Luís Gales

Prenylated derivatives of baicalein and 3,7-dihydroxyflavone: Synthesis and study of their effects on tumor cell lines growth, cell cycle and apoptosis

Fourteen baicalein and 3,7-dihydroxyflavone derivatives were synthesized and evaluated for their inhibitory activity against the in vitro growth of three human tumor cell lines. The synthetic approaches were based on the reaction with prenyl or geranyl bromide in alkaline medium, followed by cyclization of the respective monoprenylated derivative. Dihydropyranoflavonoids were also obtained by one-pot synthesis, using Montmorillonite K10 clay as catalyst combined with microwave irradiation. In vitro screening of the compounds for cell growth inhibitory activity revealed that the presence of one geranyl group was associated with a remarkable increase in the inhibitory activity. Moreover, for the 3,7-dihydroxyflavone derivatives a marked increase in growth inhibitory effect was also observed for compounds with furan and pyran fused rings. The most active compounds were also studied regarding their effect on cell cycle profile and induction of apoptosis. Overall the results point to the relevant role of the prenylation of flavone scaffold in the growth inhibitory activity of cancer cells.

Removal of acetone, ethyl acetate and ethanol vapors from air using a hollow fiber PDMS membrane module

Abstract Polyetherimide (PEI) membranes coated with polydimethylsiloxane (PDMS) are frequently used for removing volatile organic compounds (VOCs) from air. An experimental and theoretical study was performed to evaluate the effects of the feed flow rate, feed VOC composition, feed and permeate total pressure using a hollow fiber membrane module for separating acetone, ethyl acetate and ethanol from air. The results are discussed on a basis of permeate flux and permeate VOC concentration. It was found that the hollow fiber module provides good separation capabilities, in spite of the observed PEI sub-layer mass transport resistance, and the proposed model fits the experimental results fairly well.

Peptide-based solids: porosity and zeolitic behavior

Among the greatest challenges in the field of microporous solids is the development of “smart” materials, displaying environment-triggered property tuning. These could be used both in traditional and new applications of microporous materials. In this context, supramolecular peptide-based solids have recently emerged as interesting alternatives to standard microporous solids, such as zeolites and carbon molecular sieves. They possess framework and conformational flexibility, are kinetically stable and reasonably thermally resistant. Important properties such as pore size and inner wall chemistry can be controlled through appropriate chemical modification of the peptide molecules. Peptide-based porous solids have permanent microporosity, often with molecularly sized cavities created by removal of co-crystallised solvent. Some have already been successfully tested as adsorbents and permselective materials, confirming their potential. This review covers the identification, synthesis, characterization techniques and properties of peptide-based microporous solids, discussing their most unique functionalities.

Human transthyretin in complex with iododiflunisal: structural features associated with a potent amyloid inhibitor

Ex vivo and in vitro studies have revealed the remarkable amyloid inhibitory potency and specificity of iododiflunisal in relation to transthyretin [Almeida, Macedo, Cardoso, Alves, Valencia, Arsequell, Planas and Saraiva (2004) Biochem. J. 381, 351-356], a protein implicated in familial amyloidotic polyneuropathy. In the present paper, the crystal structure of transthyretin complexed with this diflunisal derivative is reported, which enables a detailed analysis of the protein-ligand interactions. Iododiflunisal binds very deep in the hormone-binding channel. The iodine substituent is tightly anchored into a pocket of the binding site and the fluorine atoms provide extra hydrophobic contacts with the protein. The carboxylate substituent is involved in an electrostatic interaction with the N(zeta) of a lysine residue. Moreover, ligand-induced conformational alterations in the side chain of some residues result in the formation of new intersubunit hydrogen bonds. All these new interactions, induced by iododiflunisal, increase the stability of the tetramer impairing the formation of amyloid fibrils. The crystal structure of this complex opens perspectives for the design of more specific and effective drugs for familial amyloidotic polyneuropathy patients.

Hysteresis in the cyclic adsorption of acetone, ethanol and ethyl acetate on activated carbon

This paper describes the adsorption behaviour of three solvents (ethyl acetate, ethanol and acetone) on BASF activated carbon at various temperatures (15–80°C). The adsorption isotherms show hysteresis which persists to very low pressures (Low Pressure Hysteresis, LPH). After prolonged outgassing (<10−2 mbar) at 473–523 K we found that LPH still remains. This LPH is more pronounced for ethyl acetate at higher temperatures. Due to its importance on Pressure Swing Adsorption (PSA) units design and operation we discuss the adsorption behaviour when adsorption/desorption cycles are applied. We concluded that after approximately five cycles the system reaches what we called ‘limiting isotherm’ where adsorption and desorption branches cannot be distinguished within experimental error. This isotherm is independent of system history if a sufficiently low pressure and/or a sufficiently high pressure is used for cycling and in these conditions the adsorbent has higher capacity than when fresh. Also the Langmuir equation correlates quite well with the limiting isotherms.

Iodine Atoms: A New Molecular Feature for the Design of Potent Transthyretin Fibrillogenesis Inhibitors

The thyroid hormone and retinol transporter protein known as transthyretin (TTR) is in the origin of one of the 20 or so known amyloid diseases. TTR self assembles as a homotetramer leaving a central hydrophobic channel with two symmetrical binding sites. The aggregation pathway of TTR into amiloid fibrils is not yet well characterized but in vitro binding of thyroid hormones and other small organic molecules to TTR binding channel results in tetramer stabilization which prevents amyloid formation in an extent which is proportional to the binding constant. Up to now, TTR aggregation inhibitors have been designed looking at various structural features of this binding channel others than its ability to host iodine atoms. In the present work, greatly improved inhibitors have been designed and tested by taking into account that thyroid hormones are unique in human biochemistry owing to the presence of multiple iodine atoms in their molecules which are probed to interact with specific halogen binding domains sitting at the TTR binding channel. The new TTR fibrillogenesis inhibitors are based on the diflunisal core structure because diflunisal is a registered salicylate drug with NSAID activity now undergoing clinical trials for TTR amyloid diseases. Biochemical and biophysical evidence confirms that iodine atoms can be an important design feature in the search for candidate drugs for TTR related amyloidosis.

Xanthones-A Structural Perspective

Xanthones, synthesized or isolated from a natural source, display a wide range of biological and pharmacological activities. In a few cases, their chemical characterization has involved the structure elucidation by single crystal X-ray diffraction. The purpose of this review is to assess in detail this three-dimensional structural data, and thus contribute to a better understanding of the molecular mechanisms involved in the different biological activities presented by xanthones.

Potential use of ultrasound to promote protein crystallization

This work shows promising applications of ultrasound in promoting protein crystallization, which is important for structure determination by X-ray crystallography. It was observed that ultrasound can be used as a nucleation promoter as it decreases the energy barrier for crystal formation. Crystallization experiments on egg-white lysozyme were carried out with and without ultrasonic irradiation using commercial crystallization plates placed in temperature-controlled water baths. The nucleation-promoting effect introduced by ultrasound is illustrated by the reduction of the metastable zone width, as measured by the isothermal microbatch technique. The same effect was confirmed by the increased number of conditions leading to the formation of crystals when vapour diffusion techniques were carried out in the presence of ultrasound. By inducing faster nucleation, ultrasound leads to protein crystals grown at low supersaturation levels, which are known to have better diffraction properties. In fact, X-ray diffraction data sets collected using 13 lysozyme crystals (seven grown with ultrasound and six without) show an average 0.1 A improvement in the resolution limit when ultrasound was used (p < 0.10). Besides the immediate application of ultrasound in nucleation promotion, the preliminary diffraction results also suggest a promising application in crystal quality enhancement.

Production and characterization of extracellular carbohydrate polymer from Cyanothece sp. CCY 0110

Cyanobacterial extracellular polymeric substances (EPS) are heteropolysaccharides that possess characteristics suitable for industrial applications, notably a high number of different monomers, strong anionic nature and high hydrophobicity. However, systematic studies that unveil the conditions influencing EPS synthesis and/or its characteristics are mandatory. In this work, Cyanothece sp. CCY 0110 was used as model organism. Our results revealed that this strain is among the most efficient EPS producers, and that the amount of RPS (released polysaccharides) is mainly related to the number of cells, rather than to the amount produced by each cell. Light was the key parameter, with high light intensity enhancing significantly RPS production (reaching 1.8 g L(-1)), especially in the presence of combined nitrogen. The data showed that RPS are composed by nine different monosaccharides (including two uronic acids), the presence of sulfate groups and peptides, and that the polymer is remarkably thermostable and amorphous in nature.

The Crystal and Solution Structures of Glyceraldehyde-3-phosphate Dehydrogenase Reveal Different Quaternary Structures.

The presence of an isoform of glyceraldehyde-3-phosphate dehydrogenase (kmGAPDH1p) associated with the cell wall of a flocculent strain of Kluyveromyces marxianus was the first report of a non-cytosolic localization of a glycolytic enzyme, but the mechanism by which the protein is transported to the cell surface is not known. To identify structural features that could account for the multiple localizations of the protein, the three-dimensional structure of kmGAPDH1p was determined by x-ray crystallography and small angle x-ray scattering. The x-ray crystallographic structure of kmGAPDH1p revealed a dimer, although all GAPDH homologs studied thus far have a tetrameric structure with 222 symmetry. Interestingly, the structure of kmGAPDH1p in solution revealed a tetramer with a 70° tilt angle between the dimers. Moreover, the separation between the centers of the dimers composing the kmGAPDH1p tetramer diminished from 34 to 30 Å upon NAD+ binding, this latter value being similar to the observed in the crystallographic models of GAPDH homologs. The less compact structure of apo-kmGAPDH1p could already be the first image of the transition intermediate between the tetramer observed in solution and the dimeric form found in the crystal structure, which we postulate to exist in vivo because of the proteins multiple subcellular localizations in this yeast species.