Probing driving forces for binding between nanoparticles and amino acids by saturation-transfer difference NMR

Numerical Study towards In Vivo Tracking of Micro-/Nanoplastic Based on X-ray Fluorescence Imaging

There is a rising awareness of the toxicity of micro- and nanoplastics (MNPs); however, fundamental precise information on MNP-biodistribution in organisms is currently not available. X-ray fluorescence imaging (XFI) is introduced as a promising imaging modality to elucidate the effective MNP bioavailability and is expected to enable exact measurements on the uptake over the physical barriers of the organism and bioaccumulation in different organs. This is possible because of the ability of XFI to perform quantitative studies with a high spatial resolution and the possibility to conduct longitudinal studies. The focus of this work is a numerical study on the detection limits for a selected XFI-marker, here, palladium, to facilitate the design of future preclinical in vivo studies. Based on Monte Carlo simulations using a 3D voxel mouse model, the palladium detection thresholds in different organs under in vivo conditions in a mouse are estimated. The minimal Pd-mass in the scanning position at a reasonable significance level is determined to be <20 ng/mm2 for abdominal organs and <16 μg/mm2 for the brain. MNPs labelled with Pd and homogeneously distributed in the organ would be detectable down to a concentration of <1 μg/mL to <2.5 mg/mL in vivo. Long-term studies with a chronic MNP exposure in low concentrations are therefore possible such that XFI measurements could, in the future, contribute to MNP health risk assessment in small animals and humans.

Protein Binding Leads to Reduced Stability and Solvated Disorder in the Polystyrene Nanoparticle Corona

Understanding the conformation of proteins in the nanoparticle corona has important implications in how organisms respond to nanoparticle-based drugs. These proteins coat the nanoparticle surface, and their properties will influence the nanoparticle's interaction with cell targets and the immune system. While some coronas are thought to be disordered, two key unanswered questions are the degree of disorder and solvent accessibility. Here, a model is developed for protein corona disorder in polystyrene nanoparticles of varying size. For two different proteins, it is found that binding affinity decreases as nanoparticle size increases. The stoichiometry of binding, along with changes in the hydrodynamic size, supports a highly solvated, disordered protein corona anchored at a small number of attachment sites. The scaling of the stoichiometry versus nanoparticle size is consistent with disordered polymer dimensions. Moreover, it is found that proteins are destabilized less in the presence of larger nanoparticles, and hydrophobic exposure decreases at lower curvatures. The observations hold for proteins on flat polystyrene surfaces, which have the lowest hydrophobic exposure. The model provides an explanation for previous observations of increased amyloid fibrillation rates in the presence of larger nanoparticles, and it may rationalize how cell receptors can recognize protein disorder in therapeutic nanoparticles.

Maximizing Aqueous Drug Encapsulation: Small Nanoparticles Formation Enabled by Glycopolymers Combining Glucose and Tyrosine

Highly potent heterocyclic drugs are frequently poorly water soluble, leading to limited or abandoned further drug development. Nanoparticle technology offers a powerful delivery approach by enhancing the solubility and bioavailability of hydrophobic therapeutics. However, the common usage of organic solvents causes unwanted toxicity and process complexity, therefore limiting the scale-up of nanomedicine technology for clinical translation. Here, we show that an organic-solvent-free methodology for hydrophobic drug encapsulation can be obtained using polymers based on glucose and tyrosine. An aqueous solution based on a tyrosine-containing glycopolymer is able to dissolve solid dasatinib directly without adding an organic solvent, resulting in the formation of very small nanoparticles of around 10 nm loaded with up to 16 wt % of drug. This polymer is observed to function as both a drug solubilizer and a nanocarrier at the same time, offering a simple route for the delivery of insoluble drugs.

Photocatalytic degradation of ciprofloxacin from water with waste polystyrene and TiO2 composites

Ciprofloxacin (CIP) is one of the widely used antibiotics with a broad antimicrobial spectrum in the fluoroquinolone type. Its concentration in water bodies has increased over the years due to its frequent use. Since ciprofloxacin in the aquatic ecosystem adversely affects human health as well as other organisms, it must be removed from wastewater. The aim of this study was to develop Polystyrene (PS) and Titanium dioxide (TiO2) composites that can be used as catalysts in CIP removal by photocatalytic process. Waste PS (obtained from disposable cutlery) was used in the synthesis of these composites. In this study, PS-TiO2 composites with different PS content (C20, C50, C80; the numbers in the names indicate the PS percentage in the composite by weight) were synthesized. This is important in terms of the use of one waste in the removal of another waste. This process was optimized using Box-Behnken design, one of the response surface method. Parameters such as the amount of polymer in the composite, pH and initial CIP concentration were studied and their effects on CIP removal were found. The validity and adequacy of the selected model were evaluated according to the relevant statistical data. These are R2 = 0.9751, adjusted R2 = 0.9565, the model's p-value <0.05 and the lack of fit-value 0.246. Optimum conditions for CIP removal were obtained when the C50 was used, with a pH value of 3 and an initial CIP concentration of 5 mg/L. In the process carried out under these conditions, the CIP removal was found to be 95.01 % at the end of 180 min. This value was predicted as 94.37 % in the model. According to these results, C50 composite synthesized with waste PS can be used effectively for CIP removal.

Protein Binding Leads to Reduced Stability and Solvated Disorder in the Polystyrene Nanoparticle Corona

Understanding the conformation of proteins in the nanoparticle corona has important implications in how organisms respond to nanoparticle-based drugs. These proteins coat the nanoparticle surface, and their properties will influence the nanoparticle's interaction with cell targets and the immune system. While some coronas are thought to be disordered, two key unanswered questions are the degree of disorder and solvent accessibility. Here, using a comprehensive thermodynamic approach, along with supporting spectroscopic experiments, we develop a model for protein corona disorder in polystyrene nanoparticles of varying size. For two different proteins, we find that binding affinity decreases as nanoparticle size increases. The stoichiometry of binding, along with changes in the hydrodynamic size, support a highly solvated, disordered protein corona anchored at a small number of enthalpically-driven attachment sites. The scaling of the stoichiometry vs. nanoparticle size is consistent disordered polymer dimensions. Moreover, we find that proteins are destabilized less severely in the presence of larger nanoparticles, and this is supported by measurements of hydrophobic exposure, which becomes less pronounced at lower curvatures. Our observations hold for flat polystyrene surfaces, which, when controlled for total surface area, have the lowest hydrophobic exposure of all systems. Our model provides an explanation for previous observations of increased amyloid fibrillation rates in the presence of larger nanoparticles, and it may rationalize how cell receptors can recognize protein disorder in therapeutic nanoparticles.

Entry of microparticles into giant lipid vesicles by optical tweezers

Entry of micro- or nanosized objects into cells or vesicles made of lipid membranes occurs in many processes such as entry of viruses into host cells, microplastics pollution, drug delivery, or biomedical imaging. Here we investigate the microparticle crossing of lipid membranes in giant unilamellar vesicles in the absence of strong binding interactions (e.g., streptavidin-biotin binding). In these conditions, we observe that organic and inorganic particles can always penetrate inside the vesicles provided an external piconewton force is applied and for relatively low membrane tensions. In the limit of vanishing adhesion, we identify the role of the membrane area reservoir and show that a force minimum exists when the particle size is comparable to the bendocapillary length.

Designing sequence-defined peptoids for fibrillar self-assembly and silicification

In the biological environment, mineral crystals exquisitely controlled by biomacromolecules often show intricate hierarchical structures and superior mechanical properties. Among these biominerals, spicules, hybrid silica/protein superstructures serving as skeletal elements in demosponges, represent an excellent example for motivating the synthesis of silica materials. Herein, by designing sequence-defined peptoids containing side chains with a strong binding to silica, we demonstrated that self-assembly of these peptoids into fiber structures enables the mimicking of both biocatalytic and templating functions of silicatein filaments for the formation of silica fibers at near-neutral pH and ambient temperature. We further showed that the presence of amino groups is significant for the nucleation of silica on self-assembled peptoid nanofibers. Molecular dynamics simulation further confirmed that having silica-binding of amino side chains is critical for self-assembled peptoid fibers in triggering silica formation. We demonstrated that tuning inter-peptoid interactions by varying carboxyl and amino side chains significantly influences the assembly kinetics and final morphologies of peptoid assemblies as scaffolds for directing silica mineralization to form silica spheres, fibers, and sheets. The formation of silica shell on peptoid fibers increased the mechanical property of peptoid hydrogel materials by nearly 1000-fold, highlighting the great potential of using silicification to enhance the mechanical property of hydrogel materials for applications including tissue engineering. Since peptoids are highly robust and programmable, we expect that self-assembly of peptoids containing solid-binding side chains into hierarchical materials opens new opportunities in the design and synthesis of highly tunable scaffolds that direct the formation of composite nanomaterials.

Binding Between Antibiotics and Polystyrene Nanoparticles Examined by NMR

Elucidating the interactions between plastic nanoparticles and small molecules is important to understanding these interactions as they occur in polluted waterways. For example, plastic that breaks down into micro- and nanoscale particles will interact with small molecule pollutants that are also present in contaminated waters. Other components of natural water, such as dissolved organic matter, will also influence these interactions. Here we use a collection of complementary NMR techniques to examine the binding between polystyrene nanoparticles and three common antibiotics, belonging to a class of molecules that are expected to be common in polluted water. Through examination of proton NMR signal intensity, relaxation times, saturation-transfer difference (STD) NMR, and competition STD-NMR, we find that the antibiotics have binding strengths in the order amoxicillin < metronidazole ≪ levofloxacin. Levofloxacin is able to compete for binding sites, preventing the other two antibiotics from binding. The presence of tannic acid disrupts the binding between levofloxacin and the polystyrene nanoparticles, but does not influence the binding between metronidazole and these nanoparticles.

Solution NMR methods for structural and thermodynamic investigation of nanoparticle adsorption equilibria

Characterization of dynamic processes occurring at the nanoparticle (NP) surface is crucial for developing new and more efficient NP catalysts and materials. Thus, a vast amount of research has been dedicated to developing techniques to characterize sorption equilibria. Over recent years, solution NMR spectroscopy has emerged as a preferred tool for investigating ligand-NP interactions. Indeed, due to its ability to probe exchange dynamics over a wide range of timescales with atomic resolution, solution NMR can provide structural, kinetic, and thermodynamic information on sorption equilibria involving multiple adsorbed species and intermediate states. In this contribution, we review solution NMR methods for characterizing ligand-NP interactions, and provide examples of practical applications using these methods as standalone techniques. In addition, we illustrate how the integrated analysis of several NMR datasets was employed to elucidate the role played by support-substrate interactions in mediating the phenol hydrogenation reaction catalyzed by ceria-supported Pd nanoparticles.

Dual Fluorescence and NMR Study for the Interaction between Xanthene Dyes and Nanoparticles

Fluorescent dyes and nanoparticles (NPs) have been widely used together to make novel biosensors, taking advantage of their unique characteristics. It is crucial to have techniques that enable us to gain detailed and high-resolution information regarding the interaction between NPs and fluorescent dyes. In this work, we chose rhodamine B (RhB) and amidine- and carboxylate-modified polystyrene (CML) NPs as models and employed both NMR (¹H and STD-NMR) and optical (UV-vis and fluorescence) techniques to investigate the interaction between NPs and fluorescent dyes. From UV-vis and fluorescence spectroscopy, we see that there are larger red shifts when rhodamine B binds to carboxylate-modified polystyrene NPs than amidine-modified NPs. Correspondingly, RhB has broader NMR peaks and a larger STD effect when binding to CML NPs than amidine NPs. Results from these two techniques validate each other. It is notable that the NMR techniques provide more reliable data than UV-vis and fluorescence methods. Moreover, we show that NMR techniques, especially STD-NMR, can provide more atomic-level binding geometry information. The higher STD effect of the smaller aromatic ring of RhB implies that this aromatic ring is closer to the surface of NPs when binding to polystyrene NPs.