Biomedical subjects

G J Blanchard

Publications and source records attributed to G J Blanchard.

18 recordsLinked to original sources

PubMed2006

Gauging the effect of impurities on lipid bilayer phase transition temperature.

We report on the gel-to-fluid phase transition behavior of unilamellar vesicles formed with 1,2-dimyristoyl-sn-phosphatidylcholine (14:0 DMPC). We have interrogated the gel-to-fluid transition temperature of these bilayer structures using the chromophore perylene incorporated in their nonpolar region. We observe a discontinuous change in the reorientation time of perylene sequestered within the bilayer at the known melting transition temperature of 14:0 DMPC, 24 degrees C. The perylene reorientation data reveal a local viscosity of 14.5 +/- 2.5 cP in the gel phase, and 8.5 +/- 1.5 cP in the fluid phase. We have also incorporated small amounts of 1,2-dimyristoleoyl-sn-glycero-3-phosphocholine (14:1 DMPC) into these unilamellar vesicles and find that the melting transition temperature for these bilayers varies in a regular manner with the amount of 14:1 DMPC present. These data demonstrate that very little "contaminant" is required to cause a substantial change in the gel-to-fluid transition temperature, even though these contaminants do not alter the viscosity of the bilayer sensed by perylene, either above or below the melting transition.

Chromogenic Compounds↗

PubMed2006

Investigating internal structural differences between micelles and unilamellar vesicles of decanoic acid/sodium decanoate.

We report on the dynamics of a chromophore sequestered within the nonpolar regions of micelles and unilamellar vesicles comprised of decanoic acid/sodium decanoate. We find that there is a measurable difference in the motional dynamics of the chromophore perylene in these two nonpolar media, with the vesicle structure forming a somewhat less viscous environment than the micelle. In all cases, the chromophore reorients as a prolate rotor, implying a local environment with a nominally similar shape for both micelle and vesicle structures. These findings demonstrate that the organization of micelles is measurably different than that of bilayers.

Journal Article↗

PubMed2006

Quantitating the association of charged molecules with ionic micelles.

We have studied micelles comprised of cationic (CTAB) and anionic (SDS) surfactants through the interactions of solution phase anionic disodium fluorescein (DSF) and cationic rhodamine 110 (R110) dyes with perylene sequestered within the micelles. Fluorescence lifetime measurements monitor energy transfer between the nonpolar optical donor within the micelle and ionic probes in the surrounding solution. The efficiency of this process is mediated by the extent to which the ionic dyes interact with the micelle palisade layer, and our fluorescence lifetime data allow us to determine the association constants for acceptor-micelle interactions.

Anions↗

PubMed2006

Probing organization and communication at layered interfaces.

We have investigated the local organization intrinsic to a variety of interfacial structures, by both electrochemical and spectroscopic means. Our focus has been on the design and construction of biomimetic interfaces, where a lipid bilayer or a hybrid bilayer membrane can be bound to an interface. The goal of this work is ultimately to create an interface on a transducer surface that can support an enzyme in its active form. To this point, we have examined the extent of organization that is achievable in monolayers that will be used to bind bilayer structures to a transducer surface. Our electrochemical data point to the important role of the substrate surface in determining adlayer organization. We have also investigated the fluidity and structural heterogeneity of lipid bilayers using time-resolved and steady state fluorescence spectroscopy. Our data point to the highly interactive nature of lipid bilayer constituents, where perturbations introduced to one region have significant consequences on other regions of the bilayer. Such information is directly relevant to the existence and properties of lipid raft structures in both model and biological bilayers.

Biomimetic Materials↗

PubMed2006

Formation of gold nanoparticles using amine reducing agents.

We report on the use of amines as reducing agents in the formation of gold nanoparticles. We can predict whether the amines will function as reducing agents in this reaction based on their redox properties. The kinetics of AuNP formation can be understood in terms of Marcus electron transfer theory, where the slower reactions proceed in the inverted region owing to the difference between the Au reduction potential and the amine oxidation potential. For a certain number of the amine reducing agents, following reduction of HAuCl4, a subsequent reaction of the amine radical cation with other reducing agent molecules in solution can form poly(amine)s. These findings point collectively to the utility of amines as reducing agents in AuNP formation and provide information on the conditions under which these reactions will proceed.

Amines↗

PubMed2006

Quantitating the dynamics of NBD hexanoic acid in homogeneous solution and in solutions containing unilamellar vesicles.

We report here on the motional and fluorescence lifetime dynamics of the chromophore NBDHA (6-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)hexanoic acid) in neat solvents and in aqueous solutions containing unilamellar vesicles of varying composition. We measure the transient response of this chromophore by time-correlated single-photon counting, using one- and two-photon excitation to resolve the Cartesian components of the rotational diffusion constant, D. Our experimental data for NBDHA in selected solvents of varying viscosity demonstrate that one- and two-photon excitation probe different components of the rotational diffusion constant and that this chromophore reorients as a prolate rotor with an aspect ratio of approximately 2. For NBDHA in aqueous solutions containing unilamellar vesicles of varying composition, we recover the same reorientation behavior regardless of vesicle composition. Fluorescence lifetime and steady-state fluorescence data show the chromophore to reside in a polar environment that is different from neat water. We understand these data in the context of the chromophore residing in close proximity to the unilamellar vesicle polar headgroups in all cases.

Caproates↗

PubMed2006

Dynamics of 4-benzylamino-7-nitrobenzofurazan in the 1-propanol/water binary solvent system. Evidence for composition-dependent solvent organization.

We report on the fluorescence lifetime and rotational diffusion dynamics of 4-benzylamino-7-nitrobenzofurazan (BBD) in a series of 1-propanol/water binary solvent systems. The fluorescence lifetime of BBD increases monotonically with increasing 1-propanol concentration. The rotational diffusion dynamics of BBD also vary with solution 1-propanol content, but this variation is not monotonic. Comparison of the BBD rotational diffusion time constant to solution viscosity and 1-propanol composition reveals the presence of a solution composition dependence of solvent-solute interactions, with a relative decrease in solvent-solute interaction strength for solvent system compositions where the 1-propanol/water azeotrope is known to exist. These data point collectively to the existence of microscopic heterogeneity in these binary solvent systems.

Journal Article↗

PubMed2005

Use of zirconium-phosphate-carbonate chemistry to immobilize polycyclic aromatic hydrocarbons on boron-doped diamond.

We report on the formation of monomolecular layers of perylene- and pyrene-alkanoic acids on boron-doped diamond (BDD) substrates. The carboxylic acid layers are bound by coordination to zirconium phosphate (ZP) functionalities on the BDD substrate surface. The resulting Zr-phosphate-carbonate (ZPC) linkages between the substrate and the adlayer are asymmetric, of the form -(OPO3(2-) Zr4+-O2C-R)+ X-. Pyrene and perylene are well-established optical probes of polarity and viscosity at interfaces. We have used electrochemical and steady-state fluorescence techniques to study the loading density and behavior of these monomolecular films, allowing comparison of BDD and indium-doped tin oxide (ITO) substrates. Electrochemical data suggest that the pyrene chromophores are positioned roughly at the same distance from the surface, regardless of the length of the anchoring alkanoic acid chain, a finding that can be explained by the pyrene lying on the substrate surface. Such a conformation is plausible given the surface coverage (5 x 10(-11) mol/cm2, ca. 0.1 monolayer) we measure for these systems.

Boron↗

PubMed2005

Probing interfacial organization in surface monolayers using tethered pyrene. 1. Structural mediation of electron and proton access to adsorbates.

We have synthesized and characterized a family of self-assembled monolayers containing pyrene derivatives on gold and indium-doped tin oxide (ITO) substrates. The covalently bound pyrene functionalities serve as either spectroscopic or electrochemical probes of their immediate environment, and we explore their electrochemical response in this paper. When these compounds are the only constituents bound to the interfaces, the molecules enjoy significant structural freedom. The addition of aliphatic adsorbates to the interfaces serves to place the pyrene derivatives in a more restricted environment. Cyclic voltammetry shows that the organization of a monolayer with pyrene derivatives, and the position of the terminal pyrene within such monolayer, depend sensitively on the length of the pyrene tether and the presence or absence of aliphatic interfacial species, as well as the identity of the substrate.

Journal Article↗

PubMed2005

Probing interfacial organization in surface monolayers using tethered pyrene. 2. Spectroscopy and motional freedom of the adsorbates.

We have studied the steady-state and time-resolved emission spectroscopy of the pyrene-containing monolayers reported in the previous article, where in this work we have bound the monolayers to SiO(x). We find that these monolayer structures are sensitive to the identity of the solvent overlayer, with the solvent playing a significant role in the organization of the surface-bound monolayers. We discuss our findings in the context of the known polarity dependence of the pyrene emission spectrum and find that the motional freedom of the chromophores varies with both the monolayer composition and the identity of the solvent overlayer. Our data point to the importance of neighbor-neighbor interactions within the monolayer structures in mediating the motional freedom of the tethered pyrene chromophores.

Journal Article↗

PubMed2005

Probing intermolecular communication with surface-attached pyrene.

We report on the covalent attachment of pyrene derivatives to solid substrates and their spectroscopic and electrochemical characterization. We have constructed several molecular assemblies attached to silica and indium-doped tin oxide surfaces where pyrene molecules are co-immobilized with other functionalities. It was shown that the addition of hydrophobic molecules to the pyrene-containing interface results in a significant decrease in the pyrene I1/I3 vibronic emission band ratio and an increase in the water drop contact angle due to increased hydrophobicity of the interface. The co-attachment of perylenedodecanoic acid, for which the absorption band overlaps with the emission spectrum of pyrene, shows significant intermolecular communication between these species. The co-immobilization of ferrocene serves as an effective fluorescence quencher for tethered pyrene. In all cases, our data point to significant intermolecular communication between adsorbate species, and the combination of spectroscopic and electrochemical interrogation provides insight into the loading density and local environment(s) characteristic of these interfaces.

Journal Article↗

PubMed2005

Oxidative transformations of surface-bound perylene.

We report on the covalent attachment of perylene derivatives to silica and indium-doped tin oxide surfaces. The spectroscopic properties of the immobilized fluorophores are studied by steady-state and time-resolved emission spectroscopy. The redox properties of the molecules are examined by electrochemical methods. It was found that the oxidation of perylene in aqueous medium results in the formation of perylenequinones. The transformation proceeds through a number of steps, with monohydroxyperylene(s) being the intermediate species. The final oxidation products are three isomeric forms of the perylenequinone/perylenehydroquinone redox couple. Understanding the mechanism of perylene transformation allows estimation of the concentration of molecules on the surface, and comparison of these results to those for pyrene and anthracene derivatives underscores the generality of this type of oxidative degradation for polycyclic aromatic hydrocarbons.

Journal Article↗

PubMed2005

Spectroscopic and electrochemical characterization of interfacial biomimetic assemblies on electrochemically generated gold oxide surfaces.

We report on the formation of a gold oxide layer and the reaction of this oxide with an acid chloride to form a stable, relatively complete monolayer bound through an ester-like bond to the gold oxide surface. We have used cyclic voltammetry, FTIR and optical ellipsometry to characterize this novel monolayer structure. The exposed functional groups of this monolayer can participate in subsequent surface reactions, opening the door to the use of oxide-based surface attachment chemistry on metallic substrates. This chemistry will allow for the formation of films tailored to contain both hydrophobic and hydrophilic regions, stacked at predetermined distances from the substrate that may serve as biomembrane mimetic assemblies.

Adipates↗

PubMed2005

Surface immobilized optical probes: pyrene molecules covalently attached to silica and indium-doped tin oxide.

We report on the covalent attachment of pyrene to quartz and indium-doped tin oxide (ITO) surfaces, and its characterization by steady-state and time-resolved emission spectroscopy. We estimate the chromophore surface coverage on the basis of their electrochemical oxidation mechanism in acidic solution. Electrochemical oxidation of immobilized pyrene results in the formation of radical cations, which are converted into hydroxypyrene and, after a second oxidation step, are transformed into isomeric forms of dihydroxypyrene/pyrenedione redox couples. Our findings demonstrate that surface-bound pyrene can be used as a spectral probe in environments that are isolated from oxidizing conditions and agents.

Indium↗

PubMed2005

Design, synthesis and characterization of monomolecular interfacial layers.

We have designed a series of monomolecular films comprised of four basic structural motifs. We have used these films for a variety of purposes, ranging from support structures for chromophore arrays to the creation of selective and biomimetic interfaces. We will discuss the several different types of interfacial binding chemistry that are used in the construction of these interfacial films, for both monomeric and polymeric layer structures. Following a discussion of the construction of the adlayers, we describe several uses of these assemblies, in areas ranging from adsorption to optical signal processing, and the formation of biomimetic interfacial structures.

Biomimetic Materials↗

PubMed2004

Electroless deposition of poly(2-alkoxyaniline)s.

The in situ deposition of poly(2-alkoxyaniline)s onto oxide surfaces is reported. It is demonstrated that the identity of the substrate can have a pronounced effect on the polymerization rate of these substituted polyanilines. Poly(2-alkoxyaniline)s deposit efficiently onto indium-doped tin oxide (ITO), but deposition onto quartz proceeds slowly. The critical stage in the deposition process is shown to be polymerization of the adsorbed oligomeric species. When this polymerization process is catalyzed by the surface, polymer growth is enhanced, and we find that conducting substrates mediate this apparent catalytic process. We demonstrate selective deposition by growing poly(2-alkoxyaniline) adlayers onto patterned ITO/quartz substrates.

Journal Article↗

PubMed2003

Covalent adlayer growth on a diamond thin film surface.

The surface of boron-doped diamond thin films can be modified by exposure to a strong oxidizing agent, resulting in the formation of -OH and =O terminated diamond. The -OH groups are reacted with an acid chloride to produce a covalently bound, modified diamond thin film surface. The demonstration of these reactions allows for the facile modification of diamond surfaces using techniques well established for oxide surfaces. Characterization of the covalently bound species shows submonolayer coverage, and time-resolved fluorescence measurements are reflective of the highly featured nature of the diamond film.

Journal Article↗

PubMed1980

Prognostic indicators in chemotherapy for head and neck carcinoma: alkaline phosphatase levels.

Serum alkaline phosphatase (AP), total bilirubin, total protein, serum albumin, and serum glutamic oxaloacetic transaminase (SGOT) were determined in 55 patients with biopsy proven carcinoma of the head and neck prior to their induction chemotherapy with cis-platinum and bleomycin. Of the 55 patients, 40 (73%) exhibited either a complete or partial response (tumor mass decreased by over 50%) to the chemotherapy. Responses were noted more frequently in patients with elevated AP levels. Nine of the 10 patients (90%) with AP levels greater than 100 mU/ml experienced a major response; whereas, only 8 of 16 patients (50%) with AP levels less than 60 mU/ml demonstrated a favorable response to the chemotherapeutic agents. The source of the elevated AP levels has not yet been established. Possible sources include liver, bone, kidney, intestinal mucosa, or the tumor itself. Total bilirubin, total protein, serum albumin, and SGOT levels did not differentiate the responders from the non-responders as accurately as did the AP levels.

Alkaline Phosphatase↗