Versatile microanalytical system with porous polypropylene capillary membrane for calibration gas generation and trace gaseous pollutants sampling applied to the analysis of formaldehyde, formic acid, acetic acid and ammonia in outdoor air

The analytical determination of atmospheric pollutants still presents challenges due to the low-level concentrations (frequently in the μg m⁻³ range) and their variations with sampling site and time. In this work, a capillary membrane diffusion scrubber (CMDS) was scaled down to match with capillary electrophoresis (CE), a quick separation technique that requires nothing more than some nanoliters of sample and, when combined with capacitively coupled contactless conductometric detection (C⁴D), is particularly favorable for ionic species that do not absorb in the UV-vis region, like the target analytes formaldehyde, formic acid, acetic acid and ammonium. The CMDS was coaxially assembled inside a PTFE tube and fed with acceptor phase (deionized water for species with a high Henry's constant such as formaldehyde and carboxylic acids, or acidic solution for ammonia sampling with equilibrium displacement to the non-volatile ammonium ion) at a low flow rate (8.3 nL s⁻¹), while the sample was aspirated through the annular gap of the concentric tubes at 2.5 mL s⁻¹. A second unit, in all similar to the CMDS, was operated as a capillary membrane diffusion emitter (CMDE), generating a gas flow with know concentrations of ammonia for the evaluation of the CMDS. The fluids of the system were driven with inexpensive aquarium air pumps, and the collected samples were stored in vials cooled by a Peltier element. Complete protocols were developed for the analysis, in air, of NH₃, CH₃COOH, HCOOH and, with a derivatization setup, CH₂O, by associating the CMDS collection with the determination by CE-C⁴D. The ammonia concentrations obtained by electrophoresis were checked against the reference spectrophotometric method based on Berthelot's reaction. Sensitivity enhancements of this reference method were achieved by using a modified Berthelot reaction, solenoid micro-pumps for liquid propulsion and a long optical path cell based on a liquid core waveguide (LCW). All techniques and methods of this work are in line with the green analytical chemistry trends.     

Strong-coupling topological Josephson effect in quantum wires

We investigate the Josephson effect for a setup with two lattice quantum wires featuring Majorana zero energy boundary modes at the tunnel junction. In the weak-coupling regime, the exact solution reproduces the perturbative result for the energy containing a contribution ～ ± cos(?/2) relative to the tunneling of paired Majorana fermions. As the tunnel amplitude g grows relative to the hopping amplitude w, the gap between the energy levels gradually diminishes until it closes completely at the critical value gc [Formula: see text]. At this point the Josephson energies have the principal values [Formula: see text], where m =- 1,0,1 and σ =± 1, a result not following from perturbation theory. It represents a transparent regime where three Bogoliubov states merge, leading to additional degeneracies of the topologically nontrivial ground state with an odd number of Majorana fermions at the end of each wire. We also obtain the exact tunnel currents for a fixed parity of the eigenstates. The Josephson current shows the characteristic 4π periodicity expected for a topological Josephson effect. We discuss the additional features of the current associated with a closure of the energy gap between the energy levels.     

Strategies for protein folding and design

Fundamental challenges in molecular biology can be addressed by using simple models on a lattice, where statistical mechanics and combinatoric techniques can be employed. The basic premise is that it is sensible to test any proposed method on the simplest of models in order to assess their validity before launching a full-scale attack on realistic problems. In this paper we follow this strategy and we present different efficient schemes to perform protein design and to extract effective amino acid interaction potentials.This work was supported in part by INFM, INFN sez. di Trieste, NASA and NATO.     

Allyl palladium complexes bearing carbohydrate-based N-heterocyclic carbenes: Anticancer agents for selective and potent in vitro cytotoxicity

Novel allyl palladium compounds stabilized by carbohydrate-based N-heterocyclic carbenes (NHCs) were prepared and characterized by nuclear magnetic resonance, high-resolution mass spectrometry and elemental analysis. The antiproliferative activity of the compounds was tested on a panel of different tumor lines, especially ovarian cancer and MRC-5 human lung fibroblasts (nontumor cells). These experiments showed that both mixed NHC/PPh₃ and NHC/PTA (PTA = 1,3,5-triaza-7-phosphaadamantane) allyl complexes have IC₅₀ (half maximal inhibitory concentration) values comparable and sometimes even significantly lower than cisplatin. Moreover, the mixed NHC/PTA allyl complexes exhibit good activity toward the seven tumor lines tested with a substantial inactivity against normal cells, a necessary condition to avoid the general cytotoxicity of a metallo-drug. Furthermore, this subclass of compounds proved particularly active on the A549 lung cancer tumor line (up to 100-fold more cytotoxic than cisplatin) and exhibited satisfactory cytotoxicity against KURAMOCHI and OVCAR3 cell lines, which are currently considered the best in vitro models for serous ovarian cancer, the most lethal tumor for women worldwide.     

Preparative Mass Spectrometry Using a Rotating-Wall Mass Analyzer

The design of functional interfaces is central to both fundamental and applied research in materials science and energy technology. We introduce a new, broadly applicable technique for the precisely controlled high-throughput preparation of well-defined interfaces containing polyatomic species ranging from small ions to nanocrystals and large protein complexes. The mass-dispersive deposition of ions onto surfaces is achieved using a rotating-wall mass analyzer, a compact device which enables the separation of ions using low voltages and has a theoretically unlimited mass range. We demonstrate an efficient deposition of singly charged Au₁₄₄(SC₄H₉)₆₀ ions (33.7 kDa), which opens up exciting opportunities for the structural characterization of nanocrystals and their assemblies using transmission electron microscopy. Our approach also enables the high-throughput deposition of mass-selected ions from multicomponent mixtures, which is of interest to the controlled preparation of surface gradients and rapid screening of molecules in mixtures for a specific property.     

Cover Picture: Angew. Chem. Int. Ed. 6/2002

The cover picture shows the electric eel, Electrophorus electricus, a source for commercially available acetylcholinesterase. In an experiment described by K. B. Sharpless and M. G. Finn and co‐workers on pp. 1053–1057, a femtomolar inhibitor was assembled by the enzyme from a collection of building blocks containing azide and alkyne functional groups, shown floating in solution. The templated 1,3‐dipolar cycloaddition reaction, producing the inhibitor, is represented by the flare of light at the center of the image.     

Fuel‐Selective Transient Activation of Nanosystems for Signal Generation

The transient activation of function using chemical fuels is common in nature, but much less in synthetic systems. Progress towards the development of systems with a complexity similar to that of natural ones requires chemical fuel selectivity. Here, we show that a self‐assembled nanosystem, composed of monolayer‐protected gold nanoparticles and a fluorogenic peptide, is activated for transient signal generation only in case the chemical fuel matches the recognition site present at the nanoparticle surface. A modification of the recognition site in the nanosystem completely changes the chemical fuel selectivity. When two nanosystems are simultaneously present, the selectivity expressed by the system depends on the concentration of nucleotide added.     

Synthesis of 2,3-dihydro-1,4-dithiinyl nucleosides via Pummerer-type glycosidation

A straightforward procedure for the preparation of nucleoside analogue 1 and its regioisomer 2 containing a dihydro-1,4-dithiin as sugar moiety has been accomplished in four steps by our readily available heterocyclic system 5. Nucleobase insertion was carried out by direct addition of N⁴-acetylcytosine to sulfoxide derivatives via Pummerer-type glycosidation reaction.     

Enhancement of gemcitabine affinity for biomembranes by conjugation with squalene: differential scanning calorimetry and Langmuir-Blodgett studies using biomembrane models

Molecular interactions between gemcitabine, alone or conjugated with squalene to form the gem-squalene prodrug, with dimyristoylphosphatidylcholine have been investigated by differential scanning calorimetry and Langmuir film balance techniques to gain information about the interaction of gemcitabine and its prodrug with mammalian cell membranes and to evaluate the potential of liposomes as a delivery system for gemcitabine prodrugs. Phospholipids assembled as multilamellar vesicles or monolayers (at the air water interface) have been used as biomembrane models. Different interactions of gemcitabine, its prodrug, and squalene with the lipid were detected by dispersing the compounds in the MLV and were compared with kinetic experiments carried out to consider the ability of the examined compounds to dissolve in an aqueous medium, to migrate through it, and to be captured by multilamellar vesicles. Their ability to be released from drug-loaded liposomes and be taken up by empty vesicles mimicking biomembranes was also considered. Analysis of the differential scanning calorimetry curves reveals that gemcitabine has very little interaction with multilamellar vesicles whereas the gem-squalene prodrug strongly interacts with multilamellar vesicles. The kinetic experiments suggest that an aqueous medium does not permit the prodrug uptake by the biomembrane models, whereas it is allowed when gem-squalene is gradually released by the liposomes. The molecular area/surface pressure isotherms of the gemcitabine/lipid, gem-squalene/lipid, and pure compound monolayers, in agreement with the calorimetric results, indicate that gem-squalene interacts with the phospholipid monolayer with the squalene moiety in contact with the phospholipid chains and gemcitabine protruding in the aqueous medium.