Ana Margarida Amado - Academia.edu (original) (raw)

Papers by Ana Margarida Amado

Research paper thumbnail of A Vibrational Raman Spectroscopic Study of Myosin and Myosin - Vanadate Interactions

Cellular Regulation by Protein Phosphorylation, 1991

Research paper thumbnail of Pseudopolymorphic transitions of Niclosamide monitored by Raman Spectroscopy

Journal of Pharmaceutical Sciences

Niclosamide suffers pseudopolymorphic transformations when exposed to different ambient condition... more Niclosamide suffers pseudopolymorphic transformations when exposed to different ambient conditions, which can lead to changes in its bioavailability. In this study, the kinetics of the pseudopolymorphic transitions of niclosamide crystals are characterized. FT-Raman spectroscopy is used to quantify the anhydrate and hydrate forms of niclosamide crystals, mostly because of its high sensitivity to the strong intermolecular interactions present in these systems. The samples are exposed to well-characterized relative humidity (RH) conditions during different periods of time and both water diffusion and polymorphic changes are monitored from the corresponding changes observed in the vibrational spectra. Both hydration and dehydration were found to be single-step processes, with a half-life time of ca. 142 and 63 h, respectively, at 24°C.

Research paper thumbnail of Vibrational Spectroscopy (FTIR-ATR and FT-Raman) - A Rapid and Useful Tool for Phycocolloid Analysis

The wide industrial application of phycocolloids (e.g. alginates, agar and carrageenans) is based... more The wide industrial application of phycocolloids (e.g. alginates, agar and carrageenans) is based on their particular properties to form gels in aqueous solution. Recently, new spectroscopic techniques have provided more accurate identification of the natural composition of the polysaccharides produced by these seaweeds. With the combination of two spectroscopic techniques (FTIR-ATR and FT-Raman) it is possible to identify the principal seaweed colloids in ground seaweed samples as in extracted material. Since the seaweed samples receive the minimum of handling and treatment (e.g. they are simply dried and ground), the composition determined represents, as accurately as possible, the native composition of the phycocolloids.

Research paper thumbnail of Weak hydrogen bonding. Part 2. The hydrogen bonding nature of short C?H ?? contacts: crystallographic, spectroscopic and quantum mechanical studies of some terminal alkynes

Journal of the Chemical Society, Perkin Transactions 2, 1995

ABSTRACT

Research paper thumbnail of H/D and D/H exchange rates in α-cyclodextrin and α-cyclodextrin inclusion compounds Raman spectroscopic study

Journal of the Chemical Society, Faraday Transactions, 1997

ABSTRACT The H/D and D/H exchange rates of hydroxy groups in crystalline α-cyclodextrin (CD) expo... more ABSTRACT The H/D and D/H exchange rates of hydroxy groups in crystalline α-cyclodextrin (CD) exposed to H 2 O and D 2 O vapour, respectively, have been studied by monitoring the relative integrated Raman intensities of the O–H and O–D stretching bands. The time-dependent Raman intensities suggest a fast diffusion-controlled H 2 O/D 2 O equilibrium process in shorter times, followed by a much slower H/D exchange for the longer times. The deuteriation process is found to be ca. 10 times slower than the reverse process, in excellent agreement with the expected isotopic effect in an exchange mechanism whose rate-determining step involves the cleavage of a O–H(–D) bond of a water molecule. The slow H/D exchange rate observed for α-CD hexahydrate in comparison with the β-CD dodecahydrate is explained by its structural rigidity, also evident from the discrete bands observed in the O–H and O–D stretching region. This structural rigidity is no longer present in the inclusion compounds of α-CD with an aromatic guest, which exhibit an H/D exchange rate much faster than the pure α-CD hexahydrate.

Research paper thumbnail of Ab initio calculations on some transition metal heptoxides by using effective core potentials

Journal of Molecular Structure: THEOCHEM, 1999

The ab initio molecular structures and vibrational frequencies for several transition metal hepto... more The ab initio molecular structures and vibrational frequencies for several transition metal heptoxides X 2 O 7 nϪ (n 0, 2, 4) were calculated using effective core potentials at the HF and DFT (B3LYP) levels. The relative merits of different valence basis set arrangements were tested by comparison with experimental results available, in particular with gas-phase Re 2 O 7 molecular structure and vibrational frequencies. The calculations were then extended to other heptoxides of the VB, VIB and VIIB transition metal groups. The results indicate that a staggered geometry (either D 3d or C 2 ) is the energy minimum for most of the heptoxides studied. The only exceptions are Mn 2 O 7 , which clearly prefers an eclipsed C 2v(syn) configuration, and Tc 2 O 7 , for which C 2 and C 2v(syn) geometries have nearly the same energy.

Research paper thumbnail of Pt(II) vs Pd(II) polyamine complexes as new anticancer drugs: A structure-activity study

Letters in Drug Design and Discovery, 2006

ABSTRACT Two homologous trinuclear polyamine chelates with either Pt(II) (Ia) or Pd(II) (Ib) were... more ABSTRACT Two homologous trinuclear polyamine chelates with either Pt(II) (Ia) or Pd(II) (Ib) were screened for their anticancer properties. Their growth-inhibition activity towards a human tongue epithelioma (HSC-3) was assessed in vitro, and the effect of the cation alteration was determined (IC50 =32 μM for Ib vs 66 μM for Ia).

Research paper thumbnail of Ab initio SCF MO calculations on triaza and tetraaza cyclic amines

Journal of the Chemical Society, Perkin Transactions 2, 1996

Research paper thumbnail of Stevens Johnson Syndrome in a patient undergoing gynaecological brachytherapy: An association or an incident?

Reports of Practical Oncology & Radiotherapy, 2011

Background: Stevens Johnson Syndrome and Erythema Multiforme are hypersensitivity skin reactions ... more Background: Stevens Johnson Syndrome and Erythema Multiforme are hypersensitivity skin reactions generally arising in the context of multiple causes. Radiation therapy is considered to be one of these causes, although most reports are hindered by concomitant medications.

Research paper thumbnail of Análise comparativa dos ficocolóides produzidos por algas carragenófitas usadas industrialmente e algas carragenófitas portuguesas

As Carragenanas (E-407) constituem um dos principais aditivos usados pela indústria alimentar, co... more As Carragenanas (E-407) constituem um dos principais aditivos usados pela indústria alimentar, como agentes gelificantes, emulsionantes, estabilizantes e espessantes. São ingredientes naturais, usados há várias décadas na área alimentar e são considerados como seguros, tendo obtido a classificação GRAS (Generally Recognised As Safe). Neste trabalho foram analisadas a percentagem de peso seco e a composição química (por FTIR e FT-Raman) das carragenanas produzidas pelas carragenófitas (Gigartinales, Rhodophyta) oriundas de diversos países: Kappaphycus alvarezzi

Research paper thumbnail of Molecular aggregation in neat 2-methoxyethanol and in 2-methoxyethanol/acrylamide solutions—A study by Raman spectroscopy and ab initio calculations

Vibrational Spectroscopy, 2006

Ab initio harmonic B3LYP/6-31G * derived force fields were used to perform normal mode analysis f... more Ab initio harmonic B3LYP/6-31G * derived force fields were used to perform normal mode analysis for the most stable monomers and dimmers of neat 2-methoxyethanol (ethyleneglycol methyl ether) and of 2-methoxyethanol/acrylamide solutions. An interpretation of the Raman spectra for the neat 2-methoxyethanol and its solutions with acrylamide were analysed and associated to the monomeric and dimeric species intermolecular interactions either in the neat compound or in the mixtures with acrylamide in terms of intra-and intermolecular hydrogen-bonded and steric effects. #

Research paper thumbnail of Simple apparatus for the measurement of mechanical properties of solids

The Physics Teacher, 2011

... Ligia R. Gomes, CIAGEB, Escola Superior de Saúde da UFP, Universidade Fernando Pessoa, Rua Ca... more ... Ligia R. Gomes, CIAGEB, Escola Superior de Saúde da UFP, Universidade Fernando Pessoa, Rua Carlos da Maia, Portugal; lrgomes@ufp.edu.pt Ana Amado, CERLAB ... Rua do Campo Alegre, 687, P-4169-007 Porto, Portugal Luís MNBF Santos, Departamento de ...

Research paper thumbnail of Doping effects in p-terphenyl molecular crystals: a study by Raman spectroscopy

Solid State Ionics, 1999

The use of doped p-terphenyl crystals as organic charge-transfer agents calls for detailed inform... more The use of doped p-terphenyl crystals as organic charge-transfer agents calls for detailed information on their structure.

Research paper thumbnail of Raman spectroscopic study of pure p-terphenyl and tetracene:p-terphenyl doped crystals

Solid State Ionics, 1997

The Raman spectra of pure p-terphenyl and tetracene:p-terphenyl doped crystals have been examined... more The Raman spectra of pure p-terphenyl and tetracene:p-terphenyl doped crystals have been examined for different guest concentrations, above and below the phase transition, at 190 K. As the temperature decreases from the α-phase to the β-phase, similar spectral changes are observed in the corresponding Raman modes of pure p-terphenyl and tetracene:p-terphenyl doped crystals for an equal decrease in temperature. The

Research paper thumbnail of C–H⋯O Hydrogen bonding in 4-phenyl-benzaldehyde: A comprehensive crystallographic, spectroscopic and computational study

Physical Chemistry Chemical Physics, 2005

The crystal structure of 4-phenyl-benzaldehyde reveals the presence of a dimer linked by the C=O ... more The crystal structure of 4-phenyl-benzaldehyde reveals the presence of a dimer linked by the C=O and C9-H groups of adjacent molecules. In the liquid phase, the presence of C-H...O bonded forms is revealed by both vibrational and NMR spectroscopy. A DeltaH value of -8.2 +/- 0.5 kJ mol(-1) for the dimerisation equilibrium is established from the temperature-dependent intensities of the bands assigned to the carbonyl-stretching modes. The NMR data suggest the preferential engagement of the C(2,6)-H and C(10/12)/C(11)-H groups as hydrogen bond donors, instead of the C(9)-H group. While ab initio calculations for the isolated dimers are unable to corroborate these NMR results, the radial distribution functions obtained from molecular dynamics simulations show a preference for C(2,6)-H and C(10/12)/C(11)-H...O contacts relative to the C(9)-H...O ones.

Research paper thumbnail of Use of FTIR, FT-Raman and 13C-NMR spectroscopy for identification of some seaweed phycocolloids

Biomolecular Engineering, 2003

Many seaweeds produce phycocolloids, stored in the cell wall. Members of the Rhodophyceae produce... more Many seaweeds produce phycocolloids, stored in the cell wall. Members of the Rhodophyceae produce polysaccharides the main components of which are galactose (galactans) */agar and carrageenan. In addition, alginic acid is extracted from members of the Phaeophyceae. This is a binary polyuronide made up of mannuronic acid and guluronic acid. The wide uses of these phycocolloids are based on their gelling, viscosifying and emulsifying properties, which generate an increasing commercial and scientific interest. In this work, the FTIR and FT-RAMAN spectra of carrageenan and agar, obtained by alkaline extraction from different seaweeds (e.g. Mastocarpus stellatus , Chondrus crispus , Calliblepharis jubata , Chondracanthus acicularis , Chondracanthus teedei and Gracilaria gracilis ), were recorded in order to identify the type of phycocolloid produced. The spectra of commercial carrageenan, alginic acid and agar samples (SIGMA and TAAB laboratories) were used as references. Special emphasis was given to the 500 Á/ 1500 cm (1 region, which presents several vibrational modes, sensitive to the type of polysaccharide and to the type of glycosidic linkage. The FT-Raman spectra present a higher resolution than FTIR spectra, this allowing the identification of a larger number of characteristic bands. In some cases, phycocolloids can be identified by FT-Raman spectroscopy alone. #

Research paper thumbnail of An Investigation of Weak CH···O Hydrogen Bonds in Maltose Anomers by a Combination of Calculation and Experimental Solid-State NMR Spectroscopy

Journal of the American Chemical Society, 2005

Two-dimensional (1)H-(13)C MAS-J-HMQC solid-state NMR spectra of the two anomeric forms of maltos... more Two-dimensional (1)H-(13)C MAS-J-HMQC solid-state NMR spectra of the two anomeric forms of maltose at natural abundance are presented. The experimental (1)H chemical shifts of the CH and CH(2) protons are assigned using first-principles chemical shift calculations that employ a plane-wave pseudopotential approach. Further calculations show that the calculated change in the (1)H chemical shift when comparing the full crystal and an isolated molecule is a quantitative measure of intermolecular C-H...O weak hydrogen bonding. Notably, a clear correlation between a large chemical shift change (up to 2 ppm) and both a short H...O distance (<2.7 A) and a CHO bond angle greater than 130 degrees is observed, thus showing that directionality is important in C-H...O hydrogen bonding.

Research paper thumbnail of Substituted Styrene Molecules Included in Cyclodextrins: a Raman Spectroscopic Study. Part II

Journal of Raman Spectroscopy, 1996

ABSTRACT

Research paper thumbnail of Meta-substituted styrene molecules included in cydodextrins: A Raman spectroscopic study

Journal of Raman Spectroscopy, 1994

ABSTRACT Raman spectra of styrene (S), 3-fluorostyrene (3FS), 3-chlorostyrene (3CS) and 3-methyls... more ABSTRACT Raman spectra of styrene (S), 3-fluorostyrene (3FS), 3-chlorostyrene (3CS) and 3-methylstyrene (3MS) and their complexes in α-, β- and γ-cyclodextrins (α-, β-, γCD) were recorded at various temperatures. The substituted styrene molecules were found to provide good group frequencies, namely, vCC and vCH, for probing the guest molecules. Generally, the CC oscillator is shown to be a good probe for studying conformational equilibria of the guest molecule perturbed by complex formation with the various CD molecules. The CH oscillators provide information concerning plausible structures for the complexes. On the whole, all the spectral observations are consistent with different types of structures for the (S, 3MS)–αCD and (3FS, 3CS)–αCD complexes. In particular, the Raman spectroscopic results suggest that, for 3MS–αCD the vinyl group keeps some rotational freedom. For 3FS–αCD and 3CS–αCD, it is suggested that the most electronegative fluorine and chlorine atoms are left outside the the CD cavity, with the vinyl group rotationally hindered. For the γCD complexes, the wider CD cavity sould be able to accommodate all the guest molecules considered keeping the conformer distributions of the pure liquids approximately. However, the inclusion process seems to hinder the internal rotation in such a way that even below 200 K the conformer distribution remains similar to that of the pure liquid at room temperature.

Research paper thumbnail of Combined Raman and 51V NMR spectroscopic study of vanadium (V) oligomerization in aqueous alkaline solutions

Journal of Raman Spectroscopy, 1993

The Raman spectra of aqueous vanadium(V) solutions at different pH values, ranging from 13.1 to 7... more The Raman spectra of aqueous vanadium(V) solutions at different pH values, ranging from 13.1 to 7.0, are presented. The dominant bands in the range 700-1100 cm-' are assigned to the VO symmetrical stretching of the different oligomers, using additional information from "V NMR spectra and empirical models. The effects of pH, concentration and ionic strength on the oligomerization equilihria are discussed. The ionic strength is found to affect significantly the oligomer composition of vanadate solutions, which is of interest in biochemical and biological studies.

Research paper thumbnail of A Vibrational Raman Spectroscopic Study of Myosin and Myosin - Vanadate Interactions

Cellular Regulation by Protein Phosphorylation, 1991

Research paper thumbnail of Pseudopolymorphic transitions of Niclosamide monitored by Raman Spectroscopy

Journal of Pharmaceutical Sciences

Niclosamide suffers pseudopolymorphic transformations when exposed to different ambient condition... more Niclosamide suffers pseudopolymorphic transformations when exposed to different ambient conditions, which can lead to changes in its bioavailability. In this study, the kinetics of the pseudopolymorphic transitions of niclosamide crystals are characterized. FT-Raman spectroscopy is used to quantify the anhydrate and hydrate forms of niclosamide crystals, mostly because of its high sensitivity to the strong intermolecular interactions present in these systems. The samples are exposed to well-characterized relative humidity (RH) conditions during different periods of time and both water diffusion and polymorphic changes are monitored from the corresponding changes observed in the vibrational spectra. Both hydration and dehydration were found to be single-step processes, with a half-life time of ca. 142 and 63 h, respectively, at 24°C.

Research paper thumbnail of Vibrational Spectroscopy (FTIR-ATR and FT-Raman) - A Rapid and Useful Tool for Phycocolloid Analysis

The wide industrial application of phycocolloids (e.g. alginates, agar and carrageenans) is based... more The wide industrial application of phycocolloids (e.g. alginates, agar and carrageenans) is based on their particular properties to form gels in aqueous solution. Recently, new spectroscopic techniques have provided more accurate identification of the natural composition of the polysaccharides produced by these seaweeds. With the combination of two spectroscopic techniques (FTIR-ATR and FT-Raman) it is possible to identify the principal seaweed colloids in ground seaweed samples as in extracted material. Since the seaweed samples receive the minimum of handling and treatment (e.g. they are simply dried and ground), the composition determined represents, as accurately as possible, the native composition of the phycocolloids.

Research paper thumbnail of Weak hydrogen bonding. Part 2. The hydrogen bonding nature of short C?H ?? contacts: crystallographic, spectroscopic and quantum mechanical studies of some terminal alkynes

Journal of the Chemical Society, Perkin Transactions 2, 1995

ABSTRACT

Research paper thumbnail of H/D and D/H exchange rates in α-cyclodextrin and α-cyclodextrin inclusion compounds Raman spectroscopic study

Journal of the Chemical Society, Faraday Transactions, 1997

ABSTRACT The H/D and D/H exchange rates of hydroxy groups in crystalline α-cyclodextrin (CD) expo... more ABSTRACT The H/D and D/H exchange rates of hydroxy groups in crystalline α-cyclodextrin (CD) exposed to H 2 O and D 2 O vapour, respectively, have been studied by monitoring the relative integrated Raman intensities of the O–H and O–D stretching bands. The time-dependent Raman intensities suggest a fast diffusion-controlled H 2 O/D 2 O equilibrium process in shorter times, followed by a much slower H/D exchange for the longer times. The deuteriation process is found to be ca. 10 times slower than the reverse process, in excellent agreement with the expected isotopic effect in an exchange mechanism whose rate-determining step involves the cleavage of a O–H(–D) bond of a water molecule. The slow H/D exchange rate observed for α-CD hexahydrate in comparison with the β-CD dodecahydrate is explained by its structural rigidity, also evident from the discrete bands observed in the O–H and O–D stretching region. This structural rigidity is no longer present in the inclusion compounds of α-CD with an aromatic guest, which exhibit an H/D exchange rate much faster than the pure α-CD hexahydrate.

Research paper thumbnail of Ab initio calculations on some transition metal heptoxides by using effective core potentials

Journal of Molecular Structure: THEOCHEM, 1999

The ab initio molecular structures and vibrational frequencies for several transition metal hepto... more The ab initio molecular structures and vibrational frequencies for several transition metal heptoxides X 2 O 7 nϪ (n 0, 2, 4) were calculated using effective core potentials at the HF and DFT (B3LYP) levels. The relative merits of different valence basis set arrangements were tested by comparison with experimental results available, in particular with gas-phase Re 2 O 7 molecular structure and vibrational frequencies. The calculations were then extended to other heptoxides of the VB, VIB and VIIB transition metal groups. The results indicate that a staggered geometry (either D 3d or C 2 ) is the energy minimum for most of the heptoxides studied. The only exceptions are Mn 2 O 7 , which clearly prefers an eclipsed C 2v(syn) configuration, and Tc 2 O 7 , for which C 2 and C 2v(syn) geometries have nearly the same energy.

Research paper thumbnail of Pt(II) vs Pd(II) polyamine complexes as new anticancer drugs: A structure-activity study

Letters in Drug Design and Discovery, 2006

ABSTRACT Two homologous trinuclear polyamine chelates with either Pt(II) (Ia) or Pd(II) (Ib) were... more ABSTRACT Two homologous trinuclear polyamine chelates with either Pt(II) (Ia) or Pd(II) (Ib) were screened for their anticancer properties. Their growth-inhibition activity towards a human tongue epithelioma (HSC-3) was assessed in vitro, and the effect of the cation alteration was determined (IC50 =32 μM for Ib vs 66 μM for Ia).

Research paper thumbnail of Ab initio SCF MO calculations on triaza and tetraaza cyclic amines

Journal of the Chemical Society, Perkin Transactions 2, 1996

Research paper thumbnail of Stevens Johnson Syndrome in a patient undergoing gynaecological brachytherapy: An association or an incident?

Reports of Practical Oncology & Radiotherapy, 2011

Background: Stevens Johnson Syndrome and Erythema Multiforme are hypersensitivity skin reactions ... more Background: Stevens Johnson Syndrome and Erythema Multiforme are hypersensitivity skin reactions generally arising in the context of multiple causes. Radiation therapy is considered to be one of these causes, although most reports are hindered by concomitant medications.

Research paper thumbnail of Análise comparativa dos ficocolóides produzidos por algas carragenófitas usadas industrialmente e algas carragenófitas portuguesas

As Carragenanas (E-407) constituem um dos principais aditivos usados pela indústria alimentar, co... more As Carragenanas (E-407) constituem um dos principais aditivos usados pela indústria alimentar, como agentes gelificantes, emulsionantes, estabilizantes e espessantes. São ingredientes naturais, usados há várias décadas na área alimentar e são considerados como seguros, tendo obtido a classificação GRAS (Generally Recognised As Safe). Neste trabalho foram analisadas a percentagem de peso seco e a composição química (por FTIR e FT-Raman) das carragenanas produzidas pelas carragenófitas (Gigartinales, Rhodophyta) oriundas de diversos países: Kappaphycus alvarezzi

Research paper thumbnail of Molecular aggregation in neat 2-methoxyethanol and in 2-methoxyethanol/acrylamide solutions—A study by Raman spectroscopy and ab initio calculations

Vibrational Spectroscopy, 2006

Ab initio harmonic B3LYP/6-31G * derived force fields were used to perform normal mode analysis f... more Ab initio harmonic B3LYP/6-31G * derived force fields were used to perform normal mode analysis for the most stable monomers and dimmers of neat 2-methoxyethanol (ethyleneglycol methyl ether) and of 2-methoxyethanol/acrylamide solutions. An interpretation of the Raman spectra for the neat 2-methoxyethanol and its solutions with acrylamide were analysed and associated to the monomeric and dimeric species intermolecular interactions either in the neat compound or in the mixtures with acrylamide in terms of intra-and intermolecular hydrogen-bonded and steric effects. #

Research paper thumbnail of Simple apparatus for the measurement of mechanical properties of solids

The Physics Teacher, 2011

... Ligia R. Gomes, CIAGEB, Escola Superior de Saúde da UFP, Universidade Fernando Pessoa, Rua Ca... more ... Ligia R. Gomes, CIAGEB, Escola Superior de Saúde da UFP, Universidade Fernando Pessoa, Rua Carlos da Maia, Portugal; lrgomes@ufp.edu.pt Ana Amado, CERLAB ... Rua do Campo Alegre, 687, P-4169-007 Porto, Portugal Luís MNBF Santos, Departamento de ...

Research paper thumbnail of Doping effects in p-terphenyl molecular crystals: a study by Raman spectroscopy

Solid State Ionics, 1999

The use of doped p-terphenyl crystals as organic charge-transfer agents calls for detailed inform... more The use of doped p-terphenyl crystals as organic charge-transfer agents calls for detailed information on their structure.

Research paper thumbnail of Raman spectroscopic study of pure p-terphenyl and tetracene:p-terphenyl doped crystals

Solid State Ionics, 1997

The Raman spectra of pure p-terphenyl and tetracene:p-terphenyl doped crystals have been examined... more The Raman spectra of pure p-terphenyl and tetracene:p-terphenyl doped crystals have been examined for different guest concentrations, above and below the phase transition, at 190 K. As the temperature decreases from the α-phase to the β-phase, similar spectral changes are observed in the corresponding Raman modes of pure p-terphenyl and tetracene:p-terphenyl doped crystals for an equal decrease in temperature. The

Research paper thumbnail of C–H⋯O Hydrogen bonding in 4-phenyl-benzaldehyde: A comprehensive crystallographic, spectroscopic and computational study

Physical Chemistry Chemical Physics, 2005

The crystal structure of 4-phenyl-benzaldehyde reveals the presence of a dimer linked by the C=O ... more The crystal structure of 4-phenyl-benzaldehyde reveals the presence of a dimer linked by the C=O and C9-H groups of adjacent molecules. In the liquid phase, the presence of C-H...O bonded forms is revealed by both vibrational and NMR spectroscopy. A DeltaH value of -8.2 +/- 0.5 kJ mol(-1) for the dimerisation equilibrium is established from the temperature-dependent intensities of the bands assigned to the carbonyl-stretching modes. The NMR data suggest the preferential engagement of the C(2,6)-H and C(10/12)/C(11)-H groups as hydrogen bond donors, instead of the C(9)-H group. While ab initio calculations for the isolated dimers are unable to corroborate these NMR results, the radial distribution functions obtained from molecular dynamics simulations show a preference for C(2,6)-H and C(10/12)/C(11)-H...O contacts relative to the C(9)-H...O ones.

Research paper thumbnail of Use of FTIR, FT-Raman and 13C-NMR spectroscopy for identification of some seaweed phycocolloids

Biomolecular Engineering, 2003

Many seaweeds produce phycocolloids, stored in the cell wall. Members of the Rhodophyceae produce... more Many seaweeds produce phycocolloids, stored in the cell wall. Members of the Rhodophyceae produce polysaccharides the main components of which are galactose (galactans) */agar and carrageenan. In addition, alginic acid is extracted from members of the Phaeophyceae. This is a binary polyuronide made up of mannuronic acid and guluronic acid. The wide uses of these phycocolloids are based on their gelling, viscosifying and emulsifying properties, which generate an increasing commercial and scientific interest. In this work, the FTIR and FT-RAMAN spectra of carrageenan and agar, obtained by alkaline extraction from different seaweeds (e.g. Mastocarpus stellatus , Chondrus crispus , Calliblepharis jubata , Chondracanthus acicularis , Chondracanthus teedei and Gracilaria gracilis ), were recorded in order to identify the type of phycocolloid produced. The spectra of commercial carrageenan, alginic acid and agar samples (SIGMA and TAAB laboratories) were used as references. Special emphasis was given to the 500 Á/ 1500 cm (1 region, which presents several vibrational modes, sensitive to the type of polysaccharide and to the type of glycosidic linkage. The FT-Raman spectra present a higher resolution than FTIR spectra, this allowing the identification of a larger number of characteristic bands. In some cases, phycocolloids can be identified by FT-Raman spectroscopy alone. #

Research paper thumbnail of An Investigation of Weak CH···O Hydrogen Bonds in Maltose Anomers by a Combination of Calculation and Experimental Solid-State NMR Spectroscopy

Journal of the American Chemical Society, 2005

Two-dimensional (1)H-(13)C MAS-J-HMQC solid-state NMR spectra of the two anomeric forms of maltos... more Two-dimensional (1)H-(13)C MAS-J-HMQC solid-state NMR spectra of the two anomeric forms of maltose at natural abundance are presented. The experimental (1)H chemical shifts of the CH and CH(2) protons are assigned using first-principles chemical shift calculations that employ a plane-wave pseudopotential approach. Further calculations show that the calculated change in the (1)H chemical shift when comparing the full crystal and an isolated molecule is a quantitative measure of intermolecular C-H...O weak hydrogen bonding. Notably, a clear correlation between a large chemical shift change (up to 2 ppm) and both a short H...O distance (<2.7 A) and a CHO bond angle greater than 130 degrees is observed, thus showing that directionality is important in C-H...O hydrogen bonding.

Research paper thumbnail of Substituted Styrene Molecules Included in Cyclodextrins: a Raman Spectroscopic Study. Part II

Journal of Raman Spectroscopy, 1996

ABSTRACT

Research paper thumbnail of Meta-substituted styrene molecules included in cydodextrins: A Raman spectroscopic study

Journal of Raman Spectroscopy, 1994

ABSTRACT Raman spectra of styrene (S), 3-fluorostyrene (3FS), 3-chlorostyrene (3CS) and 3-methyls... more ABSTRACT Raman spectra of styrene (S), 3-fluorostyrene (3FS), 3-chlorostyrene (3CS) and 3-methylstyrene (3MS) and their complexes in α-, β- and γ-cyclodextrins (α-, β-, γCD) were recorded at various temperatures. The substituted styrene molecules were found to provide good group frequencies, namely, vCC and vCH, for probing the guest molecules. Generally, the CC oscillator is shown to be a good probe for studying conformational equilibria of the guest molecule perturbed by complex formation with the various CD molecules. The CH oscillators provide information concerning plausible structures for the complexes. On the whole, all the spectral observations are consistent with different types of structures for the (S, 3MS)–αCD and (3FS, 3CS)–αCD complexes. In particular, the Raman spectroscopic results suggest that, for 3MS–αCD the vinyl group keeps some rotational freedom. For 3FS–αCD and 3CS–αCD, it is suggested that the most electronegative fluorine and chlorine atoms are left outside the the CD cavity, with the vinyl group rotationally hindered. For the γCD complexes, the wider CD cavity sould be able to accommodate all the guest molecules considered keeping the conformer distributions of the pure liquids approximately. However, the inclusion process seems to hinder the internal rotation in such a way that even below 200 K the conformer distribution remains similar to that of the pure liquid at room temperature.

Research paper thumbnail of Combined Raman and 51V NMR spectroscopic study of vanadium (V) oligomerization in aqueous alkaline solutions

Journal of Raman Spectroscopy, 1993

The Raman spectra of aqueous vanadium(V) solutions at different pH values, ranging from 13.1 to 7... more The Raman spectra of aqueous vanadium(V) solutions at different pH values, ranging from 13.1 to 7.0, are presented. The dominant bands in the range 700-1100 cm-' are assigned to the VO symmetrical stretching of the different oligomers, using additional information from "V NMR spectra and empirical models. The effects of pH, concentration and ionic strength on the oligomerization equilihria are discussed. The ionic strength is found to affect significantly the oligomer composition of vanadate solutions, which is of interest in biochemical and biological studies.