Equal Abundance Research Articles

Ultrafast Chelation Dynamics of Cyclopentadienyl Manganese Tricarbonyl Derivatives with Pendant Sulfides

The photoinduced dynamics of two new [η5-C5H4C(O)R]Mn(CO)3 complexes 2 (R = CH(SCH3)2) and 3 (R = C(SCH3)3) have been investigated in n-heptane solution on the ps to μs time scale by UV-pump IR-probe transient absorption spectroscopy. Irradiation of 2 at 266 or 289 nm induces CO loss to yield two initial products in approximately equal abundance, assigned by their CO-stretching bands to be a heptane solvate of the unsaturated Mn fragment and a ring-formed product in which the pendant sulfide moiety is coordinated to the metal center. In direct analogy with the previously observed behavior of [η5-C5H4C(O)CH2(SCH3)]Mn(CO)3 (1), the solvate reacts through a secondary pathway to afford the S-bound product within 200 ns. Irradiation of 3 under identical conditions yields the chelated product exclusively, with no evidence of a competing solvation pathway.

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Fractal nature of stratigraphic sequences

Research Article| March 01, 2004 Fractal nature of stratigraphic sequences Wolfgang Schlager Wolfgang Schlager 1Earth and Life Sciences, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, Netherlands Search for other works by this author on: GSW Google Scholar Author and Article Information Wolfgang Schlager 1Earth and Life Sciences, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, Netherlands Publisher: Geological Society of America Received: 07 Oct 2003 Revision Received: 05 Nov 2003 Accepted: 12 Nov 2003 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2004) 32 (3): 185–188. https://doi.org/10.1130/G20253.1 Article history Received: 07 Oct 2003 Revision Received: 05 Nov 2003 Accepted: 12 Nov 2003 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Wolfgang Schlager; Fractal nature of stratigraphic sequences. Geology 2004;; 32 (3): 185–188. doi: https://doi.org/10.1130/G20253.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Orders of stratigraphic sequences are being used loosely and with widely varying definitions. The orders seem to be subdivisions of convenience rather than an indication of natural structure. It is proposed that, at least at time scales of 103–106 yr, sequences and systems tracts are scale-invariant fractal features in which units bounded by exposure surfaces and units bounded by flooding surfaces are about equally likely. Support for this conceptual model derives from the well-known facts that (1) sediment architecture is largely scale invariant over a wide range of scales in time and space; (2) first-order trends of sea-level movements and sedimentation rates are fractal on all geologically relevant time scales; and (3) detailed studies in carbonates indicate approximately equal abundance of flooding surfaces and demonstrable exposure surfaces among unit boundaries. Finally, traces of prograding shelf edges that step up and step down in response to sea-level changes are demonstrated in this study to have a fractal nature. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Theoretical and experimental prospects for protein identification based solely on accurate mass measurement.

We discuss the theoretical and experimental potential and limitations of protein identification by mass measurement of proteolytic peptides and database searching. For peptides differing in composition by one (or two or three) amino acids, a surprisingly high number turn out to have isomers: 10% (or 29% or 53%), considering the 20 common amino acids with equal relative abundance. Even if isomers differing by leucine/isoleucine are excluded, the latter numbers are 14% and 38%--those isomeric peptides cannot be distinguished based on mass alone, and tandem mass spectrometry and/or other additional constraints are needed. However, for nominally isobaric peptides, the mass accuracy and resolving power of broadband Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry theoretically and experimentally suffice to resolve virtually all peptide doublets differing by up to two amino acids--including the smallest mass difference of 3.4 mDa. We demonstrate experimental resolution of another pair of peptides differing by 11 mDa, even when present in a complex mixture of hundreds of other peptides.

Peat amendment and production of different crop plants affect earthworm populations in field soil

A field experiment was conducted to study the effects of peat amendment and crop production system on earthworms. The experiment was established on a field previously cultivated with oats and with silt as the main soil type. Perennial crops strawberry, timothy and caraway, and annual crops rye, turnip rape, buckwheat, onion and fiddleneck were cultivated with conventional methods. All the crops were grown with and without soil amendment with peat. Earthworms were sampled twice: 4 and 28 months after establishment of the experiment. In the former case part of the experimental plots were soil sampled and hand sorted for estimation of earthworms. In the latter case all experimental plots were sampled and both soil sampling and mustard extraction was carried out. Soil organic carbon and microbial biomass was measured at 14 and 28 months. Peat increased the abundance of juvenile Aporrectodea caliginosa by 74% in three growing seasons, but had no effect on adult numbers. Lumbricus terrestris numbers were not increased by peat treatment. Three season cultivation of caraway favoured both A. caliginosa and L. terrestris. An equal abundance of A. caliginosa was also found in plots cultivated with turnip rape and fiddleneck. Total earthworm and especially A. caliginosa numbers were very small in plastic-mulched strawberry beds. This was mainly attributed to repeated use of the insecticide endosulfan. With the strawberry plots omitted there was a significant correlation between soil microbial N measured at 14 months and juvenile Aporrectodea spp. and Lumbricus spp. numbers measured at 28 months. Adult earthworm numbers were not associated with either soil organic C or microbial biomass.

Chronic lithium nephropathy: MR imaging for diagnosis.

To evaluate the appearance of lithium nephropathy at magnetic resonance (MR) imaging. Sixteen patients with renal insufficiency and clinical and laboratory evidence of nephropathy secondary to therapy with lithium salts were examined with a 1.5-T MR imaging unit with T1-weighted, T2-weighted fast imaging with steady-state precession (true FISP), rapid acquisition with relaxation enhancement, half-Fourier turbo spin-echo, and gadolinium-enhanced (FISP three-dimensional MR angiographic) sequences. Renal size and the presence, number, location and size of parenchymal cysts were analyzed. The cysts in each kidney were defined as rare (fewer than 10 cysts), sparse (between 10 and 30 cysts), abundant (30-60 cysts), or very abundant (more than 60 cysts). The mean length of both kidneys was 104 mm +/- 9 in seven cases, and one or both kidneys were less than 90 mm in length in nine cases. Renal microcysts measuring from 1 to 2 mm were detected in all patients. They were either very abundant (n = 12), abundant (n = 2), or sparse (n = 2). The cysts were located with equal abundance in both the cortex and the medulla in 11 cases and were predominantly located in the renal cortex in five cases. No renal artery stenosis was present. Microcysts secondary to long-term lithium therapy can be detected with MR imaging.

Molecular structure of alcohol-water mixtures.

We use x-ray emission spectroscopy to elucidate the molecular structure of liquid methanol, water, and methanol-water solutions. We find that molecules in the pure liquid methanol predominantly persist as hydrogen-bonded chains and rings with six and/or eight molecules of equal abundance. For water-methanol solutions we find evidence of incomplete mixing at the microscopic level. Our results provide a new explanation for a smaller entropy increase in the solution due to water molecules bridging methanol chains to form rings.

Fragmentation of dihydroxyacetone kinase 1 from Saccharomyces cerevisiae indicates a two-domain structure.

Global protein expression in Saccharomyces cerevisiae strains either deleted for both yeast dihydroxyacetone kinases (DAK1 and DAK2) or overexpressing DAK1, was characterized by two-dimensional polyacrylamide gel electrophoresis (2-D PAGE). We found protein expression in the double deletion strain to be highly similar to wild-type. In the strain overexpressing Dak1p, nine spots representing fragments of the Dak1p protein in the size range 40-20 kDa and amounting to approximately 30% of total Dak1p, were discovered (native size Dak1p migrates at roughly 60 kDa). Fragments were characterized by matrix-assisted laser desorption/ionization mass spectrometry and electrospray mass spectrometry analyses to represent either the N- or the C-terminal part of the DAK1 protein. Cleavage points, predicted from mass spectrometry and 2-D PAGE data, mapped almost exclusively in the middle region showing low sequence conservation between Dak1p and its closest homologues. We hypothesize that observed Dak1p fragments represent stable structural domains shielded from access by native endoproteases. Furthermore, overexpressing Dak1p with the non-native N-terminus (M)A-, resulted in native size Dak1p and N-terminal Dak1p fragments appearing in two major 2-D PAGE forms of approximately equal size and abundance, but with slightly different isoelectric points. However, when overexpressing Dak1p with the native N-terminus (M)S-, only the more acidic 2-D PAGE form appeared. In the N-terminal acetyltransferase mutant nat1delta, (M)A-Dak1p species were converted into the basic form, arguing twin spots to represent forms with acetylated and deacetylated N-termini. Data thus indicated that (M)A-N-termini, in the Dak1p context, were NatA substrates recognized with 50% lower efficiency than (M)S-N-termini.

PREDICTING THE NUMBER OF NEW SPECIES IN FURTHER TAXONOMIC SAMPLING

In evaluating the effectiveness of further sampling in species taxonomic surveys, a practical and important problem is predicting the number of new species that would be observed in a second survey, based on data from an initial survey. This problem can also be approached by estimating the corresponding expected number of new species. A. R. Solow and S. Polasky recently proposed a predictor (or estimator), with the form of a sum of many terms, that was derived under the assumption that all unobserved species in the initial sample have equal relative abundances. We show in this paper that the summation can be expressed as only one term. We provide a direct justification for the simplified estimator and connect it to an extrapolation formula based on a special type of species accumulation curve. Using the proposed justification, we show that, for large sample sizes, the estimator is also valid under an alternative condition, i.e., species that are represented the same number of times in the initial sample have equal relative abundances in the community. This condition is statistically justified from a Bayesian approach, although the estimator exhibits moderate negative bias for predicting larger samples in highly heterogeneous communities. In such situations, we recommend the use of a modified estimator that incorporates a measure of heterogeneity among species abundances. An example using field data from the extant rare vascular plant species patterns in the southern Appalachians is presented to compare the various methods. Corresponding Editor: A. R. Solow

Unique Amino Acid Composition of Proteins in Halophilic Bacteria

The amino acid compositions of proteins from halophilic archaea were compared with those from non-halophilic mesophiles and thermophiles, in terms of the protein surface and interior, on a genome-wide scale. As we previously reported for proteins from thermophiles, a biased amino acid composition also exists in halophiles, in which an abundance of acidic residues was found on the protein surface as compared to the interior. This general feature did not seem to depend on the individual protein structures, but was applicable to all proteins encoded within the entire genome. Unique protein surface compositions are common in both halophiles and thermophiles. Statistical tests have shown that significant surface compositional differences exist among halophiles, non-halophiles, and thermophiles, while the interior composition within each of the three types of organisms does not significantly differ. Although thermophilic proteins have an almost equal abundance of both acidic and basic residues, a large excess of acidic residues in halophilic proteins seems to be compensated by fewer basic residues. Aspartic acid, lysine, asparagine, alanine, and threonine significantly contributed to the compositional differences of halophiles from meso- and thermophiles. Among them, however, only aspartic acid deviated largely from the expected amount estimated from the dinucleotide composition of the genomic DNA sequence of the halophile, which has an extremely high G+C content (68%). Thus, the other residues with large deviations (Lys, Ala, etc.) from their non-halophilic frequencies could have arisen merely as “dragging effects” caused by the compositional shift of the DNA, which would have changed to increase principally the fraction of aspartic acid alone.

Characterization and quantitation of differential Tsix transcripts: implications for Tsix function.

In dosage compensation of female mammals, the accumulation of Xist RNA initiates silencing of one X-chromosome. Xist action is repressed by the antisense gene, Tsix, whose full-length RNA product is complementary to Xist RNA in mice. While previous work showed that Tsix transcription blocks the accumulation of Xist RNA, it is still unclear whether this repression requires the antisense RNA product or whether the antisense transcriptional movement is sufficient. A better understanding of potential mechanisms requires elucidation of Tsix RNA structure and determination of Tsix RNA copy number relative to that of Xist RNA. Previous work indicated that at least some of murine Tsix is spliced and that human TSIX truncates within the 3' end of XIST. Here, further characterization and quantitation of murine Tsix RNA reveal three new findings: first, in undifferentiated embryonic stem cells, Tsix RNA is present at 10-100-fold molar excess over Xist RNA. Second, only 30-60% of Tsix RNA is spliced at known exon-intron junctions. The nearly equal abundance of spliced and unspliced species leaves open possible roles for both isoforms. Finally, Tsix is spliced heterogeneously at the 5' end and most detectable splice variants exhibit only a 1.9 kb region of complementarity between sense and antisense RNAs. Implications for Tsix's possible mechanisms of action are discussed.

Geographical range and impact of five biocontrol agents established on Lantana camara in South Africa

A survey was conducted todetermine the present status of five biocontrolagents established on Lantana camara L.(Verbenaceae) in South Africa. Three ofthe five agents, Calycomyza lantanae(Frick), Ophiomyia lantanae Froggatt andTeleonemia scrupulosa Stal areestablished throughout the range of L.camara. The two hispine beetles, Octotomascabripennis Guerin-Menevilleand Uroplata girardi Pic are restrictedto the warm, subtropical regions in the easternrange of the weed, and are unable to cope withthe plants becoming seasonally leafless in dryand temperate areas. The two beetles and T. scrupulosa are rated as the most damagingagents on L. camara. The impact of O. lantanae is uncertain, and due to lowpopulations, the impact of C. lantanae isnegligible. Insect populations typicallyaccumulate to maximise their impact on plantsby midsummer, giving plants the opportunity tocompensate for the cumulative agent damageaccrued at the end of the previous growingseason. A number of parasitoids were rearedfrom U. girardi, O. lantanae andC. lantanae, but only those adapted toC. lantanae are expected to significantlyreduce its field density. The agents feed anddevelop on a wide range of lantana varieties,and where two or more varieties co-exist,insects occurred in equal abundance on thedifferent varieties. The importance of varietalpreferences appears to have beenover-estimated, but needs consideration whennew candidates are evaluated. The impact ofthese biocontrol agents is insufficient toreduce L. camara to a manageablesituation, and additional candidates arenecessary to control this weed in South Africa.

Photoluminescence and positron annihilation measurements of nitrogen doped CVD diamond

A range of techniques have been used, to determine the nitrogen levels in a series of polycrystalline diamonds. The crystals were grown by the chemical vapour deposition (CVD) technique and EPR measurements indicate that they have a single substitutional nitrogen ( N s) concentration between 10 ppb and 50 ppm. Photoluminescence (PL) spectroscopy provides an extremely sensitive way of detecting the nitrogen vacancy complex, in both the neutral (N–V) 0 and negative charge states (N–V) −, down to the 10 ppb range and below. It has been observed that for diamonds with a single substitutional nitrogen content of approximately (0.5–2.0) ppm, the nitrogen vacancy complex exists in both charge states, with an almost equal abundance. Below this level, the complex exists with greater regularity in the neutral charge state, with the (N–V) − centre dominating at ( N s) levels greater than 2 ppm. Electron irradiation of so-called ‘high nitrogen’ films, with an ( N s) value in excess of 15 ppm, show an incredibly high abundance of the interstitial related 3H centre. Such samples show little sign of the neutral vacancy, GR1, although some absorption is evident in the tail of the (N–V) − centre. No evidence of the negative vacancy, the ND1 centre, was observed in PL spectra. For equivalent electron doses on ‘low N’ samples, typically with an ( N s) level of below 1 ppm, the GR1 centre completely dominates the PL spectra. For all diamonds the intensity of the nitrogen vacancy complexes are seen to reduce within the irradiated region. Annealing studies of high N samples reveal that by 900 °C all the vacancies are annealed with many being trapped at the nitrogen to form a large concentration of the (N–V) 0 centre. Positron annihilation measurements have been performed on the samples. As positron annihilation is sensitive to vacancy concentrations, it is expected to yield lifetime measurements that are strongly dependent on the bulk (N–V) concentration. Doppler broadening spectra have been recorded as the samples were illuminated with light varying from 325 to 785 nm. The shape ‘ S’ parameter was found to increase upon illumination and relax back to its ground state, post-illumination. The relaxation time was found to vary between 30 and 200 hours and be strongly dependent on both the nitrogen concentration and the wavelength of light used. Work is currently on-going, and includes angular correlation of annihilation experiments. Lifetime measurements show clear evidence of the formation of positronium in the voids that are present in the CVD material.

The effects of clearcutting and wildfire on grasshoppers and crickets (Orthoptera) in an intermountain forest ecosystem

Members of 3 families of Orthoptera (Acrididae, Gryllacrididae, Tettigoniidae) were sampled in clearcuts, burned forest, and undisturbed forest in a coniferous forest ecosystem in northern Utah, USA. Sampling was conducted during July and August, 1995 to 1997, by use of pitfall traps. The camel cricket Ceuthophilus fusiformis (Gryllacrididae: Rhaphidophorinae) was the most commonly trapped species in forested plots, where otherwise very few orthopterans were collected. Many more orthopterans were taken in clearcuts and burns and these had equal species richness and total orthopteran abundance. However, the orthopteran assemblages differed between these two treatments. Band-winged grasshoppers (Acrididae: Oedopodinae) tended to be trapped more frequently in clearcuts, especially Camnula pellucida. Burned plots provided greater numbers of Ceuthophilus fusiformis and Steiroxys pallidipalpus (Tettigoniidae: Decticinae).

Regulation of α 1-adrenoceptor-linked phosphoinositide metabolism in cultured glia: involvement of protein phosphatases and kinases

Noradrenaline-stimulated phosphoinositide breakdown in cultured glia was found to be mediated by α 1A-adrenoceptors. The α 1A-selective agonist A61603 was as effective as noradrenaline in eliciting 3H-inositol phosphate (IP) accumulation but was approximately 50-fold more potent. In addition, the use of selective antagonists revealed a clear rank order of potency in the ability of these drugs to reverse the effect of noradrenaline on phosphoinositide breakdown: RS17053 (α 1A-selective)≫AH11110A (α 1B-selective)>BMY7378 (α 1D-selective). Pre-treatment of cultured glia with the protein phosphatase inhibitor okadaic acid resulted in a concentration- and time-dependent reduction in noradrenaline-evoked 3H-IP accumulation. This effect was mimicked by, but was not additive with, a phorbol ester, was reversed by protein kinase C (PKC) inhibitors and was not evident in cells which had been PKC depleted. The ability of cell extracts to dephosphorylate radiolabelled glycogen phosphorylase revealed the presence of the phosphatases PP1 and PP2A in almost equal abundance. Okadaic acid pre-treatment of intact cultures elicited a marked reduction in total phosphatase activity, particularly that mediated by PP2A. We also determined the effect of okadaic acid pre-treatment on PKC and cyclic AMP-dependent protein kinase (PKA) activities in these cells. PKC and PKA activities in cell extracts were assessed by determining the incorporation of 32P into histone and kemptide, respectively. Okadaic acid elicited increases in both Ca 2+-dependent and Ca 2+-independent PKC activity; in addition, increases in both initial and total PKA activities were also recorded. The effect of okadaic acid on noradrenaline-stimulated 3H-IP accumulation were not, however, mimicked by either forskolin or 8-bromo-cyclic AMP, suggesting that this event is not regulated by PKA. Our data point to roles for both PKC and PP2A in the regulation of α 1A-adrenoceptor-linked phosphoinositide metabolism in cultured cortical glia.

Variation in Foraging Behavior and Body Mass in Broods of Emperor Geese (Chen Canagica): Evidence for Interspecific Density Dependence

Abstract Broods of geese spend time feeding according to availability and quality of food plants, subject to inherent foraging and digestive constraints. We studied behavioral patterns of broods of Emperor Geese (Chen canagica) on the Yukon–Kuskokwim Delta, Alaska, and examined how feeding and alert behavior varied in relation to habitat and goose density. During 1994–1996, time spent feeding by Emperor Goose goslings and adult females was positively related to multispecies goose densities near observation blinds, and not to just Emperor Goose density. Similarly, body mass of Emperor Goose goslings was more strongly related (negatively) to multispecies goose densities than intraspecific densities. A grazing experiment in 1995 indicated that most above ground primary production by Carex subspathacea, a preferred food plant, was consumed by grazing geese. Those results demonstrate that interspecific competition for food occurred, with greatest support for goslings whose behavioral repertoire is limited primarily to feeding, digesting, and resting. Although the more abundant Cackling Canada Geese (Branta canadensis minima) differed from Emperor Geese in their preferred use of habitats during brooding rearing (Schmutz 2001), the two species occurred in equal abundance in habitats preferred by Emperor Goose broods. Thus, Cackling Canada Geese were a numerically significant competitor with Emperor Geese. Comparing these results to an earlier study, time spent feeding by goslings, adult females, and adult males were greater during 1993–1996 than during 1985–1986. During the interval between those studies, densities of Cackling Canada Geese increased two to three times whereas Emperor Goose numbers remained approximately stable, which implies that interspecific competition affected foraging behavior over a long time period. These density-dependent changes in foraging behavior and body mass indicate that interspecific competition affects nutrient acquisition and gosling growth, which has a demonstrated effect (Schmutz 1993) on juvenile survival of Emperor Geese. Management of Emperor Geese should consider interspecific relations and densities of all goose species occurring on the Yukon–Kuskokwim Delta, Alaska.

Capillary isoelectric focusing–mass spectrometry: analysis of protein mixtures from human body fluids

Isoelectric focusing within a fused silica capillary (cIEF) has proved to be a powerful and practical method for high-resolution separation of analytes from complex biological mixtures. This technique overcomes many of the problems of isoelectric focusing within slab gel media. However current cIEF systems commonly utilize UV detection which limits the detail of analyte structural information that is obtained during analysis. The use of mass spectrometry (MS) as the detection system provides much greater structural information about the detected analytes allowing accurate relative molecular mass (M(r)) determination for proteins and polypeptides. We have constructed a cIEF-MS interface and compared the separation of standard proteins analyzed by cIEF-UV with cIEF-MS. This allowed rapid optimization of the cIEF-MS system performance. Further we have demonstrated the use of MS as a detection system provides accurate M(r) information and can provide analyte modification details. These factors increase the likelihood of absolute identification for physiological proteins within complex in vivo-derived mixtures. To demonstrate the value of cIEF-MS in such analyses we have undertaken an examination of cerebrospinal fluid (CSF), and tentatively identified a number of constituent proteins. We have also analyzed whole blood from control and diabetic patients. We show that glycated alpha- and beta- chains of hemoglobin are found in almost equal abundance in diabetic patient blood. From these results we suggest cIEF-MS is an efficient and useful tool for the separation and examination of in vivo-derived analytes within physiological fluids.

Mitochondrial gene expression in stamens is differentially regulated during male gametogenesis in Arabidopsis

Patterns of mitochondrial (mt) gene expression in male reproductive tissues and the correlation of such gene expression with developmental events have been studied to a limited extent in only a few plant species. In the present paper, expression of the mitochondrial genes atp1 and cox3, coding for the α subunit of the F1F0 ATP synthase and subunit 3 of cytochrome oxidase, respectively, was characterized during stamen development in Arabidopsis by RNA gel blot and in situ hybridization. Two atp1 transcripts were seen, which showed organ-specific expression levels. In contrast, a single size class of cox3 transcript was found which showed an equal abundance in roots, leaves and flowers. Atp1 transcripts were detected in all tissues of pre-meiotic flower buds and were particularly abundant in pollen mother cells and in the tapetum during meiosis. However, no atp1 transcripts were detected in post-meiotic anthers. In contrast, cox3 transcripts were abundant in the tapetum of late meiotic and post-meiotic anthers and persisted until tapetal degeneration. The results demonstrate that the timing and cell-specificity of mt gene expression are differentially regulated during the development of stamens and pollen and may reflect a changing respiratory status of mitochondria during male gametophyte development.

Infrared spectra of 6-thioguanine tautomers. An experimental and theoretical approach

Both amino-thiol N9H and amino-thiol N7H tautomeric forms of 6-thioguanine have been identified in approximately equal abundance in infrared studies of these molecules isolated in the hydrophobic environment of an argon matrix at 12 K. The relative concentrations of the amino-thiol N9H and amino-thiol N7H ([SH, N9H]/[SH, N7H]=K N9H−N7H=1.00±0.02) are estimated from the observed relative infrared absorbances. From these relative concentrations, the difference in the Gibbs free energy of these two tautomers (Δ G 500 N9H−N7H=−0.012±0.005 kJ mol −1) have been estimated. The infrared and Raman spectra of 6-thioguanine in solid state are also discussed in terms of hydrogen bonding and stacking interactions in the crystal which are not considered in the calculation. In an effort to interpret the experimental results, ab initio calculation of the infrared spectrum has been made for the amino-thione N7H tautomer at 3-21G level. Comparison with experimental spectra is of some help in the assignment of the infrared and Raman spectra for 6-thioguanine in the solid state.

Comparison of Avian Communities on Restored and Natural Wetlands in North and South Dakota

We compared avian use of 39 restored and 39 natural wetlands in North and South Dakota during spring and summer of 1997 and 1998. Wetlands were widely distributed, but restored- and natural-wetland pairs were from the same geographic locale and had similar characteristics, including wetland size. We conducted paired comparisons between restored and natural wetlands for wetland-bird density, waterfowl-breeding pairs, and wetland-avian abundance, species richness, and diversity. We also compared abundance, species richness, and diversity of birds on upland areas adjacent to wetlands. Canada goose (avian scientific names in Appendix A), mallard, redhead, and ruddy duck had higher densities on restored wetlands. We failed to detect differences in overall avian abundance, species richness, or diversity between restored and natural wetlands. We conclude that restored wetlands in the Prairie Pothole Region supported similar avian communities with equal or higher abundances than those of natural wetlands.