Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 281
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
J Phys Chem Lett ; 11(5): 1873-1880, 2020 Mar 05.
Artigo em Inglês | MEDLINE | ID: mdl-32040318

RESUMO

Lead halide perovskites have recently shown great potential as X-ray scintillators; however, the toxicity of the lead element seriously restricts their applications. Herein we report a new lead-free and self-absorption-free scintillator based on Rb2CuCl3 metal halide. The Rb2CuCl3 exhibits a near-unity photoluminescence quantum yield (99.4%) as well as a long photoluminescence lifetime (11.3 µs). Furthermore, Rb2CuCl3 demonstrates an appreciable light yield of 16 600 photons per megaelectronvolt and a large scintillation response with a linear range from 48.6 nGyair s-1 to 15.7 µGyair s-1. Notably, the detection limit is as low as 88.5 nGyair s-1, enabling a reduced radiation dose to the human body when a medical and security check is conducted. In addition, Rb2CuCl3 exhibits good stability against the atmosphere, continuous ultraviolet light, as well as X-ray irradiation. The combination of the decent scintillation performance, low toxicity and good stability suggests the Rb2CuCl3 could be a possible promising X-ray scintillator.


Assuntos
Cobre/química , Espectroscopia Fotoeletrônica , Teoria Quântica , Rubídio/química , Raios Ultravioleta , Difração de Raios X
2.
ACS Appl Mater Interfaces ; 11(35): 31693-31699, 2019 Sep 04.
Artigo em Inglês | MEDLINE | ID: mdl-31339687

RESUMO

Fluorescent detection of glutathione (GSH) in the living system has attracted much attention, but current fluorescent probes are usually exposed to the exterior environment, leading to photobleaching and premature leakage and subsequently limiting the sensitivity and photostability. Herein, luminescent metal-organic frameworks [Ru(bpy)32+ encapsulated in UiO-66] coated with manganese dioxide nanosheets [MnO2 NS@Ru(bpy)32+-UiO-66] were prepared by an in situ growth method and further explored to construct a GSH-switched fluorescent sensing platform. Because of the splendid fluorescence quenching ability, special probe leakage blocking role and distinguished recognition of the MnO2 NS, and the improved fluorescence of Ru(bpy)32+ by UiO-66, a low background, highly sensitive and selective detection of GSH with a low limit of detection as 0.28 µM was realized. At the same time, the preparation of MnO2 NS@Ru(bpy)32+-UiO-66 nanocomposites is simple and less toxic, and there was no notable loss of cell survivability after being exposed to MnO2 NS@Ru(bpy)32+-UiO-66 below the concentrations of 120 µg mL-1 for 24 h. Consequently, the results coming from this effort suggest that the new sensing platform will have a great potential in the detection of GSH in living cells.


Assuntos
Glutationa/metabolismo , Compostos de Manganês , Estruturas Metalorgânicas , Nanocompostos/química , Óxidos , Células HeLa , Humanos , Compostos de Manganês/química , Compostos de Manganês/farmacologia , Estruturas Metalorgânicas/química , Estruturas Metalorgânicas/farmacologia , Microscopia de Fluorescência , Óxidos/química , Óxidos/farmacologia , Rubídio/química , Rubídio/farmacologia
3.
Proc Natl Acad Sci U S A ; 116(15): 7232-7237, 2019 04 09.
Artigo em Inglês | MEDLINE | ID: mdl-30898884

RESUMO

Ferroquadrupole order associated with local [Formula: see text] atomic orbitals of rare-earth ions is a realization of electronic nematic order. However, there are relatively few examples of intermetallic materials which exhibit continuous ferroquadrupole phase transitions, motivating the search for additional materials that fall into this category. Furthermore, it is not clear a priori whether experimental approaches based on transport measurements which have been successfully used to probe the nematic susceptibility in materials such as the Fe-based superconductors will be as effective in the case of [Formula: see text] intermetallic materials, for which the important electronic degrees of freedom are local rather than itinerant and are consequently less strongly coupled to the charge-carrying quasiparticles near the Fermi energy. In the present work, we demonstrate that the intermetallic compound [Formula: see text] exhibits a tetragonal-to-orthorhombic phase transition consistent with ferroquadrupole order of the Yb ions and go on to show that elastoresistivity measurements can indeed provide a clear window on the diverging nematic susceptibility in this system. This material provides an arena in which to study the causes and consequences of electronic nematicity.


Assuntos
Germânio/química , Rubídio/química , Supercondutividade , Itérbio/química
4.
Molecules ; 23(10)2018 Sep 24.
Artigo em Inglês | MEDLINE | ID: mdl-30250000

RESUMO

Ion association is an important process in aqueous dissolution, precipitation, and crystallization of ionic inorganic, organic, and biological materials. Polyoxometalates (POMs) are good model compounds for understanding the complex relationships between lattice energy, ion-pairing in solution, and salt solubility. Here we perform calorimetric measurements to elucidate trends in cluster stability, lattice energy, and ion-pairing behavior studies of simple hexatantalate salts in neat water, parent hydroxide solutions, and molybdate melts, extending previous studies on the isostructural hexaniobates. High temperature calorimetry of alkali salts of hexatantalate reveals that the enthalpies of formation from oxides of the K, Rb, and Cs salts are more similar to each other than they are for their niobate analogues and that the tantalate cluster is energetically less stable than hexaniobate. Aqueous dissolution calorimetry reveals that the cesium salt of hexatantalate has a similar concentration dependence on its dissolution enthalpy to that of hexaniobate. However, unlike rubidium hexaniobate, rubidium hexatantalate also exhibits increased concentration dependence, indicating that hextantalate can undergo increased ion-pairing with alkali salts other than cesium, despite the dilute environments studied. Dissolution enthalpies of POM salts in the parent alkali hydroxides shows that protonation of clusters stabilizes lattices even more than the strongly associating heavy alkali cations do. Additionally, neither weak nor strong lattice ion associations necessarily correlates with respectively high or low aqueous solubility. These studies illuminate the importance of considering ion-pairing among the interrelated processes in the aqueous dissolution of ionic salts that can be extended to serving as a model of cation association to metal oxide surfaces.


Assuntos
Césio/química , Metais Alcalinos/química , Rubídio/química , Compostos de Tungstênio/química , Calorimetria , Temperatura Alta , Íons/química , Sais/química , Termodinâmica , Água/química
5.
Sci Rep ; 8(1): 13342, 2018 09 06.
Artigo em Inglês | MEDLINE | ID: mdl-30190568

RESUMO

Shape-selective recognition of nucleic acid structures by supramolecular drugs offers the potential to treat disease. The Trans Activation Response (TAR) region is a region of high secondary structure within the human immunodeficiency virus-1 (HIV-1) RNA that complexes with the virus-encoded Transactivator protein (TAT) and regulates viral transcription. Herein, we explore different metallo-supramolecular triple stranded helicates (cylinders) that target the TAR bulge motif and inhibit the formation of TAR-TAT complexes and HIV infection. Cylinders that incorporate Ni(II) and Ru(II) showed the most potent anti-viral activity with limited evidence of cellular cytotoxicity. These metallo-supramolecular compounds provide an exciting avenue for developing a new class of anti-viral agents.


Assuntos
Antivirais , Complexos de Coordenação , HIV-1 , Níquel , RNA Viral , Sequências Reguladoras de Ácido Ribonucleico , Rubídio , Produtos do Gene tat do Vírus da Imunodeficiência Humana , Antivirais/química , Antivirais/farmacologia , Linhagem Celular , Complexos de Coordenação/química , Complexos de Coordenação/farmacologia , HIV-1/química , HIV-1/metabolismo , Humanos , Níquel/química , Níquel/farmacologia , RNA Viral/metabolismo , Rubídio/química , Rubídio/farmacologia , Produtos do Gene tat do Vírus da Imunodeficiência Humana/química , Produtos do Gene tat do Vírus da Imunodeficiência Humana/metabolismo
6.
ChemSusChem ; 11(16): 2758-2765, 2018 Aug 22.
Artigo em Inglês | MEDLINE | ID: mdl-30009402

RESUMO

The complete transformation of lignocellulosic biomass into valuable platform chemicals is of great significance. Herein, a catalytic process for the upgrading of lignocellulose to arenes, 5-hydroxymethylfurfural (HMF), and furfural is reported. Firstly, the lignin fraction in lignocellulosic biomass is selectively converted into lignin oil (82.9 mol % yield of lignin monomers from birch wood) over a Pd/C catalyst and then further hydrodeoxygenated to arenes in catalytic hydrogen-transfer reactions over a Ru/Nb2 O5 catalyst. High yields of C7 -C9 hydrocarbons (95.6 mol %) with 85.6 wt % selectivity to arenes based on lignin oil are achieved owing to the synergistic effect between Ru and Nb2 O5 , which enables direct hydrogenolysis of the Caromatic -OH bond in phenolics. Secondly, the cellulose and hemicellulose fractions in the Pd/C-containing solid residue, as well as methylated C5 sugars produced during the stripping of lignin, are converted into HMF and furfural with a total yield of up to 24.5 wt % (based on the amount of birch wood) in a THF/concentrated seawater (ca. 30 wt % salts) biphasic reaction system. Here, seawater played a key role in the conversion of cellulose and hemicellulose into HMF and furfural, respectively; more importantly, it made the separation and reuse of the Pd/C catalyst easier. With this catalytic process, the complete and efficient transformation of lignocellulose into highly value-added products with recycling of each catalyst and solvent has been realized.


Assuntos
Furaldeído/análogos & derivados , Furaldeído/química , Hidrocarbonetos/química , Lignina/química , Catálise , Nióbio/química , Óxidos/química , Rubídio/química , Água do Mar , Solventes/química , Madeira/química
7.
Acta Crystallogr B Struct Sci Cryst Eng Mater ; 74(Pt 3): 274-286, 2018 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-29927390

RESUMO

The leucite tectosilicate mineral analogues K2X2+Si5O12 (X = Fe2+, Co, Zn) and Rb2X2+Si5O12 (X = Mn) have been synthesized at elevated temperatures both dry at atmospheric pressure and at controlled water vapour pressure; for X = Co and Zn both dry and hydrothermally synthesized samples are available. Rietveld refinement of X-ray data for hydrothermal K2X2+Si5O12 (X = Fe2+, Co, Zn) samples shows that they crystallize in the monoclinic space group P21/c and have tetrahedral cations (Si and X) ordered onto distinct framework sites [cf. hydrothermal K2MgSi5O12; Bell et al. (1994a), Acta Cryst. B50, 560-566]. Dry-synthesized K2X2+Si5O12 (X = Co, Zn) and Rb2X2+Si5O12 (X = Mn) samples crystallize in the cubic space group Ia{\overline 3}d and with Si and X cations disordered in the tetrahedral framework sites as typified by dry K2MgSi5O12. Both structure types have tetrahedrally coordinated SiO4 and XO4 sharing corners to form a partially substituted silicate framework. Extraframework K+ and Rb+ cations occupy large channels in the framework. Structural data for the ordered samples show that mean tetrahedral Si-O and X-O bond lengths cover the ranges 1.60 Š(Si-O) to 2.24 Š(Fe2+-O) and show an inverse relationship with the intertetrahedral angles (T-O-T) which range from 144.7° (Si-O-Si) to 124.6° (Si-O-Fe2+). For the compositions with both disordered and ordered tetrahedral cation structures (K2MgSi5O12, K2CoSi5O12, K2ZnSi5O12, Rb2MnSi5O12 and Cs2CuSi5O12 leucites) the disordered polymorphs always have larger unit-cell volumes, larger intertetrahedral T-O-T angles and smaller mean T-O distances than their isochemical ordered polymorphs. The ordered samples clearly have more flexible frameworks than the disordered structures which allow the former to undergo a greater degree of tetrahedral collapse around the interframework cavity cations. Multivariant linear regression has been used to develop equations to predict intertetrahedral T-O-T angle variation depending on the independent variables Si-O and X-O bond lengths, cavity cation ideal radius, intratetrahedral (O-T-O) angle variance, and X cation electronegativity.


Assuntos
Silicatos de Alumínio/química , Cátions/química , Cobalto/química , Cristalografia por Raios X , Ferro/química , Modelos Moleculares , Estrutura Molecular , Oxigênio/química , Potássio/química , Rubídio/química , Silício/química , Zinco/química
8.
Int J Mol Sci ; 19(2)2018 Feb 04.
Artigo em Inglês | MEDLINE | ID: mdl-29401704

RESUMO

Lithium, sodium, potassium, rubidium and caesium salts of 5-O-caffeoylquinic acid (chlorogenic acid, 5-CQA) were synthesized and described by FT-IR (infrared spectroscopy), FT-Raman (Raman spectroscopy), UV (UV absorption spectroscopy), ¹H (400.15 MHz), 13C (100.63 MHz) NMR (nuclear magnetic resonance spectroscopy). The quantum-chemical calculations at the B3LYP/6-311++G** level were done in order to obtain the optimal structures, IR spectra, NBO (natural bond orbital) atomic charges, HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) orbitals and chemical reactivity parameters for 5-CQA and Li, Na and K 5-CQAs (chlorogenates). The DPPH (α, α-diphenyl-ß-picrylhydrazyl) and FRAP (ferric reducing antioxidant power) assays were used for the preliminary estimation of the antioxidant properties of alkali metal chlorogenates and chlorogenic acid. In the DPPH assay the EC50 parameter were equal to 7.39 µM for 5-CQA and was in the range of 4.50-5.89 µM for salts. The FRAP values for two different concentrations (5 and 2.5 µM) of the studied compounds were respectively 114.22 and 72.53 µM Fe2+ for 5-CQA, whereas for salts they were 106.92-141.13 and 78.93-132.00 µM Fe2+. The 5-CQA and its alkali metal salts possess higher antioxidant properties than commonly applied antioxidants (BHA, BHT, l-ascorbic acid). The pro-oxidant action of these compounds on trolox oxidation was studied in the range of their concentration 0.05-0.35 µM. The lipophilicity (logkw) of chlorogenates and chlorogenic acid was determined by RP-HPLC (reverse phase-high performance liquid chromatography) using five different columns (C8, PHE (phenyl), CN (cyano), C18, IAM (immobilized artificial membrane)). The compounds were screened for their in vitro antibacterial activity against E. coli, Bacillus sp., Staphylococcus sp., Streptococcus pyogenes and antifungal activity against Candida sp. The 5-CQA possessed lower antibacterial (minimal inhibitory concentration, MIC = 7.06 mM) and antifungal (MIC = 14.11 mM) properties than its alkali metal salts (MIC values: 6.46-2.63 mM and 12.91-5.27mM, respectively). The synthesized chlorogenates possessed better antioxidant, lipophilic, antimicrobial as well as lower pro-oxidant properties than the ligand alone. Moreover, a systematic change of the activity of alkali metal salts along the series Li→Cs suggests that there are correlations between the studied biological properties. The type of metal cation in the carboxylate group of chlorogenate is crucial for the activity of studied compounds.


Assuntos
Anti-Infecciosos/química , Antioxidantes/química , Ácido Clorogênico/análogos & derivados , Ácido Clorogênico/química , Metais Alcalinos/química , Oxidantes/química , Ácido Quínico/análogos & derivados , Sais/química , Anti-Infecciosos/síntese química , Anti-Infecciosos/farmacologia , Antioxidantes/síntese química , Antioxidantes/farmacologia , Ácido Ascórbico/farmacologia , Bacillus/efeitos dos fármacos , Bacillus/crescimento & desenvolvimento , Compostos de Bifenilo/antagonistas & inibidores , Hidroxianisol Butilado/farmacologia , Hidroxitolueno Butilado/farmacologia , Candida/efeitos dos fármacos , Candida/crescimento & desenvolvimento , Césio/química , Ácido Clorogênico/farmacologia , Cromanos/química , Escherichia coli/efeitos dos fármacos , Escherichia coli/crescimento & desenvolvimento , Interações Hidrofóbicas e Hidrofílicas , Lítio/química , Testes de Sensibilidade Microbiana , Oxidantes/síntese química , Oxidantes/farmacologia , Picratos/antagonistas & inibidores , Potássio/química , Teoria Quântica , Ácido Quínico/química , Ácido Quínico/farmacologia , Rubídio/química , Sais/farmacologia , Sódio/química , Staphylococcus/efeitos dos fármacos , Staphylococcus/crescimento & desenvolvimento , Streptococcus pyogenes/efeitos dos fármacos , Streptococcus pyogenes/crescimento & desenvolvimento
9.
J Biol Chem ; 293(4): 1373-1385, 2018 01 26.
Artigo em Inglês | MEDLINE | ID: mdl-29191836

RESUMO

Procedures to define kinetic mechanisms from catalytic activity measurements that obey the Michaelis-Menten equation are well established. In contrast, analytical tools for enzymes displaying non-Michaelis-Menten kinetics are underdeveloped, and transient-state measurements, when feasible, are therefore preferred in kinetic studies. Of note, transient-state determinations evaluate only partial reactions, and these might not participate in the reaction cycle. Here, we provide a general procedure to characterize kinetic mechanisms from steady-state determinations. We described non-Michaelis-Menten kinetics with equations containing parameters equivalent to kcat and Km and modeled the underlying mechanism by an approach similar to that used under Michaelis-Menten kinetics. The procedure enabled us to evaluate whether Na+/K+-ATPase uses the same sites to alternatively transport Na+ and K+ This ping-pong mechanism is supported by transient-state studies but contradicted to date by steady-state analyses claiming that the release of one cationic species as product requires the binding of the other (ternary-complex mechanism). To derive robust conclusions about the Na+/K+-ATPase transport mechanism, we did not rely on ATPase activity measurements alone. During the catalytic cycle, the transported cations become transitorily occluded (i.e. trapped within the enzyme). We employed radioactive isotopes to quantify occluded cations under steady-state conditions. We replaced K+ with Rb+ because 42K+ has a short half-life, and previous studies showed that K+- and Rb+-occluded reaction intermediates are similar. We derived conclusions regarding the rate of Rb+ deocclusion that were verified by direct measurements. Our results validated the ping-pong mechanism and proved that Rb+ deocclusion is accelerated when Na+ binds to an allosteric, nonspecific site, leading to a 2-fold increase in ATPase activity.


Assuntos
Modelos Químicos , Potássio/química , Rubídio/química , ATPase Trocadora de Sódio-Potássio/química , Sódio/química , Humanos , Transporte de Íons , Cinética
10.
J Biol Chem ; 293(3): 941-952, 2018 01 19.
Artigo em Inglês | MEDLINE | ID: mdl-29180448

RESUMO

Clostridium difficile infection is the leading cause of hospital-acquired diarrhea and is mediated by the actions of two toxins, TcdA and TcdB. The toxins perturb host cell function through a multistep process of receptor binding, endocytosis, low pH-induced pore formation, and the translocation and delivery of an N-terminal glucosyltransferase domain that inactivates host GTPases. Infection studies with isogenic strains having defined toxin deletions have established TcdB as an important target for therapeutic development. Monoclonal antibodies that neutralize TcdB function have been shown to protect against C. difficile infection in animal models and reduce recurrence in humans. Here, we report the mechanism of TcdB neutralization by PA41, a humanized monoclonal antibody capable of neutralizing TcdB from a diverse array of C. difficile strains. Through a combination of structural, biochemical, and cell functional studies, involving X-ray crystallography and EM, we show that PA41 recognizes a single, highly conserved epitope on the TcdB glucosyltransferase domain and blocks productive translocation and delivery of the enzymatic cargo into the host cell. Our study reveals a unique mechanism of C. difficile toxin neutralization by a monoclonal antibody, which involves targeting a process that is conserved across the large clostridial glucosylating toxins. The PA41 antibody described here provides a valuable tool for dissecting the mechanism of toxin pore formation and translocation across the endosomal membrane.


Assuntos
Anticorpos Neutralizantes/metabolismo , Toxinas Bacterianas/metabolismo , Clostridium difficile/metabolismo , Enterotoxinas/metabolismo , Anticorpos Monoclonais/metabolismo , Toxinas Bacterianas/química , Células CACO-2 , Clostridium difficile/enzimologia , Cristalografia por Raios X , Citosol/metabolismo , Enterotoxinas/química , Humanos , Concentração de Íons de Hidrogênio , Microscopia Eletrônica , Rubídio/química , Proteínas rac1 de Ligação ao GTP/química , Proteínas rac1 de Ligação ao GTP/metabolismo
11.
Water Res ; 123: 321-331, 2017 10 15.
Artigo em Inglês | MEDLINE | ID: mdl-28675845

RESUMO

The ultimate goal of seawater reverse osmosis (SWRO) brine management is to achieve minimal liquid discharge while recovering valuable resources. The suitability of an integrated system of membrane distillation (MD) with sorption for the recovery of rubidium (Rb+) and simultaneous SWRO brine volume reduction has been evaluated for the first time. Polymer encapsulated potassium copper hexacyanoferrate (KCuFC(PAN)) sorbent exhibited a good selectivity for Rb+ sorption with 10-15% increment at 55 °C (Langmuir Qmax = 125.11 ± 0.20 mg/g) compared to at 25 °C (Langmuir Qmax = 108.71 ± 0.20 mg/g). The integrated MD-KCuFC(PAN) system with periodic membrane cleaning, enabled concentration of SWRO brine to a volume concentration factor (VCF) of 2.9 (65% water recovery). A stable MD permeate flux was achieved with good quality permeate (conductivity of 15-20 µS/cm). Repeated cycles of MD-KCuFC(PAN) sorption with SWRO brine enabled the extraction of 2.26 mg Rb+ from 12 L of brine (equivalent to 1.9 kg of Rb/day, or 0.7 tonne/yr from a plant producing 10,000 m3/day brine). KCuFC(PAN) showed a high regeneration and reuse capacity. NH4Cl air stripping followed by resorcinol formaldehyde (RF) resin filtration enabled to recover Rb+ from the desorbed solution.


Assuntos
Rubídio/química , Purificação da Água , Destilação , Membranas Artificiais , Osmose , Sais , Água do Mar
12.
J Inorg Biochem ; 174: 37-44, 2017 09.
Artigo em Inglês | MEDLINE | ID: mdl-28599130

RESUMO

The interaction between a ruthenium - based water soluble oxygen probe ([Ru(Phen)3]2+, phen - phenanthroline) and human serum albumin (HSA) was investigated with the aim of describing the influence of HSA on the [Ru(Phen)3]2+ luminescence properties. Nowadays, several oxygen sensitive luminescent probes are used to determine the oxygen level in different compartments of living organisms. However, they can interact, depending on their hydrophilic/hydrophobic characters, with various serum proteins, and/or lipids, during their utilization for invivo oxygen measurement. Since HSA is the most abundant serum protein in most biological organisms, its presence may affect the spectral properties of the employed probes and, consequently, the determination of the oxygen concentration. Having this in mind, we have applied several spectroscopic and calorimetric techniques to study [Ru(Phen)3]2+ - HSA mixtures. Only a negligible effect of HSA on the absorption and luminescence spectra of [Ru(Phen)3]2+ was observed. In addition, differential scanning calorimetric studies showed that [Ru(Phen)3]2+ does not significantly influence HSA thermal stability. Importantly, [Ru(Phen)3]2+ retained a reliable luminescence lifetime sensitivity to the oxygen concentration in solutions supplemented with HSA and in U87 MG cancer cells. Finally, the biodistribution of [Ru(Phen)3]2+ in the presence of serum proteins in the blood stream of chick embryo's chorioallantoic membrane (CAM) was investigated. Fast [Ru(Phen)3]2+ and similar extravasations were observed in the presence or absence of CAM-serum. We can conclude that HSA-[Ru(Phen)3]2+ complex interaction does not significantly influence the potential of [Ru(Phen)3]2+ to be a suitable candidate for a reliable oxygen probe in living organisms.


Assuntos
Substitutos Sanguíneos , Complexos de Coordenação , Imagem Óptica , Fenantrolinas , Rubídio , Albumina Sérica Humana , Animais , Substitutos Sanguíneos/síntese química , Substitutos Sanguíneos/química , Substitutos Sanguíneos/farmacologia , Embrião de Galinha , Complexos de Coordenação/síntese química , Complexos de Coordenação/química , Complexos de Coordenação/farmacologia , Humanos , Oxigênio/química , Oxigênio/metabolismo , Fenantrolinas/química , Fenantrolinas/farmacologia , Rubídio/química , Rubídio/farmacologia , Albumina Sérica Humana/química , Albumina Sérica Humana/farmacologia
13.
Assay Drug Dev Technol ; 15(4): 167-177, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-28631939

RESUMO

A high-throughput screening (HTS) assay was developed for cotransporter, NKCC1, which is a potential target for the treatment of diverse disorders. This nonradioactive rubidium flux assay coupled with ion channel reader series provides a working screen for this target expressed in human embryonic kidney (HEK) cell line. An eightfold window of detection was achieved with the optimized assay. This new functional assay offered a robust working model for NKCC1 in determining reliable and concordant rank orders of the test compounds supporting its sensitivity and specificity. The robustness of manual assay indicated by Z' of 0.9 qualified its amenability to automation. The Z' of 0.7 was displayed by automated assay employed in high-throughput screening of compound libraries against this target. Being electrically neutral, the NKCC1 screening is difficult to achieve by both manual and automated electrophysiological techniques. These techniques, although considered gold standard, suffer from their inherent problems of being too slow to be in high-throughput format and with high running costs. In addition to being a functional assay for NKCC1, it is nontoxic as compared with thallium flux assay, which is prone to generate high number of false-positive/false-negative rates because of its innate fluorescence issues.


Assuntos
Ensaios de Triagem em Larga Escala , Rubídio/análise , Membro 2 da Família 12 de Carreador de Soluto/análise , Células HEK293 , Ensaios de Triagem em Larga Escala/instrumentação , Humanos , Rubídio/química , Membro 2 da Família 12 de Carreador de Soluto/metabolismo
14.
Biophys J ; 112(11): 2280-2290, 2017 Jun 06.
Artigo em Inglês | MEDLINE | ID: mdl-28591601

RESUMO

Telomeric DNA consists of tandem repeats of the sequence d(TTAGGG) that form G-quadruplex structures made of stacked guanines with monovalent cations bound at a central cavity. Although different ions can stabilize a G-quadruplex structure, the preferred bound ions are typically K+ or Na+. Several different strand-folding topologies have been reported for Q-quadruplexes formed from telomeric repeats depending on DNA length and ion solution condition. This suggests a possible dependence of the ion selectivity of the central pore on the folding topology of the quadruplex. Molecular dynamics free energy perturbation has been employed to systematically study the relative affinity of the central quadruplex pore for different cation types and the associated energetic and solvation contributions to ion selectivity. The calculations have been performed on two different common quadruplex folding topologies. For both topologies, the same ion selectivity was found with a preference for K+ followed by Rb+ and Na+, which agrees with the experimentally determined preference for most investigated quadruplexes. The selectivity is determined by a balance between attractive Coulomb interactions and loss of hydration but also modulated by van der Waals contributions. Specificity is mediated by the central guanines and no significant contribution of the nucleic acid backbone. The simulations indicate that different topologies might be stabilized by ions bound at the surface or alternative sites of the quadruplex because the ion specificity of the central pore does not depend on the strand folding topology.


Assuntos
Cátions/metabolismo , Quadruplex G , Telômero/metabolismo , Cátions/química , Césio/química , Césio/metabolismo , Guanina/química , Guanina/metabolismo , Lítio/química , Lítio/metabolismo , Simulação de Dinâmica Molecular , Potássio/química , Potássio/metabolismo , Rubídio/química , Rubídio/metabolismo , Sódio/química , Sódio/metabolismo , Soluções , Telômero/química
15.
J Phys Chem B ; 121(16): 3997-4014, 2017 04 27.
Artigo em Inglês | MEDLINE | ID: mdl-28363025

RESUMO

Stacking of guanine quartets (GQs) can trigger the formation of DNA or RNA quadruple helices, which play numerous biochemical roles. The GQs are stabilized by alkali cations, mainly K+ and Na+, which can reside in, or channel through, the central axis of the GQ stems. Further, ion conduction through GQ wires can be leveraged for nanochemistry applications. G-quadruplex systems have been extensively studied by classical molecular dynamics (MD) simulations using pair-additive force fields or by quantum-chemical (QC) calculations. However, the non-polarizable force fields are very approximate, while QC calculations lack the necessary sampling. Thus, ultimate description of GQ systems would require long-enough simulations using advanced polarizable molecular mechanics (MM). However, to perform such calculations, it is first mandatory to evaluate the method's accuracy using benchmark QC. We report such an evaluation for SIBFA polarizable MM, bearing on the channeling (movement) of an alkali cation (Li+, Na+, K+, or Rb+) along the axis of two stacked G quartets interacting with either one or two ions. The QC energy profiles display markedly different features depending upon the cation but can be retrieved in the majority of cases by the SIBFA profiles. An appropriate balance of first-order (electrostatic and short-range repulsion) and second-order (polarization, charge-transfer, and dispersion) contributions within ΔE is mandatory. With two cations in the channel, the relative weights of the second-order contributions increase steadily upon increasing the ion size. In the G8 complexes with two K+ or two Rb+ cations, the sum of polarization and charge-transfer exceeds the first order terms for all ion positions.


Assuntos
Quadruplex G , Guanina/química , Lítio/química , Potássio/química , Rubídio/química , Sódio/química , Álcalis/química , Anisotropia , Cátions Monovalentes/química , Modelos Moleculares , Termodinâmica
16.
Proc Natl Acad Sci U S A ; 114(12): 3234-3239, 2017 03 21.
Artigo em Inglês | MEDLINE | ID: mdl-28265056

RESUMO

Mode-shift or hysteresis has been reported in ion channels. Voltage-shift for gating currents is well documented for voltage-gated cation channels (VGCC), and it is considered a voltage-sensing domain's (VSD) intrinsic property. However, uncoupling the Shaker K+ channel's pore domain (PD) from the VSD prevented the mode-shift of the gating currents. Consequently, it was proposed that an open-state stabilization of the PD imposes a mechanical load on the VSD, which causes its mode-shift. Furthermore, the mode-shift displayed by hyperpolarization-gated cation channels is likely caused by structural changes at the channel's PD similar to those underlying C-type inactivation. To demonstrate that the PD of VGCC undergoes hysteresis, it is imperative to study its gating process in the absence of the VSD. A back-door strategy is to use KcsA (a K+ channel from the bacteria Streptomyces lividans) as a surrogate because it lacks a VSD and exhibits an activation coupled to C-type inactivation. By directly measuring KcsA's activation gate opening and closing in conditions that promote or halt C-type inactivation, we have found (i) that KcsA undergoes mode-shift of gating when having K+ as the permeant ion; (ii) that Cs+ or Rb+, known to halt C-inactivation, prevented mode-shift of gating; and (iii) that, in the total absence of C-type inactivation, KcsA's mode-shift was prevented. Finally, our results demonstrate that an allosteric communication causes KcsA's activation gate to "remember" the conformation of the selectivity filter, and hence KcsA requires a different amount of energy for opening than for closing.


Assuntos
Proteínas de Bactérias/química , Proteínas de Bactérias/metabolismo , Ativação do Canal Iônico , Canais de Potássio/química , Canais de Potássio/metabolismo , Conformação Proteica , Proteínas de Bactérias/genética , Césio/química , Íons Pesados , Cinética , Potenciais da Membrana , Modelos Moleculares , Mutação , Canais de Potássio/genética , Rubídio/química , Relação Estrutura-Atividade
17.
Comput Math Methods Med ; 2017: 6810626, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-28293274

RESUMO

Purpose. Myocardial blood flow (MBF) quantification with 82Rb positron emission tomography (PET) is gaining clinical adoption, but improvements in precision are desired. This study aims to identify analysis variants producing the most repeatable MBF measures. Methods. 12 volunteers underwent same-day test-retest rest and dipyridamole stress imaging with dynamic 82Rb PET, from which MBF was quantified using 1-tissue-compartment kinetic model variants: (1) blood-pool versus uptake region sampled input function (Blood/Uptake-ROI), (2) dual spillover correction (SOC-On/Off), (3) right blood correction (RBC-On/Off), (4) arterial blood transit delay (Delay-On/Off), and (5) distribution volume (DV) constraint (Global/Regional-DV). Repeatability of MBF, stress/rest myocardial flow reserve (MFR), and stress/rest MBF difference (ΔMBF) was assessed using nonparametric reproducibility coefficients (RPCnp = 1.45 × interquartile range). Results. MBF using SOC-On, RVBC-Off, Blood-ROI, Global-DV, and Delay-Off was most repeatable for combined rest and stress: RPCnp = 0.21 mL/min/g (15.8%). Corresponding MFR and ΔMBF RPCnp were 0.42 (20.2%) and 0.24 mL/min/g (23.5%). MBF repeatability improved with SOC-On at stress (p < 0.001) and tended to improve with RBC-Off at both rest and stress (p < 0.08). DV and ROI did not significantly influence repeatability. The Delay-On model was overdetermined and did not reliably converge. Conclusion. MBF and MFR test-retest repeatability were the best with dual spillover correction, left atrium blood input function, and global DV.


Assuntos
Processamento de Imagem Assistida por Computador/métodos , Tomografia por Emissão de Pósitrons , Rubídio/química , Adulto , Idoso , Idoso de 80 Anos ou mais , Algoritmos , Estudos de Coortes , Doença da Artéria Coronariana/diagnóstico por imagem , Doença da Artéria Coronariana/fisiopatologia , Circulação Coronária , Dipiridamol/química , Feminino , Hemodinâmica , Humanos , Cinética , Masculino , Pessoa de Meia-Idade , Imagem de Perfusão do Miocárdio , Radioisótopos , Reprodutibilidade dos Testes , Tomografia Computadorizada por Raios X
18.
Biochem Biophys Res Commun ; 482(4): 1233-1239, 2017 Jan 22.
Artigo em Inglês | MEDLINE | ID: mdl-27939886

RESUMO

Multidrug transporters play key roles in cellular drug resistance to toxic molecules, yet these transporters are also involved in natural product transport as part of biosynthetic clusters in bacteria and fungi. The genotoxic molecule colibactin is produced by strains of virulent and pathobiont Escherichia coli and Klebsiella pneumoniae. In the biosynthetic cluster is a multidrug and toxic compound extrusion protein (MATE) proposed to transport the prodrug molecule precolibactin across the cytoplasmic membrane, for subsequent cleavage by the peptidase ClbP and cellular export. We recently determined the X-ray structure of ClbM, and showed preliminary data suggesting its specific role in precolibactin transport. Here, we define a functional role of ClbM by examining transport capabilities under various biochemical conditions. Our data indicate ClbM responds to sodium, potassium, and rubidium ion gradients, while also having substantial transport activity in the absence of alkali cations.


Assuntos
Proteínas de Escherichia coli/genética , Escherichia coli/genética , Proteínas de Transporte de Cátions Orgânicos/genética , Peptídeos/genética , Peptídeos/metabolismo , Policetídeos/metabolismo , Antiporters/metabolismo , Proteínas de Bactérias/metabolismo , Produtos Biológicos/química , Transporte Biológico , Transporte Biológico Ativo , Cátions , Cristalografia por Raios X , Citoplasma/metabolismo , Escherichia coli/metabolismo , Proteínas de Escherichia coli/metabolismo , Ligações de Hidrogênio , Concentração de Íons de Hidrogênio , Transporte de Íons , Klebsiella pneumoniae/metabolismo , Microbiota , Família Multigênica , Mutação , Proteínas de Transporte de Cátions Orgânicos/metabolismo , Peptídeo Hidrolases/metabolismo , Potássio/química , Pró-Fármacos , Estrutura Secundária de Proteína , Rodaminas/química , Rubídio/química , Sódio/química , Água/química
19.
J Phys Chem B ; 120(51): 13039-13046, 2016 12 29.
Artigo em Inglês | MEDLINE | ID: mdl-27976904

RESUMO

The unimolecular chemistries and structures of gas-phase (ProLeu)M+ and (LeuPro)M+ complexes when M = Li, Na, Rb, and Cs have been explored using a combination of SORI-CID, IRMPD spectroscopy, and computational methods. CID of both (LeuPro)M+ and (ProLeu)M+ showed identical fragmentation pathways and could not be differentiated. Two of the fragmentation routes of both peptides produced ions at the same nominal mass as (Pro)M+ and (Leu)M+, respectively. For the litiated peptides, experiments revealed identical IRMPD spectra for each of the m/z 122 and 138 ions coming from both peptides. Comparison with computed IR spectra identified them as the (Pro)Li+ and (Leu)Li+, and it is concluded that both zwitterionic and canonical forms of (Pro)Li+ exist in the ion population from CID of both (ProLeu)Li+ and (LeuPro)Li+. The two isomeric peptide complexes could be distinguished using IRMPD spectroscopy in both the fingerprint and the CH/NH/OH regions. The computed IR spectra for the lowest energy structures of each charge solvated complexes are consistent with the IRMPD spectra in both regions for all metal cation complexes. Through comparison between the experimental spectra, it was determined that in lithiated and sodiated ProLeu, metal cation is bound to both carbonyl oxygens and the amine nitrogen. In contrast, the larger metal cations are bound to the two carbonyls, while the amine nitrogen is hydrogen bonded to the amide hydrogen. In the lithiated and sodiated LeuPro complexes, the metal cation is bound to the amide carbonyl and the amine nitrogen while the amine nitrogen is hydrogen bonded to the carboxylic acid carbonyl. However, there is no hydrogen bond in the rubidiated and cesiated complexes; the metal cation is bound to both carbonyl oxygens and the amine nitrogen. Details of the position of the carboxylic acid C═O stretch were especially informative in the spectroscopic confirmation of the lowest energy computed structures.


Assuntos
Césio/química , Dipeptídeos/química , Lítio/química , Rubídio/química , Sódio/química , Sítios de Ligação , Cátions Monovalentes , Estrutura Molecular , Soluções , Espectrofotometria Infravermelho , Termodinâmica
20.
J Nanosci Nanotechnol ; 16(1): 654-7, 2016 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-27398503

RESUMO

We investigated how surface roughness of a Ta/Ru buffer layer affects the degradation characteristics on MgO-based magnetic tunnel junctions (MTJs). MTJs with worse surface roughness on the buffer layer showed increased resistance drift and degraded time-dependent dielectric breakdown (TDDB) characteristics. We suggest that this resulted from reduced MgO thickness on the MTJ with worse surface roughness on the buffer layer, which was estimated by the TDDB and analytic approach. As a result, surface roughness of the buffer layer is a critical factors that impacts the reliability of MTJs, and it should be controlled to have the smallest roughness value as possible.


Assuntos
Óxido de Magnésio/química , Rubídio/química , Tantálio/química
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA