Chapter 18: Q6TY (page 443)
Describe a different set of dilutions to produce 3 mg Fe/mL from 1 000 mg
Fe/mL
Short Answer
Dilute 10 mL of stock to 100 mL to get. Dilute of the new solution up to 100 mL to get
Chapter 18: Q6TY (page 443)
Describe a different set of dilutions to produce 3 mg Fe/mL from 1 000 mg
Fe/mL
Dilute 10 mL of stock to 100 mL to get. Dilute of the new solution up to 100 mL to get
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Get started for free18-29. 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.
18-9 Why does a compound whose visible absorption maximum is at 480 nm (blue-green) appear to be red?
18-10. Color and absorption spectra. Color Plate 17 shows coalored solutions and their spectra. From Table 18-1, predict the color of each solution from the wavelength of maximum absorption. Do observed colors agree with predicted colors?
18-26. A 2.00mL solution of apotransferrin was titrated as illustrated in Figure 18-11. It required 163L of 1.43 mM ferric nitrilotriacetate to reach the end point.
(a) Why does the slope of the absorbance versus volume graph change abruptly at the equivalence point?
(b) How many moles of Fe(III) (= ferric nitrilotriacetate) were required to reach the end point?
(c) Each apotransferrin molecule binds two ferric ions. Find the molar concentration of apotransferrin in the 2.00mL solution.
(a) A solution of compound A exhibited an absorbance of 0.624 at 238nmin a 1.000 cmcuvet; a blank solution containing only solvent had an absorbance of 0.029at the same wavelength. Find the molar absorptivity of compound A.
(b) The absorbance of an unknown solution of compound A in the same solvent and cuvet was 0.375 at 238 nm. Find the concentration of A in the unknown.
(c) A concentrated solution of compound A in the same solvent was diluted from an initial volume ofto a final volume of 25.00mLand then had an absorbance of 0.733. What is the concentration of A in the concentrated solution?
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