An economic theory of public facilities in space

This paper deals with the determination of the number and locations of facilities in which a public service is made available to consumers. The solutions obtained by planning and voting are characterized and compared for both a benefit taxation, based on consumers' locations, and an income taxation.     

Observation of the surface photoelectric effect of metals: Surface photoyield spectra of aluminum

Surface photoemission spectra of metals have been discussed theoretically since Sommerfeld developed his model of a metal in 1928, the so-called jellium model. The subject is still highly controversial among theorists. A spectroscopic technique — surface photoemission spectroscopy on jellium (SPJ) — which fully exploits the properties of synchrotron radiation, made it possible to separate unambiguously the photoyield caused by the surface photoelectric effect of metals optically excited byp-polarized light from other contributions to the yield. The technique was applied to aluminum and surface photoyield spectra were obtained for the first time. The extreme surface sensitivity, which is implicit in the transition matrix element of the surface photoexcitation process of metals, was experimentally confirmed. The new technique, therefore, provides one of the most powerfull tools for the investigation of the charge distribution and the dielectric response at metal surfaces.     

5-Amino-1,2,3,4-thiatriazole: Its acylation with chloroformates and chlorothioformates as a route to 1,2,4-thiadiazoles and 1,6,6a,Δ4-trithia-3,4-diazapentalenes

Summary Pyridine catalyzed acylation of 5-amino-1,2,3,4-thiatriazole with chloroformates and chlorothioformates afforded 3,5-bis(ethoxycarbonylamino)-1,2,4-thiadiazoles in the former and 2,5-bis(phenoxy)-1,6,6a,⁴-trithia-3,4-diazapentalenes in the latter case. An unstable, but isolable intermediate 2-phenoxy-1-aza-3,4-dithiolium-5-imide has been found if the chlorothioformate acylation was performed in acetonitrile in the absence of pyridine. The bis(phenoxy)trithiapentalenes are prone to nucleophilic displacement reactions at positions 2 and 5, exchanging in a stepwise manner one or both phenoxy groups. The structures of the compounds described could be inferred from their¹H-NMR¹³C-NMR, and mass spectra and were corroborated by the comparison with the data of authentic and similar derivatives as well as by chemical means.

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Die Acylierung von 5-Amino-1,2,3,4-thiatriazol mit Chlorformiaten und Chlorthioformiaten als Route zu 1,2,4-Thiadiazolen und 1,6,6a,⁴-Trithia-3,4-diazapentalenen

Zusammenfassung Die durch Pyridine katalysierte Acylierung von 5-Amino-1,2,3,4-thiatriazol mit Chlorameisensäureethylester führt zu 3,5-bis-(ethoxycarbonylamino)-1,2,4-thiadiazolen, während mit Chlorthioameisensäureethylester 2,5-bis(phenoxy)-1,6,6a,⁴-trithia-3,4-diazapentalene erhalten werden. Ohne Pyridin entsteht bei letzterer Reaktion ein wenig stabiles, aber isolierbares Zwischenprodukt: 2-Phenoxy-1-aza-3,4-dithiolium-5-imid. Die Bis(phenoxy)trithiadiazapentalene reagieren leicht mit nukleophilen Reagenzien und tauschen dabei schrittweise eine oder beide Phenoxygruppen aus.

     

Salt-induced swelling-to-shrinking transition in polyelectrolyte multilayer capsules

We study the size of polyelectrolyte multilayer capsules as a function of ionic strength, temperature, and time. A dynamic micromechanical model is developed which successfully describes the experiments. The model includes the polymer-solvent surface tension, an electrostatic force which is strongly ionic strength dependent, and a temperature-dependent mobility parameter. The activation of >50 kT suggests that multiple ion pairs must be broken simultaneously in the process of chain rearrangement. In support of our physical model capsules can repeatedly swell and shrink by varying ionic strength.     

Ionization state and structure of l-1,2-dipalmitoylphosphatidylglycerol monolayers at the liquid/air interface

Phosphatidylglycerols are components of biological membranes. The phase behavior of these phospholipids was extensively investigated. However, there is still no definite picture about the dependence of the ionization state and monolayer structure on subphase composition. The major problem of previous investigations is that none of the methods used allow obtaining the ionization degree directly. In the present work we apply techniques developed in the past decades for Langmuir monolayers: infrared reflection absorption spectroscopy (IRRAS) as well as X-ray diffraction and reflectivity techniques, which provide straightforward information about structure and ionization state of a L-1,2-dipalmitoylphosphatidylglycerol (DPPG) monolayer. The Gouy-Chapman model is applied to evaluate the intrinsic pKa. Therewith, the ionization degree can be determined even at low pH values. The experimental titration curves are in good agreement with theoretical curves based on the Gouy-Chapman model. The obtained instrinic pKa amounts to 1. The ionization degree of a DPPG monolayer is independent of the monovalent cation size. In contrast, the structure of a DPPG monolayer is strongly affected by the type of divalent cations.     

Analysis of recognition of fructose by imprinted polymers

Binding of fructose to the fructose imprinted polymer (MIP(Frc)) and pinacol imprinted polymer (control) were studied both in batch and a flow through mode. The influence of the cross-linkers ethylene glycol dimethacrylate (EDMA) and trimethylolpropane trimethacrylate (TRIM) on the binding characteristics was analysed. TRIM cross-linked MIPs showed a lower (unspecific) binding for the control polymer (pinacol imprinted) and higher binding of fructose as compared with the EDMA-MIPs. Furthermore interactions of a TRIM cross-linked molecularly imprinted polymer against fructose and its corresponding template were studied using a thermistor. Label-free detection of fructose was realised in the range of 0.5-10mM. The difference in enthalpy changes between specific binding of fructose to boronic acid moieties of the MIP and non-specific binding to the matrix leads to an 18-fold higher apparent imprinting factor than batch binding studies. Cross-reactivity studies using MIP sensor indicate that the interaction of fructose to MIP generates higher signal than disaccharides. The studies described in this paper demonstrate the potential of direct characterisation of molecular binding events.     

Structure of the Langmuir monolayers with fluorinated ethyl amide and ethyl ester polar heads creating dipole potentials of opposite sign

This study experimentally checks our previous hypothesis (Petrov, J. G.; Polymeropoulos, E. E.; Moehwald, H. Langmuir 2007, 23, 2623) that different conformations of the fluorinated heads of RCONHCH(2)CF(3) and RCOOCH(2)CF(3) monolayers cause the opposite signs and the striking difference of 1.480 V between their surface potentials Delta V. In situ X-ray diffraction at grazing incidence (GIXD) shows that both monolayers form orthorhombic lattices with closely packed chains tilted to the next-nearest neighbors in the RCONHCH(2)CF(3) film and upright in the RCOOCH(2)CF(3) monolayer. The packing of the chains in the plane perpendicular to them, which excludes the effect of the tilt, shows the same distance between the next-nearest neighbors, but significantly closer nearest neighbors in the RCONHCH(2)CF(3) film. This difference implies a specific anisotropic attraction between the adjacent amide heads. IR reflection absorption spectroscopy (IRRAS) shows that the -CONHCH(2)CF(3) heads have trans conformation and participate in H-bonds forming a -NH...O=C- lateral network. We speculate that such structure hinders the energetically optimal orientation of the hydrophobic -CH(2)CF(3) terminals toward air, so that the (delta+)C-(F (delta-))(3) dipoles at the monolayer/water boundary yield a strong positive contribution to Delta V. In contrast, most of the unbounded by H-bonds -COOCH(2)CF(3) heads statistically orient their hydrophobic (delta+)C-(F (delta-))(3) dipoles toward air, yielding a negative average dipole moment at the monolayer/water boundary and negative surface dipole potential.     

Sonochemical intercalation of preformed gold nanoparticles into multilayered clays

Multilayered Na (+)-montmorillonite clays intercalated with Au nanoparticles were synthesized by direct ultrasonic impregnation of preformed gold colloid into the clay matrix. The sonicated composite product then consists of Au nanoparticles homogeneously dispersed in the clay. The resulting clay/nano-Au composite was calcined at 800 degrees C and characterized by BET surface area analysis, transmission electron microscopy, scanning electron microscopy, X-ray diffraction, and Fourier transform infrared measurements. Nearly spherical-shaped gold nanoparticles, with a size of 6 +/- 0.5 nm, are located in the pores of clay calcined at 800 degrees C. Their nanocomposites are thermally stable as was shown by thermogravimetric analysis. No aggregation of the gold nanoparticles was observed during calcination. The proposed ultrasonic intercalation approach is an universal one and can be employed for synthesis of catalytically active metal-clay nanocomposites stable at high temperatures with high dispersability of the metal nanoparticles in the clay matrix.     

Embedded silver ions-containing liposomes in polyelectrolyte multilayers: cargos films for antibacterial agents

A new antibacterial coating made of poly(L-lysine)/hyaluronic acid (PLL/HA) multilayer films and liposome aggregates loaded with silver ions was designed. Liposomes filled with an AgNO 3 solution were first aggregated by the addition of PLL in solution. The obtained micrometer-sized aggregates were then deposited on a PLL/HA multilayer film, playing the role of a spacer with the support. Finally, HA/PLL/HA capping layers were deposited on top of the architecture to form a composite AgNO 3 coating. Release of encapsulated AgNO 3 from this composite coating was followed and triggered upon temperature increase over the transition temperature of vesicles, found to be equal to 34 degrees C. After determination of the minimal inhibitory concentration (MIC) of AgNO 3 in solution, the antibacterial activity of the AgNO 3 coating was investigated against Escherichia coli. A 4-log reduction in the number of viable E. coli cells was observed after contact for 120 min with a 120 ng/cm (2) AgNO 3 coating. In comparison, no bactericidal activity was found for PLL/HA films previously dipped in an AgNO 3 solution and for PLL/HA films with liposome aggregates containing no AgNO 3 solution. The strong bactericidal effect could be linked to the diffusion of silver ions out of the AgNO 3 coating, leading to an important bactericidal concentration close to the membrane of the bacteria. A simple method to prepare antibacterial coatings loaded with a high and controlled amount of AgNO 3 is therefore proposed. This procedure is far superior to that soaking AgNO 3 or Ag nanoparticles into a coating. In principle, other small bactericidal chemicals like antibiotics could be encapsulated by this method. This study opens a new route to modify surfaces with small solutes that are not permeating phospholipid membranes below the phase transition temperature.