Transverse pore gradient gel electrophoresis of lipoprotein [a] using methylenebisacrylamide gradients.

We describe a modification of transverse pore gradient gel electrophoresis in which pore size is regulated by crosslinker proportion (%C) rather than by total monomer concentration (%T). We electrophoresed plasma lipoprotein [a] transversely across linear N,N'-methylenebisacrylamide gradients and measured mobility as a function of %C. This method allows for the simultaneous assessment of pore sizes generated over a wide range of crosslinker proportions.     

Mechanism of white phosphorus activation by three-coordinate molybdenum(III) complexes: a thermochemical, kinetic, and quantum chemical investigation

White phosphorus (P(4)) reacts with three-coordinate molybdenum(III) trisamides or molybdaziridine hydride complexes to produce either bridging or terminal phosphide (P(3)(-)) species, depending upon the ancillary ligand steric demands. Thermochemical measurements have been made that place the MoP triple bond dissociation enthalpy at 92.2 kcal.mol(-)(1). Thermochemical measurements together with computational analysis rule out simple P-atom abstraction from P(4) as a step in the phosphorus activation mechanism. Kinetic measurements made by the stopped-flow method show that the reaction between the monomeric molybdenum complexes and P(4) is first-order both in metal complex and in P(4). Cyclo-P(3) complexes can be obtained when ancillary ligand steric demands are small, but kinetic measurements rule them out as monometallic intermediates in the P(4) activation mechanism. Also studied by calorimetric, kinetic, and in one case variable-temperature NMR methods is the process of mu-phosphide bridge formation. Post-rate-determining steps of the P(4) activation process were examined in a search for minima on the reaction's potential energy surface, leading to the proposal of two plausible, parallel, bimetallic reaction channels.     

An empirical retention model for the optimization of on-line normal-phase LC-GC for the multi-analyte determination of hydrophobic compounds in fatty samples

Summary Normal-phase LC (NPLC) is a powerful method for the clean-up of fatty samples in the determination of organochlorine pesticides (OCPs). The injected sample deactivates the stationary phase and the triglyceride matrix therefore serves as a polarity modifier in the NPLC separation. Thus, the amount of sample injected is the key to both selectivity and sensitivity in matrixmodified LC coupled to capillary GC. In coupled LC-GC the NPLC separation becomes particularly critical because only a limited amount of the LC eluent can be transferred to the GC and the triglyceride matrix must be prevented from entering the GC, because it degrades the performance of the injector and the column. In previous applications method development was seriously hampered by these boundary conditions and tedious and lengthy trial-and-error experiments were required to determine suitable experimental conditions. In this study an empirical model was developed that describes the NPLC separation process in terms of column dimensions and fat loadability. The output is given as the probability of achieving successful LC-GC analysis of a particular set of analytes, thus furnishing a useful tool for the development of new applications in the field of exposure assessment and analysis of residues of apolar compounds in fatty samples. The limitations of current procedures—maximum transfer volumes and minimal separation—are also discussed.     

1H,13C and 19F NMR data of N‐substituted 6‐(4‐methoxyphenyl)‐7H‐pyrrolo[2,3‐d]pyrimidin‐4‐amines in DMSO‐d6

Chemical shift assignment of seven N‐substituted 6‐(4‐methoxyphenyl)‐7H‐pyrrolo[2, 3‐d]pyrimidin‐4‐amines, six of which are fluorinated, have been performed based on ¹H, ¹³C, ¹⁹F, and 2D COSY, HMBC and HSQC experiments. Copyright © 2009 John Wiley & Sons, Ltd.     

Spectroscopic detection and theoretical confirmation of the role of Cr2(CO)5(C5R5)2 and .Cr(CO)2(ketene)(C5R5) as intermediates in carbonylation of N=N=CHSiMe3 to O=C=CHSiMe3 by .Cr(CO)3(C5R5) (R = H, CH3)

Conversion of N=N=CHSiMe3 to O=C=CHSiMe3 by the radical complexes .Cr(CO)3C5R5 (R = H, CH3) derived from dissociation of [Cr(CO)3(C5R5)]2 have been investigated under CO, Ar, and N2 atmospheres. Under an Ar or N2 atmosphere the reaction is stoichiometric and produces the Cr[triple bond]Cr triply bonded complex [Cr(CO)2(C5R5)]2. Under a CO atmosphere regeneration of [Cr(CO)3(C5R5)]2 (R = H, CH3) occurs competitively and conversion of diazo to ketene occurs catalytically as well as stoichiometrically. Two key intermediates in the reaction, .Cr(CO)2(ketene)(C5R5) and Cr2(CO)5(C5R5)2 have been detected spectroscopically. The complex .Cr(13CO)2(O=13C=CHSiMe3)(C5Me5) has been studied by electron spin resonance spectroscopy in toluene solution: g(iso) = 2.007; A(53Cr) = 125 MHz; A(13CO) = 22.5 MHz; A(O=13C=CHSiMe3) = 12.0 MHz. The complex Cr2(CO)5(C5H5)2, generated in situ, does not show a signal in its 1H NMR and reacts relatively slowly with CO. It is proposed to be a ground-state triplet in keeping with predictions based on high level density functional theory (DFT) studies. Computed vibrational frequencies are also in good agreement with experimental data. The rates of CO loss from 3Cr2(CO)5(C5H5)2 producing 1[Cr(CO)2(C5H5)]2 and CO addition to 3Cr2(CO)5(C5H5)2 producing 1[Cr(CO)3(C5H5)]2 have been measured by kinetics and show DeltaH approximately equal 23 kcal mol(-1) for both processes. Enthalpies of reduction by Na/Hg under CO atmosphere of [Cr(CO)n(C5H5)]2 (n = 2,3) have been measured by solution calorimetry and provide data for estimation of the Cr[triple bond]Cr bond strength in [Cr(CO)2(C5H5)]2 as 72 kcal mol(-1). The complex [Cr(CO)2(C5H5)]2 does not readily undergo 13CO exchange at room temperature or 50 degrees C implying that 3Cr2(CO)5(C5H5)2 is not readily accessed from the thermodynamically stable complex [Cr(CO)2(C5H5)]2. A detailed mechanism for metalloradical based conversion of diazo and CO to ketene and N2 is proposed on the basis of a combination of experimental and theoretical data.     

Adamantyl Side Chains as Anti-Aggregating Moieties in Dyes for Dye-Sensitized Solar Cells

Designing and evaluating novel dye concepts is crucial for the development of the field of dye-sensitized solar cells (DSSCs). In our recent report, the novel concept of tethering the anti-aggregation additive chenodeoxycholic acid (CDCA) to dyes for DSSC was introduced. Based on the performance improvements seen for this modification, the aim of this study is to see if a simplified anti-aggregation unit could achieve similar results. The following study reports the synthesis and photovoltaic characterization of two novel dyes decorated with the steric ethyladamantyl moiety on the π-spacer, and on the triarylamine donor. This modification is demonstrated to be successful in increasing the photovoltages in devices employing copper-based electrolytes compared to the non-modified reference dye. The best photovoltaic performance is achieved by a device prepared with the adamantyl decorated donor dye and CDCA, this device achieves a power conversion efficiency of 6.1 % (Short-circuit current=8.3 mA cm⁻², Open-circuit voltage=1054 mV, Fill factor=0.69). The improved photovoltaic performance seen for the adamantyl decorated donor demonstrate the potential of ethyladamantyl side chains as a tool to ensure surface protection of TiO₂.     

The heats of reaction of phosphines and phosphites with toluene-molybdenum tricarbonyl. Importance of both steric and electronic factors in determining the Mo---PR3 bond strength

The heats of reaction of tolueneMo(CO)₃ with a series of phosphines and phosphites have been measured by solution calorimetry. The order of stability toward formation of fac-(PR₃)₃Mo(CO)₃ in THF solution is: P(OCH₃)₃s> PMe₃ > PⁿBu₃ > PMe₂Ph> PEt₃ > triphos> P(OPh)₃ > PMePh₂ > PPh₃ > PCl₃ and spans a range of 25 kcal/mol reflecting individual bond strength differences up to 8 kcal/mol. The bulky phosphines PCy₃ and P^tBu₃ react with tolueneMo(CO)₃ in THF, but 30–40 kcal/mol less heat is evolved in these reactions than with the other phosphines and phosphites. The coordinately unsaturated five-coordinate complexes (PR₃)₂Mo(CO)₃ are proposed as the reaction products. The importance of both steric and electronic factors in the Mo---P bond is discussed.     

Clean-up of some organochlorine and pyrethroid insecticides by automated solid-phase extraction cartridges coupled to capillary GC-ECD

The ASPEC (Automatic Sample Preparation with Extraction Columns) system has been coupled on-line to capillary GC-ECD by means of a loop-type interface equipped with a solvent vapour exit. Both ASPEC and GC conditions have been optimized leading to an effective clean-up of the extracts analyzed. By means of solid-phase extraction cartridges filled with silica, it has been possible to analyze concentrated surface water extracts for a group of 18 electron-capturing compounds present in the water at ppt levels. ASPEC-GC has also been applied to the determination of synthetic pyrethroids at ppt levels in surface water. The complete analytical procedure is greatly facilitated by automation and miniaturization. Miniaturization results in a considerable decrease in the sample volume required. The potential of the method for the analysis of other pesticides is estimated.     

Simple Two-Pulse Detection Scheme in Pulsed EPR for Studying Low-Frequency Nuclear Coherences

A microwave two-pulse sequence with a weak and long 180° first pulse and a hard 90° second pulse is employed to detect nuclear coherences in pulsed EPR. The coherences created by the first pulse are transferred after an evolution periodTinto an observable FID by the second pulse. The free induction is measured at some fixed delay after the second pulse; it is modulated whenTis varied. As the second pulse may be switched on immediately after the first pulse, the nuclear coherences may be detected immediately as they start to freely oscillate, without loss of information within the instrumental dead time. The method is demonstrated for a sample of the radical cation of¹⁵N-labeled bacteriochlorophylla.     

The decay of84As

The decay properties of⁸⁴As have been investigated with mass separated sources. Only one β-decaying state is seen, contradictory to previous observations. The halflife is found to be 4.5±0.2 s. A detailed decay scheme has been constructed, and 33 excited states in⁸⁴Se have been determined.