Chapter 1 Multiple Choice Questions

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. NMR spectroscopy is nowadays one of the most routine analytical techniques used to study host-guest binding in solution. Which of the following statements about this technique is incorrect?

NMR spectroscopy can give information on where the guest is binding on the host molecule. correct incorrect

For host-guest complexes in fast exchange on the ¹H NMR timescale, host-guest binding constants can be obtained by determining the chemical shifts of selected proton environments at increasing quantities of the added guest and fitting the data to an appropriate binding model. correct incorrect

NMR titrations can accurately determine the binding affinities between any host and guest in any deuterated solvent regardless of how strong the binding is. correct incorrect

For host compounds possessing fluorinated groups (e.g. perfluoroarenes) which can interact with a guest upon binding, it is possible to use ¹⁹F NMR titration experiments to determine the binding affinities. correct incorrect

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. Consider the following binding isotherm obtained when a guest molecule is added to a host solution (initial host concentration = 1.0 mM) in CDCl₃. Which of the following pairs of molecules is most likely to account for the shape of the isotherm?

correct incorrect

correct incorrect

correct incorrect

correct incorrect

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. Which of the following amino acids would you expect to be important in binding and recognising SO₄^2- within the binding cavity of a sulfate-binding protein? Assume that the amides on the peptide backbone do not play a role in binding.

1, 2, and 3 only correct incorrect

1 and 2 only correct incorrect

2, 3, and 4 only correct incorrect

All of the listed amino acids correct incorrect

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. A host and guest molecule have diffusion coefficients of logD = -9.5 and -8.5 respectively. When an excess of guest molecule was added to the host in CDCl₃, DOSY NMR revealed that the resulting host-guest complex has a diffusion coefficient of logD = -9.8. Which of the following is likely to be happening in solution?

Formation of host-guest 2:1 complex correct incorrect

Formation of host-guest 1:1 complex correct incorrect

Formation of host-guest 1:2 complex correct incorrect

Tight coiling of the host molecule around the guest correct incorrect

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. Which of the following halogen bonding interactions is most likely to be observed crystallographically in the solid state?

correct incorrect

correct incorrect

correct incorrect

correct incorrect

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. In order to determine the thermodynamics of the interactions between a host and guest molecule, a researcher measured the following association constants by ¹H NMR spectroscopy at different temperatures. The data are as shown (assume errors are very small):



Which of the following statements is consistent with these data?
(1) The host-guest binding is driven by both entropy and favourable enthalpy.
(2) The host-guest binding is driven solely by entropy.
(3) Desolvation of the host and guest molecules is likely to be necessary for complexation to take place.
(4) At temperatures below -70 ° C, formation of the host-guest complex will never occur.

Statement 1 only correct incorrect

Statements 2 and 3 only correct incorrect

Statements 2, 3, and 4 only correct incorrect

Statements 1, 3, and 4 only correct incorrect

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. The cyclophano-crown ether host (shown below) is known to form complexes with 6-methoxy-2-napthonitrile (logK_a = 2.6) and K⁺ (logK_a = 1.9) in methanol/ water 3:2 v/v. Which of the following statements is likely to be correct?

When the methanol/ water ratio is changed to 9:1 v/v, there is a large increase in the napthonitrile binding affinity but little change to K⁺ binding strength. correct incorrect

If the cyano group in the napthonitrile guest is replaced with a dimethylamino (-N(CH₃)₂₎ group, the binding affinity of the resulting molecule with the host molecule in the same solvent of methanol/ water 3:2 v/v is likely to increase. correct incorrect

In the solvent mixture of acetone/ water 3:2 v/v, the binding affinities of both K⁺ and the naphthonitrile guest are expected to increase. correct incorrect

In 100 % water, K⁺ binds much more weakly while the napthonitrile binds much more strongly correct incorrect

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. Two molecules are known to form a 1:1 stoichiometric host-guest complex in CDCl₃. When a solution containing 1.0 μmol of the host and 1.25 μmol of the guest in exactly 1.0 mL of CDCl₃ is analysed by ¹H NMR spectroscopy, the spectrum shows a peak for the host-guest complex and a separate peak for the unbound host. The area under the peak for the complex is exactly three times that of the unbound host. Calculate the K_a of the host-guest complex.

3 M^-1 correct incorrect

6 M^-1 correct incorrect

2400 M^-1 correct incorrect

6000 M^-1 correct incorrect

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. Pillararenes are macrocyclic compounds composed of a number of hydroquinone units joined together to form a ring. For the pillararene whose structure is as shown, which of the following guest compounds is least likely to bind within its cavity?

correct incorrect

correct incorrect

correct incorrect

correct incorrect

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. Beta-cyclodextrin is known to form a supramolecular complex with certain vitamins, such as vitamin d₃ (cholecalciferol), in water. The structures and dimensions of both molecules are shown below. Which of the following statements about the complex is likely to be incorrect?

The complex is more likely to form at low concentrations of cyclodextrin and cholecalciferol, as compared to high concentrations. correct incorrect

The complexation is driven by the hydrophobic effect in water. correct incorrect

When bound within the cyclodextrin, cholecalciferol can be stabilized from isomerization and oxidation reactions which can change its overall shape and dimensions. correct incorrect

Release of cholecalciferol from its bound complex can be triggered by adding ethanol. correct incorrect