Improved proton affinity measurements for proline and modified prolines using triple quadrupole and ion trap mass spectrometers

Proton affinity (PA) of compounds such as proline, cis-3-methylproline, cis-3-ethylproline, cis-3-isopropylproline and cis-3-isopentanylproline was determined by kinetic method with amines as the reference bases. The effective temperatures determined using ion trap and triple quadrupole mass spectrometers were found to be significantly different. In the case of the triple quadrupole instruments, the effective temperature depends significantly on the collision energy. The influence of the apparent basicity (GBapp) on the effective temperature may be used to estimate the difference in protonation entropy (DeltaDeltaS degrees) between the sample and reference compounds. In case of the ion trap mass spectrometer, the variation of the effective temperature as a function of the excitation amplitude is small, so it is difficult to account for the contribution of the entropy effects to the proton affinity value. A better estimation of the PA and DeltaDeltaS degrees values for the investigated molecules is obtained by combining the GBapp and Teff data pairs that are obtained from both the mass spectrometers.     

Detection of toluene diisocyanate in air with a coated piezoelectric crystal: Part 1. A Study of Coating Materials

A method for the detection of toluene diisocyanate vapour down to its threshold limit value (0.02 ppm) is presented; the sorption of the vapour onto a piezoelectric quartz crystal coated with polyethylene glycol is utilized. The resulting change in weight of the crystal is monitored by the associated change in the oscillation frequency. An investigation into the nature of the sorption process is described, and different coatings and chemical modifications to the PEG to minimize the effect of water vapour are indicated.     

Proton affinity of diastereoisomers of modified prolines using the kinetic method and density functional theory calculations: role of the cis/trans substituent on the endo/exo ring conformation

The proton affinity (PA) of cis/trans-3-prolinoleucines and cis/trans-3-prolinoglutamic acids have been studied by the kinetic method and density functional theory (DFT) calculations. Several conformations of the neutral and the protonated modified prolines, in particular the endo and exo ring conformations, were analyzed with respect to their contribution to the PA values. When the substituent is an alkyl, both the diastereoisomers have the same PA value. However, the PA values for the diastereoisomers are different when the substituted chain contains functional groups (e.g. a carboxyl group). This variation in PA values could be attributed to the existence of intramolecular hydrogen bonds.     

Extraction and determination of sulfonamides, macrolides, and trimethoprim in sewage sludge

Pressurized liquid extraction (PLE) was optimized and validated for the determination of sulfonamide and macrolide antimicrobials and trimethoprim in sewage sludge samples. A mixture of water/methanol (50:50, v/v) was found as the most efficient extraction solvent. A temperature of 100 degrees C and a pressure of 100 bar were chosen for extraction. Two cycles of 5 min each efficiently extracted at least 97% of the total extractable amount of all studied analytes from activated sludge. The limits of quantification (S/N= 10) varied between 3 and 41 microg/kg dry weight (dw) and the relative recoveries ranged between 78 and 142%. Additionally, the influence of pH and different LC/MS/MS systems on the absolute recoveries was assessed. Of the investigated antimicrobials sulfapyridin, sulfamethoxazole, trimethoprim, azithromycin, clarithromycin and roxithromycin were detected in municipal sewage sludge samples. Concentrations in activated sludge ranged up to 197 microg/kgdw. In comparison, results obtained by ultrasonic solvent extraction were significantly lower for sulfonamides and in tendency lower for macrolides.     

Plectranthone A,B, C und D. Diterpenoide Phenanthren-1,4-dione aus Blattdrüsen einer Plectranthuus sp. (Labiatae)

Plectranthons A, B, C, and D. Diterpenoid Phenanthrene-1,4-diones from Leaf-glands a Plectranthus sp. (Labiatae) The following structures of four new 1,4-phenanthraquionones, isolated in minute amounts from the coloured leaf-glands of a Plectranthus sp. obtained from the borders of Lake Kiwu₂, Rwanda, are proposed: plectranthon A ( 1 ; 3-hydroxy-5, 7,8-trimethyl-2-(2-propenyl)phenanthrene-1, 4-dione), plectranthon B ( 2 ; 2-(2ξ-acetoxypropyl)-3-hydroxy-5,7,8-trimethylphenanthrene-1,4-dione), plextranthon C ( 3 ; 3-hydroxy- 7,8-diemethyl-2-(2-propenyl)phenanthrene-1,4-dione), and plectranthon D ( 4 ; 3-hydroxy-7,8,10-trimethyl-2-(2-propenyl)phenanthrene-1,4-dione). 2-(2ξ-Hydroxypropyl)-3,6-dihydroxy-5,7,8-trimethylphenanthrene-1,4-dione ( 11 ), a compound very similar to 1–4 , was prepared by a Wagner-Meerwein, rearrangement of coleon E (⁵). Biogenetically, the plectranthons are derived from abietanoic precursors. The compounds 1, 2 and 4 are the first natural C₂₀-phenanthrenes of diterpenoid origin.     

Layer by layer self-assembled polyelectrolyte multilayers with embedded phospholipid vesicles obtained by spraying: integrity of the vesicles

In a previous paper (Michel, M.; Vautier, D.; Voegel, J.-C.; Schaaf, P.; Ball, V. Langmuir 2004, 20, 4835), we showed that phospholipid vesicles can be incorporated into poly(glutamic-acid)/poly(allylamine) (PGA/PAH) multilayered polyelectrolyte films built by the alternated dipping of a surface in polyanion and polycation solutions. AFM imaging, quartz crystal microbalance, and ellipsometry suggested that the vesicles remain intact when adhering on the surface. In the present paper, we show that such films can also be realized by spraying both the polyelectrolyte solutions and the vesicles onto the surface. Using such vesicles filled with ferrocyanide ions, we prove by cyclic voltammetry that the sprayed vesicles remain intact when embedded in the multilayers. We show that multilayers containing two distinct layers of intact vesicles separated by several polyanion/polycation bilayers can also be constructed. Polyelectrolyte multilayers containing layers of phospholipid vesicles could act as reservoirs for drug or other biologically active molecules in controlled release bioactive coatings.     

Radical-promoted Stone-Wales rearrangements

The mechanism of the known Stone-Wales rearrangement of bifluorenylidene to dibenzo[g,p]chrysene is assessed with the aid of B3LYP/6-31G(d) density functional calculations, and it is shown that a radical-promoted mechanism involving a sequence of homoallyl-cyclopropylcarbinyl rearrangement steps gives a realistic activation energy and can explain experimental observations, whereas a unimolecular mechanism has an improbably high activation energy. Radical-promoted mechanisms are then applied to the hypothetical Stone-Wales rearrangements of diindeno[1,2,3,4-defg;1',2',3',4'-mnop]chrysene and C(60) itself. Severe steric constraints in these cases raise the activation energy for the radical-promoted pathways substantially, but they are still strongly preferred to uncatalyzed, unimolecular pathways     

Molecular dynamics simulation studies of the conformation and lateral mobility of a charged adsorbate biomolecule: implications for estimating the critical value of the radius of a pore in porous media

The conformations, the values of the lateral transport coefficient of a charged biomolecule (desmopressin) in the adsorbed layer and in the liquid layers above the adsorbed layer, the potential energies of the interaction between the biomolecules located in different liquid layers with the charged solid surface and with the biomolecules in the adsorbed layer, the potential energies of the interaction between water molecules in the hydration layers surrounding the conformations of the biomolecules in different layers, as well as the structure and number of hydration layers between the different conformations of desmopressin, were determined by molecular dynamics simulation studies. The results show that the lateral mobility of the adsorbed desmopressin is approximately equal to zero and the value of the lateral transport coefficient of the biomolecule in the liquid layers located above the adsorbed layer increases as the distance of the liquid layer from the charged solid surface increases. But the values of the lateral transport coefficient of the biomolecule in the liquid layers above the adsorbed layer are lower in magnitude than the value of the transport coefficient of desmopressin along the direction normal to the charged solid surface in the liquid phase located above the vacant charged sites of the solid surface, and these differences in the values of the transport coefficients have important implications with respect to the replenishment of the biomolecules in the inner parts of a channel (pore), the overall rate of adsorption, and the form of the constitutive equations that would have to be used in macroscopic models to describe the mechanisms of mass transfer and adsorption in the pores of adsorbent media. Furthermore, a novel method is presented in this work that utilizes the information about the sizes of the conformations of the biomolecule in the adsorbed layer and in the liquid layers above the adsorbed layer along the direction that is normal to the charged solid surface, as well as the number and size of the hydration layers along the same direction, and could be used to estimate the value of the lower bound of the linear characteristic dimension of a pore (i.e., pore radius) in porous adsorbent media (e.g., porous adsorbent particles; skeletons of porous monoliths) in order to realize effective transport and overall adsorption rate.     

Alkynes as masked ylides: gold-catalysed intermolecular reactions of propargylic carboxylates with sulfides

The in situ-generation of sulfur ylides by the gold-catalysed rearrangement of propargylic carboxylates in the presence of sulfides has resulted in highly efficient and novel transformations.     

Gas-phase fragmentation of half- and first-generation polyamidoamine dendrimers by electrospray mass spectrometry using a quadrupole ion trap

Polyamidoamine (PAMAM) dendrimers are nanopolymers that can bind with biomolecules such as DNA, drugs or proteins. In order to study these complexes, we first fragmented half- and first-generation PAMAM, G0.5 and G1, respectively, using a quadrupole ion trap (QIT) equipped with an electrospray ionisation source. For both G0.5 and G1 we observed a series of impurities that only can stem from synthesis defects and that are principally due to missing branches and intramolecular cyclisations. Fragmentations of G1 showed regularity in the product ions. These ions result from the loss of 60 Da, obtained by an intramolecular cyclisation, and from the loss of 114 Da, obtained by a four-centred hydrogen transfer or a retro-Michael reaction. The fragmentations stemmed either from competitive or from consecutive reactions, even though resonant fragmentation QIT was used. It is shown that the principal fragmentation reaction is a retro-Michael rearrangement for both G1 and G0.5. In addition, by fragmenting totally deuterated [G1-d28]Na+ we were able to establish fragmentation pathways.