Dansyl chloride method

B 1. Study the details of the Edman and dansyl chloride methods for amino-terminal analysis of proteins. Discuss the advantages and disadvantages of each method. 

Polypeptide chain end-group analysis, (a) Amino-terminal group identification. A more sensitive method, the dansyl chloride method, is described in Methods of Biochemical Analysis 3B. (b) Carboxyl-terminal group identification. Identification of this amino acid is considerably more difficult. 

Gray, W. R., End group analysis using dansyl chloride. Methods. Enzymol. 25 121-138, 1972. This volume of Methods in Enzymology contains several chapters on end-group analysis. 

The dansyl chloride method provides an alternative to the Sanger method for N-terminal amino acid determination. Because it is considerably more sensitive than the Sanger method, it has become the method of choice. The reaction is... 

Gray, R. "Sequence Analysis with Dansyl Chloride", In "Methods In Enzymology", p. 333, Vol. XXV, "Enzyme Structure, Part B", C. H. W. Hlrs and S. N. Tlmasheff, Editors, Academic Press, New York, 1972. 

The Af-dansylated amino acid (e.g., glycine, leucine, proline) exhibits a yellow fluorescence. The sensitivity of detection for amino acids by this method is about 10 9 mol of amino acid. The advantage of this prodecure in comparison with that using dansyl chloride is the fact that it can be carried out in homogenous aqueous solution without addition of a cosolvent. 191... 

Amines are another important group of analytes. Mellbin and Smith [72] compared three different fluorescent reagents, dansyl chloride, 4-chloro-7-nitrobenzo-1,2,5-oxadiazole, and o-phthaldialdehyde, for derivatization of alkylamines. The dansyl tag was found to be the most effective. Hamachi et al. [73] described the application of an HPLC-POCL method for determination of a fluorescent derivative of the synthetic peptide ebiratide. Another comparative study was done by Kwakman et al. [74], where naphthalene-2,3-dialdehyde and anthracene-2,3-dial-dehyde were evaluated as precolumn labeling agents for primary amines. The anthracene-2,3-dialdehyde derivatives were not stable, especially in the presence of hydrogen peroxide, and the POCL detection of these derivatives was therefore... 

Most HPLC instruments monitor sample elution via ultraviolet (UV) light absorption, so the technique is most useful for molecules that absorb UV. Pure amino acids generally do not absorb UV therefore, they normally must be chemically derivatized (structurally altered) before HPLC analysis is possible. The need to derivatize increases the complexity of the methods. Examples of derivatizing agents include o-phthaldehyde, dansyl chloride, and phenylisothiocyanate. Peptides, proteins, amino acids cleaved from polypeptide chains, nucleotides, and nucleic acid fragments all absorb UV, so derivatization is not required for these molecules. 

Dansyl chloride (dimethylaminonaphthalene-5-sulphonyl chloride) will react with free amino groups in alkaline solution (pH 9.5-10.5) to form strongly fluorescent derivatives (Figure 10.14). This method can also be used in combination with chromatographic procedures for amino acid identification in a similar manner to the FDNB reagent but shows an approximately 100-fold increase in sensitivity. This makes it applicable to less than 1 nmol of material and more amenable for use with very small amounts of amino acids liberated after hydrolysis of peptides. The dansyl amino acids are also very resistant to hydrolysis and they can be located easily after chromatographic separation by viewing under an ultraviolet lamp see Procedure 10.1. 

Dansyl chloride (5-dimethylaminonaphthlene-l-sulphonyl chloride) and the related dabsyl chloride (4-dimethyl-aminoazobenzene-4 -sulphonyl chloride) have also been used. Sensitivity of the latter method is poor and both suffer problems from interference with reagent excess. 

A comparative study was made of the RP-HPLC analysis of free amino acids in physiological concentrations in biological fluids, with pre-column derivatization by one of the four major reagents o-phthalaldehyde (73) in the presence of 2-mercaptoethanol, 9-fluorenylmethyl chloroformate (90), dansyl chloride (92) and phenyl isothiocyanate (97, R = Ph) (these reagents are discussed separately below). Duration of the analysis was 13-40 min. Sensitivity with the latter reagent was inferior to the other three however, its use is convenient in clinical analysis, where sample availability is rarely a problem. The derivatives of 73 were unstable and required automatized derivatization lines. Only 92 allowed reliable quantation of cystine. All four HPLC methods compared favorably with the conventional ion-exchange amino acid analysis188. 

Ab initio SCRF/MO methods have been applied to the hydrolysis and methanol-ysis of methanesulfonyl chloride (334). ° The aminolysis by aromatic amines of sulfonyl and acyl chlorides has been examined in terms of solvent parameters, the former being the more solvent-dependent process.Solvent effects on the reactions of dansyl chloride (335) with substituted pyridines in MeOH-MeCN were studied using two parameters of Taft s solvatochromatic correlation and four parameters of the Kirkwood-Onsager, Parker, Marcus and Hildebrand equations. MeCN solvent molecules accelerate charge separation of the reactants and stabilize the transition... 

Nelson et al. [60] published a method for estrone and estradiol measurement using the dansyl derivatives with analysis by APCI. After adding di-estrone and ck-estradiol to 0.5 ml serum, the steroids are extracted with 6 ml methylene chloride. After drying the solvent, 50 pi of sodium bicarbonate and (100 mmol/1, pH 10.5) 50 pi of dansyl chloride (1 g/1) are added. The samples can be injected after heating at 60 C for 1 min. 

A related and more sensitive method makes a sulfonamide of the terminal NH2 group with a reagent called dansyl chloride. As with 2,4-dinitrofluorobenzene, the peptide must be destroyed by hydrolysis to release the N-sulfonated amino acid, which can be identified spectroscopically in microgram amounts ... 

Dansylation is often used for the determination of free and N-terminal amino acids. Dansyl chloride (5-dimethylaminonaphthalene-l-sulfonyl chloride, DNS-C1) reacts with the amino substituent of amino acids to form highly fluorescent derivatives [75,76]. The method is particularly useful for the analysis of trace components due to the high sensitivity of the products. The derivatives are usually separated by TLC on various types of layers. Separations of DNS-amino acids by flat-bed techniques have been reviewed [77]. Separations by column chromatography have been examined on polyamide [78] and Amberlite IRC-SO [79]. Although many variations of the dansylation reaction with amino acids have been reported, the one described below [77] appears to be the most common. 

Comparison with in vivo procedures Although the FDNB procedure proved to be a suitable reference method, there is no doubt that all methods should be ultimately compared to in vivo procedures. For this reason selected samples were also analyzed by plasma amino acid and digestibility methods. Preliminary results ( Table II ) show that plasma lysine results correlated very well with results for lysine digestibility and FDNB lysine ( r =0.95 ), reasonably well with those for dansyl chloride lysine, succinic anhydride reactive lysine and dye binding lysine, but poorly with total lysine. Although the absolute values were in many cases very different, it is apparent that all methods except total lysine can be used to at least indicate the extent of lysine damage. 

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