Automated capillary electrophoresis with on-line preconcentration by solid phase extraction using a sequential injection manifold and contactless conductivity detection

An extension of a capillary electrophoresis instrument coupled to a sequential injection analysis manifold was developed for automated measurements with on-line solid-phase extraction preconcentration. An in-house built capacitively coupled contactless conductivity detector was employed for sensitive detection with narrow capillaries of 25 μm internal diameter. The system was assembled into standardized 19 in. frames and racks for easy transport and mobile deployment. The system can be left running unattendedly without manual intervention with good operation stability. To demonstrate the application of the system, a method for the determination of four drugs, namely ibuprofen, diclofenac, naproxen and bezafibrate, was developed with enrichment factors of up to several hundreds. Detection of the drug residues down to the nM-scale was found possible and the method was found suitable for the detection of ibuprofen in the waste water of a hospital in Hanoi.     

First-principles calculations of stable local structures and electronic structures of magnesium secondary battery cathode materials,MgCo2−xMnxO4 (x = 0, 0.5), in second charged state after first discharge

Journal of Solid State Electrochemistry - The stable structures associated with the second charge of MgCo2−xMnxO4 (x = 0, 0.5), where Mg is removed from the stable first-discharge...     

SYNTHESIS OF SOME NEW 4-AMINO-1,2,4-TRIAZOLE DERIVATIVES AS POTENTIAL ANTI-HIV AND ANTI-HBV

Some novel [1,2,4]triazolo[3,4-b][1,3,4]thiadiazolylisoindole-1,3-dione 2a–c were prepared by heating 4-amino-5-aryl-1,2,4-triazole-3-thiones 1a–c with different (1,3-dioxo-1,3-dihydro-isoindol-2-yl) carboxylic acids in POCl₃. Compounds 2a, b were hydrolyzed using HCl to yield [1,2,4]triazolo[3,4-b][1,3,4]thiadiazolyl-alkylamines 3a, b. Coupling 1a, c with 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide (ABG) afforded the corresponding S-glucosides 4a, b, which on oxidation with KMnO₄ gave the corresponding sulfone 5. Treatment 1b, c with diphenyl diazomethane afforded benzhydrylsulfanyltriazolylamines 7a, b. 1,8-Bis-(4-chloro-phenyl)-bis[1,2,4]triazolo[3,4-c-,4′,3′-e][1,2,4,5]dithiadiazine 8 was formed by oxidation of 1b with lead tetracetate. Compound 1c reacted with morpholine in the presence of KI and I₂ to give the triazolodisulfide ⁹ El-Barbary, A. A., Fahmy, M., El-Badawi, M., El-Brembaly, K. and El-Brollosi, N. R. 1991. Rev. Roum. Chim., 36(619) [Google Scholar].     

Solanopubamine,a rare steroidal alkaloid from Solanum schimperianum: Synthesis of some new alkyl and acyl derivatives,their anticancer and antimicrobial evaluation

Solanopubamine (3β-amino-5α, 22αH, 25βH-solanidan-23β-ol), a steroidal alkaloid was isolated from the alkaloidal fraction of Solanum schimperianum in significant yield. Its structure was established by IR, positive ESI-MS, 1D and 2D NMR. The presence of -3β-NH₂ and -23β-OH groups was achieved through methylation, acetylation or coupling with octadecanoic and undec-11-enoic acids to produce six derivatives (2–7). Their structures were confirmed by spectroscopic analyses. Solanopubamine and semi-synthetic analogs are investigated for their in vitro cytotoxicity against a panel of human cancer cell lines and anti-microbial activity. Solanopubamine showed good antifungal activity only against Candida albicans and C. tenuis with MIC of 12.5 μg/mL. Semi-synthesized compounds (2–7) have failed to show anti-tumor and anti-microbial activities.     

Effect of Discrete Macroion Charge Distributions on Electric Double Layer of a Spherical Macroion

The effect of replacing the conventional uniform macroion surface charge density with discrete macroion charge distributions on the structure of electric double layer (EDL) of a spherical macroion has been investigated by Monte Carlo (MC) simulations. Two discrete models have been investigated in addition to the central macroion charge: point charges localized on the macroion surface and finite-sized charges protruding into the solution. Both models have been studied with fixed and mobile macroion charges. The radial functions of local densities and electrostatic potential in EDL, are calculated and compared to the results obtained for the central macroion charge distribution. It is concluded that the model of charge distribution significantly affects the EDL structure close to the macroion, while the effect is much weaker at larger distances. With point charges localized on the macroion surface, counterions become stronger accumulated to the macroion, as a result the absolute values of surface potential ?₀ and zeta ξ potential are decreased. With protruding charges, the excluded volume effect dominates over the increased correlation ability; hence the counterions are less accumulated near the macroions and the absolute values of ?₀ and ξ potentials are increased.     

Two new cycloartanes from the leaves of Combretum quadrangulare growing in Vietnam and their biological activities

Two new cycloartanes, combretanones G and H (1 and 2), were isolated from the leaves of Combretum quadrangulare. Their structures were elucidated by applying a set of spectroscopic methods, while their relative configurations were determined using DFT-NMR chemical shift calculations and subsequent assignment of DP4 probabilities. Compounds 1 and 2 are C-23/C-24 stereoisomers of the previously-reported euphonerin E. Both exhibited moderate cytotoxicity against three human cancer cell lines. Compound 2 was shown to be a potent antiparasitic. Our results confirm the traditional medicinal uses of Combretum quadrangulare in Vietnam.