Protein conformations can be probed in top-down HDX MS experiments utilizing electron transfer dissociation of protein ions without hydrogen scrambling

Electron-transfer dissociation (ETD) is evaluated as a technique to provide local information on higher order structure and dynamics of a whole protein molecule. Isotopic labeling of highly flexible segments of a model 18 kDa protein is carried out in solution under mildly denaturing conditions by means of hydrogen/deuterium exchange (HDX), followed by transfer of intact protein ions to the gas phase by means of electrospray ionization, and mass-selection of a precursor ion for subsequent reactions with fluoranthene radical anions. The ETD process gives rise to abundant fragment ions, whose deuterium content can be measured as a function of duration of the HDX reaction in solution. No backbone protection is detected for all protein segments spanning the 25-residue long N-terminal part of the protein, which is known to lack structure in solution. At the same time, noticeable protection is evident for segments representing the structured regions of the protein. The results of this work suggest that ETD of intact protein ions is not accompanied by detectable hydrogen scrambling and can be used in tandem with HDX to probe protein conformation in solution.     

Urea nitrate, an exceptionally easy-to-make improvised explosive: studies towards trace characterization

Urea nitrate is a powerful improvised explosive, frequently used by terrorists in the Israeli arena. It was also used in the first World Trade Center bombing in New York in February 1993. It is difficult to identify urea nitrate in post-explosion debris, since only a very small fraction survives the blast. Also, in the presence of water, it readily decomposes to its original components, urea and nitric acid. It is suspected that post-blast debris of urea nitrate can be confused with ammonium nitrate, the main solid product of urea nitrate thermal decomposition. In a comprehensive study towards identification of urea nitrate in post-blast traces, a spectrophotometric technique for quantitative determination of urea nitrate was developed, and conditions were found for extraction and separation of un-exploded traces of urea nitrate with minimal decomposition. Nevertheless, out of 28 samples collected from a series of three controlled firings of urea nitrate charges, only one gave the typical adduct ion by liquid chromatography/mass spectrometry analysis. We found that urea nitrate can be extracted from solid mixtures to organic solvents by using Crown ethers as “host compounds.” The adducts thus formed are solid, crystalline compounds that can be characterized by microanalysis and spectroscopic techniques. Figure Adduct formation between urea nitrate and 18-crown-6     

A phase-shift analysis of elastic pion-deuteron scattering

Recent data on differential and total cross sections in the region 82 < T_π (MeV) < 292 from SIN and CERN and an isolated polarization measurement formed the material for a πd phase-shift analysis. For virtually all cases χ² < 1 could be reached, but extracted phase parameters are not unique. We emphasize the strong constraints polarization data would exert on presently ambiguous phase parameters. We present our results in Argand plots and briefly discuss their behaviour.     

Testing the three step excited state proton transfer model by the effect of an excess proton

In a previous work, we proposed an extended model for intermolecular excited-state proton transfer to the solvent. The model invoked an intermediate species, the contact ion-pair RO(-)...H(3)O(+), where a proton is strongly hydrogen bonded to the conjugated photabase RO(-). In this study we tested the extended model by measuring the transient absorption and emission of 8-hydroxypyrene-1,3,6-trisulfonate (HPTS) in an aqueous solution in the presence of a large concentration of mineral acids. In a neutral pH solution, the pump-probe signal consists of three time components, <1, 4, and 100 ps. The 4 ps time component, with a relative amplitude of about 0.3, was attributed to the formation of the contact ion-pair and the long 100 ps component to the dissociation of the ion-pair to a free proton and RO(-). In the presence of acid, the recombination of an excess proton competes with the geminate recombination. At a high acid concentration, the recombination process alters the time-dependent concentrations of the reactant, product and intermediate contact ion-pair. We observed that when the acid concentration increases, the amplitude of both the long and intermediate time components decreases. At about 3 M of acid, both components almost disappear. Model calculations of the acid effect on the transient HPTS signal indeed showed that the amplitude of the intermediate time component decreases as the excess proton concentration increases.     

Controlled Release of Farmazin from Thermosensitive Gels Based on Poly(N-vinylcaprolactam)

With the aim to prolong the effect of a wide-spectrum antimicrobial agent, Farmazin (tylosine tartrate), this drug was immobilized on a gel of N-vinylcaprolactam-sodium itaconate copolymer, which undergoes a phase transition on heating. The phase transition, accompanied by a change in volume, in aqueous solutions of the pure copolymer gel and that with the immobilized drug was studied.     

Synthesis and Antiviral Activity of Camphene Derivatives against Different Types of Viruses

To date, the ‘one bug-one drug’ approach to antiviral drug development cannot effectively respond to the constant threat posed by an increasing diversity of viruses causing outbreaks of viral infections that turn out to be pathogenic for humans. Evidently, there is an urgent need for new strategies to develop efficient antiviral agents with broad-spectrum activities. In this paper, we identified camphene derivatives that showed broad antiviral activities in vitro against a panel of enveloped pathogenic viruses, including influenza virus A/PR/8/34 (H1N1), Ebola virus (EBOV), and the Hantaan virus. The lead-compound 2a, with pyrrolidine cycle in its structure, displayed antiviral activity against influenza virus (IC₅₀ = 45.3 µM), Ebola pseudotype viruses (IC₅₀ = 0.12 µM), and authentic EBOV (IC₅₀ = 18.3 µM), as well as against pseudoviruses with Hantaan virus Gn-Gc glycoprotein (IC₅₀ = 9.1 µM). The results of antiviral activity studies using pseudotype viruses and molecular modeling suggest that surface proteins of the viruses required for the fusion process between viral and cellular membranes are the likely target of compound 2a. The key structural fragments responsible for efficient binding are the bicyclic natural framework and the nitrogen atom. These data encourage us to conduct further investigations using bicyclic monoterpenoids as a scaffold for the rational design of membrane-fusion targeting inhibitors.     

Do ionic charges in ESI MS provide useful information on macromolecular structure?

Multiple charging is an intrinsic feature of electrospray ionization (ESI) of macromolecules. While multiple factors influence the appearance of protein ion charge state distributions in ESI mass spectra, physical dimensions of protein molecules in solution are the major determinants of the extent of multiple charging. This article reviews the information that can be obtained by analyzing ionic charge state distributions in ESI MS, as well as potential pitfalls and limitations of this powerful technique. We also discuss future areas of growth with particular emphasis on applications in structural biology, biotechnology (protein-polymer conjugates), and nanomedicine.     

Salts of Anionic Metal Carbonyl Clusters with Cryptand[2.2.2](Na+), DB‐18‐crown‐6(Na+), and Paramagnetic Cp*2Cr+ Cations Obtained by Reduction

Reduction of neutral metal clusters (Co₄(CO)₁₂, Ru₃(CO)₁₂, Fe₃(CO)₁₂, Ir₄(CO)₁₂, Rh₆(CO)₁₆, {CpMo(CO)₃}₂, {Mn(CO)₅}₂) by decamethylchromocene (Cp*₂Cr) or sodium fluorenone ketyl in the presence of cryptand[2.2.2] and DB‐18‐crown‐6 was studied. Nine new salts with paramagnetic Cp*₂Cr⁺, cryptand[2.2.2](Na⁺), and DB‐18‐crown‐6(Na⁺) cations and [Co₆(CO)₁₅]^2– ( 1 , 2 ), [Ru₆(CO)₁₈]^2– ( 3 – 4 ) dianions, [Rh₁₁(CO)₂₃]^3– ( 6 ) trianions, and new [Ir₈(CO)₁₈]^2– ( 5 ) dianions were obtained and structurally characterized. The increase of nuclearity of clusters under reduction was shown. Fe₃(CO)₁₂ preserves the Fe₃ core under reduction forming the [Fe₃(CO)₁₁]^2– dianions in 7 . The [CpMo(CO)₃]₂ and [Mn(CO)₅]₂ dimers dissociate under reduction forming mononuclear [CpMo(CO)₃]^– ( 8 ) and [Mn(CO)₅]^– ( 9 ) anions. In all anions the increase of negative charge on metal atoms shifts the bands attributed to carbonyl C–O stretching vibrations to smaller wavenumbers in agreement with the elongation of the C–O bonds in 1 – 9 . In contrast, the M–C(CO) bonds are noticeably shortened at the reduction. Magnetic susceptibility of the salts with Cp*₂Cr⁺ is defined by high spin Cp*₂Cr⁺ (S = 3/2) species, whereas all obtained anionic metal clusters and mononuclear anions are diamagnetic. Rather weak magnetic coupling between S = 3/2 spins is observed with Weiss temperature from –1 to –11 K. That is explained by rather long distances between Cp*₂Cr⁺ and the absence of effective π–π interaction between them except compound 7 showing the largest Weiss temperature of –11 K. The {DB‐18‐crown‐6(Na⁺)}₂[Co₆(CO)₁₅]^2– units in 2 are organized in infinite 1D chains through the coordination of carbonyl groups of the Co₆ clusters to the Na⁺ ions and π–π stacking between benzo groups of the DB‐18‐crown‐6(Na⁺) cations.     

Generation of magnetic field by combined action of turbulence and shear

The feasibility of a mean-field dynamo in nonhelical turbulence with a superimposed linear shear is studied numerically in elongated shearing boxes. Exponential growth of the magnetic field at scales much larger than the outer scale of the turbulence is found. The characteristic scale of the field is lB proportional S(-1/2) and the growth rate is gamma proportional S, where S is the shearing rate. This newly discovered shear dynamo effect potentially represents a very generic mechanism for generating large-scale magnetic fields in a broad class of astrophysical systems with spatially coherent mean flows.     

Push-pull molecules bearing a hydrazonocyclopentadiene acceptor moiety: from the synthesis to organic photovoltaic applications

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