Selenium, colloidal

Occurrence, Extraction and Purification—The Allotropy of Selenium—Colloidal Selenium—General Physical Properties of Selenium—Chemical Properties— Applications of Element—Physiological Action—Atomic Woighl—Valency— Constitution of Selenium Molecule—Detection and Estimation of Selenium. 

SEBACIC ACID, coapd. with 3-(2-AMINOETHYL)INDOL-5-OL, ACETATE (1 2 2) SELENIUM (COLLOIDAL)... 

Mechanisms of electrochemical and photoelectrochemical deposition of metal selenide clusters (Me = Pb, Cd, Zn, Bi, In) onto the surface as well as into the selenium films have been studied. These clusters are formed as a result of underpotential and overpotential deposition of the metals onto Se. Photoinduced underpotential deposition of Bi onto Se was used to cover selenium colloidal particles with BiiSes clusters. The PbSe and Bi2Sc3 clusters modify the Se surface and form electronic surface states in the Se bandgap, thus promoting electron exchange processes between the valence band and redox species in solution and the rise of the subbandgap photocurrent. 

Colloidal manganese. See Manganese Colloidal mercury. See Mercury Colloidal selenium. See Selenium Colloidal silica. See Silica, colloidal Silica, fumed... 

Adsorb monoclonal antibody against biotin onto colloidal selenium by mixing 5 pL of goat antibiotin antibody (4.6 mg/mL) with 0.4 mL of phosphate buffered saline and then adding 5 mL of the above selenium colloid. 

Place the bottom of the nitrocellulose strips in this incubation solution and allow the selenium colloid-antibiotin oligonucleotide complex to migrate up the strip (approx 5 min). Only LCR products that contain both fluorescein and biotin will be captured at the antifluorescein zone and will be indicated by a red color. 

This treatment converts the selenium from the red, colloidal form into the more easily filterable black modification. 

Colloidal sulfur (selenium) can be produced readily from the disproportionation of aqueous thiosulfate (selenosulfate) with dilute acids ... 

When colloidal selenium was heated with mercuric trifluoroacetate or silver trifluoroacetate, bis(trifluoromethyl)diselenide was formed (43). Later work with selenium/silver carboxylate, RC02Ag (R = CF3, C2F5, or C3F7), mixtures at 280° C in a vacuum produced a mixture of the bis(perfluoroalkyl)selenide and the bis(perfluoroalkyl)diselenide (44). Formation of a polyselenium trifluoroacetate, which decarboxylates to produce the trifluoromethylselenides, was the proposed mechanism for R = CF3 (44). However, silver trifluoroacetate is a source of trifluoromethyl radicals when heated above 260° C (21), hence the trifluoromethylselenides may be formed by reaction of trifluoromethyl radicals with selenium, as in the reaction of CF3I with selenium [Eq. (34)] (45). 

Selenium Adsorption colloid flotation Spectrophotometry of methylene blue complex - [517,546]... 

Selenium, in the form of selenate or selenite, is toxic to D. desulfuricans (Tomei et al. 1995) and Wolinella succinogenes (Tomei et al. 1992) at elevated levels. At sublethal levels of 0.1-1. OmM selenite or 10 mM selenate, minimal levels of growth is observed with both D. desulfuricans and Wolinella succinogenes. With both selenate and selenite, colloidal elemental selenium (Se°) is produced inside the cell and released into the culture fluid after cell death. This reduction of Se(VI) and Se(IV) by these anaerobes is not coupled to growth and proceeds by mechanisms that have not yet been identified. Selenite and selenate reduction with formation of elemental selenium by these nonrespiratory processes serve to detoxify the environment for future bacteria and may be important for the geochemical cycle of selenium. 

Hayes, KF. Papelis, C. Leckie, J.O. (1988) Modeling ionic strength Effects on anion adsorption at hydrous oxide/solution interfaces. J. Colloid Interface Sd. 78 717—726 Hayes, KF. Roe, A.L. Brown, G.E. Hodgson, KO. Leckie, J.O. Parks, G.A. (1987) In-situ X-ray absorption study of surface complexes Selenium oxyanions on a-FeOOH. Sdence 238 783-786... 

Selenium is readily obtained in the form of a colloidal solution, red by reflected light and blue by transmitted light. Such solutions were first obtained by Schulze 3 by the reduction of selenium dioxide in dilute aqueous solution by means of the requisite quantity of sulphur dioxide ... 

When superheated selenium vapour is passed into air-free water, colloidal solutions are formed which are usually rose-coloured, but at first of a blue tint and cloudy. Under the most favourable conditions clear yellowish-red or deep red sols may be obtained,4 the former being the more highly dispersed. The blue sols after dialysis are extremely stable, but non-dialysed sols decompose after a few days, selenious acid being detected except in the yellowish-red sols. The dialysed sols may be frozen to an almost colourless ice which at the ordinary temperature thaws and decomposes. The sols are negative and are readily coagulated by the addition of chlorides. 

Caoutchouc mixed and warmed with finely divided black amorphous selenium assumes the dark red colour of colloidal selenium. This is the first observed case of the direct reduction of an element to the colloidal condition by intimate contact with a colloid.5 The effect is probably due in large measure to stresses produced and heat generated during the mechanical working of the mixture. The presence of another colloidal substance such as albumen, gum arabic or the sodium salt of protalbic acid, renders the colloidal selenium more stable, so that it may even be separated in a solid state without losing its power of again yielding a colloidal solution on the addition of water.6... 

When warmed with neutral organic substances selenium frequently passes into colloidal solution and remains in this condition even after solidification of the solvent. Even when the solid suspension in anthracene or phthalic acid is melted the selenium does not pass into the grey crystalline condition although the points of fusion of these solvents are higher than the transformation temperature. The higher the temperature reached in the preparation of these solutions and the slower the cooling the smaller are the selenium particles.7... 

Selenium prepared by the reduction of selenious acid with sodium or ammonium hydrogen sulphite forms colloidal solutions, that precipitated... 

Very stable colloidal solutions of selenium may be prepared by the regulated action of concentrated hydrazine hydrate solution on selenium dioxide or grey crystalline selenium and subsequent dilution of the solutions with water and purification by dialysis. According to the degree of dispersion the colour of the solutions varies from intense yellow to blood red. These sols are completely irreversible. The dilute solutions are stable at the boiling-point, but are readily coagulated by barium sulphate. Sodium and potassium carbonates appear to increase the stability of the system. 

Colloidal selenium produced by means of hydrazine hydrate can be frozen to a blue ice which melts with complete coagulation, but the presence in the solution of hydrogen chloride, sodium carbonate or potassium chloride, exerts a protective action which is a maximum at certain definite concentrations.2... 

Stable selenium sols may be obtained by the reducing action of quadrivalent titanium. If a solution of titanium trichloride (1-5 per cent.) is boiled for some time, hydrolysis and oxidation occur on addition of this solution to one of selenium dioxide (0-2 per cent.) reduction to selenium occurs and any unchanged titanic acid, Ti(OII)4, remains in colloidal solution and exerts a protective action.4... 

Tire electrical method, commonly applied to the preparation of colloidal metals, can also be extended to selenium. When an electric discharge is made to pass under pure water between a platinum anode and a cathode prepared by fusing a small piece of selenium on to platinum foil, colloidal selenium is slowly formed.6 When a dilute solution of selenious anhydride is electrolysed using platinum electrodes, a colloidal solution of selenium and a black cathodic deposit of selenium... 

With selenium sols prepared by means of hydrazine hydrate at the ordinary temperature, by pouring into a large volume of water it has been shown that the stability of the colloid depends mainly on the degree of dispersion. An optimum concentration of electrolyte is necessary for the stability of the hydrosols. In the absence of electrolytes the system is quite unstable towards freezing. 

The rate of flocculation of selenium sols by solutions of potassium or barium chloride of various concentrations at temperatures between 15° and 20° C. has been determined.8 Results show that a very high concentration of these electrolytes is necessary for rapid flocculation. Smoluchowski s theory holds when the velocity of flocculation is not far removed from that obtaining when the colloidal particles are totally discharged. The results, however, deviate largely from this theory when the concentrations of the electrolytes are lower.3... 

The adsorption of crystal-violet on colloidal selenium has been studied by van der Grrnten, J. Chim. phys., 1926, 23, 209. 

Still another method for the detection of small quantities of selenious acid consists in adding sodium hydrosulphite, NaaS jO, to the solution,2 which is then neutralised with solid sodium carbonate. The presence of the least trace of selenium causes a red coloration due to the colloidal element. 

---