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Photoacid for Extremely Long-Lived and Reversible pH-Jumps
Nunes, Rui M. D.; Pineiro, Marta; Arnaut, Luís G.The ability to change the acidity of an aqueous solution within the time of a short laser pulse and use the resulting low pH to drive acid-catalyzed reactions in the irradiated volume opens news perspectives for the spatial and temporal control of a variety of processes. Persistent and reversible acidification of an aqueous solution is achieved with a new molecule, 1-(2-nitroethyl)-2-naphthol, that combines the...
Synthesis of amphiphilic sulfonamide halogenated porphyrins: MALDI-TOFMS charac...
Monteiro, Carlos J. P.; Pereira, Mariette M.; Pinto, Sara M. A.; Simões, Ana V. C.; Sá, Gonçalo F. F.; Arnaut, Luís G.; Formosinho, Sebastião J.Porphyrins are key precursors for development of photosensitizers for photodynamic therapy. A new series of ortho-halogenated tetraarylporphyrins with sulfonamide substituents have been synthesized via chlorosulfonation reaction and characterized by MALDI-TOFMS. To predict their partition properties, log KOW of a selected range of the synthesized halogenated amphiphilic porphyrins is described. A significant ef...
Understanding Chemical Reactivity: The Case for Atom, Proton and Methyl Transfers
Arnaut, Luís G.; Formosinho, Sebastião J.The concept of ldquochemical reactivityrdquo assumes that atoms and molecules contain the necessary information to describe their evolution over time as they transform from reactants to products. This concept was useful in the past to rationalize reactivity trends and predict the behavior of new systems. Free-energy relationships have played a central role in this field. However, electronic effects often counte...
A chemical understanding for the enhanced hydrogen tunnelling in hydroperoxidat...
Barroso, Mónica; Arnaut, Luís G.; Formosinho, Sebastião J.The reaction path of the Interacting-State Model (ISM) is used with the Transition-State Theory (TST) and the semiclassical correction for tunnelling (ISM/scTST) to calculate the rates of H-atom abstraction from C(11) of linoleic acid catalysed by soybean lipoxygenase-1 (SLO), as well as of an analogous uncatalysed reaction in solution. The calculated hydrogen-atom transfer rates, their temperature dependency a...
Photoacoustic Measurement of Electron Injection Efficiencies and Energies from ...
Serpa, Carlos; Schabauer, Johann; Piedade, Ana P.; Monteiro, Carlos J. P.; Pereira, Mariette M.; Douglas, Peter; Burrows, Hugh D.; Arnaut, Luís G.Time-resolved photoacoustic calorimetry is used to measure the energy released upon injection of an electron from an electronically excited dye adsorbed to nanocrystalline TiO2 into the conduction band of this material. More energy is released when the environment of the dye is made less polar, because the energy of the dye-oxidized state has a more pronounced solvent dependence than the edge of the conduction ...
The Rates of SN2 Reactions and Their Relation to Molecular and Solvent Properties
Arnaut, Luís G.; Formosinho, Sebastião J.The energy barriers of symmetrical methyl exchanges in the gas phase have been calculated with the reaction path of the intersecting/interacting-state model (ISM). Reactive bond lengths increase down a column of the Periodic Table and compensate for the decrease in the force constants, which explains the near constancy of the intrinsic barriers in the following series of nucleophiles: F-≈Cl-≈Br-≈I-. Th...
The Triplet State of Indigo13
Melo, J. Sérgio Seixas de; Burrows, Hugh D.; Serpa, Carlos; Arnaut, Luis G.No Abstract ; http://dx.doi.org/10.1002/ange.200604679
Absolute Rate Calculations. Proton Transfers in Solution
Barroso, Mónica; Arnaut, Luís G.; Formosinho, Sebastião J.The reaction path of the intersecting-state model is used in transition-state theory with the semiclassical correction for tunneling (ISM/scTST) to calculate the rates of proton-transfer reactions from hydrogen-bond energies, reaction energies, electrophilicity indices, bond lengths, and vibration frequencies of the reactive bonds. ISM/scTST calculations do not involve adjustable parameters. The calculated prot...
(More) About biphenyl first excited triplet state energy
Gomes, Paulo J. S.; Serpa, Carlos; Arnaut, Luís G.Biphenyl photophysics was extensively studied in the past and much attention was given to the measurement of its first excited triplet state energy. Phosphorescence and the corresponding T1 <-- S0 absorption give triplet energies that differ by 10 kcal mol-1. We revisited biphenyl photophysics using photoacoustic calorimetry (PAC), a technique that directly measures the thermochemistry and kinetics of short...
1,3-Dipolar cycloaddition of azomethine ylides generated from aziridines in sup...
Gomes, Paulo J. S.; Nunes, Cláudio M.; Pais, Alberto A. C. C.; Melo, Teresa M. V. D. Pinho e; Arnaut, Luis G.The 1,3-dipolar cycloaddition of azomethine ylides with DMAD in supercritical carbon dioxide is reported. The photolysis reaction conditions were optimized with a suitable adjustment of pressure, temperature, irradiation time and co-solvent concentration leading to a more efficient reaction than in neat acetonitrile. Similar results were observed using thermal reaction conditions. Supercritical carbon dioxide w...
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