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981.
982.
983.
Mechanochemical reaction of solid piracetam with the inorganic salts LiCl and LiBr yields ionic co-crystals which are also co-drugs, characterized by markedly different thermal properties with respect to pure components, also depending on the method for preparation and/or conditions of measurements; single crystal and powder X-ray diffraction at variable temperatures, DSC, TGA, hot stage microscopy (HSM) and intrinsic dissolution rate have been used to fully characterize the solid products.  相似文献   
984.
Covalent attachment of thiolated probes to conducting polymers such as polyaniline (PANI) is a promising approach towards the development of electrochemical sensors and biosensors. However, thiolation alters the conjugated polymer backbone and influences the electrochemical behavior of the conducting polymer. PANI studied in this work was electropolymerized on glassy carbon (GC) electrodes from a solution of 0.1 M aniline in 0.5 or 1.0 M H2SO4. The GC/PANI electrodes were then functionalized by covalent attachment of 2-mercaptoethanol to the PANI backbone. The progress of thiolation was studied by cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Thiolation of PANI was found to cause an initial decrease in electroactivity at 0–0.25 V and an increase in electroactivity at 0.25–0.6 V. However, prolonged thiolation caused a loss of electroactivity of PANI, which could be seen from EIS measurements as a dramatic decrease in the bulk redox capacitance of PANI.  相似文献   
985.
Immunizing: to evoke highly potent immune responses against recombinant antigens, hollow capsules consisting of layers of dextran sulphate and poly-L-arginine that encapsulate the antigen ovalbumin (orange circles) were coated with immune-activating CpG-containing oligonucleotides (green). These capsules were readily internalized by dendritic cells and showed activity in further immunization experiments.  相似文献   
986.
987.
Kinetic and thermodynamic properties of the aminoxyl (NH2O*) radical   总被引:1,自引:0,他引:1  
The product of one-electron oxidation of (or H-atom abstraction from) hydroxylamine is the H2NO* radical. H2NO* is a weak acid and deprotonates to form HNO-*; the pKa(H2NO*) value is 12.6+/-0.3. Irrespective of the protonation state, the second-order recombination of the aminoxyl radical yields N2 as the sole nitrogen-containing product. The following rate constants were determined: kr(2H2NO*)=1.4x10(8) M-1 s-1, kr(H2NO*+HNO-*)=2.5x10(9) M-1 s-1, and kr(2HNO-*)=4.5x10(8) M-1 s-1. The HNO-* radical reacts with O2 in an electron-transfer reaction to yield nitroxyl (HNO) and superoxide (O2-*), with a rate constant of ke(HNO-*+O2-->HNO+O2-*)=2.2x10(8) M-1 s-1. Both O2 and O2-* seem to react with deprotonated hydroxylamine (H2NO-) to set up an autoxidative chain reaction. However, closer analysis indicates that these reactions might not occur directly but are probably mediated by transition-metal ions, even in the presence of chelators, such as ethylenediamine tetraacetic acid (EDTA) or diethylenetriamine pentaacetic acid (DTPA). The following standard aqueous reduction potentials were derived: E degrees (H2NO*,2H+/H3NOH+)=1.25+/-0.01 V; E degrees (H2NO*,H+/H2NOH)=0.90+/-0.01 V; and E degrees (H2NO*/H2NO-)=0.09+/-0.01 V. In addition, we estimate the following: E degrees (H2NOH+*/H2NOH)=1.3+/-0.1 V, E degrees (HNO, H+/H2NO*)=0.52+/-0.05 V, and E degrees (HNO/HNO-*)=-0.22+/-0.05 V. From the data, we also estimate the gaseous O-H and N-H bond dissociation enthalpy (BDE) values in H2NOH, with BDE(H2NO-H)=75-77 kcal/mol and BDE(H-NHOH)=81-82 kcal/mol. These values are in good agreement with quantum chemical computations.  相似文献   
988.
Strong electrolytes are described in the framework of the primitive model in which the solvent is regarded as a dielectric continuum, using the mean spherical approximation. The analytical solution of the equilibrium and transport properties is dependent on the ions' diameters and valencies. For hydrated or nonspherical ions, an effective diameter must be fitted. A sensitivity study of the osmotic coefficient and the transport coefficients is performed on theoretical 1-1, 2-1, and 3-1 electrolytes, up to a total ion concentration of 2 mol/L.  相似文献   
989.
As it has been shown by pump-probe experiments electron injection at the interface between a dye molecule and mesoporous TiO2 proceeds with rates exceeding 1 x 10(13) s(-1). However, similar dye-TiO2 systems exhibit residual dye emission with lifetimes extending into the long nanosecond range. To address this inhomogeneity of injection rates time-correlated single photon counting microscopy was used to compare the emission behavior of dye-sensitized mesoporous films of TiO2 with that of individual anatase nanoparticles that had undergone extensive dialysis. The sensitized films produce intense residual emission with multiexponential decay components as long as 220 ns. The channels of mesoporous films contain physisorbed and trapped dye, which is the dominant source of the emission. It is likely that the wide range of lifetimes reflects the distribution of mean free paths experienced by the loose dye molecules diffusing within the film prior to undergoing oxidative quenching. In contrast, the intensity of emission from individual nanoparticles from which the loose dye was removed by dialysis is orders of magnitude lower. The lifetimes obtained from such particles are much shorter, with the primary component on a sub-nanosecond time scale. The presence of residual emission with a 230 ps lifetime shows that even on the surfaces of dialyzed nanoparticles there is a fraction of sensitizer molecules that do not inject electrons with the same high rate as is observed in ultrafast pump-probe experiments on films. Since the physisorbed dye was removed from these samples by dialysis, the residual emission is likely to originate from dye molecules bound to surface defects. Unusual collective emission bursts were observed in some of the measurements on sensitized nanoparticles. We attribute this behavior to stimulated emission from individual nanocrystallites.  相似文献   
990.
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