Dissertation > Excellent graduate degree dissertation topics show

Design and Synthesis of Magnetic Resonance Imaging (MRI)Contrast Agents&Catalyst-Enhanced Chemical Vapor Deposition (CECVD) of Palladium, Platinum, Palladium-Platinum Bilayer and Their Bimetal on Polymer Surface

Author: Haroon-Ur-Rashid
Tutor: KaichaoYu
School: Huazhong University of Science and Technology
Course: Organic Chemistry
Keywords: Magnetic Resonance Imaging (MRI) Contrast agents Relaxivity Photodynamic therapy (PDT) Photosensitizer PorphyrinCatalyst Enhanced Chemical Vapor Deposition (CECVD) Polyimide Polysulfone Platinum Palladium Bilayer Bimetal Alloy
CLC: TB383
Type: PhD thesis
Year: 2012
Downloads: 23
Quote: 0
Read: Download Dissertation

Abstract

Magnetic Resonance Imaging (MRI) has become a prominent imaging technique inmedicine. MRI contrast agents are used to increase the sensitivity of this technique.Efficient contrast agents have high relaxivity and therefore cause significant contrastbetween the diseased and normal tissues. The most common method for relaxivityenhancement is to increase the rotational correlation time (τR). This in turn can be achievedby increasing the molecular weight of the ligands to be complexed with the paramaeticmetal Ion.1,4,7,10-teraazacyclododecane (Cyclen), aza analogue of the crown ether is widelyused for the design and synthesis of novel ligands. In our work, cyclen was synthesized viaRichman and Atkin’s method. It was then used to synthesize a novel ligand1-(methyl,2-ethoxybenzoate)-4,7,10-tris(carboxylic acid)-1,4,7,10-tetraazacyclododecane.Recently, a new method for cancer treatment with less side-effect called photodynamictherapy (PDT) has been introduced. In this method cancer tissues are selectively destroyedwithout injuring the surrounding healthy cells. However, for the successful use of thismethod, selection of an appropriate photosensitizer is important. Hence, it will significantlypromote the diagnosis-treat union of MRI and PDT if a new family of bi-functional agents isfound which combines the effect of contrast agent in MRI and that of photosensitizer inPDT. It will bring great improvement to the cancer diagnosis and treatment.Porphyrins have proved to be useful photosensitizing agents in PDT due to theirpromising photophysical efficiency and less side effect. This work briefly describes theresearch development of porphyrin as photosensitizer applied in PDT, and also highlightsthe recent progress of research on bi-functional agents of MRI-PDT. DTPA units wereincorporated at meso-position of the porphyrin ring to synthesize new bifunctional agents ofMRI-PDT with sufficient water solubility, high relaxation potency and improved tumorselection ability. Gd3+complexes were prepared by the reaction of the high molecularweight porphyrin based ligands with GdCl3·6H2O. Longitudinal relaxivity measurementindicated154%and251%enhancement compared to that widely used MRI contrast agent, Gd-DTPA. These results indicate that the two complexes are hopefully the bi-functionalagents of MRI-PDT.Chemical vapor deposition (CVD) is a complex process of depositing thin coatings on asubstrate surface via chemical reactions of gaseous materials. It is a useful process toproduce materials of high purity, high density and high strength. CVD process is carried outat a high temperature ordinarily. Sometimes it is desirable to minimize the temperature toperform CVD process on thermally sensitive substrates. For this purpose metal catalysts areused in CVD process. Catalyst Enhanced Chemical Vapor Deposition (CECVD) is a type ofenhancement process. In CECVD co-deposition of catalytically active material causescatalysis of the CVD of a noncatalytic material. In this process a small amount of thecatalyst metal is used along with the major precursor to be deposited on the substrate. It is auseful process for the production of high quality, thin, pure films on thermally sensitivesubstrates at low temperature. CECVD of noble metals has great importance for practicalapplications in semiconductor industry, protective coatings, electronics, catalyst industries,optoelectronics and refractory ceramic materials. CECVD is particularly useful for thedeposition of thin films on polymer surface due to its low melting point as compared to theglass or silicon.In this work, chemical Vapor Deposition (CVD) of Pd, Pt, Pd-Pt bilayer and bimetalliccoatings under the carrier gas (N2, O2) on polyimide is depicted. Sequential deposition andco-deposition of Pd and Pt metals are used for deposition of bilayer and bimetallic filmsrespectively. The polyimide substrate temperature was maintained at250-3000C during thedeposition. X-ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscopy(SEM) were used for the analysis of the prepared films. Coatings quality was dependent ontheir growth temperature. During the CVD of palladium-platinum bimetal, the Pd/Pt atomicratios vary at different co-deposition conditions. Co-deposition of Pd((3-allyl)(hfac) andPt(COD)Me2under O2at300oC produced palladium-platinum bimetal with the content ofpalladium37.2%and platinum62.8%respectively without the contamination of carbon andfluorine. Only platinum was deposited for the co-deposition of platinum and palladiumwhen Pd (hfac)2and Pt(COD)Me2were used as precursors in the same chamber. The films showed firm adhesion to the polyimide surface. The electrical conductivity measurement ofthese films indicated that they are of high metallic quality.Metallic films formed on polysulfone have excellent thermal and dielectric properties.Chemical vapor deposition (CVD) of Pd, Pt, Pd-Pt bilayer and bimetallic films under thecarrier gas (N2, O2) on polysulfone is reported. The particle size of the Pd and Pt films onpolysulfone surface is about15-30nm. Sequential deposition and co-deposition of twometals were used for the deposition of bilayer and bimetallic films respectively. Catalystwas necessary for the deposition of Platinum. When a mixture of PtMe2(COD) andPd(hfac)2was used for the deposition at2500C, only Platinum was deposited with a highestpercentage of85.4%. During the CVD of Palladium-Platinum bimetal, the Pd/Pt atomicratios vary at different co-deposition conditions. Co-deposition of Pd((3-allyl)(hfac) andPt(COD)Me2under O2and N2at280oC produced Palladium-Platinum bimetallic film withthe content of palladium58.1%and Platinum34.9%. Only Platinum was deposited for theco-deposition of platinum and palladium when Pd(hfac)2and Pt(COD)Me2were used asprecursors in the same chamber. The particle size of the Pd-Pt bimetallic film onpolysulfone is in the range of20nm, much smaller than that on glass surface. Further SEMimage of the bimetallic film revealed its excellent conformity. All the films grown onpolysulfone in this work showed good adhesion to its surface.Palladium naoparticles were used as catalysts for the chemical vapor deposition ofpalladium-platinum bimetal on different polymers surfaces. The results revealed that use ofpalladium nanoparticles as catalyst greatly improved the efficiency of palladium-platinumbimetal CVD on polymer surface. CVD time was considerably decreased when palladiumnaoparticles were applied on the substrate surface.

Related Dissertations

CLC: > Industrial Technology > General industrial technology > Materials science and engineering > Special structural materials
© 2012 www.DissertationTopic.Net Mobile