Prediction of paper permanence by accelerated aging II. Comparison of the predictions with natural aging results

Accelerated aging tests are credible and useful to predict paper permanence only if such tests can be shown to correlate with natural aging. In the first part of this study, a kinetic model was developed based on the accelerated aging results. In this report, we have shown that this kinetic model can indeed predict the natural aging results of lignin-free sheets with a statistical confidence. This is the first quantitative comparison of accelerated aging with natural aging.     

On-column amperometric detection in capillary electrophoresis with an improved high-voltage electric field decoupler

The analysis of polyamide-6 oligomers and polymer is usually performed with expensive fluorinated alcohols like 2,2,2-trifluoroethanol (TFE) or 1,1,1,3,3,3-hexafluoroisopropanol (HFIP). Formic acid is well known as a mobile phase additive to adjust pH in reversed-phase high-performance liquid chromatography. However, formic acid is seldom used as a modifier to perform gradient elution chromatography on octadecyl-modified silica-based columns. Here we demonstrate the determination of cyclic and linear polyamide-6 oligomers using formic acid as a modifier on an octadecyl-modified silica-based column. This column was shown to be stable for more than 5000 column volumes, even when a mobile phase of 65-95% formic acid in water at a flow of 1 ml/min is applied. With formic acid under the conditions used (65-95% formic acid in water) the oligomers are retained on the column, while the polymer does not precipitate. In comparison, during adsorption and separation with a HFIP gradient, precipitation of the polymer occurs. The implications of the different separation mechanisms, i.e., adsorption vs. precipitation chromatography are discussed. Loadability is shown to be much better with the formic acid system. However, with formic acid as a modifier UV detection below 250 nm is not feasible. The less sensitive evaporative light scattering detector is used to detect the polyamide oligomers in the formic acid phase. In addition it is shown that capillary zone electrophoresis (CZE) with UV-absorbance detection using HFIP is an attractive combination as HFIP is UV-transparent and CZE allows low modifier consumption.     

Screening and analysis of bioactive compounds with biofingerprinting chromatogram analysis of traditional Chinese medicines targeting DNA by microdialysis/HPLC

Biofingerprinting chromatogram analysis, which is defined as the comparison of fingerprinting chromatograms of the extract of traditional Chinese medicines (TCMs) before and after the interaction with biological systems (DNA, protein, cell, etc.), was proposed for screening and analysis of the multiple bioactive compounds in TCMs. A method of microdialysis sampling combined with high performance liquid chromatography (HPLC) was applied to the study of DNA-binding property for the extracts of TCMs. Seven compounds were found to bind to calf thymus DNA (ct-DNA) from the TCMs of Coptis chinensis Franch (Coptis), but only three ones from Phellodendron amurense Rupr. (Phellodendron) and none from Sophoraflavescens Ait. (Sophora) to bind to ct-DNA, respectively. Three of them were identified as berberine, palmatine and jatrorrhizine and their association constants (K) to ct-DNA were determined by microdialysis/HPLC. Competitive binding behaviors of them to ct-DNA were also investigated.     

Solution structure and thermolysis of Cobeta-5'-deoxyadenosylimidazolylcobamide, a coenzyme B12 analogue with an imidazole axial nucleoside

The solution structure of Cobeta-5'-deoxyadenosylimidazolylcobamide, Ado(Im)Cbl, the coenzyme B(12) analogue in which the axial 5,6-dimethylbenzimidazole (Bzm) ligand is replaced by imidazole, has been determined by NMR-restrained molecular modeling. A two-state model, in which a conformation with the adenosyl moiety over the southern quadrant of the corrin and a conformation with the adenosyl ligand over the eastern quadrant of the corrin are both populated at room temperature, was required by the nOe data. A rotation profile and molecular dynamics simulations suggest that the eastern conformation is the more stable, in contrast to AdoCbl itself in which the southern conformation is preferred. Consensus structures of the two conformers show that the axial Co-N bond is slightly shorter and the corrin ring is less folded in Ado(Im)Cbl than in AdoCbl. A study of the thermolysis of Ado(Im)Cbl in aqueous solution (50-125 degrees C) revealed competing homolytic and heterolytic pathways as for AdoCbl but with heterolysis being 9-fold faster and homolysis being 3-fold slower at 100 degrees C than for AdoCbl. Determination of the pK(a)'s for the Ado(Im)Cbl base-on/base-off reaction and for the detached imidazole ribonucleoside as a function of temperature permitted correction of the homolysis and heterolysis rate constants for the temperature-dependent presence of the base-off species of Ado(Im)Cbl. Activation analysis of the resulting rate constants for the base-on species show that the entropy of activation for Ado(Im)Cbl homolysis (13.7 +/- 0.9 cal mol(-1) K(-1)) is identical with that of AdoCbl (13.5 +/- 0.7 cal mol(-1) K(-1)) but that the enthalpy of activation (34.8 kcal mol(-1)) is 1.0 +/- 0.4 kcal mol(-1) larger. The opposite effect is seen for heterolysis, where the enthalpies of activation are identical but the entropy of activation is 5 +/- 1 cal mol(-1) K(-1) less negative for Ado(Im)Cbl. Extrapolation to 37 degrees C provides a rate constant for Ado(Im)Cbl homolysis of 2.1 x 10(-9) s(-1), 4.3-fold smaller than for AdoCbl. Combined with earlier results for the enzyme-induced homolysis of Ado(Im)Cbl by the ribonucleoside triphosphate reductase from Lactobacillus leichmannii, the catalytic efficiency of the enzyme for homolysis of Ado(Im)Cbl at 37 degrees C can be calculated to be 4.0 x 10(8), 3.8-fold, or 0.8 kcal mol(-1), smaller than for AdoCbl. Thus, the bulky Bzm ligand makes at best a <1 kcal mol(-1) contribution to the enzymatic activation of coenzyme B(12).     

Large third-order nonlinear optical properties of C70 fullerene in the infrared regime

The nonlinear third-order optical susceptibility of C₇₀ in a toluene solution is measured for the first time by the method of degenerate four-wave mixing using 10 ns laser pulses at 1.06 m. The third-order susceptibility X _in ⁽³⁾ is 5.6×10^–12 esu for a C₇₀ toluene solution at a concentration of 0.476 g/l. The correspondent magnitude of the hyperpolarizability ₁₁₁₁ of the C₇₀ molecule is 1.2×10^–30 esu which is in a good agreement with the prediction given by the model of a free electron in a spherical box.     

基于三维静电势参数研究C60溶解性的构效关系

在量子化学从头算基础上,对一系列溶剂化合物分子进行了结构优化和三维静电势参数计算,运用多元线性回归分析和神经网络方法对C60在121种不同溶剂的溶解性与计算的结构参数进行了构效关系研究.用建立起来的QSPR 关系式对15种不同结构类型溶剂进行了预测,并阐述了C60溶质与不同溶剂之间的相互作用,获得了满意的结果.     

Furostanol saponins with inhibitory action against COX-2 production from Tupistra chinensis rhizomes

Two furostanol saponins were obtained from the n-butanol fraction of methanol extract from Tupistra chinensis rhizomes,a folk medicine of Shennongjia Forest District of Hubei Province.Their structures were determined as (25S)-26-O-(β-D-glucopyranosyl)- furost-1β,3β,22α,26-tetrol-3-O-β-D-glucopyranosyl-(1→4)-β-D-glucopyranosyl-(1→2)-β-D-glucopyranoside (1) and (25R)- 26-O-(β-D-glucopyranosyl)-furost-1β,3β22α,26-tetrol 3-O-β-D-glucopyranosyl-(1→4)-β-D-glucopyranosyl-(1→2)-β-D-glu- copyranoside (2),on basis of chemical and spectroscopic evidences.1 and 2 displayed marked inhibitory action towards COX-2 production in macrophages of the rat abdomen induced by LPS at 20μg/mL.     

Electrochemical and surfaced-enhanced Raman spectroscopic investigation of CO and SCN- adsorbed on Au(core)-Pt(shell) nanoparticles supported on GC electrodes

Core-shell Au-Pt nanoparticles were synthesized by using a seed growth method and characterized by transmission electron microscopy, X-ray diffraction, and UV-vis spectroscopy. Au(core)-Pt(shell)/GC electrodes were prepared by drop-coating the nanoparticles on clean glassy carbon (GC) surfaces, and their electrochemical behavior in 0.5 M H2SO4 revealed that coating of the Au core by the Pt shell is complete. The electrooxidation of carbon monoxide and methanol on the Au(core)-Pt(shell)/GC was also examined, and the results are similar to those obtained on a bulk Pt electrode. High quality surface-enhanced Raman scattering (SERS) spectra of both adsorbed CO and thiocyanate were observed on the Au(core)-Pt(shell)/GC electrodes. The potential-dependent SERS features resemble those obtained on electrochemically roughened bulk Pt or Pt thin films deposited on roughened Au electrodes. For thiocyanate, the C-N stretching frequency increases with the applied potential, yielding two distinctly different dnu(CN)/dE. From -0.8 to -0.2 V, the dnu(CN)/dE is ca. 50 cm(-1)/V, whereas it is 90 cm(-1)/V above 0 V. The bandwidth along with the band intensity increases sharply above 0 V. At the low-frequency region, Pt-NCS stretching mode at 350 cm(-1) was observed at the potentials from -0.8 to 0 V, whereas the Pt-SCN mode at 280 cm(-1) was largely absent until around 0 V and became dominant at more positive potentials. These potential-dependent spectral transitions were attributed to the adsorption orientation switch from N-bound dominant at the negative potential region to S-bound at more positive potentials. The origin of the SERS activity of the particles is briefly discussed. The study demonstrates a new method of obtaining high quality SERS on Pt-group transition metals, with the possibility of tuning SERS activity by varying the core size and the shell thickness.     

Infrared (1.2-1.6 microm) luminescence in Cr4+:Yb3Al5O12 single crystal with 940 nm diode pumping

Infrared (1.2-1.6 microm) luminescence in a ytterbium aluminium garnet (YbAG) crystal, doped with Cr (0.05at.%) ions, was investigated under CW laser diode pumping (lambda=940 nm). The Cr4+ emission band was observed with its peak at 1.34 microm and measured to be about 1.3 times with respect to Yb3+ IR luminescence (lambda=1.03 microm). We demonstrate that for the excitation wavelength of 940 nm Yb3+ ions act as sensitizers of the 3B2(3T2)-3B1(3A2) emission of Cr4+ ions. This crystal is promising as a high-efficient system for tunable laser (1.2-1.6 microm) output.