Identification of proteinaceous binding media of easel paintings by gas chromatography of the amino acid derivatives after catalytic hydrolysis by a protonated cation exchanger

Summary A procedure for the hydrolysis of proteins, based on catalysis by the protonated form of a strong cation exchanger, was established for proteinaceous binding media (e.g. casein, egg, animal collagene) used for objects of art. The experimental parameters for the hydrolysis (temperature, time) were optimized, as well as the conditions for sorption and desorption of the amino acids on the cation exchanger. The results for the identification of proteins by the gas chromatographic pattern of the amino acid derivatives, after hydrolysis by the ion exchanger and by hydrochloric acid were compared. The former method proved to be more efficient due to the mild conditions, avoiding the formation of humins in the presence of carbohydrates, and reducing the dissolution of pigments. The method was applied to identify the proteinaceous vehicles of samples from priming and paint layers of easel and wall paintings from the 16th and 18th century.     

Study of the oxidative half‐reaction catalyzed by a non‐heme ferrous catalytic center by means of structural and computational methodologies

Deacetoxycephalosporin C synthase (DAOCS) is a mononuclear ferrous enzyme that catalyzes the expansion of the five‐membered thiazolidine ring of the penicillin nucleus into the six‐membered dihydrothiazine ring of the cephalosporins. In the first half‐reaction with dioxygen and 2‐oxoglutarate, a reactive iron–oxygen species is produced that can subsequently react with the penicillin substrate to yield the cephalosporin. We describe quantum mechanical calculations of the first part of the reaction based on the high‐resolution structures of the active site of DAOCS and its complexes with ligands. These studies are aimed at understanding how the reactive species can be produced and contained in the active site of the enzyme. The results demonstrate the priming of the active site by the co‐substrate for oxygen binding and hint to the presence of a stable iron–peroxo intermediate in equilibrium with a more reactive ferryl species and the formation of CO₂ as a leaving group by decarboxylation of 2‐oxoglutarate. A conclusion from these studies is that substitution of CO₂ by the penicillin substrate triggers the oxidation reaction in a booby‐trap‐like mechanism. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

A new multi-residue method for analysis of pesticide residues in fruit and vegetables using liquid chromatography with tandem mass spectrometric detection

A new multi-residue method for determination of pesticide residues in a wide variety of fruit and vegetables, using the National Food Administration (NFA) ethyl acetate extraction and determination by means of LC-MS/MS, is presented. The method includes pesticides normally detected by LC-UV or LC-fluorescence such as benzimidazoles, carbamates, N-methylcarbamates and organophosphorus compounds with an oxidisable sulphide group as well. After extraction with ethyl acetate, the extract is concentrated and an aliquot of the extract is evaporated to dryness and redissolved in methanol before injection on LC-MS/MS. The method has been validated for 57 different pesticides and metabolites. Representative species from different commodity groups were chosen as matrices in order to study the influence from different matrices on recoveries. The fortification levels studied were 0.01-0.5 mg kg(-1). Matrix effects were tested for all matrices by means of standard addition to blank extracts. The matrix effect, expressed as signal in solvent compared to signal in matrix, was in general found to be small. The obtained recoveries are, with a few exceptions, in the range 70-100%. The proposed method is quick and straightforward and no additional clean-up steps are needed. The method can be used for the analysis of all 57 pesticides in one single determination step at 0.01 mg kg(-1).     

7-Deazaguanosine: Synthesis of an oligorbonucleotide building block and disaggregation of the U-G-G-G-G-U G4 structure by the modified base

Building blocks derived from 7-deazaguanosine (c⁷G, 1 ) were prepared for solid-phase oligoribonucleotide synthesis. Compound 1 was converted into the isobutyurl derivative 2b and the (dimethylamino)methylidene compound 3 (Scheme 1). After tritylation (→ 4a , b ), silylation was studied with regard to regioselectivity. It was found that the triisopropylsilyl group in combination with the (dimethylamino)methylidene residue gave the highest 2′ -selectivity (→ 5e ). The 2′ -O -silyl derivative 5e was reacted with PCl₃ affording the 3′ -phosphonate 7 which was used in solid-phase oligoribonucleotide synthesis. Oligonucleotides derived from U-G-G-G-G-U with an increasing number of c⁷G residues instead of G were synthesized. Aggregation was studied by polyacrylamidegel electrophoresis and CD Spectroscopy. Disaggregation of the G₄-structure of U-G-G-G-G-U was observed when c⁷G replaced G, demonstrating that guanine N(7) participates in the aggregation process.     

Orientierungsverhalten von segmentierten Polyurethanen in Abhängigkeit von der Folienpräparation und dem Zeitpunkt der Orientierungsbestimmung

Zusammenfassung Bei der Drehung von entmischten Block-Copolymeren treten kontinuums- und molekularmechanische Dremomente an den Domänen der härteren Phase auf. Dies führt im Fall der segmentierten Polyurethane zu einer anfänglichen Negativorientierung der Hartsegmente, die als Hinweis auf eine stark anisotrope Domänenform zu verstehen ist, wobei die Hartsegmente in Richtung der kurzen Domänenachse liegen. Hiervon ausgehend werden in der vorliegenden Arbeit Zusammenhänge zwischen der Probenpräparation (ca. 6m dicke Folien) und der Negativorientierung erarbeitet, um so ein Kriterium für die von Fall zu Fall unterschiedliche Domänenmorphologie zu gewinnen. Gleichzeitig ergeben sich Hinweise auf unterschiedliche Relaxationsmechanismen, die sich überlagern und so teilweise eine Erhöhung, teilweise eine Erniedrigung der Orientierung bedingen.Herrn Prof. Dr. F. H. Müller gewidmet.     

Polysulfonylamine. LXXIII [1]. Metall(II)-dimesylamid-Tetrahydrate: Das Dimesylamid-Anion als einzähniger O-Ligand und tetrafunktioneller Wasserstoffbrücken-Akzeptor in den isotypen Komplexen [M(H2O)4 {(CH3SO2)2N}2] mit M = Magnesium,Nickel, Kupfer und Zink

Polysulfonyl Amines. LXXIII. Metal(II) Dimesylamide Tetrahydrates: The Dimesylamide Anion as a Monodentate O-Ligand and a Tetrafunctional Hydrogen Bond Acceptor in the Isotypic Complexes [M(H₂O)₄{(CH₃SO₂)₂N}₂], where M = Magnesium, Nickel, Copper, or Zinc By treating aqueous HN(SO₂CH₃)₂ solutions with the appropriate metal hydroxides, oxides, or carbonates, the crystalline tetrahydrates M[(CH₃SO₂)₂N]₂ · 4 H₂O (M = Mg, Ca, Mn, Co, Ni, Cu, Zn, Cd) were obtained and analytically characterized. The crystal structures of the Mg, Ni, Cu and Zn compounds, as determined by single-crystal X-ray diffraction at low temperatures, reveal an isotypic series (triclinic, space group P1 , Z = 1). The structures consist of centrosymmetric trans-octahedral [M(H₂O)₄{(CH₃SO₂)₂N}₂] molecules in which the anionic ligand acts as a monodentate O-donor. For the Mg, Ni and Zn complexes, the M? OH₂ and M? O(anion) distances lie in the ranges 203–206 pm and 209–214 pm, respectively. The copper compound features a marked Jahn-Teller distortion with Cu? OH₂ = 195.8 and 197.7 pm and Cu? O(anion) = 232.5 pm. The cis-angles O? M? O of the four molecules do not deviate appreciably from 90°. The complex units are associated through a highly organized three-dimensional hydrogen bond network in which all the water protons act as donors and the non-coordinating oxygen atoms and the nitrogen atom of the anionic ligand are involved as acceptors. The H-bond pattern is subjected to a graph-theoretical analysis at the first and second levels.     

Multi-parameter investigation of tandem mass spectrometry in a linear ion trap using response surface modelling

The feasibility of experimental design in combination with subsequent response surface modelling was illustrated for the prediction and interpretation of tandem mass spectrometric (MS/MS) fragmentation data using a linear quadrupole ion trap under various experimental conditions. The instrumental parameters included were (i) the pressure of the collision gas, (ii) the collision energy, (iii) the fill time of the linear ion trap and (iv) the scan rate. The spectral intensity and width of five fragment ions of the doubly charged neuro-active peptide bombesin were used for evaluation, and all experiments were performed so as to resemble the results obtained from a liquid chromatographic peak. The reported results show how fairly simple mathematical tools can be utilized successfully to describe fundamental mechanisms associated with multiple collisional activation and collision-induced dissociation processes without an extensively controlled experimental environment. Most beneficial, using the suggested approach, is the ability to study interaction (synergistic) effects between various parameters. As was realized from the results, many interaction effects are indeed significant. For example, the effect on the signal intensity of different collision gas pressure settings is strongly dependent on the settings of the other parameters. The described approach can easily be adopted for optimization purposes of any MS/MS experiment.     

Stereoselective synthesis of chiral, non-racemic 1,2,3-tri- and 1,3-disubstituted ferrocene derivatives

Chiral, non-racemic 1,2,3-trisubstituted ferrocene derivatives are accessible from monosubstituted ferrocenes through two sequential ortho-deprotonation reactions; removal of the central substituent gives 1,3-disubstituted ferrocenes.     

Bridging the gap between in vitro and in vivo imaging: isostructural Re and 99mTc complexes for correlating fluorescence and radioimaging studies

A bifunctional ligand that is capable of forming Re and 99mTc complexes as complementary fluorescent and radioactive probes was developed. The tridentate bis(quinoline) amine ligand, which is referred to as the SAACQ system, was prepared in a single step from Fmoc protected lysine in high yield. Reaction of the SAACQ ligand with [Re(CO)3Br3]2- resulted in the formation of the SAACQ-(Re(CO)3)+complex which exhibits favorable fluorescence properties including a long lifetime and a large Stoke's shift. Because the SAACQ ligand is derived from an amino acid, it can readily be linked to or incorporated within peptides as a means of targeting the probe to specific receptors. To demonstrate this feature, the SAACQ ligand and the SAACQ-Re complex were incorporated into fMLFG, a peptide that binds to the formyl peptide receptor (FPR). Uptake of the fMLF[(SAACQ-Re(CO)3)+]G conjugate into human leukocytes in vitro was visualized by fluorescence microscopy, and the observed distribution of the peptide was similar to that of a well-established fluorescent FPR probe. The corresponding Tc complex, fMLF[(SAACQ-99mTc(CO)3)+]G, was prepared in excellent yield from [99mTc(CO)3(OH2)3]+, which affords the opportunity to correlate the results of the microscopy experiments with in vivo radioimaging studies because the probes are isostructural.