Further Increase In Ionic Strength Research Articles

Formation of multi-compartmental particles by controlled aggregation of liposomes

The formation of multi-compartmental colloidal particles by controlled aggregation of 100nm cationic liposomes was investigated. The aggregation was performed under quiescent (perikinetic) conditions and was controlled by the ionic strength of the solution. The time required for obtaining 500nm particles by liposome aggregation ranged from several hours to a few minutes when increasing the NaCl concentration from 50mM to 100mM. It was shown that the aggregation process can be effectively terminated by capping the liposome clusters by a biocompatible non-ionic polymeric surfactant (Poloxamer 188). The clusters were stable in time and resistant to further increase in ionic strength as well as to mechanical agitation. These results demonstrate that multi-compartmental liposome-based carriers with a controlled size can be prepared in a relatively simple and robust way, and used for further studies in environments with variable salinity and hydrodynamic conditions.

The influence of serum phase on the whipping time of unhomogenised cream

The objective of this study was to investigate how the properties of the serum phase, including ionic strength, protein content and specific milk salts, influence the whipping time of unhomogenised cream. This study showed that decreasing the protein content of the serum phase in cream resulted in shorter whipping time. However, addition of UF permeate to both deproteinated and proteinated creams indicated that other components than the protein fraction also influence whipping time of unhomogenised cream. Increasing the ionic strength by addition of NaCl, KCl and CaCl2 decreased whipping time, with the largest effect being found for CaCl2. A further increase in ionic strength by addition of NaCl and KCl resulted in an unfavourable effect on whipping time, whereas a pronounced effect, with shorter whipping times, was found for addition of CaCl2.

INVESTIGATIONS OF THE LEVEL OF OLIGONUCLEOTIDE IMMOBILIZATION ON THE SURFACE OF GOLD NANOPARTICLES USING EXPERIMENTAL APPROACH WITH FLUOROPHORE Cy3

The level of oligonucleotide immobilization on the surface of gold nanoparticles for the nanobiosensor development was studied using a proposed experimental approach. This approach for evaluation of the amount of immobilized material is based on the measurement of the residual concentration of free (unimmobilized) thiolated oligonucleotides with covalently attached fluorophore Cy3. It was shown that the efficiency of immobilization of oligonucleotides on the surface of citratestabilized gold nanoparticles is strongly dependent on the ionic strength of the medium as well as on the temperature and time of immobilization. Along with increase of ionic strength of the medium, two processes are observed: change in ionic strength (from 0 to 15-20 mM) leads to more effective immobilization of oligonucleotides, and a further increase of ionic strength leads to aggregation of gold nanoparticles, which impedes further effective immobilization of oligonucleotides.

Equilibrium, Kinetic, and Thermodynamic Studies on the Adsorption of Triclosan onto Multi‐Walled Carbon Nanotubes

AbstractThe increased accumulation of toxic pharmaceuticals and personal care products in the environment is a concern of worldwide relevance. Efficient technologies are needed to mitigate the level of such chemicals in natural waters. The suitability of multi‐walled carbon nanotubes (MWCNTs) to remove aqueous triclosan (a widely used anti‐microbial agent) was investigated in the present study. Tested operational parameters included the pH (3.0–11.0) value and the ionic strength (10−3, 10−2, and 10−1 M). Kinetic and thermodynamic studies were conducted at different initial concentrations (4, 8, and 10 mg/L) and temperatures (288, 298, and 308 K). Results showed higher triclosan adsorption at pH 3.0 (157.7 mg/g) than at pH 11.0 (103.9 mg/g). With an increase of ionic strength from 10−3 to 10−2 M, the adsorption capacity increased from 136.1 to 153.1 mg/g and from 80.8 to 105.8 mg/g at pH 3.0 and 10.0, respectively, while further increase of ionic strength to 10−1 M slightly reduced the triclosan adsorption to 149.9 and 94.7 mg/g due to the aggregation of MWCNTs. The Polanyi–Manes model (PMM) provided a best fitting of adsorption isotherms to the experimental data, and the kinetic process was well described by the pseudo second‐order kinetic model. The calculated thermodynamic parameters (ΔH0 = −88.08 kJ/mol, ΔS0 = −173.38 J/mol K) suggested that the adsorption of triclosan is spontaneous and exothermic in nature. The findings of the present work have significant implications for the removal of triclosan from aqueous solution with MWCNTs.

Conformational Transitions of Flexible Hydrophobic Polyelectrolytes in Solutions of Monovalent and Multivalent Salts and Their Mixtures

Conformations of cationic polyelectrolytes (PEs), a weak poly(2-vinylpyridine) (P2VP) and a strong poly(N-methyl-2-vinylpyridinium iodide) (qP2VP), adsorbed on mica from saline solutions in the presence of counterions of different valences are studied using in situ atomic force microscopy (AFM). Quantitative characteristics of chain conformations are analyzed using AFM images of the adsorbed molecules. The results of the statistical analysis of the chain contour reveal collapse of the PE coils when ionic strength is in a range from tens to hundreds of millimoles per kilogram and re-expansion of the coils with a further increase of ionic strength up to a region of the saturated saline solutions. The competition between monovalent and multivalent counterions simultaneously present in solutions strongly affects conformations of PE chains even at a very small fraction of multivalent counterions. Shrinkage of PE coils is steeper for multivalent counterions than for monovalent counterions. However, the re-expansion is only incremental in the presence of multivalent counterions. Extended adsorbed coils at low salt concentrations and at very high concentrations of monovalent salt exhibit conformation corresponding to a 2D coil with 0.95 fraction of bound segments (segments in "trains") in the regime of diluted surface concentration of the PE. Shrunken coils in the intermediate range of ionic strength resemble 3D-globules with 0.8 fraction of trains. The incrementally re-expanded PE coils at a high ionic strength remain unchanged at higher multivalent salt concentrations up to the solubility limit of the salt. The formation of a strong PE complex with multivalent counterions at high ionic strength is not well understood yet. A speculative explanation of the observed experimental result is based on possible stabilization of the complex due to hydrophobic interactions of the backbone.

On the functional properties of globulin and albumin protein fractions and flours of African locust bean ( Parkia biglobossa)

Albumin (ALBa) and globulin (ALBg) fractions of African locust bean were isolated and the functional properties were compared with its defatted (ALBdf) and undefatted flours (ALBf). Albumin had minimum % solubility (56.7%) at pH5, while minimum solubility was observed at pH4 for globulin and the flours. In all the samples studied, maximum solubility was observed at pH 10. A pH-dependent gelation study revealed that all of the samples had the highest least gelation concentration at pH10 apart from ALBf which had 16% w/v LGC at pH 2. Initial increase in ionic strength of the medium, to 0.4 and 0.6 M, enhanced the gelation capacity of protein fractions and flours, respectively, while further increase in ionic strength reduced it. Oil absorption capacity was maximal in ALBa while ALBf had the least value of 1.05 ml/g. Initial increase in ionic strength, up to 0.4 M, increased the water absorption capacity (WAC) of albumin fractions while WACs of the globulin fraction and flours were reduced when the ionic strength of the media reached 0.4 M. Foam capacity increased as the concentration of protein solution increased but was reduced by 6% w/v in ALBf. Initial increase in ionic strength enhanced both foam capacity and stability. Maximum EA was observed at pH 10 in all samples apart from ALBf, which reached a peak EA value at pH 2. ES (emulsion stability) was maximal at pH 10 for ALBa and ALBg while the same values were observed for ALBdf and ALBf at pH 2 and 10. Increasing the ionic strength, to 0.4 M, enhanced the EA and ES of ALBa while further increase in ionic strength, to 0.7 M, improved EA of ALBf but reduced the ES. Both EA and ES of ALBf reached peak values in 0.2 M solutions but no fixed pattern was observed in the response of ALBdf to various ionic strengths of the solutions.

Functionality of native and succinylated Lablab bean ( Lablab purpureus) protein concentrate

Lablab bean protein concentrate was acylated with succinic anhydride and resultant changes in some functional properties such as protein solubility index; oil absorption capacity, emulsifying properties and foaming properties were investigated. The result indicate that addition of succinic anhydride at 0.1, 0.25, 0.5, 0.75, and1.0 g/g of protein acylated 42.6, 61.3, 84.6, 89.1 and 92.4%, respectively of the ε-amino groups. Succinylation reduced solubility of native protein (nLPC) at pH values below its isoelectric point (4.5). However, marked improvement in solubility were observed at pH 4.5–10 following succinylation. Emulsifying activity (EA) increased with increase in concentration up to 4 and 6%, w/v for nLPC and succinylated protein (SLPC) respectively but further increase in concentration put the EA on the decline. Increase in ionic strength of the media to 0.2 M and 0.4 M significantly ( P<0.05) increased the EA of nLPC and SLPC respectively. Further increase in ionic strength however reduced the EA of protein solutions. Succinylation reduced the emulsion stability (ES) of nLPC at pH 2. However, in the pH 4–10, all succinylated protein concentrates showed improved ES over the native protein concentrate. A direct relationship was observed between increase in concentration of the protein concentrate and increase in foam capacity. Foam stability reduced after succinylation at all concentration studied. Succinylation improved foam capacity at pH 4–10 but reduced it at pH 2. Native lablab protein had better foam stability compared with the succinylated derivatives.

Effect of acetylation and succinylation on solubility profile, water absorption capacity, oil absorption capacity and emulsifying properties of mucuna bean (Mucuna pruriens) protein concentrate.

Mucuna protein concentrate was acylated with succinic and acetic anhydride. The effects of acylation on solubility, water absorption capacity, oil absorption capacity and emulsifying properties were investigated. The pH-dependent solubility profile of unmodified mucuna protein concentrate (U-mpc) showed a decrease in solubility with decrease in pH and resolubilisation at pH values acidic to isoelectric pH (pH 4). Apart from pH 2, both acetylated mucuna protein concentrates (A-mpc) and succinylated mucuna protein concentrate (S-mpc) had improved solubility over the unmodified derivative. Acylation increased the water absorption capacity (WAC) at all levels of ionic strength (0.1-1.0 M). WAC of the protein samples increased with increase in ionic strength up to 0.2 M after which a decline occurred with increase in ionic strength from 0.4-1.0 M. When protein solutions were prepared in salts of various ions, increase in WAC followed the Hofmeister series in the order: NaSCN < NaClO4 < NaI < NaBr < NaCl < Na2SO. Acetylation improved the oil absorption capacity while the lipophilic tendency reduced the following succinylation. Emulsifying capacity increased with increase in concentration up to 2, 4 and 5% w/v for U-mpc, A-mpc and S-mpc, respectively, after which an increase in concentration reduced the emulsifying capacity. Both acetylation and succinylation significantly (P < 0.05) improved the emulsifying capacity at pH 4-10. Initial increase in ionic strength up to 0.4 M for U-mpc and 0.4 M for A-mpc and S-mpc increased the emulsion capacity progressively. Further increase in ionic strength reduced emulsion capacity (EC). Contrary to the effect of various salts on WAC, increase in EC generally follows the series Na2SO4 < NaCl < NaBr < NaI < NaClO4 < NaSCN. At all levels of ionic strength studied, S-mpc had a better emulsifying activity (EA) than both A-mpc and U-mpc. EA and emulsifying stability (ES) were pH-dependent. Maximum EA and ES were recorded at pH 10. ES of protein derivatives were higher than those of U-mpc in the range of pH 4-10 but lower at pH 2. Studies revealed that both A-mpc and S-mpc had better ES and EA than the unmodified derivative when protein solutions were prepared in salts of various anions.

Comparative study of the functional properties of bambarra groundnut ( Voandzeia subterranean), jack bean ( Canavalia ensiformis) and mucuna bean ( Mucuna pruriens) flours

Functional properties of bambarra groundnut flour (BGF), jack bean flour (JBF) and mucuna bean (MBF) were determined. pH dependent protein solubility profile revealed that highest solubility in all flours was at pH 10, while minimum solubility was obtained at pH 4, which correspond to the isoelectric point. Gelation capacity was minimal at pH 4 for all of the flours. Increase in ionic strength of the medium at low salt concentration (⩽0.4 M) improved the gelation properties of the flours. Maltose, lactose, sucrose and starch when added to the flours enhanced the gelation capacity of all flours. Oil absorption capacity of JBF, MBF and BGF were 1.7, 1.6 and 1.3 ml g −1, respectively. Water absorption capacity of flours increased between ionic strength ranges of 0–0.2 M but reduced with further increase in ionic strength. Emulsifying activity (EA) decreased as the concentration of flour in solution increased. Maximum EA and emulsion stability (ES) were obtained at pH 10, while minimum values were read at isoelectric pH. EA and ES of flours increased in the ionic strength range 0–0.4 M but reduced afterwards with further increase in NaCl concentration. Foam stability (FS) of the flours increased as the concentration of flour solution increased and maximum values of 80.5%, 74.7% and 77.0% were observed for JBF, BGF and MBF at 10% flour concentration. MBF had highest foam capacity (FC) of 68% at pH 2, while JBF and BGF recorded highest value of 50% and 61%, respectively, at pH 10. Foam stability was maximal at pH 4 for all the fours. Low ionic strength ( μ⩽0.2 M) improved both foam capacity and stability of JBF while increases were recorded in FS and FC of BGF and MBF up to μ=0.4 M, after which further increase in ionic strength reduced the foaming properties of the flours.

Functionality of African locust bean ( Parkia biglobossa) protein isolate: effects of pH, ionic strength and various protein concentrations

A protein isolate was prepared from African locust bean (ALBPI) and the functional properties were investigated under the influence of pH, ionic strength and varying protein concentration. Protein solubility diminished as the pH increased from 2 to 4.5, after which further increase in pH increased it progressively. The oil absorption capacity of ALBPI was 1.97 ml/g protein. Water absorption capacity increased when ionic strength of the medium increased to 0.2 M but diminished with further increase in ionic strength. Gelation properties improved at pH 4. The results indicate improvement in gelation capacity as the ionic strength of protein solution increased from 0.1 to 0.2 M while further increase in ionic strength caused the gelation tendency to decline. Increase in concentration favoured emulsifying activity (EA) and stability (ES) up to 4% (w/v) concentration, while further increase from 6% to 10% (w/v) diminished emulsifying properties. Also, initial increase in ionic strength, up to 0.2 M, improved both emulsifying activity and stability while further increase in ionic strength progressively reduced emulsifying properties. Maximum emulsifying activity and stability were at pH 10 while minimum values were obtained at pH 4. Foam capacity and stability increased as the protein concentration increased. Increase in ionic strength from 0 to 0.2 M increased the foam capacity (FC) and stability (FS) but foam capacity was reduced as the ionic strength increased further. Foam capacity and stability were pH-dependent. A minimum value of 32.7% was recorded at pH 4 while further increase in pH increased the foam capacity progressively until it reached a maximum (86.8%) at pH 10. Contrarily, maximum foam stability was recorded at pH 4 while foam stability diminished as the pH of the protein solution increased.

Modeling adsorption-desorption processes of Cu on edge and planar sites of montmorillonite.

The effect of the ionic strength on adsorption of Cu on calcium montmorillonite was studied at concentrations ranging from 31 to 516 microM. An adsorption model was employed in the analysis of the data. When the background electrolyte was NaClO4, the ionic exchange was suppressed at 0.5 M concentration, and Cu adsorption took place on edge sites, reaching a plateau at about 24 mmol/kg. A further increase in ionic strength did not have any effect on Cu adsorption, suggesting that the heavy metal was adsorbed by inner-sphere complexes on the edge sites of the clay. A binding coefficient for Cu2+ on the edge sites K = 2 x 10(4) M(-1) was determined, indicating very high affinity of Cu2+ for these sites. When the electrolyte used was NaCl, the amounts of Cu adsorbed were reduced. The model predicted well the adsorption data by considering the adsorption of CuCl+ species. Adsorption-desorption processes of Cu on calcium montmorillonite in media of 0.01 and 0.1 M NaCl showed hysteresis. Model calculations also predict the desorption fairly well. According to the model, the hysteresis is mainly attributed to the heterogeneity of sites for the adsorption of Cu. The hysteresis arising from the planar sites is largely due to reduced competition of ion species for adsorption and enhancement in the magnitude of the surface potential.

Flocculation and characterization of protein by anionic copolymer containing reactive functional groups

Two types of anionic copolymers with reactive functional groups of amido, carboxyl and sulfonate were prepared and used to study the flocculation and characterization of lysozyme in aqueous solution. Initial increase of the ionic strength promotes flocculation, but no flocculation occurs with further increase of ionic strength. High ionic strength in solution also makes the aggregates of protein–copolymer sensitive to shear. The two types of flocculants require high pH to achieve high charge density for interacting with lysozyme effectively. Adsorption of lysozyme to the anionic copolymers was influenced strongly by pH and ionic strength. The results reveal an understanding of the types of zeta ( ζ) potential when lysozyme aggregates with copolymers. The performances of the anionic copolymers are related to their compositions when they are used as flocculants. The results confirm the mechanism of charge neutralization that prevails for highly charged polymers.

Effect of salt concentration of buffer on the binding of sodium dodecyl sulfate and on the viscosity behavior of the protein polypeptide derived from bovine serum albumin in the presence of the surfactant

The complex between SDS and a protein polypeptide derived from bovine serum albumin was characterized with respect to binding of SDS and viscosity behavior. The amount of bound SDS increased from 1.0 to 2.2 g/g with increase of the buffer concentration from 10 to 220 mM. A logarithmic plot of the amount of bound SDS against the buffer concentration gave a linear relation like in the plot where the number of SDS molecules constituting a spherical micelle of SDS is plotted similarly. The increase in the buffer concentration up to 25 mM, from 25 to 100 mM and beyond 100 mM, was accompanied by a sharp rise, monotonic decrease and levelling-off of the intrinsic viscosity in the respective region. In the region 45-175 mM, a linear relation was found between the intrinsic viscosity and reciprocal square root of the buffer concentration. The observed changes can be interpreted as follows: (1), the electrostatic repulsion between charges introduced by the bound SDS caused the initial increase; (2), shielding of the charges as the result of ion condensation with further increase in ionic strength caused the viscosity drop and subsequent levelling-off. The characteristics of the plots are consistent with the necklace model proposed previously for such complexes in which SDS is bound to a protein polypeptide forming micelle-like clusters and which behave like a flexible polyelectrolyte (Shirahama, K., Tsujii, K. and Takagi, T. (1974) J. Biochem. 75, 309-319).

Susceptibility of Baboon Aorta Elastin to Proteolysis

Elastin was purified from baboon aorta using Achromobacter collagenase and its susceptibility to proteolysis by various enzymes was studied. Human leukocyte elastase (HLE) hydrolysed baboon aortic elastin 8 times faster than human cathepsin G. Bovine chymotrypsin had virtually no activity against this substrate. The kinetic constants V and [S50] of aortic elastin hydrolysis by HLE (0.15 microM) were 0.00286 mg x ml-1 x min-1 and 0.158 mg x ml-1, respectively. One mg of this elastin could be saturated with 5.6 micrograms of HLE. As with elastins isolated from other sources, the hydrolysis of baboon aortic elastin by HLE was highly sensitive to ionic strength, and a biphasic effect was obtained with increasing NaCl concentrations. A nearly 2-fold stimulation of elastolysis was observed at a 0.15M NaCl concentration. Further increase in ionic strength led to a continuous decrease of the rate of elastolysis which paralleled the decrease of adsorption of elastase to baboon aortic elastin. Cathepsin G, but not bovine alpha-chymotrypsin, was able to stimulate the rate of hydrolysis of baboon aortic elastin by HLE. A 1.7 fold stimulation was observed for a 1:1 molar ratio of the two proteinases and rose to 2.1 for a HLE/Cat. G ratio equal to 8.

Supranucleosomal organization of chromatin. Electron microscopic visualization of long polynucleosomal chains.

A systematic study of the effect of different ionic conditions on the morphology of the 25-30 nm chromatin fiber from chicken erythrocytes has revealed that, as the ionic strength is increased, knobby fibers with a clear superbead structure are formed in the presence of either Mg++ or Na+, or both. A further increase in ionic strength results in smooth chromatin fibers due to a tight packing of superbeads. Cross-linking such fibers with formaldehyde and reversal of the ionic conditions, demonstrates the superbead structures underlying the smooth fibers observed at high ionic concentrations. The average size of the superbeads is 34 nm along the length of the fibers, in agreement with the value found in embedded sea cucumber chromatin. A second class of superbeads has an average length of 25 nm and probably corresponds to partially disrupted structures.

Higher-order structures of chromatin in solution.

Neutron scatter studies have been made on gently prepared chicken erythrocyte chromatin over a range of ionic strength. At low ionic strength the mass per unit length of the '10 nm nucleofilament corresponds to one nucleosome per 8--12 nm and a DNA packing ratio of between 6 and 9. From the contrast dependence of the cross-section radius of gyration of the nucleofilament the following parameters have been obtained; RgDNA' the cross-section radius of gyration (Rg) when DNA dominates the scatter; RgP, the cross-section Rg when protein dominates the scatter; Rc, the cross-section Rg at infinite contrast and alpha, the constant which describes the dependence of the cross-section Rg on contrast variation. From our understanding of the structure of the core particle, various arrangement of core particles in the nucleofilament have been tested. In models consistent with the above parameters the core particles are arranged edge-to-edge or with the faces of the core particles inclined to within 20 degrees to the axis of the nucleofilament. With increase of ionic strength the transition to the second-order chromatin structure has been followed. This gave the interesting result that above 20 microM NaCL or 0.4 mM MgCL2 the cross-section Rg increases abruptly to about 9 nm with a packing ratio of 0.2 nucleosome/mn and with further increase of ionic strength the Rg increases to 9.5 nm while the packing ratio increases threefold to 0.6 nucleosome/nm. This suggests a family of supercoils of nucleosomes which contract with increasing ionic strength. In its most contracted form the diameter of the hydrated supercoil has been found from the radial distribution function to be 34 nm. Models for the arrangements of core particles in the 34-nm supercoil are discussed.

RNA polymerase-DNA complexes: IV. Influences of the ionic strength on the integrity of the complexes

Dissociation of a complex of Escherichia coli RNA polymerase with DNA “keg”, which was resistant to DNAase digestion under varying ionic strength conditions was studied by gel filtration and sedimentation. This complex-like RNA polymerase lends itself to reversible dimerisation as the ionic strength of the solution varies from 0.02 to 0.1 M. Further increase in ionic strength up to 0.25–1.0 M results in dissociation of the keg into DNA and the enzyme. The relative stability of the keg in this transition range is proportional to the square root of the reciprocal of the ionic strength value. The same is valid for the dependence of the relative rate of the initiation and elongation of RNA synthesis on ionic strength. The present experiments support the hypothesis that the active form of RNA polymerase is a monomer.

Adsorption of bacteriophage on bacterial surface and on the surface of Hg dropping electrode.

The influence of the ionic strength of the medium on the adsorption of bacteriophage T 2 to the surfaces of a mercury dropping electrode on one hand and ofbacteria E. coli B on the other hand was studied. The adsorption on the mercury surface was determined by measurement of the differential capacity of the electrode double layer, the adsorption to bacteria was estimated from the decrease of free phage particles in a bacterial suspension with time. The adsorption to the mercury electrode increases with increasing ionic strength of the medium, but adsorption to the surface of bacteria increases at first, has a maximum at concentrations between 0,1 to 0,5 M and decreases with further increase of ionic strength. The decrease of adsorption of phage to the bacterial surface is assumed to be caused by the blocking of specific sites on the bacterial surface by adsorbed ions which sterically prevent the adsorption of the phage. Such specific sites are not present on the electrode surface, therefore adsorption increases further with increasing ionic strength probably due to the neutralization of surface charges of the phage and of the electrode. The saturated surface-concentration of the phageγ s was calculated from the dependence of the differential capacity on the concentration. It is concluded fromγ s value obtained that the phage particles are scattered with wide intervals on the electrode surface with a degree of coverage of approximately 1∶40.