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J A Cavaleiro

Publications and source records attributed to J A Cavaleiro.

13 recordsLinked to original sources
PubMed2001

Phenolic constituents from the core of kenaf (Hibiscus cannabinus).

Four lignans, boehmenan H [2-(4-hydroxy-3-methoxyphenyl)-5-[3-(4-hydroxy-3-methoxycinnamoyloxy)propyl]-3-hydroxymethyl-7-methoxybenzodihydrofuran], boehmenan K [2-(4-hydroxy-3-methoxyphenyl)-5-[3-(4-hydroxycinnamoyloxy)-1-propenyl]-3-(4-hydroxy-3-methoxycinnamoyloxymethyl)-7-methoxybenzodihydrofuran], threo-carolignan H [threo-1-(4-hydroxy-3-methoxyphenyl)-2-[4-[3-(4-hydroxy-3-methoxycinnamoyloxy)propyl]-2-methoxyphenoxy]-1,3-propanodiol], and threo-carolignan K [threo-1-(4-hydroxy-3-methoxyphenyl)-3-(4-hydroxy-3-methoxycinnamoyloxy)-2-[4-[3-(4-hydroxycinnamoyloxy)-1-propenyl]-2-methoxyphenoxy]-1-propanol] as well as several other lignans, aldehydes and a tyramine derivative were isolated from the acetone extract of core of kenaf (Hibiscus cannabinus). All the structures were established by spectroscopic methods. The hitherto unreported 13C NMR spectra of some compounds are also presented and discussed. 2D NMR techniques have allowed the revision of certain previously reported 13C NMR assignments of some scarce naturally occurring compounds.

Lignans↗
PubMed2001

Lignanamides and other phenolic constituents from the bark of kenaf (Hibiscus cannabinus).

Two new acyclic phenylpropane lignanamides, grossamide K and erythro-canabisine H, and the naphthol glucoside 2,5-dimethyl-3-O-beta-D-glucopyranosylnaphthol, along with six known compounds were isolated from the acetone extract of bark of Hibiscus cannabinus. All structures were established by spectroscopic methods including 2D NMR techniques, which allowed the correction of certain previously reported 13C NMR assignments of grossamide.

Amides↗
PubMed2001

Differentiation of positional isomers of nitro meso-tetraphenylporphyrins by tandem mass spectrometry.

We studied by tandem mass spectrometry two isomers of nitro meso-tetraphenylporphyrin, one with a nitro group in the para position of a phenyl ring and the other with the same group in a beta-pyrrolic position, and their copper complexes. Collisional activation of the molecular ions of both free-base porphyrins and of their copper complexes produces an array of product ions that permit ready differentiation of the two positional isomers. The diagnostic ions, when the nitro group is in a beta-pyrrolic position, may be produced through intramolecular and double cyclization processes, triggered by the interaction of the nitro substituent with the neighboring meso-phenyl ring. These diagnostic ions do not form when the nitro group is in the para position. The gas-phase processes have precedents in solution chemistry.

Copper↗
PubMed2000

Liquid secondary ion mass spectrometry of porphyrin dimers: reduction reactions and structural characterisation.

New synthesised porphyrin dimers, with an amide or ester linkage between the two porphyrin units, were studied using liquid secondary ion mass spectrometry (LSIMS). The formation of reduced species was observed for all the compounds and it was found that the extent of reduction is dependent on the matrix used and on the structure of the porphyrin dimer. The main fragmentation pathways lead to monomer fragments resulting from cleavage of the amide or ester linkage between the two porphyrin units. The consistency of the fragmentations for all the dimers studied leads to the proposal of a common designation for the fragment ions. LSIMS, in addition to molecular weight determination, can provide important structural information for this type of compound.

Dimerization↗
PubMed2000

Structural characterization of the lignin from the nodes and internodes of Arundo donax reed.

Milled wood lignin (MWL) and dioxane lignin (DL) from different morphological regions (nodes and internodes) of Arundo donax reed were subjected to a comprehensive structural characterization by (13)C, (1)H NMR, FTIR, and UV spectroscopies and functional analysis. The permanganate and nitrobenzene oxidation methods were also applied to the in situ lignins. Both node and internode lignins are HGS-type lignins, with a significant amount of H units (including p-coumaric acid type structures). The S/G ratio (1.13-1.32), the weight-average molecular weight (20,400-24,500), the methoxyl group content (0.90-0.98), the phenolic hydroxyl group content (0.23-0.27), and the aliphatic hydroxyl group content (1.00-1.09) are not very different in the lignins from nodes and internodes. However, some structural differences between node and internode lignins were observed. The former has much more phenolic acids (p-coumaric and ferulic), 8.8% in node versus 1.2% in internode and less beta-O-4 (0. 32 and 0.49 per aromatic unit in node and internode, respectively). In situ node lignin is more condensed than internode lignin.

Dietary Fiber↗
PubMed2000

meso-tetraphenylporphyrin dimer derivatives as potential photosensitizers in photodynamic therapy. Part 2.

Studies on the synthesis, singlet oxygen and fluorescence yields and pharmacokinetic properties of three different dimeric porphyrins with an amide linkage (D2-D4) are described and compared with the results recently reported for a dimeric porphyrin (D1). The pharmacokinetic behavior of all dimers were examined in Balb/c mice bearing MS-2 fibrosarcomas. The maximal efficiency and selectivity of photosensitizer accumulation in each tumor tissue takes place at 24 h after drug administration of 1.0 mg kg-1 into DL-alpha-dipalmitoylphosphatidylcholine liposomes by intravenous injection. Since the dimeric porphyrins exhibit high quantum yields of singlet oxygen generation, long triplet lifetimes and high photostability, the results obtained suggest that the evaluated dimeric structures may be promising candidates for further use in PDT experiments. The results also allow the possibility to establish a correlation between the chemical structure of the dyes and the efficiency/selectivity of the tumor accumulation and can be used for building up optimal photosensitizing agents for tumors.

Animals↗
PubMed1999

Do charge-remote fragmentations occur under matrix-assisted laser desorption ionization post-source decompositions and matrix-assisted laser desorption ionization collisionally activated decompositions?

The precursor ions of tetraphenylporphyrins that are substituted with fatty acids can be introduced into the gas phase by matrix-assisted laser desorption ionization (MALDI) and undergo post-source and collisionally activated decompositions (CAD) in a time-of-flight mass spectrometer. The goal of the research is to obtain a better understanding of post-source decompositions (PSD); specifically, we asked the question of whether ions undergoing PSD have sufficient energy to give charge-remote fragmentations along an alkyl chain. We chose the porphyrin macrocycle because we expected it to act as an inert "support," allowing the molecule to be desorbed by MALDI and to be amenable to charge-remote fragmentation. MALDI-PSD and MALDI-CAD spectra are similar to high-energy CAD spectra and considerably more informative than low-energy CAD spectra, showing that charge-remote fragmentations of the fatty acid moieties do occur upon MALDI-PSD and MALDI-CAD.

Fatty Acids↗
PubMed1998

High- and low-energy collisionally activated decompositions of octaethylporphyrin and its metal complexes.

High-energy (HE) and low-energy (LE) collisionally activated decompositions of octaethylporphyrin (OEP) and its metal complexes (ZnOEP and CuOEP) depend on whether the precursor is produced by electrospray ionization as protonated molecules or by fast atom bombardment as radical cations or protonated molecules. LE activation leads to such simple product-ion spectra that a complete picture of fragmentation emerges only after nine stages of tandem mass spectrometry (MS). HE activation, on the other hand, gives product-ion spectra that afford an integrated view of all the decomposition channels in a single MS/MS experiment. These results are the basis of a recommendation that OEP is an appropriate model compound for investigating energy effects in the collisional activation of organic and bioorganic molecule ions.

Gas Chromatography-Mass Spectrometry↗
PubMed1997

Meso-tetraphenylporphyrin dimer derivative as a potential photosensitizer in photodynamic therapy.

Studies on the synthesis, preliminary in vivo biological activity, singlet oxygen and fluorescence yields of a dimeric porphyrin (D1) are described. The pharmacokinetic behavior and photodynamic properties of the dimer D1 were examined in Balb/c mice bearing an MS-2 fibrosarcoma. Compound D1 shows a high selectivity for tumor localization (tumor/peritumoral tissue ratios of dye concentration ranging between ca 100 and 140 at 24 h after drug administration of 5.0-1.0 mg kg-1 into DL-alpha-dipalmitoylphosphatidylcholine liposomes). The phototherapeutic efficiency of dimer D1 was evaluated by following the growth curves of fibrosarcoma irradiated with red light (600-700 nm) with a total dose of 400 J cm-2, at 24 h after intravenous injection. Photodynamic therapy-treated tumors showed a significant delay in growth as compared to untreated control mice. The results obtained suggest that the porphyrin dimer D1 may be a promising candidate for further use in PDT experiments.

Animals↗