Fluorescence titrations

Diederich and coworkers [10] synthesized so-called dendrophanes (Figure 13.6) containing a paracyclophane core embedded in dendritic poly(ether-amide) shells. X-ray crystal-structure analysis indicated that these dendrimers had an open cavity binding site in the center, suitable for the binding of aromatic guests. NMR and fluorescence titration experiments revealed a site specific binding between these dendrimers and 6-(p-toluidino)naphthalene-2-sulfonate (TNS) with a 1 1 association. Also, the fluorescence spectral shift of TNS, which is... 

The conversion of squaraine 19a to the rotaxane 18 D 19a causes a modest red-shift only in both absorption (10 nm) and emission (7 nm) but an approximately threefold decrease in quantum yield. The addition of two triazole rings (dye 19b) did not significantly alter the quantum yield of 17b (Table 4). A macrocycle-induced quenching effect was verified by fluorescence titration experiments adding aliquots of 18 to a solution of squaraine 17b in methylene chloride [58]. Treatment of the 18 d 17b psuedorotaxane system with the tetrabutylammonium salts of chloride, acetate, or benzoate leads to the displacement of squaraine 17b from the macrocyclic cavity and the nearly complete restoration of its fluorescence intensity. The 18-induced quenching of 17b does not support the utility of this system as a bioimaging probe however, the pseudorotaxane system 18 Z> 17b acts as an effective and selective anion sensor with NIR fluorescence. 

Figure 3.22. Fluorescence titrations of anthrylboronic acid 16 (0.75 jiM) at pH 7.4 (20 mAf phosphate buffer) as a function of polyol concentration (+, fructose , t,l,l-tris(hydroxymethyl)ethane a, glucose +, ethylene glycol). All solutions contain 1% (v/v) dimethylsulfoxide (DMSO). (Reproduced from Ref. 26. Copyright 1992 American Chemical Society.)...

For the determination of the dissociation constant in the excited state, several methods have been used the Forster cycle,(109 m) the fluorescence titration curve/113 the triplet-triplet absorbance titration curve,014 but all involve the assumption that the acid-base equilibrium may be established during the lifetime of the excited state, which is by no means a common occurrence. A dynamic analysis using nanosecond or picosecond time-resolved spectroscopy is therefore often needed to obtain the correct pK a values.1(n5)... 

De Pauw, E. Determination of binding constants of oligonucleotide complexes with minor groove binders by electrospray ionization mass spectrometry. Comparison with fluorescence titration data. Adv. Mass Spectrom. 2001, 15, 795-796. 

Selected entries from Methods in Enzymology [vol, page(s)] Determination of FMN and FAD by fluorescence titration with apoflavodoxin, 66, 217 purification of flavin-adenine dinucleotide and coenzyme A on p-acetoxymercurianiline-agarose, 66, 221 a convenient biosynthetic method for the preparation of radioactive flavin nucleotides using Clostridium kluyveri, 66, 227 isolation, chemical synthesis, and properties of roseoflavin, 66, 235 isolation, synthesis, and properties of 8-hydroxyflavins, 66, 241 structure, properties and determination of covalently bound flavins, 66, 253 a two-step chemical synthesis of lumiflavin, 66, 265 syntheses of 5-deazaflavins, 66, 267 preparation, characterization, and coenzymic properties of 5-carba-5-deaza and 1-... 

The immediate goal of fully characterizing the parent Hg +-responsive fluorescent chemosensor, which will entail NMR and fluorescence titration experiments, isolation and characterization of the 1 1 Hg + ligand complex, and fluorescence lifetime measurements of the simple diol/carbonate pair, is expected to be complete within 6 months. (This work will be the primary responsibility of the graduate student currently on the project, Sherri McFarland.)... 

Association Constants of Two Anti-galactan Immunoglobulins and Their Fab Fragments as Determined by Fluorescence Titration 1... 

Association constants between a number of these anti-PnC myeloma proteins and phosphorylcholine have been determined79 by equilibrium dialysis and found to range from 104 to 105 liter.moL. Values of K obtained by fluorescence titration have been found to be in close agreement.80,81... 

Values of KD have been estimated by fluorescence titration and by measurement of the rate of inactivation as a function of chelator concentration (13). In general, those chelators that form the most stable complexes with Mg2 also bind most strongly to the metalloenzyme, though far less strongly than to free Mg2. Chelators with bulky non-... 

Fluorescence titration measurements are based on the proportion of fluorescence intensity to fluorophore concentration (concentration of fluorescent species in solution this is often a fluorescent guest, G). For a 1 1 complex with host, H, with stability constant Ku = [HG]/[H] [G] the fluorescence intensity Fis given by ... 

Upon pH-dependent fluorescence titration, the fluorescence of the dansyl group increased 8.5 times as the pH value increased. The quantum yield at pH 11.0 was 6 times higher than at pH 7.4. The fluorescence emission was greatly enhanced by the presence of yttrium(III) and lanthanum(III) ion (8.6 times and 3.8 times, respectively). On the other hand, the fluorescence was not affected by the presence of a great many similar cations. This means the ligand was a selective probe for Y31 and La3+ working in aqueous solutions. 

Similar dendritic building blocks have been used to prepare dendrophanes [193b (dendrimer + cyclophane), which possess cyclophane cores. Internal Complexation of naphthalene derivatives was subsequently examined by NMR and fluorescence titration. 

This method for obtaining p f(T )-values was introduced by Jackson and Porter (1961). It is even more time-consuming compared to the Forster cycle than the fluorescence titration method and relatively few direct determinations have been made of pA (T1). The experimental techniques have recently been described by Chibisov (1970) and Labhartand Heinzelmann (1973). Developments in instrumentation, including the introduction of laser excitation, have been reviewed by Porter and West (1973). 

Owing to the longer lifetime of the triplet state it is expected that the protolytic reaction will usually reach equilibrium within the lifetime of the state. Unlike the fluorescence titration method for pAr(S1) described above, the triplet-triplet absorption technique leads directly to pA"(T ]) without the necessity for a knowledge of lifetimes. Phosphorescence titration studies, on the other hand, will involve the lifetime term log t0/To just as for fluorescence. 

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