Multivalent System Research Articles

Thioether-Polyglycidol as Multivalent and Multifunctional Coating System for Gold Nanoparticles.

Thiofunctional polymers are the established standard for the coating and biofunctionalization of gold nanoparticles (AuNPs). However, the nucleophilic and oxidative character of thiols provokes polymeric crosslinking and significantly limits the chemical possibilities to introduce biological functions. Thioethers represent a chemically more stable potential alternative to thiols that would offer easier functionalization, yet a few studies in the literature report inconclusive data regarding the efficacy of thioethers to stabilize AuNPs in comparison to thiols. A systematic comparison is presented of mono- versus multivalent thiol- and thioether-functional polymers, poly(ethylene glycol) versus side chain functional poly(glycidol) (PG) and it is shown that coating of AuNPs with multivalent thioether-functional PG leads to superior colloidal stability, even under physiological conditions and after freeze-drying and resuspension, as compared to thiol analogs at comparable polymer surface coverages. In addition, it is shown that a wide range of functional groups can be introduced in these polymers. Using diazirine functionalization as example, it is demonstrated that proteins can be covalently immobilized, and that conjugation of antibodies via this strategy enables efficient targeting and laser-irradiation induced killing of cells.

Coexistence of magnetic order and valence fluctuations in the Kondo lattice systemCe2Rh3Sn5

We report on the electronic band structure, structural, magnetic and thermal properties of Ce$_2$Rh$_3$Sn$_5$. Ce $L_{\mathrm{III}}$-edge XAS spectra give direct evidence for an intermediate valence behaviour. Thermodynamic measurements reveal magnetic transitions at $T_{\mathrm{N1}}\approx$ 2.9 K and $T_{\mathrm{N2}}\approx$ 2.4 K. Electrical resistivity shows behaviour typical for Kondo lattices. The coexistence of magnetic order and valence fluctuations in a Kondo lattice system we attribute to a peculiar crystal structure in which Ce ions occupy two distinct lattice sites. Analysis of the structural features of Ce$_2$Rh$_3$Sn$_5$, together with results of electronic band structure calculations and thermodynamic data indicate that Ce2 ions are in an intermediate valence state with the ground state electronic configuration close to 4$f^0$, whereas Ce1 ions are trivalent (4$f^1$) and contribute to the low temperature magnetic ordering. Thus, our joined experimental and theoretical investigations classify Ce$_2$Rh$_3$Sn$_5$ as a multivalent charge-ordered system.

Solvation Structure of Zinc-Based Electrolytes from X-Ray Absorption Spectroscopy

Multivalent (e.g., Mg2+, Ca2+ and Zn2+) metal cells using a nonaqeous electrolyte are potential candidates for post-lithium-ion batteries. However, the development of multivalent electrolytes is challenging due to its poor compatibility with both the metal anode and higher voltage cathode chemistries, leading to poor coulombic efficiency, formation of passivation layer on the metal anode, etc. Defining the connection between the electrochemical properties of a multivalent electrolyte system with its molecular scale structure is a crucial step for developing these new chemistries. Here we use X-ray absorption fine structure (XAFS) spectroscopy to determine the solvation structure of zinc-based electrolytes with varying solvent species and concentrations. To explore the role of ion-pairing, the results are compared to first principle simulations of the electrolyte and electrochemical data.

Mechanistic Insight into Nanomolar Binding of Multivalent Neoglycopeptides to Wheat Germ Agglutinin.

Multivalent carbohydrate-protein interactions are frequently involved in essential biological recognition processes. Accordingly, multivalency is often also exploited for the design of high-affinity lectin ligands aimed at the inhibition of such processes. In a previous study (D. Schwefel et al., J. Am. Chem. Soc. 2010, 132, 8704-8719) we identified a tetravalent cyclopeptide-based ligand with nanomolar affinity to the model lectin wheat germ agglutinin (WGA). To unravel the structural features of this ligand required for high-affinity binding to WGA, we synthesized a series of cyclic and linear neoglycopeptides that differ in their conformational freedom as well as the number of GlcNAc residues. Combined evidence from isothermal titration calorimetry (ITC), enzyme-linked lectin assays (ELLA), and dynamic light scattering (DLS) revealed different binding modes of tetra- and divalent ligands and that conformational preorganization of the ligands by cyclization is not a prerequisite for achieving high binding affinities. The high affinities of the tetravalent ligands rather stem from their ability to form crosslinks between several WGA molecules. The results illustrate that binding affinities and mechanisms are strongly dependent on the used multivalent system which offers opportunities to tune and control binding processes.

Investigation of Reagent Delivery Formats in a Multivalent Malaria Sandwich Immunoassay and Implications for Assay Performance.

Conventional lateral flow tests (LFTs), the current standard bioassay format used in low-resource point-of-care (POC) settings, have limitations that have held back their application in the testing of low concentration analytes requiring high sensitivity and low limits of detection. LFTs use a premix format for a rapid one-step delivery of premixed sample and labeled antibody to the detection region. We have compared the signal characteristics of two types of reagent delivery formats in a model system of a sandwich immunoassay for malarial protein detection. The premix format produced a uniform binding profile within the detection region. In contrast, decoupling the delivery of sample and labeled antibody to the detection region in a sequential format produced a nonuniform binding profile in which the majority of the signal was localized to the upstream edge of the detection region. The assay response was characterized in both the sequential and premix formats. The sequential format had a 4- to 10-fold lower limit of detection than the premix format, depending on assay conjugate concentration. A mathematical model of the assay quantitatively reproduced the experimental binding profiles for a set of rate constants that were consistent with surface plasmon resonance measurements and absorbance measurements of the experimental multivalent malaria system.

A genetically adjuvanted influenza B virus vector increases immunogenicity and protective efficacy in mice.

The existence of multiple antigenically distinct types and subtypes of influenza viruses allows the construction of a multivalent vector system for the mucosal delivery of foreign sequences. Influenza A viruses have been exploited successfully for the expression of extraneous antigens as well as immunostimulatory molecules. In this study, we describe the development of an influenza B virus vector whose functional part of the interferon antagonist NS1 was replaced by human interleukin 2 (IL2) as a genetic adjuvant. We demonstrate that IL2 expressed by this viral vector displays immune adjuvant activity in immunized mice. Animals vaccinated with the IL2 viral vector showed an increased hemagglutination inhibition antibody response and higher protective efficacy after challenge with a wild-type influenza B virus when compared to mice vaccinated with a control virus. Our results demonstrate that it is feasible to construct influenza B vaccine strains expressing immune-potentiating foreign sequences from the NS genomic segment. Based on these data, it is now hypothetically possible to create a trivalent (or quadrivalent) live attenuated influenza vaccine in which each component expresses a selected genetic adjuvant with tailored expression levels.

Perspectives on mucosal vaccine against botulism

Clostridium botulinum toxin is one of the potent and classic molecules known to this modern scientific research field. It has dualistic characters: on one hand it causes botulism by blocking release of acetylcholine at the cholinergic nerve endings and on the other hand the same toxin molecule when administered locally at sub-lethal dose relieves various neuromuscular disorders. If the toxin is used intentionally as an act of terrorism, FDA approved therapeutic agents would be needed to recover from the illness. In addition, to prevent from such situations in the future and to protect public from botulism, there is a strong need for a mucosal vaccine. Creating a multivalent mucosal vaccine delivery system would ease the burden at the time of delivery and reduce the cost.

Synthesis and optoelectronic properties of Janus-dendrimer-type multivalent donor-acceptor systems.

A convergent, multistep protocol was employed for the synthesis of a Janus-type multivalent donor-acceptor system. The synthetic approach is based on a Sonogashira cross-coupling of two differently ferrocene-(Fc) substituted dendrons and a final sixfold [2 + 2] cycloaddition-retroelectrocyclization (CA-RE) reaction with tetracyanoethene, which occurs regioselectively at only one of the rigidly linked dendrons. The structural and optoelectronic properties of the compounds were investigated by X-ray analysis, UV/vis spectroscopy, and electrochemistry. The target Janus-system displays redox-amphoteric behavior. The nonalkynylated Fc end groups in one dendron are readily and reversibly oxidized. The second dendron, in which the terminal Fc-activated alkynes underwent the CA-RE reaction to give tetracyanobuta-1,3-dienes in the final step of the synthesis, undergoes four reversible 3-e(-) reductions in the very narrow potential range of 1 V. A spontaneous intramolecular charge transfer from the donor into the acceptor hemisphere was not observed. Furthermore, the oxidation potential of the Fc donors in one hemisphere is hardly perturbed by the push-pull acceptors in the other, which suggests that electronic communication along the π-system, with several meta-connectivities, is not efficient. Therefore, the charge-transfer bands seen in the Janus-type system originate from the interaction of the Fc donors with the directly connected tetracyanobuta-1,3-diene acceptors in the same hemisphere.

Evaluating binding avidities of populations of heterogeneous multivalent ligand-functionalized nanoparticles.

Ligand-functionalized, multivalent nanoparticles have been extensively studied as targeted carriers in biomedical applications for drug delivery and imaging. The chemical synthesis method used, however, generates nanoparticles that are heterogeneous with respect to the number of ligands on each nanoparticle. This article examines the role this heterogeneity in ligand number plays in multivalent interactions between nanoparticle ligands and targeted receptors. We designed and synthesized a model heterogeneous multivalent nanoparticle system and developed a unique kinetic analysis to quantify the avidity interactions. This system used mono-dispersed poly(amidoamine) (PAMAM) dendrimers that were then chemically functionalized with ssDNA oligonucleotides as to yield the heterogeneous nanoparticle platform (ligand valencies n = 1.7, 3.1, 6), and employed complementary oligonucleotides as targeted receptors on a surface plasmon resonance (SPR) biosensor to evaluate the multivalent binding of the nanoparticle population. Kinetic analysis of both parallel initial rate and dual-Langmuir analyses of SPR binding curves was performed to assess avidity distributions. We found that batches of multivalent nanoparticles contain both fast- and slow-dissociation subpopulations, which can be characterized as having "weak" and "strong" surface interactions ("binding"), respectively. Furthermore, we found that the proportion of "strong" binders increased as a function of the mean oligonucleotide valence of the nanoparticle population. These analyses allowed an assessment of how avidity distributions are modulated by the number of functionalized ligands and suggested that there are threshold valences that differentiated fast- and slow-dissociation nanoparticles.

DNA-scaffolded multivalent ligands to modulate cell function.

We report a simple, versatile, multivalent ligand system that is capable of specifically and efficiently modulating cell-surface receptor clustering and function. The multivalent ligand is made of a polymeric DNA scaffold decorated with biorecognition ligands (i.e., antibodies) to interrogate and modulate cell receptor signaling and function. Using CD20 clustering-mediated apoptosis in B-cell cancer cells as a model system, we demonstrated that our multivalent ligand is significantly more effective at inducing apoptosis of target cancer cells than its monovalent counterpart. This multivalent DNA material approach represents a new chemical biology tool to interrogate cell receptor signaling and functions and to potentially manipulate such functions for the development of therapeutics.

In vitro Decrease of the BCL-2 Protein Levels in Lymphoma Cells Induced by Gold Nanoparticles and Gold Nanoparticles- Anti-CD20

Apoptosis inhibition has been demonstrated as a characteristic of the Non- Hodgkin's Lymphoma (NHL). The up-regulation of anti- apoptotic BCL-2 family proteins allows the survival of cancer cells. Therefore, the strategy to induce apoptosis by targeting BCL-2 proteins is the base to propose new therapeutic probes for NHL. The aim of this research was to prepare a multimeric and multivalent system of gold nanoparticles (20 nm) conjugated to Anti-CD20 and to evaluate its biological potential to decrease the anti-apoptotic BCL-2 protein levels. The Anti-CD20 monoclonal antibody was conjugated to gold nanoparticles (AuNP) by means of spontaneous reaction of the thiol groups of cysteine. To obtain AuNP-AntiCD20, the AntiCD20 was added to 1.0 mL of AuNP solution (1 nM) at 18°C with stirring for 10 min. The nanosystem was characterized by TEM, DLS, FT-IR and UV Vis. In vitro studies were carried out in lymphoma cells. The BCL-2 protein concentration was quantified by enzymatic immune assay after treatment with AuNP or AuNP-Anti-CD20 or Anti-CD20 (positive control). TEM and spectroscopic techniques demonstrated that AuNPs were functionalized with Anti-CD20. Raji cells treated with AuNP-Anti- CD20 showed the lower BCL-2 concentration (13.07 ± 0.02ng/mL) with respect to that of incubated with the non-functionalized AuNP (14.45 ± 0.31ng/mL) or AntiCD-20 (19.85 ± 0.63ng/mL), indicating that the multimeric and multivalent Anti-CD20 nanosystem enhanced the BCL-2 concentration reduction with the possible apoptosis increasing. AuNP-Anti-CD20 demonstrates properties suitable for using as a target-specific agent useful for the NHL treatment.

A single-layer peptide nanofiber for enhancing the cytotoxicity of trastuzumab (anti-HER)

A multivalent system is often employed to enhance the effectiveness of a targeted therapy. In the present study, we report a single-layer peptide nanofiber (NFP) as a multivalent targeting platform to improve the cytotoxicity of trastuzumab (anti-HER), a monoclonal antibody targeting the human epidermal growth factor receptor 2 (HER-2) in approximately 20 % of breast cancer patients. The trastuzumab-conjugated nanofiber (anti-HER/NFP) was 100 × 4 nm in size and was assembled from multiple peptide units (mPEG-BK(FITC)SGASNRA-kldlkldlkldl-CONH2). The optimized preparation was attached with approximately 10 antibodies at the surface. Because of an increase in the multivalency, anti-HER/NFP was able to truncate more cell surface HER-2 and, thus, showed an enhanced cytotoxicity toward HER-2 positive SKBr-3 human breast cancer as compared to the free anti-HER. Western blot analysis and fluorescence microscopic studies confirmed that there was a significant downregulation of the HER-2 level and also inhibition of the cell survival cell signaling pathways including the phosphatidylinositol 3-kinase (PI3K) and the mitogen activated protein kinase (MAPK) pathway. Our data suggested that NFP can be useful as a multivalent platform for immunotherapy, especially in combination with other chemotherapeutic agents in the future.

Autonomous Agents as Tools for Modeling and Building Complex Control Systems that Operate in Dynamic and Unpredictable Environment

Complex control systems that operate in not entirely predictable environment have to deal with this environment in an autonomous manner using adaptability, the ability to predict environmental changes, and to maintain their integrity. Elements of the system must be able to find a new solution in a dynamic way. In this paper, we present the modeling of a traffic lights’ control system using a multivalent system. This is a large-scale distributed system, consisting of autonomous and rational traffic light agents, in which there is no centre imposing an outcome. Multiagent system brings another kind of organization of the distributed control. The information is distributed over the agents. The behavior of the other agents is incorporated into the making decision process of the agent. We apply different control algorithms in our multiagent simulation environment and show that using multiagent systems in dynamic and unpredictable environment the control will be adoptable.

YbPtGe2: A multivalent charge-ordered system with an unusual spin pseudogap

We performed a study of the structural and physical properties of YbPtGe${}_{2}$. This compound is a multivalent charge-ordered system presenting an unusual spin pseudogap below 200 K. The crystal structure of YbPtGe${}_{2}$ is refined from single-crystal and powder high-resolution synchrotron x-ray diffraction data at different temperatures. Analysis of the structural features of YbPtGe${}_{2}$, together with a combined study of Yb ${L}_{\mathrm{III}}$ x-ray absorption spectroscopy, magnetic susceptibility $\ensuremath{\chi}(T)$, thermopower $S(T)$, and ${}^{171}$Yb and ${}^{195}$Pt NMR indicate half of the Yb atoms to be in an intermediate valence state with an electronic configuration close to 4${f}^{13}$ (Yb${}^{3+}$), while for the remaining Yb atoms the 4${f}^{14}$ (Yb${}^{2+}$) configuration with almost no valence fluctuations is most likely. A drastic drop of the magnetic susceptibility and a decrease of the isotropic shift ${}^{195}{K}_{\mathrm{iso}}(T)$ with decreasing temperature in the temperature range of 50--200 K evidence the opening of a spin pseudogap with an activation energy of $\ensuremath{\Delta}/{k}_{\mathrm{B}}$ $\ensuremath{\sim}$ 200 K. Surprisingly, transport properties do not show clear evidence for the opening of a charge gap, thus excluding a standard Kondo-insulator scenario. Possible origins for this unusual electronic (valence) behavior are discussed.

A High-Throughput Technique Reveals the Load- and Site Density-Dependent Kinetics of E-Selectin.

The kinetics of bond rupture between receptors and ligand are critically dependent on applied mechanical force. Force spectroscopy of single receptor-ligand pairs to measure kinetics is a laborious and time-consuming process that is generally performed using individual force probes and making one measurement at a time when typically hundreds of measurements are needed. A high-throughput approach is thus desirable. We report here a magnetic bond puller that provides high-throughput measurements of single receptor-ligand bond kinetics. Electromagnets are used to apply pN tensile and compressive forces to receptor-coated magnetic microspheres while monitoring their contact with a ligand-coated surface. Bond lifetimes and the probability of forming a bond are measured via videomicroscopy, and the data are used to determine the load dependent rates of bond rupture and bond formation. The approach is simple, customizable, relatively inexpensive, and can make dozens of kinetic measurements simultaneously. We used the device to investigate how compressive and tensile forces affect the rates of formation and rupture, respectively, of bonds between E-selectin and sialyl Lewisa (sLea), a sugar on P-selectin glycoprotein ligand-1 to which selectins bind. We confirmed earlier findings of a load-dependent rate of bond formation between these two molecules, and that they form a catch-slip bond like other selectin family members. We also make the novel observation of an "ideal" bond in a highly multivalent system of this receptor-ligand pair.

Measurement of Aptamer–Protein Interactions with Back-Scattering Interferometry

We report the quantitative measurement of aptamer-protein interactions using backscattering interferometry (BSI) and show that BSI can determine when distinct binding regions are accessed. As a model system, we utilized two DNA aptamers (Tasset and Bock) that bind to distinct sites of a target protein (human α-thrombin). This is the first time BSI has been used to study a multivalent system in free solution wherein more than one ligand binds to a single target. We measured aptamer equilibrum dissociation constants (K(d)) of 3.84 nM (Tasset-thrombin) and 5.96 nM (Bock-thrombin), in close agreement with the literature. Unexpectedly, we observed allosteric effects such that the binding of the first aptamer resulted in a significant change in the binding affinity of the second aptamer. For example, the K(d) of Bock aptamer binding to preformed Tasset-thrombin complexes was 7-fold lower (indicating higher affinity) compared to binding to thrombin alone. Preliminary modeling efforts suggest evidence for allosteric linkage between the two exosites.

A Review on Intelligent Agent Systems

Multi-agent system (MAS) is a common way of exploiting the potential power of agent by combining many agents in one system. Each agent in a multivalent system has incomplete information and is in capable of solving entire problem on its own. Multi-agent system offers modularity. If a problem domain is particularly complex, large and contain uncertainty, then the one way to address, it to develop a number of functional specific and modular agent that are specialized at solving various problems individually. It also consists of heterogeneous agents implemented by different tool and techniques. MAS can be defining as loosely coupled network of problem solvers that interact to solve problems that are beyond the individual capabilities or knowledge of each problem solver. These problem solvers, often ailed agent are autonomous and can be heterogeneous in nature. MAS is followed by characteristics, Future application, What to be change, problem solving agent, tools and techniques used, various architecture, multi agent applications and finally future Direction and conclusion. Various Characteristics are limited viewpoint, effectively, decentralized; computation is asynchronous, use of genetic algorithms. It has some drawbacks which must be change to make MAS more effective. In the session of problem solving of MAS, the agent performance measure contains many factors to improve it like formulation of problems, task allocation, organizations. In planning of multivalent this paper cover self-interested multivalent interactions, modeling of other agents, managing communication, effective allocation of limited resources to multiple agents with managing resources. Using of tool, to make the agent more efficient in task that are often used. The architecture o MAS followed by three layers, explore, wander, avoid obstacles respectively. Further different and task decomposition can yield various architecture like BDI (Belief Desire Intension), RETSINA. Various applications of multi agent system exist today, to solve the real-life problems, new systems are being developed two distinct categories and also many others like process control, telecommunication, air traffic control, transportation systems, commercial management, electronic commerce, entertainment applications, medical applications. The future aspect of MAS to solve problems that are too large, to allow interconnection and interoperation of multiple existing legacy systems etc.

Monte Carlo Simulation on Growth of Antibody-Antigen Complexes: the Role of Unequal Reactivity

Growth of Antibody-Antigen complexes in a multivalent Antibody-Antigen system is studied by the Monte Carlo simulation method. The validity of the algorithm is first demonstrated for the case of the equal reactivity, then the simulation is presented for the case of unequal reactivity. It is shown that the influence of the unequal reactivity on the critical point, size distribution and the weight-average binding degree is significant. Especially, the gelation regions for the cases of unequal reactivity are studied, which can provide some useful clues for the immunological experiments.

Fluorescent Conjugated Polyfluorene with Pendant Lactopyranosyl Ligands for Studies of Ca2+-Mediated Carbohydrate−Carbohydrate Interaction

A well-defined fluorescent conjugated polyfluorene with pendant lactopyranosyl ligands was easily prepared through Cu(I)-catalyzed azide/alkyne "click" ligation and Suzuki coupling polymerization. As a fluorescent multivalent model system of glycoconjugates, the polymer was first used for studies of metal ion-mediated carbohydrate-carbohydrate interaction based on fluorescence spectroscopy. A significant fluorescence quenching of the lactosyl-bearing polyfluorene was observed upon addition of calcium ion, which is attributed to the polymer aggregation derived from Ca(2+)-mediated complex formation. Dynamic light scattering can also prove Ca(2+)-induced aggregation of the polymer based on determination of the corresponding hydrodynamic diameters. The calcium-mediated lactose-lactose interaction was reversible when treated with EDTA. In control studies, Ca(2+)-induced fluorescence quenching can not be observed for cellobiosyl- or galactosyl-functionalized polymer analogues, which show that specific sugar structures are critical for carbohydrate-metal complex formation.

Increased Efficacies of an Individual Catalytic Site in Clustered Multivalent Dendritic Catalysts

AbstractIn the studies reported so far on dendrimer‐mediated catalysis, the efficacies of the catalytic units were studied and compared primarily across the generations. In order to identify the efficacy of an individual catalytic unit with respect to the number of such units present within a given generation, a series of catalysts were prepared within a generation. Dendrimers incorporated with phosphine‐metal complexes were chosen for the study and as many as 11 catalysts within three generations were synthesized. The CC bond‐forming reactions, namely, the Heck and the Suzuki coupling reactions, were then selected to study the catalytic efficiencies of the series of partially and fully phosphine‐metal complex functionalized dendrimers. The efficacies of the formation of cinnamate and biphenyl, catalyzed by the dendritic catalysts, were compared. The comparative analyses show that an individual catalytic site is far more effective in its catalytic activity when presented in multiple numbers, i.e., in a multivalent dendritic system, than as a single unit within the same generation, i.e., in a monovalent dendritic system. The study identifies the beneficial effects of the multivalent presentation of the catalytic moieties, both within and across the dendrimer generations.