Luminescence quenching of tris(2,2′-bipyridine)ruthenium(II) by 2,6-dimethylphenol and 4-bromo-2,6-dimethylphenol in sol–gel-processed silicate thin films

The luminescence properties of tris(1,2-bipyridine)ruthenium(II) (Ru(bpy)(3)(2+)), included in different organically modified silicate gel matrixes were investigated. Spin and dip-coated thin films were prepared from methyltrimethoxysilane (MTMOS) and methyltriethoxysilane (MTEOS). A blue shift in the emission spectrum of the MLCT excited state of Ru(bpy)(3)(2+) with respect to the aqueous solution was observed in all the films, practically independent of the reaction pH used to prepare the "sol," silane-derived precursor, and procedure used (dip-coating or spin-coating) to obtain the film. A bimodal distribution of probe sites in the films was obtained from modeling of the emission decays by a double exponential and from application of the exponential series method. The parameters of the decay components depended principally on the thermal treatment used in the processing of the films. The lifetimes decreased with the increase in the drying temperature of the films; at the same time, the emission spectra showed a red shift and the luminescence efficiency decreased. A luminescence quenching of the ruthenium complex in the films by 4-bromo-2,6-dimethylphenol and 2,6-dimethylphenol in aerated aqueous solution at pH 12 in contact with the film was also observed. The quenching plots obtained from luminescence intensities or luminescence intensity decay measurements showed a downward curvature. These plots could be fitted satisfactorily by a sum of two Stern-Volmer terms with quenching constants K(SV1) and K(SV2) associated with two different binding sites of the ruthenium complex. This result is indicative of the matrix microheterogeneity in the films and is fully consistent with the biexponential nature of the luminescence intensity decay profiles. The Stern-Volmer parameter values for both sites in the films suggest that only a low percentage of the probe is accessible to the quencher and its respective constant K(SV1) is lower than in water.

Human CD1d-glycolipid tetramers generated by in vitro oxidative refolding chromatography

CD1 molecules are specialized in presenting lipids to T lymphocytes, but identification and isolation of CD1-restricted lipid specific T cells has been hampered by the lack of reliable and sensitive techniques. We here report the construction of CD1d-glycolipid tetramers from fully denatured human CD1d molecules by using the technique of oxidative refolding chromatography. We demonstrate that chaperone- and foldase-assisted refolding of denatured CD1d molecules and beta(2)-microglobulin in the presence of synthetic lipids is a rapid method for the generation of functional and specific CD1d tetramers, which unlike previously published protocols ensures isolation of CD1d tetramers loaded with a single lipid species. The use of human CD1d-alpha-galactosylceramide tetramers for ex vivo staining of peripheral blood lymphocytes and intrahepatic T cells from patients with viral liver cirrhosis allowed for the first time simultaneous analysis of frequency and specificity of natural killer T cells in human clinical samples. Application of this protocol to other members of the CD1 family will provide powerful tools to investigate lipid-specific T cell immune responses in health and in disease.

Characterization by single strand conformation polymorphism of mutations in the rpoB gene of rifampin-resistant Mycobacterium tuberculosis in strains from Vancouver, Mexico City and New Delhi

OBJECTIVE

The study was conducted to evaluate usefulness of single strand conformation polymorphism (SSCP) over DNA sequencing in the diagnosis of rifampicin (Rif)-resistant tuberculosis.

METHODS

Forty seven isolates of Mycobacterium tuberculosis (MTB) Rif-resistant and 25 Rif-sensitive were obtained from Vancouver, Mexico city and New Delhi and were analyzed by polymerase chain reaction (PCR) amplification of rpoB gene and the mutations were identified by DNA sequencing and SSCP.

RESULTS

The mutations observed by DNA sequencing in 47 RIF-resistant isolates showed that the most common mutation among Vancouver isolates was in codon 526, Hist-->Arg and in Mexico isolates was in codon 531, Ser-Leu and New Delhi isolates was in codon 516, Asp-->Val. Using fluorescence based PCR-SSCP, it was possible to distinguish Rif-resistant isolates from Rif-sensitive isolates.

CONCLUSION

DNA sequencing is a highly accurate method for the detection of mutations associated with drug resistance in tuberculosis but is more expensive and requires special equipment and personnel. SSCP is a simple, accurate method and suitable for analysis of large number of samples and the results are available in less than 72 hours.

Identification of hepatitis C virus genotypes among hospitalized patients in British Columbia, Canada

The distribution pattern of hepatitis C virus (HCV) genotypes among patients from British Columbia has been investigated by reverse transcription polymerase chain reaction (PCR) amplification of the 5' noncoding region (NCR) and direct DNA sequencing of the PCR product. The sequence data obtained from the British Columbia isolates were compared with HCV sequences for the NCR obtained from GenBank for the construction of a phylogenetic tree using the GDE program, version 2.2. The data show that in British Columbia there are 7 subtypes distributed among major genotypes 1, 2, and 3. The study also shows a new subtype of genotype 1 that represents 29% of the analyzed cases.

Mutations in the catalase-peroxidase gene from isoniazid-resistant Mycobacterium tuberculosis isolates

Isoniazid resistance in Mycobacterium tuberculosis has been associated with total deletion of the katG gene, which codes for catalase-peroxidase production. To determine whether this is a common mechanism of drug resistance, 9 isolates of isoniazid-resistant and 1 of isoniazid-sensitive M. tuberculosis were analyzed by polymerase chain reaction amplification of a 237-bp sequence of the katG gene. Amplification was observed in the isoniazid-sensitive isolate and in 8 resistant isolates; in only 1 isoniazid-resistant isolate was there no amplification of the expected band, suggesting gene deletion. DNA sequencing showed that 8 of the 9 isolates had point mutations, deletions, or insertions of 1-3 bases. Evidence corroborating the presence of mutations in the katG gene was obtained by single-strand conformation polymorphism analysis in these 8 isolates. Thus, mutations as well as insertions and deletions in the katG gene can account for inactive catalase peroxidase, leading to isoniazid resistance; gene deletion occurs only infrequently, in approximately 11% of cases.

Characterization of a DNA probe for detection of Mycobacterium tuberculosis complex in clinical samples by polymerase chain reaction

We cloned and sequenced a DNA fragment from Mycobacterium tuberculosis for use in the identification of members of the M. tuberculosis complex. The DNA probe for culture confirmation had a sensitivity and a specificity of 100%. By using primers developed from this probe, the polymerase chain reaction detected 20 mycobacteria by ethidium bromide staining. This polymerase chain reaction system demonstrated 98% sensitivity and 100% specificity for detection of the M. tuberculosis complex in 200 sputum specimens.

The photobiological activity of 5-geranoxypsoralen and its photoproducts

5-geranoxypsoralen (Bergamottin) does not photosensitize bacteria or a bacterial virus. It does, however, photosensitize mammalian cells in tissue culture. Irradiation with either black light (300-400 nm) or fluorescent ceiling lights produced at least four photobiologically active degradation products, the chemical nature of which still remains to be elucidated. Prolonged exposure to black light resulted in the formation of inactive molecule(s).

Analysis in vitro of two biologically distinct strains of murine cytomegalovirus

The two biologically distinct strains of murine cytomegalovirus, "Smith" and "K181", showed slightly different restriction-endonuclease profiles; but we could not detect strain differences in the numbers or sizes of the major immediate-early, early or late viral proteins. It is possible however that some of the minor late proteins may differ.

Sister-chromatid exchanges induced by some chromium compounds in human lymphocytes in vitro

Treatments with various concentrations of K2Cr2O7, CaCrO4 and CrO3 were given to human lymphocytes cultured in presence of BrdUrd for 2 replicative cycles. Sister-chromatid exchanges (SCEs) were visualized by a combination of fluorescent and Giemsa techniques. In all cases, the higher the concentrations the higher the frequencies of SCEs per metaphase and per chromosome. On a concentration basis, the order of effectiveness in producing SCEs was: CaCrO4 much greater than CrO3 greater than K2Cr2O7.

Interstitial fluid pressure and alkaline gastric secretion

The interstitial fluid pressure of the submucosa of the gastric fundus was monitored by means of Guyton's capsules in dogs anesthetized with pentobarbital. The intracapsular pressure (ICP) was measured during secretion produced by: a) hypertonic solutions placed inside the stomach; b) arterial hypertension (200 mmHg) applied during intra-arterial infusion of histamine, and c) intra-arterial infusion of acetylcholine. The first procedure did not modify the ICP. On the other hand, whenever interstitial fluid appeared in the gastric lumen during hypertension plus histamine, the mean ICP increased, mostly due to augmented capillary filtration. The hydraulic coefficient measured in these experiments was at least 4 orders of magnitude larger than the respective osmotic coefficient. The action of acetylcholine was complex: large doses enlarged the net capillary filtration, but small doses increased the mean ICP by muscle stimulation only. Contraction of the muscularis mucosae might be the most important mechanism underlying bulk flow of interstitial fluid in physiological conditions. It is concluded that hydraulic gradients across the epithelium might account for the "secretion" of "alkaline" juice.

Interstitial fluid pressure in canine gastric mucosa

Guyton's capsules were implanted in the submucosa of the gastric corpus of dogs. The pressure of the fluid inside the capsule (ICP) was measured between 12 and 42 days later after mounting the piece of the corpus in a Plexiglas chamber. The capsule was always filled with saline. In two out of three experiments, the ICP did not change significantly when the saline was replaced by isotonic glucose or blood plasma. Changes of pressure exerted on the surface of the stomach were accurately monitored by the ICP recordings. Changes of circulation produced by compression of the artery or the vein connected to the piece of mucosa, or by intra-arterial injections of epinephrine, norepinephrine, isoproterenol, or hypertonic mannitol, modified the ICP as predicted by Starling's law of capillary filtration. Spontaneous activity of the gastric muscles or the activity, which followed intra-arterial injections of acetylcholine, prostigmine, or histamine, changed the ICP significantly. Intra-arterial atropine usually decreased the ICP by 3--5 mmHg. The mean value of the ICP in 49 animals was 0.53 +/- 0.34 mmHg (SEM); it was negative in 43% of the experiments.

Osmotic concentration of the gastric juice of dogs

1. The freezing point of the gastric juice, produced by histamine stimulation in anaesthetized dogs, of the arterial plasma and of the plasma obtained from a gastric vein were measured.2. The osmolality of the blood that passes through the gastric mucosa increases during secretion of acid juice.3. The amount of water that should be removed from the arterial plasma to obtain a solution isosmolal to the gastric venous plasma is equivalent to the amount of water required to dilute the secreted H(+). From this result it is concluded that the increase of osmolality of the venous plasma is a consequence of the clearance of water free of solute by the gastric mucosa.4. The gastric juice was hyposmotic to the venous plasma in twenty out of thirty dogs, being isosmotic to that plasma in seven dogs. Even in the last group of animals, the gastric secretion might be considered as slightly hypotonic to the venous blood that passes through the secretory part of the mucosa.5. Considerations based on available data suggest that the ;primary' acid juice is usually hyposmotic to the extracellular fluid in the vicinity of the oxyntic cells.

The permeability of the gastric mucosa of dog

1. Tritiated water, [(14)C]urea, [(14)C]thiourea, [(14)C]sucrose and [(59)Fe]-haemoglobin were used to study the permeability of a semi-isolated piece of the great curvature of the canine stomach.2. The osmotic pressure of the solutions placed in contact with the secretory surface of the epithelium was changed by means of dextrose or urea. The mucosa behaved as a semi-permeable membrane, meaning that water flowed under gradients of osmotic pressure. Regardless of the solute used, about 45 x 10(-6) ml. of water flowed/cm(2)/min under a gradient of one atmosphere.3. The permeability constants of the probing molecules were determined under zero net volume flow obtained by placing isosmotic dextrose or isosmotic urea in the chamber. The constants decreased as the molecular volume of the probing molecules increased.4. The transport of all the non-electrolytes across the epithelium decreased significantly when the chamber contained isosmotic dextrose. Basically, this effect seems to be a result of the reduction of the area available for diffusion caused by the high molecular volume of dextrose.5. The increased hindrance to diffusion of the probing molecules caused by the added solutes is considered as good evidence that the probing molecules diffuse by way of pores filled with water.6. The equation derived by Renkin (1954) fits the results obtained if we assume that the equivalent membrane has pores of at least two different radii. The calculated radii vary somewhat with the solute placed in the chamber, though about 88% of the area available for diffusion consists of pores with radii smaller than 2.5 A.7. The equivalent pore radius, calculated from Kedem & Katchalsky's (1961) formula for pores of one single radius, contradicts some experimental findings. Once again, the results obtained would be reproduced more accurately by an equivalent membrane pierced by parallel pores of at least two different diameters.8. A procedure is suggested for calculating the proportion of pores of different radii. It seems likely that the pore radii vary in a continuous distribution from the large pores which allow the diffusion of haemoglobin, to pores hardly permitting the passage of water. The wide pores would form a small fraction of the total area available for the diffusion of water.