Electron transfer-induced fragmentation of thymine and uracil in atom-molecule collisions

Ion-pair formation has been studied in hyperthermal (30-100 eV) neutral potassium collisions with gas phase thymine (C(5)H(6)N(2)O(2)) and uracil (C(4)H(4)N(2)O(2)). Negative ions formed by electron transfer from the alkali atom to the target molecule were analysed by time-of-flight (TOF) mass spectrometry. The most abundant product anions are assigned to CNO(-) and (U-H)(-)/(T-H)(-) and the associated electron transfer mechanisms are discussed. Special emphasis is given to the enhancement of ring breaking pathways in the present experiments, notably CNO(-) formation, compared with free electron attachment measurements.     

Dissociative Electron Attachment to the Nitroamine HMX (Octahydro-1,3,5,7-Tetranitro-1,3,5,7-Tetrazocine)

In the present study, dissociative electron attachment (DEA) measurements with gas phase HMX, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, C₄H₈N₈O₈, have been performed by means of a crossed electron-molecular beam experiment. The most intense signals are observed at 46 and 176 u and assigned to NO₂ ^? and C₃H₆N₅O₄ ^?, respectively. Anion efficiency curves for 15 negatively charged fragments have been measured in the electron energy region from about 0–20 eV with an energy resolution of ~0.7 eV. Product anions are observed mainly in the low energy region, near 0 eV, arising from surprisingly complex reactions associated with multiple bond cleavages and structural and electronic rearrangement. The remarkable instability of HMX towards electron attachment with virtually zero kinetic energy reflects the highly explosive nature of this compound. Substantially different intensity ratios of resonances for common fragment anions allow distinguishing the nitroamines HMX and royal demolition explosive molecule (RDX) in negative ion mass spectrometry based on free electron capture.      

NCO–, a Key Fragment Upon Dissociative Electron Attachment and Electron Transfer to Pyrimidine Bases: Site Selectivity for a Slow Decay Process

We report gas phase studies on NCO^– fragment formation from the nucleobases thymine and uracil and their N-site methylated derivatives upon dissociative electron attachment (DEA) and through electron transfer in potassium collisions. For comparison, the NCO^– production in metastable decay of the nucleobases after deprotonation in matrix assisted laser desorption/ionization (MALDI) is also reported. We show that the delayed fragmentation of the dehydrogenated closed-shell anion into NCO^– upon DEA proceeds few microseconds after the electron attachment process, indicating a rather slow unimolecular decomposition. Utilizing partially methylated thymine, we demonstrate that the remarkable site selectivity of the initial hydrogen loss as a function of the electron energy is preserved in the prompt as well as the metastable NCO^– formation in DEA. Site selectivity in the NCO^– yield is also pronounced after deprotonation in MALDI, though distinctly different from that observed in DEA. This is discussed in terms of the different electronic states subjected to metastable decay in these experiments. In potassium collisions with 1- and 3-methylthymine and 1- and 3-methyluracil, the dominant fragment is the NCO^– ion and the branching ratios as a function of the collision energy show evidence of extraordinary site-selectivity in the reactions yielding its formation.

Improved Solvent‐Free Dakin Oxidation Protocol

A solvent‐free Dakin reaction with mCPBA was accomplished with various aromatic aldehydes, resulting in an easy and improved methodology for the preparation of corresponding phenols. 3,4‐Methylenedioxyphenol, 3,4‐dimethoxyphenol, 4‐methoxyphenol, 4‐chlorophenol, and other functionalized phenols were obtained in high yields from the corresponding aromatic aldehydes in a few minutes. This new methodology represents an efficient alternative for this important synthetic conversion.     

Controlling biotinylation of microgels and modeling streptavidin uptake

Compared are two approaches for the biotinylation of poly(N-isopropylacrylamide-co-vinylacetic acid) microgels, 300-nm diameter, water swollen particles with a corona of carboxyl groups. The biotinylated microgels are a platform for bioactive water-based ink. Streptavidin binding was measured as a function of biotin density, and the results were interpreted with a new model that predicts the minimum local density of biotins required to capture a streptavidin. An amino-polyethylene glycol derivative of biotin gave higher biotin contents than a biotin hydrazide. However, the streptavidin content versus biotin content results for both biotin derivatives fell on the same master curve with maximum biotin coverage of 0.11?mg of bound streptavidin per milligram of biotinylated microgel. Exclusion experiments showed that streptavidin was too big to penetrate the cross-linked microgel structure; thus, the conjugated streptavidin was restricted to the microgel surface. The colloidal stability of the microgels was preserved, and the biotinylated products showed good hydrolytic stability.     

Tracing pore-space heterogeneities in X-type zeolites by diffusion studies

Pore-space homogeneity of zeolite NaX was probed by pulsed field gradient (PFG) NMR diffusion studies with n-butane as a guest molecule. At a loading of 0.75 molecules per supercage, a wide spectrum of diffusivities was observed. Guest molecules in the (well-shaped) zeolite crystallites were thus found to experience pore spaces of quite different properties. After loading enhancement to 3 molecules per supercage, however, molecular propagation ideally followed the laws of normal diffusion in homogeneous media. At sufficiently high guest concentrations, sample heterogeneity was thus found to be of no perceptible influence on the guest mobilities anymore.     

Clastogenic plasma factors in psoriasis--comparison of phototherapy and anti-TNF-α treatments

As previously described, Psoralen plus UVA (PUVA) therapy induces chromosome damage in psoriatic patients. This study evaluates whether these effects are transitory or persistent. In addition, we studied these effects after narrowband UVB (nUVB) and anti-tumor necrosis factor (TNF)-α treatments. Among 40 responder patients, 10 received PUVA, 10 nUVB, 10 Infliximab and 10 Etanercept. Disease activity was determined with Psoriasis Area and Severity Index. Chromosomal breakage was evaluated by the clastogenic factor (CF) test. Potential clastogenic agents, malondialdehyde (MDA) and TNF-α were measured. Before treatment, the plasma-adjusted clastogenic scores (ACS) of patients were increased. During treatment, a further increase in ACS was observed in both phototherapy groups. Chromosome damage persisted for PUVA patients at week 32, while it diminished after nUVB to ACS values lower than before treatment. MDA and TNF-α values were also increased at baseline. MDA decreased during treatment in all groups, but without reaching normal levels. Plasma TNF-α remained unchanged in PUVA and nUVB but decreased in both anti-TNF-α treatment groups. Psoriasis is accompanied by CF-induced chromosomal breakage that increases during PUVA and nUVB treatments. Plasma clastogenic activity persisted in the follow-up after PUVA, while after nUVB ACS returned to values even lower than baseline. Clastogenic activity during the induction phase with anti-TNF-α remained unchanged.     

The Introduction of Pyrrolotetrathiafulvalene into Conjugated Architectures: Synthesis and Electronic Properties

A series of new conjugated copolymers incorporating the redox‐active pyrrolo‐TTF unit has been synthesised. The properties of the polymers have been investigated by cyclic voltammetry and electronic absorption spectroscopy, revealing that the pyrrolo‐TTF behaves very differently to its thieno‐TTF variant. In comparison to thieno analogues, the band gaps of the new polymers are wider than expected due to a decrease in the polarizability of the heteratom (nitrogen vs. sulfur) and steric interactions between repeat units. Whilst the pyrrolo‐TTF units are stronger electron donors than thieno‐TTFs in related structures, the two redox active elements of the new polymers (TTF and conjugated chain) function independently under oxidative conditions.

     

Lipase-catalyzed diacylglycerol production under sonochemical irradiation

The present paper describes a protocol for production of diacylglycerol by the partial hydrolysis of soybean oil catalyzed by lipase under ultrasound irradiation. Better yields and shorter reaction times were obtained under sonication as compared to the thermal process.