Browsing by Author "Dorn, Harry C."

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    The 1H and 13C dynamic nuclear polarization (DNP) enhancement for novel silica phase immobilized nitroxide (SPIN) samples
    Gitti, Rossitza K. (Virginia Tech, 1991-12-06)
    The solid/liquid intermolecular transfer (SLIT) flow dynamic nuclear polarization (DNP) experiment potentially provides new methodology for studying interfacial phenomena (e.g., weak hydrogen bonding). In addition, the high efficiency of the transfer also ensures dramatically enhanced NMR signals. These large DNP enhancements could alleviate sensitivity limitations in various flow NMR experiments. Previous studies have established that silica phase immobilized nitroxide (SPIN) radical system are advantageous in the SLIT experiment. In favorable cases (e.g. DCCI₃/SPIN system) a ¹³C DNP enhancement 60 times in excess of the high magnetic field (4.7 T) magnetization has been achieved.¹² However a number of factors still limit the SPIN system presently available. For example, low magnetogyric ratio nuclides, ¹³C, ¹⁵N, which are not dominated by scalar relaxation mechanism require high surface radical concentrations. The focal point of the present study is the preparation and characterization of several new SPIN radical systems and can be divided into two parts: 1). Preparation, EPR, and DNP Characterization of Achiral SPIN Radicals: a number of SPIN samples were prepared in order to examine the dependence of the observed SLIT DNP enhancements as a function of the surface spin concentration and also isotope-substitution of the immobilized radicals. The SPIN samples were characterized by EPR and DNP. The results show that the increase in the spin concentration does not offer any advantage for ¹H DNP studies. In contrast, ¹³C SLIT DNP results in improved SPIN sample demonstrate the possibility of monitoring dipolar dominated ¹³C DNP enhancements as a result of better leakage factors and suppressed three-spin effects at higher radical concentration. The effect of substitution of deuterons for protons in the immobilized radical also suggest an appreciable contribution of a solid-state three-spin effect. 2). Preparation, EPR, and DNP Characterization of Chiral SPIN Samples: This part of the study provides a chiral SPIN radical suitable for monitoring enantioselective ¹³C DNP enhancements. The DNP results suggest that selective enantiomer/chiral SPIN interactions are feasible. Specifically, differences in the ¹³C DNP enhancements for a model system: (R)- and (S)- enantiomers of bromocamphor, and a (R) chiral SPIN sample were observed.
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    The acid-catalyzed self-condensation reaction of b-diketones in the presence of 2,2,2-trifluorodiazoethane
    Roy, John Thomas (Virginia Polytechnic Institute and State University, 1984)
    A novel acid-catalyzed self-condensation reaction of 6-diketones in the presence of 2,2,2-trifluorodiazoethane (TFD) has been discovered. This reaction is of interest because not many methods are available for the preparation of cyclized products (e.g., aromatic natural products) from 6-dicarbonyl units. Acid-catalyzed reactions of 1-phenyl-1,3-butanedione and several substituted derivatives of 1- phenyl-1,3-butanedione with TFD afforded two groups of substituted biphenyl compounds. One of these groups could be an important synthon for the preparation of larger polycyclic aromatic compounds. Several cyclized products have also been obtained from the reaction of 2, 4-pentanedione with TFD. Two potential mechanisms have been suggested to describe this cyclization process. Mechanistic studies utilizing dienophiles suggest that the previously described cyclized products have originated from Michael addition reactions. Several NMR techniques have been utilized to characterize the reaction products which were obtained in this study. These techniques include ¹³C labeling, the ¹³C NMR INADEQUATE pulse experiment, and applications of lanthanide shift reagents. The results that were obtained from the lanthanide shift reagent studies illustrate that certain oxygen atoms can be converted to 2, 2, 2-trifluoroethyl ethers to prevent complexation with lanthanide shift reagents. This methodology was successfully utilized to simplify the interpretation of lanthanide shift reagent results that were obtained from polyfunctional molecules. The reactions of several additional β-diketones have also been studied to better understand the cyclization process.
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    Antioxidant studies of fullerene and metallofullerene derivatives and fluorescence studies of terbium-containing metallofullerene derivatives
    Huang, Rong (Virginia Tech, 2022-02-10)
    Fullerenes and metallofullerenes have been discovered to have a lot of applications in the biomedical area, for instance, they have been shown to have antioxidant, anti-virus, anti-cancer, immunological properties, etc. However, the hydrophobicity nature of fullerenes and metallofullerenes raises the need for functionalized hydrophilic fullerenes and metallofullerenes. Also, the advancement of the purification techniques of fullerenes and metallofullerenes makes the isolation of new fullerenes and metallofullerenes possible. Therefore, discovering the biomedical applications of these newly found fullerenes and metallofullerenes is also of vital importance. In Chapter 1, we provided a comprehensive background on the history of fullerenes and metallofullerenes, synthesis and purification methods of fullerenes and metallofullerenes, and some of their biological applications, including antioxidant applications and fluorescence applications. Some important fullerene and metallofullerenes and milestones in this area were also discussed. In Chapter 2, we demonstrated the antioxidant and anti-inflammation ability of a conjugate, FIFIFK(Cy5)PEG24K(NH2)CONH2-C60, that consisted of a peptide that binds specifically to a formyl peptide receptor-1 (FPR-1), which expresses on activated macrophages, and a carboxyl-group-functionalized C60, which is the first discovered and most used fullerene is history. We showed that the fullerene-peptide conjugate had great ability as a radical scavenger and to reduce the volume of inflammatory tissue. In Chapter 3, we demonstrated the antioxidant and anti-inflammation ability of several metallofullerene derivatives, including amino-Gd3N@C80, amino-Sc3N@C80, carboxy-Gd3N@C80, and carboxyl-Sc3N@C80. Amino-group-functionalized metallofullerenes were found to have higher radical scavenging ability and anti-inflammation ability. In Chapter 4, we developed fluorescent metallofullerene derivatives, including Tb3N@C80(NH2)9(OH)4NO2 and Tb3N@C80(CH2CH2COOH)21(OH)18. The fluorescence properties of the derivatives of fullerenes or metallofullerenes were normally realized by the addition of fluorescent moieties on the carbon cage of fullerenes or metallofullerenes. However, the fluorescence of our newly developed metallofullerene derivative was realized by the tri-terbium nitride cluster inside the carbon cage. This saved the multi-step synthesis of the fluorescence probe and maintained the simplicity of the structure of the metallofullerene derivative. These derivatives of terbium-containing metallofullerene also showed radical scavenging ability towards hydroxyl radicals. In Chapter 5, we developed another fluorescent Tb3N@C80 derivative, Tb3N@C80[DiPEG2000]. The advantage of this fluorescent metallofullerene derivative was that it was easier to purify compared to small-functional-groups-functionalized Tb3N@C80 derivatives. This newly developed fluorescent Tb3N@C80 derivative also showed great fluorescent ability and radical scavenging ability. In Chapter 6, we provided a summary of the studies on the antioxidant and fluorescent properties of fullerenes and metallofullerenes' derivatives that were discussed in this dissertation.
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    Applications of high resolution solid state carbon-13 NMR to the study of multicomponent polymer systems
    Lin, Tso-Shen (Virginia Polytechnic Institute and State University, 1983)
    The technique of high resolution solid state carbon-13 NMR, achieved with magic angle spinning (MAS) and high power 13c-1H dipolar decoupling and cross polarization, was applied to a number of multicomponent polymer systems. Specific problems which were addressed are: (1) the nature of domain structure and molecular motion of two thermoplastic elastomer systems, including a series of styrene isoprene-styrene linear triblock copolymers (SIS’s) of various compositions, molecular weights and sample histories, and a poly(ester)- urethane based on poly(1,4-butylene adipate) and 4,4¹ -diphenylmethane diisocyanate, (2) the compatibility at the molecular level of polymer blends containing poly{vinylidene fluoride) (PVF2), including solution and mechanical blends with poly{methyl methacrylate) {PMMA}, poly(vinyl acetate} (PVAc) and poly(vinyl methyl ether) (PVME). For the thermoplastic copolymers, higher degree of phase separation between the hard and soft domains was indicated by two facts: First, ¹³C resonances of either domain could be selectively observed with different experimental conditions. Second, there was a one-component, first-order, spin-lattice relaxation behavior of the ¹³C nuclei in the soft domains. For the SIS copolymers, results of T₁ and T₂* determinations (beth with MAS) suggest that molecular motion, in terms of frequency, was independent of composition, molecular weight and selective casting solvents. However, from static spectra, molecular motion of the isoprene blocks was found to be more anisotropic for the samples cast from a poor solvent for polyisoprene {MEK) in contrast to samples cast from a good solvent of polyisoprene (hexane). For the polymer blends of poly(vinylidene fluoride), the level of molecular intermixing was reflected through the degree of ¹³C NMR signal attenuations of the non-PVF₂ polymers. These attenuations are mainly due to undecoupled intermolecular ¹³C-¹⁹F dipolar interactions. With a MAS rate of 2KHz, resolution of the intimacy of mixing between the two constituent polymers in the blends was estimated to be in the range of 3 to 4 angstroms. Varying degrees of NMR signal attenuations among the individual chemically different carbons of a polymer support a postulation of weak intermolecular 'acid-base' association between the acidic protons of PVF₂ and basic carbonyl groups in the case of both the PMMA and PVAc.
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    Applications of modifiers in supercritical fluid extraction and chromatograph
    Mulcahey, Leah J. (Virginia Tech, 1991)
    The use of modifiers in supercritical fluid chromatography and extraction has become quite common due to the inability of pure carbon dioxide alone to solvate many of the compounds of interest. The effects of modifiers in supercritical fluid chromatography have been more thoroughly studied than the effects of modifier in supercritical fluid extraction. The effects of modifier on trapping efficiencies for off-line supercritical fluid extraction have been evaluated in this work. Sorbent and solid phase traps were investigated with pure carbon dioxide in order to determine the effect of stationary phase identity, pretreatment, and rinse solvent on the recoveries of a test mixture of compounds of varying vapor pressure and molecular weight. The solid phase traps, which were polyethylene frits, performed as well as the sorbent traps in most cases, and significantly better than the sorbent traps in many cases. The ability to cool these traps to -20°C allowed for efficient trapping of volatile compounds without the benefit of sorptive interactions. Sorbent and solid phase traps were then studied with the addition of 1%, 2%, 4%, and 8% methanol to the mobile phase. The sorbent trap explored consisted of 40 µm ODS packing material, while the solid phase trap consisted of 100 yum stainless steel beads. In this work trap temperatures ranged from 5-80°C. It was found that trap temperature, modifier concentration, and trap type influenced recoveries of the test mixture components. Applications of these solid phase and sorbent traps explored were the extraction of polychlorinated biphenyls from river sediment and the extraction of the active components from a drug formulation. The separation of some compounds of pharmaceutical interest was also explored, where the addition of modifier, and in some cases an additive, was required to elute compounds from the chromatographic column.
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    Approaches to intermolecular structure elucidation utilizing NMR and DNP parameters
    Tsiao, Candy (Virginia Polytechnic Institute and State University, 1989)
    This thesis is divided into two parts. The first part involves the study of molecular structure utilizing Ianthanide induced shift (LIS) and lanthanide induced relaxation (LIR) nuclear magnetic resonance (NMR). It the course of these studies, it was found that the trifluoroethoxy group is a good deactivating group towards lanthanide shift reagents (LSR) and can be used to selectively deactivate multifunctional molecules. The second part of the thesis involves the utilization of liquid-liquid intermolecular transfer (LLIT) dynamic nuclear polarization (DNP) to study the microwave power needed to achieve saturation using deuterated and nondeuterated 2,4,6-tri-tert-butylphenoxy and galvinoxyl radicals, and ¹⁴N labelled, nondeuterated and ¹⁴N labelled, deuterated 4-hydroxy-TEMPO radicals. Also, selective ¹H DNP enhancements for taxol in solid-liquid intermolecular transfer (SLIT) DNP low-to-high field transfer experiments were obtained. Finally, the syntheses of compounds with both a LSR moiety and a nitroxide radical moiety in the same molecule were examined. LLIT DNP transfer experiments for the intramolecular LSR-nitroxide radicals molecular system and the intermolecular LSR—radicals systems were studied. Conclusions based on this study provide new insight regarding approaches for new LIS and DNP studies.
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    Assembly of Bio-Nanoparticles for Double Controlled Drug Release
    Huang, Wei; Zhang, Jianfei; Dorn, Harry C.; Zhang, Chenming (PLOS, 2013-09-06)
    A critical limiting factor of chemotherapy is the unacceptably high toxicity. The use of nanoparticle based drug carriers has significantly reduced the side effects and facilitated the delivery of drugs. Source of the remaining side effect includes (1) the broad final in vivo distribution of the administrated nanoparticles, and (2) strong basal drug release from nanoparticles before they could reach the tumor. Despite the advances in pH-triggered release, undesirable basal drug release has been a constant challenge under in vivo conditions. In this study, functionalized single walled carbon nanohorn supported immunoliposomes were assembled for paclitaxel delivery. The immunoliposomes were formulated with polyethylene glycol, thermal stable and pH sensitive phospholipids. Each nanohorn was found to be encapsulated within one immunoliposome. Results showed a highly pH dependent release of paclitaxel in the presence of serum at body temperature with minimal basal release under physiological conditions. Upon acidification, paclitaxel was released at a steady rate over 30 days with a cumulative release of 90% of the loaded drug. The drug release results proved our hypothesized double controlled release mechanism from the nanoparticles. Other results showed the nanoparticles have doubled loading capacity compared to that of traditional liposomes and higher affinity to breast cancer cells overexpressing Her2 receptors. Internalized nanoparticles were found in lysosomes.
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    Assembly, characterization and evaluation of a 3rd generation nanoparticle based drug carrier for metastatic breast cancer treatment
    Huang, Wei (Virginia Tech, 2013-06-03)
    Cancer is one of the leading causes of death in the world. For women in the U.S. and the European countries, breast cancer is the most common type and it continuously threatens the lives of the patients and causes huge economic losses. Chemotherapy and endocrine therapy are the common treatments for recurrence prevention and metastatic cancer symptom palliation. However, the uses of these therapies are meanwhile largely limited because their toxic side effects and non-specificity usually lead to low quality lives of the patients. Low aqueous solubility, multi-drug resistance, degradation of drug, limited intra-tumor diffusion and etc. are other limitations of conventional chemotherapies and endocrine therapies. Nanoparticle based drug carriers were extensively studied for therapeutic drug delivery. Many carriers could be loaded with high dose of hydrophobic and hydrophilic drugs, protect the drug from the surrounding in vivo environment during the transportation, specifically target and enter the tumor cells and slowly release the drug thereafter. Advanced nanoparticle drug carriers are studied driven by the need of a more efficient drug delivery. The 3rd generation of nanoparticle based drug carriers are recently developed. They usually consist of more than one type of nanoparticles. Different part of the particle has more specialized functions. Therefore, by carefully selecting from the conventional nanoparticle carriers, a 3rd generation particle could have the properties such as high loading capacity of multiple drugs, prolonged half-life in circulation, higher tendency of accumulating at the tumor site, improved specificity to the tumor cells, higher cell uptake rate and accurately triggered controlled release, and combination of the above-mentioned properties. In our study, a paclitaxel loaded nanoparticle supported immunoliposome was assembled for metastatic breast cancer drug delivery. Functionalized single walled carbon nanohorn or poly(lactic-co-glycolic acid) was encapsulated in the polyethylene glycol (PEG) coated liposome for high drug loading and controlled release. Anti-Her2 antibody or Herceptin® was grafted onto the surface of the liposome for a higher affinity to the Her2 overexpressing breast cancer cells. Firstly, the conjugation of protein to the surface of liposome and PEGylated liposomes were investigated. Proteins with or without membrane binding domain were conjugated to liposome and PEGylated liposomes through covalent and non-covalent binding for comparison. A modified enzyme-linked immune sorbent assay was developed for surface grafted protein quantification. Secondly, the encapsulation of solid nanoparticle into PEGylated immunoliposome was investigated. Results showed a new structure of solid nanoparticle in PEGylated immunoliposome at a 1:1 ratio was formed during the repeated freeze-thawing process. Supported immunoliposomes with high homogeneity in size and structure were purified by sucrose density gradient centrifugation. Thirdly, the drug loading, triggered release, cell binding, cell uptake and cell toxicities of the supported immunoliposome were studied. Release results showed a minimum drug leakage in serum at body temperature from the particle. The release was initiated with a minor burst trigged by low pH inside the tumor cell and followed with a long term linear pattern. Cell assay results showed the highest binding affinity of the antibody or Herceptin® grafted nanoparticles to Her2 overexpressing cell lines and a lysosomal intracellular distribution of the endocytosised particles. In the final study, a fabrication process for polymeric material nanoparticles was established. The process was capable of providing accurate control of the particle size with significant high output rates, thus largely extends the scope of materials for supporting the immunoliposome.
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    The biosynthesis of ravidomycin
    Keyes, Robert F. (Virginia Tech, 1989-07-01)
    Ravidomycin is a yellow antitumor antibiotic produced by Streptomyces ravidus. Ravidomycin shows strong antitumor activity against P388 lymphocytic leukemia, the colon 38 tumor, and the CD8Fl mammary tumor. It is also very active against Gram positive bacteria. Biosynthetic studies have shown that the aglycone unit comes from the folding of a polyketide chain with the vinyl unit arising from propionic acid. Since this vinyl functionality is believed to playa role in the antitumor activity of the antibiotic, it is of interest to elucidate the stereochemical selectivity in its formation from propionic acid. The synthesis of (R) and (S)-L2-²H₁ j propionate, incorporation of the labelled material, and chemical analysis of the resulting antibiotic was be used to determine the stereochemistry of formation of the vinyl side chain. It was found that propionate was incorporated with ravidomycin with stereospecific loss of the 2-(pro-R)-proton.
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    Block Copolymer Derived Porous Carbon Fiber for Energy and Environmental Science
    Serrano, Joel Marcos (Virginia Tech, 2022-04-26)
    As the world population grows, a persistent pressure on natural resources remains. Resource requirements have extensively expanded due to industrialization. Several technological advancements continually aim to alleviate these resource shortages by targeting existing shortcomings in effective and efficient material design. Practical, high-performing, and economical materials are needed in several key application areas, including energy storage, energy harvesting, electronics, catalysis, and water purification. Further development into high-performing and economical materials remain imperative. Innovators must seek to develop technologies that overcome fundamental limitations by designing materials and devices which address resource challenges. Carbon serves as a versatile material for a wide range of applications including purification, separation, and energy storage owing to excellent electrical, physical, and mechanical properties. One-dimensional (1D) carbon fiber in particular is renowned for excellent strength with high surface-to-volume ratio and is widely commercially available. Although an exceptional candidate to address current energy and environmental needs, carbon fibers require further investigation to be used to their full potential. Emerging strategies for carbon fiber design rely on developing facile synthetic routes for controlled carbon structures. The scientific community has shown extensive interest in porous carbon fabrication owing to the excellent performance enhancement in separation, filtration, energy storage, energy conversion, and several other applications. This dissertation both reviews and contributes to the recent works of porous carbon and their applications in energy and environmental sciences. The background section shows recent development in porous carbon and the processing methods under investigation and current synthetic methods for designing porous carbon fibers (PCF). Later sections focus on original research. A controlled radical polymerization method, reversible addition-fragmentation chain transfer (RAFT), enabled a synthetic design for a block copolymer precursor, poly(methyl methacrylate) (PMMA) and polyacrylonitrile (PAN). The block copolymer (PMMA-b-PAN) possesses a unique microphase separation when electrospun and develop narrowly disperse mesopores upon carbonization. The PMMA and PAN domains self-assemble in a kinetically trapped disordered network whereby PMMA decomposes and PAN cross-links into PCF. The initial investigation highlights the block copolymer molecular weight and compositional design control for tuning the physical and electrochemical properties of PCF. Based on this study, mesopore (2 – 50 nm) size can be tuned between 10 – 25 nm while maintaining large surface areas, and the PAN-derived micropores (< 2 nm). The mesopores and micropores both contribute to the development of the unique hierarchical porous carbon structure which brings unprecedented architectural control. The pore control greatly contributes to the carbon field as the nano-scale architecture significantly influences performance and functionality. The next section uses PCF to clean water sources that are often tainted with undesirable ions such as salts and pollutants. Deionization or electrosorption is an electrochemical method for water purification via ion removal. I employed the PCFs as an electrode for deionization because of their high surface area and tunable pore size. Important for deionization, the adsorption isotherms and kinetics highlight the capacity and speed for purification of water. I studied PCF capacitive filtration on charged organic salts. Because PCF have both micropores and mesopores, they were able to adsorb ions at masses exceeding their own weight. The PFC adsorption efficiency was attributed to the diffusion kinetics within the hierarchical porous system and the double layer capacitance development on the PCF surface. In addition, based on the mechanism of adsorption, the PCFs showed high stability and reusability for future adsorption/desorption applications. The PCF performance as an electrosorption material highlights the rational design for efficient electrodes by hierarchical interconnected porosity. Another application of PFCs is updating evaporative desalination methods for water purification. Currently distillation is not widely used as a source of potable water owing to the high cost and energy requirement. Solar desalination could serve as a low-cost method for desalination; however, the evaporation enthalpy of water severely limits practical implementation. Here I apply the pore design of PCF as a method for water nano-confinement. Confinement effects reduce water density and lowers evaporation enthalpy. Desalination in PCF were studied in pores < 2 nm to 22 nm. The PCF pore size of ~ 10 nm was found to be the peak efficiency and resulted in a ~ 46% reduction in enthalpy. Interestingly, the PCF nano-confinement also contributed to the understanding in competing desorption energy for evaporation in micropores. The pore design in PCF also shows confinement effects that can be implemented in other environmental applications. Lastly, the block copolymer microphase morphology was explored in a vapor induced phase separation system. The resulting PCF properties showed a direct influence from the phase separation caused by nonsolvent. At low nonsolvent vapor, a disordered microphase separation occurred, however upon application of nonsolvent vapor, the polymer chains reorganized. The reorganization initially improved mechanical properties by developing more long-range ordered graphic chains in the PAN-derived carbon. However, at higher nonsolvent vapor concentrations, the fibers experienced polymer precipitation which resulted in bead and clump formation in the fiber mats. The beads and clumps lowered both mechanical properties and electrochemical performance. The vapor induced phase separation showed a method for enhancing mechanical properties without compromising electrochemical performance in flexible carbon fibers.
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    The catalytic activity of anodic oxides on aluminum
    Madeleine, Teresa Catherine (Virginia Polytechnic Institute and State University, 1988)
    The dehydration of isopropanol over anodic oxides was studied. The catalytic activity of the anodic oxides prepared in phosphoric, sulfuric, and oxalic acid was compared to the activity of ν-Al₂O₃. The effect of various thermal treatments on the catalytic activity was examined. IR spectroscopy proved useful for the study of the effect of thermal treatment on the acidity of the oxides. X-ray photoelectron spectroscopy (XPS) was employed to examine the oxide surfaces both before and after use as a catalyst. The acidity of the oxides was studied by various methods and related to the activity of the oxides. The acidity of the oxide surfaces was studied by the adsorption of pH indicators on the oxide surfaces. The adsorption of gaseous bases, ammonia and pyridine, was studied by IR spectroscopy and temperature programmed desorption mass spectrometry. It was thus possible to differentiate between Lewis and Brønsted acid sites and to determine the quantity of the acid sites on the various oxides.
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    Chemical Reactivity and Regioselectivity of Trimetallic Nitride Endohedral Metallofullerenes
    Cai, Ting (Virginia Tech, 2008-03-26)
    Endohedral metallofullerenes (EMF) have attracted increasing attention during past decades for their potential applications in the fields of biomedicine and nanomaterials. Trimetallic nitride template endohedral metallofullerenes (TNT EMFs) are some of the most promising fullerene-based materials (e.g., as MRI and X-ray contrast agents) because of their high yields compared to classic endohedral metallofullerenes. This dissertation addresses the chemical reactivity and regioselectivity of TNT EMFs. Based on the extraordinarily high stability of TNT EMFs relative to empty cage fullerenes and classic endohedral metallofullerenes, macroscopic quantities of high purity TNT EMFs were obtained directly from crude soot in a single facile step by using a cyclopentadiene-functionalized resin to trap the more reactive species via Diels-Alder reactions, allowing the TNT EMFs to pass through. We also developed a support-free chemical separation method of TNT EMFs from Sc- and Lu-based soot extract that makes use of the differing solubilities of unreacted TNT EMFs versus 9-methylanthracene-derivatized empty cage fullerenes. The exohedral functionalization of metallofullerenes can fine-tune their chemical and physical properties. The first N-methylpyrrolidino derivatives of TNT EMFs (Ih Sc3N@C80 and Ih Er3N@C80) were synthesized via 1,3-dipolar cycloaddition of N-methylazomethine ylides (Prato reaction). The demonstration of planar symmetry in the N-methylpyrrolidino derivatives by 13C NMR spectroscopy suggested that the reaction exclusively took place at the 5,6-ring junction. However, both 5,6-ring and 6,6 ring junction adducts were obtained when Ih Sc3N@C80 reacted with N-triphenylmethyl-5-oxazolidinone, as characterized by NMR spectroscopy and X-ray crystallography. The kinetically favored 6,6-ring junction adduct was converted to the thermodynamic product, the 5,6-ring junction adduct, upon thermal equilibration. The synthesis of pyrrolidino derivatives was also extended to two other Sc-based TNT EMFs, D5h Sc3N@C80 and Sc3N@C78. The reactivity and regioselectivity of D5h Sc3N@C80 and Sc3N@C78 were demonstrated by NMR spectroscopy, X-ray crystallography and theoretical calculations. Another type of reaction, the Bingel-Hirsch cyclopropanation was carried out with D3h Sc3N@C78 for the first time, yielding a single Cs-symmetric monoadduct and a dominant C2v-symmetric diadduct for the first time. The symmetric diadduct clearly demonstrates the remarkable regioselectivity control exerted by the encapsulated Sc3N cluster. We employed a LUMO electron density surface computational approach to predict multiadduct docking sites on the ellipsoidal fullerene cage surface. We also successfully synthesized the first derivative of a non-IPR fullerene, the diethyl malonate derivative of Sc3N@C68 by a Bingel-Hirsch reaction. The reactivity and regioselectivity of Sc3N@C68 were investigated by NMR spectroscopy and theoretical calculations.
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    The Chemistry of Fullerenes, Polymers, and Host/Guest Interactions
    Schoonover, Daniel Vernon (Virginia Tech, 2015-03-03)
    The exploitation of the relationship between the chemical and physical properties of materials is the hallmark of advancing science throughout the world. The basic understanding of how and why molecules react and interact with each other in different environments allows for the discovery and implementation of new materials and devices that not only advance the state of human life but continually change the planet. The work described in this dissertation generally falls under three diverse categories: functionalization of fullerenes, investigation of host/guest interactions in solution, and the synthesis and characterization of ion containing polymers. The separation and functionalization of fullerenes is a recent and exciting area of research. The separation methods outlined are intended to increase the availability of endohedral metallofullerenes by decreasing their cost of production. Functionalized fullerene species were achieved through Bingel and Prato reactions to provide materials with novel functional groups. These materials may be further utilized in photovoltaic or other organic electronic devices. The characterization of noncovalent interactions between different molecules in solution is the focus of supramolecular chemistry. Isothermal Titration Calorimetry stands out as one of the best, among the many methods used to elucidate the characteristics of these systems. The binding of bis- imidazolium and paraquat guests with macrocyclic host molecules has been explored in this work. The measurements of the association constants for these systems will aid in the ongoing synthesis of new host/guest systems. Ion containing polymers were synthesized and characterized for their use in electroactive devices. Imidazolium containing polymers with bulky anions were synthesized on low glass transition polymer chains. These materials had enhanced ion conductivity and may eventually be used in electronic actuator materials.
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    Chromatography and purification of endohedral metallofullerenes
    Stevenson, Steven A. (Virginia Tech, 1995)
    At the conception of this research, a separation methodology for obtaining purified mctallofullerene [Am@C2n, m = # of metal atoms, A, and C2n = # of carbons in the surrounding cage] samples was not yet developed. Isolation of these metal-encapsulated fullerenes was strongly desired for characterization of their physical and chemical properties. Predicted applications for these novel species include their use as possible superconductors, catalysts, and non-linear optical devices. However, initial purification efforts have been hindered by several difficulties. These factors include a low abundance (< 1%) in the raw extract, uncertain stability in aerobic environments, co-elution of Am@C2n with empty-cage fullerenes, and the need for selective chromatographic detection. In this research, these difficulties have been overcome with the development of a continuous-flow, on-line HPLC-EPR apparatus. Advantages include a selective, non-invasive detector with chromatographic separations being performed in a controlled anaerobic environment. This on-line approach permits the selective detection of only those metallofullerenes with an odd-number of encapsulated atoms. The ability to continually monitor separations of these paramagnetic species ultimately permits the optimization of chromatographic parameters. The methodology developed from this on-line HPLC-EPR approach has ultimately resulted in purified empty-cage (C₆₀, C₇₀...C₉₆) and metallofullerene samples (Sc₂@C₇₄, Sc₂@C₇₆, Sc₂@C₇₈, Sc₂@C₈₀, Sc₂@C₈₂, Sc₂@C₈₄ - two isomers, Sc₂@C₈₆, Sc₂@C₈₈, Sc₂@C₉₀, Sc₃@C₈₂, Sc₄@C₈₂, La₂@C₇₂, Er@C₈₂, Er₂@C₈₂ - two isomers, and Er₂@C₉₂).
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    Computational Study of the Properties and Stabilities of Endohedral Metallofullerenes
    Fuhrer, Timothy J. (Virginia Tech, 2013-04-23)
    The chemistry of fullerenes, which are a class of carbon allotropes that can be prepared by vaporization of graphite in an electric arc in a low pressure atmosphere,1 has become a topic of much experimental and theoretical study over the past 25 years.  Herein we present a series of theoretical studies related to recently discovered or studied endohedral metallofullerenes (EMF) and a theory as to the selective stability of certain isomers of EMFs. Computational treatments of the anions of C80 and C94 are presented and compared in an effort to gain an understanding and predictive model for which isomers of each cage size EMF will be most stable.  A model is proposed in which the pentagons of fullerene anions are seen as charge localization centers that repel one another, making the pyracyclene bonding motif much more unstable for fullerene anions than for fullerene neutral cages. Computational treatments are also presented for two newly discovered EMFs, Y2C2@C92 and Gd2@C79N.  Y2C2@C92 is reported to exhibit a previously undiscovered mode of internal cluster rotation, while Gd2@C79N is shown to have unusual stability for an azofullerene with a large spin quantum number (15/2). Finally, computational techniques are employed to predict the thermodynamic feasibility of a chemical reaction replacing one metal atom in a trimetallic-nitride template (TNT) endohedral metallofullerene with different metal atom.  At least two of these are predicted to be thermodynamically practical.
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    Design and Characterization of Central Functionalized Asymmetric tri-Block Copolymer Modified Surfaces
    Wang, Jianli (Virginia Tech, 2001-10-30)
    Well-defined central functionalized asymmetric tri-block copolymers (CFABC) were designed as a new type of polymer brush surface modifier, with a short central functionalized block that can form chemical bonds with a suitable substrate surface. A combination of sequential living anionic polymerization and polymer modification reactions were used for the synthesis of two CFABCs: PS-b-poly(4-hydroxystyrene)-b-PMMA and PS-b-poly(4-urethanopropyl triethoxysilylstyrene)-b-PMMA. GPC and NMR characterization indicated that the block copolymers possessed controlled molecular weights and narrow molecular weight distributions. CFABC polymer brushes were successfully prepared by chemically grafting PS-b-poly(4-urethanopropyl triethoxysilylstyrene)-b-PMMA onto silicon wafer surfaces. AFM, XPS and ellipsometry were used to confirm the CFABC polymer brush structures and thickness. The surface properties of CFABC polymer brush modified silicon wafer substrates subjected to different environmental parameters were studied. Reversibly switchable surface energies were observed when the polymer brush modified surfaces were exposed to solvents with different polarities. The phenomenon was attributed to the chain configuration auto-adjustment in the polymer brush systems. The same mechanism was also used to explain the enhanced adhesion capability between the modified surfaces and different polymer materials (PS and PMMA). Phase behaviors of polymer thin films on unmodified and CFABC polymer brush modified silicon wafer surfaces were also studied. For thin films of polymer blends, PS blend PS-co-PMMA, the effects of film thickness, chemical composition and temperature on the phase separation mechanism were investigated. The phase behavior in thin films of triblock copolymers with or without central functionalities were compared to reveal the role of the central functionalized groups in controlling film structures. Finally, the presence of CFABC polymer brush at the interface between PS-b-PMMA diblock copolymer thin film and silicon wafer substrate was found to decrease the characteristic lamellar thickness in the thin film. A mechanism of tilted chain configurations in the thin film due to the interactions with the CFABC polymer brushes was proposed.
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    Design and Modification of Polyazine-Bridged Ru(II),Rh(III) Bimetallic and Trimetallic Supramolecular Complexes Applicable in Solar Energy Harvesting for the Photocatalytic Reduction of Water to Hydrogen
    White, Travis Azor (Virginia Tech, 2012-09-17)
    The goal of this research was to develop a series of mixed-metal supramolecular complexes through systematic component variation to better understand the role of structural modification on basic chemical and photochemical properties including photocatalysis of H₂O to H₂. Varying bidentate polypyridyl terminal ligands (TL), non-chromophoric halides (X), or number of Ru(II) light absorbers (LA) tunes the electrochemical, spectroscopic, photophysical, and photochemical properties within the supramolecular architecture. Ru(II),Rh(III),Ru(II) trimetallics of the design [{(TL)₂Ru(dpp)}₂RhX₂](PF₆)₅ (TL = phen = 1,10-phenanthroline or Ph₂phen = 4,7-diphenyl-1,10-phenanthroline; dpp = 2,3-bis(2-pyridyl)pyrazine; X = Cl⁻ or Br⁻) covalently couple two Ru(II) LAs to a central Rh(III) electron collector (EC) through dpp polyazine bridging ligands (BL). Ru(II),Rh(III) bimetallics of the design [(TL)₂Ru(dpp)RhCl₂(TL′)](PF₆)₃ (TL = Ph₂phen or bpy = 2,2′-bipyridine; TL′ = Ph₂phen or tBu2bpy = 4,4′-Di-tert-butyl-2,2′-bipyridine) couple only one Ru(II) LA to a Rh(III) metal center through the dpp BL. The Ru(II),Rh(III),Ru(II) trimetallic and Ru(II),Rh(III) bimetallic complexes are synthesized using a building block approach, permitting facile modification of the supramolecular architecture throughout molecular assembly. Electrochemical analysis of both architectures displays a Ru-based HOMO tuned by TL identity (RuII/III = +1.62 V and +1.58 V vs. Ag/AgCl for TL = phen and Ph₂phen, respectively) and a Rh-based LUMO tuned by X identity (RhIII/II/I = -0.35 V and -0.32 V vs. Ag/AgCl for X = Cl⁻ and Br⁻, respectively). Modification of TL′ at Rh(III) within the bimetallics provided varying LUMO identity. The trimetallics and bimetallics are efficient light absorbers throughout the UV and visible with π⟶ π* intraligand (IL) transitions in the UV and Ru(dπ)⟶ligand(π*) metal-to-ligand charge transfer (MLCT) transitions in the visible. While X identity does not vary the light absorbing properties within Ru(II),Rh(III),Ru(II) trimetallics, TL identity and the number of Ru(II) LAs strongly impacts spectral coverage and the extinction coefficient. Photoexcitation of the Ru(dπ)⟶dpp(π*) ¹MLCT results in near unity population of the weakly emissive, short-lived Ru(dπ)⟶dpp(π*) ³MLCT excited state, which is efficiently quenched by intramolecular electron transfer to populate a non-emissive Ru(dπ)⟶Rh(dσ*) metal-to-metal charge transfer (³MMCT) excited state. Photolysis of the complexes in the presence of the sacrificial electron donor N,N-dimethylaniline (DMA) results in multi-electron collection at Rh, thereby converting Rh(III) to Rh(II) to Rh(I) accompanied by halide loss at each step. This establishes the Ru(II),Rh(III),Ru(II) and Ru(II),Rh(III) complexes as photochemical molecule devices (PMD) for photoinitiated electron collection (PEC). The ability of these systems to undergo multiple redox cycles, absorb light efficiently, populate photoreactive excited states, and collect electrons at a reactive Rh metal center fulfills the requirements for H₂O reduction photocatalysts. Photolysis of trimetallic or bimetallic complexes at 470 nm in the presence of DMA and H₂O substrate yields photocatalytic H2 production. Within [{(TL)₂Ru(dpp)}₂RhX₂]⁵⁺ trimetallics (TL = phen or Ph₂phen; X = Cl⁻ or Br⁻), varying the TL from phen to Ph₂phen and X from Cl⁻ to Br⁻ yielded the most active and robust photocatalyst with [{(Ph₂phen)₂Ru(dpp)}₂RhBr₂]⁵⁺ producing 44 ± 6 mL H₂, 610 ± 90 mol H₂/mol Rh catalyst, and 7.3% maximum quantum efficiency (max. ΦH₂) in a DMF solvent system after 20 h photolysis. The proposed mechanism of PEC suggests bimetallic systems might be prepared that are active photocatalysts. Ru(II),Rh(III) bimetallics are synthetically more challenging and the energetic proximity of dpp(π*) and Rh(dσ*) orbitals make electronic tuning with steric protection of the photogenerated Rh(I) difficult. Within [(TL)₂Ru(dpp)RhCl₂(TL′)]³⁺ bimetallics (TL = Ph₂phen or bpy; TL′ = Ph₂phen or tBu₂bpy), a careful balance of steric and electronic effects was required to produce active photocatalysts. The bimetallic [(Ph₂phen)₂Ru(dpp)RhCl₂(Ph₂phen)]³⁺ produces 1.1 ± 0.07 mL H₂, 81 ± 5 TON, and 0.88% max. ΦH₂ in a DMF solvent system after 20 h photolysis. This establishes the [(Ph₂phen)₂Ru(dpp)RhCl₂(Ph₂phen)]³⁺ complex as the first Ru(II),Rh(III) bimetallic to function as a homogeneous single-component H₂O reduction photocatalyst. This dissertation reports the detailed analysis of the electrochemical, spectroscopic, photophysical, and photocatalytic properties of [{(TL)₂Ru(dpp)}₂RhX₂]⁵⁺ trimetallic (TL = phen or Ph₂phen; X = Cl or Br) and [(TL)₂Ru(dpp)RhCl₂(TL′)]³⁺ bimetallic (TL = Ph₂phen or bpy; TL′ = Ph₂phen or tBu₂bpy) supramolecular complexes. The design of the molecular architecture and the intrinsic properties of each component contribute to the overall function and efficiency of these systems. The careful design, meticulous synthesis and purification, detailed characterizations, and methodical experimentation have led to an in-depth understanding of the properties and factors needed for more efficient photocatalytic reduction of H₂O to H₂.
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    Design, Preparation and Characterization of Novel Pseudorotaxanes, Semirotaxanes, Rotaxanes, Non-Covalent Supramolecular Polymers and Polycatenanes
    Niu, Zhenbin (Virginia Tech, 2011-09-06)
    Design and preparation of novel host/guest systems, such as pseudorotaxanes, semirotaxanes, rotaxanes and catenanes, with high association constants, enhanced yields and the abilities to respond to external stimuli are of great importance and significance due to their topological novelty and potential application. The convergence of supramolecular chemistry with polymer science provides an important way to extend the scope of polymer and material sciences by incorporating designed host/guest systems into polymers, and the resulting non-covalently linked supramolecular polymers are expected to have unusual properties due to their unique architectures compared with traditional polymers. After discovery of bis(meta-phenylene)-32-crown-10 (BMP32C10) derivative/paraquat complexes, for about a quarter century only “taco”-shaped complexes were observed by X-ray crystallography. Here, by the self-assembly of a BMP32C10 bearing two electron-donating groups (carbazoles) with electron-accepting paraquat derivatives, the first [2]pseudorotaxane and the first pseudocryptand-type poly[2]pseudorotaxane based on BMP32C10 were isolated as crystalline solids as shown by X-ray analyses. The first dual component pseudocryptand-type [2]pseudorotaxanes were designed and prepared via the self-assembly of synthetically easily accessible BMP32C10 pyridyl, quinolyl and naphthyridyl derivatives with paraquat. The formation of the pseudocryptand structures in the complexes remarkably improved the association constants by forming the third pseudo-bridge via H-bonding with the guest and π-stacking of the heterocyclic units. A pseudocryptand-type [2]pseudorotaxane was formed via the self-assembly of a dipyridyl BMP32C10 derivative and a paraquat derivative. Due to the basicity of the pyridyl group, which forms the third pseudo-bridge of the pseudocryptand, this pseudorotaxane represents the first system with acid-base adjustable association constants, i. e., finite both under acidic and neutral conditions. The first pseudocryptand-type supramolecular [3]pseudorotaxane was designed and prepared via the self-assembly of a bispicolinate BMP32C10 derivative and a bisparaquat. The complexation behavior was cooperative. In addition, the complex comprised of the BMP32C10 derivative and a cyclic bisparaquat demonstrated strong binding; interestingly, a poly[2]pseudocatenane structure was formed in the solid state for the first time. Two novel BMP32C10 cryptands, bearing covalent and metal complex linkages, were designed and prepared. By employing the self-assembly of these biscryptands, which can be viewed as AA monomers, and a bisparaquat, which can be viewed as a BB monomer, the first AA/BB-type linear supramolecular polymers with relatively high molecular weights were successfully prepared. Via the self-assembly of two BMP32C10-based cryptands, bearing covalent and metal complex (ferrocene) linkages, with dimethyl paraquat, novel [3]pseudorotaxanes were formed statistically and anticooperatively, respectively. From a hydroxyl-functionalized secondary ammonium salt a [2]semirotaxane and a [2]rotaxane were prepared successfully with dibenzo-24-crown-8 (DB24C8). X-ray analysis of a single crystal of the [2]semirotaxane confirmed its semirotaxane nature. In addition, the formation of the [2]semirotaxane can be reversibly controlled by adding KPF6 and 18C6 sequentially. This system affords a way to prepare novel supramolecular polymers. Dibenzo-30-crown-10 (DB30C10) derivatives and pyridine-based DB30C10 cryptands were prepared by employing the templating method established by our group. A [2]pseudorotaxane was prepared based on DB30C10 diol and paraquat diol. The [3]pseudorotaxane formed via the self-assembly between DB30C10 cryptand and bisparaquat diol occurred in a cooperative manner. In addition, a bromo-functionalized DB30C10 cryptand was successfully designed and prepared. An alkyne-functionalized DB30C10 cryptand was designed and is under preparation; its precursors have been prepared successfully. In the future, based on these functionalized cryptands and paraquat salts, AA and AB type monomers will be prepared. Via the self-assembly between these monomers, non-covalent supramolecular polymers with high molecular weight will be afforded. A novel DB30C10 cryptand bearing an organometallic bridge, ferrocene, was prepared via 1-(3'-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDCI) coupling of the crown ether diol with ferrocene dicarboxylic acid. The cryptand is dimerized in the solid state via π, π-stacking and hydrogen bonds. The ferrocene-based cryptand formed novel [2]pseudorotaxanes with paraquat and diquat PF₆ salts with association constants (Kₐ) of 1.7 ± 0.1 x 10³ and 4.2 ± 0.3 x 10⁴ M⁻¹ in acetone-d₆, respectively. In order to prepare linear polycatenanes, the preparation of which represent a real synthetic challenge, a series phenanthroline derivatives were designed and prepared. A “U” shaped monomer was successfully prepared in relative high yield with good solubility. In the future, real linear polycatenanes will be prepared. In addition, a novel diphenanthroline-based BMP32C10 derivative was prepared in high yield and the complexation behavior between it and dimethyl paraquat was studied.
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    Design, Syntheses and Biological Activities of Paclitaxel Analogs
    Zhao, Jielu (Virginia Tech, 2011-01-31)
    The conformation of paclitaxel in the bound state on the protein has been proposed to be the T-taxol conformation, and paclitaxel analogs constrained to the T-taxol conformation proved to be significantly more active than paclitaxel in both cytotoxicity and tubulin polymerization assays, thus validating the T-taxol conformation as the tubulin-binding conformation. In this work, eight compounds containing an aza-tricyclic moiety as a mimic of the baccatin core of paclitaxel have been designed and synthesized as water-soluble simplified paclitaxel analogs, among which 3.50-3.52 and 3.55 were conformationally constrained analogs designed to bind to the paclitaxel binding site of tubulin, based on their similarity to the T-taxol conformation. The open-chain analogs 3.41-3.43 and 3.57 and the bridged analogs 3.50-3.52 and 3.55 were evaluated for their antiproliferative activities against the A2780 cell lines. Analogs 3.50-3.52 and 3.55 which were designed to adopt the T-taxol conformation showed similar antiproliferative activities compared to their open-chain counterparts. They were all much less active than paclitaxel. In the second project, a series of paclitaxel analogs with various thio-containing linkers at C-2′ and C-7 positions were designed and synthesized in our lab. These analogs were attached to the surfaces of gold nanoparticles by CytImmune Sciences for the development of mutifunctional tumor-targeting agents. The native analogs and the gold bound analogs were evaluated for their antiproliferative activities against the A2780 cell line. All the compounds tested showed comparable or better activities than paclitaxel. Stability studies were performed for selected analogs in hydrolysis buffer, which showed that the analogs released paclitaxel in buffer over time. In the third project, the synthesis of a conformationally constrained paclitaxel analog which was designed to mimic the REDOR-taxol conformation was attempted. Two synthetic routes were tried and significant progress was made toward the synthesis of the conformationally constrained analog. However, both of the current synthetic routes failed to produce the key intermediate that would serve as the precursor for a ring-closing metathesis reaction to furnish the macrocyclic ring.
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    The development of laboratory sessions for a introductory course in nuclear magnetic resonance spectroscopy
    Iannaccone, Gennaro A. (Virginia Tech, 1991-11-05)
    The history and philosophy underlying the design of the experimental component of an intensive introductory course in Nuclear Magnetic Resonance Spectroscopy (NMR) is presented. The concept of a "hands on" experience is used to transform the complete NMR novice into a competent operator. In addition to exposing the student to classical elucidation tools, advanced techniques, such as two dimensional and solid state NMR, are introduced. Through the use of unknowns, participants are encouraged to develop practical problem solving strategies. The detailed contents of the twenty-six experiments developed for the laboratory sessions are reviewed. The five day course schedule, and a coversheet, containing pertinent references for each experiment, is included. An examination of the unknowns utilized in the course, and a glossary of NMR terms is also presented.