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71.
72.
Lhiaubet-Vallet V Encinas S Miranda MA 《Journal of the American Chemical Society》2005,127(37):12774-12775
Time-resolved measurements using nanosecond laser flash photolysis have revealed significant enantiodifferentiation in the interaction between ketoprofen (a chiral benzophenone derivative) and two relevant nucleosides, namely, thymidine and 2'-deoxyguanosine. In both cases, the highest quenching rate constants have been observed for (R)-ketoprofen, the enantiomer with lower pharmacological activity. Photoproduct studies performed in the case of thymidine suggest that the enantiodifferentiating process corresponds to a Paterno-Büchi reaction, leading to the formation of oxetanes. With 2'-deoxyguanosine, the quenching is associated with an electron-transfer process monitored through the generation of a ketyl radical. 相似文献
73.
A robust tandem HPLC method coupling size-exclusion (Shodex Asahipak GS-320HQ) and reversed phase (Vydac 218TP54) columns with ultraviolet detection was developed for quantitative determination of interferon-gamma (IFN-gamma) in Chinese hamster ovary cell culture supernatant. The 2D-HPLC system was linked up by a 6-port 2-position low hold-up volume switch valve. Compared to a commercial ELISA kit for IFN-gamma, the coupled column LC approach was able to detect and quantify soluble IFN-gamma, regardless of the glycoprotein's molecular/conformational variability and sample background. Each LC-LC analysis took 90 minutes inclusive of column regeneration. The relative standard deviation of measurements (n = 5) was less than 3%. The limit of detection (LOD) was determined to be 0.35 microg IFN-gamma. 相似文献
74.
Netto-Ferreira JC Lhiaubet-Vallet V de Oliveira Bernardes B Ferreira AB Miranda MA 《Photochemistry and photobiology》2009,85(1):153-159
The photochemical reactivity of β-lapachone ( 1 ), nor -β-lapachone ( 2 ) and 1,2-naphthoquinone ( 3 ) towards amino acids and nucleobases or nucleosides has been examined employing the nanosecond laser flash photolysis technique. Excitation (λ = 355 nm) of degassed solutions of 1 – 3 , in acetonitrile, resulted in the formation of their corresponding triplet excited states. These transients were efficiently quenched by l -tryptophan, l -tryptophan methyl ester, l -tyrosine, l -tyrosine methyl ester and l -cysteine ( k q ≈ 109 L mol−1 s−1 ). For l -tryptophan, l -tyrosine and their methyl esters new transients were formed in the quenching process, which were assigned to the corresponding radical pair resulting from an initial electron transfer from the amino acids or their esters to the excited quinone, followed by a fast proton transfer. No measurable quenching rate constants could be observed in the presence of thymine and thymidine. On the other hand, efficient rate constants were obtained when 1 – 3 were quenched by 2'-deoxyguanosine ( k q ≈ 109 L mol−1 s−1 ). The quantum efficiency of singlet oxygen (1 O2 ) formation from 1 to 3 was determined employing time-resolved near-IR emission studies upon laser excitation and showed considerably high values in all cases (ΦΔ = 0.6), which are fully in accord with the ππ* character of these triplets in acetonitrile. 相似文献
75.
Photocyclization of 2-chloroacetyl-1,2,3,4,5,6-hexahydro-1, 5-methanoazocino[4,3-b]indole () takes place at the indole 4-position to give a 1 ,2 ,3 ,4 , 5 ,6-hexahydro-2 ,11-ethano-1 ,5-methanoazocino [4 , 3-6] indole system. Consequently, the method appears to be unsuitable for constructing the pyrrolidine ring of pentacyclic Strychnos indole alkaloids. 相似文献
76.
The standard (p(o) = 0.1 MPa) molar enthalpy of formation of crystalline 2H-1,3-benzoxazine-2,4(3H)dione was measured, at T= 298.15 K, by static bomb calorimetry and the standard molar enthalpy of sublimation, at T= 298.15 K, was obtained using Calvet microcalorimetry. These values were used to derive the standard molar enthalpy of formation in the gaseous phase, T= 298.15 K, of -(401.0 +/- 3.5) kJ mol(-1). The standard molar enthalpy of sublimation of isatoic anhydride was recalculated, and our recommended experimental value for the standard molar enthalpy of formation in the gaseous phase, T= 298.15 K, is -(406.2 +/- 3.4) kJ mol(-1). Density functional calculations for the two isomers 2H-1,3-benzoxazine-2,4(3H)dione and isatoic anhydride, in which the ring nitrogen and oxygen have been transposed, confirm the experimental evidence of nearly identical thermochemical stability for these isomers. 相似文献
77.
Pérez-Prieto J Galian RE Miranda MA Catalina F Martín-Vargas N López-Ortiz F 《Organic letters》2004,6(4):561-564
[reaction: see text] Several benzo[d]-1,2-oxaphosphole 2-oxides were examined as potential precursors of stabilized C-centered radicals. The transient absorption spectra obtained after laser flash photolysis in the presence of di-tert-butyl peroxide showed the features of benzylic radicals with formation and decay kinetics not significantly influenced by the presence of oxygen. In the case of compounds with two possible diastereomeric forms, the C-H bond of the trans-isomers [corrected] is more reactive toward hydrogen abstraction. 相似文献
78.
Jambrina PG Aldegunde J de Miranda MP Sáez-Rábanos V Aoiz FJ 《Physical chemistry chemical physics : PCCP》2012,14(28):9977-9987
This article presents a methodology for the determination of the k-j-k' three-vector correlation assuming a statistical model for atom-diatom reactions; k and k' are the reagent-approach and product-recoil directions, respectively, and j is the rotational angular momentum of the reagent diatomic. Although the polarization of reagent angular momentum is in most cases negligible, conservation of the triatomic parity imposes a certain polarization for some combinations involving low reagent and product rotational states. Statistical and quantum-mechanical polarization-dependent differential cross sections were calculated for the barrierless D(+) + H(2)(v = 0,j) → HD(v' = 0,j') + H(+) reaction. The agreement between the two is in most cases excellent, confirming the statistical character of the reaction at low and moderate collision energies. 相似文献
79.
Santamaria R Mondragón-Sánchez JA Bokhimi X 《The journal of physical chemistry. A》2012,116(14):3673-3680
We investigate the behavior of a model methane clathrate cage under high hydrostatic pressures. The methane clathrate cage consists of 20 water molecules forming 12 pentagonal faces, with a methane molecule positioned at the cage center. The clathrate compound is located inside a fullerene-type arrangement of 180 He atoms to simulate an isotropic pressure. Different pressures are simulated by decreasing the radius of the He array. The minimal energy of the total system for each configuration is calculated by using density functional theory. The variation of the energy with the volume of the imprisoned clathrate cage leads to the proposal of a (cold) equation of state in the pressure range [0,60] GPa. The elastic parameters of the state equation are found in agreement with equivalent quantities measured on clathrates in their sI conformation. Special attention is given to the distribution of the confined atoms and the eventual symmetry lost from the clathrate cage with the pressure, as the clathrate cage constitutes a basic structural unit of the crystal. Finally, the strengths and limitations of the model are discussed. 相似文献
80.
Sharpe RB Burdinski D Huskens J Zandvliet HJ Reinhoudt DN Poelsema B 《Langmuir : the ACS journal of surfaces and colloids》2007,23(3):1141-1146
Self-assembled monolayers were investigated for their suitability as two-dimensional scaffolds for the selective growth of alkanethiol edge structures. Heterostructures with chemical contrast could be grown, whose dimensions were governed by both the initial pattern sizes and the process time. n-Octadecanethiol (ODT) was made to expand from the edges of 16-mercaptohexadecanoic acid (MHDA) monolayer patterns. Likewise, 11-mercaptoundecanol (MUD) was grown on MHDA and on ODT monolayer edges. The results of these experiments are in accordance with the moving boundary model for monolayer spreading. In addition to such surface-bound spreading, a vapor-phase contribution to lateral monolayer growth was identified. MUD was observed to be an excellent ink for creating chemical contrast by means of regioselective deposition from a vapor phase. As a proof of principle, ribbons of 11-mercaptoundecanol with submicrometer widths were grown on pentaerythritol-tetrakis(3-mercaptopropionate) edges, and submicrometer wide gold lines were produced by subsequent wet-chemical etching. 相似文献