Thomas C. Keane

CLASS I METHANOL MASERS: SIGNPOSTS OF STAR FORMATION?

Class I methanol masers appear to probe very early stages of star formation. An observational survey of the 44 and 36 GHz methanol lines toward several star-forming regions was conducted using the Haystack Observatory 37 m telescope. Examining the intensities of the 36 GHz Class I maser line as compared to the 44 GHz maser line, it is seen that the 36 GHz line is enhanced toward sources where there is no apparent sign of star formation. Sources where the 36 GHz emission is absent, but the 44 GHz emission is strong, appear to be those where ultracompact H II regions and millimeter continuum sources are present. Existing models for the excitation of Class I methanol masers show strong temperature and density dependences for the presence or lack of certain methanol transitions. The 36 GHz masers appear in regimes where the temperatures are low—below 100 K. The 44 GHz masers are excited in a wider range of gas temperatures (80-200 K), supporting the hypothesis that these transitions are still masing even when the 36 GHz masers are quenched.

Synthesis and optical properties of co-doped ZnO submicrometer tubes from electrospun fiber templates.

Submicrometer ZnO tubes have been synthesized by a polymer based template approach using sol-gel deposition. Zinc acetate, a precursor to ZnO, was deposited on catalytically active electrospun polycarbonate fibers approximately 250+/-100 nm in diameter. Thermal degradation of the core fibers resulted in the oxidation of zinc acetate to produce ZnO nanotubes with diameters of approximately 500+/-100 nm and an average wall thickness of approximately 100+/-50 nm. Scanning electron microscopy (SEM), Energy dispersive spectroscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and UV-visible spectroscopy were used to characterize the composition, structure, and morphology of the tubes. Powder X-ray diffraction results showed that a wurtzite crystalline phase was obtained. The UV-visible absorption spectrum was red-shifted by 25 nm due to narrowing of the ZnO band gap (approximately 3.22 eV) as a result of Co doping. Similarly, green band emission was not observed in the emission spectrum, while emission lifetime was determined to be 620 ps from photoluminescence studies.

Investigation of riboflavin sensitized degradation of purine and pyrimidine derivatives of DNA and RNA under UVA and UVB

DNA and RNA undergo photodegradation in UVC (200-290nm) due to direct absorption by the purine and pyrimidine bases. Limited effects are observed under UVB (290-320nm) or UVA (320-400nm). We have observed that an endogenous photosensitizer, riboflavin (RF), upon exposure to UVB or UVA can extensively damage the DNA and RNA bases. Guanine, uracil, thymine, adenine and cytosine were degraded by 100%, 82%, 60.4%, 46.3% and 10.3% under UVA (12J) and by 100%, 54.1%, 38.9%, 42.2% and <1.0% under UVB (6J), respectively. Guanosine and deoxyguanosine were degraded by 98±1.0% and 80±1.0% under UVA (4J) and UVB (12J), respectively. With an exception of GMP (53-82%), dGMP (51-88%) and to some extent TMP (3-4%) the remaining nucleosides and nucleotides were resistant to RF-induced photodecomposition. The photodegradation of G derivatives by RF was 2-fold higher than a well known photodynamic agent rose bengal. A comparison of the intensities of UVA and UVB sources used in this study with natural sunlight suggests that exposure with the latter along with an endogenous photosensitizer can have similar effects on DNA and RNA depending upon the duration of exposure.

On the abundance of non-cometary HCN on Jupiter

Using one-dimensional thermochemical/photochemical kinetics and transport models, we examine the chemistry of nitrogen-bearing species in the Jovian troposphere in an attempt to explain the low observational upper limit for HCN. We track the dominant mechanisms for interconversion of N2-NH3 and HCN-NH3 in the deep, high-temperature troposphere and predict the rate-limiting step for the quenching of HCN at cooler tropospheric altitudes. Consistent with some other investigations that were based solely on time-scale arguments, our models suggest that transport-induced quenching of thermochemically derived HCN leads to very small predicted mole fractions of hydrogen cyanide in Jupiters upper troposphere. By the same token, photochemical production of HCN is ineffective in Jupiters troposphere: CH4-NH3 coupling is inhibited by the physical separation of the CH4 photolysis region in the upper stratosphere from the NH3 photolysis and condensation region in the troposphere, and C2H2-NH3 coupling is inhibited by the low tropospheric abundance of C2H2. The upper limits from infrared and submillimetre observations can be used to place constraints on the production of HCN and other species from lightning and thundershock sources.

Protection of riboflavin and UVB sensitized degradation of DNA and RNA bases by natural antioxidants

Riboflavin (RF) is a potent photosensitizer producing extensive degradation of purine and pyrimidine derivatives of nucleic acids under UVA, UVB and sunlight. In this study we have demonstrated that reactive O(2) species generated by photosensitized RF under UVB were responsible for the degradation of DNA and RNA bases. While (1)O(2) accounted for the degradation of adenine, guanine, thymine and uracil, O(2)(-·)also contributed to partial degradation of adenine. Cytosine remained unaffected by the synergistic action of RF and UVB. Ascorbic acid, glutathione, glycolic acid and quercetin showed remarkable protection (88-100%) against photodegradation of bases. Sorbitol was effective in preventing photodegradation of guanine. These naturally occurring antioxidants are potential candidates for prevention against oxidative stress caused by photosensitization.

Total inhibition of 1O2-induced oxidative damage to guanine bases of DNA/RNA by turmeric extracts

The guanine base of nucleic acids is known to be very reactive towards degradation by (1)O2-induced oxidative stress. Oxidative reactions of DNA are linked to many human diseases including cancer. Among the various forms of reactive O2 species (OH, (1)O2 or O2(-)), the oxidative stress caused by (1)O2 is of particular physiologic importance because of its selectively long life in aqueous medium and its ability to diffuse through a cell membrane. In this study we investigated the degradation of a model compound guanosine (Guo) by (1)O2, which was generated by riboflavin-induced photosensitization and by molybdate ion catalyzed disproportionation of H2O2. We observed the remarkable ability of an aqueous and alcoholic extracts of Turmeric (Curcuma longa) as an extraordinary scavenger of (1)O2 to completely inhibit the degradation of Guo. The alcoholic extracts were more effective in their antioxidant activity than the corresponding water extract. This naturally occurring antioxidant offers a most economical supplement to protect biologically significant molecules from the oxidative stress induced by (1)O2.