Site-specific hydrogen abstraction in the electrochemical oxidation of ketones

Electrochemical oxidation of saturated ketones involves specific abstraction from one γ hydrogen by the carbonyl oxygen in a six-membered ring cyclic transition state, reminiscent of the first chemical steps of the McLafferty rearrangement and Norrish type II photofragmentation.     

Bystander effects in cell death induced by photodynamic treatment UVA radiation and inhibitors of ATP synthesis

Confluent layers of MDCK II cells were treated with four different photosensitizers (a purified version of hematoporphyrin derivative [Photofrin], tetra(3-hydroxyphenyl)porphine [3-THPP], meso-tetra(4-sulphonatophenyl)porphine [TPPS4] and ALA-induced Protoporphyrin IX) and irradiated with blue light, with UVA without exogenous photosensitizers, or incubated with the metabolic inhibitors carbonyl cyanide m-chlorophenylhydrazone and 2-deoxy-D-glucose. Necrotic and apoptotic cells were detected about 4 h later by fluorescence microscopy. Dead cells appeared in distinct clusters in the confluent layers. The number of dead cells in these clusters was determined by manual counting and image analysis. Forty-one of the 43 experimental distributions of dead cells in clusters were found to be significantly different from a Monte Carlo simulation of the distribution of independently inactivated cells. However, a Monte Carlo simulation model, assuming that each dead cell increased the probability of inactivation of adjacent cells, fitted 34 of the 43 observed distributions of dead cells in clusters, indicating a significant bystander effect for all the investigated treatments. The bystander-effect model parameter, defined as a cell's increase in probability of dying when it has dead neighbors, was significantly lower for 3-THPP-PDT and TPPS4-PDT than for Photofrin-PDT, ALA-PDT and treatment with metabolic inhibitors.     

Optically active aromatic and heteroaromatic alpha-amino acids by a one-pot catalytic enantioselective addition of aromatic and heteroaromatic C-H bonds to alpha-imino esters

The development of a practical one-pot catalytic enantioselective procedure for the synthesis of non-natural aromatic and heteroaromatic alpha-amino acids is reported. Starting from readily available starting materials and application of a chiral BINAP-Cu(I) catalyst, the optically active products are formed with readily removable N-protecting groups. The scope of the reaction is demonstrated by the addition of substituted furans, thiophenes, pyrroles, and aromatic compounds to N-alkoxycarbonyl-alpha-imino esters in good yields and with enantioselectivities up to 96% ee for the furans, 93% ee for the thiophenes, and 98% for the aromatic compounds. The protecting groups are readily removed, and various transformations of the aromatic and heteroaromatic alpha-amino acids are demonstrated. The coordination of the N-alkoxycarbonyl alpha-imino ester to the chiral BINAP-Cu(I) complex and the enantioselectivity of the catalyst is discussed on the basis of the DFT calculations and X-ray crystallographic data.     

Electron capture and collisionally activated dissociation mass spectrometry of doubly charged hyperbranched polyesteramides

Electron capture dissociation (ECD) of doubly protonated hyperbranched polyesteramide oligomers (1100-1900 Da) was examined and compared with the structural information obtained by low energy collisionally activated dissociation (CAD). Both the ester and amide bonds of the protonated species were cleaved easily upon ECD with the formation of odd electron (OE(.+)) or even electron (EE(+)) fragment ions. Several mechanistic schemes are proposed that describe the complex ECD fragmentation behavior of the multiply charged oligomers. In contrast to studies of biomolecules, the present results indicate that consecutive cleavages induced by intramolecular H-shifts are significant for ECD and of less importance for low energy CAD. The capture of an electron by the ionized species results in fragmentation associated with a redistribution of the excess internal energy over the products and the subsequent bond cleavage. Low energy, multiple collision CAD is found to be a more selective dissociation method than ECD in view of the observation that only amide bonds are cleaved for most of the hyperbranched polymers examined with CAD in this study. ECD appears not to provide complementary structural information compared to CAD in the study of hyperbranched polymers, even though a significantly more complex ECD fragmentation behavior is observed. ECD is shown to be of use for the structural characterization of large oligomers that may not dissociate upon low energy CAD. This is a direct result of the fact that ECD produces ionized hyperbranched oligomers with a relatively high internal energy.     

New approaches for fabrication of microfluidic capillary electrophoresis devices with on-chip conductivity detection

In practice, microfluidic systems are based on the principles of capillary electrophoresis (CE), for a large part due to the simplicity of electroosmotic pumping. In this contribution, a universal conductivity detector is presented that allows detection of charged species down to the microM level. Additionally, powderblasting is presented as a novel technique for direct etching of microfluidic networks. This method allows creation of features down to 50 microm with a total processing time (design to device) of less than one day. The performance of powderblasted devices with integrated conductivity detection is illustrated by the separation of lithium, sodium, and potassium ions and that of fumaric, malic, and citric acid.     

Synthesis and molecular structure of [Rh3(μ-PPh2)3(CO)6(PPh2-H)], an unusual six-membered inorganic ring complex

Reaction of [{Rh(μ-Cl)(CO)₂}₂] with PPh₂H in CO-saturated ethanol yields [Rh₃(μ-PPh₂)₃ (CO)₆ (PPh₂H)], a red trinuclear cluster of rhodium containing a near-planar six-membered Rh₃P₃ ring; this compound reversibly undergoes elimination of CO and PPh₂H to afford [Rh₃(μ-PPh₂)₃(CO)₅].     

LUMINESCENCE OF L-TRYPTOPHAN IN THE DRY STATE AND IN AQUEOUS SOLUTION INDUCED BY X-RAYS AND U.V.-LIGHT AT 77°K

Abstract— The luminescence from tryptophan in the dry state and in aqueous glass. induced by u.v.-light and X-rays at 77°K, has been studied. The spectra of the luminescence from the dry material, which were identical for the two types of irradiation, were attributed to the same excited singlet level as that giving rise to the fluorescence from the aqueous sample. The strong phosphorescence exhibited by the latter. could not be detected for the dry material with either type of irradiation. This was attributed to a strong quenching of the radiative triplet level occurring upon crystallization of the substance. The yield of X-ray induced fluorescence of tryptophan in aqueous glass was found to be similar to that observed in the dry state. It was concluded that there is no extensive transfer of energy between the solvent and the solute molecules contributing to the fluorescence yield of tryptophan in aqueous glass.     

Radioluminescence of H2O and D2O ice spectral characteristics

The spectra of the radiofluorescence RF, afterglow AG and the thermoluminescence TL of H₂O and D₂O ice are reported. The RF spectrum of D₂O exhibits two bands, whereas for H₂O only one of these is seen. The spectrum of TL is different from that of RF and AG. It is argued that if any of these spectra are due to de-excitation of the triplet state of water it is that of the TL. This spectrum is peaked at 335 ± 3 nm and has a width of 46 nm.     

The substitution structure of ethyleneimine

The substitution structure (r_s) of ethyleneimine (aziridine) has been found by analysis of microwave gas spectra of the parent molecule and of the necessary number (5) of mono-isotopically substituted species, all of which were chemically enriched. Two coordinates (<0.1 Å) had to be derived using the conditions Σm_ic_i = Σm_ib_ic_i = 0. Data from microwave spectra of two double-isotopically substituted species [1-D]-, [1−¹⁵N]-ethyleneimine, and [2,2'-D₂]-ethyleneimine were applied as a further check. The agreement was satisfactory. In the resulting r_s structure the C-C distance is shorter than the C-N distance, in accordance with the larger nuclear charge of nitrogen compared to carbon, but qualitatively disagreeing with the results of earlier investigations. Also, the plane defined by H(2), C(2), H(2') is not perpendicular to the N(1), C(2), C(3) plane as assumed earlier. The former plane forms and angle of 87° with the latter which, however, almost exactly bisects the HCH angle. The CH₂ groups may, therefore, be described as slightly “twisted”.     

Gas-phase ion-molecule reactions of the CH3O+ cation

The methoxy cation, CH₃0⁺, formed by collision-induced charge reversal of methoxr anions with a kinetic energy of 8 keY, has been differentiated from the isomenric CH₂OH⁺ ion by performing low kinetic energy ion-molecule reactions In the radiofrequency-only quadrupole of a reverse-geometry double-focusing quadrupole hybrid mass spectrometer. The methoxy cation reacts with CH₃SH, CH₃?CH=CH₂, (CH₃)₂O, and CH₃CH₂Cl by electron transfer, whereas the CH₂OH⁺ ion reacts by proton transfer with these substrates