Sodium-alizarin-3-sulphonate as a colloidal electrolyte

Summary During the study of the composition of metal chelates of sodium alizarin-3-sulphonate, it was realized that the colloidal nature of the reagent, especially in concentrated solutions, masks the true composition of the chelate. An investigation of the electrical conductance at various dilutions and temperatures shows that the reagent belongs to the class of colloidal electrolytes. It is recommended that for the study of the composition of chelates involving such chelating agents, extremely dilute solutions should be employed for physicochemical investigation, because under these conditions the reagent would behave as a true electrolyte.     

Solochrome Green V as a new analytical reagent

Summary The acid-base properties of Solochrome Green V have been studied with the object of testing its use as a metal indicator or colorimetric reagent. The pK values of the three steps of ionisation of the free acid were evaluated. The dye has proved to be a suitable indicator in EDTA titrations of zinc and manganese as well as a colorimetric reagent for the microdetermination of zinc. The method is highly sensitive that by its application 0.05 ppm Zn can be determined with fair accuracy.     

Migration of a colloidal particle in a gradient of electrolyte concentration

When a charged colloidal particle is placed in a solution which is macroscopically nonuniform in electrolyte composition, polarization of the diffuse part of the double layer surrounding the particle propels it through the fluid. In one experiment, gradients of ion concentration in the diffusion boundary layer next to a rapidly dissolving steel panel cause negatively charged latex particles to deposit on the metal at rates comparable to those achieved by electrodeposition. In a second experiment, diffusion of a salt through a filter membrane into a dilute agitated dispersion of latex causes the latex particles to deposit on the filter. Results of both experiments are consistent with a mechanism in which the charged particles migrate with a velocity equal to their electrophoretic velocity in a spontaneously generated electric field having that strength and direction required to prevent an electric current from accompanying diffusion of the ions.     

Solochrome violet R.S. as a new colorimetric reagent

Summary Solochrome violet R.S. has proved to be a sensitive colorimetric reagent for the microdetermination of vanadium in the limits of 0.05 to 6 ppm with a sensitive filter photometer or a spectrophotometer, at 580 nm. A large number of cations up to 100 fold the vanadium amount do not interfere with its determination. The present work comprises a comparative study on the behaviour of solochrome violet and Fast Grey, based upon the great similarity in the molecular structure of the two dyes and the influence of the orthonitrophenolic group in the molecule of Fast Grey.Part I: See Z. analyt. Chem. 178, 184 (1960).     

Solochrome Black P.V. as a new reagent in chelatometry

Summary Solochrome Black P.V. has proved to be a suitable metallochromic indicator in direct titrations of Mg, Zn, Cd and Mn^II with EDTA or in back titrating Pb, M and Co at p_H 10. By its aid together with the application of masking agents as potassium cyanide and ammonium fluoride and the mercuric nitrate procedure, fifteen binary mixtures were analysed using simple procedures which gave precise, reproducible and highly accurate results. It can be used as a substitute for Eriochrome Black T in determining micro and milligram amounts of the above mentioned cations.Part I: Khalifa, H., and S. W. Bishra: Z. analyt. Chem. 183, 108 (1961).     

7-iodo 8-hydroxy quinoline 5-sulphonic acid (Ferron) as a colloidal electrolyte

Summary Electrical conductance studies have been performed to investigate the nature of aqueous solutions of 7-iodo 8-hydroxy quinoline 5-sulphonic acid (Ferron). The reagent has been found to behave as a colloidal electrolyte and does not obeyBeer's law in concentrated solutions. The curve between the square root of concentration and equivalent conductance is not linear and resembles those of colloidal electrolytes. The temperature of zero conductance has also been determined to be –32 C. The temperature coefficient per degree centrigrade per 100 of the conductance at 35 C ranges between 1.56 and 1.72.

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Zusammenfassung Elektrische Leitfähigkeitsuntersuchungen wurden an wä\rigen Lösungen von Ferron (7-Jod-8-hydroxyquinolin-5-sulfonsäure) durchgefÜhrt, um die Natur dieser Lösungen aufzuklären. Das Reagenz benimmt sich wie ein kolloider Elektrolyt und folgt nicht demBeerschen Gesetz in konzentrierten Lösungen. Der Zusammenhang zwischen Leitfähigkeit und Quadratwurzel aus Konzentration ist nicht linear und ähnelt dem kolloider Elektrolyte. Die Temperatur der Leifähigkeit 0 liegt bei –32 C. Der Temperaturkoeffizient in Prozenten der Leitfähigkeit bei 35 C liegt zwischen 1,56 und 1,72.

     

Solochrome Violett R. S. as a new colorimetric reagent

Summary The reaction between molybdenum and the sulphonic acid azo dye Solochrome Violet R.S. has proved to be a suitable one for the microdetermination of Mo amounts covering the range of 0.3 to 10 ppm in purely aqueous solutions. The variation of extinction with concentration conforms satisfactorily with Beer's law throughout the whole range. Very many cations and anions do not interfere with such a determination. Ferric iron up to 2 mg per 25 ml is completely masked with ascorbic acid.Part II: Khalifa, H., and S. W. Bishara: Z. analyt. Chem. 178, 345 (1960).     

Solochrome Black P. V. as a new reagent in chelatometry

Summary Solochrome Black P. V. with its distinct acid-base properties has proved to be a suitable reagent for the spectrophotometric microdetermination of magnesium either alone or in the presence of zinc, calcium, cobalt, or copper. Interference due to many cations is simply eliminated. Spectrophotometric titration of magnesium with EDTA is investigated. Sensitivity of the method allows determining of 0.05 to 3 ppm Mg with reasonable accuracy.

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Zusammenfassung Solochromschwarz P. V., das als Säure-Base-Indicator verwendet werden kann, ist auch ein geeignetes Reagens zur spektrophotometrischen Mikrobestimmung von Magnesium. Zink, Calcium, Kobalt, Kupfer und andere Kationen können in einfacher Weise maskiert werden. Die spektrophotometrische Titration des Magnesiums mit ÄDTA-Lösung wird ebenfalls untersucht. 0,05–3 ppm Mg können mit guter Genauigkeit bestimmt werden.

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Part II:Khalifa, H., and M. M.Khater: Z. analyt. Chem.183, 241 (1961).     

Solochrome Black P.V. as a new reagent in chelatometry

Summary The acid-base properties of Solochrome Black P.V. have been studied with the object of applying it as a metallochromic or as a chromophoric indicator. The pK values of 4.1, 7.0 and 11 corresponding to the three steps of ionisation of the free acid were evaluated by aid of the relation between log (acid)/(salt) and p_H values obtained during the course of the potentiometric titration of the free acid with a free base together with the E-p_H relation. The molecular ratio of the magnesium-dye chelate and its mode of chelation are given.

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Zusammenfassung Die Eigenschaften des Farbstoffs Solochrome Black P.V. werden im Hinblick auf seine Verwendung als Metalloder Farbindicator untersucht. Entsprechend den drei Dissoziationsstufen der freien Säure werden pK-Werte von 4,1, 7,0 und 11 gefunden. Diese werden mit Hilfe der Beziehungen zwischen log [Säure]/[Salz] und p_H sowie zwischen E und p_H ausgewertet. Bildung und Zusammensetzung des Mg-Farbstoffchelats werden näher untersucht.

     

Complete phase behavior of the symmetrical colloidal electrolyte

We computed the complete phase diagram of the symmetrical colloidal electrolyte by means of Monte Carlo simulations. Thermodynamic integration, together with the Einstein-crystal method, and Gibbs-Duhem integration were used to calculate the equilibrium phase behavior. The system was modeled via the linear screening theory, where the electrostatic interactions are screened by the presence of salt in the medium, characterized by the inverse Debye length, kappa (in this work kappasigma=6). Our results show that at high temperature, the hard-sphere picture is recovered, i.e., the liquid crystallizes into a fcc crystal that does not exhibit charge ordering. In the low temperature region, the liquid freezes into a CsCl structure because charge correlations enhance the pairing between oppositely charged colloids, making the liquid-gas transition metastable with respect to crystallization. Upon increasing density, the CsCl solid transforms into a CuAu-like crystal and this one, in turn, transforms into a tetragonal ordered crystal near close packing. Finally, we have studied the ordered-disordered transitions finding three triple points where the phases in coexistence are liquid-CsCl-disordered fcc, CsCl-CuAu-disordered fcc, and CuAu-tetragonal-disordered fcc.     

Diffusiophoresis of a cylindrical colloidal particle oriented parallel to an electrolyte concentration gradient field

We derive the general expression for the diffusiophoretic mobility of a cylindrical particle oriented parallel to an applied electrolyte concentration gradient field in a symmetrical electrolyte solution. From the general mobility expression as combined with an approximate analytic expression with negligible error for the electric potential distribution around a cylinder, an accurate analytic mobility expression is obtained, which is applicable for arbitrary values of the particle zeta potential and the electrical double layer thickness. It is also found that the low zeta potential approximation is an excellent approximation for low-to-moderate values of the particle zeta potential.     

Blue silver: a very sensitive colloidal Coomassie G-250 staining for proteome analysis

A modified Neuhoff's colloidal Coomassie Blue G-250 stain is reported, dubbed "blue silver" on account of its considerably higher sensitivity, approaching the one of conventional silver staining. The main modifications, as compared to Neuhoff's protocol, were: a 20% increment in dye concentration (from 0.1% up to 0.12%) and a much higher level of phosphoric acid in the recipe (from 2% up to 10%). The "blue silver" exhibits a much faster dye uptake (80% during the first hour of coloration, vs. none with a commercial preparation from Sigma). Even at equilibrium (24 h staining), the "blue silver" exhibits a much higher sensitivity than all other recipes, approaching (but lower than) the one of the classical silver stain. Measurements of stain sensitivity after sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of bovine serum albumin (BSA) gave a detection limit (signal-to-noise ratio > 3) of 1 ng in a single zone. The somewhat lower sensitivity of "blue silver" as compared to classical silvering protocols in the presence of aldehydes is amply compensated for by its full compatibility with mass spectrometry of eluted polypeptide chains, after a two-dimensional map analysis, thus confirming that no dye is covalently bound (or permanently modifies) to any residue in the proteinaceous material. It is believed that the higher level of phosphoric acid in the recipe, thus its lower final pH, helps in protonating the last dissociated residues of Asp and Glu in the polypeptide coils, thus greatly favoring ionic anchoring of dye molecules to the protein moiety. Such a binding, though, must be followed by considerable hydrophobic association with the aromatic and hydrophobic residues along the polypeptide backbone.     

On the limiting electrophoretic mobility of a highly charged colloidal particle in an electrolyte solution

The electrophoretic mobility of a spherical charged colloidal particle in an electrolyte solution with large kappaa (where kappa= Debye-Hückel parameter and a= particle radius) tends to a nonzero constant value in the limit of high zeta potential. It is demonstrated that this is caused by the fact that counterions condensed near the highly charged particle surface do not contribute to the electrophoretic mobility and only co-ions govern the mobility. A simple method to derive the limiting electrophoretic mobility expression is given. The present method is also applied to cylindrical particles, showing that the leading term of the limiting electrophoretic mobility of a cylindrical particle in a transverse field with large kappaa is the same as that of a spherical particle. The electrophoretic mobility of a cylindrical particle in a tangential field, on the other hand, is proportional to the particle zeta potential and does not exhibit a constant limiting value for high zeta potentials.     

氯酸钾氧化酸性铬深蓝催化光度法测定痕量钒

基于硫酸介质中,酒石酸作活化剂,钒催化氯酸钾氧化酸性铬深蓝,建立了催化光度法测定痕量钒的新方法并讨论了其动力学条件。灵敏度1.47×10~(11)g/ml,测定范围0～9ng/ml。方法简便快速,用于水及食品中痕量钒的测定,结果满意。     

A Diketopyrrolopyrrole-Based Dimer as a Blue Pigment

1,4-Diketopyrrolo[3,4-c]pyrroles (DPPs) constitute a class of hydrogen-bonded pigments covering a color range from yellow–orange to dark violet. We report facile dimerization of a Boc-substituted 3,6-dithienyl-DPP. The formed dimer shows brilliantly blue color as a result of the expansion of the chromophore. The soluble dimer acts as latent pigment and is converted to the corresponding pigment either via thermocleavage or acidic deprotection of the Boc groups. The synthesized pigment is characterized by high migrational stability in a polymer matrix and a clear blue color.     

Electrochemical Investigation of Heterogeneous Affinity Behaviour of Methylene Blue and G-quadruplex

The heterogeneous binding behaviour between methylene blue (MB) and G-quadruplex, one kind of single-stranded (ss) DNA with specific guanine tetrads, has been thoroughly studied via electrochemical techniques. Positively charged MB interacted electrostatically with both G-quadruplex and normal ssDNA but the binding and dissociation kinetics between them were significantly different. Compared with ssDNA, G-quadruplex had a slower binding rate constant and dissociation rate constant with MB since there existed other different binding mechanisms between G-quadruplex and MB besides electrostatic interaction. This work might provide valuable information in the design and development of DNA sensors.     

Cyanobacterial chlorophyll as a sensitizer for colloidal TiO2

Chlorophyll has been extracted from cyanobacteria. The adsorption of chlorophyll on the surface of colloidal TiO(2) through electrostatic interaction was observed. The apparent association constant (K(app)) of chlorophyll-TiO(2) obtained from absorption spectra is 3.78x10(4)M(-1). The K(app) value of chlorophyll-TiO(2) as determined from fluorescence spectra is 1.81x10(4)M(-1), which matches well with that determined from the absorption spectra changes. These data indicate that there is an interaction between chlorophyll and colloidal TiO(2) nanoparticle surface. The dynamics of photoinduced electron transfer from chlorophyll to the conduction band of colloidal TiO(2) nanoparticle has been observed and the mechanism of electron transfer has been confirmed by the calculation of free energy change (DeltaG(et)) by applying Rehm-Weller equation as well as energy level diagram. Lifetime measurements gave the rate constant (k(et)) for electron injection from the excited state chlorophyll into the conduction band of TiO(2) is 4.2x10(8)s(-1).     

Zein as a source of functional colloidal nano- and microstructures

The application of colloidal particles from natural materials for purposes ranging from the delivery of bioactives to interfacial stabilisation and bulk structuring have recently gained a lot of interest for applications in the field of fast moving consumer goods, nutraceuticals, agricultural formulations and medicine. Zein-a proline rich water insoluble protein obtained from natural and sustainable source has been recently researched to generate colloidal structures that can find a wide range of applications. In this paper, we review the recent progress in the preparation of colloidal structures and their further application as functional materials in the field of delivery of functional ingredients and structuring of bulk phases and interfaces.