Showing papers by "Jennifer M. Heemstra published in 2004"
TL;DR: The methylation rate for a series of pyridine-containing phenylene ethynylene oligomers shows a nonlinear dependence on chain length, with a significant rate enhancement observed for oligomers that adopt a folded, helical conformation.
Abstract: The methylation rate for a series of pyridine-containing phenylene ethynylene oligomers shows a nonlinear dependence on chain length, with a significant rate enhancement observed for oligomers that adopt a folded, helical conformation. The folded structure provides a microenvironment that lowers the energy barrier for the methylation reaction. Of these noncovalent interactions, the largest stabilization may arise from binding of methyl iodide in the hydrophobic cavity of the folded oligomer, in close proximity to the pyridine nucleophile.
57 citations
TL;DR: The folded structure of a m-phenylene ethynylene oligomer is tolerant to single-site modifications to both the backbone sequence and end groups, allowing the oligomer sequence to be customized without a significant change in stability.
41 citations
TL;DR: Intramolecular cation-pi interactions between a methyl pyridinium ion and a phenyl ring stabilize the folded structure of a phenyleneethynylene oligomer.
31 citations
TL;DR: Incorporation of a pyridine monomer into the backbone of a m-phenylene ethynylene oligomer allows functionalization of the interior binding cavity of the folded oligomer, granting access to a pK(a) range of 5-14 in acetonitrile.
30 citations
TL;DR: A N,N-(dimethylamino)pyridine monomer is incorporated into the backbone of a m-phenyleneethynylene oligomer such that the pyridine nitrogen is located on the interior surface of the binding cavity in the folded structure of the oligomer.
Abstract: A N,N-(dimethylamino)pyridine monomer is incorporated into the backbone of a m-phenyleneethynylene oligomer such that the pyridine nitrogen is located on the interior surface of the binding cavity in the folded structure of the oligomer. For an oligomer having a chain length of 13 monomer units, competitive inhibition experiments reveal that methyl iodide binds weakly within the oligomer cavity with an association constant Ka = 2 M-1, and the oligomer−methyl iodide complex reacts with unimolecular rate constant ku = 0.082 s-1 to provide the methylated product. The effective molarity is calculated to be 230 M by comparison of ku for the 13-mer with the second-order rate constant for a 3-mer that is too short to fold and thus unable to bind methyl iodide.
26 citations
TL;DR: In this paper, a series of substituted azobenzene dyes was found to span a range of 8 p K a units in acetonitrile, and the UV absorption spectra of the dyes are responsive to protonation, changing in both absorption maximum and intensity.
8 citations