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This article aims to explain the mechanism of silting in the natron basins in the lake region in western Chad. Indeed, Chad is one of the largest countries in Africa which covers an area of 1,284,000 km2 of which its northern part, almost half of the country (600,350 km2) or 46.76% is a desert area. This characteristic means that the arid climate of the north inevitably contributes to desertification and especially to the silting up of Chad for several decades through the process of erosion, transport and deposition of living dunes. The methodological approach is based on field observations and measurements, surveys with the Global Positioning System (GPS), the survey of 70 operators, 20 merchants, 10 officials in charge of the environment at the Lake, 04 mining and energy officials, 06 customary officials of the Lake. The results of this study showed that the phenomenon of silting in the lake and particularly that of the natron basins invaded 2,135 m2 of usable surfaces. However, these natron valleys are spaces that allow local populations to live. This harms the environment and the socio-economic life of the Lake region and the actors of natron. [ABSTRACT FROM AUTHOR]

Five pyrazagalloles bearing H and CH3 substituents on the gallium atom and/or in the pyrazole ring have been calculated. The theoretical results have been compared with literature results concerning geometries from the Cambridge Data Base with very good agreement. 1H and 13C NMR results from the literature, scarce, and unpublished from our group are also well reproduced from GIAO calculations. The most important conclusion from this work is the assignment to a pz3Ga3 trimer as the isomer present in the 1H NMR spectra of dimeric pyrazagalloles. A mechanism connecting dimers and trimers has been found and the transition states identified. [ABSTRACT FROM AUTHOR]

Anemia is a common clinical problem in daily clinical practice. Anemia could be the only expression of a subclinical celiac disease. Iron deficiency is the most important background of this anemia. Sometimes, iron deficiency anemia with no identifiable cause can be the only sign of an undiagnosed celiac disease. The pathogenic mechanism of anemia in gluten-sensitive enteropathy deserves consideration for a proper and faster diagnosis, especially in cases with atypical presentation – iron deficiency anemia. [ABSTRACT FROM AUTHOR]

• Hollow fiber and flat membrane energy accumulators are designed and tested. • Compared with HFMEAs, FMEAs have higher mass transfer efficiency. • The mass transfer mechanism in MEA is analyzed. • Effects of thermodynamic characters on solution mass transfer are obtained. An experimental platform was set up to test the heat and mass transfer performance inside the membrane energy accumulator (MEA). Hollow fiber MEAs (HFMEAs) and flat MEAs (FMEAs) were designed and tested. Compared with HFMEAs, FMEAs have higher mass transfer efficiency. The average mass transfer speed of the water vapor increased by 108.34% when the evaporation temperature increased from 4.5 °C to 12.3 °C for HFMEA. When the evaporation temperature increased from 7.88 °C to 19.51 °C, the change in mass fraction of lithium bromide (LiBr) in FMEA increased by 62.36%. Compared with a 60% solution, the average mass transfer rate of water vapor molecules in a 70% LiBr solution increased by 49.83% for FMEA. In addition, the water vapor absorbed by the 70% LiBr solution in 30 min increased by 18.63% compared to that of the 60% solution for FMEA. The effect of the initial solution temperature on the mass transfer rate is closely related to the mass fraction of LiBr. Both the mass transfer rate and crystallization melting process of the LiBr solution will accelerate by increasing the initial mass fraction and evaporation temperature. [ABSTRACT FROM AUTHOR]

La psychologie anglo-saxonne a produit un nombre conséquent d'études mettant en évidence l'implication de mécanismes psychologiques dans le développement et le maintien des hallucinations acoustico-verbales (HAVs), aussi appelées phénomène d'entente de voix. S'il est souvent considéré, pour des raisons historiques, que les HAVs sont une des caractéristiques principales des troubles psychotiques et notamment schizophréniques, les études épidémiologiques montrent que celles-ci sont également extrêmement prévalentes dans de nombreuses autres populations cliniques (e.g. trouble bipolaire, trouble de stress post-traumatique, trouble de personnalité borderline) et neurologiques (e.g. Maladie de Parkinson), tout comme au sein de la population générale. Cependant, les HAVs restent encore, en pratique courante, associées à la psychose, et d'un point de vue étiologique à des « dysfonctionnements neurobiologiques complexes ». L'objectif principal de cette revue est de faire une synthèse narrative et intégrative des différents modèles psychologiques faisant actuellement consensus sur les HAVs. Plus précisément, nous décrirons (1) le rôle des croyances à propos de l'expérience d'entente de voix et les croyances à propos de soi, (2) l'expérience d'entente de voix comme devant être comprise comme un phénomène fondamentalement relationnel entre l'entendeur de voix et la voix elle-même, (3) le rôle des émotions et des stratégies de régulation émotionnelle, et (4) le rôle des expériences passées traumatiques et de la dissociation. Nous terminons cette revue par une brève critique argumentée de la conception des HAVs telle qu'elle est actuellement adoptée en psychiatrie. Anglo-Saxon psychology has produced a significant number of studies showing the involvement of psychological mechanisms in the development and maintenance of auditory hallucinations (voice-hearing). Likewise, numerous studies have shown that hallucinations are also described in other psychiatric (e.g. post-traumatic stress disorder) and neurodegenerative (e.g. Parkinson's disease) clinical populations as well as in a minority of the general population. However, despite these advances, hallucinations are still considered as a specific characteristic of schizophrenia, which in most cases, is understood from a biological point of view. For this reason, in this review, we are specifically interested in the psychological models of auditory hallucinations from a transdiagnostic point of view. More specifically, we will describe (1) the role of beliefs about voices and self-schemas, (2) the experience of voice understood as a fundamentally relational phenomenon between the voice hearer and the voices, (3) the role of emotions and emotional regulation strategies, and, finally, (4) the role of past traumatic experiences and dissociation. Regarding the role of beliefs about voices and self-schemas, numerous studies are showing that more important than the experience of hearing voices it is how the individual appraisal their experience that will ultimately impact on how they will cope with the experiences and how they will feel about it (distressed or not). Voices appraised as malevolent and powerful are more often associated with avoidant, escape, confrontation, and compliance coping strategies. Moreover, they are also associated with higher levels of depression and anxiety regardless of the frequency of hallucinations and duration of the disorder. Besides the beliefs about the voices, how the individual perceives him/herself is also essential. It has been shown, for example, that the more individuals feel depressed and inferior in comparison to others in interpersonal relationships, the more inferior they feel about their voices. The relational approach proposed that the experience of voice understood as a fundamentally relational phenomenon between the voice hearer and the voices. Indeed, phenomenological studies have been able to show that voice-hearers describe voices as possessing human characteristics. As a result, voice-hearers often develop a relationship of virtual intimacy with their voices, which often seems to be complex and characterised by a certain ambivalence similar to the interpersonal relationships encountered in everyday life. Thus, current research suggests that it is essential to take into account these relational aspects when working with voice-hearers. Alongside cognitive and relational variables, emotional states and processes play a significant role in the development and maintenance of auditory hallucinations. Indeed, it has been shown that stress, anxiety and depression are predictors of hallucinations. Also, increased use of non-adaptive emotion regulation strategies may play a major role in the phenomenon of voice agreement. Studies have demonstrated that emotional regulation strategies such as experiential avoidance and abstract rumination seem to contribute to the increased frequency of hallucinations and associated distress. Finally, there is now strong evidence showing the involvement of past adverse experiences in the onset and content of hallucinations. In this framework, dissociation is seen as a protective mechanism that allows individuals to psychologically detach themselves from events that they cannot cope with. Consequently, the experience is attributed to external sources, ultimately leading to the phenomenon of voice-hearing. In summary, in this brief review, we have tried to present the best validated psychological models for understanding the experience of voice agreement. The goal is to provide information on how these psychological processes can help us to the adoption of a person-centred approach in mental health care that allows the person to describe their experiences in their own words and thus formulate an understanding of their suffering. [ABSTRACT FROM AUTHOR]

This study aims to reveal the role of dominant social institutions in building and shaping awareness of security risks, from Ulrich Beck's perspective, which provides insight into the relationship between dominant social institutions, the production and management of security risks. It concluded that Ulrich Beck offers a mechanism for understanding the social construction of security risks. It reflects the way in which you understand security risks, both in academia and in the broader community. This mechanism highlights the different contradictions (conflicts) in risk perception. [ABSTRACT FROM AUTHOR]

This paper proposes a reflection on the epistemological status of psychoanalysis created by Freud. It was developed through a critical confrontation of the insertion of his metapsychology within a framework some authors have called vitalism, which would have been the result of a deviation from his academic education when resuming and updating the 19th-century concept of vitalism with the notion of Trieb. In response, this article discusses some topics, such as Freud's scientific training environment, the status of the notion of Trieb - which is considered conventional and entropic - and finally, resorting to Canguilhem, inserts Freud's metapsychology in a framework of mechanistic materialism elevated to the ultimate consequences, which would have been the result of his true epistemological procedure, in addition to his most daring and refined scientific contribution at the time. [ABSTRACT FROM AUTHOR]

The increasing incidence of drug-related renal pathology represents a pressing problem for medical specialties and clinical pharmacology, which requires a multilateral approach. The elucidation and analysis of the mechanisms of drug nephrotoxicity, the processes that influence them and the specific biomarkers that allow the early detection of reversible renal lesions will significantly reduce the undesirable consequences of the drugs on the kidneys. The review of nephrotoxic drugs and of the responsible pathogenic mechanisms will allow the development of principles for monitoring, prevention and correction of renal disorders, which will complement the pharmacovigilance compartment of clinical pharmacology. [ABSTRACT FROM AUTHOR]

Epilepsy can be caused by several factors. Seizures contribute to progressive neurodegeneration with mild neurofunctional and psychosocial consequences, but epilepsy in the child can often be refractory to existing antiepileptic medications. Development of epilepsy takes place in a complex neurobiological environment characterized by continuous processes of secondary lesions induced by seizures. One of the mechanisms that determine the development of epilepsy is related to the changes in activity of neurons, i. e., hypersynchronic activity, and excitability, i. e., processes of excitation and inhibition. Older conceptions about exclusive participation of neurons in epileptogenesis are now changed, and currently special attention is given to the role in the pathogenesis of epilepsy of glia and neuroinflammatory immune factors. It is suggested that immune and inflammatory reactions occur in the epileptic brain, being closely linked to the presence of cerebral vascular barrier that strictly regulates infiltration with blood monocytes and lymphocytes. According to current concepts, from a clinical point of view, neuroinflammation is considered as a distinctive phenomenon of epileptogenic foci outbreaks in various types of refractory epilepsy. These processes are determined probably by immune mediators that are characteristic for the brain and peripheral leukocytes that infiltrate the brain. Understanding the immune neuroinflammation mechanisms in refractory epilepsy in humans will help to correctly use immunotherapeutic medications to resolve the causes of the disease. The present study describes a clinical case of a child with convulsive seizures refractory to antiepileptic therapy. [ABSTRACT FROM AUTHOR]

The objective of this work is to perform a theoretical analysis of the antioxidant properties of a series of 8-hydroxyquinolines (8-HQs) to rationalize the available experimental results and to design new potent 8-HQ derivatives. The study was carried out in gas phase and in methanol at the DFT/B3LYP/ 6-311++G(d,p) computational level. The formation of stable ArO• radicals is discussed on the basis of different mechanisms, namely, hydrogen atom transfer (HAT), single electron transfer followed by proton transfer (SET-PT), and single proton loss electron transfer (SPLET). The obtained results show that the HAT mechanism is, thermodynamically, more favoured in gas phase, whereas the SPLET pathway is more favoured in polar solvents. The calculated thermochemical descriptors allow classification of the antioxidant power of the studied compounds. [ABSTRACT FROM AUTHOR]

Joint "cracking" is common but not a clearly understood audible phenomenon. In this brief report we propose an in-vitro model to potentially assist in revealing a mechanism for, and therefore source of, this phenomenon. Using a suction cup under tension and de-nucleated fluid to simulate synovial fluid, an audible release with intra-articular cavity formation was elicited. This was followed by a refractory period during which no audible crack could be elicited until the observed cavity had slowly reabsorbed back into the joint fluid. Conversely, if regular fluid containing pre-existing nuclei was used, a cavity formation occurred but with neither an audible release nor subsequent refractory period. With this simple in-vitro model, we were able to reproduce the characteristic audible release, cavity formation and related refractory period typically observed in related elimexperiments in human joints. This simple in-vitro model may be of use in helping to discern both the timing and precise nature of other yet to be discerned mechanisms related to joint cracking. [ABSTRACT FROM AUTHOR]

In this review are presented, under a synthetic mini-course, the main concepts related to digestive diseases in animals. Introductory concepts are presented with brief anatomical - histo - physiological recollections; data about specific bacterial flora present in the digestive tract, about digestive disease: the defense mechanisms; pathogenesis, diagnosis and semiotics. Due to space parsimony of this work we have not presented exhaustively all notions of the gastrointestinal tract, but insisted only on main entities responsible for digestive disorders that were present most often in animals. In the second part are presented in detail the main medicinal remedies against the digestive tract disease in animals, under a suggestive table form. [ABSTRACT FROM AUTHOR]

Density functional theory calculations were employed to study the catalytic mechanism, modes of activation, and origin of enantioselectivity of guanidine-catalyzed asymmetric Strecker reaction of N-benzhydryl imine with hydrogen cyanide. Two types of bifunctional activation mode were identified, namely conventional bifunctional Brønsted acid activation and unconventional bifunctional Brønsted-Lewis acid activation. The lowest-energy transition states correspond to the conventional bifunctional mode of activation. The calculated enantiomeric excess, based on eight lowest-energy C-C bond forming transition states, is in good accord with observed enantioselectivity. NCI (noncovalent interaction) analysis of the key transition states reveals extensive noncovalent interactions, including aromatic interactions and hydrogen bonds, between the guanidinium catalyst and substrates. Multiple aryl-aryl interactions between the phenyl groups of guanidine catalyst and the phenyl rings of N-benzhydryl imine are the key stabilizations in the most stable ( R)-inducing transition state. Differential attractive aryl-aryl stabilization is the major factor for stereoinduction. [ABSTRACT FROM AUTHOR]

The kinetics of the gas-phase thermolysis reaction of seven β-lactams and their thione analogues were investigated over the temperature range 533-603 K for the β-lactams and 463-542 K for the β-thiolactams. The average values of the energy of activation ( Ea) (kJ mol−1) and Arrhenius log A (s-1) were, respectively, 170.8 ± 18.6 and 12.4 ± 1.6 for the lactams and 131.7 ± 18.2 and 11.0 ± 2.0 for the thione analogues. The entropy of activation (Δ S#) was negative for of the substrates and slightly positive for three. The rate constants ( k) (s−1) were calculated for 510 K and compared for the two series of azetidinones. The effects of substituents on rates and the novel role played by the C=O and C=S moieties on the relative reactivities of the cyclic amides are rationalized on the basis of a formal retro[2+2]cycloaddition mechanism used earlier to explain the products of the gas-phase thermolysis reaction of the present azetidinones. [ABSTRACT FROM AUTHOR]

Heavy metals, such as cobalt, copper, manganese, molybdenum, and zinc, are essential in trace amounts for growth by plants and other living organisms. However, in excessive amounts these heavy metals have deleterious effects. Like other organisms, plants possess a variety of detoxification mechanisms to counter the harmful effects of heavy metals. These include the restriction of heavy metals by mycorrhizal association, binding with plant cell wall and root excretions, metal efflux from the plasma membrane, metal chelation by phytochelatins and metallothioneins, and compartmentalization within the vacuole. Phytoremediation is an emerging technology that uses plants and their associated rhizospheric microorganisms to remove pollutants from contaminated sites. This technology is inexpensive, efficient, and ecofriendly. This review focuses on potential cellular and molecular adaptations by plants that are necessary to tolerate heavy metal stress. [ABSTRACT FROM AUTHOR]

Radiotherapy induced cardiovascular disease may be very heterogeneous and it is considered, in the present, as the most important cause of mortality not related to the cancer itself in cancer survivors. Radiotherapy, even modern techniques, isolated or especially associated with chemotherapy and/or biological agents, increase the risk of cardiovascular disease in these patients. The potential mechanisms by which radiotherapy may induce cardiovascular lesions and, subsequently, clinical manifestations, are extremely complex and only partially known. Anyway, cardiovascular risk is significantly increased in patients that associate cardiovascular risk factors or who already have cardiac diseases. In the meantime, the onset of pathological changes seems to be related to other several factors, as genetic polymorphism, the modality and the dose of irradiation. [ABSTRACT FROM AUTHOR]

The aim of this bibliographic essay is to refresh the knowledge of veterinarians in the field of therapy and bacterial resistance. Are summarized, in a didactic manner: the bacteria classification, the overall structure of the cell wall, the general characterization of antibiotics, the fundamental modes of action of antibiotics, the main interactions and side phenomena antibiotics and toxic products. Installing and effects of bacterial resistance to antibiotics is presented in detail, being given the basic concepts about resistance mechanisms as: the drug inactivation or misappropriation of the pathway, enzyme target altering or structure, low accumulation of antibiotic resistance in bacterial cells. They are also presented: the natural antibiotic resistance (epigenetic), the gained antibiotic resistance, the genetic adaptation (by mutation and selection) and the genetic acquisition. By means of resistance means all the mechanisms by which bacteria can reduce or total inactivate the antimicrobial activity. In this regard are presented: phases of the resistance installation and antibiotics’ modification / inactivation, not being omitted also the trends in the evolution of resistance to antibiotics and environmental impacts analysis, the results of the imprudent using of the anti-infectives (like veterinary antibiotics in soil and water, the antibiotic resistance in the genetic modiffied crops or the long-term effects on ecosystems) and them consequences. [ABSTRACT FROM AUTHOR]

When lactose was incubated with G794A-β-galactosidase (a variant with a 'closed' active site loop that binds transition state analogs well) an allolactose was trapped with its Gal moiety in a 4H3 conformation, similar to the oxocarbenium ion-like conformation expected of the transition state. The numerous interactions formed between the 4H3 structure and β-galactosidase indicate that this structure is representative of the transition state. This conformation is also very similar to that of d-galactono-1,5-lactone, a good transition state analog. Evidence indicates that substrates take up the 4H3 conformation during migration from the shallow to the deep mode. Steric forces utilizing His418 and other residues are important for positioning the O1 leaving group into a quasi-axial position. An electrostatic interaction between the O5 of the distorted Gal and Tyr503 as well as C-H-π bonds with Trp568 are also significant. Computational studies of the energy of sugar ring distortion show that the β-galactosidase reaction itinerary is driven by energetic considerations in utilization of a 4H3 transition state with a novel 4C1-4H3-4C1 conformation itinerary. To our knowledge, this is the first X-ray crystallographic structural demonstration that the transition state of a natural substrate of a glycosidase has a 4H3 conformation. [ABSTRACT FROM AUTHOR]

Here we describe the measurement of the inactivation rate constants for the mechanism-based inactivator 2,3-difluorosialic acid acting upon the sialidase from Micromonospora viridifaciens. Using double mixing stopped-flow experiments conducted in a 3-( N-morpholino)propanesulfonic acid buffer (100 mmol/L, pH 7.00) at 25 °C, the derived kinetic parameters are kinact/ Ki = (3.9 ± 0.8) × 106 (mol/L)-1 s-1 and Ki = 1.7 ± 0.4 μmol/L. We demonstrate that the inhibitory efficiency of the inactivation event is similar to the catalytic efficiency for this sialidase acting upon a typical substrate, 4-methylumbelliferone α- d-sialoside, kcat/ Km = (7.2 ± 2.8) × 106 (mol/L)-1 s-1. Furthermore, we show that the catalytic efficiencies for inactivation and hydrolysis by the Kdnase from Aspergillus fumigatus are similar for the corresponding Kdn-analogues. We conclude that the deactivating effect of incorporating an axial 3-fluoro substituent onto the sialic acid scaffold is comparable to the enhanced activation that occurs when the 4-methylumbelliferone leaving group is changed to the more nucleofugal fluoride ion. [ABSTRACT FROM AUTHOR]

In acid media ([H+] = 0.01-0.06 M), 2-mercaptoethanol (HSCH2CH2OH, abbreviated as MERCAP) and thioglycolic acid (HSCH2COOH, abbreviated as TGA) reduce the superoxo complex [(en)(dien)CoIII(O2)CoIII(en)(dien)]5+ ( 1) to the corresponding peroxo complex [(en)(dien)CoIII(μ-O2)CoIII(en)(dien)]4+ ( 2). The observed rate ( ko), although proportional to both [MERCAP] and [TGA], is higher for TGA than for MERCAP, which is contrary to the expected trend on the basis of standard reduction potential (-0.14 versus -0.26 V, respectively). Moreover, ko values decrease with increasing media ionic strength ( I) and [H+] and thus, thiolate anions are supposed to be the reactive forms of the reductants. Under the experimental conditions, the concentrations of such reductants (-SCH2CH2OH and HOOCCH2S-, respectively) from MERCAP (p Ka = 9.7) and TGA (p Ka1, p Ka2 = 3.53, 10.10) are very small. However, for TGA, the tautomerization between HSCH2COO- and -SCH2COOH (p Ki = 7.0) plays a significant role in increasing the concentration of HOOCCH2S-. The rates of both of the reactions are limited by the rate of solvent diffusion and this fact is also supported by the relatively low activation energy ( Ea), for the reactions. The Ea values for the reactions with MERCAP and TGA are close enough (29.6 ± 1.3 and 27.0 ± 0.4 kJ M−1 respectively) to suggest a common reaction mechanism for both. [ABSTRACT FROM AUTHOR]

The development of molecular biology placed in the foreground a mechanistic and deterministic conception of the functioning of macromolecules. In this article, I show that this conception was neither obvious, nor necessary. Taking Jacques Monod as a case study, I detail the way he gradually came loose from a statistical understanding of determinism to finally support a mechanistic understanding. The reasons of the choice made by Monod at the beginning of the 1950s can be understood only in the light of the general theoretical schema supported by the concept of mechanistic determinism. This schema articulates three fundamental notions for Monod, namely that of the rigidity of the sequence of the genetic program, that of the intrinsic stability of macromolecules (DNA and proteins), and that of the specificity of molecular interactions. [ABSTRACT FROM AUTHOR]

Le but de notre étude est de décrire les mécanismes lésionnels et les aspects anatomo-cliniques des traumatismes par accident de cyclomoteur. C'est une étude transversale menée au niveau du Centre Hospitalier Régional de Kaffrine sur une période de 12 mois. Elle portait sur les patients admis au service d'accueil pour accident de la voie publique impliquant un cyclomoteur. Il s'agissait de 129 patients (112 hommes et de 17 femmes). L'âge moyen était de 30,5 ans. Soixante-treize patients étaient conducteurs de cyclomoteur, 31 piétons et 25 passagers arrière. Le mécanisme le plus fréquent était une chute de moto. Les lésions prédominaient au niveau des membres. Les accidents de cyclomoteur sont un problème de santé publique. [ABSTRACT FROM AUTHOR]

Electroplating industries in Madurai city produce approximately 49 000 L of wastewater and 1200 L of sludge every day revealing 687-5569 ppm of nickel (Ni) with other contaminants. Seventeen Ni-tolerant bacterial strains were isolated from nutrient-enriched effluents. Among them one hyper Ni accumulating strain was scored and identified as Bacillus cereus VP17 on the basis of morphology, biochemical tests, 16S rDNA gene sequencing, and phylogenetic analysis. Equilibrium data of Ni(II) ions using the bacterium as sorbent at isothermal conditions (37 °C) and pH 6 were best adjusted by Langmuir ( R2 = 0.6268) and Freundlich models ( R2 = 0.9505). Experimental validation reveals Ni sorption takes place on a heterogeneous surface of the biosorbent, and predicted metal sorption capacity is 434 ppm. The pseudo-second-order kinetic model fitted the biosorption kinetic data better than the pseudo-first-order kinetic model ( R2 = 0.9963 and 0.3625). Scanning electron microscopy, energy dispersive X-ray, and Fourier transform infrared spectroscopy studies of the bacterial strain with and without Ni(II) ion reveals the biosorption mechanism. The results conclude possibilities of using B. cereus VP17 for Ni bioremediation. [ABSTRACT FROM AUTHOR]

The transition state for the hydronium-ion-promoted hydrolysis of α- d-glucopyranosyl fluoride in water has been characterized by combining multiple kinetic isotope effect measurements with theoretical modelling. The measured kinetic isotope effects for the C1-deuterium, C2-deuterium, C5-deuterium, anomeric carbon-13, and ring oxygen-18 are 1.219 ± 0.021, 1.099 ± 0.024, 0.976 ± 0.014, 1.014 ± 0.005, and 0.991 ± 0.013, respectively. The transition state for the hydronium ion reaction is late with respect to both C-F bond cleavage and proton transfer. [ABSTRACT FROM AUTHOR]

The hydrolytic reactivity of simple phosphate diesters with very good leaving groups is known to be practically independent of the nonleaving group at 100 °C. Calculations on the (too slow to measure) hydrolysis at 25 °C of a series of p-nitrophenyl diesters ROPO2--OpNP with a wide range of nonleaving group OR indicate a small but significant effect at the lower temperature, making the R = methyl ester the most reactive. This is in the opposite sense to the much larger effect observed for the reactions of triesters and consistent with a reaction driven primarily by leaving group departure. The calculations use a continuum model with up to four discrete water molecules: two or three waters give the best results. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) and the coupled cluster method have been used to study the mechanism of the cycloaddition of acetylene to silene, H2Si=CH2, and germene, H2Ge=CH2, at the B3LYP/6-311++G(d,p) and CCSD/6-311++G(d,p) levels of theory. Diradical, zwitterionic, and concerted pathways were located for both metallenes. The computational results were compared to experimental data to propose the most likely reaction pathway for each metallene. [ABSTRACT FROM AUTHOR]

This article is a contribution to the study of the causes, characterization, and numerical modeling, using finite elements, of the landslide affecting the coastal slope at the edge of the Mediterranean Sea near the city center of Tigzirt (Algeria). This slope is characterized by a relatively low inclination (13°-15°) and composed of two main geological formations (marly bedrock overlain by recent Quaternary deposits). Several factors have acted jointly and explain the activity of Tigzirt landslide: it is the effect of geological, morphological, and hydrogeological site contexts combined to triggering factors of various origins (human, climatic, and seismic). The landslide is characterized by a planar failure surface, which involves a global translational deformation towards the sea. [ABSTRACT FROM AUTHOR]

A variety of terminal alkynes were added to dimesitylfluorenylidenegermane, Mes2Ge=CR2 (where CR2 = fluorenylidene). The addition of phenylacetylene and 1-hexyne to Mes2Ge=CR2 gave a germacyclohexene via a cycloaddition where the germene acts as the 4π component and the alkyne as the 2π component. Through the use of a mechanistic probe, trans-(2-phenylcyclopropyl)-acetylene, the reaction was postulated to proceed through a concerted [2+4] cycloaddition. The addition of ethoxyacetylene to the germene produced both a [2+2] cycloadduct, a germacyclobutene, and a [2+4] cycloadduct, a germacyclohexene. The results of this study are compared to the results of the addition of alkynes to Mes2Ge=CHCH2- t-Bu. [ABSTRACT FROM AUTHOR]

Plaque is a bacterial aggregation adhering to the tooth surface, to mobile or fixed prostheses, orthodontic appliances and implants. In bacterial plaque composition are between 200-400 different species of bacteria. The pathogen is represented by a microorganism that is capable of producing disease. Pathogenicity is the ability to produce disease in a host organism. Microbes show their pathogenicity in virulence. We know two types of mechanisms involved in the pathogenesis of periodontal disease: direct mechanisms related to bacterial factors and indirect mechanisms related to the immune response of the host tissue. Direct mechanisms that steps: adherence, bacteria colonization; invasion of periodontal tissues; harmful action of bacterial cell structure factors; harmful action of factors synthesized and released from the bacterial cell. [ABSTRACT FROM AUTHOR]

Selective Pt−Me bond activation of dimethylplatinum(II) complexes [PtMe2(PP)] (PP = dppm (bis(diphenylphosphino)methane), dppe (1,2-bis(diphenylphosphino)ethane), dppp (1,3-bis(diphenylphosphino)propane)) was achieved by SnMe2Cl2 to yield the corresponding platinum(II) complexes [PtMeCl(PP)] (PP = dppm, dppe, dppp) and cis-[PtCl2(PP)] (PP = dppm, dppp). On the other hand, the reactions of complexes [PtMe2(PP)] (PP = dppm, dppe, dppp) with SnPh3Cl resulted in the selective cleavage of the Pt−Me bond to afford the methylplatinum(II) complexes [PtMeCl(PP)]. Notably, the reaction of [PtMe2(dppm)] with SnMe2Cl2 and SnPh3Cl also gave the ionic A-frame complex [Pt2Me2(μ-Cl)(μ-dppm)2]Cl. The variable-temperature 1H and 31P NMR spectroscopy shows that the cleavage of the Pt−Me bond occurs very rapidly and the short-lived platinum(IV) intermediate is difficult to detect during the reaction. An explanation is presented on the basis of the nature of the strong π-acceptance of the phosphine ligand, which resulted in the formation of a very unstable platinum(IV) intermediate. [ABSTRACT FROM AUTHOR]

Abstract: The study of refrigerant-based nanofluid boiling and two-phase flow phenomena is still in its infancy. This field of research provides many opportunities to study new frontiers but also poses great challenges. To summarize the current status of research in this newly developing interdisciplinary field and to identify the future research needs as well, this paper presents a comprehensive review of nucleate pool boiling, flow boiling, condensation and two-phase flow of refrigerant-based nanofluids. The effects of nanolubricants on boiling and two phase flow phenomena are presented as well. Furthermore, studies of applications and challenges of refrigerant-based nanofluids are presented and future research needs are identified. For the limited studies done so far, there are some controversies from one study to another. Conclusions and contradictions on the available refrigerant-based studies of physical properties, boiling and two phase flow are presented. According to this review, it has been realized that the physical properties have significant effects on the refrigerant-based nanofluid boiling and two-phase flow characteristics but the lack of the accurate knowledge of these physical properties has greatly limited the study in this interdisciplinary field. Furthermore, the limited available experiments and quite contradictive results have limited the understanding of the fundamentals of boiling and two phase flow phenomena. Flow regimes are very important in understanding the phenomena but less investigated so far. Apparently it is still a long way to go to achieve systematic fundamental knowledge and theory in the relevant subject. Therefore, effort should be made to contribute to the physical property database of nanofluids as a first priority. Secondly, systematic accurate experiments and flow regime observations on boiling and two-phase flow phenomena under a wide range of test conditions and nanofluid types should be emphasized to understand the fundamentals. Finally, physical mechanisms and prediction methods for boiling heat transfer and two phase flow characteristics should be targeted and applied research should also be focused on in the future. [Copyright &y& Elsevier]

It has been shown recently that most ethers hydrolyze in aqueous acid media not by the traditional A1 or A2 process, but by a mechanism involving rate-determining proton transfer to the substrate, concerted with C-O bond cleavage. The reactions of azoethers are more complicated, because the azo group can be protonated in the acid reaction medium as well. This protonation has to be accounted for in the kinetic analysis. Often it simply ties up the substrate in an unreactive form; the hydrolysis reaction slows down as a result of the azo-protonated compound not being the reactant in the hydrolysis. However, there are other possibilities. If the ether group is suitably located in the substrate the azo-protonated compound can react with three water molecules (a 'water wire') in a fast reaction, and the alkoxy group is lost as a result. Depending on the acidity, in this mechanism either the initial three-water attack, or the breakup of the resulting intermediate, can be rate-determining, and both of these were observed. A third possibility is that ring protonation of suitable substrates can occur, giving delocalized carbocations that can form a hydrolysis product in subsequent fast reactions. Thus, three different hydrolysis mechanisms for azoethers in acidic media can be observed. Six azoethers were studied, one of which contained two methoxy groups. Both of these hydrolyzed, but by different mechanisms. [ABSTRACT FROM AUTHOR]

It has been shown recently that many supposed reaction intermediates in aqueous media do not have lifetimes long enough for them to serve this purpose. Among these are oxygen-protonated species where the positive charge is not delocalized, primary and secondary carbocations, and the commonly written species H3O+ and HO-. This means that the mechanisms for many of the organic reactions that take place in aqueous media are in need of revision. This paper concerns the acid hydrolysis of simple ethers, many of which cannot form carbocations stable enough to exist in water. Rather than an A1 process in which an oxygen-protonated species dissociates into an alcohol and a carbocation, which is then quenched by water, or an A2 process in which a water molecule or another nucleophilic species assists in this, the mechanism for most ethers is a general-acid-catalyzed process in which proton transfer to oxygen is concerted with C-O bond cleavage in cases where a stable carbocation can exist, or additionally concerted with nucleophilic attack for those cases in which stable carbocation formation is not possible. All of the cases for which rate constant data could be found in the literature are analyzed and discussed in this paper, with the exception of the hydrolyses of several azoethers, where additional hydrolysis mechanisms are possible. These will be discussed in a subsequent paper. [ABSTRACT FROM AUTHOR]

Several recent models of probabilistic causal reasoning in adults propose the existence of multiple interactions between ascending and descending factors. The aim of the present study is to evaluate the potential interactions between knowledge about generative and preventive mechanisms, the delta p of the data, and the relative importance given to the type of data provided. Two experiments involving 54 participants each are conducted, in which participants are invited to quantify the nature of a potential link (causal or associative) between adding a chemical substance to the asphalt of the roads and the formation of a slippery road in the winter, after being given information suggestive of (1) a generative mechanism, (2) a preventive mechanism, or (3) nothing special. Results show an influence of the suggested mechanisms on the reading of data that were provided, especially those with a delta p that is compatible with the a priori mechanism. These results are interpreted and discussed in line with the importance of considering multiple factors in probabilistic causal reasoning. [ABSTRACT FROM AUTHOR]

Abstract: The follow-up of the advance of the reaction of polymerization of resorcinol with formaldehyde in acid or basic medium by NMR shows that the structure of the obtained xerogel in both cases is the same one. Indeed, the junction between the aromatic nuclei is of type OCH2OCH2. While basing itself on the structure of the xerogel, we propose the mechanism for the polymerization reaction between resorcinol and formaldehyde. [Copyright &y& Elsevier]

Abstract: Idiopathic scoliosis is a three-dimensional deformation of the spine. As its name suggests, its pathogenesis remains poorly understood. Enhanced comprehension of its pathogenesis would be likely to improve current therapeutic results. While the hereditary and genetic origin of scoliosis appears unassailable and several chromosomes are known to be involved in transmission, the role assumed by each individual chromosome remains uncertain, and the mechanisms leading to the expression of scoliosis have yet to be determined. Even though a large number of pathogenetic hypotheses have been put forward and numerous studies carried out, none of these hypotheses have won unanimous approval, and the controversy remains persistent. Objective: The objective of this paper is to identify the existing hypotheses and to group them within large-scale etiological categories. Methods: We examined the Pubmed and Goggle databases using as keywords “idiopathic scoliosis” and “pathogenesis”. The search was limited to articles in English and French. Results: The vicious cycle hypothesis is markedly preponderant. However, no existing pathogenetic model adequately accounts for the formation of scolioses. Conclusion: We are proposing four main pathogenetic mechanisms: asymmetric bone growth dysregulation, susceptibility of bones to deformation, abnormal passive spinal system maintenance and disturbed active spinal system maintenance. [Copyright &y& Elsevier]

Arterial hypertension in old age is an important cause of morbidity and mortality throughout the world, its frequency being on the rise due to the aging of the population and modern means of treatment. The kidney's intervention as a central pivot in the ethiopathogenesis of arterial hypertension through the secretion of renin, pressure natriuresis and volemic shock, as well as the intervention of the cardiovascular system through increased vascular resistance, endothelial disfunctions and myocardic hypertrophy allow the condition to be addressed by general physicians, cardiologists and nephrologists. Given the associated comorbidities, arterial hypertension in old age remains a poorly defined entity, open to speculations regarding both the pathogenic mechanisms involved and the possibilities of treatment. [ABSTRACT FROM AUTHOR]

Abstract: Palmar dislocation of the metacarpophalangeal joint of the long finger is a rare injury. The authors report a case of palmar dislocation of the metacarpophalangeal joint of the ring finger. The presumed mechanism is a combination of active flexion and forceful hyperextension. The dislocation was treated successfully by closed reduction shortly after injury. Closed reduction should be attempted in all cases of this injury. [Copyright &y& Elsevier]

Catalytic ethene trimerization at a chromium(I) indolate-AlR2Cl centre has been studied by density functional theory (DFT) methods. The reaction is found to follow the standard metallacycle mechanism. At most stages of the reaction, coordination of Cr to the pyrrole ring of the indolate is preferred. In all 13-e intermediates, coordination of the Al-bound chloride to Cr provides additional stabilization: the chloride behaves as a hemilabile ligand. Benzene is found to compete with ethene for coordination to CrI. The final hexene-forming step involves direct Cβ → Cα′ hydrogen transfer; reductive elimination from a possible (hydride)(hexenyl) intermediate is more difficult. The kinetic isotope effect calculated for the direct hydrogen transfer (4.1) agrees well with the experimental value for a bis(phosphino)amide chromium catalyst. Side products obtained in such systems (methylenecyclopentane, methylcyclopentane) can plausibly be explained through routes not involving any (hydride)(alkyl) reductive elimination. Our results indicate that a CrI/CrIII trimerization cycle is possible for some chromium trimerization catalysts, and also suggest that direct hydrogen transfer is most likely a general feature of trimerization at Cr centres. [ABSTRACT FROM AUTHOR]

The cleavage of seven RNA model 2-hydroxypropyl aryl phosphates (1) catalyzed by a dinuclear Zn(II) complex of bis[1,4-N1,N1′(1,5,9-triazacyclododecanyl)]butane (4) was studied in methanol and ethanol at 25 °C under pH controlled conditions. The results are compared with what was reported earlier for the dinuclear Zn(II) complex of the lower homologue bis[1,3-N1,N1′(1,5,9-triazacyclododecanyl)]propane (3). In methanol, the higher homologue exhibits saturation binding with substrates having poor aryloxy leaving groups. With good leaving groups there is an observed linear dependence of kobs versus complex concentration without saturation binding over the catalyst concentration range investigated. In ethanol, strong saturation binding between the active form of the catalyst ((RO–):Zn(II)2:4) and all substrates is observed, the results observed in both solvents being similar to what was reported for the lower (RO–):Zn(II)2:3 homologue. Energetics calculations are presented for the (RO–):Zn(II)2:4-catalyzed cleavage of each substrate in both solvents to assess the catalytic efficiency via the ΔΔG‡ for catalyst binding a transition state comprising [RO–:1]‡ or its kinetic equivalent. Opérant dans des conditions de pH contrôlé, à 25 C, en solution dans le méthanol et l’éthanol, on a étudié la réaction de clivage de sept phosphates d’aryle et de 2-hydroxypropyle (1), des modèles de l’ARN, catalysé par un complexe dinucléaire du Zn(II) et le bis[1,4-N1,N1′(1,5,9-triazacyclododécanyl)]butane (4). On compare les résultats avec ceux rapportés antérieurement pour le complexe dinucléaire du Zn(II) l’homologue inférieur bis[1,3-N1,N1′(1,5,9-triazacyclodécanyl)]propane (3). Dans le méthanol, l’homologue supérieur on observe qu’il y a saturation du site de fixation avec les substrats pour lesquels l’habilité à partir des groupes aryloxy est faible. Avec de bons groupes partant, pour toute la plage de concentration de catalyseur utilisée dans ce travail, on observe une dépendance linéaire de kobs en fonction de la concentration du complexe. Dans l’éthanol, on observe une forte saturation des sites de fixation entre tous les substrats et la forme active du catalyseur [(RO–):Zn(II)2:4]; dans les deux solvants, les résultats sont similaires à ceux rapportés pour l’homologue inférieur [(RO–):Zn(II)2:3]. Afin d’évaluer l’efficacité catalytique par le biais du ΔΔG‡ de la fixation par le catalyseur d’un état d’activation comportant [RO–:1]‡ ou son équivalent cinétique, on a effectué des calculs d’énergie pour le clivage de chacun des substrats, catalysés par [(RO–):Zn(II)2:4]. [ABSTRACT FROM AUTHOR]

The addition of amines or aziridines to prenylacetate is catalyzed by palladium phosphine complexes. The first-formed products have recently been shown to be the branched olefins R2NCMe2CH=CH2, R = alkyl, or R2 = 1,2-C6H10, for example. DFT calculations using the MPW1K functional were performed on reactions of the suspected intermediate η3-prenyl complex [Pd(η3-Me2CCHCH2)(PH3)2]+ with dimethylamine and ethylene imine. The activation barrier for the nucleophilic attack by the amine or the aziridine is calculated to be similar for either the sterically hindered site of the π-allyl ligand to produce the branched olefin complex or the unhindered site to give the linear olefin complex. Therefore, these calculations do not reveal the experimentally observed preference for attack. This observation, along with the experimental observation of lack of isomerization of the branched olefin product of the aziridine reactions, appears to rule out the intermediacy of a π-allyl complex [Pd(η3-Me2CCHCH2)L2]+, L = phosphine or L2 = diphosphine in the C–N bond-forming reaction. [ABSTRACT FROM AUTHOR]

Oxidation of phenyl PtII complexes K[(dpms)PtIIPh2], 1, (dpms)PtIIPh(MeOH), 2, (dpms)PtIIPh(OH2), 3, and methyl PtII complex (dpms)PtIIMe(NH2Ph), 6, with O2 in aqueous or methanol solutions under ambient conditions leads to corresponding (dpms)PtIVR(X)OH complexes (R = X = Ph, 7; R = Ph, X = OH, 8; R = Ph, X = OMe, 9; R = Me, X = NHPh; 11; dpms = di(2-pyridyl)methanesulfonate). Complexes 7–9 could be isolated in high yield. Complex 11 as well as its phenyl analogue (dpms)PtIVPh(NHPh)OH, 10 can be prepared in high yield by oxidation of corresponding (dpms)PtIIR(NH2Ph) with H2O2 in methanol. Phenyl PtII complexes (dpms)PtIIPh(HX) derived from HX = aniline and DMSO, 4 and 5, respectively, are inert toward O2. The rate of oxidation of 1–5 with O2 decreases in the order 1 > 3 ~ 2 » 4, and 5 is unreactive. Methyl analogues are significantly more reactive compared with their phenyl counterparts. Proposed mechanism of oxidation with O2 includes formation of anionic species (dpms)PtIIR(X)– responsible for reaction with dioxygen. Attempts at C–O and C–N reductive elimination from phenyl PtIV complexes 7–10 do not lead to phenyl derivatives PhX at 80–100 °C, consistent with the results of the DFT estimates of corresponding activation barriers, ΔG0 exceeding 28 kcal/mol. [ABSTRACT FROM AUTHOR]

Tandem catalysis and olefin metathesis are powerful tools in the development of sustainable synthetic practices. This Award Lecture describes our advances in designing new tandem metathesis-hydrogenation methodologies for the synthesis of “designer materials” and Ru-pseudohalide metathesis catalysts that amplify opportunities for tuning catalyst activity, selectivity, and lifetime. Also discussed is the operation of a previously unrecognized oligomerization-backbiting pathway in ring-closing metathesis of conformationally flexible α,ω-dienes, which has important implications for the sustainable synthesis of medium and large rings. [ABSTRACT FROM AUTHOR]

Recently it has become apparent that the mechanism of amide hydrolysis in relatively dilute strong acid media is the same as the one observed for ester and benzimidate hydrolysis, two water molecules reacting with the O-protonated amide in the rate-determining step. This is not the whole story, however, at least for benzamide, N-methylbenzamide, and N,N-dimethylbenzamide, since the observed rate constants for these substrates deviate upwards from the observed excess acidity correlation lines at acidities higher than about 60% H2SO4, meaning that another, faster, reaction with a different mechanism is taking over at higher acidities. It has never been clear what this latter mechanism was until the work reported in this paper. An exhaustive excess acidity analysis of all the available measured reaction rate constants for the three substrates in three different acidic media, aqueous H2SO4, aqueous HClO4, and aqueous HCl, shows that this second mechanism involves a second rate-determining proton transfer to the O-protonated benzamide, followed by (or possibly concerted with) irreversible loss of +NH4 to give an acylium ion. Subsequent reaction of this with water (or bisulfate, etc.) eventually gives the observed carboxylic acid product. This latter reaction mechanism has never been previously considered for amide hydrolysis, but it may not be uncommon; at least one other reaction with a similar mechanism is known, and another possible case is suggested. [ABSTRACT FROM AUTHOR]

This paper presents two new and fast methods of determining product ratios for kinetic schemes leading to more than one product on which the Acree–Curtin–Hammett (ACH) principle is based. The methods involve rewriting a given kinetic scheme as a directed graph with nodes and arrows connecting the nodes and takes advantage of the directionality of the kinetic arrows and the enumeration of paths to the various target product nodes. The first, based on path divergent trees, is computationally simpler but works under a specific set of conditions, whereas the second, based on an adapted version of Chou’s graphical method, works for all cases. By means of illustrated examples, both methods are shown to be completely verifiable with conventional more tedious treatments based on rate law determinations. The directed graph concept also works for kinetic schemes that involve entirely equilibrated species. In addition, the paper extends these ideas to variants of the basic ACH scheme, thereby testing the validity of the ACH principle and bringing about a deeper understanding of it. Generalization of the results yields a new parameter, called degree of kinetic plasticity, which completely describes the dynamics of kinetic resolution between the boundary limits of ACH behaviour (100% kinetic plasticity) and anti-ACH behaviour (100% kinetic rigidity). It is shown that this parameter is a good descriptor of all possible scenarios between and including these limits and can be determined experimentally by conducting a new kind of product study that tracks the behaviour of final product excesses as a function of initial substrate excesses. The resulting plot is always linear with a positive slope. The degree of kinetic plasticity is found by simply subtracting the slope from unity. These ideas are tested on complex kinetic schemes exhibiting dynamic kinetic resolution (DKR) by means of organocatalysis. [ABSTRACT FROM AUTHOR]

4-R-Substituted 2-nitro-1-nitrosoethylbenzenes (R = H, CH3, OCH3, Cl, F) have been synthesized under solvent-free conditions and the mechanism of their tautomerization to 2-isonitroso-1-nitro-2-phenylethanes have been investigated by 1H NMR spectroscopy.Key words: tautomerization, pseudonitrosite, mechanism, 2-nitro-1-nitrosoethylbenzene, 1H NMR spectroscopy Opérant dans des conditions n’impliquant aucun solvant, on a réalisé la synthèse de 2-nitro-1-nitrosoéthylbenzènes substitués en position 4 par des groupes R = H, CH3, OCH3, Cl et F et, faisant appel à la spectroscopie RMN du 1H, on a étudié leur tautomérisation en 2-isonitroso-1-nitro-2-phényléthanes.Mots-clés : tautomérisation, pseudonitrosite, mécanisme, 2-nitro-1-nitrosoéthylbenzène, spectroscopie RMN du 1H.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

The regioselective Friedländer reaction of 3-amino-4-cyanopyrroles with a series of cyclic ketones has enabled the first reported synthesis of substituted 4-azaisoindoles. Structurally, this new class of compounds stands for the first reported 4-azaisoindole tacrine analogues. A reaction mechanism for the formation of the reported 4-azaisoindoles is proposed. [ABSTRACT FROM AUTHOR]

A detailed study of the lithium dialkylamide induced deprotonation of β,β-disubstituted α,β-unsaturated amides is presented. The preferential γ-Z-deprotonation and stereochemical outcome of substituents on the γ-Z carbon atom are rationalized in terms of a cyclic eight-membered transition state, which is supported by DFT calculations. Analogous deprotonations on cyclohexylidenecarboxamides reveal a delicate balance of the preference for the eight-membered cyclic transition state with the effects of existing substituents on the ring and the intervention of a twist-boat transition state. [ABSTRACT FROM AUTHOR]

The β-scission mechanisms of catalytically chemisorbed carbenium ions are further investigated using density functional theory computations and explicit-contact modelling, but with slightly larger catalyst fragment models than in our previous work. Some variations are seen, including the existence of formal one-step and three-step (rather than two-step) mechanisms. The activation barriers are most affected by the basicity of the catalyst model than by any other characteristics: the stronger the base, the greater the barrier. A general mechanism for β scission is presented, as are the specific mechanisms for all the step variations observed from computations to date. [ABSTRACT FROM AUTHOR]

The Claisen-like condensation of a series of 1-arylacetyl-6-acetyl-3,4,7,8-tetramethylglycolurils (Ar = Ph, p-OMeC6H4, and p-ClC6H4) was studied in preparative experiments and by analysis of kinetic data. The reactions proceeded in virtually quantitative yield and were highly regioselective: the corresponding N-(2′-aryl-3′-ketobutanoyl)-3,4,7,8-tetramethylglycolurils were obtained in all cases, with none of the 4′-aryl regioisomers being detected. Clean bimolecular kinetics were observed for each conversion using UV spectroscopy. Reaction rates followed the order Ar = p-OMeC6H4 < Ph < p-ClC6H4. The results are explained by a mechanism in which the deprotonation of the substrates is rate-limiting; thus, deprotonation of the arylacetyl groups is favoured. The ensuing enolate reacts rapidly in the C–C bond-forming step. [ABSTRACT FROM AUTHOR]