Luminescence Properties of Eu3+ Complexes of Tripode and Tetrapode Ligands Containing 2,2′-Bipyridine Units

The Eu³⁺ complexes of the tripode and tetrapode ligands 1 and 2 , respectively, containing 2,2′-bipyridine coordinating units have been prepared. The UV absorption and luminescence spectra, lifetimes, and quantum yields have been measured under a variety of experimental conditions. The contributions of different paths to the decay of the luminescent excited state are evaluated, and the structures of the complexes are discussed on the basis of spectroscopic and photophysical data.     

Kinetics of base hydrolysis ofO-bonded pentaammineglycinatocobalt(III) and pentaammine-β-alaninatocobalt(III) ions

Transition Metal Chemistry - The kinetics and mechanism of the base hydrolysis ofO-bonded pentaammineglycinatocobalt(III) and pentaammine-β-alaninatocobalt(III) ions have been studied...     

Unrestricted Hartree-Fock spin density distributions in nitro aromatic radical anions

The spin density distributions in the radical anions of nitrobenzene and some para substituted nitrobenzenes are calculated using the unrestricted Hatree-Fock formalism of Amos and Snyder. A parameter scheme which gives satisfactory account of the electronic transitions and molecular ionisation potentials of substituted benzenes (nitrobenzene, toluene, aniline, benzaldehyde and benzonitrile) is used for spin density calculations of the nitro radical anions. The importance of spin densities on neighbouring atoms on the hyperfine splitting of nitrogen atom is discussed. It is seen that although Karplus-Fraenkel theory gives a better estimate of¹⁴N splitting constant, the simple McConnell-type of relation is approximately valid for the nitro group-nitrogen. The--parameters for use with unrestricted Hartree-Fock spin densities for the prediction of nitrogen hyperfine couplings in nitro, amino and cyano groups are summarised.

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Zusammenfassung Die Spindichteverteilungen in den Radikalanionen des Nitrobenzols und einiger parasubstituierter Nitrobenzole werden mit Hilfe des UHF-Formalismus von Amos und Snyder berechnet. Zur Ermittlung der Spindichte der nitroaromatischen Radikalanionen wird ein Parameterschema benutzt, das zufriedenstellende Darstellung der Elektronenübergänge und der molekularen Ionisationspotentiale von substituierten Benzolen (Nitrobenzol, Toluol, Anilin, Benzaldehyd, Benzonitril) gestattet. Der Einfluß der Spins von benachbarten Atomen auf die Hyperfeinaufspaltung des Stickstoffatoms wird diskutiert. Es zeigt sich, daß zur näherungsweisen Beschreibung des Stickstoffs der Nitrogruppe eine einfache Gleichung des McCornell-Typs ausreicht, wenn auch die Karplus-Fraenkel-Theorie eine bessere Abschätzung der¹⁴N-Aufspaltungskonstanten ermöglicht. Die --Parameter, die zur Voraussage der Stickstoff-Hyperfeinkopplung in Nitro-, Amino- und Cyanogruppen mit Hilfe der UHF-Spindichten erforderlich sind, werden zusammengestellt.

     

Thermodynamic model for the size-dependent melting of prism-shaped nanoparticles

We report on the size-dependent melting of prism-shaped nanoparticles based on thermodynamic model and applied to understand the melting of prism-shaped indium nanoparticles. It is shown here that the bulk melting temperature cannot be extrapolated from the nanoscale and the extrapolated value will always be lower than the bulk melting temperature as has been observed experimentally.     

Studies on ion association. Calorimetric study of the formation of monoazido complexes of Ni(II), Zn(II) and Cd(II)

From rehydration experiments the hydrates Ba(OH)₂ · 8 H₂O, Ba(OH)₂ · 3 H₂O β-Ba(OH)₂, · 1 H₂O, and γ-Ba(OH)₂ · 1 H₂O have been found in the system Ba(OH)₂-H₂O. Thermoanalytical measurements (DTA, TG, DTG, high temperature X-ray diffraction, high temperature Raman scattering) on these hydrates are reported. Thermal decomposition of Ba(OH)₂ · 8 H₂O and Ba(OH)₂ · 3 H₂O always results in the formation of β-Ba(OH)₂ · 1 H₂O, the stable form of the monohydrates at ambient temperature. Dehydration of β- and γ-Ba(OH)₂ · 1 H₂O, both of which form anhydrous β-Ba(OH)₂ as the first product of decomposition, starts at 105 and 115°C, respectively. Single crystals of Ba(OH)₂ · 3 H₂O and γ-Ba(OH)₂ · 1 H₂O were prepared from Ba(OH)₂ · 8 H₂O meltings and from ethanolic solutions of Ba(OH)₂ , respectively. The crystal data are: Ba(OH)₂ · 3 H₂O (orthorhombic, Pnma): a = 764.0(2), b = 1140,3(5), c = 596.5(1) pm, Z = 4; γ-Ba(OH)₂ · 1 H₂O (monoclinic, P2₁/m or P2₁): a = 704.9(2), b = 418.4(1), c = 633.3(1) pm, β = 111.45(2)°, Z = 2.     

Effect of oxygen partial pressure on the growth of zinc micro and nanostructures

Zinc micro and nanostructures were synthesized in vacuum by condensing evaporated zinc on Si substrate at different gas pressures. The morphology of the grown Zn structures was found to be dependent on the oxygen partial pressure. Depending on oxygen partial pressure it varied from two-dimensional microdisks to one-dimensional nanowire. The morphology and structural properties of the grown micro and nanostructures were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Transmission electron microscopy (TEM) studies on the grown Zn nanowires have shown that they exhibit core/shell-like structures, where a thin ZnO layer forms the shell. A possible growth mechanism behind the formation of different micro and nanostructures has been proposed. In addition, we have synthesized ZnO nanocanal-like structures by annealing Zn nanowires in vacuum at 350 °C for 30 min.     

Fabrication of Luminescent CdS Nanoparticles on Short‐Peptide‐Based Hydrogel Nanofibers: Tuning of Optoelectronic Properties

The pH‐induced self‐assembly of three synthetic tripeptides in water medium is used to immobilize luminescent CdS nanoparticles. These peptides form a nanofibrillar network structure upon gelation in aqueous medium at basic pH values (pH 11.0–13.0), and the fabrication of CdS nanoparticles on the gel nanofiber confers the luminescent property to these gels. Atomic force microscopy, field‐emission scanning electron microscopy, and high‐resolution transmission electron microscopy clearly reveal the presence of CdS nanoparticles in a well‐defined array on the gel nanofibers. This is a convenient way to make organic nanofiber–inorganic nanoparticle hybrid nanocomposite systems. The size of the CdS nanoparticles remains almost same before and after deposition on the gel nanofiber. Photoluminescence (PL) measurement of the CdS nanoparticles upon deposition on the gel nanofibers shows a significant blue shift in the emission spectrum of the nanoparticles, and there is a considerable change in the PL gap energy of the CdS nanoparticles after immobilization on different gel nanofibrils. This finding suggests that the optoelectronic properties of CdS nanoparticles can be tuned upon deposition on gel nanofibers without changing the size of the nanoparticles.     

Polar networks control oligomeric assembly in membranes

Polar interactions have a profound influence on membrane stability and structure. A membrane-solubilized GCN4 peptide, MS-1, is used to study the impact of polar networks. Amide functionalities from amino acid side chains have been shown to promote peptide oligomerization, but lacked specificity. Herein, the hydrogen bonding interactions of an Asn side chain are coupled with the hydroxyl of Ser or Thr to generate a polar network. Analytical ultracentrifugation and fluorescence resonance energy transfer studies indicate that a trimer assembly is established where each membrane-embedded hydrogen bond contributes 1 kcal mol-1.