Effect of noble gases on sonoluminescence temperatures during multibubble cavitation

Sonoluminescence spectra were collected from Cr(CO)6 solutions in octanol and dodecane saturated with various noble gases. The emission from excited-state metal atoms serves as an internal thermometer of cavitation. The intensity and temperature of sonoluminescence increases from He to Xe. The intensity of the underlying continuum, however, grows faster with increasing temperature than the line emission. Dissociation of solvent molecules within the bubble consumes a significant fraction of the energy generated by the collapsing bubble, which can limit the final temperature inside the bubble.     

Liquid Chromatography Analysis of Reactive Oxoammonium Cations

This study presents the first liquid chromatography method for the quantitative and qualitative analysis of highly reactive oxoammonium cations based on a simple derivatization reaction. Rapid 1,2-electrophilic addition reactions with olefins were used to transform these reactive species into analyzable derivates. Three model substances were chosen to represent each of the main application fields of oxoammonium cations and to demonstrate the versatility of the method. The measuring protocol was validated according to the ICH and USP guidelines. The method revealed an excellent linearity (R²?=?0.9980–0.9990) with a low limit of detection (0.16–0.14 mmol L^?1) and a low limit of quantification (0.55–0.43 mmol L^?1). The protocol was finally used to determine the oxoammonium cations in the presence of their corresponding radical, showing a robustness against impurity concentration of up to approx. 30%.

     

Spectroscopic characterization of novel polycyclic aromatic polymers

A series of novel polyphenylenevinylene (PPV) derivative polymers were studied by absorption and photoluminescence spectroscopies. The effect of the sequential introduction of polycyclic aromatic ring substituents into the delocalized backbone was examined with relation to hypsochromatic and bathochromatic shifting. While the replacement of the phenyl units by naphthyl units results in a substantial hypsochromic shift of both the absorption and emission spectra, their subsequent substitution by anthryl units results in a bathochromic shift. The system is modeled according to, and is found to be consistent with, a previous study of donor-acceptor polyenes of varying length. The electronic structure of the backbone is found to be a balance between that of the high electron affinity polycyclic ring system and the contribution to conjugation across the linking vinyl unit. The model is adapted based on electron affinities of the constituent units, and a clear structure-property relationship for the absorption and emission properties of the system is elucidated. The Stokes shift is examined and is seen to be well-correlated with the vinyl contribution to the electron affinity total (EAtotal). The trends observed in the optical properties of the polymeric system are supported by Raman spectroscopy, whereby the spectral signature of the connecting vinyl bond is seen to soften in a fashion which is correlated with the modeled electron affinity parameters.     

A comparison of ionic liquids to molecular organic solvents as additives for chiral separations in micellar electrokinetic chromatography

In this study, we report the effects of adding ionic liquids (ILs), as compared to adding conventional molecular organic solvents (MOSs), to aqueous buffer solutions containing molecular micelles in the separation of chiral analyte mixtures in micellar EKC (MEKC). The molecular micelle used in this study was polysodium oleyl-L-leucylvalinate (poly-L-SOLV). The ILs were 1-alkyl-3-methylimidazolium tetrafluoroborate, where the alkyl group was ethyl, butyl, hexyl, or octyl. These ILs were chosen due to their hydrophobicity, good solvating, and electrolyte properties. Thus, it was expected that these ILs would have favorable interactions with chiral analytes and not adversely affect the background current. Common CE buffers, mixed with a molecular micelle, and an IL or a MOS, were used for these chiral separations. The buffers containing an IL in the concentration range of 0.02-0.1 v/v were found to support a reasonable current when an electric field strength of 500 V/cm was applied across the capillary. However, a current break down was observed for the buffers containing more than 60% v/v MOS on application of the above-mentioned electric field. The chiral resolution and selectivity of the analytes were dependent on the concentration and type of IL or MOS used.     

Reduction in growth rate in Phaeodactylum tricornutum (Bacillariophyceae) and Dunaliella tertiolecta (Chlorophyceae) induced by UV-B radiation

The effect of UV-B radiation (UVBR, 280-315 nm) on growth rate during 72 h of incubation, was measured for two marine microalgae -Dunaliella tertiolecta (Chlorophyceae) and Phaeodactylum tricornutum (Bacillariophyceae). The resulting inhibition of growth rate was analysed by calculating biological weighting functions (BWFs). The growth rate of D. tertiolecta was slightly more inhibited by UVBR (over the whole range of the spectrum) than was the growth rate of P. tricornutum, but the wavelength dependencies were the same. Our results were compared with results from photosynthesis experiments of Andreasson and W?ngberg [1] , where two methods, pulse amplitude modulation (PAM) fluorescence and carbon fixation, were measured for these same algae. The BWF for the growth rate, here, showed more wavelength dependency than the BWF for the previous two photosynthesis measurements - except for the carbon fixation BWF in P. tricornutum, which was closer to the BWF for growth rate. The wavelength dependency of the growth rate inhibition showed less variation between the species than the inhibition of the photosynthesis.     

Catalyst-assisted solution-liquid-solid synthesis of CdS/CdSe nanorod heterostructures

We report the synthesis and characterization of axial nanorod heterostructures composed of cadmium selenide (CdSe) and cadmium sulfide (CdS). The synthesis employs a solution-liquid-solid (SLS) mechanism with the assistance of bismuth nanocrystals adhered to a substrate (silicon or a III-V semiconductor). Transmission electron microscopy (TEM) and diffraction studies show that CdSe and CdS segments exhibit the wurtzite (hexagonal) crystal structure with <5% stacking faults. Both of these segments grow along the [002] direction with an epitaxial interface between them. Energy-dispersive X-ray (EDX) spectrometry using a high-resolution TEM operating in scanning mode confirms the alloy-free composition modulation in the nanorod heterostructures, showing that Se and S are localized in the CdSe and CdS portions of the nanorod heterostructures, respectively. This study demonstrates that SLS synthesis provides an alternate route to prepare axial nanorod heterostructures that have been difficult to generate using either vapor-liquid-solid growth or catalyst-free solution-phase synthesis.     

Formate dehydrogenase--a biocatalyst with novel applications in organic chemistry

In the field of industrial biocatalysis, formate dehydrogenase (FDH) is well established, in particular for its broad application in cofactor regeneration. Further applications have been limited by the enzyme's narrow range of substrates. These restrictions have been overcome now by the finding, that the enzyme is capable of selectively cleaving formic acid esters to the respective alcohol. Five homologous alkyl formates and phenyl formate as an aromatic ester were converted quantitatively by FDH from Candida boidinii in a batch reaction within 3 to 5 h. The substrates were turned irreversibly into carbon dioxide and the respective alcohol through hydride abstraction from the formyl group with full conversion. The mechanism shows parallels to hydrolysis reactions of the A(AC)1-type. K(M)-values and reactions rates of the tested formic acid esters display a tendency to higher conversion rates with increasing chain length. FDH emerged to be a superior deformylation catalyst compared to hydrolases as well as classical catalysts, as was shown by the selective deformylation of 1-acetoxy-4-formoxy butane (92%) and 1,3-bis(3-formoxypropyl)tetramethyldisiloxane. In particular its capability to distinguish between formic acid esters and non-formic acid esters renders the method particularly suitable for protective group chemistry. Furthermore the completeness of deformylation allows for converting substrates highly incompatible with aqueous media like siloxanes within a few hours.     

Synthesis, structure and magnetic properties of nanocrystalline YMnO3

Nanocrystalline YMnO(3) has been prepared by wet chemical synthesis routes to obtain crystallites with sizes from 20 nm to bulk material. The crystal structure of hexagonal YMnO(3) nanocrystallites smaller than 80 nm deviates from bulk material in terms of unit cell distortion and unit cell volume. The ferrielectric displacements of Y(3+) cations along the polar c-axis decays progressively with decreasing size below 100 nm. Indications of weak ferromagnetism in the form of a narrow hysteresis loop and enhanced magnetic susceptibility below 43 K in 20 nm YMnO(3) nanoparticles is attributed to extrinsic effects. Low-temperature annealing of the 20 nm crystallites in an oxidizing atmosphere removed all traces of ferromagnetism, showing that this is not a size-induced property. Finally, formation of the competing metastable orthorhombic phase and the thermodynamically stable hexagonal phase is discussed with respect to oxidizing or reducing conditions during synthesis.