Bond dissociation of the dipeptide dialanine and its derivative alanine anhydride induced by low energy electrons

Dissociative electron attachment to dialanine and alanine anhydride has been studied in the gas phase utilizing a double focusing two sector field mass spectrometer. We show that low-energy electrons (i.e., electrons with kinetic energies from near zero up to 13 eV) attach to these molecules and subsequently dissociate to form a number of anionic fragments. Anion efficiency curves are recorded for the most abundant anions by measuring the ion yield as a function of the incident electron energy. The present experiments show that as for single amino acids (M), e.g., glycine, alanine, valine, and proline, the dehydrogenated closed shell anion (M-H)(-) is the most dominant reaction product. The interpretation of the experiments is aided by quantum chemical calculations based on density functional theory, by which the electrostatic potential and molecular orbitals are calculated and the initial electron attachment process prior to dissociation is investigated.     

A highly stereoselective synthesis of new styryl-π-conjugate organosilicon compounds

This work describes very precise and controlled catalytic transformations as useful tools for the synthesis of new trans-π-conjugated molecular and macromolecular organosilicon compounds. Several distyryl-arenes were obtained efficiently via silylative coupling in high yields and with excellent selectivity for new E,E-bis(silyl)arenes.     

Chromatographic determination of hydrophobicity of dialkylimidazolium ionic liquids using selected stationary phase

The determination of hydrophobicity of ionic liquids (ILs) is essential for the reason that some of these salts' classes are of toxic character. The conventional shake flask method of logP estimation fails in case of ILs. This is connected with their ionic character. Therefore other methods need to be developed and optimized. Chromatographic methods seem to be the proper ones. For that reason, several specific stationary phases (octadecyl, octyl, aminopropyl, alkylamide, cholesterolic, immobilized artificial membrane, phenyl) have been used for the determination of logk(w) of alkylimidazolium ILs. Then, logk(w) were used for the correlation with calculated logP for ILs. Depending on applied calculation procedure, high values of determination coefficient were obtained for alkyl-based silica stationary phases or for more specific column packing. This result is very promising as it has already been proven that several, different in nature, stationary phases can be successfully used for estimation of logP of IL cations.     

Mobile-phase pH influence on the retention of some benzoic acid derivatives in reversed-phase chromatography

Five end-capped octadecyl RP stationary phases, among which one was a polar embedded stationary phase, were tested for the analysis of benzoic acid derivatives using two mobile phases with or without addition of formic acid (water pH was measured by a common approach; pH of water with addition of formic acid was 3.0 and without formic acid 5.8). The influence of mobile-phase pH on the retention of benzoic acid derivatives was under study. Consequently, Purospher-STAR and Alltima columns provided symmetrical peaks for benzoic acid derivatives at pH 3.0 and also at pH 5.8. Reprosil and Symmetry stationary phases showed poor peak shapes at higher pH of the mobile phase. Differences between the tested columns may be caused by surface heterogeneity. Another reason may be the presence of some atoms creating additional adsorption sites on the surface of Reprosil and Symmetry stationary phases. This can lead to enhanced silanol activity resulting in peak tailing. The addition of formic acid into the mobile phase improved peak shapes. The polar embedded C18 stationary-phase Synergi-Fusion-RP appeared as not a suitable column for the analysis of benzoic acid derivatives. Synergi-Fusion-RP provided asymmetrical peaks even if formic acid was added into the mobile phase.     

Hydrophilic interaction liquid chromatography (HILIC)—a powerful separation technique

Hydrophilic interaction liquid chromatography (HILIC) provides an alternative approach to effectively separate small polar compounds on polar stationary phases. The purpose of this work was to review the options for the characterization of HILIC stationary phases and their applications for separations of polar compounds in complex matrices. The characteristics of the hydrophilic stationary phase may affect and in some cases limit the choices of mobile phase composition, ion strength or buffer pH value available, since mechanisms other than hydrophilic partitioning could potentially occur. Enhancing our understanding of retention behavior in HILIC increases the scope of possible applications of liquid chromatography. One interesting option may also be to use HILIC in orthogonal and/or two-dimensional separations. Bioapplications of HILIC systems are also presented.     

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.

X-ray induced damage in DNA monitored by X-ray photoelectron spectroscopy

In this work, the chemical changes in calf thymus DNA samples were analyzed by X-ray photoelectron spectroscopy (XPS). The DNA samples were irradiated for over 5 h and spectra were taken repeatedly every 30 min. In this approach the X-ray beam both damages and probes the samples. In most cases, XPS spectra have complex shapes due to contributions of C, N, and O atoms bonded at several different sites. We show that from a comparative analysis of the modification in XPS line shapes of the C 1s, O 1s, N 1s, and P 2p peaks, one can gain insight into a number of reaction pathways leading to radiation damage to DNA.     

Poly(ether amine) and cross-linked poly(propylene oxide) diacrylate thin-film polymer electrolyte for 3D-microbatteries

This paper presents a novel thin-film electrolyte of a 2:1 blend of polyetheramine (glyceryl poly(oxypropylene)) and cross-linked oligomeric poly(propylene oxide) diacrylate with LiTFSI. The polyetheramine acts as a surfactant, and can thereby be applied as a conformal coating on complex surfaces—here demonstrated for porous LiFePO₄ cathodes—making it useful for 3D-microbatteries. The poly(propylene oxide) diacrylate blends with the surfactant and is easily UV cross-linked, thereby ensuring good mechanical stability. Electrolytes, ~ 2 μm thick, were casted onto LiFePO₄ cathodes and cycled against metallic lithium, displaying stable discharge capacities of ~ 8 mAh/g at room temperature and ~ 120 mAh/g at 60 °C. The electrolyte showed conductivities of 3.45 × 10^? 6 and 5.80 × 10^? 5 S cm^? 1 at room temperature and 60 °C, respectively.     

A simple economic and heat transfer analysis of the nanoparticles use

In this paper, a review of the impact of most common nanoparticles on the Leidenfrost temperature T _Leid in heat transfer applications is delivered. Moreover, a simple economic analysis of the nanoparticles use is proposed. When coolant is distilled water, T _Leid can range 150–220 °C; occasionally, it can even amount to over 400 °C. When the base liquid is modified by additives, considerable changes in the character of heat transfer are observed. Out of five nanofluids under consideration in this study, the best thermal effect (up to 50%) is obtained when Al₂O₃ nanofluid having particle sizes ~39 nm and volume concentration of 0.1% is used. Conversely, the fluid containing TiO₂ particles, 20–70 nm in size, seems to be the worst of the analysed fluid, giving only 7% heat transfer enhancement in comparison with water. However, when TiO₂ nanoparticles are far smaller, very good thermal effects are obtained (23–25%). In a majority of the cases analysed, the temperature that marks the onset of film boiling is inversely proportional to concentrations of nanoparticles, which is relevant from the economic standpoint.