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Dendrimers: Highly Branched Macromolecules
Transcript of Dendrimers: Highly Branched Macromolecules
the gap between homogeneous
and heterogeneous catalysis"
Periphery Core Figures: D. Méry, D. Astruc / Coordination Chemistry Reviews 250 (2006) 1965–1979
Catalyst species easily accessible to reactants Reaction rates are similar to homogeneous systems High catalyst concentrations allow for cooperative interactions between catalyst sites Local Antiviral and Antibacterial drugs Solubilisation of Guest Molecules Dendrimers with hydrophobic interiors and hydrophilic exteriors can be used to carry hydrophobic molecules in aqueous solution
Viruses attach to cells by binding specific receptors on the cell's anionic surface poly (aryl ether) dendrimer Hydrophilic carboxylate groups Hydrophobic cavities Hydrophobic guest polycyclic aromatic Opposites! Fluorinated shell dendrimers have been shown to extract dyes from water and carry them in liquid carbon dioxide [Meijer et al.]
Bacteria also have an anionic surface, with specific receptors not found on host cells A Dendritic Box Nanotechnology Precisely adjustable nanoscale dimensions
Ease of multi-functionalisation Nano-scale applications Consider Azobenzene... Azobenzene undergoes E-Z isomerization when exposed to different wavelengths of UV light Dendrimers in nature Scaffolds for tissue repair Wait . . . what? Geckos' feet are made of dendritic networks that use Van der Waals forces... 1 mm x 1 mm 14 000 setae 100 - 1000 spatulae Dendrimers as injectable sealants for wounds caused by trauma, infection and inflammation Can lead to scarring, infection, cataract formation, glaucoma and blindness Usually repaired with sutures Corneal lacerations: Maximum intraocular pressures before rupture were comparable with those obtained by suturing Imagine a dendrimer with growth factors on the surface! trans cis hv Antiviral Mechanism Azobenzene groups can support dendritic branches Nanoscale Impellers Azobenzene groups with terminal hydrocarbon groups have been fixed into silicone dioxide nanotubes
Light driven passage of ions may be possible with switchable nanoimpellers hv hv hv Photo-isomerization of azobenzene SiO2 Nanotube
(3.8nm) Vogtle, F et al. "Azobenzene-Functionalized Cascade Molecules:
Photoswitchable Supramolecular Systems", Chem. Eur. J. 4, 699-706 (1998) An Overview... What is a dendrimer? Highly branched polymer
Consists of a core, branches and end groups
globular shape Dendrimers can be functionalized with hydrophobic exteriors and hydrophilic interiors Ex: Poly(propylene imine) dendrimer "Unimolecular Micelles" Reversible accomodation of guests
No Critical micelle concentration
Entrapment of guest molecules possible t Boc-L-phenylanaline surface traps guest molecules (Bengal Rose) (p-nitrobenzoic acid) http://www.uni-ulm.de/nawi/nawi-anorg2/forschungsgebiete/dendrizymes.html Sterically bulky H-bonded shell makes entrapment permanent Synthesis Dykes G.M. "Dendrimers: a review of their appeal and
applications." J Chem Technol Biotechnol. 76. pp903-918. (2001) Dykes G.M. "Dendrimers: a review of their appeal and
applications." J Chem Technol Biotechnol. 76. pp903-918. (2001) Hierarchical synthesis
Exponential growth Starburst Limit Eventually the dendrimer must stop growing Dendritic structure causes a
site isolation effect The steric and electronic environment surrounding the catalyst site results in
enantioselective catalysis Cooperation between two neighbouring sites on the surface of the dendrimer
Enhanced enantioselective activity through steric isolation inside the dendrimer
Improved solubility and recovery in solutions The Dendritic Effect Different: Similar: Dendron Immobilisation Catalyst Group Location Molecular Structure A third generation dendrimer schematic Core Internal Cavities periphery . is the number of active sites available
. can cause shape changes
comparison to linear polymers Multiplicity Divergent Convergent Growth starts at what will become the periphery of the dendrimer and proceeds inwards Growth starts at the core and proceeds radially outward toward the dendrimer periphery Figure from: http://www.rsc.org/ebooks/archive/free/BK9780854048526/BK9780854048526-00001.pdf Construction 1. Coupling of monomer to reactive core
2. Activation of monomer end-group to create a reactive surface 1. Works inwards by linking surface units together with more monomers done by one to one coupling
2. Ends at the core, where dendritic segments are joined together. Construction Intermolecular interactions Comparison to linear polymers "Dendron is greek for tree!" Active Site starting at the periphery steric hindrance prevents further generations catalyst site Remember: Enantiomers have the same molecular formula but different bond orientation in space polymer support Highly symmetric dendrimer molecules
Large variety of dendrimers synthesizeable
Successful for the production of large quantities of dendrimers large dendrimers experience incomplete growth steps and side reactions
Virtually impossible to isolate pure from their side products Advantages Disadvantages Disadvantages Advantages Ability to synthesize asymmetric dendrimers, or dendrimers having mixed structural elements
Fewer simultaneous reactions required
Minimal number of reactive sites during proliferation allows faster reaction rates and yields
Easier separation of reactants from the product Low overall yields due to fewer active sites Potential nanoscale impeller photo-isomerizable azobenzene Zinc, De Cola, Vogtle et al. "Photoisomerization of Azobenzene Derivatives in Nanostructured Silica". J. Phys. Chem. B 110, pp24390-24398 (2006) Find this presentation: http://prezi.com/aypsewcr4h1c/dendrimers-highly-branched-macromolecules/ Or go to prezi.com
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