Ag Interactions Research Articles

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.

On-surface formation of metal–organic coordination networks with C⋯Ag⋯C and C=O⋯Ag interactions assisted by precursor self-assembly

Surface-bound reactions are commonly employed to develop nanoarchitectures through bottom-up assembly. Precursor molecules are carefully designed, and surfaces are chosen with the intention to fabricate low-dimensional extended networks, which can include one-dimensional and two-dimensional structures. The inclusion of functional groups can offer the opportunity to utilize unique chemistry to further tune the bottom-up method or form novel nanostructures. Specifically, carbonyl groups open up new avenues for on-surface coordination chemistry. Here, the self-assembly and formation of an organometallic species via the thermally induced reaction of 3,6-dibromo-9,10-phenanthrenequinone (DBPQ) molecules were studied on Ag(100) and Ag(110). Low-temperature ultrahigh vacuum scanning tunneling microscopy revealed the room temperature formation of self-assemblies defined by hydrogen and halogen bonds on Ag(100). Following a thermal anneal to 300 °C, DBPQ on Ag(100) was found to form metal-organic coordination networks composed of a combination of organometallic species characteristics of Ullmann-like coupling reactions and carbonyl complexes. On Ag(110), the C-Br bonds were found to readily dissociate at room temperature, resulting in the formation of disordered organometallic species.

Development and Immunological Function of Lymph Node Stromal Cells.

Stromal cells have for a long time been viewed as structural cells that support distinct compartments within lymphoid tissues and little more. Instead, an active cross-talk between endothelial and fibroblastic stromal cells drives the maturation of lymphoid niches, a relationship that is recapitulated during lymph node organogenesis, steady-state conditions, and following inflammation. In this review, we go over recent advances in genetic models and high-resolution transcriptomic analyses that have propelled the finer resolution of the stromal cell infrastructure of lymph nodes, revealing that the distinct subsets are strategically positioned to deliver a catered mixture of niche factors to interacting immune cell populations. Moreover, we discuss how changes in the activation state of poised stromal cell-underpinned niches rather than on-demand differentiation of new stromal cell subsets govern the efficient interaction of Ag, APC, and cognate B and T lymphocytes during adaptive immune responses.

Studies on the interactions of Ag(i) with DNA and their implication on the DNA-templated synthesis of silver nanoclusters and on the interaction with complementary DNA and RNA sequences.

Silver nanoclusters (AgNCs) prepared by the reduction of silver ions in the presence of DNA oligonucleotides have attracted great interest as potential diagnostic tools for their tunable and high fluorescent properties. In this work, three DNA sequences that consist of a 12-nucleotide long probe sequence at the 5′-end linked to the complementary sequence to three miRNAs are studied. First, the interaction of these sequences with Ag(i) was characterized by means of circular dichroism spectroscopy. By applying multivariate methods to the analysis of spectroscopic data, two complexes with different Ag(i) : DNA ratios were resolved. Secondly, the impact of several experimental variables, such as temperature, borohydride concentration and reaction time, on the formation of AgNCs templated by these three sequences was studied. Finally, the fluorescence properties of the duplexes formed by DNA probes with complementary DNA or miRNA sequences were studied. The results presented here highlight the role of the secondary structure adopted by the DNA probe on the fluorescence properties of DNA-stabilized AgNCs which, in turn, affect the development of methods for miRNA detection.

Effects of sponge-derived Ageladine A on the photosynthesis of different microalgal species and strains

Fluorescent natural compounds have been identified in several marine hosts of microalgae. Their prevalence, and the energy the host is expending on their synthesis, suggests an important, yet poorly understood ecological role. It has been suggested that some of these natural products may enhance the photosynthesis of microbial symbionts. In this study, the effect of Ageladine A (Ag A), a pH-dependent fluorophore found in sponges of the genus Agelas, on the photosynthesis of nine microalgal species and strains was examined. The data showed that the variety of effects of Ag A additions differed between species, and even strains within a species. While in one strain of Synechococcus sp., the presence of Ag A increased gross photosynthesis under UV light exposure, it decreased in another. And while in the chlorophyte T. chuii overall metabolic activity was greatly reduced under all forms of lighting, photosynthesis in T. lutea was positively affected by the addition of Ag A. The variety of effects of Ag A on photosynthesis observed in this study indicate a complex interaction of Ag A with microalgal cells and suggests that a host may be able to shape its own symbiotic microbiome with self-produced natural products.

Promising effect of Ag/Rh paired mesoporous composite-oxide for low temperature NO[sbnd]CO reaction

A promising effect of the silver and rhodium binary precious metals added composite oxide was investigated for NO-CO redox reaction. The interaction of Ag and Rh enhanced the catalytic property of the overall composite catalyst which brought to 100% conversion of NO and CO at significantly low temperature of 150 °C. Additionally, mesoporous structure composed of such active nano-particles leads in high oxygen mobility and CO reactivity on catalyst surface, showing a good agreement with catalytic performance. Such catalytic enhancement conveys the transfer of electronic cloud from Ag to Rh which is pointing towards good synergy between active AgRh pairs.

Mechanochemical P-derivatization of 1,3,5-Triaza-7-Phosphaadamantane (PTA) and Silver-Based Coordination Polymers Obtained from the Resulting Phosphabetaines.

We have described earlier that in aqueous solutions, the reaction of 1,3,5-triaza-7-phosphaadamantane (PTA) with maleic acid yielded a phosphonium-alkanoate zwitterion. The same reaction with 2-methylmaleic acid (citraconic acid) proceeded much slower. It is reported here, that in the case of glutaconic and itaconic acids (constitutional isomers of citraconic acid), formation of the corresponding phosphabetaines requires significantly shorter reaction times. The new phosphabetaines were isolated and characterized by elemental analysis, multinuclear NMR spectroscopy and ESI-MS spectrometry. Furthermore, their molecular structures in the solid state were determined by single crystal X-ray diffraction (SC-XRD). Synthesis of the phosphabetaines from PTA and unsaturated dicarboxylic acids was also carried out mechanochemically with the use of a planetary ball mill, and the characteristics of the syntheses in solvent and under solvent-free conditions were compared. In aqueous solutions, the reaction of the new phosphabetaines with Ag(CF3SO3) yielded Ag(I)-based coordination polymers. According to the SC-XRD results, in these polymers the Ag(I)-ion coordinates to the N and O donor atoms of the ligands; however, Ag(I)-Ag(I) interactions were also identified. The Ag(I)-based coordination polymer (CP1.2) formed with the glutaconyl derivative of PTA (1) showed considerable antimicrobial activity against both Gram-negative and Gram-positive bacteria and yeast strains

Features of Chemical Interactions in Silver Chalcogenides Responsible for Their High Plasticity

A possibility of the existence of metallophilic Ag–Ag interactions in silver chalcogenides and their influence on the properties of these compounds were analyzed.

A new ladder-type silver(I) coordination polymer with 4,4'-bipyridine and 4-[(4-carboxybenzyloxy)methyl]benzoate ligands: synthesis, crystal structure, fluorescence properties and Hirshfeld surface analysis.

A novel ladder-type coordination polymer (CP), poly[(μ-4,4'-bipyridine-κ2N:N'){μ-4-[(4-carboxybenzyloxy)methyl]benzoato-κO}silver(I)](Ag-Ag), [Ag(C16H13O5)(C10H8N2)]n or [Ag(HL)(4,4'-bpy)]n {H2L is 4,4'-[oxybis(methylene)]dibenzoic acid and 4,4'-bpy is 4,4'-bipyridine}, was synthesized using hydrothermal methods. The complex was characterized by IR spectroscopy, elemental analysis and single-crystal X-ray diffraction, and is a ladder-type CP which exhibits an obvious Ag-Ag interaction. The legs of the ladder are formed by parallel 4,4'-bipy ligands and silver ions, and the rungs are constructed by Ag-Ag interactions. A Hirshfeld surface analysis was carried out and is discussed in detail. The complex also displays favourable fluorescence properties.

Effect of Ag on toluene oxidation over Ag supported wire-like MnO2 catalysts

Ag/MnO2 two-component catalysts with different loading of Ag are synthesized by liquid-phase chemical reduction and the synergistic catalytic effect mechanism for toluene oxidation is investigated. The catalytic performance is significantly affected by the addition of silver and the reaction activity is directly related to the loading amount of silver. 4% Ag/MnO2 catalyst exhibits the best catalytic performance for toluene oxidation and the complete oxidation temperature for toluene into water and carbon dioxide occurs at temperature of 220°C. More importantly, the activity at temperature lower than 200°C becomes quite high because of the interaction of Ag and MnO2. The redox ability and the amount of surface lattice oxygen in catalyst rise firstly and then drop with the increasing amount of Ag. 4% Ag/MnO2 shows the lowest reduction temperature, and gives the most amount of surface lattice oxygen and toluene desorption, therefore proper amount of Ag species is essential for the promotion of MnOx structure properties and catalytic performance. The Ag loading improves the activation of toluene molecules to be oxidized into carboxylate intermediate species, which directly causes the high activity at low temperature on 4% Ag/MnO2.

Efficient synthesis of sub-5 nm Ag nanoparticles by the desorption effect of supercritical CO2 in SBA-15

Herein, the desorption effect of supercritical CO2 (scCO2) was utilized to obtain sub-5 nm Ag nanoparticles (NPs) with a high Ag loading in SBA-15. The size of the Ag NPs decreased from 3.54 ± 0.79 nm (Ag loading of 25.3 wt.% wt.%) to 2.38 ± 0.68 (Ag loading of 10.5 wt%) nm by changing the depressurization curve from 0.1 MPa min−1 (20–14 MPa) to 3 MPa min−1 (20–12 MPa). Meanwhile, the intensity of the crystalline Ag characteristic peaks was obviously higher than the latter sample from the x-ray diffraction (XRD) patterns. However, compared with the adsorption kinetics of the two precursors of AgNO3 and Cu(NO3)2 on SBA-15, under the same deposition and depressurization conditions, when the two depositional systems used water as a co-solvent, the time taken to reach the adsorption equilibrium of Ag+ on the supports was longer than the time taken by Cu2+, which existed in the water as [Cu(H2O)4]2+. The surface of SBA-15 was hydrophilic, and then the interaction of Ag+ and the surface was weaker compared with Cu2+, making Ag+ highly dispersed on the surface under the scCO2 desorption effect. After calcination, the size of the Ag NPs decreased, but the morphology of CuO was mainly characterized by nanorods (NRs). Moreover, by comparing the experiments of wetness impregnation, the dispersion ability of the bulk scCO2 of the reactor was inefficient for Ag+ adsorbed on the channels in the depressurization process.

Probing the Kinetic and Thermodynamic Fingerprints of Anti-EGF Nanobodies by Surface Plasmon Resonance.

Despite the widespread use of antibodies in clinical applications, the precise molecular mechanisms underlying antibody–antigen (Ab–Ag) interactions are often poorly understood. In this study, we exploit the technical features of a typical surface plasmon resonance (SPR) biosensor to dissect the kinetic and thermodynamic components that govern the binding of single-domain Ab or nanobodies to their target antigen, epidermal growth factor (EGF), a key oncogenic protein that is involved in tumour progression. By carefully tuning the experimental conditions and transforming the kinetic data into equilibrium constants, we reveal the complete picture of binding thermodynamics, including the energetics of the complex-formation transition state. This approach, performed using an experimentally simple and high-throughput setup, is expected to facilitate mechanistic studies of Ab-based therapies and, importantly, promote the rational development of new biological drugs with suitable properties.

Subnanomolar detection of ions using thin voltammetric membranes with reduced Exchange capacity

Herein, we report on a new strategy to improve the limit of detection of ionophore-based thin membranes interrogated under accumulation/stripping electrochemical protocol. Accordingly, we demonstrate subnanomolar detection of silver ion (Ag+) in water samples by re-formulating the membrane content with a reduced amount of the cation exchanger sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (Na+TFPB–), i.e. 10 mmol kg–1 compared to 40 mmol kg–1 commonly used in previous thin cation-selective membranes. Thoughtfully, by decreasing the amount of NaTFPB in the membrane phase, a diminution of its total ion-exchange capacity is to be seen. Essentially, a lower exchange capacity causes that the saturation of the membrane occurs at a lower concentration of Ag+, allowing us to reach a lower limit of detection. This effect is indeed promoted by achieving the total replacement of the Na+ present in the membrane by Ag+ entering from the solution (even at the subnanomolar level) at shorter accumulation times in the readout protocol. For the silver-selective electrode, we found a linear range of response with the peak current from 0.05–10 nM Ag+ concentration. The developed silver-selective electrode is successfully applied to the determination of Ag+ at the (sub)nanomolar level in different water samples (i.e., tap water, seawater and freshwater samples), with the results validated using inductively coupled plasma mass spectrometry as well as recovery studies. In addition, the electrode is suitable for dynamic studies involving the interaction of Ag+ with compounds forming natural organic matter in aquatic resources such as humic acid.

Effect of Al2O3 phase on the catalytic performance for HCHO oxidation over Ag/Al2O3 catalysts

The effect of different crystalline phases of Al2O3 (γ-Al2O3, γ, θ-Al2O3) on HCHO oxidation over Ag catalysts is investigated, and the silver state and particle size strongly depend on the Al2O3 crystalline phase. The various coordinatively unsaturated Al3+ (AlⅢ, AlⅤ) involves in the formation of Ag-O-Al entities. Ag species is mainly anchored on AlⅤ sites for γ-Al2O3, whereas mainly on AlⅢ sites for γ, θ-Al2O3. The weaker interaction of Ag, O and AlⅤ on γ-Al2O3 compared with that of Ag, O and AlⅢ on γ, θ-Al2O3 and the larger surface area of γ-Al2O3 result in the formation of more Ag0 with high dispersion. The higher fraction of coordinated AlⅥ on γ-Al2O3 provides more adjacent hydroxyl groups for HCHO adsorption and formation of intermediates. And the synergistic effect of OH group and the high activation ability for oxygen on smaller Ag0 particles give the high HCHO oxidation activity on Ag/γ-Al2O3 (T100 = 85 °C).

OR24-02 Identification of Membrane Proteins That Enhance the Responsiveness of the Ghrelin Receptor

Ghrelin, a 28-amino acid peptide gut hormone, occurs in acylated (AG) and unacylated (UAG) variants. AG is a GH secretagogue as well as being orexigenic and diabetogenic, acting via the growth hormone secretagogue receptor (GHSR1a) in the hypothalamus and pituitary. UAG counteracts these metabolic effects through unknown mechanisms. While screening for potential UAG receptor(s) we discovered previously uncharacterised interactions of AG and UAG with five cell membrane proteins (MPs), three of which are known to modulate metabolism. Here, we studied if two of these MPs (MP1 & 2) could modulate GHSR1a signalling by expressing their transgenes in HEK293 cells. As GHSR1a is coupled with calcium signalling via Gq proteins, aequorin luminescence was used to evaluate Ca2+ influx into the cells. Transfected cells were treated with either AG, UAG, or soluble parts of the MPs, or combinations thereof.MP2 markedly enhanced the efficacy (~5.5-fold), but not the potency, of AG-induced Ca2+ influx, whereas MP1 had no effect on Ca2+ influx. Neither MP1 nor MP2 overexpression altered cellular GHSR1a levels. In the absence of GHSR1a, MP2 was unable to stimulate an AG-induced Ca2+ influx. UAG treatment (100nM) had no effect on GHSR1a-mediated Ca2+ influx in the presence or absence of MP2. MP2 is post-translationally modified and we suspected this to be important for its activity. However, removal or blockade of these modifications had no effect on the ability of MP2 to enhance GHSR1a signalling. Moreover, incubating the cells with soluble ectodomain of MP2 did not alter its effect on GHSR1a signalling. Nevertheless, induction of ectodomain shedding with PMA (0.4-1µM) dose-dependently reduced the AG-induced Ca2+ response to 0.5-0.2 of control levels (DMSO) in MP2-GHSR1a co-transfected cells. Unlike MP2, which has a transmembrane and intracellular domain, MP1 is attached to the plasma membrane via a glycosylphosphatidylinositol (GPI) anchor and lacks an intracellular domain. Since MP1 is otherwise structurally similar to MP2, we suspected that the intracellular domain of MP2 may be important for its function. Therefore, we expressed chimeras of MP2 and MP1 in which the GPI linkage site and the transmembrane/intracellular domains were exchanged. The MP2 ectodomain with a GPI-anchor had similar stimulatory effects on GHSR1a signalling as full-length MP2, whereas the MP1 ectodomain with MP2 transmembrane and intracellular domain only enhanced GHSR1a signalling by approximately 3-fold.In conclusion, we have identified a membrane protein as a novel component of the ghrelin signalling pathway that markedly enhances the response of the ghrelin receptor to AG. Our current data suggest its ectodomain is important in mediating this effect. Studies are ongoing to fully delineate the mode of interaction and to determine the role of MP2 in ghrelin signalling in vivo.

Modification-free amperometric biosensor for the detection of wild-type p53 protein based on the in situ formation of silver nanoparticle networks for signal amplification

Sensitive and accurate quantification of wild-type p53 protein is of great importance for biological research and clinical diagnosis. Herein, a modification-free amperometric biosensor was proposed for sensitive detection of wild-type p53 protein by the signal amplification of silver nanoparticles (AgNPs) networks formed in situ on electrode surface. Double-stranded DNA (dsDNA) probe containing two consensus sites was immobilized on gold electrode surface to capture wild-type p53 protein. The cysteine thiol and amine groups on the exterior of the protein allowed for the attachment of bare AgNPs through the AgS or AgN interactions. Meanwhile, benzene-1,4-dithiol (BDT) molecules in solution triggered the assembly of more AgNPs on electrode surface through the AgS interactions, thus leading to the in situ formation of AgNPs networks for signal amplification. The target at the concentration as low as 0.1 pM can be readily determined. This method was further applied to determine wild-type p53 protein in spiked human serum and cell lysates with satisfactory results. Moreover, the biosensor is regenerative and does not require the modification of AgNPs with recognition element for signal readout. The modification-free strategy can potentially be applied to develop novel biosensors for detection of other biological macromolecules.

Crystal design, thermal and dielectric behavior of novel silver (Ag) co-ordinated thiourea single crystals

Novel silver co-ordianted thiourea adducts was synthesized by mechanochemical stirring process. Structural data of TuAgN (1:1) and TuAgN (4:1) were collected with the help of single crystal X-ray diffractometer and their unique structural properties were studied and compared. The ratio of the compounds 1:1 and 4:1 represents the mole ratio of thiourea and silver nitrate which has taken for the synthesis. i.e. TuAgN (1:1) indicates, 1 mole of thiourea and 1 mole of silver nitrate and TuAgN (4:1) reveals, 4 mole of thiourea and 1 mole of silver nitrate. The crystalline materials belong to Triclinic and Tetragonal systems with a space group of P-1 and I41 respectively. In both the crystal systems, a single Ag atom co-ordinate with three thiourea ligands and the chain is continued through Ag to Ag interactions. TG/DTA study provides the details of thermal stability and thermal decomposition behavior of the crystals. Electrical characterizations like dielectric constant, dielectric loss and their importance were studied at different temperatures (40, 60 and 80 °C) in the frequency range from 50 Hz to 5 MHz.

Features of Extended XPS Spectra of C2FBr0.15 Intercalate and Silver Foil

The possibility to obtain novel data by standard electron spectroscopy and quantum chemical techniques is exemplified by C2FBr0.15 intercalate and silver foil. The features of extended X-ray photoelectron spectra are interpreted by electronic transitions in the valence band of similar unit cells. The analysis of experimental and calculated spectra reveals two states of intercalated Br2: molecular and chain-like. The interaction of Ag with NO2 at 300–520 K is limited by the formation of an oxidized state in the near-surface layer with a thickness of ∼6 A, with the metallic state of silver dominating in the Ag3d И Ag MNN spectra. Geometric parameters, states of atoms, and the character of bonds between them are consistent with the previously obtained results.

Changes in Spectral Properties of Aqueous Silver Sols Induced by Complexation on the Surface of Nanoparticles

The interaction of Ag+ ions existing on the surface of silver nanoparticles with complexing agents, such as ammonia, ammonium thiocyanate, and sodium thiosulfate, has been studied. Both the presence of complexing agents in the initial reaction mixture and their introduction into preliminarily synthesized sols of silver nanoparticles lead to a small shift of the absorption maximum toward long wavelengths and its considerable broadening. In both cases, there is a correlation of the absorption band width with the logarithm of formation constants of corresponding silver complexes. This can be evidence of analogous chemical processes that occur on the surface of nanoparticles. The surface complexation is of interest both for a fundamental understanding of the interaction nature and in the applied aspect for the determination of complexing agents in aqueous systems.