Doubly charged ion mass spectra: VI—Amines

Doubly charged ion mass spectra of 22 amines (2–10 carbon atoms) were determined using an Hitachi RMU-7L double focusing mass spectrometer. Molecular ions were not observed in the spectra of aliphatic amines. The most intense product ion peaks in the spectra of lower molecular weight amines resulted from hydrogen elimination from the molecular ion; however, as amine molecular weight increased the largest peaks resulted from both hydrogen and heavy atom elimination from the molecular ion. Dominant ions in the doubly charged ion spectra of lower molecular weight aliphatic amines were from reactions of [C_nH₃N]²⁺ (n:=2, 3, 4) type ions. The spectra of higher molecular weight aliphatic amines spanned a wide mass range. Appearance energies for some of the more prominent ions were measured in the range from 25 to 49 eV. A geometry optimized quantum mechanical self-consistent field molecular orbital treatment was used to compute the energies and structural parameters of prominent ions in the doubly charged ion mass spectra.     

Recognition of G-1:C73 atomic groups by Escherichia coli histidyl-tRNA synthetase

This work focuses on the RNA-protein interactions necessary for efficient aminoacylation of tRNAHis by Escherichia coli histidyl-tRNA synthetase (HisRS). The E. coli tRNAHis acceptor stem is characterized by a unique "extra" G-1:C73 base pair. Previous in vivo and in vitro studies showed that G-1:C73 is a major recognition element for E. coli HisRS. To further probe the role of the G-1:C73 base pair in specific aminoacylation, we carried out atomic group "mutagenesis" studies. Systematic base analogue substitutions at the -1:73 position of chemically synthesized microhelixHis substrates suggest that the G-1 base serves to position the 5'-monophosphate, which is critical for aminoacylation. Additionally, the C73 and G-1 bases contain major groove exocyclic atomic groups that contribute to HisRS recognition.     

Synthesis,characterization and antioxidant,antibacterial activity Zn2+, Cu2+, Ni2+ and Co2+, complexes of ligand [2-(thiophen-2-yl)-1-(thiophen-2-ylmethyl)-1H-benzo[d]imidazole]

New metal complexes of (Zn(II), Co(II), Ni(II) and Cu(II)) based on the ligand 2-(thiophen-2-yl)-1-(thiophen-2-ylmethyl)-1H-benzo[d]imidazole] were synthesized, whose structures were determined with the different spectroscopic techniques ¹H NMR,¹³C NMR, FT-IR, UV–Visible and by mass spectrometry. The thermal analysis was performed by TG-DTA. The antioxidant activity of the ligand and its complexes was evaluated by DPPH (2,2-diphenyl-1-picrylhydrazyl) method, in comparison with the synthetic antioxidant, ascorbic acid. The results obtained showed that the antioxidant activity of the ligand and its complexes is moderate and that the copper complex has a high activity that exceeds that of ascorbic acid. Antimicrobial activity of the ligand and its metal complexes was studied against two Gram-positive bacteria: Bacillus subtilis ILP1428B, Staphylococcus aureus CIP543154 and two Gram-negative bacteria: Pseudomonas aeruginosa ATCC27653, Escherichia coli CIP5412 (American Type Culture Collection)the activity data show that the metal complexes are more potent than the free ligand.     

Determination of thorium in rocks : The arsenazo III reaction in perchlorate medium

savvin's reagent, arsenazo III, has been examined for the determination of traces of thorium in rocks. The superior sensitivity and selectivity of the arsenazo III reaction, over the thorin reaction have been confirmed. Sensitivity and stability have been improved by working in a perchlorate medium. Anomalous effects were observed in the presence of relatively large amounts of titanium. Silicate samples are decomposed by rafter's peroxide sinter, the sinter cake leached with water, and the residue dissolved in acid. Thorium is collected on a calcium oxalate precipitate, and determined photometrically in perchloratc medium at 660 mm. The normal working range is 0 to 25 μg of thorium on a 0.5-g sample.     

Membrane admittance measurements under computer control

The application of the elegant Fourier transform method of Smith et al.^3,4 to measurements on ultrathin, “black” lipid membrane is described. A digital computer generates a waveform containing many frequencies, applies it to the measurement cell containing an artificial, ultrathin membrane, collects the resulting electrical response, extracts the cell admittance by a substitution method, and facilitates subsequent numerical data analysis. The performance of the instrument is illustrated.     

Diversity through isosterism: the case of boron-substituted 1,2-dihydro-1,2-azaborines

The first general synthesis of boron-substituted 1,2-dihydro-1,2-azaborines is described. The versatile 1,2-dihydro-1,2-azaborine precursor 4 is synthesized through a ring-closing metathesis-oxidation sequence. Treatment of 4 with a wide range of anionic nucleophiles furnishes the desired adducts 5 in good yields. The scope includes hydrogen- and a variety of carbon- and heteroatom-based nucleophiles. Furthermore, the boron-containing isostere (7) of the potent hypolipidemic agent, methyl 2-ethylphenoxyacetate (8), is readily prepared through our method.