Rapid determination of polyprenylated xanthones in gamboge resin of Garcinia hanburyi by HPLC

A rapid ion-pair HPLC method was developed and validated for the determination of eight polyprenylated xanthones including three pairs of epimers, namely morellic acid (MA), 30-hydroxygambogic acid (HGA), 30-hydroxyepigambogic acid (HEGA), isogambogic acid (IGA), epiisogambogic acid (EIGA), gambogenic acid (GNA), gambogic acid (GA), and epigambogic acid (EGA), in gamboge resin of Garcinia hanburyi. The separation was performed on a narrow bore C8 column with isocratic elution using a mixture of methanol-ACN-40 mM KH2PO4 buffer (37.5:37.5:25 v/v/v, containing 0.1% tetradecyltrimethylammonium bromide). The newly developed method was used to determine the contents of the eight compounds present in the gamboge. Results showed that GA and EGA are the dominant components of gamboge. The content ratio of each epimer pair remained constant, indicating that the content ratio of epimers can be used as a specific characteristic for the quality control of gamboge.     

Encapsulation of a highly sensitive EPR active oxygen probe into sonochemically prepared microspheres

High-power ultrasound (20 kHz) was used to encapsulate a solution of perchlorotriphenylmethyl triester (PTM-TE, a stable organic free radical) dissolved in hexamethyldisiloxane (HMDS) into a polymerized shell of bovine serum albumin (BSA). The size distribution of the microspheres was between 0.5 and 3 microm with a maximum at approximately 1.2 microm. The electron paramagnetic resonance spectrum of PTM-TE consists of a single, sharp line which is sensitive to the surrounding concentration of oxygen. It was found that the technique of encapsulating a solution of PTM-TE dissolved in HMDS into the BSA microspheres resulted in an overall loss of EPR signal intensity from the washed suspension of microspheres. However, the encapsulated PTM-TE/HMDS solution remained sensitive to the partial pressure of oxygen in the surrounding environment. The microspheres were found to be useful for determining the partial pressure of oxygen in the muscle and tumor tissue of mice.     

Simultaneous determination of phenylglyoxylic acid, mandelic acid, styrene glycol and hippuric acid in primary culture of rat hepatocytes incubate by high-performance liquid chromatography

A simple HPLC method for the simultaneous determination of phenylglyoxylic acid (PGA), mandelic acid (MA), styrene glycol (SG) and hippuric acid (HA) in cell culture medium was developed. Analysis was performed on a C(18) column with a mobile phase composed of methanol-potassium dihydrogen phosphate (pH 2.5; 10 mM; 10:90, v/v) at 220 nm. The flow-rate of mobile phase was set at 0.5 mL/min. The mean absolute recoveries of PGA, MA, SG and HA were 95.9, 98.4, 98.0 and 97.1%, respectively. The inter-day and intra-day precisions, determined at three concentration levels, were less than 10% of RSD. The limits of quantification for PGA, MA, SG and HA were 13.2, 13.1, 14.5 and 11.2 microM with RSD less than 20%. The limits of detection for PGA, MA, SG and HA were 4.6, 4.6, 5.1 and 3.9 microM, respectively. The method was successfully applied to study the stereoselective metabolism of SG and MA in primary culture of rat hepatocytes. The results show that there is stereoselective metabolism for both of MA and SG in primary culture of rat hepatocytes. The extent of biotransformation from S-MA to PGA is significantly greater than that from the R enantiomer and the main metabolites are PGA and HA for S-SG and R-SG, respectively.     

Direct detection method of oligosaccharides by high-performance liquid chromatography with charged aerosol detection

A simple and rapid detection method of oligosaccharides using high-performance liquid chromatography with a charged aerosol detection (HPLC-CAD) was studied. The direct detection of a sialylglycopeptide (SGP) derived from egg yolk was accomplished by HPLC-CAD using an amido-silica column, and its limit of detection was 0.40 pmol [signal-to-noise ratio (S/N) = 3]. The sensitivity of this method was lower than that of the fluorescence detection; however, the method showed approximately 5 times higher sensitivity than that using the conventional UV absorbance detection. Furthermore, this method was used for the analysis of the acid hydrolysis products of SGP. Monosialo- and asialo-oligosaccharides as well as free sialic acid were detected without using fluorescent derivatization. These results indicate that the present method is a new tool for the analysis of oligosaccharides.     

Thermal behavior of 1,1-diamino-2,2-dinitroethylene

The thermal behavior of 1,1-diamino-2,2-dinitroethlene (DADNE) was followed by differential scanning calorimetry (DSC) and thermogravimetry (TG). In addition, it was further investigated by the combination techniques of in situ thermolysis cell or fast thermolysis probe with rapid-scan Fourier transform infrared spectroscopy (thermolysis/RSFT-IR and fast thermolysis/RSFT-IR) and by mass spectroscopy (MS). The results showed that there was a phase transition (beta-DADNE to gamma-DADNE) at the temperature of 119 degrees C, and that the gas products of DADNE consisted of CO2, CO, NO2, NO, N2O, HCN, and HNCO, of which CO2, NO, N2O, and HCN present themselves in both the first and second stages of DADNE decomposition process, whereas CO, NO2, and HNCO are only caused by the second stage, in air atmosphere. The C=C and C-NH2 bonds of DADNE molecules are broken in the first stage of the decomposition process in open air, and one of the C-NO2 and one of the C-NH2 bonds of the molecules are broken in the same stage under electrospray ionization condition.     

Copper- and ligand-free Sonogashira reaction catalyzed by palladium in microemulsion

An oil-in-water microemulsion containing PdCl2 and NaOH can be used as an effective catalyst system for rapid copper- and ligand-free Sonogashira reaction of aryl halides and phenylacetylene. Excellent yield of the Sonogashira reaction catalyzed by 0.5 mol% palladium could be achieved within 5 min. The types of base have an intense influence on the reaction. The reaction rate was increased with increased aqueous content in the microemulsions, and dispersed palladium nanoparticles can be in situ formed without other reductants.     

Time-course expression of DNA repair-related genes in hepatocytes of zebrafish (Danio rerio) after UV-B exposure

The objective of this study was to evaluate the time-course effects of UV-B exposure on expression of genes involved in the DNA repair system of zebrafish ( Danio rerio ) hepatocytes, a highly competent species in terms of damage repair induced by UV radiation. For gene expression analysis (RT-PCR), cells were exposed to 23.3 mJ cm⁻² UV-B, which was the dose that affected viable cell number (reduction of 30% when compared with the control group) and produced no visual alteration on cell morphology. The early response observed (6 h) showed induction in the expression of the CDKI gene (cyclin-dependent kinase inhibitor) and genes related to DNA damage repair (mainly XPC and DDB2 ), while the late response observed (24 h) was more related to up-regulation of p53 and genes involved in cell cycle arrest ( gadd45a , cyclinG1 ). In all times analyzed, the anti-apoptotic gene Bcl-2 was down-regulated. Another interesting result observed was the up-regulation of the Apex- 1 gene after UV-B exposure, which could indicate the induction of oxidative lesions in the DNA molecule. In conclusion, these results demonstrate an activation of the DNA repair system in hepatocytes of zebrafish exposed to UV-B radiation, mainly involving the participation of p53.     

Unraveling the aflatoxin-FAPY conundrum: structural basis for differential replicative processing of isomeric forms of the formamidopyrimidine-type DNA adduct of aflatoxin B1

Aflatoxin B1 (AFB) epoxide forms an unstable N7 guanine adduct in DNA. The adduct undergoes base-catalyzed ring opening to give a highly persistent formamidopyrimidine (FAPY) adduct which exists as a mixture of forms. Acid hydrolysis of the FAPY adduct gives the FAPY base which exists in two separable but interconvertible forms that have been assigned by various workers as functional, positional, or conformational isomers. Recently, this structural question became important when one of the two major FAPY species in DNA was found to be potently mutagenic and the other a block to replication [Smela, M. E.; Hamm, M. L.; Henderson, P. T.; Harris, C. M.; Harris, T. M.; Essigmann, J. M. Proc. Natl. Acad. Sci. U.S.A. 2002, 99, 6655-6660]. NMR studies carried out on the AFB-FAPY bases and deoxynucleoside 3',5'-dibutyrates now establish that the separable FAPY bases and nucleosides are diastereomeric N5 formyl derivatives involving axial asymmetry around the congested pyrimidine C5-N5 bond. Anomerization of the protected beta-deoxyriboside was not observed, but in the absence of acyl protection, both anomerization and furanosyl --> pyranosyl ring expansion occurred. In oligodeoxynucleotides, two equilibrating FAPY species, separable by HPLC, are assigned as anomers. The form normally present in duplex DNA is the mutagenic species. It has previously been assigned as the beta anomer by NMR (Mao, H.; Deng, Z. W.; Wang, F.; Harris, T. M.; Stone, M. P. Biochemistry 1998, 37, 4374-4387). In single-stranded environments the dominant species is the beta anomer; it is a block to replication.     

Thermodynamic investigation of n-hexane thin films adsorbed on magnesium oxide

The thermodynamic properties of n-hexane adsorption on MgO(100) were determined using high-resolution volumetric adsorption isotherms in the temperature range 195-255 K. Two distinct layering transitions are observed in the isotherms. The isotherms are used to calculate the two-dimensional compressibility, the differential enthalpy and entropy, the heat of adsorption, and the isosteric heat of adsorption. Neutron Diffraction is used to identify where melting of the n-hexane monolayer takes place.     

Nonadiabatic reactant-product decoupling calculation for the F(2P(1/2)) + H2 reaction

In this paper we present a theoretical study using time-dependent nonadiabatic reactant-product decoupling method for the state-to-state reactive scattering calculation of F((2)P(1/2))+H(2) (nu=j=0) reaction on the Alexander-Stark-Werner potential energy surface. In this nonadiabatic state-to-state calculation, the full wave function is partitioned into reactant component and a sum of all product components. The reactant and product components of the wave function are solved independently. For the excited state reaction, the state-to-state reaction probabilities for J=0.5 are calculated. Comparing the state-to-state reaction probabilities, it is found that the vibrational population of the HF product is dominated by vibrational levels nu=2 and 3. The rotation specific reaction probabilities of HF product in j=1 and 2 are larger than those in other rotational levels. As the rotation quantum number j increases, the positions of the peak in the rotational reaction probability of HF product in nu=3 shift to higher collision energy.