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BACKGROUND The solubility limitation and poor gelation properties of myofibrillar proteins at low ionic strength are the most challenging obstacle to limit salt reduction in meat products. In the present study, five amino acids with different concentrations of 5, 10 15, and 20 mmol L–1, l‐lysine (Lys), l‐arginine (Arg), l‐histidine (His), l‐proline (Pro) and l‐glycine (Gly), were introduced into myofibrillar protein (MP) suspensions at low ionic strength to improve solubility and gelation properties. RESULTS: The dynamic rheological analysis showed that the MPs at 100 mmol L–1 NaCl containing 15/20 mmol L–1 Lys/Arg exhibited similar gelling behaviors to MPs at 600 mmol L–1 NaCl. Similarly, 15/20 mmol L–1 Lys/Arg significantly increased the solubility of MPs and the water holding capacity (WHC) and gel strength of MP gels, which was comparable to those of MPs at 600 mmol L–1 NaCl. Furthermore, Lys and Arg promoted the formation of aggregation‐type gel with a dense and compact structure observed by scanning electron microscopy. The gels containing 15/20 mmol L–1 Lys/Arg exhibited a significant increase in the proportion of immobilized water (P21). CONCLUSION: The enhancement of WHC, gel strength, and P21 was closely associated with the increased solubility and the dense microstructure induced by Lys and Arg with high concentrations of 15 and 20 mmol L–1. The knowledge obtained from this study may be useful for the improvement of gelation properties of MPs at low ionic strength using l‐lysine and l‐arginine. © 2021 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

The specific molecular behavior of myofibrillar proteins (MPs) in low-salt media limits the development of muscle protein-based emulsions. This study aimed to evaluate the potential of high-intensity ultrasound (HIU; 150, 300, 450, and 600 W) to improve the physical stability of MP emulsion at low ionic strength and decipher the underlying mechanism. According to the physical stability analysis, HIU pretreatment, especially at 450 W power, significantly improved the physical stability of MP emulsions, as evidenced by the reduced particle size, enhanced inter-droplet interactions, and increased uniformity of the droplet size distribution (p

Salt-soluble myofibrillar proteins (MPs) form the major protein component of meat and have several advantages over plant-derived proteins, including high digestibility and the presence of all the essential amino acids. However, MPs are not widely used because the presence of myosin filaments limits their functionality in low ionic strength media. Hence, an approach for effectively inhibiting or disrupting the formation of myosin filaments is a challenging issue in the development of novel meat protein based products. To develop a strategy for inhibiting or destroying the formation of myosin filaments, an understanding of the process of myosin self-association is needed at the molecular level. Hence, the present review systematically elaborates the assembly mechanism of myosin filaments and its relation to the functionality of MPs. Additionally, the review focuses on the description of several chemical and physical strategies, with an emphasis on advantages, disadvantages, and recent progress. The assembly of myosin into filaments has been shown to be mediated by sequentially distributed charges in the myosin tail. Moreover, the dissociation of myosin filaments, leading to improved functional properties of the MPs, has been demonstrated by amino acid treatment, glycation, high-intensity ultrasonication (HIU), and high-pressure homogenization (HPH) in low ionic strength media. Nevertheless, these strategies still face a number of limitations and, hence, further research is needed in order to achieve large-scale industrial production. In addition, the enhanced development of novel meat protein based products requires a consideration of the thermal stability of MPs throughout the entire process from product sterilization through to preservation and consumption. • The assembly mechanism of myosin filaments is elaborated systematically. • The myosin filaments limit the functionality of MPs in low ionic strength media. • Several strategies can effectively inhibit or disrupt the assembly of myosin filaments. • Large-scale industrial production continues to face technical limitations. • Further studies need to consider the thermal stability of MPs during heat sterilization. [ABSTRACT FROM AUTHOR]

Abstract This work demonstrates that anodic stripping voltammetry at a microdisc electrode allows the detection of silver in the absence of added supporting electrolyte. The voltammetry however becomes distorted under low-support conditions. A semi-analytical model is developed to investigate the effects of the lack of supporting electrolyte on the voltammetric responses. First, the alteration in the double-layer kinetics is studied. In particular, we show that the classical Frumkin correction cannot explain the distorted shape of the voltammetry and only accounts for no more than ~50% of the shift in the voltammetric peaks. Second, compared to the Frumkin correction, Ohmic drop contributes much more significantly to the shift in the peak potential and the distorted wave shape upon lowering electrolyte concentrations. The Ohmic drop determined on the basis of predicted constriction resistance as expressed by Newman gives a reasonable approximation to the solution resistances, especially at ionic strengths above 200 μM. In deionized water or ultra-low conductivity water with the ionic strength of sub-micromolar level, a discrepancy in the resistances of up to a factor of 25 was observed. This discrepancy likely arises due to the assumptions made in applying the Newman model to the experimental system. Finally, we show that a model which considers simultaneously the electrode kinetics and the ohmic drop effects give a consistent fit with experimental data, when the values of the resistances are appropriately adjusted to account for the inaccuracy in the approximation of constriction resistances. Highlights • Silver detection in the absence of added supporting electrolyte • Anodic stripping voltammetry at a microdisc electrode under low-support conditions • Semi-analytical models for systems with insufficient electrolytes • Frumkin correction and extended electron tunnelling • Ohmic drop effects on the basis of constriction resistances [ABSTRACT FROM AUTHOR]

Charged food hydrocolloids provide structure and texture in manufactured foods by their organization and electrostatic interactions with other species and small ions. These electrostatic interactions depend on their actual charge density which cannot be predicted from pK a values of weakly charged monomers. In practice, this is circumvented by the use of an ‘apparent pK a ’ (pK a (app) ) which depends on solution ionic strength and type of counter-ions. pK a (app) values for food hydrocolloids are poorly documented, especially in low ionic strength solvents. Titration of a metachromatic alginate-ortho-toluidine blue complex revealed a sigmoidal, pH-dependent, dye metachromasy response with its centre located at pH = pK a (app) . To test the suitability of this approach for the determination of pK a (app) , five food hydrocolloids and a synthetic polyanion are analysed and the results are compared to classical methods such as potentiometric titration. Metachromasy is shown to occur when the polymer inter-charge distance is 4.5 Å; the complex stoichiometry depending on inter-charge distance. pK a (app) of stoichiometric complexes at low ionic strength (1 mM phosphate buffer) were successfully determined (alginate 4.5, sodium carboxymethylcellulose 4.6, κ-carrageenan 1.2, polyphosphate 2.1 and polyacrylic acid 5.8) and are comparable to values obtained by potentiometric titration. Further, it is shown that pK a (app) determination by metachromatic dye titration is feasible for stoichiometric polymer-dye complexes at low concentrations (20–200 μM) in low ionic strength (<10 mM) aqueous solutions. Unlike classical methods, the metachromatic dye titration approach is suitable for low polymer concentrations in aqueous solutions at low ionic strength. [ABSTRACT FROM AUTHOR]

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The qualitative characteristics of meat products are closely related to the functionality of muscle proteins. Myofibrillar proteins (MPs), comprising approximately 50% of total muscle proteins, are generally considered to be insoluble in solutions of low ionic strength (< 0.2 M), requiring high concentrations of salt (> 0.3 M) for solubilization. These soluble proteins are the ones which determine many functional properties of meat products, including emulsification and thermal gelation. In order to increase the utilization of meat and meat products, many studies have investigated the solubilization of MPs in water or low ionic strength media and determining their functionality. However, there still remains a lack of systematic information on the functional properties of MPs solubilized in this manner. Hence, this review will explore some typical techniques that have been used. The main procedures used for their solubilization, the fundamental principles and their functionalities in water (low ionic strength medium) are comprehensively discussed. In addition, advantages and disadvantages of each technique are summarized. Finally, future considerations are presented to facilitate progress in this new area and to enable water soluble muscle MPs to be utilized as novel meat ingredients in the food industry. [ABSTRACT FROM AUTHOR]

The presence of a simple surfactant, sodium n-dodecyl sulfate (SDS), at a particular concentration provided a suitable hydrophobic pocket for heme-imidazole moiety, which produced a peroxidase active site containing negative charges distributed on the colloidal surface. It is important that which aggregation structure of SDS encompasses the heme-imidazole as peroxidase active site. Ionic strength variation is an important key that can be used to obtain wide range of hydrophobic pocket in different structures. Here heme-imidazole complex was embedded into SDS micelles in different ionic strengths via phosphate buffer solution (PBS) variation and it has been investigated structurally and functionally. The critical micelle concentrations (CMC) of SDS were determined in different ionic strengths of PBS by using condutometry. The catalytic activity of triple-component: SDS-heme-imidazole, indicated that the catalytic efficiency of the novel “nanozyme” at PBS 0.2 mM was 28.7% of native horseradish peroxidase (HRP) which is related to the formation of a unique and discrete nano-structure of peroxidase-like biocatalyst at low ionic strength which obtained by Transmission Electron Microscopy (TEM) and Differential Scanning Calorimetery (DSC) experiments. The important role of hydration layer force in assembling the particular colloid structure that causes the suitable structural thermal profile in special low PBS concentration (0.2 mM) determined by DSC method. The final biomimetic structure of micellar SDS-Heme-imidazole as an efficient artificial peroxidase as well as imidazole role on nanozyme stability was resolved by molecular dynamics simulation based on hydrodynamic radii measured by Dynamic Light Scattering (DLS). [ABSTRACT FROM AUTHOR]

Human red blood cells (RBCs) when suspended in a Low Ionic Strength medium (LIS) demonstrate characteristic triphasic shape changes (morphological response, MR) and become reduced in volume. Tahitian Tabari Noni juice (Tb), after being given during the terminal phase of MR, was shown to initiate an unusual cell response. This response can be described as a volumetric four-phasic response including first a shrinking phase, attributed to the initial sucrose-induced shrinkage during typical MR, a rapid first swelling phase, induced by application of the juice, followed spontaneously by the occurrence of a more prolonged second shrinking phase, which culminated in the swelling and hemolysis of the cells. All the phases of volumetric response can be independently regulated by chloride, DIDS, cations Ca2+, Ag+, Hg2+ or plasma. The second shrinking phase is not inhibited by clotrimazole, a known inhibitor of Gardos channels, and can be replicated by a mixture of two ionophores (valinomycin and CCCP), suggesting the involvement of the putative K+/H+ exchanger as a mechanism of this phase. We suggest that the erythrocyte membrane is equipped with additional molecular systems, poorly characterized at present, that regulate the cell shape and volume. The cell should, therefore, be considered as an “active” responsive system instead of a “passive” osmometer-like structure.

Background/Aims: In a variety of investigations described in the literature it was not clear to what extent the transmembrane potential red blood cells (RBCs) was changed after the cells have been transferred into low ionic strength (LIS) solutions. Another open question was to find out how fast the transmembrane potential of RBCs in LIS solution will change and which final new equilibrium value will be reached. Methods: The transmembrane potential of human and bovine RBCs was investigated using the potential-sensitive fluorescent dye DIBAC4(3) (bis(1,3-dibutylbarbituric acid) trimethine oxonol) as well as the CCCP (carbonylcyanide-m-chlorophenylhydrazone) method. Results: Under physiological conditions the transmembrane potential was about -10 mV in agreement with literature data. However, when the RBCs were transferred into an isosmotic low ionic strength medium containing sucrose the transmembrane potential increased to +73 mV and +81 mV for human and bovine RBCs, respectively. In case of human RBCs it continuously decreased reaching finally an equilibrium state of -10 mV again after 30 - 60 min. For bovine RBCs the transmembrane potential declined more slowly reaching a value of +72 mV after 30 min. Conclusions: Investigations of parameters of RBCs depending on transmembrane potential cannot be performed with human RBCs in LIS media.

In this study, the earlier used method to measure the dynamics of shape changes in red blood cells (RBCs), based on an analysis of light fluctuations in the suspension, was modified to allow for the simultaneous recording of cell volume changes after appropriate recalculation of the raw absorbance and shape index data. With this improved methodology, we investigated the morphological and volume responses triggered by cell environment changes. In a low ionic strength medium (LIS), the characteristic triphasic shape changes (morphological response, MR) were accompanied with a gradual shrinking of the cells without any re-swelling phase. The addition of hyperosmotic NaCl during the terminal MR phase restored the discoid RBC shape inducing cell swelling resembling regulatory volume increase. The cell volume was greater than that before salt addition; however, it was lower than the initial isotonic cell volume. This re-swelling phase was inhibited by the external DIDS, acetozolamide and bicarbonate, and was slightly dependent upon pH ranging from 5 to 7.2. The analysis shows that chloride-induced re-swelling cannot be directly explained by the reversion of OH or HCO3 gradients which drive the Cl inside the cells against the concentration gradient, and indicates the significant role of the external bicarbonate ions in shape and volume responses in LIS.

The development of myofibrillar proteins drinks (MPDs) can provide meat protein nutrition to specific groups of people. However, one major challenge is that myofibrillar proteins (MPs) are insoluble in solutions with a low ionic strength. Another functional constraint is the susceptibility of MPs to heat-induced aggregation. Currently, the primary approach used to improve the water solubility of MPs is to inhibit the assembly of myofilaments. Increasing the thermostability of MPs primarily inhibits the aggregation of myosin or oxidizes myosin to soluble substances. This review focuses on the description of several chemical and physical strategies, with an emphasis on the advantages, disadvantages, and recent progress. Under the myosin filament assembly process and the cross-linking aggregation mechanism, this summary helps improve our understanding of the solution and thermostability of MPs in low-ionic-strength solutions, thus providing new ideas to the development of MPDs. [ABSTRACT FROM AUTHOR]

The fact that the porosity and permeability of intervessel pit pathways are significantly reduced by low ionic strength (deionized water) evokes the question of to what degree the pit membrane permeability can be reduced, and whether the network of laterally connected vessels can be affected by low ionic strength. Isolated stem segments of Tamarix gallica were used to (1) evaluate the effect of low ionic strength on lateral pit pathways in xylem of the halophytic plant; (2) visualize the blocked pathways by tracing the vessel network before and after treatments, using two apoplastic tracers. The results showed that the degree of intervessel contacts was significantly decreased by deionized water. Blockage of some laterally connected vessels could be clearly visualized in samples perfused with deionized water. These results suggested that some intervessel pit pathways might be blocked under low ionic strength, causing a reduction in the intervessel connectivity. Also, our results supported the idea that pit membranes might differ in their structure and/or chemical nature within the same xylem network. This study may contribute to an understanding of the complex interactions among sap salinity, pit pathways, and intervessel connectivity. [ABSTRACT FROM AUTHOR]

Background/Aims: In a variety of investigations described in the literature it was not clear to what extent the transmembrane potential red blood cells (RBCs) was changed after the cells have been transferred into low ionic strength (LIS) solutions. Another open question was to find out how fast the transmembrane potential of RBCs in LIS solution will change and which final new equilibrium value will be reached. Methods: The transmembrane potential of human and bovine RBCs was investigated using the potential-sensitive fluorescent dye DIBAC4(3) (bis(1,3-dibutylbarbituric acid) trimethine oxonol) as well as the CCCP (carbonylcyanide-m-chlorophenylhydrazone) method. Results: Under physiological conditions the transmembrane potential was about -10 mV in agreement with literature data. However, when the RBCs were transferred into an isosmotic low ionic strength medium containing sucrose the transmembrane potential increased to +73 mV and +81 mV for human and bovine RBCs, respectively. In case of human RBCs it continuously decreased reaching finally an equilibrium state of -10 mV again after 30 - 60 min. For bovine RBCs the transmembrane potential declined more slowly reaching a value of +72 mV after 30 min. Conclusions: Investigations of parameters of RBCs depending on transmembrane potential cannot be performed with human RBCs in LIS media. Copyright © 2013 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Abstract: The determination of free metal ion concentrations of heavy metals, like Zn2+ or Cd2+, with AGNES (Absence of Gradients and Nernstian Equilibrium Stripping) requires an adequate selection of parameters such as deposition potential (linked to the gain, [M0]/[M2+]) and deposition time. In systems with low ionic strength, the peak potential of the Differential Pulse Polarogram (DPP) measured with low supporting electrolyte is not always suitable for the computation of the gain with existing expressions. The application of AGNES with a constant potential (regardless of the ionic strength) provides a direct measurement of the metal ion activity. When working with low ionic strength solutions, the selection of appropriate instrumentation is important to avoid changes in liquid junction potentials or leakages from the employed electrodes. The deposition times (for a given gain) have not been found to be greatly affected by the probed ionic strengths when working with just metal. A new strategy for the practical implementation of AGNES to measure free metal ion concentrations in samples with low KNO3 or Ca(NO3)2 concentrations consists in the computation of the deposition potential (to reach a certain gain) from the DPP peak potential at a sufficiently high ionic strength using a new expression. A speciation experiment with Zn2+ and glycine at pHs between 4 and 7.5, where [KNO3]=0.001M, shows that this methodology works well and also proves that it is possible to perform AGNES in systems with very low ionic strength. [Copyright &y& Elsevier]

Abstract: A moderately hydrophobic ionic liquid, tributyl(2-methoxyethyl)phosphonium bis(pentafluoroethanesulfonyl)amide ([TBMOEP+][C2C2N−]), shows a very stable liquid junction potential upon contact with an aqueous solution whose ionic strength is as low as 1μmoldm−3. The stability with the maximum excursion of the potential within ±0.5mV for 30min is very promising for accurate determination of pH and other single ion activities potentiometrically. [ABSTRACT FROM AUTHOR]

Abstract: Morphological response (MR) of red blood cells represents a triphasic sequence of spontaneously occurring shape transformation between different shape states upon transfer the cells into isotonic sucrose solution in the order: S0 (initial discoid shape in physiological saline)→S1 (echinocytic shape at the beginning of MR, phase 1)→S2 (intermediate discoid shape, phase 2)→S3 (final stomatocytic shape, phase 3). In this paper, the dynamics of cell shape changes was investigated by non-invasive light fluctuation method and optical microscopy. Among 12 possible transitions between four main shape states, we experimentally demonstrate here an existence of nine transitions between neighbour or remote states in this sequence. Based on these findings and data from the literature, we may conclude that red blood cells are able to change their shape through direct transitions between four main states except transition S1 →S0, which has not been identified yet. Some shape transitions and their temporal sequence are in accord with predictions of bilayer couple concept, whereas others for example transitions between remote states S3 →S1, S1 →S3 and S3 →S0 are difficult to explain based solely on the difference in relative surface areas of both leaflets of membrane suggesting more complex mechanisms involved. Our data show that MR could represents a phenomenon in which the major role can play pH and chloride-sensitive sensor and switching mechanisms coupled with transmembrane signaling thus involving both cytoskeleton and membrane in coordinated shape response on changes in cell ionic environment. [ABSTRACT FROM AUTHOR]

Abstract: The dynamics of red cell shape changes following transfer into sucrose media having a low chloride content was studied. Based on a large number of measurements, six types of morphological response (MR), differing both in the degree of shape changes and the time course of the process, were identified. The most prominent type of response is a triphasic sequence of shape changes consisting of a fast transformation into a sphere (phase 1), followed by restoration of the discoid shape (phase 2) and final transformation into spherostomatocytes (phase 3), with individual parameters which could vary significantly. It was found that individual morphological response exhibited day to day variations, depending on the initial state of the red blood cells and the donor, but to a larger extent depended on the composition of the sucrose solution, such as concentration and type of buffers, the presence of EDTA, calcium, as well as very small amounts of extracellular hemoglobin. MR shows strong pH and ionic strength dependence. Low pH inhibited phase 1 and high pH changed dramatically the time course of the response. Increasing ionic strength inhibited all phases of MR, and at concentrations above 10–20 mM NaCl it was fully suppressed. Tris and phosphate were also inhibitory whereas HEPES, MOPS and Tricine were less effective. MR occurred also in hypertonic or hypotonic sucrose solutions, with exception of extreme hypotonicity due to volume restrictions. It is concluded that strong membrane depolarization per se is not a causal factor leading to MR, and its different phases could be regulated independently. For some types of morphological response the fast shape transformation from sphere to disc and back to sphere occurs within a 10 s time interval and could be accelerated several fold in the presence of a small amount of hemoglobin. It is suggested that MR represents a type of general cell reaction that occurs upon exposure to low ionic strength. [Copyright &y& Elsevier]

Abstract: When red blood cells (RBCs) are placed in isotonic sucrose solution with low chloride content dynamic shape response is observed. Generally, it consists of three phases: i) fast spherulation (phase 1), ii) restoration of shape close to discoid one (phase 2), followed by a second slower spherulation in stomatocyte direction (phase 3). This morphological transformation (morphological response (MR)) is rather a fast process, usually comprises 1–2 min interval with disc retransformation time within 20–30 s. We have found that low concentration of extracellular hemoglobin (Hb) in the range 14–44 nM derived from cell lysate significantly accelerated MR at any stage of process. Increasing NaCl concentration up to 10 mM completely eliminated any influence of Hb. Other inhibitors EDTA and chlorpromazine while retarding some phases of MR did not prevent its activation by Hb. It was established that at conditions of low ionic strength Hb strongly binds to native RBC membrane. The number of binding sites was found to be 1–1.6×106 molecules per cell and the equilibrium dissociation constant was less than 2×10−8 M. After heat denaturation of Hb at 70–72 °C an ability of Hb to affect MR was lost. Our data provide evidence that extracellular Hb could be involved in shape regulation of red blood cells at least in low ionic strength solutions. [Copyright &y& Elsevier]

Abstract: The effect of the presence of charged amphiphiles during the incubation of human erythrocytes in a sucrose-substituted low-Cl− solution on the shift of the osmotic resistance profile and the net K+ efflux was investigated. Osmotic fragility was determined by fitting the complementary error function to the haemolysis resistance curve. K+ efflux was calculated from the increase in the K+ concentration in supernatant measured by inductively coupled plasma atomic emission spectrometry (ICP-AES). The cationic amphiphile hexadecyltrimethylammonium bromide (CTAB) at 14 μM decreases, whereas the anionic amphiphile sodium dodecyl sulfate (SDS) at 50 μM increases the shift of the haemolysis resistance curve of erythrocytes incubated in isotonic sucrose by 0.069 and 0.079 %NaCl, respectively. Both the positively and the negatively charged amphiphile caused a significant change in the K+ efflux into isotonic sucrose solution: CTAB decreased and SDS increased K+ efflux by about 40%. In view of the lack of effect of the investigated compounds on the haemolysis resistance curve and K+ efflux from human erythrocytes incubated in isotonic NaCl solution, these results suggest that the insertion of charged amphiphiles into the erythrocyte membrane modulates the properties of the K+ transport pathway which is activated under low ionic strength (LIS) conditions. [Copyright &y& Elsevier]

Residual K+ fluxes in red blood cells can be stimulated in conditions of low ionic strength. Previous studies have identified both the non-selective, voltage-dependent cation (NSVDC) channel and the K+ (Na+)/H+ exchanger as candidate pathways mediating this effect, although it is possible that these pathways represent different modes of operation of a single system. In the present study the effects of HOE642, recently characterised as an inhibitor of the K+(Na+)/H+ exchanger, on NSVDC has been determined to clarify this question. Radioisotope flux measurements and conductance determinations showed that HOE642 exerted differential effects on the NSVDC channel and the K+(Na+)/H+ exchanger, confirming that the salt loss observed in low ionic strength solutions represents contributions from at least two independent ion transport pathways. The findings are discussed in the context of red blood cell apoptosis (eryptosis) and disease. Copyright © 2007 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Digital simulation of steady-state voltammetry of diffusion–migration systems with the reactant involved in the complexation reaction has been carried out using a FIFD-related algorithm.It has been found, that in the case of neutral ligands, the shift of the halfwave potential caused by the formation of the complex has the same magnitude in solutions with and without supporting electrolyte. The measurement data can thus be interpreted using the standard methods for voltammetric analysis, like, e.g. De Ford–Hume scheme. For charged ligands it is possible to find a value for the ligand:reactant concentration ratio above which the migrational effects can be neglected. This allows one to use classic methods also to the systems with charged ligands. The simulation results show that the limiting ligand:reactant concentration ratio mentioned above differs for different charge numbers of species and for different complex formation constants, but for the majority of the considered systems this ratio should be not less than 5 in the total absence of supporting electrolyte.The proposed approach has been applied to the experimental results obtained for Tl+ with 18-crown-6 ligand in water without addition of supporting electrolyte. [Copyright &y& Elsevier]

Electroanalytical aspects of voltammetric behavior of diferrocenemethanol, sodium diferrocenemethanolan, (diferrocenyl)methyltrimethylammonium hexafluorophosphate, and 1,2-diferrocenyloethane were studied. Special attention was paid to the differences in the wave heights caused by the presence and absence of supporting electrolyte. Linear scan voltammetry (LSV) and normal pulse voltammetry (NPV) were employed in the investigation. The differocenes synthesized differ in charge and in the interactions between the two redox centers. They have both iron atoms at the +2 oxidation number. The charged diferrocenes offer not only a good internal potential scale in electroanalysis, as does the uncharged diferrocene, but are also sensitive to ionic strength in the solution. In the absence of supporting electrolyte, no second voltammetric wave was obtained for the (diferrocenyl)methyltrimethylammonium cation. The IR and UV-VIS spectroscopic characteristic have been done for all diferrocenes studied. [ABSTRACT FROM AUTHOR]

Standard methods of analysis based on the dependence of current magnitudes and waveshapes on scan rate (cyclic voltammetry) and rotation rate (rotating risk electrode voltammetry) are available to interpret processes of the form Az+⇌, upper limit E°f,ks,α A(z+n)++ne− when the migration current is negligible. Using analysis of simulated voltammograms, the present study shows that when a migration current is present, it simply acts as a scaling factor with respect to current magnitudes and introduces a small potential shift. The effects are equivalent to altering the diffusion coefficient in the fully supported case. Experimental detection of migration can be confirmed by examining the concentration dependence of a process, but not by dependence on scan rate or rotation rate. [Copyright &y& Elsevier]

The objective of this study was to relate the rheological behavior of ovalbumin gels at low pH and low ionic strength to their mesoscopic structure, using rheological measurements and Transmission Electron Microscopy (TEM). Varying pH, ionic strength and protein concentration, we obtained transparent solutions, transparent gels, opaque gels, or turbid gels, upon heating and subsequent cooling of the ovalbumin solutions. At equal pH and increasing salt concentration we found an increase in turbidity, suggesting that the structure of the aggregates changed from linear or branched to more clustered aggregates. The gel strength increased with increasing salt concentration. A similar trend was observed at equal ionic strength and increasing pH. TEM micrographs of ovalbumin aggregates at pH 2 and 15 mM NaCl show that the ovalbumin aggregates are linear. Increasing the pH from 2 to 3.5 results in structures that are still linear, but with a higher degree of clustering. No random aggregates were observed. TEM micrographs of the gel phase at pH 3.5 and 30 mM NaCl (turbid) show that the structure consists of linear aggregates organized in large clusters of approximately 230–350 nm. At pH 2 and 30 mM NaCl (transparent) the gel consists of single strands with a diameter of about 3.3–3.9 nm, i.e. one or at most two monomers thick. [Copyright &y& Elsevier]

The use of cresol red (CR) indicator for determination of freshwater pH is evaluated. Ionic strength effects and indicator pH perturbation are discussed and quantified using theoretical and empirical approaches. Spectrophotometric and potentiometric methods are directly compared by repeated analyses of a low ionic strength pH buffer. The mean and standard deviation of the two methods were 7.618±0.008 (spectrophotometric) and 7.484±0.040 (potentiometric) (N=18) with systematic errors of 0.003 and 0.137 pH units relative to the true pH (7.621). Field data from an alkaline river (pH∼7.8–8.8) show that measurement reproducibility is better than 0.01 pH units, making it possible to resolve very small spatial and temporal changes in riverine pH. Uncertainty in the indicator apparent dissociation constant limits the accuracy of the pH measurement to ∼0.05 pH units. An alternative method for estimating the dissociation constant, based on calculation of pH from two other carbonate parameters, is proposed. [Copyright &y& Elsevier]

Bacteria and archaea (prokaryotes) are vital components for maintaining healthy function of groundwater ecosystems. The prokaryotic community composition and associated putative functional processes were examined in a shallow sandy aquifer in a wet-dry tropical environment. The aquifer had a contaminated gradient of saline mine-water, which primarily consisted of elevated magnesium (Mg2+) and sulfate (SO 4 2−), although other major ions and trace metals were also present. Groundwaters were sampled from piezometers, approximately 2 m in depth, located in the creek channel upstream and downstream of the mine-water influence. Sampling occurred during the dry-season when only subsurface water flow was present. Next generation sequencing was used to analyse the prokaryote assemblages using 16S rDNA and metabolic functions were predicted with FAPROTAX. Significant changes in community composition and functional processes were observed with exposure to mine-waters. Communities in the exposed sites had significantly lower relative abundance of methanotrophs such as Methylococcaceae and methanogens (Methanobacteriaceae), but higher abundance in Nitrososphaeraceae, associated with nitrification, indicating potentially important changes in the biogeochemistry of the exposed sites. The changes were most strongly correlated with concentrations of SO 4 2−, Mg2+ and Na+. This knowledge allows an assessment of the risk of mine-water contamination to groundwater ecosystem function and aids mine-water management. [Display omitted] • Prokaryotes are rarely considered in environmental assessments. • Metabarcoding was used to assess mine-water impacts on groundwater prokaryotes. • Saline mine-waters altered prokaryote community composition and function. • Changes were strongly correlated with elevated concentrations of SO 4 2+, Mg+ and Na+. Saline mine-waters with elevated concentrations of SO 4 2−, Mg2+ and Na + resulted in changes in prokaryote community composition and functional processes. [ABSTRACT FROM AUTHOR]

Horse heart cytochrome c at pH 7 and low ionic strength is present as two conformers, as evidenced by 1H-NMR spectroscopy. The two structures have been calculated using NOE and pseudocontact shift constraints. They have the same folding patterns and are essentially equal, within the rmsd of the families. The two average structures have rmsd values of 0.049 nm and 0.093 nm for the backbone and the heavy atoms, respectively. Such a difference has been analyzed through a detailed analysis of the NOEs. It appears that the species at low ionic strength differs from the species present at high ionic strength by the displacement of some external residues, such as Gln16, Ile81 and Glu90. Other changes are monitored by the chemical shifts but they cannot be quantified at the present level of resolution. Ionic-strength-dependent structural rearrangements may be relevant with respect to the problem of molecular recognition. [ABSTRACT FROM AUTHOR]

Concentrations of soluble aluminum (Al) and manganese (Mn) frequently reach phytotoxic levels in acid soils. While dose response relationships for these metals are well documented, the effects of combined exposure have received less attention. We have examined the effect of combinations of Al and Mn on growth and metal accumulation in Vigna unguiculata (L.) Walp. grown in solution culture under conditions of low ionic strength (conductivities typically < 100 µS cm-1). The nature of interaction between these metals varied with the specific physiological response, the part of the plant investigated, and the relative amount of stress imposed. Analysis of growth data provided evidence for amelioration of metal toxicity (antagonistic effects), although this effect was dose dependent. Analysis of metal content data provided evidence for antagonistic and synergistic (exacerbation of toxicity) effects, again depending on dose. Analysis of foliar symptoms also provided evidence for antagonisms and synergisms, with the nature of the response dependent on the specific physiological response and specific plant part investigated. In contrast with previous reports, evidence for antagonistic, synergistic, and multiplicative effects on growth, metal uptake, and expression of foliar symptoms have been obtained under physiologically and environmentally relevant conditions. These results suggest a more detailed analysis of the potential for interactions between metals in the environment is required. [ABSTRACT FROM AUTHOR]

[Display omitted] • The assembly behavior of myosin molecules limits the development of interfacial proteins. • High-intensity ultrasound (HIU) disrupted the filamentous myosin structure. • HIU improved the physical stability of myofibrillar protein (MPs) emulsion. • HIU pretreatment promoted the adsorption and rearrangement of MPs at the O/W interface. • HIU pretreatment enhanced the inter-droplet interactions. The specific molecular behavior of myofibrillar proteins (MPs) in low-salt media limits the development of muscle protein-based emulsions. This study aimed to evaluate the potential of high-intensity ultrasound (HIU; 150, 300, 450, and 600 W) to improve the physical stability of MP emulsion at low ionic strength and decipher the underlying mechanism. According to the physical stability analysis, HIU pretreatment, especially at 450 W power, significantly improved the physical stability of MP emulsions, as evidenced by the reduced particle size, enhanced inter-droplet interactions, and increased uniformity of the droplet size distribution (p < 0.05). The results of interfacial protein composition, Fourier transform infrared spectroscopy analysis, and microscopic morphology observation of the aqueous MP suspension suggested that HIU induced the depolymerization of filamentous myosin polymers and inhibited the subsequent self-assembly behavior. These effects may facilitate protein adsorption and molecular rearrangement at the oil–water interface, forming a complete interfacial layer and, thus, droplet stabilization. Confocal laser scanning microscopy observations further confirmed these results. In conclusion, these findings provide direct evidence for the role of HIU in improving the physical stability of MP emulsions at low ionic strength. [ABSTRACT FROM AUTHOR]

Self-assembly of rat tail collagen type I was investigated by means of turbidity measurements and molecular dynamics simulations. Turbidity curves collected at different pH values show that the rate of aggregation was not linear in dependence from pH, with the fastest kinetics at pH 5.0 and the lowest at neutral pH. MD simulations were carried out on two regions with different hydropathicity, monitoring the aggregation of up to four staggered tropocollagen fragments at different ionic strength. At physiological conditions, association of lowly charged regions occurs more easily than for highly charged ones, the latter seeming to aggregate in a sequential way. The first contacts indicate for both regions that the driving force is hydrophobic, the electrostatic contribution becoming relevant at short distance. The direct inter-tropocollagen H-bonds confirm that fibrillogenesis is driven by loss of surface water from the monomers and involves in large percentage hydroxyproline residues. Low ionic strength dynamics leads to the formation of incorrect assemblies, driven by not shielded pairwise charge interactions. Unlabelled Image • Turbidity curves of collagen fibrillogenesis show kinetics with not linear dependence from pH. • Lowly charged and highly charged regions show different ability to associate. • The driving force is hydrophobic and the aggregation mainly sequential. • Fibrillogenesis involves in large part hydroxyproline residues with direct H-bonds. • At low ionic strength incorrect assemblies are formed. [ABSTRACT FROM AUTHOR]