Fluorescent 2-naphthol

Premchandran RS, Banerjee S, Wu XK, John VT, McPherson GL, Ayyagari M, Kaplan D (1996) Enzymatic synthesis of fluorescent naphthol-based polymers. Macromolecules 29(20) 6452-6460... 

Fluorescent naphthol-based polymers were prepared by HRP-catalyzed polymerization of 2-naphthol in AOT/isooctane reverse micelles to give the polymer microspheres.31 The precipitated polymer was soluble in a range of polar and nonpolar organic solvents and possessed quinonoid structure. The reverse micellar system induced the peroxidase-catalyzed copolymerization of p-hydroxythiophenol and />ethylphenol, yielding the thiol-containing polyphenol particles.32 The attachment of CdS to the particles gave the CdS—polymer nanocomposite showing fluorescence characteristics. 

Colorations with resorcinol and naphthol. Dissolve about 0-2 g. of resorcinol in I ml. of 30% aqueous NaOH solution, add i ml. of chloroform and warm gently the aqueous layer turns red and shows a slight fluorescence. 

Bromo-2-pyridyla2o)-5-diethylamiQophenol (5-Br-PADAP) is a very sensitive reagent for certain metals and methods for cobalt have been developed (23). Nitroso-naphthol is an effective precipitant for cobalt(III) and is used in its gravimetric determination (24,25). Atomic absorption spectroscopy (26,27), x-ray fluorescence, polarography, and atomic emission spectroscopy are specific and sensitive methods for trace level cobalt analysis (see... 

Purified by recrystn from xylene. Gives yellow-green fluorescent solutions at pH 8.2-9.5, [IR Schnopper et al. Anal Chem 31 1542 7959.] With AcCl naphthol AS-D acetate is obtained m 168-169°, and with... 

The reaction course has not been elucidated (cf. also sodium hydroxide reagent). Hydrolyzation reactions and aromatizations are probably primarily responsible for the formation of colored and fluorescent derivatives. Substituted nitrophenols - e.g. the thiophosphate insecticides — can probably be hydrolyzed to yellow-colored nitro-phenolate anions by sodium hydroxide or possibly react to yield yellow Meisenheimer complexes. Naphthol derivatives with a tendency to form radicals, e.g. 2-naphthyl benzoate, react with hydrolysis to yield violet-colored mesomerically stabilized 1,2-naph-thalenediol radicals. 

In addition, there is a large number of studies involving aromatic alcohols such as phenol [166] or naphthol, which have in part been reviewed before [21], These include time-resolved studies [21], proton transfer models [181], and intermolecular vibrations via dispersed fluorescence [182]. Such doubleresonance and more recently even triple-resonance studies [183] provide important frequency- and time-domain insights into the dynamics of aromatic alcohols, which are not yet possible for aliphatic alcohols. 

If pK is greater than 2, a plateau is observed for the relative fluorescence quantum yield of the acidic form and the basic form for pH ranging from pK to pK (Figure 4.10A) because of the absence of diffusional recombination. In fact, Eqs (4.59) and (4.60) which are relevant to this case show that /HA and IA- are constants. A typical example is 2-naphthol (pK = 9.3, pK = 2.8). 

The aqueous cores of reverse micelles are of particular interest because of their analogy with the water pockets in bioaggregates and the active sites of enzymes. Moreover, enzymes solubilized in reverse micelles can exhibit an enhanced catalytic efficiency. Figure B4.3.1 shows a reverse micelle of bis(2-ethylhexyl)sulfosuccinate (AOT) in heptane with three naphthalenic fluorescent probes whose excited-state pK values are much lower than the ground-state pK (see Table 4.4) 2-naphthol (NOH), sodium 2-naphthol sulfonate (NSOH), potassium 2-naphthol-6,8-disulfonate (NSOH). The spectra and the rate constants for deprotonation and back-recombination (determined by time-resolved experiments) provide information on the location of the probes and the corresponding ability of their microenvironment to accept a proton , (i) NDSOH is located around the center of the water pool, and at water contents w = [H20]/[A0T] >... 

The crucial requirement of excited-state proton transfer (ESPT) is suggested by the failure of 1-naphthyl methyl ether to undergo self-nitrosation under similar photolysis conditions. The ESPT is further established by quenching of the photonitrosation as well as 1-naphthol fluorescence by general bases, such as water and triethylamine, with comparable quenching rate constants and quantum yield. ESPT shows the significance in relation to the requirement of acid in photolysis of nitrosamines and acid association is a photolabile species. 

The pK of tyrosine explains the absence of measurable excited-state proton transfer in water. The pK is the negative logarithm of the ratio of the deprotonation and the bimolecular reprotonation rates. Since reprotonation is diffusion-controlled, this rate will be the same for tyrosine and 2-naphthol. The difference of nearly two in their respective pK values means that the excited-state deprotonation rate of tyrosine is nearly two orders of magnitude slower than that of 2-naphthol.(26) This means that the rate of excited-state proton transfer by tyrosine to water is on the order of 105s 1. With a fluorescence lifetime near 3 ns for tyrosine, the combined rates for radiative and nonradiative processes approach 109s-1. Thus, the proton transfer reaction is too slow to compete effectively with the other deactivation pathways. 

W. R Laws and L. Brand, Analysis of two-state excited-state reactions. The fluorescence decay of 2-naphthol, J. Phys. Chem. 83, 795-802 (1979). 

Fig. 16.20 Fluorescence quenching (FQ) of 1-naphthol in the presence of HA as a function of pH and reaction time (1-naphthol = 8pmol LHA = 11 ppm C ionic strength of O.IM LiQ) F and F denote fluorescence intensities in the absence and in the presence of the quencher (HA), respectively. Reprinted with permission from Karthikeyan KG, Chorover J (2000) Effects of solution chemistry on the oxidative transformation of 1-naphtol and its complexation with humic acid. Environ Sci Technol 34 2939-2946. Copyright 2000 American Chemical Society...

Naphthol AS-D (3-hydroxy-2-naphthoic-o-toluide) [135-61-5] M 277.3, m 1196-198 . Purified by recrystn from xylene. Gives yellow-green fluorescent solutions at pH 8.2-9.5, [IR Schnopper et al. AC 31 1542 1959]. With AcCl naphthol AS-D acetate is obtained m 168-169 , and with chloroacetyl chloride naphthol AS-D-chloroacetate is obtained [Moloney et al. J His toe hem Cytochem 8 200 1960 Burstone Arch Pathology 63 164 1957],... 

Naphthol AS-acetate (3-acetoxynaphthoic acid anilide] [1163-67-3] M 305.3, m 152°, 160°. Recrystd from hot MeOH and dried in vacuo over P2O5. It is slightly soluble in AcOH, EtOH, CHCI3 or CgHg. It is a fluorogenic substrate for albumin esterase activity. [Chen and Scott Analyt Letters 17 857 1984], At kgx 320nm it had fluorescence at 500nm. [Brass and Sommer B 61 1000 1928]. 

Morra, M. J., Corapcioglu, M. O., von Wandruszka, R. M. A., Marshall, D. B. Topper, K. (1990). Fluorescence quenching and polarization studies of naphthalene and 1-naphthol interaction with humic acid. Soil Science Society of America Journal, 54, 1283—9. 

For 0-naphtholate at 25 °C. the quantum yield of fluorescence is about 0.2 of solvated electron formation about 0.1. This solvated electron formation is a major factor competing with fluorescence for that part of the original quantum energy reaching the lowest singlet state. As previously stated (37), it may be a major factor leading to fluorescence quenching in polar solvents, and particularly in aqueous solutions. 

The addition of electrons to an aromatic system can be accomplished by adding electron-donating groups or by changing the pH of the solution. The effect of pH on the fluorescence of 1-naphthol is well known. In acidic or neutral media the molecule exists as the form 1 ... 

In a basic medium, structures 2-4 exist. The fluorescence maxima of 1-naphthol shift from 306 (excitation) and 362 nm (emission) in acidic or neutral solution to 338 (excitation) and 462 nm (emission) in base [29]. The increase in wavelength is attributed to the naphthoquinone structures of the ionized forms. These structures are supported by the fact that other stable naphthoquinone compounds exhibit, in neutral solution, almost identical fluorescence spectra as 1-naphthol in basic media. Menadione (2-methyl-1,4-naphthoquinone), for example, has excitation and emission maxima at 335 and 480 nm, respectively, in 95% ethanol [30]. 

Most of the older methods of fluorimetric analysis of pesticides involved hydrolysis to form fluorescent anions. Co-ral (coumaphos) [147] was hydrolyzed in alkali to the hydroxybenzopyran, which was subsequently determined by means of its fluorescence. Guthion (azinphosmethyl) was hydrolyzed to anthranilic acid for fluorimetric analysis [148,149]. A method was developed [150] for Maretin (N-hydroxynaphthalimide diethyl phosphate) in fat and meat which involved hydrolysis in 0.5 M methanolic sodium hydroxide followed by determination of the fluorescence of the liberated naphthalimide moiety. Carbaryl (1-naphthyl N-methylcarbamate) and its metabolites have been determined by a number of workers using base hydrolysis and the fluorescence of the resulting naphtholate anion [151-153]. Nanogram quantities of the naphtholate anion could be detected. Zectran (4-dimethylamino-3,5-xylyl N-methylcarbamate) has been determined by the fluorescence of its hydrolysis product [154]. The fluorescence behaviour of other carbamate insecticides in neutral and basic media has been reported [155]. Gibberellin spray used on cherries has been determined fluorimetrically after treatment with strong acid [156]. Benomyl (methyl N-[l-(butylcarbamoyl)-2-benzimidazolyl]carbamate) has been analyzed by fluorimetry after hydrolysis to 2-aminobenzimidazole [157]. 

---