Pinheiro, C, Parola AJ, Pina F, Laia CAT.
2009.
Electrochromism of Crystal Violet Lactone in the presence of Fe(III)/Fe(II) redox pair, 2009. Electrochimica Acta. 54:5593-5597.
AbstractSelective interaction between Crystal Violet Lactone and Fe(3+)/Fe(2+) in methanol leads to a reversible ionochromic colour change. This interaction can be controlled electrochemically, in order to achieve reversible colour changes with high contrast between colourless and dark blue solutions. The presented system is proposed as an alternative electrochromic solution. (C) 2009 Elsevier Ltd. All rights reserved.
Petrov, V, Gomes R, Parola AJ, Pina F.
2009.
Flash photolysis and stopped flow studies of the 2'-methoxyflavylium network in aq. acidic and alkaline solution, 2009. Dyes and Pigments. 80:149-155.
AbstractThe rate and equilibrium constants of the network of chemical species involving the dye 2'-methoxyflavylium tetrafluoroborate were characterized using stopped flow and flash photolysis in both acidic and alkaline aqueous solution. The trans-chalcone is the thermodynamic stable species in acidic solutions 2 < pH < 7; irradiation of trans-chalcone at low pH leads to the corresponding coloured flavylium cation. The system reverts to its initial state in a few hours, in the dark. The kinetics of the various steps in the system were determined; flash photolysis revealed that the rate determining process of flavylium formation is the ring closure to give the corresponding hemiketal. In alkaline medium the ionized transchalcone is the stable form and clear evidence for the existence of a hemiketal species was obtained. A write-read-erase cycle can be performed with this compound. (c) 2008 Elsevier Ltd. All rights reserved.
Gomes, R, Parola AJ, Bastkowski F, Polkowska J, Klarner FG.
2009.
Host-Guest Interactions between Molecular Clips and Multistate Systems Based on Flavylium Salts, 2009. Journal of the American Chemical Society. 131:8922-8938.
AbstractFlavylium salts contain the basic structure and show a pH-dependent sequence of reactions identical to natural anthocyanins, which are responsible for most of the red and blue colors of flowers and fruits. In this work we investigated the effect of the water-soluble molecular clips C1 and C2 substituted by hydrogen phosphate or sulfate groups on the stability and reactions of the flavylium salts 1-4 by the use of UV-vis absorption, fluorescence, and NMR spectroscopy as well as of the time-resolved pH jump and flash photolysis methods. Clip C1 forms highly stable host-guest complexes with the flavylium salts 1 and 2 and the quinoidal base 3A in methanol. The binding constants were determined by fluorometric titration to be log K = 4.1, 4.7, and 5.6, respectively. Large complexation-induced (1)H NMR shifts of guest signals, Delta delta(max), indicate that in the case of the flavylium salts 1 and 2 the pyrylium ring and in the case of the quinoidal base 3A the o-hydroxyquinone ring are preferentially bound inside the clip cavity. Due to the poor solubility of these host-guest complexes in water, the association constants could be only determined in highly diluted aqueous solution by UV-vis titration experiments for the complex formation of clip C1 with the flavylium salt 3AH(+) at pH = 2 and the quinoidal base 3A at pH = 5.3 to be log K = 4.9 for both complexes. Similar results were obtained for the formation of the complexes of the sulfate-substituted clip C2 with flavylium salt 4AH(+) and its quinoidal base 4A which are slightly better soluble in water (log K = 4.3 and 4.0, respectively). According to the kinetic analysis (performed by using the methods mentioned above) the thermally induced trans-cis chalcone isomerization (4Ct -> 4Cc) and the H(2)O addition to flavylium cation 4AH(+) followed by H(+) elimination leading to hemiketal 4B are both retarded in the presence of clip C2, whereas the photochemically induced trans-cis isomerization (4Ct -> 4Cc) is not affected by clip C2. The results presented here are explained with dominating hydrophobic interactions between the molecular clips and the flavylium guest molecules. The other potential interactions (ion-ion, cation-pi, pi-pi, and CH-pi), which certainly determine the structures of these host-guest complexes to a large extent, seem to be of minor importance for their stability.
Pinheiro, C, Parola AJ, Laia CAT, Camara A, Pina F.
2009.
Multiresponsive chromogenic systems operated by light and electrical inputs, 2009. New Journal of Chemistry. 33:2144-2147.
AbstractIn the framework of supramolecular chemistry, a three component system constituted by Fe(3+)/Fe(2+), crystal violet lactone (CVL) and a spiropyran (SPI) leads to three coloured states, cyan, magenta and yellow, as well as a transparent state, each independently addressable by light and electrical input. The system profits from fine speciation Fe(3+)/Fe(2+) complexes with CVL and SPI. Redox stimulus operates the metal, leading to different coloured complexes (ionochromism), while light stimulus operates the SPI component (photochromism).
Diniz, AM, Gomes R, Parola AJ, Laia CAT, Pina F.
2009.
Photochemistry of 7-Hydroxy-2-(4-hydroxystyryl)-1-benzopyrylium and Related Compounds, 2009. Journal of Physical Chemistry B. 113:719-727.
Abstract2-Styryl-1-benzopyrylium derivatives exhibit deeper hues and absorption spectra that are substantially red-shifted when compared with their 2-phenyl-1-benzopyrylium analogues. They follow the same pH and light-dependent network of chemical reactions previously described for 2-phenyl-1-benzopyrylium compounds. In this work, the photochromic properties of 7-hydroxy-2-(4-hydroxystyryl)-1-benzopyrylium chloride are reported. This compound was fully characterized by UV-vis absorption, fluorescence emission, pH jumps, and flash photolysis, and its properties were compared with the analogue 7,4'-dihydroxyflavylium (7-hydroxy-2-(4-hydroxyphenyl)-1- benzopyrylium). The trans-chalcones of both compounds lacking the hydroxyl in position 2 were synthesized and used as model compounds since they exhibit cis-trans isomerization but cannot be involved in the other processes resulting from the ring closure. The transient absorption of two triplets attributed to the chalcones Ct/Ct(-), and a tautomer was detected by nanosecond flash photolysis, independent of the existence of the 2-hydroxyl substituent. The experimental results are compatible with the main formation of cis-chalcone from the singlet state. In the case of the styryl derivatives, the fraction of triplet formed from excitation of Ct is much higher, and the fraction of isomerization is much smaller. For this reason, the photochemistry of 7-hydroxy-2-(4-hydroxystyryl)-1-benzopyrylium in water is much less efficient than that of its parent 7,4'-dihydroxyflavylium; however, in the presence of CTAB micelles, intense red colors can be obtained upon irradiation, confirming the usefulness of this family of compounds as photochromic systems.
Gomes, R, Diniz AM, Jesus A, Parola AJ, Pina F.
2009.
The synthesis and reaction network of 2-styryl-1-benzopyrylium salts: An unexploited class of potential colorants, 2009. Dyes and Pigments. 81:69-79.
AbstractThe syntheses, thermodynamic and kinetic properties of a series of 2-styryl-1-benzopyrylium compounds are reported. This family of compounds was found to follow the same pH- and light-dependent network of chemical reactions previously described for flavylium (2-phenyl-1-benzopyrylim) compounds. However, 2-styryl-1-benzopyrylium compounds exhibit absorption spectra substantially red shifted when compared with flavylium analogues (up to 90 nm). In particular, a photochromic system switching from yellow to light blue based on derivatives of natural anthocyanins is for the first time documented. (C) 2008 Elsevier Ltd. All rights reserved.
Roque, ACA, Bispo S, Pinheiro ARN, Antunes JMA, Gonçalves D, Ferreira HA.
2009.
Antibody immobilization on magnetic particles. Journal of Molecular Recognition. 22:77–82., Number 2
AbstractMagnetic particles {(MNPs)} offer attractive possibilities in biotechnology. {MNPs} can get close to a target biological entity, as their controllable sizes range from a few nanometres up to tens of nanometres, and their surface can be modified to add affinity and specificity towards desired molecules. Additionally, they can be manipulated by an external magnetic field gradient. In this work, the study of ferric oxide {(Fe3O4)} {MNPs} with different coating agents was conducted, particularly in terms of strategies for antibody attachment at the surfaces (covalent and physical adsorption) and the effects of blocking buffer composition and incubation times on the specific and non-specific interactions observed. The considered biological model system consisted of a coating antibody (goat {IgG)}, bovine serum albumin {(BSA)} as blocking agent, and a complementary antibody labelled with {FITC} (anti-goat {IgG).} The detection of antibody binding was followed by fluorescence microscopy and the intensity of the signals quantified. The ratio between the mean grey values of negative and positive controls, as well as the maximum intensity attainable in positive controls, were considered in the evaluation of the assays efficiency. The covalent immobilization of the coating antibody was more successful as opposed to protein adsorption. For covalent immobilization, silica-coated {MNPs}, a 5% (w/v) concentration of {BSA} in the blocking buffer and incubation times of 1 h produced the best results in terms of assay sensitivity. However, when conducting the assay for incubation periods of 10 min, the fluorescence signal was reduced by 44% but the assay specificity was maintained.
Hussain, A, Pina AS, Roque ACA.
2009.
Bio-recognition and detection using liquid crystals. Biosensors and Bioelectronics. 25:1–8., Number 1
AbstractLiquid crystals {(LCs)} are used extensively by the electronics industry as display devices. Advances in the understanding of the liquid crystalline phase and the chemistry therein lead to the development of {LC} exhibiting faster switching speed with greater twist angle. This in turn lead to the emergence of liquid crystal displays, rendering dial-and-needle based displays (such as those used in various meters) and cathode ray tubes obsolete. In this article, we review the history of {LC} and their emergence as an invaluable material for display devices and the more recent discovery of their use as sensing elements in biosensors. This new application of {LC} as tools in the development of fast and simple biosensors is envisaged to gain more importance in the foreseeable future.
Ribeiro, MP, Espiga A, Silva D, Baptista P, Henriques J, Ferreira C, Silva JC, Borges JP, Pires E, Chaves P, Correia IJ.
2009.
Development of a new chitosan hydrogel for wound dressing. Wound repair and regeneration. 17(6):817–824., Number 6: Blackwell Publishing Inc
AbstractWound healing is a complex process involving an integrated response by many different cell types and growth factors in order to achieve rapid restoration of skin architecture and function. The present study evaluated the applicability of a chitosan hydrogel (CH) as a wound dressing. Scanning electron microscopy analysis was used to characterize CH morphology. Fibroblast cells isolated from rat skin were used to assess the cytotoxicity of the hydrogel. CH was able to promote cell adhesion and proliferation. Cell viability studies showed that the hydrogel and its degradation by-products are noncytotoxic. The evaluation of the applicability of CH in the treatment of dermal burns in Wistar rats was performed by induction of full-thickness transcutaneous dermal wounds. Wound healing was monitored through macroscopic and histological analysis. From macroscopic analysis, the wound beds of the animals treated with CH were considerably smaller than those of the controls. Histological analysis revealed lack of a reactive or a granulomatous inflammatory reaction in skin lesions with CH and the absence of pathological abnormalities in the organs obtained by necropsy, which supported the local and systemic histocompatibility of the biomaterial. The present results suggest that this biomaterial may aid the re-establishment of skin architecture.
Pina, AS, Hussain A, Roque ACA.
2009.
An historical overview of drug discovery. Ligand-Macromolecule Interactions in Drug Discovery. (
Roque, A. C. A., Ed.).:3-12., USA: Humana Press Inc.
AbstractDrug Discovery in modern times straddles three main periods. The first notable period can be traced to the nineteenth century where the basis of drug discovery relied on the serendipity of the medicinal chemists. The second period commenced around the early twentieth century when new drug structures were found, which contributed for a new era of antibiotics discovery. Based on these known structures, and with the development of powerful new techniques such as molecular modelling, combinatorial chemistry, and automated high-throughput screening, rapid advances occurred in drug discovery towards the end of the century. The period also was revolutionized by the emergence of recombinant DNA technology, where it became possible to develop potential drugs target candidates. With all the expansion of new technologies and the onset of the "Omics" revolution in the twenty-first century, the third period has kick-started with an increase in biopharmaceutical drugs approved by FDA/EMEA for therapeutic use.
Albuquerque, SS, Carret C, Grosso AR, Tarun AS, Peng X, Kappe SHII, Prudêncio M, Mota MM.
2009.
Host cell transcriptional profiling during malaria liver stage infection reveals a coordinated and sequential set of biological events. BMC Genomics. 10:270., Number 1
AbstractBACKGROUND:
Plasmodium sporozoites migrate to the liver where they traverse several hepatocytes before invading the one inside which they will develop and multiply into thousands of merozoites. Although this constitutes an essential step of malaria infection, the requirements of Plasmodium parasites in liver cells and how they use the host cell for their own survival and development are poorly understood.
RESULTS:
To gain new insights into the molecular host-parasite interactions that take place during malaria liver infection, we have used high-throughput microarray technology to determine the transcriptional profile of P. berghei-infected hepatoma cells. The data analysis shows differential expression patterns for 1064 host genes starting at 6 h and up to 24 h post infection, with the largest proportion correlating specifically with the early stages of the infection process. A considerable proportion of those genes were also found to be modulated in liver cells collected from P. yoelii-infected mice 24 and 40 h after infection, strengthening the data obtained with the in vitro model and highlighting genes and pathways involved in the host response to rodent Plasmodium parasites.
CONCLUSION:
Our data reveal that host cell infection by Plasmodium sporozoites leads to a coordinated and sequential set of biological events, ranging from the initial stage of stress response up to the engagement of host metabolic processes and the maintenance of cell viability throughout infection.
Godinho, MH, Canejo JP, Pinto LFV, Borges JP, Teixeira PIC.
2009.
How to mimic the shapes of plant tendrils on the nano and microscale: spirals and helices of electrospun liquid crystalline cellulose derivatives. Soft Matter. 5(14):2772–2776., Number 14: Royal Society of Chemistry
AbstractWe show that suspended nano and microfibres electrospun from liquid crystalline cellulosic solutions will curl into spirals if they are supported at just one end, or, if they are supported at both ends, will twist into a helix of one handedness over half of its length and of the opposite handedness over the other half, the two halves being connected by a short straight section. This latter phenomenon, known as perversion, is a consequence of the intrinsic curvature of the fibres and of a topological conservation law. Furthermore, agreement between theory and experiment can only be achieved if account is taken of the intrinsic torsion of the fibres. Precisely the same behaviour is known to be exhibited by the tendrils of climbing plants such as Passiflora edulis, albeit on a lengthscale of millimetres, i.e., three to four orders of magnitude larger than in our fibres. This suggests that the same basic, coarse-grained physical model is applicable across a range of lengthscales.
Pokkuluri, PR, Londer YY, Wood SJ, Duke NEC, Morgado L, Salgueiro CA, Schiffer M.
2009.
Outer membrane cytochrome c, OmcF, from Geobacter sulfurreducens: High structural similarity to an algal cytochrome c6. Proteins: Structure, Function, and Bioinformatics. 74(1):266-270.
Abstract
Fonseca, BM, Saraiva IH, Paquete CM, Soares CM, Pacheco I, Salgueiro CA, Louro RO.
2009.
The tetraheme cytochrome from Shewanella oneidensis MR-1 shows thermodynamic bias for functional specificity of the hemes. Journal of Biological Inorganic Chemistry. 14(3):375-385.
AbstractBacteria of the genus Shewanella contain an abundant small tetraheme cytochrome in their periplasm when growing anaerobically. Data collected for the protein isolated from S. oneidensis MR-1 and S. frigidimarina indicate differences in the order of oxidation of the hemes. A detailed thermodynamic characterization of the cytochrome from S. oneidensis MR-1 in the physiological pH range was performed, with data collected in the pH range 5.5-9.0 from NMR experiments using partially oxidized samples and from redox titrations followed by visible spectroscopy. These data allow the parsing of the redox and redox-protonation interactions that occur during the titration of hemes. The results show that electrostatic effects dominate the heme-heme interactions, in agreement with modest redox-linked structural modifications, and protonation has a considerable influence on the redox properties of the hemes in the physiological pH range. Theoretical calculations using the oxidized and reduced structures of this protein reveal that the bulk redox-Bohr effect arises from the aggregate fractional titration of several of the heme propionates. This detailed characterization of the thermodynamic properties of the cytochrome shows that only a few of the multiple microscopic redox states that the protein can access are significantly populated at physiological pH. On this basis a functional pathway for the redox activity of the small tetraheme cytochrome from S. oneidensis MR-1 is proposed, where reduction and protonation are thermodynamically coupled in the physiological range. The differences between the small tetraheme cytochromes from the two organisms are discussed in the context of their biological role.
Morgado, L, Fernandes AP, Londer YY, Pokkuluri PR, Schiffer M, Salgueiro CA.
2009.
Thermodynamic characterization of the redox centres in a representative domain of a novel c-type multihaem cytochrome. Biochemical Journal. 420(3):485-492.
AbstractMultihaem cytochromes that could form protein “nanowires” were identified in the Geobacter sulfurreducens genome, and represent a new type of multihaem cytochrome. The sequences of these proteins, two with 12 haems (GSU1996, GSU0592) and one with 27 haems (GSU2210), suggest that they are formed with domains homologous to the trihaem cytochrome c7. Although all three haems have bis-His co-ordination in cytochromes c7, in each domain of the above polymers, the haem equivalent to haem IV has His-Met co-ordination. We previously determined the structure and measured the macroscopic redox potential of one representative domain (domain C) of a dodecahaem cytochrome (GSU1996). In the present study, the microscopic redox properties of the individual haem groups of domain C were determined using NMR and UV–visible spectroscopies. The reduction potentials of the haems for the fully reduced and protonated protein are different from each other (haem I, −106 mV; haem III, −136 mV; and haem IV, −125 mV) and are strongly modulated by redox interactions. This result is rather surprising since the His-Met co-ordinated haem IV does not have the highest potential as was expected. The polypeptide environment of each haem group and the strong haem pairwise redox interactions must play a dominant role in controlling the individual haem potentials. The strong redox interactions between the haems extend the range of their operating potentials at physiological pH (haem I, −71 mV, haem III, −146 mV and haem IV, −110 mV). Such a modulation in haem potentials is likely to have a functional significance in the metabolism of G. sulfurreducens.
Pessanha, M, Rothery EL, Miles CS, Reid GA, Chapman SK, Louro RO, Turner DL, Salgueiro CA, Xavier AV.
2009.
Tuning of functional heme reduction potentials in Shewanella fumarate reductases. Biochimica et Biophysica Acta (BBA) - Bioenergetics. 1787(2):113-120.
AbstractThe fumarate reductases from S. frigidimarina NCIMB400 and S. oneidensis MR-1 are soluble and monomeric enzymes located in the periplasm of these bacteria. These proteins display two redox active domains, one containing four c-type hemes and another containing FAD at the catalytic site. This arrangement of single-electron redox co-factors leading to multiple-electron active sites is widespread in respiratory enzymes. To investigate the properties that allow a chain of single-electron co-factors to sustain the activity of a multi-electron catalytic site, redox titrations followed by NMR and visible spectroscopies were applied to determine the microscopic thermodynamic parameters of the hemes. The results show that the redox behaviour of these fumarate reductases is similar and dominated by a strong interaction between hemes II and III. This interaction facilitates a sequential transfer of two electrons from the heme domain to FAD via heme IV.
Abrantes, M, Paz FAA, Valente AA, Pereira CCL, Gago S, Rodrigues AE, Klinowski J, Pillinger M, Goncalves IS.
2009.
Amino acid-functionalized cyclopentadienyl molybdenum tricarbonyl complex and its use in catalytic olefin epoxidation. Journal of Organometallic Chemistry. 694:1826-1833., Number 12
Abstractn/a