Effects of ampholyte concentration on protein behavior in on-chip isoelectric focusing

The effects of mobility corrections on carrier ampholytes are studied at various ampholyte concentrations to understand protein behavior during IEF. IEF simulations are conducted in the presence of 25 biprotic carrier ampholytes within a pH range of 6-9 after applying the Onsager-Debye-Hückel correction to the carrier ampholytes. Two model proteins with ten charge states but without ionic strength corrections are allowed to focus under an electric field of 300 V/cm in a 1 cm long channel. The IEF simulation results show that higher ionic strengths (50 - 100 mM) cause significant changes in the transient movement as well as the final focused profiles of both ampholytes and proteins. The time required for a single, well-defined peak to form increases with ionic strength when Onsager corrections are applied to the carrier ampholytes. For a particular ampholyte concentration, the space-averaged conductivity does not change during the final focusing stage, but the magnitude of space averaged conductivity is different for different ampholyte concentration. The simulation results also reveal that at steady-state ionic strength profiles remain flat throughout the channel except at the locations of proteins where a significant change in ampholyte concentration is obtained.     

Anti-Proliferative Naphthalene Glucoside from Aerial Part of Neanotis wightiana

Chemistry of Natural Compounds - A new bioactive naphthalene glucoside, named neanoside C (1), was isolated from the aerial part of Neanotis wightiana. The structure of neanoside C (1) was...     

A method to determine quasi-steady state in constant voltage mode isotachophoresis

Identification of the steady state is very challenging in isotachophoresis (ITP); especially in complex microgeometries, such as dog-leg channels or cross-channel junctions. In this work, an elastic matching method is applied to determine the quasi-steady state in microscale ITP. In the elastic matching method, the similarity between two profiles is calculated by comparing intensity distribution of two images or profiles. To demonstrate this similarity-based analysis technique for ITP, a constant voltage mode ITP model is developed and applied to a five-component ITP system. Hydrochloric acid and caproic acid are used as the leader and terminator, respectively, while histidine is used as the counter-ion. Two sample components, acetic acid and benzoic acid, are separated under the action of an applied electric field in both straight and dog-leg microchannels. This analysis shows that conductivity profiles provide a better measure to determine the quasi-steady state in an ITP process. For a straight microchannel, the quasi-steady state is achieved in less than a minute with a total potential drop of 100?V in a 2?cm long channel. In a straight channel, a true steady state can be achieved for ITP with appropriate countercurrent flow where stationary zones are formed, but the time it takes to reach the steady state is much longer than the without counter flow case. The numerical results indicate that a steady state cannot be reached in a dog-leg microchannel because of sample dispersion and refocusing at and near the intersections and at the branch channels. However, the elastic matching method can be used to determine the quasi-steady state in a dog-leg microchannel.     

Mono- and binuclear ruthenium(II) trifluoroacetato complexes containing monodentate co-ligands

Summary The syntheses of new dinuclear and mononuclear complexes of Ru^II trifluoroacetate containing monodentate co-ligands, namely [Ru₂(-O₂CCF₃)₄L₂] (L = py, 2-Mepy or 3-Mepy); trans-[Ru(O₂CCF₃)₂L₄] (L = 2-Mepy or 3-Mepy); [Ru(O₂CCF₃)(PPh₃)₄](O₂CCF₃) and [Ru(O₂CCF₃)₂(CO)(MPh₃)₃] (M = P or As), are described. The complexes have been characterized by physical and electrochemical studies.     

On electrophoresis of a pH‐regulated nanogel with ion partitioning effects

The electrophoresis of a polyelectrolyte nanoparticle, whose charge condition depends on the salt concentration and pH of the suspended medium as well as the dielectric permittivity difference, is analyzed. The present nonlinear model for the electrophoresis of this pH‐regulated polyelectrolyte (PE) particle is based on the consideration of full set of governing equations of fluid and ion transport coupled with the equation for electric field. The Born energy of the ions are incorporated to account for the difference in the dielectric permittivity of the PE and the electrolyte. The governing equations are computed numerically through a control volume approach. The nonlinear effects are highlighted by comparing with the existing linear model as well as results based on the first‐order perturbation analysis valid for a weak applied field. The ion partitioning effect arising due to the difference in self energy of ions between the two media, have a strong impact on the mobility of the PE. The ion partitioning effect attenuates the penetration of counterions in the PE, which enhances the electric force and hence, results in a larger mobility of the PE. The nonlinear effects due to the double layer polarization and relaxation are intensified due to the ion partitioning effect. The ion partitioning effect influences the association/dissociation of PE functional group by tuning the hydrogen/hydroxide ions. Present study shows that the ion partitioning effect is profound for higher salt concentration and/or higher volume density of PE functional groups.     

Electrophoretic transport and dynamic deformation of bio‐vesicles

Study of the deformation dynamics of cells and other sub‐micron vesicles, such as virus and neurotransmitter vesicles are necessary to understand their functional properties. This mechanical characterization can be done by submerging the vesicle in a fluid medium and deforming it with a controlled electric field, which is known as electrodeformation. Electrodeformation of biological and artificial lipid vesicles is directly influenced by the vesicle and surrounding media properties and geometric factors. The problem is compounded when the vesicle is naturally charged, which creates electrophoretic forcing on the vesicle membrane. We studied the electrodeformation and transport of charged vesicles immersed in a fluid media under the influence of a DC electric field. The electric field and fluid‐solid interactions are modeled using a hybrid immersed interface‐immersed boundary technique. Model results are verified with experimental observations for electric field driven translocation of a virus through a nanopore sensor. Our modeling results show interesting changes in deformation behavior with changing electrical properties of the vesicle and the surrounding media. Vesicle movement due to electrophoresis can also be characterized by the change in local conductivity, which can serve as a potential sensing mechanism for electrodeformation experiments in solid‐state nanopore setups.     

An unsteady analysis of non-Newtonian blood flow through tapered arteries with a stenosis

The problem of non-Newtonian and nonlinear blood flow through a stenosed artery is solved numerically where the non-Newtonian rheology of the flowing blood is characterised by the generalised Power-law model. An improved shape of the time-variant stenosis present in the tapered arterial lumen is given mathematically in order to update resemblance to the in vivo situation. The vascular wall deformability is taken to be elastic (moving wall), however a comparison has been made with nonlinear visco-elastic wall motion. Finite difference scheme has been used to solve the unsteady nonlinear Navier-Stokes equations in cylindrical coordinates system governing flow assuming axial symmetry under laminar flow condition so that the problem effectively becomes two-dimensional. The present analytical treatment bears the potential to calculate the rate of flow, the resistive impedance and the wall shear stress with minor significance of computational complexity by exploiting the appropriate physically realistic prescribed conditions. The model is also employed to study the effects of the taper angle, wall deformation, severity of the stenosis within its fixed length, steeper stenosis of the same severity, nonlinearity and non-Newtonian rheology of the flowing blood on the flow field. An extensive quantitative analysis is performed through numerical computations of the desired quantities having physiological relevance through their graphical representations so as to validate the applicability of the present model.