PubMed Health⌕ Search

Biomedical subjects

J Rocha

Publications and source records attributed to J Rocha.

At least 37 records · Page 2Linked to original sources
PubMed2000

Structural characterization of glassy phases in the system Na2O-Ga2O3-P2O5 by MAS and solution NMR and vibrational spectroscopy: II. Structure of the phosphate network.

The structure of the phosphate network of glasses in the system Na2O-Ga2O3-P2O5 has been investigated as a function of the Na/Ga molar ratio and the phosphate composition corresponding to a mono, di, tri, tetra and meta phosphate stoichiometry. The glass is made of phosphate molecular groups of different lengths linked by the cations with rather ionic (Na) or more covalent (Ga) bonds except in the case of the orthophosphate composition for which we only found isolated PO4(3-) ions. The vibrational spectra are sensitive to composition variations but the band width and the couplings between the different groups prevent any quantitative determination. 31P MAS-NMR gives an in-situ information on the P environment in the glass but the signals are often large and ill defined so that the assignment is not at all straightforward. On the other hand, 31P solution NMR gives sharper signals, allowing more quantitative determinations but the dissolution process always introduces some indeterminacy on the real glass structure which can be minimized by a careful preparation of the solution.

Diphosphates↗
PubMed2000

Structural characterization of glassy phases in the system Na2O-Ga2O3-P2O5 by MAS-NMR, EXAFS and vibrational spectroscopy. I. Cations coordination.

The cationic coordinations of phosphate based gallium sodium glasses in the system Na2O-Ga2O3-P2O5 have been studied by several techniques (71Ga and 23Na MAS-NMR, EXAFS and vibrational spectroscopies) in order to study the relationship between the structure and the chemical composition. We found that three different environments are available for the gallium ions while it is very difficult to get accurate information on the sodium coordinations. Our data show that in orthophosphate glasses, gallium is mainly tetrahedral but when the mean phosphate chain length increases, its coordination becomes more and more octahedral. In these glassy structure, it becomes then possible to dissolve large amounts of typically octahedral cations like Fe3+ or Cr3+.

Cations↗
PubMed1999

Identification of a novel R21X mutation in the liver-type arginase gene (ARG1) in four Portuguese patients with argininemia.

Argininemia is a rare autossomal recessive disorder caused by deficiency in the cytosolic liver-type arginase enzyme (L-arginine urea-hydrolase; E.C. 3.5.3.1). In order to investigate the molecular basis for argininemia in four unrelated Portuguese patients (two from northern Portugal and two from Madeira Island) we performed a DNA sequence analysis of all the exons and exon/intron boundaries of the liver-type arginase gene (ARG1). All patients were found to be homozygous for a newly identified C ->T transition in codon 21 (exon 2) substituting arginine for a premature stop codon (R21X: CGA to TGA) and generating a NlaIII restriction site. Restriction digestion following PCR amplification of ARG1 exon 2 confirmed the presence of the mutation.

Amino Acid Metabolism, Inborn Errors↗
PubMed1999

Very high-resolution 1H MAS NMR of a natural polymeric material.

The use of ultrafast magic angle spinning (> 30 kHz) in tandem with delayed echo acquisition is shown to yield very high-resolution lH MAS NMR spectra of complex natural organic materials. For the first time, very high-resolution 1H MAS NMR spectra are reported for cork and wood components, two natural materials with great economic importance. The effect of the spinning rate on the 1H NMR spectra was evaluated with single-pulse acquisition and delayed-echo acquisition. The delayed-echo acquisition spectra presented linewidths as sharp as 67 and 25 Hz. The narrow peaks, characterised by proton spin-spin and spin-lattice relaxation, were assigned to the isotropic chemical shifts and the general spectral features were shown to correlate with the sample chemical structure. The tentative assignments of cork 1H MAS NMR signals were presented.

Biopolymers↗
PubMed1999

Identification in Portugal and Brazil of a mtDNA lineage containing a 9-bp triplication of the intergenic COII/tRNALys region.

Although the deletion of one of the 9-bp repeats in region V of mitochondrial DNA is very common in Asians, Asian-derived populations and Africans, the triplication of the 9-bp segment was described only a few times, mostly on individuals from Asian origin. Here, we report for the first time the presence of the 9-bp triplication in Europeans. The triplication was initially found in one Brazilian individual. Sequencing of the hypervariable segments I (HVSI) and II (HVS2) of the control region and RFLP analysis of the coding region classified the mtDNA as belonging to the European haplogroup H. Since white Brazilians are predominantly of Portuguese descent, we screened 96 unrelated Northern Portuguese for the 9-bp triplication and found its presence in two of them (2.1%). One of these had an mtDNA haplotype identical to that of the Brazilian individual, while the other differed in a single base change in HVS2. The fact that the 9-bp triplication has reached polymorphic frequencies in Northern Portugal and that it has apparently differentiated into at least two lineages defined by the mutuation in HVS2 suggests that it probably occurred a long time ago.

Base Sequence↗
PubMed1999

Haplotype analysis of the apolipoprotein E and apolipoprotein C1 loci in Portugal and São Tomé e Príncipe (Gulf of Guinea): linkage disequilibrium evidence that APOE*4 is the ancestral APOE allele.

The joint distributions of phenotypes from the apolipoprotein E gene (APOE) and from a closely linked restriction site polymorphism at the apolipoprotein C1 locus (APOC1) were studied in population samples from Portugal and São Tomé e Príncipe (Gulf of Guinea), a former Portuguese colony that was originally populated by slaves imported from the African mainland. The frequencies of the APOE alleles (*2, *3, and *4) in Portugal and São Tomé fitted the ranges of variation generally observed in European and African populations, respectively. Haplotype analysis showed that in both populations the strength of linkage disequilibrium was highest for the APOE*2 allele and lowest for the APOE*4 allele, suggesting that the origin of the APOE alleles followed a 4-->3-->2 pathway and thus providing independent confirmation of the results from sequence homology studies with nonhuman primates. In accordance with global trends in the distribution of human genetic variation, the European sample from Portugal presented more intense linkage disequilibrium between APOE and APOC1 than the African sample from São Tomé where, despite the short 4-kb distance that separates the 2 loci, the level of association between the APOC1 alleles and APOE*4 was nonsignificant.

Apolipoprotein C-I↗
PubMed1999

Adenosine deaminase polymorphisms at the protein and DNA levels.

Adenosine deaminase (ADA, E.C. 3.5.4.4) exhibits a well-known polymorphism at the protein level. We have studied ADA and an STR polymorphism exhibiting variation of a TTTA repeat motif at intron 3 of the ADA gene in random samples from northern Portugal (N = 218) and southwestern Germany (N = 114). The ADA phenotype distribution and population data on the worldwide distribution of ADA favor recurrent mutation as an explanation for the maintenance of the ADA*2 gene product at polymorphic frequencies.

Adenosine Deaminase↗
PubMed1998

Pancreatitis and primary hyperparathyroidism: forty cases.

BACKGROUND: Pancreatitis is associated with primary hyperparathyroidism (PHPT) in 1.5-7% of cases. The relationship of cause and effect between the two diseases has been debated. METHODS: To evaluate this relationship, the clinical, biochemical and pathological data on 1435 patients operated on for hyperparathyroidism (HPT) over the past 30 years were retrospectively reviewed. A total of 1224 of these patients had biologically proven and cured PHPT and 211 patients had renal HPT (RHPT). The diagnosis of pancreatitis (PTS) was based on a high serum amylase level and/or abnormalities on ultrasound or computed tomography (CT) scan explorations. Only patients without biliary stones were included in the PTS group associated with HPT. RESULTS: A total of 3.2% (n = 40) of patients with PHPT had PTS, which was acute in 18 cases, subacute in 8 cases and chronic in 14 cases. This rate of PTS is higher than in a random hospital population. Surgical cure of HPT was followed by the spontaneous healing of 17/18 acute PTS, whereas six of the 22 patients with subacute or chronic PTS developed complications due to the evolution of their disease (diabetes, pancreatic duct stenosis treated by surgery). A single diseased gland was found in 27 patients with PTS, which is in favour of primary parathyroid disease, being responsible for, and not a consequence of, PTS. Only the serum calcium (13.0 vs 12.1 g/dL) level was significantly increased in PHPT patients with PTS, when compared to those without PTS. The calcium level is probably of major importance in the development of PTS, which was never encountered in 211 patients with RHPT, who had low calcium and high PTH levels. CONCLUSIONS: The data suggest that (i) the PTS-PHPT association is not incidental; (ii) PTS is the consequence and not the cause of PHPT; (iii) hypercalcaemia seems to be a major factor in the development of PTS in PHPT patients; and (iv) cure of PHPT leads to the healing of acute PTS, whereas it does not affect the evolution of subacute and chronic PTS.

Acute Disease↗
PubMed1997

Analysis of the allelic diversity of a (CA)n repeat polymorphism among alpha 1-antitrypsin gene products from northern Portugal.

The level of molecular heterogeneity associated with alpha 1-antitrypsin gene products was assessed in the population of northern Portugal using three restriction fragment length polymorphisms (RFLPs) corresponding to specific amino acid substitutions and a highly variable (CA)n repeat polymorphism located at the 5' end of the PI gene. The allelic affinities inferred from the analysis of the DNA polymorphisms essentially agree with the evolutionary pattern proposed for the PI gene products on the basis of their amino acid sequences. PI*Z can be considered the most recent common PI allele and was found to be associated with the same predominant haplotype previously reported in northern European populations, thus confirming the hypothesis that most European Z alleles are derived from a single mutation. However, a rare deficient variant that is the likely result of a recurrent Z mutation on an M2 or M4 background was additionally observed. PIS was also found to be associated with a strongly predominant haplotype and seems to be the second most recent PI common allele, while M2 and M3 show weaker associations, suggesting more ancient origins of their corresponding mutations. M1Ala213 and M1Vat213 display more homogeneous (CA)n allele frequency distributions, M1Ala213 representing the most ancient PI allele as inferred from its highest variance in (CA)n allele length.

Alleles↗
PubMed1997

A 13C solid state nuclear magnetic resonance spectroscopic study of cork cell wall structure: the effect of suberin removal.

Solid state 13C NMR measurements of cork, before and after suberin removal, showed that aliphatic suberin is spatially separated from carbohydrate and lignin and experiences higher motional freedom. Two types of chain methylenes, differing in chemical shift and in dynamic properties, were identified in aliphatic suberin. Experimental evidence indicated that the more motionally hindered methylenes are those situated nearer the linkages of aliphatic suberin to the cell wall. These linkages were shown to involve -CH2O- groups, probably engaged in ester linkages to phenylpropane units and carbohydrate C6 carbons. Spectral intensity changes indicated that, during the first steps of alkaline desuberization, these linkages are broken and the shorter aliphatic suberin chains removed. Longer chains require hydrolysis of the ester linkages within the chains and are removed upon stronger alkaline treatment. T1(C), T1 rho (H) and T1 rho (C) relaxation times have shown that the removal of suberin from cork leads to a motionally restricted and more compact environment, on the megahertz and mid-kilohertz timescales. The properties of cork suberin showed that suberin organization in cork is distinct from that in potato tissue.

Carbohydrates↗
PubMed1997

Solid-state NMR studies of interstitial phosphorus atoms in rhodium carbonyl clusters.

Pure samples and as-prepared mixtures of Rh9 and Rh10 carbonyl clusters with interstitial P atoms have been studied quantitatively by 31P MAS and 1H-31P CP/MAS NMR. Information on the 31P chemical shift tensor of the Rh9 and Rh10 clusters has been derived from spinning sideband simulations. The chemical shift anisotropy is slightly larger in the Rh10 clusters (340-400 ppm) than in the Rh9 clusters (230-300 ppm), while the asymmetry parameters are similar (eta = 0.1-0.4). The results contribute to the understanding of the relationship between the shielding anisotropy and the structure of the cluster cavity.

Anisotropy↗
PubMed1995

Transient bisalbuminemia: separation by isoelectric focusing of human albumin fractions linked to different numbers of benzylpenicilloyl groups.

The behavior of modified human serum albumin (HSA) from penicillin-treated patients and in vitro conjugated samples was studied by isoelectric focusing in the absence and presence of 8 M urea. It is shown that samples classified as bisalbuminemic after separation under native conditions display a spectrum of several major bands with decreasing pIs when focusing is done in the presence of 8 M urea. In this spectrum, the distances between two consecutive major bands are as expected from a 2-unit charge difference. Since this result is compatible with the blockage of a lysine residue with a benzylpenicilloyl (BPO) group, each major band can be interpreted as representing an HSA fraction covalently linked to different numbers of benzylpenicilloyl groups. The separation methods presented therefore seem to constitute simple and reliable tools for a detailed assessment of the extent of BPO covalent binding to HSA both in vivo and in vitro.

Benzeneacetamides↗
PubMed1995

Anterior evacuation of a spontaneous cervical epidural hematoma.

The case of a spontaneous cervical epidural hematoma treated by anterior corporectomy and arthrodesis is reported. An anterior approach is preferable when an epidural hematoma is anterior to the dural sac and when MRI shows an aspect of old clotted blood that can not be easily evacuated by a posterior laminectomy.

Cervical Vertebrae↗
PubMed1995

13C solid-state nuclear magnetic resonance and Fourier transform infrared studies of the thermal decomposition of cork.

The thermal decomposition of cork has been studied by Fourier transform infrared (FTIR) spectroscopy and 13C solid-state nuclear magnetic resonance (NMR) spectroscopy with cross-polarization and magic-angle spinning (CP-MAS), high-power 1H decoupling (HPDEC) and cross-polarization depolarization-polarization (CPDP). Waxes and other soluble components of cork begin to decompose at ca. 150 degrees C. This is accompanied by partial decomposition of suberin, probably initiated at the points of attachment to the cell wall. The carbohydrates begin to decompose at ca. 200 degrees C. The decomposition of lignin begins at 250-300 degrees C, while suberin undergoes further degradation. Significant amounts of coke are formed in the process. At 400 degrees C cork has been transformed into coke with traces of partially decomposed suberin. The thermal decomposition of cork is dependent on the calcination time, particularly in the 200-350 degrees C range.

Hot Temperature↗