Performance of a fast fiber based UV/Vis multiwavelength detector for the analytical ultracentrifuge

The optical setup and the performance of a prototype UV/Vis multiwavelength analytical ultracentrifuge (MWL-AUC) is described and compared to the commercially available Optima XL-A from Beckman Coulter. Slight modifications have been made to the optical path of the MWL-AUC. With respect to wavelength accuracy and radial resolution, the new MWL-AUC is found to be comparable to the existing XL-A. Absorbance accuracy is dependent on the light intensity available at the detection wavelength as well as the intrinsic noise of the data. Measurements from single flashes of light are more noisy for the MWL-AUC, potentially due to the absence of flash-to-flash normalization in the current design. However, the possibility of both wavelength and scan averaging can compensate for this and still give much faster scan rates than the XL-A. Some further improvements of the existing design are suggested based on these findings.     

Calculation of vacancy transfer probabilities from K to L shell using the X-ray fluorescence parameters

The probabilities for vacancy transfer from the K to the L shell (η_KL), have been calculated for eleven high atomic number elements using the measured K and L shells X-ray production cross-sections. The targets were excited by 123.6 keV photon from a ⁵⁷Co annular radioactive source. K and L X-rays emitted by samples were counted with a Si(Li) detector. The measured values of η_KL were compared with the theoretical values and our early papers.     

Determination of the surfactant density on SWCNTs by analytical ultracentrifugation

We report on the extensive characterization of single-walled carbon nanotubes (SWCNTs) dispersed in a variety of surfactants, such as sodium dodecyl benzene sulfonate (SDBS), sodium cholate (SC), and three synthesized perylene-based surfactants, by using differential sedimentation in H(2)O and D(2)O. Multidimensional evaluation of the absorption profiles over radius, wavelength, and time allows the determination of the anhydrous specific volumes of the SWCNT-surfactant complexes as well as the concentration of the surfactant reservoir in free micelles with very slow sedimentation coefficients (<1 Svedberg). Among the perylene bisimide surfactants, the smallest derivative is densely adsorbed on the nanotube backbone with an anhydrous specific volume significantly above that of SC or SDBS. Bulky Newkome dendritic groups on one or both ends of the perylene moiety gradually reduce the adsorption density, in accord with the absolute adsorption between 0.66 and 1.7 mmol surfactant per gram SWCNTs. Furthermore, hydrodynamic analysis reveals that SDBS favors the "tails-on" configuration. The distribution of sedimentation coefficients of SWCNTs prepared by high-pressure carbon monoxide decomposition (HiPco) is broader and shifted to faster sedimentation than those prepared by using cobalt-molybdenum catalysis (CoMoCAT), which reflects the polydispersity in diameter and length.     

Evaluation and discrimination of simvastatin-induced structural alterations in proteins of different rat tissues by FTIR spectroscopy and neural network analysis

Statins are commonly used to control hypercholesterolemia and to prevent cardiovascular diseases. Among the statins, Simvastatin is one of the most frequently prescribed statins because of its efficacy in reducing LDL lipoprotein cholesterol levels, its tolerability, and its reduction of cardiovascular risk and mortality. Conflicting results have been reported with regard to benefits (pleiotropic effects) as well as risks (adverse effects) of simvastatin on different soft and hard tissues. In the current study, Attenuated Total Reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy was used to obtain detailed information about protein conformational changes due to simvastatin therapy of soft tissues namely liver, testis, sciatic nerve and hard tissues such as femur and tibia. Protein secondary structural changes were predicted by intensity calculations from second derivative spectra and neural network (NN) analysis, using the amide I band (1700-1600 cm(-1)) of FTIR spectra. Moreover, based on protein secondary structural differences, hierarchical cluster analysis was carried out in the 1700-1600 cm(-1) region. The results of our study in liver, testis and sciatic nerve tissues revealed that simvastatin treatment significantly decreased alpha helix structure and beta sheet structure at 1638 cm(-1), while increased the anti-parallel and aggregated beta sheet and random coil structures implying a simvastatin-induced protein denaturation in treated groups. Different to soft tissues, the results of hard tissue studies on femur and tibia bones revealed increased alpha helix structure and decreased anti-parallel beta sheet, aggregated beta sheet and random coil structures implying more strengthened bone tissues in simvastatin-treated groups. Finally, the simvastatin-treated and control groups for all soft and bone tissues were successfully differentiated using cluster analysis. According to the heterogeneity values in the cluster analysis of these tissues, the sciatic nerve tissue was found to be the most affected tissue from simvastatin treatment among the studied soft tissues. In addition, the high heterogeneity value implied high secondary structural difference between control and simvastatin-treated groups in tibia bone tissues. These findings reveal that FTIR spectroscopy with bioinformatic analyses such as neural network and hierarchical clustering, allowed us to determine the simvastatin-induced protein conformational changes as adverse and pleiotropic effects of the drug on different soft and hard tissues.     

Signal ratio amplification via modulation of resonance energy transfer: proof of principle in an emission ratiometric Hg(II) sensor

Boradiazaindacene dyads designed as energy transfer casettes can be modified to signal cation concentrations ratiometrically. If the energy transfer efficiency is increased via changing spectral overlap on cation binding, an enhancement of emission signal ratios can be obtained. A larger range of ratios results in highly improved sensitivity to analyte concentrations. We demonstrate this approach in a de novo design of a novel and highly selective ratiometric chemosensor for Hg(II) ions.     

Dissection of aminoglycoside-enzyme interactions: a calorimetric and NMR study of neomycin B binding to the aminoglycoside phosphotransferase(3')-IIIa

In this work, for the first time, we report pKa values of the amino functions in a target-bound aminoglycoside antibiotic, which permitted dissection of the thermodynamic properties of an enzyme-aminoglycoside complex. Uniformly enriched 15N-neomycin was isolated from cultures of Streptomyces fradiae and used to study its binding to the aminoglycoside phosphotransferase(3')-IIIa (APH) by 15N NMR spectroscopy. 15N NMR studies showed that binding of neomycin to APH causes upshifts of approximately 1 pKa unit for the amines N2' and N2' ' while N6' experienced a 0.3 pKa unit shift. The pKa of N6' ' remained unaltered, and resonances of N1 and N3 showed significant broadening upon binding to the enzyme. The binding-linked protonation and pH dependence of the association constant (Kb) for the enzyme-aminoglycoside complex was determined by isothermal titration calorimetry. The enthalpy of binding became more favorable (negative) with increasing pH. At high pH, binding-linked protonation was attributable mostly to the amino functions of neomycin; however, at neutral pH, functional groups of the enzyme, possibly remote from the active site, also underwent protonation/deprotonation upon formation of the binary enzyme-neomycin complex. The Kb for the enzyme-neomycin complex showed a complicated dependence on pH, indicating that multiple interactions may affect the affinity of the ligand to the enzyme and altered conditions, such as pH, may favor one or another. This work highlights the importance of determining thermodynamic parameters of aminoglycoside-target interactions under different conditions before making attributions to specific sites and their effects on these global parameters.     

Active ruthenium‐(N‐heterocyclic carbene) complexes for hydrogenation of ketones

Four ruthenium‐N‐heterocyclic carbene complexes ( 3–6 ) have been prepared and the new compounds characterized by C, H, N analyses, ¹H‐NMR and ¹³C‐NMR. The reduction of ketones to alcohols via transfer hydrogenation was achieved with catalytic amounts of complexes 3–6 in the presence of t‐BuOK. Copyright © 2006 John Wiley & Sons, Ltd.     

Synthesis of novel palladium N‐heterocyclic‐carbene complexes as catalysts for Heck and Suzuki cross‐coupling reactions

Novel palladium‐1,3‐dialkylperhydrobenzimidazolin‐2‐ylidene (2a–c) and palladium‐1,3‐dialkylimidazolin‐2‐ylidene complexes (4a,b) have been prepared and characterized by C, H, N analysis, ¹H‐NMR and ¹³C‐NMR. Styrene or phenylboronic acid reacts with aryl halide derivatives in the presence of catalytic amounts of the new palladium‐carbene complexes, PdCl₂(1,3‐dialkylperhydrobenzimidazolin‐2‐ylidene) or PdCl₂(1,3‐dialkylimidazolin‐2‐ylidene) to give the corresponding C? C coupling products in good yields. Copyright © 2006 John Wiley & Sons, Ltd.     

Radioactivity in groundwater along the borders of Oman and UAE

Characterizing the quality and radioactivity of groundwater is vital as it represents valuable resource in arid regions. Here we present radioactivity level in groundwater collected from wells in a region along the border between Sultanate of Oman and United Arab Emirates (UAE). The aquifers are alluvium deposits (silt, sand and gravel) and the measured groundwater radioactivity (including ²³²Th, ²³⁸U, ²³⁵U, ²²⁶Ra, ²²²Rn, gross-α and gross-β) indicates values below the WHO permissible limits for drinking water. The results also show large difference in radioactivity fingerprints, in particular for ²²⁶Ra and ²²²Rn within the investigated aquifers. The data further indicate lower radioactivity in groundwater of the alluviums compared to the carbonate aquifers in the region. This feature makes the alluvium aquifers valuable reservoirs that should be carefully exploited as a source of groundwater. As this is the first investigation on the radioactivity of groundwater in alluvial aquifers in the region, it suggests that other alluvial deposits, particularly those inland and far from the marine water intrusion or seepage from carbonate rocks would have low radioactivity fingerprints.