Ag Interactions Research Articles

Fabrication of electrochemical immunosensor based on GCN-β-CD/Au nanocomposite for the monitoring of vitamin D deficiency

Serum 25-hydroxyvitamin D (25(OH)D) has been clinically considered as a novel biomarker for vitamin D deficiency. The current standard technologies for the detection of 25(OH)D are performed in sophisticated laboratories exhibiting the practical limitations for onsite and affordable testing. Therefore, the development of a cost-effective device for Vitamin D is extremely necessary to provide an earlier diagnosis. Herein, for the first time, we propose a novel label-free impedimetric immunosensor for the detection and quantification of 25-hydroxyvitamin D3 (25(OH)D3) biomarker in serum samples based on the Au nanoparticles functionalized GCN–β-CD nanocomposite. To fabricate the sensing probe, Ab-25(OH)D3 antibodies were covalently immobilized on GCN–β-CD@Au/GCE using carbodiimide chemistry. The surface morphology and structural properties of constructed immunosensor were confirmed by different analytical techniques. Electrochemical impedance spectroscopy technique (EIS) has been selected as the main detection method to measure the Antibody (Ab) and Antigen (Ag) interaction at the immunosensor surface because it is label-free, less destructive to the activities of the biomolecule, and highly sensitive. The as-prepared immunosensor exhibited an excellent concentration range from 0.1 ng/ml to 500 ng/ml with the lowest limit of detection of 0.01 ng/ml. Furthermore, the sensing probe was validated in serum samples and obtained results were compared with the standard CLIA technique. The results have revealed that the sensing probe could be used for clinical diagnosis of Vitamin D deficiency in the clinical laboratories.

Photothermal and colorimetric dual-readout silver ions determination utilizing the oxidase-mimicking activity of MnO2 nanosheets

Accurate and sensitive sensing of silver ions (Ag+) is meaningful to environmental safety and human health. However, many of the analytical methods for Ag+ usually rely on large analytical instruments for quantitative reading. Herein, we report a portable assay for Ag+ based on the excellent colorimetric and photothermal properties of a dye 3,3′,5,5′-tetramethylbenzidine (TMB). As an oxidase-like activity nanomaterial, MnO2 nanosheets (NSs) were employed to catalyze the oxidation of TMB into oxTMB. Nevertheless, the reduction of MnO2 NSs by glutathione (GSH) could minimize the catalytic ability of the MnO2 NSs. In this approach, the specific interaction of Ag+ and GSH was utilized to suppress this reduction process. According to this principle, Ag+ concentrations could be transformed to temperature and color signals. So that, Ag+ could be identified with naked-eyes, and also sensitive determined with a portable thermometer. The proposed sensor exhibited a high selectivity, making it a sensitive, portable, and accurate new Ag+ detection system.

Green synthesis of Phenothiazinium Schiff base and its nano silver complex using egg white as a catalyst under solvent free condition

In the current study, an efficient method was developed for the preparation of phenothiazinium Schiff base ligand followed by the attachment to nanosilver mediated by egg white (lysozyme) as a catalyst and reductant under solvent-free conditions. The synthesized Schiff base ligand, nanosilver, and its complex were characterized by UV, IR, XRD, and NMR. Biological studies for Schiff base ligand, nanosilver, and its complex were investigated. The advantages of this method are environmentally benign process; the product can be isolated simply by filtration, simplicity, elimination of solvents, high product yields, and short reaction times. The synthesized compounds were tested for their in vitro antimicrobial activity using the broth dilution method against Staphylococcus aureus (gram-positive) and E. coli (gram-negative) bacteria. From the results the silver nanocomplex exhibits enhanced antibacterial activity which may be due to the interaction of Schiff base and nano Ag on the bacterial cell wall. The silver complex can be utilized in the future for drug delivery and biomedical applications.

Cover Feature: Structural Diversity and Argentophilic Interactions in Small Phosphine Silver(I) Thiolate Clusters (Eur. J. Inorg. Chem. 27/2021)

The Cover Feature shows the Ag⋅⋅⋅Ag interactions in various small phosphine silver(I) thiolate clusters. The argentophilic contacts can be either attractive or repulsive as a function of the electronic and geometric environment of the silver centers, which is in turn modulated by the ligand effects. The real space electron density (QTAIM and NCI-index) and energy decomposition (IQA) analyses deliver insights into these effects. Our investigation provides new tools for the precise atomic design and construction of higher nuclearity clusters. The background was adapted from the image The Crab Nebula in Taurus (Credit: ESO). More information can be found in the Full Paper by G. Moreno-Alcántar and co-workers.

Structural Diversity and Argentophilic Interactions in Small Phosphine Silver(I) Thiolate Clusters

AbstractSilver(I) coordination compounds display an interesting geometrical diversity, the possibility of having distinct coordination numbers (typically from 2 to 4) and the capability of forming argentophilic (Ag⋅⋅⋅Ag) interactions. These properties complicate the accurate prediction of structures of silver complexes under certain experimental conditions. In this work, we show how subtle modifications in thiolate and phosphine ligands exert important effects on the nuclearity and geometry of phosphine caped clusters [Ag(SR)]n(n=4, 6 and 8). We rationalize these effects in terms of the electronic environment of silver centers by analyzing the electronic density of the single‐crystal X‐ray structures via the Quantum Theory of Atoms in Molecules (QTAIM) and the Non‐Covalent Interaction (NCI)‐Index. Furthermore, we characterized attractive and repulsive argentophilic contacts by means of the Interacting Quantum Atoms (IQA) energy partition. Our results provide insights on the effects of ancillary ligands in controlling the structure of silver‐thiolate clusters. Such control is relevant towards a bottom‐up approach to the atomic precise construction of higher nuclearity clusters.

Chemical Interface Damping of Silver‐coated Gold Nanorods Using Supramolecular Host–Guest Chemistry

We present the chemical interface damping (CID) of single Ag‐coated Au nanorods (AuNRs@Ag) using cucurbit[7]uril (CB[7])‐based host–guest chemistry. The chemisorption of CB[7]‐NH2 onto an AuNR@Ag surface resulted in a redshift of its localized surface plasmon resonance (LSPR) scattering peak, with a considerably increased linewidth. This LSPR broadening was ascribed to CID caused by the formation of a strong nitrogen–Ag interaction during the chemisorption of CB[7]‐NH2 onto the AuNR@Ag surface. Furthermore, we observed additional broadening of the LSPR linewidth when the guest molecule (oxaliplatin) was encapsulated into CB[7]‐NH2 chemisorbed onto the AuNR@Ag surface.

Interaction of Ag+ with corannulene: Experimental and theoretical study

By using electrospray ionization mass spectrometry (ESI-MS), it was proven experimentally that the silver cation Ag+ forms with corannulene (C20H10) the cationic complex [Ag(C20H10)2]+. Further, applying quantum chemical DFT calculations, the most probable structures of the [Ag(C20H10)2]+ complex were derived. In the resulting complex the “central” cation Ag+, is located between two molecules of the corannulene ligand. Finally, the interaction energy, E(int), of the considered cation-π complex [Ag(C20H10)2]+ was found to be −335.0 to −306.9 kJ/mol.

A label-free Exonuclease I-assisted fluorescence aptasensor for highly selective and sensitive detection of silver ions

Based on the specific interaction of Ag+ and cytosine-cytosine (C-C) base mismatch and using berberine (Ber) as the fluorescent probe and Exonuclease I (Exo I) as the background fluorescence reducing tool, a label-free Exo I-assisted fluorescence aptamer sensing platform was established for the detection of silver ions with high sensitivity and selectivity. Exo I reduced the fluorescence background of the Ber/Ag+-aptamer complex to a level similar to that of Ber itself in the absence of Ag+. After introducing Ag+ into the sensing system, it induces the aptamer rich in base C to form C-Ag+-C i-motif structure which are resistant to degradation mediated by Exo I. The concentration of Ber, Ag+-aptamer, Exo I and the temperature and reaction time for Exo I were all optimized. Under the optimal experimental conditions, the detection limit of Ag+ was 4.4 nM and the linear range was from 0.0059 μM to 235.48 μM with a coefficient of determination (R2) > 0.99. Moreover, the proposed strategy had been successfully applied to the detection of Ag+ in tap water and human serum with a good recovery ranging from 88.4% to 106.9%.

Functional and in silico Characterization of Neutralizing Interactions Between Antibodies and the Foot-and-Mouth Disease Virus Immunodominant Antigenic Site.

Molecular knowledge of virus–antibody interactions is essential for the development of better vaccines and for a timely assessment of the spread and severity of epidemics. For foot-and-mouth disease virus (FMDV) research, in particular, computational methods for antigen–antibody (Ag–Ab) interaction, and cross-antigenicity characterization and prediction are critical to design engineered vaccines with robust, long-lasting, and wider response against different strains. We integrated existing structural modeling and prediction algorithms to study the surface properties of FMDV Ags and Abs and their interaction. First, we explored four modeling and two Ag–Ab docking methods and implemented a computational pipeline based on a reference Ag–Ab structure for FMDV of serotype C, to be used as a source protocol for the study of unknown interaction pairs of Ag–Ab. Next, we obtained the variable region sequence of two monoclonal IgM and IgG antibodies that recognize and neutralize antigenic site A (AgSA) epitopes from South America serotype A FMDV and developed two peptide ELISAs for their fine epitope mapping. Then, we applied the previous Ag–Ab molecular structure modeling and docking protocol further scored by functional peptide ELISA data. This work highlights a possible different behavior in the immune response of IgG and IgM Ab isotypes. The present method yielded reliable Ab models with differential paratopes and Ag interaction topologies in concordance with their isotype classes. Moreover, it demonstrates the applicability of computational prediction techniques to the interaction phenomena between the FMDV immunodominant AgSA and Abs, and points out their potential utility as a metric for virus-related, massive Ab repertoire analysis or as a starting point for recombinant vaccine design.

Probing the Ag – liquid gallium system and its interaction with redox active solutions for catalysis and AgTCNQ formation

The creation of liquid metal alloys that are reacted with species in solution is a relatively new approach to the synthesis of functional nanomaterials. In this work we explore the liquid Ag–Ga system and its interaction with redox active species in aqueous solution in the areas of heterogeneous catalysis and charge transfer complex formation. It was found that when Ag is alloyed with Ga that solid microwires of Ag2Ga were formed over time with a width of ca. 1–1.5 µm of up to 160 µm in length. This Ga/Ag2Ga composite was then investigated for the discolouration of methylene blue dye in both the liquid and solid state where little difference in activity was found resulting in 40% discolouration after 30 min. However, if nitrogen gas was passed through the liquid form of the catalyst the conversion efficiency of the catalyst increased significantly up to 99% after 1 min and could be re-used for up to 10 cycles. In addition, the catalytic conversion of 4-nitrophenol to 4-aminophenol at the liquid Ga/Ag2Ga catalyst was significantly greater than liquid Ga and could be reused for up to 5 cycles. The interaction of liquid Ag–Ga with the well-known electron acceptor 7,7,8,8-tetracyanoquinodimethane (TCNQ) was also studied where it was found that a reaction only occurred immediately after mixing Ag microparticles with liquid Ga and before any Ag2Ga microwires were formed. The reaction conditions of bubbling nitrogen gas through the liquid Ag–Ga catalysts in an acetonitrile solution of TCNQ resulted in the time dependent formation of various morphologies of the semi-conducting charge transfer complex AgTCNQ. This work shows that alloying metals with Ga can result in the time dependent formation of a variety of materials under different reaction conditions when exposed to solution based redox active species.

Hydrophilic Character of Single-Layer MoS2 Grown on Ag(111).

The study of MoS2/metal interfaces is crucial for engineering efficient semiconductor–metal contacts in 2D MoS2-based devices. Here we investigate a MoS2/Ag heterostructure fabricated by growing a single MoS2 layer on Ag(111) by pulsed laser deposition under ultrahigh vacuum (UHV) conditions. The surface structure is observed in situ by scanning tunneling microscopy, revealing the hexagonal moiré pattern characteristic of the clean MoS2/Ag(111) interface. Ex situ Raman spectroscopy reveals an anomalous behavior of vibrational modes, induced by the strong MoS2–Ag interaction. After few-hours exposure to ambient conditions the Raman response significantly changes and the formation of molybdenum oxysulfides is revealed by X-ray photoelectron spectroscopy. These effects are due to the interplay with water vapor and can be reversed by a moderate UHV annealing. A polymeric (PMMA) capping is demonstrated to hinder water-induced modifications, preserving the original interface quality for months.

Interactions of Ag+ ions and Ag-nanoparticles with protein. A comparative and multi spectroscopic investigation

UV–visible and florescence spectroscopic methods have been applied to analyze the binding capabilities of Ag+ ions and AgNPs with bovine serum albumin (BSA). UV–visible studies revealed that BSA acted as a ligand towards both Ag+ and AgNPs, and provides potential site for coordination. BSA fluorescence was quenched significantly by the quenchers (Ag+ and AgNPs). The binding constant, quenching constant, quantum yield, and coordination sites were evaluated. The Ag+ ions has strong binding and quenching efficiency towards BSA than that of AgNPs. The distance between the tryptophan and acceptor decreases from 127 Å to 72 Å with Ag+ ions from 0.6 to 20.0 × 10-5 mol/L. The energy transfer from BSA to ligand (Ag+ ions and AgNPs) follows a surface energy transfer process with a 1/d4 distance dependence. This is found to be according to strong coordinating affinity of metal ions with structural unit of protein, which helps to understand the mechanism of bacterial cell death in presence of metal ions and/or metal NPs.

Probing the Surface Chemistry of Nanoporous Gold via Electrochemical Characterization and Atom Probe Tomography.

Surface chemistry information is crucial in understanding catalytic and sensing mechanisms. However, resolving the outermost monolayer composition of metallic nanoporous materials is challenging due to the high tortuosity of their morphology. In this study, we first elaborate on the capabilities and limitations of atom probe tomography (APT) in resolving interfaces. Subsequently, an electrochemical approach is designed to characterize the surface composition of nanoporous gold (NPG), developed from dealloying an inexpensive precursor (95 at. % Ag, 5 at. % Au), by the means of aqueous electrochemical measurements of the selective electrosorption of sulfide ions, which react strongly with Ag, but to a significantly lesser extent with Au. Accordingly, cyclic voltammetry was performed at various scan rates on NPG in alkaline aqueous solutions (0.2 M NaOH; pH 13) in the presence and absence of 1 mM Na2S. Calibrations via similar voltammetric measurements on pure polycrystalline Ag and Au surfaces allowed for a quantitative estimation for the Ag surface coverage of NPG. The sensitivity threshold for the detection of the adsorbate–Ag interaction was assessed to be approximately 2% Ag surface coverage. As curves measured on NPG only showed featureless capacitive currents, no faradaic charge density associated with sulfide electrosorption could be detected. This study opens a new avenue to gain further insight into the monolayer surface coverage of metallic nanoporous materials and assists in enhancement of the interpretation of APT reconstructions.

A novel silver(I) di-iso-butyldithiocarbamate: Unusually complicated 1-D polymeric structure, multiple ligand-supported Ag–Ag interactions and its capability to bind gold(III). Preparation, structural organisation and (13C, 15N) CP-MAS NMR of [Ag6(S2CNiBu2)6]n and [Au(S2CNiBu2)2][AgCl2

We have synthesised three new complexes of [Ag6{S2CN(iso-C4H9)2}6]n (1), [Au{S2CN(iso-C4H9)2}2][AgCl2] (2) and [Au{S2CN(iso-C4H9)2}2][Ag0.69Au0.31Cl2] (3), chemically identified these compounds using solution (1H, 13C) and solid-state (13C, 15N) CP-MAS NMR and FT-IR spectroscopy, and structurally characterised them by single-crystal X-ray diffraction analysis. There are six structurally inequivalent silver(I) centres in the former compound, whose unusually complicated, monodimensional polymeric structure is generally stabilised by six unequal iBuDtc ligands acting as bridges, along with numerous ligand-supported Ag–Ag interactions. Studying the capability of the precipitated AgiBuDtc to bind gold(III) from a [AuCl4]–/5.15 M NaCl solution, the double pseudo-polymeric heterometallic dithiocarbamato-chlorido complexes 2 and 3 were successfully obtained as individual fixation modes of gold to the solid phase. In the self-assembly of a bidimensional supramolecular structure of the latter two compounds, numerous interionic secondary bonds (Au···S, Ag···S and S···Cl), the anagostic HC···Ag interactions and the Cl···HC hydrogen bonds play a key role. To study the thermal behaviour of crystalline compounds 1 and 2, we additionally used simultaneous thermal analysis (STA). During the thermolysis of 1/2, the formation of Ag2S/AgCl,Au0 was supported, respectively, by energy dispersive X-ray (EDX) spectroscopy, while the dispersity and morphology of residual substances were studied using scanning electron microscopy.

Two 1D double-chain silver coordination polymers constructed by Ag-Ag bonds: Synthesis, structure and properties

Two new one-dimensional (1D) double-chain Ag(I) coordination polymers, namely: {[Ag(Hcn)(bpy)]·2CH3OH}n (1), [Ag2(Hidc)(H2O)2]n (2) (Hcn = 2-hydroxycinnamate, bpy = 4,4′-bipyridine, Hidc = 4,5-imidazoledicarboxylate), were synthesized by volatilization method and characterized by single-crystal X-ray diffraction, elemental analysis, IR and UV–vis spectra. Single-crystal analyses show that although two Ag(I) CPs are both 1D double-chain structure constructed by Ag-Ag bonds, CP 1 is linear, while CP 2 is zigzagged. This difference in the structure may be due to the symmetry of the repeat unit of the Ag(I) CPs and the linkage pattern of the Ag-Ag bonds, in which the repeat unit of CP 1 is symmetric, whereas that of CP 2 is asymmetric. The fluorescence properties of the ligands and CPs 1-2 in the solid-state were studied. The fluorescence peaks of the two Ag(I) CPs were weakened compared to the ligands, which is attributed to ligand-centered fluorescence. The partial quenching of the aggregates may be due to the Ag-Ag interactions. In addition, cyclic voltammograms of CPs 1-2 indicated an irreversible Ag+/Ag couple with the order of reversibility being 1 > 2.

Effects of Both Methyl and Pyrimidine Groups in Fe-Ag Spin-Crossover Hofmann-Type Complex {Fe(4-Methylpyrimidine)2[Ag(CN)2]2}.

The spin-crossover (SCO) phenomenon is an active area of research. This paper describes the synthesis of an Fe-Ag Hofmann-type complex, {Fe(4-methylpyrimidine)2[Ag(CN)2]2}, which demonstrates a one-step SCO and single-layer Hofmann-type structure with Ag-N interactions and no Ag-Ag interactions, which is strikingly different from the previously synthesized complex {Fe(4-methylpyrimidine)2[Au(CN)2]2} that contains Au-Au interactions and no Au-N interactions. This difference can be explained in terms of the lack of relativistic effect in the Ag atoms and the different cooperative effects caused by their different structures. A scan-rate-dependent hysteresis is observed using magnetic measurement whereas not using 57Fe Mössbauer spectroscopy, suggesting that the spin transition is relatively slow.

A new silver 1D-coordination polymer with bridging 2-aminopyrimidine, synthesis, characterization and antibacterial activity

A new silver(І) complex formulated as [Ag(μ-amp)(ONO2)]n (1) (amp = 2-aminopyrimidine) was synthesized and characterized by elemental analysis, IR spectroscopy, and single-crystal X-ray diffraction. Its thermal stability was studied by TGA/DTA. The bridging 2-aminopyrimidine ligands connect Ag(I) ions into a polymeric chain extended along the a axis; the chains are connected by nitrate anions and Ag…Ag interactions into 2 D arrays parallel with ac; these arrays are finally connected by hydrogen bonds into a three-dimensional network. In vitro antibacterial activities of 1 on Staphylococcus aureus (ATCC25923), Enterococcus faecalis (ATCC29219), Pseudomonas aeruginosa (ATCC27853) and Escherichia coli (ATCC25922) as important pathogens in producing infection in humans were investigated. Antibacterial activities were studied by determining minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The silver 1 D-coordination polymer with appropriate concentrations has good efficacy on these microorganisms. Escherichia coli is most sensitive to the complex (MIC: 0.009 µg/mL).

Novel synthesis, structural characterization, DFT and TDDFT investigation of ‘Butterfly’ like Ag(I)- complex supported by 3-pyrazinyl [1-methyl)imidazolium hexaflurophosphate

1-methyl-3-(3-pyrazine)imidazolium hexafluorophosphate, (1.HPF6) and its Ag(I) complexes (2 and 3) have been synthesized and characterized by a series of spectroscopic techniques. Complex 2 has been synthesized using proligand 1.HPF6 after floating the same in methanolic solution of AgPF6 (in 2:1 ratio); whereas complex 3 has been prepared from acetonitrile solution. Finally the solid state structures of 2 and 3 have been established by single crystal X-ray diffraction studies. Interestingly, single crystal X-ray diffraction studies establish 2 as a mononuclear and complex as dinuclear complex where two Ag(I) bridged by two CH3CN (μ2-patern). The asymmetric unit possesses two different types of molecules. Theoretical studies have been performed to inside into the structure. DFT and AIM studies also support the weak Ag–Ag interaction.

Synthesis and Structural Characterization of a Silver(I) Pyrazolato Coordination Polymer.

Coinage metal(I)···metal(I) interactions are widely of interest in fields such as supramolecular assembly and unique luminescent properties, etc. Only two types of polynuclear silver(I) pyrazolato complexes have been reported, however, and no detailed spectroscopic characterizations have been reported. An unexpected synthetic method yielded a polynuclear silver(I) complex [Ag(μ-L1Clpz)]n (L1Clpz− = 4-chloride-3,5-diisopropyl-1-pyrazolate anion) by the reaction of {[Ag(μ-L1Clpz)]3}2 with (nBu4N)[Ag(CN)2]. The obtained structure was compared with the known hexanuclear silver(I) complex {[Ag(μ-L1Clpz)]3}2. The Ag···Ag distances in [Ag(μ-L1Clpz)]n are slightly shorter than twice Bondi’s van der Waals radius, indicating some Ag···Ag argentophilic interactions. Two Ag–N distances in [Ag(μ-L1Clpz)]n were found: 2.0760(13) and 2.0716(13) Å, and their N–Ag–N bond angles of 180.00(7)° and 179.83(5)° indicate that each silver(I) ion is coordinated by two pyrazolyl nitrogen atoms with an almost linear coordination. Every five pyrazoles point in the same direction to form a 1-D zig-zag structure. Some spectroscopic properties of [Ag(μ-L1Clpz)]n in the solid-state are different from those of {[Ag(μ-L1Clpz)]3}2 (especially in the absorption and emission spectra), presumably attributable to this zig-zag structure having longer but differently arranged intramolecular Ag···Ag interactions of 3.39171(17) Å. This result clearly demonstrates the different physicochemical properties in the solid-state between 1-D coordination polymer and metalacyclic trinuclear (hexanuclear) or tetranuclear silver(I) pyrazolate complexes.

A “nucleophilic” iodine in a halogen-bonded iodonium complex manifests an unprecedented I+···Ag+ interaction

Summary When an electron is removed from a halogen atom, it forms a halenium ion X+ (X = I, Br, Cl). In halogen bonding (XB), X+ is considered as a strong XB donor, and when interacting with two XB acceptors (e.g., pyridine), it forms a halonium XB complex with a [N–I–N] three-center-four-electron bond with the two XB acceptors. An unprecedented I+···Ag+ interaction occurs between a [L1–I–L1]+ halogen-bonded complex and a [L2–Ag–L2]+ complex in which the iodonium ion acts like a nucleophile and donates electrons to the silver(I) cation. The X-ray diffraction analysis reveals a short contact [3.4608(3) A] between the I+ and Ag+ cations, and ITC measurements give a ΔG of −6.321 kcal/mol and Ka∼37,000 M−1 for the 1:1 complex. The DFT computational study on the nature of the I+···Ag+ interaction indicates that the I+ is nucleophilic in character, manifesting an unusual and strongly attractive interaction between the I+ and Ag+ cations.