SCIENCE-Module 6

• Self-assembly


  The organization of components into structures without human intervention
• Self-assembly

  • Can occur with components having sizes from the molecular to the macroscopic
  • Components can be distinct/separate or linked
  • Different kinds of interactions between the components are involved
  • Formation of aggregates requires suitable conditions
  • Structures or aggregates formed are ordered/stable
  • The structure and characteristics of the components usually determine the structure and characteristics of the assembled product
  • The process is reversible or adjustable
• Self-assembly has a wide range of applications in nanotechnology, manufacturing, robotics, netted sensors, computer networks, etc.
• Levels of self-assembly


  • Atomic
  • Molecular
  • Nanoscale
  • Mesoscopic to macroscopic
• Molecular self-assembly


  The spontaneous assembly of molecules into supramolecules
• Examples of molecular self-assembly

  • Formation of molecular crystals
  • Colloids
  • Lipid bilayers, micelles
  • Phase-separated polymers
  • Self-assembled monolayers
  • Folding of polypeptide chains into proteins
  • Folding of nucleic acids
  • Association of a ligand with a receptor
• Molecular self-assembly


  • Components are a group of molecules or segments of a macromolecule which can be the same or different
  • Interactions are generally weak and noncovalent or relatively weak covalent bonds
  • Association of components must be reversible or must allow the adjustment of positions within an aggregate once it has formed
  • Normally is carried out in solution or at an interface to allow the required motion of the components
  • The components must be mobile (usually provided by thermal motion in solutions)
• Electrostatic interactions


  Interactions between charged species, including ionic (full charges) and van der Waals (dipoles)
• van der Waals forces

  Electrostatic interactions involving permanent or induced dipoles
• Hydrogen bonds


  Bonds between molecules that have an H atom bonded to a small, highly electronegative atom with lone electron pairs, specifically N, O, or F
• Hydrophobic interactions


  The tendency of nonpolar molecules to aggregate in aqueous solutions in order to separate from water
• Coordination bonds


  Weak covalent bonds wherein the bonding electrons are derived from one of the atoms sharing the bond, usually between a metal and a species with lone pairs
• Interactions in macroscopic self-assembly

  • Gravitational attraction
  • External electromagnetic fields
  • Magnetic interactions
  • Capillary interactions
  • Entropic interactions
  • Dynamic self-assembly
• Static self-assembly


  Requires energy but the structures are stable once formed
• Dynamic self-assembly


  Interactions responsible for the formation of structures only occur when energy is dissipated
• Types of self-assembly


  • Static (S)
  • Dynamic (D)
  • Templated (T)
  • Biological (B)
• Examples of self-assembly


  • Crystallization at all scales
  • Assembly of parts with nano- and micrometer dimensions for robotics and manufacturing
  • Synthesis of nanostructures (colloids, nanotubes, and wires) for nanoscience and technology
  • Fabrication of three-dimensional microelectronic devices
  • Interconnected networks of computers, sensors, and controllers that communicate and collaborate with each other and configure or self-assemble themselves into functional systems based on the flow of information
• Atomic


  Usually involves metal atoms.
• Intramolecular


  within a complex molecule forming a well-defined stable structure.
• Intermolecular


  among molecules to form supramolecular assemblies.
• Nanoscale


  Colloids, nanowires and nanospheres, and related structures.
• Mesoscopic to macroscopic


  Objects with dimensions from micrometers to centimeters and bigger.
• Molecular self-assembly has five characteristics.
• Components


  Group of molecules or segments of a macromolecule which can be the same or different.
• Interactions


  Balance of attractive and repulsive interactions
• Reversibility/Adjustability


  Association of components must be reversible or must allow the adjustment of positions within an aggregate once it has formed.
• Environment


  Normally is carried out in solution or at an interface to allow the required motion of the components.
• Mass Transport and Agitation

  The components must be mobile (usually provided by thermal motion in solutions).
• Electrostatic interactions


  -Interactions between charged species.

  • Ionic (full charges) or van der Waals (dipoles).
• Hydrogen bonds


  Between molecules that have an H atom bonded to a small, highly electronegative atom with lone electron pairs, specifically N, O, or F.
• Hydrogen bonds


  Between molecules that have an H atom bonded to a small, highly electronegative atom with lone electron pairs, specifically N, O, or F.
• Hydrophobic interactions


  Tendency of nonpolar molecules to aggregate in aqueous solutions in order to separate from water.
• Coordination bonds


  Weak covalent bond wherein the bonding electrons are derived from one of the atoms sharing the bond.

  ○

  Usually between a metal and a species with lone pairs.
• Gravitational attraction


  Attraction between objects that have mass.
• External electromagnetic fields


  Electromagnetic field (combination of invisible electric and magnetic fields generated by electric current) outside of a system that can influence the behavior of charged particles within their vicinity.
• Magnetic interactions


  Interactions between magnetic materials via magnetic fields.
• Capillary interactions


  Involves minimizing the contribution of interfaces by minimizing surface areas.
• Entropic interactions


  Interactions between particles or molecules resulting in the tendency to increase entropy.
• Static self-assembly (S)


  Requires energy but the structures are stable once formed.
• Dynamic self-assembly (D)


  Interactions responsible for the formation of structures only occur when energy is dissipated.