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Biomedical subjects

Jeffrey S Moore

Publications and source records attributed to Jeffrey S Moore.

13 recordsLinked to original sources
PubMed2026

Ultrasound-driven mechanophore activation in living plants.

This study presents a biocompatible, ultrasound-responsive platform for remotely activating mechanochemical reactions within live plant tissue. Fluorogenic Mechanophore-embedded silica NanoParticles (FMNPs) that are thermally stable were engineered to emit blue fluorescence at 440 nm upon mechanical activation. In Solanum lycopersicum (tomato) leaves, activation was achieved through the synergistic combination of gas vesicles (GVs) and high-frequency focused ultrasound (FUS, 550 kHz), enabling spatially localized and minimally invasive stimulation. Low-frequency ultrasound (25 kHz) triggered activation but caused extensive tissue damage, while high-frequency FUS alone was biocompatible yet insufficient to activate FMNPs. Incorporation of GVs as a cavitation amplifier significantly boosted activation efficiency under mild acoustic conditions without observable tissue disruption. In planta fluorescence imaging confirmed that FMNPs retained their functionality after injection into leaf vasculature, and only the combination of GV and FUS produced a statistically significant fluorescence increase, indicating successful mechanochemical activation. This represents a demonstration of noninvasive and biocompatible ultrasound-induced mechanophore activation in live plants. This modular and noninvasive strategy opens possibilities for programmable release of regulatory and metabolic chemicals, biosensing, and synthetic molecular control in plant systems.

Plant Leaves↗
PubMed2002

Hydrogen bond-stabilized helix formation of a m-phenylene ethynylene oligomer.

[reaction: see text] Incorporation of a single hydrogen bonded beta-turn mimic in the backbone of a m-phenylene ethynylene oligomer is shown to affect the thermodynamic properties of the folding reaction. Oligomers 1 and 2 both undergo solvophobic helix formation, but hydrogen bonded oligomer 1 was found to form a more stable helix with a higher tolerance to solvent denaturation than isomeric, non-hydrogen bonded oligomer 2.

Alkynes↗
PubMed2002

Helical pitch of m-phenylene ethynylene foldamers by double spin labeling.

To investigate the helical conformation of oligo(m-phenylene ethynylene)s, a pair of TEMPO spin labels were appended to the backbone. The two TEMPO radicals were separated by the four, five, and six repeating units. ESR spectra of the labeled oligomers were measured in chloroform and in ethyl acetate solvents in which the oligomers are disordered and folded, respectively. The measurement and analysis of ESR spectra revealed that six repeating units make one helical turn.

Journal Article↗
PubMed2002

Reversible polymerization driven by folding.

Bisfunctionalized m-phenylene ethynylene imine oligomers were polymerized in the polar solvent acetonitrile, resulting in high-molecular weight poly(m-phenylene ethynylene imine)s. It is hypothesized that this polymerization, which proceeds through the reversible metathesis of imine bonds, is driven by the folding of the long m-phenylene ethynylene imine chains. Upon conducting the polymerization in a series of solvents in which the m-phenylene ethynylene oligomers exhibit different folding stabilities, it was possible to correlate the molecular weight of the resulting poly(m-phenylene ethynylene imine)s with the helical stability of the corresponding oligomers. The polymerization was also demonstrated to be reversible and responsive to solvent and temperature changes.

Journal Article↗
PubMed2002

Principles of surface-directed liquid flow in microfluidic channels.

To direct liquid flow inside microchannels, surface free energies were patterned by use of self-assembled monolayers (SAMs) in combination with either multistream laminar flow or photolithography. For the photolithographic method, two photocleavable SAMs were designed and synthesized. Carboxylic acid-terminated monolayers were obtained by photodeprotection, which was confirmed by contact angle and X-ray photoelectron spectroscopy. Using either of these patterning methods, we show that aqueous liquids flow only along the hydrophilic pathways when the pressure is maintained below a critical value; the liquids are referred to as being confined by virtual walls. Several principles of liquid flow in surface-patterned channels were derived analytically and verified experimentally. These principles include the maximum pressure that virtual walls can withstand, the critical width of the hydrophilic pathway that can support spontaneous flow, the smallest width of the liquid streams under an external pressure, the critical radius of curvature of turns that can be introduced into the hydrophilic pathway without liquid crossing the hydrophilic-hydrophobic boundary, and the minimal distance for two liquid streams to remain separated under the maximum pressure. Experimental results are in good agreement with the analytical predictions.

Biotechnology↗
PubMed2002

Molecular packing and morphology of oligo(m-phenylene ethynylene) foldamers.

Understanding and controlling solid-state morphologies and molecular conformations is the key to optimizing the properties of materials. As an example for the influence of small chemical changes on solid-state structures, we studied oligo(m-phenylene ethynylene) foldamers, where the introduction of an endo-methyl group induces a transition from an extended all-transoid to a helical all-cisoid conformation. The resulting structural changes were analyzed by X-ray diffraction (XRD), polarized optical microscopy (POM), and low-dose high-resolution electron microscopy (LD-HREM) over several length scales from the molecular to the mesoscopic level. The strong tendency of the endo-methyl oligomer 1 to form stable compact helices in solution resulted in round droplets with an ordered hexagonal columnar (Col(ho)) liquid crystalline structure, where shrinkage during the crystallization resulted in the formation of a banded texture. On the other hand, the endo-hydrogen oligomer 2 exhibited a very different morphology; its extended linear shape was maintained during crystallization and resulted in an extended lamellar structure, which was determined by a compromise between crystalline packing and minimization of the surface area. Another pronounced difference between both molecular structures was the ability of the extended lamellar "crystals" to bend, whereas the helices form either straight or disordered domains. In addition, both materials exhibit strong surface effects, which extend considerably inside the droplet and induce uniform bending of the supramolecular structures.

Journal Article↗
PubMed2002

Synthesis and self-association of an imine-containing m-phenylene ethynylene macrocycle.

The purpose of this study was to test the suitability of the imine bond as a structural unit within the backbone of phenylene ethynylene macrocycles and oligomers by determining the ability of m-phenylene ethynylene macrocycle 1 to form pi-stacked aggregates in both solution and the solid state. Macrocycle 1, with two imine bonds, was synthesized in high yield from diamine 4 and dialdehyde 5. The imine-forming macrocyclization step was carried out under a variety of conditions, with the best yield obtained simply by refluxing the reactants in methanol. The self-association behavior of 1 in various solvents was probed by (1)H NMR. The association constants (K(E)) in acetone-d(6) and tetrahydrofuran-d(8) were determined by fitting the concentration-dependent chemical shifts with indefinite self-association models. The results showed that solvophobically driven intermolecular pi-pi stacking could be preserved in the imine-containing m-phenylene ethynylene macrocycles. Interestingly, in acetone macrocycle 1 exhibited a stronger tendency to form a dimer rather than higher aggregates. We postulate that this behavior may be due to electrostatic attraction between dipolar imine groups. The solid-state packing of 1 was studied by wide- and small-angle X-ray powder diffraction (WAXD and SAXD). Bragg reflections of 1 were consistent with a hexagonal packing motif similar to our previous studies on m-phenylene ethynylene macrocycles that formed columnar liquid crystal phases.

Journal Article↗
PubMed2002

The size-selective synthesis of folded oligomers by dynamic templation.

A dynamic pool of m-phenylene ethynylene oligomers generated by sequence ligation using the imine metathesis reaction was equilibrated under a variety of conditions, and the mixture of products was analyzed by HPLC. The equilibration was performed in the presence and absence of rodlike ligand 2b, which exhibits an affinity for the helical oligomers that is very length specific. Among the eight oligomers generated during metathesis equilibrium, the formation of 22-mer 6b was enhanced in acetonitrile in the presence of 2b. This particular oligomer has the highest binding affinity for 2b. Quantitative analysis by HPLC of the products indicated that 6b was produced in 66% yield in the presence of 2 equiv 2b while a 37% yield was produced in the absence of 2b. Judging from the binding affinities of oligomers 6 with 2b, the equilibrium shifting was driven by the selective binding of 6b with 2b.

Journal Article↗
PubMed2002

Control and applications of immiscible liquids in microchannels.

Photolithography was used in combination with photocleavable self-assembled monolayers to pattern surface free energies inside microchannels enabling the control of the boundary between immiscible liquids. While aqueous solutions are confined to the hydrophilic pathways by surface forces alone, organic liquids are confined to the hydrophobic region only if the aqueous liquid first occupies the hydrophilic region. In this way, stable liquid boundaries between immiscible liquids are possible as long as the pressures are maintained below critical values. The maximum pressures are determined by the interfacial tension of the aqueous solution and organic liquid, channel depth, and advancing contact angle (theta;(a)). Experimental results on maximum pressures are in good agreement with the analytical values. The ability to confine and position the boundary between immiscible liquids inside microchannels leads to a broad range of applications in microfluidic systems, which is exemplified by fabrication of a semipermeable membrane in a surface-patterned channel via interfacial polymerization.

Journal Article↗
PubMed2002

Helicogenicity of solvents in the conformational equilibrium of oligo(m-phenylene ethynylene)s: implications for foldamer research.

A (R)-binaphthol tethered bis-hexameric oligo(m-phenylene ethynylene) foldamer was examined in 30 solvents to correlate the unfolded-folded conformational equilibrium to bulk solvent properties and specific solvent-chain interactions. The oligomer is soluble in a variety of solvents of intermediate polarity, with the majority of these solvents being helicogenic. The amphiphilic nature of the chain allows the solvophobic backbone to be solubilized in a wide range of solvents through the polar triethylene glycol side chains. As demonstrated through UV and CD spectroscopic experiments, the helical conformation is increasingly stabilized with increasing solvent polarity in the absence of specific solvent-chain interactions. Surprisingly, very few solvents are capable of fully denaturing the helix, indicating the strength of the solvophobic driving forces in this cooperative system. The folding reaction for this amphiphilic oligomer can be described as a compromise in solubility properties, where chains collapse intramolecularly into helical conformations to minimize solvent-backbone contacts while maintaining favorable solvent-side chain interactions for solvation. In terms of mimicking the properties of biomacromolecules, foldamers using solvophobic driving forces must be tempered with functionalities that promote solubility of the folded state while at the same time allowing access to the unfolded state through the use of denaturants.

Alkynes↗