Detection of coexisting protein conformations in capillary zone electrophoresis subsequent to transient contact with sodium dodecyl sulfate solutions

Non-native conformations of proteins were generated by temporary contact with aqueous solutions of sodium dodecyl sulfate (SDS) and separated from the native state with capillary zone electrophoresis (CZE) in alkaline borate buffer deficient of SDS. Nine proteins at concentrations of 2.0 or 3.0 mg.L(-1) were compared in terms of their susceptibility to SDS. For superoxide dismutase and ferritin the tendency of unfolding was modest with < 25% of the protein being transformed to the non-native state at 10 mmol.L(-1) SDS. Highest susceptibility was observed for albumin, myoglobin (Mb), and hemoglobin with > 75% in the non-native state even at 2.0 mmol.L(-1) SDS. The influence of varying SDS concentrations on the conformational state of Mb was tested. Increasing the SDS concentration, circular dichroism revealed a reduction in alpha-helix, an increase in random coil, and an introduction of beta-sheet, which is absent in native structure. Modifications in the secondary structure were in agreement with distinct changes in the shape of the non-native Mb peak in CZE and make a gradual unfolding/refolding process with several coexisting molten globules instead of two-state transition of conformations most plausible for Mb. CZE was found to contribute to a further understanding of holo-Mb transformation towards a population of non-native conformations (i) by means of calculated peak area ratios of native to non-native states, which showed sigmoid transition, (ii) by detecting the release of the prosthetic heme group, and (iii) by changes in the effective electrophoretic mobility of the Mb-SDS peaks. Reconstituted holo-Mb forms differed in the Soret band around 410 nm, indicating diversity in the conformation of the heme pocket.     

Determination of total selenium and selenium distribution in the milk phases in commercial cow’s milk by HG-AAS

A procedure has been developed for determining the selenium in cows milk using hydride generation–atomic absorption spectrometry (HG-AAS) following microwave-assisted acid digestion. The selenium distributions in milk whey, fat and micellar casein phases were studied after separating the different phases by ultracentrifugation and determining the selenium in all of them. The detection limits obtained by HG-AAS for the whole milk, milk whey and micellar casein were 0.074, 0.065 and 0.075 g l^–1, respectively. The accuracy for the whole milk was checked by using a Certified Reference Material CRM 8435 whole milk powder from NIST, and the analytical recoveries for the milk whey and casein micelles were 100.9 and 96.9%, respectively. A mass balance study of the determination of selenium in the different milk phases was carried out, obtaining values of 95.5–100.8%. The total content of selenium was determined in 37 milk samples from 15 different manufacturers, 19 whole milk samples and 18 skimmed milk samples. The selenium levels found were within the 8.5–21 g l^–1 range. The selenium distributions in the different milk phases were studied in 14 whole milk samples, and the highest selenium levels were found in milk whey (47.2–73.6%), while the lowest level was found for the fat phase (4.8–16.2%). A strong correlation was found between the selenium levels in whole milk and the selenium levels in the milk components.     

High resolution atomic coherent control via spectral phase manipulation of an optical frequency comb

We demonstrate high resolution coherent control of cold atomic rubidium utilizing spectral phase manipulation of a femtosecond optical frequency comb. Transient coherent accumulation is directly manifested by the enhancement of signal amplitude and spectral resolution via the pulse number. The combination of frequency comb technology and spectral phase manipulation enables coherent control techniques to enter a new regime with natural linewidth resolution.     

Rearranged icetexane diterpenoids from the roots of Salvia thymoides (Labiatae)

From the roots of Salvia thymoides Benth., three new rearranged icetexane diterpenoids (2-4) were isolated together with the previously described quinone tilifolidione (1). The proposed structures were established by extensive NMR analysis, including HMBC and HMQC pulse sequences.     

Determination of macrolide antibiotics in porcine and bovine urine by high-performance liquid chromatography coupled to coulometric detection

A high-performance liquid chromatography method coupled to coulometric detection has been applied for the determination, in a single run, of up to eight macrolide antibiotics (erythromycin [ERY], tylosin [TYL], tilmicosin [TILM], spiramycin 2 [SPI 2], spiramycin 3 [SPI 3], josamycin [JOS], kitasamycin [KIT], and rosamicin [ROS]) in spiked porcine and bovine urine. Quantification was performed using matrix-matched calibration with roxithromycin (ROX) as the internal standard. The detection limits for each drug were below 3.5 ng injected (equivalent to an initial concentration below 0.07 mg L^–1) for porcine urine and below 5 ng injected (equivalent to an initial concentration below 0.10 mg L^–1) for bovine urine. Recoveries from urine samples spiked at three different concentrations within the linear range were not significantly dependent on concentration. The entire procedure provides average macrolide recoveries ranging from 69.7 to 96.6% for bovine urine and from 75.5 and 96.1% for porcine urine.     

Direct frequency comb measurements of absolute optical frequencies and population transfer dynamics

A phase-stabilized femtosecond laser comb is directly used for high-resolution spectroscopy and absolute optical frequency measurements of one- and two-photon transitions in laser-cooled 87Rb atoms. Absolute atomic transition frequencies, such as the 5S1/2 F=2-->7S1/2 F"=2 two-photon resonance measured at 788,794 768,921 (44) kHz, are determined without a priori knowledge about their values. Detailed dynamics of population transfer driven by a sequence of pulses are uncovered and taken into account for the measurement of the 5P states via resonantly enhanced two-photon transitions.     

PIXE and PIGE assessment of in vivo elemental and physical changes of a composite from a dental filling

Simultaneous particle‐induced x‐ray emission (PIXE) and particle‐induced gamma‐ray emission (PIGE) measurements in the 0–270 keV range with a low‐energy hyperpure Ge detector have been performed on the outer surface and on an inner section of a dental composite filling extracted from a patient. The biomaterial has been identified as the fluorine‐releasing Tetric Ceram dental composite. Compared to the native material, the dental filling evidenced changes occurring during the in vivo oral use. These included mainly Cl and K accumulation and loss of Zr, Ba, Yb (by PIXE), and F (in the PIGE region). The changes were similar at the surface and inside of the dental filling for most of the above elements, indicating an unexpectedly high permeability of the material, maybe due to microscopic bulk fracture of the dental composite filling throughout its use. The PIGE spectra detected also Al and traces of Hf and Sm possibly associated with Zr and Yb. Changes in the ratio of the L lines of Yb and in the ratio of the 110‐ and 197‐keV lines of F evidenced alterations in the matrix physical properties of the composite, associated with factors such as surface roughening by wear, grain size decrease by slow dissolution, and compositional variations. Further studies are needed to gain a deeper insight into the complex changes taking place in a dental composite filling. Copyright © 2009 John Wiley & Sons, Ltd.     

Perov type results in gauge spaces and their applications to integral systems on semi-axis

In this paper we present Perov type fixed point theorems for contractive mappings in Gheorghiu’s sense on spaces endowed with a family of vector-valued pseudo-metrics. Applications to systems of integral equations are given to illustrate the theory. The examples also prove the advantage of using vector-alued pseudo-metrics and matrices that are convergent to zero, for the study of systems of equations.     

Application of a poly(dithiocarbamate) resin to the determination of trace copper,iron and zinc in natural waters

A chelating poly(dithiocarbamate) resin with macroreticular support is shown to be effective for the preconcentration of copper, iron and zinc in natural waters. The retained ions can be eluted efficiently in 5 ml of 8M nitric acid from 1–20-cm columns of resin.This poly(dithiocarbamate) resin is used for the preconcentration and determination of copper, iron and zinc by flame atomic absorption spectrophoto-metry. Common ions present in natural waters do not interfere. The detection limits were 0.50, 0.21 and 0.04 g 1^–1 for Cu, Fe and Zn respectively.     

Determination of traces of silver in human scalp hair slurries by electrothermal atomic absorption spectrometry

A simple and rapid method for the determination of traces of silver in human hair by slurry sampling and electrothermal atomic absorption spectrometry was optimized. Hair pulverization and the particle size reduction were achieved using a vibrational zirconia mill ball for 20 min. Palladium nitrate, magnesium nitrate and palladium-magnesium nitrate were investigated as chemical modifiers to thermally stabilize silver. Glycerol was used as wetting agent to stabilize the hair slurries. A limit of detection of 21.6 g kg^–1 was obtained for the use of palladium nitrate as best chemical modifier. The repeatibility of the overall procedure (slurry preparation and atomic absorption spectrometric determination) corresponding to eleven measurements was 14.3%. Matrix effect was significant and so, the standard addition method was used to determine silver in hair samples from healthy people. The levels found varied between 0.10 and 1.62 mg kg^–1.