Reactive dications: the superacid-catalyzed reactions of alkynes bearing adjacent N-heterocycles or amine groups

A variety of aminoalkynes and related heterocycles are reacted in the Bronsted superacid CF(3)SO(3)H (triflic acid), and products are obtained in generally good yields (69-99%) from Friedel-Crafts-type reactions. The reactions are consistent with the formation of novel dicationic intermediates having a vinyl cationic site and an adjacent protonated N-heterocycle or ammonium cation.     

Reactions of Charged Substrates. 4. The Gas-Phase Dissociation of (4-Substituted benzyl)dimethylsulfoniums and -pyridiniums

The relative rates for the gas-phase dissociation RX(+) --> R(+) + X degrees of five (4-Y-substituted benzyl)dimethysulfoniums (Y = MeO, Me, H, Cl, and NO(2)) and 24 (4-Y-substituted benzyl)-3'-Z-pyridiniums (complete series for Z = CN, Cl, CONH(2), and H, and 4-methoxy- and 4-nitrobenzyls for Z = F and CH(3)CO) were measured using liquid secondary ion mass spectrometry. The Hammett plot (vs deltaDeltaG degrees or sigma(+)) is linear for the sulfoniums, but plots for the four pyridinium series have a drastic break between the 4-Cl and 4-NO(2) substrates. Br?nsted-like plots for the pyridiniums show a strong leaving group effect only for 4-nitrobenzyls. An analysis of these linear free energy relations with supporting evidence from semiempirical computations suggests that collisionally activated pyridinium substrates dissociate by two pathways, direct dissociation and through an ion-neutral complex intermediate. Comparison of these results with results for the solution reactions of some of these compounds shows that the mechanism is different in the gas and solution phases. Sufficient experimental data are not available to assign a mechanism for dissociation to the sulfonium series, but computational results show characteristics of a direct dissociative mechanism.     

CERTAIN SINGLET OXYGEN QUENCHERS AFFECT THE PHOTOREACTION BETWEEN 8-MOP and DNA

The effect of certain chemicals known as singlet oxygen quenchers on the photoreaction between 8-MOP and DNA has been studied in vitro; sodium azide, l,4-diazabicyclo-(2,2,2)-octane, p-carotene and dimethylsolfoxide (used as a solvent) appeared to be capable of reducing significantly the 8-MOP ability to induce both monoadducts and cross-links in DNA. Therefore, these chemicals seem to be not useful in studying the singlet oxygen implication in the induction of biological effects of 8-MOP sensitization.     

Measurement of natural environmental radioactivity and estimation of population exposure in Bihac,Bosnia and Herzegovina

Journal of Radioanalytical and Nuclear Chemistry - This work presents measurements of activity concentrations and estimation of population exposure from the naturally occurring radionuclides 238U,...     

Highly Diastereoselective [3+2] Cycloadditions Between Non-Racemic p-Tolylsulfinimines and Iminoesters: An Efficient Entry to Enantiopure Imidazolidines and Vicinal Diaminoalcohols

Abstract

Readily available p-tolylsulfinimines undergo highly stereoselective [3 + 2] cycloadditions with azomethine ylides generated from α -iminoesters and LDA to produce N-sulfinylimidazolidines. In the presence of Lewis acids, p-tolylsulfinimines react with glycine iminoester enolates to produce N-sulfinylimidazolidines, after cyclization of open chain intermediates. These mechanistically diverse processes take place with excellent regio-, stereo-, and facial selectivities, and the latter is opposite to most known reactions involving sulfinimines. Some of the resulting imidazolidines have been transformed into examples of a novel class of nonsymmetrical vicinal diamines using reductive and/or hydrolytic protocols.     

Search of sequence databases with uninterpreted high-energy collision-induced dissociation spectra of peptides

We have broadened the utility of the SEQUEST computer algorithms to permit correlation of uninterpreted high-energy collision-induced dissociation spectra of peptides with all sequences in a database. SEQUEST now allows for the additional fragment ion types observed under high-energy conditions. We analyzed spectra from peptides isolated following trypsin digestion of 13 proteins. SEQUEST ranked the correct sequence first for 90% (18/20) of the spectra in searches of the OWL database, without constraint by enzyme cleavage specificity or species of origin. All false-positives were flagged by the scoring system. SEQUEST searches databases for sequences that correspond to the precursor ion mass ±0.5 u. Preliminary ranking of the top 500 candidates is done by calculation of fragment ion masses for each sequence, and comparison to the measured ion masses on the basis of ion series continuity, summed ion intensity, and immonium ion presence. Final ranking is done by construction of model spectra for the 500 candidates and constructing/performing of a cross-correlation analysis with the actual spectrum. Given the need to relate mounting genome sequence information with corresponding suites of proteins that comprise the cellular molecular machinery, tandem mass spectrometry appears destined to play the leading role in accelerating protein identification on the large scale required.     

Separation and quantification of double‐ and triple‐layered rotavirus‐like particles by CZE

Virus‐like particles have been successfully used as safe vaccines, as their structure is identical to their native counterparts but devoid of the viral genetic material. However, production of these complex structures is not easy, as recombinant proteins must assemble into virus‐like particles. Techniques to differentiate assembled and soluble proteins, as well as assembly intermediaries often present in a sample, are required. An example of complex virus‐like particles mixture occurs when rotavirus proteins are recombinantly expressed. Rotavirus‐like particles (RLP) can be single (sl), double (dl), or triple layered (tl). The use of RLP preparations as vaccines requires their complete characterization, including separation and quantification of each RLP in a sample. In this work, CZE was evaluated for the separation and quantification of dl and triple‐layered rotavirus‐like particles (tlRLP). A fused‐silica capillary with a deoxycholate running buffer efficiently separated dl and tlRLP in RLP preparations, as they migrated in two discrete peaks with electrophoretic mobilities of 1.24±0.04 and 2.95±0.03 Ti, respectively. Standard curves for dl and tlRLP were generated, and the response was linearly proportional to analyte concentration. The methodology developed was quantitative, specific, accurate, precise, and reproducible. CZE allowed the quantitative characterization of RLP preparations, which is required for evaluation of immunogens, for process development, and for quality control protocols.     

Syntheses and characterization of Cu,Ni and Zn binding capability of histidinehydroxamic acid derivatives

Two histidinehydroxamic acid derivatives (N-methyl-histidinehydroxamic acid, N-Me-Hisha and Z-histidinehydroxamic acid, Z-Hisha) have been synthesized and their complexation with Cu²⁺-, Ni²⁺- and Zn²⁺-ions has been studied by using pH-potentiometric, UV–Vis, CD, ¹H NMR, EPR and ESI-MS methods. Both of the two new derivatives contain one donor atom less compared to the histidinehydroxamic acid (Hisha). In the case of N-Me-Hisha the hydroxamate-N as donor is eliminated, while the coordination of the amino-N of Z-Hisha is not possible at all.