6.6 First Steps Towards a “Central Dogma” for Synthetic
Nanochemistry: Dendrimer-Based Nanochemistry
One of the highest priority challenges and barriers hindering continued progress of
the international nanoscience technology movement is the absence of a “central
paradigm and a Mendeleev-like periodic system” for unifying and defining
nanoscience.
Historically, the development of such a central paradigm and systematic framework was absolutely critical for the seminal transformation in the early nineteenth
century of an empirical alchemy movement to a systematic, highly predictable
scientific discipline recognized as traditional small-molecule chemistry [134].
As described in this chapter and elsewhere, substantial progress has been made
toward resolving this challenge by the introduction of a systematic, unifying
framework based on the first principles of traditional chemistry [137, 138]. In
review, this concept was inspired by the pervasive heuristic “atom mimicry”
behavior observed for a broad range of monodisperse, well-defined nanoparticle
categories [137, 138]. Ample evidence has now emerged that supports the premise
that CADPs such as size, shape, surface chemistry, flexibility/rigidity, composition,
and architecture may be conserved and translated hierarchically from the picoscale
to the nanoscale level if suitable structure-controlled, bottom-up synthesis strategies are employed [137]. These conserved features were first observed with welldefined bottom-up structure-controlled, soft nanoparticles such as dendrons,
dendrimers, and dendronized polymers [138, 151, 169]. An abundance of literature
data has now shown that at least 12 categories of both soft and hard nano-elements
(i.e., SNE, HNE) exhibit atom mimicry features and pervasive nano-periodic
property patterns or trends related to their CNDPs. Hard and soft nanomodule
categories (i.e., atom collections of 10
3 –10
9 atoms) have been shown to behave
heuristically like “nanosized superatoms” by exhibiting remarkably well-defined
stoichiometries and mass-combining ratios to form covalent nanocompounds and
non-bonding nano-assemblies. Furthermore, as predicted in the original concept
paper [137] and described briefly in this chapter, both the hard and soft nanoelement categories (designated [HNE-n] and [SNE-n]), as well as their resulting
nanocompounds and assemblies appear to manifest both physico-chemical and
functional/ application property trends reminiscent of Mendeleev-like property
patterns normally associated with the atomic elements (Fig. 32).
We now examine recent progress reported by Percec, Rosen and colleagues
[151] that has clearly demonstrated the first working examples of predictive,
Mendeleev-like nano-periodic tables. These Percec nano-periodic tables clearly
demonstrate a priori predictions for the mode of [S-1]-type amphiphilic dendron
self-assembly into supramolecular dendrimers with 85–90% accuracy. Quite
remarkably, as proposed in the original concept [137], these self-assembly modes
may be accurately predicted based on simply knowing the CNDPs (size, shape,
surface chemistry, and flexibility) for the amphiphilic dendron primary structure, as
will be described in the next section.
372
D.A. Tomalia
Nanochemistry: Dendrimer-Based Nanochemistry
One of the highest priority challenges and barriers hindering continued progress of
the international nanoscience technology movement is the absence of a “central
paradigm and a Mendeleev-like periodic system” for unifying and defining
nanoscience.
Historically, the development of such a central paradigm and systematic framework was absolutely critical for the seminal transformation in the early nineteenth
century of an empirical alchemy movement to a systematic, highly predictable
scientific discipline recognized as traditional small-molecule chemistry [134].
As described in this chapter and elsewhere, substantial progress has been made
toward resolving this challenge by the introduction of a systematic, unifying
framework based on the first principles of traditional chemistry [137, 138]. In
review, this concept was inspired by the pervasive heuristic “atom mimicry”
behavior observed for a broad range of monodisperse, well-defined nanoparticle
categories [137, 138]. Ample evidence has now emerged that supports the premise
that CADPs such as size, shape, surface chemistry, flexibility/rigidity, composition,
and architecture may be conserved and translated hierarchically from the picoscale
to the nanoscale level if suitable structure-controlled, bottom-up synthesis strategies are employed [137]. These conserved features were first observed with welldefined bottom-up structure-controlled, soft nanoparticles such as dendrons,
dendrimers, and dendronized polymers [138, 151, 169]. An abundance of literature
data has now shown that at least 12 categories of both soft and hard nano-elements
(i.e., SNE, HNE) exhibit atom mimicry features and pervasive nano-periodic
property patterns or trends related to their CNDPs. Hard and soft nanomodule
categories (i.e., atom collections of 10
3 –10
9 atoms) have been shown to behave
heuristically like “nanosized superatoms” by exhibiting remarkably well-defined
stoichiometries and mass-combining ratios to form covalent nanocompounds and
non-bonding nano-assemblies. Furthermore, as predicted in the original concept
paper [137] and described briefly in this chapter, both the hard and soft nanoelement categories (designated [HNE-n] and [SNE-n]), as well as their resulting
nanocompounds and assemblies appear to manifest both physico-chemical and
functional/ application property trends reminiscent of Mendeleev-like property
patterns normally associated with the atomic elements (Fig. 32).
We now examine recent progress reported by Percec, Rosen and colleagues
[151] that has clearly demonstrated the first working examples of predictive,
Mendeleev-like nano-periodic tables. These Percec nano-periodic tables clearly
demonstrate a priori predictions for the mode of [S-1]-type amphiphilic dendron
self-assembly into supramolecular dendrimers with 85–90% accuracy. Quite
remarkably, as proposed in the original concept [137], these self-assembly modes
may be accurately predicted based on simply knowing the CNDPs (size, shape,
surface chemistry, and flexibility) for the amphiphilic dendron primary structure, as
will be described in the next section.
372
D.A. Tomalia