Quenching of nucleotide-derived radicals by bis benzimidazole derivative Hoechst-33258 in aqueous solution

The pulse radiolysis technique has been employed to investigate the reaction of DNA-minor-groove ligand bisbenzimidazole Hoechst 33258 with pyrimidine and purine nucleotide-derived radicals. Formation of an N-centred Hoechst-33258 radical is observed. Bimolecular rate constants and the yields of Hoechst-33258 radical have been evaluated. While the rate constant for the reaction of pyrimidine-derived radicals with Hoechst-33258 remained the same (1–2) × 10⁹ dm³ mol⁻¹ s⁻¹, the yields of the Hoechst-33258 radical varied from 25% (5′-cytidine monophosphate) to 75% (5′-guanosine monophosphate) under anoxic conditions. The rate constant values for the reaction of purine-derived radicals with Hoechst-33258, under oxic and anoxic conditions, remained the same whereas with pyrimidine-derived radicals, the rate constant value under oxic conditions was about two orders of magnitude lower than under anoxic conditions. The difference in the yields of Hoechst-33258 radical with various nucleotide-derived radicals suggest the formation of different types of radicals and that the reaction mainly occurs by electron transfer from Hoechst-33258 to the nucleotide radicals.     

Comparative analysis of the composition of essential oils and supercritical carbon dioxide extracts from the berries and needles of Estonian juniper (Juniperus communis L.)

The composition of the volatile oil of the common juniper (Juniperus communis L.) from Estonia was analyzed by gas chromatography (GC-FID) and gas chromatography-mass spectrometry (GC-MS). The yield and composition of the oil obtained by different methods (micro-distillation and extraction, SDE, and supercritical carbon dioxide extraction, SFE) from various parts of juniper (berries, needles) were compared. The oil yield ranged from 0.7 to 2.1%. The content of α-pinene of juniper-berry essential oil was 47.9, that of juniper needleoil, 36.4%. The oil yields and composition obtained by SDE and SFE from juniper needles were similar. The oil obtained by SFE from juniper berries contained more sesquiterpenes and high boiling compounds than that obtained by SDE.     

Microwave induced synthesis of the thiazolidine‐2,4‐dione motif and the efficient solvent free‐solid phase parallel syntheses of 5‐benzylidene‐thiazolidine‐2,4‐dione and 5‐benzylidene‐2‐thioxo‐thiazolidine‐4‐one compounds

Novel microwave induced method for the synthesis of thiazolidine‐2,4‐dione motif under solvent phase conditions is developed. Further we report an efficient, microwave assisted method for the parallel syntheses of biologically important 5‐benzylidene‐thiazolidine‐2,4‐dione and 5‐benzylidene‐2‐thioxothiazolidine‐4‐one compounds under solid‐phase and solvent‐free conditions. A comparative study between the developed microwave methods and the conventional methods is described. We have also illustrated the possible mechanism behind to address the reason why piperidine, acetic acid and silica gel enhanced the Knoevenagel condensation reaction.     

A novel approach to increase emission wavelength of InAs/GaAs quantum dots by using a quaternary capping layer

In this paper, we present a new approach to obtain large size dots in an MBE grown InAs/GaAs multilayer quantum dot system. This is achieved by adding an InAlGaAs quaternary capping layer in addition to a high growth temperature (590°C) GaAs capping layer with the view to tune the emission wavelength of these QDs towards the 1.3 μm/0.95 eV region important for communication devices. Strain driven migration of In atoms from InAlGaAs alloy to the InAs QDs effectively increases the size of QDs. Microscopic investigations were carried out to study the dot size and morphology in the different layers of the grown samples. Methods to reduce structural defects like threading dislocations in multilayer quantum dot samples are also studied.     

Synthesis and optical characterization of c-axis oriented GaN thin films on amorphous quartz glass via sol–gel process

c-Axis oriented GaN nanocrystalline thin films were fabricated by nitridation of three different thin films of -GaO(OH), -Ga₂O₃ or β-Ga₂O₃ obtained by sol–gel technique on amorphous quartz glass substrates. All these GaN thin films showed near band edge emission at 390 nm and yellow luminescence at 570 nm. The crystalline nature and c-axis orientation as well as luminescence properties of the GaN thin films increased by several times by using a buffer layer of GaN on the substrate.     

Determination of urinary 5-hydroxy-3-indoleacetic acid by an automated HPLC method

A HPLC method for the quantitative determination of 5-hydroxy-3-indoleacetic acid (5-HIAA) in urine is described. The method is based on ion-pair chromatography, reversed phase (RP) column material and specific fluorimetric detection at 300 nm and 355 nm. Sample preparation and gradient elution were avoided by using a column-switching technique. The sensitivity of the assay was excellent for clinical routine analysis, with a detection limit of 0.2 mg/L 5-HIAA. No endogenous or exogenous interference problems arose. Intra- and interassay precision was good, with observed coefficients of variation of 1.5 to 2.6% and 2.1%, respectively. Recoveries were 93 to 98%. The system described can be used for clinical diagnosis and therapy follow-up of carcinoid tumors. It has been running for over a year without disturbances and with a minimum of technical attendance.     

Interference of O Kα ghost features in X-ray-excited Auger spectra

We have noted the interference of O Kα ghost peaks in spectra obtained using unmonochromatized X-ray sources, particularly in C(KVV) and O(KVV) X-ray-excited Auger spectra. The source of the undesirable O Kα photons is a surface oxide on the Mg or Al anode of the polychromatic X-ray sources used. A calculation of the oxide thickness required to give the observed ghost intensity in measurements on a gold sample using a heavily oxidized Mg anode is given and the estimated oxide thickness found plausible. Since it may be impossible to operate the anode with no oxide present, the use of a standard Au sample is suggested as an excellent test for the presence of O Kα X-radiation from unmonochromatized X-ray sources.     

A temperature programmed desorption study of the reaction of methylacetylene on Pt(111) and Sn/Pt(111) surface alloys

The adsorption and reaction of methylacetylene (H₃CC≡CH) on Pt(111) and the p(2×2) and

Full-size image

surface alloys were investigated with temperature programmed desorption, Auger electron spectroscopy and low energy electron diffraction. Hydrogenation of methylacetylene to form propylene is the most favored reaction pathway on all three surfaces accounting for ca 20% of the adsorbed monolayer. Addition of Sn to the Pt(111) surface to form these two ordered surface alloys suppresses the decomposition of methylacetylene to surface carbon. The alloy surfaces also greatly increase the amount of reversibly adsorbed methylacetylene, from none on Pt(111) to 60% of the adsorbed layer on the

Full-size image

surface alloy. Methylacetylene reaction also leads to a small amount of desorption of benzene, along with butane, butene, isobutylene and ethylene. There is some difference in the yield of these other reaction products depending the Sn concentration, with the (2×2)-Sn/Pt(111) surface alloy having the highest selectivity for these. Despite previous experiments showing cyclotrimerization of acetylene to form benzene on the Pt–Sn surface alloys, the analogous reaction of methylacetylene on the alloy surfaces was not observed, that is, cyclotrimerization of methylacetylene to form trimethylbenzene. It is proposed that this and the high yield of propylene is due to facile dehydrogenation of methylacetylene because of the relatively weak H–CH₂CCH bond compared to acetylene. The desorption of several C₄ hydrocarbon products at low (<170 K) temperature indicates that some minor pathway involving C–C bond breaking is possible on these surfaces.     

Specific background electrolytes for nonaqueous capillary electrophoresis

The use of organic solvents or mixture of solvents in capillary electrophoresis is gaining wider attention. The electroosmotic flow mobility of eight organic solvents (acetonitrile, acetone, dimethylformamide, dimetylsulphoxide, propylene carbonate, methanol, ethanol, n-propanol) and of mixtures of several solvents (methanol-acetonitrile, methanol-propylene carbonate, acetonitrile-propylene carbonate) has been studied. The influence of 1,3-alkylimidazolium salts in different solvents on the separation of different analytes has been investigated. Some of these salts have shown usefulness for matrix-assisted laser desorption ionization matrices and off-line analysis of electrophoresis fractions. It also appears that nonaqueous capillary electrophoresis with 1,3-alkylimidazolium salts as background electrolytes is suitable for separation small inorganic ions.