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Biomedical subjects

Manuel Marquez

Publications and source records attributed to Manuel Marquez.

At least 19 recordsLinked to original sources
PubMed2007

Theoretical evidence for C-F bond activation by a fluoro-calix[4]pyrrole-tert-amine macrocycle.

Density functional theory as well as highly correlated ab initio molecular orbital theory was used to explore the possibility of activating C-F bonds in fluoroalkanes by organic macrocycles. The results indicate that the reaction between fluoro-calix [4]pyrrole-tert-amine and CH3F via a Menshutkin displacement mechanism is highly favorable and competitive from a thermochemical point of view with the very efficient C-Cl activation by a simple macrocyclic amine recently reported in the literature (Stanger, L. J.; Noll, B. C.; Gonzalez, C.; Marquez, M.; Smith, B. D. J. Am. Chem. Soc. 2005, 127, 4184).

Journal Article↗
PubMed2007

Temperature-responsive semipermeable capsules composed of colloidal microgel spheres.

We present semipermeable, hollow capsules (colloidosomes) that expand and contract upon heating and cooling. The capsules are composed of micrometer-sized poly(N-isopropylacrylamide)-co-acrylic acid microgel particles, which exhibit a reversible size transition near 34 degrees C. The microgel particles assemble on the surfaces of water droplets in oil. Addition of the diblock copolymer poly(butadiene-b-N-methyl 4-vinyl pyridinium iodide) to the oil results in soft, elastic membranes of microgel particles that remain intact after the droplet interfaces are dissolved. Under heating, the capsules contract reversibly by 13% or irreversibly by 40% in radius. These stimulus-responsive colloidosomes might be useful for controlled release or as microscopic actuators.

Biocompatible Materials↗
PubMed2007

Photo-, thermally, and pH-responsive microgels.

Microgels with photo-, thermally, and pH-responsive properties in aqueous suspension have been synthesized and characterized using dynamic light scattering and UV-visible spectroscopy. The new route involved first preparing poly(N-isopropylacrylamide) (PNIPAM)-allylamine copolymer microgels and a spiropyran photochrome (SP) bearing a carboxylic acid group. Then the functionalized spiropyran was coupled to the microgel via an amide bond. The dark-equilibrated gel particles feature spiropyran molecules in the polar, merocyanine form. After irradiation of visible light, the particle size becomes smaller because spiropyran changes to the relatively nonpolar, closed spiro form. The PNIPAM-SP microgels undergo a volume phase transition in water from a swollen state to a collapsed state with increasing temperature under all light conditions. However, the transition temperature range of the PNIPAM-SP is much broader than that for the PNIPAM without SP. The PNIPAM-SP microgels are monodisperse and self-assemble into a crystalline lattice while in suspension. The UV-visible spectra of an aqueous suspension of PNIPAM-SP microgel in the dark-adapted, merocyanine form showed both an absorption peak around 512 nm due to the merocyanine (giving a reddish color to the suspension) and two sharp peaks from Bragg diffraction of colloidal crystallites. Upon visible irradiation, the 512-nm band bleached significantly due to spiropyran photoisomerization. The spiropyran photoisomerization and accompanying color changes of the suspension were reversible upon alternating dark, UV, and visible light irradiation. Due to the residues of amine groups, the swelling capability of PNIPAM-SP microgels reduces as the pH value is changed from 7 to 10.

Acrylic Resins↗
PubMed2006

Optical imaging of bacterial infection in living mice using a fluorescent near-infrared molecular probe.

An optical imaging probe was synthesized by attaching a near-infrared carbocyanine fluorophore to an affinity group containing two zinc(II) dipicolylamine (Zn-DPA) units. The probe has a strong and selective affinity for the surfaces of bacteria, and it was used to image infections of Gram-positive S. aureus and Gram-negative E. coli bacteria in living nude mice. After intravenous injection, the probe selectively accumulates at the sites of localized bacterial infections in the thigh muscles of the mice.

Animals↗
PubMed2006

Optical properties of Au-Ag nanoboxes studied by single nanoparticle spectroscopy.

The optical properties of two Au-Ag nanobox samples with average edge lengths of 44 and 58 nm and wall thicknesses of 6 and 8 nm, respectively, have been studied by single particle spectroscopy. The measurements gave an average line width of Gamma = 306 +/- 7 meV with a standard deviation of sigma = 30 meV for the 44-nm boxes, and Gamma = 350 +/- 9 meV with sigma = 35 meV for the 58-nm boxes. These line widths are much broader than those of gold nanorods with comparable resonance energies. The increased broadening is attributed to a combination of surface scattering of electrons, as well as increased radiation damping for the nanoboxes. Discrete dipole approximation calculations have been performed with and without surface scattering of electrons to compare with the experimental spectra. The calculations confirm that both electron-surface scattering and radiation damping are important effects in this system.

Algorithms↗
PubMed2006

Microfluidic assembly of homogeneous and Janus colloid-filled hydrogel granules.

The microfluidic assembly of colloid-filled hydrogel granules of varying shape and composition is described. First, drops are formed by shearing a concentrated colloidal microsphere-acrylamide suspension in a continuous oil phase using a sheath-flow device. Both homogeneous and Janus (hemispherically distinct) spheres and disks are produced by confining the assembled drops in microchannels of varying geometry. Next, photopolymerization is carried out shortly after drop breakup to preserve their morphology. Representative wet and dried granules are characterized using fluorescence and scanning electron microscopy, respectively. Our approach offers a facile route for assembling colloid-filled hydrogel granules with controlled shape and composition.

Colloids↗
PubMed2006

Stable jets of viscoelastic fluids and self-assembled cylindrical capsules by hydrodynamic focusing.

We demonstrate formation of long-lived cylindrical jets of a viscoelastic fluid using hydrodynamic focusing. A solution of polyacrylamide in water is driven coaxially with immiscible oil and subjected to strong extensional flow. At high flow rates, the aqueous phase forms jets that are 4-90 microm in diameter and several centimeters long. The liquid surfaces of these jets are then used as templates for assembly of microspheres into novel rigid and hollow cylinders.

Acrylic Resins↗
PubMed2006

Gold nanostructures: engineering their plasmonic properties for biomedical applications.

The surface plasmon resonance peaks of gold nanostructures can be tuned from the visible to the near infrared region by controlling the shape and structure (solid vs. hollow). In this tutorial review we highlight this concept by comparing four typical examples: nanospheres, nanorods, nanoshells, and nanocages. A combination of this optical tunability with the inertness of gold makes gold nanostructures well suited for various biomedical applications.

Biomedical Engineering↗
PubMed2006

First-principles study of hydrogen storage on Li12C60.

Solid state materials capable of storing hydrogen with high gravimetric (9 wt %) and volumetric density (70 g/L) are critical for the success of a new hydrogen economy. In addition, an ideal storage system should be able to operate under ambient thermodynamic conditions and exhibit fast hydrogen sorption kinetics. No materials are known that meet all these requirements. While recent theoretical efforts showed some promise for transition-metal-coated carbon fullerenes, later studies demonstrated that these metal atoms prefer to cluster on the fullerene surface, thus reducing greatly the weight percentage of stored hydrogen. Using density functional theory we show that Li-coated fullerenes do not suffer from this constraint. In particular, we find that an isolated Li(12)C(60) cluster where Li atoms are capped onto the pentagonal faces of the fullerene not only is very stable but also can store up to 120 hydrogen atoms in molecular form with a binding energy of 0.075 eV/H(2). In addition, the structural integrity of Li(12)C(60) clusters is maintained when they are allowed to interact with each other. The lowest energy structure of the dimer is one where the Li atom capped on the five-member ring of one fullerene binds to the six-member ring of the other. The binding of hydrogen to the linking Li atom and the potential of materials composed of Li(12)C(60) building blocks for hydrogen storage are discussed.

Journal Article↗
PubMed2006

Highly porous fibers by electrospinning into a cryogenic liquid.

Highly porous fibers of various polymers were created by electrospinning with a modified collector. A bath of liquid nitrogen was used to freeze the fibers, inducing a phase separation between the polymer and the solvent. When the solvent was removed in vacuo, highly porous fibers were obtained. Poly(styrene), poly(acrylonitrile), poly(vinylidene fluoride), and poly(epsilon-caprolactone) were all electrospun into porous fibers using this simple method. These porous fibers have a range of potential applications in encapsulation, controlled release, superhydrophobic coating, and lightweight reinforcement.

Journal Article↗
PubMed2006

Ultrafast laser studies of the photothermal properties of gold nanocages.

Au nanocages were synthesized via a galvanic replacement reaction. The extinction peak of these hollow structured particles is shifted into the near-IR compared with the Ag nanocube templates. Energy transfer from the Au nanocages into the surrounding environment (water) as well as the coherently excited vibrational modes of the nanocages were studied by femtosecond pump-probe spectroscopy. The time scale for energy relaxation was found to increase with the size of the particles, with the relaxation time being independent of the laser intensity. The time scales for relaxation are comparable to those for solid spherical gold particles and are consistent with energy relaxation being controlled by heat dissipation in the solvent. The period of the coherently excited vibrational mode is proportional to the dimensions of the nanocages. Intensity-dependent measurements show that in solution the nanocages maintain their integrity up to lattice temperatures of 1100 +/- 100 K.

Gold↗
PubMed2006

Growth of columnar hydrogel colloidal crystals in water-organic solvent mixture.

A novel emulsion method has been demonstrated to grow columnar hydrogel colloidal crystals by mixing an aqueous suspension of poly-N-isopropylacrylamide-co-allylamine microgels with organic solvent, driven by the coalescence of micelles consisting of organic oil droplets coated by many microgels. This method leads to microgel colloidal crystals of several centimeters growing from the top to the bottom along the gravity direction. Both temperature and polymer concentration play critical roles for the formation of columnar crystals. A phase diagram has been determined, and it can be used as a guide to selectively grow different crystals, including columnar crystals and randomly oriented crystals, and enable the coexistence of columnar crystals and randomly oriented crystals.

Journal Article↗
PubMed2006

Chemisorption-induced spin symmetry breaking in gold clusters and the onset of paramagnetism in capped gold nanoparticles.

We present a simple model to describe the induction of magnetic behavior on gold clusters upon chemisorption of one organic molecule with different chemical linkers. In particular, we address the problem of stability of the lowest lying singlet and show that for some linkers there exists a spin symmetry-breaking that lowers the energy and leads to preferential spin density localization on the gold atoms neighboring the chemisorption site. The model is basically an adaptation of the Stoner model for itinerant electron ferromagnetism to finite clusters and it may have important implications for our understanding of surface magnetism in larger nanosystems and its relevance to electronic transport in electrode-molecule interfaces.

Journal Article↗
PubMed2006

Encapsulation and suspension of hydrophobic liquids via electro-hydrodynamics.

There are situations in which bioactive products of interest in biotechnology turn out to be hydrophobic. To reach high uniform levels of such products in water-based host fluids, such as those existing in many biological environments, one strategy consists on dividing the bioactive product into tiny micrometer (or sub-micrometer) pieces, since these are much more amenable of being uniformly dispersed and stabilized in the host fluid. On the other hand, if the bioactive product must act at specific locations, these micrometer pieces need to be hold in place, an objective that may be achieved by encapsulating them in mats of fibers. Here we demonstrate how these tasks may be accomplished by resorting to the generation and control of electrified coaxial jets of a hydrophilic liquid surrounding the hydrophobic liquid carrying the bioactive substance. When the process is carried out inside a dielectric liquid, double oil/water/oil and simple oil/water emulsions may be formed. On the other hand, when the process runs in air and a biopolymer is added to the hydrophilic liquid, then non woven mats of beaded nanofibers, encapsulating the bioactive product in the beads, are generated.

Biocompatible Materials↗
PubMed2006

Melt coaxial electrospinning: a versatile method for the encapsulation of solid materials and fabrication of phase change nanofibers.

We have developed a method based on melt coaxial electrospinning for fabricating phase change nanofibers consisting of long-chain hydrocarbon cores and composite sheaths. This method combines melt electrospinning with a coaxial spinneret and allows for nonpolar solids such as paraffins to be electrospun and encapsulated in one step. Shape-stabilized, phase change nanofibers have many potential applications as they are able to absorb, hold, and release large amounts of thermal energy over a certain temperature range by taking advantage of the large heat of fusion of long-chain hydrocarbons. We have focused on compounds with melting points near room temperature (octadecane) and body temperature (eicosane) as these temperature ranges are most valuable in practice. We have produced thermally stable, phase change materials up to 45 wt % octadecane, as measured by differential scanning calorimetry. In addition, the resultant fibers display novel segmented morphologies for the cores due to the rapid solidification of the hydrocarbons driven by evaporative cooling of the carrier solution. Aside from the fabrication of phase change nanofibers, the melt coaxial method is promising for applications related to microencapsulation and controlled release of drugs.

Journal Article↗
PubMed2005

Simple electrooptical sensors for inorganic anions.

[reaction: see text] Electrooptical sensors consisting of a conjugated chromophore undergoing a change in color and a redox-active moiety such as quinone fused to the chromophore were synthesized. Strong changes in colorimetric and electrochemical properties were observed in the presence of inorganic anions. A unique anion-specific response was observed for fluoride, pyrophosphate, and acetate. DFT (B3LYP/6-31G) calculations performed for both "on/off" states of a sensor-fluoride model are in good agreement with the observed electrochemical and spectroscopic data.

Journal Article↗