The [4Fe-4S](2+) cluster in reconstituted biotin synthase binds S-adenosyl-L-methionine

The combination of resonance Raman, electron paramagnetic resonance and M?ssbauer spectroscopies has been used to investigate the effect of S-adenosyl-l-methionine (SAM) on the spectroscopic properties of the [4Fe-4S]2+ cluster in biotin synthase. The results indicate that SAM interacts directly at a unique iron site of the [4Fe-4S]2+ cluster in BioB and support the hypothesis of a common inner-sphere mechanism for the reductive cleavage of SAM in the radical SAM family of Fe-S enzymes.     

Review of stationary phases for microelectromechanical systems in gas chromatography: feasibility and separations

This review covers the recent development of stationary phases for chip-based gas chromatography (GC). Portable systems for rapid and reliable analysis are urgently needed. One way to achieve this is to miniaturize the entire analysis. Because the column is the central component of the GC system and determines the feasibility and quality of separation, this review focuses on stationary phases reported in the literature and their use in different fields during the last two decades, with emphasis on different methods for introducing the stationary phase into the GC column.     

Chemical isolation of element 106 from aqueous solutions according to model experiments with short-lived tungsten isotopes

The short-lived isotopes of W and their descendants have been isolated from the products of the bombardment of¹⁴⁴Sm with²⁴Mg by a fast continuous ion-exchange method, using HF solution media. The feasibility of this method for isolation of element 106 is discussed.     

Use of disposable open tubular ion exchange pre-columns for in-line clean-up of serum and plasma samples prior to capillary electrophoretic analysis of inorganic cations

A simple analytical system using disposable, open-tubular ion exchange clean-up precolumns coupled in-line to capillary electrophoresis for direct injection of biological samples is presented. The clean-up precolumns were prepared from fused silica capillaries by thermally initiated layer-by-layer polymerization of poly(butadiene-maleic acid) (PBMA) directly on the capillary wall. Typically, 6 cm long precolumns with 4-layers of PBMA were used for sample pretreatment. A robust and reproducible coupling between the precolumn (75 μm ID) and the analytical capillary (50 μm ID) was achieved using an inexpensive, commercially available low dead volume union. No extra dispersion of the analyte zones was observed. Proteins and other high molecular weight compounds from biological sample matrices were retained on the cation-exchanger sites of the precolumn, which eliminated their adsorption on analytical capillary walls and ensured stable electroosmotic flow and migration times of target analytes. Unretained small inorganic cations migrated freely into the analytical capillary for separation and detection. Applicability of the sample clean-up procedure was proved by determination of major inorganic cations in blood serum and plasma samples using capillary electrophoresis with contactless conductivity detection. Separations were performed in background electrolyte solution consisting of 15 mM L-arginine, 12.5 mM maleic acid, 3 mM 18-crown-6 at pH 5.5 and repeatabilities of migration times and peak areas were below 1.5% and 7.3%, respectively. Less than 1 μL of biological sample was required for injection.     

Iron(II)-catalyzed amidation of aldehydes with iminoiodinanes at room temperature and under microwave-assisted conditions

A method for the amidation of aldehydes with PhI=NTs/PhI=NNs as the nitrogen source and an inexpensive iron(II) chloride + pyridine as the in situ formed precatalyst under mild conditions at room temperature or microwave assisted conditions is described. The reaction was operationally straightforward and accomplished in moderate to excellent product yields (20-99%) and with complete chemoselectivity with the new C-N bond forming only at the formylic C-H bond in substrates containing other reactive functional groups. By utilizing microwave irradiation, comparable product yields and short reaction times of 1 h could be accomplished. The mechanism is suggested to involve insertion of a putative iron-nitrene/imido group to the formylic C-H bond of the substrate via a H-atom abstraction/radical rebound pathway mediated by the precatalyst [Fe(py)(4)Cl(2)] generated in situ from reaction of FeCl(2) with pyridine.     

Comparison between 2-hydroxypropyl-��-cyclodextrin and 2-hydroxypropyl-��-cyclodextrin for inclusion complex formation with danazol

Complexation in solution between danazol and two different cyclodextrins [2-hydroxypropyl-??-cyclodextrin (HP-??-CD) and 2-hydroxypropyl-??-cyclodextrin (HP-??-CD)] was studied using phase solubility analysis, and one- and two-dimensional ¹H-NMR. The increase of danazol solubility in the aqueous cyclodextrin solutions showed a linear relationship (A_L profile). The apparent stability constant, K _1:1, of each complex was calculated and found to be 51.7 × 10³ and 7.3 × 10³ M^?1 for danazol?CHP-??-CD and danazol?CHP-??-CD, respectively. ¹H-NMR spectroscopic analysis of varying ratios of danazol and the different cyclodextrins in a mixture of EtOD?CD₂O confirmed the 1:1 stoichiometry. Cross-peaks, from 2D ROESY ¹H-NMR spectra, between protons of danazol and H3?? and H5??of cyclodextrins, which stay inside the cyclodextrin cavity, proved the formation of an inclusion complex between danazol and the cyclodextrins. For HP-??-CD, the inclusion complex is formed by entrance of the isooxazole and the A rings of danazol in the cyclodextrin cavity. For HP-??-CD, two different inclusion structures may exist simultaneously in solution: one with the isooxazole and A ring in the cavity and the other with the C and D ring inside the cavity. DLS showed that self-aggregation of the CD??s was absent in the danazol HP-??-CD system up to a CD concentration of 10% and in the danazol HP-??-CD system up to a CD concentration of 5%.     

On-chip multi-electrochemical sensor array platform for simultaneous screening of nitric oxide and peroxynitrite

In this work we report on the design, microfabrication and analytical performances of a new electrochemical sensor array (ESA) which allows for the first time the simultaneous amperometric detection of nitric oxide (NO) and peroxynitrite (ONOO(-)), two biologically relevant molecules. The on-chip device includes individually addressable sets of gold ultramicroelectrodes (UMEs) of 50 μm diameter, Ag/AgCl reference electrode and gold counter electrode. The electrodes are separated into two groups; each has one reference electrode, one counter electrode and 110 UMEs specifically tailored to detect a specific analyte. The ESA is incorporated on a custom interface with a cell culture well and spring contact pins that can be easily interconnected to an external multichannel potentiostat. Each UME of the network dedicated to the detection of NO is electrochemically modified by electrodepositing thin layers of poly(eugenol) and poly(phenol). The detection of NO is performed amperometrically at 0.8 V vs. Ag/AgCl in phosphate buffer solution (PBS, pH = 7.4) and other buffers adapted to biological cell culture, using a NO-donor. The network of UMEs dedicated to the detection of ONOO(-) is used without further chemical modification of the surface and the uncoated gold electrodes operate at -0.1 V vs. Ag/AgCl to detect the reduction of ONOOH in PBS. The selectivity issue of both sensors against major biologically relevant interfering analytes is examined. Simultaneous detection of NO and ONOO(-) in PBS is also achieved.     

Tuning the electronic properties of cyclopentadienyl analogs with CB2N2 frameworks: 1,2-diphenyl-1,2-diaza-3,5-diborolyl ligands and their alkali metal salts

Two heterocyclic cyclopentadienyl analogs with a CB2N2 skeleton, 4-methyl-1,2,3,5-tetraphenyl-1,2-diaza-3,5-diborolidine and 4-methyl-3,5-dimethylamino-1,2-diphenyl-1,2-diaza-3,5-diborolidine were prepared through cyclocondensation of the corresponding 1,1-bis(organochloroboryl)ethane with 1,2-diphenylhydrazine. The former diazadiborolidine featured a cyclopentadiene-like structure with short B-N bonds and a planar ring framework, while in the latter the B-N bonds were noticeably longer and the ring framework was considerably folded as a result of the interaction between boron and the electron donating NMe2 groups. The dimethylamino substituted diazadiborolidine could not be deprotonated due to the reduced acidity of the ring proton, however, the B-phenylated analog was easily deprotonated and the lithium, sodium and potassium 1,2-diaza-3,5-diborolyls were isolated and structurally characterized. The solid state structures of the lithium and sodium salts were similar, with an eta(1)-coordinated pi ligand and three THF molecules completing the coordination sphere of the metal. The potassium salt featured a highly unusual mono-dimensional polymeric structure with the metal pi-coordinated by the CB2N2 ligand and two of the phenyl groups on boron and nitrogen, and sigma-coordinated by one THF molecule.