Chemical ionization desorption mass spectrometry of some quaternary ammonium salts

The ammonia chemical ionization desorption spectra of N,N-dimethyl quaternary ammonium iodides in addition to high protonated molecular ion [M + H]⁺ intensity, show signals for an ion radical composed of N-methyl abstracted salt cation and ammonia [C + NH₃? CH₃]^+˙. These ions corresponding to the cation +2 show increased importance in the chemical ionization mode, using the same reagent gas. The technique of chemical ionization desorption appears suitable for the analysis of salts, and thus for the determination of the molecular weight of both anion and cation.     

The colors of polydiacetylenes: a commentary

Polydiacetylenes (PDA) can take several colors, mostly "red" and "blue", and blue-to-red color transitions are usually considered as transitions from a well ordered state to a disordered one. Recent work on single isolated PDA chains shows that this is not correct: red chains can be quasi-perfect quantum wires. The transition is between two different chain conformations, and each may, or may not, be perfectly ordered. Disorder, when it occurs, is a side-product of the transformation.     

Réactivité de spirochromènes et de mérocyanines azahétérocycliques vis-à-vis de quelques agents nucléophiles

Under the action of nucleophile reagents such as water, hydrogen sulfide and sodium borohydride, the saturated azaheterocyclic spirochromenes are opened either on the azaheterocyclic side or on the benzopyran side or on both parts simultaneously. The merocyanines are either partially reduced or decomposed by the sodium borohydride.     

Galactose Oxidase models: 19F NMR as a powerful tool to study the solution chemistry of tripodal ligands in the presence of copper(II)

In copper(ii) complexes of tripodal ligands, the protonation state of the phenol moiety, and its position (axial vs. equatorial), are easily assessed by (19)F NMR.     

Dual biosensor immunoassay-directed identification of fluoroquinolones in chicken muscle by liquid chromatography electrospray time-of-flight mass spectrometry

Fluoroquinolones (FQs) are synthetic antibiotics of broad-spectrum antibacterial activity widely used to treat infections in farmed fish, turkeys, pigs, calves and poultry. Monitoring these substances residues is therefore regulated by law. For the detection of FQs, we studied the feasibility of coupling the simultaneous screening of several FQs, using a dual surface plasmon resonance (SPR) biosensor immunoassay (BIA), in parallel, with an analytical chemical methodology for their identification. Six FQs were simultaneously screened at or below their maximum residue level (MRL) in chicken muscle using a multi-FQ BIA for norfloxacin, ciprofloxacin, enrofloxacin, difloxacin and sarafloxacin, and a specific BIA for flumequine. The two BIAs were serially coupled in a multi-channel SPR biosensor featuring a dual BIA in a competitive inhibition format. The samples non-compliant during the screening with the dual BIA were further concentrated and fractionated with gradient liquid chromatography (LC). The effluent was splitted toward two 96-well fraction collectors resulting in two identical 96-well plates. One was re-screened with the dual BIA to identify the immunoactive fractions and direct the identification efforts toward the relevant fractions in the second well-plate with high resolution LC-electrospray time-of-flight mass spectrometry (ESI-TOFMS). The system not only allows the possibility to screen and identify known FQs, but also to discover unknown chemicals of similar structure which show activity in the dual BIA.     

"ENERGY"-DEPENDENT QUENCHING OF CHLOROPHYLL FLUORESCENCE and THERMAL ENERGY DISSIPATION IN INTACT LEAVES DURING INDUCTION OF PHOTOSYNTHESIS

Abstract— Intact leaves, previously adapted to darkness for a prolonged period of time, were suddenly illuminated with a strong, photosynthetically saturating, white light (ca 1500 μmol m⁻² s^_1), resulting in the rapid establishment of a large energy-dependent chlorophyll fluorescence quenching (q_E) as shown by in vivo fluorescence measurements with a pulse amplitude modulation technique. Two different photothermal methods, photoacoustic spectroscopy and photothermal deflection spectroscopy, were used to monitor thermal deactivation of excited pigments during the dark-light transitions. The in vivo photothermal signals measured with both techniques were shown to remain constant during induction of photosynthesis under high light conditions, suggesting that, in contrast to current hypotheses, energy-dependent quenching q_E is not associated with significant changes in thermal dissipation of absorbed light energy in the chloroplasts. When photosynthesis was induced with a low-intensity modulated light, a noticeable decrease in the heat emission yield was observed resulting from the progressive activation of the competing photochemical processes.     

Utilization of cyclotron produced fast neutrons in the activation analysis for oxygen

The possible application of cyclotron-produced fast neutrons to activation analysis for oxygen based on the¹⁶O(n, p)¹⁶N reaction has been investigated. Neutrons were produced by bombarding a thick beryllium target with 22 to 45 MeV deuterons. It was found that the sensitivity increases rapidly with the energy of the deuterons. Using 45 MeV deuterons and a 10 μA beam current a sensitivity of about 20 counts per 1 μg oxigen could be achieved, enabling the determination of less than 1 μg oxigen. In a direct comparison it was experimentally established that the sensitivity for cyclotron-produced neutrons assuming a deuteron beam of about 10 μA, is up to two orders of magnitude higher than that achievable for 14 MeV neutrons with a flux of about 10¹⁰ n/s. The interference of fluorine is at about the same level for both the cyclotron-produced and 14 MeV neutrons. Using cyclotron-produced fast neutrons in the investigated energy range, sodium and magnesium can also interfere, but only to a very much lower extent.     

Silver versus gold catalysis in tandem reactions of carbonyl functions onto alkynes: a versatile access to furoquinoline and pyranoquinoline cores

An efficient and versatile tandem process of acetalization and cycloisomerization reactions has been developed for the reactions of 1-alkynyl-2-carbonylquinoline substrates. The reaction occurs thanks to Au(I) and Ag(I) catalysis. Silver(I) catalysis has been extensively studied (11 different silver species) on a broad range of quinoline derivatives (variation of alkyne substituent, of carbonyl function and of nucleophiles), leading to a variety of furoquinoline and pyranoquinoline moieties. An insight is given for the presumed mechanism along with DFT-B3 LYP/6-31G** calculations to address the 6-endo and 5-exo regioselectivities observed.     

Xylooligosaccharides Production from Alkali-Pretreated Sugarcane Bagasse Using Xylanases from Thermoascus aurantiacus

Sugarcane bagasse hemicellulose was isolated in a one-step chemical extraction using hydrogen peroxide in alkaline media. The polysaccharide containing 80.9% xylose and small amounts of l-arabinose, 4-O-methyl-d-glucuronic acid and glucose, was hydrolyzed by crude enzymatic extracts from Thermoascus aurantiacus at 50?°C. Conditions of enzymatic hydrolysis leading to the best yields of xylose and xylooligosaccharides (DP 2-5) were investigated using substrate concentration in the range 0.5–3.5% (w/v), enzyme load 40–80 U/g of the substrate, and reaction time from 3 to 96 h, applying a 2² factorial design. The maximum conversion to xylooligosaccharides (37.1%) was obtained with 2.6% of substrate and xylanase load of 60 U/g. The predicted maximum yield of xylobiose by a polynomial model was 41.6%. Crude enzymatic extract of T. aurantiacus generate from sugarcane bagasse hemicellulose 39% of xylose, 59% of xylobiose, and 2% of other xylooligosaccharides.     

Microscopic study of hydroxyapatite dissolution as affected by fluoride ions

Fluoride ions play a critical role in preventing tooth decay. We investigated the microscopic effects of fluoride ions on hydroxyapatite (100) surface dissolution using in situ atomic force microscopy. In the presence of 10 mM NaF, individual surface step retraction velocities decreased by about a factor of 5 as compared to NaF-free conditions. Importantly, elongated hexagonal etch pits, which are characteristic of (100) surface dissolution, were no longer observed when NaF was present. The alteration of pit shape is more distinct at a higher NaF concentration (50 mM) where triangular etch pits evolved during dissolution. Furthermore, in a fluoride concentration typical for tap water (10 μM), we observed roughening of individual step lines, resulting in the formation of scalloped morphologies. Morphological changes to individual steps across a wide range of fluoride concentrations suggest that the cariostatic capabilities of fluoride ions originate from their strong interactions with molecular steps.