Aggregate structure of hydroxyproline-rich glycoprotein (HRGP) and HRGP assisted dispersion of carbon nanotubes

Self-assembly of misfolded proteins into ordered fibrillar structures is a fundamental property of a wide range of proteins and peptides. This property is also linked with the development of various neurodegenerative diseases such as Alzheimer’s and Parkinson’s. Environmental conditions modulate the misfolding and aggregation processes. We used a peptide, CGNNQQNY, from yeast prion protein Sup35, as a model system to address effects of environmental conditions on aggregate formation. The GNNQQNY peptide self-assembles in fibrils with structural features that are similar to amyloidogenic proteins. Atomic force microscopy (AFM) and thioflavin T (ThT) fluorescence assay were employed to follow the aggregation process at various pHs and ionic strengths. We also used single molecule AFM force spectroscopy to probe interactions between the peptides under various conditions. The ThT fluorescence data showed that the peptide aggregates fast at pH values approaching the peptide isoelectric point (pI = 5.3) and the kinetics is 10 times slower at acidic pH (pH 2.0), suggesting that electrostatic interactions contribute to the peptide self-assembly into aggregates. This hypothesis was tested by experiments performed at low (11 mM) and high (150 mM) ionic strengths. Indeed, the aggregation lag time measured at pH 2 at low ionic strength (11 mM) is 195 h, whereas the lag time decreases ∼5 times when the ionic strength is increased to 150 mM. At conditions close to the pI value, pH 5.6, the aggregation lag time is 12 ± 6 h under low ionic strength, and there is minimal change to the lag time at 150 mM NaCl. The ionic strength also influences the morphology of aggregates visualized with AFM. In pH 2.0 and at high ionic strength, the aggregates are twofold taller than those formed at low ionic strength. In parallel, AFM force spectroscopy studies revealed minimal contribution of electrostatics to dissociation of transient peptide dimers.

Sorption of Metal Ions on Clay Minerals: II. Mechanism of Co Sorption on Hectorite at High and Low Ionic Strength and Impact on the Sorbent Stability

Deposition of nanomaterials onto surfaces is a key process governing their transport, fate, and reactivity in aquatic systems. We evaluated the transport and deposition behavior of carboxyl functionalized single-walled carbon nanotubes (SWNTs) in a well-defined porous medium composed of clean quartz sand over a range of solution chemistries. Our results showthat increasing solution ionic strength or addition of calcium ions result in increased SWNT deposition (filtration). This observation is consistent with conventional colloid deposition theories, thereby suggesting that physicochemical filtration plays an important role in SWNT transport. However, the relatively insignificant change of SWNT filtration at low ionic strengths (< or = 3.0 mM KCl) and the incomplete breakthrough of SWNTs in deionized water (C/Co = 0.90) indicate that physical straining also plays a role in the capture of SWNTs within the packed sand column. It is proposed that SWNT shape and structure, particularly the very large aspect ratio and its highly bundled (aggregated) state in aqueous solutions, contribute considerably to straining in flow through porous media. We conclude that both physicochemical filtration and straining play a role at low (< 3.0 mM) ionic strength, while physicochemical filtration is the dominant mechanism of SWNT filtration at higher ionic strengths. Our results further show that deposited SWNTs are mobilized (released) from the quartz sand upon introduction of low ionic strength solution following deposition experiments with monovalent salt (KCl). In contrast, SWNTs deposited in the presence of calcium ions were not released upon introduction of low ionic strength solution to the packed column, even when humic acid was present in solution during SWNT deposition.

The viscosity of histone‐depleted nucleohistone has been measured at high and low ionic strength. Native nucleohistone at low ionic strength and f1‐depleted nucleohistone at both low and high ionic strength all have the same intrinsic viscosity of 10.0 dl/g. This implies that these molecules are not flexible but behave in solution as rigid particles. On the assumption that they are rods they have a weight‐average length of 1160 ± 120 nm and diameter 5.6 ± 0.3 nm. The DNA is compressed in the rod to give an increase in mass per unit length for the DNA of 5.0 ± 0.5.By contrast the intrinsic viscosity of nucleohistone depleted of f1, f2a2 and 75% of F2b and F3, varies with ionic strength in the manner typical of a flexible polyelectrolyte. The shapes of the sedimentation boundaries measured at high ionic strength of depleted nucleohistone show that the dissociation of histone from DNA takes place so that all molecules are depleted to the same extent. It thus has a conformation intermediate between that of native nucleohistone and DNA.Polyacrylamide gel electrophoresis of histones removed by 1.0 M NaCl using a technique capable of resolving all five main histone fractions, shows that if one fraction only is responsible for supercoiling nucleohistone it must be f2a2.

Zinc isotope fractionation during adsorption to calcite at high and low ionic strength

The reduction of tetravalent manganese (Mn-(IV)) to trivalent manganese (Mn-(III)) by HEPES Good's buffer is often used to modify the reactivity of δ-MnO2 and to distinguish between the Mn-(III) and Mn-(IV) oxidants in redox reactions. However, the structure of HEPES-reacted δ-MnO2 has remained elusive, hindering a detailed understanding of interfacial electron transfer between adsorbed species and structural Mn. Here, we characterized the structure of δ-MnO2 reacted with HEPES at pH 6 and 8 under low and high NaCl ionic strength, using chemical analysis, high-energy X-ray diffraction, pair distribution function (PDF), extended X-ray absorption fine structure (EXAFS) spectroscopy, and high-resolution transmission electron microscopy (HRTEM) coupled with selected area electron diffraction (SAED). The average Mn oxidation state (AMOS) decreases from 3.92-3.87 to 3.71-3.59 after HEPES addition, depending on pH and ionic strength. HEPES-reacted δ-MnO2 has a distinctly different structure at low and high ionic strength. At low ionic strength, the δ-MnO2 HE crystallites are 3-6 nm across, and the MnO2 layers have approximately 23% vacant sites capped with mainly Mn-(III) and some Mn-(II). At high ionic strength and pH 8, δ-MnO2 HE contains large crystals, several hundred nanometers across, made up of crystallographically oriented nanodomains. Most SAED patterns show streaks along the [100]* direction, indicating a high degree of disorder in the close packing of the anionic sheets, in the Na position within the interlayer, and in the Mn-(IV)-Mn-(III) distribution within the layer. Some nanodiffraction patterns show distinct superstructure reflections along the streaks with A* = 3a*, as seen in well-crystallized triclinic birnessite, and A* = 6a*. High-ionic-strength δ-MnO2 HE has no interlayer Mn-(III), and the Na-(I) ions, along with the layer Mn-(III) and Mn-(IV) cations, are semiordered at the short- to medium-range scales and essentially disordered over longer distances. Identifying the two distinct structures of HEPES-reacted δ-MnO2 clarifies structural ambiguities reported in the literature and provides a solid foundation for exploring its redox reactivity and electrochemical performance.

Foam Fractionation of Binary Mixtures of Lysozyme and Albumin

Strain engineering for thermal conductivity of single-walled carbon nanotube forests

Recent atomic 3-D reconstructions of the acto-myosin interface suggest that electrostatic interactions are important in the initial phase of cross-bridge formation. Earlier biochemical studies had also given strong evidence for the ionic strength dependence of this step in the cross-bridge cycle. We have probed these interactions by altering the ionic strength (Gamma/2) of the medium mainly with K+, imidazole+ and EGTA2- to vary charge shielding. We examined the effect of ionic strength on the kinetics of rigor development at low Ca2+ (experimental temperature 18-22 degrees C) in chemically skinned single fast-twitch fibres of mouse extensor digitorum longus (EDL) muscle. On average the delay before rigor onset was 10 times longer, the maximum rate of rigor tension development was 10 times slower, the steady-state rigor tension was 3 times lower and the in-phase stiffness was 2 times lower at high (230 mM) compared to low (60 mM) ionic strength. These results were modelled by calculating ATP depletion in the fibre due to diffusional loss of ATP and acto-myosin Mg.ATPase activity. The difference in delay before rigor onset at low and high ionic strength could be explained in our model by assuming a 15 times higher Mg.ATPase activity and a threefold increase in Km in relaxing conditions at low ionic strength. Activation by Ca2+ induced at different time points before and during onset of rigor confirmed the calculated time course of ATP depletion. We have also investigated ionic strength effects on rigor development with the activated troponin/tropomyosin complex. ATP withdrawal at maximum activation by Ca2+ induced force transients which led into a "high rigor" state. The peak forces of these force transients were very similar at low and high ionic strength. The subsequent decrease in tension was only 10% slower and steady-state "high rigor" tension was reduced by only 27% at high compared to low ionic strength. Addition of 10 mM phosphate to lower cross-bridge attachment strongly suppressed the transient increases in force at high ionic strength and reduced the steady-state rigor tension by 17%. A qualitatively similar but smaller effect of phosphate was observed at low ionic strength where steady-state rigor force was reduced by 10%. The data presented in this study show a very strong effect of ionic strength on rigor development in relaxed fibres whereas the ionic strength dependence of rigor development after thin filament activation was much less. The data confirm the importance of electrostatic interactions in cross-bridge attachment and cross-bridge-attachment-induced activation of thin filaments.

The reconstitution of glucose oxidase on a flavin-adenine-dinucleotide (FAD)-functionalized single-walled carbon nanotube (SWCNT) associated with an Au electrode yields an electrically contacted biocatalyst (see picture). The efficiency of the electrical contact is controlled by the length of the SWCNT.

Transport and deposition of microplastic particles in saturated porous media: Co-effects of clay particles and natural organic matter

We report discoveries from a series of molecular dynamics simulations that single-walled carbon nanotubes, with different diameters, lengths, and chiralities, can coaxially self-assemble into multiwalled carbon nanotubes in water via spontaneous insertion of smaller tubes into larger ones. The assembly process is tube-size-dependent, and the driving force is primarily the intertube van der Waals interactions. The simulations also suggest that a multiwalled carbon nanotube may be separated into single-walled carbon nanotubes under appropriate solvent conditions. This study suggests possible bottom-up self-assembly routes for the fabrication of novel nanodevices and systems.

Surfaces based on amino acid functionalized polyelectrolyte films towards active surfaces for enzyme immobilization.

ABSTRACTNine combinations of sodium chloride (NaCl), potassium chloride (KCI), and magnesium chloride (MgCl2,) at high and low ionic strengths (IS) (0.42 and 0.21 respectively) and low IS with 0.13% tripotassium phosphate (K3PO4) were used to determine the effects of a reduction or partial replacement of sodium on bologna characteristics and acceptability. The NaCl‐MgCl2 had significantly (P &lt; 0.05) less stable and firm emulsion and compression hardness than NaCl or NaCl‐KCl treatments. Low IS treatments had significantly less stable and firm emulsions and lower compression hardness than high IS treatments. Adding PO4 to low IS treatments produced products similar to high IS treatments. Only slight textural changes occurred in products after 14 days of cooler (1°C) storage. High IS NaCl and NaCl‐KCl and low IS NaCl‐PO4, NaCl‐MgCl2 ‐PO4 and NaCl‐KCl‐PO4 were found acceptable for flavor, texture, and color by consumer panels.

Probe is a key part of atomic force microscopy (AFM) and the curvature radius of its tip limits the lateral resolution. Furthermore, as an expendable, its life has a direct effect on operation cost. Single-walled carbon nanotubes (SWNTs) are ideal materials for the probe tips used in atomic force microscopy (AFM), since they have intrinsically small diameters, high aspect ratios and unique wearability. Herein, the fabrication of AFM SWNT tips is systemically investigated, including mechanical method and direct growth method. In the former, substrates with isolated SWNTs are first prepared by chemical vapor deposition and then scanned with conventional silicon probes under AFM. During scanning, SWNTs can be picked up from substrates and attached to the pyramid of silicon probes via attractive Van del Waals forces. Preparation of substrates is decisive to this method, since only the SWNTs disengaged from surface are possible to pick up. Different substrates have been compared and the results show that the substrates full of gaps are prior to the planar ones. SWNTs are suspended across gaps and suitable to the following assembly. The mechanical method is easily implemented and can produce AFM SWNT tips one by one, while the direct growth method is promising to manufacture them in a large scale, in spite of more difficulty. In the latter, catalyst for the growth of SWNTs is directly placed on individual commercial probes or pyramid arrays. Through chemical vapor deposition, grown SWNTs protrude from the original tips and create new ones. Due to the random orientation of SWNT growth, the yield of successful SWNT tips is generally low for the direct growth method. In this article, Electric filed is used to direct the growth orientation of SWNTs during chemical vapor deposition. Both electrodes are located in the furnace to apply a static electric field along the pyramid axis during growth. The intensity can be varied from 0.1V/um to IV/um, and the direction is towards the surface of wafers. The growth of SWNTs is oriented by electric field and the yield of SWNT tips is raised. The AFM SWNT tips derived from the above two methods have been utilized to image Au layers in the tapping mode. Compared with conventional silicon probes, SWNT tips are longer lasting to keep a high resolution.