The affinity of hemoglobin for CO relative to O₂ is decreased compared to simple iron-porphyrin systems mainly due to electronic effects. Hydrogen-bond formation with the His E7 residue of hemoglobin has been revealed to stabilize the bound dioxygen. This thesis describes the development of a series porphyrin models, benzene-4/4 (49a), benzene-5/5 (49b), amidobenzene-4/4 (49c) and amidobenzene-5/5 (49d) capped porphyrins, which serve as simple models to imitate the hydrogen bonding in hemoglobin. The chain linked bis pyrroles 38 were synthesized by Friedel-Crafts acylation of the benzene and nitrobenzene diacid chain derivatives with two equivalents of the β-unsubstituted pyrrole 36, followed by diborane reduction of the ketonic groups. After the nitro functions were transformed to the acetamides, modification of the ethyl ester functions of 38a, 38b and 39 via the benzylesters 40, the carboxypyrroles 41 and the α-unsubstituted pyrroles 42 afforded the important bis formyl pyrroles 43. The cyanoacrylate protected formyl pyrrole derivatives 44 were subjected to monochlorination at the α-methyl groups followed by condensation with two equivalents of the α-unsubstituted pyrrole 46 to give dipyrromethane dimers 47. Strong aqueous alkali caused saponification of the two ester groups and deprotection of the formyl functions to give 48. The α formyl-α′-unsubstituted dipyrromethane dimer, resulting from the thermal decarboxylation of 48, was cyclized to produce the porphyrin 49 in acidic medium. The interactions of CO and O₂ with the heme derivatives, Fe[superscript]Ⅱ(porphyrin)(DcIm), have been studied. The CO binding constant of the amide substituted heme is two foldlarger than that of the non-amide substituted heme. In contrast, the low temperature (-45°C) O₂ binding constants of the hemes have shown a 6-8 fold increase from nonamide to amide substituted hemes, probably because of a hydrogen bonding between the amide function and bound dioxygen similar to the hydrogen bonding in hemoglobin. [formula omitted] / Science, Faculty of / Chemistry, Department of / Graduate

The reaction of Rh(OEP)(H) (OEP - 2,3 J,8,12,13,17,18-octaemylporphyrin) with O₂ in organic solvents was examined by visible, proton and phosphorus nuclear magnetic resonance spectroscopy (nmr) as a candidate system for the net insertion of O₂ into the metal-hydride bond. The nmr data for a thermally unstable Rh[superscript]Ⅲ(OEP)(OOHXH₂0) mtennediate were obtained at -40 °C in CD₂C1₂- Addition of O₂ to CH₂CI₂ solutions of Rh(OEP)(H) with triphenylphosphine resulted in reaction with solvent forming Rh(OEP)(Cl)(PPh₃) and Rh(OEP)(CH₂Cl)(PPh₃) as the major species (in equimolar amounts), without concomitant formation of OPPh₃. The sensitivity of the reaction of Rh(OEP)(H) with O₂ to initial conditions, and the observation of products containing Rh (Ⅱ) and Rh-CH₂Cl, suggest a radical mechanism. Initiation/tenniriation: 2Rh(OEP)(H) ⇌ [Rh(OEP)]₂ + H₂ [Rh(OEP)]₂ ⇌ 2Rh(OEP)- and in the presence of PPh₃ [Rh(OEP)]₂+ PPh₃ ⇌ -Rh(OEP)(PPh₃) + Rh(OEP)- Propagation: Rh(OEP)- + O₂ ⇌ Rh(OEP)(O₂) Rh(OEP)( O₂) + Rh(OEP)(H) → Rh(OEP)(OOH) + Rh(OEP)- Teimination: Rh(OEP)(OOH) + Rh(OEP)(H) →[Rh(OEP)]₂ + H₂O +½O₂ and in the presence of PPh₃ •Rh(OEP)(PPh₃) + CH₂CI₂ ⇌ Rh(OEP)(Cl)(PPh₃) + ∙CH₂C1 Rh(OEP)∙ + ∙CH₂C1 ⇌Rh(OEP)(CH₂Cl) The reaction of Et₃N with Rh(por)(a)(L) (por = OEP or 5,10,15,20-tetramesitylporphyrin(TMP), L = H₂O, (CH₃)₂CHOH, CH₃CN) gave products, identified by visible (scanning and stopped-flow) and proton nmr spectroscopy to be Rh(por)(CH(Me)NEt₂), Et₂NH as Rh(por)(Cl)(Et₂NH), and Rh(por)(CH₂CHO). This indicated amine C-H and C-N cleavage and net one-electron reduction of Rh(Ⅲ) to Rh(Ⅱ) species ([Rh(OEP)]₂). Of other amines examined, aniline, N-methyl-diphenylamine and N-ethyl piperidine all formed complexes of the type Rh(OEP)(Cl)(amine). Proton Sponge and tributylamine with Rh(OEP)(Cl)(H₂O) give [Rh(OEP)]₂ as a major product under anaerobic conditions. Only the mechanism of the Et₃N system was examined in detail. Stopped-flow data indicated that Et₃N initially replaced L in the Rh[superscript]Ⅲ(por)(Cl)(L) species to form a Rh[superscript]Ⅲ(por)(Cl)(Et₃N) complex. An equilibrium involving reduction of Rh[superscript]Ⅲ to Rh[superscript]Ⅱ resulted and, in aromatic solvents under anaerobic conditions, slow reaction of Rh[superscript]Ⅱ(por) with Et₃N occurred to give Rh(por)(CH(Me)NEt₃). In CH₂CI₂, reaction of Et₃N with Rh(por)(Cl)(L) was fast, giving a mixture principally of Rh(por)(CH₂Cl)(amine) and the ɳ¹-ylidic enamine complex, Rh(por)(Cl)(CH₂CH=NEt₂) with minor mounts of Rh(por)(CH(Me)NEt₃). The Rh(por)(Cl)(CH₂CH=NEt₂) and Rh(por)(CH(Me)NEt₃) species were unstable, both ultimately giving Rh[superscript]Ⅲ(por)(Cl)(Et₂NH). The synthesis, along with characterization by visible, proton and phosphorus nmr spectroscopy, of the previously structurally characterised, mono-phosphine complex Rh(OEP)(Cl)(PPh₃) are presented. Additionally, spectroscopic evidence is presented for solution equilibria of Rh(OEP)(Cl)(PPh₃) involving formation of Rh(OEP)(L)₂+ (L = PPh₃, P[superscript]nBu₃) via thermal reactions, and Rh(OEP)(Cl)(L') (L'= CO, THF, CH₃CN) via photochemical processes. Thermodynamic data (ΔH⁰ = -33 ± 2 kJ mol⁻¹ and ΔS⁰ = -146 ±8 J K⁻¹mol⁻¹) have been estimated for formation of the bis(triphenylphospnine) species in CH₂CI₂: Rh(OEP)(Cl)(PPh₃) + PPh₃ [symbol omitted] [Rh(OEP)(PPh₃)₂]+ + Cl- Some complexes of Rh[superscript]Ⅲ(OEP) containing l,4-bis(diphenylphosphino)butane (dppb), l,2-bis((diphenylphospliino)ethane (dppe), bis(diphenylphosphino)methane (dppm) and 1,3-bis(diphenylphosphho)propane (dppp) have been characterized in situ using visible, proton and phosphorus nmr spectroscopy. The diphosphines (PP) are bound to Rh(Ⅲ) porphyrins in a monodentate dangling fashion (Rh[superscript]Ⅲ(OEP)(Cl)(PP) and [Rh[superscript]Ⅲ(OEP)(PP)₂]+), or a bridging mode between two metal centers ([Rh[superscript]Ⅲ(OEP)(Cl)]-μPP-[Rh[superscript]Ⅲ(OEP)(Cl)]). / Science, Faculty of / Chemistry, Department of / Graduate

Porphyrins are a class of natural and synthetic aromatic macrocycles that have received extensive investigation because of their unique chemical and optoelectronic properties. They are excellent ligands, photosensitizers and catalysts and serve critical roles in numerous biochemical reactions. Their properties and diverse applications have fascinated chemists from multiple fields, and porphyrins have been investigated in applications such as dye-sensitized solar cells, cancer treatments, and conjugated polymers among others. While porphyrins have made in-roads in multiple fields they have received at best minimal attention in the field of polysiloxane chemistry. Polysiloxanes are a class of inorganic polymers widely used in industrial applications that possess properties including low glass transition temperatures, high thermal and oxidative stabilities, high optical transparency, and low refractive indices that are largely unmatched by organic polymers. These properties, if properly utilized, could compliment those possessed by porphyrins and lead to the development of new applications in the fields of porphyrin and polysiloxane chemistry. Unfortunately, porphyrins and polysiloxanes are not readily compatible with one another and synthetic techniques must be developed to allow for the reliable incorporation of porphyrins into polysiloxane matrices. The objectives of this thesis are to develop strategies that allow for the ready incorporation of porphyrins into polysiloxane materials to improve existing and develop new applications for porphyrin-polysiloxane materials. These investigations led to the development of two techniques for the incorporation of porphyrins into polysiloxanes, the Piers-Rubinsztajn reaction, and ionic crosslinking. Several siloxane and polysiloxane porphyrins were prepared utilizing the Piers-Rubinsztajn reaction. These porphyrins were easily incorporated into silicone elastomers that could be utilized as dielectric, or reactive oxygen species-generating elastomers. Alternatively, ionic crosslinks could be utilized to incorporate the natural porphyrin hemin into silicone elastomers. Elastomers manufactured via this method retained the catalytic capabilities of hemin, opening the door to a new class of synthetic peroxidases. Regardless of the method of application controlling the natural tendency of porphyrins to aggregate was essential to achieving the desired properties. / Thesis / Doctor of Philosophy (PhD) / Porphyrins have attracted the attention of scientists for generations who have sought to exploit their unique chemical, physical, optical, and electronic properties. Their unique properties have led to them being utilized in a multitude of applications. Despite the wide array of applications investigated, the utilization of porphyrins in polysiloxane (silicone) chemistry has received comparatively little attention. Polysiloxanes and porphyrins possess potentially mutually beneficial properties that could lead to the development of interesting materials. Unfortunately, their development is not straightforward, as porphyrins and polysiloxanes are not naturally compatible with one another. Therefore, to realize the potential benefit of porphyrin-polysiloxane materials synthetic techniques must be first developed that allow for the reliable incorporation of porphyrins into polysiloxane matrices Two techniques were investigated for the incorporation of porphyrins into polysiloxanes. The Piers-Rubinsztajn reaction and ionic crosslinking. These methods allowed for the development of materials that had interesting applications including dielectric elastomers, reactive oxygen species generating materials and catalytic elastomers.

No description available.

Spectrophotometric titrations for a full series of 4-aminophenyl/4-pyridyl meso-substituted porphyrins were carried out using methanesulfonic acid in DMSO to study the hyperporphyrin effect across different substitution patterns. The series included zero, one, two (cis and trans), three, and four meso(4-aminophenyl) groups, with the remaining meso substituents being 4-pyridyl groups. The peripheral pyridyl groups consistently protonate before the interior porphyrin pyrrole nitrogens, which protonate before the aminophenyl groups. Aminophenyl substituents increase the basicity of the pyrrole nitrogens and lead to distinctive hyperporphyrin spectra with a broad Soret band and a strong red absorption. The structure proposed to give rise to these spectra is the previously proposed charge-transfer interaction between the aminophenyl and the protonated pyrrole. A novel hyperporphyrin structure involving charge-transfer interactions between two peripheral substituents is also proposed in one case - the triply protonated (+3) porphyrin with three aminophenyl and one pyridyl substituents; two of the aminophenyl groups delocalize the charges on the interior nitrogens while the third aminophenyl group delocalizes with the protonated pyridyl. The NMR titrations for a full series of 4-aminophenyl/4-pyridyl meso-substituted porphyrins were also performed by methanesulfonic acid in DMSO. Zero, one, two (cis), three, and four meso(4-aminophenyl) groups, with the remaining meso substituents being 4-pyridyl groups are the primary compounds studied here. The inductive effect of the meso-substituents and the π system of the macrocycle both determine the hyperporphyrin spectra, in which inductive effect has stronger influence on cis-A2Py2P and APy3P. TAPP and A3PyP both show slow exchanges from free base to hyperporphyrin, indicating these hyperporphyrin structures are stable. Both 1H-NMR and 2D NOESY spectra further validate the existence of the novel D-type hyperporphyrin from A3PyPH3+3. Electrochemical studies of these hyperporphyrins were also performed. The porphyrins involved here are zero, two (cis & trans), three, and four meso (4-aminophenyl) groups, with the remaining meso substituents being 4-pyridyl groups. The acid titrations were done in DMSO using methanesulfonic acid. Both TAPP and A3PyP can be extensively reduced with up to five distinct reduction waves. The hyperporphyrin from A3PyP, unlike that from TAPP, shows stable structures during the reduction, and A3PyPH3+3 was proposed to have the ability to reduce protons into hydrogen in a catalytic cycle.

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

No description available.

The work described in this thesis is mainly concerned with the accurate measurement of redox potentials for a series of covalently linked porphyrin-quinone molecules (P-Q), in non-aqueous media. These compounds (synthesised by Prof. J.R. Bolton and co-workers of the University of Western Ontario, Canada) are of interest as models for the primary photochemical step in the photosynthetic process. The redox potentials were measured by cyclic voltammetry and differential pulse voltammetry. These electrochemical redox potentials were used to estimate the energy of the excited charge-separated state (P<SUP>.+</SUP>-Q<SUP>.-</SUP>), and confirm that this state is likely to be photochemically produced from the excited singlet state of P-Q rather than the triplet state. As a prelude and postscript to the studies of the P-Q compounds, the electrochemical behaviour of several related but simpler compounds, both porphyrins and quinones, is described. This includes an invesigation of the solvent dependence of quinone reduction potentials in non-aqueous media. A simple linear equation, based on Swain's A+B solvent parameters, is proposed as a means of predicting quinone reduction potentials in different solvents. Finally, the electrode kinetics of some simple metallorporphyrin oxidations are studied using an a.c. technique. A non-linear fitting routine was used to optimise the rate constant values obtained.

No description available.