Mass spectrometric analysis of cyclofenil and its metabolites in human urine

Using gas chromatography/electron impact-mass spectrometry (GC/EI-MS) and high performance liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometry (HPLC/APCI-MS/MS), the structures of cyclofenil metabolites in human urine have been assigned. The hydroxyl metabolites liberated from the glucuronide conjugates after acid hydrolysis were characterized as the trimethylsilyl (O-TMS) derivatives using GC/MS. The conjugate glucuronide forms were detected without hydrolysis by HPLC/MS. Cyclofenil was not observed in urine. Tentative structures for the two metabolites are proposed.     

The isotropic and anisotropic EPR spectra of the tetrafluoroethylene radical anion

The tetrafluoroethylene radical anion has been generated in solid solutions by electron addition to the parent molecule. Both its isotropic and anisotropic EPR spectra have been observed, including the isotropic ¹³C satellite lines in natural abundance. The isotropic EPR parameters are a_F = 94.3 G, a_C = 48.7 G, and g = 2.0027. Two possible geometries, planar and chair, are discussed for this radical anion. The magnitude of the ¹⁹F and ¹³C hyperfine coupling constants are consistent with a planar (D_2h) structure provided that the unpaired electron occupies the 5b_1u (σ*) rather than the 2b_1g (π*) molecular orbital which is predicted by ab initio calculations to be the LUMO of the parent molecule. On the other hand, the EPR parameters do not rule out a chair (C_2h) structure if the bending of the CF₂ groups introduces only a small distortion from planarity.     

The polymerization of actin: extent of polymerization under pressure, volume change of polymerization, and relaxation after temperature jumps

The protein actin can polymerize from monomeric globular G-actin to polymeric filamentary F-actin, under the regulation of thermodynamic variables such as temperature, pressure, and compositions of G-actin and salts. We present here new measurements of the extent of polymerization (phi) of actin under pressure (P), for rabbit skeletal muscle actin in H2O buffer in the presence of adenosine triposphate and calcium ions and at low (5-15 mM) KCl concentrations. We measured phi using pyrene-labeled actin, as a function of time (t) and temperature (T), for samples of fixed concentrations of initial G-actin and KCl and at fixed pressure. The phi(T,P) measurements at equilibrium have the same form as reported previously at 1 atm: low levels of polymerization at low temperatures, representing dimerization of the actin; an increase in phi at the polymerization temperature (Tp); a maximum in phi(T) above Tp) with a decrease in phi(T) beyond the maximum, indicating a depolymerization at higher T. From phi(T,P) at temperatures below Tp, we estimate the change in volume for the dimerization of actin, DeltaVdim, to be -307+/-10 ml/mol at 279 K. The change of Tp with pressure dTp/dP=(0.3015+/-0.0009) K/MPa=(30.15+/-0.09) mK/atm. The phi(T,P) data at higher T indicate the change in volume on propagation, DeltaVprop, to be +401+/-48 ml/mol at 301 K. The phi(t) measurements yield initial relaxation times rp(T) that reflect the behavior of phi(T) and support the presence of a depolymerization temperature. We also measured the density of polymerizing actin with a vibrating tube density meter, the results of which confirm that the data from this instrument are affected by viscosity changes and can be erroneous.     

Allosteric control through mechanical tension

Conformational changes of proteins modulate their function. In allosteric control, the conformational change is induced by the binding of a signaling molecule. Here we insert a "molecular spring" on the enzyme guanylate kinase, to control the conformation of this protein. The stiffness of the spring can be varied externally, which allows one to exert a controlled mechanical tension between the two points on the protein's surface where the spring is attached. We show that by applying and releasing the tension we can reversibly turn the enzyme off and on.     

Artificial allosteric control of maltose binding protein

We demonstrate the allosteric control of a protein based on mechanical tension. When substrate binding is accompanied by a significant change of conformation of the protein, a mechanical tension favoring one or the other conformation will alter the binding affinity for the substrate. We have constructed a chimera where the two lobes of the maltose-binding protein are covalently coupled to the ends of a DNA oligomer. The mechanical tension on the protein is controlled externally by exploiting the difference in stiffness between single stranded and double stranded DNA. We report that the binding affinity of the protein for its substrates is significantly altered by the tension.     

Purification of carbon single-wall nanotubes by potassium intercalation and exfoliation

A purification procedure for single-wall carbon nanotubes prepared by the arc-discharge method is described that employs a new step of potassium intercalation. Thermogravimetric analysis, Raman spectroscopy, X-ray diffraction, and transmission electron microscopy were used to characterize the results of each purification step. This potassium intercalation step is particularly useful for exfoliating the graphitic shell structure that typically surrounds the metal catalyst particles that remain from the nanotube synthesis. By exfoliating the shell structure, subsequent treatments are more efficacious for removing the metal catalyst particles. By testing full purification procedures, it is demonstrated that with potassium intercalation the number of purification steps can be reduced. PACS 81.05.Tp; 33.20.Fb; 81.07.De; 81.20.Ym; 71.20.Tx     

Sonolytic degradation of hazardous organic compounds in aqueous solution

Benzene, chlorobenzene, 1,2-, 1,3-, 1,4-dichlorobenzene, biphenyl, and polychlorinated biphenyls such as 2-, 4-chlorobiphenyl and 2,2′-dichlorobiphenyl in aqueous solutions have been subjected to sonolysis with 200 kHz ultrasound at an intensity of 6 W cm⁻² under an argon atmosphere. 80–90% of initial amount of these compounds were degraded by 30–60 min of sonication when the initial concentrations were 10–100 μmol l⁻¹. The degradation rate of these compounds increased with increase in their vapor pressures. In all cases of sonolysis of chlorinated organic compounds, an appreciable amount of liberated chloride ion was observed.     

Bile Salt Anion Sorption by Polymeric Resins: Comparison of a Functionalized Polyacrylamide Resin with Cholestyramine

Cholestyramine and a cross-linked polyacrylamide resin with lateral alkyl quaternary ammonium groups (QPDA12) were used to study their ability to bind several bile salt anions (including the cholate, glycocholate, taurocholate, and chenodeoxycholate), individually and competitively, from phosphate buffer solutions at room temperature. The latter resin showed high affinities for all the bile salt anions examined, while cholestyramine exhibited a high affinity only for the more hydrophobic chenodeoxycholate. However, for the binding with cholestyramine, cooperative effects were more pronounced, leading to the enhancement of sorption at higher concentrations. The Langmuir equation and its modified versions were used in the interpretation of both individual and competitive binding of bile salts. The data from competitive binding studies indicated that the presence of the tightly bound chenodeoxycholate did not significantly diminish the ability of QPDA12 resin to bind cholate. However, for cholestyramine, the sorption of chenodeoxycholate increased the relative binding affinity for the more hydrophilic cholate, revealing a novel "cooperative" effect involving different bile salt anions. The latter results suggest that the observed higher affinity of QPDA12 is brought about predominantly through the hydrophobic interactions with the pendant alkyl groups rather than with the resin backbone. Copyright 2000 Academic Press.     

Optical properties of Al‐doped ZnO thin films deposited by two different sputtering methods

Aluminum‐doped zinc oxide (AZO) thin films were deposited on sapphire (002) and glass substrates by two different sputtering techniques radio frequency magnetron cosputtering of AZO and ZnO targets and sputtering of an AZO target. The dependence of the photoluminescence (PL) and transmittance properties of the AZO films deposited by cosputtering and sputtering on the AZO/ZnO target power ratio, R and the O₂/Ar flow ratio, r were investigated, respectively. Only a deep level emission peak appears in the PL spectra of cosputtered AZO films whereas both UV emission and deep level emission peaks are observed in the PL spectra of sputtered AZO films. The absorption edges in the transmittance spectra of the AZO films shift to the lower wavelength region as R and r increase. Also effects of crystallinity, surface roughness, PL on the transmittance of the AZO films were explained using the X‐ray diffraction (XRD), atomic force microscopy (AFM), and PL analysis results. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects of cooling rate and post-heat treatment on properties of ZnO thin films deposited by sol-gel method

Sol-gel spin-coated ZnO thin films are cooled with different rates after the pre-heat treatment. Atomic force microscopy (AFM), X-ray diffraction (XRD), Raman, and photoluminescence (PL) were carried out to investigate the effects of the cooling rate during pre-heat treatment on structural and optical properties of the ZnO thin films. The ZnO thin films cooled slowly exhibit mountain chain structure while the ones cooled rapidly have smooth surface. The ZnO thin films cooled rapidly have higher c-axis orientation compared to the ones cooled slowly. The narrower and the higher near-band-edge emission (NBE) peaks are observed in the ZnO thin films cooled rapidly.