Highly efficient formation of halodiazoacetates and their use in stereoselective synthesis of halocyclopropanes

Halogenated analogues of ethyl diazoacetate are synthesised by a novel and highly efficient procedure and give halocyclopropanes in good to excellent yields when exposed to a Rh(ii) catalyst in the presence of alkenes.     

Superparamagnetic gamma-Fe(2)O(3) nanoparticles with tailored functionality for protein separation

Polymer coated superparamagnetic gamma-Fe(2)O(3) nanoparticles were derivatized with a synthetic double-stranded RNA [poly(IC)], a known allosteric activator of the latent (2-5)A synthetase, to separate a single 35 kDa protein from a crude extract which cross reacted with antibodies raised against the sponge enzyme.     

The existence of NRB[v,k] where k + 1 is an even prime power

The existence of NRB[v,k] where k ≥ 7 and k + 1 is an even prime power is considered. We will show that there exists an NRB[kn + 1, k] for all n > (3k)^b-1(kb)^3kb(b-1)+1, where k + 1 is an even prime power, k ≥ 7 and . The tools used to construct this bound include the frames extracted from a construction of J. X. Lu's for resolvable balanced incomplete block designs © 1998 John Wiley & Sons, Inc. J Combin Designs 6:43–49, 1998     

The DFS-heuristic for orthogonal graph drawing

In this paper, we present a new heuristic for orthogonal graph drawings, which creates drawings by performing a depth-first search and placing the nodes in the order they are encountered. This DFS-heuristic works for graphs with arbitrarily high degrees, and particularly well for graphs with maximum degree 3. It yields drawings with at most one bend per edge, and a total number of m−n+1 bends for a graph with n nodes and m edges; this improves significantly on the best previous bound of m−2 bends.     

Improved voltage transfer coefficients for nonconductive materials in radiofrequency glow discharge optical emission spectrometry

In radiofrequency glow discharge emission spectrometry (RF-GDOES), the excitation voltage used to create the plasma is applied to the back or front end of the sample to be analyzed. In this paper we focus on back-applied voltage systems (a configuration that represents about half of the instruments available on the market), and on applied voltage problems (the power coupling efficiency and materials analysis are beyond the scope of this study). In the RF-GDOES of nonconductive samples, a voltage drop develops inside the material. The voltage transfer coefficient is defined as the ratio between the peak voltage in front of the sample (facing the plasma) and the peak voltage applied to the back of the sample. In this work, we show that it is possible to increase the voltage transfer coefficient by increasing the capacitance of the sample. The capacitance of a given nonconductive material depends on its surface, its thickness and its permittivity. Increasing the voltage transfer coefficient permits higher power deposition in the plasma. This study is based on an electrical equivalent circuit for the discharge device, which takes into account the sample and reactor capacitances as well as the voltage probes used for the measurements. This circuit, when modeled by a commercial electrical circuit simulator, gives the voltage transfer coefficient as a function of the sample capacitance. Different approaches to increasing the sample capacitance and their influence on the voltage transfer coefficient are presented and related to the 750.4 nm argon line intensity, which is correlated to the electron density.     

β-Shielded Michael systems whose H–C(sp2) deprotonation and 1,2-addition reactions compete for organolithiums

Steric shielding of an α,β-unsaturated nitrile R₂C?=?CH–CN by tert-alkyl β-substituents (R) prevented 1,4-additions of organolithiums and showed a remarkably solvent-dependent selectivity of tert-butyllithium (tBuLi): 1,2-addition at CN and α-deprotonation occurred almost equally fast in THF, while CN addition was exclusive in Et₂O. The resultant N-lithioimine was cleanly α-deprotonated (albeit with unusual slowness) in situ by an excess of tBuLi. The imine was hydrolyzed to produce an enone R₂C?=?CH–C(R')?=?O with bulky substituents R and R', which admitted CO addition but did not undergo α-deprotonation by mesityllithium, n-butyllithium (nBuLi), and even the very strong base tBuLi. 2,4,6-Tri-tert-butylphenyllithium (“Mes*Li”) did not add or deprotonate the enone. With N-lithio-2,2,6,6-tetramethylpiperidine (LTMP) as the catalyst, however, Mes*Li achieved α-deprotonation simultaneously with the known Mes* radical rearrangement and a subsequent carbonyl addition. With KOH or KOtBu as a base in [D₆]DMSO (but not in DOCH₃), the enone accomplished a rapid α-H/α-D exchange reaction at rt.     

Following the excited state relaxation dynamics of indole and 5-hydroxyindole using time-resolved photoelectron spectroscopy

Time-resolved photoelectron spectroscopy was used to obtain new information about the dynamics of electronic relaxation in gas-phase indole and 5-hydroxyindole following UV excitation with femtosecond laser pulses centred at 249 nm and 273 nm. Our analysis of the data was supported by ab initio calculations at the coupled cluster and complete-active-space self-consistent-field levels. The optically bright (1)L(a) and (1)L(b) electronic states of (1)ππ? character and spectroscopically dark and dissociative (1)πσ? states were all found to play a role in the overall relaxation process. In both molecules we conclude that the initially excited (1)L(a) state decays non-adiabatically on a sub 100 fs timescale via two competing pathways, populating either the subsequently long-lived (1)L(b) state or the (1)πσ? state localised along the N-H coordinate, which exhibits a lifetime on the order of 1 ps. In the case of 5-hydroxyindole, we conclude that the (1)πσ? state localised along the O-H coordinate plays little or no role in the relaxation dynamics at the two excitation wavelengths studied.     

Design and Synthesis of Pyrrolidinyl Ferrocene-Containing Ligands and Their Application in Highly Enantioselective Rhodium-Catalyzed Olefin Hydrogenation

Herein, we report the design and synthesis of a series of chiral pyrrolidine-substituted ferrocene-derived ligands. The proficiency of this novel structural motif was demonstrated in the Rh-catalyzed asymmetric hydrogenation of dehydroamino acid esters and α-aryl enamides. The products were obtained with full conversions and excellent levels of enantioselectivities of up to >99.9% ee and 97.7% ee, respectively, using a BINOL-substituted phosphine-phosphoaramidite ligand which possesses planar, central, and axial chirality elements.