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H Barrios

Publications and source records attributed to H Barrios.

15 recordsLinked to original sources
PubMed2005

(1)H, (13)C NMR and X-ray crystallographic studies of highly polyhalogenated derivatives of costunolide lactone.

The costunolide lactone, a sesquiterpene compound isolated from Zaluzania triiloba species, reacted with several dihalocarbene sources produced by trihaloform-NaOH under successive phase transfer reactions yielding mono-, bis- and tris-dihalocyclopropane adducts. The structures, as well as the configurational assignments of the different derivatives, were established by (1)H and (13)C NMR spectroscopy and assisted by X-ray crystallographic and molecular modelling studies. The specific shielding of protons in the neighbourhood of different halogens on the cyclopropane moieties was correlated to the pseudocontact interactions.

Anthelmintics↗
PubMed2003

1H,13C 2D NMR and X-ray studies of the products of the reaction between dibenzylidencyclohexanone and 6-amino-1,3-dimethyl uracil.

The reaction of the 6-amino-1,3-dimethyl uracil with the dibenzylidencyclohexanone (1), provided three adducts whose structures result from nucleophilic attack yielding the monoadduct 3 and two isomeric bisadducts (4 and 5) in moderate yields (50-60%). The structures obtained in this study were elucidated with 2D high resolution NMR experiments, variable temperature NMR and X-ray crystallographic studies. In compound 3, the tricyclic skeleton is essentially planar and the cyclohexane ring addopts an envelope conformation. The structures 4 and 5 correspond to two isomeric spiro compounds.

Crystallography, X-Ray↗
PubMed2002

2D 1H and 13C NMR evidences of the [2 + 2] autodimerization of 2-benzyl-5-benzylidene cyclopentanone yielding two different diphenyl, dispiro cyclobutane derivatives.

The ene-ene [2 + 2] cycloaddition of 2-benzyl-5-benzylidenecyclopentanone proceeds smoothly and spontaneously in benzene-d6 or deuteriochloroform solution to give two different diphenyl dispiro [4.1.4.1] dodecan-4,11-diones. Detailed 1H and 13C 2DNMR spectroscopy (COSY, HMQC, HMBC) were performed in order to prove the existence in solution of two cyclobutane derivatives, one a previously described photodimer obtained by the UV irradiation of crystals of 2-benzyl-5-benzylidenecyclopentanone.

Carbon Isotopes↗
PubMed2001

RepA negatively autoregulates the transcription of the repABC operon of the Rhizobium etli symbiotic plasmid basic replicon.

The basic replicon of Rhizobium etli CE3, like other members of the repABC plasmid family, is constituted by the repABC operon. RepC is essential for replication, and RepA and RepB play a role in plasmid segregation. It has been shown that deletion derivatives lacking the repAB genes have an increased copy number, indicating that these genes participate in the control of plasmid copy number. RepA is also a trans-incompatibility factor. To understand the regulation of the repABC operon, in this paper: (i) the transcription start site of the repABC operon was determined; (ii) the promoter region was identified by site-directed mutagenesis of the putative -35 and -10 hexameric elements; and (iii) RepA was recognized as a negative regulator of the transcription of the repABC operon.

Bacterial Proteins↗
PubMed2000

13C and 1H NMR of 2,6-diaryl-1-hydroxy piperidin-4-one oximes; substituent effects on cis/trans ratio and conformational equilibria.

The reaction of substituted diarylidene acetones with hydroxylamine hydrochloride affords isomeric N-hydroxy diaryl piperidinone oximes as main products. The structures as well as conformational equilibria of these products were established by 1H and 13C NMR spectroscopy and further studied by variable temperature NMR. It was found that the cis/trans ratio of 2,6-substituted piperidine derivatives depended on the position of the substituent on the aromatic ring.

Acetone↗
PubMed1999

Compilation and analysis of sigma(54)-dependent promoter sequences.

Promoters recognized by the RNA-polymerase with the alternative sigma factor sigma(54) (Esigma54) are unique in having conserved positions around -24 and -12 nucleotides upstream from the transcriptional start site, instead of the typical -35 and -10 boxes. Here we compile 186 -24/-12 promoter sequences reported in the literature and generate an updated and extended consensus sequence. The use of the extended consensus increases the probability of identifying genuine -24/-12 promoters. The effect of several reported mutations at the -24/-12 elements on RNA-polymerase binding and promoter strength is discussed in the light of the updated consensus.

Bacteria↗
PubMed1998

In vivo genomic footprinting analysis reveals that the complex Bradyrhizobium japonicum fixRnifA promoter region is differently occupied by two distinct RNA polymerase holoenzymes.

The Bradyrhizobium japonicum fixRnifA operon is transcribed from two promoters: fixRp1, a -24/-12 promoter recognized by the sigma54-holoenzyme form of the RNA polymerase, and fixRp2, a -35/-10 promoter that is transcribed by a second, unidentified, form of RNA polymerase holoenzyme. The fixRp1 promoter is autoregulated during microaerobiosis by NifA, whereas fixRp2 is also activated, but by a different regulatory protein. The main transcription start sites for these promoters are just two nucleotides apart, such that the conserved -12 and -10 regions of fixRp1 and fixRp2, respectively, must overlap each other, whereas the -24 and -35 regions lie one DNA helical turn apart. Using in vivo genomic dimethyl sulfate and KMnO4 footprinting, we showed that the promoter region is differentially protected, depending upon which holoenzyme is bound. Mutagenesis analyses indicated that positions from -12 to -14 are critical for the activity of both promoters, whereas mutations at -10 and -11 affected mainly fixRp2 expression. When the sequence of the putative -35 region of fixRp2 was modified to match the putative consensus, expression from this promoter was increased 3-fold and the reactivity toward KMnO4, but not the transcriptional start site, moved two nucleotides further upstream, indicating that the altered promoter forms a different open complex. Additionally, we detected NifA-dependent methylation protection of two atypical NifA binding sites and protection of guanine -75. The latter residue is located in a region critical for fixRp2 promoter activation. The results present direct physical evidence of the complexity of the organization, regulation, and function of the fixRnifA promoter region.

Bacterial Proteins↗
PubMed1998

2D 1H and 13C NMR evidence for stereoselective formation of a new bond C-N, C-S or C-C in the reaction of ivalin acetate with substituted pyrimidines.

Several pyrimidine derivatives of ivalin acetate were synthesized as potential anti HIV agents. High stereoselective Michael addition to ivaline acetate was observed and a new C-C, C-N or C-S bond was formed. 2D NMR 1H and 13C as well as X-ray crystallographic studies were performed on the compounds herein described to establish the structure and stereochemistry.

Alkylation↗
PubMed1995

Overlapping promoters for two different RNA polymerase holoenzymes control Bradyrhizobium japonicum nifA expression.

The Bradyrhizobium japonicum NifA protein, the central regulator for nitrogen fixation gene expression, is encoded in the fixRnifA operon. This operon is activated during free-living anaerobic growth and in the symbiotic root nodule bacteroid state. In addition, it is expressed in aerobic conditions, albeit at a low level. Here, we report that this pattern of expression is due to the presence of two overlapping promoters: fixRp1, which is of the -24/-12 class recognized by the RNA polymerase sigma 54, and fixRp2, which shares homology with the -35 and -10 regions found in other putative B. japonicum housekeeping promoters. Primer extension analyses showed that fixRp1 directed the synthesis of a transcript, P1, that starts 12 nucleotides downstream of the -12 region. In addition to sigma 54, P1 was dependent on NifA and low oxygen tension. Transcripts originating from fixRp2 started at two sites: one coincided with P1, while the most abundant, P2 initiated just two nucleotides further downstream of P1. Expression from fixRp2 was dependent on the upstream -68 promoter region, a region known to bind a putative activator protein, but it was independent of sigma 54 and NifA. This promoter was expressed in aerobic and anaerobic conditions but was not expressed in 30-day-old bacteroids. Mutations in the conserved 12 region for the sigma 54 promoter did not show any transcript, because these mutations also disrupted the overlapping -10 region of the fixRp2 promoter. Conversely, mutations at the -24 region only affected the sigma 54-dependent P1 transcript, having no effect on the expression of P2. In the absence of omega(54), anaerobic expression from the fixRp(2) promoter was enhanced threefold, suggesting that in the wild-type strain, the two RNA polymerase holoenzymes must compete for binding to the same promoter region.

Bacterial Proteins↗
PubMed1982

New attenuation marker for junin virus based on immunologic responses of guinea pigs.

A new attenuation marker to distinguish a virulent strain (XJJV) from an attenuated strain (XJC13JV or XJOJV) of Junin virus by means of the humoral and cellular responses to unrelated antigens was studied in guinea pigs. Strain XJJV suppressed the humoral immune response, as shown by the lower titers of precipitating antibody to ovalbumin. The concomitant decrease in serum complement level contributed to a milder Arthus cutaneous reactivity. In contrast, the attenuated strains did not decrease the humoral response. The pathogenic strain suppressed cell-mediated immunity, as demonstrated by decreased contact sensitivity to 2,4-dinitro-1-fluorobenzene and by depression of delayed skin reactions to tuberculin purified protein derivative. When attenuated strains were used, such suppressive effects were not observed. For virulent strain XJJV, virus replication in lymphoid organs and immunosuppressive effects were correlated. These findings provide a further means to differentiate between virulent and attenuated strains of Junin virus for the purpose of vaccine control of Argentine hemorrhagic fever.

Animals↗
PubMedDate not supplied

[Serotypes of Salmonella isolated from the Luján River, Argentina].

In this work, the serotypes of Salmonella genus polluting the waters of Lujan River, situated in the north east of the province of Buenos Aires, Argentina, were studied. A total of 690 samples of water were collected and analysed from February 1988 through December 1989, at three different sites. They were obtained according to the Moore technique and then preenriched in buffered peptone water and enriched in Rappaport-Vassiliadis Soya peptone broth was carried out. The isolations were realised in brilliant green-desoxycholate agar and bismuth sulphite agar and the presumptive colonies to be Salmonella were tested by the standard biochemical identification. Salmonella spp. was isolated in 434 samples (62.9%). The predominant serotype was S. Anatum, followed in a decreasing order by S. Montevideo, S. Newport and S. Bredeney. A large amount of serotypes that are isolated with very low frequency and very rarely in other hidric courses in the country were: S. Westhampton, S. Poona and S. Saintpaul were found.

Argentina↗
PubMedDate not supplied

[Incidence of rotavirus in intensive-production poultry farms].

Rotavirus are the major etiological agent of acute gastroenteritis in various species of mammals and birds. This study was aimed to explore the frequency of rotavirus in flocks of commercial laying hens and industrial broiler chicken. Feces and caecal content were sampled from 589 birds belonging to 17 farms located in the neighbourhood of Lujan National University. RNA patterns were explored by polyacrylamide gel electrophoresis. Viral particles were found with moderate frequency throughout the period of study: 7.06% in 1987; 7.45% in 1988; 12.57% in 1989. This finding demonstrates the permanence of rotavirus infection in the farm under study and emphasizes the importance of routine rotavirus screening in industrial poultry farms.

Animal Husbandry↗
PubMedDate not supplied

[Comparative study of 4 methods for isolating Salmonella from surface waters].

The study presented here is the first stage of a project designed to determine the presence of Salmonella serotypes in Lujan river waters, which flow beside the urban area of the homonymous city, in the province of Buenos Aires. It consisted in a comparative study of four methods for Salmonellae detection in 200 samples: Tetrathionate-brilliant green; mannitol-selenite; Rappaport 25 and modified Rappaport-Vassiliadis broth, each of them with and without pre-enrichment in buffered peptone water. The submerged gauze technique was applied to the sampling in three different spots of the river: at the town center, two km water above, and two down-stream from the city. Best results were obtained when modified Rappaport-Vassiliadis enrichment broth and brilliant green agar with 0.25% of sodium deoxycholate were used, after pre-enrichment of the samples in buffered peptone water. Salmonella were isolated from 46% of the samples studied, and 16 serotypes were identified: S. Typhimurium, S. Enteritidis, S. Infantis, S. Mbandaka, S. Israel and S. Subspecies IV 18 z36: z38:-, among them.

Bacteriological Techniques↗