Chemical Characterization of Pigments

There are two groups of triarylcarbonium pigments inner salts of triphenyl-methane sulfonic acids, and complex salts with heteropolyacids containing phosphorus, tungsten, molybdenum, silicon, or iron. 

Quinophthalone pigments have a polycyclic structure derived from quinaldine and phthalic anhydride. 

A few members of this class have gained commercial recognition for their very good temperature resistance. The main markets for their mostly greenish yellow shades are in the plastics and coatings industries. 

In this chapter, the correlation between chemical constitution and pigment performance is outlined in terms of empirical rules. These correlations essentially apply independently from the application medium for all industrial uses of pigments. 

While the properties of (soluble) dyes are determined almost exclusively by their chemical constitution, application characteristics of pigments—which are by definition insoluble in the medium in which they are applied (see Sec. 1.1) — are largely controlled by their crystalline constitution, i.e., by their physical characteristics. This is discussed in the next chapter. 

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Clark et al, (1969) Clark, J.R. Appleman, D.E. Papike, J.J. Crystal-chemical characterization of clinopyroxenes based on eight new structure refinements Mineralogical Society of America Special Papers 2 (1969) 31-50 Clark et al (1995) Clark, R.J.H. Synthesis, structural characterization and Raman spectroscopy of the inorganic pigments lead tin yellow types I and II and lead antimonate yellow their identification on Medieval paintings and manuscripts Journal of the Chemical Society. Dalton Transactions 16 (1995) 2577-2582 Clarke (1976) Clarke, J. Two Aboriginal rock art pigments from Western Australia their properties, use and durability Studies in Conservation 21 (1976) 134-142, 159-160... 

Campoy, S. et ah. Characterization of an hyperpigmenting mutant of Monascus purpureas IBl identification of two novel pigment chemical structures, Appl. Microbiol. Biotechnol, 70, 488, 2006. 

The chemical composition of the macular yellow pigment was originally characterized by Wald as being a leaf xanthophyll carotenoid (Wald 1945). It took another 40 years until the molecules lutein and zeaxanthin were identified as its main constituents by Bone et al. (1985), and in 1993 the same authors reported that macular zeaxanthin is itself comprised of two stereoisomers, (3/f,37f)-/eaxan(hin and (3/f,3. S )-/eaxan(hin (Bone et al. 1993), this compound will be called (meso)-zeaxanthin throughout this article. These three molecules are often collectively called the macular xanthophylls (for their chemical formulas see Figure 13.2). 

The most common measurements of pigment properties comprise elemental analysis, impurity content, ciystal structure, particle size and shape, particle size distribution, density, and surface area. These parameters are measured so that pigments producers can better contiol production, and set up meaningful physical and chemical pigments specifications. Measurements of these properties are not specific only to pigments. The techniques applied are commonly used to characterize powders and solid materials, and the measuring methods have been standardized in various industries. 

Typical of many members of the botanical plant family Solanaceae, which also includes the tomato, eggplant, and pepper, goji is phytochemically rich, characterized by having both major classes of pigments—carotenoids and polyphenols, identified in laboratory research as having antidisease mechanisms. Goji appears to be one of the richest plant sources of the carotenoid zeaxanthin (closely related in chemical structure to the... 

The example of the polymorphs (allotropes) of carbon illustrate the key messages of this chapter different crystal forms of a substance can possess very different properties and behave as different materials. This concept has important implications in all fields of chemistry associated with the production and commercialization of molecules in the form of crystalline materials (drugs, pigments, agrochemicals and food additives, explosives, etc). The producer, in fact, needs to know not only the exact nature of the material in the production and marketing process, but also its stability with time, the variability of its chemical and physical properties as a function of the crystal form, etc. In some areas, e.g. the pharmaceutical industry, the search for and characterization of crystal forms of the API has become a crucial step for the choice of the best form for formulation, production, stability and for intellectual property protection. 

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