Line Tension and Line Activity in Mixed Monolayers Composed of Aliphatic and Terphenyl-Containing Surfactants

Custom-designed surfactants, known as “linactants”, have the ability to reduce the line tension between coexisting phases within mixed monolayers of chemically dissimilar compounds at the air–water interface. Thus far, linactants have been successfully identified for only one type of chemical dissimilarity, involving mixed monolayers of hydrocarbon and fluorocarbon surfactants. In the present work, we have pursued a more general interpretation of linactant compounds by extending the concept to a new system that is comprised of a mixture of aliphatic (pentadecanoic acid) and aromatic (<i>p</i>-terphenyl carboxylic acid) compounds. We found that the “bare” line tension between phases of this mixed monolayer was ∼4 pN, and within the same order of magnitude as our previous measurement in mixed monolayers containing hydrocarbons and fluorocarbons. Furthermore, we examined a homologous series of potential linactant compounds possessing an aliphatic tail of variable length and a <i>p-</i>terphenyl block. We determined that linactants with longer tails were able to reduce the line tension more efficiently and effectively. In particular, the addition of only 0.14% of a linactant with an 11-carbon chain reduced the line tension by more than a factor of 2. We hypothesize that the efficiency of this particular linactant is associated with its long tail; this creates strong van der Waals interactions with the aliphatic chains and enables the tail to adopt conformations that facilitate π-stacking interactions with the aromatic compounds within the monolayer

Stability and phase transfer of catalytically active platinum nanoparticle suspensions

In this work, we present a robust synthesis protocol for platinum nanoparticles that yields a monomodal dispersion of particles that are approximately 100 nm in diameter. We determine that these particles are actually agglomerates of much smaller particles, creating a “raspberry” morphology. We demonstrate that these agglomerates are stable at room temperature for at least 8 weeks by dynamic light scattering. Furthermore, we demonstrate consistent electrocatalytic activity for methanol oxidation. Finally, we quantitatively explore the relationship between dispersion solvent and particle agglomeration; specifically, particles are found to agglomerate abruptly as solvent polarity decreases

Single-Molecule Resolution of Protein Dynamics on Polymeric Membrane Surfaces: The Roles of Spatial and Population Heterogeneity

Although polymeric membranes are widely used in the purification of protein pharmaceuticals, interactions between biomolecules and membrane surfaces can lead to reduced membrane performance and damage to the product. In this study, single-molecule fluorescence microscopy provided direct observation of bovine serum albumin (BSA) and human monoclonal antibody (IgG) dynamics at the interface between aqueous buffer and polymeric membrane materials including regenerated cellulose and unmodified poly­(ether sulfone) (PES) blended with either polyvinylpyrrolidone (PVP), polyvinyl acetate-<i>co</i>-polyvinylpyrrolidone (PVAc-PVP), or polyethylene glycol methacrylate (PEGM) before casting. These polymer surfaces were compared with model surfaces composed of hydrophilic bare fused silica and hydrophobic trimethylsilane-coated fused silica. At extremely dilute protein concentrations (10^–3–10^–7 mg/mL), protein surface exchange was highly dynamic with protein monomers desorbing from the surface within ∼1 s after adsorption. Protein oligomers (e.g., nonspecific dimers, trimers, or larger aggregates), although less common, remained on the surface for 5 times longer than monomers. Using newly developed super-resolution methods, we could localize adsorption sites with ∼50 nm resolution and quantify the spatial heterogeneity of the various surfaces. On a small anomalous subset of the adsorption sites, proteins adsorbed preferentially and tended to reside for significantly longer times (i.e., on “strong” sites). Proteins resided for shorter times overall on surfaces that were more homogeneous and exhibited fewer strong sites (e.g., PVAc-PVP/PES). We propose that strong surface sites may nucleate protein aggregation, initiated preferentially by protein oligomers, and accelerate ultrafiltration membrane fouling. At high protein concentrations (0.3–1.0 mg/mL), fewer strong adsorption sites were observed, and surface residence times were reduced. This suggests that at high concentrations, adsorbed proteins block strong sites from further protein adsorption. Importantly, this demonstrates that strong binding sites can be modified by changing solution conditions. Membrane surfaces are intrinsically heterogeneous; by employing single-molecule techniques, we have provided a new framework for understanding protein interactions with such surfaces

Power, potential, and pitfalls in global health academic partnerships: review and reflections on an approach in Nepal.

BackgroundGlobal health academic partnerships are centered around a core tension: they often mirror or reproduce the very cross-national inequities they seek to alleviate. On the one hand, they risk worsening power dynamics that perpetuate health disparities; on the other, they form an essential response to the need for healthcare resources to reach marginalized populations across the globe.ObjectivesThis study characterizes the broader landscape of global health academic partnerships, including challenges to developing ethical, equitable, and sustainable models. It then lays out guiding principles of the specific partnership approach, and considers how lessons learned might be applied in other resource-limited settings.MethodsThe experience of a partnership between the Ministry of Health in Nepal, the non-profit healthcare provider Possible, and the Health Equity Action and Leadership Initiative at the University of California, San Francisco School of Medicine was reviewed. The quality and effectiveness of the partnership was assessed using the Tropical Health and Education Trust Principles of Partnership framework.ResultsVarious strategies can be taken by partnerships to better align the perspectives of patients and public sector providers with those of expatriate physicians. Actions can also be taken to bring greater equity to the wealth and power gaps inherent within global health academic partnerships.ConclusionsThis study provides recommendations gleaned from the analysis, with an aim towards both future refinement of the partnership and broader applications of its lessons and principles. It specifically highlights the importance of targeted engagements with academic medical centers and the need for efficient organizational work-flow practices. It considers how to both prioritize national and host institution goals, and meet the career development needs of global health clinicians

Power, potential, and pitfalls in global health academic partnerships: review and reflections on an approach in Nepal

ABSTRACT Background:: Global health academic partnerships are centered around a core tension: they often mirror or reproduce the very cross-national inequities they seek to alleviate. On the one hand, they risk worsening power dynamics that perpetuate health disparities; on the other, they form an essential response to the need for healthcare resources to reach marginalized populations across the globe. Objectives:: This study characterizes the broader landscape of global health academic partnerships, including challenges to developing ethical, equitable, and sustainable models. It then lays out guiding principles of the specific partnership approach, and considers how lessons learned might be applied in other resource-limited settings. Methods:: The experience of a partnership between the Ministry of Health in Nepal, the non-profit healthcare provider Possible, and the Health Equity Action and Leadership Initiative at the University of California, San Francisco School of Medicine was reviewed. The quality and effectiveness of the partnership was assessed using the Tropical Health and Education Trust Principles of Partnership framework. Results:: Various strategies can be taken by partnerships to better align the perspectives of patients and public sector providers with those of expatriate physicians. Actions can also be taken to bring greater equity to the wealth and power gaps inherent within global health academic partnerships. Conclusions:: This study provides recommendations gleaned from the analysis, with an aim towards both future refinement of the partnership and broader applications of its lessons and principles. It specifically highlights the importance of targeted engagements with academic medical centers and the need for efficient organizational work-flow practices. It considers how to both prioritize national and host institution goals, and meet the career development needs of global health clinicians