Sulfur Compounds as Chromophores

Sulfur dyes are a special class of dyes with regard to both preparation and application, and knowledge of their chemical constitution [1], They are made by heating aromatic or heterocyclic compounds with sulfur or species that release sulfur. Sulfur dyes are classified by method of preparation as sulfur bake, polysulfide bake, and polysulfide melt dyes. Sulfur dyes are not well-defined chemical compounds but mixtures of structurally similar compounds, most of which contain various amounts of both heterocyclic and thiophenolic sulfur. 

Pseudo sulfur dyes are dyes that can be applied in the same way as sulfur dyes but are not prepared by classical sulfurization. 

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Note that palmitic acid does not have a chromophore and would, therefore, not be visible in the UV trace. In general, negative ion APCI and ESI are sensitive to those compounds that can easily deprotonate (e.g., acids and phenols) or attach a negative ion either in the gas phase or in solution, while positive ion APCI and ESI are sensitive to compounds with relatively high proton affinity (e.g., amines and low oxidation state sulfur compounds). As ESI and APCI can be complementary, so positive ion and negative ion can be as well. Consider Fig. 11 which shows a more... 

This chapter is devoted to the chemical chromophores of dyes, but the term chromophore is used here in a somewhat extended manner that also considers dye classes such those as based on cationic, di- and triarylcarbonium, and sulfur compounds, and metal complexes. 

The possibility that this chromophore was a tertiary-alkyl carbonium ion formed in a rapid isomerization of the other ion precursors in the acid solution cannot be correct for the following reasons (a) Cryoscopic data for alcohols in sulfuric acid indicate a process more complex than that expected for ionization of these compounds as secondary bases (236) (b) evolution of SO 2 from sulfuric acid solutions of octene-1 was observed to closely parallel the appearance of the 3000 A band in this system (137), indicating that an oxidation process was involved in forming the chromophore from olefins (c) the lowest electronic transition for the isoelectronic alkylborines occurs in the 2000 A-2200 A region (138). 

Highly nonpolar compounds such as fatty acids, glycerides, alkanes, and some lower terpenoids require simple nonpolar solvent systems (e.g., cyclohexane, hexane, pentane, diethyl ether.hexane mixtures) and may be difficult to detect by UV (i.e., no chromophore) or by spray detection (use charring reagents, e.g., vanillin-sulfuric acid). 

The ability to selectively enhance the modes of the resonant chromophore has fueled the steady development of RR spectroscopy and its transient RR and TR variants as exquisite probes of active site structure and dynamics in a wide range of metalloproteins and enzymes. Inasmuch as this remarkable potential has been more fully realized in the study of heme proteins than for any other class of metalloproteins, it is natural that the illustrative applications presented here be focused on these systems. However, excellent summaries of applications to other metalloproteins and their model compounds are available, including copper proteins,iron-sulfur proteins, and non-heme oxo-iron clusters. ... 

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