Synthesis of Quinoline Analogs: Search for Antimalarial Agents

Summary. Novel synthesis routes for the promising antimalarial agents 4(3-hydroxypyrrolidin-1-yl) and 4(3-hydroxypiperidine-1-yl)-2,8-bis(trifluoromethyl)quinoline have been developed.     

Metal-doped ethylene complexes for hazardous gas molecule sensing

Structural Chemistry - Adsorption of hazardous gas molecules viz. NH3, HCN and Cl2 on C2H4M (M?=?Li, Ti) complex is studied using first-principle calculations and atom-centred density...     

Conformational analysis of c3′-c8 connected biflavones

Two biflavones isolated from Taxus cuspidata were identified with ginkgetin (1) and sciadopitysin (2) which belong to C3′-C8 connected biflavones. The conformation of 2 in the solid state was determined by X-ray analysis and the conformations of 1 and 2 in the liquid state were discussed using nmr techniques. Complete assignments of ¹H and ¹³C nmr spectra about 1 were made on the basis of COSY, HMQC, HMBC and nOe experiments.     

Surface Molding of Microscale Hydrogels with Microactuation Functionality

This work describes the fabrication of numerous hydrogel microstructures (μ‐gels) via a process called “surface molding.” Chemically patterned elastomeric‐assembly substrates were used to organize and manipulate the geometry of liquid prepolymer microdroplets, which, following photo‐initiated crosslinking, maintained the desired morphology. By adjusting the state of strain during the crosslinking process, a continua of structures could be created using one pattern. These arrays of μ‐gels have stimuli‐responsive properties that are directly applicable to actuation where the basis shape and array geometry of the μ‐gels can be used to rationally generate microactuators with programmed motions. As a method, “surface molding,” represents a powerful addition to the soft‐lithographic toolset that can be readily applied to the simultaneous synthesis of large numbers of geometrically and functionally distinct polymeric microstructures.     

High-performance liquid chromatography column switching applied to the trace determination of herbicides in environmental and drinking water samples

A selective and sensitive coupled-column high-performance liquid chromatographic method is developed for the simultaneous determination of 5 phenylurea herbicides (monuron, linuron, isoproturon, monolinuron, and diuron) in environmental and drinking water samples. Sample clean-up is performed automatically by means of a column switching technique. Using 2 octadecyl silica columns connected via two programmable 6-port valves and ultraviolet detection at 244 nm, the aforementioned compounds can be determined at the low concentration levels required for pesticide residue analysis in water samples. A mobile phase consisting of a mixture of methanol-water (55:45, v/v) is pumped at 1 mL/min. For the 5 phenylureas, high recoveries ranging from 94.9 to 101.6%, good reproducibility with relative standard deviations lower than 5%, and wide linear ranges up to 20 micrograms/L are observed with determination limits of 0.05 microgram/L. The method is successfully applied to the screening of different environmental water samples such as surface, ground, rain, and drinking water.     

Determination of ofloxacin in tablets by room-temperature phosphorimetry on a poly(vinyl alcohol) solid substrate

An easy and sensitive method for the quantitative determination of ofloxacin (OFLX), a new fluoroquinolone antimicrobial agent, in a pharmaceutical formulation, tablet, was developed by using solid-substrate room-temperature phosphorimetry (RTP) on a poly(vinyl alcohol) substrate. The method did not require a dry gas flush during the measurement of phosphorescence. The influence of different conditions such as solution pH and concentrations of heavy atoms, used as the enhancer, were studied. The phosphorescence intensity of OFLX was enhanced using NaOH and KI as enhancers. A linear relationship between concentration and RTP intensity for each standard solution was obtained in the concentration range of 4-18000 ng/ml, and the determination limit was 4 ng/ml. The proposed method was applied to a determination of OFLX in a commercial tablet, and the results were compared with those of fluorescence and UV methods. It was proven that OFLX in a commercial tablet can be accurately measured by this method with a very small amount of sample solution.     

Binding of the general anesthetics chloroform and 2,2,2-trichloroethanol to the hydrophobic core of a four-alpha-helix bundle proteins

The structural features of general anesthetic binding sites on proteins are being examined using a defined model system consisting of a four-alpha-helix bundle scaffold with a hydrophobic core. Previous work suggested that halothane binding to the four-alpha-helix bundle was improved by (1) introducing a cavity into the hydrophobic core and (2) substituting a methionine side-chain in place of an alpha-helical heptad e position leucine. In this study, the ability of the general anesthetics chloroform and 2,2,2-trichloroethanol to bind to the hydrophobic core of the four-alpha-helix bundle (Aalpha2-L38M)2 is explored. The halogenated alkane chloroform binds with a dissociation constant (Kd) = 1.4 +/- 0.2 mM, whereas 2,2,2-trichloroethanol binds with a Kd = 19.5 +/- 1.2 mM. The affinity of both general anesthetics for the hydrophobic core of the four-alpha-helix bundle approximates their whole animal effective concentration in 50% of test subjects' (EC50) values, as shown previously for halothane. Tryptophan phosphorescence decay rates at 77 K are accelerated by a factor of 4.5 by both bound halothane and chloroform, indicating that the heavy-atom effect is responsible for a portion of the observed fluorescence quenching. Because heavy-atom effects are operative only at short distances, the findings indicate that these general anesthetics are binding in the vicinity of the indole rings of W15 in the hydrophobic core of the four-alpha-helix bundle scaffold. The results indicate that chloroform, halothane and 2,2,2-trichloroethanol may occupy the same sites on protein targets.     

Molecular mechanics analysis of polymer conformation, 4. Local chain motions and molecular relaxations of poly(parabanic acids)

The structure of the repeating units of poly(parabanic acid) (PPA), a polyimide-like glassy heat resistant polymer, was analyzed by MM2 using various model compounds of PPA-M and PPA-T consisting of M (1,3-diazolidine-2,4,5-trione-1,3-diyl-1,4-phenylenemethylene-1,4-phenylene) and T (1,3-diazolidine-2,4,5-trione-1,3-diyl-3,3′-dimethyl-4,4′-biphenylylene) units, respectively. Based on the most stable structures obtained, the subunit rotations of the methylene, phenylene, and diazolidine groups were evaluated. The potential mobilities estimated for these subunits can reasonably be correlated with the dynamic mechanical and dielectric properties of PPA. The γ relaxation mode of both PPA-M and a copolymer PPA-TM is reasonably explained by the rotation of the methylene group. The major mode of the β relaxations of both PPAs is ascribed to the rotation of the phenylene ring of the M unit, while the β^* dielectric relaxation is attributed to the torsional vibration of the parabanic ring involving the adjacent aromatic moieties. These data suggest that PPA is similar to polycarbonate rather than polyimide in terms of the local chain motion. It is shown that the conformational analysis by MM2 is quite informative to understand the structure property relationships of polymers.     

2D NMR Spectroscopic Studies of the Toxic Alkaloid from Oxytropis Glabra D C.

The Oxytropis, legume genus, is native in the northwest of China, and some of its members have been reported to be toxic to grazing livestock. In the course of studying toxic reason of this legume, a toxic alkaloid was isolated from Oxytropis glabra D C. grown in the Inner Mongolian Autonomous Region. The LD+(50) of (—)-thermopsine(Ⅰ) was shown to be 89.98 mg/kg(in mice). This paper reports an approach to the structure elucidation of(-)-thermopsine by combining 2D NMR[~1H-~1H and ~1H-~(13)C (one-bond and long-range) COSY] and other physicochemical methods. The stereochemistry of compound Ⅰ is also discussed.     

Multiresidue Analysis of Phenylurea Herbicides in Environmental and Drinking Water by Capillary Electrophoresis

The present paper describes the application of capillary electrophoresis in the micellar mode to the separation and quantitative determination of five phenylurea herbicides, viz. monuron, linuron, diuron, isoproturon, and monolinuron, in water samples. Using uncoated fused silica capillary and phosphate-borate buffer (pH 7.0) containing SDS, the five pesticides are resolved in less than 15 min and quantitatively determined by an ultraviolet detector at 244 nm. Method optimization and validation parameters are presented. Good linearity and repeatability were observed for all the compounds studied (correlation coefficients 0.999). The feasibility of the method developed was tested by simultaneous determination of these herbicides in environmental and drinking water samples at the minimum residue levels (MRLs) (0.1 μg/L) after solid-phase extraction (SPE) preconcentration procedure.