394 research outputs found

    Accurate static electric dipole polarizability calculation of +3 charged lanthanide ions

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    An accurate determination of the heavy element static atomic dipole polarizability is a challenge for theoretical methods. We present in this paper computed values of the dipole polarizability of the lanthanide ions from La3+ to Lu3+. The results were obtained by performing fully relativistic and pseudopotential calculations including the treatment of open-shell systems. We have shown that, in order to obtain accurate results, it is essential to take into account scalar relativistic effects, core polarization and flexibility of the basis sets. Finally, we present a database of reference values of dipole polarizability for the Ln3+ ions

    Vibrational mode assignment of finite temperature infrared spectra using the AMOEBA polarizable force field †

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    International audienceThe calculation of infrared spectra by molecular dynamics simulations based on the AMOEBA polarizable force field has recently been demonstrated [Semrouni et al., J. Chem. Theory Comput., 2014, 10, 3190]. While this approach allows access to temperature and anharmonicity effects, band assignment requires additional tools, which we describe in this paper. The Driven Molecular Dynamics approach, originally developed by Bowman, Kaledin et al. [Bowman et al. J. Chem. Phys., 2003, 119, 646, Kaledin et al. J. Chem. Phys., 2004, 121, 5646] has been adapted and associated with AMOEBA. Its advantages and limitations are described. The IR spectrum of the Ac-Phe-Ala-NH 2 model peptide is analyzed in detail. In addition to differentiation of conformations by reproducing frequency shifts due to non-covalent interactions, DMD allows visualizing the temperature-dependent vibrational modes

    Evaluation of the impact of antibiotics and pesticides used in livestock and agriculture on the safety of bovine meat consumed in the North-East of Benin

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    The presence of antibiotic and pesticide residues in food can cause health problems for consumers. However, no study has quantified residues of veterinary antibiotics and pesticides in meat of cattle massively bred in North Benin. This is why the overall objective of this thesis is to evaluate the impact of the use of veterinary antibiotics and pesticides on the safety of cattle meat consumed in North-East of Benin. The first chapter is a compilation of three review papers that were titled, respectively: “production, importation and quality of meat consumed in Benin”; “quality of veterinary antibiotics used in West Africa and methods for detecting of their residues in foodstuffs” and “review on the modes of action, impacts and detection of pesticides used in agriculture”. In chapter 2, a survey was first conducted among 98 farmers in the communes of Banikoara, Kandi, Bembereke and Kalale located in North-East of Benin. This first study showed that the antibiotics used in cattle breeding belonged to the groups of tetracyclines, beta-lactams, sulphonamides, aminoglycosides and macrolides, which were used per 100; 88; 56; 44 and 35% of breeders, respectively, in the study area. Fifty-eight percents of these farmers bought these drugs in the illegal market, 57% of them practiced “self-medication” and 93% of them did not respect the withdrawal times for antibiotics before putting foodstuffs from treated animals on the market. These risky practices led to the contamination of cattle meat with antibiotic residues, as was shown in the second study. The kidney and muscle tissues of 50 cattle carcasses from the Parakou city, in north-east of Benin, were samples to determine antibiotic residues (tetracyclines, beta-lactams and sulfonamides), using a semi-quantitative screening method adapted from the New Two Plates Test (NTPT) of Pham Kim et al. (2011). This modified NTPT showed that 60 % of the 50 carcasses analyzed contained residues of tetracyclines, beta-lactams and sulfonamides. Positive results were confirmed by liquid chromatography - mass spectrometry (LC-MS) analyzes. The maximum levels observed for oxytetracycline, epi-oxytetracycline, tetracycline and epi-tetracycline residues in the kidney were 1380, 350, 190 and 230 ÎŒg kg-1, respectively. In one of the bovine carcasses, very high levels of sulfamethazine residues were found: 3900 ÎŒg kg-1 in the kidney and 2220 ÎŒg kg-1 in the muscle. Overall, 38 % of the carcasses submitted to confirmation analyzes by LC-MS showed antibiotic residue levels that exceeded the maximum residue limits (MRLs) applied in the European legislation. The modified NTPT method was then used to evaluate the quality of veterinary antibiotic drugs used in cattle breeding in the study area. The results of this third study showed that the 28 products tested contained the active ingredient as indicated on the drug labels. However, quantitatively, only 61 % of these drugs contained active substance at levels ranging from 90 to 120 %, 90-115 % and ≄ 90 % of the concentrations mentioned on the labels (for oxytetracycline, penicillin G and tylosin drugs, respectively), and could therefore be declared compliant with the requirements of USP (United States Pharmacopeia). The results of the studies reported in this chapter 2 have shown that veterinary practices, resulting in the presence of residues in the meat, and the poor quality of veterinary antibiotics could promote the development of bacterial resistance to antibiotics in the study area. Chapter 3 presents the results of studies 4 and 5. The inventory realized in study 4 showed that 56 commercial pesticides (including 21 herbicides and 35 insecticides) were used in agriculture in the study area. As regards the active ingredients contained in these products, 13 were herbicides and 14 were insecticides. Seventy-eight percents of farmers bought these pesticides both in the illegal circuit and in the official agricultural inputs selling structures. Only 53 % of these farmers knew the instructions for use of these dangerous products. These practices have led to the contamination of natural ecosystems and the food chain with pesticide residues. Indeed, study 5 revealed traces of glyphosate residues in pasture waters. In addition, three of 25 cattle carcasses that samples were subjected to the analyzes by gas chromatography - mass spectrometry, were contaminated with insecticide residues such as beta-endosulfan (98.6-139.5 ÎŒg kg-1) and dichlorodiphenyldichloroethylene (DDE) (4.6 ÎŒg kg-1). Overall, only beta-endosulfan found in two carcasses showed concentrations above the MRL established by European Regulation (EC) 396/2005. Finally, chapter 4 presents a general discussion of the results obtained in the five studies. As a general conclusion and recommendation, it can be said that all the veterinary and agricultural practices as described in studies 1 and 4 clearly impact the safety of cattle meat consumed in North-East of Benin, and the results of these studies are benchmarks for future monitoring of the food chain in Benin.La prĂ©sence de rĂ©sidus d’antibiotiques et de pesticides dans les aliments peut ĂȘtre Ă  l’origine de problĂšmes de santĂ© pour les consommateurs. Pourtant, aucune Ă©tude n’avait quantifiĂ© les rĂ©sidus d’antibiotiques vĂ©tĂ©rinaires et de pesticides dans les viandes de bovins massivement Ă©levĂ©s au Nord du BĂ©nin. C’est pourquoi l’objectif global de cette thĂšse est d’évaluer les impacts de l’utilisation des antibiotiques vĂ©tĂ©rinaires et des pesticides sur la qualitĂ© sanitaire des viandes bovines consommĂ©es au Nord-Est BĂ©nin. Le premier chapitre est une compilation de trois articles de synthĂšse bibliographique qui sont respectivement titrĂ©s : « production, importation et qualitĂ© des viandes consommĂ©es au BĂ©nin » ; « qualitĂ© des antibiotiques vĂ©tĂ©rinaires utilisĂ©s en Afrique de l’Ouest et mĂ©thodes de dĂ©tection de leurs rĂ©sidus dans les denrĂ©es alimentaires » et « revue sur les modes d’action, impacts et dĂ©tection des pesticides utilisĂ©s en agriculture ». Dans le chapitre 2, une enquĂȘte a d’abord Ă©tĂ© menĂ©e auprĂšs de 98 Ă©leveurs rĂ©partis dans les communes de Banikoara, Kandi, BembĂšrĂškĂš et KalalĂ© situĂ©es au Nord-Est BĂ©nin. Il ressort de cette premiĂšre Ă©tude que les antibiotiques utilisĂ©s en Ă©levage de bovins appartenaient aux groupes des tĂ©tracyclines, bĂȘta-lactames, sulfamidĂ©s, aminoglycosides et macrolides, qui Ă©taient respectivement employĂ©s par 100 ; 88 ; 56 ; 44 et 35 % des Ă©leveurs de la zone d’étude. Cinquante-huit pourcents de ces Ă©leveurs achetaient ces mĂ©dicaments dans le marchĂ© illĂ©gal, 57 % parmi eux pratiquaient l’automĂ©dication et 93 % d’entre eux ne respectaient pas les dĂ©lais d’attente des antibiotiques avant de mettre en consommation les denrĂ©es alimentaires issues des animaux traitĂ©s. Ces pratiques Ă  risque ont engendrĂ© la contamination des viandes bovines par des rĂ©sidus d’antibiotiques, comme cela a Ă©tĂ© montrĂ© dans la deuxiĂšme Ă©tude. Les tissus rĂ©nal et musculaire de 50 carcasses bovines provenant de la ville de Parakou, au Nord-Est BĂ©nin, ont fait l’objet d’une recherche de rĂ©sidus d’antibiotiques (tĂ©tracyclines, bĂȘta-lactames et sulfamidĂ©s), grĂące Ă  une mĂ©thode de screening semi-quantitatif adaptĂ©e du ‘‘New Two Plates Test’’ (NTPT) de Pham Kim et al. (2011). Ce NTPT modifiĂ© a permis de montrer que 60 % des 50 carcasses analysĂ©es contenaient des rĂ©sidus de tĂ©tracyclines, de bĂȘta-lactames et de sulfamidĂ©s. Les rĂ©sultats positifs ont Ă©tĂ© confirmĂ©s par des analyses de chromatographie en phase liquide couplĂ©e Ă  un spectromĂštre de masse (CL-SM). Les teneurs maximales observĂ©es pour les rĂ©sidus d’oxytĂ©tracycline, Ă©pi-oxytĂ©tracycline, tĂ©tracycline et Ă©pi-tĂ©tracycline dans le rein Ă©taient respectivement de 1380, 350, 190 et 230 ”g kg-1. Dans une des carcasses bovines, des niveaux trĂšs Ă©levĂ©s de rĂ©sidus de sulfamĂ©thazine ont Ă©tĂ© trouvĂ©s : 3900 ”g kg-1 dans le rein et 2220 ”g kg-1 dans le muscle. Dans l’ensemble, 38 % des carcasses soumises aux analyses de confirmation par CL-SM prĂ©sentaient des concentrations en rĂ©sidus d’antibiotiques supĂ©rieures aux limites maximales de rĂ©sidus (LMR) appliquĂ©es dans la lĂ©gislation europĂ©enne. La mĂ©thode NTPT modifiĂ©e a Ă©tĂ© ensuite utilisĂ©e pour l’évaluation de la qualitĂ© des mĂ©dicaments antibiotiques vĂ©tĂ©rinaires utilisĂ©s en Ă©levage de bovins dans la zone d’étude. Les rĂ©sultats de cette troisiĂšme Ă©tude ont montrĂ© que les 28 produits analysĂ©s contenaient la matiĂšre active conformĂ©ment Ă  ce qui Ă©tait indiquĂ© sur l’emballage du mĂ©dicament. Cependant, sur le plan quantitatif, seulement 61 % de ces mĂ©dicaments prĂ©sentaient des teneurs en substances actives comprises dans une fourchette de 90 Ă  120 %, 90-115 % et ≄ 90 % des concentrations mentionnĂ©es sur les Ă©tiquettes (respectivement pour les produits Ă  base d’oxytĂ©tracycline, de pĂ©nicilline G et de tylosine), et pouvaient donc ĂȘtre dĂ©clarĂ©s conformes aux exigences de l’USP (United States Pharmacopeia). Les rĂ©sultats des Ă©tudes consignĂ©es dans ce chapitre 2 ont montrĂ© que les pratiques vĂ©tĂ©rinaires, rĂ©sultant en la prĂ©sence de rĂ©sidus dans la viande, et la qualitĂ© mĂ©diocre des antibiotiques vĂ©tĂ©rinaires pourraient favoriser le dĂ©veloppement de rĂ©sistances bactĂ©riennes aux antibiotiques dans la zone d’étude. Le chapitre 3 prĂ©sente les rĂ©sultats des Ă©tudes 4 et 5. L’inventaire rĂ©alisĂ© dans l’étude 4 (dont la mĂ©thode est similaire Ă  celle de la premiĂšre Ă©tude) a montrĂ© que 56 pesticides commerciaux (dont 21 herbicides et 35 insecticides) Ă©taient utilisĂ©s en agriculture dans la zone d’étude correspondante. En ce qui concerne les matiĂšres actives contenues dans ces produits, 13 ont Ă©tĂ© recensĂ©es pour les herbicides et 14 pour les insecticides. Septante-huit pourcents des agriculteurs achetaient ces pesticides aussi bien dans le circuit illĂ©gal que dans les structures officielles de vente d’intrants agricoles. Seulement 53 % de ces producteurs maĂźtrisaient le mode d’emploi de ces produits dangereux. Ces pratiques ont induit une contamination des Ă©cosystĂšmes naturels et de la chaĂźne alimentaire en rĂ©sidus de pesticides. En effet, l’étude 5 a rĂ©vĂ©lĂ© des traces de rĂ©sidus de glyphosate dans les eaux de pĂąturage. De plus, 3 des 25 carcasses bovines dont les Ă©chantillons ont Ă©tĂ© soumis aux analyses par chromatographie en phase gazeuse couplĂ©e Ă  un spectromĂštre de masse prĂ©sentaient des rĂ©sidus d’insecticides tels que le bĂȘta-endosulfan (98,6 Ă  139,5 ”g kg-1) et le dichlorodiphĂ©nyldichloroĂ©thylĂšne (DDE) (4,6 ”g kg-1). Dans l’ensemble, seul le bĂȘta-endosulfan retrouvĂ© dans deux carcasses prĂ©sentait des concentrations supĂ©rieures Ă  la LMR fixĂ©e par le RĂšglement EuropĂ©en (CE) 396/2005. Enfin, le chapitre 4 prĂ©sente une discussion gĂ©nĂ©rale des rĂ©sultats obtenus dans les cinq Ă©tudes. En guise de conclusion gĂ©nĂ©rale et de recommandations, on peut dire que l’ensemble des pratiques vĂ©tĂ©rinaires et agricoles telles que dĂ©crites dans les Ă©tudes 1 et 4 impactent clairement la qualitĂ© sanitaire des viandes bovines consommĂ©es au Nord-Est du BĂ©nin, et les rĂ©sultats de ces Ă©tudes constituent des repĂšres pour des actions de surveillance futures de la chaĂźne alimentaire au BĂ©nin

    Autonomisation de la femme en milieu rural au BĂ©nin : une contextualisation par les projets & programmes d’alphabĂ©tisation

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    The so-called “empowerment” of rural women remains one of the strategies for combating their situation of poverty and vulnerability. It has been the subject of several studies which have attempted to measure it to know the effects of development actions in their favor. A polysemic and multidimensional concept, empowerment is complex; its measurement is difficult and presents challenges related particularly to its subjective and contextual characteristics, which suggest an operational and contextual definition of the concept. Through literacy programs, women are likely to become self-sufficient. One of the defining aspects of these programs is “when participants are asked to profile what an empowered woman should be in her own context”. This article attempts to answer the following question: what is the perception of empowerment of rural women in the context of Benin, where several literacy programs have been implemented? In this perspective, an exploratory, qualitative and participatory approach was adopted and supported by six (06) group interviews of seven (07) rural women each in six (06) departments of Benin. Through the content analysis method, the concept of empowerment is contextualized with an appropriate measurement framework and a local definition as they perceived it: Empowerment is a process of change that takes place in women's lives, by which they access/acquire (to) more economic and social resources, gain access to new knowledge and skills to improve their well-being and that of their families, as well as to increase their negotiation skills with men/spouses, negotiation that leads to mutual consultation and results in freer decision-making. The results found could serve as a starting point for future research aimed at assessing the effects or impact of rural women's participation in literacy projects and programs on their level of empowerment.   Keywords: Empowerment, literate woman, participating woman, rural environment, measurement. JEL Classification: C83, I 25, I28, I38, I31, J16 Type of paper: empirical researchL’autonomisation dite « empowerment Â» des femmes rurales reste l’une des stratĂ©gies de lutte contre leur situation de pauvretĂ© et de vulnĂ©rabilitĂ©.  Elle a fait l’objet de plusieurs Ă©tudes qui ont tentĂ© de la mesurer pour connaĂźtre des effets des actions de dĂ©veloppement en leur faveur. Concept polysĂ©mique et multidimensionnel, l’autonomisation est complexe ; sa mesure est difficile et prĂ©sente des dĂ©fis liĂ©s, notamment, Ă  ses caractĂšres subjectif et contextuel qui suggĂšrent une dĂ©finition opĂ©rationnelle et contextuelle du concept. Par les programmes d’alphabĂ©tisation, les femmes sont susceptibles de devenir autonomes. Un des aspects dĂ©terminants de ces programmes est « le moment oĂč les participantes sont invitĂ©es Ă  Ă©tablir le profil de ce que devrait ĂȘtre une femme autonome dans le contexte qui lui est propre Â». Cet article tente de rĂ©pondre Ă  la question suivante : quelle est la perception de l’autonomisation des femmes rurales dans le contexte du BĂ©nin oĂč plusieurs programmes d’alphabĂ©tisation ont Ă©tĂ© mis en Ɠuvre ? Dans cette optique, une approche exploratoire, qualitative et participative fut adoptĂ©e et soutenue par six (06) entrevues de groupe de sept (07) femmes rurales chacun dans six (06) dĂ©partements du BĂ©nin. Par la mĂ©thode d’analyse du contenu, le concept d’autonomisation est contextualisĂ© avec un cadre de mesure adaptĂ©e et une dĂ©finition locale telle qu’elles l’ont perçue : l’autonomisation est un processus de changement qui intervient dans la vie des femmes, par lequel elles accĂšdent/acquiĂšrent (Ă ) plus de ressources Ă©conomiques et sociales, accĂšdent Ă  de nouvelles connaissances et compĂ©tences pour amĂ©liorer leur bien-ĂȘtre et celui de leur famille, ainsi que pour renforcer leurs capacitĂ©s de nĂ©gociation avec les hommes/conjoints, nĂ©gociation qui conduit Ă  une consultation mutuelle et aboutit Ă  des prises de dĂ©cisions plus libres. Les rĂ©sultats obtenus pourraient servir de point de dĂ©part pour des recherches futures visant Ă  Ă©valuer les effets ou l’impact de la participation des femmes rurales aux projets et programmes d’alphabĂ©tisation sur leur niveau d’autonomisation.   Mots clĂ©s : Autonomisation, femme alphabĂ©tisĂ©e, femme participante, milieu rural, mesure. Classification JEL: C83, I 25, I28, I38, I31, J16 Type de l’article : Recherche empiriqu

    Tourisme et Croissance Inclusive au BĂ©nin: Une Analyse d’AprĂšs l’Indice SynthĂ©tique de Croissance Inclusive

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    Cette Ă©tude vise Ă  examiner le type de relation entre tourisme et croissance inclusive au BĂ©nin de 1995 Ă  2021 en utilisant comme variable dĂ©pendante, contrairement Ă  plusieurs Ă©tudes,  l’Indice SynthĂ©tique de Croissance Inclusive  (ISCI). En nous appuyant sur des donnĂ©es chronologiques, nous avons effectuĂ© des estimations Ă  l'aide du ModĂšle Vectoriel Ă  Correction d'Erreur (VECM), du test de causalitĂ© de Granger et du ModĂšle Ă  Correction d'Erreur (MCE) sous STATA 15. Les rĂ©sultats rĂ©vĂšlent une relation significative positive entre le ratio des recettes touristiques rĂ©elles et l'Indice SynthĂ©tique de Croissance Inclusive (ISCI), dĂ©montrant que le tourisme contribue Ă  la croissance inclusive jusqu'Ă  un certain seuil. En outre,  la nature bidirectionnelle de cette relation (entre tourisme et croissance inclusive) a Ă©tĂ© Ă©galement mise en Ă©vidence.   This study aims to examine the type of relationship between tourism and inclusive growth in Benin from 1995 to 2021 using as a dependent variable, unlike several studies, the Synthetic Inclusive Growth Index (ISCI). Based on historical data, we carried out estimations using the Vector Error Correction Model (VECM), the Granger causality test and the Error Correction Model (ECM) under STATA 15. The results reveal a significant positive relationship between the ratio of real tourism receipts and the Synthetic Inclusive Growth Index (ISCI), demonstrating that tourism contributes to inclusive growth up to a certain threshold. Furthermore, the bidirectional nature of this relationship (between tourism and inclusive growth) was also highlighted

    Tourisme et Croissance Inclusive au BĂ©nin: Une Analyse d’AprĂšs l’Indice SynthĂ©tique de Croissance Inclusive

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    Cette Ă©tude vise Ă  examiner le type de relation entre tourisme et croissance inclusive au BĂ©nin de 1995 Ă  2021 en utilisant comme variable dĂ©pendante, contrairement Ă  plusieurs Ă©tudes,  l’Indice SynthĂ©tique de Croissance Inclusive  (ISCI). En nous appuyant sur des donnĂ©es chronologiques, nous avons effectuĂ© des estimations Ă  l'aide du ModĂšle Vectoriel Ă  Correction d'Erreur (VECM), du test de causalitĂ© de Granger et du ModĂšle Ă  Correction d'Erreur (MCE) sous STATA 15. Les rĂ©sultats rĂ©vĂšlent une relation significative positive entre le ratio des recettes touristiques rĂ©elles et l'Indice SynthĂ©tique de Croissance Inclusive (ISCI), dĂ©montrant que le tourisme contribue Ă  la croissance inclusive jusqu'Ă  un certain seuil. En outre,  la nature bidirectionnelle de cette relation (entre tourisme et croissance inclusive) a Ă©tĂ© Ă©galement mise en Ă©vidence.   This study aims to examine the type of relationship between tourism and inclusive growth in Benin from 1995 to 2021 using as a dependent variable, unlike several studies, the Synthetic Inclusive Growth Index (ISCI). Based on historical data, we carried out estimations using the Vector Error Correction Model (VECM), the Granger causality test and the Error Correction Model (ECM) under STATA 15. The results reveal a significant positive relationship between the ratio of real tourism receipts and the Synthetic Inclusive Growth Index (ISCI), demonstrating that tourism contributes to inclusive growth up to a certain threshold. Furthermore, the bidirectional nature of this relationship (between tourism and inclusive growth) was also highlighted

    Tourisme et Croissance Inclusive au BĂ©nin : Une Analyse d’AprĂšs l’Indice SynthĂ©tique de Croissance Inclusive

    Get PDF
    Cette Ă©tude vise Ă  examiner le type de relation entre tourisme et croissance inclusive au BĂ©nin de 1995 Ă  2021 en utilisant comme variable dĂ©pendante, contrairement Ă  plusieurs Ă©tudes, l’Indice SynthĂ©tique de Croissance Inclusive (ISCI). En nous appuyant sur des donnĂ©es chronologiques, nous avons effectuĂ© des estimations Ă  l'aide du ModĂšle Vectoriel Ă  Correction d'Erreur (VECM), du test de causalitĂ© de Granger et du ModĂšle Ă  Correction d'Erreur (MCE) sous STATA 15. Les rĂ©sultats rĂ©vĂšlent une relation significative positive entre le ratio des recettes touristiques rĂ©elles et l'Indice SynthĂ©tique de Croissance Inclusive (ISCI), dĂ©montrant que le tourisme contribue Ă  la croissance inclusive jusqu'Ă  un seuil donnĂ©. En outre, la nature bidirectionnelle de cette relation (entre tourisme et croissance inclusive) a Ă©tĂ© Ă©galement mise en Ă©vidence. This study aims to examine the type of relationship between tourism and inclusive growth in Benin from 1995 to 2021 using as a dependent variable, unlike several studies, the Synthetic Inclusive Growth Index (ISCI). Based on historical data, we carried out estimations using the Vector Error Correction Model (VECM), the Granger causality test and the Error Correction Model (ECM) under STATA 15. The results reveal a significant positive relationship between the ratio of real tourism receipts and the Synthetic Inclusive Growth Index (ISCI), demonstrating that tourism contributes to inclusive growth up to a given threshold. Furthermore, the bidirectional nature of this relationship (between tourism and inclusive growth) was also highlighted

    Molecular dynamics study of the hydration of lanthanum(III) and europium(III) including many-body effects

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    Lanthanides complexes are widely used as contrast agents in magnetic resonance imaging (MRI) and are involved in many fields such as organic synthesis, catalysis, and nuclear waste management. The complexation of the ion by the solvent or an organic ligand and the resulting properties (for example the relaxivity in MRI) are mainly governed by the structure and dynamics of the coordination shells. All of the MD approachs already carried out for the lanthanide(III) hydration failed due to the lack of accurate representation of many-body effects. We present the first molecular dynamics simulation including these effects that accounts for the experimental results from a structural and dynamic (water exchange rate) point of view

    Theoretical study of the hydrated Gd3+ ion: Structure, dynamics, and charge transfer

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    The dynamical processes taking place in the first coordination shells of the gadolinium (III) ion are important for improving the contrast agent efficiency in magnetic-resonance imaging. An extensive study of the gadolinium (III) ion solvated by a water cluster is reported, based on molecular dynamics simulations. The AMOEBA force field [P. Y. Ren and J. W. Ponder, J. Phys. Chem. B 107, 5933 (2003)] that includes many-body polarization effects is used to describe the interactions among water molecules, and is extended here to treat the interactions between them and the gadolinium ion. In this purpose accurate ab initio calculations have been performed on Gd3+-H2O for extracting the relevant parameters. Structural data of the first two coordination shells and some dynamical properties such as the water exchange rate between the first and second coordination shells are compared to available experimental results. We also investigate the charge transfer processes between the ion and its solvent, using a fluctuating charges model fitted to reproduce electronic structure calculations on [Gd(H2O)n]3+ complexes, with n ranging from 1 to 8. Charge transfer is seen to be significant (about one electron) and correlated with the instantaneous coordination of the ion
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