Diffusion Of Aqueous Solutions Research Articles

Tracing Molecular Propagation in Dextran Solutions by Pulsed Field Gradient NMR.

We have exploited the pulsed field gradient (PFG) technique of NMR to measure molecular diffusion in aqueous solutions of a mixture of dextran molecules. From detailed studies by fluorescence correlation spectroscopy (FCS), the lighter component of such mixtures is known to undergo subdiffusion, up to diffusion path lengths on the order of 0.5 μm. Our studies provide clear evidence of a crossover to normal diffusion for diffusion path lengths from this range up to about 1 μm.

Hydrogen bond dynamics and vibrational spectral diffusion in aqueous solution of acetone: A first principles molecular dynamics study#

We present an ab initio molecular dynamics study of vibrational spectral diffusion and hydrogen bond dynamics in aqueous solution of acetone at room temperature. It is found that the frequencies of OD bonds in the acetone hydration shell have a higher stretch frequency than those in the bulk water. Also, on average, the frequencies of hydration shell OD modes are found to increase with increase in the acetone–water hydrogen bond distance. The vibrational spectral diffusion of the hydration shell water molecules reveals three time scales: A short-time relaxation (~80fs) corresponding to the dynamics of intact acetone–water hydrogen bonds, a slower relaxation (~1.3ps) corresponding to the lifetime of acetone–water hydrogen bonds and another longer time constant (~12ps) corresponding to the escape dynamics of water from the solute hydration shell. The present first principles results are compared with those of available experiments and classical simulations. Vibrational spectral diffusion and hydrogen bond dynamics in aqueous solution containing an acetone molecule are studied through ab initio molecular dynamics simulations and time series analysis. The present theoretical results are also compared with those of available experiments and classical simulations.

Molecular Modeling of Organophosphorous Agents and Their Aqueous Solutions

Using molecular dynamics simulations, we modeled solvation and diffusion in aqueous solutions of organophosphorous compounds, including nerve G-agents sarin and soman (methylphosphonofluoridates) and their common simulants DMMP (dimethyl methylphosphonate) and DIFP (diisopropyl fluorophosphate). The aqueous solutions of the organophosphorous compounds were found to display complex molecular scale structures and dynamic properties due to competing interactions between strongly hydrophobic and hydrophilic groups. The mixing of agents with water was proved to be exothermic with negative excess mixing volume, indicating a strongly hydrophilic solvation. This effect was confirmed in a specially performed experiment. We discuss to what extent DMMP and DIFP are suitable simulants for G-agents in experimental studies, as far as their interactions with water are concerned. We also focus on the relevance of the structural features and mobilities of agents in water to their interactions with permselective polyelectrolyte membranes that may be employed as protective barriers against chemical warfare agents.

Transport of Neutral and Ionic Solutes: The Gel/Electrode and Gel/Electrolyte Interfaces

Transport through a polysaccharide gel phase has been investigated voltammetrically using both redox voltammetry at a gel covered electrode and ion transfer voltammetry across the gel/liquid interface (Gel/L). The apparent diffusion coefficients, D(app), of a range of neutral and ionic electroactive species have been determined in both uncharged and anionic polysaccharide media, agar, and kappa-carrageenan, respectively. It is shown that the diffusion of electroactive species in agar gel occurs at a rate similar to that of diffusion in aqueous solution for a range of redox couples. In the kappa-carrageenan medium, by contrast, the diffusion coefficient obtained for cationic solutes was found to be approximately an order of magnitude lower than the value in aqueous solution. The difference in D(app) is attributed to two independent processes: electrostatic interactions between the charge of the sulfonate groups of the kappa-carrageenan gel and the charge of the solute, as well a change in hydration of the solute molecules.

Uptake swelling and thermal expansion of CFRP tendons

Carbon-fibre-reinforced polymer (CFRP) tendons can be used as a corrosion-resistant alternative to steel for reinforcing or prestressing concrete in aggressive marine environments. The design lives of many civil marine structures often span decades and so the long-term durability of the internal reinforcement is important. One significant, yet overlooked, aspect of CFRP tendon durability is its susceptibility to swell on absorption of aqueous solutions including water and salt water. This paper reviews uptake-induced swelling in CFRP materials and draws comparisons with studies of swelling caused by thermal effects. The diffusion of aqueous solutions and their interaction with the polymer matrix are identified as the primary mechanisms responsible for the swelling. Experimental details are presented that correlate the uptake of water and salt water to swelling observed in CFRP tendons. The results are contrasted with both uptake- and thermal-driven behaviour cited in the literature. Lamé's equations are used to estimate the magnitude of the resulting stresses induced in the surrounding concrete. The practical significance of the findings is discussed, including the potential for cracking in the surrounding concrete cover and the implications for the tendon–concrete bond.

DNA diffusion in aqueous solution in presence of suspended particles

AbstractAlthough nanoparticles, which are comparable in size to polymer chains, are widely used as fillers to polymer matrices for developing functional and high performance materials, the dynamics of polymers constrained between solid particles has not been well elucidated. In this study, dynamics of individual polymer under such condition was investigated with fluorescent microscopy using DNA solutions as model systems. For individual T4 and λ DNA molecules in aqueous suspensions of spherical polystyrene particles with diameter of 1 μm, it was found that (i) the radius of gyration of DNA is independent of the particle volume fraction, ϕp, (ii) DNA diffusion is not sensitive to ϕp up to a certain critical ϕp where the average distance between particle surfaces is close to DNA size, and (iii) the DNA diffusion becomes slower at higher ϕp. The diffusion coefficient of DNA was larger, by a factor of 2, in the suspensions at intermediate ϕp than in the corresponding confined geometry (channel/slit between fixed walls), whereas this difference asymptotically vanished with increasing ϕp. This result suggested that the DNA diffusion in the suspensions with intermediate ϕp is accelerated by the particle motion. In fact, the diffusion coefficient measured for DNA in the suspensions was semiquantitatively described by the Rouse constraint‐release model considering the matrix effect on the probe chain diffusion. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1103–1111, 2009

Evaluation of amylopectin clusters and their interaction with nonionic surfactants

The interaction between polyoxyethylene (7 and 23) dodecyl ether (Unitol L-70 and L-230, respectively) and polyoxyethylene (9.5) nonylphenol ether (Renex 95) with amylopectin was studied employing the relative intensities of pyrene fluorescence emission bands 1 to 3, and excimer to monomer ratios. The pyrene concentration was very low (1 μmol/L), and the probe was added to amylopectin solution by two different methods. These experimental conditions have given information about how amylopectin branch structure affects the molecular diffusion in aqueous solution. Amylopectin clusters are formed from the biopolymer outer branches. The cluster polarity is similar to ethylene glycol, confirmed by the Reichardt dye measurements. Inside the clusters, amylopectin-Unitol surfactant complexes can form with cac and cmc dependent on the biopolymer concentration. The micellar aggregation number of 60 ± 5 was determined through pyrene steady-state fluorescence quenching experiments.

Ion-Specific Isotopic Fractionation of Molybdenum during Diffusion in Aqueous Solutions

Experiments modeling diffusion of Mo in aqueous solutions have been performed and, using multicollector ICP-MS, the ratios of the diffusivities of Mo isotopes, D97Mo/ D95Mo, in aqueous solutions have been determined. Diffusion of MoO42- ions in solution was concomitant with Mo isotopic fractionation with D97Md/D95Mo = 0.99988+/-0.00004 (2sigma for n = 3). In contrast, during diffusion of Mo polyanions, such as Mo70246- and Mo8O264-, no measurable isotope fractionation has been found with D97Mo/D95MO = 1.00000 +/- 0.00002 (2sigma for n = 3). These results indicate the need for due consideration to Mo speciation when attempting to interpret the role of diffusive fluxes in the formation of Mo isotopic signatures in nature. They also raise the possibility that the various chemical forms of other transition metals may be characterized by species-specific isotopic fractionation effects during physicochemical reactions.

Fluorescence relaxation in 3D from diffraction‐limited sources of PAGFP or sinks of EGFP created by multiphoton photoconversion

The relaxation of fluorescence from diffraction-limited sources of photoactivatable green fluorescent protein (PAGFP) or sinks of photobleached enhanced GFP (EGFP) created by multiphoton photo-conversion was measured in solutions of varied viscosity (eta), and in live, spherical Chinese hamster ovary (CHO) cells. Fluorescence relaxation was monitored with the probing laser fixed, or rapidly scanning along a line bisected by the photoconversion site. Novel solutions to several problems that hamper the study of PAGFP diffusion after multiphoton photoconversion are presented. A theoretical model of 3D diffusion in a sphere from a source in the shape of the measured multiphoton point-spread function was applied to the fluorescence data to estimate the apparent diffusion coefficient, D(ap). The model incorporates two novel features that make it of broad utility. First, the model includes the no-flux boundary condition imposed by cell plasma membranes, allowing assessment of potential impact of this boundary on estimates of D(ap). Second, the model uses an inhomogeneous source term that, for the first time, allows analysis of diffusion from sources produced by multiphoton photoconversion pulses of varying duration. For diffusion in aqueous solution, indistinguishable linear relationships between D(ap) and eta(-1) were obtained for the two proteins: for PAGFP, D(aq)= 89 +/- 2.4 microm2 s(-1) (mean +/- 95% confidence interval), and for EGFP D(aq)= 91 +/- 1.8 microm2 s(-1). In CHO cells, the application of the model yielded D(ap)= 20 +/- 3 microm2 s(-1) (PAGFP) and 19 +/- 2 microm2 s(-1) (EGFP). Furthermore, the model quantitatively predicted the decline in baseline fluorescence that accompanied repeated photobleaching cycles in CHO cells expressing EGFP, supporting the hypothesis of fluorophore depletion as an alternative to the oft invoked 'bound fraction' explanation of the deviation of the terminal fluorescence recovery from its pre-bleach baseline level. Nonetheless for their identical diffusive properties, advantages of PAGFP over EGFP were found, including an intrinsically higher signal/noise ratio with 488-nm excitation, and the requirement for approximately 1/200th the cumulative light energy to produce data of comparable signal/noise.

The Effect of Salt Stoichiometry on Protein−Salt Interactions Determined by Ternary Diffusion in Aqueous Solutions

We report the four diffusion coefficients for the lysozyme-MgCl2-water ternary system at 25 degrees C and pH 4.5. The comparison with previous results for the lysozyme-NaCl-water ternary system is used to examine the effect of salt stoichiometry on the transport properties of lysozyme-salt aqueous mixtures. We find that the two cross-diffusion coefficients are very sensitive to salt stoichiometry. One of the cross-diffusion coefficients is examined in terms of common-ion, excluded-volume, and protein-preferential hydration effects. We use the four ternary diffusion coefficients to extract chemical-potential cross-derivatives and protein-preferential interaction coefficients. These thermodynamic data characterize the protein-salt thermodynamic interactions. We demonstrate the presence of the common-ion effect (Donnan effect) by analyzing the dependence of the preferential-interaction coefficient not only with respect to salt concentration but also with respect to salt stoichiometry. We conclude that the common-ion effect and the protein-preferential hydration are both important for describing the lysozyme-MgCl2 thermodynamic interaction.

The Effect of Salt on Protein Chemical Potential Determined by Ternary Diffusion in Aqueous Solutions

We use accurate thermodynamic derivatives extracted from high-precision measurements of the four volume-fixed diffusion coefficients in ternary solutions of lysozyme chloride in aqueous NaCl, NH4Cl, and KCl at pH 4.5 and 25 degrees C to (a) assess the relative contributions of the common-ion and nonideality effects to the protein chemical potential as a function of salt concentration, (b) compare the behavior of the protein chemical potential for the three salts, which we found to be consistent with the Hofmeister series, and (c) discuss our thermodynamic data in relation to the dependence of the protein solubility on salt concentration. The four diffusion coefficients are reported at 0.6 mM lysozyme chloride and 0.25, 0.5, 0.9, 1.2, and 1.5 M KCl and extend into the protein-supersaturated region. The chemical potential cross-derivatives are extracted from diffusion data using the Onsager reciprocal relation and the equality of molal cross-derivatives of solute chemical potentials. They are compared to those calculated previously from diffusion data for lysozyme in aqueous NaCl and NH4Cl. We estimate the effective charge on the diffusing lysozyme cation at the experimental concentrations. Our diffusion measurements on the three salts allowed us to analyze and interpret the four diffusion coefficients for charged proteins in the presence of 1:1 electrolytes. Our results may provide guidance to the understanding of protein crystallization.

(Sodium Alginate/Acrylamide) Semi‐Interpenetrating Polymer Networks and their Usability on Removal of Lead, Cadmium, Nickel Ions

In this study, (sodium alginate (NaAlg)/acrylamide (AAm)) interpenetrating polymer networks (IPN) have been prepared at three different compositions, where the sodium alginate composition varies 1, 2, and 3% (w/v) in 50% (w/v) acrylamide solutions. These solutions have been irradiated with a 60Co‐γ source at different doses. The percent conversion was determined gravimetrically and 100% gelation was achieved at the 10.0 kGy dose. The swelling results at pH 7.0 and 9.0 indicated that (NaAlg/AAm)3IPN hydrogel, containing 3% NaAlg showed maximum % swelling in water, with swelling increasing in the order of Ni2+>Cd2+>Pb2+. Diffusion in aqueous solutions of metal ions within (NaAlg/AAm)IPN hydrogels was found to be Fickian character. Diffusion coefficients of (NaAlg/AAm)IPN hydrogels in water and aqueous solutions of metal ions were calculated. The maximum weight loss temperature and half life temperature for NaAlg, PAAm, (NaAlg/AAm)IPN and (NaAlg/AAm)IPN‐metal ion systems were found from thermal analysis studies. In the adsorption experiments, the efficiency of (NaAlg/AAm)IPN hydrogels to adsorb nickel, cadmium and lead ions from water was studied. (NaAlg/AAm)IPN hydrogels showed different adsorption for different aqueous solution of metal ion at pH 7.0. Adsorption isotherms were constructed for the (NaAlg/AAm)IPN‐metal ion systems. S type adsorption in the Giles classification system was found.

Quaternary mutual diffusion coefficients for aqueous solutions of a cationic–anionic mixed surfactant from moments analysis of Taylor dispersion profiles

Taylor dispersion is used to measure mutual diffusion in aqueous solutions of dodecyltrimethylammonium bromide (DTAB) + sodium octanoate (NaOct), a cationic–anionic mixed surfactant. Diffusion of the four different constituent ions (DTA+, Br−, Na+, Oct−) constrained only by electroneutrality produces three independent solute fluxes. Mutual diffusion in these solutions is therefore a quaternary process described by nine Dik coefficients. Injecting excess DTAB or NaOct into DTAB + NaOct carrier solutions produces remarkable refractive-index profiles with three maxima and two minima. Least-squares analysis of these profiles failed to converge, prompting the development of a procedure for the evaluation of quaternary Dik coefficients from the heights, areas, first moments, and second moments of dispersion profiles. The reported Dik coefficients describe the coupled diffusion of DTAB(1) + NaOct(2) + NaBr(3) components in solutions containing 40 mmol dm−3 total surfactant at 25 °C and four different DTAB:NaOct ratios. The results show that the unusual profile shapes are caused by strongly coupled diffusion, as indicated by large negative D12, D21 values and large positive D32, D31 values which exceed the magnitude of main-coefficients D11 and D22. Binary mutual diffusion coefficients for aqueous DTAB solutions and critical micelle concentration for DTAB + NaOct solutions are also reported.

The effect of precursor concentration on the size of the CdS nanoparticles synthesized in a chicken egg membrane

Results of the studies on the effect of concentration of the precursors on the size of CdS nanoparticles formed in a chicken egg membrane are presented in this article. CdS is formed by the diffusion of aqueous solutions of cadmium acetate and thiourea across the membrane. The optical absorption spectra of the samples exhibit a blue shift in the absorption edge indicating the formation of CdS particles with the size lying in the nanoscale regime. The band gaps of the samples with small reaction times were higher than that of the bulk value, approaching the bulk band gap value with the increase in reaction time for a fixed concentration. Particle sizes were estimated from the band gap values. At lower concentrations, smaller particles are formed even at large reaction times and offer a better control over the size of the particles. At very low concentrations, it takes some time for the absorption edge to evolve after the membrane is removed from the reaction bath. The particle size saturates at higher reaction time possibly due to an equilibrium being established in the system, resulting in stoppage of the diffusion of the reacting ions. Absorption edge could not be detected even days after the removal of the membrane from the reaction bath at still lower concentrations, despite allowing the reaction to take place for large periods of time.

水溶液‐無機・生体鉱物間微量元素分配とその環境問題への応用

Partitioning of trace elements between abiotic and biotic minerals (carbonates and sulfates) and aqueous solutions was theoretically considered. The effects of diffusion in aqueous solution, rate of precipitation, and physical properties of crystals (ionic radii, Poisson's ratio, Young's modulus) on the partitioning are discussed. Some examples of application of the partitioning of trace elements to environmental problems are given.

Diffusion of Aqueous Solutions of CoCl 2 , Co(NO 3 ) 2 , and Cu(NO 3 ) 2 in Porous Glass Membranes

Diffusion coefficients of CoCl2, Co(NO3)2, and Cu(NO3)2 salts, characterizing permeation of their aqueous solutions across glass membranes with predominant pore radius in the range from 70 to 4.5 nm are determined. With pores in the membranes becoming narrower, the diffusion mobility of the electrolytes decreases.

Dynamically observing intratumor injection of laser-absorbing dye and immunoadjuvant using digital x-ray imaging technique

WeiR.ChenUniversity of Central OklahomaDepartment of Physics and EngineeringEdmond, Oklahoma 73034andUniversity of OklahomaDepartment of Physics and AstronomyNorman, Oklahoma 73109E-mail: wchen@ucok.eduHong LiuUniversity of OklahomaCenter for Bioengineering and School ofElectrical EngineeringNorman, Oklahoma 73019Wei YueJiping WangUniversity of VirginiaDepartment of Internal MedicineCharlottesville, Virginia 22908Robert E. NordquistUniversity of OklahomaDepartment of OphthalmologyOklahoma City, Oklahoma 73104andWound Healing of Oklahoma, Inc.3945 North Walnut StreetOklahoma City, Oklahoma 73105Abstract. Selective laser-tissue interaction is a promising method fornoninvasive treatment of deep tumors. Using a laser beam with a wave-length in the near-infrared region and an intratumoral injection of a laser-absorbing dye, the laser energy can destroy targeted tumor cells whilesparing normal surrounding tissue. Introducing an immunoadjuvant canachieve possible systemic antitumor immune response, hence augment-ing the selective laser-tissue interaction. Administration of the dye andthe immunoadjuvant, and the time window for optimal laser application,are crucial in determining the outcome of the treatment. To determinethe dynamic distribution of intratumor-injected laser-absorbing dye andimmunoadjuvant, a digital x-ray imaging technique was employed. In-docyanine green as the laser-absorbing dye and glycated chitosan asthe immunoadjuvant were injected into the center of a rat tumor, and thetransmitted x-ray signals through tumor tissue and surrounding normaltissue, before and after the injection, were acquired and analyzed. Thetransmitted signals through tissue were reduced due to the injection ofeither dye or immunoadjuvant solution. The diffusion of aqueous solu-tions in tissue was a function of time and of the properties of the solutes.The indocyanine green solution, due to its low molecular weight, diffusedthrough the tumor almost immediately after injection, then gradually dis-persed into the surrounding tissue. The glycated chitosan, on the otherhand, due to its high molecular weight and high viscosity, dispersedslowly and took about 20 to 25 min to reach maximum accumulation atthe edge of the tumor. Our results showed that the digital x-ray imagescould be used to guide the precise positioning of the injecting needle,and to determine the distributions of the dye and immunoadjuvant in thetumor and in the surrounding normal tissue. Apparently, the dynamicobservation of dye and immunoadjuvant administration and their diffu-sion process could be used to optimize the parameters for laser treat-ment of deep tumors.

Thermal Diffusivity of Aqueous Solutions of Magnesium Chloride in the Temperature Range from 294 to 371 K

The thermal diffusivity of aqueous solutions of magnesium chloride was determined in the temperature range 294 to 371 K and at atmospheric pressure. Using a noninvasive optical technique—laser-induced thermal grating (LTG)—the measurements were carried out in aqueous solutions of weight fractions of 5, 10, 15, and 20% magnesium chloride. The measurement results for the aqueous solutions are presented as a function of temperature and weight fraction.

Movement and localization of RNA in the cell nucleus.

The movement of various RNAs from their sites of chromosomal synthesis to their functional locations in the cell is an important step in eukaryotic gene readout, though one less well understood than the transcription, RNA processing, and various functions of RNA. The segregation of the many classes of RNA out into to their appropriate sites in the cell is, from a physical chemical point of view, a remarkable phenomenon. This paper summarizes investigations my colleagues and I have undertaken over the past 7 years to describe the intracellular traffic and localization of RNA in living cells. One approach we have developed is to glass-needle microinject approximately 0.01 pl of fluorescent RNA solutions into the nucleus or cytoplasm of cultured mammalian cells. This 'fluorescent RNA cytochemistry' approach has resolved intranuclear sites ('speCkles') for which premessenger RNAs (pre-mRNA) have high affinity and has revealed very rapid movements of certain other RNAs from their nucleoplasmic injection sites to the nucleoli. One of these rapidly trafficking nucleolar RNAs is the signal recognition particle (SRP) RNA, and further results indicate that the nucleolus is a site of SRP RNA processing or ribonucleoprotein assembly prior to export to the cytoplasm. In these fluorescent RNA microinjection studies, we have also used mutant RNA molecules to identify specific nucleotide sequences that function as targeting elements for the localization of RNAs at their respective intranuclear sites. In a second approach, we have used fluorescent correlation spectroscopy (FCS), a classical biophysical method for measuring molecular motion in vitro, coupled with confocal fluorescence microscopy to measure the movement of poly(A) RNA in the nucleus, with the interesting finding that these RNAs appear to move about inside the nucleus at rates comparable to diffusion in aqueous solution. Parallel experiments using the method of fluorescence recovery after photobleaching (FRAP) revealed a diffusion coefficient for intranuclear poly(A) RNA close to that measured by FCS. These results bear on the structure of the nucleoplasmic ground substance-an extremely controversial and unsolved problem in cell biology (29). The methods we have developed and these initial results represent the first major step toward a comprehensive understanding of RNA traffic in the cell nucleus.

Structures, Ferromagnetic Ordering, Anisotropy, and Spin Reorientation for Two- and Three-Dimensional Cyano-Bridged Mo3±-Mn2± Compounds

The compounds K2Mn3(H2O)6[Mo(CN)7]2·6H2Oand Mn2(H2O)5Mo(CN)7·nH2O (α phase, n = 4; β phase, n = 4.75) have been synthesized in the form of well shaped single crystals by slow diffusion of aqueous solutions containing [Mo(CN)7]K2·2H2O and [Mn(H2O)6](NO3), respectively. The first compound has been obtained in the presence of an excess of K± ions. The crystal structures have been determined. K2Mn3(H2O)6[Mo(CN)7]2·6H2O is two-dimensional, and Mn2(H2O)5Mo(CN)7 ·nH2O (α and β phases) are three-dimensional. The magnetic properties have been studied in great detail through single crystal magnetic measurements, and the magnetic phase diagrams have been determined. The three compounds exhibit a long-range ferromagnetic ordering along with a field-induced spin reorientation. Furtuthermore, the last two compounds show an additional magnetically ordered state which disappears when applying a suffeciently large magnetic field. The magnetic properties have been found to be dramatically modified when the non-coordinated water molecules are released. For instance, Tc is shifted from 39 to 72 K for K2Mn3(H2O)6 [Mo(CN)7]2·6H2O, and a pronounced coercivity is observed after partial dehydration.