scholarly journals Aggregation dynamics of charged peptides in water: effect of salt concentration

2019 ◽  
Author(s):  
Susmita Ghosh ◽  
T Devanand ◽  
Upayan Baul ◽  
Satyavani Vemparala
Keyword(s):  
Early Stage ◽  
Potassium Ions ◽  
Sodium Ions ◽  
Magnesium Ions ◽  
Compact Structure ◽  
Biologically Relevant ◽  
Kinetics And Dynamics ◽  
Aggregate Morphology ◽  
Dynamics Simulations ◽  
Charged Peptides

Extensive molecular dynamics simulations have been employed to probe the effects of salts on the kinetics and dynamics of early-stage aggregated structures of steric zipper peptides in water. The simulations reveal that the chemical identity and valency of cation in the salt play a crucial roles in aggregate morphology of the peptides. Sodium ions induce the most aggregated structures but this is not replicated by potassium ions which are also monovalent. Divalent Magnesium ions induce aggregation, but to a lesser extent than that of sodium and their interactions with the charged peptides are also significantly different. The aggregate morphology in the presence of monovalent sodium ions is a compact structure with interpenetrating peptides, which differs from the more loosely connected peptides in the presence of either potassium or magnesium ions. The different ways in which the cations effectively renormalize the charges of peptides is suggested to be the cause of the differential effects of different salts studied here. These simulations underscore the importance of understanding both the valency and nature of of salts in biologically relevant aggregated structures.

scholarly journals Kinetics of charged polymer collapse: effects of additional salt

2020 ◽  
Author(s):  
Susmita Ghosh ◽  
Satyavani Vemparala
Keyword(s):  
Charge Density ◽  
Early Stage ◽  
Finite Size ◽  
Long Distance ◽  
Charged Polymers ◽  
Kinetics And Dynamics ◽  
Polymer Models ◽  
Charged Polymer ◽  
Dynamics Simulations ◽  
Kinetics Of

Extensive molecular dynamics simulations, using simple charged polymer models, have been employed to probe the kinetics and dynamics of early-stage collapse of charged polymers and the effect of additional monovalent salt on such kinetics. The exponents characterizing the coarsening dynamics during such early-collapse stage via finite size scaling for the case of charged polymers are found to be different from the neutral polymers, suggesting that the collapse kinetics of charged polymers are inherently different from that neutral polymers. The kinetics of coarsening of the clusters along the collapsed trajectory also depends significantly on the counterion valency and for higher valency counterions, multiple regimes are observed and unlike the neutral polymer case, the collapse kinetics are a function of charge density along the charged polymer. Inclusion of additional salt affects the kinetics and conformational landscape along the collapse trajectory. Addition of salt increases the value of critical charge density required to initiate collapse for all the counterion valencies, though the effect is more pronounced for monovalent counterion systems. The addition of salt significantly affects the collapse trajectory in the presence of trivalent counterions via promotion of transient long-distance loop structures inducing a parallel and hierarchical local collapsed conformation leading to faster global collapsed states. This may play a role in understanding the fast folding rates of biopolymers such as proteins and RNA from extended state to a collapsed state in the presence of multivalent counterions before reorganizing into a native fold.

scholarly journals CHEMICAL ANTAGONISM OF IONS

1928 ◽  
Vol 12 (2) ◽  
pp. 241-258 ◽  
Author(s):  
Henry S. Simms
Keyword(s):  
Ionic Strength ◽  
Oxalic Acid ◽  
Quantitative Data ◽  
Marked Decrease ◽  
Short Chain ◽  
Potassium Ions ◽  
Sodium Ions ◽  
Magnesium Ions ◽  
Biological Interest ◽  
Wide Range

Magnesium ions decrease the activity of divalent organic anions much more than the normal decrease produced by sodium ions. The effect is very large with short chain acids, particularly oxalic acid. The addition of sodium or potassium ions produces a marked decrease in the effect of magnesium diions on the activity of oxalate diions. Quantitative data on 0.005 molar solutions of oxalic diion over a wide range of concentrations of MgCl2 and of NaCl (or KCl) show that the following equation is obeyed: See PDF for Equation where A is an empirical value dependent on the concentration of oxalate diion (0x=). This equation has been shown to hold down to zero ionic strength of Na+ and K+, and hence to be valid in the physiological range. These observations are of biological interest since the activity of proteins should (like oxalic acid) show a similar antagonism.

Sodium and Potassium Fluxes in the Abdominal Nerve Cord of the Cockroach, Periplaneta Americana L

1961 ◽  
Vol 38 (2) ◽  
pp. 315-322
Author(s):  
J. E. TREHERNE
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Nerve Cord ◽  
Periplaneta Americana ◽  
Unit Area ◽  
Potassium Ions ◽  
Sodium Ions ◽  
Nerve Sheath ◽  
The Central Nervous System ◽  
Sodium And Potassium

1. The influx of sodium and potassium ions into the central nervous system of Periplaneta americana has been studied by measuring the increase in radioactivity within the abdominal nerve cord following the injection of 24NA and 42K. into the haemolymph. 2. The calculated influx of sodium ions was approximately 320 mM./l. of nerve cord water/hr. and of potassium ions was 312 mM./l. of nerve cord water/hr. These values are very approximately equivalent to an influx per unit area of nerve cord surface of 13.9 x 10-2 M cm. -2 sec.-1 for sodium and 13.5 x 10-12 M cm. -2 sec.-1 for potassium ions. 3. The relatively rapid influxes of these ions are discussed in relation to the postulated function of the nerve sheath as a diffusion barrier. It is suggested that a dynamic steady state rather than a static impermeability must exist across the sheath surrounding the central nervous system in this insect.

scholarly journals A Comprehensive Review of Winding Short Circuit Fault and Irreversible Demagnetization Fault Detection in PM Type Machines

Energies ◽  
2018 ◽  
Vol 11 (12) ◽  
pp. 3309 ◽  
Author(s):  
Zia Ullah ◽  
Jin Hur
Keyword(s):  
Fault Diagnosis ◽  
Early Stage ◽  
Short Circuit ◽  
Industrial Applications ◽  
Operational Environment ◽  
Compact Structure ◽  
Torque Density ◽  
Prime Concern ◽  
Attractive Option ◽  
The Impact

Contemporary research has shown impetus in the diagnostics of permanent magnet (PM) type machines. The manufacturers are now more interested in building diagnostics features in the control algorithms of machines to make them more salable and reliable. A compact structure, exclusive high-power density, high torque density, and efficiency make the PM machine an attractive option to use in industrial applications. The impact of a harsh operational environment most often leads to faults in PM machines. The diagnosis and nipping of such faults at an early stage have appeared as the prime concern of manufacturers and end users. This paper reviews the recent advances in fault diagnosis techniques of the two most frequently occurring faults, namely inter-turn short fault (ITSF) and irreversible demagnetization fault (IDF). ITSF is associated with a short circuit in stator winding turns in the same phase of the machine, while IDF is associated with the weakening strength of the PM in the rotor. A detailed literature review of different categories of fault indexes and their strengths and weaknesses is presented. The research trends in the fault diagnosis and the shortcomings of available literature are discussed. Moreover, potential research directions and techniques applicable for possible solutions are also extensively suggested.

DNA KNOT FORMATION IN AQUEOUS SOLUTIONS

1994 ◽  
Vol 03 (03) ◽  
pp. 287-298 ◽  
Author(s):  
STANLEY Y. SHAW ◽  
JAMES C. WANG
Keyword(s):  
Aqueous Solutions ◽  
Experimental Test ◽  
Attractive Potential ◽  
Sodium Ions ◽  
Magnesium Ions ◽  
Close Apposition ◽  
Closed Chain ◽  
Solvent Properties

The knotting probability of a closed chain has been calculated as a function of chain dimensions and solvent properties in a number of studies. We have measured the probability of DNA knot formation upon random cyclization of linear DNA in vitro to provide an experimental test of the various theoretical treatments of the problem; parameters of these models, such as the effective chain diameter of DNA, were calculated in different concentrations of counterions. Our results in the presence of sodium ions agree well with theoretical treatments of DNA as a polyelectrolyte; knotting data in the presence of divalent magnesium ions indicate that moderate concentrations of magnesium ions can induce an attractive potential between DNA segments, resulting in negative values of the calculated effective DNA helix diameter. We discuss structures in which the divalent magnesium counterion facilitates the close apposition of two DNA segments, and review the effect of chemical- and protein-mediated crosslinks between DNA segments on DNA knot formation. Finally, we consider DNA knot formation in vivo.

scholarly journals Biochemical and Molecular Studies on the Role of Rosemary (Rosmarinus officinalis) Extract in Reducing Liver and Kidney Toxicity Due to Etoposide in Male Rats

2019 ◽  
pp. 1-11
Author(s):  
Majd Almakhatreh ◽  
Ezar Hafez ◽  
Ehab Tousson ◽  
Ahmed Masoud
Keyword(s):  
Dna Damage ◽  
Calcium Ions ◽  
Chloride Ions ◽  
Male Rats ◽  
Control Group ◽  
Potassium Ions ◽  
Sodium Ions ◽  
Total Proteins ◽  
Kidney Toxicity ◽  
Liver And Kidney

Aims: Etoposide (Vepesid) is chemotherapeutic drugs that inhibit topoisomerase II activity and long been used for treatment of human malignancies, where it is a semi-synthetic compound derived from the plant Podophyllum peltatum. The current study was designed to investigate the possible protective effect of rosemary extract against Etoposide -induced changes in liver and kidney functions, and DNA damage in rats. Materials and Methods: A total of 50 male Wistar albino rats were divided randomly into four groups (1st group was control; 2nd group was treated with rosemary, 3rd group was received etoposide, and 4th & 5th groups was co- and post treated groups respectively). Results: The administration of Etoposide revealed a significant increase in serum ALT, AST, ALP, creatinine, urea, potassium ions, chloride ions, and DNA damage. In contrast; a significant decrease in albumen, total proteins, sodium ions, and calcium ions were when compared with control group. This increased in ALT, AST, ALP, creatinine, urea, potassium ions, chloride ions, and DNA damage was reduced after administration of rosemary when co-treated with etoposide (G4), or post-treated after etoposide  (G5) for four weeks with lowest damage in G4. Also, this decreased in albumen, total proteins, sodium ions, and calcium ions was increased after administration of rosemary when co-treated with etoposide (G4), or post-treated after etoposide (G5) for four weeks with lowest damage in G4. Conclusion: It could be concluded that rosemary has a promising role and it worth to be considered as a natural substance for protective the liver and kidney toxicity induced by etoposide (Vepesid) chemotherapy.

scholarly journals Icephobicity of Functionalized Graphene Surfaces

2016 ◽  
Vol 2016 ◽  
pp. 1-8 ◽  
Author(s):  
Xiang-Xiong Zhang ◽  
Min Chen
Keyword(s):  
Molecular Dynamics ◽  
Freezing Temperature ◽  
Ice Nucleation ◽  
Chloride Ions ◽  
Water Molecules ◽  
Sodium Ions ◽  
Functionalized Graphene ◽  
Functionalized Surfaces ◽  
The Difference ◽  
Dynamics Simulations

Manipulating the ice nucleation ability of liquid water by solid surface is of fundamental importance, especially in the design of icephobic surfaces. In this paper, the icephobicity of graphene surfaces functionalized by sodium ions, chloride ions, or methane molecules is investigated using molecular dynamics simulations. The icephobicity of the surface is evaluated by the freezing temperature. The freezing temperature on surface functionalized by methane molecules decreases at first and then increases as a function of the number groups, while the freezing temperature increases monotonically as a function of the number groups upon surfaces functionalized by sodium ions or chloride ions. The difference can be partially explained by the potential morphologies near the surfaces. Additionally, the validity of indicating the ice nucleation ability of water molecules using the number of six rings in the system is examined. Current study shows that the ice nucleation upon functionalized surfaces is inhibited when compared with smooth graphene substrate, which proves the feasibility of changing the icephobicity of the surfaces by functionalizing with certain ions or molecules.

EFFECTS OF CATIONS ON SUGAR ABSORPTION BY ISOLATED SURVIVING GUINEA PIG INTESTINE

1958 ◽  
Vol 36 (3) ◽  
pp. 347-362 ◽  
Author(s):  
E. Riklis ◽  
J. H. Quastel
Keyword(s):  
Guinea Pig ◽  
Glucose Transport ◽  
Active Transport ◽  
Glucose Absorption ◽  
Ion Concentration ◽  
Potassium Ions ◽  
Magnesium Ions ◽  
Sugar Absorption ◽  
Rate Of Absorption ◽  
High Concentrations

The rate of absorption of glucose from isolated surviving guinea pig intestine increases with increase of the concentration of glucose in the lumen until a maximum rate is obtained. The relation between absorption rate of glucose and initial glucose concentration conforms to an equation of the Michaelis–Menten type. The apparent Km(half saturation concentration) is 7 × 10−3M. Increase of the concentration of potassium ions in the Ringer–bicarbonate solution bathing the intestine leads to an increase of the rate of glucose absorption, this being most marked with 15.6 meq./liter K+and 14 mM glucose. No such stimulating action of potassium ions is observed on glucose absorption under anaerobic conditions. The effect of increased potassium ion concentration is to accelerate the rate of transport found with low concentrations of glucose to the maximum value found with high concentrations of the sugar. Sodium ions must be present for glucose absorption to take place and omission of magnesium ions from a Ringer–bicarbonate solution, containing 15.6 meq./liter K+, brings about a decreased rate of active glucose transport. Magnesium ions are necessary for the stimulated rate of glucose absorption obtained in the presence of potassium ions. The presence of ammonium ions decreases the rate of glucose absorption. Potassium ions may be effectively replaced by rubidium ions for stimulation of glucose transport. Cesium ions do not activate. The proportion of glucose to fructose appearing in the serosal solution, when fructose is absorbed from the mucosal solution, depends on the concentration of fructose present. The proportion may be as high as 9:1 with low (7 mM) fructose concentrations; it decreases with increasing fructose concentrations. The active transport of fructose, as demonstrated by the conversion of fructose in the isolated surviving guinea pig intestine, is enhanced by the presence of potassium ions (15.6 meq./liter). The rate of transport of fructose itself is unaffected by potassium. Using radioactive glucose and fructose, it is shown that the total amount of sugar transferred through the intestine as estimated by the radioactivity appearing in the serosal solution is approximately that calculated from chemical analyses. Potassium ions have no activating action on the transport of sugars such as sorbose, mannose, and D-glucosamine, but have a marked effect on galactose transport. The results support the conclusion that potassium ions do not influence active transport of glucose, fructose, and galactose by a change of intestinal permeability to these sugars, but do so by affecting a specific phase involved in the mechanism of active transport of sugars. The presence of L-glutamine stimulates active transport of glucose, whereas that of L-glutamate tends to diminish it.

Sign in / Sign up

Export Citation Format

Share Document