Real-time kinetic analysis of hCG-monoclonal antibody interaction using radiolabeled hCG probe: presence of two forms of Ag-mAb complex as revealed by solid phase dissociation studies

Real-time kinetics of ligand-ligate interaction has predominantly been studied by either fluorescence or surface plasmon resonance based methods. Almost all such studies are based on association between the ligand and the ligate. This paper reports our analysis of dissociation data of monoclonal antibody-antigen (hCG) system using radio-iodinated hCG as a probe and nitrocellulose as a solid support to immobilize mAb. The data was analyzed quantitatively for a one-step and a two-step model. The data fits well into the two-step model. We also found that a fraction of what is bound is non-dissociable (tight-binding portion (TBP)). The TBP was neither an artifact of immobilization nor does it interfere with analysis. It was present when the reaction was carried out in homogeneous solution in liquid phase. The rate constants obtained from the two methods were comparable. The work reported here shows that real-time kinetics of other ligand-ligate interaction can be studied using nitrocellulose as a solid support. (C) 2002 Elsevier Science B.V. All rights reserved.

A numerical model of a liquid-feed solid polymer electrolyte DMFC and its experimental validation

A one-dimensional, biphasic, multicomponent steady-state model based on phenomenological transport equations for the catalyst layer, diffusion layer, and polymeric electrolyte membrane has been developed for a liquid-feed solid polymer electrolyte direct methanol fuel cell (SPE- DMFC). The model employs three important requisites: (i) implementation of analytical treatment of nonlinear terms to obtain a faster numerical solution as also to render the iterative scheme easier to converge, (ii) an appropriate description of two-phase transport phenomena in the diffusive region of the cell to account for flooding and water condensation/evaporation effects, and (iii) treatment of polarization effects due to methanol crossover. An improved numerical solution has been achieved by coupling analytical integration of kinetics and transport equations in the reaction layer, which explicitly include the effect of concentration and pressure gradient on cell polarization within the bulk catalyst layer. In particular, the integrated kinetic treatment explicitly accounts for the nonhomogeneous porous structure of the catalyst layer and the diffusion of reactants within and between the pores in the cathode. At the anode, the analytical integration of electrode kinetics has been obtained within the assumption of macrohomogeneous electrode porous structure, because methanol transport in a liquid-feed SPE- DMFC is essentially a single-phase process because of the high miscibility of methanol with water and its higher concentration in relation to gaseous reactants. A simple empirical model accounts for the effect of capillary forces on liquid-phase saturation in the diffusion layer. Consequently, diffusive and convective flow equations, comprising Nernst-Plank relation for solutes, Darcy law for liquid water, and Stefan-Maxwell equation for gaseous species, have been modified to include the capillary flow contribution to transport. To understand fully the role of model parameters in simulating the performance of the DMCF, we have carried out its parametric study. An experimental validation of model has also been carried out. (C) 2003 The Electrochemical Society.

Mass spectrometric and electrochemical studies of thermodynamic properties of liquid and solid phases in the CaO Al2O3 system

The activities of CaO and Al2O3 in lime-alumina melts were studied by Knudsen cell-mass spectrometry at 2060 K. Emf of solid state cells, with CaF2 as the electrolyte, was measured from 923 to 1223 K to obtain the free energies of formation of the interoxide compounds. The results are critically evaluated in the light of data reported in the literature on phase equilibria, activities in melts, and stabilities of compounds. A coherent set of data is presented, including the previously unknown free energy of formation of CaO.6Al2O3 and the temperature dependence of activities in the liquid phase.

Studying electrons on curved surfaces by trapping and manipulating multielectron bubbles in liquid helium

Investigations of two-dimensional electron systems (2DES) have been achieved with two model experimental systems, covering two distinct, non-overlapping regimes of the 2DES phase diagram, namely the quantum liquid phase in semiconducting heterostructures and the classical phases observed in electrons confined above the surface of liquid helium. Multielectron bubbles in liquid helium offer an exciting possibility to bridge this gap in the phase diagram, as well as to study the properties of electrons on curved flexible surfaces. However, this approach has been limited because all experimental studies have so far been transient in nature. Here we demonstrate that it is possible to trap and manipulate multielectron bubbles in a conventional Paul trap for several hundreds of milliseconds, enabling reliable measurements of their physical properties and thereby gaining valuable insight to various aspects of curved 2DES that were previously unexplored.

Origin of the Spin-Orbital Liquid State in a Nearly J=0 Iridate Ba3ZnIr2O9

We show using detailed magnetic and thermodynamic studies and theoretical calculations that the ground state of Ba3ZnIr2O9 is a realization of a novel spin-orbital liquid state. Our results reveal that Ba3ZnIr2O9 with Ir5+ (5d(4)) ions and strong spin-orbit coupling (SOC) arrives very close to the elusive J = 0 state but each Ir ion still possesses a weak moment. Ab initio density functional calculations indicate that this moment is developed due to superexchange, mediated by a strong intradimer hopping mechanism. While the Ir spins within the structural Ir2O9 dimer are expected to form a spin-orbit singlet state (SOS) with no resultant moment, substantial frustration arising from interdimer exchange interactions induce quantum fluctuations in these possible SOS states favoring a spin-orbital liquid phase down to at least 100 mK.

Studies on two-phase co-current air/non-Newtonian shear-thinning fluid flows in inclined smooth pipes

In this work. co-current flow characteristics of air/non-Newtonian liquid systems in inclined smooth pipes are studied experimentally and theoretically using transparent tubes of 20, 40 and 60 turn in diameter. Each tube includes two 10 m lone pipe branches connected by a U-bend that is capable of being inclined to any angle, from a completely horizontal to a fully vertical position. The flow rate of each phase is varied over a wide range. The studied flow phenomena are bubbly, plug flow, slug flow, churn flow and annular flow. These are observed and recorded by a high flow. stratified flow. -speed camera over a wide range of operating conditions. The effects of the liquid phase properties, the inclination angle and the pipe diameter on two-phase flow characteristics are systematically studied. The Heywood-Charles model for horizontal flow was modified to accommodate stratified flow in inclined pipes, taking into account the average void fraction and pressure drop of the mixture flow of a gas/non-Newtonian liquid. The pressure drop gradient model of Taitel and Barnea for a gas/Newtonian liquid slug flow was extended to include liquids possessing shear-thinning flow behaviour in inclined pipes. The comparison of the predicted values with the experimental data shows that the models presented here provide a reasonable estimate of the average void fraction and the corresponding pressure drop for the mixture flow of a gas/ non-Newtonian liquid. (C) 2007 Elsevier Ltd. All rights reserved.

Synthesis and spectroscopy of ruthenium-modified nucleic acids

Redox-active probes are designed and prepared for use in DNA-mediated electron transfer studies. These probes consist of ruthenium(II) complexes bound to nucleosides that possess metal-binding ligands. Low- and high-potential oxidants are synthesized from these modified nucleosides and display reversible one-electron electrochemical behavior. The ruthenium-modified nucleosides exhibit distinct charge-transfer transitions in the visible region that resemble those of appropriate model complexes. Resonance Raman and time-resolved emission spectroscopy are used to characterize the nature of these transitions.

The site-specific incorporation of these redox-active probes into oligonucleotides is explored using post-synthetic modification and solid-phase synthetic methods. The preparation of the metal-binding nucleosides, their incorporation into oligonucleotides, and characterization of the resulting oligonucleotides is described. Because the insertion of these probes into modified oligonucleotides using post-synthetic modification is unsuccessful, solid-phase synthetic methods are explored. These efforts lead to the first report of 3'-metallated oligonucleotides prepared completely by automated solid-phase synthesis. Preliminary efforts to prepare a bis-metallated oligonucleotide by automated synthesis are described.

The electrochemical, absorption, and emissive features of the ruthenium-modified oligonucleotides are unchanged from those of the precursor metallonucleoside. The absence of any change in these properties upon incorporation into oligonucleotides and subsequent hybridization suggests that the incorporated ruthenium(II) complex is a valuable probe for DNA-mediated electron transfer studies.

Experimental study on inertial effects in liquid-solid flows

This thesis presents experimental measurements of the rheological behavior of liquid-solid mixtures at moderate Reynolds (defined by the shear rate and particle diameter) and Stokes numbers, ranging from 3 ≤ Re ≤ 1.6 × 10³ and 0.4 ≤ St ≤ 195. The experiments use a specifically designed Couette cylindrical rheometer that allows for probing the transition from transporting a pure liquid to transporting a dense suspension of particles. Measurements of the shear stress are presented for a wide range of particle concentration (10 to 60% in volume) and for particle to fluid density ratio between 1 and 1.05. The effective relative viscosity exhibits a strong dependence on the solid fraction for all density ratios tested. For density ratio of 1 the effective viscosity increases with Stokes number (St) for volume fractions (φ) lower than 40% and becomes constant for higher φ. When the particles are denser than the liquid, the effective viscosity shows a stronger dependance on St. An analysis of the particle resuspension for the case with a density ratio of 1.05 is presented and used to predict the local volume fraction where the shear stress measurements take place. When the local volume fraction is considered, the effective viscosity for settling and no settling particles is consistent, indicating that the effective viscosity is independent of differences in density between the solid and liquid phase. Shear stress measurements of pure fluids (no particles) were performed using the same rheometer, and a deviation from laminar behavior is observed for gap Reynolds numbers above 4× 10³, indicating the presence of hydrodynamic instabilities associated with the rotation of the outer cylinder. The increase on the effective viscosity with Stokes numbers observed for mixtures with φ ≤ 30% appears to be affected by such hydrodynamic instabilities. The effective viscosity for the current experiments is considerably higher than the one reported in non-inertial suspensions.

Structure of coexisting liquid phases of supercooled water: analogy with ice polymorphs.

The structural changes occurring in supercooled liquid water upon moving from one coexisting liquid phase to the other have been investigated by computer simulation using a polarizable interaction potential model. The obtained results favorably compare with recent neutron scattering data of high and low density water. In order to assess the physical origin of the observed structural changes, computer simulation of several ice polymorphs has also been carried out. Our results show that there is a strict analogy between the structure of various disordered (supercooled) and ordered (ice) phases of water, suggesting that the occurrence of several different phases of supercooled water is rooted in the same physical origin that is responsible for ice polymorphism.

Calorimetric study on two biphenyl liquid crystals

The molar heat capacities of the two biphenyl liquid crystals, 3BmFF and 3BmFFXF3, with a purity of 99.7 mol% have been precisely measured by a fully automated precision adiabatic calorimeter in the temperature range between T = 80 and 350 K. Nematic phase-liquid phase transitions were found between T = 297 K and 300 K with a peak temperature of T-peak = (298.071 +/- 0.089) K for 3BmFF, and between T = 316 and 319 K with a peak temperature of T-peak = (315.543 +/- 0.043) K for 3BmFFXF3. The molar enthalpy (Delta(trs)H(m)) and entropy (Delta(trs)S(m)) corresponding to these phase transitions have been determined by means of the analysis of the heat capacity curves, which are (15.261 +/- 0.023) U mol(-1) and (51.202 +/- 0.076) J K-1 mol(-1) for 3BmFF, (31.624 +/- 0.066) kJ mol(-1) and (100.249 +/- 0.212) J K-1 mol(-1) for 3BmFFXF3, respectively. The real melting points (TI) and the ideal melting points (TO) with no impurities of the two compounds have been obtained from the fractional melting method to be (298.056 +/- 0.018) K and (298.165 +/- 0.038) K for 3BmFF, (315.585 +/- 0.043) K and (315.661 +/- 0.044) K for 3BmFFXF3, respectively. In addition, the transitions of these two biphenyl liquid crystals from nematic phase to liquid phase have further been investigated by differential scanning calorimeter (DSC) technique; the repeatability and reliability for these phase transitions were verified. (C) 2004 Elsevier B.V. All rights reserved.

Observation of Nucleation and Growth of CdS Nanocrystals in a Two-phase System

The nucleation and growth kinetics of CdS nanocrystals in a two-phase synthesis system have been investigated. It was found that the nucleation process is quite lengthy and overlapped with the growth process; nevertheless, as formed nanocrystals show extremely narrow size distribution owing to the unique heterogeneous reacting environment and Ostwald ripening growth. The nucleation and growth kinetics of the nanocrystals were also influenced strongly by the monomer concentration, capping agent concentration, and solvent polarity. It was also found that a high monomer concentration, a low capping agent concentration, and low solvent polarity lead to a higher maximum nucleus concentration and nanocrystal concentration, while high polarity solvents are favorable for the formation of nanocrystals with narrower size distribution and higher photoluminescence quantum yield.