Titration fluorimetric

Daniel E, Weber G (1966) Cooperative effects in binding by bovine serum albumin. I. The binding of l-anilino-8-naphthalenesulfonate. Fluorimetric titrations. Biochemistry 5 1893-1900... 

Weller s work [5-7] on the kinetics of ESPT brought out the importance of competition between the rates of deactivation of the excited states and the rates of proton transfer. In cases where the deactivation rates are slow enough for a complete establishment of excited-state equilibrium, fluorimetric titrations provide a method for experimental determinations of pK a. However, it has been realized that for a fairly large number of ESPT molecules, there is a frequent mismatch of pA"f, values obtained from Forster cycle and fluorimetric titrations methods. There are also examples of extended fluorimetric titration curves resulting from low proton availability in the mid-pH region (4-10). Various modifications of the Forster cycle and extensions of Weller s original kinetic considerations have been made from time to time and have been reviewed periodically. Some of the earlier important ones include those by Weller [7] in 1961, Vander Donckt [8] in 1970, Schulman [9] in 1974, and Klopffer [10] in 1977. The review by Ireland and Wyatt [11] contains extensive references of experimental results available in the literature until 1976. 

Fluorimetric titration in water was applied to estimate acidity constants of some well-known antihypertensive drugs containing in their structure an NH-unsubstituted tetrazole fragment governing their acid properties pKa 3.15 (losartan 29), 4.70 (irbesartan 83), and some others <2001MI477>. 

Figure 23. Fluorimetric titration curves of receptor 15 with tripeptides. Excitation wavelength = 320 nm. (CFG = gly-phe-gly CGC = gly-gly-gly GGF = gly-gly-phe GWG = giy-trp-giy). ...

Lahri has reviewed the determination of acidity constants in excited singlet states as well as providing an extensive compilation of pK data. Schulman, Vogt, and Lovell have measured rate constants for the protonation of the excited base and deprotonation of the weak base acridone by fluorimetric titrations in moderately concentrated acid media using bromide ion as a quencher. 

A new instrument for automatic colorimetric and fluorimetric titrations is described. Titrant delivery is automatically stopped at the end point by the use of a microammeter with a built-in relay which stops a motor-driven buret equipped with digital read-out or a gravity driven buret equipped with solenoid control. Monochromatic light is used to excite fluorescence, which is received at 90° by a photomultiplier tube with the microammeter in its anode circuit. Light transmitted through the titration vessel is detected by a barrier-layer photocell, the output of which is fed to the microammeter. 

An ideal fluorimetric titration is one performed in such a manner that a highly f luorescent product is formed... 

Kowalczyk, A. Boens, N. Meuwis, K. Ameloot, M. Potential misevaluation of the ground-state dissociation constant from fluorimetric titrations ... 

Note pK, a = Determined by the dynamic analyses with fluorimetry pK, b = Estimated by the midpoint of fluorimetric titration of RNH pK, c = Estimated by the Forster cycle. 

This conclusion is borne out by other evidence. Fluorimetric alkaline titration gives a simple curve with a pX of 10.3 similar to the first part of the usual spectral titration. The phenolate ion is nonfluorescent. By itself the observed effect could represent quenching by nonfluorescent free tyrosines of fluorescent buried ones. This is particularly unlikely in view of the action of dioxane. The fluorescence of simple tyrosine peptides increases linearly with volume per cent of dioxane in the solvent. 

Support for a concerted model for the yeast enzyme has come from X-ray small angle scattering experiments (162) as well as from hydro-dynamic and optical rotation studies (163, 164). A. volume contraction of about 5% occurs on binding of NAD to the apoenzyme, presumably related to tightening of the tetramer and expulsion of water mojecules. The relation between NAD bound (R) and change of volume (Y) was hyperbolic, in accord with the concerted model. It was lator shown (166) from buoyant density and preferential hydration studies that water is indeed excluded from the yeast enzyme on binding to NAD, such that a volume contraction of about 6% occurs. Furthermore, fluorimetric and calorimetric titrations over the range 6°-40° showed independence of... 

Luminescence titration has extensively been described in several mono-graphs4-6, u 708 Fluorimetric and chemiluminescence indicators are used for the determination of about 30 elements (Fig. 3). 

A new method for the determination sulfldes is based on titration by precipitation and fluorimetric detection of the end-point [102]. The indicator is a dye derived from acridine, the fluorescence of which is statically quenched by sulfide The concentrations measured range between 1 and 10 mM by titration with silver nitrate. 

When monochlorobenzene was Irradiated in 2U ueous solution at 253.7 nm, the formation of phenol was pointed out using fluorimetric measurements ( emission at 295 nm ). The qumtitative titrations were carried out by HPLC. The formation of an equivalent quemtity of hydrogen chloride was demonstrated using potentlometrlc measurements (18). ... 

There are two standard procedures for vitamin C determination in vegetables and legumes. The sample preparation is common to both and involves macer-ation/dilution of the sample in a stabilizing solution, such as 5% metaphosphoric acid or trichloroacetic acid, followed by filtration. The ascorbic acid can then be determined by titration with 2,6-dichloroin-dophenol, where the ascorbic acid reduces the oxidation/reduction indicator dye to a colorless solution or by fluorimetric detection, in which the ascorbic acid is oxidized to dehydroascorbic acid, which then reacts with o-phenylenediamine (1,2-diamino benzene) to produce a fluorophore. The latter method has the advantages that it is suitable for colored solutions and can be used to measure levels of naturally occurring dehydroascorbic acid as well as ascorbic acid. Many other methods are available for determination of vitamin C with the use of LC techniques, currently the subject of much interest. Reversed-phase LC techniques can be used to determine dehydroascorbic acid, ascorbic acid, and their isomers. 

Titration methods. A diluted sample of the fluid is titrated with EDTA in the presence of an indicator dye (e.g. calcein, murexide, Eriochrome Black T) which is bound as a complex to calcium. When all the calcium present has been chelated by EDTA the spectral characteristics of the dye are changed and this can be detected fluorimetrically or colorimetrically. Magnesium interference in some of these methods can be eliminated by titration at an alkaline pH at which magnesium is precipitated as magnesium hydroxide. 

The methods of assay for aneurine in complex galenicals have been developed from the original colorimetric or fluorimetric methods necessary for the small concentrations present in natural sources microbiological methods can also be used for small amounts. For tablets and injection solutions where the amounts are greater Adamson and Handisyde have shown that a gravimetric technique is more accurate. Titration in non-aqueous solvents is also applicable (see p. 792). 

Used as 1% soln. in EtOH for fluorimetric detn. of B used as a metallochromic indicator in titration of Fe(//7) with CyDTA (pH 1-2) photometric detn. of F . 

Bacteriological stain, antioxidant. Used as C H soln. for extraction-photometric detn. of Ge as a 0.05% aq. soln. for photometric detn. of Ga and as an indicator in visual titrations with TiClj soln fluorimetric detn. of S indicator in complexonometric titrimetric detn. of Al. Blackish-green needles (HCl aq.). Sol. hot H2O, H2SO4 si. sol. cold H2O. Blue or violet soln. in H2O, A 602.5 nm. Forms colourless leuco-dye on redn. with Zn/H or Na2S204 derivs. behave similarly. Used as a mixture with Methylene blue, M-00175 (Azure II) for extraction-photometric detn. of Hg(/7), Sb(F). 

Used for extraction-photometric detn. of Ga (CHCI3), Sc (Amax 520 nm, e 15000, Et20) as an aq. soln. as an indicator in complexometric indicator in EDTA titrations (Ca, Mg) photometric detn. of codeine, Nb (Amax 540 nm, e 16000), as 0.1% soln. in Me2CO for extraction-fluorimetric detn. of Al (pH 3.2-5.3, butanol). Orange-red cryst. Sol. H2O, Me2CO, EtOH, CHCI3,... 

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