Affinity For Ag Research Articles

Reconstruction of a helical trimer by the second transmembrane domain of human copper transporter 2 in micelles and the binding of the trimer to silver

The second transmembrane domain of human copper transporter 2 (hCtr2-TMD2) forms a trimer with a weaker intermolecular interaction and a lower affinity for Ag(I) than hCtr1-TMD2 trimer.

A subset of AID-dependent B-1a cells initiates hypersensitivity and pneumococcal pneumonia resistance.

We propose that there is a special B-1a B cell subset ("sB-1a" cells) that mediates linked processes very early after immunization to initiate cutaneous contact sensitivity (CS), delayed-type hypersensitivity (DTH), and immune resistance to pneumococcal pneumonia. Our published data indicate that in CS and DTH, these initiating processes are required for elicitation of the delayed onset and late-occurring classical T cell-mediated responses. sB-1a cells resemble memory B2 cells, as they are stimulated within 1 h of immunization and depend on T helper cytokines-uniquely IL-4 from hepatic iNKT cells--for activation and rapid migration from the peritoneal cavity to the spleen to secrete IgM antibody (Ab) and Ab-derived free light chains (FLCs) by only 1 day after immunization. Unlike conventional B-1a (cB-1a) cell-produced IgM natural Ab, IgM Ab produced by sB-1a cells has high Ag affinity owing to immunoglobulin V-region mutations induced by activation-induced cytidine deaminase (AID). The dominant cB-1a cells are increased in immunized AID-deficient mice but do not mediate initiation, CS, or pneumonia resistance because natural Ab has relatively low Ag affinity because of unmutated germ-line V regions. In CS and DTH, sB-1a IgM Ag affinity is sufficiently high to mediate complement activation for generation of C5a that, together with vasoactive mediators such as TNF-α released by FLC-sensitized mast cells, activate local endothelium for extravascular recruitment of effector T cells. We conclude by discussing the possibility of functional sB-1 cells in humans.

Complexation of silver and dissolved organic matter in soil water extracts

An important aspect of the behaviour and fate of silver (Ag) in soils is the interaction with dissolved organic matter (DOM). The complexation and strength of binding of Ag+ with DOM in soil water extracts was examined and modelled based on a range of chemical and quality DOM measurements. Silver ion binding measured by addition of the 110mAg radioisotope in addition to a cation exchange resin technique were used to determine strongly complexed Ag in solutions. Silver was found to be up to 70% strongly complexed. The variability in Ag+ binding by DOM across different soils was closely related (R2 = 0.8) to the mid-infrared spectra of these extracts. The affinity of Ag+ for DOM was stronger in solutions containing a greater content of humic and aromatic structures. The ability of Ag+ to complex with DOM could result in increased mobilisation of this metal in the soil environment.

A signal-off sandwich photoelectrochemical immunosensor using TiO2 coupled with CdS as the photoactive matrix and copper (II) ion as inhibitor

In this work, a novel sandwich photoelectrochemical (PEC) biosensor was developed based on a signal-off strategy using TiO2 coupled with CdS quantum dots (QDs) as the photoactive matrix and copper (II) ion (Cu2+) as inhibitor. TiO2/CdS modified indium tin oxide (ITO) electrode was employed for primary antibody (Ab1) immobilization and the subsequent sandwich-type antibody–antigen (Ab–Ag) affinity interactions. Flower-like copper oxide (CuO) was used as labels of secondary antibody (Ab2) and immobilized on the modified electrode via specific affinity interactions between Ab2 and Ag. Cu2+ was released by dissolving CuO with HCl, and then reacted with CdS to form CuxS (x=1, 2), which would create new energy levels for electron–hole recombination and resulted in a decrease of the photocurrent. CuO, as the labels of Ab2, was first applied in PEC biosensor based on the signal-off strategy of the Cu2+ for CdS. Greatly enhanced sensitivity was achieved through the coupling of CdS QDs with TiO2. Besides, the introduction of polythiophene (PT-Cl) on the surface of TiO2 made the PEC signal more stable. Under 405nm irradiation at 0.1V, the PEC biosensor for H–IgG determination exhibited a linear range from 0.1pgmL−1 to 100ngmL−1 with a low detection limit of 0.03pgmL−1. The proposed biosensor showed high sensitivity, stability and selectivity, which opens up a new promising signal-off PEC platform for future bioassay.

Comparative Study of Materials-Binding Peptide Interactions with Gold and Silver Surfaces and Nanostructures: A Thermodynamic Basis for Biological Selectivity of Inorganic Materials

Controllable 3D assembly of multicomponent inorganic nanomaterials by precisely positioning two or more types of nanoparticles to modulate their interactions and achieve multifunctionality remains a major challenge. The diverse chemical and structural features of biomolecules can generate the compositionally specific organic/inorganic interactions needed to create such assemblies. Toward this aim, we studied the materials-specific binding of peptides selected based upon affinity for Ag (AgBP1 and AgBP2) and Au (AuBP1 and AuBP2) surfaces, combining experimental binding measurements, advanced molecular simulation, and nanomaterial synthesis. This reveals, for the first time, different modes of binding on the chemically similar Au and Ag surfaces. Molecular simulations showed flatter configurations on Au and a greater variety of 3D adsorbed conformations on Ag, reflecting primarily enthalpically driven binding on Au and entropically driven binding on Ag. This may arise from differences in the interfacial sol...

Polyacrylic acid sodium salt film entrapped Ag-nanocubes as molecule traps for SERS detection

Surface-enhanced Raman spectroscopy (SERS) is a fast analytical technique for trace chemicals; however, it requires the active SERS-substrates to adsorb analytes, thus limiting target species to those with the desired affinity for substrates. Here we present networked polyacrylic acid sodium salt (PAAS) film entrapped Ag-nanocubes (denoted as Ag-nanocubes@PAAS) as an effective SERS-substrate for analytes with and without high affinity. Once the analyte aqueous solution is cast on the dry Ag-nanocubes@PAAS substrate, the bibulous PAAS becomes swollen forcing the Ag-nanocubes loose, while the analytes diffuse in the interstices among the Ag-nanocubes. When dried, the PAAS shrinks and pulls the Ag-nanocubes back to their previous aggregated state, while the PAAS network “detains” the analytes in the small gaps between the Ag-nanocubes for SERS detection. The strategy has been proven effective for not only singleanalytes but also multi-analytes without strong affinity for Ag, showing its potential in SERS-based simultaneous multi-analyte detection of both adsorbable and non-adsorbable pollutants in the environment.

Impact ionisation mass spectrometry of polypyrrole-coated pyrrhotite microparticles

Cation and anion impact ionization mass spectra of polypyrrole-coated pyrrhotite cosmic dust analogue particles are analysed over a range of cosmically relevant impact speeds. Spectra with mass resolutions of 150–300 were generated by hypervelocity impacts of charged particles, accelerated to up to 37kms−1 in a Van de Graaff electrostatic accelerator, onto a silver target plate in the Large Area Mass Analyzer (LAMA) spectrometer. Ions clearly indicative of the polypyrrole overlayer are identified at masses of 93, 105, 117, 128 and 141u. Organic species, predominantly derived from the thin (20nm) polypyrrole layer on the surface of the particles, dominate the anion spectra even at high (>20kms−1) impact velocities and contribute significantly to the cation spectra at velocities lower than this. Atomic species from the pyrrhotite core (Fe and S) are visible in all spectra at impact velocities above 6kms−1 for 56Fe+, 9kms−1 for 32S+ and 16kms−1 for 32S− ions. Species from the pyrrhotite core are also frequently visible in cation spectra at impact speeds at which surface ionisation is believed to dominate (<10kms−1), although the large number of organic peaks complicates the identification of characteristic molecular species. A thin oxidised surface layer on the pyrrhotite particles is indicated by weak spectral features assigned to iron oxides and iron oxy-hydroxides, although the definitive identification of sulfates and hydrated sulfates from the oxidation process was not possible. Silver was confirmed as an excellent choice for the target plate of an impact ionization mass spectrometer, as it provided a unique isotope signature for many target-projectile cluster peaks at masses above 107–109u. The affinity of Ag towards a dominant organic fragment ion (CN−) derived from fragmentation of the polypyrrole component led to molecular cluster formation. This resulted in an enhanced sensitivity to a particular particle component, which may be of great use when investigating astrobiologically relevant chemicals, such as amino acids.

Responsive Lanthanide Coordination Polymer for Hydrogen Sulfide

Metal organic coordination polymers have received great attention because of their flexible compositions and architecture. Here, we report the design and synthesis of a responsive lanthanide coordination polymer (LCP) for hydrogen sulfide (H2S), utilizing self-assembling of biomolecule nucleotide with luminescent terbium ion (Tb(3+)) and sensitizing silver ion (Ag(+)) in aqueous solution. LCP is highly fluorescent due to the inclusion of Ag(+) ions, which sensitized the fluorescence of Tb(3+) ions. H2S can strongly quench the fluorescence of LCP through its high affinity for Ag(+) ions. Such configurated LCP material from initial building blocks showed high sensitivity and selectivity for H2S and was applied to the determination of H2S in human serum. LCP with Tb(3+) ions also has a long fluorescence lifetime, which allows for time-resolved fluorescence assays, possessing particular advantages to probing H2S in biological systems with autofluorescence.

Di-substituted azocalix[4]arenes containing chromogenic groups: synthesis, characterization, extraction, and thermal behavior

In this study, the synthesis of chromogenic di-substituted azocalix[4]arene derivatives is described. Six novel azocalix[4]arenes (4a–f)were prepared by linking 4-methoxy, 4-methyl, 4-ethyl, 4-chloro, 4-bromo, and 4-nitroaniline to 25,26,27,28-tetrahydroxy-11,23-di-(tert-butyl)calix[4]arene through a diazo-coupling reaction, and were characterized by elemental analysis, FTIR, 1H NMR spectra and thermogravimetric analysis (TGA). The complexing properties of these compounds were studied by the liquid–liquid extraction of selected metal cations (Sr2+, Ag+, Hg+, Hg2+, Co2+, Ni2+, Cu2+, Pb2+, Cr3+, Al3+). It has been observed that di-substituted azocalix[4]arenes showed a high affinity for Ag+, Hg+, and Hg2+ ions, but almost no affinity to other metals. The colors of these azocalix[4]arenes were compared with respect to effect of varying pH on the absorption ability. Thermal behaviors of these compounds were also reported by means of thermogravimetry (TG) and thermal analysis (DTA).

High-Affinity IgG Antibodies Develop Naturally in Ig-Knockout Rats Carrying Germline Human IgH/Igκ/Igλ Loci Bearing the Rat CH Region

Mice transgenic for human Ig loci are an invaluable resource for the production of human Abs. However, such mice often do not yield human mAbs as effectively as conventional mice yield mouse mAbs. Suboptimal efficacy in delivery of human Abs might reflect imperfect interaction between the human membrane IgH chains and the mouse cellular signaling machinery. To obviate this problem, in this study we generated a humanized rat strain (OmniRat) carrying a chimeric human/rat IgH locus (comprising 22 human V(H)s, all human D and J(H) segments in natural configuration linked to the rat C(H) locus) together with fully human IgL loci (12 Vκs linked to Jκ-Cκ and 16 Vλs linked to Jλ-Cλ). The endogenous Ig loci were silenced using designer zinc finger nucleases. Breeding to homozygosity resulted in a novel transgenic rat line exclusively producing chimeric Abs with human idiotypes. B cell recovery was indistinguishable from wild-type animals, and human V(D)J transcripts were highly diverse. Following immunization, the OmniRat strain performed as efficiently as did normal rats in yielding high-affinity serum IgG. mAbs, comprising fully human variable regions with subnanomolar Ag affinity and carrying extensive somatic mutations, are readily obtainable, similarly to conventional mAbs from normal rats.

Applying Surface Charge Attraction to Synthesizing TiO2/Ag Composition for VOCs Photodegradation

This study utilized a unique method to prepare TiO2/Ag composites by operating the pH value of synthesis solution, which causes the opposite charges on the surface between TiO2 and Ag to enhance the combination affinity of TiO2 and Ag due to electron attraction. The results showed that the TiO2/Ag prepared in solution at pH 5.8 was characterized as high TiO2 dispersibility and the optimal combination between TiO2/Ag, due to the opposite surface charges and the greatest difference in zeta potentials between TiO2 and Ag. The prepared TiO2/Ag was utilized to process acetone photodegradation, and the results illustrated that TiO2/Ag prepared in solution at pH 5.8 showed the best performance in photodegrading acetone. With increasing TiO2 coated on Ag in TiO2/Ag, the photodegradation efficiency of acetone was enhanced. In terms of the average efficiency via TiO2 coating amount, 10 wt% was the most optimal efficient proportion of TiO2/Ag for the photodegradation of acetone.

1,3-Disubstitutedp-tert-Butylcalix[4]arene Derivatives Bearing Phenanthroline Moieties：Synthesis and Selective Recognition of Silver Ion

p-tert-Butylcalix(4)arene-1,3-dialdehydes were firstly obtained by two step alkylations of p-tert-butylcalix(4)arene with alkylene dihalide and hydroxyl-substituted benzaldehydes. Then p-tert-butylcalix(n)arene 1,3-disubstituted phenanthroli- nes were successfully prepared by condensation of active calixarene dialdehydes with 1,10-phenanthroline-5,6-dione. The structures of the prepared hoters were characterized with IR, NMR, and HRMS techniques. The recogination of calixarene 1,3-disubstituted phenanthroline for metal ions was studied with UV-Vis spectroscopy. A great affinity for Ag + ions that can

Negative Feedback Regulation of Antigen Receptors through Calmodulin Inhibition of E2A

Signaling from the BCR is used to judge Ag-binding strengths of the Abs of B cells. BCR signaling enables the selection for successive improvements in the Ag affinity over an extremely broad range of affinities during somatic hypermutation. We show that the mouse BCR is subject to general negative feedback regulation of the receptor proteins, as well as many coreceptors and proteins in signal pathways from the receptor. Thus, the BCR can downregulate itself, which can enable sensitive detection of successive improvements in the Ag affinity over a very large span of affinities. Furthermore, the feedback inhibition of the BCR signalosome and most of its proteins, as well as most other regulations of genes by BCR stimulation, is to a large extent through inhibition of the transcription factor E2A by Ca(2+)/calmodulin.

Mechanical Interactions between Dendritic Cells and T Cells Correlate with T Cell Responsiveness

Ag recognition is achieved through the communication across intercellular contacts between T cells and APCs such as dendritic cells (DC). Despite remarkable progress in delineating detailed molecular components at the intercellular contacts, little is known about the functional roles of physical cross-junctional adhesion between T and DC in shaping T cell responses. In addition, the mechanisms underlying sensitivity and specificity of Ag discrimination by T cells at intercellular contacts remain to be elucidated. In this study, we use single-cell force spectroscopy to probe the mechanical interactions between DC and T cells in response to stimulation with a panel of altered peptide ligands. The results show that intercellular interactions of DC-T cell conjugates exhibited different ranges of interaction forces in peptide-dependent manners that match the ability of the peptides to activate T cells. Elevated calcium mobilization and IL-2 secretion by T cells were only promoted in response to antigenic peptides that induce strong interaction forces, suggesting that mechanically stable DC-T cell contacts are crucial for driving T cell activation. Strong interactions were not solely dependent on cell-surface molecules such as TCRs and the adhesion molecule LFA-1, but were also controlled by cytoskeletal dynamics and the integrity of membrane lipid rafts. These data provide novel mechanical insights into the effect of Ag affinity on intercellular contacts that align with T cell responsiveness.

The effect of B cell receptor affinity on lipid mediated B cell receptor antigen microclustering (109.1)

Abstract After encountering antigens (Ags), B-cell receptors(BCRs) with bound Ags assemble into microclusters then into a macrocluster. BCR recognition of antigen results in a monotonically increasing graded signaling response with increasing affinity for Ag, a robust feature that seems to be characterizing BCR-Ag affinity discrimination. Recent experiments indicate an important role of very early (within seconds) signaling events, such as formation of BCR-Ag microclusters, in this affinity discrimination process. Our current studies improve upon our most recent biophysical models for BCR-Ag microcluster and macrocluster formation by incorporating lipid-mediated BCR attraction factors. We examine the effect of (a) lipid and BCR concentration, and (b) varying attractive forces between different lipid and BCR pairings. Our studies indicate that a weak attraction between pairs of BCR molecules does not lead to microclusters. However, strong coupling between BCR and lipid (sphingolipids) molecules, that possibly arises upon antigen binding, generates microclusters of size similar to what has been observed in experiments. Our results indicate that microcluster size and number increase with increasing affinity while the formation times of such early BCR-Ag clusters decrease. These features can have important implications for the B cell affinity discrimination problem.

Characterization of [peptide+(Ag)n]+ complexes using matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry

Silver ion complexes of peptides [M + (Ag)(n) ](+) , M = angiotensin I or substance P where n = 1-8 and 17-23 for angiotensin I and n = 1-5 for substance P, are identified and characterized using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). The Ag(+) coordination number exceeds the number of available amino acid residues in angiotensin I whereas the number of observed complexes in substance P is less than the number of amino acid residues in it. The larger coordination number of angiotensin I with Ag(+) indicates the simultaneous binding of several Ag(+) ions to the amino acid residue present in it. The lower number of observed complexes in substance P suggests the binding of two or more residues to one Ag(+) ion. The presence of trifluoroacetic acid in the peptide samples reduces the Ag(+) coordination ability in both the peptides which indicates that the basic residues in it are already protonated and do not participate in the Ag(+) -binding process. The Ag(+) ion also forms a complex with the α-cyano-4-hydroxycinnamic acid (CHCA) matrix and is observed in the MALDI mass spectra and the formation of [CHCA + Ag](+) , [CHCA + AgNO(3) ](+) and [(CHCA)(2) + Ag](+) ions is due to the high binding affinity of Ag(+) to the CN group of CHCA.

A sensitive immunoassay based on direct hapten coated format and biotin–streptavidin system for the detection of chloramphenicol

A novel enzyme liked immunosorbent assay (ELISA) was developed for the detection of chloramphenicol (CAP). In this assay, the small molecular hapten (Hap) was directly coated on the surface of microtiter plates and biotin–streptavidin system (BSAS) was employed to improve the sensitivity of immunoassay (BSAS-direct Hap coated ELISA). The surface of microtiter plates was treated with glutaraldehyde (GA) polymer network to introduce aldehyde group, which was used to cross-link with amino group of CAP. Compared with conventional ELISA (the plates were coated with Hap–carrier protein conjugates), the modified plates presented significantly high antibody and antigen (Ab–Ag) affinity and showed excellent stability. And then the biotinylated monoclonal antibody (mAb) and HRP-labeled streptavidin were employed in this assay for amplification of signals. The sensitivity of BSAS-direct Hap coated ELISA was increased by approximately 20-folds and the stability was also improved greatly compared to conventional ELISA. Its 50% inhibition concentration (IC 50) for CAP was 10.5 ng mL −1 and the limit of detection (LOD) was 0.2 ng mL −1 after optimization of reaction conditions. To our knowledge, this was one of the most sensitive immunoassay for CAP yet reported. In sample analysis, the results of CAP detected by this assay were in accordance with which obtained by conventional ELISA and high performance liquid chromatography (HPLC). Therefore, it is an attractive alternative compared to conventional immunoassays in routine supervision for residue detection in food and environment.

The Strength of B Cell Interaction with Antigen Determines the Degree of IgM Polymerization

The induction of variable disulfide polymerization of IgM in the trout (Oncorhynchus mykiss) and its effect on its half-life were examined. An association between greater Ab affinity and increased disulfide polymerization was first indicated by the observation of this increased IgM disulfide polymerization during the process of affinity maturation. A direct association between Ab affinity and disulfide polymerization was then established by the fractionation of individual sera into high- and low-affinity subpopulations, which also resulted in the partitioning of high and low degrees of disulfide polymerization. The ability of high-affinity B cells to produce more highly polymerized Abs upon Ag induction was demonstrated by in vitro Ag-driven selection. Low Ag concentrations, which elicited only high-affinity Abs, also possessed the highest degree of polymerization, whereas higher concentrations of Ag elicited a broader array of Ab affinities, yielding a lower average affinity and degree of polymerization. Half-life studies revealed that the high-affinity, highly polymerized Abs possessed longer half-lives than the lower-affinity, lightly polymerized Abs. Finally, although the affinity for Ag is associated with elevated levels of polymerization, analysis of naive Ig revealed that the degree of polymerization alone, not affinity, appears sufficient to prolong Ig half-life.

Antigen Affinity Controls Rapid T-Dependent Antibody Production by Driving the Expansion Rather than the Differentiation or Extrafollicular Migration of Early Plasmablasts

To optimize the initial wave of Ab production against T-dependent Ags, primary B cell clones with the highest Ag affinity are selected to generate the largest extrafollicular plasmablast (PB) responses. The mechanism behind this remains undefined, primarily due to the difficulty of analyzing low frequency Ag-specific B cells during the earliest phases of the immune response when key differentiation decisions are made. In this study, a high resolution in vivo mouse model was used to characterize in detail the first 6 days of a T-dependent B cell response and to identify the steps at which initial Ag affinity has a major impact. Ag-specific B cells proliferated within splenic follicles from days 1.0 to 3.0 before undergoing a dynamic phase of multilineage differentiation (days 3.0-4.0) that generated switched and unswitched populations of germinal center B cells, early memory B cells, and extrafollicular PBs. PB differentiation was marked by synchronous up-regulation of CXCR4 and down-regulation of CXCR5 and the adoption of a unique BCR(high) phenotype by unswitched PBs. Differences in Ag affinity of >50-fold did not markedly affect the early stages of the response, including the differentiation and extrafollicular migration of PBs. However, high affinity PBs underwent significantly greater expansion within the splenic bridging channels and red pulp, due to both increased proliferation and decreased apoptosis. Extrafollicular PBs maintained class II MHC, but not IL-21R expression, and interacted directly with Ag-specific extrafollicular Th cells, suggesting that IL-21-independent T cell help may drive extrafollicular PB expansion in responses to foreign Ag.

Investigation of Ag in the king scallop Pecten maximus using field and laboratory approaches

The bioaccumulation, tissue and subcellular distributions of Ag were investigated in the king scallop Pecten maximus from the Bay of Seine fishery area (France) in laboratory and in field conditions. Experimental investigations with the radiotracer 110mAg showed that the scallop readily concentrated Ag when exposed via seawater and to a much lower extent when exposed via sediment. Retention of the metal incorporated via all tested contamination pathways was shown to be very strong, but the assimilation efficiency of Ag ingested with food was found to be tightly depending on the phytoplankton strain used to feed the scallops (74 and 33% with Skeletonema costatum and Isochrysis galbana, respectively). The uptake and depuration kinetic parameters determined in the laboratory experiments were used to run a global bioaccumulation model. The latter indicated that the major uptake pathway of Ag in P. maximus was strongly depending on the food quality. Indeed, when fed the diatom S. costatum which was characterised by a high affinity for Ag (high distribution constant K df) the relative contribution of the feeding pathway reached 98% of the global Ag bioaccumulation. In contrast, when fed I. galbana which displayed a lower K df than S. costatum, dietary Ag was retained to a lesser extent by P. maximus, and seawater appeared as the major contributing uptake pathway. In wild scallops collected from reference and contaminated sites, Ag was mainly concentrated in the digestive gland and secondarily in the gills, and was mainly found associated with the insoluble subcellular fraction in all the scallop tissues.