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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
61

Síntese, caracterização e estudo do comportamento térmico dos glicolatos de lantanídeos e ítrio no estado sólido / Synthesis, characterization and study of the thermal behavior of glycolates of lanthanides and yttrium in solid form

Gomes, Danilo José Coura [UNESP] 17 March 2016 (has links)
Submitted by DANILO JOSÉ COURA GOMES null (danilogomes26@yahoo.com.br) on 2016-03-21T17:46:23Z No. of bitstreams: 1 Versão eletrônica.pdf: 37219010 bytes, checksum: 3db084a502fe18628a8958b5523753bd (MD5) / Rejected by Ana Paula Grisoto (grisotoana@reitoria.unesp.br), reason: Solicitamos que realize uma nova submissão seguindo as orientações abaixo: No campo “Versão a ser disponibilizada online imediatamente” foi informado que seria disponibilizado o texto completo porém no campo “Data para a disponibilização do texto completo” foi informado que o texto completo deverá ser disponibilizado apenas 24 meses após a defesa. Caso opte pela disponibilização do texto completo apenas 24 meses após a defesa selecione no campo “Versão a ser disponibilizada online imediatamente” a opção “Texto parcial”. Esta opção é utilizada caso você tenha planos de publicar seu trabalho em periódicos científicos ou em formato de livro, por exemplo e fará com que apenas as páginas pré-textuais, introdução, considerações e referências sejam disponibilizadas. Se optar por disponibilizar o texto completo de seu trabalho imediatamente selecione no campo “Data para a disponibilização do texto completo” a opção “Não se aplica (texto completo)”. Isso fará com que seu trabalho seja disponibilizado na íntegra no Repositório Institucional UNESP. Por favor, corrija esta informação realizando uma nova submissão. Agradecemos a compreensão. on 2016-03-22T16:56:26Z (GMT) / Submitted by DANILO JOSÉ COURA GOMES null (danilogomes26@yahoo.com.br) on 2016-03-22T17:53:54Z No. of bitstreams: 1 Versão eletrônica.pdf: 37215484 bytes, checksum: d91d471547bea0cdb42d7b423b2d9455 (MD5) / Approved for entry into archive by Juliano Benedito Ferreira (julianoferreira@reitoria.unesp.br) on 2016-03-23T14:24:19Z (GMT) No. of bitstreams: 1 gomes_djc_dr_araiq_par.pdf: 3387049 bytes, checksum: c79b9767bc573eb1f988cb8e70b185a6 (MD5) / Made available in DSpace on 2016-03-23T14:24:19Z (GMT). No. of bitstreams: 1 gomes_djc_dr_araiq_par.pdf: 3387049 bytes, checksum: c79b9767bc573eb1f988cb8e70b185a6 (MD5) Previous issue date: 2016-03-17 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Foram sintetizados, no estado sólido, os compostos LnL3∙nH2O, sendo que Ln representa os lantanídeos trivalentes (La ao Lu) e o ítrio(III) e o L representa o glicolato (C2H4O2-). Os compostos foram sintetizados por adição de ligeiro excesso do ácido glicólico com carbonato básico de lantanídeos e ítrio, sob agitação e aquecimento. A caracterização dos compostos foi realizada utilizando técnicas como difratometria de raios X pelo método do pó, complexometria e as técnicas termoanalíticas como termogravimetria e calorimetria exploratória diferencial simultânea (TG-DSC) e termogravimetria acoplada à espectroscopia de absorção na região do infravermelho com transformada de Fourier (TG-FTIR). Também foram realizados cálculos teóricos para a elaboração de modelos estruturais mais prováveis e energeticamente favoráveis dos compostos sintetizados e a partir dessas estruturas foram gerados os espectros teóricos de infravermelho, para isso foram aplicados métodos da Teoria do Funcional de Densidade Eletrônica (DFT). Os resultados forneceram informações sobre o comportamento térmico, cristalinidade, estequiometria, sítios de coordenação e também pode identificar os principais produtos gasosos liberados durante o aquecimento dos compostos estudados. / Solid-state LnL3∙nH2O compounds, where Ln stands for trivalent lanthanides (La to Lu) or yttrium(III) and L is glycolate (C2H4O2 - ) have been synthesized. The compounds were synthesized by addition of slight excess of glycolic acid with basic carbonate of yttrium and lanthanides, under stirring and heating. The characterization of the compounds was performed using X-ray powder diffratometry, complexometry and thermoanalytical techniques such as simultaneous thermogravimetry and differential scanning calorimetry (TG-DSC) and thermogravimetry coupled to absorption spectroscopy in the region of infrared with Fourier transform (TG-FTIR). Theoretical calculations were also performed to elaborate more probable and energetically favorable structural models of the synthesized compounds and from these structures the theoretical infrared spectra were generated, with the application of methods of Functional Theory of Electron Density (DFT). The results provided information about thermal behaviour, crystallinity, stoichiometry, coordination sites and could also identify the main gaseous products released during heating of the compounds studied. / CNPq: 146916/2013-1
62

Síntese, caracterização e estudo do comportamento térmico dos 4-metoxibenzoatos de lantanídeos(III) e ítrio(III), no estado sólido /

Rodrigues, Emanuel Carlos. January 2006 (has links)
Orientador: Massao Ionashiro / Banca: Mario Cilense / Banca: Mercedes de Moraes / Banca: Lázaro Moscardini D'Assunção / Banca: Jeosadaque José de Sene / Resumo: Foram sintetizados os 4-metoxibenzoatos de lantanídeos e ítrio trivalentes e no estado sólido. Esses compostos foram caracterizados e estudados utilizando-se as técnicas de análise elementar, complexometria, difratometria de raios x pelo método do pó, espectroscopia de absorção na região do infravermelho, termogravimetria-análise térmica diferencial simultânea (TG-DTA) e calorimetria exploratória diferencial (DSC). Os resultados permitiram obter informações sobre a estequiometria, desidratação, transformação polimórfica (transição de fase), modo de coordenação, comportamento térmico e decomposição térmica. / Abstract: Solid 4-methoxybenzoates of trivalent lanthanides and yttrium have been synthesized. Elemental analysis, complexometry, X-ray powder diffractometry, infrared spectroscopy, simultaneous thermogravimetry and differential thermal analysis (TG-DTA), and differential scanning calorimetry (DSC) were used to characterize and to study the thermal behaviour of these compounds. The results led to information about the composition, dehydration, polymorphic transformation (phase transition), coordination mode, thermal behaviour and thermal decomposition of the isolated compounds. / Doutor
63

Íons lantanídeos atuando simultaneamente como catalisadores e sondas luminescentes: inesperada clivagem seletiva da n-acetilbenzamida

Lima, Geórgia Batista Vieira de 21 December 2014 (has links)
Made available in DSpace on 2015-05-14T13:21:37Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 3266029 bytes, checksum: 4d92a2fca508ea7c2bb15c9e2b4c72b7 (MD5) Previous issue date: 2014-12-21 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / This work reports, for the first time, the catalytic action of trivalent lanthanide ions, Ln3 +, on the cleavage of imides. In addition to accelerating the N-acetylbenzamide reaction with the nucleophile, the Ln3+ induces an unusual regioselectivity of it. The concentrations of NABZ and benzamide, investigated by gas chromatography over time, fit well to a first order kinetics, but the reactions half-life are dependent on the proportion Ln3+: imide, tending to decrease with increasing amount of Ln3+ ions. The cleavage of the Nacetylbenzamide mediated by Ln3+ ions is highly solvent dependent, suggesting that it acts as a nucleophile in the reaction. It is also dependent on the Ln3+ ion type, with the reaction rate order as follows: Yb3+ > Tb3+ > Eu3+. Unlike what occurs with the NABZ, nor phthalimide neither N-benzoyl-N-(pyridin-2-yl)benzamide undergo cleavage mediated by ions Ln3+ under the same conditions, suggesting that the reaction reported in this work is only operative with acyclic R1CONHCOR2 imides. Both Eu3+ and Tb3+ ions could be used as catalysts, as well as luminescent probes for monitoring qualitatively the N-acetylbenzamide cleavage reaction in ethanol. Finally, a mechanism consistent with the experimental observations above was proposed. / No presente trabalho, é reportada, pela primeira vez, a ação catalítica de íons lantanídeos trivalentes, Ln3+, na clivagem de imidas. Além de acelerar a reação da Nacetilbenzamida com o nucleófilo, os Ln3+ induzem uma regiosseletividade não usual para a mesma. As concentrações de NABZ e benzamida, ao longo do tempo, investigadas por cromatografia gasosa, se ajustam bem a uma cinética de primeira ordem, mas o tempo de meia vida das reações são dependentes da proporção Ln3+:imida, tendendo a diminuir com o aumento da quantidade do íon Ln3+. A clivagem da N-acetilbenzamida mediada pelos íons Ln3+ é altamente dependente do solvente, o que sugere que o mesmo atua como nucleófilo na reação. Ela também é dependente do tipo de íon Ln3+, a velocidade da reação segue a ordem: Yb3+ > Tb3+ > Eu3+. Ao contrário do que ocorre com a NABZ, nem a ftalimida nem a Nbenzoil- N-(piridina-2-il)benzamida sofrem clivagem mediada pelos íons Ln3+ nas mesmas condições, o que sugere que a reação reportada neste trabalho só é operante em imidas acíclicas do tipo R1CONHCOR2. Ambos os íons Eu3+ e Tb3+ puderam ser utilizados, além de catalisadores, como sondas luminescentes para o monitoramento qualitativo da reação de clivagem da N-acetilbenzamida em etanol. Finalmente, um mecanismo consistente com as observações experimentais supracitadas foi proposto.
64

Design and Synthesis of Lanthanide Single-Molecule Magnets Using the Schiff Base Approach

Lacelle, Thomas January 2017 (has links)
Single-Molecule Magnets (SMMs) are discrete molecules that exhibit slow relaxation of magnetization. Unlike conventional magnets that rely on the long range magnetic ordering in the form of domains, these molecules act as magnets independently, that is without the influence of neighbouring molecules. SMMs have intrigued physicists and chemists alike for over twenty years with their potential future applications in data storage quantum computing, and with this communal interest there has been significant collaboration between the two fields of research. SMMs have brought forth an opportunity for coordination chemists to muster their creativity and synthetic expertise in the rational design and development of these magnetic materials. From these new and fascinating compounds, both experimental and theoretical physicists have sought to develop and refine our understanding of the aspects of these molecular magnets in order to improve their performance at higher temperatures. In this work, new topologies for lanthanide complexes are explored using a novel Schiff base ligand. The magnetic properties of dinuclear, tetranuclear and octanuclear lanthanide complexes are discussed and correlated to their structural properties. The rational design of tetrazine-based Schiff base ligands for magnetic studies is also discussed in hopes of developing high performance SMMs.
65

Intercalação de íons lantanídeos e de poli(óxido de etileno) assistida por tensoativo na matriz hospedeira VOPO4.2H2O / Intercalation of ions Lanthanides and Poly (ethylene oxide) assisted by surfactant in host matrix of VOPO4.2H2O

João Paulo Ligabó Ferreira 02 October 2008 (has links)
Compostos de vanádio são extensivamente estudados, devido suas propriedades redox, eletroquímicas, catalíticas, magnéticas e biológicas. Nesta dissertação tivemos como foco de nosso trabalho o composto VOPO4.2H2O que apresenta uma forma lamelar com suas lamelas unidas por interações de Van der Waals. Essas fracas interações interlamelares fazem do fosfato de vanadila e de seus componentes análogos excelentes matrizes para a síntese de compostos de intercalação. A morfologia do VOPO4.2H2O mostrou-se sensível a alterações de temperatura e tempo durante síntese. Através da alteração destes parâmetros obtivemos um sólido lamelar com um grau de organização inferior a matriz sintetizada à 130oC e 16 horas, devido a existência da fase II-VOPO4 que foi constatada por difração de raios-X. A quantidade de dois mols de água por mol de VOPO4 manteve-se constante segundo as análises termogravimétricas. As imagens de microscopia eletrônica de varredura confirmaram a estrutura lamelar dos produtos, no entanto uma forma rosácea foi constatada em VOPO4/160oC, sugerindo a presença da fase VOHPO4.0,5H2O, precursora da fase (VO)2P2O7 que atua como catalisador seletivo na reação de oxidação do n-butano à anidrido malêico. A intercalação de íons lantanídeos na matriz VOPO4.2H2O produziu sólidos lamelares com cristalinidade inferior a matriz hospedeira, devido a distorção dos octaedros ocasionado pela redução dos íons vanádio (V) à (IV) apresentando uma diminuição na distância interlamelar com concomitante inserção de íons lantanídeos visando o balanceamento de carga na matriz. A reação de intercalação da matriz VOPO4.2H2O utilizando os tensoativos CTAB e CPC apresentaram resultados satisfatórios confirmados por difração de raios-X e espectrofotometria na região infravermelho. A intercalação de poli(óxido de etileno) assistida com brometo de cetiltrimetilamônio mostrou-se mais adequada apresentando sólidos organizados devido as moléculas de CTAB atuarem como agente diretivo. / Vanadium compounds are intensively studied due to their electrochemical, catalytic, magnetic and biological properties. In this work, our goal was to investigate the VOPO4.2H2O (vanadyl phosphate), which has a lamellar structure formed by VOPO4 sheets interconnected by weak interactions. Taking advantage of this structure, it is possible to synthesize several different intercalation compounds in which the guest species can vary from simple ions to polymeric species. The morphology of VOPO4.2H2O is very sensitive to temperature and time of reaction changes. By varying both parameters, several lamellar matrices have been synthesized. X-ray diffraction, thermal analysis and scanning electronic microscopy showed that depending on the synthetic conditions the arrangements VOPO4.2H2O can change the shape. For instance, in one of the experiments, a rose-like structure was produced, suggesting the presence of VOHPO40.5H2O phase, precursor of (VO)2P2O7 phase, which acts as oxidation catalyst of the n-butane to maleic anhydride. Intercalation of lanthanide ions leads to lamellar solids with low crystallinity in relation to the matrix due to octahedric distortion caused by reduction of vanadium ions (VV to VIV). Besides, it was observed a decrease of the interlamellar distance in function of the electroneutrality balance between the lamellar sheets. Intercalation compounds were produced by reacting surfactants molecules directly with the matrix under hydrothermal conditions. Surfactant-assisted intercalation of poly(ethylene oxide) into VOPO4.2H2O was conducted under soft conditions with the surfactant/matrix compound as a suspension in an aqueous polymer solution.
66

Propriedades fotofísicas de complexos de íons lantanídeos no estado sólido e em solução aquosa : imageamento e atividade citotóxica / Photo-physical properties of lanthanide ions complexes in the solid state or aqueous solution : imaging and cytotoxic activity

Monteiro, Jorge Henrique Santos Klier, 1985- 08 January 2014 (has links)
Orientadores: Fernando Aparecido Sigoli, André Luiz Barboza Formiga / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-25T19:44:19Z (GMT). No. of bitstreams: 1 Monteiro_JorgeHenriqueSantosKlier_D.pdf: 54893672 bytes, checksum: 68dcf83b484b6ed57a8eac7493d1ef01 (MD5) Previous issue date: 2014 / Resumo: Neste trabalho sintetizaram-se os ligantes 4-azidadipicolinato (dipicN3), 4-aminodipicolinato (dipicNH2) e 4-aminopiridina-bis(oxazolina) (pyboxNH2), bem como seus complexos com íons lantanídeos(III) solúveis em água. Sintetizaram-se também complexos insolúveis em água, contendo ligantes derivados dos ácidos benzóico, fenilselenínico e fenilfosfínico. A coordenação dos complexos foi verificada utilizando espectroscopia de absorção no infravermelho, enquanto que a estequiometria dos complexos foi confirmada utilizando análise elementar de carbono e hidrogênio, titulação complexométrica, espectrometria de massas e 1H-RMN. Também foram obtidas as estruturas de alguns complexos por difração de raios X de monocristal. Com os complexos análogos de gadolínio(III) foram obtidos os espectros de fosforescência do ligante a ?77 K com resolução temporal para determinação da energia do nível tripleto, a qual foi obtida pelo método da tangente ou da transição 0-0 fônon. Os complexos de európio(III) foram classificados, comparativamente, em função da simetria pontual, utilizando os espectros de emissão, parâmetros de intensidade de Judd-Ofelt e razão assimétrica, e também em função do grau de covalência da ligação Eu ¿ O, obtido pelo baricentro da transição 5D0 ? 7F0. Foi também medido o tempo de vida de emissão e o rendimento quântico dos complexos contendo os íons európio(III) ou térbio(III). As geometrias do estado fundamental foram determinadas utilizando o método Sparkle/PM3, sendo assim possível explicar alguns dos resultados experimentais obtidos, tal como a alta eficiência de sensitização de alguns complexos. Os complexos de európio(III) e térbio(III) com os ligantes dipicN3, dipicNH2 e pyboxNH2 apresentaram luminescência em solução aquosa, tempo de vida > 1 ms e rendimento quântico na faixa 15 ¿ 40 %, qualificando-os como marcadores luminescentes em sistemas biológicos. Os ligantes e seus complexos tiveram suas citotoxicidades testadas contra células normais (NIH/3T3) e células neoplásicas (NG97, câncer de cérebro e PANC1, câncer de pâncreas). Somente os complexos apresentaram atividade citotóxica e esta é seletiva para células NG97 e PANC1. O complexo K3[Eu(dipicNH2)3] foi capaz de atravessar a barreira hemato-encefálica e foi utilizado como marcador luminescente para células NG97 e PANC1 / Abstract: Water-soluble lanthanide complexes with the ligands 4-azidodipicolinate (dipicN3), 4-aminodipicolinate (dipicNH2) and 4-aminopyridine bis-oxazoline (pyboxNH2) were synthesized, a long with water-insoluble lanthanide complexes with ligands derived from benzoic, phenylseleninic or phenylphosphinic acids. The coordination modes of the carboxylic ligands were verified by FT-IR. The stoichiometries of the complexes were confirmed by carbon and hydrogen elemental analysis, complexometric titration and mass spectrometry. The crystal structures of some complexes were determined by single crystal X-ray diffraction. The time-resolved phosphorescence spectra of the ligands were obtained at ?77 K using the gadolinium(III) analogs complexes in order to obtain the energies of triplet levels. The triplet energies were determined by the tangent method or the 0-0 phonon transition. The europium(III) complexes were classified, comparatively, as a function of the point symmetry, using the emission spectra, Judd-Ofelt intensity parameters and the asymmetric ratio, and as a function of the Eu ¿ O bond covalence degree, obtained from the centroid of the 5D0 ? 7F0 transition. The emission lifetimes and quantum yields for the europium(III) and terbium(III) complexes were also determined. The ground state geometries were calculated using the Sparkle/PM3 method and were used to explain some of the experimental results such as the high sensitization efficiency of some complexes. The europium(III) and terbium(III) complexes with the ligands dipicN3, dipicNH2 and pyboxNH2 showed luminescence in water, emission lifetimes > 1 ms and quantum yields in the range 15 ¿ 40 %, qualifying them as potential luminescent markers for biological systems. Cytotoxic assays using the ligands and their complexes against normal cells (NIH/3T3) and neoplastic cells (NG97, brain¿s cancer and PANC1, pancreatic cancer) were performed. Only the complexes showed selective cytotoxicity against NG97 and PANC1 cells. The complex K3[Eu(dipicNH2)3] was able to cross a simulated blood-brain barrier and was also used as a luminescent marker for NG97 and PANC1 cells / Doutorado / Quimica Inorganica / Doutor em Ciências
67

Interlocked host structures for anion recognition and sensing in aqueous solutions

Langton, Matthew J. January 2014 (has links)
This thesis describes the synthesis of interlocked anion host systems which exploit hydrogen bonding, halogen bonding, and lanthanide-coordination for anion recognition and sensing in aqueous solution. Chapter 1 introduces the field of anion supramolecular chemistry, with particular focus on areas of particular relevance to this thesis, namely anion recognition and sensing, anion templation and the synthesis of interlocked structures. Chapter 2 describes the synthesis of hydrogen bonding rotaxane and catenane hosts for recognising and sensing oxoanions in aqueous solvent media. The novel use of nitrate anion templation for the synthesis of interlocked molecules is reported, and the unprecedented selective recognition of nitrate in aqueous solvent media is demonstrated. Chapter 3 details the preparation of water soluble permethylated β-cyclodextrin-stoppered rotaxane hosts that utilise halogen bonding and hydrogen bonding interactions to bind anions in pure water. The first thermodynamic investigation into halogen bonding in water is reported, and the relative capabilities of halogen and hydrogen bonding for anion recognition in water are compared. Chapter 4 investigates the incorporation of lanthanide cations into rotaxane hosts for optical anion sensing. The seminal use of lanthanide cation templation for interlocked molecule synthesis is described, before anion templation approaches towards the synthesis of lanthanide-based rotaxanes are discussed. The luminescence anion sensing capabilities of these interlocked hosts are investigated. Chapter 5 describes the experimental procedures used in this work, and details the characterisation of compounds presented in Chapters 2–4. Chapter 6 summarises the conclusions of this thesis.
68

The Synthesis, Structure and Magnetic Properties of O-Vanillin-Derived Schiff Base Polynuclear Lanthanide Single-Molecule Magnets

Jiang, Yu Ting January 2015 (has links)
This thesis describes the synthesis, characterization and magnetic investigation of homometallic lanthanide complexes based on two different o-vanillin-derived Schiff base ligands: H2ovph and H2ovgrd. The studies were performed using single crystal X-ray diffractometry, Powder XRD and SQUID magnetometry. Chapter 2 focuses on dinuclear systems 1-8 coordinated to the ligand H2ovph and presents their structural and magnetic properties, mainly with respect to their intramolecular interactions. Chapter 3 describes two hexanuclear systems, 9 (DyIII) and 10 (GdIII), with trigonal prism-assembled core structures. A structural comparison to other similar complexes in the literature is performed. A series of dinuclear complexes, 11-15, based on the ligand H2ovgrd are described in Chapter 4, focusing on the synthetic strategy, crystal structures and magnetism. The presence of the lanthanide contraction is evident in this system of complexes and is consistent with the intrinsic lanthanide contraction property.
69

Metody značení těla a potravy hmyzu a jejich využití u včel (Anthophila) / Methods of insect body and food marking and their utilization in bees (Anthophila)

Macháčková, Lenka January 2021 (has links)
Marking methods represent often an essential part of many studies which target on insect biology. These marking techniques sometimes represent the only possible way to obtain new and important informations. In the first part of the thesis I deal with individual insect labeling, which was used for marking of solitary bees and their nests as a tool of obtaining informations about nesting bee dynamics in aggregation. Our study show that nest owner replacements are very common in all four species. However, a large percentage of the nests were abandoned by the female owners before owner change. Only a part of all the nests were trully usurped on the nesting site. The true usurpations thus represent rather minor part of observed nest owner replacement situations. The bees surprisingly often abandon their nests and found the new ones. The frequent contacts of the females on a nesting site occur as a result of common nest owner replacements. High tolerance of bees to each other together with tolerance of usurpations and low level of aggression may thus represent one of the possible ways towards communality and other types of social behaviour. In the second part of the thesis I focus on the possibilities of food marking in bees. Effectivity of sugar and pollen utilization are not yet fully understood in...
70

Makrobicyklické ligandy pro aplikace v MRI / Macrobicyclic ligands for use in MRI

Pniok, Miroslav January 2011 (has links)
4 Title: Macrobicyclic ligands for use in MRI Author: Bc. Miroslav Pniok Department: Department of Inorganic Chemistry, Faculty of Science Supervisor: doc. RNDr. Jan Kotek, Ph.D. Supervisor's e-mail address: modrej@natur.cuni.cz Abstract: The aim of this project is to synthesize new kind of macrobicyclic ligands for Ln3+ ions, especially Gd3+ ion. Gadolinium(III) complexes are widely used in the clinical practice as contrast agents for MR imaging and an improvement of their properties is in the center of interest of many scientific teams. The macrobicyclic ligands have been designed to make possible coordination of two water molecules in the first coordination sphere with fast water exchange. The macrocyclic core (cyclen) is combined with a linking phosphinate chain in N1 ,N4 - and N1 ,N7 -positions forming a cryptand-like structure. The N1 ,N7 -isomer Et2L1 was synthesized in a small amount so only the N1 ,N4 -isomer H2L3 has been studied. The protonation constants have been determined by pH 31 P NMR titration. Keywords: cyclen, chelating agent, cryptand, MRI, phosphinate

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