Studies of gas-jet assisted RF-glow discharge atomic absorption spectrometry

The gas jet assisted glow discharge source has been employed for the RF-glow discharge atomic absorption spectrometry (RF-GDAAS). Data are described to illustrate the role of discharge power, pressure as well as gas flow rate on the sample loss rate, absorbance and self-bias potential. Results show that the optimum discharge conditions depend not only on the pressure and discharge power but also on the gas flow rate. The absorbance increases as much as 1 order of magnitude as the gas flow rate increases from 50 mL/min to 500 mL/min at a pressure of 3 mbar. The use of a gas-jet source allows the direct analysis of solids by RF-GDAAS.     

An ultraviolet-curable mold for sub-100-nm lithography

We describe a novel UV-curable mold that is stiff enough for replicating dense sub-100-nm features even with a high aspect ratio. It also allows for flexibility when the mold is prepared on a flexible support such that large area replication can be accomplished. The composite material of the mold is inert to chemicals and solvents. The surface energy is made low with a small amount of releasing agent such that the mold can be removed easily and cleanly after patterning. In addition, the material allows self-replication of the mold. These unique features of the mold material should make the mold quite useful for various patterning purposes.     

Redetermination of (6R,7S,9S,11S)‐(–)‐sparteinium monoperchlorate

The structure of the title compound, C₁₅H₂₇N₂⁺·ClO₄^?, consists of a monoprotonated sparteinium cation and a perchlorate anion. The two tertiary N atoms of the cation, one perchlorate O atom and a H atom form a bifurcated hydrogen bond, the four hydrogen‐bonding atoms being nearly in the same plane.     

Copper coupling of 1-chloro-2-iodo- and 1,2-di-iodo-perfluorocycloalkenes

Reductive coupling of 1-chloro-2-iodoperfluorocyclobutene (I), cyclopentene (III) and cyclohexene (VI) has been carried out with copper powder and a trace amount of dimethylformamide to give the corresponding 2,2′-dichloroperfluoro-(bi-1-cycloalken-1-yl) derivatives in 69%, 36% and 73% yield, respectively. A reduced by-product, 2H,2′H-dodecafluoro-(bi-1-cyclopenten-1-yl) was also obtained in the copper coupling of (III). Coupling of 1,2-di-iodoperfluorocyclobutene (IX) and cyclopentene (XII) under similar conditions gave good yields of cyclic trimers and tetramers. Mass spectra, infrared and ¹⁹F NMR data are discussed.     

CONTRASTING STRUCTURAL IMPACTS INDUCED BY cis-syn CYCLOBUTANE DIMER AND (6–4) ADDUCT IN DNA DUPLEX DECAMERS: IMPLICATION IN MUTAGENESIS AND REPAIR ACTIVITY

Abstract—
The relative biological importance of cis-syn cyclobutane dimer and pyrimidine(6–4)pyr-imidone photoadduct ([6–4] photoadduct) appears to be dependent on the biological species, dipyrimidine sites and the local conformational variation induced at the damaged sites. The single-stranded deoxyn-ucleotide 10-mers containing the site-specific (6–4) adduct or cis-syn cyclobutane dimer of thymidylyl (3'-5')-thymidine were generated by direct photolysis of d(CGCATTACGC) with UVC (220–260 nm) irradiation or UVB (260–320 nm) photosensitization. Three-dimensional structures of the duplex cis-syn and (6–4) decamers of d(CGCATTACGC)d(GCGTAATGCG) were determined by NMR spectroscopy and the relaxation matrix refinement method. The NMR data and structural calculations establish that Watson-Crick base pairing is still intact at the cis-syn dimer site while the hydrogen bonding is absent at the 3'-side of the (6–4) lesion where the T → C transition mutation is predominantly targeted. Overall conformation of the duplex cis-syn decamer was B-DNA and produced a 9° bending in the DNA helix, but a distinctive base orientation of the (6–4) lesion provided a structural basis leading to 44° helical bending. The observed local structure and conformational rigidity at the (6–4) adduct of the thymidylyl(3'-5')-thymidine (T-T [6–4]) lesion site suggest the potential absence of hydrogen bonding at the 3' sides of the (6–4) lesion with a substituted nucleotide during replication under SOS conditions. Contrasting structural distortions induced by the T-T (6–4) adduct with respect to the T-T cis-syn cyclobutane pyrimidine photodimer may explain the large differences in mutation spectrum and repair activities between them.