bluuebunny/crossref_metadata_2025 huggingface dataset:
The turnover of carbohydrate carbon in a cultivated soil estimated by 13C natural abundances
Authors: Derrien D. , Marol C. , Balabane M. , Balesdent J.
Published: May 2006

Understanding the chemical composition of soil organic matter (SOM) requires the determination of the dynamics of each class of compounds. We measured the dynamics of carbon in neutral carbohydrates by use of natural 13C labelling in an experimental wheat and maize sequence extending over 23 years. The isotopic composition of individual neutral monosaccharides was determined in hydrolysed particle‐size fractions by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) of trimethylsilyl (TMS) derivatives. The sensitivity in terms of 13C/12C ratios ranged between 1 and 2‰ depending on the monosaccharide. The age distribution of neutral sugar carbon was very similar to that of total soil carbon. Particulate organic matter (POM) was characterized by the predominance of glucose and xylose of vegetal origin. In POM > 200 µm, the mean age of sugar‐C (5 years) was slightly less than that of total carbon (7 years). Xylose was younger than glucose. The fine fraction 0–50 µm contained mainly glucose, arabinose, galactose, xylose, fucose and mannose, which had predominantly microbial origins. The mean age of carbohydrate carbon in the fraction 0–50 µm was between 60 and 100 years and was similar to that of total organic carbon (OC). No difference in the age of carbon between the individual monosaccharides was found. The POM fraction 50–200 µm had an intermediate signature and turnover. Considering the typical lability of carbohydrates, the relatively great age of carbohydrate carbon may be explained by physical or chemical protection from degradation, as well as by recycling of soil organic matter carbon by soil microbes.
Involving mental health service users in quality assurance
Authors: Weinstein Jenny
Published: May 2006

Objective  This study compares the process and outcomes of two approaches to engaging mental health (MH) service users in the quality assurance (QA) process.

Background  QA plays a significant role in health and care services, including those delivered in the voluntary sector. The importance of actively, rather than passively, involving service users in evaluation and service development has been increasingly recognized during the last decade.

Design  This retrospective small‐scale study uses document analysis to compare two QA reviews of a MH Day Centre, one that took place in 1998 as a traditional inspection‐type event and one that took place in 2000 as a collaborative process with a user‐led QA agenda.

Setting and participants  The project was undertaken with staff, volunteers and service users in a voluntary sector MH Day Centre.

Intervention  The study compares the management, style, evaluation tools and service user responses for the two reviews; it considers staff perspectives and discusses the implications of a collaborative, user‐led QA process for service development.

Results  The first traditional top–down inspection‐type QA event had less ownership from service users and staff and served the main purpose of demonstrating that services met organizational standards. The second review, undertaken collaboratively with a user‐led agenda focused on different priorities, evolving a new approach to seeking users’ views and achieving a higher response rate.

Conclusions  Because both users and staff had participated in most aspects of the second review they were more willing to work together and action plan to improve the service. It is suggested that the process contributed to an evolving ethos of more effective quality improvement and user involvement within the organization.
Mortality predictions for colon and anorectal cancer for Ireland, 2003–17
Authors: O'Lorcain P. , Deady S. , Comber H.
Published: May 2006

Objective  Colorectal cancer mortality predictions for Ireland are presented for all ages and for the age group 0–64 years.

Methods  Log and log‐linear Poisson regression modelling was fitted to colorectal cancer mortality data for each year between 1950 and 2002 to predict average European age standardized mortality rates (EASMRs) per 100 000 person years (100 000 PY−1) and average numbers of deaths.

Results  EASMRs for colon cancer are predicted to fall to 17.3 100 000 PY−1 (95%PI 14.4, 20.2) in men and to 8.4 100 000 PY−1 (95%PI 6.9, 10.2) in women by 2013–17. EASMRs for anorectal cancer are also predicted to fall to 8.0 100 000 PY−1 (95%PI 6.6, 9.5) in men and to 3.0 100 000 PY−1 (95%PI 2.3, 3.8) in women by this time. Truncated EASMRs for colon cancer for those aged between 0 and 64 years are predicted over the next 15 years to fall from their current levels to 4.4 100 000 PY−1 (95%PI 3.0, 5.8) in men and to 2.3 100 000 PY−1 (95%PI 1.5, 3.2) in women. For anorectal cancer, truncated EASMRs for those aged between 0 and 64 years are also predicted over the next 15 years to fall from their current levels to 2.9 100 000 PY−1 (95%PI 2.0, 3.8) in men and to 0.9 100 000 PY−1 (95%PI 0.4, 1.3) in women.

Conclusions  Ireland currently has one of the highest colorectal mortality rates in the developed world but recent downward trends, the advent of new screening tests and well targeted public health promotion programmes may lead to further reductions.
Characterizing regime shifts in the marine environment
Authors: Lees Kathryn , Pitois Sophie , Scott Catherine , Frid Chris , Mackinson Steven
Published: May 2006

Recent years have seen a plethora of studies reporting that ‘regime shifts’ have occurred in the North Atlantic and Pacific Oceans during the last century. In many cases, the criteria used to distinguish a regime shift have not been explicitly stated. In other cases, a formal definition has been proposed and the data set assessed against it. Developing a universal quantitative definition for identifying and distinguishing between purported climatic and ecological regime shifts has proved problematic as many authors have developed criteria that seem unique to the system under study. Consequently, they throw little light on the drivers of ecological regime shifts. Criteria used to define regime shifts are reviewed and on the basis of evidence from purported regime shifts, common characteristics in the speed and amplitude of the changes and the duration of quasi‐stable states are used to propose a more clearly defined set of criteria for defining climatic and ecological regime shifts. Causal drivers of regime shifts are explored using correlation analysis. Limitations of these methods are discussed.
Achieving Compliance when Legal Sanctions are Non‐deterrent*
Authors: Tyran Jean‐Robert , Feld Lars P.
Published: May 2006

Law backed by non‐deterrent sanctions (mild law) has been hypothesized to achieve compliance because of norm activation. We experimentally investigate the effects of mild law in the provision of public goods by comparing it to severe law (deterrent sanctions) and no law. The results show that exogenously imposing mild law does not achieve compliance, but compliance is much improved if mild law is endogenously chosen, i.e., self‐imposed. We show that voting for mild law induces expectations of cooperation, and that people tend to comply with the law if they expect many others to do so.
Brightness contrast perception in the mesopic region
Authors: Freyssinier J. P. , Rea M. S. , Bullough J. D.
Published: May 2006

Subjective evaluations of brightness contrast were obtained for Munsell chips of varying hues, lightness values and sizes against a white background illuminated in turn by four white illuminants at four background luminances in the mesopic region. Chip lightness was the strongest variable, resulting in a family of monotonic functions relating brightness contrast ratings to chip lightness. At the lowest light levels a nearly linear relationship was found between chip lightness and subjective ratings. As light levels increased, the relationship became curvilinear such that at the lowest contrast, chromatic brightness became important for subjective ratings. Within the level of precision for this experiment, chip hue and size as well as the spectral power distribution of the illuminants did not significantly impact the overall brightness contrast ratings. The subjective ratings of brightness contrast were analysed as a function of the luminance contrast of the stimuli as determined by conventional photometry and by three models of mesopic vision. The response functions relating subjective rating to the stimulus characterized in terms of these models were similar to those obtained with conventional photometry.
Clinical disorders affecting mesopic vision
Authors: Petzold Axel , Plant Gordon T.
Published: May 2006

Vision in the mesopic range is affected by a number of inherited and acquired clinical disorders. We review these conditions and summarize the historical background, describing the clinical characteristics alongside the genetic basis and molecular biological mechanisms giving rise to rod and cone dysfunction relevant to twilight vision. The current diagnostic gold standards for each disease are discussed and curative and symptomatic treatment strategies are summarized.
Multiple Mutations in or Adjacent to the Conserved Penicillin‐Binding Protein Motifs of the Penicillin‐Binding Protein 1A Confer Amoxicillin Resistance to Helicobacter pylori
Authors: Gerrits Monique M. , Godoy Anita P. O. , Kuipers Ernst J. , Ribeiro Marcelo L. , Stoof Jeroen , Mendonça Sergio , Van Vliet Arnoud H. M. , Pedrazzoli José , Kusters Johannes G.
Published: May 2006

Background:  Amoxicillin‐based therapies are highly effective for the treatment of Helicobacter pylori infections, but the efficacy may decrease as the incidence of amoxicillin resistance is increasing. So far, the molecular mechanism underlying stable amoxicillin resistance has only been identified for a few naturally occurring amoxicillin‐resistant (AmxR) H. pylori isolates, and is mediated by mutations in penicillin‐binding protein 1A (PBP1A). In this study the molecular mechanism underlying amoxicillin resistance of seven additional AmxR H. pylori isolates has been established.

Methods:  H. pylori strain 26695 (minimal inhibitory concentration (MIC) 0.125 mg/l) was naturally transformed with total DNA and pbp1A polymerase chain reaction (PCR) products from the seven AmxR H. pylori isolates, and the MIC of amoxicillin and pbp1A gene sequence of the obtained AmxR transformants were determined.

Results:  Replacement of the wild‐type pbp1A gene of H. pylori reference strain 26695 by the pbp1A gene of the AmxR H. pylori isolates resulted in an increased MIC (0.5–1.0 mg/l). Sequence analysis of the smallest PBP1A fragments able to transfer the resistance indicated that several amino acid substitutions in or adjacent to the second (SKN402−404) and third (KTG555−557) conserved penicillin‐binding protein motifs (PBP‐motifs) mediate amoxicillin resistance in H. pylori. This was confirmed by site‐directed mutagenesis using oligonucleotides that contained defined mutations in or adjacent to these PBP‐motifs.

Conclusion:  In naturally occurring AmxR H. pylori isolates, amoxicillin resistance is mediated by various mutational changes located in or adjacent to the second and third PBP‐motifs of the PBP1A. Although we cannot exclude the role of the other genes in amoxicillin resistance, it is likely that multiple mutational changes in the PBP1A gene are the predominant cause of amoxicillin resistance in H. pylori. The findings of this study currently preclude the rapid detection of amoxicillin resistance in H. pylori by molecular tests.
Cracking During Lateral Drying of Alumina Suspensions
Authors: Holmes Derek M. , Vasant Kumar R. , Clegg William J.
Published: May 2006

The onset of cracking during drying of alumina suspensions cast onto a substrate has been studied experimentally. It is shown that the capillary pressure would impose a compressive stress on the particle array and cannot itself cause cracking. Based on experimental observations, it is proposed that the driving force for cracking arises from a misfit strain that occurs when repulsive layers between the particles collapse completely, after the particles have adhered to the substrate. This predicts that cracking should occur while the space between the particles is still filled with liquid, which is consistent with observations using laser speckle interferometry.
C‐reactive protein in patients with coexistent periodontal disease and acute coronary syndromes
Authors: Czerniuk Maciej R. , Górska Renata , Filipiak Krzysztof J. , Opolski Grzegorz
Published: May 2006

Aim: To evaluate periodontal disease (PD) influence on changes in high‐sensitivity C‐reactive protein (hsCRP) concentrations in patients with acute coronary syndromes and coexistent PD.

Materials and Methods: Dental examinations were carried out in a group of 50 consecutive patients, less than 60 years old, hospitalized as a result of acute coronary syndromes. The patients were divided into two groups on the basis of own‐constructed combined PD score (group 2: more advanced; and group 1: less advanced PD) as well as clinical attachment loss (CAL) – group 4: CAL >3 mm; group 3: CAL 3 mm. Blood samples for hsCRP estimation were taken at admission, after 10/12 days and long term after acute coronary syndromes.

Results: A statistically significant decrease in hsCRP was observed among three consecutive blood sample examinations in groups 2 and 4, whereas it was only seen between examination 1 and examination 2 in groups 1 and 3.

Conclusions: Although no statistically significant difference of hsCRP was found between studied groups, patients with less advanced PD, either estimated with the use of own‐constructed combined score or on the basis of CAL, have significantly longer diminution of inflammatory response monitored with hsCRP concentrations.
Insulin induces heme oxygenase‐1 through the phosphatidylinositol 3‐kinase/Akt pathway and the Nrf2 transcription factor in renal cells
Authors: Harrison Ewen M. , McNally Stephen J. , Devey Luke , Garden O. J. , Ross James A. , Wigmore Stephen J.
Published: May 2006

Heme oxygenase‐1 catalyzes the breakdown of heme and is protective in models of kidney transplantation. In this study we describe the induction of heme oxygenase‐1 mRNA and protein by insulin. Following treatment with insulin, a five‐fold increase in heme oxygenase‐1 mRNA and a four‐fold increase in protein expression were observed in renal adenocarcinoma cells; insulin‐induced heme oxygenase‐1 expression was also demonstrated in mouse primary tubular epithelial cells. The induction of heme oxygenase‐1 in renal adenocarcinoma cells was blocked by actinomycin D and cycloheximide and was abolished by the phosphatidylinositol 3‐kinase inhibitor, LY294002, but not by the inactive analog LY303511. Overexpressing a dominant‐negative form of Akt abrogated the heme oxygenase‐1‐inducing effects of insulin, whereas cells transfected with a constitutively active Akt construct demonstrated an increase in heme oxygenase‐1 promoter activity and protein expression. The transcription factor NF‐E2‐related factor‐2 was found to translocate to the nucleus following insulin treatment in a phosphatidylinositol 3‐kinase‐dependent manner. Pretreatment with NF‐E2‐related factor‐2 small‐interfering RNA abolished insulin‐induced heme oxygenase‐1 induction. Insulin was also found to activate the mitogen‐activated protein kinase cascades p38 and extracellular signal‐related kinase; however, inhibition of these pathways with SB202190 and PD98059 did not alter insulin‐induced heme oxygenase‐1 expression. Thus, insulin induces heme oxygenase‐1 mRNA and protein expression in renal cells in a phosphatidylinositol 3‐kinase/Akt and NF‐E2‐related factor‐2‐dependent manner.
Global Change and Southern Africa
Authors: MEADOWS MICHAEL E.
Published: May 2006

The developing nations of southern Africa have previously been identified as vulnerable to the vagaries of global change, particularly in terms of future climate change. This paper explores recent climate change scenarios for the region in terms of some representative sectors of the environment‐society interface, namely biodiversity, agriculture and related land uses, water resources and health issues. It is concluded that the impacts of predicted climate changes over the next century are likely to be very marked indeed. Biome distribution, agriculture, rangelands and water resources are highlighted as being negatively impacted in ways that will increase the vulnerability of the great majority of the region's population to natural hazards. The potential impact of these changes on the prolific biodiversity of southern Africa is clear. Holistic policy responses, incorporating both environmental and human development concerns, are required in the near future if a crisis is to be averted.
Changes in Activation States of Murine Polymorphonuclear Leukocytes (PMN) during Inflammation: a Comparison of Bone Marrow and Peritoneal Exudate PMN
Authors: Itou Takuya , Collins L. Vincent , Thorén Fredrik B. , Dahlgren Claes , Karlsson Anna
Published: May 2006

To study different activation states in polymorphonuclear leukocytes (PMN) in mice, we compared the function of murine PMN obtained from the bone marrow (BMPMN) with those of PMN obtained by intraperitoneal induction with thioglycolate (TGPMN) or uric acid (UAPMN). When stimulated with chemotactic peptides, e.g., formyl-methionyl-leucyl-phenylalanine (fMLF), WKYMVM, or WKYMVm, the TGPMN and UAPMN showed greatly enhanced generation of reactive oxygen species (ROS) compared with BMPMN, which suggests that exudation to the peritoneum per se induces a primed state in the cells. The WKYMVm peptide was the most potent stimulant of ROS generation, and it desensitized for subsequent stimulation with fMLF or WKYMVM. This desensitization was broken by the addition of cytochalasin B. The TGPMN and UAPMN appeared to be fully primed, since no increase in response was induced by pretreatment with tumor necrosis factor α (TNF-α). In contrast, the BMPMN response was increased 2.5- to 3-fold. The differences in oxidative responses were supported by degranulation studies. Preincubation with TNF-α promoted CR3 expression on BMPMN, and this level of expression was also enhanced by WKYMVm. In contrast, CR3 expression on untreated TGPMN and UAPMN was already similar to that on TNF-α-primed BMPMN and could be only slightly enhanced by TNF-α treatment. Taken together, these results indicate that BMPMN are in a resting state and have the capacity to become primed, while peritoneal exudate PMN are already fully primed upon isolation. These results have major implications for murine neutrophil research and show the importance of defining which PMN subsets to use when investigating murine models.
Expression of a Mitochondrial Peroxiredoxin Prevents Programmed Cell Death inLeishmania donovani
Authors: Harder Simone , Bente Meike , Isermann Kerstin , Bruchhaus Iris
Published: May 2006

Leishmaniapromastigote cells transmitted by the insect vector get phagocytosed by macrophages and convert into the amastigote form. During development and transformation, the parasites are exposed to various concentrations of reactive oxygen species, which can induce programmed cell death (PCD). We show that a mitochondrial peroxiredoxin (LdmPrx) protectsLeishmania donovanifrom PCD. Whereas this peroxiredoxin is restricted to the kinetoplast area in promastigotes, it covers the entire mitochondrion in amastigotes, accompanied by dramatically increased expression. A similar change in the expression pattern was observed during the growth ofLeishmaniafrom the early to the late logarithmic phase. Recombinant LdmPrx shows typical peroxiredoxin-like enzyme activity. It is able to detoxify organic and inorganic peroxides and prevents DNA from hydroxyl radical-induced damage. Most notably,Leishmaniaparasites overexpressing this peroxiredoxin are protected from hydrogen peroxide-induced PCD. This protection is also seen in promastigotes grown to the late logarithmic phase, also characterized by high expression of this peroxiredoxin. Apparently, the physiological role of this peroxiredoxin is stabilization of the mitochondrial membrane potential and, as a consequence, inhibition of PCD through removal of peroxides.
Kinetic study of the spin orbit states of atomic germanium, Ge(43P0,1,2), by time-resolved attenuation of atomic resonance radiation
Authors: Brown Adam , Husain David
Published: May 2006

Germanium atoms in all the three spin orbit states arising from the 4p2 ground state configuration, 43P0, 43P1 (557 cm−1), and 43P2 (1410 cm−1), have been generated by the pulsed irradiation of GeBr4 and monitored photoelectrically in absorption by time-resolved attenuation of atomic resonance radiation derived from a microwave discharge. The decays have been monitored in the presence of added gases and absolute second order rate constants for the removal of all three atomic states reported for the collision partners, He, Xe, O2, CO, NO, and GeBr4. These rate constants constitute the first detailed rate data for germanium atoms in any specific quantum state.
1,3-Dipolar cycloadditions with diazomethylphosphonates. Double pyrazolines derived from norbornadiene
Authors: Cohen Huguette , Benezra Claude
Published: May 2006

Four new exo- double pyrazolines 3–5 have been prepared from norbornadiene and dimethyl phenyldiazomethylphosphonate; their structures have been proven by nmr spectroscopy. There is a strong predominance of the isomers with the two aryl groups syn to the bridge. When the two aryl groups were different no electronic interaction between them could be detected by uv spectroscopy. Direct photolysis of the double pyrazolines leads to the corresponding double cyclopropanes with retention of configuration.
Etude comparée du rapport isomérique du 84m,fRb produit dans une cible d'yttrium 89 par des protons et des particules α
Authors: Krupa Jean-Claude
Published: May 2006

A physical method for separation of alkali metals, carried out inside a surface ionization ion source of an electromagnetic isotope separator, was used to determine the isomeric ratio of 84m,fRb produced in 89Y targets bombarded by protons and α-particles of energies between 40 and approximately 160 MeV.The variation of isomeric ratio with energy of the incident particles enabled the principal reaction to be differentiated from other possible mechanisms. With compound nucleus formation as the mechanism and the use of a statistical Fermi-gas model, the spin cut-off parameters were deduced, based on the Huizenga–Vandenbosch formalism. The kinetic momentum effect was investigated by a comparison of the proton and α-particle induced reactions.
Spin trapping of radicals formed during radiolysis of aqueous solutions. Direct electron spin resonance observations
Authors: Sargent Frederick Peter , Gardy Edward Michael
Published: May 2006

It is shown that esolv, H•, and OH formed by the radiolysis of water by 3 MeV electrons are trapped by nitroso and nitrone compounds to give nitroxides with well defined esr spectra. Three spin trapping agents were used, nitroso-t-butane, phenyl-t-butyl nitrone, and 5,5′-dimethyl pyrroline-1-oxide. The latter was shown to be an excellent compound for these studies. Complications due to the instability of some of the nitroxides were overcome by coupling the electron accelerator to the esr spectrometer to permit direct observation of the spectra.
Reactions of sodium tetrahydroborate and cyanotrihydroborate with ruthenium(II) and (III) systems in the presence of tertiary phosphines
Authors: Holah David G. , Hughes Alan N. , Hui Benjamin C.
Published: May 2006

The first tetrahydroborato–phosphine complexes of Ru(II) are reported and a number of new cyanotrihydroborato and hydrido complexes of Ru(II) are also recorded. Among the more interesting complexes prepared are RuH(BH4)(PPh3)3, RuH(BH4)(CO)(PPh3)3, RuH(BH4)(CO)2[P(C6H11)3]2, and RuH(BH3CN)(CO)2(DBP)2 (DBP is the ligand 5-phenyl-5H-dibenzophosphole). It is shown that unlike Rh(III), Ru(III) is not stabilized by phosphine complex formation towards reduction by tetrahydroborate ion although Ru(II) is not reduced further by this reagent. A stepwise mechanism is proposed for the reduction of phosphine–dichloro Ru(II) systems to hydrido–tetrahydroborato and dihydro complexes. Nuclear magnetic resonance studies show that certain of the products are mixtures of geometrical isomers and, in several cases, detailed nmr assignments are made.
The use of ceric ammonium nitrate in pyrrole chemistry
Authors: Paine III John B. , Dolphin David
Published: May 2006

Ceric ammonium nitrate, in aqueous acetic acid buffered with sodium acetate, rapidly oxidizes 2,2′-dipyrromethanes to the corresponding 2,2′-dipyrroketones.
A facile synthesis of sulfonyl chlorides
Authors: Langler Richard F.
Published: May 2006

Benzylic sulfides have been shown to furnish sulfonyl chlorides in excellent yields, upon reaction with molecular chlorine in aqueous acetic acid. The reaction most likely proceeds through the intermediacy of the corresponding sulfenyl chloride.
The photochemistry of some bisethylenediamine and cyclam complexes of rhodium(III)
Authors: Sellan James , Rumfeldt Robert
Published: May 2006

The visible and uv photolysis of trans-[Rh(A4)X2]+ and cis-[Rh(A4)Y2]+ have been studied where A4 is the macromolecule 1,4,8,11-tetraazacyclotetradecane (cyclam) or two ethylenediamine (en) molecules, X is Cl, Br, or I, and Y is Cl. With the exception of cis-[Rh(en)2Cl2]+, all photoreactions proceeded via halide aquation with complete isomeric retention for both ligand field and charge transfer excitation. In the case of cis-[Rh(en)2Cl2]+, amine aquation is the principal reaction with some isomerization occurring through a secondary reaction. The quantum yield of halide increased in the order Cl < Br < I for trans-[Rh(A4)X2]+, but was found to be almost equally sensitive to the degree of chelation of the amine system so that the photoactivity of trans-[Rh(NH3)4Cl2]+ and trans-[Rh(cyclam)I2]+ were nearly equal [Formula: see text] These systems were also found to be more sensitive to charge transfer excitation than ligand field excitation with cis-[Rh(cyclam)Cl2]+ being the most sensitive complex [Formula: see text]The photochemistry of the systems studied has been interpreted in terms of a dominant influence of electronic factors in determining the type of photoreaction with the quantitative aspects being significantly influenced by mechanistic factors.
Potential energy calculations of the mechanisms of self-diffusion in molecular crystals: adamantane
Authors: Fyfe C. A. , Harold-Smith D.
Published: May 2006

A simple but physically well–defined model for self-diffusion in molecular solids is described. This is combined with semi-empirical atom–atom pair potentials for nonbonded atoms to test various possible diffusion mechanisms in the two phases of adamantane. For adamantane it is found that (1) diffusion occurs by jumps to single-vacancy holes at nearest-neighbor lattice sites, (2) the four molecules closest to the midpoint of the jumps are cooperatively distributed among their equilibrium orientations, and (3) the jump trajectory is curved. The computed enthalpy of activation is in good agreement with the experimental value obtained from T1ρ and vapor pressure measurements. The rate of self-diffusion in β-adamantane has not been reported, but the enthalpy of activation has been calculated for various mechanisms and indicates the critical role of lattice disorder in the self-diffusion of plastic crystals.
A comparison of methods for pKa determination in strongly basic systems applied to the deprotonation of some heterocyclic methiodide salts
Authors: Cox Robin A. , Stewart Ross , Cook Michael J. , Katritzky Alan R. , Tack Robert D.
Published: May 2006

Ionization values for the deprotonation of the methiodide salts 1–8, which occurs in strongly basic DMSO/water mixtures containing 0.047 M base, are used to determine pKa values by the Bunnett–Olsen and Marziano–Cimino–Passerini techniques, which involve extrapolation to the purely aqueous state. The resulting values are compared with those obtained using the H0q acidity function; agreement is good in most cases.
Intramolecular vibrational energy relaxation. Decomposition of chemically activated alkylcyclobutanes
Authors: Wang Fa-Mei , Rabinovitch B. S.
Published: May 2006

This paper describes an approach to the study of intramolecular energy relaxation of highly vibrationally excited complex molecules. The features of the decomposition of a series of chemically activated alkylcyclobutanes are outlined, including variable selectivity of the initial, non-randomized state of excitation. It is shown how this can afford both a qualitative test of the postulate of internal energy randomization employed in the Rice–Ramsperger–Kassel–Marcus treatment of unimolecular reactions, as well as a quantitative measure of the rate of relaxation. The study of the first members of this series, ethyl and dimethyl cyclobutane, is described. As expected, the first members can provide a lower limit to the relaxation rate, namely, λ > 1012 s−1.
Milieux hyperbasiques: préparation et alkylation de carbanions en α d'amides N,N-disubstitués. Application à la synthèse de la d,l-pipéritone
Authors: Hullot Pierre , Cuvigny Thérèse , Larchevêque Marc , Normant Henri
Published: May 2006

The anions α to N,N-disubstituted amides can be conveniently prepared by treatment with very powerful bases, "activated dialkylamides" in HMPT. These anions may react with various electrophiles especially with halogenated compounds. The use of functional halides (chloro or bromo compounds) affords functional amides. Lithiated amides are very useful intermediates in organic synthesis because they give regiospecific alkyl ketones by reacting with organo lithium compounds. In this way, we succeeded in obtaining the 1,5-diketone which was cyclised by intramolecular aldolization into d,l-piperitone.
A re-examination of the nitrobenzene – 2,2,4-trimethyl pentane system in the consolute region and of the thermodynamical considerations concerning the value of ε′ at the consolute point
Authors: Halliwell R. , Hutchinson D. A. , McIntosh R.
Published: May 2006

Failure to find maxima in ε′and ε″for aniline–cyclohexane in the consolute region by Lubezky and McIntosh (8) led to re-examination of the system nitrobenzene–2,2,4-trimethyl pentane for which anomalous values of ε′and ε″ have been reported. Earlier results by Lubezky and McIntosh (6) could not be repeated. A re-examination of thermodynamical arguments was then undertaken and the conclusion reached that these do not predict anomalous values of ε′.
Reaction rates of electrons in liquid methanol and ethanol: effects of pressure
Authors: Bolton Gerald L. , Robinson Maurice G. , Freeman Gordon R.
Published: May 2006

The value of the rate constant k1 for the reaction e−solv → RO−solv + H, [1], at 295 K and 1 bar is ≤1.4 × 105 s−1 in methanol and ≤8 × 104 s−1 in ethanol. The respective volumes of activation averaged between 1 bar and 2 kbar are ΔV1≠ ≤ −21 and ≤ −22 cm3 mol−1. A high concentration of potassium hydroxide (1 M) or water (5 M) decreases the apparent value of k1 somewhat but has little or no effect on the value of ΔV1≠. The effect of pressure on the rate constant of e−solv + S → product, [2], was also measured for a series of solutes that displays a wide range of reactivity. Experimental values of ΔV2≠ depend on the relative contributions of the effects of solvent density on the reactant diffusion rates, the concentrations of the actual reacting species, and the relative energies of the reactant and intermediate states. For reactions whose rates are near the diffusion controlled limit, k2 ≈ 1010 M−1 s−1 in methanol and ethanol, the values of ΔV2≠ are positive and similar to those for the diffusion of simple ions. ΔV≠(e−solv diffusion) = 4 cm3 mol−1 in methanol and 6 cm3 mol−1 in ethanol. Cadmium chloride is apparently not completely dissociated in alcohols, and k(e−solv + CdCl2) < k(e−solv + CdCl+) < k(e−solv + Cd2+). For a series of compounds with lower rate constants there is a correlation between log k2 and ΔV2≠, the latter being negative for very low values of k2. The products of electron capture by benzene, toluene, ethyl acetate, and possibly acetonitrile appear to be stabilized by protonation: [Formula: see text] S−solv + ROH → SH + RO−slov, [4]. The results indicate that the decomposition of e−solv in a pure alcohol occurs by protonation of the electron site, e−solv + ROH → H + RO−slov, [4′], rather than by electron transfer to an alcohol molecule followed by decomposition of the anion.
Empirical equations for predicting 13C chemical shifts in nuclear magnetic resonance spectra of certain types of amino acids
Authors: MacDonald James C. , Bishop Gregory G. , Mazurek Mytosk
Published: May 2006

13C chemical shift data were obtained for amino acids related to glycine which had the following types of substituents on C-2: alkyl, branched chain alkyl, ω-amino alkyl, and ω-guanido alkyl. Such data were obtained for aqueous solutions at a pH between the pK values of the carboxyl and 2-amino groups (zwitterion form). The data were subjected to graphical and statistical analysis to obtain separate predictive equations for C-1, C-2, and other carbon atoms. Data for the change in chemical shifts on titration with acid were also obtained to aid in 13C assignments and to elucidate configuration.
Reactions of trifluoromethyl radicals with iodine and nitric oxide
Authors: Amphlett J. C. , Macauley L. J.
Published: May 2006

The reactions 2 and 3 have been studied by competitive methods. Use of previous Arrhenius[Formula: see text][Formula: see text]parameters for reaction 2 leads to k3 = 1.3 × 1010 exp −[(700 ± 100J)/RT]. Arrhenius parameters of reactions 2 and 3 are compared with those for reactions of other radicals with I2 and NO.
The thermal (dark) decomposition of 2-(2′,4′-dinitrophenylamino)-2-deoxy-D-glucose (DNP-glucosamine) in alkaline borate buffer
Authors: Okotore R. O.
Published: May 2006

The thermal lability of 2-(2′ 4′-dinitrophenylamino)-2-deoxy-D-glucose (DNP-glucosamine) in alkaline borate buffer is reported. This was dependent on borate ion concentration at constant pH. Of the many reaction products, 2,4-dinitroaniline was isolated and identified by spectroscopic and other means. It was formed in 20% yield. A mechanism of reaction is suggested.
The hydrolysis of maleimide in alkaline solution
Authors: Barradas Remigio Germano , Fletcher Stephen , Porter John Douglas
Published: May 2006

The hydrolysis of maleimide has been investigated in the pH range 8.5–14. Polarographic limiting currents were well-defined, so that the bulk concentration of reactant during reduction could be clearly followed as a function of time. Logarithmic analysis of derived data indicated an arrest in the rate of reaction at circa pH 12, and a reaction scheme is proposed to explain this. In this scheme, the neutral maleimide molecule exists in equilibrium with its anion, and both of these species may undergo hydrolysis at the appropriate pH. From derived rate equations, the pKa of maleimide was found to be 10.0, whilst estimates of the rates of hydrolysis were also calculated.
Structure of radicals produced by γ-radiolysis. Part 5. Radicals derived from some aliphatic alkene molecules
Authors: Linder R. E. , Winters D. L. , Ling A. Campbell
Published: May 2006

Adamantane isolation matrices have been used to determine the structure of radicals produced by room temperature γ-radiolysis of certain selected alkene systems. The molecules studied include linear 1-ene homologues, linear 2-ene homologues, 2-methylpropene (2MPr), 2-methylbutene-1 (2MB1), 3-methylbutene-1 (3MB1), 2-methylbutene-2 (2MB2), 2-methylpentene-1 (2MP1), 2-methylpentene-2 (2MP2), 4-methylpentene-2 (4MP2), 2,3-dimethylbutene-2 (DMB2), 3,3-dimethylbutene-1 (33DMB), and 2,4,4-trimethylpentene-1 (TMPE). The general mode of reaction is allylic radical formation, with one isomer predominating, and structures have been either confirmed or assigned for the radicals derived from butene-1, butene-2, 2MPr, 2MB1, 2MB2, 2MP1, 4MP2, DMB2, and a listing of hfsc values have been obtained for each radical studied.
A stereochemical investigation of substituted ethylene sulfites via 13C nuclear magnetic resonance
Authors: Buchanan Gerald W. , Hellier Desmond G.
Published: May 2006

13C nmr chemical shifts for ethylene sulfite and 17 derivatives are presented. From the magnitudes of the γ shifts and the tenets of conformational analysis, support is gained for the existence of twist-envelope conformations in solution. Pseudorotational paths are suggested which do not involve inversion at the sulfur atom.
Etude par résonance magnétique nucléaire des propriétés acides de l'éthyltrifluoroacétoacétate d'uranium(IV)
Authors: Paris J. , Folcher G.
Published: May 2006

The compound (CF3COCHCOOC2H5)4U has been prepared. The chemical shifts of the ethyl protons are very important and were found to be very sensitive to interactions with the solvent. From their study certain correlations were established with physical quantities available elsewhere. These displacements can be interpreted as resulting from the variation of the sharing of the non-paired electrons of uranium between the chelate and the base. [Journal translation]
Olefin cycloadditions to 2′,3′,5′-triacetyluridine
Authors: Charlton James L. , Lai Hoi Kiong
Published: May 2006

Photocycloadditions of 2′,3′,5′-triacetyluridine to tetramethylethylene, isopropenyl acetate, 1,1-diethoxyethylene, and vinylene carbonate are described. The rearrangement of the vinylene carbonate adduct to 2′,3′,5′-triacetyl-5-formylmethyluridine followed by oxidation to the 5-carboxymethyl or decarbonylation to the 5-methyl (ribothymidine) derivative is also described.
The total synthesis of coccinelline and precoccinelline
Authors: Ayer William A. , Furuichi Kimiaki
Published: May 2006

The synthesis of the ladybug defensive substances precoccinelline and coccinelline, starting from 2,6-lutidine, is described.
Condensation of cis-9-methyl-2-decalone with cyclic β-amino esters: synthesis and X-ray crystallography of perhydroazacyclopentaanthracenes and perhydroazabenzanthracenes
Authors: Kelly Ronald B. , Beckett Barry A. , Mumtaz Ijaz , Stanley Eric , White Peter S.
Published: May 2006

Condensation of cis-9-methyl-2-decalone, 9, with ethyl 2-pyrrolidineacetate, 10, afforded a mixture of two isomeric vinylogous amides, 11. Oxidation of either one pure isomer, 11a, or the mixture 11 to the same pyridone, 12, revealed that the two condensation products were stereoisomeric at a single carbon atom and not structural isomers. Reduction of 11a afforded the amino ketone 13. The structures assigned to 11, 12, and 13 are based on X-ray crystallographic analysis of 13.Similarly, condensation of 9 with ethyl 2-piperidineacetate, 14, afforded the isomers 15a and 15b both of which were oxidized to the same pyridone, 16. Reduction of 15a afforded 17. The structures assigned to 15, 16, and 17 are based on X-ray crystallographic analysis of 17.
Effect of aging on properties of polynuclear hydroxyaluminum cations
Authors: Turner Robert C.
Published: May 2006

Very slow partial neutralization of 5 × 10−4 to 6 × 10−2 M solutions of AlCl3 and Al(ClO4)3, using either finely ground dolomite or NH3 as the base, resulted in the formation of polynuclear hydroxyaluminum cations without the appearance of any solid phases. Certain properties of the polynuclear cations did not change and no solids formed during an aging period of two years. The properties of the polynuclear cations examined were their rate of reaction with 8-hydroxy-quinoline and hydrolysis constants using formulas suggested in the literature. In contrast, the concentration of the polynuclears decreased, although very slowly, during aging. This decrease was accompanied by the appearance of a second type of polynuclear hydroxyaluminum cation, which apparently has the same OH/Al mole ratio but is much less reactive than the first type.
Highly excited 1sns states of the helium atom
Authors: Kuriyan Mary , Pritchard Huw O.
Published: May 2006

Variational calculations are reported on the 1sns singlet and triplet states of the helium atom, up to and including n = 26. By suitable choice of terms in the expansion for the wave function, significant economies in computer time are possible, and we quote an example of a 12-term uncorrelated wave function which gives a lower energy than Pekeris' 220-term correlated wave function. The problems of extending these calculations to much higher n (e.g. n > 100) to include states of astrophysical interest are enumerated.
Calculation of electro-optical parameters, a new approach. Part III. Applications to X2CZ molecules (X = H, F, Cl, Br and Z = O, S)
Authors: Prasad P. L. , Singh Surjit
Published: May 2006

Calculations of electro-optical parameters by the modified first order approximation (MFOA) method have been extended to X2CZ (X = H, F, Cl, Br; Z = O, S) molecules with a view to investigate the transferability of these parameters. The diagonal and cross elements of the bond moment derivative matrix have been evaluated. Unique values of µC−X are obtained for the A1 species. The bond moment derivatives are found to be transferable among A1 and B1 species. Transferability of the µC−Z in B1 and B2 species is obtained for thiocarbonyl halides. Bond moment derivatives with respect to angle deformations are not found to be very significant whereas other cross elements of the bond moment derivative matrix are found to be of high magnitude.
Kinetics of radical exchange in the reaction of CF3 radicals with tin tetramethyl
Authors: Bell T. N. , Young P. J.
Published: May 2006

The reaction of CF3 radicals with SnMe4 leads to hydrogen abstraction and also radical exchange.[Formula: see text]We propose the exchange reaction proceeds via a five coordinate intermediate. The Arrhenius parameters for the exchange reaction are,[Formula: see text]Additional data for the H abstraction reaction[Formula: see text]combined with previous data yields an improved rate constant for abstraction,[Formula: see text]
Action of Grignard reagents on hexuronic esters and attempted dehydration of tertiary alcohols to give hex-5-enopyranosides
Authors: Aspinall Gerald O. , Igarashi Osamu , Krishnamurthy Thinnayam N. , Mitura Walter , Funabashi Masuo
Published: May 2006

The attempted formation of hex-5-enopyranosides from glycosiduronates by the action of Grignard reagents followed by dehydration affords hex-6-enopyranosides or 1,6-anhydrohexopyranoses as major products. 13C nmr spectra of 6,6-di-C-substituted hexose derivatives are compared with those of a number of structurally related compounds. The formation of a hex-5-enopyranoside and the selective cleavage of its glycosidic linkage is illustrated by the synthesis and controlled hydrolysis of methyl 6-O-(6-deoxy-2,3,4-tri-O-methyl-β-L-arabino-hex-5-enopyranosyl)-2,3,4-tri-O-methyl-β-D-glucopyranoside(2).
Preparation and characterization of salts containing the triply bridged dimeric iridium(III) ion, [H(Ar3P)2Ir(SAr′)2ClIr(PAr3)2H]+
Authors: Kelly Timm L. , Senoff Caesar V.
Published: May 2006

The dimeric iridium(III) hydride complexes [IrHCl(SAr′)(PAr3)2]2 where Ar = 4-CH3C6H4 or C6H5 and Ar′ = 4-CH3C6H4, 4-CH3OC6H4, 4-FC6H4, or C6H5 have been shown to react in halogenated solvents such as chloroform or 1,2-dichloroethane to form triply bridged dimeric hydrated complexes of the type, [H(Ar3P)2Ir(SAr′)2ClIr(PAr3)H]Cl•2H2O. When PAr3 = (4-FC6H4)3P, no triple bridge formation was observed. However, the dimeric complexes, [IrHCl(SAr′)(PAr3)2]2 including PAr3 = (4-FC6H4)3P all react with AgClO4 in acetone to form the complexes, [H(Ar3P)2Ir(SAr′)2ClIr(PAr3)2H]ClO4•x(CH3)2CO (x = 0–3). The isolation and characterization of these triply bridged dimeric iridium(III) hydrides are discussed.
An R.K.R.-like estimate of the effective non-adiabatic internuclear potential for the hydrogen molecule
Authors: Kuriyan Mary , Pritchard Huw O.
Published: May 2006

An effective internuclear potential for the hydrogen molecule is deduced from the experimental energy levels; this potential is valid in the sense that it reproduces the rotation–vibration energy levels to an accuracy of the order of ±0.1 cm−1, and is unique in the sense that it is equally accurate for all observed values of the rotational quantum number J.The implied corrections to the adiabatic relativistic internuclear potential are consistent with the estimated values for the non-adiabatic coupling correction over the whole range of internuclear separation.
A second species of polynuclear hydroxyaluminum cation, its formation and some of its properties
Authors: Turner Robert C.
Published: May 2006

When a solution of Al(ClO4)3 or AlCl3 with total Al concentration between 5 × 10−4 and 6 × 10−2 M is partially neutralized very slowly with a base, it is possible to produce a solution of polynuclear hydroxyaluminum cations with no solid phases present. When such a solution is aged, the polynuclear hydroxyaluminum cations, AlP1, disappear very slowly at 25 °C and a second type of polynuclear hydroxyaluminum cations, AlP2, is formed. The second type, AlP2, has some properties that are the same as those of AlP1, e.g. they both have an OH/Al mole ratio equal to or very nearly equal to 2.5, diffuse readily across a dialysis membrane, and are removed from solution by the clay mineral bentonite in an exchangeable form. Some of their properties, however, are entirely different, e.g. AlP1 reacts with 8-hydroxyquinoline about 250 times faster with a much lower energy of activation than does AlP2, is much less resistant to attack by HCl, and is precipitated at a pH about 0.5 pH units lower than AlP2. The transformation of AlP1 to AlP2 is a first order process with an energy of activation of 20.8 kcal per mol. The specific rate constant seems to be affected somewhat by the extraneous anion present and the degree of neutralization; experimental values varied from 0.57 × 10−3 to 3.5 × 10−3 day−1 at 25 °C.
Application of photoelectron spectroscopy to intramolecularly hydrogen-bonded systems. Part III. The photoelectron spectra of cis and trans 2-substituted cyclopentanols and cis and trans 2-substituted cyclohexanols
Authors: Brown R. S.
Published: May 2006

The photoelectron spectra of several well defined molecules exhibiting intramolecular hydrogen bonding has been determined and the analysis of the spectra is in accord with recent molecular orbital calculations of related systems. The experimentally determined enthalpies of the hydrogen bonds in cis-2-aminocyclopentanol and cis- and trans-2-aminocyclohexanol do not correlate in any simple fashion with the shifts in the ionization energies of the nO and nN orbitals compared to a model which precludes hydrogen bonding. The spectral differences attributed to hydrogen bonding in the cis and trans 2-substituted cyclanols cannot be attributed to differences in the through-bond interaction of the n orbitals on either atom since the cis and trans isomers of 1,2-dimethoxycyclopentane and 1,2-dimethoxycyclohexane show virtually identical pe spectra. A discussion of the applicability of Koopmans' theorem and the effect of the hydrogen bond in both the ion and ground states is presented.