Test of variational transition state theory against accurate quantal results for a reaction with very large reaction-path curvature and a low barrier

We present three sets of calculations for the thermal rate constants of the collinear reaction I+HI-->IH+I: accurate quantum mechanics, conventional transition state theory (TST), and variational transition state theory (VTST). This reaction differs from previous test cases in that it has very large reaction-path curvature but hardly any tunneling. TST overestimates the accurate results by factors of 2×10^10, 2×10^4, 57, and 19 at 40, 100, 300, and 1000 K, respectively. At these same four temperatures the ratios of the VTST results to the accurate quantal ones are 0.3, 0.8, 1.1, and 1.4, respectively. We conclude that the variational transition states are meaningful, even though they are computed from a reaction-path Hamiltonian with large curvature, which is the most questionable case

Hydrogeology and Development Pressures

Guidebook for field trips in southern and west-central Maine, October 13, 14 and 15, 1989: New England Intercollegiate Geological Conference 81st annual meeting: Trip A-3; C-

Stand Analysis of an Invading Firetree (Myrica faya Aiton) Population, Hawaii

Since 1971, the exotic firetree (Myricafaya) has been invading a native ohia tree (Metrosideros collina subsp. polymorpha Rock) habitat in the 1959 Kilauea Iki devastation area, Hawaii Volcanoes National Park. Ninetysix trees of the invading population were analyzed as to structural and fruiting characteristics. Data were collected from two permanent transects that were designed to provide for continued study of the fire tree and ohia community. Initial findings reveal that the present firetree spread depends on an outside seed source, and successful seedling establishment is dependent on favorable microhabitat conditions beneath ohia trees. As yet, no competitive replacement of ohia trees by fire trees has been observed. On the contrary, firetrees over 2 m tall that had grown up and into ohia tree crowns were exhibiting poor vigor. Additionally, there is a high positive correlation between fire tree loss of vigor and diameter increase beyond 4-5 em. Preliminary observations suggest that fire tree seed dispersal depends on birds, primarily, the exotic Japanese white-eye (Zosterops japonica)

Skyglow extends into the world’s Key Biodiversity Areas

This is the author accepted manuscript. The final version is available from Wiley / Zoological Society of London via the DOI in this record.The proportion of the Earth’s surface that experiences a naturally dark environment at night is rapidly declining with the introduction of artificial light. Biological impacts of this change have been documented from genes to ecosystems, and for a wide diversity of environments and organisms. The likely severity of these impacts depends heavily on the relationship between the distribution of artificial nighttime lighting and biodiversity. Here, we carry out a global assessment of the overlap between areas of conservation priority and the most recent atlas of artificial skyglow. We show that of the world’s Key Biodiversity Areas (KBAs), less than a third have completely pristine nighttime skies, about a half lie entirely under artificially bright skies, and only about a fifth contain no area in which nighttime skies are not polluted to the zenith. The extent of light pollution of KBAs varies by region, affecting the greatest proportion of KBAs in Europe and the Middle East. Statistical modelling revealed associations between light pollution within KBAs and associated levels of both gross domestic product and human population density. This suggests that these patterns will worsen with continued economic development and growth in the human populationNatural Environment Research Council (NERC)Natural Environment Research Council (NERC

The Prey of Common Barn Owls (Tyto alba) in Dry Limestone Scrub Forest of Southern Jamaica

A collection of common barn-owl (Tyto alba Scopoli) pellets from caves on the Portland Ridge of Jamaica reveals that whereas introduced rodents constitute approximately 90% of the total prey, bats and birds are also frequent prey items. Of the bats, frugivorous species predominate with Ariteus flavescens Gray and Artibeus jamaicensis Leach accounting for the largest portion of the bat prey. Insectivorous bats are markedly under-represented with respect to the known diversity of insectivorous species in the habitat

Metallothionein isoform 3 and proximal tubule vectorial active transport

Metallothionein isoform 3 and proximal tubule vectorial active transport.BackgroundMetallothionein isoform 3 (MT-3) is expressed in the proximal tubule cells of the human kidney. The goal of the present study was to further characterize the basal expression of MT-3 in the proximal tubule and to determine if MT-3 participates in the maintenance of proximal tubule cell function.MethodsExpression of MT-3 mRNA was determined in the intact proximal tubule using microdissection and reverse transcription-polymerase chain reaction (RT-PCR). Basal expression of MT-3 mRNA and protein was determined in cultured human proximal tubule (HPT) cells and an immortalized proximal tubular cell line, HK-2 cells, using RT-PCR and immunoblotting. The MT-3 gene was stably transfected into the HK-2 cell line using the pcDNA3.1/Hygro (+) vector.ResultsMT-3 mRNA was detected in the proximal tubule of the in situ kidney with relative expression in excess to that of the β-actin housekeeping gene. The mortal HPT cells were shown to express both MT-3 mRNA and protein and to form domes, while immortal HK-2 cells were shown to have no expression of MT-3 mRNA and protein nor to form domes. The stable transfection of MT-3 in HK-2 restored MT-3 expression and dome formation to the HK-2 cells.ConclusionsMT-3 mRNA is present in the human proximal tubule, and MT-3 expression is involved in the transport function of a human renal cell line that retains properties of the proximal tubule

Variational Transition State Theory Evaluation Of The Rate Constant For Proton Transfer In A Polar Solvent

Variational transition state theory (VTST) is used to calculate rate constants for a model proton transfer reaction in a polar solvent. We start from an explicit description of the reacting solute in a solvent, and we model the effects of solvation on the reaction dynamics by a generalized Langevin equation (GLE) for the solute. In this description, the effects of solvation on the reaction energetics are included in the potential of mean force, and dynamical, or nonequilibrium, solvation is included by solvent friction. The GLE solvation dynamics are approximated by a collection of harmonic oscillators that are linearly coupled to the coordinates of the reacting system. This approach is applied to a model developed by Azzouz and Borgis [J. Chem. Phys. 98, 7361 (1993)] to represent proton transfer in a phenol-amine complex in liquid methyl chloride. In particular, semiclassical VTST, including multidimensional tunneling contributions, is applied to this model with three explicit solute coordinates and a multioscillator GLE description of solvation to calculate rate constants. We compare our computed rate constants and H/D kinetic isotope effects to previous calculations using other approximate dynamical theories, including approaches based on one-dimensional models, molecular dynamics with quantum transitions, and path integrals. By examining a systematic sequence of 18 different sets of approximations, we clarify some of the factors (such as classical vibrations, harmonic approximations, quantum character of reaction-coordinate motion, and nonequilibrium solvation) that contribute to the different predictions of various approximation schemes in the literature. (C) 2001 American Institute of Physics

Expression of hsp 27, hsp 60, hsc 70, and hsp 70 stress response genes in cultured human urothelial cells (UROtsa) exposed to lethal and sublethal concentrations of sodium arsenite.

The stress response is one mechanism that the bladder urothelium could potentially employ to protect itself from cellular damage after exposure to arsenic and, in so doing, influence the shape of the dose-response curve at low concentrations of exposure to this environmental pollutant. In the present study, we used the cultured human urothelial cell line UROtsa, a model of human urothelium, to determine the expression of heat shock proteins hsp 27, hsp 60, hsc 70, and hsp 70 after acute and extended exposure of the cells to lethal and sublethal levels of sodium arsenite (NaAsO2). Acute exposure was modeled by exposing confluent cultures of UROtsa cells to 100 micro M NaAsO2 for 4 hr followed by a 48-hr recovery period. Extended exposure was modeled by exposing confluent UROtsa cells to 1, 4, and 8 micro M NaAsO2 for 16 days, with the highest concentration producing cell death by 4 days of exposure. The expression of hsp 27, hsp 60, hsc 70, and hsp 70 mRNA and protein was determined by reverse-transcription polymerase chain reaction and Western analysis. Cell viability was determined by the MTT [(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay. The results demonstrated that the expression of hsp 27, hsp 60, and hsc 70 mRNA and protein were not consistently increased by either acute or extended exposure to NaAsO2. In contrast, hsp 70 expression was induced by NaAsO2 after both acute and extended exposure. The degree and duration of the induction of the hsp 70 protein in the extended time course of exposure to NaAsO2 correlated directly with UROtsa cell cytotoxicity. The substantial level of basal expression of hsp 27, hsp 60, and hsc 70 shown previously in human bladder urothelium, coupled with the inducible expression of hsp 70, could provide the human urothelium with a mechanism to withstand and recover from a low level of arsenite exposure

Metallothionein Isoform 3 Expression in Human Skin, Related Cancers, and Human Skin Derived Cell Cultures

Human skin is a well known target site of inorganic arsenic with effects ranging from hyperkeratosis to dermal malignancies. The current study characterizes the expression of a protein known to bind inorganic, As3+, metallothionein 3 (MT-3). Expression of this protein was assessed immunohistochemically with a specific MT-3 antibody on human formalin-fixed, paraffin-embedded biopsy specimens in normal skin, squamous cell carcinoma (SCC), basal cell carcinoma (BCC) and melanoma. Assessment in normal skin using nine normal specimens showed moderate to intense MT-3 staining in epidermal karatinocytes with staining extending into the basal cells and moderate to intense staining in melanocytes of nevi. MT-3 immunoexpression was shown to be moderate to intense in 12 of 13 of SCC, low to moderate in 8 of 10 BCC, and moderate to intense in 12 melanoma samples. MT-3 expression in cell culture models (normal human epidermal keratinocytes, normal human melanocytes, and HaCaT cells) showed only trace expression of MT-3, while exposures to the histone deacytalase inhibitor, MS-275, partially restored expression levels. These results indicate that the epidermis of human skin and resulting malignancies express high level of MT-3 and potentially impact on the known association of arsenic exposure and the development of skin disorders and related cancers