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1.
Anal Biochem ; 450: 30-6, 2014 Apr 01.
Article in English | MEDLINE | ID: mdl-24433980

ABSTRACT

A simple and sensitive method for quantification of nanomolar copper with a detection limit of 1.2×10(-10)M and a linear range from 10(-9) to 10(-8)M is reported. For the most useful analytical concentration of quantum dots, 1160µg/ml, a 1/Ksv value of 11µM Cu(2+) was determined. The method is based on the interaction of Cu(2+) with glutathione-capped CdTe quantum dots (CdTe-GSH QDs) synthesized by a simple and economic biomimetic method. Green CdTe-GSH QDs displayed the best performance in copper quantification when QDs of different sizes/colors were tested. Cu(2+) quantification is highly selective given that no significant interference of QDs with 19 ions was observed. No significant effects on Cu(2+) quantification were determined when different reaction matrices such as distilled water, tap water, and different bacterial growth media were tested. The method was used to determine copper uptake kinetics on Escherichia coli cultures. QD-based quantification of copper on bacterial supernatants was compared with atomic absorption spectroscopy as a means of confirming the accuracy of the reported method. The mechanism of Cu(2+)-mediated QD fluorescence quenching was associated with nanoparticle decomposition.


Subject(s)
Copper/analysis , Escherichia coli/cytology , Quantum Dots/chemistry , Spectrometry, Fluorescence/methods , Biological Transport , Biomimetics , Cadmium Compounds/chemistry , Cells, Cultured , Copper/chemistry , Copper/metabolism , Culture Media/chemistry , Escherichia coli/growth & development , Escherichia coli/metabolism , Glutathione/chemistry , Limit of Detection , Spectrometry, Fluorescence/economics , Tellurium/chemistry , Time Factors , Water/chemistry
2.
Appl Environ Microbiol ; 72(1): 963-7, 2006 Jan.
Article in English | MEDLINE | ID: mdl-16391146

ABSTRACT

The ubiE gene of Geobacillus stearothermophilus V, with its own promoter, was cloned and introduced into Escherichia coli. The cloned gene complemented the ubiE gene deficiency of E. coli AN70. In addition, the expression of this gene in E. coli JM109 resulted in the evolution of volatile selenium compounds when these cells were grown in selenite- or selenate-amended media. These compounds were dimethyl selenide and dimethyl diselenide.


Subject(s)
Bacillaceae/enzymology , Escherichia coli K12/enzymology , Methyltransferases/genetics , Methyltransferases/metabolism , Selenium Compounds/metabolism , Bacillaceae/genetics , Culture Media , Escherichia coli K12/drug effects , Escherichia coli K12/genetics , Organoselenium Compounds/metabolism , Selenic Acid , Volatilization
3.
Appl Environ Microbiol ; 66(11): 4849-53, 2000 Nov.
Article in English | MEDLINE | ID: mdl-11055934

ABSTRACT

Cultures of a purple nonsulfur bacterium, Rhodobacter sphaeroides, amended with approximately 1 or approximately 100 ppm selenate or selenite, were grown phototrophically to stationary phase. Analyses of culture headspace, separated cells, and filtered culture supernatant were carried out using gas chromatography, X-ray absorption spectroscopy, and inductively coupled plasma spectroscopy-mass spectrometry, respectively. While selenium-amended cultures showed much higher amounts of SeO(3)(2-) bioconversion than did analogous selenate experiments (94% uptake for SeO(3)(2-) as compared to 9.6% for SeO(4)(2-)-amended cultures from 100-ppm solutions), the chemical forms of selenium in the microbial cells were not very different except at exposure to high concentrations of selenite. Volatilization accounted for only a very small portion of the accumulated selenium; most was present in organic forms and the red elemental form.


Subject(s)
Rhodobacter sphaeroides/metabolism , Selenium Compounds/metabolism , Sodium Selenite/metabolism , Chromatography, Gas/methods , Culture Media/chemistry , Rhodobacter sphaeroides/growth & development , Selenic Acid , Spectrum Analysis/methods
4.
J Biol Inorg Chem ; 4(6): 791-4, 1999 Dec.
Article in English | MEDLINE | ID: mdl-10631611

ABSTRACT

The selenium K-edge X-ray absorption spectra of selenomethionine, selenocysteine, selenocystine, and sulfo-selenocystine in solution are compared with the corresponding sulfur K-edge spectra of the sulfur analogues of these compounds. The selenium and sulfur spectra follow similar trends, although the latter are significantly sharper owing to the longer core hole lifetime at the lower energies where sulfur absorbs. The spectra of the selenium compounds are sufficiently distinct that it is reasonable to expect that curve fitting will allow the speciation of the forms of selenium in complex biological samples.


Subject(s)
Amino Acids/chemistry , Selenium/chemistry , Spectrum Analysis/methods , X-Rays
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