Ground and Excited State Electron Transfer Reaction Between a few Anthracene Appended Tertiary Amines and Suitable Electron Acceptors

the thesis entitled “Ground and Excited State Electron Transfer Reaction Between a few Anthracene Appended Tertiary Amines and Suitable Electron Acceptors” portrays our attempts to explore the solvent, concentration and temperature effect of the reaction between a few (anthracen-9- yl)methanamines with electron acceptors like DMAD, DBA and DBE. We have also studied the effect of solvent and percentage fluorescence quenching in the photoinduced electron transfer reactions of these ‘donor-spacer-acceptor’ systems. Finally we look in to the intramolecular electron transfer reactions of a few tertiary amine appended dibenzobarrelenes and bisdibenzobarrelenes

Statistics and kinetics of single-molecule electron transfer dynamics in complex environments: A simulation model study

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Dynamical calculation of direct muon-transfer rates from thermalized muonic hydrogen to C6+ and O8+

Moun-transfer reactions from muonic hydrogen to carbon and oxygen nuclei employing a full quantum-mechanical few-body description of rearrangement scattering were studied by solving the Faddeev-Hahn-type equations using close-coupling approximation. The application of a close-coupling-type ansatz led to satisfactory results for direct muon-transfer reactions from muonic hydrogen to C6+ and O8+.

New structures in the continuum of C-15 populated by two-neutron transfer

The C-13(O-18,O-16)C-15 reaction has been studied at 84 MeV incident energy. The ejectiles have been detected at forward angles and C-15 excitation energy spectra have been obtained up to about 20 MeV. Several known bound and resonant states of C-15 have been identified together with two unknown structures at 10.5 MeV (FWHM = 2.5 MeV) and 13.6 MeV (FWHM = 2.5 MeV). Calculations based Oil the removal of two uncorrelated neutrons from the projectile describe a significant part of the continuum observed in the energy spectra. In particular the structure at 10.5 MeV is dominated by a resonance of C-15 near the C-13 + n + n threshold. Similar structures are found in nearby nuclei such as C-14 and Be-11. (c) 2012 Elsevier BM. All rights reserved.

Real-time observation of the charge-transfer-to-solvent dynamics

Intermolecular electron-transfer reactions have a crucial role in biology, solution chemistry and electrochemistry. The first step of such reactions is the expulsion of the electron to the solvent, whose mechanism is determined by the structure and dynamical response of the latter. Here we visualize the electron transfer to water using ultrafast fluorescence spectroscopy with polychromatic detection from the ultraviolet to the visible region, upon photo-excitation of the so-called charge transfer to solvent states of aqueous iodide. The initial emission is short lived (~60 fs) and it relaxes to a broad distribution of lower-energy charge transfer to solvent states upon rearrangement of the solvent cage. This distribution reflects the inhomogeneous character of the solvent cage around iodide. Electron ejection occurs from the relaxed charge transfer to solvent states with lifetimes of 100–400 fs that increase with decreasing emission energy.

Large kinetic isotope effects in enzymatic proton transfer and the role of substrate oscillations

We propose an interpretation of the experimental findings of Klinman and coworkers [Cha, Y., Murray, C. J. & Klinman, J. P. (1989) Science 243, 1325–1330; Grant, K. L. & Klinman, J. P. (1989) Biochemistry 28, 6597–6605; and Bahnson, B. J. & Klinman, J. P. (1995) Methods Enzymol. 249, 373–397], who showed that proton transfer reactions that are catalyzed by bovine serum amine oxidase proceed through tunneling. We show that two different tunneling models are consistent with the experiments. In the first model, the proton tunnels from the ground state. The temperature dependence of the kinetic isotope effect is caused by a thermally excited substrate mode that modulates the barrier, as has been suggested by Borgis and Hynes [Borgis, D. & Hynes, J. T. (1991) J. Chem. Phys. 94, 3619–3628]. In the second model, there is both over-the-barrier transfer and tunneling from excited states. Finally, we propose two experiments that can distinguish between the possible mechanisms.

Kinetic coupling between electron and proton transfer in cytochrome c oxidase: simultaneous measurements of conductance and absorbance changes.

Bovine heart cytochrome c oxidase is an electron-current driven proton pump. To investigate the mechanism by which this pump operates it is important to study individual electron- and proton-transfer reactions in the enzyme, and key reactions in which they are kinetically and thermodynamically coupled. In this work, we have simultaneously measured absorbance changes associated with electron-transfer reactions and conductance changes associated with protonation reactions following pulsed illumination of the photolabile complex of partly reduced bovine cytochrome c oxidase and carbon monoxide. Following CO dissociation, several kinetic phases in the absorbance changes were observed with time constants ranging from approximately 3 microseconds to several milliseconds, reflecting internal electron-transfer reactions within the enzyme. The data show that the rate of one of these electron-transfer reactions, from cytochrome a3 to a on a millisecond time scale, is controlled by a proton-transfer reaction. These results are discussed in terms of a model in which cytochrome a3 interacts electrostatically with a protonatable group, L, in the vicinity of the binuclear center, in equilibrium with the bulk through a proton-conducting pathway, which determines the rate of proton transfer (and indirectly also of electron transfer). The interaction energy of cytochrome a3 with L was determined independently from the pH dependence of the extent of the millisecond-electron transfer and the number of protons released, as determined from the conductance measurements. The magnitude of the interaction energy, 70 meV (1 eV = 1.602 x 10(-19) J), is consistent with a distance of 5-10 A between cytochrome a3 and L. Based on the recently determined high-resolution x-ray structures of bovine and a bacterial cytochrome c oxidase, possible candidates for L and a physiological role for L are discussed.

Pressure and temperature effects on metal-to-metal charge transfer in cyano-bridged Co-III-Fe-II complexes

The effects of pressure and temperature on the energy (E-op) of the metal-to-metal charge transfer (MMCT, Fe-II --> Co-III) transition of the cyano-bridged complexes trans - [(LCoNCFe)-Co-14(CN)(5)](-) and cis-[(LCoNCFe)-Co-14(CN)(5)](-) (where L-14 = 6-methyl-1,4,8,11-tetraazacyclotetradecan-6-amine) were examined. The changes in the redox potentials of the cobalt and iron metal centres with pressure and temperature were also examined and the results interpreted with Marcus Hush theory. The observed redox reaction volumes can mainly be accounted for in terms of localised electrostriction effects. The shifts in E-op due to both pressure and temperature were found to be less than the shifts in the energy difference (E degrees) between the Co-III-Fe-II and Co-II-Fe-III redox isomers. The pressure and temperature dependence of the reorganisational energy, as well as contributions arising from the different spin states of Co-II, are discussed in order to account for this trend. To study the effect of pressure on Co-III electronic absorption bands, a new cyano-bridged complex, trans - [(LCoNCCo)-Co-14(CN)(5)], was prepared and characterised spectroscopically and structurally. X-Ray crystallography revealed this complex to be isostructural with trans -[(LCoNCFe)-Co-14(CN)(5)] center dot 5H(2)O.

Leading coordinate analysis of reaction pathways in proton chain transfer: Application to a two-proton transfer model for the green fluorescent protein

The ‘leading coordinate’ approach to computing an approximate reaction pathway, with subsequent determination of the true minimum energy profile, is applied to a two-proton chain transfer model based on the chromophore and its surrounding moieties within the green fluorescent protein (GFP). Using an ab initio quantum chemical method, a number of different relaxed energy profiles are found for several plausible guesses at leading coordinates. The results obtained for different trial leading coordinates are rationalized through the calculation of a two-dimensional relaxed potential energy surface (PES) for the system. Analysis of the 2-D relaxed PES reveals that two of the trial pathways are entirely spurious, while two others contain useful information and can be used to furnish starting points for successful saddle-point searches. Implications for selection of trial leading coordinates in this class of proton chain transfer reactions are discussed, and a simple diagnostic function is proposed for revealing whether or not a relaxed pathway based on a trial leading coordinate is likely to furnish useful information.

Chiral Triphenylprolinol Ligands for the Efficient Catalytic Asymmetric Arylation of Aldehydes

The synthesis of new chiral amino alcohols by Heck arylation of an enecarbamate is described. These compounds were used as chiral ligands for the catalytic asymmetric arylation of aldehydes and can be easily recovered. Chiral, nonracemic diarylmethanols were obtained in high yields and enantioselectivities.

Discrete cyanide-bridged mixed-valence Co/Fe complexes: Outer-sphere redox behaviour

The outer-sphere redox behaviour of a series of [LnCoIII-NCFeII(CN)(5)](-) (L-n = n-membered pentadentate aza-macrocycle) complexes have been studied as a function of pH and oxidising agent. All the dinuclear complexes show a double protonation process at pH approximate to 2 that produces a shift in their UV/Vis spectra. Oxidation of the different non-protonated and diprotonated complexes has been carried out with peroxodisulfate, and of the non-protonated complexes also with trisoxalatocobaltate(III). The results are in agreement with predictions from the Marcus theory. The oxidation of [Fe(phen)(3)](3+) and [IrCl6](2-) is too fast to be measured, although for the latter the transient observation of the process has been achieved at pH = 0. The study of the kinetics of the outer-sphere redox process, with the S2O82- and [Co(ox)(3)](3-) oxidants, has been carried out as a function of pH, temperature, and pressure. As a whole, the values found for the activation volumes, entropies, and enthalpies are in the following margins, for the diprotonated and non-protonated dinuclear complexes, respectively: DeltaV(not equal) from 11 to 13 and 15 to 20 cm(3) mol(-1); DeltaS(not equal) from 110 to 30 and -60 to -90 J K-1 mol(-1); DeltaH(not equal) from 115 to 80 and 50 to 65 kJ.mol(-1). The thermal activation parameters are clearly dominated by the electrostriction occurring on outer-sphere precursor formation, while the trends found for the values of the volume of activation indicate an important degree of tuning due to the charge distribution during the electron transfer process. The special arrangement on the amine ligands in the isomer trans[(L14CoNCFeII)-N-III(CN)(5)](-) accounts for important differences in solvent-assisted hydrogen bonding occurring within the outer-sphere redox process, as has been established in redox reactions of similar compounds. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).

Capacidade antioxidante de bebidas comerciais

Mestrado em Engenharia Química

Preparação e análise estrutural de complexos de samário

Trabalho Final de Mestrado para obtenção do grau de Mestre em Engenharia Química e Biológica - Ramo de Bioprocessos

Periplasmic nitrate reductases: structural and spectroscopic studies

Dissertação apresentada para obtenção do grau de Doutor em Bioquímica, especialidade Bioquímica-Física, pela Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa

Metal ions and protein folding: conformational and functional interplay

Dissertation presented to obtain a PhD degree in Biochemistry at Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa