VTechWorks Repository :: Browsing by Author "Merola, Joseph S."

Browsing by Author "Merola, Joseph S."

Now showing 1 - 20 of 134

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.
(2S,4R)-4-Fluoro-pyrrolidinium-2-carboxyl-ate.
Hobart, David B. Jr.; Merola, Joseph S. (International Union of Crystallography, 2012-08-01)
The crystal structure of the title compound, C(5)H(8)FNO(2), at 100 K, displays inter-molecular N-H⋯O hydrogen bonding between the ammonium and carboxyl-ate groups as a result of its zwitterionic nature in the solid state. The five-membered ring adopts an envelope conformation with the C atom at the 3-position as the flap. The compound is of inter-est with respect to the synthesis and structural properties of synthetic collagens. The absolute structure was determined by comparison with the commercially available material.
Analysis of wood pulp extracts utilizing gas chromatography-mass spectroscopy
Sequeira, Anna J. (Virginia Tech, 1991)
Wood pulp mill effluents continue to attract much attention due to environmental consequences. However, in comparison, very little work has been published on wood pulp extracts themselves. In this investigation, chemithermomechanical (CTMP) pulps as well as Kraft (BKP) pulps were Soxhlet extracted with solvents of different polarity. These two types of pulp extracts were then compared qualitatively using GC-FID and GC-MSD as well as quantitatively based on the percent of extractives obtained. For all the pulps studied, the percent extractives of water > ethyl acetate > cyclohexane. The CTMP extracts exhibited many more components as compared to BKP extracts for all the extractions solvents. The presence of trace chlorinated phenolics in the above wood pulp extracts was also addressed utilizing GC-ECD, GC-EIMS and GC-NCIMS. 4-MCG, 4,5-DCG, 4,5,6-TCG, 3,4,5-TCG, 2,4,6- TCP, 2,3,4,6-TeCP, PCP and 6-MCVN were discovered. Due to a lack of knowledge of the complete history of the wood pulps studied, the exact causes for their discoveries are unknown. Attempts were also made to study the feasibility of Supercritical Fluid Extraction of the above mentioned wood pulps due to the difficulties faced with Soxhlet extractions. The percent extractives obtained using SF-CO₂ and cyclohexane were found to be comparable.
The application of thin film planar waveguides as a refractive index detector for microscale high performance liquid chromatography
Kang, Lee (Virginia Tech, 1991-01-15)
Thin film planar waveguides were originally introduced in microwave engineering. The spectroscopist began to use such waveguides as tools to solve chemical characterization problems since Harrick and Fahrenfort introduced the Attenuated Total'Reflection (ATR) in the early 1960's. Today, planar waveguides are playing an important and ever-increasing role in modem chemistry. In this thesis, a novel design for a refractometer involving the application of a thin film planar waveguide and coupling prism was demonstrated. This device shows the feasibility of refractive index measurements in a flowing stream. Therefore, an online detector for High Performance Liquid Chromatography (HPLC) was chosen as the vehicle to test out the concepts. The research works were devoted to studies of waveguide properties and flow dynamics in a chromatographic situation. It was found that microscale detection is possible. The sensitivity can be enhanced by using the highest propagation mode as the probe, and by selecting a proper refractive index liquid as the solvent carrier. A description of the investigation and the various factors involved in designing and optimizing a planar waveguide for refractive index detection is included. The results provide guidelines for the device as a realistic analytical detector.
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.
Aqua-bis-(4-methyl-benzene-sulfonato-κO)(η(5)-penta-methyl-cyclo-penta-dien-yl)rhodium(III) monohydrate.
Roy, Christopher P.; Boyer, Pauline M.; Merola, Joseph S. (International Union of Crystallography, 2013-05-01)
The title half-sandwich rhodium(III) complex, [Rh(C10H15)(C7H7O3S)2(H2O)]·H2O, consists of a π-bonded penta-methyl-cyclo-penta-dienyl group, two σ-bonded tosyl-ate groups and an aqua ligand. The structure displays both inter- and intra-molecular O-H⋯O hydrogen bonding. The inter-molecular hydrogen bonding results in an extended helical chain along a 21 screw axis parallel to c, due to hydrogen bonding from the coordinating water ligand to the lattice water mol-ecule and then to a sulfonate O atom of a different asymmetric unit.
Aspects of the microwave induced plasma as an element selective detector for supercritical fluid chromatography and supercritical fluid extraction
Ducatte, Gerald Roger (Virginia Tech, 1993-12-05)
The introduction of supercritical CO₂ at packed column supercritical fluid chromatography (SFC) flow rates is shown to significantly affect the excitation characteristics of a helium microwave induced plasma (He MIP). In this work, the influence of CO₂ on specific atomic and ionic transitions of Cl, Br, I, P, and S is described. Also presented is the determined relationship between transition energy and degree of signal depression resulting from the introduction of CO₂ to the plasma. Attempts to enhance the emission signals of non-metals by introducing H₂ into a He MIP are discussed. The inadequacy of excitation temperature, ionization temperature, rotational temperature, and electron number density measurements to determine the effect of CO₂ on the excitation characteristics of a He MIP is also described. However, application of kinetic theory and a recently developed theory on charge transfer allows a reasonable series of mechanisms to be developed that describe the excitation processes of a He MIP to which supercritical CO₂ is added. The remainder of this work describes a direct interface between a supercritical fluid extraction (SFE) vessel and an Ar MIP for the purpose of element selective detection. The response of the plasma to the introduction of sample via SFE at a variety of extraction temperatures, pressures, and sample concentrations is presented.
Base catalysis by alkali modified zeolites
Hathaway, Paul Edward (Virginia Polytechnic Institute and State University, 1989)
The development, characterization, and catalytic application of a novel zeolite with solid base properties has been completed. From isopropanol decomposition to acetone and propylene, the acid/base properties of various alkali exchanged, faujasite-type zeolites are explored. It is found that upon impregnation of CsNaY with cesium hydroxide or cesium acetate, acetone production (normally attributed to base sites) is promoted by an order of magnitude above the untreated (not impregnated) CsNaY zeolite. Furthermore, selectivity to acetone is above 97% and on a surface area basis, acetone activity is found to be comparable to MgO. Impregnation of CsNaX shows little promotion in acetone activity resulting in acetone activity comparable to the untreated CsNaY zeolite and acetone selectivity at 62%. From numerous characterization studies of the impregnated CsNaY zeolite (many in situ) it appears that a highly dispersed intracrystalline cesium oxide is formed from the decomposition of the occluded salt and is believed to be the active site for acetone formation. Evidence is provided also to indicate the presence of an isopropoxide intermediate which is responsible for the acetone and the minor amounts of propylene formed by the acetate impregnated CsNaY zeolite. The cesium acetate impregnated CsNaY catalyst was tested for activity by the base catalyzed alkylation of toluene, acetone, ethane, and methane with methanol. For toluene alkylation, it is determined that little improvement is gained over previous faujasite-type catalysts. This appears to be a result of the rapid decomposition of formaldehyde, i.e., the alkylating agent derived from the dehydrogenation of methanol. MgO is demonstrated to possess base properties similar to the acetate impregnated CsNaY zeolite, yet MgO is found to be inactive in toluene alkylation. Neither ethane or methane is alkylated at 425°C or 465°C by the acetate impregnated zeolites. Acetone is alkylated slightly to methylvinylketone and methylethylketone at 425°C but the majority of the reacted acetone appears to form aldol condensation products.
Bis-(η(2)-ethyl-ene)(η(5)-inden-yl)iridium(I).
Merola, Joseph S. (2013)
The asymmetric unit of the title compound, [Ir(C9H7)(C2H4)2], consists of two independent mol-ecules. The bonding between iridium and the five-membered ring of the indenyl ligand shows the usual asymmetry associated with the typical ring slippage responsible for the enhanced activity of indenyl metal compounds when compared with the analogous cyclo-penta-dienyl metal compound. There are three short Ir-C bonds of 2.210 (3), 2.190 (4) and 2.220 (3) Å and two long Ir-C bonds to the C atoms that are part of the fused six-membered ring of 2.349 (4) and 2.366 (3) Å for one of the independent mol-ecules [2.208 (4), 2.222 (3), 2.197 (4) Å for the short distances and 2.371 (3) and 2.358 (3) Å for the long distances in the second mol-ecule]. This results in both indenyl ligands being slightly kinked, with dihedral angles of 6.8 (4)° and 6.5 (4)°.
Bis[bis-(penta-methyl-cyclo-penta-dien-yl)cobalt(III)] tetra-chlorido-cobaltate(II) di-chloro-methane disolvate.
Merola, Joseph S.; Ngo, Mai; Karpin, George W. (International Union of Crystallography, 2013)
The title compound, [Co(C10H15)2]2[CoCl4]·2CH2Cl2, was isolated as a dichloromethane solvate and was formed in the reaction between lithium pentamethylcyclopentadienide and anyhydrous cobalt(II) chloride in tetrahydrofuran. There are two decamethylcobaltocenium cations, one tetrachloridocobaltate(II) anion and two dichloromethane solvent molecules in the formula unit. There is a slight disorder of the dichloromethane solvent which was treated with a two-site model [occupancy rates = 0.765 (4) and 0.235 (4)]. The dichloromethane molecules display significant C-HCl interactions with the tetrachloridocobaltate(II) dianion. The cobalt atom of the decamethylcobaltocenium cation sits on a twofold rotation axis, with only one pentamethylcyclopentadiene ligand being unique and the second generated by symmetry. The cobalt atom of the [CoCl4]-2 ion sits on a special site with -4 symmetry, with one unique chloride ligand and the others generated by the fourfold inversion axis.
C-H activation: oxidative addition to an iridium(I) center and reactivity of the resulting iridium(III) species
Selnau, Henry Edward (Virginia Tech, 1992)
Thermal reactions of the iridium complex, [Ir(COD)(PMe₃)₃]Cl (COD=1, 5 Cyclooctadiene), with benzene, benzaldehyde, pyridine, and furan yield the C-H addition products of mer-(Me₃P)₃Ir(Phenyl)(H)C! (1), mer-(Me₃P)₃Ir(COC₆H₅)(H)Cl (II), mer-(Me₃P)₃Ir(Pyridyl)(H)Cl (IID, and mer-(Me₃P)₃Ir(furyl)Cl (IV), respectively. Each of these complexes was characterized by 1H, 13C, 31P NMR spectroscopy and single crystal X-ray diffraction. Thermal reaction of the [Ir(COD)(PMe₃)₃]CI with thiophene and benzothiophene produced the C-S addition products forming thiometallacycles of (Me₃P)₃Ir-(CH=CHCH=CHS)CI(V), and (Me₃P)₃Ir(CH=CH-C₆H₄S)Cl (VI). The C-H addition products are unreactive and require the aid of TI[PF6] to remove the chloride ligand to provide an open coordination site. Complex (I) and 3,3-dimethyl-1-butyne, produced a 1,4-di-t-butyldienyl complex (VIII) by a double insertion of the alkyne with one t-butyl group forming an agostic interaction with iridium. Deuterium labeling experiments revealed the mechanism to involve: initial acetylene coordination after the chloride ligand was removed by TI⁺ followed by a hydride migration forming a vinyl complex and allowing a second alkyne to coordinate, rearrangement of the second alkyne into a vinylidene and finally a migratory-insertion of the vinyl group unto the vinylidene to form (VIII). Complex (III) and two equivalence of 3,3-dimethyl-1-butyne produced a trans diacetylide complex (XII). The pyridyl ligand was able to remove acidic protons via the nitrogen lone pair, thus altering the course of the reaction. Initial investigations have led to a possible mechanism. Complex (IV) and 3,3-dimethyl-1-butyne gave an interesting hydrido metallo-vinyl complex (XIV) with the t-butyl group forming an agostic CH-Ir interaction. A deuterium labeling experiment revealed the alkyne to initially coordinate and rearrange into a vinylidene, followed by migratory-insertion of the furan group unto the vinylidene to give (XIV). The furyl group is believed to stabilize the initial intermediate by forming a five coordinate square pyramidal complex through the donation of a pair of electrons from the oxygen atom. Reductive elimination of (XIV) using elevated temperatures gave exclusively the trans 3,3-dimethyl-1-(2 furanyl) -1-butyne (XV). The resonance structure found in (IV) is the most important feature of this work. While most insertions occur between the M-H bond, the resonance structure found in (IV) provides the necessary means for insertion of unsaturates to occur between the M-C bond, leaving the M-H bond intact. In conclusion, it appears that the reactivity of the phenyl complex (I) is dependent on the alkyne used. While the reactivity of the pyridyl complex (III) is governed by the nitrogen lone pair; the reactivity of the furanyl complex (IV) follows a different pathway due to resonance stability of the furanyl ligand.
Catalytic hydroboration: a study of model hydridoiridium and hydridorhodium boron complexes
Knorr, Joseph Robert (Virginia Tech, 1991-07-15)
The mechanism of catalytic hydroboration was studied through the use of iridium and rhodium model complexes. Oxidative addition of the B-H bond in (1,2-phenylenedioxy) borane (catecholborane) to (Me₃P)₃Ir(Cl)(H) (BO₂C₆H₄ (II) produces mer-(Me₃P}₃Ir(Cl)(H)(B0₂C₆H₄) (II), which was characterized by ¹H NMR spectroscopy and single crystal X-ray diffraction. Compound II reacted with alkynes to form vinyliridium complexes and will catalyze the hydroboration of alkynes with (1,2- phenylenedioxy)borane. The reaction of II with acetylenes was inhibited by the presence of free Lewis bases indicating that the reaction proceeds by a dissociative mechanism. Exchange of the chloride ligand in II occurred with other Lewis bases, indicating that chloride dissociation was responsible for opening up the vacant coordination site on the complex and thus providing for acetylene coordination. When the chloride ligand on II was replaced with other Lewis bases, the reactivity towards trimethylsiliylacetylene was qualitatively determined to be inversely proportional to the strength of the new ligand. The above experiments indicated that the mechanism of catalytic hydroboration of acetylenes with catecholborane involves: oxidative addition of the B-H bond to the iridium center, followed by chloride dissociation and acetylene coordination, migratory-insertion into the Ir-H bond to form the metallo-vinyl complex, and finally reductive elimination to produce trans-alkylvinylborole esters. The stable metallo-vinyl complex, IX, produced in the reaction of II with dimethyl acetylene dicarboxylate produced twO isomers in solution, one of which showed fluxional behavior. Single crystal X-ray diffraction elucidated a single solid state structure, but the structures of the isomers in solution and the fluxional properties observed have not yet been explained. The rhodium complex was synthesized by oxidative addition of the B-H bond in (1,2- phenylenedioxy) borane to (Me₃P)₃RhCl producing mer-(Me₃Rh(CI)(H)(BO₂C₆H-₄) (XXIV), which was characterized by ¹H NMR spectroscopy. This complex reacted with acetylenes, but more slowly than the iridium complex, II. The resulting vinyl products were also different than those produced in the iridium case. Phosphine dissociation in XXIV was observed, indicating the possibility of a different mechanism than proposed for the iridium complex.
Characterization, toxicity, and biological activities of organometallic compounds and peptide nucleic acids for potential use as antimicrobials
Ernst, Marigold Ellen Bethany (Virginia Tech, 2019-04-29)
Bacterial antibiotic resistance is a globally recognized problem that has prompted extensive research into novel antimicrobial compounds. This dissertation describes research focusing on two types of potential antimicrobial molecules, organometallic compounds (OMC) and peptide nucleic acids (PNA). Organometallic compounds show promise as antimicrobial drugs because of their structural difference from conventional antibiotics and antimicrobials, and because of the ability to "tune" their chemical and biological properties by varying ligand attachments. Peptide nucleic acids, when linked to a cell-penetrating peptide (CPP), can suppress bacterial gene expression by an antisense mechanism and are attractive candidates for antimicrobial drugs because they bind strongly to target nucleic acids and are resistant to nucleases. Chapters 1 and 2 of the dissertation provide an introduction and broad literature review to frame the experimental questions addressed. Chapter 3 describes work to test the cytotoxicity and cellular penetration capabilities of novel OMCs by evaluating their effects on J774A.1 murine macrophage-like cells that were either uninfected or were infected with Mycobacterium bovis BCG. Results indicate that OMCs with an iridium (Ir) metal center and an amino acid ligand show minimal cytotoxicity against eukaryotic cells but likely do not penetrate the intracellular compartment in significant amounts. Chapter 4 presents research into in vitro effects of CPP-PNAs targeting the tetA and tetR antibiotic resistance genes (CPP-anti-tetA PNA and CPP-anti-tetR PNA, respectively) in tetracycline-resistant Salmonella enterica ssp. enterica serovar Typhimurium DT104 (DT104). Through the use of modified minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) assays it was shown that both the CPP-anti-tetA PNA and CPP-anti-tetR PNA increase tetracycline susceptibility in DT104. Chapter 5 explores the molecular mechanism of the CPP-anti-tetA PNA and CPP-anti-tetR PNA through the use of reverse transcriptase quantitative polymerase chain reaction (RT-qPCR). Results indicate good specificity of the CPP-anti-tetA PNA for its nucleic acid target as evidenced by suppression of tetA mRNA expression in DT104 cultures treated with a combination of tetracycline and the PNA. Chapter 6 describes the development of a mouse model of DT104 infection using BALB/c mice, followed by implementation of that model to test in vivo antimicrobial effects of the CPP-anti-tetA PNA and the CPP-Sal-tsf PNA, which targets expression of the essential tsf gene. An optimal dose of DT104 was identified that causes clinical illness within 2-4 days. At the doses tested, concurrent treatment of infected mice with tetracycline and the CPP-anti-tetA PNA or with the CPP-Sal-tsf PNA alone did not have a protective effect. Final conclusions are 1) that further research with the OMCs should focus on compounds with an Ir center and an amino acid ligand, and should explore ways to enhance intracellular penetration, 2) that the in vitro results of the PNA studies suggest that PNAs targeting expression of antibiotic resistance genes could allow for repurposing of antibiotics to which bacteria are resistant, and 3) additional study of the behavior of PNAs in vivo is advised.
A chemical sensor based on surface plasmon resonance on surface modified optical fibers
Bender, William John Havercamp (Virginia Tech, 1993-02-12)
A sensor is described which utilizes the phenomenon of surface plasmon resonance to detect changes in refractive index of chemical or biochemical samples applied to a surface modified optical fiber. The sensor is constructed by polishing a short section of the lateral surface of an optical fiber to its evanescent field surrounding the fiber core. One or more thin films are applied to the polished section of the fiber to produce the sensing element. One of the films is the metal silver, which acts as the support for the surface plasmon. Under the proper conditions, TM polarized energy propagating in the fiber can be coupled to a surface plasmon electromagnetic mode on the metal film. This coupling depends on the wavelength, the nature of the fiber, the refractive index and thickness of the thin films applied to the fiber, and the refractive index of a chemical sample in contact with the modified surface. The fiber to plasmon coupling is seen as a large attenuation of the light reaching the distal terminus of the fiber.
Chemical studies of the C-4 position of baccatin III and taxol
Neidigh, Kurt Alan (Virginia Tech, 1995)
Because of the efficacy of taxol against a wide variety of cancers, the demand for this drug has vastly increased during the last decade. Due to its limited natural supply, a number of alternative sources of taxol continue to be investigated. One approach toward alleviating the taxol supply problem is by the systematic investigation of the structure-activity relationships of the molecule, in order to establish the structural features and functionalities necessary for biological activity. Research efforts during the last decade have led to the establishment of the molecular domains and functionalilties which are crucial for biological activity, however at the inception of this work, the structure-activity relationships of the C-4 position of taxol were unknown. It was thus the major goal of this work to prepare 4-deacetyltaxol, in order to assess the importance of the C-4 acetate for overall activity, as well as to have a template molecule with which to begin studies aimed at determining the effect on activity rendered by replacement of the C-4 acetate with other acyl groups. Preliminary studies of the deacylation and reacylation of baccatin III were carried out in order to find conditions necessary for the preparation of 4-deacetylbaccatin III, and hence 4-deacetyltaxol. 4-Deacetyltaxol has now been prepared from baccatin III via two synthetic approaches and from taxol via one synthetic approach, and has been shown to be significantly less potent than taxol, suggesting that the C-4 acetate is necessary for biological activity. From the investigation of several potential synthetic approaches toward the formation of 4-acyltaxol analogs, one methodology has been developed which has allowed the preparation of 4-acyltaxol derivatives from baccatin III] or the more readily available 10- deacetylbaccatin III. This particular methodology can be extended to the preparation of other 4-acvitaxol or 4-acyltaxotere derivatives. Two C-5a halogenated oxetane ring-opened compounds have been prepared from a 4-deacetyltaxol derivative, offering the opportunity to investigate the potential effects on biological activity generated by modifications to the oxetane ring.
cis-Arenediols as versatile chiral synthons in the synthesis of prostaglandins, cyclitols, carbohydrates, and alkaloids
Contla, Hector Luna (Virginia Tech, 1992-09-15)
The oxidation of simple benzene derivatives by a mutant of Pseudomonas putida, called 39-D, produces cis-arenediols (1). The diols are enantiomerically pure and can be used as synthons for the preparation of a variety of interesting compounds because of their stereochemistry and the special array of functional groups. See: Figure 1 cis -Toluenedio] (2) served as a chiral intermediate in an efficient synthesis of enone (3). which has been used to attain prostaglandin Fra and Neplanocin A. The same diol (2) was transformed into both enantiomers of a terpene synthon (4). See: Figures 2, 3, 4 Oxidative functionalization of cis-chlorobenzenediol (5) afforded intermediates suitable for transformation into L-erythrose (6), conduritol C (7), dihydroconduritol C (8) and aminoconduntol F-4 (9). See: Figures 5, 6, 7, 8 The application of this versatile synthetic protocol culminated in an approach to kifunensine (10), an important glycosidase inhibitor, which was approached according to the following retrosynthetic analysis: See: Figures 10, 11, 12, 5, 14, 13 A detailed study of the nucleophilic opening of epoxide 13 was carried out in order to better understand the parameters of the diastereoselective functionalization of arenediols. Details are provided for the oxidative functionalization of chlorobenzenediol (5), the key compound in all of the projects discussed.
Comparative Electrochemistry, Electronic Absorption Spectroscopy and Spectroelectrochemistry of the Monometallic Ruthenium Polypyridyl Complexes, [Ru(Bpy)(Dpb)2](Pf6)2, [Ru(Bpy)2(Dpb)](Pf6)2, [Ru(Bpy)2(Dpq)](Pf6)2, [Ru(Bpy)(Dpq)2](Pf6)2
Duchovnay, Alan (Virginia Tech, 2011-04-13)
The novel compound [Ru(bpy)(dpb)–(PFâ )â was synthesized, in a manner similar to the literature synthesis of [Ru(bpy)(dpq)â (PFâ )â . For the sake of completeness, the related analogs, [Ru(bpy)â (dpb)](PFâ )â , [Ru(bpy)â (dpq)](PFâ )â and [Ru(bpy)(dpq)â ](PFâ )â were also synthesized. Alumina adsorption chromatography was used for purification purposes. Liquid secondary ion mass spectroscopy was used to confirm identity of compounds. The new compound contained 1% electroactive impurity as determined by OSWV. Spectroelectrochemical studies were conducted with both a bulk H-cell and a ~0.2 mm pathlength, optically transparent thin layer electrode (OTTLE) cell. High reversibility (a 99%) is possible with dilute solutions (ca 10â »â ´ M) and the OTTLE cell as compared to ca 50% with the H-cell. Spectroelectrochemical data supported the following electronic transitions for the new compound [Ru(bpy)(dpb)â ](PFâ )â : (1) the Ru (dÏ ) â dpb MLCT at 552 nm, (2) a d â d at 242 nm, a bpy Ï â Ï * at 285 nm. (3) The location of the Ru (dÏ ) â bpy MLCT peak is obscured by shoulders from 390-420 nm. (4) The strong peak at 316 nm may be dpb Ï â Ï â *, the location of the lower energy intraligand dpb Ï â Ï â * is uncertain. Upon oxidation of the metal center, no LMCT was observed within the UV-VIS range. This is in direct contrast to the results of Gordon et al. This author hypothesizes that their LMCT found in the visible region was actually the result of incomplete electrochemical conversion and that a LMCT should be seen in the NIR. The spectroelectrochemical properties of [Ru(bpy)(dpq)â ](PFâ )â were also presented for the first time. These results indicated that the 256 nm transition was d â d and not bpy Ï â Ï â * as suggested by Rillema et al.
Coupled solid phase extraction-supercritical fluid extraction on-line gas chromatography of explosives from water
Slack, Gregory C. (Virginia Tech, 1992)
A method has been developed for the quantitative extraction of nitrotoluenes (2,6-dinitrotoluene, 2,4-dinitrotoluene, and trinitrotoluene) from water. Three types of solid sorbents were investigated: two 47 mm Empore disks™ - octadecylsilane (C18) and styrene-divinylbenzene (SDVB); and one Bakerbond spe*™ Phenyl stationary phase. The phenyl sorbent yielded the highest recoveries. The average SPE recoveries for spike standards ranged from 80 to 95 percent for Millipore water and 55 to 95 percent from well and surface water in the low ppb and ppt levels. After the nitrotoluenes were trapped on the solid sorbents they were quantitatively eluted by first doping the bed with toluene and then extracting with supercritical carbon dioxide. Doping with toluene was found to increase the rate of extraction. The extracts were analyzed off-line via GC-ECD using an internal standard. Extraction losses are due to analyte break through, and not from poor SFE recoveries. This demonstrates that supercritical fluid extraction is a suitable elution technique for analytes trapped on solid phase extraction (SPE) cartridges. A method has also been developed and evaluated for the direct on-line coupling of SPE to GC. SPE-SFE-GC-ECD analysis eliminates off-line collection and subsequent handling of hazardous materials. SFE is an ideal means of directly coupling SPE to GC, since carbon dioxide is a gas at ambient temperatures and pressures and thus easily removed. One potential problem for SPE-SFE on-line GC is the presence of residual water trapped on the active sites of the bonded silica sorbent. The presence of water can interfere with the cryogenic trapping of the analytes on the capillary GC column. The water becomes ice at cryogenic temperatures and in large quantities blocks the GC column. This problem has been avoided by using a split injection interface previously described by Hawthorne. The quantitative reproducibility of this interface will be investigated for nanogram quantities of nitroaromatics.
Creating a Positive Departmental Climate at Virginia Tech: A Compendium of Successful Strategies
Finney, Jack W.; Finkielstein, Carla V.; Merola, Joseph S.; Puri, Ishwar; Taylor, G. Don; Van Aken, Eileen M.; Hyer, Patricia B.; Savelyeva, Tamara (Virginia Tech, 2008-05-05)
“Creating a Positive Departmental Climate at Virginia Tech: A Compendium of Successful Strategies” was created as part of the AdvanceVT Departmental Climate Initiative (DCI). The Department Climate Committee collected policies and practices from a variety of sources to provide department chairs and heads with opportunities to learn about departmental issues at Virginia Tech, to understand more fully the ways in which these issues manifest themselves within departments, and to share both successful and unsuccessful strategies illustrative of the different approaches departments have taken towards promoting effective, efficient, and pleasant work environments.
Crystal structure of chlorido-(η(2)-phenyl iso-thio-cyanate-κ(2) C,S)-mer-tris-(tri-methyl-phosphane-κP)iridium(I).
Merola, Joseph S.; Grieb, Aarthur W. (International Union of Crystallography, 2014-11-01)
The molecule of the title compound, [IrCl(C7H5NS)(C3H9P)3], is a distorted octa-hedral iridium complex with three PMe3 ligands arranged in a meridional geometry, a chloride ion cis to all three PMe3 groups and the phenyl iso-thio-cyanate ligand bonded in an η(2)-fashion through the C and S atoms. The C atom is trans to the chloride ion and the S atom is responsible for a significant deviation from an ideal octa-hedral geometry. The geometric parameters for the metal-complexing phenyl isothiocyanate group are compared with other metal-complexed phenyl iso-thio-cyanates, as well as with examples of uncomplexed aryl iso-thio-cyanates.

Browsing by Author "Merola, Joseph S."

Results Per Page

Sort Options