Joana Oliveira - Academia.edu (original) (raw)

Papers by Joana Oliveira

Research paper thumbnail of Mid-infrared observations of young stellar objects in the vicinity of sigma Orionis

We present new mid-infrared observations of objects in the vicinity of the O-star sigma Orionis, ... more We present new mid-infrared observations of objects in the vicinity of the O-star sigma Orionis, obtained with TIMMI-2 at ESO. By constraining their near- and mid-infrared spectral energy distributions, we established the nature of previously known IRAS sources and identified new mid-infrared sources as young stellar objects with circumstellar disks, likely massive members of the sigma Ori cluster. For two of these objects we have obtained spectroscopy in the 8-13 micron range in order to investigate the chemistry of the dust grains. TX Ori exhibits a typical silicate emission feature at 10 micron, with a feature at about 11.2 micron that we identify as due to crystalline olivine. The IRAS 05358-0238 spectrum is very unusual, with a weak silicate feature and structure in the range 10-12 micron that may be explained as due to self-absorbed forsterite. We also provide the first evidence for the presence of circumstellar disks in the jet sources Haro 5-39/HH 447, V510 Ori/HH 444 and V603 Ori/HH 445.

Research paper thumbnail of Screening of Portisins (Vinylpyranoanthocyanin Pigments) in Port Wine by LC/DAD-MS

Food Science and Technology International, 2005

Samples of a two-year-old Port red wine were fractionated by Toyopearl gel column chromatography ... more Samples of a two-year-old Port red wine were fractionated by Toyopearl gel column chromatography yielding different coloured fractions. Anthocyanin-derived compounds were tentatively identified by LC/DAD-MS in the different eluted fractions. Several pigments were found to correspond to a recently reported family of pyranoanthocyanin compounds named portisins, supposedly arising from the reaction between anthocyanin-pyruvic acid adducts and flavanols in the presence

Research paper thumbnail of The SMC as a probe of dust in the early Universe (GTO)

We propose a comprehensive spectroscopic survey of the Small Magellanic Cloud (SMC), using the IR... more We propose a comprehensive spectroscopic survey of the Small Magellanic Cloud (SMC), using the IRS and MIPS-SED. The SMC has a metallicity similar to high-redshift galaxies, and its proximity makes it a spatially resolved proxy for star-forming galaxies in the distant, early Universe. The sensitivity of the Spitzer Space Telescope allows us to to observe dust in nearly every stage of its life cycle in the SMC so that we can study how the interactions of dust and its host galaxy differ from more metal-rich systems like the Galaxy and the LMC. Our proposed observations concentrate on important classes underrepresented in the archive of SMC spectra such as young stellar objects, compact H II regions, objects in transition to and from the asymptotic giant branch, and supergiants. These observations, in combination with those already in the archive, will give us a complete picture of the dust in a metal-poor star-forming galaxy similar to those in the early Universe. We request 116 hours, 62 as IRS GTO time and 54 as GO time.

Research paper thumbnail of New Family of Bluish Pyranoanthocyanins

Journal of biomedicine & biotechnology, 2004

Research paper thumbnail of Dust Production and Mass Loss in the Galactic Globular Cluster NGC 362

We investigate dust production and stellar mass loss in the Galactic globular cluster NGC 362. Du... more We investigate dust production and stellar mass loss in the Galactic globular cluster NGC 362. Due to its close proximity to the Small Magellanic Cloud (SMC), NGC 362 was imaged with the IRAC and MIPS cameras onboard the Spitzer Space Telescope as part of the Surveying the Agents of Galaxy Evolution (SAGE-SMC) Spitzer Legacy program. We detect several cluster members near the tip of the Red Giant Branch that exhibit infrared excesses indicative of circumstellar dust and find that dust is not present in measurable quantities in stars below the tip of the Red Giant Branch. We modeled the spectral energy distribution (SED) of the stars with the strongest IR excess and find a total cluster dust mass-loss rate of 3.0(+2.0/-1.2) x 10^-9 solar masses per year, corresponding to a gas mass-loss rate of 8.6(+5.6/-3.4) x 10^-6 solar masses per year, assuming [Fe/H] = -1.16. This mass loss is in addition to any dust-less mass loss that is certainly occurring within the cluster. The two most extreme stars, variables V2 and V16, contribute up to 45% of the total cluster dust-traced mass loss. The SEDs of the more moderate stars indicate the presence of silicate dust, as expected for low-mass, low-metallicity stars. Surprisingly, the SED shapes of the stars with the strongest mass-loss rates appear to require the presence of amorphous carbon dust, possibly in combination with silicate dust, despite their oxygen-rich nature. These results corroborate our previous findings in omega Centauri.

Research paper thumbnail of The State of the Gas and the Relation between Gas and Star Formation at Low Metallicity: The Small Magellanic Cloud

Astrophysical Journal, 2011

We compare atomic gas, molecular gas, and the recent star formation rate (SFR) inferred from H-al... more We compare atomic gas, molecular gas, and the recent star formation rate (SFR) inferred from H-alpha in the Small Magellanic Cloud (SMC). By using infrared dust emission and local dust-to-gas ratios, we construct a map of molecular gas that is independent of CO emission. This allows us to disentangle conversion factor effects from the impact of metallicity on the formation and star formation efficiency of molecular gas. On scales of 200 pc to 1 kpc we find a characteristic molecular gas depletion time of ~1.6 Gyr, similar to that observed in the molecule-rich parts of large spiral galaxies on similar spatial scales. This depletion time shortens on much larger scales to ~0.6 Gyr because of the presence of a diffuse H-alpha component, and lengthens on much smaller scales to ~7.5 Gyr because the H-alpha and H2 distributions differ in detail. We estimate the systematic uncertainties in our measurement to be a factor of 2-3. We suggest that the impact of metallicity on the physics of star formation in molecular gas has at most this magnitude. The relation between SFR and neutral (H2+HI) gas surface density is steep, with a power-law index ~2.2+/-0.1, similar to that observed in the outer disks of large spiral galaxies. At a fixed total gas surface density the SMC has a 5-10 times lower molecular gas fraction (and star formation rate) than large spiral galaxies. We explore the ability of the recent models by Krumholz et al. (2009) and Ostriker et al. (2010) to reproduce our observations. We find that to explain our data at all spatial scales requires a low fraction of cold, gravitationally-bound gas in the SMC. We explore a combined model that incorporates both large scale thermal and dynamical equilibrium and cloud-scale photodissociation region structure and find that it reproduces our data well, as well as predicting a fraction of cold atomic gas very similar to that observed in the SMC.

Research paper thumbnail of A novel synthetic pathway to vitisin B compounds

Tetrahedron Letters, 2009

The hemi-synthesis of vitisin B compounds is described herein for the first time through a new, s... more The hemi-synthesis of vitisin B compounds is described herein for the first time through a new, simple and suitable reaction of malvidin-3-glucoside and malvidin-3-O-coumaroylglucoside with vinyloxy-trimethylsilane. The obtained compounds were identified by LC/DAD-MS and fully characterized by NMR analysis for the first time.

Research paper thumbnail of ChemInform Abstract: Previous and Recent Advances in Pyranoanthocyanins Equilibria in Aqueous Solution

Research paper thumbnail of Flavanols: Catechins and Proanthocyanidins

Natural Products, 2013

Flavanols are a wide group of polyphenols that include flavan-3-ols (e.g., catechin and proanthoc... more Flavanols are a wide group of polyphenols that include flavan-3-ols (e.g., catechin and proanthocyanidins), flavan-4-ols, and flavan-3,4-diols. They arise from plant secondary metabolism through condensation of phenylalanine derived from the shikimate pathway with malonyl-CoA obtained from citrate that is produced by the tricarboxylic acid cycle, leading to the formation of the key precursor in the flavonoids biosynthesis: the naringenin chalcone. The exact nature of the molecular species that undergo polymerization and the mechanism of assembly in proanthocyanidins are still unknown. From a structural point of view, flavanols comprise a C15 (C6-C3-C6) general structure composed by a benzopyran moiety (A and C rings) with an additional aromatic ring (B ring) linked to carbon C-2 of C ring. Flavanols are present in nature in monomeric, oligomeric, and polymeric forms and differ from each other essentially in the configuration of carbon C-2, the hydroxylation/methoxylation pattern of the rings, the type of linkage between each unit, and the degree of galloylation. Flavanols in foods are described to present several beneficial effects such as antioxidant and anticarcinogenic properties and also contribute to the sensory properties of some food products, such as astringency and color. Some of these aspects are discussed herein.

Research paper thumbnail of SAGE-SMC: Surveying the Agents of Galaxy Evolution in the Tidally-Disrupted, Low-Metallicity Small Magellanic Cloud

Research paper thumbnail of Unusual Color Change of Vinylpyranoanthocyanin−Phenolic Pigments

Journal of Agricultural and Food Chemistry, 2010

Research paper thumbnail of Oxovitisins: A New Class of Neutral Pyranone-anthocyanin Derivatives in Red Wines

Journal of Agricultural and Food Chemistry, 2010

A new class of stable yellowish pigments with similar unique spectral features, displaying only a... more A new class of stable yellowish pigments with similar unique spectral features, displaying only a pronounced broad band around 370 nm in the UV-vis spectrum, was detected in an aged Port wine fraction obtained by a combination of chromatography on TSK Toyopearl HW-40(s) and Polyamide resins. These compounds were identified by liquid chromatography-diode array detector/electrospray ionization mass spectrometry (LC-DAD/ESI/MS) and shown to be direct oxidative derivatives of carboxy-pyranoanthocyanins (vitisins A) by synthesis experiments performed in a wine model solution. Their structures were fully characterized by MS and NMR spectroscopy ((1)H, gCOSY, gHSQC, and gHMBC) and found to correspond to alpha-pyranone-anthocyanins (lactone or pyran-2-one-anthocyanins). Their formation involves first the nucleophilic attack of water into the positively charged C-10 position of vitisins, followed by decarboxylation, oxidation, and dehydration steps, yielding a new and neutral pyranone structure. The occurrence of these novel pigments in aged wines points to a new pathway involving anthocyanin secondary products (vitisins A) as precursors of new pigments in subsequent stages of wine aging that may contribute to its color evolution.

Research paper thumbnail of Chemical Behavior of Methylpyranomalvidin-3- O -glucoside in Aqueous Solution Studied by NMR and UV−Visible Spectroscopy

The Journal of Physical Chemistry B, 2011

In the present work, the proton-transfer reactions of the methylpyranomalvidin-3-O-glucoside pigm... more In the present work, the proton-transfer reactions of the methylpyranomalvidin-3-O-glucoside pigment in water with different pH values was studied by NMR and UV-visible spectroscopies. The results showed four equilibrium forms: the methylpyranomalvidin-3-O-glucoside cation, the neutral quinoidal base, the respective anionic quinoidal base, and a dianionic base unprotonated at the methyl group. According to the NMR data, it seems that for methylpyranomalvidin-3-O-glucoside besides the acid-base equilibrium between the pyranoflavylium cation and the neutral quinoidal base, a new species is formed at pD 4.88-6.10. This is corroborated by the appearance of a new set of signals in the NMR spectrum that may be assigned to the formation of hemiketal/cis-chalcone species to a small extent. The two ionization constants (pK(a1) and pK(a2)) obtained by both methods (NMR and UV-visible) for methylpyranomalvidin-3-O-glucoside are in agreement (pK(a1) = 5.17 ± 0.03; pK(a2) = 8.85 ± 0.08; and pK(a1) = 4.57 ± 0.07; pK(a2) = 8.23 ± 0.04 obtained by NMR and UV-visible spectroscopies, respectively). Moreover, the fully dianionic unprotonated form (at the methyl group) of the methylpyranomalvidin-3-O-glucoside is converted slowly into a new structure that displays a yellow color at basic pH. On the basis of the results obtained through LC-MS and NMR, the proposed structure was found to correspond to the flavonol syringetin-3-glucoside.

Research paper thumbnail of NMR structure characterization of a new vinylpyranoanthocyanin–catechin pigment (a portisin)

Tetrahedron Letters, 2004

Research paper thumbnail of A novel synthetic pathway to vitisin B compounds

Tetrahedron Letters, 2009

The hemi-synthesis of vitisin B compounds is described herein for the first time through a new, s... more The hemi-synthesis of vitisin B compounds is described herein for the first time through a new, simple and suitable reaction of malvidin-3-glucoside and malvidin-3-O-coumaroylglucoside with vinyloxy-trimethylsilane. The obtained compounds were identified by LC/DAD-MS and fully characterized by NMR analysis for the first time.

Research paper thumbnail of Influence of anthocyanins and derivative pigments from blueberry ( Vaccinium myrtillus) extracts on MPP + intestinal uptake: A structure–activity approach

Food Chemistry, 2008

The aim of the present study was to investigate the influence of an anthocyanin extract (extract ... more The aim of the present study was to investigate the influence of an anthocyanin extract (extract I), and two other derivative extracts (extracts II and III), which are being developed aiming to be further applied in the food industry, on intestinal uptake of organic cations. For this purpose, the effect of these compounds on 3H-MPP+ uptake was evaluated in Caco-2 cells (an enterocyte-like cell line derived from a human colonic adenocarcinoma).Extracts I and III did not present any effect on 3H-MPP+ uptake. Extract II, an anthocyanin–pyruvic acid adduct extract, decreased organic cation uptake. Some phenolic molecules were also tested, aiming to study possible structural features responsible for these effects. The results are compatible with the hypothesis of phenolic molecules bearing a carboxylic group with extended electronic conjugation being the responsible feature for the inhibitory effect on 3H-MPP+ uptake.The use of these compounds in foodstuffs must be carefully assessed since interactions with organic cations present in the diet, as nutrients or xenobiotics, may affect their absorption and bioavailability. Type and complexity of the ingested compounds are important factors in this regard, and should be taken into consideration.

Research paper thumbnail of The phase-field model in tumor growth

Philosophical Magazine, 2011

Tumor growth is becoming a central problem in biophysics both from its social and medical interes... more Tumor growth is becoming a central problem in biophysics both from its social and medical interest and, more fundamentally, because it is a remarkable example of an emergent complex system. Focusing on the description of the spatial and dynamical features of tumor growth, in this paper we review recent tumor modeling approaches using a technique borrowed from materials science: the

Research paper thumbnail of Fluorescence Approach for Measuring Anthocyanins and Derived Pigments in Red Wine

Journal of Agricultural and Food Chemistry, 2013

A novel fluorescence approach to monitor the evolution of anthocyanins and derivatives in red win... more A novel fluorescence approach to monitor the evolution of anthocyanins and derivatives in red wine was developed. Some red table wines and Port wine with different vintage years were first tested with the aim to determine the ideal fluorescent conditions. The fluorescence contribution of both monomeric and polymeric anthocyanins was studied by comparing their emission spectra. By measuring the F700/F560 ratio on different wine samples and applying an inverted exponential function, it was possible to estimate the monomeric/polymeric anthocyanin absorbance ratio that is proportional to the relative content of the two classes of compounds. The methodology was further developed by using pure compounds representative of monomeric anthocyanins and anthocyanin-pyruvic acid adducts, namely, by using malvidin-3-O-glucoside and vitisin A. A fluorescence excitation ratio (FER350/550) was considered for estimating the absorbance ratio between vitisin A and malvidin-3-O-glucoside. Overall, this work aims to use fluorescence to monitor the evolution of anthocyanin derivatives and to distinguish them from their anthocyanin precursors, thereby allowing the evolution of anthocyanin pigments during wine aging to be monitored, but it also may be useful to determine age markers or even geographical markers.

Research paper thumbnail of Pyranoanthocyanin Dimers: A New Family of Turquoise Blue Anthocyanin-Derived Pigments Found in Port Wine

Journal of Agricultural and Food Chemistry, 2010

Research paper thumbnail of Reaction between Hydroxycinnamic Acids and Anthocyanin−Pyruvic Acid Adducts Yielding New Portisins

Journal of Agricultural and Food Chemistry, 2007

Three new anthocyanin-derived pigments were found to occur in a 2-year-old Port red wine. Their s... more Three new anthocyanin-derived pigments were found to occur in a 2-year-old Port red wine. Their structures were elucidated through LC/DAD-MS and NMR analysis and were found to correspond to a pyranoanthocyanin moiety linked to substituted cinnamyl substituents. The structures of these compounds are very similar to the one already reported for portisins, with a phenolic moiety replacing the catechin moiety. The newly formed anthocyanin-derived compounds display a bathochromic shift of the lambdamax ( approximately 540 nm) when compared with their anthocyanin-pyruvic acid adduct precursor (lambdamax = 511 nm), which may be due to the extended conjugation of the pi electrons in the structures of those pigments. Studies performed in model solutions helped to clarify the formation mechanism of these pigments that can result from the nucleophilic attack of the olefinic double bond of a hydroxycinnamic acid to the eletrophilic C-10 position of the anthocyanin-pyruvic acid adduct, followed by the loss of a formic acid molecule and decarboxylation. The chromatic characterization of these malvidin-3-glucoside-derived compounds revealed a higher resistance to discoloration against the nucleophilic attack by water and bisulfite when compared to malvidin-3-glucoside that is almost converted into its colorless hemiacetal form. However, the resistance to discoloration of these new pigments is not as high as the one reported for catechin-derived portisins. This could be explained by the presence of a smaller group (hydroxycinnamyl group), which does not protect so efficiently the chromophore against nucleophilic attack at the C-2 position. The occurrence of these pigments in red wine highlights new chemical pathways involving anthocyanin-pyruvic acid derivatives as precursors for the formation of new pigments in subsequent stages of wine aging that may contribute to its color evolution.

Research paper thumbnail of Mid-infrared observations of young stellar objects in the vicinity of sigma Orionis

We present new mid-infrared observations of objects in the vicinity of the O-star sigma Orionis, ... more We present new mid-infrared observations of objects in the vicinity of the O-star sigma Orionis, obtained with TIMMI-2 at ESO. By constraining their near- and mid-infrared spectral energy distributions, we established the nature of previously known IRAS sources and identified new mid-infrared sources as young stellar objects with circumstellar disks, likely massive members of the sigma Ori cluster. For two of these objects we have obtained spectroscopy in the 8-13 micron range in order to investigate the chemistry of the dust grains. TX Ori exhibits a typical silicate emission feature at 10 micron, with a feature at about 11.2 micron that we identify as due to crystalline olivine. The IRAS 05358-0238 spectrum is very unusual, with a weak silicate feature and structure in the range 10-12 micron that may be explained as due to self-absorbed forsterite. We also provide the first evidence for the presence of circumstellar disks in the jet sources Haro 5-39/HH 447, V510 Ori/HH 444 and V603 Ori/HH 445.

Research paper thumbnail of Screening of Portisins (Vinylpyranoanthocyanin Pigments) in Port Wine by LC/DAD-MS

Food Science and Technology International, 2005

Samples of a two-year-old Port red wine were fractionated by Toyopearl gel column chromatography ... more Samples of a two-year-old Port red wine were fractionated by Toyopearl gel column chromatography yielding different coloured fractions. Anthocyanin-derived compounds were tentatively identified by LC/DAD-MS in the different eluted fractions. Several pigments were found to correspond to a recently reported family of pyranoanthocyanin compounds named portisins, supposedly arising from the reaction between anthocyanin-pyruvic acid adducts and flavanols in the presence

Research paper thumbnail of The SMC as a probe of dust in the early Universe (GTO)

We propose a comprehensive spectroscopic survey of the Small Magellanic Cloud (SMC), using the IR... more We propose a comprehensive spectroscopic survey of the Small Magellanic Cloud (SMC), using the IRS and MIPS-SED. The SMC has a metallicity similar to high-redshift galaxies, and its proximity makes it a spatially resolved proxy for star-forming galaxies in the distant, early Universe. The sensitivity of the Spitzer Space Telescope allows us to to observe dust in nearly every stage of its life cycle in the SMC so that we can study how the interactions of dust and its host galaxy differ from more metal-rich systems like the Galaxy and the LMC. Our proposed observations concentrate on important classes underrepresented in the archive of SMC spectra such as young stellar objects, compact H II regions, objects in transition to and from the asymptotic giant branch, and supergiants. These observations, in combination with those already in the archive, will give us a complete picture of the dust in a metal-poor star-forming galaxy similar to those in the early Universe. We request 116 hours, 62 as IRS GTO time and 54 as GO time.

Research paper thumbnail of New Family of Bluish Pyranoanthocyanins

Journal of biomedicine & biotechnology, 2004

Research paper thumbnail of Dust Production and Mass Loss in the Galactic Globular Cluster NGC 362

We investigate dust production and stellar mass loss in the Galactic globular cluster NGC 362. Du... more We investigate dust production and stellar mass loss in the Galactic globular cluster NGC 362. Due to its close proximity to the Small Magellanic Cloud (SMC), NGC 362 was imaged with the IRAC and MIPS cameras onboard the Spitzer Space Telescope as part of the Surveying the Agents of Galaxy Evolution (SAGE-SMC) Spitzer Legacy program. We detect several cluster members near the tip of the Red Giant Branch that exhibit infrared excesses indicative of circumstellar dust and find that dust is not present in measurable quantities in stars below the tip of the Red Giant Branch. We modeled the spectral energy distribution (SED) of the stars with the strongest IR excess and find a total cluster dust mass-loss rate of 3.0(+2.0/-1.2) x 10^-9 solar masses per year, corresponding to a gas mass-loss rate of 8.6(+5.6/-3.4) x 10^-6 solar masses per year, assuming [Fe/H] = -1.16. This mass loss is in addition to any dust-less mass loss that is certainly occurring within the cluster. The two most extreme stars, variables V2 and V16, contribute up to 45% of the total cluster dust-traced mass loss. The SEDs of the more moderate stars indicate the presence of silicate dust, as expected for low-mass, low-metallicity stars. Surprisingly, the SED shapes of the stars with the strongest mass-loss rates appear to require the presence of amorphous carbon dust, possibly in combination with silicate dust, despite their oxygen-rich nature. These results corroborate our previous findings in omega Centauri.

Research paper thumbnail of The State of the Gas and the Relation between Gas and Star Formation at Low Metallicity: The Small Magellanic Cloud

Astrophysical Journal, 2011

We compare atomic gas, molecular gas, and the recent star formation rate (SFR) inferred from H-al... more We compare atomic gas, molecular gas, and the recent star formation rate (SFR) inferred from H-alpha in the Small Magellanic Cloud (SMC). By using infrared dust emission and local dust-to-gas ratios, we construct a map of molecular gas that is independent of CO emission. This allows us to disentangle conversion factor effects from the impact of metallicity on the formation and star formation efficiency of molecular gas. On scales of 200 pc to 1 kpc we find a characteristic molecular gas depletion time of ~1.6 Gyr, similar to that observed in the molecule-rich parts of large spiral galaxies on similar spatial scales. This depletion time shortens on much larger scales to ~0.6 Gyr because of the presence of a diffuse H-alpha component, and lengthens on much smaller scales to ~7.5 Gyr because the H-alpha and H2 distributions differ in detail. We estimate the systematic uncertainties in our measurement to be a factor of 2-3. We suggest that the impact of metallicity on the physics of star formation in molecular gas has at most this magnitude. The relation between SFR and neutral (H2+HI) gas surface density is steep, with a power-law index ~2.2+/-0.1, similar to that observed in the outer disks of large spiral galaxies. At a fixed total gas surface density the SMC has a 5-10 times lower molecular gas fraction (and star formation rate) than large spiral galaxies. We explore the ability of the recent models by Krumholz et al. (2009) and Ostriker et al. (2010) to reproduce our observations. We find that to explain our data at all spatial scales requires a low fraction of cold, gravitationally-bound gas in the SMC. We explore a combined model that incorporates both large scale thermal and dynamical equilibrium and cloud-scale photodissociation region structure and find that it reproduces our data well, as well as predicting a fraction of cold atomic gas very similar to that observed in the SMC.

Research paper thumbnail of A novel synthetic pathway to vitisin B compounds

Tetrahedron Letters, 2009

The hemi-synthesis of vitisin B compounds is described herein for the first time through a new, s... more The hemi-synthesis of vitisin B compounds is described herein for the first time through a new, simple and suitable reaction of malvidin-3-glucoside and malvidin-3-O-coumaroylglucoside with vinyloxy-trimethylsilane. The obtained compounds were identified by LC/DAD-MS and fully characterized by NMR analysis for the first time.

Research paper thumbnail of ChemInform Abstract: Previous and Recent Advances in Pyranoanthocyanins Equilibria in Aqueous Solution

Research paper thumbnail of Flavanols: Catechins and Proanthocyanidins

Natural Products, 2013

Flavanols are a wide group of polyphenols that include flavan-3-ols (e.g., catechin and proanthoc... more Flavanols are a wide group of polyphenols that include flavan-3-ols (e.g., catechin and proanthocyanidins), flavan-4-ols, and flavan-3,4-diols. They arise from plant secondary metabolism through condensation of phenylalanine derived from the shikimate pathway with malonyl-CoA obtained from citrate that is produced by the tricarboxylic acid cycle, leading to the formation of the key precursor in the flavonoids biosynthesis: the naringenin chalcone. The exact nature of the molecular species that undergo polymerization and the mechanism of assembly in proanthocyanidins are still unknown. From a structural point of view, flavanols comprise a C15 (C6-C3-C6) general structure composed by a benzopyran moiety (A and C rings) with an additional aromatic ring (B ring) linked to carbon C-2 of C ring. Flavanols are present in nature in monomeric, oligomeric, and polymeric forms and differ from each other essentially in the configuration of carbon C-2, the hydroxylation/methoxylation pattern of the rings, the type of linkage between each unit, and the degree of galloylation. Flavanols in foods are described to present several beneficial effects such as antioxidant and anticarcinogenic properties and also contribute to the sensory properties of some food products, such as astringency and color. Some of these aspects are discussed herein.

Research paper thumbnail of SAGE-SMC: Surveying the Agents of Galaxy Evolution in the Tidally-Disrupted, Low-Metallicity Small Magellanic Cloud

Research paper thumbnail of Unusual Color Change of Vinylpyranoanthocyanin−Phenolic Pigments

Journal of Agricultural and Food Chemistry, 2010

Research paper thumbnail of Oxovitisins: A New Class of Neutral Pyranone-anthocyanin Derivatives in Red Wines

Journal of Agricultural and Food Chemistry, 2010

A new class of stable yellowish pigments with similar unique spectral features, displaying only a... more A new class of stable yellowish pigments with similar unique spectral features, displaying only a pronounced broad band around 370 nm in the UV-vis spectrum, was detected in an aged Port wine fraction obtained by a combination of chromatography on TSK Toyopearl HW-40(s) and Polyamide resins. These compounds were identified by liquid chromatography-diode array detector/electrospray ionization mass spectrometry (LC-DAD/ESI/MS) and shown to be direct oxidative derivatives of carboxy-pyranoanthocyanins (vitisins A) by synthesis experiments performed in a wine model solution. Their structures were fully characterized by MS and NMR spectroscopy ((1)H, gCOSY, gHSQC, and gHMBC) and found to correspond to alpha-pyranone-anthocyanins (lactone or pyran-2-one-anthocyanins). Their formation involves first the nucleophilic attack of water into the positively charged C-10 position of vitisins, followed by decarboxylation, oxidation, and dehydration steps, yielding a new and neutral pyranone structure. The occurrence of these novel pigments in aged wines points to a new pathway involving anthocyanin secondary products (vitisins A) as precursors of new pigments in subsequent stages of wine aging that may contribute to its color evolution.

Research paper thumbnail of Chemical Behavior of Methylpyranomalvidin-3- O -glucoside in Aqueous Solution Studied by NMR and UV−Visible Spectroscopy

The Journal of Physical Chemistry B, 2011

In the present work, the proton-transfer reactions of the methylpyranomalvidin-3-O-glucoside pigm... more In the present work, the proton-transfer reactions of the methylpyranomalvidin-3-O-glucoside pigment in water with different pH values was studied by NMR and UV-visible spectroscopies. The results showed four equilibrium forms: the methylpyranomalvidin-3-O-glucoside cation, the neutral quinoidal base, the respective anionic quinoidal base, and a dianionic base unprotonated at the methyl group. According to the NMR data, it seems that for methylpyranomalvidin-3-O-glucoside besides the acid-base equilibrium between the pyranoflavylium cation and the neutral quinoidal base, a new species is formed at pD 4.88-6.10. This is corroborated by the appearance of a new set of signals in the NMR spectrum that may be assigned to the formation of hemiketal/cis-chalcone species to a small extent. The two ionization constants (pK(a1) and pK(a2)) obtained by both methods (NMR and UV-visible) for methylpyranomalvidin-3-O-glucoside are in agreement (pK(a1) = 5.17 ± 0.03; pK(a2) = 8.85 ± 0.08; and pK(a1) = 4.57 ± 0.07; pK(a2) = 8.23 ± 0.04 obtained by NMR and UV-visible spectroscopies, respectively). Moreover, the fully dianionic unprotonated form (at the methyl group) of the methylpyranomalvidin-3-O-glucoside is converted slowly into a new structure that displays a yellow color at basic pH. On the basis of the results obtained through LC-MS and NMR, the proposed structure was found to correspond to the flavonol syringetin-3-glucoside.

Research paper thumbnail of NMR structure characterization of a new vinylpyranoanthocyanin–catechin pigment (a portisin)

Tetrahedron Letters, 2004

Research paper thumbnail of A novel synthetic pathway to vitisin B compounds

Tetrahedron Letters, 2009

The hemi-synthesis of vitisin B compounds is described herein for the first time through a new, s... more The hemi-synthesis of vitisin B compounds is described herein for the first time through a new, simple and suitable reaction of malvidin-3-glucoside and malvidin-3-O-coumaroylglucoside with vinyloxy-trimethylsilane. The obtained compounds were identified by LC/DAD-MS and fully characterized by NMR analysis for the first time.

Research paper thumbnail of Influence of anthocyanins and derivative pigments from blueberry ( Vaccinium myrtillus) extracts on MPP + intestinal uptake: A structure–activity approach

Food Chemistry, 2008

The aim of the present study was to investigate the influence of an anthocyanin extract (extract ... more The aim of the present study was to investigate the influence of an anthocyanin extract (extract I), and two other derivative extracts (extracts II and III), which are being developed aiming to be further applied in the food industry, on intestinal uptake of organic cations. For this purpose, the effect of these compounds on 3H-MPP+ uptake was evaluated in Caco-2 cells (an enterocyte-like cell line derived from a human colonic adenocarcinoma).Extracts I and III did not present any effect on 3H-MPP+ uptake. Extract II, an anthocyanin–pyruvic acid adduct extract, decreased organic cation uptake. Some phenolic molecules were also tested, aiming to study possible structural features responsible for these effects. The results are compatible with the hypothesis of phenolic molecules bearing a carboxylic group with extended electronic conjugation being the responsible feature for the inhibitory effect on 3H-MPP+ uptake.The use of these compounds in foodstuffs must be carefully assessed since interactions with organic cations present in the diet, as nutrients or xenobiotics, may affect their absorption and bioavailability. Type and complexity of the ingested compounds are important factors in this regard, and should be taken into consideration.

Research paper thumbnail of The phase-field model in tumor growth

Philosophical Magazine, 2011

Tumor growth is becoming a central problem in biophysics both from its social and medical interes... more Tumor growth is becoming a central problem in biophysics both from its social and medical interest and, more fundamentally, because it is a remarkable example of an emergent complex system. Focusing on the description of the spatial and dynamical features of tumor growth, in this paper we review recent tumor modeling approaches using a technique borrowed from materials science: the

Research paper thumbnail of Fluorescence Approach for Measuring Anthocyanins and Derived Pigments in Red Wine

Journal of Agricultural and Food Chemistry, 2013

A novel fluorescence approach to monitor the evolution of anthocyanins and derivatives in red win... more A novel fluorescence approach to monitor the evolution of anthocyanins and derivatives in red wine was developed. Some red table wines and Port wine with different vintage years were first tested with the aim to determine the ideal fluorescent conditions. The fluorescence contribution of both monomeric and polymeric anthocyanins was studied by comparing their emission spectra. By measuring the F700/F560 ratio on different wine samples and applying an inverted exponential function, it was possible to estimate the monomeric/polymeric anthocyanin absorbance ratio that is proportional to the relative content of the two classes of compounds. The methodology was further developed by using pure compounds representative of monomeric anthocyanins and anthocyanin-pyruvic acid adducts, namely, by using malvidin-3-O-glucoside and vitisin A. A fluorescence excitation ratio (FER350/550) was considered for estimating the absorbance ratio between vitisin A and malvidin-3-O-glucoside. Overall, this work aims to use fluorescence to monitor the evolution of anthocyanin derivatives and to distinguish them from their anthocyanin precursors, thereby allowing the evolution of anthocyanin pigments during wine aging to be monitored, but it also may be useful to determine age markers or even geographical markers.

Research paper thumbnail of Pyranoanthocyanin Dimers: A New Family of Turquoise Blue Anthocyanin-Derived Pigments Found in Port Wine

Journal of Agricultural and Food Chemistry, 2010

Research paper thumbnail of Reaction between Hydroxycinnamic Acids and Anthocyanin−Pyruvic Acid Adducts Yielding New Portisins

Journal of Agricultural and Food Chemistry, 2007

Three new anthocyanin-derived pigments were found to occur in a 2-year-old Port red wine. Their s... more Three new anthocyanin-derived pigments were found to occur in a 2-year-old Port red wine. Their structures were elucidated through LC/DAD-MS and NMR analysis and were found to correspond to a pyranoanthocyanin moiety linked to substituted cinnamyl substituents. The structures of these compounds are very similar to the one already reported for portisins, with a phenolic moiety replacing the catechin moiety. The newly formed anthocyanin-derived compounds display a bathochromic shift of the lambdamax ( approximately 540 nm) when compared with their anthocyanin-pyruvic acid adduct precursor (lambdamax = 511 nm), which may be due to the extended conjugation of the pi electrons in the structures of those pigments. Studies performed in model solutions helped to clarify the formation mechanism of these pigments that can result from the nucleophilic attack of the olefinic double bond of a hydroxycinnamic acid to the eletrophilic C-10 position of the anthocyanin-pyruvic acid adduct, followed by the loss of a formic acid molecule and decarboxylation. The chromatic characterization of these malvidin-3-glucoside-derived compounds revealed a higher resistance to discoloration against the nucleophilic attack by water and bisulfite when compared to malvidin-3-glucoside that is almost converted into its colorless hemiacetal form. However, the resistance to discoloration of these new pigments is not as high as the one reported for catechin-derived portisins. This could be explained by the presence of a smaller group (hydroxycinnamyl group), which does not protect so efficiently the chromophore against nucleophilic attack at the C-2 position. The occurrence of these pigments in red wine highlights new chemical pathways involving anthocyanin-pyruvic acid derivatives as precursors for the formation of new pigments in subsequent stages of wine aging that may contribute to its color evolution.