General synthesis and aggregation behaviour of a series of single-chain 1,omega-bis(phosphocholines)

The synthesis and physicochemical characterisation of a series of polymethylene-1,omega-bis(phosphocholines) with even-numbered chain lengths between 22 and 32 carbon atoms is described. Two new synthetic strategies for the preparation of long-chain 1,omega-diols as hydrocarbon building blocks are presented. The temperature-dependent self-assembly of the single-chain bolaamphiphiles was investigated by cryo transmission electron microscopy (cryo-TEM), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR).     

Efficient palladium(II) catalysis under air. Base-free oxidative heck reactions at room temperature or with microwave heating

Scope and limitations of the base-free oxidative Heck reaction with arylboronic acids have been explored. Under our conditions, the dmphen-palladium(II)-catalyzed arylation proceeded with air or p-benzoquinone as reoxidants of palladium(0). We found that ambient temperature and mild aerobic conditions allow for the use of substrates sensitive to palladium(II)-catalyzed oxidation. Oxidative Heck couplings, employing different arylboronic acids, were smoothly and regioselectively conducted with both electron-rich and electron-poor olefins, providing high yields even with disubstituted butyl methacrylate, sensitive acrolein, and a vinylboronate ester. Controlled microwave processing was used to reduce reaction times from hours to minutes both in small scale and in 50 mmol scale batch processes.     

Determination of OH number densities outside of a platinum catalyst using cavity ringdown spectroscopy

It is demonstrated that cavity ringdown spectroscopy (CRDS) can be used to probe reaction intermediates desorbing from the surface during a heterogeneous catalytic reaction and provide information valuable in understanding the reaction kinetics. During water formation from H2 and O2, desorbed OH molecules outside of a polycrystalline platinum catalyst were quantified as a function of the relative hydrogen concentration, alphaH2 using CRDS. The temperature of the catalyst was 1500 K, the total pressure was 26 Pa, and the flow was set to 100 sccm. At a distance of 6.5 mm from the Pt catalyst, the maximum OH concentration was found to be 1.5+/-0.2x10(12) cm(-3) at an alphaH2 value of 10%, and the rotational temperature was determined to be 775+/-24 K. The desorbed OH molecules were also probed using laser-induced fluorescence (LIF), and the alphaH2-dependent OH abundance was compared with the CRDS results. The relative concentration of OH probed with LIF appeared to be lower at alphaH2=30-50% compared to what was determined by CRDS. The observed discrepancy is suggested to be due to electronic quenching, as was indicated by a shorter fluorescence lifetime at alphaH2=30% compared to at alphaH2=10%.     

Microwave-enhanced copper-catalyzed N-arylation of free and protected amino acids in water

A microwave-enhanced copper-catalyzed protocol for N-arylation using water as the solvent is reported. This fast transformation allows the reaction between various amino acids or amino acid esters and a diverse set of substituted aryl bromides in less than 40 min, affording good yields of non-protected N-arylated amino acids with only minor racemization (6% or less). In addition, online ESI-MS and MS/MS analysis were used to "fish-out" an anionic Cu-containing amino acid complex directly from an ongoing N-arylation reaction.     

Level algebras with bad properties

This paper can be seen as a continuation of the works contained in the recent article (J. Alg., 305 (2006), 949-956) of the second author, and those of Juan Migliore (math. AC/0508067). Our results are:

1). There exist codimension three artinian level algebras of type two which do not enjoy the Weak Lefschetz Property (WLP). In fact, for , we will construct a codimension three, type two -vector of socle degree such that all the level algebras with that -vector do not have the WLP. We will also describe the family of those algebras and compute its dimension, for each .

2). There exist reduced level sets of points in of type two whose artinian reductions all fail to have the WLP. Indeed, the examples constructed here have the same -vectors we mentioned in 1).

3). For any integer , there exist non-unimodal monomial artinian level algebras of codimension . As an immediate consequence of this result, we obtain another proof of the fact (first shown by Migliore in the above-mentioned preprint, Theorem 4.3) that, for any , there exist reduced level sets of points in whose artinian reductions are non-unimodal.

     

An Oxofluoride Catalyst Comprised of Transition Metals and a Metalloid for Application in Water Oxidation

The application of the recently discovered oxofluoride solid solution (Co_xNi_1?x)₃Sb₄O₆F₆ as a catalyst for water oxidation is demonstrated. The phase exhibits a cubic arrangement of the active metal that forms oxo bridges to the metalloid with possible catalytic participation. The Co₃Sb₄O₆F₆ compound proved to be capable of catalyzing 2H₂O→O₂+4H⁺+4e^? at 0.33 V electrochemical and ≤0.39 V chemical overpotential with a TOF of 4.4?10^?3, whereas Ni₃Sb₄O₆F₆ needs a higher overpotential. Relatively large crystal cubes (0.3–0.5 mm) are easily synthesized and readily handled as they demonstrate both chemical resistance to wear after repeated in situ tests under experimental conditions, and have a mechanical hardness of 270 V0.1 using Vickers indentation. The combined properties of this compound offer a potential technical advantage for incorporation to a catalytic interface in future sustainable fuel production.     

Designing a new Diels-Alderase: a combinatorial, semirational approach including dynamic optimization

A computationally inexpensive design strategy involving 'semirational' screening for enzymatic catalysis is presented. The protocol is based on well-established computational methods and represents a holistic approach to the catalytic process. The model reaction studied here is the Diels-Alder, for which a successful computational design has recently been published (Siegel, J. B. et al. Science 2010, 329, 309-313). While it is a leap forward in the field of computational design, the focus on designing only a small fraction of the active site gives little control over dynamics. Our approach explicitly incorporates mutagenesis and the analysis of binding events and transition states, and a promising enzyme-substrate candidate is generated with relatively little effort. We estimate catalytic rate accelerations of up to 10?.     

A rapid synthesis of asymmetric alkyl- and aryl-2,9-disubstitued 1,10-phenanthrolines

The finding that alkyl- and aryllithium reagents add almost instantly to the N-C2/C9 bond of 1,10-phenanthrolines led us to the development of a reaction scheme where the C2 and C9 positions of 1,10-phenanthroline can be functionalized by two different alkyl or aryl groups in a one-pot reaction. Furthermore, the total synthetic and work-up time needed for the entire transformation from unsubstituted 1,10-phenanthrolines into asymmetric 2,9-disubstituted 1,10-phenanthrolines was under 2 h and produced very high yields.     

Electrochemical control of growth factor presentation to steer neural stem cell differentiation

Let it grow: The conjugated polymer poly(3,4-ethylenedioxythiophene) (PEDOT) was synthesized with heparin as the counterion to form a cell culture substrate. The surface of PEDOT:heparin in the neutral state associated biologically active growth factors. Electrochemical in?situ oxidation of PEDOT during live cell culture decreased the bioavailability of the growth factor and created an exact onset of neural stem cell differentiation.