Chapter 18: Q36P (page 460)
What is the difference between a fluorescence excitation spectrum and a fluorescence emission spectrum? Which one resembles an absorption spectrum?
The fluorescence excitation spectrum resembles an absorption spectrum.
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Gold nanoparticles (Figure 17-31) can be titrated with the oxidizing agent TCNQ in the presence of excess ofto oxidize in deaerated toluene. Gold atoms in the interior of the particle are Au(0) . Gold atoms bound to - (dodecanethiol) ligands on the surface of the particle are Au(I) and are not titrated.
The table gives the absorbance at $856 0.700 mL of in toluene is titrated with gold nanoparticles (1.43 g/Lin toluene) from a microsyringe with a Teflon-coated needle. Absorbance in the table has already been corrected for dilution.
(a) Make a graph of absorbance versus volume of titrant and estimate the equivalence point. Calculate the Au(0) in 1.00 g of nanoparticles.
(b) From other analyses of similarly prepared nanoparticles, it is estimated that 25 % of the mass of the particle is dodecanethiol ligand. Calculate mmol of localid="1667559229564" in 1.00 g of nanoparticles.
(c) The Au(I) content of 1.00 g of nanoparticles should be 1.00 mass of Au(0) - mass of . Calculate the micromoles of Au(I) in 1.00 g of nanoparticles and the mole ratio Au(I) :. In principle, this ratio should be 1: 1. The difference is most likely because was not measured for this specific nanoparticle preparation.
18-27. The iron-binding site of transferrin in Figure 18-8 can accommodate certain other metal ions besides Fe and certain other anions besidesData are given in the table for the titration of transferrin ( 3.57 mg in 2.00 mL ) with 6.64 mM solution in the presence of the anion oxalate, , and in the absence of a suitable anion. Prepare a graph similar to Figure 18-11, showing both sets of data. Indicate the theoretical equivalence point for the binding of one and two ions per molecule of protein and the observed end point. How many ions are bound to transferrin in the presence and in the absence of oxalate?
18-8: What is an absorption spectrum?
18-29. Biotin-streptavidin fluorescence titration. Biotin is a cofactor in enzymatic carboxylation reactions. Biotin activatesfor biosynthetic reactions.
Streptavidin is a protein isolated from the bacterium Streptomyces avidinii that binds biotin with a formation constant of . The biotin-streptavidin complex is widely used in biotechnology because the noncovalent complex is stable in the presence of detergents, protein denaturants, and organic solvents, and at extremes of pH and temperature.
The stoichiometry of the biotin-streptavidin complex was measured by a fluorescence titration. Fluorescein (page 453 ) covalently attached to biotin via the biotin carboxyl group fluoresces at 520 nm when irradiated at 493 nm. When biotin-fluorescein (BF) binds to streptavidin (SA), fluorescence decreases. The table gives emission intensity for addition of BF to SA and also for addition of SA to BF. Data are already corrected for dilution.
(a) Make a graph of fluorescence versus mole ratio for each titration and state the stoichiometry of binding of biotin to streptavidin.
(b) Explain the shape of each titration curve.
18-7: How do transmittance, absorbance, and molar absorptivity differ? Which one is proportional to concentration?
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