masculino (n = 5693) y 56% <20 años (n = 7752). El porcentaje global de resultados positivos fue 4% (n = 524), la mitad de los hombres obtuvieron un resultado positivo (OR 0,49; IC95% 0,40­0,60; P < 0,001) y se observó una mayor tasa de resultados positivos en las personas ⩾20 años (6% en los hombres y 8% en las mujeres). En dos tercios de los casos se trató de una primera prueba y la probabilidad de haber tenido una prueba en el pasado fue de 50% en los hombres (OR 0,43; IC95% 0,40­0,47; P < 0,001).Conclusión: Las pruebas diagnósticas del VIH practicadas de puerta a puerta pueden ser un método eficaz de alcanzar a las poblaciones con alta prevalencia de la infección VIH en regiones rurales remotas, que no cuentan con un acceso adecuado a los establecimientos de salud. Esta estrategia ofrece una mejor posibilidad de llegar a los jóvenes y los hombres que las pruebas institucionales u otras estrategias comunitarias y puede detectar a los niños pequeños positivos frente al VIH que se han pasado por alto con otros métodos.

Paederus dermatitis: an outbreak on a medical mission boat in the Amazon.

Paederus dermatitis is a peculiar, irritant contact dermatitis characterized by a sudden onset of erythematobullous lesions on exposed areas of the body. The disease is provoked by an insect belonging to the genus Paederus. This beetle does not bite or sting, but accidental brushing against or crushing the beetle over the skin provokes the release of its coelomic fluid, which contains paederin, a potent vesicant agent. This article describes this dermatitis, which occurred in three healthcare personnel aboard a medical mission boat on the Amazon River. The epidemiology and pathogenesis of paederus dermatitis is reviewed as well its treatment and prevention.