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The image of an 80 to 90 percent underexposed medical radiograph can be increased to readable density and contrast by autoradiographic image intensification. The technique consists of combining the image silver of the radiograph with a radioactive compound, thiourea labeled with sulfur-35, and then making an autoradiograph from the activated negative.
In this study, a 101-kb IncF plasmid from an avian pathogenic Escherichia coli (APEC) strain (APEC O2) was sequenced and analyzed, providing the first completed APEC plasmid sequence. This plasmid, pAPEC-O2-R, has functional transfer and antimicrobial resistance-encoding regions. The resistance-encoding region encodes resistance to eight groups of antimicrobial agents, including silver and other heavy metals, quaternary ammonium compounds, tetracycline, sulfonamides, aminoglycosides, trimethoprim, and beta-lactam antimicrobial agents. This region of the plasmid is unique among previously described IncF plasmids in that it possesses a class 1 integron that harbors three gene cassettes and a heavy metal resistance operon. This region spans 33 kb and is flanked by the RepFII plasmid replicon and an assortment of plasmid maintenance genes. pAPEC-O2-R also contains a 32-kb transfer region that is nearly identical to that found in the E. coli F plasmid, rendering it transferable by conjugation to plasmid-less strains of bacteria, including an APEC strain, a fecal E. coli strain from an apparently healthy bird, a Salmonella enterica serovar Typhimurium strain, and a uropathogenic E. coli strain from humans. Differences in the G+C contents of individual open reading frames suggest that various regions of pAPEC-O2-R had dissimilar origins. The presence of pAPEC-O2-R-like plasmids that encode resistance to multiple antimicrobial agents and that are readily transmissible from APEC to other bacteria suggests the possibility that such plasmids may serve as a reservoir of resistance genes for other bacteria of animal and human health significance.
To facilitate identification and preservation of the auditory nerve during cerebello-pontine angle surgery, bipolar recording of cochlear nerve compound action potentials (CNAPs) was performed. Two silver wires insulated with teflon up to the exposed ends were utilized as electrodes. They were twisted together, the distance between the two tips being 1 mm or less. Rarefaction polarity clicks (31/s) ranging from the psychoacoustical threshold to 120 dB pe SPL were used as stimuli. The investigation was performed in three groups of patients. The first group consisted of 9 patients submitted to vestibular neurectomy and 4 patients operated on by microvascular decompression of the eighth nerve. The second group comprised 8 patients with acoustic tumors smaller than 2 mm and serviceable hearing. Postoperative audiometric results in the subjects in the second group were compared with those obtained in well-matched homogeneous controls consisting of patients with acoustic neuroma operated on without the aid of CNAP recording. Bipolar recording from the eighth nerve was extremely selective, a good response being obtained only when positioning the electrode on the cochlear portion of the eighth nerve. During removal of the acoustic neuroma, repeated bipolar probing of the tumor and eighth nerve facilitated the task of distinguishing the cochlear nerve from other nervous structures and from the tumor, and contributed to preserving hearing in most patients.
Nineteen guinea pigs were chosen to measure the compound action potential (CAP) using the silver-ball electrode before and after explosion and 48 h after perfusion of acidic fibroblast growth factor (aFGF) and basic fibroblast growth factor (bFGF). After explosion the average CAP thresholds in the group perfused with bFGF and aFGF were 88.7 dB and 93.2 dB SPL respectivery, the CAP threshold in the control group was 119.4 dB SPL. The difference was significant. The results of the hair cell count from the surface preparation of the cochlea showed that hair cell damage in the control group was more severe than that in the group perfused with aFGF and bFGF. It suggests that aFGF and bFGF perfused to the cochlea may facilitate recovery processes of hearing loss and help to repair the hair cell following acoustic trauma.
A method of elemental determination is put forward in this paper. Namely, Pt, Pd, Au in 10-20 g samples were preconcentrated in milligram microgranular silver alloy by using fire assay. When compounded in solution, trace platinum, palladium, and gold in the solution were determined by ICP-AES. The detection limits of this method were 0.01, 0.005, and 0.01 microg x mL(-1) for Pt, Pd and Au, respectively. Recoveries of standard were more than 97% with precision of 0.1%, 0.12%, and 0.09% of RSD (n=10), respectively. It has proven that this analysis method is quick, simple and accurate. The method has been applied to the determination of contents of Pt, Pd and Au in samples.
The accumulation and physico-chemical forms of metals were determined by atomic absorption spectrometry in the whole soft tissues of oysters, by histological and microanalytical techniques in tissue sections, by gel permeation chromatography of soft tissue homogenates. Oysters were reared according to four types of experimental conditions: exposed to silver (20 micrograms Ag/l) or unexposed, in sea water (33%) or brackish water (8%). Copper, zinc and silver accumulation in oysters are inversely related to salinity. Amoebocytes, which play a key role in accumulating copper and zinc in natural sea water, are able to sequester an important part of added silver as Ag2S. In brackish water an increase of the number of amoebocytes may be considered as responsible for the enhancement of Cu and Zn concentrations in the whole soft tissues. In such conditions, additional silver is concentrated in these cells rather than in the basement membranes which are target structures for Ag2S accumulation in sea water. If the global fluctuations of metal concentrations in the soft tissue are ascribable mainly to changes at the histological level, the fate of metals in the soluble fraction must not be neglected since the speciation of metals influences their toxicity. The freshening of sea water induced a change in the distribution of cytosolic silver and zinc but in no case were the molecular masses of compounds associated with each metal perfectly identical. From these results, it is concluded that the accumulation of silver by oysters is not mediated by the same mechanisms as those for copper and zinc.
The complexation properties of the ligand bis(3,5-dimethylpyrazol-1-yl)methane (L) towards group 11 metals have been studied. The reaction in a 1 : 1 molar ratio with [Cu(NCMe)4]PF6 or Ag(OTf) complexes gives the mononuclear [CuL(NCMe)]PF6 (1), with crystallographic mirror symmetry, or dinuclear [Ag2(mu-L)2](OTf)2 (2) (OTf = trifluoromethanesulfonate) in which the ligand bridges both silver centres, an unprecedented mode of coordination for this type of ligands. Compound 2 crystallizes with two water molecules and forms a supramolecular structure through classical hydrogen bonding. The reaction in a 2 : 1 ratio affords in both cases the four-coordinated derivatives [ML2]X (M = Cu, X = PF6 (3); Ag, X = OTf 4). The treatment of [Ag(OTf)(PPh3)] with the ligand L gives [AgL(PPh3)]OTf (5). The gold(I) derivative [Au2(C6F5)2(mu-L)] (6) has also been obtained by reaction of L with two equivalents of [Au(C6F5)(tht)]. These complexes present a luminescent behaviour at low temperature; the emissions being mainly intraligand but enhanced after coordination of the metal. Compounds 1-4 have been characterized by X-ray crystallography. DFT studies showed that, in the silver complex 2, coordination of H2O to Ag in the binuclear complex is favoured by formation of a hydrogen-bonding network, involving the triflato anion, and releasing enough energy to allow distortion of the Ag2 framework.
Metal ions or metal ions in complexes or compounds have been used for centuries to disinfect fluids, solids and tissues. The biocidal effect of silver, with its broad spectrum of activity including bacterial, fungal and viral agents, is particularly well known and the term "oligodynamic activity" was coined for this phenomenon. Silver ions have an affinity to sulfhydryl groups in enzyme systems of the cell wall, through which they interfere with the transmembranous energy transfer and electron transport of bacterial microorganisms. Silver ions also block the respiratory chain of microorganisms reversibly in low concentrations and irreversibly in higher concentrations. Binding to the DNA of bacteria and fungi increases the stability of the bacterial double helix and thus inhibits proliferation. There is no cross resistance with antibiotics and also no induction of antimicrobial resistance by silver ions. The concentrations required for bactericidal activity are in the range 10(-9) mol/l. These concentrations can be achieved in solution by the interaction of metallic silver with electrolytes only if there is a large enough surface of silver. By a novel technology, metallic silver is distributed in submicron particles in polyurethane and results in a concentration of 0.8% in an active surface of 450 cm2/g polyurethane. Polyurethane is hygroscopic and rapidly attracts water; the interaction of electrolyte solutions with the extremely finely distributed silver throughout the polyurethane releases bactericidal concentrations of silver ions over a period of years to the surface of the material. The electronegatively charged surface of bacteria attracts the positively charged silver ions. The concentrations released from the polyurethane are far below the toxic concentrations for humans.
Inhibition of the growth of nerve fibers by mercurials was quantitatively estimated by measuring the length of fibers in the cultured chick dorsal root ganglion. Morphological changes in nonneuronal cells were also evaluated. The growth rates of nerve fibers were constant for 2 to 6 days after the start of incubation. Methylmercury depressed nerve fiber growth dose- and time-dependently by 50% and completely at 3 x 10(-6) M and 7 x 10(-6) M, respectively. About 10-fold higher concentrations of inorganic mercury were required for the same extent of inhibition. The nerve fibers exposed to inorganic mercury shrank at an early stage of exposure and thereafter grew again within 24 hours. Electron microscopic examination revealed that methylmercury decreased microtubule mass extensively in nerve fibers, while inorganic mercury markedly altered surface membrane structure. These results suggested that microtubule disruption is involved in methylmercury-induced depression of nerve fibers but not in that induced by inorganic mercury. Characteristic effects on the growth of nerve fibers and the proliferation of nonneuronal cells were observed on the treatment with other metals such as cadmium, silver and chromium. Thus, dorsal root ganglion culture seems to be useful for the evaluation of toxic effects of metals in vitro.
This account reviews our efforts over the past 37 years to understand the chemistry of a select group of sulfur-nitrogen compounds including sulfinimines (N-sulfinyl imines) and N-sulfonyloxaziridines. Our early exploration of the thermal properties of sulfenamides, a class of sulfur-nitrogen compounds about which little was known, resulted in a new procedure, the silver-assisted method, for the construction of sulfenimines (N-sulfenyl imines). Selective oxidations of these compounds resulted in the production of N-sulfinyl imines (sulfinimines) and N-sulfonyloxaziridines. N-Sulfonyloxaziridines turned out to be a new class of aprotic neutral oxidizing reagents. Enantiomerically pure examples afford high ee values in the oxidation of enolates to alpha-hydroxy carbonyl compounds and in the oxidation of sulfides and selenides to sulfoxides and selenoxides. Additions of organometallic reagents to enantiomerically pure sulfinimines provide the best and most versatile method for the asymmetric construction of the carbon-nitrogen stereocenters found in many biologically active compounds. Sulfinimine-derived chiral building blocks provide efficient access to many classes of nitrogen heterocycles including aziridines, 2H-azirines, pyrrolidines, and piperidines.
Nonspecific background staining of the gel matrix is the limiting factor in the differentiation of proteins using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It is caused by nonspecific binding of silver ions in the gel matrix, either to nonprotein compounds or through the chemistry of the polyacrylamide gel itself. The resulting stain of the gel produces a stain baseline, making differentiation of protein bands with a laser densitometer difficult. We have therefore developed a modified silver staining method for the PhastSystem to reduce such nonspecific background staining. Apart from slowing the development program by lowering the temperature to 15 degrees C and shortening the incubation time to 4 min, the essential step in the modification is the combined use of an EDTA and Tris-acetate buffer solution which stops the reduction of silver ions. The reduced background staining leads to an improved detection of protein bands and virtually identical zero lines for the laser densitograms and the stain baselines. The total staining time is 91 min. All steps in the program are fully automated and continuous, employing the PhastSystem staining unit.
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2 histochemical methods were used to analyse the carbohydrates in the human oviductal epithelium, namely the periodic acid-semicarbazide-silver proteinate and the 'mild' periodic acid-thiosemicarbazide-silver proteinate technique. It was possible to detect periodate reactive substances and sialic acid-containing compounds, namely separately. The 'mild' periodic acid oxidation is a selective technique for the histochemical demonstration of the existence of unsubstituted acylneuraminic acids. The ultrahistochemical results show that, firstly, periodate reactive particles are located in the cytoplasm of ciliated and nonciliated cells. The material appears in form of beta-granula (glycogen). Secondly, we could observe fine granular reactive products in the lysosomal-like and lipid droplet-like structures. In these subjects the positive granula encircling ring-like the homogeneous matrix occur in the peripheral zone of the morphological substrate investigated. By the way, these granula situated in the periphery of organelles are alone reacting after staining with 'mild' periodic acid-thiosemicarbazide-silver proteinate; this means, the glycogen particles are unstained. Thus the findings indicate that, in the cells of the human oviductal epithelium, sialic acid-containing compounds are ultrahistochemically visualized by 'mild' periodic acid oxidation in combination with thiosemicarbazide and silver proteinate.
Reaction of 3-aminomethylpyridine (3-amp) with silver(I) salts of triflate (OTf-) and trifluoroacetate (tfa-) produce a variety of multidimensional coordination networks whose structures depend on the stoichiometry of the components present. A 1:1 ratio of 3-amp to AgX produces a linear polymer, 1, when X = tfa- and a planar sheet, 2, when X = OTf-. Addition of a second equivalent of ligand increases the dimensionality of both structures by one to form a two-dimensional sheet, 3, and a three-dimensional system, 4, for their respective anions. Addition of 2,2'-bipyridine (bipy) to solutions of any of the previous compounds produces the fixed-ratio complexes 5 (tfa- salt) and 6 (OTf- salt). The bipyridyl ligand halts the polymerization of compounds 1-4 by cutting the chain after each silver(I) link and forcing a 1:2:2 ratio of 3-amp to AgX to bipy. Compound 5, however, remains polymeric in nature due to the closed-shell Ag-Ag interactions of the planar metals holding the monomers together. Differences between structures of each ratio stem from the differences in basicity and in the extra degree of H-bonding ability that the OTf- anion has over tfa-.
Silver(I) complexes of the two closely related linear bis-bidentate pyridazine-based Schiff-base ligands 5 and 6 exhibit very different solid state molecular architectures, easily deformed grid vs. side-by-side, due to steric and electronic factors.