Rupture energy of a pendular liquid bridge

We propose a simple expression for the rupture energy of a pendular liquid bridge between two spheres, taking into account capillary and viscous (lubrication) forces. In the case of capillary forces only, the results are in accordance with curve fitting expressions proposed by Simons et al. [2] and Willett et al. [5]. We performed accurate measurements of the force exerted by liquid bridges between two spheres. Experimental results are found to be close to theoretical values. A reasonable agreement is also found in the presence of viscous forces. Finally, for small bridge volumes, the rupture criterion given by Lian et al. [10] is modified, taking into account additional viscous effects. Received 18 September 2000 and Received in final form 10 June 2001     

The use of acridine orange base (AOB) as molecular probe to characterize nonaqueous AOT reverse micelles

The behavior of acridine orange base (AOB) in nonaqueous reverse micelles composed of n-heptane/AOT/polar solvent has been performed. Ethylene glycol (EG), propylene glycol (PG), glycerol (GY), formamide (FA), dimethylformamide (DMF), and dimethylacetamide (DMA) were employed as water substitutes. The studies were performed by static and time-resolved emission spectroscopy. Thus, the distribution of AOB between the two pseudophases of the aggregates was quantified by measuring the partition constants from emission spectra at different surfactant concentration. Similar values to those obtained by means of absorption spectroscopy were obtained. This match is indicating that AOB is not experiencing partition during the lifetime of the excited state. Partitioning to the micelles is strongly favored in micelles containing hydrogen-bond donor (HBD) solvents rather than non-HBD solvents. Variations of fluorescence lifetimes with AOT concentration confirm these results. By the solvatochromic behavior of AOB in the different systems it is shown that the microenvironment at the interface is distinct from that of the bulk polar solvent, indicating that the probe senses no "free" solvent. The steady state anisotropy (r) was measured for EG/AOT/n-heptane and DMF/AOT/n-heptane systems as representatives for HBD and non-HBD polar solvents, respectively. The value of r is higher in the micelles containing EG than that obtained with DMF, and increases with AOT concentration. This is explained as due to highly structured polar solvents in the inner core. EG is interacting with the polar heads of AOT through hydrogen-bond interaction, while DMF can only interact with the Na+ counterions. This is confirmed by the time-resolved emission spectra (TRES) of the probe in the micellar systems, in comparison with the bulk solvents.     

Chemo-differentiating MCRs based on alpha-ketoesters and terminal alkynoates. A homoaldol-based ABB' system

A novel ABB' 3 component reaction (3-CR) system based on the organocatalyzed homoaldolic condensation of alpha-ketoesters in the presence of terminal conjugated alkynoates is described.     

Divergent reactivity of allene-containing α-diazoesters using Cu and Rh catalysis

A versatile intramolecular reaction of allene-containing diazomalonates that exhibits excellent chemoselectivity for either allenic C–H insertion or cyclopropanation is demonstrated. The identity of the product depends on the transition metal catalyst that is employed for the reaction. Rh catalysts promote exclusive C–H insertion with good diastereoselectivity for the trans product, while Cu catalysis enables intramolecular cyclopropanation to yield methylenecyclopropanes with moderate to good E:Z ratios.     

Energy decompositions according to physical space partitioning schemes: treatments of the density cumulant

This article is a continuation of our previous paper on schemes of energy decompositions of molecular systems in the real space [D. R. Alcoba et al., J. Chem. Phys. 122, 074102 (2005)] now using correlated state functions. We study, according to physical arguments, the appropriate management of the density cumulant arising from the second-order reduced density matrix at correlated level, whose contributions can be assigned to one-center or to two-center terms in the energy partitioning. Our treatments are applied within two physical space partitioning schemes: the Bader partitioning into atomic basins and the fuzzy atom procedure. The results obtained in selected molecules are analyzed and discussed in detail.     

Quantitative measurement of different ceramide species from crude cellular extracts by normal-phase high-performance liquid chromatography coupled to atmospheric pressure ionization mass spectrometry

Normal-phase high-performance liquid chromatography (NP-HPLC) coupled to atmospheric pressure ionization mass spectrometry (APCI-MS) allows quantitative analysis of endogenous ceramide and dihydroceramide species from crude lipid extracts. Qualitative information for the species comes from observation of differences in chromatographic and mass spectrometric behavior between species (Pettus et al. Rapid Commun. Mass Spectrom. 2003; 17: 1017-1026). Quantitative analysis is achieved by (1) use of a synthetic internal standard as an extraction and injection control, (2) lack of salt adduction, ion suppression, or other matrix effects in APCI mode, and (3) consistent fragmentation and ionization of external standards across the physiologically relevant concentration range found in endogenous lipid samples. Application to the analysis and quantitation of ceramide and dihydroceramide from various cell lines is demonstrated. The results from APCI-MS analysis corroborate and enhance information acquired from use of the diacylglycerol kinase assay for total ceramide measurement. This technique readily allows simultaneous quantitation of ceramide and dihydroceramide species.     

Continuous photochemical generation of catalytically active [CpRu]+ complexes from CpRu(η6-C6H6)PF6

Inter- and intramolecular ene-yne coupling reactions catalyzed by a species generated in situ via photolysis of CpRu(η(6)-C(6)H(6))PF(6)--an inexpensive, readily available, and shelf-stable complex--have been demonstrated under conditions of continuous flow. Importantly, the catalyst can be recovered quantitatively at the end of the reaction. Various functional groups are tolerated by the reaction, which affords skipped diene products in high yields.     

Stability of Plasma Treated Non-vulcanized Polybutadiene Surfaces: Role of Plasma Parameters and Influence of Additives

Surface modification studies of non-vulcanized BR elastomers (butadiene rubber) by low-pressure air plasma treatment and the effect on ageing and adhesion performances are presented in this paper. In particular, the influence of discharge power and distance from the glow discharge, and impact of antioxidant molecules in the BR formulation were examined. To characterize the changes to the BR surface, XPS spectroscopy, contact angle measurements, AFM nanoindentation experiments and tack measurements were utilized. Oxidation and crosslinking were the main mechanisms observed on the polymer chains regardless of the plasma conditions used. Beyond a certain threshold of plasma energy (in our case, discharge power of ~60 W and exposure time of ~30 s), a steady state was reached irrespective of the distance from the glow discharge. The presence of antioxidant molecules considerably reduced crosslinking phenomena while maintaining oxidation processes on polymer chains and increasing the nitrogen content in the near surface region. The mechanisms responsible for these differences have been identified. Interestingly, the COOH/C=O ratio changed according to the balance between oxidation and crosslinking. The hydrophobic recovery rate was mainly driven by temperature-dependent dynamics and varied according to the degree of crosslinking in the surface region. It was found to be lower in air atmosphere in the presence of antioxidant molecules. Finally, the presence of antioxidant molecules in the BR formulation allowed the adhesion performances after plasma exposure to significantly increase.