Nanostructural Architectures from Molecular Building Blocks

 Molecular building blocks:  MBBs are the link between classical synthsis chemistry from in theory the smallest possible unit, and large structures.  MBBs are molecules that self assemble into larger units.  The limitations of this method are:  Availability of the units, connectivity, and suitable linkers

Nanostructural Architectures from Molecular Building Blocks  Bonding and connectivity –Covalent bonding –Covalent bonds are formed by the sharing of pairs of electrons between atoms. –Best example is the covalent bond between two C atoms. –Sigma bonding along the axis between the two atoms, provides a means of low energy rotation in linear molecules and low energy angle twisting in cyclic molecules. –Sigma bonding defines the general connectivity and framework of the molecule

Nanostructural Architectures from Molecular Building Blocks

 Covalent bonding has many advantages: –Covalent bonds lead to extremely stable intermolecular connections, as compared to electrostatic interactions (temperature, ionic strength, pH) –Covalnet bonds are dependable, they do not reorganise, like hydrogen bonds –Protocols exist to form all kinds of covalent bonds for all kinds of building blocks, allowing all possible connectivities

Nanostructural Architectures from Molecular Building Blocks  Coordination complexes –In between the covalent bonds and the other interamolecular interactions are the coordination complexes between organic molecules and metal ions. –The initial description of these metal ligand molecules stems from the ability of metal ions to coordinate ligands electron donating molecules

Nanostructural Architectures from Molecular Building Blocks

 Dative bonds: –Interaction of a lone pair with an atom centered molecular orbital. Strength comparable to a sigma bond. –E.g. Bonding between B and N. –Coupling of a molecule to B with a lone pair leads to change in boron from trigonal planar (sp2) to tetrahedral (sp3).

Nanostructural Architectures from Molecular Building Blocks

Boroadamantane is a special case, because B is already in sp3 hybridisation and has the final conformation already built in the molecule.

Nanostructural Architectures from Molecular Building Blocks   Interactions –They play a role in base stacking in DNA –Molecular crystals –Polymer chemistry –Foramtion, shape and function of proteins

Nanostructural Architectures from Molecular Building Blocks

 Molecular building block approaches –The ultimate goal is the assembly of nanostructures or nanoscale materials through the manipulation of a subunit by chemical modification –The MBB is devisible into one or more chemically/electrostaically active region  Supramolecular Chemistry  Science of electrostatic interaction at the molecular level

Nanostructural Architectures from Molecular Building Blocks  Hydrogen bonding  It is used extensively in Supramolecular Chemistry  Easy means to self assemble large units from smaller subunits, can rearrange  Stability increases with the total amount of Hydrogen bonds

Nanostructural Architectures from Molecular Building Blocks

 Crystal Engineering –Hydrogen Bonding has been extensively used in the stabilisation of crystal lattices. –Hydrogen bonding is one of the main bonding in biological molecules –Stabilisation of structures and backbones –Secondary structure stabilisation

Nanostructural Architectures from Molecular Building Blocks

 Supramolecular structures  Whole families of Supramolecular structures are known that have been built up only by Hydrogen bonding  Mixing the units in te correct ratios will lead to the self assembly of the desired structures  Cavities, sheets, triangular structures,…..

Nanostructural Architectures from Molecular Building Blocks

 Catenanes –Catenanes are a very special class of supramolecular molecules –They come into existence when two macrocycles interpenetrate each other. –The first catenane has been synthesised in very poor yields

Nanostructural Architectures from Molecular Building Blocks

 Molecular Zippers –Molecular zippers are formed by amide oliomers –They maximise the amount of Hydrogen bonding and  -stacking –Stabiloity increases with oligomer length –Decrease in stability in polar solvents (methanol)

Nanostructural Architectures from Molecular Building Blocks

 Covalent Architectures  The Tinkertoy chemist  Idea behind the concept to build all possible structures and shapes from a limited set of molecules where all possible connectivities of each single are known  LEGO block system for organic chemistry

Nanostructural Architectures from Molecular Building Blocks

 Stability: –Stability and reactivity are the most important factors –The MBBS should only react during the formation of the structure and result in an inert structure at the end of the reaction  Size –Control over the size is better the smaller the single building blocks are.

Nanostructural Architectures from Molecular Building Blocks  Chemical reactivity –From the box of the 24 molecules the reactivity and reaction chemistry is known and described. –Protocols for all possible linking reactions are known –Engineering all possible shapes is possible

Nanostructural Architectures from Molecular Building Blocks

Honeycomb lattices

Nanostructural Architectures from Molecular Building Blocks

 Symmetry interaction model –Symmetry interaction model builds on the understanding that many highly symmetric naturally occuring structures are formed as a consequence of lock and key interactions between the subunits. –Metal complex chemistry uses these principles to generate new metal-ligand assemblies

Nanostructural Architectures from Molecular Building Blocks

 2 Dimensional structures  Virtually no limit in structural combinations

Nanostructural Architectures from Molecular Building Blocks

 3D structures  Spotaneous self assembly from non covalent self assembly is a known principle in biological structures  Proteins  Ladders  Rods

Nanostructural Architectures from Molecular Building Blocks