Protein interactions with silver nanoparticles: Green synthesis, and biophysical approach

Regulating Enzyme Catalysis by Tailored Silver Nanocrystals Fabricated with Holigarna arnottiana-Synthesis, Characterization, and Performance Optimization

Modification of catalytic expression of enzymes and regulating their in vivo activity are the goals of novel treatment strategies. A green synthetic nanostructured silver with potent trypsin inhibitory properties has not yet been developed, despite the fact that silver nanoparticles possess unique properties that allow them to efficiently block enzymes. The present study demonstrates for the first time a facile, safe, economic, and eco-friendly synthetic route for silver nanoparticles using an aqueous extract of Holigarna arnottiana bark engineered to interact with trypsin and hinder its activity effectively. The studies carried out to examine the interaction between these biofabricated AgNPs (HaAgNPs) and trypsin by UV-visible spectrophotometry and FTIR spectroscopy suggest that the formation of trypsin-HaAgNP complex is responsible for diminishing the catalytic efficiency of trypsin. In vivo studies on Aedes aegypti larval serum support these instrumental results of HaAgNP-induced trypsin inhibition and proves its application as a biopesticide. It is noteworthy that the bioengineered HaAgNPs were also found to have good inhibition potential against pepsin and urease as well. A variety of methods have been employed to characterize the synthesized biocompatible HaAgNPs and it possesses a characteristic absorption maximum of 420 nm. Their shelf life of above 7 years is noticeable, since none of the reported green synthesized AgNPs possess a shelf life of more than 1 year. Altogether, this work demonstrates that biofabricated HaAgNPs are multifunctional and cost-resilient biological tools that can be used as enzyme regulators possessing antioxidant, antimicrobial, and insecticidal features.

Green synthesis of zinc ferrite nanoparticles from Nyctanthes arbor-tristis: unveiling larvicidal potential, protein binding affinity and photocatalytic activities

Environmental pollution, being a major concern worldwide, needs a unique and ecofriendly solution. To answer this, researchers are aiming in utilizing plant extracts for the synthesis of nanoparticles. These NPs synthesized using plant extracts provide a potential, environmentally benign technique for biological and photocatalytic applications. Especially, plant leaf extracts have been safe, inexpensive, and eco-friendly materials for the production of nanoparticles in a greener way. In this work, zinc ferrite nanoparticles (ZnFe2O4 NPs) were prepared using Nyctanthes arbor-tristis leaf extract by hydrothermal method, and its biological and photocatalytic properties were assessed. The synthesized ZnFe2O4 NPs were characterized using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy (FT-IR). X-ray diffraction confirmed the arrangement of the fcc crystal structure of the nanoparticles and that some organic substances were encapsulated within the zinc ferrite. According to the SEM analysis, the resulting nanoparticles got agglomerated and spherical in shape. The ZnFe2O4 nanoparticles are in their pure form, and all of their elemental compositions were shown by the energy-dispersive X-ray analysis (EDAX) spectrum. The FTIR results revealed that the produced nanoparticles contained distinctive functional groups. Fluorescence spectroscopy was used to examine the binding affinities between bovine serum albumin (BSA) and ZnFe2O4 nanoparticles in terms of protein binding, stability, and conformation. The interaction between BSA and ZnFe2O4 NPs was examined using steady-state and time-resolved fluorescence measurements, and it was evident that static quenching occurred. The ability of ZnFe2O4 nanoparticles to kill Culex quinquefasciatus (C. quinquefasciatus) larvae was evaluated. The synthesized NPs demonstrated a noteworthy toxic effect against the fourth instar larvae of C. quinquefasciatus with LC50 values of 43.529 µg/mL and LC90 values of 276.867 µg/mL. This study revealed the toxicity of green synthesized ZnFe2O4 NPs on mosquito larvae, proving that these NPs are good and effective larvicides. Furthermore, the ZnFe2O4 NPs were utilized for dye degradation of methylene blue under visible light treatment and achieved 99.5% degradation.

Fibrous Conductive Metallogels with Hybrid Electron/Ion Networks for Boosted Extreme Sensitivity and High Linearity Strain Sensor

Fibrous strain sensing materials with both high sensitivity and high linearity are of significant importance for wearable sensors, yet they still face great challenges. Herein, a photo-spun reaction encapsulation strategy is proposed for the continuous fabrication of fibrous strain sensor materials (AMGF) with a core-sheath structure. Metallogels (MOGs) formed by bacterial cellulose (BC) nanofibers and Ag nanoparticles (AgNPs), and thermoplastic elastomers (TPE) are employed as the core and sheath, respectively. The in situ ultraviolet light reduction of Ag+ ensured AgNPs to maintain the interconnections between the BC nanofibers and form electron conductive networks (0.31 S m-1 ). Under applied strain, the BC nanofibers experience separation, bringing AMGF a high sensitivity (gauge factor 4.36). The concentration of free ions in the MOGs uniformly varies with applied deformation, endowing AMGF with high linearity and a goodness-of-fit of 0.98. The sheath TPE provided AMGF sensor with stable working life (>10 000 s). Furthermore, the AMGF sensors are demonstrated to monitor complex deformations of the dummy joints in real-time as a wearable sensor. Therefore, the fibrous hybrid conductive network fibers fabricated via the photo-spun reaction encapsulation strategy provide a new route for addressing the challenge of achieving both high sensitivity and high linearity.

Adsorption and volumetric properties of some nonionic surfactants and their mixtures with quercetin and rutin

The adsorption and volumetric properties of the Triton X-114 (TX114), Tween 80 (T80), quercetin (Q) and rutin (Ru) at the different temperatures in relation to above properties of the TX114 and T80 mixtures with quercetin and rutin in the absence and presence of alcohol were discussed based on the studies reported in the literature. The adsorption isotherms of the mixtures of the nonionic surfactants with flavonoids in the presence and absence of alcohol were analyzed based on the isotherms of the surface tension of the particular mixture components and thermodynamic parameters of the adsorption of these components at the water-air interface. The surface tension isotherms of the particular component of the mixtures were taken into account while considering the surface tension isotherms of the mixtures and the composition of the mixed surface layer at the water-air interface. Different ways of the mixed surface layer composition determination were shown. The values of the surface tension and composition of the mixed surface layers obtained using different methods were discussed in the light of the intermolecular interactions and their contribution to the surface tension of the surfactants mixture with flavonoids and alcohol. The composition of the mixed monolayer and the bulk phase were compared and the differences between them were explained. The behaviour of the nonionic surfactants and flavonoids in the presence and absence of alcohol was analyzed in relation to the micelle formations and molar volumes of the mixtures and their components. Moreover, the micelles composition and their size as well as the thermodynamic parameters of the micellization process were analyzed.

“Soft Protein Corona” as the Stabilizer of the Methionine-Coated Silver Nanoparticles in the Physiological Environment: Insights into the Mechanism of the Interaction

The study of the interactions between nanoparticles (NPs) and proteins has had a pivotal role in facilitating the understanding of biological effects and safe application of NPs after exposure to the physiological environment. Herein, for the first time, the interaction between L-methionine capped silver nanoparticles (AgMet), and bovine serum albumin (BSA) is investigated in order to predict the fate of AgMet after its contact with the most abundant blood transport protein. The detailed insights into the mechanism of interaction were achieved using different physicochemical techniques. The UV/Vis, TEM, and DLS were used for the characterization of the newly formed “entity”, while the kinetic and thermodynamic parameters were utilized to describe the adsorption process. Additionally, the fluorescence quenching and synchronous fluorescence studies enabled the prediction of the binding affinity and gave us insight into the influence of the adsorption on the conformation state of the BSA. According to the best of our knowledge, for the first time, we show that BSA can be used as an external stabilizer agent which is able to induce the peptization of previously agglomerated AgMet. We believe that the obtained results could contribute to further improvement of AgNPs’ performances as well as to the understanding of their in vivo behavior, which could contribute to their potential use in preclinical research studies.

Investigation on Green Synthesis, Biocompatibility, and Antibacterial Activity of Silver Nanoparticles Prepared Using Cistus incanus

This paper describes the plant-mediated preparation of silver nanoparticles with aqueous extract and infusion of Cistus incanus leaves. To evaluate aqueous extract and infusion antioxidant capacity and total phenolic content the DPPH and Folin-Ciocalteau methods were utilized. The antioxidant capacity and total phenolic content of extract and infusion were equal to 85.97 ± 6.54 mg gallic acid equivalents per gram of dry weight.; 10.76 ± 0.59 mg/mL and 12.65 ± 1.04 mg gallic acid equivalents per gram of dry weight.; 3.10 ± 0.14 mg/mL, respectively. The formed nanoparticles displayed the characteristic absorption band in the 380-450 nm wavelength range. The average size of particles was in the 68.8-71.2 nm range. Morphology and phase composition analysis revealed the formation of spherical nanoparticles with a face-centred cubic structure. Immune compatibility tests of nanoparticles and plant extracts showed no activation of the THP1-XBlue™ monocyte. Cytotoxicity tests performed with L929 mice fibroblasts showed that nanoparticles should be utilized at a concentration of 16 ppm. The minimum inhibitory concentrations determined with the microdilution method for nanoparticles prepared with plant infusion for S. aureus and S. epidermidis were 2 ppm and 16 ppm, respectively.

Biocompatible silver nanoparticles: An investigation into their protein binding efficacies, anti-bacterial effects and cell cytotoxicity studies

Green synthesis of silver nanoparticles (AgNPs) has garnered tremendous interest as conventional methods include the use and production of toxic chemicals, products, by-products and reagents. In this regard, the synthesis of AgNPs using green tea (GT) extract and two of its components, (-)-epigallocatechin gallate (EGCG) and (+)-catechin (Ct) as capping/stabilizing agents, is reported. The synthesized AgNPs showed antibacterial activity against the bacterial strains Staphylococcus aureus and Escherichia coli, along with anticancer activity against HeLa cells. After administering nanoparticles to the body, they come in contact with proteins and results in the formation of a protein corona; hence we studied the interactions of these biocompatible AgNPs with hen egg white lysozyme (HEWL) as a carrier protein. Static quenching mechanism was accountable for the quenching of HEWL fluorescence by the AgNPs. The binding constant (K b) was found to be higher for EGCG-AgNPs ((2.309 ± 0.018) × 104 M-1) than for GT-AgNPs and Ct-AgNPs towards HEWL. EGCG-AgNPs increased the polarity near the binding site while Ct-AgNPs caused the opposite effect, but GT-AgNPs had no such observable effects. Circular dichroism studies indicated that the AgNPs had no such appreciable impact on the secondary structure of HEWL. The key findings of this research included the synthesis of AgNPs using GT extract and its constituent polyphenols, and showed significant antibacterial, anticancer and protein-binding properties. The -OH groups of the polyphenols drive the in situ capping/stabilization of the AgNPs during synthesis, which might offer new opportunities having implications for nanomedicine and nanodiagnostics.

Synthesis of cationic carbon dots and their effects on human serum proteins and in vitro blood coagulation

Cationic carbon dots (CCDs) are a promising alternative to gene-delivery systems, and good biosafety levels are crucial for their in vivo use. In this study, spherical and monodispersed CCDs with an average surface potential of +28.7 mV were prepared using sucrose and glutamate (denoted SG-CCDs) using a one-pot autoclave-assisted method. Molecular interactions between the SG-CCDs and four major human serum proteins (albumin, immunoglobulin G, fibrinogen, and transferrin) were investigated. The results were further verified on human serum, and the effect of the SG-CCDs on in vitro blood coagulation was examined. The results showed that the fluorescence of human serum was clearly quenched by the SG-CCDs through a dynamic collision mechanism. Moreover, SG-CCDs at a concentration of 20 μM exhibited minor effects on the secondary structure of human serum. The activated partial thromboplastin and prothrombin time as well as the fibrinogen concentration were not changed, indicating that the SG-CCDs did not interfere with the coagulation process. This study provided an understandable background on the behaviour of CCDs in clinical applications.

Silver-incorporating peptide and protein supramolecular nanomaterials for biomedical applications

The natural biomolecules of peptides and proteins are able to form elegant metal incorporating supramolecular nanomaterials through multiple weak non-covalent interactions. The use of toxic chemical reagents to fabricate silver nanoparticles poses a danger to apply them in various biomedical applications. Peptide and protein biomolecules have the potential to overcome this barrier by the supramolecular chemistry approach. In this review, we focus on the self-assembly of peptides and proteins to synthesize silver incorporating supramolecular nanoarchitectures, which in turn enhance the biological properties of these silver nanomaterials being used in nanomedicine. This review aims to illustrate the recent developments in amphiphilic peptides, oligopeptides, collagen, bovine serum albumin (BSA), and human serum albumin (HSA) as capping, stabilizing, and reducing agents to form silver incorporating supramolecular nanostructures. Finally, we provide some biomedical applications of silver-incorporating supramolecular nanomaterials along with future perspectives.

Facile Bio-Fabrication of Ag-Cu-Co Trimetallic Nanoparticles and Its Fungicidal Activity against Candida auris

Candida auris is an emergent multidrug-resistant pathogen that can lead to severe bloodstream infections associated with high mortality rates, especially in hospitalized individuals suffering from serious medical problems. As Candida auris is often multidrug-resistant, there is a persistent demand for new antimycotic drugs with novel antifungal action mechanisms. Here, we reported the facile, one-pot, one-step biosynthesis of biologically active Ag-Cu-Co trimetallic nanoparticles using the aqueous extract of Salvia officinalis rich in polyphenols and flavonoids. These medicinally important phytochemicals act as a reducing agent and stabilize/capping in the nanoparticles' fabrication process. Fourier Transform-Infrared, Scanning electron microscopy, Transmission Electron Microscopy, Energy dispersive X-Ray, X-ray powder diffraction and Thermogravimetric analysis (TGA) measurements were used to classify the as-synthesized nanoparticles. Moreover, we evaluated the antifungal mechanism of as-synthesized nanoparticles against different clinical isolates of C. auris. The minimum inhibitory concentrations and minimum fungicidal concentrations ranged from 0.39-0.78 μg/mL and 0.78-1.56 μg/mL. Cell count and viability assay further validated the fungicidal potential of Ag-Cu-Co trimetallic nanoparticles. The comprehensive analysis showed that these trimetallic nanoparticles could induce apoptosis and G2/M phase cell cycle arrest in C. auris. Furthermore, Ag-Cu-Co trimetallic nanoparticles exhibit enhanced antimicrobial properties compared to their monometallic counterparts attributed to the synergistic effect of Ag, Cu and Co present in the as-synthesized nanoparticles. Therefore, the present study suggests that the Ag-Cu-Co trimetallic nanoparticles hold the capacity to be a lead for antifungal drug development against C. auris infections.

Interactions of insulin with tragacanthic acid biopolymer: Experimental and computational study

Alternative methods for insulin delivery instead of subcutaneous injection in diabetic patients is of great essential, and biocompatible polymers are one of the most efficient vehicles for this purpose. This research aims to investigate the capability of tragacanthic acid (TA) to bind insulin and release it under physiological conditions without alteration in the structure and conformation of insulin. Interactions between TA and insulin were studied using spectroscopic techniques and computational modeling by docking and molecular dynamics simulations. Our results demonstrate an entropy-driven spontaneous interaction between insulin and TA, where hydrogen bonds act as the main enthalpic contribution. According to our findings, the weak interaction between insulin and TA provides the basis for efficient capture and appropriate release of insulin by TA as a potential part of the insulin delivery system. In conclusion, tragacanth acid can be a proper candidate for insulin delivery.

Phytomediated Photo-Induced Green Synthesis of Silver Nanoparticles Using Matricaria chamomilla L. and Its Catalytic Activity against Rhodamine B

The bio-fabrication of silver nanoparticles (AgNPs) was carried out through the facile green route, using the aqueous extract of Matricaria chamomilla L. Herein, we have developed a cost-efficient, ecofriendly, and photo-induced method for the biomolecule-assisted synthesis of AgNPs using an aqueous extract of Matricaria chamomilla L. as a bio-reducing and capping/stabilizing agent. The biomolecule-capped AgNPs were confirmed from the surface plasmon resonance (SPR) band at λmax = 450 nm using a UV-visible spectrometer. The stability of the AgNPs was confirmed by recording the UV-visible spectra for a more extended period, and no precipitation was observed in the sol. The morphology and structure of photo-induced biomolecule-capped AgNPs were characterized by different microscopic and spectroscopy techniques such as TEM, SEM, EDX, XRD, and FTIR analysis. The role of phytochemicals as reducing and stabilizing agents was confirmed by comparative FTIR analysis of the AgNPs and pure Matricaria chamomilla L. aqueous extract. The obtained result shows that the AgNPs are mostly spherical morphology with an average size of about 26 nm. Furthermore, the thermal stability of biomolecule-capped AgNPs was examined by TGA-DTG analysis that showed a weight loss of approximately 36.63% up to 800 °C. Moreover, the potential photocatalytic activity of photo-induced AgNPs against Rhodamine B (RB) was examined in the presence of UV light irradiation. The catalyst reusability, the effect of catalyst dosage and initial dye concentration, and the effect of the temperature and pH of the reaction medium were also assessed.

Structure, stability and chaperone function of Mycobacterium leprae Heat Shock Protein 18 are differentially affected upon interaction with gold and silver nanoparticles

Gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs) have several biomedical applications. However, the effective usage of these two nanoparticles is impeded due to limited understanding of their interaction with proteins including small heat shock proteins (sHSPs). Specifically, no evidences of interaction of these two nanoparticles with HSP18 (an antigenic protein) which is an important factor for the growth and survival of M. leprae (the causative organism of leprosy) are available in the literature. Here, we report for the first time evidences of "HSP18-AuNPs/AgNPs interaction" and its impact on the structure and chaperone function of HSP18. Interaction of citrate-capped AuNPs/AgNPs (~20 nm diameter) to HSP18 alters the secondary and tertiary structure of HSP18 in a distinctly opposite manner; while "HSP18-AuNPs interaction" leads to oligomeric association, "HSP18-AgNPs interaction" results in oligomeric dissociation of the protein. Surface hydrophobicity, thermal stability, chaperone function of HSP18 and survival of thermally stressed E. coli harbouring HSP18 are enhanced upon AuNPs interaction, while all of them are reduced upon interaction with AgNPs. Altogether, our study reveals that HSP18 is an important drug target in leprosy and its chaperone function may possibly plays a vital role in the growth and survival of M. leprae pathogen in infected hosts.

Influence of pH on interaction of silver nanoparticles - protein: Analyses by spectroscopic and thermodynamic ideology

To investigate the interaction between bovine serum albumin (BSA) and silver nanoparticles (AgNPs) at five different pHs (below (3.0 and 4.0), above (7.4 and 9.2) and at the isoelectric point (4.7) of BSA) by spectroscopic (viz., UV-vis, fluorescence, circular dichroism (CD)), microscopic (viz., atomic force microscopy (AFM), transmission electron microscopy (TEM), field emission scanning electron microscope (FESEM)) and thermodynamic (viz., isothermal titration calorimetry (ITC)) methods. The fluorescence quenching spectra provided binding constants via Stern-Volmer plot, quenching constant (K_sv) and rate constant (K_q) were calculated. From the CD spectra, it is clear that the α-helix decreases by increasing the AgNP's concentration. However, at isoelectric point (pH = 4.7), BSA shows more helicity in the presence of AgNPs, which indicates that the structures of BSA become more ordered and stable, and aggregation occurs at strong acidic (3.0), and basic medium (9.2) Fluorescence spectra also indicate the aggregation of the protein at strong acidic (pH = 3.0) and basic medium (pH = 9.2). Furthermore, the morphological and topographical evolute ion upon the interaction was examined using TEM, FESEM, and AFM. The studies conclude the effect of the pH in the medium and behavior of AgNPs with BSA by using different spectroscopic and microscopic techniques.

Silver Nanoparticle Surface Enabled Self-Assembly of Organic Dye Molecules

Fluorescence titration of methylene blue, rhodamine B and rhodamine 6G (R6G) by silver nanoparticle (AgNP) all resulted in an initial steep quenching curve followed with a sharp turn and a much flatter quenching curve. At the turn, there are about 200,000 dye molecules per a single AgNP, signifying self-assembly of approximately 36-layers of dye molecules on the surface of the AgNP to form a micelle-like structure. These fluorescence-quenching curves fit to a mathematical model with an exponential term due to molecular self-assembly on AgNP surface, or we termed it "self-assembly shielding effect", and a Stern-Volmer term (nanoparticle surface enhanced quenching). Such a "super-quenching" by AgNP can only be attributed to "pre-concentration" of the dye molecules on the nanoparticle surface that yields the formation of micelle-like self-assembly, resulting in great fluorescence quenching. Overall, the fluorescence quenching titration reveals three different types of interactions of dye molecules on AgNP surface: 1) self-assembly (methylene blue, rhodamine B and R6G), 2) absorption/tight interaction (tryptamine and fluorescein), and 3) loose interaction (eosin Y). We attribute the formation of micelle-like self-assembly of these three dye molecules on AgNP to their positive charge, possession of nitrogen atoms, and with relatively large and flat aromatic moieties.

Methylene blue dye removal on silver nanoparticles reduced by Kyllinga brevifolia

Silver nanoparticles (AgNPs) were prepared by reacting Kyllinga brevifolia extract (KBE) with AgNO₃ aqueous solution at room temperature (22 ± 3 °C). The phytochemical constituents in KBE responsible for the reduction process were identified as carbohydrate, protein, and plant sterols (stigmasterol and campesterol). KBE was also found to function as a capping agent for stabilization of AgNPs. The AgNPs were stable at room temperature and had a quasi-spherical shape with an average particle size 22.3 nm. The use of KBE offers not only eco-friendly and non-pathogenic path for AgNPs formation, it also induced rapid formation of the AgNPs. Methylene blue (MB) removal was then done on the AgNPs in the presence of either KBE or NaBH₄. Ninety-three percent removal of MB was achieved with a rate of reaction 0.2663 min^-1 in the solution with KBE+AgNPs (pH 2). However, in NaBH₄+AgNPs system, 100% MB removal was achieved at pH 8-10. The reaction rate was 2.5715 min^-1 indicating a fast removal rate of MB dye. The process of reduction occurs via electron relay effect whereas in KBE+AgNPs system, sedimentation occurred along with the reduction process. Nevertheless, the use of KBE+AgNPs system is preferred as the reducing agent is more benign to the environment.

Study of Intermolecular Interactions of CTAB with Amino Acids at Different Temperatures: A Multi Technique Approach

The densities, ρ, viscosities, η and specific conductivities κ, of (0.0002, 0.0004, 0.0006 and 0.0008 m) CTAB in 0.1 m aqueous valine, leucine and isoleucine were measured at different temperatures. The measured data were used to calculate various useful thermodynamic parameters. A complete characterization of any mixture can be performed by means of these thermodynamic properties. The apparent molar volume, ϕv , partial molar volume, ϕ v 0 $\phi _v^0$ and partial molar isobaric expansibilities, ϕ E 0 , $\phi _E^0,$ were calculated using density data. The viscosity data were analyzed using Jones–Dole equation to obtain viscosity coefficients, A- and B-, free energy of activation per mole of solvent, Δμ 1°∗, and solute, Δμ 2°∗, enthalpy, ΔH ∗ and entropy, ΔS ∗ of activation of viscous flow. Measuring the changes in these properties has been found to be an excellent qualitative and quantitative way to obtain information regarding the molecular structure and intermolecular interactions occurring in these mixtures. Various structure-making/breaking ability of solute (cetyltrimethylammonium bromide) in presence of aqueous amino acid solutions were discussed. In addition, fluorescence study using pyrene as a photophysical probe has been carried out, the results of which support the conclusions obtained from other techniques.

Seedless synthesis and efficient recyclable catalytic activity of Ag@Fe nanocomposites towards methyl orange

This work demonstrates a competitive reduction method of synthesis of nanomaterials. In this method along cetyltrimethylammonium bromide (CTAB), the reduction of Ag+ and Fe3+ ions is achieved by ascorbic acid-to-bimetallic Ag@Fe yellow-colored nanomaterials. The shape of UV–visible spectra and wavelengths absorbed of Ag@Fe can be tuned from ca. 290–600 nm by controlling [CTAB] and [Ag+]. The apparent first-order rate constants were calculated within the approximation of 6.1 × 10−3 s−1. The as-prepared Ag@Fe NPs have been found to be very important catalyst in terms of depredate methyl orange in vicinity of sodium borohydride (NaBH4), which exhibits excellent efficiency and re-usability in the prototypical reaction. The cmc of cationic surfactant CTAB has been determined by conductivity method under different experimental conditions. In the presence of CTAB, Ag+ and Fe3+ ions reduce to Ag@Fe core/shell nanoparticles, comprehend a change in wavelength and intensity of SRP band. The apparent first-order rate constant, activation energy, and turnover frequency for the methyl orange reduction catalyzed by Ag@Fe NPs were found to be 1.6 × 10−3 s−1, 58.2 kJ mol−1, and 1.1 × 10−3 s−1, respectively.