Electronic structural dependence of the photophysical properties of fluorescent heteroditopic ligands - implications in designing molecular fluorescent indicators

Two fluorescent heteroditopic ligands (2a and 2b) for zinc ion were synthesized and studied. The efficiencies of two photophysical processes, intramolecular charge transfer (ICT) and photoinduced electron transfer (PET), determine the magnitudes of emission bathochromic shift and enhancement, respectively, when a heteroditopic ligand forms mono- or dizinc complexes. The electron-rich 2b is characterized by a high degree of ICT in the excited state with little propensity for PET, which is manifested in a large bathochromic shift of emission upon Zn(2+) coordination without enhancement in fluorescence quantum yield. The electron-poor 2a displays the opposite photophysical consequence where Zn(2+) binding results in greatly enhanced emission without significant spectral shift. The electronic structural effects on the relative efficiencies of ICT and PET in 2a and 2b as well as the impact of Zn(2+)-coordination are probed using experimental and computational approaches. This study reveals that the delicate balance between various photophysical pathways (e.g. ICT and PET) engineered in a heteroditopic ligand is sensitively dependent on the electronic structure of the ligand, i.e. whether the fluorophore is electron-rich or poor, whether it possesses a donor-acceptor type of structure, and where the metal binding occurs.     

Self-assembly of zwitterionic molecules on a Au(23 23 21) surface at low temperature

The adsorption of zwitterionic (E) 4-methoxy-4′-(3-n-sulfonatopropyl)stilbazolium (MSPS) molecules on the stepped vicinal Au(23 23 21) surface was studied by scanning tunneling microscopy (STM) at low temperature as a function of the molecular coverage. At the sub-half monolayer, a supramolecular network based on MSPS is preferentially adsorbed onto face-centered cubic stacking regions. At the monolayer, a complete periodic supramolecular film is obtained.     

New tungstate fluorophosphate glasses

A new class of tungstate fluorophosphate glasses was identified in the NaPO₃-BaF₂-WO₃ ternary system. The variation of several physical properties was determined with respect to chemical composition. Characteristic temperatures, density and refractive index increase as tungsten oxide content increases. The optical transmission range and specially the energy bandgap depend of the WO₃ amount. No crystallization could be observed for the most WO₃ concentrated vitreous samples (?20% molar). Color and optical properties of the glasses depend of the melting time because of the presence of reduced tungsten species like W⁵⁺ and W⁴⁺. In addition, photodarkening is observed in tungsten rich glass samples under UV laser illumination and this phenomenon can be reversible by heat treatment near the glass transition temperature.     

Room‐Temperature Electronic Template Effect of the SmSi(111)‐8×2 Interface for Self‐Alignment of Organic Molecules

This work describes an innovative concept for the development of organized molecular systems based on the template effect of the pre‐structured semi‐conductive SmSi(111) interface. This substrate is selected because Sm deposition in the submonolayer range leads to a 8×2‐reconstruction, which is a well‐defined one‐dimensional semi‐metallic structure. Adsorption of aromatic molecules [1,4‐di‐(9‐ethynyltriptycenyl)‐benzene] on SmSi(111)‐ 8×2 and Si(111)‐7×7 interfaces is investigated by scanning tunneling microscopy (STM) at room temperature. Density functional theory (DFT) and semi‐empirical (ASED+) calculations define the nature of the molecular adsorption sites of the target molecule on SmSi as well as their self‐alignment on this interface. Experimental data and theoretical results are in good agreement.     

Aluminoxane–epoxi–siloxane hybrids waveguides

Boehmite–GPTS (GPTS-glycidoxypropyltrimethoxysilane) hybrids (BGS) have been prepared by the sol–gel methodology. Spectroscopic properties and structural features have been evaluated from the initial sols to xerogels as a function of composition. Eu³⁺-containing BGS samples were also prepared, and the Eu^{3+ 5}D₀ state emission quantum efficiency was observed to depend on the boehmite–siloxane interactions. Boehmite–siloxane heterocondensation was inferred from vibrational spectroscopy and ¹³C, ²⁹Si, and ²⁷Al nuclear magnetic resonance results. Unreacted epoxi groups could be identified in the final material being an important characteristic for the future applications. Good optical quality and mechanical properties lead to the preparation of thin films deposited on glass substrates by dip and spin-coating. Refractive index could be tuned by the relative boehmite and GPTS content. Waveguide properties have also been studied by m-lines spectroscopy and guided modes together with attenuation measurements suggest potential application of the prepared films in integrated optics.     

Spectroscopic study and local coordination of polyphosphate colloidal systems

The interaction between metaphosphate chains and the metal ions Ca2+ and Eu3+ has been studied in water by Eu3+ luminescence, infrared absorption, and 31P NMR spectroscopy. Two main families of sites could be identified for the metal ions in the aqueous polyphosphate colloidal systems: (1) cagelike sites provided by the polyphosphate chain and (2) a family which arises following saturation of cagelike sites. Occupation of this second family leads to supramolecular interactions between polyphosphate chains and the consequent destabilization of the colloidal system. In the polyphosphate-Ca2+ system, this destabilization appears as a coacervation process. Equilibrium existing between colloidal species as a function of the compositions could be reasoned based on the spectroscopic measurements. The determination of coordination numbers and the correlation of the results with the observation of coacervates show that Eu3+ luminescence properties can be used to probe in a unique way the coacervation process.     

Study of the effect of mechanical working on the rheological properties of some potential artificial lubricants for human joints

Conclusion The effect of mechanical working on polyethylene oxide suggests that, although this substance fulfils many of the criteria for an artificial lubricant in human joints, it is unlikely to be successful in vivo over a prolonged period. This is probably due to the weak linkages present. The simplicity of the structure might have led one to think that it would withstand mechanical degradation more satisfactorily than a more complex molecule, but the experiments demonstrate that this is not so. Sodium carboxymethyl cellulose, on the other hand, shows a high degree of resistance to mechanical degradation and a successful artificial lubricant is likely to be closer to this configuration in which bonds are less exposed.

---

Zusammenfassung Die Bio-Ingenieur-Gruppe für das Studium von menschlichen Gelenken an der Universität Leeds hat angedeutet, daß Osteoarthrosis in leicht angegriffenen lasttragenden Gelenken mit künstlichen Schmiermitteln erleichtert werden könnte. Wenn das künstliche Schmiermittel erfolgreich die Schmierfunktion übernehmen soll, die die normale Synovialflüssigkeit erfüllt, dann sollte es ähnliche Theologische Eigenschaften aufweisen. In dieser Veröffentlichung werden die Ergebnisse einer Studie über die Theologischen Eigenschaften einiger potentieller künstlicher Schmiermittel aufgezeichnet.Einige Polymerlösungen zeigen insgesamt ein rheologisches Verhalten, das der Synovialflüssigkeit sehr ähnlich ist; der Einfluß der Konzentration, der Schubbelastung und der Arbeitsmechanik auf dieses Verhalten wird beobachtet werden. Die Viskosität der Polymerlösung wird unter verschiedenen Bedingungen mit einemFerranti-Shirley-Viskosimeter (Konus auf Platte)gemessen. Das Schmiermittel wurde auch in einem besonderen Hüftgelenk-Simulator getestet, der für Belastungen und Geschwindigkeiten, ähnlich der einer natürlichen Gehbewegung, programmiert war. Es wird gezeigt, daß die Viskosität abnimmt und daraufhin sich teilweise wieder erholt.

---

---

Paper presented to the British Society of Rheology Conference on Rheology in Medicine and Pharmacy, London, April 14–15, 1970.     

Dual-seeded dispersion polymerization: Effect of different polymerization conditions on the shape of the produced particles

Dual-seeded dispersion polymerization (DSDP) of 2-ethylhexyl methacrylate with polystyrene (PS) and poly(methyl methacrylate) (PMMA) seed beads in the presence of saturated hydrocarbon droplets followed by evaporation of the hydrocarbon was studied. The effect of various polymerization conditions including initiator type and content, stabilizer type and concentration, and different hydrocarbon’s content on the shape of the obtained particles was investigated. The increase of concentration of 2,2'-azobis(isobutyronitrile) (AIBN) had no effect on the shape of the produced almond-shell-like PS particles, although it contributes in the formation of associated composite particles along with larger poly(2-ethylhexyl methacrylate) (PEHMA) beads produced by secondary nucleation. The experimental results showed that other initiators led to the formation of stable golf-ball-like PMMA particles as well as PS ones with symmetric shape. The type of stabilizer did not affect the shape of the particles. This observation suggests that unique almond-shelllike PS particles can be produced through a stabilizer-free DSDP process. The lowering of the concentration of hydrocarbons with long alkyl chains yielded stable disc-like PMMA particles. The formation of functional almond-shell-like particles by using light hydrocarbons was another interesting finding of this research.     

Scrap Tires Pyrolysis: Product Yields,Properties and Chemical Compositions of Pyrolytic Oil

This investigation involves an experimental study on the pyrolysis of scrap tires under different operating conditions such as feedstock size and pyrolysis temperature by highlighting the properties of the whole liquid products generated during each thermal degradation process. The complete conversion temperature for the pyrolysis of used tires was close to 500?550°C. The characteristics of liquid fraction were determined by elemental analysis, chromatographic and spectroscopic techniques and distillation data. All the obtained atomic ratios are around 1,4 which is significant that such pyrolytic liquids are a mixture of aliphatic and aromatic compounds derived from polymeric materials. Analysis of the pyrolytic oil (pyro-oil) by chromatographic analysis showed that it was a complex mixture of organic compounds C₅?C₂₆, aromatics and a large proportion of light hydrocarbons that can be used as liquid fuels. Furthermore, the comparison distillation data indicates that more than 40% of such pyrolytic oil fraction with the boiling point range between 180?360°C is specified for diesel. It is noted that the viscosity decreases obviously from 4.87 to 1.79 with the increase in temperature.