Effects of Poly(ethylene glycol) Doping on the Behavior of Pyrene, Rhodamine 6G, and Acrylodan-Labeled Bovine Serum Albumin Sequestered within Tetramethylorthosilane-Derived Sol-Gel-Processed Composites

We investigate the effects of controlled poly(ethylene glycol) (PEG) doping on the behavior of pyrene, rhodamine 6G (R6G), and acrylodan-labeled bovine serum albumin (BSA-Ac) sequestered within tetramethylorthosilicate (TMOS)-derived sol-gel-processed materials. To probe the dipolarity of the local environment within the composite we performed static fluorescence measurements on pyrene as the composites aged. We found that small levels of PEG loading effected significant enhancements in the local dipolarity surrounding the average pyrene molecule. Time-resolved fluorescence anisotropy measurements were used to follow the rotational reorientation dynamics of R6G as the composites aged. As the PEG loading increased, the R6G reorientational mobility increased. Nitrogen adsorption techniques were used to quantify the effects of PEG doping level on the surface area and final xerogel pore features. A large reduction in surface area was observed with PEG doping, but no detectable change in pore size was noted. The effects of PEG doping on a biomolecule were probed by following the time-resolved fluorescence anisotropy decay of BSA-Ac. These results showed that PEG doping resulted in increased biomolecule dynamics relative to that found for a neat, undoped TMOS-derived composites. Together these results show that PEG doping can be used to tune the sol-gel-processed composite dipolarity, alter the mobility of dopants sequestered within the composite, control analyte acessibility to the sensing chemistry, and modulate the internal dynamics within a biodopant.     

Conjugation, hybridization, and steric hindrance in relation to bond lengths

Three theories which have been proposed to explain the observed shortening of a single bond when it is adjacent to a double bond are discussed. Possible predictions from these theories are examined, especially for comparison with various quantities measurable by microwave spectroscopy. It is concluded that the steric theory is probably untenable, that some conjugation appears necessary to explain observed barries to internal rotation, and that it is difficult to find testable predictions from the hybridization theory.     

A metabonomic investigation of the biochemical effects of mercuric chloride in the rat using 1H NMR and HPLC-TOF/MS: time dependent changes in the urinary profile of endogenous metabolites as a result of nephrotoxicity

The effects of the administration of a single dose of the model nephrotoxin mercuric chloride (2.0 mg kg(-1), subcutaneous) to male Wistar-derived rats on the urinary metabolite profiles of a range of endogenous metabolites has been investigated using (1)H NMR and HPLC-MS. Urine samples were collected daily for 9 days from both dosed and control animals. Analysis of these samples revealed marked changes in the pattern of endogenous metabolites as a result of HgCl(2) toxicity. Peak disturbances in the urinary metabolite profiles were observed (using both NMR and HPLC-MS) at 3 days post dose. Thereafter the urinary metabolite profile gradually returned to a more normal composition. Markers of toxicity identified by (1)H NMR spectroscopy were raised concentrations of lactate, alanine, acetate, succinate, trimethylamine (TMA), and glucose. Reductions in the urinary excretion of citrate and alpha-ketoglutarate were also seen. Markers identified by HPLC-MS, in positive ion mode, were kynurenic acid, xanthurenic acid, pantothenic acid and 7-methylguanine which decreased after dosing. In addition an ion at m/z 188, probably 3-amino-2-naphthoic acid, was observed to increase after dosing. As well as these identified compounds other ions at m/z 297 and 267 decreased after dosing. In negative ion mode a range of sulfated compounds were observed, including phenol sulfate and benzene diol sulfate, which decreased after dosing. As well as the sulfated components an unidentified glucuronide at m/z 326 was also observed to decrease after dosing. The results of this study demonstrate the complementary nature of the NMR and MS-based techniques for metabonomic analysis.     

On eigenvalue calculations for radiative transfer models that include polarization effects

Several representations of the dispersion matrix (z) basic to analytical solutions for a theory of radiative transfer that includes the effects of polarization are reported, and a method for computing the zeros of det (z) is discussed. Numerical results are given for several specific models.

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Zusammenfassung Verschiedene Darstellungen der Dispersionsmatrix (z), welche grundlegende Bedeutung für die analytischen Lösungen der Theorie der Strahlungsübertragung mit Polarisation hat, werden angegeben. Eine Methode zur Berechnung der Nullstellen von det (z) wird diskutiert. Es werden numerische Ergebnisse für verschiedene Modelle angegeben.

     

Sol-gel-derived micron scale optical fibers for chemical sensing

We report for the first time on the preparation of organically-doped room temperature processed sol-gel-derived micron scale optical fibers as platforms for chemical- and bio-sensors. Micron scale optical fibers are drawn from fluorescent dye-doped tetraethoxysilane (TEOS)-derived sol-gel solution processed under ambient conditions. Such a simple methodology to entrap organic and even bioactive species within the optical fiber offers many advantages over more conventional ways of immobilizing organic probes for the development of optical sensors. Specifically, we report on the photophysical properties of fluorescein (a pH sensitive fluorescent dye) and rhodamine 6G (R6G; laser dye) entrapped within sol-gel-derived optical fibers. We present the preliminary results on the viability of such doped optical fibers for chemical sensing. Our results demonstrate that a fluorescein-doped sol-gel-derived optical fiber responds to ammonia and acid vapors with a response time of 1–2 seconds.     

Dendrimeric organochalcogen catalysts for the activation of hydrogen peroxide: origins of the "dendrimer effect" with catalysts terminating in phenylseleno groups

Several scenarios were evaluated to explain the large "dendrimer effect" observed in the bromination of cyclohexene with H(2)O(2) and NaBr catalyzed by the addition of Frechét-type dendrimers terminating in -O(CH(2))(3)SePh groups. Although phenylseleninic acid was an efficient catalyst for the oxidation of NaBr with H(2)O(2), first-order rate constants for the selenoxide elimination were too small to produce PhSeO(2)H at a rate sufficient to explain the rates of catalysis and no dendrimer effect was observed in the rates of selenoxide elimination. An induction period was observed using 1-SePh as a catalyst for the oxidation of Br(-) with H(2)O(2). The addition of preformed selenoxide 1-Se(=O)Ph gave immediate catalysis with no induction period. However, rates of oxidation of the selenides with H(2)O(2) under homogeneous or biphasic conditions or with t-BuOOH under homogeneous conditions were too slow to account for the rates of catalysis, and no dendrimer effect was observed in the rates of oxidation. The primary oxidant for converting selenides to selenoxides was "Br(+)" produced initially by the uncatalyzed background reaction of H(2)O(2) with NaBr and then produced catalytically following formation of selenoxide groups. Autocatalysis is observed, and the rate of oxidation increases with the number of SePh groups. Autocatalysis is the source of the large dendrimer effect observed with the SePh series of catalysts.     

Molecular dynamics simulation of the spontaneous formation of a small DPPC vesicle in water in atomistic detail

Molecular dynamics simulations have been used to study the spontaneous aggregation of a concentrated solution of dipalmitoylphosphatidylcholine (DPPC) molecules in water into a small vesicle. The molecules were represented in atomistic detail. Starting from a DPPC solution in water, an oblong vesicle with a long axis of 15 nm and short axes of 10 nm was formed spontaneously. After 90 ns of simulation, the vesicle contained a number of water pores. Water pores were shown to facilitate exchange of lipids between inner and outer leaflets. Lipid tails were shown to be less ordered in the inner leaflet of the vesicle, as compared to those in the outer leaflet of the vesicle and an equilibrated lamellar bilayer.     

Integrated chemical sensor array platform based on a light emitting diode, xerogel-derived sensor elements, and high-speed pin printing

We report a new, solid-state, integrated optical array sensor platform. By using pin printing technology in concert with sol-gel-processing methods, we form discrete xerogel-based microsensor elements that are on the order of 100 μm in diameter and 1 μm thick directly on the face of a light emitting diode (LED). The LED serves as the light source to excite chemically responsive luminophores sequestered within the doped xerogel microsensors and the analyte-dependent emission from within the doped xerogel is detected with a charge coupled device (CCD). We overcome the problem of background illumination from the LED reaching the CCD and the associated biasing that results by coating the LED first with a thin layer of blue paint. The thin paint layer serves as an optical filter, knocking out the LEDs red-edge spectral tail. The problem of the spatially-dependent fluence across the LED face is solved entirely by performing ratiometric measurements. We illustrate the performance of the new sensor scheme by forming an array of 100 discrete O₂-responsive sensing elements on the face of a single LED. The combination of pin printing with an integrated sensor and light source platform results in a rapid method of forming (∼1 s per sensor element) reusable sensor arrays. The entire sensor array can be calibrated using just one sensor element. Array-to-array reproducibly is <8%. Arrays can be formed using single or multiple pins with indistinguishable analytical performance.     

Comparison of thermodynamic properties of coarse-grained and atomic-level simulation models.

Thermodynamic data are often used to calibrate or test amomic-level (AL) force fields for molecular dynamics (MD) simulations. In contrast, the majority of coarse-grained (CG) force fields do not rely extensively on thermodynamic quantities. Recently, a CG force field for lipids, hydrocarbons, ions, and water, in which approximately four non-hydrogen atoms are mapped onto one interaction site, has been proposed and applied to study various aspects of lipid systems. To date, no extensive investigation of its capability to describe salvation thermodynamics has been undertaken. In the present study, a detailed picture of vaporization, solvation, and phase-partitioning thermodynamics for liquid hydrocarbons and water was obtained at CG and AL resolutions, in order to compare the two types or models and evaluate their ability to describe thermodynamic properties in the temperature range between 263 and 343 K. Both CG and AL models capture the experimental dependence of the thermodynamic properties on the temperature, albeit a systematically weaker dependence is found for the CG model. Moreover, deviations are found for solvation thermodynamics and for the corresponding enthalpy-entropy compensation for the CG model. Particularly water/oil repulsion seems to be overestimated. However, the results suggest that the thermodynamic properties considered should be reproducible by a CG model provided it is reparametrized on the basis of these liquid-phase properties.