On the enantioselective hydrogenation of isomeric β-acylamido β-alkylacrylates with chiral Rh(I) complexes—comparison of phosphine ligands and substrates

The rhodium(I)-catalyzed enantioselective hydrogenation of E- and Z-configured β-acylamido β-alkylacrylates as well as of isomeric mixtures has been investigated. As ligands 1,2-bisphospholanes like DuPHOS, BPE and Me₄-BASPHOS have been tested, but also diphosphines forming seven-membered chelates such as DIOP. The effect of additional oxy groups in the diphosphine ligand on rate and enantioselectivity was likewise elucidated. In general, with all catalysts screened the hydrogenation is strongly sensitive to the E/Z-geometry of the substrate. E-Substrates are converted with good or excellent enantioselectivites into the desired β-amino acid derivatives. The hydrogenation of Z-substrates showed the known H₂-pressure dependency of the ee.     

Kinetics of acid-induced spectral changes in the GFPmut2 chromophore

We have used a nanosecond pH-jump technique, coupled with simultaneous transient absorption and fluorescence emission detection, to characterize the dynamics of the acid-induced spectral changes in the GFPmut2 chromophore. Disappearance of the absorbance at 488 nm and the green fluorescence emission occurs with a thermally activated, double exponential relaxation. To understand the source of the two transients we have introduced mutations in amino acid residues that interact with the chromophore (H148G, T203V, and E222Q). Results indicate that the faster transient is associated with proton binding from the solution, while the second process, smaller in amplitude, is attributed to structural rearrangement of the amino acids surrounding the chromophore. The protonation rate shows a 3-fold increase for the H148G mutant, demonstrating that His148 plays a key role in protecting the chromophore from the solvent. The deprotonation rate for T203V is an order of magnitude smaller, showing that the hydrogen bond with the hydroxyl of Thr203 is important in stabilizing the deprotonated form of the chromophore. A kinetic model suggests that, in addition to protecting the chromophore from the solvent, His148 may act as the primary acceptor for the protons on the way to the chromophore.     

Synthesis of alpha-P-modified nucleoside diphosphates with ethylenediamine

This report describes a one-pot synthesis of alpha-P-borano-, alpha-P-thio-, and alpha-P-seleno-modified nucleoside diphosphate analogues that are otherwise difficult to obtain. The key step involves the intramolecular nucleophilic attack by an amino group in 5 to remove the gamma-phosphate. The absolute configurations of P-diastereomers were confirmed by analysis of their 1H NMR. Affinity studies revealed that the nucleoside boranodiphosphates are potentially useful in antiviral research.     

An automated, sheathless capillary electrophoresis-mass spectrometry platform for discovery of biomarkers in human serum

A capillary electrophoresis-mass spectrometry (CE-MS) method has been developed to perform routine, automated analysis of low-molecular-weight peptides in human serum. The method incorporates transient isotachophoresis for in-line preconcentration and a sheathless electrospray interface. To evaluate the performance of the method and demonstrate the utility of the approach, an experiment was designed in which peptides were added to sera from individuals at each of two different concentrations, artificially creating two groups of samples. The CE-MS data from the serum samples were divided into separate training and test sets. A pattern-recognition/feature-selection algorithm based on support vector machines was used to select the mass-to-charge (m/z) values from the training set data that distinguished the two groups of samples from each other. The added peptides were identified correctly as the distinguishing features, and pattern recognition based on these peptides was used to assign each sample in the independent test set to its respective group. A twofold difference in peptide concentration could be detected with statistical significance (p-value < 0.0001). The accuracy of the assignment was 95%, demonstrating the utility of this technique for the discovery of patterns of biomarkers in serum.     

Synthesis of chiral self-assembling rhombs and their characterization in solution, in the gas phase, and at the liquid-solid interface

Chiral, enantiopure metallo-supramolecular rhombs self-assemble in solution through coordination of bis-pyridyl-substituted ligands with (en)M(NO3)2 (en = ethylenediamine, M = Pd(II), Pt(II)). Characterization by NMR and CD spectroscopy in solution and by ESI-FT-ICR mass spectrometry in the gas phase suggests that an equilibrium exists in water/methanol of a major 2:2 complex and a minor 3:3 complex of ligands and metal corners. In the gas phase, doubly charged 2:2 complexes fragment into two identical singly charged halves followed by metal-mediated C-H and C-C bond activation reactions within the ethylenediamine ligands. Electrochemical scanning tunneling microscopy (EC-STM) provides in situ imaging of the complexes even with submolecular resolution. Flat-lying rhombs are deposited under potential control from an aqueous electrolyte on a Cu(100) electrode surface precovered by a tetragonal pattern of chloride anions from the supporting electrolyte. Chirality induces the formation of only one domain orientation. Density functional calculations help to interpret the STM images.     

ON THE NATURE OF THE INTERMEDIATE ELECTRON ACCEPTOR (A1) IN THE PHOTOSYSTEM I REACTION CENTER

Abstract— A sodium dodecyl sulfate-Photosystem I (PSI) complex has been prepared and characterized with respect to its electron acceptors. Component X and iron-sulfur centers A and B are absent from this preparation but the intermediate electron acceptor (A₁) is present. Flash-induced absorbance changes at 25°C show charge separation, followed by a back-reaction with a half-time of 5 µs. The spectrum of the flash-induced change from 350 to 550 nm indicates a contribution from the intermediate electron acceptor, A₁, as well as from P700⁺. EPR studies show that A₁ is associated with a free-radical signal having a g-value of 2.0025 and a linewidth of 12 gauss. A, would appear to be associated with a monomeric form of either Chi α or pheophytin a.     

Stereoregular polymerization of 1-vinylnaphthalene, 2-vinylnaphthalene,and 4-vinylbiphenyl

1-Vinylnaphthalene, 2-vinylnaphthalene, 4-vinylbiphenyl, and styrene were polymerized with Et₃Al–TiCl₄, Et₂AlCl–TiCl₃, and Et₃Al–TiCl₃ catalyst systems. The latter catalyst system gave polymers in 75–95% conversion which were at least 90% isotactic. Extraction with 2-butanone (MEK) separated the atactic from the isotactic fractions. The polymers were characterized by infrared and nuclear magnetic resonance spectroscopy.     

Short and diverse route toward complex natural product-like macrocycles

[reaction: see text] A general strategy toward macrocyclic compounds using multicomponent reaction (MCR) chemistry, e.g., Passerini and Ugi variants, and ring-closing metathesis (RCM) is introduced. The corresponding bifunctional isocyanides carboxylic acids bearing a terminal olefin are easy to prepare from the corresponding commercially available starting materials. Advantageously, this strategy allows fast access to a diverse conformational space of natural product-like macrocycles and could thus be of interest in the discovery of novel bioactive agents.     

Oxidation of small alkenes at high temperature

If the mechanism of formation of alkenes, the main primary products of the combustion of alkanes above 1000 K, is now well understood, their ways of degradation have been much less studied. Following a previous modeling of the oxidation of propene in a static and a jet‐stirred reactors by using an automatically generated mechanism, the present paper shows new validations of the same mechanism for ignition delays in a shock tube. It also describes the extension of the rules used for the automatic generation to the case of 1‐butene. The predictions of the mechanism produced for the oxidation of 1‐butene are compared successfully with two sets of experimental results: the first obtained in a jet‐stirred reactor between 900 and 1200 K; the second being new measurements of ignitions delays behind reflected shock waves for temperatures from 1200 up to 1670 K, pressures from 6.6 to 8.9 atm, equivalence ratios from 0.5 to 2, and with argon as bath gas. Flux and sensitivity analyses show that the role of termination reactions involving the very abundant allylic radicals is less important for 1‐butene than for propene. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 666–677, 2002     

A miniature biofuel cell operating in a physiological buffer

A glucose-O2 biofuel cell, consisting only of two electrocatalyst coated 7-mum diameter, 2-cm long carbon fibers is reported. The cell operated continuously at 0.52 V at 37 degrees C in a physiological buffer solution for a week, producing 1.9 muW during the first and 1.0 muW during the last day, generating in the period 0.9 J of electrical energy while passing a charge of 1.7 C. If a similar dimension zinc fiber were utilized in a battery at 100% current efficiency, only 0.016 C would have been generated.