Synthesis and reduction of some 1H-2,1,3-benzothiadiazin-4(3H) one 2,2-dioxides

Several 2,1,3-benzothiadiazin-4(3H) one 2,2-dioxides were synthesized as possible sweetening agents by reacting sulfamoyl chloride with various anthranilic acid derivatives. The isolation of 1-methyl-4-methoxy-2,1,3-benzothiadiazine 2,2-dioxide and preparation of 3,4-dihydro-2,1,3-benzothiadiazine 2,2-dioxide is also reported.     

Structural studies of the allelic wheat glutenin subunits 1Bx7 and 1Bx20 by matrix-assisted laser desorption/ionization mass spectrometry and high-performance liquid chromatography/electrospray ionization mass spectrometry

Structural studies of the high molecular mass (HMM) glutenin subunits 1Bx7 (from cvs Hereward and Galatea) and 1Bx20 (from cv. Bidi17) of bread wheat were conducted using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) and reversed-phase high-performance liquid chromatography/electrospray ionization mass spectrometry (RP-HPLC/ESI-MS). For all three proteins, MALDI-TOFMS analysis showed that the isolated fractions contained a second component with a mass about 650 Da lower than the major component. The testing and correction of the gene-derived amino acid sequences of the three proteins were performed by direct MALDI-TOFMS analysis of their tryptic peptide mixture. Analysis of the digest was performed by recording several MALDI mass spectra of the mixture at low, medium and high mass ranges, optimizing the matrix and the acquisition parameters for each mass range. Complementary data were obtained by RP-HPLC/ESI-MS analysis of the tryptic digest. This resulted in coverage of about 98% of the sequences. In contrast to the gene-derived data, the results obtained demonstrate the insertion of the sequence QPGQGQ between Trp716 and Gln717 of subunit 1Bx7 (cv. Galatea) and a possible single amino acid substitution within the T20 peptide of subunit 1Bx20. Moreover, the mass spectrometric data demonstrated that the lower mass components present in all the fractions correspond to the major components but lack about six amino acid residues, which are probably lost from the protein C-terminus. Finally, the results obtained provide evidence for the lack of glycosylation or other post-translational modifications of these subunits.     

Structural studies of glutenin subunits 1Dy10 and 1Dy12 by matrix-assisted laser desorption/ionisation mass spectrometry and high-performance liquid chromatography/electrospray ionisation mass spectrometry

Structural studies of the high molecular weight (HMW) glutenin subunits 1Dy10 and 1Dy12 of bread wheat were conducted using matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOFMS) and reversed-phase high-performance liquid chromatography/electrospray ionisation mass spectrometry (RP-HPLC/ESI-MS). For both proteins, MALDI-TOFMS analysis showed that the isolated fractions contained a second component with a mass about 500-540 Da lower than the major component. The testing and correction of the gene-derived amino acid sequences of both proteins were performed by direct MALDI-TOFMS analysis of their tryptic peptide mixture and analysis of the digests was performed by recording several MALDI mass spectra of the mixture at low, medium and high mass ranges, optimising the matrix and the acquisition parameters for each mass range. Complementary data were obtained by RP-HPLC/ESI-MS analysis of the tryptic digest. This resulted in the coverage of the whole protein sequences except for two short fragments (T1 and T8), which are identical in the two homologous subunits, and for an additional dipeptide (T14) in subunit 1Dy12, which were not detected. It also demonstrated that, in contrast to the gene-derived data, the sequence of subunit 1Dy12 does not include the dipeptide Gly-Gln between residues Gln(454) and Pro(455), and that the lower mass components present in both fractions correspond to the same sequences lacking short peptides that are probably lost from the protein N- or C-termini. Finally, the results obtained provide evidence for the lack of a substantial level of glycosylation or other post-translational modifications of the two subunits, and demonstrate that mass spectrometric mapping is the most useful method presently available for the direct verification of the gene-derived sequences of HMW glutenin subunits and similar proteins.     

Transference numbers for ultra concentrated solutions of aqueous hydrochloric acid at 25°C

Transference numbers of HCl(aq) solutions at 25°C, from 0.01 to 13.6 mol-kg^–1(m) have been obtained by measuring the emf of cells with transference using hydrogen gas/platinum electrodes. Good agreement is obtained at concentrations up to 1 m with all previous data, and our results strongly corroborate those of King and Spiro over the 2–8m concentration range. The transference numbers of the hydronium ion fit the empirical equation, _H ^HCl = 0.821 + 0.0457m ^1/2 – 2.476×10^–2m – 1.90×10^–4 m ² – 1.45×10^–5 m ³ the maximum deviation in T _H ^HCl being 0.003.     

THE PHOTOPHYSICS OF p-AMINOBENZOIC ACID

Abstract— The lowest-lying allowed UV transition in p -aminobenzoic acid (PABA) is assigned Γ→¹L_a based on quantitative absorption and fluorescence studies, as well as semiempirical PM3 multielec-tron configuration interaction calculations. The oscillator strengths, fluorescence quantum efficiencies and lifetimes are reported for PABA in several polar, nonpolar, protic and aprotic solvents (aerated) at 296 K. Reasonable agreement is found between the observed radiative rate constant and that calculated from the absorption and fluorescence spectra. Shifts in the absorption and fluorescence spectra in aprotic solvents are analyzed in terms of the Onsager reaction field model; results are consistent with an increase in dipole moment of ca 4 D between the relaxed S₀ and S₁, states. No evidence is found for the emission from the amino-twisted form of PABA in all solvents studied although calculations show that the amino-twisted S, state is highly polar, but higher in energy by ca 35 kJ/mol ( in vacuo ). The fluorescence efficiency is excitation wavelength independent in both methylcyclohexane and water. The temperature dependence of the nonradiative rate constant (from S₁) was studied in several solvents. Nonradiative decay may be due to intersystem crossing, which would be fast enough to compete with thermally activated intramolecular NH₂ twisting. The phosphorescence spectrum and lifetime obtained in an EPA glass at 77 K are reported, and the triplet energy of PABA is estimated.     

Determination of fluoride in wine by fluoride selective ion electrode, standard addition method: collaborative study

The accuracy, precision, and reproducibility of a rapid method for determination of fluoride in wine, using a fluoride selective ion electrode, were established by a collaborative study involving 12 laboratories, 5 in Europe and 7 in the United States. The laboratories assayed 6 Youden pairs of fluoride-fortified, red and white wine samples with fluoride concentrations ranging from 0.2 to 3.0 mg/L. The relative standard deviations of repeatability ranged from 1.94 to 4.88%; relative standard deviations of reproducibility ranged from 4.15 to 18.40%. HORRAT values ranged from 0.30 to 0.97. The average recovery was 99.97%. Based on the statistical results of this collaborative study, the Study Director recommends that this method be adopted First Action.     

Copper(II)-catalyzed aerobic oxidation of primary alcohols to aldehydes in ionic liquid [bmpy]PF6

A room-temperature aerobic oxidation of primary alcohols to aldehydes catalyzed by the three-component system acetamido-TEMPO/Cu(ClO(4))(2)/DMAP in the ionic liquid [bmpy]PF(6) has been developed, and the catalysts can be recycled and reused for five runs without any significant loss of catalytic activity. [reaction: see text]