Specific buffer effects on the formation of BSA protein corona around amino-functionalized mesoporous silica nanoparticles

The effect of buffer species on biomolecules and biomolecule-nanoparticle interactions is a phenomenon that has been either neglected, or not understood. Here, we study the formation of a BSA protein corona (PC) around amino-functionalized mesoporous silica nanoparticles (MSN-NH2) in the presence of different buffers (Tris, BES, cacodylate, phosphate, and citrate) at the same pH (7.15) and different concentrations (10, 50, and 100 mM). We find that BSA adsorption is buffer specific, with the adsorbed amount of BSA being 4.4 times higher in the presence of 100 mM Tris (184 ± 3 mg/g) than for 100 mM citrate (42 ± 2 mg/g). That is a considerable difference that cannot be explained by conventional theories. The results become clearer if the interaction energies between BSA and MSN-NH2, considering the electric double layer (EEDL) and the van der Waals (EvdW) terms, are evaluated. The buffer specific PC derives from buffer specific zeta potentials that, for MSN-NH2, are positive with Tris and negative with citrate buffers. A reversed sign of zeta potentials can be obtained by considering polarizability-dependent dispersion forces acting together with electrostatics to give the buffer specific outcome. These results are relevant not only to our understanding of the formation of the PC but may also apply to other bio- and nanosystems in biological media.

Understanding the Phase Behavior of a Multistimuli-Responsive Elastin-like Polymer: Insights from Dynamic Light Scattering Analysis

Elastin-like polymers are a class of stimuli-responsive protein polymers that hold immense promise in applications such as drug delivery, hydrogels, and biosensors. Yet, understanding the intricate interplay of factors influencing their stimuli-responsive behavior remains a challenging frontier. Using temperature-controlled dynamic light scattering and zeta potential measurements, we investigate the interactions between buffer, pH, salt, water, and protein using an elastin-like polymer containing ionizable lysine residues. We observed the elevation of transition temperature in the presence of the common buffering agent HEPES at low concentrations, suggesting a "salting-in" effect of HEPES as a cosolute through weak association with the protein. Our findings motivate a more comprehensive investigation of the influence of buffer and other cosolute molecules on elastin-like polymer behavior.

Anion Binding to Ammonium and Guanidinium Hosts: Implications for the Reverse Hofmeister Effects Induced by Lysine and Arginine Residues

Anions have a profound effect on the properties of soluble proteins. Such Hofmeister effects have implications in biologics stability, protein aggregation, amyloidogenesis, and crystallization. However, the interplay between the important noncovalent interactions (NCIs) responsible for Hofmeister effects is poorly understood. To contribute to improving this state of affairs, we report on the NCIs between anions and ammonium and guanidinium hosts 1 and 2, and the consequences of these. Specifically, we investigate the properties of cavitands designed to mimic two prime residues for anion-protein NCIs─lysines and arginines─and the solubility consequences of complex formation. Thus, we report NMR and ITC affinity studies, X-ray analysis, MD simulations, and anion-induced critical precipitation concentrations. Our findings emphasize the multitude of NCIs that guanidiniums can form and how this repertoire qualitatively surpasses that of ammoniums. Additionally, our studies demonstrate the ease by which anions can dispense with a fraction of their hydration-shell waters, rearrange those that remain, and form direct NCIs with the hosts. This raises many questions concerning how solvent shell plasticity varies as a function of anion, how the energetics of this impact the different NCIs between anions and ammoniums/guanidiniums, and how this affects the aggregation of solutes at high anion concentrations.

Cation Adsorption in TiO2 Nanotubes: Implication for Water Decontamination

TiO2 nanotubes constitute very promising nanomaterials for water decontamination by the removal of cations. We combined a range of experimental techniques from structural analyses to measurements of the properties of aqueous suspensions of nanotubes, with (i) continuous solvent modeling and (ii) quantum DFT-based simulations to assess the adsorption of Cs+ on TiO2 nanotubes and to predict the separation of metal ions. The methodology is set to be operable under realistic conditions, which, in this case, include the presence of CO2 that needs to be treated as a substantial contaminant, both in experiments and in models. The mesoscopic model, based on the Poisson-Boltzmann equation and surface adsorption equilibrium, predicts that H+ ions are the charge-determining species, while Cs+ ions are in the diffuse layer of the outer surface with a significant contribution only at high concentrations and high pH. The effect of the size of nanotubes in terms of the polydispersity and the distribution of the inner and outer radii is shown to be a third-order effect that is very small when the nanotube layer is not very thick (ranging from 1 to 2 nm). Besides, DFT-based molecular dynamics simulations demonstrate that, for protonation, the one-site and successive association assumption is correct, while, for Cs+ adsorption, the size of the cation is important and the adsorption sites should be carefully defined.

Cation and buffer specific effects on the DNA-lipid interaction

Knowledge of DNA - lipid layer interactions is key for the development of biosensors, synthetic nanopores, scaffolds, and gene-delivery systems. These interactions are strongly affected by the ionic composition of the solvent. We have combined quartz crystal microbalance (QCM) and ellipsometry measurements to reveal how pH, buffers and alkali metal chloride salts affect the interaction of DNA with lipid bilayers (DOTAP/DOPC 30:70 in moles). We found that the thickness of the DNA layer adsorbed onto the lipid bilayer decreased in the order citrate > phosphate > Tris > HEPES. The effect of cations on the thickness of the DNA layer decreased in the order (K⁺ > Na⁺ > Cs⁺ ∼ Li⁺). Rationalization of the experimental results requires that adsorption, due to cation specific charge screening, is driven by the simultaneous action of two mechanisms namely, the law of matching water affinities for kosmotropes (Li⁺) and ion dispersion forces for chaotropes (Cs⁺). The outcome of these two opposing mechanisms is a ^"bell-shaped" specific cations sequence. Moreover, a superimposed buffer specificity, which goes beyond the simple effect of pH regulation, further modulated cation specificity. In summary, DNA-lipid bilayer interactions are maximized if citrate buffer (50 mM, pH 7.4) and KCl (100 mM) are used.

Perspectives on weak interactions in complex materials at different length scales

Nanocomposite materials consist of nanometer-sized quantum objects such as atoms, molecules, voids or nanoparticles embedded in a host material. These quantum objects can be exploited as a super-structure, which can be designed to create material properties targeted for specific applications. For electromagnetism, such targeted properties include field enhancements around the bandgap of a semiconductor used for solar cells, directional decay in topological insulators, high kinetic inductance in superconducting circuits, and many more. Despite very different application areas, all of these properties are united by the common aim of exploiting collective interaction effects between quantum objects. The literature on the topic spreads over very many different disciplines and scientific communities. In this review, we present a cross-disciplinary overview of different approaches for the creation, analysis and theoretical description of nanocomposites with applications related to electromagnetic properties.