Biomedical subjects
Publications and source records attributed to Dominic V McGrath.
A series of 3,5-poly(aryl ether) dendrons was prepared up to the third generation using inexpensive 3,5-di-tert-butyl-4-hydroxytoluene (BHT, 1) as a starting material.
The first incorporation of quinacridone, a technologically important organic electroluminescent emitter, into dendrimers increases solubility, decreases aggregation, retards heterogeneous electron transfer, and enhances luminescence in condensed phases (powders and thin films).
Two analogous classes of dendrimers with a single azobenzene moiety at the core have been prepared. Flexible benzyl aryl ether dendrimers 1a-e were obtained in good yields by direct alkylation of diphenolic azobenzene 3 with benzyl aryl ether dendrons [G-n]-Br (n = 0-4). In rigid dendrimers 2a-e, the azobenzene configurational switch was linked to phenylacetylene dendrons through acetylenic linkages to maintain the shape-persistent nature of these dendrimers. A comparison of these two different classes of dendrimers with azobenzene cores reveals a difference in the properties of the photochromic moiety upon dendritic incorporation as well as a significant difference in the photomodulation of dendrimer properties. The E --> Z photoisomerization quantum yield decreased markedly with increasing generation for dendrimers 1a-e but only slightly for dendrimers 2a-e. However, increasing generation did not significantly alter thermal isomerization kinetics or activation barriers. The hydrodynamic volumes of azobenzene-containing dendrimers 2b-e were significantly modulated when the azobenzene unit is subjected to irradiation, while those of dendrimers 1b-e were only slightly affected.
Geometric disassembly of dendritic structures was realized by a cascade cleavage reaction triggered by an initially stimulated group at the dendrimer core. Release of an exponential number of dendrimer fragments was a result of the branching nature of the cleavage pathway. Evidence for the completion of the disassembly process was provided by the absorbance peak of the p-nitrophenoxide ion that was covalently installed at the periphery of the dendrons for this purpose. The release by dendrimer disassembly of an exponential number of dendrimer fragments that serve to alter the properties of a system is termed dendritic amplification.
The disassembly of dendritic structures was realized by a cascade cleavage reaction triggered by an initially stimulated group in the dendrimer periphery. A depolymerizable backbone was engineered into prototypical dendritic structures. Evidence for the completion of the disassembly process is provided by the absorbance peak of the p-nitrophenoxide ion that was intentionally installed at the focal point of the dendrons. Observation of the UV spectra during the disassembly process supports a stepwise cascade cleavage proceeding from the periphery into the core.
Eight poly(aryl) ether dendritic wedges attached to the periphery of a phthalocyanine significantly decreases self-association of these chromophores in solution and the condensed state.
We prepared a rigid, chiral polymer (1) from optically active hydrobenzoin-based subunits. Nonracemic monomer units 6 and 8 were prepared by asymmetric dihydroxylation (AD) methodology and polymerization was carried out under Sonagashira coupling conditions. Polymer 1 was obtained in good yield with a molecular weight M(n) = 5,100 (PDI = 2.3). Modeling suggests that polymer 1 could form a stable helical mainchain conformation in solution or the solid state. The chiroptical data of the polymer and a low-molecular weight model compound (9) are compared.
We present an overview of an entirely new concept in nanotechnology, dendrimer disassembly. Dendrimer disassembly is a process that relies on a single triggering event to initiate multiple cleavages throughout a dendritic structure that result in release of individual dendrimer subunits or larger dendrimer fragments. The potential of this process lies in (1) the nature of dendrimers as covalent assemblages of active species, and using the chemistry of disassembly to release these species into a system; and (2) the role of dendritic components of a system in influencing solubility, energy harvesting, or insulating capabilities, etc., and using the chemistry of disassembly to reverse those contributions to a system. This is a powerful construct, in that dendrimers and dendritic structures can be made up of a wide variety of subunits, compatibilized with many different environments, and incorporated into countless systems. We anticipate that dendritic materials with disassembly capabilities will (a) be useful for traditional polymer degradation technologies and (b) have potential applications in nanotechnology, biomedicine, sensors, etc.