Recent advances in the histochemical staining of heavy metals by means of chelating agents, with special reference to cadmium

Abstract

This review discusses the way of improving the sensitivity and specificity of chelating agents used for the histochemical demonstration of trace amounts of heavy metals in cells and tissues. In the search for a more sensitive and specific agent, various chelating agents have been prepared and their staining properties for various metals examined. Of those developed 1-(2-benzothiazolylazo)-2-naphthol (BTAN), 2-(8-quinolylazo)-4,5-(diphenyl)imidazole (QAI), and 2-(5-bromo-2-pridylazo)-5-(diethylamino)phenol (BrPADAP) were far superior to conventional staining agents in staining sensitivity. This was particularly so for staining cadmium. When modifying chelating agents to increase staining sensitivity, hydrophobicity of the agent molecules, selection of substituent groups, and the position of the groups added to the agent molecules must be taken into consideration. The most frequently mentioned factors in a staining mechanism are complex-tissue attractive forces, and recent studies have made it clear that weak interactions, such as hydrogen bonds and hydrophobic interactions, contribute significantly. The Hansch pi values were a useful indication of the hydrophobicity of metal staining agents. The published values for stability constants of metal complexes were found to be unreliable guides for choosing a masking agent to block interfering metals. The polyphosphates, aminopolycarboxylic acids, and alkylamines were among the most useful masking agents for metal staining from a practical standpoint.

Responses induced by high concentration of cadmium in Phragmites australis roots

“…After several washing steps with distilled water, freehand control and Cd‐treated‐roots sections, taken approximately 100 mm from the apex, were washed with 50 m M borate buffer, pH 10. Samples were incubated for 15 min in each of two masking solutions constituted by TRIS (2‐aminoethyl)amine 0.33 m M and triethylenetetramine 0.66 m M , to prevent a staining effect of other metals such Zn, Cr, Cu, and Pb (Sumi and Suzuki 2002). Sections were then placed in the QAI staining solution for 3 h. This solution was prepared by dissolving 3 mg QAI in 0.5 ml dimethylsulfoxide containing one drop of 0.5 N NaOH and then diluting with 29 ml of distilled water.…”

Selective colorimetric sensing of Co2+ and Cu2+ using 1-(2-pyridylazo)-2-naphthol derivative immobilized polyvinyl alcohol microspheres

“…[16][17][18][19] Azo compounds are wellknown aromatic dyes that have the ability to form colored complexes with heavy metals. [20][21][22][23] Taking advantage of this ability, we employed 4-(2-pyridylazo)-1,3-benzenediol for the detection of Cu 2+ and developed a sensor with excellent detection performance. 24 Sedghi et al 25 prepared a colorimetric sensor based on TiO 2 /poly(acrylamide-co-methylenebisacryl amide) nanocomposites, which could simultaneously detect Hg 2+ and Pb 2+ .…”

Synthesis and characterization of stable thiazolylazo anion radical complexes of ruthenium(II)

“…Among the various azo heterocycles, thiazolylazo compounds have attracted much attention due to their versatile applications in various fields such as analytical chemistry, biological chemistry, the dye industry, and in many high technology areas [40][41][42][43][44][45][46][47]. These thiazolylazo derivatives have been used in spectrophotometric determinations of trace metals in alloys or ores due to their good selectivity and sensitivity over a wide range of pH [40,41].…”

“…They have been used in resin beds for the separation of different metal ions because of the specific affinity of thiazolyl sulfur towards soft or borderline metal ions [42,43]. Further applications include nonlinear optical materials [44,45], structure-function relationships in biologically active molecules [46], and as agents for the histochemical demonstration of trace amounts of heavy metals in cells and tissues [47].…”