Biomedical subjects

JS Moore

Publications and source records attributed to JS Moore.

6 recordsLinked to original sources

PubMed2000

Conformational ordering of apolar, chiral m-phenylene ethynylene oligomers

A series of m-phenylene ethynylene oligomers containing nonpolar, (S)-3,7-dimethyl-1-octanoxy side chains have been synthesized and studied. In apolar alkane solvents, oligomers of sufficient length (n > 10) were found to adopt a helical conformation with a large twist sense bias. In contrast, in chloroform the oligomers adopt a random coil conformation. Surprisingly, the strong twist sense bias was determined to be highly time dependent and is partially attributed to intermolecular aggregation.

Journal Article↗

PubMed2000

"Masterpiece" copolymer sequences by targeted equilibrium-shifting

We describe an equilibrium model to determine whether a random population of dynamic copolymer sequences could be driven by molecular recognition to a subset of sequences that tightly bind a specific ligand. The model predicts that the population's mean binding constant can be shifted, but because of competitive binding, only to a limited degree (ca. 2 orders of magnitude larger than the original mean). True chemical evolution will require a mechanism for selection and amplification.

Journal Article↗

PubMed2000

Functional hydrogel structures for autonomous flow control inside microfluidic channels

Hydrogels have been developed to respond to a wide variety of stimuli, but their use in macroscopic systems has been hindered by slow response times (diffusion being the rate-limiting factor governing the swelling process). However, there are many natural examples of chemically driven actuation that rely on short diffusion paths to produce a rapid response. It is therefore expected that scaling down hydrogel objects to the micrometre scale should greatly improve response times. At these scales, stimuli-responsive hydrogels could enhance the capabilities of microfluidic systems by allowing self-regulated flow control. Here we report the fabrication of active hydrogel components inside microchannels via direct photopatterning of a liquid phase. Our approach greatly simplifies system construction and assembly as the functional components are fabricated in situ, and the stimuli-responsive hydrogel components perform both sensing and actuation functions. We demonstrate significantly improved response times (less than 10 seconds) in hydrogel valves capable of autonomous control of local flow.

Journal Article↗

PubMed2000

Helical twist sense bias in oligo(phenylene ethynylene)s induced by an optically active flexible tether

[graph and structure: see text] A series of tethered phenylene ethynylene oligomers, which undergo a solvent-dependent conformational transition from a random coil to a helix, has been synthesized. The use of trimethylsilyl ether protecting groups on the (+)-tartaric acid-derived tether results in the formation of helices with a large twist sense bias. In contrast, an isopropylidene ketal protecting group or no protecting group is not only ineffective at helical discrimination but may even inhibit helix formation.

Journal Article↗

PubMed2000

Synthesis and characterization of monodendrons based on 9-phenylcarbazole

A series of 9-phenylcarbazole ethynylene monodenrons have been prepared by palladium-catalyzed coupling reactions creating well-organized arrays of redox centers. The tert-butyl groups attached to the 3,6-positions of peripheral 9-phenylcarbazole monomers provide adequate solubility to a limited degree. Trimer and 7-mer monodendrons were prepared using a monomer with 3, 3-diethyltriazene at its focal point. To facilitate purification, the synthesis of 15-mer monodendron, however, required a monomer bearing a 3-hydroxy-3-methyl-but-1-ynyl group at its focal point as a masking group for the terminal acetylene functionality. Although the solubility was limited, high generation monodendrons were found to be readily soluble in carbon disulfide, a solvent of high polarizability. Spectroscopic studies showed that there is limited through-bond conjugation over the monodendrons, but fluorescence studies suggested the presence of long-range through-space interactions in the higher members of the series.

Journal Article↗

PubMed2000

Twist Sense Bias Induced by Chiral Side Chains in Helically Folded Oligomers.

Cooperative interactions among the side chains of the helically folded phenylene-ethynylene oligomer shown (n=2, 4, 6, 8, 10, 12, 14, 16, 18) can induce a twist sense bias. Therefore, the side chains can play more than just an ancillary role in these conformationally ordered oligomers. The onset of the twist sense bias lags significantly behind the appearance of helical conformations, possibly because a large ensemble of "collapsed" conformations is initially formed.

Journal Article↗