Titration of mixtures of acids of nearly equal strengths

Accurate and precise experimental methods that were developed for the purpose of determining stability constants in aqueous solutions are employed in titrations of acids which have nearly equal strengths. A computer program capable of handling five acids simultaneously has been designed to evaluate the titration data. The results show that it is possible to determine two acids which have stability constants differing by only about one logarithmic unit with an accuracy better than 1%. If the conditions are favourable, it is even possible to analyse a mixture of two acids with about 2% accuracy when the constants differ by as little as 0.2 logarithmic units.     

S(H)2 reaction vs hydrogen abstraction/expulsion in methyl radical-methylsilane reactions: effects of prereactive complex formation

A quantum chemical study has been undertaken to elucidate the cause of the recently observed S(H)2 reaction between the deuterated methyl radical (*CD3) and methylsilane (SiD3CH3) following the photolysis of CD3I. [Komaguchi, K.; Norberg, D.; Nakazawa, N.; Shiotani, M.; Persson, P.; Lunell, S. Chem. Phys. Lett. 2005, 410, 1-5.] It is found that the backside S(H)2 mechanism may proceed favorably for C-Si-C angles deviating with up to 40 degrees from linearity. The competitive hydrogen abstraction reaction is predicted to be active in the range of 90 degrees 相似文献   

Limited configuration interaction calculation of the optical spectrum for the permanganate ion

A series of limited configuration interaction calculations based upon an extended basis set is presented for the permanganate ion. The configurations have been selected so that they describe initial and final states equally well, and the size of the expansion has been increased until a reasonable convergence in the results has been assured. Both singlet and triplet states have been treated. Electron density changes occurring at the so-called charge-transfer transitions have been studied, and relaxation turns out to play an important role. The agreement with experimental spectra is satisfactory.     

ESR and theoretical studies of trimer radical cations of coronene

Highly resolved ESR spectra of monomer, dimer and trimer radical cations of coronene (C24H12) were observed at room temperature for a solution of 1,1,1,3,3,3-hexafluoro-2-propan-2-ol (HFP) containing thallium(III) trifluoroacetate as oxidant. The spectra consisting of multiple lines with isotropic 1H-hyperfine splitting (hfs) constants of 0.0766 mT (24H) and 0.013 mT (6H) were attributable to a mixture of the dimer with the trimer radical cations, (C24H12)2+ and (C24H12)3+. For (C24H12)2+, the 1H-hfs constant agreed well with the reported value, 0.077 mT. However, for (C24H12)3+, the values were significantly different from the reported ones, 0.117 mT (12H) and 0.020 mT (24H), by Ohya Nishiguchi et al. [H. Ohya-Nishiguchi, H. Ide, N. Hirota, Chem. Phys. Lett. 66 (1979) 581], but rather similar to those reported by Willigen et al. [H. van Willigen, E. De Boer, J.T. Cooper, W.F. Forbes, J. Chem . Phys. 49 (1968) 1190]. In conflict with Willigen's report, however, no ESR line broadening which has been ascribed to a low stationary concentration of (C24H12)3+ was detected. Based on ab initio MO calculations for benzene as a compact model of C24H12, the structure of (C24H12)3+ was investigated in terms of the observed 1H-hfs constants. A staggered sandwich C(2v) structure was suggested being at the "global" minimum for the benzene trimer cation. In the structure, the unpaired electron spin is predominantly localized to the central ring, which is qualitatively in agreement with the previous ESR results of (C24H12)3+ by Ohya-Nishiguchi et al. In addition, as a "local" minimum, the benzene trimer was indicated to have a slipped sandwich Cs structure, which is less stable by ca. 19 kJ mol(-1) than the "global" minimum. In this structure, the unpaired electron spin was nearly equally distributed on both the central and one of the two side C24H12 molecules. The observed 1H-hfs constants were possibly attributable to the (C24H12)3+ cation with the analogous slipped sandwich Cs structure.     

Two photon QED corrections in helium like highly charged ions

An overview of calculations and measurements of the energy levels of helium-like ions is presented. We focus on the two-photon QED effects, and conclude that measurements of the excited states of large Z helium-like ions are desired. This revised version was published online in August 2006 with corrections to the Cover Date.     

Immobilized lipodisks as model membranes in high-throughput HPLC-MS analysis

Lipodisks, also referred to as polyethylene glycol (PEG)-stabilized bilayer disks, have previously been demonstrated to hold great potential as model membranes in drug partition studies. In this study, an HPLC-MS system with stably immobilized lipodisks is presented. Functionalized lipodisks were immobilized on two different HPLC support materials either covalently by reductive amination or by streptavidin–biotin binding. An analytical HPLC column with immobilized lipodisks was evaluated by analysis of mixtures containing 15 different drug compounds. The efficiency, reproducibility, and stability of the system were found to be excellent. In situ incorporation of cyclooxygenase-1 (COX-1) in immobilized lipodisks on a column was also achieved. Specific binding of COX-1 to the immobilized lipodisks was validated by interaction studies with QCM-D. These results, taken together, open up the possibility of studying ligand interactions with membrane proteins by weak affinity chromatography.     

Production and Kinetics of Swelling in Water of Biocompatible Branched Polyvinyl Alcohol Films

Russian Journal of Applied Chemistry - The interrelation of the synthesis conditions of polyvinyl alcohol chain branching products under the action of epichlorohydrin in an alkaline medium was...     

On the dimerization of chlorophyll in photosystem II

In photosystem II, absorbed light energy is transferred to a reaction centre consisting of chlorophyll units. Release of an electron from the reaction centre is the starting point for the charge separation and electron transport chain in PSII. Crystal structures of the reaction centre have identified two chlorophyll monomers forming a dimer with a partial structural overlap, thus being stabilized by van der Waals interactions. However, the magnitude of this interaction is not accurately known. In this work, the structure of the chlorophyll dimer has been optimized for the first time using dispersion-corrected density functional theory (B3LYP-DCP) revealing the magnitude of dimerization to be approximately -17 kcal mol(-1). The dispersion interaction is shown to be of great significance for the chlorophyll dimer stabilization. In addition, the redox potential of the chlorophyll dimer is calculated to be 1283 mV in good agreement with recent experimental data.