Luís Mafra

Characterization of an extracellular polysaccharide produced by a Pseudomonas strain grown on glycerol.

A new extracellular charged polysaccharide composed mainly by galactose, with lower amounts of mannose, glucose and rhamnose, was produced by the cultivation of Pseudomonas oleovorans NRRL B-14682 using glycerol as the sole carbon source. Thermal and solid-state NMR analysis showed that this polymer is essentially amorphous, with a glass transition temperature of 155.7 degrees C. The exopolysaccharide aqueous solutions have viscoelastic properties similar to that of Guar gum, but with affinity to salts as a result of its polyelectrolyte character. In addition, the exopolysaccharide has demonstrated good flocculating and emulsifying properties and film-forming capacity. These properties make this polymer a good alternative to more expensive natural polysaccharides, such as Guar gum, in several applications in the food, pharmaceutical, cosmetic, textile, paper and petroleum industries.

Packing Interactions in Hydrated and Anhydrous Forms of the Antibiotic Ciprofloxacin: a Solid-State NMR, X-ray Diffraction, and Computer Simulation Study

We present an experimental NMR, X-ray diffraction (XRD), and computational study of the supramolecular assemblies of two crystalline forms of Ciprofloxacin: one anhydrate and one hydrate forming water wormholes. The resonance assignment of up to 51 and 54 distinct (13)C and (1)H resonances for the hydrate is reported. The effect of crystal packing, identified by XRD, on the (1)H and (13)C chemical shifts including weak interionic H-bonds, is quantified; (1)H chemical shift changes up to ∼-3.5 ppm for CH···π contacts and ∼+2 ppm (CH···O((-))); ∼+4.7 ppm (((+))NH···O((-))) for H-bonds. Water intake induces chemical shift changes up to 2 and 5 ppm for (1)H and (13)C nuclei, respectively. Such chemical shifts are found to be sensitive detectors of hydration/dehydration in highly insoluble hydrates.

Multi-functional rare-earth hybrid layered networks: photoluminescence and catalysis studies

Hydrothermal reactions between rare-earth (RE) chloride salts and N-(carboxymethyl)iminodi(methylphosphonic acid) (H5cmp) led to the isolation of a series of layered networks formulated as [RE(H2cmp)(H2O)] [RE3+ = Y3+, La3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+ and Er3+]. All compounds were isolated as micro-crystalline powders (many of which were nano-sized in thickness), with the plate-like crystallites found to exhibit preferential growth perpendicular to the [002] vector, a feature which seems to favour catalytic performance. Full structural elucidation was attained by the combination of synchrotron radiation (micro-crystal and powder) diffraction data, solid-state NMR studies (1H, 13C and 31P) and photophysical measurements. Materials consist of ∞2[RE(H2cmp)(H2O)] layers in the ab plane of the unit cell, constructed from a single RE3+ centre (in a highly distorted dodecahedral coordination environment with one water molecule in the first coordination sphere) and one H2cmp3− ligand present in a zwitterionic form. Connections between layers along the c-axis are assured by strong and highly directional O–H⋯O hydrogen bonds involving the protonated phosphonate group (donor) of one layer and one oxygen atom (acceptor) of the carboxylate group in the adjacent layer. The network is an unprecedented 12-connected uninodal plane net with total Schafli symbol 330.434.52. The Eu3+ material is photoluminescent at room temperature and 12 K with 5D0 lifetimes of 0.86 ± 0.01 ms and 0.89 ± 0.01 ms, respectively. Studies of the mixed-lanthanide diluted [(Gd0.95Eu0.05)(H2cmp)(H2O)] material showed that Gd3+-to-Eu3+ energy transfer occurs within the layers. The coordinated water molecule plays a decisive role in the non-radiative relaxation process of the Eu3+ emission. All synthesised materials were further tested in the cyclodehydration of xylose to furfural, with the observed results comparing quite favourably with those from other solid acid catalysts used in the same reaction under similar conditions. A detailed catalytic study was performed for [Y(H2cmp)(H2O)]: selectivity increased to 84% as the conversion reached 83%; this solid was also re-used successfully in three consecutive 4 h runs after separation from the liquid phase by centrifugation and regeneration using either thermal treatment at 280 °C or repeated washing with solvents. All materials have been routinely characterized using vibrational spectroscopy (ATR-FT-IR and FT-Raman), thermogravimetric analyses, SEM investigations and CHN elemental composition.

High-resolution 1H homonuclear dipolar recoupling NMR spectra of biological solids at MAS rates up to 67 kHz

Two-dimensional (1)H homonuclear correlation NMR spectra of solids of biological interest have been recorded at high magnetic fields (14.1 and 18.8 T) and MAS rates up to 67 kHz, using RN(n)(nu) symmetry-based homonuclear recoupling and CRAMPS decoupling; this method affords exceptional spectral resolution and is well suited to probe (1)H-(1)H proximities in powdered solids.

Sulfonated Graphene Oxide as Effective Catalyst for Conversion of 5‐(Hydroxymethyl)‐2‐furfural into Biofuels

The acid-catalyzed reaction of 5-(hydroxymethyl)-2-furfural with ethanol is a promising route to produce biofuels or fuel additives within the carbohydrate platform; specifically, this reaction may give 5-ethoxymethylfurfural, 5-(ethoxymethyl)furfural diethylacetal, and/or ethyl levulinate (bioEs). It is shown that sulfonated, partially reduced graphene oxide (S-RGO) exhibits a more superior catalytic performance for the production of bioEs than several other acid catalysts, which include sulfonated carbons and the commercial acid resin Amberlyst-15, which has a much higher sulfonic acid content and stronger acidity. This was attributed to the cooperative effects of the sulfonic acid groups and other types of acid sites (e.g., carboxylic acids), and to the enhanced accessibility to the active sites as a result of the 2D structure. Moreover, the acidic functionalities bonded to the S-RGO surface were more stable under the catalytic reaction conditions than those of the other solids tested, which allowed its efficient reuse.

Practical aspects of Lee-Goldburg based CRAMPS techniques for high-resolution 1H NMR spectroscopy in solids: implementation and applications.

Elucidating the local environment of the hydrogen atoms is an important problem in materials science. Because (1)H spectra in solid-state nuclear magnetic resonance (NMR) suffer from low resolution due to homogeneous broadening, even under magic-angle spinning (MAS), information of chemical interest may only be obtained using certain high-resolution (1)H MAS techniques. (1)H Lee-Goldburg (LG) CRAMPS (Combined Rotation And Multiple-Pulse Spectroscopy) methods are particularly well suited for studying inorganic-organic hybrid materials, rich in (1)H nuclei. However, setting up CRAMPS experiments is time-consuming and not entirely trivial, facts that have discouraged their widespread use by materials scientists. To change this status quo, here we describe and discuss some important aspects of the experimental implementation of CRAMPS techniques based on LG decoupling schemes, such as FSLG (Frequency Switched), and windowed and windowless PMLG (Phase Modulated). In particular, we discuss the influence on the quality of the (1)H NMR spectra of the different parameters at play, for example LG (Lee-Goldburg) pulses, radio-frequency (rf) phase, frequency switching, and pulse imperfections, using glycine and adamantane as model compounds. The efficiency and robustness of the different LG-decoupling schemes is then illustrated on the following materials: organo-phosphorus ligand, N-(phosphonomethyl)iminodiacetic acid [H(4)pmida] [I], and inorganic-organic hybrid materials (C(4)H(12)N(2))[Ge(2)(pmida)(2)OH(2)] x 4H(2)O [II] and (C(2)H(5)NH(3))[Ti(H(1.5)PO(4))(PO(4))](2) x H(2)O [III].

KCa4(BO3)3:Ln3+ (Ln = Dy, Eu, Tb) phosphors for near UV excited white–light–emitting diodes

A series of doped KCa4(BO3)3:Ln3+ (Ln: Dy, Eu and Tb) compositions were synthesized by solid–state reaction method and their photoluminescent properties were systematically investigated to ascertain their suitability for application in white light emitting diodes. The X–ray diffraction (XRD) and nuclear magnetic resonance (MAS–NMR) data indicates that Ln3+–ions are successfully occupied the non–centrosymmetric Ca2+ sites, in the orthorhombic crystalline phase of KCa4(BO3)3 having space group Ama2, without affecting the boron chemical environment. The present phosphor systems could be efficiently excitable at the broad UV wavelength region, from 250 to 350 nm, compatible to the most commonly available UV light–emitting diode (LED) chips. Photoluminescence studies revealed optimal near white–light emission for KCa4(BO3)3 with 5 wt.% Dy3+ doping, while warm white–light (CIE; X = 0.353, Y = 0.369) is obtained at 1wt.% Dy3+ ion concentration. The principle of energy transfer between Eu3+ and Tb3+ also demonstr...

Clean synthesis of molecular recognition polymeric materials with chiral sensing capability using supercritical fluid technology. Application as HPLC stationary phases

Molecularly imprinted polymers (MIPs) of poly(ethylene glycol dimethacrylate) and poly(N-isopropylacrylamide-co-ethylene glycol dimethacrylate) were synthesized for the first time in supercritical carbon dioxide (scCO(2)), using Boc-L-tryptophan as template. Supercritical fluid technology provides a clean and one-step synthetic route for the preparation of affinity polymeric materials with sensing capability for specific molecules. The polymeric materials were tested as stationary HPLC phases for the enantiomeric separation of L- and D-tryptophan. HPLC results prove that the synthesized MIPs are able to recognize the template molecule towards its enantiomer which opens up potential applications in chromatographic chiral separation.

Solid acids with SO3H groups and tunable surface properties: versatile catalysts for biomass conversion

Acid catalysis plays an important role in biomass conversion processes for producing chemicals and fuels. We report a relatively simple procedure for synthesizing versatile, strong acid catalysts based on carbon and carbon–silica composites with sulfonic acid groups. The process involves chemical activation of a sulfonic acid organic precursor at low temperature. The synthesis conditions can be modified to tune the surface composition, texture, and the acid properties of the materials towards superior catalytic performances. Molecular level insights into the nature and strength of the acid sites were gained by combining high resolution XPS and 1H-decoupled 31P MAS NMR spectroscopy of adsorbed triethylphosphine oxide. These materials are effective acid catalysts for the conversion of different biomass-derived chemicals to useful bio products such as furanic ethers and levulinate esters.

Combining Multinuclear High-Resolution Solid-State MAS NMR and Computational Methods for Resonance Assignment of Glutathione Tripeptide

We present a complete set of experimental approaches for the NMR assignment of powdered tripeptide glutathione at natural isotopic abundance, based on J-coupling and dipolar NMR techniques combined with (1)H CRAMPS decoupling. To fully assign the spectra, two-dimensional (2D) high-resolution methods, such as (1)H-(13)C INEPT-HSQC/PRESTO heteronuclear correlations (HETCOR), (1)H-(1)H double-quantum (DQ), and (1)H-(14)N D-HMQC correlation experiments, have been used. To support the interpretation of the experimental data, periodic density functional theory calculations together with the GIPAW approach have been used to calculate the (1)H and (13)C chemical shifts. It is found that the shifts calculated with two popular plane wave codes (CASTEP and Quantum ESPRESSO) are in excellent agreement with the experimental results.