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1.
Licere (Online) ; 26(1): 104-132, abril2023. ilus, graf
Artigo em Francês | LILACS | ID: biblio-1437737

RESUMO

Os indivíduos constantemente tomam decisões de consumo, que também impactam na cadeia que participa direta ou indiretamente para a criação daquele produto ou serviço. Assim, compreender melhor os perfis dos consumidores de jogos digitais auxiliam os desenvolvedores locais a produzir jogos que despertem e mantenham o interesse desses gamers, tornando esse, o principal objetivo desta pesquisa. Para tal, utilizou-se a Análise de Clusters, através do método K-means para variáveis categóricas, onde foram encontradas quatro personas. Os grupos com mais idade e com renda mensal de R$ 2.200,01 a R$ 4.400,00 expressou um comportamento prudente em relação aos gastos com jogos (gastaram de 0 a 100 reais, nos últimos 6 meses). Os outros dois grupos restantes, mais jovens, apresentaram características financeiras distintas: o de menor renda mensal (até R$ 1.100,00) não foi o que menos gastou com jogos eletrônicos nos últimos 6 meses (101 a 250 reais). A pesquisa também concluiu que "autonomia para seguir vários caminhos" foi bastante valorizada pelos 4 perfis, nomeados de "jogador retraído", "jogador apaixonado", "jogador nostálgico" e "jogador vontade", refletindo as características principais de cada perfil.


Individuals constantly make consumption decisions, which impact not only the consumer, but also the entire chain that participates directly or indirectly in the creation of that product or service. Thus, there is a need to better understand the profiles of consumers of digital entertainment games, so that local developers can produce games that arouse and maintain the interest of these gamers, making this the main objective of this research. For this, Cluster Analysis was used, through the K-means method for categorical variables, where four personas were found, which were translated by their reference profiles (detailed in D descriptions), and represented a set of similar profiles in the sample space of the respondents, with homogeneous characteristics to this "focal profile". The groups composed of the oldest age group (31 ­ 40 years old) and with a monthly income of BRL 2,200.01 to BRL 4,400.00 expressed a prudent behavior in relation to spending on games (they spent from BRL 0.00 to BRL 100.00 in the last 6 months). The other two remaining groups, formed by the younger age group (21 ­ 30 years), had different financial characteristics: the one with the lowest monthly income (up to BRL 1,100.00) was not the one who spent the least on electronic games in the last 6 months. (BRL 101.00 to BRL 250.00). The survey also concluded that "autonomy to follow several paths" was highly valued by the 4 profiles, named "withdrawn player", "passionate player", "nostalgic player" and "willing player"" to reflect the main characteristics of each profile.


Assuntos
Adulto , Jogos de Vídeo , Comportamento do Consumidor
2.
mBio ; 11(5)2020 09 29.
Artigo em Inglês | MEDLINE | ID: mdl-32994335

RESUMO

Klebsiella pneumoniae is an important cause of multidrug-resistant infections worldwide. Understanding the virulence mechanisms of K. pneumoniae is a priority and timely to design new therapeutics. Here, we demonstrate that K. pneumoniae limits the SUMOylation of host proteins in epithelial cells and macrophages (mouse and human) to subvert cell innate immunity. Mechanistically, in lung epithelial cells, Klebsiella increases the levels of the deSUMOylase SENP2 in the cytosol by affecting its K48 ubiquitylation and its subsequent degradation by the ubiquitin proteasome. This is dependent on Klebsiella preventing the NEDDylation of the Cullin-1 subunit of the ubiquitin ligase complex E3-SCF-ßTrCP by exploiting the CSN5 deNEDDylase. Klebsiella induces the expression of CSN5 in an epidermal growth factor receptor (EGFR)-phosphatidylinositol 3-kinase (PI3K)-protein kinase B (AKT)-extracellular signal-regulated kinase (ERK)-glycogen synthase kinase 3 beta (GSK3ß) signaling pathway-dependent manner. In macrophages, Toll-like receptor 4 (TLR4)-TRAM-TRIF-induced type I interferon (IFN) via IFN receptor 1 (IFNAR1)-controlled signaling mediates Klebsiella-triggered decrease in the levels of SUMOylation via let-7 microRNAs (miRNAs). Our results revealed the crucial role played by Klebsiella polysaccharides, the capsule, and the lipopolysaccharide (LPS) O-polysaccharide, to decrease the levels of SUMO-conjugated proteins in epithelial cells and macrophages. A Klebsiella-induced decrease in SUMOylation promotes infection by limiting the activation of inflammatory responses and increasing intracellular survival in macrophages.IMPORTANCEKlebsiella pneumoniae has been singled out as an urgent threat to human health due to the increasing isolation of strains resistant to "last-line" antimicrobials, narrowing the treatment options against Klebsiella infections. Unfortunately, at present, we cannot identify candidate compounds in late-stage development for treatment of multidrug-resistant Klebsiella infections; this pathogen is exemplary of the mismatch between unmet medical needs and the current antimicrobial research and development pipeline. Furthermore, there is still limited evidence on K. pneumoniae pathogenesis at the molecular and cellular levels in the context of the interactions between bacterial pathogens and their hosts. In this research, we have uncovered a sophisticated strategy employed by Klebsiella to subvert the activation of immune defenses by controlling the modification of proteins. Our research may open opportunities to develop new therapeutics based on counteracting this Klebsiella-controlled immune evasion strategy.


Assuntos
Interações Hospedeiro-Patógeno/imunologia , Evasão da Resposta Imune , Imunidade Inata , Klebsiella pneumoniae/imunologia , Klebsiella pneumoniae/metabolismo , Sumoilação , Células A549 , Animais , Feminino , Humanos , Interferon Tipo I/imunologia , Infecções por Klebsiella/microbiologia , Pulmão/microbiologia , Macrófagos Alveolares/imunologia , Camundongos , Camundongos Endogâmicos C57BL , Transdução de Sinais/imunologia
3.
Acta Med Port ; 33(3): 161-165, 2020 Mar 02.
Artigo em Inglês | MEDLINE | ID: mdl-32130094

RESUMO

INTRODUCTION: Obstructive sleep apnea is a clinical entity that is associated with an increase in morbidity and mortality and it is estimated that it is significantly undiagnosed. The objective of this study was to assess the risk of undiagnosed obstructive sleep apneain obese individuals. MATERIAL AND METHODS: A descriptive and analytical cross-sectional study; the risk of obstructive sleep apnea's was assessed over a period of 11 months by applying the STOP-Bang questionnaire to all individuals who attended a family health unit who were aged ≥ 18 years and had body mass index of ≥ 30 kg/m2 and who had not yet been diagnosed with obstructive sleep apnea and agreed to participate; the risk of an undiagnosed moderate to severe obstructive sleep apnea was considered for any STOP-Bang score of ≥ 3. RESULTS: The risk of undiagnosed obstructive sleep apnea was assessed in 888 individuals (59.3% females) with an average age of 59.6 ± 14.68 years and a mean body mass index 33.6 ± 3.43 kg/m2; the mean STOP-Bang score was 3.5 ± 1.74, 70.9% scored ≥ 3; the frequency of all STOP-Bang questionnaire parameters was higher (p < 0.004) within the group with score ≥ 3. DISCUSSION: The studied population is one of the main strengths, since it is in obese people that the incidence of this disease is higher. There are some limitations related to this sample coming from a single family health unit, as well as the patients' follow-up being carried out throughout routine appointments for diseases that are closely related with obstructive sleep apnea. CONCLUSION: The level of underdiagnosis of obstructive sleep apnea's in obese individuals can be significantly high and a large proportion of them may have the disease at a moderate to severe stage; Family Physicians can have a very important role in screening and diagnosis.


Introdução: A apneia obstrutiva do sono é uma entidade clínica que condiciona aumento da morbimortalidade e estima-se que exista um elevado subdiagnóstico. Foi objetivo deste estudo avaliar o risco de apneia obstrutiva do sono não diagnosticada em indivíduos obesos. Material e Métodos: Estudo transversal descritivo e analítico; durante um período de 11 meses foi avaliado o risco de apneia obstrutiva do sono aplicando o questionário STOP-Bang a todos os indivíduos com idade ≥ 18 anos e índice de massa corporal ≥ 30 kg/m2 que frequentaram uma unidade de saúde familiar, sem o diagnóstico de apneia obstrutiva do sono e que aceitaram participar; considerou-se risco de apneia obstrutiva do sono não diagnosticada para score STOP-Bang ≥ 3. Resultados: Foi avaliado o risco de apneia obstrutiva do sono não diagnosticada em 888 indivíduos (59,3% do género feminino), com idade média de 59,6 ± 14,68 anos e índice de massa corporal médio de 33,6 ± 3,43 kg/m2; o score STOP-Bang médio foi de 3,5 ± 1,74, 70,9% apresentaram score ≥ 3; a frequência de todos os parâmetros do questionário STOP-Bang foi superior (p < 0,004) no grupo com score ≥ 3. Discussão: A população estudada é uma das principais forças, pois é nas pessoas obesas que a incidência dessa doença é maior. Existem algumas limitações relacionadas com a amostra ser de uma única unidade de saúde, bem como o seguimento dos pacientes ser por doenças relacionadas com a apneia obstrutiva do sono. Conclusão: O subdiagnóstico da apneia obstrutiva do sono nos indivíduos obesos pode ser muito elevado e uma grande parte destes pode apresentar doença moderada a grave; os médicos de Medicina Geral e Familiar podem ter um papel muito importante no rastreio e diagnóstico.


Assuntos
Obesidade/complicações , Atenção Primária à Saúde , Apneia Obstrutiva do Sono/etiologia , Índice de Massa Corporal , Estudos Transversais , Feminino , Inquéritos Epidemiológicos , Humanos , Masculino , Pessoa de Meia-Idade , Portugal/epidemiologia , Medição de Risco , Apneia Obstrutiva do Sono/diagnóstico , Apneia Obstrutiva do Sono/epidemiologia
4.
PLoS Pathog ; 13(11): e1006696, 2017 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-29112952

RESUMO

Klebsiella pneumoniae is a significant cause of nosocomial pneumonia and an alarming pathogen owing to the recent isolation of multidrug resistant strains. Understanding of immune responses orchestrating K. pneumoniae clearance by the host is of utmost importance. Here we show that type I interferon (IFN) signaling protects against lung infection with K. pneumoniae by launching bacterial growth-controlling interactions between alveolar macrophages and natural killer (NK) cells. Type I IFNs are important but disparate and incompletely understood regulators of defense against bacterial infections. Type I IFN receptor 1 (Ifnar1)-deficient mice infected with K. pneumoniae failed to activate NK cell-derived IFN-γ production. IFN-γ was required for bactericidal action and the production of the NK cell response-amplifying IL-12 and CXCL10 by alveolar macrophages. Bacterial clearance and NK cell IFN-γ were rescued in Ifnar1-deficient hosts by Ifnar1-proficient NK cells. Consistently, type I IFN signaling in myeloid cells including alveolar macrophages, monocytes and neutrophils was dispensable for host defense and IFN-γ activation. The failure of Ifnar1-deficient hosts to initiate a defense-promoting crosstalk between alveolar macrophages and NK cell was circumvented by administration of exogenous IFN-γ which restored endogenous IFN-γ production and restricted bacterial growth. These data identify NK cell-intrinsic type I IFN signaling as essential driver of K. pneumoniae clearance, and reveal specific targets for future therapeutic exploitations.


Assuntos
Interferon Tipo I/imunologia , Células Matadoras Naturais/imunologia , Infecções por Klebsiella/imunologia , Macrófagos Alveolares/imunologia , Transdução de Sinais/imunologia , Animais , Resistência a Múltiplos Medicamentos/imunologia , Klebsiella pneumoniae/crescimento & desenvolvimento , Klebsiella pneumoniae/imunologia , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Receptor Cross-Talk/imunologia , Infecções Respiratórias/imunologia
5.
Solid State Nucl Magn Reson ; 84: 210-215, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-28624184

RESUMO

The present study has investigated the structure of four niobium phosphates compounds using 31P MAS NMR spectroscopy. Niobium 93Nb decoupling, applied during 31P NMR acquisition led to a resolution enhancement by a factor of 2-3, which allowed distinguish phosphorous sites separated by 1 ppm or less. The assignment of 31P spectra has been completed by use of first-principles calculations derived from the original XRD structures. One of the compounds, Na3.04Nb7P4O29, contains a sodium vacancy, clearly revealed in the 31P MAS spectrum obtained with 93Nb decoupling. A series of structural models were proposed to account for the sodium distribution in the structure of Na3.04Nb7P4O29 and the assignment was possible using DFT calculation and a statistical analysis of the NMR parameters.

6.
J Chem Phys ; 139(1): 014109, 2013 Jul 07.
Artigo em Inglês | MEDLINE | ID: mdl-23822295

RESUMO

Two finite-field implementations for the calculation of chemical shieldings of molecular systems using a plane-wave basis set and the Gauge-Including Projector-Augmented-Wave method are presented. The direct approach mimics the nuclear magnetic resonance experiment in that it puts the molecule in a uniform magnetic field and obtains shieldings from the current response. The other is based on the recently introduced "converse method" [T. Thonhauser, D. Ceresoli, A. A. Mostofi et al., J. Chem. Phys. 131, 101101 (2009)]. In both methods two-center contributions to the shieldings can be included via a numerically simple augmentation construction. Results obtained with both methods are discussed as well as (dis)similarities in their behaviors.

7.
J Phys Condens Matter ; 25(25): 255402, 2013 Jun 26.
Artigo em Inglês | MEDLINE | ID: mdl-23719213

RESUMO

The extended Czjzek model (ECM) is applied to the distribution of NMR parameters of a simple glass model (sodium metaphosphate, NaPO3) obtained by molecular dynamics (MD) simulations. Accurate NMR tensors, electric field gradient (EFG) and chemical shift anisotropy (CSA) are calculated from density functional theory (DFT) within the well-established PAW/GIPAW framework. The theoretical results are compared to experimental high-resolution solid-state NMR data and are used to validate the considered structural model. The distributions of the calculated coupling constant C(Q) is proportional to |V(zz)| and the asymmetry parameter η(Q) that characterize the quadrupolar interaction are discussed in terms of structural considerations with the help of a simple point charge model. Finally, the ECM analysis is shown to be relevant for studying the distribution of CSA tensor parameters and gives new insight into the structural characterization of disordered systems by solid-state NMR.

8.
J Chem Phys ; 135(19): 194503, 2011 Nov 21.
Artigo em Inglês | MEDLINE | ID: mdl-22112088

RESUMO

We study the influence of the softness of the interparticle interactions on the fragility of a glass former by considering three model binary mixture glass formers. The interaction potential between particles is a modified Lennard-Jones type potential, with the repulsive part of the potential varying with an inverse power q of the interparticle distance, and the attractive part varying with an inverse power p. We consider the combinations (12,11) (model I), (12,6) (model II), and (8,5) (model III) for (q,p) such that the interaction potential becomes softer from model I to III. We evaluate the kinetic fragilities from the temperature variation of diffusion coefficients and relaxation times, and a thermodynamic fragility from the temperature variation of the configurational entropy. We find that the kinetic fragility increases with increasing softness of the potential, consistent with previous results for these model systems, but at variance with the thermodynamic fragility, which decreases with increasing softness of the interactions, as well as expectations from earlier results. We rationalize our results by considering the full form of the Adam-Gibbs relation, which requires, in addition to the temperature dependence of the configurational entropy, knowledge of the high temperature activation energies in order to determine fragility. We show that consideration of the scaling of the high temperature activation energy with the liquid density, analyzed in recent studies, provides a partial rationalization of the observed behavior.

9.
Phys Chem Chem Phys ; 13(28): 13082-95, 2011 Jul 28.
Artigo em Inglês | MEDLINE | ID: mdl-21677972

RESUMO

Carbazole functionalized polyisocyanides are known to exhibit excellent electronic properties (E. Schwartz, et al., Chemistry of Materials, 2010, 22, 2597). The functionalities and properties of such materials crucially depend on the organization and stability of the polymer structure. We combine solid-state Nuclear Magnetic Resonance (NMR) experiments with first-principles calculations of isotropic chemical shifts, within the recently developed converse approach, to rationalize the origin of isotropic chemical shifts in the crystalline monomer l-isocyanoalanine 2-(9H-carbazol-9-yl) ethyl amide (monomer 1) and thereby gain insight into the structural organization of its polymer (polymer 2). The use of state-of-the-art solid-state NMR experiments combined with Density Functional Theory (DFT) based calculations allows an unambiguous assignment of all proton and carbon resonances of the monomer. We were able to identify the structure stabilising interactions in the crystal and understand the influence of the molecular packing in the crystal structure on the chemical shift data observed in the NMR spectra. Here the Nuclear Independent Chemical Shift (NICS) approach allows discriminating between 'physical' interactions amongst neighboring molecules such as ring-current effects and 'chemical' interactions such as hydrogen bonding. This analysis reveals that the isocyanide monomer is stabilized by multiple hydrogen bonds such as a bifurcated hydrogen bond involving -N-H, -C-H and O=C- moieties and Ar-H···C≡N- hydrogen bonding (Ar = aromatic group). Based on the geometrical arrangement it is postulated that the carbazole units are involved in the weak σ-π interactions giving rise to a Herringbone packing of the molecules. The chemical shift analysis of the polymer spectra readily establishes the existence of N-H···O=C hydrogen bonds despite the limited resolution exhibited by the polymer spectra. It is also elucidated that the relative arrangement of the carbazole units in the polymer differs significantly from that of the monomer.

10.
Magn Reson Chem ; 48 Suppl 1: S142-50, 2010 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-20821412

RESUMO

In this short review, we discuss the ability to reproduce NMR parameters in the case of phosphates materials through electronic structure calculation within density functional theory linear response. Indeed, the gauge-including projector-augmented wave is today largely used by the solid-state NMR community as a tool for structural determination and it has been applied to a large variety of materials. We emphasise on the crucial points that should be taken into account to perform such calculations. In particular, we discuss the influence of the electronic structure and of the geometry on the calculation of NMR parameters. To illustrate the review, we present experimental and theoretical comparison of (31)P, (1)H and (23)Na NMR data on a series of sodium phosphate systems.


Assuntos
Simulação por Computador , Fosfatos/química , Cristalografia por Raios X , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Conformação Molecular , Estereoisomerismo
11.
Phys Chem Chem Phys ; 12(31): 9053-62, 2010 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-20559592

RESUMO

In the present study, we used a combination of (17)O NMR methods at a high magnetic field with first-principles calculations in order to characterize the oxygen sites in a series of hydroxylated sodium phosphate compounds, namely the hydrogen pyrophosphate Na(2)H(2)P(2)O(7) and the hydrogen orthophosphates NaH(2)PO(4), NaH(2)PO(4) x H(2)O and NaH(2)PO(4) x 2 H(2)O. The chemical shifts and quadrupolar parameters of these compounds were interpreted in terms of local and semi-local environment, i.e., the chemical composition of the immediate surroundings and the nature of the bonds, e.g. hydrogen bonding. The magnitude of the quadrupolar interaction and its asymmetry were revealed to be a precise indicator of the local structure in sodium hydrogen phosphates. Our (17)O NMR experimental and computing approach allowed for identification and quantification of the different crystalline phases involved in the weathering mechanism of a sodium phosphate glass, even in small amount.


Assuntos
Oxigênio/química , Fosfatos/química , Cristalografia por Raios X , Espectroscopia de Ressonância Magnética , Conformação Molecular , Isótopos de Oxigênio/química
12.
J Microbiol ; 48(3): 331-6, 2010 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-20571951

RESUMO

Thermophilic fungi produce thermostable enzymes which have a number of applications, mainly in biotechnological processes. In this work, we describe the characterization of a protease produced in solidstate (SSF) and submerged (SmF) fermentations by a newly isolated thermophilic fungus identified as a putative new species in the genus Myceliophthora. Enzyme-production rate was evaluated for both fermentation processes, and in SSF, using a medium composed of a mixture of wheat bran and casein, the proteolytic output was 4.5-fold larger than that obtained in SmF. Additionally, the peak of proteolytic activity was obtained after 3 days for SSF whereas for SmF it was after 4 days. The crude enzyme obtained by both SSF and SmF displayed similar optimum temperature at 50 degrees C, but the optimum pH shifted from 7 (SmF) to 9(SSF). The alkaline protease produced through solid-state fermentation (SSF), was immobilized on beads of calcium alginate, allowing comparative analyses of free and immobilized proteases to be carried out. It was observed that both optimum temperature and thermal stability of the immobilized enzyme were higher than for the free enzyme. Moreover, the immobilized enzyme showed considerable stability for up to 7 reuses.


Assuntos
Proteínas de Bactérias/metabolismo , Endopeptidases/metabolismo , Proteínas Fúngicas/metabolismo , Sordariales/enzimologia , Alginatos , Proteínas de Bactérias/isolamento & purificação , Endopeptidases/isolamento & purificação , Estabilidade Enzimática , Enzimas Imobilizadas/metabolismo , Fermentação , Proteínas Fúngicas/isolamento & purificação , Ácido Glucurônico , Ácidos Hexurônicos , Concentração de Íons de Hidrogênio , Cinética , Filogenia , Sordariales/classificação , Sordariales/genética , Sordariales/isolamento & purificação , Temperatura
13.
Open Microbiol J ; 4: 75-82, 2010 Aug 17.
Artigo em Inglês | MEDLINE | ID: mdl-21253464

RESUMO

Mammalian electron transfer flavoproteins comprise a mitochondrial matrix heterodimer, and an electron transfer flavoprotein dehydrogenase localized in the mitochondrial inner membrane. Electrons from primary acyl-CoA dehydrogenases, of mitochondrial metabolism of fatty acids and amino acids, are transferred to the matricial heterodimer and, subsequently, to the electron transfer flavoprotein dehydrogenase, which transfers electrons to ubiquinone of the mitochondrial electron transport chain. Several evidences suggest that these proteins may convey electrons directly to molecular oxygen, yielding reactive oxygen species. In this work, we investigated phenotypes of the yeast mutants affected in the orthologous genes of the matrix heterodimer (AIM45 and YGR207c/CIR1) and of the electron transfer flavoprotein dehydrogenase (YOR356w/CIR2). The mutant strains aim45 and yor356w/cir2 displayed better growth on several non-fermentable carbon sources, which depended on the component of the electron transport chain that accepts the electrons resulting from its mitochondrial oxidation. Furthermore, upon heat shock, the mutant strains presented decreased intracellular oxidation, suggesting that these flavoproteins are a source of reactive oxygen species. Other phenotypes identified suggest that AIM45, YGR207c/CIR1 and YOR356w/CIR2 can protect cells from oxidative and heat stress, which encompass increased heat stress sensitivity, superoxide sensitivity, both only on non-fermentable carbon sources.

14.
J Phys Chem A ; 113(46): 12864-78, 2009 Nov 19.
Artigo em Inglês | MEDLINE | ID: mdl-19905016

RESUMO

We present a comprehensive comparison of through-space heteronuclear correlation techniques for solid state NMR, combining indirect detection and single-channel recoupling method. These techniques, named D-HMQC and D-HSQC, do not suffer from dipolar truncation and can be employed to correlate quadrupolar nuclei with spin-1/2 nuclei. The heteronuclear dipolar couplings are restored under magic-angle spinning by applying supercycled symmetry-based pulse sequences (SR412) or simultaneous frequency and amplitude modulation (SFAM). The average Hamiltonian theory (AHT) of these recoupling methods is developed. These results are applied to analyze the performances of D-HMQC and D-HSQC sequences. It is shown that, whatever the magnitude of spin interations, D-HMQC experiment offers larger efficiency and higher robustness than D-HSQC. Furthermore, the spectral resolution in both dimensions of proton detected two-dimensional D-HMQC and D-HSQC spectra can be enhanced by applying recently introduced symmetry-based homonuclear dipolar decoupling schemes that cause a z-rotation of the spins. This is demonstrated by 1H-13C and 1H-23Na correlation experiments on l-histidine and NaH2PO4, respectively. The two-dimensional heteronuclear 1H-23Na correlation spectrum yields the assignment of 23Na resonances of NaH2PO4. This assignment is corroborated by first-principles calculations.


Assuntos
Histidina/química , Fosfatos/química , Prótons , Simulação por Computador , Espectroscopia de Ressonância Magnética/normas , Modelos Químicos , Padrões de Referência , Sódio/química
15.
Inorg Chem ; 47(16): 7327-37, 2008 Aug 18.
Artigo em Inglês | MEDLINE | ID: mdl-18642900

RESUMO

The assignment of high-field (18.8 T) (17)O MAS and 3QMAS spectra has been completed by use of first-principles calculations for three crystalline sodium phosphates, Na 3P 3O 9, Na 5P 3O 10, and Na 4P 2O 7. In Na 3P 3O 9, the calculated parameters, quadrupolar constant ( C Q), quadrupolar asymmetry (eta Q), and the isotropic chemical shift (delta cs) correspond to those deduced experimentally, and the calculation is mandatory to achieve a complete assignment. For the sodium tripolyphosphate Na 5P 3O 10, the situation is more complex because of the free rotation of the end-chain phosphate groups. The assignment obtained with ab initio calculations can however be confirmed by the (17)O{ (31)P} MAS-J-HMQC spectrum. Na 4P 2O 7 (17)O MAS and 3QMAS spectra show a complex pattern in agreement with the computed NMR parameters, which indicate that all of the oxygens exhibit very similar values. These results are related to structural data to better understand the influence of the oxygen environment on the NMR parameters. The findings are used to interpret those results observed on a binary sodium phosphate glass.

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