Ionic Strength-Independent Potentiometric Cation Concentration Sensing on Paper Using a Tetrabutylammonium-based Reference Electrode

When the reference electrode liquid junction of a Nova 2 analyser was changed to isotonic potassium chloride, increasing the ionic strength of aqueous solutions containing a constant total calcium concentration had a negligible effect on measured ionised calcium. In contrast, measurements using hypertonic potassium chloride, hypertonic sodium formate and isotonic sodium chloride liquid junctions showed significant sample ionic strength effects. Interferences by sample protein concentration and haematocrit were marked with hypertonic, but negligible with isotonic junctions. Ionised calcium values in samples containing 25 mmol/L acetate, bicarbonate, β-hydroxybutyrate, lactate or pyruvate were all lower by 6–7% with an isotonic than a hypertonic potassium chloride junction. Thus, anions that replace bicarbonate during metabolic acidosis have a similar effect on residual liquid junction potential. The clinical usefulness of an isotonic potassium chloride liquid junction needs to be evaluated.

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Calculating Melting Temperature of Native and Modified Oligonucleotide Complexes at Various Cation Concentrations with the Use of Enhanced Counterion Condensation Model

Siberian Journal of Physics ◽

10.54362/1818-7919-2008-3-2-61-75 ◽

2010 ◽

Vol 3 (2) ◽

pp. 61-75

Author(s):

Aleksandr A. Lomzov ◽

Dmitriy V. Pyshnyi

Keyword(s):

Thermal Stability ◽

Ionic Strength ◽

Melting Temperature ◽

Binding Constants ◽

Data Sets ◽

Dna Duplexes ◽

Counterion Binding ◽

Cation Concentration ◽

Wide Range ◽

Thermal Stability Of

A new model describing the influence of ionic strength on thermal stability of DNA comlexes of oligonucleotides is proposed. This model assumes that binding of cations with DNA polyanions influences solely the entropy of hybridization and has a saturating mode. The efficacy of counterion binding with single- and double-stranded DNA is different, and the number of cations which bind additionally with the oligonucleotide at duplex formation depends on bulk cation concentration. Analytical equations describing the influence of cation concentration on melting temperature of DNA-duplexes as function of the length of oligonucleotide, its GC-composition and presence of the modification (non-nucleotide insert) were obtained. The values of melting temperature (Tm ) and thermodynamic parameters ( o ∆H , o ∆S ) characterizing the hybridization of both native and «bridged» oligonucleotides (bearing non-nucleotide insert on the basis of diethylene glycol phosphodiester) with DNA in various concentrations of NaCl (0,01÷1 М) were obtained using the UV-melting technique. Based on both the data obtained and presented in literature the database (695 data sets) characterizing the influence of ionic strength on the thermal stability of oligonucleotide complexes of various structure is developed. The database analysis allows us to obtain the values of the equilibrium binding constants for condensation of caions on DNA and the number of ions required for saturation of a discrete binding site. The proposed enhanced model of cation condensation utilizing unified thermodynamic increments of dsDNA formation allows us to calculate melting temperatures of DNAduplexes in the wide range of ionic strength ([Na+] = 0,01÷1 М) with high accuracy.

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The ionic strength dependence of chromatin folding

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100081966 ◽

1978 ◽

Vol 36 (2) ◽

pp. 220-221

Author(s):

F. Thoma ◽

TH. Koller

Keyword(s):

Electron Microscopy ◽

Electron Microscope ◽

Ionic Strength ◽

Specimen Preparation ◽

Preparation Technique ◽

Carbon Supports ◽

Ionic Strength Dependence ◽

Chromatin Folding ◽

Strength Dependence ◽

Preparation Techniques

Under a variety of electron microscope specimen preparation techniques different forms of chromatin appearance can be distinguished: beads-on-a-string, a 100 Å nucleofilament, a 250 Å fiber and a compact 300 to 500 Å fiber.Using a standardized specimen preparation technique we wanted to find out whether there is any relation between these different forms of chromatin or not. We show that with increasing ionic strength a chromatin fiber consisting of a row of nucleo- somes progressively folds up into a solenoid-like structure with a diameter of about 300 Å.For the preparation of chromatin for electron microscopy the avoidance of stretching artifacts during adsorption to the carbon supports is of utmost importance. The samples are fixed with 0.1% glutaraldehyde at 4°C for at least 12 hrs. The material was usually examined between 24 and 48 hrs after the onset of fixation.

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Conformational Transitions in Escherichia coli Ribosomal RNAs as Visualized by Dedicated STEM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100102961 ◽

1988 ◽

Vol 46 ◽

pp. 176-177

Author(s):

J.S. Wall ◽

V. Maridiyan ◽

S. Tumminia ◽

J. Hairifeld ◽

M. Boublik

Keyword(s):

Ionic Strength ◽

Three Dimensional ◽

Conformational Transitions ◽

Dark Field ◽

Dimensional Structure ◽

Ribosomal Rnas ◽

Field Mode ◽

Freeze Dried ◽

High Resolution Images ◽

Low Ionic Strength

The high contrast in the dark-field mode of dedicated STEM, specimen deposition by the wet film technique and low radiation dose (1 e/Å2) at -160°C make it possible to obtain high resolution images of unstained freeze-dried macromolecules with minimal structural distortion. Since the image intensity is directly related to the local projected mass of the specimen it became feasible to determine the molecular mass and mass distribution within individual macromolecules and from these data to calculate the linear density (M/L) and the radii of gyration.2 This parameter (RQ), reflecting the three-dimensional structure of the macromolecular particles in solution, has been applied to monitor the conformational transitions in E. coli 16S and 23S ribosomal RNAs in solutions of various ionic strength.In spite of the differences in mass (550 kD and 1050 kD, respectively), both 16S and 23S RNA appear equally sensitive to changes in buffer conditions. In deionized water or conditions of extremely low ionic strength both appear as filamentous structures (Fig. la and 2a, respectively) possessing a major backbone with protruding branches which are more frequent and more complex in 23S RNA (Fig. 2a).

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The three-dimensional structure of frozen-hydrated left- and right-handed forms of bacterial flagellar filaments from an identical serotype

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100143110 ◽

1986 ◽

Vol 44 ◽

pp. 298-299

Author(s):

S. Trachtenberg ◽

D. J. DeRosier

Keyword(s):

Ionic Strength ◽

Basal Body ◽

Three Dimensional ◽

Dimensional Structure ◽

Protein Species ◽

Liquid Environment ◽

Bacterial Flagellum ◽

Left And Right ◽

Rotary Motor ◽

Helical Parameters

The bacterial cell is propelled through the liquid environment by means of one or more rotating flagella. The bacterial flagellum is composed of a basal body (rotary motor), hook (universal coupler), and filament (propellor). The filament is a rigid helical assembly of only one protein species — flagellin. The filament can adopt different morphologies and change, reversibly, its helical parameters (pitch and hand) as a function of mechanical stress and chemical changes (pH, ionic strength) in the environment.

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