SELF-ASSEMBLYAND MOLECULAR SELF-ASSEMBLY Flashcards
What do you put into the term “self-assembly”? (Hint –see lecture notes molecular self-assembly.) Give some examples connected to the curriculum of this course.
Phenomenon where the components of a system assemble themselves to form a larger functional unit.
Emulsions, homogeneous nucleation NP synthesis, packing of NPs, molecular self assembly,..
Suggest why we observe Au clusters with the magic numbers Au13, Au55, Au147 whereas Na form stable clusters as Na2, Na8, Na18, Na20, Na3+, Na9+, Na19+, Na7- and Na17-.
Au – surface minimization
Na – electronic electron configuration (full shell of electrons according to periodic table)
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? Hint – look up your lecture notes to get data on type of crystal structure and unit cell dimensions.
Same crystals structure end members, equal atomic size (within 15%), similar electronegativity elements or charge cations-anions
Au –Ag: Both ccp; Au (a = 4.078 Å) Ag (a = 4.086)(metallic atomic radii for Au and Ag approx. 1.44 Å)
Yes, we would expect them to form a solid solution, which also is confirmed by checking up the phase diagram.
Suggest why the various Au nanoparticle distributions, as reported in Kiely et al. (Nature 1998), pack in different configurations. What may be the driving force? (Hint –look up lecture notes “molecular self-assembly”).
Depletion attraction (particles with more similar size have a better match in overlap volume) and Weak van der Waals forces between particles.
Whitesides et al. (Science, 1991) talk about organic synthesis at four different levels. Describe each of them briefly.
Sequential covalent synthesis: generate arrays of covalently linked atoms with well-defined composition, connectivity, and shape.
covalent polymerization: 6). A relatively simple, reactive low molecular weight substance (a monomer) is caused to react with itself in a process that produces a molecule (a polymer) comprising many covalently connected monomer.
“self-organizing syntheseis”: The distinguishing feature of these methods is self-organization. The molecules or ions adjust their own positions to reach a thermodynamic minimum; the chemist does not specify these positions.
molecular self-assembly: the spontaneous assembly of molecules into structured, stable, non-covalently joined aggregates. Molecular self-assembly combines features of each of the preceding strategies to make large, structurally well-defined assemblies of atoms.
Explain in short, how Mother Nature produce DNA utilizing the forth-level strategy as outlined by Whitesides et al.
- Include an explanation to how a protein form, secondary structures, tertiary structures and quaternary structures to your explanation.
- What is the molecular mass of Hemoglobin (in Dalton)? What is the maximum mass (in Dalton) of laboratory synthesized molecular self-assemblies?
Covalent bonds along each helix, disulfide bonds between helixes, stabilized by hydrophobic interactions outwards. Protein primary structure is covalent, secondary is hydrogen bonds between side groups on AA’s, tertiary is van der Waal between groups of AA’s, and quatinary is van der Waal between tertiary groups.
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?
Self assembly is driven by having a lower free energy. In the example for DNA, the helixes want to bind through hydrophobic interactions inwards and hydrophilic interactions outwards. This is difficult to tune in the lab, because the chemist can’t decide the free energy of the material. It is what it is.
With basis in the lecture notes “Molecular self-assembly”, 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.
The free electrons if the Au NP will oscillate with incoming em waves. Different sizes will have different resonance frequency, and will therefore have different color. Protonation/deprotonation if carboxylic side chains OR connecting nanorods can be one of the reason why there is pH tuning of color.
