Stability in an overdetermined problem for the Green’s function

In the plane, we consider the problem of reconstructing a domain from the normal derivative of its Green’s function (with fixed pole) relative to the Dirichlet problem for the Laplace operator. By means of the theory of conformal mappings, we derive stability estimates of Hölder type.     

Influence of gel-phase microdomains and lipid rafts in lipid monolayers on the electron transfer of a lipophilic redox probe: dioctadecylviologen

Gel-phase microdomains and lipid rafts form spontaneously in monolayers of lipid mixtures of dioleoylphosphatidylcholine (DOPC), palmitoylsphingomyelin (PSM) and cholesterol (Chol), self-assembled on mercury. The influence of microdomains on the electron transfer properties of 2 mol% dioctadecylviologen (DODV), incorporated in these lipid monolayers, was investigated by cyclic voltammetry. In pure DOPC, the DODV molecules tend to aggregate, giving rise to strong attractive lateral interactions. With an increase in the PSM mole fraction in DOPC/PSM binary mixtures, the edges of the resulting gel-phase microdomains act as docking sites for the DODV molecules, decreasing lateral interactions and modifying the DODV redox properties. A similar behavior is shown by lipid rafts formed by adding Chol to the above binary mixtures. By varying the DOPC/PSM molar ratio, the midpoint between the peak potentials of the DODV reduction and oxidation peaks shifts in parallel with the surface dipole potential of the lipid mixture. This behavior indicates that the formal (half-reduction) potential of a redox pair, as measured versus a given reference electrode, may include a surface dipole potential if one or both members of the redox pair are embedded in a medium different from the bulk phase containing the reference electrode.     

Tethered bilayer lipid micromembranes for single-channel recording: the role of adsorbed and partially fused lipid vesicles

A mercury-supported bilayer lipid micromembrane was prepared by anchoring a thiolipid monolayer to a mercury cap electrodeposited on a platinum microdisc about 20 μm in diameter; a lipid monolayer was then self-assembled on top of the thiolipid monolayer either by vesicle fusion or by spilling a few drops of a lipid solution in chloroform on the cap and allowing the solvent to evaporate. Single-channel recording following incorporation of the alamethicin channel-forming peptide exhibits quite different features, depending on the procedure followed to form the distal lipid monolayer. The "spilling" procedure, which avoids the formation of adsorbed or partially fused vesicles, yields very sharp single-channel currents lasting only one or two milliseconds. These are ascribed to ionic flux into the hydrophilic spacer moiety of the thiolipid. Conversely, the vesicle-fusion procedure yields much longer single-channel openings analogous to those obtained with conventional bilayer lipid membranes, albeit smaller. This difference in behavior is explained by ascribing the latter single-channel currents to ionic flux into vesicles adsorbed and/or partially fused onto the tethered lipid bilayer, via capacitive coupling.     

Synthesis of Novel Carbohydrate Acridinone Derivatives with Potential Biological Activities using 1,3‐Dipolar Cycloaddition

Novel 10‐{[3‐(6‐hydroxy‐2,2‐dimethyltetrahydrofuro[2,3‐d][1,3]dioxol‐5‐yl)‐4,5‐dihydro‐5‐isoxazolyl]methyl}‐9(10H)‐acridinone derivatives (13–16) were synthesized by 1,3‐dipolar cycloaddition using the carbohydrate derivative as dipole and different 10‐allyl‐9(10H)‐acridinone derivatives (9–12) as dipolarophiles. The new cycloadducts as well as the dipolarophiles precursors were characterized spectroscopically.     

Synthesis of 11H-Pyrido[2,1-b]quinazolin-11-one and Derivatives

The synthesis of 11H-pyrido[2,1-b]quinazolin-11-one (IV) and derivatives, by the condensation of o-chlorobenzoic acid and 2-aminopyridine in DMF is reported.     

Solvent dependence of the photophysical properties of 2-chlorothioxanthone, the principal photoproduct of chlorprothixene

2‐chlorothioxanthone (CTX) is used as photoinitiator for the reticulation of synthetic resins and for the preparation of pharmaceuticals. It was previously determined that CTX is the primary photoproduct of z‐chlorprothixene (CPTX) when irradiated at 313 nm and is formed in an autocatalyzed reaction through an energy‐transfer mechanism (Piñero et al. [2009] Photochem. Photobiol., 85 , 895–900). In this work, the photophysical properties of CTX were measured in acetonitrile/water solutions to determine if their magnitude can affect the side effects of CPTX. The results show that CTX has higher absorption coefficients in the visible region (400–420 nm) and higher triplet quantum yields than its parent compound. Similar to TX, both properties strongly depend on the solvent polarity/hydroxylicity. The quantum yield of the triplet intermediate is very close to the value of the phenothiazine triplets. The phenothiazines are the most phototoxic antidepressants. Therefore, given the appropriate microenvironment, the photosensitization side effects of CPTX can be intensified on the production of CTX.     

Two-dimensional Fourier transform ion cyclotron resonance mass spectrometry: reduction of scintillation noise using Cadzow data processing

In two-dimensional Fourier transform ion cyclotron resonance mass spectrometry (2D FTICR-MS), scintillation noise, caused mostly by fluctuations in the number of ions in the ICR cell, is the leading cause for errors in spectrum interpretation. In this study, we adapted an algorithm based on singular value decomposition and first introduced by Cadzow et al. (IEE Proceedings Pt. F 1987, 134, 69) to 2D FTICR-MS and we measured its performance in terms of noise reduction without losing signal information in the 2D mass spectrum.     

Traceless solid-phase synthesis of bicyclic dihydropyrimidones using multidirectional cyclization cleavage

Solid-phase and solution-phase protocols for the synthesis of furo[3,4-d]pyrimidines, pyrrolo[3,4-d]pyrimidines, and pyrimido[4,5-d]pyridazines are reported. The multistep solid-phase sequence involves the initial high-speed, microwave-promoted acetoacetylation of hydroxymethylpolystyrene resin with methyl 4-chloroacetoacetate. The immobilized 4-chloroacetoacetate precursor was subsequently subjected to three-component Biginelli-type condensations employing urea and a variety of aromatic aldehydes. The resulting 6-chloromethyl-functionalized resin-bound dihydropyrimidones served as common chemical platforms for the generation of the desired heterobicyclic scaffolds using three different traceless cyclative cleavage strategies. The corresponding furo[3,4-d]pyrimidines were obtained by microwave flash heating in a rapid, thermally triggered, cyclative release. Treatment of the chloromethyl dihydropyrimidone intermediates with a variety of primary amines followed by high-temperature microwave heating furnished the anticipated pyrrolo[3,4-d]pyrimidine scaffolds via nucleophilic cyclative cleavage. In a similar way, reaction with monosubstituted hydrazines resulted in the formation of pyrimido[4,5-d]pyridazines. All compounds were obtained in moderate to good overall yields and purities.