Arylidene imidazothiazoles. Synthesis,structure and benzodiazepine receptor binding

A series of arylidene imidazo[2,1-b]thiazoles was synthesized, in order to investigate the influence of different spatial arrangements of the arylidene substituent towards the bicyclic structure of imidazo[2,1-b]-thiazole on benzodiazepine receptor affinity. 1,2- And 2,3-cyclized derivatives of mono- and di-substituted Z-5-arylidene-2-thiohydantoins were investigated. As an example of E isomers E-5-benzylidene-2,3-dihydroimidazo[2,1-b]thiazol-6(5H)-one was obtained. The spatial arrangement of the arylidene sub stituent toward the bicyclic structure as well as the character of isomers had little influence on the benzo diazepine receptor affinity of the compounds. It seems that the greatest influence on biological activity has the nature and the number of substituents on the phenyl ring. All investigated imidazo[2,1-b]thiazoles were less active than previously described arylidene imidazo[2,1-b]thiazepinones.     

An Improved Synthesis of L-Homohistidine

Bloemhoff - Kerling's method of L-homohistidine synthesis was modified by employing formamidine acetate in liquid ammonia for imidazole ring formation. The improved procedure significantly shortened the synthetic pathway and resulted in enhanced yield.     

Copper- or manganese-doped ZnS quantum dots as fluorescent probes for detecting folic acid in aqueous media

3-Mercaptopropionic acid-capped core/shell ZnS:Cu/ZnS and ZnS:Mn/ZnS doped quantum dots (QDs) prepared through hydrothermal methods exhibit high photoluminescence intensity as well as good photostability. These water-dispersible nanoparticles exhibit high fluorescence sensitivity to folic acid due to the high affinity of the carboxylate groups and nitrogen atoms of folic acid towards the Zn surface atoms of the doped dots. Quenching of the fluorescence intensity of the QDs allows the detection of folic acid concentrations as low as 11 μM, thus affording a very sensitive system for the sensing of this biologically active molecule in aqueous solution. The possible quenching mechanism is discussed.     

The circumference of the square of a connected graph

The celebrated result of Fleischner states that the square of every 2-connected graph is Hamiltonian. We investigate what happens if the graph is just connected. For every n ≥ 3, we determine the smallest length c(n) of a longest cycle in the square of a connected graph of order n and show that c(n) is a logarithmic function in n. Furthermore, for every c ≥ 3, we characterize the connected graphs of largest order whose square contains no cycle of length at least c.     

Characterisation of silica nanoparticles prior to in vitro studies: from primary particles to agglomerates

The size, surface charge and agglomeration state of nanoparticles under physiological conditions are fundamental parameters to be determined prior to their application in toxicological studies. Although silica-based materials are among the most promising candidates for biomedical applications, more systematic studies concerning the characterisation before performing toxicological studies are necessary. This interest is based on the necessity to elucidate the mechanisms affecting its toxicity. We present here TEM, SAXS and SMPS as a combination of methods allowing an accurate determination of single nanoparticle sizes. For the commercial material, Ludox TM50 single particle sizes around 30 nm were found in solution. DLS measurements of single particles are rather affected by polydispersity and particles concentration but this technique is useful to monitor their agglomeration state. Here, the influence of nanoparticle concentration, ionic strength (IS), pH and bath sonication on the agglomeration behaviour of silica particles in solution has been systematically investigated. Moreover, the colloidal stability of silica particles in the presence of BSA has been investigated showing a correlation between silica and protein concentrations and the formation of agglomerates. Finally, the colloidal stability of silica particles in standard cell culture medium has been tested, concluding the necessity of surface modification in order to preserve silica as primary particles in the presence of serum. The results presented here have major implications on toxicity investigations because silica agglomeration will change the probability and uptake mechanisms and thereby may affect toxicity.     

Excitation-wavelength Dependent Fluorescence of Ethyl 5-(4-aminophenyl)-3-amino-2,4-dicyanobenzoate

The excitation wavelength dependence of the steady-state and time-resolved emission spectra of ethyl 5-(4-aminophenyl)-3-amino-2,4-dicyanobenzoate (EAADCy) in tetrahydrofuran (THF) at room temperature has been examined. It is found that the ratio of the fluorescence intensity of the long-wavelength and short-wavelength fluorescence bands strongly depends on the excitation wavelength, whereas the wavelengths of the fluorescence excitation and fluorescence bands maxima are independent on the observation/excitation wavelengths. The dynamic Stokes shift of fluorophore in locally excited (LE) and intramolecular charge transfer (ICT) states has been studied with a time resolution about 30 ps. The difference between Stokes shift in the LE and ICT states was attributed to the solvent response to the large photoinduced dipole moment of EAADCy in the fluorescent charge transfer state. On this base we can state that, the relaxation of the polar solvent molecules around the fluorophore was observed.     

A theoretical model for evaluation of configurational entropy of mixing with respect to shape and size of particles

A general method of evaluation of configurational entropy of a liquid mixture is presented. It is based on a generalized lattice model with no restrictions due to particle shape being introduced. A general formula for the entropy is derived. Achieved results open a way for a rigorous analysis of particle shape effect on mixing process. As an example, a new formula for the entropy of mixing of hard spheres in continuous space is derived which may respect a physical bound for packing ratio. A systematic approach to improve the model accuracy is proposed. The resultant alternative models are discussed in details. A comparison with literature data and the Mansoori-Carnahan-Starling formula is presented. Very good agreement is shown.     

Probing plasmonic nanostructures by photons and electrons

We discuss recent developments for studying plasmonic metal nanostructures. Exploiting photons and electrons opens up new capabilities to probe the complete plasmon spectrum including bright and dark modes and related local optical fields at subnanometer spatial resolution. This comprehensive characterization of plasmonic properties of metal nanostructures provides new basic insight into the fundamental physics of “surface enhanced” spectroscopy in hottest hot spots and enables us to optimize plasmon supported processes and devices.