Eight ABC heterotrimers whose self-assembly are directed through electrostatic interactions were studied here. Oppositely charged pairs of amino acids, with varying side chain length, were assessed for their ability to stabilize a triple helix. Aspartate-lysine was found to result in the most thermally stable helix followed by lysine-glutamate, ornithine-aspartate and finally ornithine-glutamate. When the sequence position of these charged amino acids was reversed from what is normally observed in nature, triple helix stability and compositional purity was significantly reduced. The effect of salt on triple helix stability was explored and it was observed that increased salt concentration reduces the thermal stability of heterotrimers by an average of 5°C, but does not disrupt helix assembly. It was also found that positively charged homotrimers can be stabilized in the presence of phosphate anions. Raman and Surface-enhanced Raman spectroscopies (SERS) are potentially important tools in the characterization of biomolecules such as proteins and DNA. In this work, SERS spectra of three cysteine containing aromatic peptides: tryptophan-cysteine, tyrosine-cysteine, and phenylalanine-cysteine, bound to Au nanoshell substrates, were obtained and compared to their respective normal Raman spectra. While the full widths at half maximum of the SERS peaks are significantly broadened (up to 70%), no significant spectral shifts (<6 cm-1) of the major Stokes modes were observed between the two modalities. It is shown that the Raman and SERS spectra of penetratin, a cell-penetrating peptide, can be evaluated quite reliably from the spectra of its constituent aromatic amino acids except in the -CH2- bending and amide I and III regions where the spectral intensities are critically dependent on the chain length and/or protein conformations. From this study we conclude that with aromatic amino acid residues provide the overwhelmingly dominant features in the Raman and SERS spectra of peptides and proteins, and that the Raman modes of these three small constructed peptides can apply directly to the assignment of Raman and SERS features in the spectra of larger peptides and proteins.

This thesis details the synthesis, characterization, and functionalization of transition metal phosphide nanomaterials from single source molecular precursors. The decomposition of the organometallic cluster, H2Fe3(CO) 9PtBu, yielded iron phosphide (Fe2P) nanomaterials of various morphologies depending on the surfactants used for the decomposition. Branched nanostructures were observed as a result of crystal splitting in a few of the surfactant systems. Cross-shaped structures were also observed and attributed to the twinning of two individual bundles during growth as the result of an interrupted growth process. The role of the solvents in particular the use of oleic acid for the formation of nanorods, in the formation of Fe2P nanoparticles will be discussed. Magnetic measurements taken of a variety of different morphologies of these iron phosphide nanoparticles will also be presented. Fe2P nanoparticles were also isolated via the decomposition of other clusters, including Fe3(CO) (P tBu)2, Fe2(CO)6(PHtBu) 2, Fe4(CO)11PtBu2, and Fe3(CO)10PtBu. In order to study the mechanism by which the clusters decompose, the decompositions were monitored using infrared spectroscopy. For all of the systems studied, the clusters rearranged in the surfactant solutions, ultimately resulting in Fe2(CO) 6(PHtBu)2 prior to decomposition. This rearrangement is believed to be a result of the interaction of the clusters with the surfactants employed, suppored by the finding that the solid state decomposition of H 2Fe3(CO)pPtBu was found to result in a combination of Fe 3P, Fe2P, and Fe3O4. In addition to the formation of the binary phases of transition metal phosphide nanomaterials, investigation into the formation of mixed metal phosphides of iron and manganese were also performed. For these experiments, H2 Fe3(CO)9PtBu with a manganese source, either Mn2(CO)10 or Mn(CO)5Br, were decomposed in a variety of surfactant systems. The resulting nanoparticles were only doped with manganese; pure stoichiometric phases were not isolated. Finally the functionalization of Fe2P split rods, T-shapes, and crosses with a gold shell was performed. Their optical properties were studied, and a redshift in the extinction maximum was seen as the shell thickness increased. This plasmon peak shift, as opposed to the trends seen in silica-Au core-shell structures as shell thickness increases, is attributed to the high permittivity of the Fe2P core.

This thesis details the synthesis and characterization of anisotropic cadmium and lead sulfide nanostructures from single-source molecular precursors. Six new precursors were synthesized for cadmium and lead sulfide each, by the reaction of the appropriate metal acetate with picolinic (HPic), 2,6-dipicolinic (H2dipic) or salicylic acid (H2sal) followed by the addition of thiourea (th) or thiosemicarbazide (ths). The precursors for CdS are [Cd(Hsal)2(tu)2] (Cd1a), [Cd(Hsal) 2(ths)2]·nH2O (Cd1b), [Cd(pic) 2(tu)2]·0.5H2O (Cd2a), [Cd(pic) 2(ths)2]·2H2O (Cd2b), [Cd(dipic)(tu) 2] (Cd3a) and [Cd(dipic)(ths)2(H2O)]·2H 2O (Cd3b) and the precursors for PbS are [Pb(Hsal) 2(th)2] (Pb1a), [Pb(Hsal)2(ths) 2] (Pb1b), [Pb(pic)2(th)2] ( Pb2a), [Pb(pic)2(ths)2] (Pb2b), [Pb(dipic)(th)(H2O)]2·2H2O ( Pb3a) and [Pb(dipic)(ths)2]·H2O ( Pb3b). All of the compounds were characterized spectroscopically and by elemental analysis. Cd1a, Cd2a, Cd2b, Cd3a, Cd3b, Pb2b Pb3a and Pb3b formed well-defined crystals and were characterized by single crystal X-ray diffraction. The precursors were decomposed at or around 170°C using n-cetyltrimethylammonium bromide (CTAB), sodium dodecylsulphate (SDS), ethylenediamine, oleic acid, oleylamine, trioctylamine or hexadecylamine as surfactants. Systematic variations of surfactants gave small spherical nanoparticles, micro-sized flowers, multipods and nanorods for CdS and nanocubes, truncated nanocubes, hexapods, octahedrons and dendritic stars for PbS. From XRPD studies it was found that most of the CdS nanostructures were of the stable hexagonal phase. However, in two cases the nanostructures were found to be predominantly of a metastable orthorhombic phase. For PbS system, all the decompositions yielded pure crystalline galena. For CdS system, TEM studies revealed planar defects (such as polysynthetic and multiplet twinning) in the nanocrystals, which gave an explanation for mechanism of growth. For PbS system, in order to elucidate the effect of single source precursors on the mechanism of growth of nanoparticles, the decomposition results were compared with PbS nanostructures synthesized from multiple-source precursors, lead acetate and thiourea or thiosemicarbazide. It was found that in the reactions of multiple source precursors, acidic components in the reaction mixture (oleic acid, acetic acid) led to etching and crystal splitting, which played a crucial role in the formation of anisotropic nanostructures.

Thesis (Ph. D.)--Indiana University, Dept. of Chemistry, 2009. / Title from PDF t.p. (viewed Feb. 4, 2010). Source: Dissertation Abstracts International, Volume: 70-04, Section: B, page: 2297. Adviser: Daniel J. Mindiola.

<p> This dissertation is based on the hydro(solvo)thermal syntheses and characterization of uranyl (UO₂²⁺) coordination polymers (CPs) via single-crystal X-ray diffraction (SC-XRD), powder X-ray diffraction (PXRD), and luminescence spectroscopy. The rich structural portfolio of uranyl CPs arises from the UO₂²⁺ cation&rsquo;s tendency to undergo hydrolysis, and form uranyl oligomeric species (or secondary building units, SBUs). Because of hydrolysis, synthetic control of SBUs is difficult and more often then not, their solid-state crystallization is random and unpredictable. Thus, it is challenging to know what building unit will be observed in a uranyl CP. </p><p> Our strategy to address such challenges and potentially thwart hydrolysis is to use N-donor chelating ligands. These ligands offer potential chelating sites that may allow for direct coordination to UO₂²⁺ and thus essentially promote specific uranyl building units. The N-donor ligands chosen in our study are 2,2&rsquo;:6,2&rdquo;-terpyridine (TPY), analogs of 2,2&rsquo;-bipyridine (BPY), 2,4,6-tripyridyl-s-triazine (TPTZ), and 2,3,5,6-tetrakis(2-pyridyl)pyrazine (TPPZ). By restricting UO₂²⁺ speciation, assembly of aromatic or aliphatic O-donor linkers to available coordination sites on UO₂²⁺ allowed us to synthesize a series of uranyl CPs containing N-donor (TPY, TPTZ, BPY analogs) and O-donor co-ligands. These coordination polymers resulted in extended structures with unique structural topologies and luminescent features. </p><p> Depending on the choice of N- and O-donors, structural variations in the local UO₂²⁺ coordination sphere and global structure within a uranyl CP were observed. N-donor chelating ligands were also explored as guest molecules, in which a series of CPs containing TPTZ, BPY analogs, or TPPZ and different O-donor aliphatic or aromatic linkers were synthesized. These guests were found to stabilize the structure through non-covalent interactions or participate as charge balancing species. Beyond structural manipulation of our materials, we also studied UO₂²⁺ luminescence and lifetimes within our uranyl CPs. We observe that modifications on either the N- or O-donor (i.e. sterics, functional groups, and/or non-covalent interactions) or a change in the local and global structure of a CP influences UO₂²⁺ luminescence thus resulting in unique spectral signatures. </p><p> Given the influence of N-donors and O-donors on the structure and luminescence of an uranyl CP, we also explored the synthesis of uranyl complexes using N-donor BPY, 5,5&rsquo;-dimethyl-2,2&rsquo;-bipyridine (MeBPY), and TPY ligands exclusively via self assembly conditions in the presence of sunlight and ambient light. Unexpectedly, we observe the presence of peroxo ligands in our crystal structures. To explore the origin of the peroxo ligand, rigorous synthetic experiments were performed in which the presence of peroxo most likely arises from a mechanism consistent to photo-excitation of UO₂²⁺.</p>

¹H NMR and EPR techniques were used to investigate the electron spin distribution and electronic ground state in several iron tetrapyrrolic macrocycles. The first macrocycle studied is corrole, including [(Me₈C)FeCl] (Me₈C = 2,3,7,8,12,13,17,18-octamethylcorrole) and [(7,13-Me₂Et₆C)FeCl] (7,13-Me₂Et₆C = 7,13-dimethyl-2,3,8,12,17,18-hexaethylcorrole) and four meso-substituted corrolates--[(TPCorr)FeCl], [(4-NO2TPCorr)FeCl], [(4-MeOTPCorr)FeCl] and [(TPCorr)FeClO₄] (TPCorr = 5,10,15-triphenylcorrole). These chloroiron corrolates were all found to be S = 3/2 intermediate-spin iron(III) π cation radical complexes, with the corrole radical strongly antiferromagnetically coupled to the spins of the iron, leading to an overall spin of 1 and large negative π spin densities on the meso positions. Upon addition of imidazole ligands, [(Me₈C)FeCl] and [(7,13-Me₂Et₆C)FeCl2] change to bis imidazole low-spin iron(III) π cation radical species at low temperature. There is little or no ferromagnetic coupling between the radical and the iron center, resulting in large position pi spin densities on the meso positions. The binding of cyanide to [(7,13-Me₂Et₆C)FeCl] causes autoreduction of the complex. An excess of cyanide in the solution can reduce the bis-cyanide complex, a low-spin iron(III) π cation radical which is produced first upon addition of cyanide, to the mono-cyanide complex, which is a normal low-spin iron(III) five-coordinate complex. The redox reaction occurs on the corrole ring instead of at the iron center. Proton relaxation times (T₁ and T₂) of a pyrrole-CH₃ peak from the heme domain of the chicken liver sulfite oxidase were measured by NMR methods. From the relaxation times, it is found that the sulfite oxidase enzyme tumbles as the whole protein rather than the larger Mo domain and the smaller heme domain tumbling somewhat independently. The last macrocycles investigated are chlorins and mono-oxochlorin. Both high-spin tetraphenylchlorinatoiron(III) chloride (TPCFeCl) and octaethylchlorinatoiron(III) chloride (OECFeCl) and their low-spin complexes with different imidazole and pyridine ligands were studied by NMR and EPR. The full peak assignments were made for all high-spin and low-spin species from COSY, NOESY, NOE difference and saturation transfer experiments. The NMR results show that, like TPPFe(III) and TMPFe(III) complexes, the low-spin TPCFe(III) complexes change their ground state from (dxy)²(dxzdyz)³ to (dxzdyz)⁴(dxy)¹ with decrease in the donor strength of the axial ligands, while OECFe(III) complexes keep their ground state unchanged (always (dxy)²(dxydyz)³) with different axial ligands in the temperature range of NMR experiments (+30°C to -90°C)). However, EPR data show that both TPCFe(III) and OECFe(III) complexes have the trend of change to (dxzdyz)⁴(dxy)¹ ground state with weak donor ligands (such 4-cyanopyridine). The electronic structure of [OECFe(t-BuNC)₂]⁺ is the (dxzdyz)⁴(dxy)¹ ground state with a low-lying (dxy)²(d xzdyz)³ excited state. The chlorin ring of [OECFe(tBuNC)₂]⁺ is probably ruffled, as in [OEPFe(t-BuNC)₂]⁺. The NMR spectrum of [OECFe(t-BuNC)₂]⁺ is characterized by the large downfield shift of the pyrrolene protons, indicating the involvement of the A-1 orbital in the spin distribution mechanism. [mono-oxo-OECFe(Im-d₄)₂]Cl (mono-oxo-OEC = 2-oxo-3,3',7,8,12,13,17,18-octaethyl-chlorin) is a low-spin Fe(III) complex with (dxy)²(dxzdyz)³ ground state. The pattern of the chemical shifts of the pyrrole-CH2 and meso protons is similar to that of [OECFe(Im-d₄)₂]Cl, except that more peaks were observed due to its lower symmetry. Finally, DFT calculation on high-spin iron (III) chlorin was carried out to predict the Fermi contact shifts and spin distribution mechanism.

<p> This dissertation describes the synthesis of a series of transition metal compounds and their reactivity with hydrogen and carbon dioxide for application in reversible hydrogen storage in organic molecules. Chapter 1 is a review of hydrogen storage molecules and discusses each from the perspectives of safety, availability, and environmental impact. Heterogeneous and homogeneous catalysts for dehydrogenation of these molecules are also discussed here. In Chapter 2, a family of PNP pincer-supported iron compounds is investigated by M&ouml;ssbauer spectroscopy and magnetic circular dichroism with the goal of elucidating the degree of solution-state flexibility of the PNP pincer ligand. Chapter 3 expands on this family of PNP pincer-supported iron compounds with the synthesis of several new compounds through reaction with hydrogen and carbon dioxide. Furthermore, these compounds are shown to be highly active catalysts for formic acid dehydrogenation in the presence of a Lewis acid co-catalyst. The action of the Lewis acid co-catalyst is further demonstrated in Chapter 4, where PNP pincer-supported iron compounds are used as catalysts for aqueous-phase methanol dehydrogenation. Chapter 5 describes the synthesis, characterization and reactivity of a family of palladium and nickel compounds supported by allyl, cyclopentadienyl, and indenyl ligands. These compounds are shown to react with simple electrophiles, although they do not show the desired reactivity with carbon dioxide.</p>

This dissertation is concerned with the chemistry of the hexarhenium selenide cluster and its use as a synthetic building block. Two themes underlay the research presented here: (1) to create of novel supramolecular arrays and (2) to provide possible solutions to problems associated with the synthesis of inorganic-organic hybrid materials. Star-shaped scaffolding was used to develop a molecular Tinkertoy kit containing pieces which incorporate a variety of angles. Further functionalization of a molecular Tinkertoy based upon TPyP by incorporation of metal ions was discussed and examined along with the new electrochemical and photophysical properties observed. A new metallodendrimer motif containing clusters a the core, within the branches, and on the periphery was developed and discussed. Also addressed is the hitherto unseen electrochemical communication between [Re6(μ3-Se)8]2+ clusters bridged by an organic moiety. Possible solutions to problems involved with the synthesis of inorganic-organic hybrid materials were provided, as well as a demonstration-of-feasibility synthesis demonstrating the successful copolymerization of [Re6(μ3-Se)8]2+ vinylpyridine derivative with styrene.

Models of the heme b centers in the cytochrome bc₁ complex based on octaalkyltetraphenyliron(III) porphyrins (OETPP, OMTPP, and TC₆TPP) with various axial ligands (4-Me₂NPy, 4-CNPy, 1-MeIm, 2-McImH, CN- and t-BuNC) have been synthesized and explored via NMR and EPR spectroscopy and X-ray crystallography. The electron spin distributions and the electronic ground states of the complexes were determined based on the NMR and EPR results. The type of ground state of Fe(III) is defined by the number and nature of the axial ligands and peripheral substituents. Five-coordinate complexes with Cl- are high-spin (HS, S = 5/2) with ∼10% of intermediate spin (IS, S = 3/2) mixed in. Bis-(4-CNPy) porphyrins at relatively high temperatures, as well as five-coordinate perchlorates, have the IS state. Finally, six-coordinate complexes with pyridines, imidazoles, cyanides and isocyanides are all low-spin (LS, S = 1/2), with the (dxy)²(d xz,dyz)³ ground state in the case of strongly and moderately basic axial ligands, and the (dxz,dyz)⁴(dxy)¹ ground state when bound to weak sigma-donors and/or strong pi-acceptors like t-BuNC or 4-CNPy (at low temperatures only). Crystal structures of more than 15 complexes have been obtained in order to establish structure-property relationships in the systems studied. All of them adopt a saddled conformation with different degrees of ruffling and non-planarity and a wide range of dihedral angles between the axial ligands. Non-planar distortion of the macrocycle induced by the steric interaction between the peripheral substituents increases in the order TC₆TPP < OMTPP < OETPP. The rate of ring inversion of the porphyrin cores decreases in the same order, as shown by NMR spectroscopy. While all bis-ligated iron(III) porphyrinate of this study with pyridine or hindered imidazole ligands have close to perpendicular axial ligand orientations, bis-(1-MeIm) complexes have perpendicular as well as close to parallel ligand arrangements both in crystals and in solutions as observed by EPR and Mössbauer spectroscopy and X-ray crystallography. Preliminary Mössbauer studies of four of the complexes of this study have been carried out in the laboratory of Professor A. X. Trautwein, Institute of Physics, University of Lubeck, Germany. The results of the work presented in this dissertation suggest that octaalkyltetraphenylporphyrinatoiron(III) complexes are promising models for the heme b centers in the cytochrome bc₁ complex.

The bonding interactions of phosphines and carbenes with a transition metal center have been explored with gas-phase photoelectron spectroscopy and computational methods. The interactions governing the electronic differences between these two species are probed in order to comment on differences in reactivity that are seen in transition-metal catalytic species. The principles governing the nature of sigma and pi bonding for phosphines and carbenes have been explored and quantified. The electronic bonding factors of the ligand L in the (L)₂(CL)₂Ru=CHPh have been probed in order to explain the catalytic reactivity differences in Grubb's first generation bisphosphine species where L = tricyclohexylphosphine (PCy₃) to the second generation ruthenium catalyst where an N-heteocyclic carbene (NHC) 1,3-dimesityl-imidazolidine-2-ylidene (H₂IMes) replaces one of the phosphines in the catalyst. To directly compare the bonding modes of PCy₃ and NHCs, the (CO)₅MoL system is utilized in order to take advantage of its high symmetry. Results indicate that the NHC ligands are stronger σ donors than phosphines, and essentially have no π-acceptor ability. These electronic differences have key implications to the differences these catalyst exhibit in terms of initiation and propagation. Next, the bonding in the Cp*Ru(Cl)L molecules, where L = PCy₃, PⁱPr₃, H₂IMes, IMes and Prⁱ₂Me₂Im, is explored by photoelectron spectroscopic investigations and supporting electronic structure calculations. The Cp*Ru(Cl)L system is a coordinatively unsaturated 16 electron system which can electronically and satirically bind small molecules. This system has been found to have electronic structure interactions similar to half-sandwich complexes. In addition, the ionization energies measured from the photoelectron spectra of Cp*Ru(C)L molecules correlate well to solution calorimetry measurements of bond energies by Nolan and co-workers. Finally, the nature of a rare "internal" transition metal iridium carbene is probed via gas-phase photoelectron spectroscopy and density functional calculations. Ionizations measured for the [IrCl(ᵗBu₂PCH₂CH₂CCH₂CH₂PᵗBu₂)] complex with the support of theoretical calculations serve to establish the valency of the iridium metal center. This internal pincer has been found to have a "covalent carbene-metal" interaction.