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Biomedical subjects

R Beltrán

Publications and source records attributed to R Beltrán.

At least 19 recordsLinked to original sources
PubMed2006

Use of multiple headspace solid-phase microextraction and pervaporation for the determination of off-flavours in wine.

The occurrence of off-flavours in wines and especially the so-called "cork taint defect" represents one of the most serious problem in wine industry in which 2,4,6-trichloroanisole has been blamed as the main responsible. The development of analytical methods for haloanisoles determination in wine/cork represent a challenge, mainly due to food matrix complexity and low taste and odour (T&O) threshold levels which are generally beyond the sensitivity of the analytical systems. In this work, a method based on the combined use of the recently developed multiple headspace solid-phase microextraction (MHS-SPME) and gas chromatography-ion-trap mass spectrometry has been optimised for the determination of haloanisoles in wines. This powerful analytical methodology is compared with several analytical approaches based on pervaporation, an innovative membrane-based technique similar to dynamic headspace. Analytical features of the methods assayed reveal their suitability for the appraisal of haloanisoles in this matrix in which threshold odor concentrations are in the range 4-40 ng l(-1). The analytical approaches have been applied to the analysis of haloanisoles in different Spanish white and red wines, in which spiking experiments showed good recoveries for the methodologies assayed.

Anisoles↗
PubMed2005

Precipitation, pH and metal load in AMD river basins: an application of fuzzy clustering algorithms to the process characterization.

In the present work, Acid Mine Drainage (AMD) processes in the Chorrito Stream, which flows into the Cobica River (Iberian Pyrite Belt, Southwest Spain) are characterized by means of clustering techniques based on fuzzy logic. Also, pH behavior in contrast to precipitation is clearly explained, proving that the influence of rainfall inputs on the acidity and, as a result, on the metal load of a riverbed undergoing AMD processes highly depends on the moment when it occurs. In general, the riverbed dynamic behavior is the response to the sum of instant stimuli produced by isolated rainfall, the seasonal memory depending on the moment of the target hydrological year and, finally, the own inertia of the river basin, as a result of an accumulation process caused by age-long mining activity.

Environmental Monitoring↗
PubMed2003

Spatial variations of heavy metals contamination in sediments from Odiel river (Southwest Spain).

The presence of heavy metal concentrations was examined in surface sediments from 27 sites within the Odiel river in the southwest Spain suffering inputs from industrial and mining activities. The interest is specially focused on the final delta located in the Odiel Natural Park, which constitutes a feeding ground of international importance for migrating birds. The behavior of 10 heavy metals (Zn, Cd, Pb, Cu, Cr, Mn, Ni, Fe, Hg) is conditioned by chemical properties of sediments such as acidity and carbonate or the presence of sulfate Very acidic sediments in the medium course of river contribute to the lower presence of metal as a consequence of leaching process. However, tidal action raises the pH in the marshes of the delta with correlative metal accumulation. In accordance with the Müller [Umschan 79 (1979) 133-149] scale for geoaccumulation index, the entire watercourse could be considered polluted by Zn and Pb, while Cu exhibits a high presence in the delta marshes of the river.

Animals↗
PubMed1993

Characterization of the zinc-induced structural transition to *H-DNA at a d(GA.CT)22 sequence.

Zinc induces transition of a d(GA.CT)22 sequence to a novel DNA conformation, called *H-DNA. In this paper, the structural characteristics of this altered DNA conformation are determined. Formation of *H-DNA is induced at zinc concentrations higher than 70 microM (Zn/P = 2) and it is favoured by negative supercoiling and low ionic strength. Two different structural conformations of the d(GA.CT)22 sequence are observed upon increasing the zinc concentration. At low zinc concentration (Zn/P < 15), half of the purine strand falls back upon itself giving rise to the formation of an RRY intramolecular triplex (H*-triplex). At higher zinc concentration, the complete pyrimidine strand is single-stranded and an RR hairpin is formed (*H-hairpin). Protection towards dimethylsulphate modification suggests that zinc binds to the N-7 group of guanine residues in the *H-hairpin with a higher affinity than in B-DNA. The dissociation constant of the *H-zinc complex is estimated to be in the range of 10(-3) M to 10(-4) M.

Base Sequence↗
PubMed1991

SV40 recombinants carrying a d(CT.GA)22 sequence show increased genomic instability.

Repetitive d(CT.GA)n sequences are commonly found in eukaryotic genomic DNA. They are frequently located in sites involved in genetic recombination or in promoter regions. To test for their possible biological function, a d(CT.GA)22 synthetic sequence was introduced into the genome of SV40, since it constitutes an appropriate model system for eukaryotic chromatin. When SV40 infects permissive cells, it proliferates in the form of a minichromosome. The simple repetitive sequence indicated above was inserted at the unique HpaII site of SV40 (at nt 346), and the genomic stability of SV40 recombinants carrying the d(CT.GA)22 sequence (SV/CT22 viruses) was analyzed. Upon serial passage through permissive CV1 cells, SV/CT22 recombinants show an increased production of defective viruses. Generation of SV/CT22 variants is likely to take place via recombination between and within viral molecules. The enhancement of the rate of recombination induced by the repetitive sequence is likely to be related to its known propensity to form triple-stranded structures. Many different variants coexist in the same viral population indicating that the mechanism by which they are produced is not unique. One variant (SV/X), showing a replicative advantage, was characterized in detail. Variant SV/X accounts for a large proportion of the total viral population. Its genomic organization corresponds to a tandem duplication of an early SV40 DNA fragment spanning from approx. nt 3200-nt 160. Variant SV/X contains a duplicated SV40 ori.

Base Sequence↗
PubMed1990

DNA-sequence and metal-ion specificity of the formation of *H-DNA.

The homopyrimidine-homopurine sequence d(CT/GA)22 undergoes, in the presence of zinc ions, transition to an altered DNA conformation (*H-DNA) which is neither H-DNA nor B-DNA. *H-DNA is characterized by a peculiar chemical reactivity pattern in which most of the polypyrimidine strand is hyperreactive to osmium tetroxide and the central part of the polypurine strand is sensitive to diethylpyrocarbonate. Formation of *H-DNA is specific of metal-ion. *H-DNA is detected in the presence of Zn++, Cd++ and Mn++. The efficiency on promoting the transition is in the order of Zn++ greater than Cd++ much greater than Mn++. Formation of *H-DNA is also specific of nucleotide sequence. From all the different homopolymeric sequences tested only the d(CT/GA)22 sequence showed the zinc-induced transition to *H-DNA. These results suggest that stabilization of *H-DNA involves the formation of a specific complex between the metal-ion and the nucleotide sequence. The biological relevance of these results is discussed in view of the important role that zinc ions play on many nucleic acids processes.

Base Sequence↗
PubMed1989

Structural polymorphism of homopurine--homopyrimidine sequences: the secondary DNA structure adopted by a d(GA.CT)22 sequence in the presence of zinc ions.

In this paper, we have analysed the conformational behaviour shown by the homopurine--homopyrimidine alternating d(GA.CT)22 sequence cloned into SV40. Our results show that, in the presence of zinc ions, the d(GA.CT)22 sequence adopts an altered secondary DNA structure (*H-DNA) which differs from either B-DNA or H-DNA. Formation of *H-DNA is facilitated by negative supercoiling and does not appear to require base protonation, since it is induced at neutral pH by approximately 0.4 mM ZnCl2. The patterns of OsO4 and DEPC modification obtained in the presence of zinc are compatible with a homopurine--homopurine--homopyridimine triplex, though other structural models for *H-DNA are also possible. The hypersensitivity to S1-cleavage of the d(GA.CT)22 sequence is reinterpreted in terms of the equilibria between the B-, H- and *H-forms of the sequence. These results reveal the high degree of structural polymorphism shown by homopurine-homopyrimidine sequences. Its biological relevance is discussed.

Animals↗
PubMed1978

[Innovative trends in dentistry: background, bases and outlook].

This article briefly analyzes the present situation in dental practice with emphasis on its inherent discrepancies, and describes the background, theoretic and methodologic bases, and prospects of the PAHO/WHO Program of Innovation in Dental Education and Care. An account is given of the conceptual framework of the Program, which is based on the hypothesis that changes in oral health in a country depend partly on the national socioeconomic situation at any given point in its history. At the same time, it is recognized that there is leeway in the general political setting for the trial and application of plans for curricula and care that can work quantitative and qualitative changes in the educational and service sectors. There follows a description of the operational arrangement and the subprograms and prpkects going forward in 16 dental schools of Latin America.

Dental Care↗
PubMed1977

Changing patterns in dental education in Latin America.

The unsatisfactory dental health situation in the majority of the Latin American population, presently not covered by existing dental services, led to a serious questioning of the educational process directed to prepare human resources in dentistry. At the present time, many dental schools in Latin America are trying to find and implement new teaching methods, different curriculum patterns, and even seeking to define new professional and non-professional profiles, in order to meet the tremendous challenge that requires the formation of a different type of dental health personnel capable of introducing definite changes in the way dentistry is conceived and performed in order to cover the needs of a constantly growing population.

Community Health Services↗