Sialic acid absorption maximum

Polythiophenes functionalized with monosaccharides have been evaluated for their ability to detect the influenza virus and E. coli (Baek et al. 2000). Copolymers of thiophene acetic acid 10 and carbohydrate-modified thiophenes 11 have been prepared via iron(III) chloride mediated polymerization. Addition of influenza virus to a sialic acid containing copolymer resulted in a blue shift of the polymer absorption maximum, resulting in an orange to red chromatic transition. Mannose-containing polythiophenes underwent color changes upon the addition of the lectin ConA or E. coli cells that contain cell surface mannose-binding receptors. A similar biotinylated pol5hhiophene afforded a streptavidin responsive material (Paid and Leclerc 1996). 

Table 1. Colorimetric analysis of the sialic acids. Molar absorption coefficients The molar absorption coefficients are noted for the different sialic acids using the commonly used colorimetric assays. The chromophore was measured at the absorption maximum, noted at the head of each column. Abbreviations of the sialic acids are those used in chapter B, Table 1... 

The method was introduced for sialic acids simultaneously by Warren (1959, 1963) and Aminoff (1959, 1961), and was earlier employed for deoxyribose measurement (Waravdekar and Saslaw 1957, 1959). The two methods are similar and generate the same chromogen which condenses with thiobarbituric acid to give a red pigment with an absorption maximum at 549 nm. Differences in the methods lie in the acidity of the initial periodate oxidation and the extraction of the pigment into cyclohexanone (Warren 1959) or acidic butan-l-ol (Aminoff 1961). 

The other widely employed colorimetric assay is the thiobarbituric acid procedure which is useful for free but not bound sialic acid. Proposed independently by Warren (1959) and Aminoff (1959), the method is based on periodate oxidation of sialic acid to )8-formylpyruvic acid (Figure 11) which then reacts with two moles of 2-thiobarbituric acid to form a chromophore (XLIX) with absorption maximum at 549 nm. The identity of this chromophore was established through synthesis... 

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