bluuebunny/crossref_metadata_2025 huggingface dataset:
Neotropical diversification: the effects of a complex history on diversity within the poison frog genus Dendrobates
Authors: Noonan Brice P. , Wray Kenneth P.
Published: May 2006

Aim  We study the Neotropical poison frogs of the genus Dendrobates Wagler, 1830 in order to clarify their phylogenetic relationships and biogeographical history. The genus Dendrobates is an excellent taxon for examining patterns of Neotropical diversification as the four major species groups appear to correspond roughly to distinct geographical regions: (1) trans‐Andean, (2) Andean foreland, (3) Brazilian Shield and (4) Guianan Shield/Central America. In order to test the agreement of five of the most prominent hypotheses of Amazonian diversification, phylogenetic patterns were examined for agreement with patterns predicted by these hypotheses.

Location  Central and South America

Methods  The phylogenetic relationships of the genus Dendrobates were examined from novel and existing (GenBank) sequences of four mitochondrial loci totalling c. 1400 bp from 40 specimens of 22 different species using maximum parsimony and Bayesian methods. Results were compared with traditional taxonomic arrangements by means of SH tests. Phylogenetic relationships and genetic distances were used to test the adequacy of various diversification hypotheses.

Results  Phylogenetic analyses support the restructuring of two species groups of Dendrobates and the creation of a new species group. Statistical tests of the traditional taxonomic arrangement indicate a significantly bad fit to the molecular data. This restructuring has important implications for the understanding of the historical biogeography of Dendrobates. Biogeographical patterns within this genus suggest that a complex interaction of biotic and abiotic factors since the Eocene have produced the diversity observed today.

Main conclusions  The current classification of Dendrobates into discrete species groups does not accurately reflect evolutionary history. Data presented here strongly support a monophyletic Brazilian Shield lineage whose members have previously been split among the quinquevittatus and tinctorius groups. Furthermore, previous attempts at elucidating the historical biogeography of this genus were compromised by incomplete sampling and conclusions drawn from a paraphyletic ingroup. Our findings demonstrate a role for numerous hypotheses of diversification (e.g. river, refuge, disturbance–vicariance) in the history of Dendrobates, supporting previous warnings about the dangers of over‐simplification in the study of Neotropical diversification.
Satellite‐based mapping of the growing season and bioclimatic zones in Fennoscandia
Authors: Karlsen Stein Rune , Elvebakk Arve , Høgda Kjell Arild , Johansen Bernt
Published: May 2006

Aim  To test whether satellite‐derived NDVI values obtained during the growing season as delimited by the onset of phenological phases can be used to map bioclimatically a large region such as Fennoscandia.

Location  Fennoscandia north of about 58° N and neighbouring parts of NW Russia.

Methods  Phenology data on birch from 15 research stations and the half‐monthly GIMMS‐NDVI data set with 8 × 8 km2 resolution from the period 1982–2002 were used to characterize the growing season. To link surface phenology with NDVI data, new algorithms on a pixel‐by‐pixel basis that show high correlation with phenophases on birch were developed. Then, time‐integrated values (TI NDVI) during the phenologically defined growing season were computed to produce a bioclimatological map of Fennoscandia, which was tested and correlated with growing degree days (GDD) obtained from 20 meteorological stations. The map was also compared vs. traditional bioclimatic maps, and analysed for error factors distorting NDVI values.

Results  The correlation between GDD and TI NDVI data during the phenologically defined growing season was very high. Therefore, the TI NDVI map could be presented as a bioclimatic map reflecting GDD. However, several major areas have interfering factors distorting NDVI values, such as the pixel heterogeneity caused by the altitudinal mosaic in western Norway, the mosaic of lakes in southeastern Finland, and the agriculture‐dominated areas in southern Fennoscandia.

Main conclusions  TI NDVI data from the phenologically defined growing season during 1982–2002 in Fennoscandia can be processed as a bioclimatic map reflecting GDD, except for the areas distorting NDVI values by their strong ground‐cover heterogeneity.
Monetary Policy, Expectations and Commitment*
Authors: Evans George W. , Honkapohja Seppo
Published: May 2006

Commitment in monetary policy leads to equilibria that are superior to those from optimal discretionary policies. A number of interest‐rate reaction functions and instrument rules have been proposed to implement or approximate commitment policy. We assess these rules in terms of whether they lead to a rational expectations equilibrium that is both locally determinate and stable under adaptive learning by private agents. A reaction function that appropriately depends explicitly on private sector expectations performs particularly well on both counts.
Design and Planned Analyses of an Ongoing Randomized Trial Assessing the Preventive Effect of Helicobacter pylori Eradication on Occurrence of New Gastric Carcinomas After Endoscopic Resection
Authors: Kikuchi Shogo , Kato Mototsugu , Katsuyama Tsutomu , Tominaga Suketami , Asaka Masahiro
Published: May 2006

Background:  A causal relationship between Helicobacter pylori infection and gastric cancer has been established. A nonrandomized study has shown eradication of H. pylori after endoscopic resection (ER) of early gastric cancer inhibits development of new carcinomas.

Subjects and Methods:  Eligible subjects are patients with H. pylori infection who are newly diagnosed with early gastric cancer and plan to have ER or who are in the post‐resection follow‐up phase after ER time of enrollment. Patients are randomly allocated to the eradication or the control arms (no eradication and standard of care). Patients will be evaluated by endoscopy at 0.5, 1, 2, and 3 years after randomization. Diagnosis of a new carcinoma at another site of the stomach is defined as primary endpoint, and recurrence of tumors at the resection site as a secondary endpoint. In addition to intention‐to‐treat and per‐protocol analyses using proportional hazards models, time to recurrence will be compared between treatment and control using multiple logistic regression analyses. In the latter two situations, the models will be adjusted for the factors exerting significant influences on the results.

Results:  Five hundred and forty‐two subjects have been enrolled into the study and are being followed‐up.

Conclusions:  This study will have the statistical power to demonstrate whether H. pylori eradication therapy exerts any clinically relevant inhibitory effects on occurrence or recurrence of gastric cancer. In addition, it will be able to test the hypothesis that H. pylori infection is a promoter in gastric carcinogenesis.
Presurgical Language fMRI in Patients with Drug‐resistant Epilepsy: Effects of Task Performance
Authors: Weber Bernd , Wellmer Jörg , Schür Simone , Dinkelacker Vera , Ruhlmann Jürgen , Mormann Florian , Axmacher Nikolai , Elger Christian E. , Fernández Guillén
Published: May 2006

Summary:  Purpose: To determine whether language functional magnetic resonance imaging (fMRI) before epilepsy surgery can be similarly interpreted in patients with greatly different performance levels.

Methods: An fMRI paradigm using a semantic decision task with performance control and a perceptual control task was applied to 226 consecutive patients with drug‐resistant localization‐related epilepsy during their presurgical evaluations. The volume of activation and lateralization in an inferior frontal and a temporoparietal area was assessed in correlation with individual performance levels.

Results: We observed differential effects of task performance on the volume of activation in the inferior frontal and the temporoparietal region of interest, but performance measures did not correlate with the lateralization of activation.

Conclusions:
fMRI, as applied here, in patients with a wide range of cognitive abilities, can be interpreted regarding language lateralization in a similar way.
Pregabalin Exerts Oppositional Effects on Different Inhibitory Circuits in Human Motor Cortex: A Double‐blind, Placebo‐controlled Transcranial Magnetic Stimulation Study
Authors: Lang Nicolas , Sueske Elke , Hasan Alkomiet , Paulus Walter , Tergau Frithjof
Published: May 2006

Summary: Purpose:To explore acute effects of pregabalin (PGB) on human motor cortex excitability with transcranial magnetic stimulation (TMS).

 Methods:PGB, 600 mg/day, was orally administered in 19 healthy subjects twice daily in a randomized, double‐blind, placebo‐controlled crossover design. Several measures of motor cortex excitability were tested with single‐ and paired‐pulse TMS.

 Results:Mean short‐interval intracortical inhibition (SICI) was reduced after PGB (74 ± 7% of unconditioned response) compared with placebo (60 ± 6% of unconditioned response). In contrast, mean long‐interval intracortical inhibition (LICI) was increased by PGB (26 ± 4% of unconditioned response) compared with placebo (45 ± 8% of unconditioned response), and mean cortical silent period (CSP) showed an increase from 139 ± 8 ms or 145 ± 8 ms after placebo to 162 ± 7 ms or 161 ± 10 ms after PGB. Motor thresholds, intracortical facilitation, and corticospinal excitability were unaffected.

 Conclusions:The observed excitability changes with oppositional effects on SICI and LICI or CSP suggest γ‐aminobutyric acid (GABA)B‐receptor activation. They are markedly distinct from those induced by gabapentin, although both PGB and gabapentin are thought to mediate their function by binding to the α(2)‐δ subunit of voltage‐gated calcium channels. Conversely, the TMS profile of PGB shows striking similarities with the pattern evoked by the GABA‐reuptake inhibitor tiagabine.
Incidence and Predictors of Seizures in Patients with Alzheimer's Disease
Authors: Amatniek Joan C. , Hauser W. Allen , DelCastillo‐Castaneda Carrie , Jacobs Diane M. , Marder Karen , Bell Karen , Albert Marilyn , Brandt Joseph , Stern Yaakov
Published: May 2006

Summary:  Purpose: To determine cumulative incidence and predictors of new‐onset seizures in mild Alzheimer's disease (AD) with a cohort followed prospectively. Limited information is available on the incidence of seizures, and no reports exist of seizure predictors in AD patients.

Methods: Mild AD patients were prospectively followed at 6‐month intervals to estimate incidence of unprovoked seizures, compare age‐specific risk of unprovoked seizures with population norms, and identify characteristics at baseline (demographics, duration and severity of AD, physical and diagnostic test findings, and comorbid medical and psychiatric conditions) influencing unprovoked seizure risk. Review of study charts and medical records supplemented coded end‐point data.

Results: The cumulative incidence of unprovoked seizures at 7 years was nearly 8%. In all age groups, risk was increased compared with a standard population, with an 87‐fold increase in the youngest group (age 50–59 years) and more than a threefold increase in the oldest group (age 85+ years). In multivariate modeling, independent predictors of unprovoked seizures were younger age [relative risk (RR), 0.89 per year increase in age; 95% confidence interval (CI), 0.82–0.97], African‐American ethnic background (RR, 7.35; 95% CI, 1.42–37.98), more‐severe dementia (RR, 4.15; 95% CI, 1.06–16.27), and focal epileptiform findings on electroencephalogram (EEG) (RR, 73.36; 95% CI, 1.75–3075.25).

Conclusions: Seizure incidence is increased in people starting with mild‐to‐moderate AD. Younger individuals, African Americans, and those with more‐severe disease or focal epileptiform findings on EEG were more likely to have unprovoked seizures.
Fabrication of Transparent Cerium‐Doped Lutetium Aluminum Garnet Ceramics by Co‐Precipitation Routes
Authors: Li Hui‐Li , Liu Xue‐Jian , Xie Rong‐Jun , Zeng Yi , Ping Huang Li
Published: May 2006

Nanosized, highly sinterable Ce‐doped lutetium aluminum garnet (LuAG:Ce) powders were synthesized by the urea homogeneous co‐precipitation routes. LuAG:Ce transparent ceramics with an average grain size of about 6 μm were successfully fabricated at 1800°C for 10 h by vacuum sintering without sintering aids using the powders calcined at 1000°C for 2 h. The transmittance in the visible light region reaches 65%. The radioluminescence spectrum displays a broad band located at 480–650 nm consisting of two emissions due to the transitions from the lowest 5d excited state to the 4f ground state of Ce3+, which is consistent with that of LuAG:Ce single crystal and well coupled with the silicon photodiodes.
Multi‐Scale Study of Sintering: A Review
Authors: Olevsky Eugene A. , Tikare Veena , Garino Terry
Published: May 2006

An integrated approach, combining the continuum theory of sintering with a kinetic Monte‐Carlo (KMC) model‐based mesostructure evolution simulation is reviewed. The effective sintering stress and the normalized bulk viscosity are derived from mesoscale simulations. A KMC model is presented to simulate microstructural evolution during sintering of complex microstructures taking into consideration grain growth, pore migration, and densification. The results of these simulations are used to generate sintering stress and normalized bulk viscosity for use in continuum level simulation of sintering. The advantage of these simulations is that they can be employed to generate more accurate constitutive parameters based on most general assumptions regarding mesostructure geometry and transport mechanisms of sintering. These constitutive parameters are used as input data for the continuum simulation of the sintering of powder bilayers. Two types of bilayered structures are considered: layers of the same particle material but with different initial porosity, and layers of two different materials. The simulation results are verified by comparing them with shrinkage and warping during the sintering of bilayer ZnO powder compacts.
Peripheral Blood Mononuclear Cells from Individuals Infected with Human T-Cell Lymphotropic Virus Type 1 Have a Reduced Capacity To Respond to Recall Antigens
Authors: Mascarenhas Rita Elizabeth , Brodskyn Cláudia , Barbosa Geisa , Clarêncio Jorge , Andrade-Filho Antônio Souza , Figueiroa Frederico , Galvão-Castro Bernardo , Grassi Fernanda
Published: May 2006

Evidence indicates that human T-cell lymphotropic virus type 1 (HTLV-1) infection leads to chronic immunosuppression and a greater susceptibility to infectious diseases. Spontaneous in vitro proliferation of peripheral blood mononuclear cells (PBMC) is an important immunological feature of HTLV-1-infected individuals. However, the association between spontaneous proliferation and immunosuppression is not clear. In this study, we evaluated the cellular immune responses of PBMC from 58 asymptomatic HTLV-1-infected individuals with PBMC showing or not showing spontaneous proliferation. Individuals with PBMC that spontaneously proliferated had increased proportions of CD4 T cells expressing CD45RO and dramatically reduced responses to recall antigens. In addition, frequencies of positive responses to recall antigens were also decreased in HTLV-infected individuals without spontaneous proliferation of PBMC. There was a polyclonal expansion of multiple T-cell receptor Vβ families of CD4
+
T lymphocytes in patients with spontaneous proliferation. We observed that HTLV-1 induced an immunosuppression characterized by a decrease in the stimulation index to a recall antigen, even in individuals who did not present spontaneous proliferation. On the other hand, only patients with PBMC presenting spontaneous proliferation showed polyclonal activation and increased proportion of CD4 T cells expressing CD45RO.
Lymphatic Tissue Fibrosis Is Associated with Reduced Numbers of Naïve CD4
+
T Cells in Human Immunodeficiency Virus Type 1 Infection
Authors: Schacker Timothy W. , Brenchley Jason M. , Beilman Gregory J. , Reilly Cavan , Pambuccian Stefan E. , Taylor Jodie , Skarda David , Larson Matthew , Douek Daniel C. , Haase Ashley T.
Published: May 2006

The organized structure of lymphatic tissues (LTs) constitutes a microenvironment referred to as a niche that plays a critical role in immune system homeostasis by promoting cellular interactions and providing access to cytokines and growth factors on which cells are dependent for survival, proliferation, and differentiation. In chronic human immunodeficiency virus type 1 (HIV-1) infection, immune activation and inflammation result in collagen deposition and disruption of this LT niche. We have previously shown that these fibrotic changes correlate with a reduction in the size of the total population of CD4
+
T cells. We now show that this reduction is most substantial within the naïve CD4
+
T-cell population and is in proportion to the extent of LT collagen deposition in HIV-1 infection. Thus, the previously documented depletion of naïve CD4
+
T cells in LTs in HIV-1 infection may be a consequence not only of a decreased supply of thymic emigrants or chronic immune activation but also of the decreased ability of those cells to survive in a scarred LT niche. We speculate that LT collagen deposition might therefore limit repopulation of naïve CD4
+
T cells with highly active antiretroviral therapy, and thus, additional treatments directed to limiting or reversing inflammatory damage to the LT niche could potentially improve immune reconstitution.
Production of an Anti-Severe Acute Respiratory Syndrome (SARS) Coronavirus Human Monoclonal Antibody Fab Fragment by Using a Combinatorial Immunoglobulin Gene Library Derived from Patients Who Recovered from SARS
Authors: Liu Jinye , Shao Hongxia , Tao Yanlin , Yang Bin , Qian Lisheng , Yang Xiaoli , Cao Brian , Hu Gengxi , Tachibana Hiroshi , Cheng Xunjia
Published: May 2006

A combinatorial human immunoglobulin gene library was constructed from the peripheral lymphocytes of two patients who recovered from severe acute respiratory syndrome (SARS). The library was screened for the production of Fab antibody fragments to a recombinant spike protein of SARS-associated coronavirus (SARS-CoV). One Fab clone, AS3-3, reacted with the spike protein in an enzyme-linked immunosorbent assay. The dissociation constant of AS3-3 was 1.98 × 10
−8
M. Immunofluorescent microscopy revealed that it reacted with SARS-CoV-infected cells. The library seems to be a potent tool for the production of human antibodies to SARS-CoV.
Synthesis and characterization of some dibasic tridentate Schiff base ligands
Authors: Alyea Elmer C. , Malek Abdul
Published: May 2006

not available
The reduction of acetals with cobalt carbonyl catalysts
Authors: Fleming Bruce I. , Bolker Henry I.
Published: May 2006

When heated with a dicobalt octacarbonyl (Co2(CO)8) catalyst under synthesis gas, acetals of aromatic aldehydes (in contrast to aliphatic acetals) gave good yields of the products of reductive cleavage, but no products of hydroformylation. A mechanism is proposed to explain the products of cyclic acetals of benzaldehyde which yielded not only the expected hydroxy-ethers, but also considerable amounts of dibenzyl ethers. The room temperature reductive cleavage of aromatic acetals by pure HCo(CO)4 in organic solvents indicates that HCo(CO)4 might be the active species in the catalytic reductions. Since acetals of benzaldehyde para-substituted with electron-releasing groups cleaved faster than those substituted with electron-withdrawing groups, the mechanism probably involves a carbonium ion intermediate.The previously observed formation of dibenzyl ether during benzaldehyde reduction with cobalt carbonyl catalysts can now be explained via the reductive cleavage of hemiacetal or acetal intermediates.
Substituent and solvent effects on organic acids: an electrostatic theory
Authors: Matsui Takeki , Hepler Loren G.
Published: May 2006

We have used an electrostatic model as basis for derived equations to represent the effects of substituents and solvents on the thermodynamics of proton transfer reactions. Equations derived in this manner are related to those based on earlier 'internal-environmental' models and are also discussed in relation to recent gas phase acidity work.
Mercury(I) chemistry. Part I. Complexes of the mercurous ion with some arenes
Authors: Dean Philip A. W. , Ibbott David G. , Stothers J. B.
Published: May 2006

not available
The heat of formation of N2H2 and the proton affinity of N2
Authors: Willis C. , Lossing F. P. , Back R. A.
Published: May 2006

not available
Defensive substances of Coccinella transversoguttata and Hippodamia caseyi, ladybugs indigenous to western Canada
Authors: Ayer William A. , Bennett Michael J. , Browne Lois M. , Purdham James T.
Published: May 2006

The defensive substances of two species of ladybug indigenous to western Canada have been isolated. The known compounds precoccinelline (1) and coccinelline (2) are present in Coccinella transversoguttata, and hippodamine (3) and convergine (4) in Hippodamia caseyi. From the latter insect we have also isolated two new alkaloids, a new base, N-oxide pair, which we have named hippocasine and hippocasine oxide. The structure of hippocasine oxide (8) was established by spectroscopic methods and confirmed by X-ray analysis of the hydrochloride (9d and Fig. 1).
The decomposition of dimethylbenzylanilinium chloride in alcoholic solvents
Authors: Ko Munan , Sato Tsuneyuki , Otsu Takayuki
Published: May 2006

The decomposition of dimethylbenzylanilinium chloride (DMBAC) was found to follow second-order kinetics in ethanol or aqueous ethanol solvents, but first-order kinetics in higher alcoholic solvents. From the activation parameters obtained at 80 °C, different isokinetic relationships were found for the ethanol series and the higher alcohol series. The dissociation constants of DMBAC in ethanol and isopropanol at 80 °C were calculated to be 7.34 × 10−3 and 2.10 × 10−4 mol/l, respectively, from conductivity measurements. Accordingly, it was concluded that in higher alcohols the major part of DMBAC exists as ion pairs, which are responsible for the decomposition reaction, but in ethanol the decomposition involves a bimolecular reaction between free ions.
Nicotinamide coenzyme regeneration. Flavin mononucleotide (riboflavin phosphate) as an efficient, economical, and enzyme-compatible recycling agent
Authors: Jones J. Bryan , Taylor Keith E.
Published: May 2006

The high cost of nicotinamide coenzymes currently acts as a deterrent to the widespread adoption of alcohol dehydrogenases as chiral catalysts for effecting stereospecific and selective [Formula: see text] oxidoreductions on a preparative scale. Attempts to overcome this problem generally involve using catalytic amounts of coenzyme together with an auxiliary system capable of continuously regenerating its active form insitu. Flavin mononucleotide has been found to be an effective, convenient, and inexpensive reagent for insitu recycling of NAD+. Using horse liver alcohol dehydrogenase-catalyzed oxidation of cyclohexanol as a representative process, up to 50-fold NAD+-regeneration levels have been achieved. This method is the most satisfactory and practical oxidative-mode recycling procedure yet developed for routine laboratory applications.
Nicotinamide coenzyme regeneration. The rates of some 1,4-dihydropyridine, pyridinium salt, and flavin mononucleotide hydrogen-transfer reactions
Authors: Jones J. Bryan , Taylor Keith E.
Published: May 2006

The rates of H-transfer between various 1,4-dihydropyridines and pyridinium salts (including NADH and NAD+), and from 1,4-dihydropyridines to FMN, have been measured. The reactions are found to be sufficiently slow for H-transfer to be rate-determining to a significant extent when such Systems are applied for nicotinamide coenzyme recycling purposes. The rates of H-transfer parallel the magnitudes of the donor–acceptor redox potential differences (ΔE0′); ΔE0′ values may therefore be used as qualitative guides in formulating and selecting redox couples of NAD/H recycling value. On the basis of deuterium isotope effects, it is concluded that formation of a complex prior to H-transfer is not rate determining for 1,4-dihydropyridine–NAD+ reactions. This behavior is in contrast to that of other model alcohol dehydrogenase Systems.
Reactions of organolithium compounds with sulfonate esters. A novel sulfone synthesis
Authors: Baarschers W. H.
Published: May 2006

The reaction of a variety of organolithium compounds with sulfonate esters leads to nucleophilic substitution on sulfur, resulting in the formation of sulfones in moderate to high yields. Several new sulfones were prepared by this method.
The photochemistry of 2-furaldehyde vapour. II. Photodecomposition: direct photolysis at 253.7 and 313 nm and Hg(3P1)-sensitized decomposition
Authors: Gandini A. , Parsons J. M. , Back R. A.
Published: May 2006

The photolysis of furaldehyde vapour at 253.7 nm, 65 °C, and pressures from about 0.2 to 7 torr, produces CO, propyne, allene, furan, cyclopropene, CO2, and C2H2. The quantum yield of CO approaches 2 at low pressure and decreases towards zero with increasing pressure of furaldehyde or added CO2. Yields of the other products also decrease but show a more complex pressure dependence. A mechanism involving excited furaldehyde and excited C4H4O and C3H4 intermediates is suggested.The Hg(3P1)-photosensitized decomposition gives products very similar to those of the direct photolysis. Photolysis at 313 and 366 nm also leads to similar products but in much lower yields, with the major product, CO, having a quantum yield of about 0.01. Some photopolymerization was observed in all Systems.
Acid dissociation constants and rates as studied by ultrasonic absorption
Authors: Green Larry W. , Kruus Peeter , McGuire M. Jacqueline
Published: May 2006

Experimental ultrasonic absorption data on solutions of H2SO4 and H3PO4 are interpreted in terms of proton transfer equilibria. The acid dissociation constants obtained are compared with those obtained using other methods and are shown to be consistently lower. A model is proposed to explain this in terms of ΔVθ and ΔHθ involved in the steps leading to recombination of the proton with the anion. This model is supported by the values of the reaction distance parameters calculated from the value of the rate constant obtained for the recombination rate. The accuracy of this rate constant is dependent on the accuracy of the ΔVθ value used for the equilibrium. Experimental density data are presented here as an aid in determining ΔVθ. Problems involving activity coefficients in such solutions are discussed in the course of checking the values used for species present in sulfuric acid solutions.
Excess energy–volume and cohesive energy density coefficients for binary systems. Comparison with constant pressure functions
Authors: Macdonald Digby D.
Published: May 2006

Excess energy–volume and cohesive energy density coefficients have been calculated for the hexane + perfluoro-hexane, water + DMSO, water + tert-butanol, water + methanol, water + acetonitrile, and methanol + DMSO Systems. These parameters are compared with other constant pressure excess functions of mixing for these binary systems, and it is proposed that they represent additional criteria for the classification of liquid mixtures.
Photosolvation of [Co(CN)6]3−, trans-[Cr(NH3)2(NCS)4]−, and trans-[Cr(en)2NCSF]+ in aqueous mixed solvent systems
Authors: Wong Carl Fook Chow , Kirk Alexander David
Published: May 2006

Photosolvation of [Co(CN)6]3−(1), trans-[Cr(NH3)2(NCS)4]−(2) and trans-[Cr(en)2NCSF]+(3) has been studied in various water/methanol, ethanol, acetonitrile, ethylene glycol, glycerol, and acetone mixtures and in aqueous solutions of polyvinylpyrolidone. The quantum yield for thiocyanate loss from 3 was found to be fairly independent of solvent, while for thiocyanate loss from 2, large, and at higher concentrations of organic solvent, specific reductions of quantum yield were observed. The study of 1 using spectrophotometric analysis for [Co(CN)5H2O]2− yielded similar data to some in the literature, but the larger range of systems studied here did not support the reported reduction of quantum yield with bulk viscosity. Furthermore evidence from this and other work suggests that many of the observed quantum yield reductions are only apparent, based on a false assumption that the photosolvation is qualitatively the same in ail mixtures. The data are reinterpreted in terms of competitive solvation by both solvent components. It is argued that this study supports a dissociative model of reaction for 1, but an associative model for the chromium complexes 2 and 3.
Transfert du champ de forces de l'isothiazole: étude des vibrations moleculaires des dérivés de l'isothiazole monosubstitués en position 3, 4 ou 5
Authors: Mille Gilbert , Chouteau Jacques , Avignon Thierry , Bouscasse Luc
Published: May 2006

The study of normal vibrations of 3-, 4-, or 5-monosubstituted isothiazole derivatives, assuming transferability of the valence force field of isothiazole, gives results which agree with the experimental data and which permit the assignment of the various vibrations.
The solubility of water in low-dielectric solvents
Authors: Kirchnerová Jitka , Cave Genille C. B.
Published: May 2006

The solubility of water has been measured in several low-dielectric solvents at 25 °C, and the values in the nonpolar solvents are treated by using a modification of the Scatchard–Hildebrand equation. The water–solvent interaction parameter in this equation is represented by a new relationship involving the separate contributions due to dispersion and polar interactions. A new method is given for calculation of the dispersion component of the solubility parameter of a polar species. Formation constants are reported for 1:1 water–solvent complexes in carbon tetrachloride, benzene, toluene, and p-xylene.
Crystal and molecular structure of difluoroboron N-methylacethydroxamate (2,2-difluoro-4,5-dimethyl-1,3-dioxa-4-azonia-2-boranatacyclopent-4-ene)
Authors: Rettig Steven J. , Trotter James , Kliegel W. , Nanninga D.
Published: May 2006

Crystals of difluoroboron N-methylacethydroxamate are monoclinic, a = 5.097(1), b = 10.653(2), c = 11.520(2) Å, β = 103.57(2)°, Z = 4, space group P21/c. The structure was solved by direct methods and was refined by full-matrix least squares procedures to a final R of 0.056 and Rw of 0.077 for 988 reflections with I ≥ 3σ(I). The structure features a planar five-membered BO2CN ring. Bond lengths (corrected for libration) are: B—F, 1.374(3) and 1.381(3), O—B, 1.496(3) and 1.497(3), O—N, 1.349(2), O—C, 1.346(2), C—N, 1.298(3) and 1.458(3), and C—C, 1.468(3) Å.
Synthesis and electron spin resonance studies of a Co(II) complex with a tetradentate macrocyclic Schiff base ligand
Authors: Reuveni Amikam , Malatesta Vincenzo , McGarvey Bruce R.
Published: May 2006

The synthesis, physical properties, and electron spin resonance of frozen solutions of CoTAAB(NO3)2 (TAAB = tetrabenzo[b,f,j,n] [1,5,9,13]tetraazacyclohexadecine) are reported. The spin Hamiltonian parameters were elucidated by simulation of spectra assuming axial g and 59Co hyperfine tensors and including nuclear quadrupole and Zeeman contributions. Electron spin resonance spectra in solvents such as methanol, acetone, and dimethylformamide are typical for a low spin complex (S = 1/2) and are nearly identical with [Formula: see text] and [Formula: see text]. In pyridine and quinoline a complex with a molar ratio solvent/ligand of 1:1 is formed with the solvent which gives [Formula: see text]and [Formula: see text] much closer to [Formula: see text]. In strong Lewis bases, such as piperidine, a 2:1 complex is formed and no esr signal is found. Evidence is presented to show that these 2:1 complexes with strong Lewis bases are S = 1/2 complexes with a low lying S = 3/2 state that is partially populated at room temperatures. This behaviour is accounted for in terms of a theory derived for a 2A1 ground state with a low lying quartet state which could become the ground state in strong basic solvents.
The para substituent dependence of the internal rotational barrier in benzenethiol
Authors: Schaefer Ted , Parr William J. E.
Published: May 2006

On the basis of the observed spin–spin coupling constants between the sulfhydryl and ring protons and a hindered rotor treatment of the twofold barrier to internal rotation in a series of para substituted benzenethiol derivatives, it is argued that V2 is essentially zero in p-amino-benzenethiol and is 2.5 ± 0.2 kcal/mol in p-nitrobenzenethiol; having intermediate values for the methoxy, fluoro, methyl, and bromo derivatives in solution. The results are based on an assumed relationship between the four-bond and the fictitious six-bond couplings to the sulfhydryl proton. The conclusions are consistent with the observed magnitudes of the couplings over six and seven bonds, respectively, between the sulfhydryl proton and the fluorine nucleus and the methyl protons in the appropriate derivatives; as well as with the coupling between the sulfhydryl and methyl protons in 4-bromo-3-methylbenzenethiol. The experimental barriers are compared with ab initio molecular orbital calculations of their substituent dependence.
Infrared studies of water in crystalline hydrates: K2HgCl4.H2O
Authors: Falk Michael , Knop Osvald
Published: May 2006

Infrared spectra of polycrystalline K2HgCl4.H2O at different degrees of deuteration were recorded, in the 4000–250 cm−1 region, at temperatures between liquid-nitrogen and 130 °C. The spectra confirm the existence of a single type of water molecule, engaged in two equivalent hydrogen bonds. The value of 2548 cm−1 for the isolated O—D stretching frequency leads to an estimate of 3.25(3) Å for the O … Cl hydrogen-bond distance, in excellent agreement with the results of X-ray and neutron diffraction. Dynamic coupling is appreciable for stretch, bend, and librational fundamentals but is weaker than in CuCl2.2H2O or K2CuCl4.2H2O, in which the water molecules in the crystal are more tightly bonded.A number of corrected values are reported of isolated O—D stretching frequencies in hydrates studied previously.
Electron mobility in nonpolar liquids: the effect of molecular structure, temperature, and electric field
Authors: Schmidt Werner F.
Published: May 2006

A survey is given on the mobility of excess electrons in liquid hydrocarbons and related compounds. It was found that the mobility is strongly influenced by the molecular structure of the liquid, by the temperature, and by the electric field strength. The mobility in hydrocarbons increases as the shape of the molecule approaches a sphere. The temperature coefficient is positive in most liquids over a limited temperature although exceptions have been observed in liquid methane. The field dependence of the mobility in high mobility liquids (>10 cm2V−1s−1) showed a decrease of the mobility at higher field strengths while in low mobility liquids (<1 cm2V−1s−1) it showed an increase. These results are discussed on the basis of the extended and the localized electron models. The predictions of these theories are compared with the experimental results and conclusions on the validity of the underlying assumptions are drawn.
Use of 13C in biosynthetic studies. Incorporation of 13C-labeled acetate into chartreusin by Streptomyceschartreusis
Authors: Canham P. L. , Vining L. C. , McInnes A. G. , Walter J. A. , Wright J. L. C.
Published: May 2006

Examination by 13C nuclear magnetic resonance spectroscopy of chartreusin produced in cultures of Streptomyceschartreusis supplemented with [1-13C] and [2-13C]acetate showed that the 19-carbon aglycone component was derived entirely from acetate. In the spectrum of chartreusin enriched from [1,2-13C]acetate the signals for 16 of the carbon atoms were accompanied by satellites due to spin–spin coupling of intact 13C—13C units. The coupled pairs were matched with the aid of homonuclear single 13C-frequency decoupling. Of the uncoupled carbon atoms, two were derived from methyl groups of acetate and the third came from an acetate carboxyl group. The arrangement of paired and unpaired 13C atoms in chartreusin suggests that the aglycone is derived from a single 22-carbon polyketide chain. Cyclization to a benzpyrene-like intermediate followed by ring cleavage and loss of three carbon atoms provides a plausible route from the polyketide to the substituted isocoumarin structure of the aglycone.
Luminescence différée d'une solution organique vitreuse photoactivée et transition vitreuse
Authors: Ceccaldi D.
Published: May 2006

A general kinetic theory is used to explain the shapes of photoionized sample luminescence curves perturbed by thermal jumps (Δ ∼ 1 K, rise time ∼ 1 s). The samples studied are photoactivated organic vitreous solutions of TMPD/MCH 10−3 M and TMPD/3-MP 10−3 M. The experiments are performed within a temperature range (63–91 K) which includes the glass transition temperature Tg. It is shown that there is a slow diffusion of the trapped electrons towards the cation and competition between thermal detrapping and tunneling. The tunneling/thermal detrapping ratio Y is not time dependent during an isothermal luminescence and is only slowly temperature dependent if T ≤ Ty. Ty is very close to Tg. For T > Ty, Y decreases rapidly with T. The activation energy for thermal detrapping shows a maximum when the temperature reaches

[Formula: see text] The glass transition temperature Tg may therefore be defined empirically as:[Formula: see text]Finally we obtain a glassy matrix relaxation time, τ, which decreases with T.
Nuclear analogs of β-lactam antibiotics. V. Synthesis of a benzo[3,4]-O-2-isocephem
Authors: Doyle Terrence William
Published: May 2006

The synthesis of 7-β-phenoxyacetamido-4′-hydroxybenzo[3,4]-O-2-isocephem 14 is described. Condensation of 5 with cinnamaldehyde gave 6 which was converted to the 3-azido-4-styrrylazetidinone 7. Ozonolysis and reduction of the resulting aldehyde 8 gave 9. Compound 9 was converted to the mesylate 12 by reduction of the azide to the amine 10, coupling of 10 with phenoxyacetic acid to give 11, and mesylation of 11. Removal of the benzyl groups of 12 by hydrogenolysis and base catalyzed ring closure of the phenol gave 14.
Derivatives of 2-pyrazolin-5-one. V. Preparation and properties of 1′,2′-dihydrospiro[[2]pyrazoline-4,3′ (4′H)-quinoline]-5-one.derivatives and related compounds
Authors: Coutts Ronald T. , El-Hawari Abdel-Monaem
Published: May 2006

1′,2′-Dihydro-3-methyl-1-phenylspiro[[2]pyrazoline-4,3′(4′H)-quinoline]-5-one (8q), the structurally related 1,3-diphenylspiro[pyrazolone-quinoline] 8r and numerous 2′-substituted derivatives of 8q and 8r are readily accessible from catalytic reduction of 3-methyl-1-phenyl- or 1,3-diphenyl-4-(2-nitrobenzyl)-2-pyrazolin-5-one (1a, 1b, respectively) in alcohols (with the incorporation of the alkylidene moiety) or by interaction of the corresponding 2-aminobenzyl precursors (3a, 3b) with appropriate aldehydes and ketones. All spiro compounds were characterized by mass, ir, and 1Hmr spectra. The products obtained by reducing the spiro compounds with sodium borohydride and with lithium aluminum hydride are described. Reduction of 1a and 1b with zinc and acetic acid gave 3-methyl-1-phenyl- and 1,3-diphenyl-1H-pyrazolo[3,4-b]quinoline (2a, 2b, respectively).
Kinetics and mechanism of the oxidation of several ketones by tris(1,10-phenanthroline)Fe(III) in aqueous acid medium
Authors: Ng Flora T. T. , Henry Patrick M.
Published: May 2006

The kinetics of the oxidation of acetone, 2-butanone, 2,4-dimethyl-3-pentanone, 3-methyl-2-butanone, and 3-pentanone by tris(1,10-phenanthroline)Fe(III) (ferriin) were determined in aqueous solutions containing either sulphuric or perchloric acid in the presence or absence of air. The kinetics are consistent only with a mechanism involving oxidation of the enol tautomer by ferriin. The rate constants of enolization calculated from this kinetic analysis agree well with the literature values. Relative reactivity of the four enols from symmetrical ketones were found to be in the order: 2,4-dimethyl-3-pentanone > 3-pentanone > cyclohexanone > acetone. The rate of oxidation of the enol form of 2,4-dimethyl-3-pentanone is approximately 1000 fold larger than that of the enol form of acetone, indicating that electron-donating methyl substituents enhance the rate of electron transfer from the enol tautomer to ferriin.Kinetics of the oxidation carried out in air were generally the same as in its absence; the rates of oxidation were found to be slower by a factor of 2 in most cases. This suggests that the initially formed enol radical reacts with O2 rather than a second ferriin to give the oxidized product. At high [ferriin] in air, pseudo zero-order kinetics were observed initially as in its absence. However, above about 50% reduction of ferriin, the reaction appears to involve auto-catalysis and was not studied further.
Lifetimes of the solvated electron in liquid alcohols
Authors: Baxendale J. H. , Wardman Peter
Published: May 2006

The solvated electron, es−, decays with first-order kinetics in pulse-irradiated aliphatic alcohols, attributed to reaction 1: es− + ROH → products. It is suggested that a recent report of curved Arrhenius plots for the temperature dependence of the rate constants for reaction 1 can be ascribed to reaction of es− with impurities.
Etude par spectroscopie infrarouge de l'ion diacétylacétylium. Rôle de AlCl3, AlBr3 et GaCl3 sur sa formation et sa structure. Mise en évidence d'une liaison hydrogène intramoléculaire dans le tétrachloroaluminate de diacétylacétylium
Authors: Germain Alain , Pascal Jean-Louis , Potier Jacqueline
Published: May 2006

The study of the reaction of formation of the diacetoacetylium ion from CH3COX (X = Cl or Br) and the Lewis acids AlCl3, AlBr3, and GaCl3 shows that the counterion is always the tetrahalogenometallate. In the solid tetrachloroaluminate the cation is a monomer with a double minimum type of intramolecular hydrogen bond: v O—H—O = v O—D—O = 1400 cm−1; d O—O = 2.48 Å. An identical behaviour is observed with the tetrabromoaluminate, but the structure of the diacetoacetylium sstetrachlorogallate is more complicated.
Raman and infrared spectral studies of polycrystalline thallium(I) halates, TIXO3
Authors: Viste Arlen , Irish Donald E.
Published: May 2006

Raman and infrared spectra have been recorded for polycrystalline samples of TIClO3, TIBrO3, and T1IO3 at room temperature. The vibrational spectra of these rhombohedral (R3m, C3v5) crystals are closely related to each other, and to single crystal Raman spectra of isomorphous RbClO3 and KBrO3 reported by others. Spectral assignments are made. The uni-molecular unit cell yields no correlation field splitting, but lack of a center of inversion leads to TO/LO splitting of each active mode in these uniaxial piezoelectric crystals. Relationships between the thallium(I) halates and the NaN3 and MXY3 perovskite structures are considered.
Cupric ion binding by coal humic acids at pH's 1–3
Authors: Green John B. , Manahan Stanley E.
Published: May 2006

The extent and mechanism of cupric ion binding by humic acid (HA) at low pH's where the material was insoluble in aqueous media was investigated. It was shown that significant amounts of Cu(II) were bound by HA even at pH's as low as 1.35. Two major types of HA—Cu2+ binding were observed. Binding which was accompanied by exchange of H+ was more prevalent at high pH's and [Cu2+]. Nonexchange bonding occurred at all pH's, but assumed greater importance at low pH's. Since the pattern of Cu(II) uptake could not be interpreted in terms of basic ion exchange or surface adsorption theory, a new model was proposed which qualitatively explained the dependence of Cu(II) on pH and [Cu2+]. The model assumed that the intermolecular bonding in flocculated HA was determined by the relative amounts of H+ and Cu2+ available for forming bridging bonds between the HA molecules. The model suggested that at high concentrations of Cu(II) and/or high pH's, the floc structure was such that the formation of copper bridge bonds was maximized.
Strong amide–halothane hydrogen-bonding observed by nuclear magnetic resonance
Authors: Brown John M. , Chaloner Penny A.
Published: May 2006

The widely-used halothane anaesthetic CF3CHBrCl exhibits a proton magnetic resonance signal in CCl4 solution which is strongly deshielded by addition of N-methylpyrrolidone. This is interpreted as a hydrogen-bonding interaction with halothane C—H as donor and carbonyl as acceptor. From the temperature dependence of the halothane C—H proton chemical shift in the presence of varying concentrations of N-methylpyrrolidone, thermodynamic parameters ΔH0 = −4.7 kcal mol−1 and ΔS0 = −14 cal mol−1deg−1 were obtained. The carbon magnetic resonance spectrum of the two components in CCl4 shows desheilding of the carbonyl carbon at higher concentrations of CF3CHBrCl the halocarbons (1-H) undecafluorobicycloheptane and (1-H,4-H)decafluorobicycloheptane show similar H-bonding behaviour which is comparable with that exhibited by CHCl3.These results are discussed in relation to their possible relevance to the mechanism of action of halocarbon anaesthetics.
Vibrational analysis of alkyl bromides. II. Secondary bromides
Authors: Crowder G. A. , Iwunze Maurice
Published: May 2006

Infrared and Raman spectra were obtained for 2-bromopentane, 3-bromopentane, 2-bromohexane, and 3-bromohexane. Vibrational assignments were made for several conformers of each compound with the aid of normal coordinate calculations. A 48 parameter modified valence force field was obtained that fit 221 frequencies of three conformers of 2-bromopentane, 4 conformers of 3-bromopentane, and 1 conformer of 2-bromobutane with an average error of 4.1 cm−1. This force field was transferred to the bromohexanes, with good results.
Etude par résonance paramagnétique électronique de la radiolyse de la pyridine N-oxyde en matrice vitreuse de methanol
Authors: Quaegebeur J. P. , Perly B. , Surpateanu G. , Lablache-Combier A.
Published: May 2006

The analysis of esr spectra derived from γ irradiated pyridine N-oxide in a methanolic vitreous matrix at 77 K shows the presence of a mixture of 2- and 4-azacyclohexadienyl N-oxide radicals (respectively 1 and 2) formed by the addition of the hydroxymethyl primary species to the pyridine ring. The structure of the different radicals was determined by comparison with spectra derived from several substituted pyridine N-oxides.
Matrix dependence of the electron spin resonance spectra of the radical trapped in different single crystals
Authors: Michaut J. P. , Roncin J.
Published: May 2006

Nitrogen and proton coupling tensors have been measured for the [Formula: see text] radical trapped in five different single crystal matrices. As all isotropic coupling constants are the same within experimental error (aN = 21.2 G, aH = 28.4 G), no measurable crystal field effect is found. In these solids the motions of the radical depend on the dimension of the trapping cage and the motions of the surrounding molecules.
Nuclear charge dispersion studies in the light-mass region formed in the fission of 238U by protons of energy 35–85 MeV
Authors: Galinier J.-L. , Dikšić M. , Yaffe L.
Published: May 2006

Cross sections for the independent formation of 76As and 78As, for the partially cumulative formation of 77As and 77Ge, and the cumulative formation of 79As, 78Ge, and 75Ge formed in the fission of 238U by protons of energies 35–85 MeV have been determined. Charge dispersion curves have been obtained. Values of (ZA – Zp) and full-widths at half-maximum of the curves show that the behaviour of these light-mass products is the same as their complementary fragment (A ≈ 152). This is inconsistent with values found at A = 96.