Biomedical subjects

Thoi D Nguyen

Publications and source records attributed to Thoi D Nguyen.

5 recordsLinked to original sources

PubMed2007

Design and optimization of molecular nanovalves based on redox-switchable bistable rotaxanes.

Redox-controllable molecular nanovalves based on mesoporous silica nanoparticles have been fabricated, using two bistable [2]rotaxanes with different spacer lengths between their recognition sites as the gatekeepers. Three different linkers with varying chain lengths have been employed to attach the bistable [2]rotaxane molecules covalently to the silica substrate. These nanovalves can be classified as having IN or OUT locations, based on the positions of the tethered bistable [2]rotaxanes with respect to the entrances to the nanopores. The nanovalves are more efficient when the bistable [2]rotaxane-based gatekeepers are anchored deep within (IN) the pores than when they are attached closer to (OUT) the pores' orifices. The silica nanopores can be closed and opened by moving the mechanically interlocked ring component of the bistable [2]rotaxane closer to and away from the pores' orifices, respectively, a process which allows luminescent probe molecules, such as coumarins, tris(2-phenylpyridine)iridium, and rhodamine B, to be loaded into or released from the mesoporous silica substrate on demand. The lengths of the linkers between the surface and the rotaxane molecules also play a critical role in determining the effectiveness of the nanovalves. The shorter the linkers, the less leaky are the nanovalves. However, the distance between the recognition units on the rod section of the rotaxane molecules does not have any significant influence on the nanovalves' leakiness. The controlled release of the probe molecules was investigated by measuring their luminescence intensities in response to ascorbic acid, which induces the ring's movement away from the pores' orifices, and consequently opens the nanovalves.

Journal Article↗

PubMed2006

Construction of a pH-driven supramolecular nanovalve.

[Structure: see text] The versatility of supramolecular chemistry has been exploited in constructing nanovalves based on mesoporous silica MCM-41 and the mutual recognition between secondary dialkylammonium ions and dibenzo[24]crown-8 (DB24C8). Naphthalene-containing dialkylammonium threads were tethered to the MCM-41, followed by loading with coumarin 460 and capping with DB24C8. Controlled release of coumarin 460 from the pores of MCM-41 was demonstrated using different bases. The rate of release of coumarin 460 from the nanovalves depends on the size of the base.

Coumarins↗

PubMed2005

A reversible molecular valve.

In everyday life, a macroscopic valve is a device with a movable control element that regulates the flow of gases or liquids by blocking and opening passageways. Construction of such a device on the nanoscale level requires (i) suitably proportioned movable control elements, (ii) a method for operating them on demand, and (iii) appropriately sized passageways. These three conditions can be fulfilled by attaching organic, mechanically interlocked, linear motor molecules that can be operated under chemical, electrical, or optical stimuli to stable inorganic porous frameworks (i.e., by self-assembling organic machinery on top of an inorganic chassis). In this article, we demonstrate a reversibly operating nanovalve that can be turned on and off by redox chemistry. It traps and releases molecules from a maze of nanoscopic passageways in silica by controlling the operation of redox-activated bistable [2]rotaxane molecules tethered to the openings of nanopores leading out of a nanoscale reservoir.

Models, Chemical↗

PubMed2003

Chemistry of constrained dioxocyclam ligands with Co(III): unusual examples of C-H and C-N bond cleavage.

The reactions between H(2)dc3 and Co(acac)(3) have been studied in the presence and absence of base. In the presence of base, a complex with an intramolecular Co-C bond, Co(dc3-C-(8))(H(2)O), 1, is formed, presumably through heterolytic C-H bond activation. An X-ray crystallographic study demonstrates the presence of a Co-C bond and shows that the diazacyclooctane (daco) subunit adopts the chair-boat conformation with respect to the metal. The cobalt-carbon bond induces strain in the macrocycle as demonstrated by bond angles significantly deviating from tetrahedral. The (13)C NMR resonance of the carbon atom bound to cobalt (-10.5 ppm) suggests significant ionic character in the cobalt-carbon bond. However, we were unable to cleave this bond in the presence of strong acid. In the absence of base, the reaction of Co(acac)(3) with H(2)dc3 resulted in C-N cleavage of the ligand and the formation of a complex of dioxocyclam, Co(dc)(acac), 2. This complex has subsequently been prepared in high yield by the reaction of Co(acac)(3) with dioxocyclam. An X-ray crystallographic study demonstrates that dioxocyclam adopts the heretofore unreported cis configuration, having folded along a N-Co-N axis that is perpendicular to the Co-acac plane.

Carbon↗

PubMed2003

Solution-state and solid-state structural characterization of complexes of a new macrocyclic ligand containing the 1,5-diazacyclooctane subunit.

The synthesis and characterization of a new constrained tetraazamacrocyclic ligand, 1,4,8,11-tetraazabicyclo[9.3.3]heptadecane (1,11-C(3)-cyclam), is reported. Because of its basicity, this ligand (pK(a) of the protonated form >13.5) requires aprotic solvents for its metalation reactions. Two complexes of this ligand, [Ni(1,11-C(3)-cyclam](OTf)(2) and [Co(1,11-C(3)-cyclam)(NCS)(2)](OTf), have been characterized by single-crystal X-ray crystallography. For the Ni(II) complex, the 1,5-diazacyclooctane (daco) subunit of the ligand is in the chair-boat conformation, whereas that same subunit in the Co(III) complex is in the chair-chair conformation. For the Ni(II) complex, C(12) and H(12a) block one of the coordination sites. The (1)H and (13)C NMR spectra of the Ni(II) complex in D(2)O have very sharp resonances, indicative of low-spin Ni(II). The resonance for H(12a) appears at 4.5 ppm, suggesting an interaction with Ni(II). In acetonitrile, the (1)H and (13)C spectra are broadened, indicative of a low-spin/high-spin equilibrium due to axial coordination by acetonitrile. C(12) experiences the greatest degree of broadening in the (13)C NMR spectrum. Variable-temperature NMR spectroscopy from -70 to +80 degrees C shows no significant change as a function of temperature. The electronic spectrum of the Ni(II) complex (lambda(max) = 449.9 nm) is consistent with steric and electronic factors for this complex.

Alkanes↗