Low Ionic Strength Conditions Research Articles

Kinetics and equilibrium partitioning of dissolved BTEX in PDMS and POM sheets.

Passive sampling of volatile organic chemicals from soil and groundwater is primarily important in assessing the status of environmental contamination. A group of low molecular weight pollutants usually found in petroleum fuels, benzene, toluene, ethylbenzene, and xylenes (BTEX) was studied for its kinetics and equilibrium partitioning with single-phase passive samplers using polydimethylsiloxane (PDMS) and polyoxymethylene (POM) as sorbing phase. PDMS (1mm) and POM (0.076mm) sheets were used for sorption of BTEX and concentrations were analyzed using GC-FID. The equilibrium absorption and desorption of PDMS in water was achieved after 120min while POM sheets absorbed up to 35days and desorbed in 7days. The kinetic rate constants in PDMS is higher than in POM up to 3 orders of magnitude. Logarithms of partition coefficient were determined to be in the range of 1.6-2.8 for PDMS and 2.1-3.1 for POM. The results indicate that POM is a stronger sorbent for BTEX and has slower equilibration time than PDMS. The partitioning process for both polymers was found to be enthalpy-driven by measurement of K d values at varying temperatures. K d values increase at low temperature and high ionic strength conditions. Presence of other gasoline components, as well as dissolved organic matter, did not significantly affect equilibrium partitioning. A good 1:1 correlation between the measured and the predicted concentrations was established on testing the potential application of the constructed PDMS sampler on natural soils and artificial soils spiked with gasoline-contaminated water.

Refinement of current monitoring methodology for electroosmotic flow assessment under low ionic strength conditions.

Current monitoring is a well-established technique for the characterization of electroosmotic (EO) flow in microfluidic devices. This method relies on monitoring the time response of the electric current when a test buffer solution is displaced by an auxiliary solution using EO flow. In this scheme, each solution has a different ionic concentration (and electric conductivity). The difference in the ionic concentration of the two solutions defines the dynamic time response of the electric current and, hence, the current signal to be measured: larger concentration differences result in larger measurable signals. A small concentration difference is needed, however, to avoid dispersion at the interface between the two solutions, which can result in undesired pressure-driven flow that conflicts with the EO flow. Additional challenges arise as the conductivity of the test solution decreases, leading to a reduced electric current signal that may be masked by noise during the measuring process, making for a difficult estimation of an accurate EO mobility. This contribution presents a new scheme for current monitoring that employs multiple channels arranged in parallel, producing an increase in the signal-to-noise ratio of the electric current to be measured and increasing the estimation accuracy. The use of this parallel approach is particularly useful in the estimation of the EO mobility in systems where low conductivity mediums are required, such as insulator based dielectrophoresis devices.

Motile properties of the bi-directional kinesin-5 Cin8 are affected by phosphorylation in its motor domain.

The Saccharomyces cerevisiae kinesin-5 Cin8 performs essential mitotic functions in spindle assembly and anaphase B spindle elongation. Recent work has shown that Cin8 is a bi-directional motor which moves towards the minus-end of microtubules (MTs) under high ionic strength (IS) conditions and changes directionality in low IS conditions and when bound between anti-parallel microtubules. Previous work from our laboratory has also indicated that Cin8 is differentially phosphorylated during late anaphase at cyclin-dependent kinase 1 (Cdk1)-specific sites located in its motor domain. In vivo, such phosphorylation causes Cin8 detachment from spindles and reduces the spindle elongation rate, while maintaining proper spindle morphology. To study the effect of phosphorylation on Cin8 motor function, we examined in vitro motile properties of wild type Cin8, as well as its phosphorylation using phospho-deficient and phospho-mimic variants, in a single molecule fluorescence motility assay. Analysis was performed on whole cell extracts and on purified Cin8 samples. We found that addition of negative charges in the phospho-mimic mutant weakened the MT-motor interaction, increased motor velocity and promoted minus-end-directed motility. These results indicate that phosphorylation in the catalytic domain of Cin8 regulates its motor function.

Adsorption characteristics of Direct Red 23 azo dye onto powdered tourmaline

The high electric field on the surface of tourmaline particles has a potential of enhancing electrostatic reactions during adsorption. However, information concerning the adsorption characteristics of dyes onto tourmaline is currently unavailable. In the present study, the behavior and efficiency of powdered tourmaline (PT) in removing the diazo Direct Red 23 (DR23) dye from aqueous solution were investigated. The observations from batch adsorption experiments indicated that the adsorption was more favorable under low adsorbate surface loading, low pH, high temperature, and low ionic strength conditions. A homogeneous particle diffusion model (HPDM) was used to characterize the process, and the rate of adsorption was found to be controlled by intra-particle diffusion. An activation energy of 4.54kcal/mol was calculated, suggesting that the adsorption proceeded with a low energy barrier and that a physisorption was involved. The functional groups binding anionic DR23 on the PT particles were also identified. A maximum adsorption capacity of 153mg/g was determined according to the Langmuir isotherm. The PT was subjected to a total of 5 regeneration runs without losing much of its dye-adsorption capacities. Due to its low price, abundant availability, and superb adsorption capacity, PT has a great potential for use as an effective adsorbent in removing DR23 from aqueous solutions.

Glycosidases Interact Selectively With Mannose-6-Phosphate Receptors of Bull Spermatozoa.

Glycosidases may play a role in sperm maturation during epididymal transit. In this work, we describe the interaction of these enzymes with bull spermatozoa. We found that β-galactosidase associated to spermatozoa can be released under low ionic strength conditions, whereas the interaction of N-acetyl-β-D-glucosaminidase and β-glucuronidase with spermatozoa appeared to be stronger. On the other hand, α-mannosidase and α-fucosidase cannot be removed from the gametes. In addition, part of N-acetyl-β-D-glucosaminidase, β-galactosidase, and β-glucuronidase can also be released by mannose-6-phosphate. Taking into account these data, we explored the presence of cation-independent- and cation-dependent-mannose-6-phosphate receptors in the spermatozoa and found that cation-independent mannose-6-phosphate receptor is highly expressed in bull spermatozoa and cation-dependent-mannose-6-phosphate receptor is expressed at a lesser extent. In addition, by immunofluorescence, we observed that cation-independent-mannose-6-phosphate receptor is mostly located at the acrosomal zone, whereas cation-dependent-mannose-6-phosphate receptor presents a different distribution pattern on spermatozoa during the epididymal transit. N-acetyl-β-D-glucosaminidase and β-glucuronidase isolated from epididymal fluid interacted mostly with cation-independent-mannose-6-phosphate receptor, while β-galactosidase was recognized by both receptors. We concluded that glycosidases might play different roles in bull spermatozoa and that mannos-6-phosphate receptors may act as recruiters of some enzymes. J. Cell. Biochem. 117: 2464-2472, 2016. © 2016 Wiley Periodicals, Inc.

Characterization of cross-linked cellulosic ion-exchange adsorbents: 2. Protein sorption and transport

Adsorption behavior in the HyperCel family of cellulosic ion-exchange materials (Pall Corporation) was characterized using methods to assess, quantitatively and qualitatively, the dynamics of protein uptake as well as static adsorption as a function of ionic strength and protein concentration using several model proteins. The three exchangers studied all presented relatively high adsorptive capacities under low ionic strength conditions, comparable to commercially available resins containing polymer functionalization aimed at increasing that particular characteristic. The strong cation- and anion-exchange moieties showed higher sensitivity to increasing salt concentrations, but protein affinity on the salt-tolerant STAR AX HyperCel exchanger remained strong at ionic strengths normally used in downstream processing to elute material fully during ion-exchange chromatography. Very high uptake rates were observed in both batch kinetics experiments and time-series confocal laser scanning microscopy, suggesting low intraparticle transport resistances relative to external film resistance, even at higher bulk protein concentrations where the opposite is typically observed. Electron microscopy imaging of protein adsorbed phases provided additional insight into particle structure that could not be resolved in previous work on the bare resins.

Influence of Charge on the Elastic Properties of Lipid Membranes

Lipid membrane elastic properties play an important role in the membrane deformations and dynamic morphological transitions necessary for cell function. A key elastic property underlying these dynamics is the bending rigidity, motivating significant research efforts to quantify the effects of lipid structure and additives on the membrane bending modulus. To date, the majority of experimental research has focused on the dynamics of model membrane systems composed of zwitterionic lipids; however, most biomembranes are negatively charged at physiological conditions due to the presence of charged lipid headgroups. Here we study the bending dynamics of negatively-charged phosphatidylglycerol (PG) bilayers using neutron spin echo spectroscopy. Our results show that the charged lipid bilayers are softer than analogous zwitterionic phosphatidylcholine (PC) bilayers in both the gel and fluid phases at low ionic strength conditions. Interestingly, theoretical predictions indicate that the opposite should be true and that the bending rigidity should increase with increasing surface charge. We propose that this discrepancy is due to charged-related differences in the area per headgroup and lipid hydration between PG and PC bilayers that are not considered by existing theoretical models. Our results provide new insights into the influence of charge on the membrane elastic properties and demonstrate how these dynamics are coupled to charge effects on the membrane structure.

Determination of Electrophoretic Forces in a Gel Matrix in Different Ionic Strength Conditions

Nanocoding, a genome analysis platform, relies on very low ionic strength conditions to elongate DNA molecules up to 1.06 (fully stretched DNA molecule = 1)1, which is the largest stretch reported in the literature. Understanding how electroosmotic and electrophoretic forces vary, as ionic strength decreases, will enable better Nanocoding devices to be developed. Using two different gel assays to determine electroosmotic and overall mobility (includes contributions from electrophoretic forces and electroosmotic forces), we were able to determine electrophoretic mobility in different ionic strength solutions. Our first gel assay relied on electrophoresising linear DNA molecules [pUC19 (2.7 kb), pBR322 (4.4 kb), φX174 (5.4 kb), and PSNAPf-H2B (6.2 kb)] in varying gel concentrations (1.5%, 1.25%, 1%, 0.75%, 0.5%) to determine the free solution mobility (overall mobility) of these molecules in dilutions of TE buffer. As the buffer concentration decreases from 2X (Ionic strength = 13.8 mM) to 1X (Ionic strength = 7.3 mM), the overall mobility increased. As we further diluted TE (< 1X TE), the overall mobility drastically decreased as the ionic strength decreased.1. Kounovsky-Shafer, K.L., Hernandez-Ortiz, J.P., Jo, K., Odijk, T., de Pablo, J.J., and David C. Schwartz, D.C. Presentation of large DNA molecules for analysis as nanoconfined dumbbells, Macromolecules, 2013, 46 (20), 8356-8368.

Determining Parameters and Mechanisms of Colloid Retention and Release in Porous Media.

A modeling framework is presented to determine fundamental parameters and controlling mechanisms of colloid (microbes, clays, and nanoparticles) retention and release on surfaces of porous media that exhibit wide distributions of nanoscale chemical heterogeneity, nano- to microscale roughness, and pore water velocity. Primary and/or secondary minimum interactions in the zone of electrostatic influence were determined over the heterogeneous solid surface. The Maxwellian kinetic energy model was subsequently employed to determine the probability of immobilization and diffusive release of colloids from each of these minima. In addition, a balance of applied hydrodynamic and resisting adhesive torques was conducted to determine locations of immobilization and hydrodynamic release in the presence of spatially variable water flow and microscopic roughness. Locations for retention had to satisfy both energy and torque balance conditions for immobilization, whereas release could occur either due to diffusion or hydrodynamics. Summation of energy and torque balance results over the elementary surface area of the porous medium provided estimates for colloid retention and release parameters that are critical to predicting environmental fate, including the sticking and release efficiencies and the maximum concentration of retained colloids on the solid phase. Nanoscale roughness and chemical heterogeneity produced localized primary minimum interactions that controlled long-term retention, even when mean chemical conditions were unfavorable. Microscopic roughness played a dominant role in colloid retention under low ionic strength and high hydrodynamic conditions, especially for larger colloids.

Critical role of surface roughness on colloid retention and release in porous media

This paper examines the critical role of surface roughness (both nano- and micro-scale) on the processes of colloid retention and release in porous media under steady-state and transient chemical conditions. Nanoscale surface roughness (NSR) in the order of a few nanometers, which is common on natural solid surfaces, was incorporated into extended-DLVO calculations to quantify the magnitudes of interaction energy parameters (e.g. the energy barrier to attachment, ΔΦa , and detachment, ΔΦd , from a primary minimum). This information was subsequently used to explain the behavior of colloid retention and release in column and batch experiments under different ionic strength (IS) and pH conditions. Results demonstrated that the density and height of NSR significantly influenced the interaction energy parameters and consequently the extent and kinetics of colloid retention and release. In particular, values of ΔΦa and ΔΦd significantly decreased in the presence of NSR. Therefore, consistent with findings of column experiments, colloid retention in the primary minimum was predicted to occur at some specific locations on the sand surface, even at low IS conditions. However, NSR yielded a much weaker primary minimum interaction compared with that of smooth surfaces. Colloid release from primary minima upon decreasing IS and increasing pH was attributed to the impact of NSR on the values of ΔΦd . Pronounced differences in the amount of colloid retention in batch and column experiments indicated that primary minimum interactions were weak even at high IS conditions. Negligible colloid retention in batch experiments was attributed to hydrodynamic torques overcoming adhesive torques, whereas significant colloid retention in column experiments was attributed to nano- and micro-scale roughness which would dramatically alter the lever arms associated with hydrodynamic and adhesive torques.

Molecular simulation study of feruloyl esterase adsorption on charged surfaces: effects of surface charge density and ionic strength.

The surrounding conditions, such as surface charge density and ionic strength, play an important role in enzyme adsorption. The adsorption of a nonmodular type-A feruloyl esterase from Aspergillus niger (AnFaeA) on charged surfaces was investigated by parallel tempering Monte Carlo (PTMC) and all-atom molecular dynamics (AAMD) simulations at different surface charge densities (±0.05 and ±0.16 C·m(-2)) and ionic strengths (0.007 and 0.154 M). The adsorption energy, orientation, and conformational changes were analyzed. Simulation results show that whether AnFaeA can adsorb onto a charged surface is mainly controlled by electrostatic interactions between AnFaeA and the charged surface. The electrostatic interactions between AnFaeA and charged surfaces are weakened when the ionic strength increases. The positively charged surface at low surface charge density and high ionic strength conditions can maximize the utilization of the immobilized AnFaeA. The counterion layer plays a key role in the adsorption of AnFaeA on the negatively charged COOH-SAM. The native conformation of AnFaeA is well preserved under all of these conditions. The results of this work can be used for the controlled immobilization of AnFaeA.

Aggregation behaviour of gold nanoparticles in presence of chitosan

Chitosan (CS) is a biocompatible polysaccharide with positive charge that is widely used as a coating agent for negatively charged nanoparticles. However, the types of structures that emerge by combining CS and nanoparticles as well as their behaviour are still poorly understood. In this work, we characterize the nanocomposites formed by gold nanoparticles (AuNPs) and CS and study the influence of CS in the expected aggregation process that should experience those nanoparticles under the favourable conditions of low pH and high ionic strength. Thus, at the working CS concentration, we observe the existence of CS structures that quickly trap the AuNPs and avoid the formation of nanoparticle aggregates in environmental conditions that, otherwise, would lead to such an aggregation.

Crystallization of interleukin-18 for structure-based inhibitor design.

Interleukin-18 (IL-18) is a pleiotropic pro-inflammatory cytokine belonging to the IL-1 superfamily. IL-18 plays an important role in host innate and acquired immune defense, with its activity being modulated in vivo by its naturally occurring antagonist IL-18 binding protein (IL-18BP). Recent crystal structures of human IL-18 (hIL-18) in complex with its antagonist or cognate receptor(s) have revealed a conserved binding interface on hIL-18 representing a promising drug target. An important step in this process is obtaining crystals of apo hIL-18 or hIL-18 in complex with small-molecule inhibitors, preferably under low ionic strength conditions. In this study, surface-entropy reduction (SER) and rational protein design were employed to facilitate the crystallization of hIL-18. The results provide an excellent platform for structure-based drug design.

Extraction of histone H1 and decondensation of nuclear chromatin with various Mg-dependent organization levels under treatment with polyglutamic acid and distamycin.

Chromatin in rat liver nuclei under conditions of low ionic strength (20-25mM) and [Mg2+] from 2 to 5mM has a condensed structure (100-200nm globules) and gives the same CD signal (320-340nm) at interaction with the antibiotic distamycin A (DM). Reducing [Mg2+] to 1mM leads to chromatin decondensation to 30nm structures and increases the CD signal. Poly-L-glutamic acid (PG) at weight ratio PG/DNA= 6 and in the presence of 5mM Mg2+ extracts only about 1/8 of nuclear histone H1, preserving a condensed chromatin structure. Removal of about 1/4 of H1 at 3mM Mg2+ leads to chromatin decondensation to 30nm fibrils. Extraction of about half of histone H1 at [Mg2+] ≤ 2mM results in chromatin refolding to nucleosome fibrils. PG-decondensation leads to a significant increase in the CD signal. The main H1 extraction occurs in 1-2min, but at all Mg2+ concentrations the more slowly PG extracted fraction is found comprising 5-7% of nuclear H1. About 25% of leaving nuclear H1 can be extracted by PG in the presence of saturating DM concentration (molar DM/DNA= 0.1). H1 release depends significantly on the PG concentration. However, even at high weight ratio PG/DNA= 30 and DM/DNA= 0.1, about 5-10% of histone H1 remained in the nuclei. Decondensation of chromatin in the nucleus is not always proportional to the yield of extracted histone H1 and is weakened in the presence of positively charged DM or high concentrations of PG. Our results show that the interaction of DM with chromatin depends primarily on chromatin packaging, while PG extraction depends on [Mg2+] supporting this packaging.

Impact of Growth Phase and Natural Organic Matter on the Attachment Kinetics of Salmonella typhimurium to Solid Surfaces

The impact of biological interactions on the transport and attachment of Salmonella typhimurium was investigated using cells grown to the mid- and late-exponential phases under a range of ionic strength (IS) conditions, ion valence (KCl vs. CaCl2), and the presence of natural organic matter (NOM). A parallel plate flow chamber was used for the observation of bacterial cell attachment kinetics onto a glass surface with an optical microscope. The physicochemical interactions occurring between the bacteria and surface, as well as the contribution of growth phase and NOM were evaluated. Results showed that none of the cells harvested at the mid- and late-exponential phases attached to glass surfaces at low IS condition (10−3 M KCl), whereas maximum attachment was observed at high IS (10−1 M KCl) for both growth phases. Meanwhile, the presence of NOM reduced the attachment of the Salmonella cells significantly under all conditions. Without NOM, attachment efficiencies (α) in KCl were similar at both growth phases; however, in the presence of the divalent ions, α decreased as the cells aged. In the presence of NOM, α was significantly lower at the late-exponential phase than the mid-exponential phase. Cellular characterization suggested that bacterial cell surface heterogeneity and functional groups due to growth phase is one of the primary contributors to the observed attachment trends, affected by both NOM and ion valence. These trends indicate the complex role of NOM in the fate and transport mechanisms of Salmonella, coupled with ion valence and growth phase.

Aggregation of growing crystals in suspension: III. Accounting for adhesion and repulsion

In this paper we modify our previously published model describing the aggregation behaviour of crystals growing in suspensions. That model considered aggregation only in terms of cementing, i.e. the growth of a neck between colliding particles.In this current work, we introduce into our model the case of aggregation of growing crystals in the presence of inter-particle forces. Here we postulate that aggregation may be augmented by adhesion between the colliding particles, or diminished by repulsion of particles. In the new model we characterise the adhesive or repulsive force by a surface energy acting along a linear contact and subsequently define an adhesion Mumtaz number, MA. In the case of simultaneous cementing and adhesion the Mumtaz number is simply the sum of the separate cementing and adhesion numbers.In this work, two crystallographic forms of calcium oxalate monohydrate (COM) and one form of calcite under both low and high ionic strength conditions were studied. Calcite crystals were found to evidence adhesion between the colliding particles, both a high and low ionic strength. Furthermore, the ionic strength also influenced the cementing parameter. The different forms of COM exhibited both different cementing and inter-particle behaviour. These effects were attributed to differences between the systems at the nano-scale and that aggregation behaviour depends on the anisotropic nature of growing crystals.

Modeling and Mechanism of the Adsorption of Proton and Copper to Natural Bamboo Sawdust Using the NICA–Donnan Model

Bamboo sawdust represents an attractive low-cost adsorbent for heavy metal removal from contaminated waters. In the present study, the binding of protons and copper (Cu) ions to purified natural bamboo sawdust was investigated through acid–base titrations and Cu adsorption isotherms. The experimental data were modeled with the nonideal competitive adsorption (NICA)–Donnan equation (the NICA–Donnan model) to account for the heterogeneity of binding sites, stoichiometry of ion binding, as well as electrostatic interaction. Our results showed that the NICA–Donnan modeling of acid–base titration curves provided more accurate fitting results than the two-site surface complexation model. The stoichiometry parameters of the adsorption for Cu were both mono-dentate and binuclear, with the latter existing mainly under low ionic strength and high pH conditions. The contribution of low proton affinity and high proton affinity sites to Cu binding was dependent on pH. For high proton affinity sites, the partial inclusion of CuOH+ species adsorption led to an increase in the Cu ion affinity constant, whereas the incorporation of species adsorption decreased the affinity constant.

Single DNA Molecule Swollen and Trapped in Nanoslit

Single DNA Molecule Swollen and Trapped in NanoslitDirect visualization of individual DNA molecules confined within a nano/microfluidic geometry has provided a new route for the study of polymer physics. Molecular confinement has been utilized to evaluate theoretical predictions developed over several decades. Particularly, nanoslit confined DNA molecules are an interesting topic to show the conformational transition from 3D to 2D depending on nanoslit heights. Although several experiments have recently reported the dependence of DNA conformation on nanoslit confinement, a controversy still remains because the results have not been consistent with one another nor with theoretical predictions. Here we present nanoslit confined DNA conformations at various low ionic strength conditions down to 0.18 mM, which increase the repulsion between DNA−DNA and DNA−nanoslit. Moreover, we derived a new theoretical explanation for most measurements of single DNA molecule size under strong nanoslit confinement. Our findings demonstrates that very low ionic strength conditions not only increase the DNA persistence length dramatically, but also cause DNA molecules to swell to the extent that the effective diameter of DNA becomes larger than the nanoslit height (h < w), which can be considered as electrostatic trapping to confine molecules to geometry smaller than the physical boundaries. Consequently, by accounting for these effects, our results and theory provide a reasonable solution for a current controversy regarding the dependence of the DNA conformation on slit height (h), persistence length (p), and effective diameter (w).1. Lee J, Kim S, Jeong H, Jung GY, Chang R, Chen YL, Jo, K (2014) Nanoslit Confined DNA at Low Ionic Strengths. ACS Macro Letters 3(9): 926-930

Site-Specific Structural Changes in Unmodified and Pyroglutamylated Amyloid Beta Peptide by Isotope-Edited Ftir

Amyloid beta-peptide (Abeta) forms cytotoxic assemblies that contribute to Alzheimer's disease. Recent evidence indicates that prefibrillar aggregates and not the fibrillar deposits exert the main toxic effect. In addition, naturally occurring N-terminally truncated and pyroglutamylated peptide (pE-Abeta) displays augmented cytotoxicity by an unknown mechanism. This study examines the conformational changes in both unmodified Abeta and pE-Abeta upon exposure to an aqueous environment. FTIR and circular dichroism were used to identify alpha-helix-to-beta-sheet conformational transitions of both peptides during aggregation. To gain site-specific structural information, the peptides were 13C,15N-labeled at residues 16-18 (KLV) or 36-39 (VGGV), followed by FTIR analysis. The peptides dried from hexafluoroisopropanol were alpha-helical (amide I peak at 1660-1657 cm-1) and showed negligible intensity of the labeled segments around 1615 cm-1, suggesting that in alpha-helical conformation the labeled amide groups behave like isolated oscillators. Upon addition of aqueous buffer (pH 7.2) both peptides rapidly adopted beta-sheet structure (amide I peak at 1637-1629 cm-1), with disproportionally prominent components around 1604-1597 cm-1 generated by the labeled segments. The intensity and the frequency of the amide I mode of the isotope-labeled segments suggest 12C-13C vibrational coupling, consistent with formation of antiparallel beta-sheet structures. Moreover, the amide I contours of the peptides under near-physiological and low ionic strength conditions were significantly different; both peptides exhibited an increased alpha-helical and decreased beta-sheet propensity under low ionic strength conditions, indicating a strong influence of the ionic strength on the aggregation kinetics and accompanying structural changes. Ongoing studies focus on structural differences between the unmodified Abeta and pE-Abeta peptides as well as their mutual structural effects when combined at various molar ratios, in an attempt to understand the structural basis of the elevated cytotoxicity of pE-Abeta.

Heteroagglomeration of oxide nanoparticles with algal cells: effects of particle type, ionic strength and pH.

Discharged oxide nanoparticles (NPs) have been shown toxic to unicellular algae, yet the research on heteroagglomeration between NPs and cells as an important precondition of the toxicity is scarce. This study for the first time investigated heteroagglomerations between various NPs and algal cells (Chlorella pyrenoidosa) and analyzed influencing factors including pH and ionic strength (IS) through cosettling experiment, transmission electron microscopic (TEM) observation, and Derjaguin–Landau–Verwey–Overbeek (DLVO) calculation. The examined NPs included anatase and rutile TiO2, microporous and spherical SiO2, and α-form and β-form Al2O3. The results of cosettling experiments coincided well with the TEM observations, whereas the DLVO theory could only partly explain the NP–cell heteroagglomerations. The NP–cell heteroagglomeration for rutile TiO2 and β-form Al2O3 was weak and insensitive to pH or IS. Preferential heteroagglomeration occurred at low pH or high IS for microporous SiO2, while marked heteroagglomeration only occurred under the neutral and low IS condition for anatase TiO2. The heteroagglomeration for spherical SiO2 was insensitive to pH but increased with increasing IS, while the heteroagglomeration for α-form Al2O3 occurred at low pH and irrelevant to IS. The work will shed new light on the bionano interfacial interaction and help to understand biological effects of NPs.