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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
101

Gegenseitige Beeinflussung von Mizellaren Strukturen und Photodimerisierung von Cumarinderivaten

Yu, Xiuling 21 April 2004 (has links)
In dieser Arbeit wurde die gegenseitige Beeinflussung von mizellaren Strukturen und Photodimerisierung von Cumarinderivaten untersucht. Als Mizellbildner wurden das kationische Cetyltrimethylammoniumbromid (CTAB) und das nicht-ionische Triton X-100, als Solubilisate Cumarinderivaten verwendet. Es wurden rheologische, thermodynamische und photochemische Untersuchungen durchgeführt. Die Viskosität der beiden Tensidsysteme steigt mit zunehmender Solubilisatkonzentration je nach Cumarinderivat unterschiedlich stark an. Dabei zeigten 6-Alkylcumarine als Solubilisate die größten "rheologischen Effekte". Die Photodimerisierung der solubilisierten Cumarine führte zu einem weiteren Anstieg oder zu einer Abnahme der Viskosität der CTAB- und Triton X-100-Lösungen - "photorheologischer Effekt". In Abhängigkeit von der Konzentration werden Strukturänderungen der mizellaren Aggregate induziert, die teilweise zu drastischen Änderungen der makroskopischen Eigenschaften der Tensidlösungen-Lösung führen. Die Photodimerisierung fungiert dabei als "large-response-trigger". Die Kettenlänge der solubilisierten 6-Alkylcumarine beeinflusst das Fießverhalten der CTAB-Lösungen und Triton X-100-Lösungen. Mit zunehmender Kettenlänge steigt die Viskosität der beiden Tensidlösungen zunächst an, um dann bei noch längeren Ketten wieder abzunehmen. In beiden Tensidsystemen liegt der Maximalwert bei 6-Oktylcumarin. Der Photodimerisierung beeinflusst die Viskosität der beiden Tensid-Systeme unterschiedlich. In CTAB-Lösungen in Anwesenheit von kürzeren Alkylcumarinen steigt die Viskosität mit der Photodimerisierung weiter. Ab Pentylcumarin nimmt die Viskosität nach der Photodimerisierung jedoch ab. Im Triton X-100 System ist der photorheologische Effekt dagegen stets positiv. Thermodynamische Untersuchungen zeigen eine Korrelation mit dem rheologischen Effekt: Je größer die Viskosität, desto negativer sind Enthalpie- und Entropiedifferenzen bei der Bildung der mizellaren Aggregate. Die Ergebnisse legen als Ursache für die Viskositätseffekte Unterschiede in der Ausdehnung der Hydratwasserschicht der Mizellen nahe. Bei der photochemischen Untersuchungen wurden mit Hilfe von NMR-Spektroskopie und Kristallstrukturanalyse die isomeren Produkte der Photodimeriserung von Cumarinderivaten charakterisiert und die Produktverteilung unter verschiedenen Bedingungen ermittelt. In CTAB-Lösung konnte eine Möglichkeit Steuerung der Selektivität der Produktbildung gefunden werden: Lange 6-Alkylsubstituenten (ab 6-Propylcumarin) steuern zu Anti- und zu KK-Dimeren, während bei kurzen Ketten bzw. beim unsubstituierten Cumarin mehr Syn- und KS-Dimere gebildet werden. Bei dem im Detail untersuchten 6-Methylcumarin steigt die relative Quantenausbeute mit fallender Temperatur, abnehmender Konzentration und mit Zugabe des Triplettsensibilisators Benzophenon. In Gegenwart des Sensibilisators entsteht vermehrt das Anti-KK-Dimer, was darauf schließen lässt, dass dieses aus dem Triplett-Zustand gebildet wird. In ionischer mizellarer Lösung CTAB bilden sich bevorzugt Syn-Dimere. In unpolaren Lösungsmitteln entsteht nur Anti-KK, während in polaren Lösungsmitteln auch kleine Mengen Syn-Dimere gebildet werden. Die Lewis-Säure BF3 beschleunigt die Photodimerisierung deutlich und steuert zu Syn-KS.
102

Kinetic Studies of the Glycerophosphate Acyltransferase From Euglena Microsomes, Including the Effects of Serum Albumin

Hershenson, Susan, Lou Ernst-Fonberg, Mary 16 May 1983 (has links)
The kinetics of the reaction catalyzed by acyl-CoA: sn-glycerol-3-phosphate O-acyltransferase solubilized from Euglena gracilis microsomes were examined. For myristoyl-, palmitoyl-, stearoyl-, and oleoyl-CoAs, the initial reaction rates rose with increasing substrate concentration up to an optimal concentration that varied from 18.5 to 25 μ M, well above the respective critical micelle concentrations. At higher substrate concentrations, reaction was progressively inhibited. Arachidoyl-CoA was a relatively poor substrate for the acyltransferase, and substrate inhibition was not seen with it. Km values for acyl-CoAs ranged from 13 to 20 μ M while the corresponding V values varied almost 40-fold. Bovine serum albumin, among other effects, caused a change in the kinetic pattern of the reaction acyl-CoA dependency. Both acyl-CoA micelles and albumin-bound acyl-CoA were substrates. The binding of palmitoyl- and oleoyl-CoA was 2.7 and 1.5 mol, respectively, per mol of albumin. The critical micelle concentration of palmitoyl-CoA under the reaction conditions was shown by low angle light scattering photometry to be 7.1 p.M. The sn-glycerol 3-phosphate concentration dependency of the acyltransferase initial velocity exhibited Michaelis-Menten kinetics with Km values of 1.3 and 2.9 mM in the presence of 12.5 and 25 μM palmitoyl-CoA, respectively. The substrate analogues sn-glyceraldehyde 3-phosphate and dihydroxyacetone phosphate inhibited the reaction.
103

SELF-ASSEMBLED POLYSTYRENE-BLOCK-POLY (ETHYLENE OXIDE) (PS-b-PEO) MICELLE MORPHOLOGIES IN SOLUTION

Bhargava, Prachur 02 October 2007 (has links)
No description available.
104

Pharmacokinetics of Ultrasonically-Released, Micelle-Encapsulated Doxorubicin in the Rat Model and its Effect on Tumor Growth

Staples, Bryant J. 15 May 2007 (has links) (PDF)
Chemotherapy is one of the most successful cancer treatments used today. Unfortunately, the amount of chemotherapy a patient can receive is limited by the associated negative side effects, such as cardiotoxicity, immune system suppression, and nephrotoxicity. Encapsulation of these drugs, Doxorubicin (DOX) in particular, in stabilized Pluronic micelles (Plurogel TM) shows success in limiting these harmful side effects. In previous studies, low-frequency ultrasound (US) has been shown, in vitro, to locally release DOX from these micelles. In this study, a novel drug delivery system involving the encapsulation of DOX in Plurogel and the release of the drug at the tumor site using ultrasound was studied in vivo using rats. These studies determined the effect of ultrasonically released drugs on tumor growth rate and drug delivery to the tumor tissue. Concurrently, different frequencies (20 kHz, 500 kHz) were tested for the same effects. Treatments consisted of micelle-encapsulated doxorubicin injected intravenously followed by ultrasound application to one of the two bilateral tumors. Also, in different experiments, pharmacokinetic studies of the drug in the heart, liver, leg muscle, and tumors were performed up to a period of one week after treatment. Results showed that tumors treated with ultrasound displayed, on average, slower growth rates than non-insonated tumors (P = 0.0047). Also, insonated tumors displayed a weak increased concentration of DOX than non-insonated tumors within the first eight hours after treatment (P = 0.064). However, comparison between tumors which received 20 kHz and 500 kHz ultrasound treatment showed no statistical difference (P = 0.9275) in tumor growth rate or DOX concentration. It is noteworthy that the insonated tumor has slower growth even though the amount of DOX was not that much greater in the non-insonated tumor. This suggests that US also affects the uptake and/or processing of the DOX by the tumor cells, and that the therapeutic effect may not be attributed solely to a higher concentration of drug released by insonation. Pharmacokinetic studies showed significant drug accumulation in the heart but no accumulation in the liver, skeletal leg muscle, or tumors over the course of four weeks of consecutive weekly injections of DOX-encapsulated Plurogel. After 24 hours, DOX concentration remains the greatest in the tumors, regardless of whether they received ultrasound or not.
105

Minor Components and Their Roles on Lipid Oxidation in Bulk Oil That Contains Association Colloids

Chen, Bingcan 01 May 2012 (has links)
The combination of water and surface active compounds found naturally in commercially refined vegetable oils have been postulated to form physical structures known as association colloids. This research studied the ability of 1,2-dioleoyl-sn-glycerol-3-phosphocholine (DOPC) and water to form physical structures in stripped soybean oil. Interfacial tension and fluorescence spectrometry results showed the critical micelle concentration (CMC) of DOPC in stripped soybean oil was 650 and 950 microM, respectively. Light scattering attenuation results indicated that the structure formed by DOPC was reverse micelles. The physical properties of DOPC reverse micelles were determined using small-angle X-ray scattering (SAXS) and fluorescence probes. These studies showed that increasing the water concentration altered the size and shape of the reverse micelles formed by DOPC. The impact of DOPC reverse micelles on the lipid oxidation of stripped soybean oil was investigated by following the formation of primary and secondary lipid oxidation products. DOPC reverse micelles had a prooxidant effect, shortening the oxidation lag phase of SSO at 55 °C. It also was not able to change the lipid oxidation of stripped soybean oil compared with DOPC reverse micelles at same concemtration ( i.e., 950 microM). 1,2-dibutyl-sn-glycerol-3-phosphocholine (DC4PC) which has the shorter fatty acid than DOPC was not able to form association colloids and did not impact lipid oxidation rates. This indicated that the choline group of the phospholipid was not responsible for the increased oxidation rates and suggested that the physical structure formed by DOPC was responsible for the prooxidant effect. The impact of the DOPC reverse micelles on the effectiveness and physical location of the antioxidants, alpha-tocopherol and Trolox was also studied. Both non-polar (alpha-tocopherol) and polar (Trolox) were able to inhibit lipid oxidation in stripped soybean oil in the presence of DOPC reverse micelles. Trolox was a more effective antioxidant than alpha-tocopherol. Fluorescence steady state and lifetime decay studies suggested that both alpha-tocopherol and Trolox were associated with DOPC reverse micelle in bulk oil. Trolox primarily concentrated in the water pool of reverse micelle since it quenched NBD-PE fluorescence intensity with increasing concentrations. A portion of alpha-tocopherol was also associated with the aqueous phase of the DOPC reverse micelles but this was likely at the oil-water interface since alpha-tocopherol is not water soluble. The addition of ferric chelator, deferoxamine (DFO) to stripped soybean oil significantly prevented the lipid oxidation caused by DOPC reverse micelles as the lag phase was extended from 2 to 7 days. DFO was also found to increase the antioxidant activity of both Trolox and alpha-tocopherol. Trolox and alpha-tocopherol were found to be rapidly decomposed by high-valence Fe(III) while low-valence-state (Fe (II) was much less reactive. Fe(III) was also consumed by both hydrophilic Trolox and lipophilic alpha-tocopherol presumably though reduction to Fe (II). DOPC reverse micelles were able to decrease antioxidants-iron interactions as evidence by a decrease in antioxidant depletion by iron and a decrease in iron reduction by the antioxidants. These results suggested that the ability of DFO to increase the antioxidant activity of alpha-tocopherol and Trolox was due to its ability to decrease free radical production and not its ability to decrease direct iron-antioxidant interactions. Overall, the results presented in this dissertation show phospholipids and water can form reverse micelles in edible oils. These reverse micelles increase lipid oxidation rates by increasing the prooxidant activity of iron. Free radical scavenging antioxidants can inhibit oxidation promoted by the reverse micelles with polar Trolox being more effective than non-polar alpha-tocopherol presumably because Trolox is more highly associated with the reverse micelle. The reverse micelles produced by DOPC protected alpha-tocopherol and Trolox from direct degradation by iron. The knowledge gained from this study will improve our understanding of the mechanism of lipid oxidation in bulk oils which will hopefully provide new technologies to improve the oxidation stability of edible oils. For example, it may be able to use oil refining technologies to remove prooxidative minor components that for physical structure in bulk oils.
106

Characterizing Bile Acid Association as a Ligand and in Micellization.

Werry, Brian Scott 21 February 2014 (has links)
No description available.
107

Designing Photo-switchable Quantum Dots for Super Resolution Imaging

Fan, Qirui January 2015 (has links)
No description available.
108

Surfactant Drag Reduction and Heat Transfer Enhancement

Shi, Haifeng 27 August 2012 (has links)
No description available.
109

DESIGN AND SYNTHESIS OF BLOCK COPOLYMERS THAT SELF ASSEMBLE INTO MICELLES WITH CONTROLLED ACID AND LIPASE CATALYZED DEGRADATION

Zhu, Xiaobo January 2013 (has links)
Poly (ε-caprolactone) block poly (ethylene glycol) (PCL-b-PEG) is typical amphiphilic block copolymer that self assembles into micelles in water where the hydrolytically stable hydrophilic PEG segment forms the exterior corona and the core contains the hydrophobic degradable PCL block. Micelles from PCL-b-PEG block copolymers are among the top candidates for application as transport and delivery systems. The efficiency for micellar transported therapeutics to reach the desired site is currently limited by processes that prematurely degrade the micelle and this issue is stimulating increased effort in evaluating how micelles respond to the conditions encountered in the digestive and circulatory systems. Drug loaded micelles introduced into the blood and digestive systems encounter a wide range of conditions, enzymes and other substances that can promote micelle precipitation, degradation and premature release of therapeutics. Furthermore, PEG-b-PCL diblock copolymer micelle stability in aqueous suspension, low drug loading content and burst drug releasing are also the critical issues in drug delivery system. One central objective for this research is to identify and utilize polymer structural features that influence the hydrolytic stability of micelles toward acid, base and enzyme catalyzed hydrolysis of the polyester cores. The strategy of by preparing a set of triblock copolymers (PEG-b-PBO-b-PCL) formed by inserting a short hydrophobic non-hydrolyzable PBO segment between the PEG and PCL blocks as an approach to increase the barrier for water to reach the sensitive interface ester at the surface of the PCL core and thus increase the micelle stability at acidic aqueous medium. However, the triblock micelle doesn't significantly reduce the rate of lipase enzyme catalyzed degradation of micelle from PCL-b-PEG-OMe. Another objective for this research is to prepare PCL-b-PEG diblock copolymer micelles that have high stability in aqueous suspensions, high drug loading content and selective reactions with lipase enzymes. The working hypothesis is that the micelles with charged groups at the terminus of PEG corona will increase the micelle dispersion stability and stabilize micelles with much larger hydrophobic cores through intermicelle electrostatic repulsions. When the micelle corona and lipase enzyme have the same charge there will be an increased barrier to reaction. The comparison of micelle dispersion stabilities micelles from HO-PCL-b-PEG-CH2CH=CH, [PCL-b-PEG-RCO2]- Na+ and [PCL-b-PEG-RSO3]-Na+ demonstrates that the micelles with ionic coronas have significantly higher suspension stability. Kinetic of lipase catalyzed degradation of micelles with corona charges shows that lipases selective reaction with corona charged micelles which could be used as design feature to selectivity for therapeutic transport and release. Modification hydrophilic-hydrophobic interface and corona charges of PCL-b-PEG diblock copolymer micelle are successful chemical strategies to increase micelle stability and control acid and lipase enzymes catalytic degradation. / Chemistry
110

Nuclear magnetic resonance and rheo-NMR investigations of wormlike micelles, rheology modifiers, and ion-conducting polymers

Wilmsmeyer, Kyle Gregory 26 October 2012 (has links)
Investigation and characterization of polymeric materials are necessary to obtain in-depth understanding of their behavior and properties, which can fuel further development. To illuminate these molecular properties and their coupling to macroscopic behavior, we have performed nuclear magnetic resonance (NMR) studies on a variety of chemical systems. In addition to versatile "traditional" NMR measurements, we took advantage of specialized techniques, such as "rheo-NMR," 2H NMR, and NMR self-diffusion experiments to analyze alignment, orientational order, elaborate rheological behavior, and ion transport in polymer films and complex fluids. We employed self-diffusion and quadrupolar deuterium NMR methods to water-swollen channels in Nafion ionomer films commonly used in fuel cells and actuators. We also correlated water uptake and anisotropic diffusion with differing degrees and types of alignment in Nafion films based on membrane processing methods. Further, we made quantitative measurements of bulk channel alignment in Nafion membranes and determined anisotropic properties such as the biaxiality parameter using these methods. Additionally, our studies made the first direct comparison of directional transport (diffusion) with quantitative orientational order measurements for ionomer membranes. These results lend insight to the importance of water content in ionomer device performance, and showed that increased control over the direction and extent of orientational order of the hydrophilic channels could lead to improved materials design. We used the same techniques, with the addition of "rheo-NMR" and solution rheology measurements, to study the complex rheological behavior of cetyltrimethylammonium bromide wormlike micelle solutions, which behave as nematic liquid crystals at sufficiently high concentration. Amphiphilic solutions of this type are used in myriad applications, from fracturing fluids in oil fields to personal care products. We investigated the phase behavior and dynamics of shear and magnetic field alignment, and made the first observations of a novel bistable shear-activated phase in these solutions. Our first reports of the complex Leslie-Ericksen viscoelastic parameters in wormlike micelles and measurements of diffusion anisotropy show the potential for increased control and understanding of materials used in tissue engineering, oil extraction, personal care products, and advanced lubricants. / Ph. D.

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