Phosphorescent transition metal complexes make up an important group of compounds that continues to attract intense research owing to their intrinsic bioimaging applications that arise from bright emissions, relatively long excited state lifetimes, and large stokes shifts. Now for biomaging assay a model organism is required which must meet certain criteria for practical applications. The organism needs to be small, with a high turn-over of progeny (high fecundity), a short lifecycle, and low maintenance and assay costs. Our model organism C. elegans met all the criteria. The ideal phosphor has low toxicity in the model organism. In this work the strongly phosphorescent platinum (II) pyrophosphito-complex was tested for biological applications as a potential in vivo hypoxia sensor. The suitability of the phosphor was derived from its water solubility, bright phosphorescence at room temperature, and long excited state lifetime (~ 10 µs). The applications branched off to include testing of C. elegans survival when treated with the phosphor, which included lifespan and fecundity assays, toxicity assays including the determination of the LC50, and recovery after paraquat poisoning. Quenching experiments were performed using some well knows oxygen derivatives, and the quenching mechanisms were derived from Stern-Volmer plots. Reaction stoichiometries were derived from …

The scope of work in this dissertation has comprised several major investigations on applications and theoretical studies of ab initio quantum mechanics and density functional theory where those techniques were applied to the following: (i) investigation of the performance of density functionals for the computations of molecular properties of 3d transition metal containing systems; (ii) guidance for experimental groups for rational design of macrometallocyclic multinuclear complexes with superior π-acidity and π-basicity that are most suitable for p- and n-type semiconductors of metal-organic molecules and nanomaterials; (iii) investigation of the metallo-aromaticity of multi-nuclear metal complexes; (iv) investigation of the kinetics and thermodynamics of copper-mediated nitrene insertion into C-H and H-H bond; and (v) accurate computations of dissociation energies of hydrogen-bonded DNA duplex moieties utilizing the resolution of identity correlation consistent composite approach (RI-ccCA).

Calculations were performed on transition-metal complexes to (1) extrapolate the structure and bonding of the ground and phosphorescent states (2) determine the luminescence energies and (3) assist in difficult assignment of luminescent transitions. In the [Pt(SCN)4]2- complex, calculations determined that the major excited-state distortion is derived from a b2g bending mode rather than from the a1g symmetric stretching mode previously reported in the literature. Tuning of excimer formation was explained in the [Au(SCN)2]22- by interactions with the counterion. Weak bonding interactions and luminescent transitions were explained by calculation of Hg dimers, excimers and exciplexes formed with noble gases.

In this research the validity of various computational techniques has been determined and applied the appropriate techniques to investigate and propose a good catalytic system for C-H bond activation and functionalization. Methane being least reactive and major component of natural gas, its activation and conversion to functionalized products is of great scientific and economic interest in pure and applied chemistry. Thus C-H activation followed by C-C/C-X functionalization became crux of the synthesis. DFT (density functional theory) methods are well suited to determine the thermodynamic as well as kinetic factors of a reaction. The obtained results are helpful to industrial catalysis and experimental chemistry with additional information: since C-X (X = halogens) bond cleavage is important in many metal catalyzed organic syntheses, the results obtained in this research helps in determining the selectivity (kinetic or thermodynamic) advantage. When C-P bond activation is considered, results from chapter 3 indicated that C-X activation barrier is lower than C-H activation barrier. The results obtained from DFT calculations not only gave a good support to the experimental results and verified the experimentally demonstrated Ni-atom transfer mechanism from Ni=E (E = CH2, NH, PH) activating complex to ethylene to form three-membered ring products but also validated …

Multiscale modeling is an effective tool for integrating different computational methods, creating a way of modeling diverse chemical and physical phenomena. Presented are studies on a variety of chemical problems at different computational scales and also the combination of different computational methods to study a single phenomenon. The methods used encompass density functional theory (DFT), molecular dynamics (MD) simulations and finite element analysis (FEA). The DFT studies were conducted both on the molecular level and using plane-wave methods. The particular topics studied using DFT are the rational catalyst design of complexes for C—H bond activation, oxidation of nickel surfaces and the calculation of interaction properties of carbon dioxide containing systems directed towards carbon dioxide sequestration studies. Second and third row (typically precious metals) transition metal complexes are known to possess certain electronic features that define their structure and reactivity, and which are usually not observed in their first-row (base metal) congeners. Can these electronic features be conferred onto first-row transition metals with the aid of non-innocent and/or very high-field ligands? Using DFT, the impact of these electronic features upon methane C—H bond activation was modeled using the dipyridylazaallyl (smif) supporting ligand for late, first-row transition metal (M) imide, oxo and …

Three different types of cage crown ethers have been prepared and their complexation properties with Ag(I) have been studied. Atomic absorption, fluorescence quenching, and UV absorption have been used to study the interaction between the hosts (cage crown ethers) and guests (Ag+). For the cage-annulated crown ethers that contain aromatic rings, cation-π and π-π interactions may contribute significantly to the overall complexation ability of the host system. Piperazine groups may cooperate, and the piperazine nitrogen atoms provide unshared electrons, which may form a complex with Ag+. In addition, relatively soft donor atoms (e.g., Br) are well-suited for complexation with Ag+, which is a softer Lewis acid than alkali metal cations.

The two major topics studied in this dissertation are the gold(I) pyrazolate trimer {[Au(3-R,5-R’)Pz]3} complexes in aqueous chitosan polymer and phosphorescent polymeric nanoparticles based on platinum(II) based complex. The first topic is the synthesis, characterization and optical sensing application of gold(I) pyrazolate trimer complexes within aqueous chitosan polymer. A gold(I) pyrazolate trimer complex, {[Au(3-CH3,5-COOH)Pz]3}, shows high sensitivity and selectivity for silver ions in aqueous media, is discussed for optical sensing and solution-processed organic light emitting diodes (OLEDs) applications. Gold(I) pyrazolate trimer complexes are bright red emissive in polymeric solution and their emission color changes with respect to heavy metal ions, pH and dissolved carbon dioxide. These photophysical properties are very useful for designing the optical sensors. The phosphorescent polymeric nanoparticles are prepared with Pt-POP complex and polyacrylonitrile polymer. These particles show excellent photophysical properties and stable up to >3 years at room temperature. Such nanomaterials have potential applications in biomedical and polymeric OLEDs. The phosphorescent hybrid composites are also prepared with Pt-POP and biocompatible polymers, such as chitosan, poly-l-lysine, BSA, pnipam, and pdadmac. Photoluminescent enhancement of Pt-POP with such polymers is also involved in this study. These hybrid composites are promising materials for biomedical applications such as protein labeling and …

A series of heteroleptic and homoleptic platinum(II) complexes has been synthesized and characterized towards their use in thin film devices such as organic light-emitting diodes (OLEDs) and organic thin film transistors (OTFTs). Pyridylpyrazolate- and pyridyltetrazolate-containing ligands were selected due to their structural rigidity and ease of functionalization. Single-crystal x-ray diffraction studies of two selected heteroleptic complexes show strong aggregation with preferential stacking into vertical columns with a varying degree of overlap of the neighboring square planar molecular units. It is shown that the close proximity of the molecules to one another in the stack increases semiconducting character, phosphorescence quantum yields, and shorter radiative lifetimes. The potential for these materials towards incorporation into high-efficiency doping free white OLEDs (DFW-OLEDs) for solid-state lighting and display applications has been realized and will be expanded upon by present and future embodiments of materials in this thesis.

A series of 28 square-planar dithiol(diimine)platinum(II) chromophoric complexes have been synthesized, characterized, and evaluated for potential efficacy in sensitization of solid state photovoltaic devices to the near-infrared regions of the electromagnetic spectrum. The effect of molecular stacking in the solid state and self-association in solution are shown to influence spectral, electronic, and magnetic properties of the chromophores. Such properties are investigated in the pure form and as partners in donor-acceptor charge transfer adducts. Finally, selected chromophores have been incorporated into single layer schottky diodes as neat films and as dopants in multi-layer organic photovoltaic devices. Evaluation of the devices internal quantum efficiency and voltage-current was measured as proof of concept.

Organometallic catalysis has attracted significant interest from both industry and academia due to its wide applications in organic synthetic transformations. Example of such transformations include the reaction of a zinc carbenoid with olefins to form cyclopropanes. The first project is a computational study using both density functional and correlated wavefunction methods of the reaction between ethylene and model zinc carbenoid, nitrenoid and oxenoid complexes (L-Zn-E-X, E = CH2, NH or O, L = X = I or Cl). It was shown that cyclopropanation of ethylene with IZnCH2I and aziridination of ethylene with IZnNHI proceed via a single-step mechanism with an asynchronous transition state. The reaction barrier for the aziridination with IZnNHI is lower than that of cyclopropanation. Changing the leaving group of IZnNHI from I to Cl, changes the mechanism of the aziridination reaction to a two-step pathway. The calculation results from the epoxidation with IZnOI and ClZnOCl oxenoids suggest a two-step mechanism for both oxenoids. Another important example of organometallic catalysis is the formation of alkyl arenes from arenes and olefins using transition metal catalysis (olefin hydroarylation). We studied with DFT methods the mechanism of a novel Rh catalyst (FlDAB)Rh(TFA)(η2–C2H4) [FlDAB = N,N’ -bis(pentafluorophenyl)-2,3-dimethyl-1,4-diaza-1,3-butadiene; TFA = trifluoroacetate] that converts …

Alkyl-arenes are important industry feedstock chemicals that are used as solvents, pharmaceutical precursors, and polymer monomer units. One alkyl-arene, ethylbenzene, is the main focus of this dissertation, and is produced in the million ton a year scale. As alkyl-arenes are important commodity chemicals, catalytic olefin hydroarylation is a lucrative alternative for their production rather than Friedel-Crafts alkylation or various coupling reactions that have lower atom economy, require strong acids, or are energetically demanding. Currently catalytic olefin hydroarylation still suffers from decomposition pathways of the active catalytic complexes, side reactions that lead to waste products, and unfavorable activation barriers, which represent high temperature and pressure. Modifications to the catalytically active system bipyridine platinum(II) (bpyPtII), through computational methods, are explored herein. The work presented here investigates catalytic olefin hydroarylation in order to mitigate the aforementioned difficulties. Included in this study are changes to the electronic profile of the supporting ligand, bpy, through the addition of electron withdrawing or electron donating R groups (methoxy, nitro), definite ligand replacements such as bpy to hydridotris(pyrazolyl)borate (Tp), changes in metal oxidation (II to IV), and replacing the metal center from Pt to Ni. Nickel was selected as a possible alternative to platinum as it is more …

A computational chemistry analysis combined with a crystallographic database study of the bonding in late transition metal N-heterocyclic carbene (NHC) complexes is reported. The results illustrate a metal-carbon bond for these complexes, approximately 4% shorter than that of a M-C single bond found in metal alkyl complexes. As a consequence of this result, two hypotheses are investigated. The first hypothesis explores the possibility of multiple-bond character in the metal-carbon linkage of the NHC complex, and the second, considers the change in the hybridization of the carbenoid carbon to incorporate more p character. The latter hypothesis is supported by the results. Analysis of these complexes using the natural bond orbital method evinces NHC ligands possessing trans influence.

Layered double hydroxides (LDH) have been principally known as anion-exchanging, clay-like materials for several decades, and continues to be the main driving force for current and future research. The chemical interactions of LDH, with transition metallocyanides, have been a popular topic of investigation for many years, partly due to the use of powder x-ray diffraction and infrared spectroscopy as the main characterization tools. Each transition metallocyanide has a characteristic infrared stretching frequency that can be easily observed, and their respective sizes can be observed while intercalated within the interlayer of the LDH. The ability of LDH to incorporate metal cations or any ions/molecules/complexes, that have a postive charge, have not been previously investigated, mainly due to the chemical and physical nature of LDH. The possibility of cationic incorporation with LDH would most likely occur by surface adsorption, lattice metal replacement, or by intercalation into the LDH interlayers. Although infrared spectroscopy finds it main use through the identification of the anions incorporated with LDH, it can also be used to study and identify the various active and inactive bending and stretching modes that the metal hydroxide layers have.

The square-planar tetracyanonickelate(II) anion was intercalated into 2:1 and 3:1 Mg-Al layered double hydroxide systems (LDHs). In the 2:1 material, the anion holds itself at an angle of about 30° to the layers, whereas in the 3:1 material it lies more or less parallel to the layers. This is confirmed by orientation effects in the infrared spectra of the intercalated materials and by X-ray diffraction (XRD) data. The measured basal spacings for the intercalated LDH hosts are approximately 11 Å for the 2:1 and approximately 8 Å for the 3:1. The IR of the 2:1 material shows a slight splitting in the ν(CN) peak, which is suppressed in that compound's oriented IR spectrum, indicating that at least some of the intercalated anion's polarization is along the z-axis. This effect is not seen in the 3:1 material. A comparison between chloride LDHs and nitrate LDHs was made with respect to intercalation of tetracyanonickelate(II) anions. Both XRD data and atomic absorption spectroscopy (AAS) data of the LDH tetracyanonickelates confirms that there are no significant differences between the products from the two types of starting materials. The presence of a weak ν(NO) peak in the IR spectra of those samples made from nitrate …

Human glutathione synthetase (hGS) is a homodimeric enzymes that catalyzes the second step in the biological synthesis of glutathione, a critical cellular antioxidant. The enzyme exhibits negative cooperativity towards the γ-glutamylcysteine (γ-GC) substrate. In this type of allosteric regulation, the binding of γ-GC at one active site significantly reduces substrate affinity at a second active site over 40 Å away. The presented work explores protein-protein interactions, substrate binding, and allosteric communication through investigation of three regions of hGS: the dimer interface, the S-loop, and the E-loop. Strong electrostatic interactions across the dimer interface of hGS maintain the appropriate tertiary and quaternary enzymatic structure needed for activity. The S-loop and E-loop of hGS form walls of the active site near γ-GC, with some residues serving to bind and position the negatively cooperative substrate. These strong interactions in the active site serve as a trigger for allosteric communication, which then passes through hydrophobic interactions at the interface. A comprehensive computational and experimental approach relates hGS structure with activity and regulation. ATP-grasp enzymes, including hGS, utilize ATP in the nucleophilic attack of a carboxylic acid in a reaction thought to proceed through the formation of an acylphosphate intermediate. Small metal cations are known …

Our country continues to demand clean renewable energy to meet the growing energy needs of our time. Thus, natural gas, which is 87% by volume of methane, has become a hot topic of discussion because it is a clean burning fuel. However, the transportation of methane is not easy because it is a gas at standard temperature and pressure. The usage of transition metals for the conversion of small organic species like methane into a liquid has been a longstanding practice in stoichiometric chemistry. Nonetheless, the current two-step process takes place at a high temperature and pressure for the conversion of methane and steam to methanol via CO + H2 (syngas). The direct oxidation of methane (CH4) into methanol (CH3OH) via homogeneous catalysis is of interest if the system can operate at standard pressure and a temperature less than 250 C. Methane is an inert gas due to the high C-H bond dissociation energy (BDE) of 105 kcal/mol. This dissertation discusses a series of computational investigations of oxy-insertion pathways to understand the essential chemistry behind the functionalization of methane via the use of homogeneous transition metal catalysis. The methane to methanol (MTM) catalytic cycle is made up of two key …

Numerous enzymatic reactions are controlled by the chemistry of metallic ions. This dissertation investigates the electronic properties of three transition metal (copper, chromium, and nickel) complexes and describes modeling studies performed on glutathione synthetase. (1) Copper nitrene complexes were computationally characterized, as these complexes have yet to be experimentally isolated. (2) Multireference calculations were carried out on a symmetric C2v chromium dimer derived from the crystal structure of the [(tBu3SiO)Cr(µ-OSitBu3)]2 complex. (3) The T-shaped geometry of a three-coordinate β-diketiminate nickel(I) complex with a CO ligand was compared and contrasted with isoelectronic and isosteric copper(II) complexes. (4) Glutathione synthetase (GS), an enzyme that belongs to the ATP-grasp superfamily, catalyzes the (Mg, ATP)-dependent biosynthesis of glutathione (GSH) from γ-glutamylcysteine and glycine. The free and reactant forms of human GS (wild-type and glycine mutants) were modeled computationally by employing molecular dynamics simulations, as these currently have not been structurally characterized.

Various gold complexes were computationally investigated, to probe their photophysical, geometric, and bonding properties. The geometry of AuI complexes (ground state singlet) is very sensitive to the electronic nature of the ligands: σ-donors gave a two-coordinate, linear shape; however, σ-acceptors yielded a three-coordinate, trigonal planar geometry. Doublet AuIIL3 complexes distort to T-shape, and are thus ground state models of the corresponding triplet AuIL3. The disproportionation of AuIIL3 to AuIL3 and AuIIIL3 is endothermic for all ligands investigated, however, σ-donors are better experimental targets for AuII complexes. For dimeric AuI complexes, only one gold center in the optimized triplet exciton displays a Jahn-Teller distortion, and the Au---Au distance is reduced versus the ground state distance (i.e., two reasons for large Stokes' shifts).

There is a high demand for the development of processes for the conversion of ubiquitous molecules into industrially useful commodities. Transition metal catalysts are often utilized for the activation and functionalization of small organic molecules due to their diverse nature and proven utility with a myriad of chemical transformations. The functionalization of methane (CH4) and dinitrogen (N2) to methanol (CH3OH) and ammonia (NH3) respectively is of particular interest; however, both methane and dinitrogen are essentially inert due to the inherit strength of their bonds. In this dissertation a series of computational studies is performed to better understand the fundamental chemistry behind the functionalization of methane and the activation of dinitrogen in a homogeneous environment. A catalytic cycle is proposed for the oxy-functionalization of methane to methanol. The cycle consists of two key steps: (1) C-H activation across a metal-alkoxide bond (M-OR), and (2) regeneration of the M-OR species through an oxy-insertion step utilizing external oxidants. The C-H activation step has been extensively studied; however, the latter step is not as well understood with limited examples. For this work, we focus on the oxy-insertion step starting with a class of compounds known to do C-H activation (i.e., Pt(II) systems). Computational studies …

The diversity of transition metal complexes allows for a wide range of chemical processes to be mediated by the metal, from catalysis to surface chemistry. Investigations into the structure and electronic configuration of transition metal complexes allow for tuning of desired species by modifications to the ligands and/or metals to achieve more efficient thermodynamics and kinetics for the process of interest. Transition metals, often used in catalysts for a number of important processes, require detailed descriptions of intermediates, transition states and products to fully characterize a reaction mechanism(s) in order to design more active and efficient catalysts. Computational investigations into inorganic catalysts are explored with the aim of understanding the activity of each species and how modifications of supporting ligands, co-ligands and metals vary the interaction along the reaction pathway. Reported results give important insight into the development of the most active complexes in addition to determining the least active complexes to aid experimental development. This report first investigates the mechanisms of two unique transfer reactions: 1) formation of low coordinate nickel-nitrene ((P~P)Ni=NR; P~P = 1,2-bis(dihydrophosphino)-ethane or 1,2-bis(difluoromethylphosphino)-ethane) complexes as catalysts for nitrogen atom transfer and 2) oxidation of a triphosphorus niobium complex, [(η2-P3SnPh3)Nb(OMe)3], for the transfer of the phosphorus …

Glutathione syntethase (GS) is an enzyme that belongs to the ATP-grasp superfamily and catalyzes the second step in the biosynthesis of glutathione. GS has been purified and sequenced from a variety of biological sources; still, its exact mechanism is not fully understood. Four highly conserved residues were identified in the binding site of human GS. Additionally, the G-loop residues that close the active site during catalysis were found to be conserved. Since these residues are important for catalysis, their function was studied computationally by site-directed mutagenesis. Starting from the reported crystal structure of human GS, different conformations for the wild type and mutants were obtained using molecular dynamics technique. The key interactions between residues and ligands were detected and found to be essential for enzyme activity.

A 13C and 6Li variable temperature NMR study of 2-ethylbutyllithium/lithium 2-ethyl-1-butoxide mixed aggregates formed from reacting 2-ethyl-1-butanol with 2-ethylbutyllithium in two O/Li ratios of 0.2/1 and 0.8/1. The 0.2/1 sample resulted in two 2-ethylbutyllithium/lithium 2-ethyl-1-butoxide mixed aggregates and seven lithium hydride/lithium 2-ethyl-1-butoxide mixed aggregates. The lithium hydride mixed aggregates were also studied using selective 1H decoupling experiments. The 0.8/1 sample resulted in six 2-ethylbutyllithium/lithium 2-ethyl-1-butoxide mixed aggregates and five lithium hydride/lithium 2-ethyl-1-butoxide mixed aggregates. A low temperature 13C NMR spectroscopy study of n-pentyllithium indicated three aggregates, most likely a hexamer, an octamer, and a nonamer. A low temperature 13C NMR study of an 0.2/1 O/Li ratio sample of n-pentyllithium mixed with 1-pentanol resulted in three n-pentyllithium/lithium n-pentoxide aggregates mixed aggregates along with the three n-pentyllithium aggregates. 13C NMR data for this mixture gave inconclusive results whether or not lithium hydride/lithium alkoxide mixed aggregates were present in the sample.

An NMR spectroscopy study of trimethylsilylmethyllilthium, TMSM-Li, indicates that TMSM-Li exists as two different aggregates in cyclopentane solution. Using previously reported colligative properties of TMSM-Li in different solutions in connection with new 13C and 6Li NMR data collected in this study, aggregation states were assigned as octamer and hexamer. Low temperature 13C and 6Li NMR peak intensities indicated an equilibrium exists between the two aggregates that shifts toward the octamer as the temperature decreases. ΔH was calculated to be 5.23 + 0.15 kcal/mol and ΔS was calculated to be 17.9 + 0.6 eu for the hexamer/octamer equilibrium system. Samples of TMSM-Li were mixed with TMSM-OH in attempts to form mixed alkyllithium/lithium alkoxide aggregates. 13C NMR data for these mixtures gave inconclusive results whether or not these compounds formed, which is different from other primary alkyllithium compounds studied in the past. A study of neopentyllithium, NpLi, indicates only one aggregate in solution with the aggregation state unknown using low temperature 13C NMR spectroscopy.

One of the main goals of computational methods is to identify reasonable geometries for target materials. Organometallic complexes have been investigated in this dissertation research, entailing a significant challenge based on transition metal diversity and the associated complexity of the ligands. A large variety of theoretical methods have been employed to determine ground state geometries of organometallic species. An impressive number of transition metals entailing diverse isomers (e.g., geometric, spin, structural and coordination), different coordination numbers, oxidation states and various numbers of electrons in d orbitals have been studied. Moreover, ligands that are single, double or triple bonded to the transition metal, exhibiting diverse electronic and steric effects, have been investigated. In this research, a novel de novo scheme for structural prediction of transition metal complexes was developed, tested and shown to be successful.