Optical detection of solid-state chiral structures with unpolarized light and in the absence of external fields.
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Electromagnetic Fields↗
Biomedical subjects
João Rocha
Publications and source records attributed to João Rocha.
Photoluminescent layered Y(III) and Tb(III) silicates doped with Ce(III).
The synthesis and structural characterization of new layered rare-earth silicates K(3)[M(1-a)Ce(a)Si(3)O(8)(OH)(2)], M = Y(3+), Tb(3+), a << 1 (AV-22 materials), have been reported. These materials combine the properties of layered silicates, such as intercalation chemistry, and photoluminescence and may find applications in new types of sensor devices. For mixed Tb/Ce-AV-22, evidence has been found for the energy transfer from the large Ce(3+) 4f( 1) --> 5d(1) broad band to the sharp Tb(3+) 4f (8) lines. This energy transfer allows the fine-tuning of the color emission in the blue-green region of the chromaticity diagram. Upon Ce(3+) excitation (342 nm), the radiance of Tb/Ce-AV-22 is approximately 2 times higher than that measured under direct Tb(3+) excitation, which reinforces the existence of effective room-temperature Ce(3+)-to-Tb(3+) energy transfer.
Cerium↗
Characterization of microporous aluminophosphate IST-1 using (1)H Lee-Goldburg techniques.
The presence of two independent methylamine species in microporous aluminophosphate IST-1 (|(CH(3)NH(2))(4)(CH(3)NH(+)(3))(4)(OH(-))(4)|[Al(12)P(12)O(48)]) has been shown previously by synchrotron powder X-ray diffraction. One of these species, [N(1)-C(1)], links to a six-coordinated framework Al-atom [Al(1)], while the other methylamine [N(2)-C(2)] is protonated and hydrogen-bonded to three O-atoms [O(1), O(2) and O(12)]. We revisit the structure of IST-1 and report the complete assignment of the (1)H NMR spectra by combining X-ray data and high-resolution heteronuclear/homonuclear solid-state NMR techniques based on frequency-switched Lee-Goldburg homonuclear decoupling and (31)P-(31)P homonuclear recoupling. Careful analysis of the 2D (1)H-X homonuclear correlation (X=(1)H) and 2D heteronuclear correlation (X=(13)C, (31)P and (27)Al) spectra allowed the distinction of both methylamine species and the assignment of all (31)P and (13)C resonances. For the first time at a relatively high (9.4 T) magnetic field, symmetric doublet patterns have been observed in the (13)C spectra, caused by the influence of the (14)N second-order quadrupolar interaction.
Journal Article↗
Effects of N-acetylcysteine plus deferoxamine in lipopolysaccharide-induced acute lung injury in the rat.
OBJECTIVES: Interventions that reduce the generation or the effects of reactive oxygen species exert controversial effects in animal models of lung injury, and these could be secondary to the pro-oxidant effects of antioxidants generally by their interaction with iron. We here describe the effects of N-acetylcysteine, deferoxamine, or both in the treatment of acute lung injury induced by intratracheal lipopolysaccharide injection. DESIGN: Prospective, randomized, controlled experiment. SETTING: Animal basic science laboratory. SUBJECTS: Male Wistar rats, weighing 200-250 g. INTERVENTIONS: Rats exposed intratracheally to lipopolysaccharide were treated with N-acetylcysteine (20 mg/kg subcutaneously 3, 6, and 12 hrs after lipopolysaccharide instillation), deferoxamine (20 mg/kg subcutaneously 3 hrs after lipopolysaccharide instillation), N-acetylcysteine (20 mg/kg, 3, 6, and 12 hrs after lipopolysaccharide instillation) plus deferoxamine (20 mg/kg 3 hrs after lipopolysaccharide instillation), or vehicle. MEASUREMENTS AND MAIN RESULTS: Acute lung injury was induced by intratracheal instillation of lipopolysaccharide in Wistar rats. The animals were randomly divided into five groups: group 1, control with instillation of isotonic saline; group 2, lipopolysaccharide treated with saline; group 3, lipopolysaccharide treated with N-acetylcysteine; group 4, lipopolysaccharide treated with deferoxamine; and group 5, lipopolysaccharide treated with N-acetylcysteine plus deferoxamine. Several times after lipopolysaccharide instillation, the rats were killed and a bronchoalveolar lavage was performed to determine thiobarbituric acid reactive species, protein carbonyls, superoxide dismutase and catalase activities, mitochondrial superoxide production (oxidative stress variables), the degree of the alveolar-capillary membrane compromise, and inflammatory infiltration. Samples from the lung were isolated and assayed for oxidative stress variables or histopathologic analyses. N-acetylcysteine plus deferoxamine decreased bronchoalveolar lavage fluid protein, inflammatory cells, oxidative damage variables, and proinflammatory cytokines. N-acetylcysteine plus deferoxamine treatment significantly attenuated lung oxidative damage, mitochondrial superoxide production, and histopathologic alterations after lipopolysaccharide instillation. CONCLUSIONS: Our data provide the first experimental demonstration that N-acetylcysteine plus deferoxamine decreases oxidative stress and mitochondrial dysfunction and limits inflammatory response and alveolar pathology induced by lipopolysaccharide in the rat.
Acetylcysteine↗
X-ray diffraction and solid-state NMR studies of a germanium binuclear complex.
A compound formulated as (C4H12N2)[Ge2(pmida)2(OH)2] x 4 H2O (where pmida(4-) = N-(phosphonomethyl)iminodiacetate and C4H12N2(2+) = piperazinedium cation), containing the anionic [Ge2(pmida)2(OH)2]2- complex, has been synthesised by the hydrothermal approach and its structure determined by single-crystal X-ray diffraction analysis. Several high-resolution solid-state magic-angle spinning (MAS) NMR techniques, in particular two-dimensional 1H-X(13C,31P) heteronuclear correlation (HETCOR) and 1H-1H homonuclear correlation (HOMCOR) experiments incorporating a frequency-switched Lee-Goldburg (FS-LG) decoupling scheme, have been employed for the first time in such a material. Using these tools in tandem affords an excellent general approach to study the structure of other inorganic-organic hybrids. We assigned the NMR resonances with the help of C...H and P...H internuclear distances obtained through systematic statistical analyses of the crystallographic data. The compound was further characterised by powder X-ray diffraction techniques, IR and Raman spectroscopy, and by elemental and thermal analyses (thermogravimetric analysis and differential scanning calorimetry).
Journal Article↗
A new titanosilicate umbite membrane for the separation of H2.
A new microporous titanosilicate umbite membrane has been synthesized on commercial porous TiO2 tubular supports. This membrane is able to separate H2/N2 mixtures (with selectivities as high as 48) even in the presence of water.
Journal Article↗
Multiplex MQMAS NMR of quadrupolar nuclei.
A multiplex phase cycling method (N. Ivchenko et al., J. Magn. Reson. 160 (2003) 52-58) has been used to record two-dimensional MQMAS spectra with a very short phase cycling. A straightforward procedure has been developed to easily process the data. Combining this Multiplex approach and the new Soft-Pulse-Adding-Mixing (SPAM) method considerably increases the signal-to-noise ratio of the conventional MQMAS experiment. The Multiplex acquisition procedure is much simpler than the echo/anti-echo method recently proposed, and has been applied with success to record (87)Rb spectra of RbNO(3) and (27)Al 3Q and 5Q MQMAS NMR of microporous aluminophosphate AlPO(4)-14.
Journal Article↗
Photoluminescent layered lanthanide silicates.
The hydrothermal synthesis and structural characterization of layered lanthanide silicates, K(3)[M(1-a)Ln(a)Si(3)O(8)(OH)(2)] (M = Y(3+), Tb(3+); Ln = Eu(3+), Er(3+), Tb(3+), and Gd(3+)), named AV-22 materials, are reported. The structure of these solids was elucidated by single-crystal (180 K) and powder X-ray diffraction and further characterized by chemical analysis, thermogravimetry, scanning electron microscopy, (29)Si MAS NMR, and photoluminescence spectroscopy. The Er-AV-22 material is a room-temperature infrared phosphor, while Tb- and Eu-AV-22 are visible emitters with output efficiencies comparable to standards used in commercial lamps. The structure of these materials allows the inclusion of a second (or even a third) type of Ln(3+) ion in the framework and, therefore, the fine-tuning of their photoluminescent properties. For the mixed Tb(3+)/Eu(3+) materials, evidence has been found of the inclusion of Eu(3+) ions in the interlayer space by replacing K+ ions, further allowing the activation of Tb(3+)-to-Eu(3+) energy transfer mechanisms. The occurrence probability of such mechanisms ranges from 0.62 (a = 0.05) to 1.20 ms(-1) (a = 0.1) with a high energy transfer efficiency (0.73 and 0.84, respectively).
Journal Article↗
Immobilization of oxomolybdenum species in a layered double hydroxide pillared by 2,2'-bipyridine-5,5'-dicarboxylate anions.
A Zn,Al layered double hydroxide (LDH) with Zn/Al = 1.45 and containing nitrate anions was prepared by coprecipitation and characterized by powder X-ray diffraction, Zn K-edge extended X-ray absorption fine structure spectroscopy (EXAFS), thermogravimetric analysis, FTIR and FT Raman spectroscopy, and (27)Al MAS NMR spectroscopy. Three Zn...O and four Zn...M (M = Zn, Al) shells could be fitted to the low-temperature (40 K) EXAFS spectrum, in accordance with a model for an ordered cationic sheet. The nitrate anions were easily exchanged by 2,2'-bipyridine-5,5'-dicarboxylate anions, resulting in an increase in the basal spacing from 9 to 18 A. The basal spacing of the pillared derivative indicates that the anions are arranged with their longest dimension nearly perpendicular to the host layers. This material exhibits a high encapsulating ability, as evidenced by its interaction with a dichloromethane solution of the dioxomolybdenum(VI) complex MoO(2)Cl(2)(THF)(2). A material with a metal loading of 11.2 wt % was obtained. Molybdenum K-edge EXAFS analysis could not substantiate the formation of a supported complex of the type MoO(2)Cl(2)(N-N) but instead indicated the formation of unidentate-bridged entities of the type [O(2)Mo-O-MoO(2)] with a metal-metal separation of 3.29 A. The molybdenum-containing LDH was active as a catalyst for the liquid-phase epoxidation of cis-cyclooctene, 1-octene, and trans-2-octene using tert-butyl hydroperoxide as the oxygen source, yielding the corresponding epoxides as the only products. For reactions carried out with no additional solvent (other than n-decane) or in the presence of 1,2-dichloroethane, the solid catalyst could be recycled with no major loss of activity. Other tests confirmed that the systems functioned as true heterogeneous catalysts.
Journal Article↗
Protective effect of N-acetylcysteine and deferoxamine on carbon tetrachloride-induced acute hepatic failure in rats.
OBJECTIVE: Carbon tetrachloride (CCl4) is a lipid-soluble potent hepatotoxic; thus, it widely is used as an animal model of severe hepatic failure. Treatment with antioxidants may modulate the toxic effects of CCl4 on liver, generally with drug administration before CCl4, which can restrict its use in the clinical setting. We here describe the effects of N-acetylcysteine, deferoxamine, or both in the treatment of CCl4-induced hepatic failure. DESIGN: Prospective, randomized, controlled experiment. SETTING: Animal basic science laboratory. SUBJECTS: Male Wistar rats, weighing 200-250 g. INTERVENTIONS: Rats exposed to CCl4 were treated with N-acetylcysteine and/or deferoxamine or vehicle. MEASUREMENTS AND MAIN RESULTS: N-acetylcysteine plus deferoxamine treatment significantly attenuated hepatic and central nervous system oxidative damage after acute hepatic failure induced by CCl4. In addition, the serum levels of alanine aminotransferase, total bilirubin, and prothrombin time in the N-acetylcysteine plus deferoxamine group were significantly lower than those in the N-acetylcysteine or deferoxamine and saline groups. After N-acetylcysteine plus deferoxamine treatment, hepatocellular necrosis and inflammatory infiltration induced by carbon tetrachloride were greatly decreased. Survival in untreated rats was 5%. Survival increased to 25% and 35%, respectively, with N-acetylcysteine and deferoxamine treatment. In rats treated with N-acetylcysteine plus deferoxamine, survival was 80%. CONCLUSIONS: Our data provide the first experimental demonstration that N-acetylcysteine plus deferoxamine reduces mortality rate, decreases oxidative stress, and limits inflammatory infiltration and hepatocyte necrosis induced by CCl4 in the rat.
Acetylcysteine↗
Novel microporous lanthanide silicates with tobermorite-like structure.
The synthesis and structural characterization of microporous lanthanide silicates (Na(1.08)K(0.5)Ln(1.14)Si(3)O(8.5).1.78H(2)O, Ln = Eu, Tb, Sm, Ce) are reported. The structure of these solids is closely related with the structure of hydrated calcium silicate minerals known as tobermorites and was solved by powder X-ray diffraction ab initio (direct) methods and further characterized by chemical analysis, thermogravimetry, scanning electron microscopy, (23)Na and (29)Si MAS NMR and luminescence spectroscopy. These materials combine microporosity with interesting photoluminescence properties, and their structural flexibility allows fine-tuning of luminescence properties, by introducing a second type of lanthanide ion in the framework. Thus, they may find applications in new types of sensors.
Journal Article↗
Molecular structure-activity relationships for the oxidation of organic compounds using mesoporous silica catalysts derivatised with bis(halogeno)dioxomolybdenum(VI) complexes.
Mo K-edge XAFS spectra have been measured for ordered mesoporous silica MCM-41 grafted with the complexes [MoO2X2(thf)2] (X=Cl, Br). For grafting reactions in the absence of triethylamine, materials with 1 wt. % Mo are obtained; the Mo K-edge EXAFS results indicate the co-existence of isolated surface-fixed monomeric species [MoO2[(-O)3SiO]2(thf)(n)] and [MoO2[(-O)3SiO]X(thf)(n)]. When Et3N is used in the grafting reactions, materials with 4 wt. % Mo are obtained. The EXAFS data for the material prepared using [MoO2Cl2(thf)2] and Et3N indicate the presence of dinuclear species with two Mo(VI) centres, each with two Mo=O groups and each linked by one or two oxo bridges (Mo...Mo 3.27 A). The molybdenum centres in the material prepared using the dibromo complex comprise mainly isolated four-coordinate dioxomolybdenum(VI) and trioxomolybdenum(VI) monomeric species, with a small contribution from dimeric species. All materials were further characterised in the solid state by powder X-ray diffraction, N2 adsorption analysis, MAS NMR (13C, 29Si) and FTIR spectroscopy. The derivatised MCMs perform differently as catalysts in the liquid-phase oxidation of various olefins and alcohols with tert-butyl hydroperoxide. The highest alkene epoxidation activity was recorded for the catalysts with low metal loading, whereas the material containing oxo-bridged dimers had the highest activity for oxidation of alcohols. The recyclability of all the catalysts was tested: the catalytic activity of the derivatised materials tended to stabilize with ageing.
Journal Article↗
Preparation and characterization of organotin-oxomolybdate coordination polymers and their use in sulfoxidation catalysis.
The organotin-oxomolybdates [(R(3)Sn)(2)MoO(4)].n H(2)O (R=methyl, n-butyl, cyclohexyl, phenyl, benzyl) have been prepared and tested as catalysts for the oxidation of benzothiophene with aqueous hydrogen peroxide, at 35 degrees C and atmospheric pressure. In all cases, the 1,1-dioxide was the only observed product. The kinetic profiles depend on the nature of the tin-bound R group and also on the addition of a co-solvent. For the tribenzyltin derivative, the apparent activation energies for sulfoxidation as a function of the co-solvent are in the order 1,2-dichloroethane (5 kcal mol(-1))<ethanol<acetonitrile<water (27 kcal mol(-1)). The solid could be recovered by centrifugation from the three-phase (solid-liquid-liquid) system containing 1,2-dichloroethane. The catalyst was reused in a second reaction cycle with no significant loss of activity. Increasing the oxidant/substrate ratio from 2:1 to 6:1 allows the corresponding sulfone to be obtained in quantitative yield within 24 h. Changing the nature of the tin-bound R group in the catalyst precursors modifies their physical properties and hence their catalytic performance. The variation in hydrophobic/hydrophilic character is important, since the Me, nBu and Cy derivatives crystallize as anhydrous compounds, whereas the other two derivatives are hydrates. The polymers also have different structures, as evidenced by Xray powder diffraction. Mo K-edge and Sn K-edge EXAFS spectroscopy confirmed that the structures arise from the self-assembly of tetrahedral [MoO(4)](2-) subunits and [R(3)Sn](+) spacers. The Mo...Sn separation in the trimethyltin derivative is a uniform 3.84 A. By contrast, the EXAFS results revealed the coexistence of short (3.67-3.79 A) and long (3.93-4.07 A) Mo.Sn separations in the other coordination polymers. The catalyst precursors were also characterized in the solid state by thermogravimetric analysis, FTIR, and Raman spectroscopy, and MAS NMR ((13)C, (119)Sn) spectroscopy.
Journal Article↗
I-STMAS, a new high-resolution solid-state NMR method for half-integer quadrupolar nuclei.
In complement to the previously proposed multiple-quantum magic-angle-spinning (MQMAS) and satellite transition MAS (STMAS) sequences, we describe a new two-dimensional high-resolution method, inverse-STMAS (I-STMAS) that allows second-order quadrupolar averaging. Like STMAS, I-STMAS correlates second-order quadrupole dephasing occurring on coherences related to the central transition (CT) and satellite transitions (STs), but does it in a reverse manner: CT evolves during the t(1) period while STs are detected during t(2). Although STMAS and I-STMAS are symmetric, there are some interesting and useful differences between the two methods. For example, we show that during the acquisition time t(2), it is possible to over-sample the data and then to process them to suppress the CT-CT correlation resonance.
Journal Article↗
An optimised method to determine the degree of acetylation of chitin and chitosan by FTIR spectroscopy.
Linking up the user-friendly and low-priced FTIR with the more sophisticated and high-priced 13C CP/MAS NMR spectroscopies, an improved method to determine the degree of acetylation (DA) of chitins and chitosans was outlined. The method was established for the most complex polymorphic form (alpha-chitin) and for the most problematic range of DA values (most acetylated samples) and can easily be extended to the other polymorphic forms (beta- and gamma-chitins) and to other ranges of DA values.
Acetylation↗
Double-resonance decoupling for resolution enhancement of 31P solid-state MAS and 27Al --> 31P MQHETCOR NMR.
27Al decoupling has been used to remove residual J-coupling interactions between 31P and 27Al in microporous aluminophosphates AlPO4-14 and AlPO4-40. In combination with 1H high-power decoupling, 27Al adapted decoupling yields 31P spectra with optimal sensitivity and resolution. The importance of double-resonance decoupling is further demonstrated by incorporating this technique in the MQHETCOR sequence. Unambiguous assignment of all the AlPO4-14 nuclear magnetic resonances is achieved by combining multiple-quantum evolution in the 27Al dimension and double-resonance decoupling in the 31P acquisition domain.
Aluminum Compounds↗
Lanthanopolyoxotungstoborates: synthesis, characterization, and layer-by-layer assembly of europium photoluminescent nanostructured films.
New lanthanopolyoxotungstoborates, K6-xHx[Ln(BW11O39)(H2O)3].nH2O, Ln(III) = Sm, Eu, Tb, Er, were prepared and characterized by spectroscopic methods (Fourier transform infrared, Fourier transform-Raman, 11B solid-state nuclear magnetic resonance, and photoluminescence) and elemental analysis. A layer-by-layer assembly method was employed to fabricate multilayered films containing the europium heteropolyanion and the polyelectrolytes poly(sodium 4-styrenesulfonate) and poly(diallydimethylammonium chloride). The photoluminescence behavior of these final nanostructures was investigated and compared with that of the starting Eu(III) polyoxometalate used as the building unit.
Adsorption↗