Transport Of Solute Molecules Research Articles

The complexities of the human placenta

The flow and transport of solute molecules in the intricate structure of the placenta make the organ a fetal life-support system.

Enhancing Surface Capture and Sensing of Proteins with Low-Power Optothermal Bubbles in a Biphasic Liquid.

Molecular binding in surface-based biosensing is inherently governed by diffusional transport of molecules in solution to surface-immobilized counterparts. Optothermally generated surface microbubbles can quickly accumulate solutes at the bubble-liquid-substrate interface due to high-velocity fluid flows. Despite its potential as a concentrator, however, the incorporation of bubbles into protein-based sensing is limited by high temperatures. Here, we report a biphasic liquid system, capable of generating microbubbles at a low optical power/temperature by formulating PFP as a volatile, water-immiscible component in the aqueous host. We further exploited zwitterionic surface modification to prevent unwanted printing during bubble generation. In a single protein-protein interaction model, surface binding of dispersed proteins to capture proteins was enhanced by 1 order of magnitude within 1 min by bubbles, compared to that from static incubation for 30 min. Our proof-of-concept study exploiting fluid formulation and optothermal add-on paves an effective way toward improving the performances of sensors and spectroscopies.

Morphology Modulation of Direct Inkjet Printing by Incorporating Polymers and Surfactants into a Sol–Gel Ink System

Many methods have been reported to prevent the nonuniformity of inkjet printing structures. Most of them depend on the balance of the capillary flow in the printing pattern during the evaporation of the solvent. However, as the relation of evaporation and capillary flow can obviously vary among different ink systems, it is difficult for a method to fit most of the situations. Therefore, it would be a promising way to eliminate any capillary flow before solvent evaporation so that morphology of the printing structure will not be affected by the evaporation behavior of the ink system. In this paper, a novel method of direct inkjet printing of a uniform metal oxide structure is reported. We introduce a polymer polyacrylamide and a surfactant FSO into a sol-gel ink system, and the new ink system can gel from the printing pattern edge to center as temperature increases because of the cross-linking of the polymer chains. By that means, transport of solute molecules and solvent molecules is limited. Meanwhile, the surfactant can ensure that the solute in the central liquid phase deposits uniformly by enhancing the Marangoni flow during the gelation process. The ZrO2 film with uniform morphology was fabricated by drying and annealing the gelating film and afforded a leakage current density of 7.48 × 10-7 A cm-2 at 1 MV and a breakdown field of 1.9 MV cm-1 at an annealing temperature of 250 °C.

Transport properties and size exclusion effects in wide-pore superficially porous particles

The effects of hydrodynamic radius on the transport of solute molecules in packed beds of wide-pore superficially porous particles (SPP) are studied using pore-scale simulation. The free molecular diffusion rate varies with radius through the Stokes-Einstein relation. Lattice Boltzmann and Langevin methods are used to model fluid motion and the transport of an ensemble of solute molecules in the fluid, providing statistics on solute concentration, flux, molecule age and residence time, as a function of depth in the SPP. Intraparticle effective diffusion and bed dispersion coefficients are calculated and correlated with the hydrodynamic radius and accessible porosity.The relative importance of convection and diffusion are found to depend on the molecule (tracer) size through the diffusion rate, and convection effects are more significant for larger, slower-diffusing molecules. When larger molecules are utilized, the intraparticle concentration is reduced in proportion to the local particle porosity, leading to a natural definition of the accessible porosity used in size exclusion chromatography (SEC). Although the pore shape is complex, the SEC constant K can be calculated directly from simulation. Simulation demonstrates that the effective diffusion coefficient is elevated near the particle hull, which is largely open to interstitial flow, and decreases with depth into the particle. All molecules studied here have transport access to the entire particle depth, although the accessible volume at a given depth depends on their size. The first passage time into the particle is well predicted by the diffusion rate, but residence time is influenced by convection, shortening the average visit duration. These results are of interest in “perfusion” chromatography where convection is thought to increase separation efficiency for large biomolecules.

A shrinking core model for seeds oil extraction with particularization to Camelina oil separation

The oil extraction from a spherical particle in an adequate solvent is analyzed by a dynamic model. The oil extraction occurs by moving the unsolubilized solid/solute-free phase interface toward the center of the particle. We assume that the transport of solute molecules has three resistances: (1) the resistance due to oil core dissolving; (2) the resistance due to the solute-free portion of the particle; (3) the resistance due to a surface layer near solid–liquid interface. Generally, the equation governing the dynamic behavior of oil extraction is numerically solved. However, sometimes analytical expressions for the time dynamics of the size of the unsolubilized oil portion can be obtained in some special cases. The present analysis on oil process extraction takes into account the effect of variable bulk solute concentration and of seed internal characteristics such as particle porosity, particle tortuosity and core oil dissolving kinetics. Result consists in a general mathematical model whose particularization is given for the case of Camelina seeds oil extraction. For Camelina seeds the oil hexane extraction has been characterized by particularization of the general modified shrinking core model. It has obtained that the particle dimensionless porosity is set to 0.08, while the constant of kinetic process from the shrinking core surface is strongly dependent on core position and on the temperature after relation kd=kd0(t)(rc/R)n with n=4 and kd0(t) in the range 4.3–8.3 10−8m/s.

Sedimentation Velocity Analysis of Large Oligomeric Chromatin Complexes Using Interference Detection.

Sedimentation velocity experiments measure the transport of molecules in solution under centrifugal force. Here, we describe a method for monitoring the sedimentation of very large biological molecular assemblies using the interference optical systems of the analytical ultracentrifuge. The mass, partial-specific volume, and shape of macromolecules in solution affect their sedimentation rates as reflected in the sedimentation coefficient. The sedimentation coefficient is obtained by measuring the solute concentration as a function of radial distance during centrifugation. Monitoring the concentration can be accomplished using interference optics, absorbance optics, or the fluorescence detection system, each with inherent advantages. The interference optical system captures data much faster than these other optical systems, allowing for sedimentation velocity analysis of extremely large macromolecular complexes that sediment rapidly at very low rotor speeds. Supramolecular oligomeric complexes produced by self-association of 12-mer chromatin fibers are used to illustrate the advantages of the interference optics. Using interference optics, we show that chromatin fibers self-associate at physiological divalent salt concentrations to form structures that sediment between 10,000 and 350,000S. The method for characterizing chromatin oligomers described in this chapter will be generally useful for characterization of any biological structures that are too large to be studied by the absorbance optical system.

The Teaching of Biochemistry: An Innovative Course Sequence Based on the Logic of Chemistry

An innovative course sequence for the teaching of biochemistry is offered, which more truly reflects the common philosophy found in biochemistry texts: that the foundation of biological phenomena can best be understood through the logic of chemistry. Topic order is chosen to develop an emerging understanding that is based on chemical principles. Preeminent biological questions serve as a framework for the course. Lipid and lipid-aggregate structures are introduced first, since it is more logical to discuss the intermolecular association of simple amphiphiles to form micelle and bilayer formations than to discuss the complexities of protein structure/folding. Protein, nucleic acid, and carbohydrate structures are studied next. Binding, a noncovalent process and the simplest expression of macromolecular function, follows. The physical (noncovalent) transport of solute molecules across a biological membrane is studied next, followed by the chemical transformation of substrates by enzymes. These are logical extensions of the expression of molecular function, first involving a simpler (physical transport) and second, a more complex (covalent transformation) process. The final sequence involves energy and signal transduction. This unique course sequence emerges naturally when chemical logic is used as an organizing paradigm for structuring a biochemistry course. Traditional order, which seems to reflect historic trends in research, or even an order derived from the central dogma of biology can not provide this logical framework.

Kinetics of hybridization of interfacial RNA homopolymer studied by thickness-shear mode acoustic wave sensor

The impedance response of RNA homopolymer hybridization on the electrode-solution interface of thickness shear mode acoustic wave sensors has been examined on a real-time basis by network analysis. The effects of blocking agents conventionally used to avoid nonspecific adsorption, solution ionic strength and temperature on the rate of interfacial hybridization have been examined quantitatively in terms of a pseudo-first order effective rate constant. A hybridization mechanism involving transport of RNA probe molecules in solution followed by duplex formation is proposed. The results suggest that the use of blocking agents is not necessary and that the biosensor is capable of the direct detection of hybridization in the present of nonspecific adsorption.

A stochastic model for adsorption in an open flow system

AbstractA stochastic model is developed to characterize flow, adsorption and transport of solute molecules through the solid phase in an open flow adsorber. The flow process is depicted as composed of n compartments with forward and backward flow connecting adjacent compartments. To account for adsorption and transport of solute molecules through the porous solid, the solid phase in each compartment is partitioned into an outer layer and an inner layer. The stochastic process model accounts for movement of solute molecules in the liquid phase, for the transfer of molecules between the liquid and the outer layer of the solid phase and for solute movement through the solid phase. From this model, one may predict the residence time distribution of a molecule in the system and the concentration profile of solute molecules in the outlet stream (breakthrough curve) and estimate the adsorption and flow parameters of the process. In addition to its usefulness in engineering treatment systems such as water and air purification, this modelling approach is useful in studying the transport of organic chemicals in the soil.