Gadolinium tagging for high-precision measurements of 6 nm distances in protein assemblies by EPR

Double electron-electron resonance (DEER) distance measurements of a protein complex tagged with two Gd(3+) chelates developed for rigid positioning of the metal ion are shown to deliver outstandingly accurate distance measurements in the 6 nm range. The accuracy was assessed by comparison with modeled distance distributions based on the three-dimensional molecular structures of the protein and the tag and further comparison with paramagnetic NMR data. The close agreement between the predicted and experimentally measured distances opens new possibilities for investigating the structure of biomolecular assemblies. As an example, we show that the dimer interface of rat ERp29 in solution is the same as that determined previously for human ERp29 in the single crystal.     

Electrospray Post-Ionization Mass Spectrometry of Electrosurgical Aerosols

The feasibility of electrospray (ES) ionization of aerosols generated by electrosurgical disintegration methods was investigated. Although electrosurgery itself was demonstrated to produce gaseous ions, post-ionization methods were implemented to enhance the ion yield, especially in those cases when the ion current produced by the applied electrosurgical method is not sufficient for MS analysis. Post-ionization was implemented by mounting an ES emitter onto a Venturi pump, which is used for ion transfer. The effect of various parameters including geometry, high voltage setting, flow parameters, and solvent composition was investigated in detail. Experimental setups were optimized accordingly. ES post-ionization was found to yield spectra similar to those obtained by the REIMS technique, featuring predominantly lipid-type species. Signal enhancement was 20- to 50-fold compared with electrosurgical disintegration in positive mode, while no improvement was observed in negative mode. ES post-ionization was also demonstrated to allow the detection of non-lipid type species in the electrosurgical aerosol, including drug molecules. Since the tissue specificity of the MS data was preserved in the ES post-ionization setup, feasibility of tissue identification was demonstrated using different electrosurgical methods.     

Some General Features in the Autocatalytic Reaction between Sulfite Ion and Different Oxidants

The autocatalytic oxidation of a weak acid is a common building block of the pH oscillators. These reactions can be described by a simple general scheme that includes a protonation equilibrium and the oxidation of the protonated form of the weak acid. Here we show that independently from the chemical nature of the oxidizing agent, these reactions bear some general features, namely (1) the change in pH (ΔpH) observed during the reaction is determined by the acidity constant (K_HA) and by the initial concentration of the unprotonated form of the weak acid (A^?): , (2) the inflection time of the autocatalytic reaction (t_i) depends reciprocally on K_HA and on the initial hydrogen ion concentration, and (3) in the presence of a competitive reversible proton‐binding component (D^?), that is not involved in the oxidation process, ΔpH follows a titration‐like curve as the concentration of D^? is increased, t_i is only slightly affected but the maximum rate of the autocatalytic process is significantly reduced. The slowing of the overall reaction is proportional to the acidity constant of the proton‐binding component.     

Free-Radical Reaction of 2-Vinylcyclopropane-1,1-dicarboxylate with Alkynes

A free-radical reaction of dimethyl 2-vinylcyclopropane-1,1-dicarboxylate with electron rich alkynes giving cyclopentene systems is described. This reaction can be achieved with p-toluenesulfonyl chloride and phenyldisulfide as radical precursors.     

Chemical defects in the highly fluorescent conjugated polymer dots

We present strong evidence for the oxidation of conjugated polymers in the formation of conjugated polymer dots (CPdots) using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Although recent studies show that folding of the polymer chain into a compact 3D structure is involved in the formation of these nanoparticles, the process by which these intrinsically hydrophobic nanoscale particles circumvent aggregation in water is still not well understood. Zeta potential results show that these dots have a negatively charged surface at neutral pH, with a zeta potential and surface charge density of approximately -40 mV and (1.39 - 1.70) × 10(-2) C/m(2), respectively. In addition, quantitative elemental analysis of CPdots indicates that oxygen composes 7-13% of these nanoparticles. The overall results support the presence of chemical defects in forming a hydrophilic surface of CPdots. As a consequence, the charged surface contributes to inhibiting the aggregation of CPdots in water, leading to colloidal stability.     

A Calibration Reaction for Rapid Freeze-Quench W-Band EPR

A simple setup for rapid freeze-quench electron paramagnetic resonance (EPR) at W-band is described. It is based on a BioLogic commercial apparatus and a modified sample collection appropriate for W-band capillaries. The standard reaction of myoglobin with azide, which converts high-spin Fe(III) to low-spin Fe(III), used for calibration of rapid freeze-quench X-band EPR is very inconvenient for high-field measurements. Here we propose a different simple calibration reaction for W-band: the reduction of a nitroxide free radical with sodium dithionite using Mn²⁺ as an internal standard. Using this calibration reaction we determined the dead time of our system to be less than 10 ms.     

Structure and properties of a new double-stranded tetranuclear [Cu(II)2]2 helicate

A novel double-stranded tetranuclear helicate composed of a pair of [Cu(II)(2)] dimers has been prepared and characterized by exploiting the flexibility, chelating ability and bridging potential of a hexadentate bis-oximate ligand.     

Hollow fiber-mediated liquid-phase microextraction of chemical warfare agents from water

Unambiguous detection and identification of chemical warfare agents (CWAs) and related compounds are of paramount importance from verification point of view of Chemical Weapons Convention (CWC). It requires development of fast, reliable, simple and reproducible sample preparation of CWAs from water which is likely to be contaminated during deliberate or inadvertent spread of CWAs. This work describes development of hollow fiber liquid-phase microextraction (HF-LPME) method for efficient extraction of CWAs (such as sarin, sulfur mustard and their analogues) from water followed by gas chromatography-mass spectrometric analysis. Extraction parameters, such as organic solvent, agitation, extraction time, and salt concentration were optimized. Best recoveries of target analytes were achieved using 1 microL trichloroethylene as extracting solvent, 1000 rpm stirring rate, 15 min extraction time, and 30% NaCl. Excellent precision was observed with less than 7.6% RSD. The limit of detection by HF-LPME was achieved up to 0.1 microg/L at 30% salt concentration.     

Electronic structure study by means of x-ray spectroscopy and theoretical calculations of the "ferric star" single molecule magnet

The electronic structure of the single molecule magnet system {M[Fe(L(1))(2)](3)}4CHCl(3) [M=Fe,Cr;L(1)=CH(3)N(CH(2)CH(2)O)(2) (2-)] has been studied using x-ray photoelectron spectroscopy, x-ray-absorption spectroscopy, soft-x-ray emission spectroscopy, as well as theoretical density-functional-based methods. There is a good agreement between theoretical calculations and experimental data. The valence band mainly consists of three bands between 2 and 30 eV. Both theory and experiments show that the top of the valence band is dominated by the hybridization between Fe 3d and O 2p bands. From the shape of the Fe 2p spectra it is argued that Fe in the molecule is most likely in the 2+ charge state. Its neighboring atoms (O,N) exhibit a magnetic polarization yielding effective spin S=52 per iron atom, giving a high-spin state molecule with a total S=5 effective spin for the case of M=Fe.     

Gas chromatography/mass spectrometric analysis of N,N-dialkylaminoethyl-2-methoxyethyl ethers as the decontamination markers of N,N-dialkylaminoethyl-2-chlorides for verification of the Chemical Weapons Convention

The detection and identification of markers of scheduled chemicals plays an important role in verification analysis of Chemical Weapons Convention (CWC). This paper describes the gas chromatography electron ionization mass spectrometric (GC/EI-MS) analysis of N,N-dialkylaminoethyl-2-methoxyethyl ethers (DAEMEs), which are identified as characteristic degradation markers of N,N-dialkylaminoethyl-2-chlorides. N,N-dialkylaminoethyl-2-chlorides produced DAEMEs on reacting with the universally used decontamination solution (DS-2). DAEMEs were prepared by condensation of N,N-dialkylaminoethyl-2-chlorides with 2-methoxy ethanol the active ingredient of DS-2. Based on the GC/EI-MS analysis of DAEMEs the generalized fragmentation routes are proposed which rationalize most of the characteristic ions in EI-MS.