 Solution

ID: past-exam-of-the-mphil-in-micro-and-nanotechnology-enterprise-course-of-the-university-of-cambridge/2023/paper-1/section-a-iii/5/ii/a/solution

The stabilizing outer groups should be compatible with the solvent, while the thiol-derived sulfur anchors the ligand shell to the gold nanoparticle.

Solvent	Thiol number	Reason
Acidic water	1	The terminal amine is protonated, favoring hydration and electrostatic repulsion between similarly charged particles.
Basic water	2	The carboxylic acid becomes carboxylate, giving a hydrated negatively charged outer group.
Hexane	4	The long hydrocarbon tail is well solvated by a hydrocarbon solvent and can provide steric protection.
Perfluorohexane	5	The fluorinated tail is compatible with the fluorous solvent, unlike a conventional hydrocarbon shell.
Toluene	3	The aromatic-containing ligand is compatible with the aromatic organic solvent.

These choices concern colloidal stability, not merely whether a free ligand dissolves. Coverage, chain packing and particle separation also matter. In the aqueous cases, high electrolyte concentrations can screen electrostatic repulsion, so ionization alone does not guarantee stability at every acid or base concentration.

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