Dominic V Mcgrath
Publications
Abstract:
Metal phthalocyanines (Fe, Co, Ni and Sn) and ruthenium tetramethylcyclam 14 and 15 were studied as cocatalysts for methanol oxidation on platinum supported catalysts. The formation of well defined monolayers of the adsorbed complexes was inferred from the Langmuirian form of the adsorption isotherms in solutions of macrocycles. The coverage at monolayer levels was low, e.g. 1.25 to 2.25 × 1013 molecules cm-2 or 400 to 800 Å2 molecule-1. Enhancement for the methanol oxidation reaction was observed for Pt co-catalyzed with Sn phthalocyanine and Ru tetramethylcyclam. Ru tetramethylcyclam showed an enhancement for methanol oxidation on a per unit weight basis over pure Pt, approaching the activity of PtRu at lower potentials. Increasing the size of the nitrogen ring from 14 to 15 resulted in a lower redox potential and increase in the activity of methanol oxidation. The activity of Pt co-catalyzed with Ru TMC 15 decreased with time suggesting that the macrocycle was desorbing from the supported catalyst surface. © 1998 Elsevier Science Ltd. All rights reserved.
Abstract:
We have prepared a series of chiral dendrons (1-4) in which chiral subunits are placed in individual generational shells at varying distances from the focal point. The optical activity of these chiral dendritic structures is successfully modeled using structurally similar low-molecular weight model compounds. In dendrons 1a and 1b a chiral subunit is directly adjacent to the focal point, whereas in dendrons 2, 3, and 4a,b the chiral subunits are incorporated in the interior of the dendron. A marked difference in optical activity between the former (1a and 1b) and latter (2, 3, 4a,b) dendrons is mirrored in the optical activities of model compounds 12a, 12b, 19a, and 19b. These model compounds directly mimic the surrounding constitution of the chiral subunits in the dendrons. This successful analysis of the chiroptical data using low-molecular weight model compounds suggests that these dendrons do not possess conformational order in solution.
Abstract:
The photoresponsive behavior of dendrimers with methyl ester exteriors and azobenzene linkers were studied. Saponification of dendrimer 6 was also accomplished to provide a water soluble dendrimer with a hydrophobic interior.
PMID: 14971953;Abstract:
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.
Abstract:
Azobenzene-containing shape-persistent dendrimers were synthesized to address the effect of the dendrimer subunit on the behavior of well-defined systems. The resulting dendrimers have rigid structures with phenylacetylene subunits. The properties of the dendrimers allow comparison with previously-prepared flexible azobenzene-containing dendrimers.