High contrast electromagnetically induced transparency in a nitrogen filled Rb vapour cell

We observe the electromagnetically induced transparency (EIT) spectra inside a nitrogen filled Rb vapour cell (Rb-N₂) in a five-level Λ-type system of D₂ transition of Rb atom. The high contrast EIT resonance in buffer gas filled Rb cell is obtained under our experimental conditions. The effect of velocity changing coherence preserving collisions to obtain the contrast resonance in buffer gas cell has been discussed. We measured the dependence of EIT width and height on pump intensity and find that the EIT width (FWHM) and peak height have a linear dependence on pump intensity. Our experimental results show that the presence of N2 buffer gas reduces the power broadening of the observed resonances.     

Rapid screening and confirmation of drugs and toxic compounds in biological specimens using liquid chromatography/ion trap tandem mass spectrometry and automated library search

Recent advances in liquid chromatography/tandem mass spectrometry (LC/MS/MS) technology have provided an opportunity for the development of more specific approaches to achieve the ‘screen’ and ‘confirmation’ goals in a single analytical step. For this purpose, this study adapts the electrospray ionization ion trap LC/MS/MS instrumentation (LC/ESI‐MS/MS) for the screening and confirmation of over 800 drugs and toxic compounds in biological specimens. Liquid‐liquid and solid‐phase extraction protocols were coupled to LC/ESI‐MS/MS using a 1.8‐µm particle size analytical column operated at 50°C. Gradient elution of the analytes was conducted using a solvent system composed of methanol and water containing 0.1% formic acid. Positive‐ion ESI‐MS/MS spectra and retention times for each of the 800 drugs and toxic compounds were first established using 1–10 µg/mL standard solutions. This spectra and retention time information was then transferred to the library and searched by the identification algorithm for the confirmation of compounds found in test specimens – based on retention time matches and scores of fit, reverse fit, and purity resulting from the searching process. The established method was found highly effective when applied to the analyses of postmortem specimens (blood, urine, and hair) and external proficiency test samples provided by the College of American Pathology (CAP). The development of this approach has significantly improved the efficiency of our routine laboratory operation that was based on a two‐step (immunoassay and GC/MS) approach in the past. Copyright © 2009 John Wiley & Sons, Ltd.     

Resolution,absolute configuration and antifilarial activity of coumarinyl amino alcohols

The resolution of racemic coumarinyl amino alcohols 5–10 was achieved by using the inexpensive and readily accessible chiral resolving agent N-carbethoxy-l-proline (S)-11. Direct esterification of rac-5–10 with (S)-11 furnished diastereomeric esters, which were easily separated by column chromatography. The obtained diastereomers yielded the desired enantiopure coumarinyl amino alcohols (S)-(+)-5–10 and (R)-(?)-5–10 in good yields with high enantiomeric excess on saponification. The absolute configurations were determined by X-ray crystal analysis and/or by comparison of the specific rotations. Furthermore, in in vitro antifilarial motility inhibition assays, enantiopure coumarins (S)-(+)-9, (R)-(?)-9 and (S)-(+)-10, (R)-(?)-10 were found to be less efficient in affecting the viability of macrofilariae of Brugia malayi than their racemic forms 9 and 10, respectively, indicating the synergistic effect of the enantiomers in evoking antifilarial action.     

A metal‐mediated dimerization of the ligand bis(N,N‐diethyl­amino)­carbeniumdi­thio­carboxyl­ate

The title compound, methylene bis[bis(N,N‐diethyl­amino)­carbeniumdi­thio­carboxyl­ate] penta­chloro­oxo­rhenium, (C₂₁H₄₂N₄S₄)[ReCl₅O], is the result of an unusual dimerization of the ligand bis(N,N‐diethyl­amino)­carbeniumdi­thio­carboxyl­ate [(Et₂N)₂C₂S₂] upon reaction with [ReOCl₃(PPh₃)₂] in chloro­form under reflux conditions. The compound was obtained as a dicationic moiety, with the molecular [ReOCl₅]²⁻ anion providing the charge compensation. The planes of the carbenium and thio­carboxyl­ate moieties are nearly perpendicular to one another and the backbone C—C bond length in the N₂CCS₂ group is the same as a normal C—C single‐bond length.     

Accelerated Poisson-Boltzmann calculations for static and dynamic systems

We report here an efficient implementation of the finite difference Poisson-Boltzmann solvent model based on the Modified Incomplete Cholsky Conjugate Gradient algorithm, which gives rather impressive performance for both static and dynamic systems. This is achieved by implementing the algorithm with Eisenstat's two optimizations, utilizing the electrostatic update in simulations, and applying prudent approximations, including: relaxing the convergence criterion, not updating Poisson-Boltzmann-related forces every step, and using electrostatic focusing. It is also possible to markedly accelerate the supporting routines that are used to set up the calculations and to obtain energies and forces. The resulting finite difference Poisson-Boltzmann method delivers efficiency comparable to the distance-dependent dielectric model for a system tested, HIV Protease, making it a strong candidate for solution-phase molecular dynamics simulations. Further, the finite difference method includes all intrasolute electrostatic interactions, whereas the distance dependent dielectric calculations use a 15-A cutoff. The speed of our numerical finite difference method is comparable to that of the pair-wise Generalized Born approximation to the Poisson-Boltzmann method.     

1H NMR detection of immobilized water molecules within a strong distal hydrogen-bonding network of substrate-bound human heme oxygenase-1

Solution 1H NMR is used to probe the environments of the donor protons of eight strong hydrogen bonds on the distal side of the heme substrate in the cyanide-inhibited, substrate-bound complex of human heme oxygenase, hHO. It is demonstrated that significant magnetization transfer from the bulk water signal to the eight labile protons does not result from chemical exchange, but from direct nuclear Overhauser effect due to the dipolar interaction of these labile protons with "ordered" water molecules. The enzyme labile proton to water proton distances are estimated at approximately 3 A. It is proposed that the role of the strong hydrogen-bonding network is to immobilize numerous water molecules which both stabilize the activated hydroperoxy species and funnel protons to the active site.     

High throughput synthesis of ester library utilizing selective molecular reactivity and recognition technology

This paper reports a new solid support reagent that showed high degrees of selective molecular reactivity and molecular recognition in homo-functional reactions (reactions having similar reactive functionality in reactants and products).     

Amphipols can support the activity of a membrane enzyme

Amphipathic polymers ("amphipols") were introduced several years ago (Tribet, C.; Audebert, R.; Popot, J.-L. Proc. Natl. Acad. Sci. U.S.A. 1996, 93, 15047-15050) as an alternative method for solubilizing integral membrane proteins in stable, nativelike conformations. However, direct maintenance of full membrane protein functionality in amphipol solutions has not previously been demonstrated in the absence of added lipid or detergent. In this contribution, the first zwitterionic amphipol "PMAL-B-100" is introduced. PMAL-B-100 not only maintains membrane protein structure and solubility, but also supports the full catalytic activity of an integral membrane enzyme, diacylglycerol kinase, in the complete absence of additional lipid or detergent. All of the roles which a lipid bilayer normally plays in maintaining diacylglycerol kinase's structure and in facilitating catalysis are satisfied by the environment and interactions supplied by PMAL-B-100.