Texas Red hydrazide

Dabcyl-N-succinimidyl ester aminofluorescein Texas Red hydrazide... 

Texas Red hydrazide is a derivative of Texas Red sulfonyl chloride made by reaction with hydrazine (Invitrogen). The result is a sulfonyl hydrazine group on the No. 5 carbon position of the lower-ring structure of sulforhodamine 101. The intense Texas Red fluorophore has a QY that is inherently higher than either the tetramethylrhodamine or Lissamine rhodamine B derivatives of the basic rhodamine molecule. Texas Red s luminescence is shifted maximally into the red region of the spectrum, and its emission peak only minimally overlaps with that of fluorescein. This makes derivatives of this fluorescent probe among the best choices of labels for use in double-staining techniques. 

Figure 9.20 Texas Red hydrazide reacts with aldehydes to create hydrazone bonds.

Texas Red hydrazide is soluble in DMF and may be dissolved as a concentrated stock solution in this solvent prior to the addition of a small aliquot to an aqueous reaction medium. The solid and all solutions made from it must be protected from light to avoid photo-decomposition. Prepare the stock solution fresh immediately before use. A suggested protocol on the use of this fluorescent probe may be obtained by following the method outlined for fluorescein-5-thi-osemicarbazide in Section 1 of this chapter. Optimization may be necessary to achieve the best level of fluorescent modification (F/P ratio) for a particular application. 

Figure 13.22. Dependence of the Texas Red Hydrazide/Bromothymol Blue phase angle on pH.

The hydrazide derivative can be used to modify aldehyde- or ketone-containing molecules, including cytosine residues using the bisulfite activation procedure described in Chapter 17, Section 2.1. The sulfonyl hydrazine group of Texas Red hydrazide reacts with aldehydes or ketones in target functional groups to form hy-drazone bonds (Fig. 218). Carbohydrates and glycoconjugates can be specifically labeled at the polysaccharide portion if the required aldehydes are first formed by periodate oxidation or another such method (Chapter 1, Section 4.4). 

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