Biomedical subjects

S S Saavedra

Publications and source records attributed to S S Saavedra.

8 recordsLinked to original sources

PubMed2000

Preparation of polyetherol-appended sulfur porphyrazines and investigations of peripheral metal ion binding in polar solvents.

We describe the complete synthesis and characterization of a new family of peripherally functionalized porphyrazines (pz's) with four, three, or two (in a trans conformation) bis[thioethoxy(ethoxy)ethanol] moieties appended at the pyrroles. These "polyetherol" groups serve as weak exocyclic binding sites for a number of metal ions and also provide solubility of the pz's in low molecular-weight alcohols and water. Electronic spectra of the modified porphyrazines exhibit distinct changes in the visible region (both absorbance and fluorescence) in response to treatment with Ag+, Pb2+, Cd2+, Cs+, and Ni2+ in solution. Such properties make these compounds intriguing candidates for incorporation into the transducer layers in optically based chemical sensors.

Ethers↗

PubMed1998

Molecular orientation distributions in protein films: III. Yeast cytochrome c immobilized on pyridyl disulfide-capped phospholipid bilayers.

Molecular orientation in a hydrated monolayer film of yeast cytochrome c, immobilized via disulfide bonding between Cys-102 and a pyridyl disulfide-capped phospholipid bilayer deposited from an air-water interface onto glass substrates, was investigated. The orientation distribution of the heme groups in the protein film was determined using a combination of absorption linear dichroism, measured in a planarintegrated optical waveguide-attenuated total reflection geometry- and fluorescence anisotropy, measured in a total internal reflection geometry. A gaussian model for the orientation distribution was used to recover the mean heme tilt angle and angular distribution about the mean, which were 40 and 11 degrees, respectively. Additional experiments showed that a large fraction of the cytochrome c was disulfide bonded to the bilayer, which correlates with the high degree of macroscopic order in the protein film. However, a subpopulation of yeast cytochrome c molecules in the film (approximately 30% of the total) appeared to be nonspecifically adsorbed. The orientation distribution of this subpopulation was found to be much broader than the specifically bound fraction.

Adsorption↗

PubMed1998

Planar integrated optical methods for examining thin films and their surface adlayers.

Thin film integrated optical waveguides (IOWs) have gained acceptance as a method for characterizing ultrathin dielectrical films and adlayers bound to the film surface. Here, we present the expressions that govern IOW methods as well as describe the common experimental configurations used in attenuated total reflection, fluorescence and Raman applications. The applications of these techniques to the study of adsorbed or surface-bound proteins to polymer and glass waveguides are reviewed.

Adsorption↗

PubMed1994

Fabrication and characterization of low-loss, sol-gel planar waveguides.

Applications of planar integrated optical waveguide (IOW) technology to problems in surface spectroscopy and optical chemical sensing have been partly limited by the difficulty of producing high-quality glass IOWs. The fabrication of IOWs by the sol-gel method from methyltriethoxysilane and titanium tetrabutoxide precursors is described here. The physical, chemical, and optical properties of the films during and after high-temperature annealing were studied using a variety of analytical techniques. The results show that the catalyst used to accelerate the sol-gel reaction strongly influenced the optical quality of the IOW. HCl catalysis produced waveguides with propagation losses of approximately 1 dB/cm, whereas in the case of SiCl4 catalysis, propagation losses were < 0.2 dB/cm, a value significantly less than any previously reported for sol-gel-derived IOWs. An examination of film surface structure and morphology by scanning electron microscopy and atomic force microscopy showed that the SiCl4-catalyzed IOWs were significantly smoother and more homogeneous on a submicrometer scale than the HCl-catalyzed IOWs. The use of SiCl4 is thought to retard formation of a microheterogeneous network containing Si-rich and Ti-rich domains, which is favored with HCl catalysis and contributes to the higher observed losses.

Fiber Optic Technology↗

PubMed1993

Effect of the conformation and orientation of adsorbed fibronectin on endothelial cell spreading and the strength of adhesion.

The effect of surface hydrophobicity upon the conformation of the cell binding domain of fibronectin (Fn) and the influence of Fn conformation on bovine aortic endothelial cell (BAEC) adhesion were examined. The free sulfhydryl group of Fn located near the cell binding domain was selectively labeled with acrylodan, a polarity sensitive fluor. Fluorescence emission was monitored in solution and upon adsorption to hydrophilic glass and hydrophobic silanized glass. The acrylodan-labeled Fn emission maximum shifted to longer wavelengths upon adsorption and the shift was greater for acrylodan-labeled Fn adsorbed to hydrophilic glass than hydrophobic silane, suggesting that the acrylodan was in a more solvent accessible environment on glass than silane. BAEC, suspended in serum-free medium, attached for 15 or 120 min onto glass or silane surfaces containing preadsorbed Fn, after which cell spreading and the strength of adhesion in a parallel plate flow chamber were measured. Cell spreading was similar on both surfaces after 15 min attachment, but BAECs were more spread on glass than silane after 120 min. At low surface concentrations of Fn, BAECs were more adherent on glass than silane. At higher surfaces concentrations, adhesion was similar. After a 2-h incubation in serum-free medium, cells on glass showed more extensive development of focal contacts as determined by immunofluorescent staining for vinculin. Cell adhesion under flow was reduced on silane by inhibition of protein synthesis with cycloheximide, suggesting that cell attachment to silane was promoted by cellular synthesis of Fn. The results indicate that changes in the conformation of the Fn cell binding domain affect Fn affinity for its cell surface receptor.

Adsorption↗

PubMed1990

Integrated optical attenuated total reflection spectrometry of aqueous superstrates using prism-coupled polymer waveguides.

Attenuated total reflection (ATR) spectrometry of aqueous solutions in contact with polystyrene integrated optical waveguides has been investigated. The mode-dependent absorption of evanescent energy by fluorescein solutions adjacent to the waveguide surface was measured and compared to theoretical predictions based on a ray optics approach. Although enhanced sensitivity was observed with increasing mode number, the sensitivity for the highest order mode was less than that predicted by theory.

Chemistry Techniques, Analytical↗

PubMed1989

Time-resolved fluorimetric detection of terbium-labelled deoxyribonucleic acid separated by gel electrophoresis.

Deoxyribonucleic acid (DNA) was reacted with a strong chelating agent and labelled with terbium, yielding a highly fluorescent conjugate with a lifetime of 1.5 ms. When a pulsed source and gated detection electronics were employed, the long-lived decay allowed effective discrimination against background fluorescence and scattered excitation. Detection limits should therefore be significantly improved in comparison with covalent labels with fluorescence lifetimes in the nanosecond regime or stains such as ethidium bromide. The conjugate is very stable, remaining fluorescent on dilution and in an electric field at elevated temperatures (60 degrees C), conditions typically encountered during polyacrylamide gel electrophoresis. As an enhancement solution is not required to develop the fluorescence, this system could be utilised in situations where on-line detection is desirable. Although only DNA was labelled, the method is equally applicable to ribonucleic acid.

Aminosalicylic Acid↗

PubMedDate not supplied

Terbium chelate membrane label for time-resolved, total internal reflection fluorescence microscopy of substrate-adherent cells.

A chelating agent conjugated to a lipid was synthesized by reacting the dianhydride form of diethylenetriaminepentaacetic acid sequentially with 4-aminosalicylate and dioleoylphosphatidylethanolamine. The product, DOPE-YAS-Tb, exhibits photophysical properties characteristic of a chelated Tb3+ ion bound to an organic triplet donor: an excitation maximum at 310 nm, narrow emission bands at 490, 545, 590, and 625 nm, and a lifetime of 1.57 ms. The suitability of DOPE-YAS-Tb as a membrane-staining agent for morphological studies of cultured cells using total internal reflection fluorescence microscopy (TIRFM) was investigated. Swiss albino mouse 3T3 cells were cultured on silica and polystyrene substrates. Time-resolved detection was employed to reject short-lived background emission (autoemission from the cells and/or the polymer substrate), which allowed the long-lived Tb3+ emission to be selectively imaged. The results show that time-resolved TIRFM of cells stained with DOPE-YAS-Tb is an effective method of quantitatively examining the cell morphology in situations where background due to autoemission from cells and/or the substrate material is problematic.

3T3 Cells↗