Archaeology and ecotourism potential of the Chácara Columbia in São Bernardo do Campo (SP, Brazil)

Diagnóstico prospectivo arqueológico realizado na Chácara Columbia, município de São Bernardo do Campo, São Paulo, em 2009. Relatório dos trabalhos entregue ao IPHAN-SP indica a existência de um sítio arqueológico com diferentes ocupações, possivelmente de diferentes épocas de povos ceramistas em função de dois tipos distintos de fragmentos cerâmicos encontrados. Há também a possibilidade desse sítio ter sido um local de passagem, talvez um sítio histórico, devido à existência de fragmentos de louça (?) ou porcelana (?), uma com as inscrições “P II”, “Rio de Janeiro” e o “Brasão do Império”. Foi encontrado também um depósito de carapaças de conchas de moluscos, provavelmente de origem marinha, no interior de uma das quadras escavadas. O artigo apresenta proposta de criação de um museu de sítio para uso ecoturístico

Autoxidation of a model membrane. A comparison of the autoxidation of egg lecithin phosphatidylcholine in water and in chlorobenzene [12]

Peer reviewed: YesNRC publication: Ye

Autoxidation of biological molecules. 2. The autoxidation of a model membrane. A comparison of the autoxidation of egg lecithin phosphatidylcholine in water and in chlorobenzene

The kinetics of the autoxidation of egg lecithin phosphatidylcholine in homogeneous solution in chlorobenzene and as a bilayer dispersion in 0.1 M aqueous NaCl has been studied at 30\ub0C under 760 torr of O2. The autoxidations were initiated by the thermal decomposition of di-tert-butyl hyponitrite. The efficiency of chain initiation, e, was determined by the induction period method using \u3b1-tocopherol as the chain-breaking antioxidant. In chlorobenzene e was ca. 0.66 but in the aqueous dispersion e was only ca. 0.091. The reduced efficiency of initiation in the bilayer is attributed to a reduction in the fraction of tert-butoxyls which escape from the solvent cage, and this in turn is due to the fact that the bilayer has a high microviscosity. The rate of autoxidation of the egg lecithin in chlorobenzene is proportional to the lecithin concentration and to the square root of the rate of chain initiation, and is virtually independent of the oxygen pressure, which means that this autoxidation follows the usual kinetic rate law. In the aqueous dispersion the concentration of egg lecithin in the bilayer cannot be altered, but since the rate of autoxidation is proportional to the square root of the rate of chain initiation and is virtually independent of the oxygen pressure, the usual kinetic rate law would also appear to be followed. The oxidizability of egg lecithin in chlorobenzene is 0.61 M-1/2 s-1/2, and in the aqueous dispension it is 0.0165 M-1/2 s-1/2. The reduction in oxidizability in the bilayer is attributed to the diffusion of the peroxyl radical center, which is a polar moiety, out of the autoxidizable, nonpolar, interior region of the bilayer and into the nonautoxidizable, polar surface region. As a consequence, chain progogation will be retarded and chain termination will be accelerated. \ua9 1981 American Chemical Society.Peer reviewed: YesNRC publication: Ye

Kinetic applications of electron paramagnetic resonance spectroscopy. XX. 2,4,6-Tri(tert-butyl)benzyl, -anilino, -phenoxy, and -phenylthiyl radicals

The title radicals have been generated, and their kinetic behavior has been examined. The EPR parameters for the benzyl and anilino radicals indicate that the benzylic and amino hydrogens are coplanar with the aromatic rings. The benzyl radical decays rapidly with second-order kinetics (k = (5 \ub1 2) 7 108 M-1 sec-1 at 24\ub0) to give the bibenzyl. The anilino radical exists in equilibrium with the hydrazine (\u394H = -13.1 \ub1 0.5 kcal/mol, \u394S = -27 \ub1 2 gibbs/mol). The rate constant for anilino decay to its dimer can be represented by log (k-1/M-1 sec-1) = 6.3(\ub11.0) - 2.5(\ub10.8)/\u3b8, where \u3b8 = 2.3RT kcal/mol, and that for decomposition of dimer to two anilino radicals by log (k1/sec-1) = 12.2 - 15.6/\u3b8. The phenylthiyl radical is also in equilibrium with its dimer at ambient temperatures (\u394H = -23.3 kcal/mol), but the phenoxy radical shows no sign of dimerization even at -100\ub0. The behavior of these four radicals is discussed in terms of the strengths of the bonds formed by head-to-head dimerization.Peer reviewed: YesNRC publication: Ye

The 2,4,6-tri-tert-butylphenyl radical [14]

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Mechanism of rearrangement of \u3b2-(acyloxy)alkyl radicals

Rate constants for the free radical rearrangement, CF 3C(O)OCMe 2\u10aH 2 (1d) \u2192 CF 3C(O)OCH 2\u10aMe 2 (2d), have been measured in CF 2ClCFCl 2 by kinetic EPR spectroscopy. This reaction is very significantly faster (k 1 75\ub0C = 7.0 7 10 4 s -1) than the related rearrangement, CH 3C(O)OCMe 2\u10aH 2 (1a) \u2192 CH 3C(O)OCH 2\u10aMe 2 (2a) (k 1 75\ub0C = 4.5 7 10 2 s -1), in hydrocarbon solvents. The potential cyclic intermediate radical, 2-(trifluoromethyl)-4,4-dimethyl-1,3-dioxolan-2-yl (3d), does not undergo ring opening to 2d, at temperatures where the 1d \u2192 2d rearangement is very fast. It is concluded that 3d is not an intermediate in the trifluoroacetoxyl migration. It is also concluded on the basis of the k 1 values for 1a and 1d that these rearrangements involved a charge-separated transition state. The 1a \u2192 2a rearrangement is very much faster in water (k 1 75\ub0C = 2.1 7 10 4 s -1) than in hydrocarbon solvents, which provides additional support for a charge-separated transition state.Peer reviewed: YesNRC publication: Ye

Kinetic applications of electron paramagnetic resonance spectroscopy. 38. Rearrangement of \u3b2-(acyloxy)alkyl and \u3b2-(benzoyloxy)alkyl radicals

Rate constants for the free-radical rearrangement, RC(O)OCMe2CH2 \u2192 RC(O)OCH2CMe2, and for the ring-opening reaction, R\u10aOCH2CMe2O \u2192 RC(O)OCH2\u10aMe2, have been measured by kinetic EPR spectroscopy. In hydrocarbon solvents at 75\ub0C with R = methyl and phenyl, the 1,2-acyloxy migrations are slower (k = 5.1 7 102 s-1 and 2.5 7 102 s-1, respectively) than the corresponding 1,3-dioxolan-2-yl ring openings (k = 7.6 7 103 s-1 and 1.0 7 103 s-1, respectively). The formation of a 1,3-dioxolan-2-yl radical as an intermediate in these two rearrangements could not, therefore, be ruled out. However, with R = cyclopropyl, the rearrangement proceeded normally (k 48 1.2 7 102 s-1 at 75\ub0C), but the corresponding 1,3-dioxolan-2-yl radical underwent opening of the cyclopropyl ring rather than the dioxolanyl ring. Since this process occurred at a much faster rate (k = 8.7 7 105 s-1 at 75\ub0C) than the rearrangement, the dioxolanyl radical cannot, in this case at least, be an intermediate in this acyloxy migration. The possible role of charge separation in the transition state for acyloxy migration is considered. \ua9 1982 American Chemical Society.Peer reviewed: YesNRC publication: Ye

Kinetic applications of electron paramagnetic resonance spectroscopy. 26. Quantum-mechanical tunneling in the isomerization of sterically hindered aryl radicals

Rate constants for the isomerization of 2,4,6-tri-tert-butylphenyl to 3,5-di-tert-butylneophyl have been measured from -26 to -160 \ub0C, and for the corresponding isomerization of 2,4,6-tri-tert-(perdeuteriobutyl)phenyl from 20 to -150 \ub0C. This pair of reactions has an exceptionally large deuterium kinetic isotope effect at all temperatures. Arrhenius plots for both reactions are nonlinear and over any range of temperature the activation energy and Arrhenius preexponential factor are much larger for deuterium than for hydrogen transfer. The experimental results can be quantitatively accounted for by quantummechanical tunneling through a potential barrier. The analogous isomerization of 2,4,6-tri(1\u2032-adamantyl)phenyl, which was studied from -28 to -167 \ub0C, also occurs by quantum-mechanical tunneling. Attempts to detect other aryl radicals by EPR spectroscopy are described.Peer reviewed: YesNRC publication: Ye

Kinetic applications of electron paramagnetic resonance spectroscopy. 32. Further studies of quantum-mechanical tunneling in the isomerization of sterically hindered aryl radicals

The isomerization of 2,4,6-tri-tert-butylphenyl, which occurs by quantum-mechanical tunneling of a hydrogen atom from an ortho tert-butyl group,5 occurs at the same rate in matrices as in solution. The rate of this process has been measured at temperatures down to 28 K. At such low temperatures the rate is virtually independent of temperature. Tri-tert-(perdeuteriobutyl)phenyl decays by deuterium atom tunneling at the same rate in matrices as in solution. A number of less hindered aryls decay by intermolecular hydrogen abstraction from the surrounding medium. However, octamethyloctahydroanthracen-9-yl decays by intramolecular hydrogen tunneling, even though the corresponding deuterated radical decays by reaction with the solvent. \ua9 1978 American Chemical Society.Peer reviewed: YesNRC publication: Ye