Browsing by Author "Medeiros, Michelle"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Dephosphorylation Reactions of Mono-, Di-, and Triesters of 2,4-Dinitrophenyl Phosphate with Deferoxamine and Benzohydroxamic Acid
    (2012) Medeiros, Michelle; Orth, Elisa S.; Manfredi, Alex M.; Pavez Guerrero, Paulina Isabel; Micke, Gustavo A.; Kirby, Anthony J.; Nome, Faruk
  • No Thumbnail Available
    Item
    Nucleophilic Neutralization of Organophosphates: Lack of Selectivity or Plenty of Versatility?
    (2021) Silva, Valmir B.; Campos, Renan B.; Pavez, Paulina; Medeiros, Michelle; Orth, Elisa S.
    Neutralization of organophosphates is an issue of public health and safety, involving agrochemicals and chemical warfare. A promising approach is the nucleophilic neutralization, scope of this review, which focuses on the molecular nucleophiles: hydroxide, imidazole derivatives, alpha nucleophiles, amines and other nucleophiles. A reactivity mapping is given correlating the pathways and reaction efficiency with structural dependence of the nucleophile (basicity) and the organophosphate (electrophilic centers, P=O/P=S shift, leaving and non-leaving group). Reactions extremely unfavorable (>20 years) can be reduced to seconds with various nucleophiles, some which are catalytic. Although there is no universal nucleophile, a lack of selectivity in some cases accounts for plenty of versatility in other reactions. The ideal neutralization requires a solid mechanistic understanding, together with balancing factors such as milder conditions, fast process, selectivity and less toxic products.
  • No Thumbnail Available
    Item
    Supramolecular kinetic effects by pillararenes: the synergism between spatiotemporal and preorganization concepts in decarboxylation reactions†
    (2021) Vieira Silveira, Eduardo; Montecinos, Rodrigo; Scorsin, Leandro; Garcia-Rio, Luis; Medeiros, Michelle; Nascimento, Vanessa; Nome, Faruk; Affeldt, Ricardo F.; Micke, Gustavo A.
    A study about spontaneous decarboxylation reactions of 3-carboxy-1,2-benzisoxazole (CBI) nitrated derivatives (6-NitroCBI and 5,6-DinitroCBI) compared with supramolecular kinetic effects promoted by two cationic pillararenes (P5A and P6A) has been carried out and brings contributions to advance current theories related to supramolecular and enzymatic catalysis/inhibition. A higher energy barrier to spontaneous hydrolysis of 6-NitroCBI relative to that of 5,6-DinitroCBI (Delta Delta G(double dagger) = 2.98 kcal mol(-1)) was determined experimentally, however similar transitions states were observed for both substrates. The host-guest complexes generated catalytic effects up to 7.1-fold on k(obs), except for 6-NitroCBI subset of P5A which is the only system that presented unprecedent inhibitory kinetic effects. The data (kinetics, H-1 NMR titration and molecular dynamic simulations) elucidated the kinetic effects of the four complexes as a result of their geometries, more specifically, by modifying 3 main factors: (1) number of hydrogen bonds between solvent and carboxyl groups of the CBIs, (2) polarization of the O-N bond of the isoxazole ring and (3) reduction of the inductive effect of NO2 groups by field effects. The data from the present study encourage the use of both spatiotemporal and preorganization theories during interpretations related to supramolecular and enzymatic catalysis.
  • Thumbnail Image
    Item
    Supramolecular phosphate transfer catalysis by pillar[5]arene
    (2016) Liz, Daiane G.; Manfredi, Alex M.; Medeiros, Michelle; Montecinos Escobar, Rodrigo Andrés; Gómez-González, Borja; García Río, Luis; Nome, Faruk