Specific determination of 20 primary aromatic amines in aqueous food simulants by liquid chromatography-electrospray ionization-tandem mass spectrometry

A multi-analyte method without any pre-treatment steps using reversed-phase liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) was developed and applied for the determination of 20 primary aromatic amines (PAA) associated with polyurethane (PUR) products or azo-colours. The method was validated in-house for water and 3% acetic acid food simulants using spiked migrates from plastic laminates. Detection limits ranged from 0.27 to 3 microg amine/L food simulants, and RSD values of within-laboratory reproducibility at the 2 microg PAA/L level ranged from 3.9 to 19%. PAA migration from plastic laminates and black nylon cooking utensils were determined with the method, and high levels of 4,4'-methylenedianiline and aniline were found in migrates from about half of the tested cooking utensils. The method fulfils present legislative demands in the EU for screening and verification of PAA migration from food contact materials.     

210Pb/210Po isotope generator

As a continuation of previous work (Kmak et al. in J Radioanal Nucl Chem 314:985–989, 2017), an isotope generator column based on the ²¹⁰Pb decay chain has been made to produce highly radiopure ²¹⁰Po. Two replicate studies were performed on AG 50Wx8 columns with an average yield of 90.4 ± 1.9%. ²¹⁰Pb breakthrough was seen at the 6 month elution for both generators.

     

Deuterium/hydrogen isotope ratio measurement of water and organic samples by continuous-flow isotope ratio mass spectrometry using chromium as the reducing agent in an elemental analyser

A rapid continuous-flow technique for quantitative determination of hydrogen isotope ratios in water and organic materials at natural abundance levels is described. Water and organic samples were reduced in a helium stream at temperatures in excess of 1000 degrees C over chromium metal. delta(2)H per thousand values of water and organic samples were determined by calibration against International Atomic Energy Agency reference materials V-SMOW and SLAP water. The accuracy of the method was demonstrated through the analysis of the intermediate water standard GISP and IAEA water intercomparison materials OH-1, OH-2 and OH-3. Values obtained using this technique compared well with reference values (maximum difference 2.2 per thousand). The precision of water analyses was less than 2.3 per thousand (1 sigma or 1 standard deviation) in all cases. No apparent memory effect was observed when measuring samples at the natural abundance level. The application of the technique to organic molecules and the salts of organic acids was successfully demonstrated by measuring the delta(2)H per thousand values of an n-hexadecane laboratory reference and anhydrous calcium formate versus water calibration materials. Copyright Crown copyright 2001. Reproduced with permission of the Controller of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.     

Synthesis of [ethylene-1-(eta(5)-4,5,6,7-tetrahydro-1-indenyl)-2- (eta(5)-4',5',6',7'-tetrahydro-2'-indenyl)]titanium dichloride, the elusive isomer of the Brintzinger-type ansa-titanocenes

We present a short synthesis of 1-(2-indenyl)-2-(3-indenyl)ethane (5) and a method for its conversion to the ansa-metallocene [ethylene(eta5-inden-1-yl)(eta5-inden-2-yl)]titanium dichloride (13). The synthetic strategy applied to prepare bisindene 5 relies on the efficient alkylation of 2-(phenylsulfonyl)indane followed by HMPA-assisted E1cB-elimination of phenylsulfinate. This tandem sequence circumvents the predisposition of indene to undergo C(1)-alkylation and enables access to C(2)-substituted indenes. The key step in the synthesis of the title ansa-titanocene (4) features a previously unreported equilibration step to generate the bis(indenide anion) of 5. Complexation with TiCl4.(THF)2 followed by hydrogenation of the product metallocene furnishes ansa-titanocene 4.     

Solid-phase synthesis of phenols and pyridinones via arylboronation/oxidation protocol using aryl bromides

A sequence of two known reactions, palladium catalyzed arylboronation of arybromide and subsequent oxidation of arylboronate with oxone, has been carried out to prepare functionalized phenols and pyridin-2(1H)-one which were later loaded on to resin for solid-phase synthesis. Using these resin-bound templates, a number of solid-phase methods were developed to generate libraries of substituted phenols and pyridin-2(1H)-one.     

Understanding the factors controlling the photo-oxidation of natural DNA by enantiomerically pure intercalating ruthenium polypyridyl complexes through TA/TRIR studies with polydeoxynucleotides and mixed sequence oligodeoxynucleotides

Ruthenium polypyridyl complexes which can sensitise the photo-oxidation of nucleic acids and other biological molecules show potential for photo-therapeutic applications. In this article a combination of transient visible absorption (TrA) and time-resolved infra-red (TRIR) spectroscopy are used to compare the photo-oxidation of guanine by the enantiomers of [Ru(TAP)₂(dppz)]²⁺ in both polymeric {poly(dG-dC), poly(dA-dT) and natural DNA} and small mixed-sequence duplex-forming oligodeoxynucleotides. The products of electron transfer are readily monitored by the appearance of a characteristic TRIR band centred at ca. 1700 cm⁻¹ for the guanine radical cation and a band centered at ca. 515 nm in the TrA for the reduced ruthenium complex. It is found that efficient electron transfer requires that the complex be intercalated at a G-C base-pair containing site. Significantly, changes in the nucleobase vibrations of the TRIR spectra induced by the bound excited state before electron transfer takes place are used to identify preferred intercalation sites in mixed-sequence oligodeoxynucleotides and natural DNA. Interestingly, with natural DNA, while it is found that quenching is inefficient in the picosecond range, a slower electron transfer process occurs, which is not found with the mixed-sequence duplex-forming oligodeoxynucleotides studied.

Efficient electron transfer requires the complex to be intercalated at a G-C base-pair. Identification of preferred intercalation sites is achieved by TRIR monitoring of the nucleobase vibrations before electron transfer.     

Acid-Catalyzed Amine-Borane Reduction of Nitrite

The rate of reduction of nitrite by trimethylamine-borane was followed by observing the decrease in nitrite absorbance under pseudo-first-order conditions. The reaction is acid-catalyzed and exhibits a first-order dependence on both amine-borane and total nitrite concentration. The molar equivalence of NaNO(2) to (CH(3))(3)NBH(3) = 2:1. Equimolar amounts of hydrogen and nitrous oxide are formed, and the molar ratio of nitrite reacted to N(2)O produced is 2:1. In concentrated HCl or H(2)SO(4), a correlation of rate with the Hammett acidity function, h(o), is observed. The reaction is subject to a pronounced inversesolvent isotope effect (k(D)()2(O)/k(H)()2(O) approximately 2.7) and a modest normal substrate effect (k((CH)()3())()3(N.BH)()3/k((CH)()3())()3(N.BD)()3 approximately 1.4). The reaction is first-order in H(3)O(+) in the region pH 0.7-2.7, but a second-order dependence is observed above pH 4 with the transition occurring at pH approximately pK(a) for HNO(2). Results are consistent with a mechanistic model involving preequilibration protonation of molecular nitrous acid followed by rate-limiting hydride attack on H(2)ONO(+) or free NO(+) to produce nitrosyl hydride as a reactive intermediate.     

Unusual photophysical switching in a Ru(II) diimine DNA probe caused by amide functionalisation

Whereas the complex [Ru(phen)2Medpq]2+(phen=1,10-phenanthroline; Medpq=2-methyldipyrido[3,2-f:2',3'-h]-quinoxaline) is luminescent in both aqueous and nonaqueous solutions, [Ru(phen)2dpqa]2+(2-pentylamidodipyrido[3,2-f:2',3'-h]-quinoxaline) does not emit in water but does so strongly in organic solvents or when bound to DNA--suggesting its use as a photochemical and photophysical probe for nucleic acids.     

Synthesis of a negatively charged dibenzofuran-based beta-turn mimetic and its incorporation into the WW miniprotein-enhanced solubility without a loss of thermodynamic stability

A versatile synthesis has been developed to functionalize the 4-(2-aminoethyl)-6-dibenzofuran propionic acid residue (1a) at the 2 and 8 positions with a variety of different substructures. The unfunctionalized version of this peptidomimetic (1a) is known to facilitate beta-hairpin formation in a variety of small peptides and proteins in aqueous solution when incorporated in place of the i + 1 and i + 2 residues of a beta-turn. In this study, we append propionate substituents on 1a at the 2 and 8 positions to successfully overcome solubility problems encountered with the incorporation of 1a in place of the i + 1 and i + 2 residues of the beta-turn in loop 1 of the WW domain. The thermodynamic stability of several WW domain analogues incorporating residues 1a and 1b was compared to that of the wild-type sequence revealing comparable DeltaG(H(2)O) unfolding values at 4 degrees C ranging from 3 to 3.6 kcal/mol. WW domains incorporating residue 1b exhibit improved solubility (exceeding 100 microM) and resistance to aggregation without compromising thermodynamic stability.     

Serum protein immunogenicity: implications for liver xenografting

The objectives of this study were threefold: (i) assess immunogenicity of donor plasma proteins following hepatic xenotransplantation, (ii) identify potential immunogens, and (iii) consider the implications of antibody formation against these plasma proteins in xenograft survival. We studied liver and heart xenografts in a concordant combination, hamster to rat. All grafts were examined at necropsy for evidence of rat immunoglobulin G (IgG) deposition. Cardiac xenografts were placed in recipients who had, or had not, been sensitized with hamster serum. Hepatic xenografts were placed in naive recipients to see if antibodies to hamster serum proteins could be eluted from the rejecting organ. Sera of immunized rats were examined for the presence of anti-hamster antibodies by immunoelectrophoresis and by Western blotting following sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) separation of hamster serum. Antibodies in sera of immunized rats were compared with those eluted from rejecting livers. Candidate antigens were identified by tandem mass spectrometry, sequence analysis, and reference to protein databases. Results showed that sera of immunized rats recognized a minimum of four different antigens in hamster serum by immunoelectrophoresis, and a minimum of seven by the more sensitive SDS-PAGE Western blot. IgG eluted from rejecting livers bound three of seven candidate antigens recognized by sera of the immunized animals. Sequence analysis searches revealed proteinase inhibitors in each of the three SDS-PAGE bands common to the above samples. All of these candidate proteinase inhibitor immunogens share a common catabolic fate, uptake via the lipoprotein-related protein (LRP/alpha 2-macroglobulin receptor (CD91). Sensitization to hamster serum proteins hastened cardiac xenograft rejection in 30-50% of recipients (depending on sensitization protocol). Vascular deposition of rat IgG occurred in all rejecting xenografts. Antibody binding to proteinase inhibitors could disturb their functional activity and contribute to the pathogenesis of delayed xenograft rejection.