Dansyl, Dns

One of the first examples describing the idea of fluorescence signal amplification in NPs was reported by Montalti et al. [197]. In an early work, silicaNPs were covered with a layer of dansyl (Dns) moieties and were evaluated for their pH response. Photophysical studies indicated that protonation had a dramatic effect on the fluorescence of the NPs, leading to the quenching of both, the protonated Dns and... 

Many N-amino add derivatives have been proposed to this purpose and the most commonly studied by TLC are 2,4-dinitrophenyl (DNP)- and 5-dimethylamino-l-naphthalene-sulfonyl (Dansyl,Dns)-amino adds, and 3-phenyl-2-thiohydantoins (PTH-amino adds). 

Figure 6.37. Dansyl-labeled cycbidcxtrin. Also shown is a schemade of the effects of l-adain nUnol, represented by the black ball, on the location of the dansyl (DNS) grtwp. Revised from Ref. 89.

Dansyl (Dns)-amino acids [Figure 11.15(b)] were separated using reversed-phase liquid chromatography with either metal chelates or (5)-histidine additives. The separation efficiency of derivatized diastereomers has been studied using many selective reagents. ... 

The identification of N-terminal amino acids in peptides and proteins is of considerable practical importance because it constitutes an essential step in the process of sequential analysis of peptide structures. Many N-amino acid derivatives have been proposed for this purpose and the ones most commonly studied by TLC are 2,4-dinitrophenyl (DNP)-and 5-dimethylaminonaphthalene-l-sulfonyl (dansyl, Dns)-amino acids, and 3-phenyl-2-thiohydantoins (PTH-amino acids). Recently, 4-(dimethylamino)azobenzaie-4/-isothio-cyanate (DABITC) and phenyl-isothiocyanate (PITC) have also been investigated as derivatizing agents of amino acids. 

In Reference 55, several positively charged CDs, i.e., 6 mono-6-alkylimidazolium p-CDs, 2 mono-6-aIkylammo-nium p-CDs, mono-6-amino-p-CD hydrochloride, and 2-amino-p-CD hydrochloride, and mono-6-substituted a- and y-CDs with alkylimidazolium, alkylammonium, and amino moieties, were successfully applied for the separation of 14 derivatized AAs, 8 hydroxyl acids, and 14 carboxyl acids. Phosphate buffers and acetate buffers both with a concentration of 50 mM, were used for basic and acidic compounds, respectively. The optimum buffer pH varied for the different CDs. For example, 2-amino-p-CD hydrochloride (20-mM BGE) could baseline resolve a mixture of 8 dansyl (Dns)-amino and hydroxyl acids, i.e., Dns-DL-a-caprylic acid, Dns-DL-a-aminobutyric acid, Dns-oL-glutamic acid,... 

Rizkov et al. ° used L-and D- 3-amino alcohols for the enantioseparation of, among others, dansylated (Dns) AAs by CZE in a low-molecular-weight organogel (LMOG)-filled capillary. This LMOG is a fibrillar gel of trans-(15,2S)-l,2-bis-(dodecylamido) cyclohexane in MeOH. Bare fused-silica capillaries with an i.d. of 100 fim and a total length of 60.0 cm (52.0 cm effective length) were used. The BGE contained 10-mM 3-amino alcohol and 5-mM cupric acetate monohydrate in MeOH with pH 5. The selector copper-valinol (2 1) performed best compared... 

Although the chromophore-modified CD adopts several conformations in aqueous solution, we can explain the conformational equilibrium by the simplified two-state model, consisting of a self-inclusion state and non-self-inclu-sion state (Fig. 3). Although the conformational interconversion occurs too rapidly to be followed by NMR spectroscopy, the analysis of the fluorescence decay of the fluorophore pendant can provide useful information with respect to the conformational features, as the fluorescence lifetimes of many fluorophores are in the range of a measurable timescale (nanoseconds). The dansyl (DNS) moiety is sensitive to the hydrophobicity around its local environment and has... 

All proteinogenic amino acids, with the only exception of proline, were resolved into their enantiomers as dansyl (DNS) derivatives by eluting with buffer A, with or without 4 mM DPA and 1 mM cupric acetate. The use of buffer A with the copper (II) complex of the chiral selector as eluent was necessary to maintain a concentration of the chiral complex on the surface of silanized silica gel sufficiently high to resolve some specific racemates. This suggested that the copper (II)-DPA complex was less adsorbed by silanized silica gel than copper (II)-hydroxydodecylproline complex proposed by Gunther et al. [3]. Detection was effected with UV light (360 nm) and dansyl amino acids appeared as fluorescent yellow-green spots. 

Retention (hRfi, h/ f2) and Resolution (a, R ) Data for Resolved Racemic Dansyl (Dns)-Amino Acids and Verapamil on Silica Gel Plates Coated (CCSP) with Erythromycin (A) and Vancomycin (B)... 

An excellent discussion on derivatization techniques has been given by Lawrence (17) including a detailed discussion on pre-column derivatization (18) and post-column derivatization (19). Probably, the more popular procedures are those that produce fluorescing derivatives to improve detector sensitivity. One of the more commonly used reagents is dansyl chloride (20), 5-dimethylamino-naphthalene-1-sulphonyl chloride (sometimes called DNS-chloride or DNS-C1). The reagent reacts with phenols and primary and secondary amines under slightly basic conditions forming sulphonate esters or sulphonamides. 

Dansyl chloride Dns-Cl Primary and secondary amines, phenols, euaino acids and imidazoles 550, 617-619... 

Figure 14 Representative fluorescence derivatization reagents used for PO-CL detection. DNS-CI, dansyl chloride DBD-F, 4-(A,A-dimethylaminosulphonyl-7-fluoro-2,l, 3-benzoxadiazole NDA, naphthalene-2,3-dicarboxaldehyde DNS-H, dansyl hydrazine DBD-H, 4-(iV,iV-dimethylaminosulphonyl-7-hydrazino-2,l,3-benzoxadiazole).

Draw a picture in your notebook of the polyamide thin-layer plate exposed under UV light after each of the two or three solvent developments. These pictures should look similar to Figure E2.7. Three fluorescent areas should be evident after solvent 2 however, better separation is achieved by solvent 3. A blue fluorescent area at the bottom of the plate is dansic acid (DNS-OH), which is a hydrolysis product of dansyl chloride. A blue-green fluorescent spot about one-third to one-half up the plate is dansyl amide (DNS-NH2), which is produced by reaction of dansyl chloride with ammonia. A third spot, which usually fluoresces green, is the dansyl derivative of the NH2-terminus amino acid. Note the positions of the standard dansyl amino acids and compare with the unknown. What is the identity of the NH2-terminal amino acid Are any other fluorescent spots evident on the plate Using polarity or nonpolarity, try to explain the position of each molecule on the thin-layer plate. 

DMQPH = 6,7-dimethoxy-l-methyl-2(177j-quinoxalinone-3-proprionylcarboxylic acid hydrazide, HCPI = 2-(4-hydrazinocarbonylphenyl)-4,5-diphenyli-midazole, DBPM = 7V-[4 (6 dimethylamino-2-benzofuranyl)phenyl]maleimide, DNS-H = dansyl hydrazine, DBD H = 4 (AA -dimethylaminosulphonyl) 7-hydrazino-2,l,3-benzoxadiazole, DETBA = l,3-diethyl-2-thiobarbituric acid, DCIA = 7-dimethylamino-3- 4-[(iodoacetyl)amino]phenyl -4-methylcou marin, m-CED = 1, 2-bjs(3-chlorophenyl)ethylenediamine. 

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. 

TLC separation of DNS-amines is usually made on layers of silica gel with solvents covering a range of polarity, e.g., chloroform, ethyl acetate, diisopropyl ether and methanol. Seiler and Wiechmann [97] developed 30 solvent systems for the separation of DNS derivatives of over 100 biogenic amines on TLC plates of silica gel. The selective reaction of DNS-C1 with the amino group of catecholamines has been examined [98]. The drugs dopamine, norepinephrine and epinephrine are adsorbed on alumina which protects their hydroxyl groups from dansylation. The N-dansylated compounds are separated with benzene-dioxane-acetic acid (90 25 4) on layers of silica gel. 

Chlorpromazine and many of its metabolites react with DNS-C1 to form fluorescent derivatives [135,136]. The reaction involves dansylation of the amino and/or the phenol groups of the molecules. The metabolites which form DNS derivatives are listed in Table 4.24. 

Fig. 4.69. Reaction scheme for the formation of DNS derivatives of carbamate and urea herbicides (example, Linuron). 1 = Hydrolysis 2 dansylation of the aniline moiety.

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