Self-assembly and Molecular Self-assembly

Question 1

What do you put into the term “self-assembly”? Give some examples connected to the curriculum of this course.

Answer 1

• Emulsions, homogeneous nucleation NP synthesis, packing of NPs, etc

Question 2

Suggest why we observe Au clusters with the magic numbers, Au_13, Au_55, Au_147 whereas Na form stable clusters as Na_2, Na_8, Na_18, Na_20, Na_3+, Na_9+, Na_19+, Na_7- and Na_17-.

Answer 2

• Au: Surface minimization

- Na: Electron configuration (full shell)

Question 3

What is the Hume-Rothery substitution rules saying? Based on this, would you expect the two metals Au and Ag to form a solid solution?

Answer 3

• H-R: Same crystal structure (similar coord. polyhedra for atoms), equal atomic size (within 15%), similar electronegativity, same oxidation state (cat/ani).

Au and Ag should be expected to form a solid solution

Question 4

Suggest why the various Au nanoparticle distributions pack in different configurations. What may be the driving force?

Answer 4

Depletion attraction and weak vdW forces between particles

Question 5

Whitesides et al talk about organic synthesis at four different levels. Describe each of them briefly.

Answer 5

1) Sequential covalent synthesis: Generate arrays of covalently linked atoms with well-defined properties.
2) Covalent polymerization: Most important for preparing molecules with high molecular weights. Monomer caused to react with itself –> molecule (polymer) comprising many covalently connected monomers.
3) Relies on weaker/less directional bonds (ionic, H-bonds, vdW). “Self-organizing synthesis”. Want to reach a thermodynamic minimum.
4) Molecular self-assembly (most relevant to nanostructures). Spontaneous assembly of molecules into structured, stable, noncovalently joined aggregates.

Question 6

Explain in short, how Mother Nature produce DNA utilizing the fourth-level strategy as outlined by Whitesides et al.

Answer 6

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Question 7

Discuss thermodynamic constraints in the formation of self-assembled molecules similar to DNA. How well do the chemist do this type of synthesis in the laboratory?

Answer 7

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Question 8

With basis in the lecture notes “Molecular self-assemblyat”, explain in short why localized surface Plasmon’s on certain metals give rise to strong colors and why pH tuning (in the Au example) induce a switch in color.

Answer 8

Localized surface plasmons (LSPs)