Metal Ion-Induced Unusual Stability of the Metastable Vesicle-like Intermediates Evolving during the Self-Assembly of Phenylalanine: Prominent Role of Surface Charge Inversion

The underlying mechanism and intermediate formation in the self-assembly of aromatic amino acids, peptides, and proteins remain elusive despite numerous reports. We, for the first time, report that one can stabilize the intermediates by tuning the metal ion-amino acid interaction. Microscopic and spectroscopic investigations of the self-assembly of carboxybenzyl (Z)-protected phenylalanine (ZF) reveal that the bivalent metal ions eventually lead to the formation of fibrillar networks similar to blank ZF whereas the trivalent ions develop vesicle-like intermediates that do not undergo fibrillation for a prolonged time. The time-lapse measurement of surface charge reveals that the surface charge of blank ZF and in the presence of bivalent metal ions changes from a negative value to zero, implying unstable intermediates leading to the fibril network. Strikingly, a prominent charge inversion from an initial negative value to a positive value in the presence of trivalent metal ions imparts unusual stability to the metastable intermediates.

Protein-based bioactive coatings: from nanoarchitectonics to applications

Protein-based bioactive coatings have emerged as a versatile and promising strategy for enhancing the performance and biocompatibility of diverse biomedical materials and devices. Through surface modification, these coatings confer novel biofunctional attributes, rendering the material highly bioactive. Their widespread adoption across various domains in recent years underscores their importance. This review systematically elucidates the behavior of protein-based bioactive coatings in organisms and expounds on their underlying mechanisms. Furthermore, it highlights notable advancements in artificial synthesis methodologies and their functional applications in vitro. A focal point is the delineation of assembly strategies employed in crafting protein-based bioactive coatings, which provides a guide for their expansion and sustained implementation. Finally, the current trends, challenges, and future directions of protein-based bioactive coatings are discussed.

Effect of lead ions on biochemical behavior of Cladophora glomerata in sterilized and non-sterilized media

Freshwater ecosystems are under peril globally due to anthropogenic influences, most notably metals. The present study aimed to evaluate the morphological and biochemical responses of Cladophora glomerata obtained from a freshwater stream to various lead concentrations (0.0, 7.5, 15, 30, and 60 mg/L Pb2+) in sterilized and non-sterilized media. Pigments, proline, malondialdehyde (MDA), total phenolic compounds (TPC), hydrogen peroxide, and protein content of the green alga were determined in response to various growing conditions. Pb2+ stress had a detrimental effect not only on biochemical components of C. glomerata but also on the algal cell's shape and surface structure. High Pb2+ concentrations significantly decreased chlorophyll-a (from 1350 μg/g in non-sterilized and 1340 μg/g in sterilized media for the control group to 1067 μg/g in non-sterilized and 1049 μg/g in sterile media at 60 mg/L Pb2+) and protein contents (from 34.47 mg/g for the sterilized and 35.89 mg/g for non-sterilized of the control to 24.82 mg/g for the sterilized and 26.18 mg/g for the non-sterilized at 60 mg/L Pb2+) of algal biomass but increased the concentrations of stress compounds (e.g., MDA, proline, and TPC). Variation in the macroalgal biomass composition was also indicated by FTIR analysis based on interactions between amino, amide, and anionic surface groups on the algal biomass and Pb2+ ions. Morphological and biochemical responses of C. glomerata reveal that non-sterile conditions encouraged the proliferation of this macroalga under Pb2+ exposure.

The Multifaceted Roles of Bovine Lactoferrin: Molecular Structure, Isolation Methods, Analytical Characteristics, and Biological Properties

Bovine lactoferrin (bLF) is widely known as an iron-binding glycoprotein from the transferrin family. The bLF molecule exhibits a broad spectrum of biological activity, including iron delivery, antimicrobial, antiviral, immunomodulatory, antioxidant, antitumor, and prebiotic functions, thereby making it one of the most valuable representatives for biomedical applications. Remarkably, LF functionality might completely differ in dependence on the iron saturation state and glycosylation patterns. Recently, a violently growing demand for bLF production has been observed, mostly for infant formulas, dietary supplements, and functional food formulations. Unfortunately, one of the reasons that inhibit the development of the bLF market and widespread protein implementation is related to its negligible amount in both major sources─colostrum and mature milk. This study provides a comprehensive overview of the significance of bLF research by delineating the key structural characteristics of the protein and elucidating their impact on its physicochemical and biological properties. Progress in the development of optimal isolation techniques for bLF is critically assessed, alongside the challenges that arise during its production. Furthermore, this paper presents a curated list of the most relevant instrumental techniques for the characterization of bLF. Lastly, it discusses the prospective applications and future directions for bLF-based formulations, highlighting their potential in various fields.

The role of available nitrogen in the adsorption of polystyrene nanoplastics on magnetic materials

Several studies have been conducted on nanoplastics (NPs). However, few studies have investigated the complexity of the interactions between NPs and other aqueous pollutants in multi-solute media. In this study, the adsorption of polystyrene nanoplastics (PSNPs) on magnetic materials (MS) in the presence of available nitrogen (AN) was studied. The results demonstrated that the adsorbed amount of PSNPs increased in the presence of ammonium nitrogen (NH₄⁺-N), whereas no significant difference was detected on the adsorbed amount of PSNPs using nitrate nitrogen (NO₃^--N) as a cosolute. The increase in the adsorbed amount of PSNPs was attributed to the formation of an MS-PSNPs-NH₄⁺-N complex. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and zeta potential analyses indicated that the PSNPs with NH₄⁺-N as a cosolute can be bound on the MS surfaces. Moreover, the change in the PSNPs amount adsorbed by MS depends on the valence state, electronegativity of the coexisting ions, and the surface properties and functional groups of PSNPs. Additionally, the ionic strength, dissolved organic matter, solution pH, metal cations and the subsequent release of MS-coated PSNPs and NH₄⁺-N changed considerably in different aquatic systems and artificial nitrating fluids. Among different natural aquatic systems, the PSNPs adsorption on MS was excellent in lake water. The results indicate high potential for the attachment of PSNPs to MS in the presence of AN and further deepen the understanding of removing NPs using magnetic materials in aqueous systems with various coexisting contaminants.

Adsorption of Cd2+ onto apatite surface: Equilibrium, kinetics and thermodynamic studies

This study examined the application of chemically synthesized apatite (CHAp) powder as a potential adsorbent for the elimination of Cd²⁺ in aqueous medium. The synthesized hydroxyapatite (HAp) powder before and after adsorption was elucidated by XRD, EDX, FT-IR, SEM, and TEM analytical techniques. The role of time, initial Cd²⁺ concentration, amount of CHAp used, temperature and solution pH on the adsorption process were investigated. Data from the adsorption process were subjected to Dubinin-Radushkevich, Langmuir, Freundlich, and Tempkin adsorption isotherms, while pseudo-first-order, pseudo-second-order, Elovich and intraparticle diffusion kinetic models were used for the kinetics investigation. Results from XRD confirmed that chief characteristic peaks of HAp powder were detected, while functional groups such as PO₄ ^3-, CO₃ ^2- and OH^- matching pure HAp were displayed in the FT-IR spectra. Round shape morphology of the CHAp was confirmed by SEM and TEM analyses. Langmuir isotherm best described the adsorption process with ceiling adsorption capacity of 195.711 mg/g, whereas, the adsorption mechanism obeys the pseudo-first-order model which suggests a physical adsorption process. The value of entropy change (ΔS) of the adsorption of Cd²⁺ onto CHAp surface was obtained to be 0.610 kJ/mol, while the value of enthalpy change obtained was 175.591 kJ/mol. Results from free energy change obtained adjudged the adsorption process to be spontaneous and endothermic in character. Thus, the chemically synthesized HAp could be an excellent adsorbent for the elimination of Cd²⁺ in bioremediation applications.

A Pragmatic Perspective of the Initial Stages of the Contact Killing of Bacteria on Copper-Containing Surfaces

A consideration of the outer structures of Gram-positive and Gram-negative bacteria, and of the surface contaminants present on Cu-containing substrates, has led to the identification of Cu2O as a potent antimicrobial. In the presence of adsorbed water, the hydrated form ionizes to CuI-O−, which is capable of degrading the protective polysaccharide layer of the outer lipopolysaccharide membranes of Gram-negative bacteria; it is equally capable of attacking the peptidoglycan lattices present in both Gram-positive and Gram-negative bacteria. This Perspective underlines the importance of CuI-O− in the early stages of contact killing, and points to information, still lacking, that would optimize contact killing and lead to broader applications in the therapeutic management of bacterial infections.

Comment on "High-Resolution Microscopical Studies of Contact Killing Mechanisms on Copper-Based Surfaces"

In the original paper, Chang and co-workers describe the contact killing of Bacillus subtilis, a Gram-positive bacterium, on copper-containing substrates and offer a mechanism for its accomplishment. The present Comment offers support for that mechanism and adds a necessary initial step, the degradation of the overlying peptidoglycan lattice. Degradation is necessary because the lattice is too thick, and its pores too small, for substrate-membrane contact without it. A suggestion is offered as to how degradation is accomplished.

La3+ and Y3+ interactions with the carboxylic acid moiety at the liquid/vapor interface: Identification of binding complexes, charge reversal, and detection limits

Specific interactions of yttrium and lanthanum ions with a fatty acid Langmuir monolayer were investigated using vibrational sum frequency spectroscopy. The trivalent ions were shown to interact with the charged form of the carboxylic acid group from nanomolar concentrations (<300 nM). Analysis of the spectral features from both the symmetric and the asymmetric carboxylate modes reveals the presence of at least three distinct coordination structures linked to specific binding configurations. Although the same species were identified for both La³⁺ and Y³⁺, they display a different concentration dependence, highlighting the ion-specificity of the interaction. From the analysis of the response of interfacial water molecules, the reversal of the surface charge, as well as the formation of yttrium hydroxide complexes, were detected upon increasing the amount of salt in solution. The binding interaction and kinetics of absorption are sensitive to the solution pH, showing a distinct ion speciation in the interfacial region when compared to the bulk. Changing the subphase pH or adding a monovalent background electrolyte that promotes deprotonation of the carboxylic acid headgroup could further improve the detection limit of La³⁺ and Y³⁺ to concentrations < 100 nM. These findings demonstrate that nM concentrations of trace metals contaminants, typically found on monovalent salts, can significantly influence the binding structure and kinetics in Langmuir monolayers.

A Pragmatic Perspective of the Antibacterial Properties of Metal-Based Nanoparticles

A consideration of the antibacterial efficacy of metal-based nanoparticles, from the point of view of their physicochemical properties, suggests that such efficacy arises from the protein coronas that form around them, and that the contents of the coronas depend on the chemical groups found on the nanoparticle surfaces. We offer a new perspective and new insights, making use of our earlier observations of the physicochemical properties of nanoparticle surfaces, to propose that the nanoparticle serves as a mediator for the formation and activation of the protein corona, which attacks the bacterium. That is, the nanoparticle enhances the body’s natural defenses, using proteins present in body fluids.

The crucial role of heavy metals on the interaction of engineered nanoparticles with polystyrene microplastics

Despite continuous research on microplastics (MPs), studies exploring the complexity of interaction between MPs and other aqueous constituents in multi-solute systems are scarce. In this study, the uptake and release of nanoceria (CeNPs) by various polystyrene MPs (PSMPs) were investigated. Results showed that PSMPs in the presence of heavy metals (HMs) exhibited a substantially higher sorption affinity for isotropic charged CeNPs than PSMPs alone; this enhanced affinity was attributed to the formation of PSMP-HM-CeNP complexes. FE-SEM imaging reaffirmed that CeNP clusters adhered to PSMP surfaces in the presence of HMs. Such attachment varied dependent on valence state, atomic size of coexisting metal cations, surface texture, and functionalities of MPs. The HM-mediated complex formation on PSMP particles was suppressed at higher ionic strength because of competitive sorption and double-layer compression. Subsequent release of MP-adhered CeNPs and HMs varied significantly between aquatic media and various simulated digestive fluids, verifying the crucial role of MPs for transfer of engineered nanoparticles (ENPs) from natural environments into biota via ingestion of MPs and trophic transfer. Our results highlight the enhanced potential for MPs to accumulate and to transport ENPs when metallic contaminants are present, which adds to the current understanding of the environmental fate and adverse effects of MPs along with various waterborne contaminants in actual environments.

Biomacromolecular-Assembled Nanoclusters: Key Aspects for Robust Colloidal SERS Sensing

Superstructures of gold nanospheres offer augmented surface-enhanced Raman scattering (SERS) activities beyond the limits of their individual building blocks. However, for application as reliable and quantitative colloidal SERS probes, some key aspects need to be considered to combine efficiency and robustness with respect to hotspot excitation, analyte adsorption, signal stability, and colloidal stability. For this purpose, we studied core/satellite superstructures with spherical cores as a simple optically isotropic model system. Superstructures of different core sizes were assembled using bovine serum albumin (BSA), which serves as a non-specific biomacromolecular linker and provides electrosteric stabilization. We show that the "noisy" spectral footprint of the protein coating may serve as an internal standard, which allows accurate monitoring of the adsorption kinetics of analytes. The SERS activity was quantified using 4-mercaptobenzoic acid (MBA) as an aromatic low-molecular-weight model analyte. The molar SERS efficiency was studied by variation of the particle (Au⁰) and analyte concentrations with a limit of detection of 10^-7 M MBA. The practical importance of colloidal stability for robust measurement conditions was demonstrated by comparing the superstructures with their citrate-stabilized or protein-coated building blocks. We explain the theoretical background of hotspot formation by a leader/follower relationship of asymmetric control between the core and the satellites and give practical guidelines for robust colloidal SERS sensing probes.

Easy colorimetric detection of gadolinium ions based on gold nanoparticles: key role of phosphine-sulfonate ligands

The possibility to easily and rapidly assess the presence of Gd3+ ions in solution is of paramount importance in many domains like magnetic resonance imaging. In that context, the use of easy to implement colorimetric sensing probes based on gold nanoparticles (AuNPs) is of special interest. Herein, AuNPs functionalized with a commercial bis(p-sulfonatophenyl)phenyl phosphine ligand (BSPP) (AuNP@BSPP), bearing negatively charged sulfonate groups are used as a colorimetric sensing probe. The addition of Gd3+ ions onto these NPs was studied through UV-visible absorbance measurements, Quartz Crystal Microbalance with Dissipation monitoring (QCM-D) and transmission electron microscopy and compared with citrate covered AuNPs. We evidenced interactions between the Gd3+ ions and their water rich coordination sphere and sulfonate groups on the surface of AuNP@BSPP via electrostatic interactions and hydrogen bonding. These interactions induce the reversible aggregation of AuNP@BSPP in the presence of concentrations of Gd3+ ions at a μM level. We took advantage of this phenomenon to develop a simple and fast bench colorimetric assay for the detection of free Gd3+ ions, based on the determination of a flocculation parameter thanks to UV-visible measurements. Limits of detection and quantification were found equal to 0.74 μM and 4.76 μM of Gd3+ ions, respectively, with a high sensitivity that competes with conventional methods used for lanthanide detection.

Multivalent ions and biomolecules: Attempting a comprehensive perspective

Ions are ubiquitous in nature. They play a key role for many biological processes on the molecular scale, from molecular interactions, to mechanical properties, to folding, to self-organisation and assembly, to reaction equilibria, to signalling, to energy and material transport, to recognition etc. Going beyond monovalent ions to multivalent ions, the effects of the ions are frequently not only stronger (due to the obviously higher charge), but qualitatively different. A typical example is the process of binding of multivalent ions, such as Ca2+ , to a macromolecule and the consequences of this ion binding such as compaction, collapse, potential charge inversion and precipitation of the macromolecule. Here we review these effects and phenomena induced by multivalent ions for biological (macro)molecules, from the "atomistic/molecular" local picture of (potentially specific) interactions to the more global picture of phase behaviour including, e. g., crystallisation, phase separation, oligomerisation etc. Rather than attempting an encyclopedic list of systems, we rather aim for an embracing discussion using typical case studies. We try to cover predominantly three main classes: proteins, nucleic acids, and amphiphilic molecules including interface effects. We do not cover in detail, but make some comparisons to, ion channels, colloidal systems, and synthetic polymers. While there are obvious differences in the behaviour of, and the relevance of multivalent ions for, the three main classes of systems, we also point out analogies. Our attempt of a comprehensive discussion is guided by the idea that there are not only important differences and specific phenomena with regard to the effects of multivalent ions on the main systems, but also important similarities. We hope to bridge physico-chemical mechanisms, concepts of soft matter, and biological observations and connect the different communities further.