Disproportionation of H2O2 Mediated by Diiron-Peroxo Complexes as Catalase Mimics

Heme iron and nonheme dimanganese catalases protect biological systems against oxidative damage caused by hydrogen peroxide. Rubrerythrins are ferritine-like nonheme diiron proteins, which are structurally and mechanistically distinct from the heme-type catalase but similar to a dimanganese KatB enzyme. In order to gain more insight into the mechanism of this curious enzyme reaction, non-heme structural and functional models were carried out by the use of mononuclear [Fe^II(L_1–4)(solvent)₃](ClO₄)₂ (1–4) (L₁ = 1,3-bis(2-pyridyl-imino)isoindoline, L₂ = 1,3-bis(4′-methyl-2-pyridyl-imino)isoindoline, L₃ = 1,3-bis(4′-Chloro-2-pyridyl-imino)isoindoline, L₄ = 1,3-bis(5′-chloro-2-pyridyl-imino)isoindoline) complexes as catalysts, where the possible reactive intermediates, diiron-perroxo [Fe^III₂(μ-O)(μ-1,2-O₂)(L₁-L₄)₂(Solv)₂]²⁺ (5–8) complexes are known and well-characterized. All the complexes displayed catalase-like activity, which provided clear evidence for the formation of diiron-peroxo species during the catalytic cycle. We also found that the fine-tuning of iron redox states is a critical issue, both the formation rate and the reactivity of the diiron-peroxo species showed linear correlation with the Fe^III/Fe^II redox potentials. Their stability and reactivity towards H₂O₂ was also investigated and based on kinetic and mechanistic studies a plausible mechanism, including a rate-determining hydrogen atom transfer between the H₂O₂ and diiron-peroxo species, was proposed. The present results provide one of the first examples of a nonheme diiron-peroxo complex, which shows a catalase-like reaction.     

Functional Food: Die Ernährung der Zukunft?: Neuartige Lebensmittel

Prevention of health risks is closely related to functional food, which is expected to provide a health benefit beyond basic nutrition.This review deals with substances which are considered as potential ingredients of functional food. Up to now little is known about their mode of action in the human body, about possible interaction with other food ingredients, and about safety, stability, resorption etc. It is discussed whether functional food reveals any benefit for people's health.     

Polymethacrylate-type monoliths functionalized with chiral amino phosphonic acid-derived strong cation exchange moieties for enantioselective nonaqueous capillary electrochromatography and investigation of the chemical composition of the monolithic polymer

In situ prepared monolithic poly(glycidyl methacrylate-co-ethylene dimethacrylate) (poly(GMA-co-EDMA)) capillary columns were activated to reactive thiol-monoliths and subsequently functionalized with (S)-N-(4-allyloxy-3,5-dichlorobenzoyl)-2-amino-3,3-dimethylbutanephosphonic acid as chiral selector by radical addition to afford enantioselective strong cation exchanger (SCX) capillary columns (100 microm inner diameter (ID)). These monolithic capillaries were devised for the enantioseparation of chiral bases by nonaqueous and aqueous capillary electrochromatography (CEC) and the results obtained for mefloquine and its tert-butylcarbamate as test compounds were compared to those obtained with particulate silica-based analogs (packed columns). Despite abolishment of nonspecific ionic interactions between the cationic solutes and residual silanols that may diminish separation factors of the silica-based chiral SCX particles, the poly(GMA-co-EDMA)-supported SCX monolith did not, as expected, show better enantioselectivities, which was assumed to be due to detrimental nonspecific interactions between the analytes and the lipophilic polymer backbone. In order to minimize these unfavorable contributions, less lipophilic monoliths were developed by copolymerization of different amounts of the hydrophilic monomer 2-hydroxyethyl methacrylate (HEMA) with GMA and EDMA, leading to GMA-co-HEMA-co-EDMA-terpolymeric monoliths. By this increase of the hydrophilicity of the monolithic support the enantioselectivity of the resultant SCX stationary phase could be enhanced and reached values comparable to the packed silica-based enantioselective SCX capillaries. Additionally, the mobile phase composition and other variables were examined and it could be shown that the separation factors are considerably affected by diverse parameters such as acetonitrile-methanol ratio and type and concentration of the counterion. Mefloquine enantiomers could be separated with alpha-values up to 1.56 and a maximum plate count of ca. 60,000 m(-1) could be achieved.     

Crown thioethers and the kinetic macrocyclic effect. Solvolysis of molybdenum(0) tricarbonyl complexes of cyclic and acyclic trithioethers

Summary Solvolysis of the macrocyclic trithioether complexes fac-[Mo(CO)₃([9]aneS₃)] ([9]aneS₃ = 1,4,7-trithiacyclononane) and fac-[Mo(CO)₃(ttob)] (ttob = 2,5,8-trithia[9]-o-benzenophane), and the acyclic trithioether complex fac-[Mo(CO)₃(ttn)] (ttn = 2,5,8-trithiononane) in dimethylsulfoxide (DMSO) solution gives the free trithioether in each case. The kinetics of these reactions were studied by ¹H-n.m.r. spectroscopy. In the absence of acid or base, the rate of solvolysis of [Mo(CO)₃([9]aneS₃)] is at least 4.6 × 10⁵ slower than that of [Mo(CO)₃(ttn)]; larger macrocycles give intermediate rates. [Mo(CO)₃-([9]aneS₃) and [Mo(CO)₃(ttob)] undergo stoichiometric reactions with acid and base in DMSO which in all cases lead to more rapid loss of the intact macrocycle than in DMSO alone. The results are discussed in terms of the structure and bonding of likely intermediate complexes.     

Platinum(II) complexes of 2-alkoxy-dibenzo[c.e][1,2]oxaphosphorines

2-Alkoxy-dibenzo[c.e][1,2]oxaphosphorines were prepared by the reaction of chloro-dibenzooxaphosphorine with alcohols and were converted to the cyclic phosphonates by oxidation and to the corresponding phosphonous boranes by reaction with borane-dimethylsulfide. Interaction of the alkoxy-dibenzooxaphosphorines with dichlorodibenzonitrileplatinum led to bis(dibenzooxaphosphorino)dichloroplatinum complexes exhibiting the P-ligands in the cis disposition. Relative energetics for the prepared cis and the theoretically possible trans isomers of the complexes along with their stereostructures were investigated by quantum chemical calculations.     

Speciation of BCxNy films grown by PECVD with trimethylborazine precursor

Films of BC _x N _y were produced in a plasma-enhanced chemical vapor deposition process using trimethylborazine as precursor and with H₂, He, N₂, and NH₃, respectively, as auxiliary gas. These films deposited on Si(100) wafers or fused quartz glass substrates were characterized chemically by X-ray photoelectron spectroscopy and by synchrotron radiation-based total-reflection X-ray fluorescence combined with near-edge X-ray absorption fine structure. Independent of the auxiliary gas, the B–N bonds are dominating. Furthermore, B–C and N–C bonds were identified. Oxygen, present in the bulk (in contrast to the surface layer of some nanometers, where molecular oxygen and/or water are absorbed) as an impurity, is bonded to boron or to carbon, respectively. The relation of boron and nitrogen changes with the character of the auxiliary gas: c _B/c _N ≈ 4:3 (for H₂ and He) and c _B/c _N ≈ 1 (for N₂ or NH₃). Furthermore, physical properties such as the refractive index and the optical band-gap energy were determined.     

Metabolic profiling of intracellular metabolites in fermentation broths from β-lactam antibiotics production by liquid chromatography–tandem mass spectrometry methods

An analytical platform comprising three LC–ESI-MS/MS methods is presented for qualitative and quantitative profiling of more than 200 intracellular metabolites. Employing a silica based zwitterionic stationary phase in the HILIC mode, in total 223 hydrophilic metabolites can be determined. In particular, amino acids, organic acids as well as nucleotide sugars were found to be well separable and detectable under acidic mobile phase conditions, while in comparison especially phosphates such as nucleotides, coenzymes or sugar phosphates as well as sugars and sugar acids performed better at higher pH. Additionally, 21 less polar analytes turned out to be amenable for separation and analysis on a pentafluorophenyl modified silica stationary phase in RP mode. Solutes were detected by tandem mass spectrometry on a triple quadrupole instrument in the selected reaction monitoring (SRM) mode and specific SRM transitions for 258 metabolites are provided. All three methods were validated with respect to the limit of quantification, linear dynamic range, precision and accuracy. Applicability of the analytical platform was evaluated by analysis of the targeted metabolites in extracts of β-lactam antibiotics fermentation broths. Thereby, 87 metabolites were determined qualitatively in penicillin fermentation broths, and 94 compounds were found in cephalosporin extracts. In addition, a number of selected metabolites that can be determined by at least two of the presented LC–MS/MS methods was analyzed quantitatively by both, external calibration using pure standards as well as by matrix-matched calibration performing standard addition. Quantitative results obtained with the different methods agreed well, however, for some analytes external calibration was found to be ill-suited due to matrix effects.     

Selective enrichment of phosphatidylcholines from food and biological matrices using metal oxides as solid-phase extraction materials prior to analysis by HPLC–ESI-MS/MS

A zirconia (ZrO₂)-modified solid-phase extraction sorbent has been evaluated for selective extraction of phosphatidylcholines from biological samples, followed by analysis of the isolated solutes by reversed-phase liquid chromatography–electrospray ionization–tandem mass spectrometry. The clean-up process was optimized using seven standard phosphatidylcholines including two lyso derivatives. Different acidic conditions were tested for the bonding and washing steps; for elution, various aqueous or methanolic bases were studied. Experiments were conducted hydrodynamically using extraction cartridges, and statically in batch mode; the performance of the sorbent was significantly better when used in the flow-through mode. The developed clean-up procedure was used to selectively enrich phosphatidylcholines from whole milk, human plasma, and mouse plasma, to show the wide applicability of the method. For the preceding extraction of total lipids from the matrix, different solvent mixtures (methanol–chloroform, methanol–methyl tert-butyl ether, and ethanol–ethyl acetate) were compared. Accuracy and reproducibility of the proposed sample-preparation procedure were evaluated. Matrix effects possibly affecting mass spectrometric analysis were studied before and after the solid-phase extraction. They were found to be significant for several analytes, stressing the importance of a sample clean-up procedure. Under identical experimental conditions, recovery of bound phosphatidylcholines by zirconia was superior to that by other metal oxides, for example titania (TiO₂) and stannia (SnO₂).     

Analytical characterization of BCxNy films generated by LPCVD with triethylamine borane

Triethylamine borane (TEAB) and He, N₂ or NH₃ were applied as additional reaction gases in the production of BC_xN_y layers by low-pressure chemical vapor deposition (LPCVD). These layers were deposited on Si(100) wafers and characterized chemically by X-ray photoelectron spectroscopy (XPS) and synchrotron radiation-based total-reflection X-ray fluorescence analysis combined with near-edge X-ray absorption fine-structure spectroscopy (TXRF-NEXAFS). The composition of the material produced without NH₃ was found to be dominated by B–C bonds with the stoichiometric formula B₂C₃N. B–N bonds with the formula B₂CN₃ were preferred when NH₃ was added. A first attempt was made to compare the results obtained by applying trimethylamine borane and TEAB as single-source precursors.