Sérgio M. Santos

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.

Development and application of a capillary electrophoresis based method for the simultaneous screening of six antibiotics in spiked milk samples.

An easy to use and low time consuming capillary electrophoresis (CE) method was developed and applied to the simultaneous determination of six antibiotics (ampicillin, amoxicillin, cloxacillin, penicillin, tetracycline and chloramphenicol) in spiked milk samples. Samples of milk were cleaned up by solid-phase extraction (with a C(18) cartridge) after protein precipitation. Analysis was performed by CE and results compared with the obtained via HPLC, both coupled to a UV-vis detector (210nm). CE employed a 58.5cm long fused-silica capillary (50cm to detector), 75microm i.d., a 2.7x10(-2)M KH(2)PO(4), 4.3x10(-2)M Na(2)B(4)O(7) separation buffer, pH 8; an applied voltage of 18kV; a hydrostatic injection of 0.5psi during 3s; and a run temperature of 25 degrees C. Under the described conditions, amoxicillin was not separated by HPLC, while CE was able to separate, and, therefore, allow detection. Regardless of amoxicillin, comparable results were obtained by HPLC and CE. The average recoveries of antibiotics, from milk fortified at 2.5 and 5microg/mL, was over 72% with R.S.D.s within 5%. Recovery levels were essentially dictated by the used SPE cartridge.

Sulfate anion templation of a neutral pseudorotaxane assembly using an indolocarbazole threading component.

The first example of anion templated pseudorotaxane formation between two neutral components in solution and in surface assembled monolayers is described.

Interlocked Host Anion Recognition by an Indolocarbazole-Containing [2]Rotaxane

The design, synthesis, structure, and anion-binding properties of the first indolocarbazole-containing interlocked structure are described. The novel [2]rotaxane molecular structure incorporates a neutral indolocarbazole-containing axle component which is encircled by a tetracationic macrocycle functionalized with an isophthalamide anion recognition motif. (1)H NMR and UV-visible spectroscopies and X-ray crystallography demonstrated the importance of pi-donor-acceptor, CH...pi, and electrostatic interactions in the assembly of pseudorotaxanes between the electron-deficient tetracationic macrocycle and a series of pi-electron-rich indolocarbazole derivatives. Subsequent urethane stoppering of one of these complexes afforded a [2]rotaxane, which was shown by (1)H NMR spectroscopic titration experiments to exhibit enhanced chloride and bromide anion recognition compared to its non-interlocked components. Computational molecular dynamics simulations provide further insight into the mechanism and structural nature of the anion recognition process, confirming it to involve cooperative hydrogen-bond donation from both macrocycle and indolocarbazole components of the rotaxane. The observed selectivity of the [2]rotaxane for chloride is interpreted in terms of its unique interlocked binding cavity, defined by the macrocycle isophthalamide and indolocarbazole N-H protons, which is complementary in size and shape to this halide guest.

Sulfate anion-templated assembly of a [2]catenane

The sulfate anions templating role in catenane formation is demonstrated for the first time; a novel bis-pyridinium nicotinamide [2]catenane is prepared in a remarkable high yield and is shown to exhibit selectivity for sulfate, the templating anion.

Anion induced and inhibited circumrotation of a [2]catenane.

The first example of a catenane capable of performing circumrotation via an anion switching methodology is described; of particular interest is a conformational locking mechanism which results from chloride coordination in the catenane binding cavity.

Production of adsorbents by pyrolysis of paper mill sludge and application on the removal of citalopram from water

This work describes the production of alternative adsorbents from industrial residues and their application for the removal of a highly consumed antidepressant (citalopram) from water. The adsorbents were produced by pyrolysis of both primary and biological paper mill sludge at different temperatures and residence times. The original sludge and the produced chars were fully characterized by elemental and proximate analyses, total organic carbon, specific surface area (BET), N₂ isotherms, FTIR, (13)C and (1)H solid state NMR and SEM. Batch kinetic and equilibrium experiments were carried out to describe the adsorption of citalopram onto the produced materials. The fastest kinetics and the highest adsorption capacity were obtained using primary sludge pyrolysed at 800 °C during 150 min. The use of pyrolysed paper mill sludge for the remediation of contaminated waters might constitute an interesting application for the valorization of those wastes.

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.

Corrole and corrole functionalized silica nanoparticles as new metal ion chemosensors: a case of silver satellite nanoparticles formation.

Corrole macrocycles are very appealing dyes for incorporation into light harvesting devices. This work shows the sensorial ability of 5,10,15-tris(pentafluorophenyl)corrole 1 and its monoanionic species toward Na(+), Ca(2+), Cu(2+), Cd(2+), Pb(2+), Hg(2+), Ag(+), and Al(3+) metal ions in toluene and acetonitrile. The photophysical studies toward metal ions were carried out by absorption and emission spectroscopy. From all metal ions studied, corrole 1 shows to be colorimetric for Hg(2+) allowing a naked-eye detection of Hg(2+) through a change of color from purple to blue in acetonitrile and from green to yellow in toluene. In addition a new β-imine corrole 4 was successful synthesized and further functionalized with 3-isocyanatopropyl-trimethoxysilane resulting in an alkoxysilane derivative 5. The grafting of alkoxysilane derivative 5 with optically transparent silica nanoparticles (SiNPs) was achieved succesfully. The new-coated silica nanoparticles with corrole 5 were studied in the presence of Cu(2+), Hg(2+), and Ag(+) as metal ion probes. Interestingly, upon addition of Ag(+), groups of satellite AgNPs were formed around the SiNPs and were checked by transmission electron microscopy (TEM). At same time, a change of color from green to yellow was observed.

Columnar discotic Pt(II) metallomesogens as luminescence multifunctional materials with chemo and thermosensor abilities

A new family of Pt(II) luminescent metallomesogens based on dicatenar pyridylpyrazolate ligands [Pt(pzR(n,n)py)2] (R(n,n) = C6H3(OCnH2n+1)2, n = 4–18) has been prepared, and their mesomorphic and photophysical properties are described. The compounds were isolated as red (n = 4–8) or yellow (n = 10–18) solids at room temperature, but the first ones were converted to yellow crystals by slow evaporation of a chloroform–acetone mixed solution. All of them behave as discotic liquid crystal materials, exhibiting hexagonal columnar mesophases (Colh) in a wide range of temperatures. Photoluminescence studies in the solid state at variable temperatures showed a high emission in the liquid crystalline phase, which was significantly red-shifted with respect to the yellow-green emission of the solid state. This photophysical change was attributed to the formation of aggregates through Pt(dz2)–Pt(dz2) interactions, thereby giving rise to the metal–metal-to-ligand charge transfers (3MMLCT) responsible for the luminescence observed. Taking advantage of these properties we have fabricated polymeric solid supports doped with the platinum complex [Pt(pzR(10,10)py)2], which can be used as temperature sensors for real technological applications. In addition, the Pt–bispyrazolate complexes and their corresponding pyrazole ligands have been proved to be useful as chemosensors towards Pd2+, Zn2+, Cd2+ and Hg2+ metal ions.