INDUCTION OF SISTER-CHROMATID EXCHANGES IN ICR 2A FROG CELLS EXPOSED TO 254 NM AND SOLAR UV WAVELENGTHS

Abstract— Exposure of ICR 2A frog cells to 254 nm UV induced the formation of sister-chromatid exchanges (SCEs) in a fluence-dependent manner. Cells were also exposed to the UV produced by a fluorescent sunlamp that was filtered through 8C Mylar in order to simulate the mid-UV(290–320 nm) portion of sunlight reaching the earth's surface. In this instance, SCEs were induced in a linear fashion at low fluences but reached a plateau at a low level of induced SCEs. In addition, pretreatment of cells with the solar UV followed by exposure to 254 nm UV resulted in a significantly lower level of SCEs than in cells exposed to 254 nm UV alone.     

Determination of regioselectivity in ring opening of tert-butylaziridinones by a combination of (15)N labeling and electrospray ionization-ion trap mass spectrometry

The ring opening of 1,3-di-tert-butylaziridinone by tert-butylamine and aniline was investigated by using electrospray ionization and collision-induced dissociation in an ion trap mass spectrometer in conjunction with (15)N labeling of the two amine nucleophiles. Using the MS(n) capabilities of the ion trap instrument, we were able to monitor the retention of the (15)N label through successive fragmentation steps. Both amines exhibited a remarkable degree of selectivity in that they both cleaved exclusively the 1,3-bond (the alkyl-nitrogen bond). This result is in contrast to that obtained previously with methylamine, which cleaved just the opposite bond, namely, the 1,2-bond (the acyl-nitrogen bond). These contrasting results could not have been predicted by previously published guidelines.     

Vinyl sulfones

Four neutral vinyl sulfones, two of which are paired with phosphonate groups, are described. The compounds are diisopropyl (2‐phenylethenylsulfonylmethyl)phosphonate, C₁₅H₂₃O₅PS, (I), diisopropyl {[2‐(7‐methoxy‐1,3‐benzodioxol‐5‐yl)ethenylsulfonyl]methylsulfonylmethyl}phosphonate, C₁₈H₂₇O₁₀PS₂, (II), bis(trans‐2‐phenylethenyl) sulfone, C₁₆H₁₄O₂S, (III), and bis(trans‐2‐phenylethenylsulfonyl)methane, C₁₇H₁₆O₄S₂, (IV). Their structures can be considered as highly functionalized mimics of mono‐, di‐ and triphosphates. These phosphate isosteres are currently of interest as agents for enzyme inhibition in both cancer and HIV therapy. All except one of the compounds has Z′ > 1. The lone exception is (IV), a disulfone with twofold crystallographic symmetry. Geometrically, the sulfone functionality is found to be a good mimic for phosphate. The principal effect of the vinyl group is to shorten the S—C(vinyl) distance relative to the S—CH₂ distance by ca 0.05 Å. The S—C—S and S—C—P backbones resemble the P—O—P backbone but are not identical because the S—C and P—C distances are longer than the P—O distance and the S—C—S and S—C—P angles are more acute than the P—O—P angle. No prior crystal structures of comparable compounds have been published.     

Vehicle impacts on the environment at different spatial scales: observations in west central Georgia, USA

Roads and vehicles change the environmental conditions in which they occur. One way to categorize these effects is by the spatial scale of the cause and the impacts. Roads may be viewed from the perspective of road segments, the road network, or roads within land ownership or political boundaries such as counties. This paper examines the hypothesis that the observable impacts of roads on the environment depend on spatial resolution. To examine this hypothesis, the environmental impacts of vehicles and roads were considered at four scales in west central Georgia in and around Fort Benning: a second-order catchment, a third-order watershed, the entire military installation, and the five-county region including Fort Benning. Impacts from an experimental path made by a tracked vehicle were examined in the catchment. Land-cover changes discerned through remote sensing data over the past three decades were considered at the watershed and installation scales. A regional simulation model was used to project changes in land cover for the five-county region. Together these analyses provide a picture of the how environmental impacts of roads and vehicles can occur at different spatial scales. Following tracked vehicle impact with a D7 bulldozer, total vegetation cover responded quickly, but the plant species recovered differently. Soils were compacted in the top 10 cm and are likely to remain so for some time. Examining the watershed from 1974 to 1999 revealed that conversion from forest to nonforest was highest near unpaved roads and trails. At the installation scale, major roads as well as unpaved roads and trails were associated with most of the conversion from forest to nonforest. For the five-county region, most of the conversion from forest to nonforest is projected to be due to urban spread rather than direct road impacts. The study illustrates the value of examining the effects of roads at several scales of resolution and shows that road impacts in west central Georgia are most important at local to subregional scales. The insights from these analyses led to several questions about resource management at different spatial scales.     

Effect of Swirling Desolvation Gas Flow in an Atmospheric Pressure Ion Source

A numerical study is performed to examine the effect of introducing a swirling desolvation gas flow on the flow transport characteristics in an electrospray and an atmospheric pressure chemical ionization (APCI) system. An ion source having three coaxial tubes is considered: (1) an inner capillary tube to inject the liquid sample, (2) a center coaxial tube to provide a room temperature gas flow to nebulize the liquid, referred to as the nebulizing gas flow, and (3) an outer coaxial tube having a converging exit to supply a high temperature gas for droplet desolvation, referred to as the desolvation gas flow. The results show that a swirling desolvation gas flow reduces the dispersion of the nebulizing gas and suppresses turbulent diffusion. The effect of swirling desolvation flow on the trajectory of a range of droplet sizes emitted from a source is also considered. Figure

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From the Membership Secretary

Abstract

As of April, 1996, paid membership of the International Liquid Crystal Society totalled 745. Over the past three years we have adopted a system of mailing renewal notices quarterly; members therefore receive their renewal notices in one of four mailings each year. Additionally, we have adopted a policy of deleting a former member's name if no response is received to a follow-up reminder letter. Therefore, the current membership total reflects an ACTIVE membership base, and a clear growth for the Society.     

Heteronuclear double resonance on formamide-15N and ammonium-15N using weak perturbing radiofrequency fields

Weak radiofrequency fields have been used to perturb nitrogen transitions in the formamide-¹⁵N and ammonium-¹⁵N molecules. Observation of the proton spectra has completed the determination of the relative signs of the coupling constants in formamide-¹⁵N. Chemical shifts precisely related to tetramethylsilane are reported and a discussion of a method for presentation of shift results is included.