Specific Electrostatic Interactions Research Articles

C9orf72 polyPR interaction with the nuclear pore complex

The C9orf72 gene associated with amyotrophic lateral sclerosis/frontotemporal dementia is translated to five dipeptide repeat proteins, among which poly-proline-arginine (PR) is the most toxic in cell and animal models, contributing to a variety of cellular defects. It has been proposed that polyPR disrupts nucleocytoplasmic transport (NCT) through several mechanisms including accumulation in the nuclear pore complex (NPC), accumulation in the nucleolus, and direct interactions with transport receptors. The NPC, which is the key regulator of transport between the cytoplasm and nucleus, plays a central role in these suggested mechanisms. Exploring polyPR interaction with the NPC provides valuable insight into the molecular details of polyPR-mediated NCT defects. To address this, we use coarse-grained molecular dynamics models of polyPR and the yeast NPC lined with intrinsically disordered FG-nucleoporins (FG-Nups). Our findings indicate no aggregation of polyPR within the NPC or permanent binding to FG-Nups. Instead, polyPR translocates through the NPC, following a trajectory through the central low-density region of the pore. In the case of longer polyPRs, we observe a higher energy barrier for translocation and a narrower translocation channel. Our study shows that polyPR and FG-Nups are mainly engaged in steric interactions inside the NPC with only a small contribution of specific cation-pi, hydrophobic, and electrostatic interactions, allowing polyPR to overcome the entropic barrier of the NPC in a size-dependent manner.

Deciphering protein-mediated underwater adhesion in an invasive biofouling ascidian: Discovery, validation, and functional mechanism of an interfacial protein

Discovering macromolecules and understanding the associated mechanisms involved in underwater adhesion are essential for both studying the fundamental ecology of benthos in aquatic ecosystems and developing biomimetic adhesive materials in industries. Here, we employed quantitative proteomics to assess protein expression variations during the development of the distinct adhesive structure - stolon in the model fouling ascidian, Ciona robusta. We found 16 adhesive protein candidates with increased expression in the stolon, with ascidian adhesive protein 1 (AAP1) being particularly rich in adhesion-related signal peptides, amino acids, and functional domains. Western blot and immunolocalization analyses confirmed the prominent AAP1 signals in the mantle, tunic, stolon, and adhesive footprints, indicating the interfacial role of this protein. Surface coating and atomic force microscopy experiments verified AAP1′s adhesion to diverse materials, likely through the specific electrostatic and hydrophobic amino acid interactions with various substrates. In addition, molecular docking calculations indicated the AAP1′s potential for cross-linking via hydrogen bonds and salt bridges among Von Willebrand factor type A domains, enhancing its adhesion capability. Altogether, the newly discovered interfacial protein responsible for permanent underwater adhesion, along with the elucidated adhesion mechanisms, are expected to contribute to the development of biomimetic adhesive materials and anti-fouling strategies. Statement of SignificanceDiscovering macromolecules and studying their associated mechanisms involved in underwater adhesion are essential for understanding the fundamental ecology of benthos in aquatic ecosystems and developing innovative bionic adhesive materials in various industries. Using multidisciplinary analytical methods, we identified an interfacial protein - Ascidian Adhesive Protein 1 (AAP1) from the model marine fouling ascidian, Ciona robusta. The interfacial functions of AAP1 are achieved by electrostatic and hydrophobic interactions, and the Von Willebrand factor type A domain-based cross-linking likely enhances AAP1’s interfacial adhesion. The identification and validation of the interfacial functions of AAP1, combined with the elucidation of adhesion mechanisms, present a promising target for the development of biomimetic adhesive materials and the formulation of effective anti-fouling strategies.

Spectroscopic and in silico characterization of the interaction between synthetic 2-substituted-naphtho-1,4-quinones and human serum albumin

The intermolecular interaction between 2-(N-phenyl-N-methyl)aminonaphtho-1,4-quinone (1) and 2-(4-N-methylaminophenyl)naphtho-1,4-quinone (2) and human serum albumin (HSA) was investigated using spectroscopic techniques combined with in silico calculations via molecular docking. Steady-state titration of HSA fluorescence by 1 and 2 (λexc 295 nm) in PBS at 305, 310, and 315 K, as well as studies employing time-resolved fluorescence emission, demonstrated that the HSA:1 and HSA:2 interaction occurs through a static quenching mechanism. The Stern-Volmer constant (Ksv) values, (1.56 ± 0.08) and (3.05 ± 0.10) × 104 L/mol at 310 K for HSA:1 and HSA:2, respectively, indicate a moderate binding affinity. Van't Hoff plots showed that HSA:1 and HSA:2 interactions are spontaneous (negative ΔGo) with a hydrophobic character (ΔSo value of 0.00707 ± 0.00106 and 0.0392 ± 0.0062 kJ/mol K for HSA:1 and HSA:2, respectively) and specific electrostatic interactions (ΔHo value of –22.7 ± 3.3 and −14.4 ± 1.9 kJ/mol for HSA:1 and HSA:2, respectively). Synchronous fluorescence results showed significant perturbation in the microenvironment of the tryptophan residue (Trp-214). Circular dichroism indicated that after interaction with naphthoquinones 1 and 2, the HSA structure remains predominantly in the α-helix form. Finally, molecular docking revealed the formation of hydrophobic, electrostatic, and hydrogen bond interactions with the surrounding amino acid residues in subdomain IIA of HSA, which contains the Trp-214 residue, validated with the experimental drug-displacement assays. Overall, spectroscopic and in silico characterization of HSA:1 and HSA:2 might reflect in a low half-life in the human bloodstream, indicating the necessity of methods to improve the bioavailability, e.g., studies on the type of administration (oral versus intravenous).

Structural characterization and binding interaction of rice glutelin fibrils complexing with curcumin

The rice glutelin (RG), the separated retentate (RGFs) and filtrate (FGFs) fractions from total glutelin fibrils (TGFs) at pH 3.5 were used as carrier for curcumin in this test. The solubility and antioxidant activities of curcumin were improved after binding with protein and fibrils. Compared to other complexes, the RGFs-curcumin complex exhibited a highest curcumin solubility (48.05%) and a superior sustained release property, probably owing to the stable hydrogen bond between the surface groups of fibrils and hydroxyl groups of polyphenols. In addition, thermodynamic parameters revealed that the RG/TGFs/RGFs-curcumin complexes were stabilized by hydrogen bonds and van der Waals forces, whereas FGFs interacted with curcumin through specific electrostatic interaction. Besides, after interacting with curcumin, the fibrils gathered into coarsened and agglutinated fibrillar aggregates, relating to the increment of a-helix and β-sheet structure. These results suggested that RGFs could be a good alternative for curcumin delivery in food industry.

Impact of specific ion effects and electrostatic interactions on a polyelectrolyte-polyampholyte complex

A complex overlay of interactions governs the conformations of polymers in solution. Among them, electrostatic interactions are the dominating factor for governing the dynamics of charged macromolecules. Salt ions further impact the conformations by inducing screening of the electrostatic interactions of the polymers. Polyelectrolytes and polyampholytes are two majorly used charged polymers for engineering hydrogels. These polymers form a complex when added together in a solution. This article emphasises the effect of salts on the polyelectrolyte-polyampholyte complex. The interactions have been analysed through the viscosity and diffusivity measurements. The in-depth analysis of the specific ion effect along with the viscous effect induced by the polymer has been carried out. It was concluded that the viscous effect tends to reverse the impact of salts on the electrostatic-dominated conformations of the polymers. The ‘Shear Dependent Generalised Intrinsic Viscosity’ (SDGIV) have been used to gain insights into the interactions between the polymers. Finally, the scaling of the viscosity with respect to the polymer concentration and the impact of the salts on the same has also been studied. It is concluded that the viscous effect of the polymers should also be considered for analysing the specific ion effects of the salts on the charged polymers.Graphical

Structural basis for the phase separation of the chromosome passenger complex.

The physical basis of phase separation is thought to consist of the same types of bonds that specify conventional macromolecular interactions yet is unsatisfyingly often referred to as 'fuzzy'. Gaining clarity on the biogenesis of membraneless cellular compartments is one of the most demanding challenges in biology. Here, we focus on the chromosome passenger complex (CPC), that forms a chromatin body that regulates chromosome segregation in mitosis. Within the three regulatory subunits of the CPC implicated in phase separation - a heterotrimer of INCENP, Survivin, and Borealin - we identify the contact regions formed upon droplet formation using hydrogen/deuterium exchange mass spectrometry (HXMS). These contact regions correspond to some of the interfaces seen between individual heterotrimers within the crystal lattice they form. A major contribution comes from specific electrostatic interactions that can be broken and reversed through initial and compensatory mutagenesis, respectively. Our findings reveal structural insight for interactions driving liquid-liquid demixing of the CPC. Moreover, we establish HXMS as an approach to define the structural basis for phase separation.

Electrostatically Mediated Attractive Self-Interactions and Reversible Self-Association of Fc-Fusion Proteins.

Attractive self-interactions and reversible self-association are implicated in many problematic solution behaviors for therapeutic proteins, such as irreversible aggregation, elevated viscosity, phase separation, and opalescence. Protein self-interactions and reversible oligomerization of two Fc-fusion proteins (monovalent and bivalent) and the corresponding fusion partner protein were characterized experimentally with static and dynamic light scattering as a function of pH (5 and 6.5) and ionic strength (10 mM to at least 300 mM). The fusion partner protein and monovalent Fc-fusion each displayed net attractive electrostatic self-interactions at pH 6.5 and net repulsive electrostatic self-interactions at pH 5. Solutions of the bivalent Fc-fusion contained higher molecular weight species that prevented quantification of typical interaction parameters (B22 and kD). All three of the proteins displayed reversible self-association at pH 6.5, where oligomers dissociated with increased ionic strength. Coarse-grained molecular simulations were used to model the self-interactions measured experimentally, assess net self-interactions for the bivalent Fc-fusion, and probe the specific electrostatic interactions between charged amino acids that were involved in attractive electrostatic self-interactions. Mayer-weighted pairwise electrostatic energies from the simulations suggested that attractive electrostatic self-interactions at pH 6.5 for the two Fc-fusion proteins were due to cross-domain interactions between the fusion partner domain(s) and the Fc domain.

Study on the adsorption performance of modified high silica fly ash for methylene blue.

Presently, there are several issues associated with solid waste fly ash, such as its accumulation and storage, low comprehensive utilization rate, lack of high-value utilization technology, environmental risk and ecological impact. Thus, based on the high silica content and adsorption characteristics of fly ash, two novel adsorbents, namely mesoporous silica-based material (MSM) and sodium dodecyl sulfate-modified fly ash (SDS-FA), were prepared using an ultrasound-assisted alkali fusion-hydrothermal method and surface modification method. Furthermore, effects of adsorbent dosage, initial pH, contact time, and initial concentration of the solution on the adsorption of the organic pollutant methylene blue (MB) by fly ash, MSM, and SDS-FA were investigated to select the optimal modified high silica fly ash adsorbent. Based on the adsorption isotherms and adsorption kinetics, together with SEM, XRD, FTIR and BET analyses, the adsorption mechanism of MSM for MB was revealed. The results showed that under the conditions of an adsorbent dosage of 2 g L-1, initial pH of 9, contact time of 150 min, and initial concentration of 100 mg L-1, MSM and SDS-FA exhibited removal efficiencies of 92.69% and 84.64% for MB, respectively, which were significantly higher than that of fly ash alone. The adsorption of MB by MSM and SDS-FA followed the Langmuir model and pseudo-second-order kinetics, indicating monolayer adsorption with chemical adsorption as the dominant mechanism. The mechanism of the adsorption of MB by MSM is mainly the result of the synergistic effect among its increased specific surface area, hydrogen bonding, ion exchange, and electrostatic interactions. After five cycles of adsorption-desorption process, the removal efficiency of MSM for MB consistently remained above 80%. Therefore, MSM can serve as a valuable reference for the resource utilization of fly ash and remediation of dye-polluted wastewater.

One-drop chemosensing of dapoxetine hydrochloride using opto-analysis by multi-channel μPAD decorated silver nanoparticles: introducing a paper-based microfluidic portable device/sensor toward naked-eye pharmaceutical analysis by lab-on-paper technology.

Dapoxetine (DPX) belongs to the selective serotonin reuptake inhibitor (SSRI) class and functions by blocking the serotonin transporter and increasing serotonin activity, thereby delaying ejaculation. Therefore, monitoring of the concentration of DPX in human biofluids is important for clinicians. In this study, application of silver nanoparticles with the morphology of prisms (AgNPrs) for the sensitive measurement of DPX using colorimetric chemosensing and the spectrophotometric method was investigated. Also, DPX was determined in real samples using the spectrophotometry method. Based on the obtained results, all of the detection process in colorimetric assay is related to morphological reform of AgNPrs after it's specific electrostatic and covalent interaction with DPX as analyte. The UV-vis results indicate that the proposed AgNPrs-based chemosensing system has a wide range of linearity (0.01 μM to 1 mM) with a low limit of quantification of 0.01 μM in human urine samples, which is suitable for clinical analysis of this drug in human urine samples. It is important to point out that, this chemosensing strategy showed inappropriate analytical results for the detection of DPX in human urine samples which is a novelty of this platform. Finally, the optimized microfluidic paper-based analytical device (μPAD) was integrated with the colorimetric analysis of DPX to provide a time/color system for estimating analyte concentration by a portable substrate toward in situ and on-site biomedical analysis. Interestingly, the analytical validation tests showed appropriate results with great stability, which may facilitate commercialization of the engineered substrate. For the first time, in order to provide a simple and portable colorimetric/spectrophotometric recognition system to sensitive determination of DPX, an optimized pump-less microfluidic paper-based colorimetric device (μPCD) was introduced and validated for the real-time biomedical analysis of this analyte. According to the obtained results, this alternative approach is suitable for therapeutic drug monitoring (TDM) and biomedical analysis by miniaturized and cost-beneficial devices.

Preparation and performance of FeCo bimetallic organic frameworks with super adsorption and excellent peroxymonosulfate activation for tetracycline removal

As bifunctional materials for adsorption and peroxymonosulfate (PMS) activation, iron − cobalt bimetallic organic frameworks (FeCo − MOF) were successfully fabricated via a facile method at room temperature, and characterized by XRD, SEM, TEM, XPS, TGA, BET and FTIR. Due to the high specific surface area and electrostatic interaction, FeCo − MOF showed excellent adsorption capacity. 30 mg of FeCo − MOF can adsorb 87.5 % of tetracycline (TC) in a 100 mL aqueous solution (70 mg/L). The adsorption data are well fitted by the Langmuir model and pseudo − second − order adsorption kinetics, indicating the TC capture probably was monolayer molecular adsorption and chemisorption. Meanwhile, FeCo − MOF/PMS had the outstanding catalytic activity for TC degradation via PMS activation. 10 mg of FeCo − MOF can remove 91 % of TC within 5 min in a 100 mL aqueous solution (20 mg/L) with PMS (0.1 mmol·L−1). Quenching experiments showed that •OH, SO4•−, O2•− and 1O2 all participate in the TC degradation. The effects of PMS concentration, pH value, reaction temperature on TC degradation were investigated. Although the coexisting inorganic anions and small molecule acids inhibited the catalytic performance of FeCo − MOF/PMS, the TC removal rates were still greater than 80 %, indicating the FeCo − MOF/PMS system has a strong anti − interference ability to complex water environments. In addition, the complete degradation of various pollutants, including TC, methylene orange (MO) and methyl blue (MB), and TC degradation in different water bodies confirmed the wide applicability of the FeCo − MOF/PMS system.

Molecular mechanism of regulation of RhoA GTPase by phosphorylation of RhoGDI

Rho-specific guanine nucleotide dissociation inhibitors (RhoGDIs) play a crucial role in the regulation of Rho family GTPases. They act as negative regulators that prevent the activation of Rho GTPases by forming complexes with the inactive GDP-bound state of GTPase. Release of Rho GTPase from the RhoGDI-bound complex is necessary for Rho GTPase activation. Biochemical studies provide evidence of a "phosphorylation code," where phosphorylation of some specific residues of RhoGDI selectively releases its GTPase partner (RhoA, Rac1, Cdc42, etc.). This work attempts to understand the molecular mechanism behind this specific phosphorylation-induced reduction in binding affinity. Using several microseconds long atomistic molecular dynamics simulations of the wild-type and phosphorylated states of the RhoA-RhoGDI complex, we propose a molecular-interaction-based mechanistic model for the dissociation of the complex. Phosphorylation induces major structural changes, particularly in the positively charged polybasic region (PBR) of RhoA and the negatively charged N-terminal region of RhoGDI that contribute most to the binding affinity. Molecular mechanics Poisson-Boltzmann surface area binding energy calculations show a significant weakening of interaction on phosphorylation at the RhoA-specific site of RhoGDI. In contrast, phosphorylation at a Rac1-specific site does not affect the overall binding affinity significantly, which confirms the presence of a phosphorylation code. RhoA-specific phosphorylation leads to a reduction in the number of contacts between the PBR of RhoA and the N-terminal region of RhoGDI, which manifests a reduction of the binding affinity. Using hydrogen bond occupancy analysis and energetic perturbation network, we propose a mechanistic model for the allosteric response, i.e., long-range signal propagation from the site of phosphorylation to the PBR and buried geranylgeranyl group in the form of rearrangement and rewiring of hydrogen bonds and salt bridges. Our results highlight the crucial role of specific electrostatic interactions in manifestation of the phosphorylation code.

Accelerated naked-eye identification of cations using non-plasmonic amplification by functionalized GQDs: A novel photochemical microfluidic sensor for environmental/mineral analysis using Lab-on-paper technology

This study describes the synthesis of various types of thiolated-graphene quantum dots (GQDs) for the simultaneous multi-sensing of heavy metal ions using one-droplet microfluidic paper-based analytical devices (OD-µPADs). For the first time, functionalized GQDs were synthesized and stabilized on the surface of hydrophobic fiber-glass with simple manufacturing and assembly strategy towards colorimetric chemosensing of ions including iron, copper, cobalt, mercury, chrome, manganese, and nickel. For this purpose, GQDs are functionalized by various organic species including cysteamine, decanethiol, and mercaptopropionic acid (MPA) towards specific electrostatic interaction with metal ions of Fe (II), Cu (II), Co(II), Hg (II), Mn (II), and Ni (II). Therefore, an innovative GQDs-based miniaturized chemo-system was proposed for the environmental analysis. Additionally, the results were confirmed using fluorescence spectrometry as an optical detection method. Finally, this simple and efficient colorimetric platform was used for facile metal ions detection in human urine models, and environmental fluids, which can provide a commercial device for sensing contaminants by non-professional users in biomedical/environmental mixture. As an economical technique, this platform presents a “mix-and-sense” system without dye (as a side substance) or chemical treatments. The low instrumental requirements, the color uniformity, and the disposability of OD-μPADs approve the commercial application of the engineered ion-chemosensor.

Regulating Electrostatic Interactions toward Thermoresponsive Hydrogels with Low Critical Solution Temperature.

Low critical solution temperature (LCST) of commonly used thermoresponsive polymers in water is basically dominated by hydrophobic interactions. Herein, a novel thermoresponsive system based on electrostatic interactions is reported. By simply loading aluminum chloride (AlCl3 ) into non-responsive poly(2-hydroxyethyl acrylate) (PHEA) hydrogels, PHEA-Al gels turn to have reversible thermoresponsive behavior between transparent and opaque without any volume change. Further investigations by changing metal ion-polymer compositions unravel the necessity of specific electrostatic interactions, namely, cation-dipole bonding interactions between hydroxy groups and trivalent metal ions. The thermoresponsive hydrogel demonstrates high transparency (≈95%), excellent luminous modulation capability (>98%), and cyclic reliability, suggesting great potential as an energy-saving material. Although LCST control by salt addition is widely known, salt-induced expression of thermoresponsiveness has barely been discussed before. This design provides a new approach of easy fabrication, low cost, and scalability to develop stimuli-responsive materials.

Structural study of acyl carrier protein of Enterococcus faecalis and its interaction with enzymes in de novo fatty acid synthesis

Enterococcus faecalis has recently shown signs of high antibiotic resistance. These bacteria can endure extremes of temperature and this may be due to the high thermostability of its proteins. E. faecalis has two acyl carrier proteins (ACPs), AcpA (EfAcpA), which is essential for de novo fatty acid synthesis (FAS), and EfAcpB, which plays an auxiliary role in the incorporation of exogenous fatty acids. Structural studies on EfAcpA and its interaction with FAS enzymes have not yet been reported. Here, we investigated the structures of EfAcpA using NMR spectroscopy, showing that EfAcpA consists of three α-helices with a long α2α3 loop, while the other ACPs have four α-helices. CD experiments showed that the melting temperature of EfAcpA is 76.3 °C and the Ala mutation for Ile10 reduced it dramatically by 29.5 °C. Highly conserved Ile10 of EfAcpA mediates compact intramolecular packing and promotes high thermostability. A docking simulation of EfAcpA and β-ketoacyl-ACP synthase III (EfKAS III) showed that the α2α3 loop of EfAcpA contributes to specific protein–protein interactions (PPI) with EfKAS III. Unconserved charged residues, Lys52 and Glu54, in the α2α3 loop of EfAcpA formed specific electrostatic interactions with Asp 226 and Arg217 of EfKAS III, respectively. Binding interactions between EfAcpA and EfKASIII may provide insights for designing PPI inhibitors targeting FAS in E. faecalis to overcome its antibacterial resistance.

Quaternary Ammonium-Tethered Phenylboronic Acids Appended Supramolecular Nanomicelles as a Promising Bacteria Targeting Carrier for Nitric Oxide Delivery.

The delivery of drugs to focal sites is a central goal and a key challenge in the development of nanomedicine carriers. This strategy can improve the selectivity and bioavailability of the drug while reducing its toxicity. To ensure the specific release of nitric oxide at the site of a bacterial infection without damaging the surrounding normal tissue, we designed a host-guest molecule containing a host molecule with a target moiety and a nitric oxide donor to release nitric oxide. The boronic acid group in the structure of this nanoparticle interacts strongly and specifically with the surface of E. coli. In addition, the quaternary amine salt can interact electrostatically with bacteria, indicating a large number of negatively charged cell membranes; altering the molecular structure of the cell membrane; increasing the permeability of the cell membrane; and causing cytoplasmic diffusion and cell lysis, resulting in lethal activity against most bacteria. The synthesised molecules were characterised by 1H NMR and mass spectrometry. The strong specific interaction of the boronic acid moiety with the surface of E. coli and the electrostatic interaction of the quaternary amine salt with the cell membrane were confirmed by antibacterial experiments on molecules with and without the targeting moiety. The targeting group-modified micelles enhanced the antibacterial effect of the micelles very effectively through specific interactions and electrostatic interactions. In addition, in vitro skin wound healing experiments also confirmed the targeting and antimicrobial effect of micelles. These results suggest that the specific release of nitric oxide at the site of bacterial infection is an important guide to further address the emergence of antibiotic-resistant strains of bacteria.

Essential Role of Loop Dynamics in Type II NRPS Biomolecular Recognition.

Non-ribosomal peptides play a critical role in the clinic as therapeutic agents. To access more chemically diverse therapeutics, non-ribosomal peptide synthetases (NRPSs) have been targeted for engineering through combinatorial biosynthesis; however, this has been met with limited success in part due to the lack of proper protein-protein interactions between non-cognate proteins. Herein, we report our use of chemical biology to enable X-ray crystallography, molecular dynamics (MD) simulations, and biochemical studies to elucidate binding specificities between peptidyl carrier proteins (PCPs) and adenylation (A) domains. Specifically, we determined X-ray crystal structures of a type II PCP crosslinked to its cognate A domain, PigG and PigI, and of PigG crosslinked to a non-cognate PigI homologue, PltF. The crosslinked PCP-A domain structures possess large protein-protein interfaces that predominantly feature hydrophobic interactions, with specific electrostatic interactions that orient the substrate for active site delivery. MD simulations of the PCP-A domain complexes and unbound PCP structures provide a dynamical evaluation of the transient interactions formed at PCP-A domain interfaces, which confirm the previously hypothesized role of a PCP loop as a crucial recognition element. Finally, we demonstrate that the interfacial interactions at the PCP loop 1 region can be modified to control PCP binding specificity through gain-of-function mutations. This work suggests that loop conformational preferences and dynamism account for improved shape complementary in the PCP-A domain interactions. Ultimately, these studies show how crystallographic, biochemical, and computational methods can be used to rationally re-engineer NRPSs for non-cognate interactions.

Sulfide modifies physicochemical properties and mercury adsorption of microplastics

Microplastics (MPs) tend to accumulate and undergo a sulfur weathering process that leads to significant surface changes in sulfur-rich anaerobic environments, such as sewage and wastewater treatment plants. Aged MPs can have a profound impact on environmental behaviors of various toxic pollutants, especially heavy metals. Although previous studies have investigated the adsorption characteristics of metal ions on MPs that are aged in aerobic environments, the sorptive interactions of sulfur-aged MPs in anaerobic environments with mercury, i.e., Hg(II), are largely unknown. In this study, laboratory investigations were conducted to study the sorptive behaviors of Hg(II) by six common MPs treated anaerobically in the presence of sulfide. Adsorption isotherms show that the sulfur aging process greatly enhances the MP sorption capacity of Hg(II). The mechanisms including changes in the specific surface area, electrostatic interactions, surface precipitation, and surface functional groups are responsible for the enhanced adsorption capacities of sulfur-aged MPs. The thiol group that forms on the MP surface plays a dominant role in enhancing the MP adsorption capacity of Hg(II), which is determined by the formation of unsaturated bonds in the molecular chains of MPs. Furthermore, the pathways of surface chemical transformation of MPs during sulfur aging have been proposed. This study promotes our understanding of the potential hazard of MPs as well as the fate and transport of heavy metals in the presence of aged MPs.

Breaking the scaling relations for efficient N2-to-NH3 conversion by a bowl active site design: Insight from LaRuSi and isostructural electrides

The design of optimal heterogeneous catalysts for N 2 -to-NH 3 conversion is often dictated by the scaling relations, which result in a volcano curve that poses a limit on the catalytic performance. Herein, we reveal a bowl active site that can break the scaling relations, through investigating the catalytic mechanisms of N 2 -to-NH 3 conversion on the lanthanide intermetallic electride catalyst LaRuSi by first-principles modeling. This bowl active site, composed of four surface La cations and one subsurface Si atom rich in electrons, plays the key role in enabling efficient catalysis. With adaptive electrostatic and orbital interactions, the bowl active site promotes the adsorption and activation of N 2 that delivers facile cleavage of N–N bond, while destabilizes the adsorptions of *NH x ( x = 1, 2, 3) species, which facilitates the release of the final NH 3 product. By comparison with other electride catalysts isostructural to LaRuSi, we confirm the breaking of scaling relations between the adsorptions of *NH x species and that of *N on the bowl active site. Thus, this bowl active site presents a design concept that breaks the scaling relations for highly efficient heterogeneous catalysis of N 2 -to-NH 3 conversion. A bowl active site on the lanthanide intermetallic electride LaRuSi, composed of four surface La cations and one subsurface Si atom, plays the key role in efficient catalysis of N 2 -to-NH 3 conversion by breaking the scaling relations through specific electrostatic and orbital interactions. This bowl active site thus presents a design concept of highly efficient heterogeneous catalyst for N 2 -to-NH 3 conversion.

Coupling humic acid in Fe-bearing montmorillonite for enhanced adsorption and catalytic degradation of tetracycline.

Clay-based materials have attracted attention owing to their dual effects of adsorption and advanced oxidation degradation in removing organic pollutants. In this study, the introduction of humic acid (HA) in the Fe-bearing montmorillonite (Fe-Mt) nano platform enhanced its tetracycline (TC) adsorption and degradation were investigated. The result showed that the adsorption and degradation efficiency of humic acid/poly-hydroxyl-iron/montmorillonite (HA-Fe-Mt) was greater than those of Fe-Mt. The adsorption performance and characterization confirmed that HA-Fe-Mt had more functional groups, stronger hydrophobic character, and higher specific surface area. The introduction of HA onto the Fe-Mt platform enhanced its specific surface area, electrostatic interaction, and hydrophobic character, therefore providing more active sites to interact with the carbonyl and amide groups of TC. Moreover, the catalytic performance and characterization results revealed that HA-Fe-Mt had greater persulfate (PS) activation, the coupled HA would speed up the transmission of electrons between Fe (III) and PS in the Fe (III) / Fe (II) cycle when PS was captured by the HA-Fe-Mt system, and the in situ generated Fe accelerates the generation of reactive oxygen species (ROS) to further degrade TC. Consequently, HA can not only promote the adsorption of TC but also promote the degradation of TC in the Fe-Mt nano platform. HA-Fe-Mt provided a feasible and promising platform with PS activation for TC adsorption and degradation.

11-Mercaptoundecanoic Acid-Functionalized Carbon Dots As a Ratiometric Optical Probe for Doxorubicin Detection

A ratiometric optical dual-mode probe was first designed for the detection of doxorubicin (DOX) based on 11-mercaptoundecanoic acid-functionalized carbon dots (MUA-CDs). The carbon dots (CDs) were synthesized via hydrothermal carbonization of m-phenylenediamine and p-aminobenzoic acid, and then it was reacted with 11-mercaptoundecanoic acid by the amide reaction to obtain the MUA-CDs. The as-synthesized MUA-CDs have a high fluorescence quantum yield (59.4%) with bright green emission. Based on a specific electrostatic interaction and the fluorescence resonance energy transfer (FRET) between MUA-CDs and DOX, a ratiometric optical dual-mode probe was constructed for the detection of DOX with good selectivity, high sensitivity, and excellent anti-interference performance. When DOX was mixed the MUA-CDs, the fluorescence of the MUA-CDs at 513 nm decreased, while the fluorescence at 590 nm increased. With this information, a ratiometric fluorescent method was established to determine DOX with a linear range and limit of detection (LOD) of 0.25–19.96 and 0.66 μM and 50.33–80.88 and 0.23 μM, respectively. Meanwhile, the color of the MUA-CDs varied from colorless to dark yellow in the presence of DOX, and therefore, a ratiometric colorimetric method was applied to determine DOX in a range of 2.50–29.80 μM with a LOD of 0.75 μM. Finally, the as-constructed probe was successfully used to determine DOX in serum, urine, and live cells with satisfactory results. This work will contribute to the specific design of functional CDs and broaden the application of functional CDs in analytical detection and biological imaging.