Encontrados 26 documentos, a visualizar página 1 de 3
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...
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...
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...
Tunnelling in low-temperature hydrogen-atom and proton transfers
Arnaut, Luís G.; Formosinho, Sebastião J.; Barroso, MónicaThe reaction path of the interacting-state model with the Lippincott-Schroeder potential for hydrogen bonds, is used in transition-state theory calculations with the semiclassical correction for tunnelling (LS-ISM/scTST) to estimate proton and hydrogen-atom transfer rates at low temperatures. Down to 100 K, the semiclassical correction leads to semi-empirical rates and isotope effects that are in good agreement...
Temperature Dependence of Ultra-Exothermic Charge Recombinations13
Serpa, Carlos; Gomes, Paulo J. S.; Arnaut, Luis G.; Melo, J. Seixas de; Formosinho, Sebastião J.We measured the temperature dependence (from +32 to -50 °C) of charge-recombination rates between contact radical ion pairs in isopropyl ether. In the systems selected for this study, aromatic hydrocarbon cations are the electron acceptors and the fumaronitrile anion is the electron donor. Nearly quantitative electron transfers occur at all temperatures. The charge recombinations have excess exothermicities of ...
Electron Transfer in Supercritical Carbon Dioxide: Ultraexothermic Charge Recom...
Serpa, Carlos; Gomes, Paulo J. S.; Arnaut, Luis G.; Formosinho, Sebastião J.; Pina, João; Melo, J. Seixas deCharge-recombination rates in contact radical-ion pairs, formed between aromatic hydrocarbons and nitriles in supercritical CO2 and heptane, decrease with the exothermicity of the reactions until they reach -70 kcal mol-1, but from there on an increase is observed. The first decrease in rate is typical of the ldquoinverted regionrdquo of electron-transfer reactions. The change to an increase in the rate for ult...
Dramatic Pressure-Dependent Quenching Effects in Supercritical CO2 Assessed by ...
Barroso, Mónica; Chattopadhyay, Nitin; Klymchenko, Andrey S.; Demchenko, Alexander P.; Arnaut, Luís G.; Formosinho, Sebastião J.Steady-state fluorescence of 4‘-dimethylamino-3-hydroxyflavone (DMA3HF) was observed in supercritical carbon dioxide (scCO2). Excited-state intramolecular proton transfer (ESIPT) occurs resulting in two well-separated emission bands corresponding to the normal and tautomer forms. As the scCO2 density exceeds 0.7 g/mL, the relative intensity of the two bands tends to a constant value, comparable to that observed...
Absolute Rate Calculations: Atom and Proton Transfers in Hydrogen-Bonded Systems13
Barroso, Mónica; Arnaut, Luis G.; Formosinho, Sebastião J.We calculate energy barriers of atom- and proton-transfer reactions in hydrogen-bonded complexes in the gas phase. Our calculations do not involve adjustable parameters and are based on bond-dissociation energies, ionization potentials, electron affinities, bond lengths, and vibration frequencies of the reactive bonds. The calculated barriers are in agreement with experimental data and high-level ab initio calc...
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