About Dendrimers

1
About Dendrimers

• Introduction
• Dendrimer Growth Modes
• Functionalization
• Synthesis
• Medical Applications
• Catalysis Applications

2
Dendrimer and its applications
3
What is dendrimer ?
Highly branched molecules that combine the
properties of polymers as well as
small discrete molecules
Allow us to demonstrate the controlled occupation
of microenvironment as a function of size,
shape, and disposition of desired organic
functionality.
4
Potential Applications
5
(No Transcript)
6
(No Transcript)
7
(No Transcript)
8
(No Transcript)
9
'Divergent' Dendrimer Growth

• The synthetic methodology employed in the early
  dendrimer syntheses came to be known as the
  'divergent' approach. This name comes from the
  way in which the dendrimer grows outwards from
  the core, diverging into space. Starting from a
  reactive core, a generation is grown, and then
  the new periphery of the molecule is activated
  for reaction with more monomers. The two steps
  can be repeated. The divergent approach is
  successful for the production of large quantities
  of dendrimers since, in each generation-adding
  step, the molar mass of the dendrimer is doubled.

10
(No Transcript)
11
Convergent' Dendrimer Growth

• The 'convergent' approach was developed as a
  response to the weaknesses of divergent
  syntheses. Convergent growth begins at what will
  end up being the surface of the dendrimer, and
  works inwards by gradually linking surface units
  together with more monomers (Scheme 4). When the
  growing wedges are large enough, several are
  attached to a suitable core to give a complete
  dendrimer. The advantages of convergent growth
  over divergent growth stem from the fact that
  only two simultaneous reactions are required

12
'Convergent' Dendrimer Growth
13

• There are also certain other advantages
  associated with convergent growth. The growth
  reactions do not have to be so stringently
  efficient, and it becomes possible to introduce
  subtle engineering into the dendritic structure.
  Convergent syntheses are not without their own
  shortcomings, however. The number of steps
  required to build up a large structure is not
  reduced compared with the divergent approach, yet
  a great deal more starting material is required.
  The convergent methodology also suffers from low
  yields in the synthesis of large structures.
  Dendritic wedges of higher generations encounter
  serious steric problems in the reactions of their
  'focal points'

14
Functionalization
15
Dendritic Architectures
16
Characterisation of the Dendritic
Microenvironment

• Many investigators have made use of functional
  probes in order to study dendritic
  microenvironments. These probes can either be
  attached covalently to the dendritic structure,
  like the photochemical, chiral, and
  solvatochromic moieties that have already been
  discussed, or they can be introduced as guest
  species. Spectroscopic methods have also produced
  information about dendritic microenvironments.
  PAMAM dendrimers have been shown to have
  decreased 13C relaxation times for internal
  generations, suggesting that these moieties are
  less mobile than the surface groups.15
  Rotational-Echo Double Resonance (REDOR)
  solid-state NMR spectroscopy has been used to
  examine the shape of the Fréchet polyethers, and
  Electron Spin Resonance (ESR)spectroscopy of
  complexed PAMAMs have been examined. Computer
  modelling of dendrimers has been used extensively
  for the purposes of visualisation and dynamics
  experiments.

17
Chemical structure of the nanostar dendrimer. The
lines indicate the chromophore couplings
considered in the Forster energy transfer
calculation. The numbers indicate distances in
angstroms for a planar geometry.
18
(No Transcript)
19
The synthesis of poly(propylene imine) dendrimers
(reactions A and B) and alternative, unwanted
reactionpaths C and D.
20
poly(propylene imine)dendrimers
21
Unimolecular Micelle
22
Medical Applications

• Enhanced carbonhydrate-protein interaction
  (Glycodendrimer)
• High Antibody response
• Gd(III) polychelate for MRI-contrast agent
• Boron neutron capture therapy(BNCT)
• Transfer biomolecules to cell (PAMAM)

23
PAMAM
24
Catalysis ACCOUNTS OF CHEMICAL RESEARCH VOL.
34, 2001, 181
25
Pd catalyzed reduction