Determination of total mercury and methylmercury in human hair by graphite-furnace atomic absorption spectrophotometry using 2,3-dimercaptopropane-1-sulfonate as a complexing agent.

For the determination of total mercury in hair, an amount (25.0 mg) of hair sample was digested with conc. HNO3 (400 microl) at 90 degrees C for 10 min in a 7-ml teflon microreaction vessel. After digestion, the pH of the acidic hair mixture was adjusted to 5.0-6.0 by NaOH and was then passed through a clean-up Sep-Pak C18 cartridge. To the eluate, 2,3-dimercaptopropane-1-sulfonate (DMPS) and sodium acetate buffer (pH = 6.0) were added to form a mercury-DMPS complex. This complex was preconcentrated on two Sep-Pak C18 cartridges in series, and each cartridge was eluted with methanol and adjusted to 2.00 ml. A portion (50 microl) was introduced into a graphite cuvette and then atomized according to a temperature program. The method detection limit (MDL, 3sigma) was 0.064 (microg g(-1)); the calibration graph was linear up to 7.52 microg g(-1). Good accuracies were obtained when testing two human hair certified reference materials (GBW 09101 and BCR-397). Six real samples were analyzed, and the recoveries were 95.8 - 98.2% with a relative standard deviation (RSD, n = 3) < 2.1%. For the determination of methylmercury (CH3Hg+), 25.0 mg of hair sample was extracted with 2.0 mol dm(-3) HCl (1.0 ml) by ultrasonicating for 1 h. The supernatant solution was used for CH3Hg+ analysis and the hair residue was used for the analysis of inorganic mercury (Hg2+). The MDL of CH3Hg+ was 0.068 microg g(-1); the calibration graph was linear up to 6.00 microg g(-1). Six real samples were analyzed, and the recoveries were 96.0-99.2% with RSD (n = 3) < 2.3%. The sum of the concentrations of CH3Hg+ and Hg2+ was very close to that of the total mercury measured with a relative error within 3.6%. The proposed method can be accurately applied to the measurement of CH3Hg+, Hg2+, and total mercury in hair samples.     

Determination of nalidixic acid by fluorometry with sodium borohydride and hydrogen peroxide

A simple and sensitive fluorometric method for the determination of nalidixic acid was established by using 0.75M sodium borohydride and 7.5% hydrogen peroxide solution as fluorogenic reagents. Analyte concentrations of 0.0232-11.6 pg/mL could be determined with high precision and accuracy by the method. A relative standard deviation of 1.75% was obtained for a nalidixic acid concentration of 0.232 pg/mL. The method was satisfactorily applied to the determination of nalidixic acid in human serum, fish muscle, and chicken muscle, and the calibration curves were linear from 0.23 to 58.00 pg/mL, from 9.28 to 32.48 mg/kg, and from 4.64 to 23.20 mg/kg, respectively. The specificity of the reaction is also discussed.     

Silica nanoparticles for separation of biologically active amines by capillary electrophoresis with laser-induced native fluorescence detection

This paper describes the analysis of biologically active amines by capillary electrophoresis (CE) in conjunction with laser-induced native fluorescence detection. In order to simultaneously analyze amines and acids as well as to achieve high sensitivity, 10 mM formic acid solutions (pH < 4.0) containing silica nanoparticles (SiNPs) were chosen as the background electrolytes. With increasing SiNP concentration, the migration times for seven analytes decrease as a result of increase in electroosmotic flow (EOF) and decrease in their electrophoretic mobilities against EOF. A small EOF generated at pH 3.0 reveals adsorption of SiNPs on the deactivated capillary wall. The decreases in electrophoretic mobilities with increasing SiNP concentration up to 0.3x indicate the interactions between the analytes and the SiNPs. Having a great sensitivity (the limits of detection at a signal-to-noise ratio (S/N) = 3 of 0.09 nM for tryptamine (TA)), high efficiency, and excellent reproducibility (less than 2.4% of the migration times), this developed method has been applied to the analysis of urinal samples with the concentrations of 0.50 +/- 0.02 microM, 0.49 +/- 0.04 microM, and 74 +/- 2 microM for TA, 5-hydroxytryptamine, and tryptophan, respectively. The successful examples demonstrated in this study open up a possibility of using functional nanoparticles for the separation of different analytes by CE.     

Migration behavior and enantioseparation of hydrobenzoin and structurally related compounds in capillary zone electrophoresis with a dual cyclodextrin system consisting of heptakis-(2,3-dihydroxy-6-O-sulfo)-beta-cyclodextrin and beta-cyclodextrin

Migration behavior and enantioseparation of racemic hydrobenzoin and structurally related compounds, including benzoin and benzoin methyl ether, in CZE with a dual CD system consisting of heptakis-(2,3-dihydroxy-6-O-sulfo)-beta-CD (SI-S-beta-CD) and beta-CD as chiral selectors in the presence and absence of borate complexation at pH 9.0 were investigated. The results indicate that enantioseparation of hydrobenzoin is mainly governed by CD complexation of hydrobenzoin-borate complexes with SI-S-beta-CD when SI-S-beta-CD concentration is relatively high. Whereas CD complexation of hydrobenzoin-borate complexes with beta-CD plays a significant role in enantioseparation when SI-S-beta-CD concentration is comparatively low. The (S,S)-enantiomer of the hydrobenzoin-borate complex was found to interact more strongly than the corresponding (R,R)-enantiomer with both SI-S-beta-CD and beta-CD. These two types of CD show the same chiral recognition pattern, but they exhibit opposite effects on the mobility of the enantiomers of hydrobenzoin-borate complexes. Enantiomer migration reversal of hydrobenzoin occurred in the presence of borate complexation when varying the concentration of beta-CD, while keeping SI-S-beta-CD at a relatively low concentration. Binding constants of the enantiomers of benzoin-related compounds to beta-CD and those of hydrobenzoin-borate complexes to SI-beta-CD were evaluated; the mobility contributions of all complex species to the effective mobility of the enantiomers of hydrobenzoin as a function of beta-CD concentration in a borate buffer were analyzed. In addition, comparative studies on the enantioseparation of benzoin-related compounds with SI-S-beta-CD and with randomly sulfate-substituted beta-CD were made.     

An Efficient Synthesis of 8-Amino-9-Benzylguanine

The reaction of 2,5-diamino-4-benzylamino-pyrimidin-6(III)-one (6) with benzoyl isothiocyanate furnished 2-amino-4-benzylamino-5-[1-(3-benzoylthioureido)]-pyrimidin-6(1H)-one (7) in good yield. The title compound I was synthesized from compound 7 via a cyclodesulfurative reaction with DCC in DMF at 80°C directly to form 8-benzoylamino-9-benzylguanine (9) which was subsequently treated with 1 N sodium hydroxide.     

Cooperatively assembled liquid crystals enable temperature-controlled Förster resonance energy transfer

Balancing the rigidity of a π-conjugated structure for strong emission and the flexibility of liquid crystals for self-assembly is the key to realizing highly emissive liquid crystals (HELCs). Here we show that (1) integrating organization-induced emission into dual molecular cooperatively-assembled liquid crystals, (2) amplifying mesogens, and (3) elongating the spacer linking the emitter and the mesogen create advanced materials with desired thermal–optical properties. Impressively, assembling the fluorescent acceptor Nile red into its host donor designed according to the aforementioned strategies results in a temperature-controlled Förster resonance energy transfer (FRET) system. Indeed, FRET exhibits strong S-curve dependence as temperature sweeps through the liquid crystal phase transformation. Such thermochromic materials, suitable for dynamic thermo-optical sensing and modulation, are anticipated to unlock new and smart approaches for controlling and directing light in stimuli-responsive devices.

A temperature-sensitive Förster resonance energy transfer system was constructed using a highly emissive liquid crystal co-assembled with Nile red, enabling thermo-optical modulation for controlling and directing light in stimuli-responsive devices.     

Tasumatrols P – T,Five New Taxoids from Taxus sumatrana

The phytochemical investigation of the more polar fractions from the leaves and twigs of Taxus sumatrana (Taxaceae) afforded five new taxane diterpene esters, tasumatrols P–T ( 1 – 5 ) possessing an 11(15→1),11(10→9)‐diabeotaxane skeleton. Compounds 1, 4 , and 5 contain an α‐hydroxy group at C(14), while 3 has no OH group at either C(13) or C(14). Compound 2 is a natural 4,5‐acetonide derivative, while 4 has an unusual spiro‐connected 2‐hydroxy‐2‐phenyl‐1,3‐dioxolane ring. Ten known taxoids, were also isolated in the course of the chromatographic fractionation. Five additional new O‐acetyl derivatives 3a, 4a, 4b, 5a , and 5b were prepared from the taxanes 3 – 5 . The structures of all new compounds were established on the basis of their spectroscopic analyses. Compound 1 showed mild cytotoxic activity against human Hela and Daoy tumor cells.     

吡咯和呋喃气相质子化过程的密度泛函理论研究

Density functional theory and ab initio calculations have been used to determine structures and stabilities of the protonated aromatics species AH^＋ and AH2^2＋ （A=pyrrole, furan）. Possible mechanisms and relative energetics for protonation of pyrrole and furan by H3O^＋ and AH^＋ in the gas phase have been explored. Calculations show that the Cα-protonated species was the most stable structure for AH^＋, and the protonated AH^＋ might accommodate the second proton to yield AH2^2＋ if the free proton was available. The gas-phase H3O^＋ could protonate pyrrole and furan with significant exothermiCity and almost without barrier. The proton transfer from AH4^＋ to pyrrole and furan has a barrier ranging from 33.5 to 39.3 kJ/mol in the gas phase.     

An algorithm for the calculation of the electrostatic repulsion between surface coated with a charge membrane

We propose a numerical procedure for the calculation of the electrostatic repulsion force between two identical, parallel surfaces immersed in anab electrolyte solution. These surfaces are coated with an ion-penetrable membrane carrying fixed charges. The amount of fixed charges is governed by the dissociation of the functional groups in the membrane phase. The effect of pH on the degree of dissociation of these functional groups is taken into account. The difficulty of extensive use of Jacobi elliptic function in the numerical treatment of Poisson-Boltzmann equation can be circumvented by resorting to the present algorithm.