Theoretical design of dendrimeric fractal patterns for the encapsulation of a family of drugs: salicylanilides

Four dendrimeric fragments (FPs) were designed to encapsulate a family of drugs known as salicylanilides (importantly acaricides/anthelminthics), mainly by H-bonding. The experimental system: PAMAM-DBNP (2,6-dibromo-4-nitrophenol) was also calculated as a reference. The efficiency of encapsulation is related to the presence of functional groups like amide and alcohol, the flexibility of the aliphatic chains, and efficient pre-organization before the encapsulation. All the geometry optimizations were carried out at DFT/LAV3P^∗ level of theory. Two hybrid functionals were tested: B3LYP and BHandHLYP. The last one shows improved performance in describing close contacts as well as better agreement with experimental observations for the complex PAMAM-BDNP.     

Preparation of Nd:YAG nanopowder in a confined environment

Nanopowder of yttrium aluminum garnet (YAG, Y3Al5O12) doped with neodymium ions (Nd:YAG) was prepared in the water/cetyltrimethylammonium bromide/1-butanol/n-heptane system. Aluminum, yttrium, and neodymium nitrates were used as starting materials, and ammonia was used as a precipitating agent. Coprecipitate hydroxide precursors where thermally treated at 900 degrees C to achieve the garnet phase. The starting system with and without reactants was characterized by means of the small-angle neutron scattering technique. The system, without reactants, is constituted by a bicontinuous structure laying near the borderline with the lamellar phase region. The introduction of nitrates stabilizes the bicontinuous structure, while the presence of ammonia induces a transformation from the bicontinuous phase to a lamellar phase. Nd:YAG nanopowder was characterized by wide-angle X-ray scattering, transmission electron microscopy, gas adsorption, and photoluminescence spectroscopy. By comparison with a sample prepared by the conventional coprecipitation method, the obtained Nd:YAG nanopowder is constituted by smaller crystalline nanoparticles showing a lower tendency to agglomerate. In addition, the nanoparticles present a well-defined spherical shape. Photoluminescence spectroscopy confirms that the doping Nd3+ ions substitute Y3+ ions in the YAG crystalline lattice. The Nd3+ lifetime value, obtained from the luminescence decay curves, was 286 +/- 10 micros, higher than the single-crystal value (255 micros) and much higher than the nanopowder value obtained by the conventional coprecipitation method (75 micros).     

Bis(heterocumulenes) derived from the 1,4-diphenyl-1,3-butadiyne framework. Synthesis of three new classes of axially chiral biheteroaryls

Bis(ketenimines) and bis(carbodiimides) derived from 1,4-bis(2-aminophenyl)-1,3-butadiynes via two independent biradical cyclizations provided, respectively, axially chiral bis(benzocarbazoles) and bis(quinindolines). Mixed biheteroaryls, consisting of benzocarbazole and quinindoline units, have been also prepared by a slightly modified strategy.     

Brønsted acid catalyzed propargylation of 1,3-dicarbonyl derivatives. Synthesis of tetrasubstituted furans

Simple Br?nsted acids such as p-toluenesulfonic acid monohydrate (PTS) efficiently catalyze a direct substitution of the hydroxyl group in propargylic alcohols with 1,3-dicarbonyl compounds. Selective propargylation or allenylation is obtained depending on the nature of the alkynol. Reactions can be performed in air in undried solvents with water being the only side product of the process. By applying this reaction as the key step, a range of interesting polysubstituted furans can easily be synthesized in a one-pot procedure. [reaction: see text].     

EPR STUDIES OF THE BISTABILITY IN CF3CNSSN

Condensation of CF₃C(═NH)NH₂ with SCl₂ yielded the dithiadiazolylium salt, [CF₃CNSSN]Cl which could be reduced to [CF₃CNSSN]₂ with Zn/Cu couple in SO₂. [CF₃CNSSN]₂ is a diamagnetic dimer in the solid state but melts at 308 K to give a paramagnetic liquid. On cooling the radical enters a metastable state before immediately re-solidifying below 295 K. The thermal hysteresis was probed by EPR spectroscopy. Metastable samples spontaneously solidified after an induction period, typically between ca. 5 and 30 min, consistent with the variable time necessary to form a seed crystal from which crystallization can occur.     

Generation of chemisorbed benzyl radicals on silica nanoparticles

Functionalized silica nanoparticles (NP) were obtained by esterification of the silanol groups of fumed silica nanoparticles with benzyl alcohol. These particles were characterized by Fourier transform infrared spectroscopy, ¹³C and ²⁹Si NMR spectroscopy, thermogravimetry, total organic carbon, Brunauer–Emmett–Teller analysis, UV-visible spectroscopy, and transmission electron microscopy. NP suspensions in water/acetonitrile mixtures were used as quenchers of benzophenone (BP) phosphorescence in time-resolved experiments at the excitation wavelength of 266 nm. The phosphorescence signals obtained in the presence of the nanoparticles were fitted to biexponential decays. Both decays were accelerated in the presence of increasing amounts of NP. A model, including the reversible adsorption of BP on the NP, which was supported by computer simulations accounts for the observed results. Laser flash-photolysis experiments with excitation at 266 nm of NP suspensions in water/acetonitrile in the presence of BP generated benzyl radicals that were attached to the silica surface. These radicals were detected at their absorption maxima (320 nm) by transient optical techniques.     

A new and efficient synthetic approach to dichlorofluoflavines. Study of the stability of isomeric fluoflavines by HF and B3LYP procedures

The first method for the synthesis of 7,10-dichloro-5,12-dihydroquinoxalino[2,3-b]quinoxalines is reported. Treatment of 3,3,6,6-tetrachloro-1,2-cyclohexanedione with diaminomaleonitrile leads to 5,8-dichloro-2,3-dicyanoquinoxaline in near quantitative yields. This compound has been found to be an excellent synthetic equivalent of unavailable 2,3,5,8-tetrachloroquinoxaline. It reacts with o-phenylenediamines providing the corresponding dichlorofluoflavines in fair to high yields. These compounds have been identified by NMR spectroscopy and X-ray crystallography. Molecular structures, chemical hardness, ΔG₂₉₈^≠-values, and relative stabilities of all possible isomeric products have been calculated by HF and B3LYP density functional theory methods.     

A new and efficient approach to pyrazolines. First synthesis of 3-aryl-5-dichloromethyl-2-pyrazolines

An efficient synthetic method for dichloromethylated pyrazolines has been established. 1-Aryl-4,4-dichlorobut-3-en-1-ones 4 were efficiently prepared by treatment of acetophenones with anhydrous chloral, followed by dehydration and reductive dechlorination. Compounds 4 reacted with hydrazine hydrate and methylhydrazine to give the respective 5-dichloromethyl-2-pyrazolines in high to quantitative yields. The molecular structure of 5-dichoromethyl-1-methyl-3-(2-naphthyl)-2-pyrazoline has been determined by X-ray crystallography.