NanoMORALs — Metal nanoparticles doped with organic molecules

A new class of nanosized metal–organic alloys (MORALs) has been synthesized for the first time. Silver nanoparticles doped with Cu(II) and Fe(III) phthalocyanines were thus synthesized in the presence of sodium dodecyl sulfate (SDS). The resulting materials were characterized by means of XRD, SEM, TEM coupled to energy dispersive X-ray analysis, and thermogravimetric analysis. No leaching of the photoactive dopant species was observed in water or in common organic solvents.

On the mechanism of nitrosoarene-alkyne cycloaddition

The thermal reaction between nitrosoarenes and alkynes produces N-hydroxyindoles as the major products. The mechanism of these novel reactions has been probed using a combination of experimental and computational methods. The reaction of nitrosobenzene (NB) with an excess of phenyl acetylene (PA) is determined to be first order in each reactant in benzene at 75 degrees C. The reaction rates have been determined for reactions between phenyl acetylene with a set of p-substituted nitrosoarenes, 4-X-C(6)H(4)NO, and of 4-O(2)N-C(6)H(4)NO with a set of p-substituted arylalkynes, 4-Y-C(6)H(4)C[triple bond]CH. The former reactions are accelerated by electron-withdrawing X groups (rho = +0.4), while the latter are faster with electron-donating Y groups (rho = -0.9). The kinetic isotope effect for the reaction of C(6)H(5)NO/C(6)D(5)NO with PhC[triple bond]CH is found to be 1.1 (+/-0.1) while that between PhC[triple bond]CH/PhC[triple bond]CD with PhNO is also 1.1 (+/-0.1). The reaction between nitrosobenzene and the radical clock probe cyclopropylacetylene affords 3-cyclopropyl indole in low yield. In addition to 3-carbomethoxy-N-hydroxyindole, the reaction between PA and o-carbomethoxy-nitrosobenzene also affords a tricyclic indole derivative, 3, likely derived from trapping of an intermediate indoline nitrone with PA and subsequent rearrangement. Computational studies of the reaction mechanism were carried out with density functional theory at the (U)B3LYP/6-31+G(d) level. The lowest energy pathway of the reaction of PhNO with alkynes was found to be stepwise; the N-C bond between nitrosoarene and acetylene is formed first, the resulting vinyl diradical undergoes cis-trans isomerization, and then the C-C bond forms. Conjugating substituents Z on the alkyne, Z-C[triple bond]CH, lower the calculated (and observed) activation barrier, Z = -H (19 kcal/mol), -Ph (15.8 kcal/mol), and -C(O)H (13 kcal/mol). The regioselectivity of the reaction, with formation of the 3-substituted indole, was reproduced by the calculations of PhNO + PhC[triple bond]CH; the rate-limiting step for formation of the 2-substituted indole is higher in energy by 11.6 kcal/mol. The effects of -NO(2), -CN, -Cl, -Br, -Me, and -OMe substituents were computed for the reactions of p-X-C(6)H(4)NO with PhC[triple bond]CH and of PhNO and/or p-NO(2)-C(6)H(4)NO with p-Y-C(6)H(4)C[triple bond]CH. The activation energies for the set of p-X-C(6)H(4)NO vary by 4.3 kcal/mol and follow the trend found experimentally, with electron-withdrawing X groups accelerating the reactions. The range of barriers for the p-Y-C(6)H(4)C[triple bond]CH reactions is smaller, about 1.5 and 1.8 kcal/mol in the cases of PhNO and p-NO(2)-PhNO, respectively. In agreement with the experiments, electron-donating Y groups on the alkyne accelerate the reactions with p-NO(2)-C(6)H(4)NO, while both ED and EW groups are predicted to facilitate the reaction. The calculated kinetic isotope effect for the reaction of C(6)H(5)NO/C(6)D(5)NO with PhC[triple bond]CH is negligible (as found experimentally) while that for PhC[triple bond]CH/PhC[triple bond]CD with PhNO (0.7) differs somewhat from the experiment (1.1). Taken together the experimental and computational results point to the operation of a stepwise diradical cycloaddition, with rate-limiting N-C bond formation and rapid C-C connection to form a bicyclic cyclohexadienyl-N-oxyl diradical, followed by fast tautomerization to the N-hydroxyindole product.

Structures from powders: diflorasone diacetate

Diflorasone diacetate, a steroid anti-inflammatory drug (marketed as Diacort or Florone by Pfizer) and used in the treatment of skin disorders, can be prepared as anhydrous form, DD1 (as deposited in the US pharmacopoeia), or as a monohydrated phase, DDW. Heating the DDW form above 90 degrees C, a mixture of DD1 and of a new anhydrous polymorph, DD2 is obtained. Further heating of this mixture, or of pure DD1, up to 230 degrees C (only a few degrees before melting!), generates an elusive anhydrous DD3 polymorph. Their crystal structures, determined uniquely from laboratory powder diffraction data, show the isomorphous character of the DDW and DD1 forms, while the DD2 and DD3 polymorphs crystallize with markedly different unit cells. Crystals of the DD1, DD2 and DDW forms are orthorhombic, P2(1)2(1)2(1), a=29.386(1)A; b=10.4310(9)A, c=8.1422(7)A, V=2495.8(3)A(3) for DD1; a=15.2639(10)A; b=11.7506(7)A, c=13.8931(11)A, V=2491.9(3)A(3) for DD2; a=30.311(2)A; b=10.6150(9)A, c=7.9337(7)A, V=2552.7(4)A(3) for DDW; while the lattice parameters for the monoclinic P2(1)DD3 species are a=11.5276(10)A; b=13.8135(11)A, c=7.8973(7)A, beta=103.053(6) degrees , V=1225.0(2)A(3). These compounds have also been fully characterized by thermo analytical methods, as well by (13)C, (19)F, and (1)H NMR spectroscopy.

Intramolecular Pd(II)-catalyzed cyclization of propargylamides: straightforward synthesis of 5-oxazolecarbaldehydes

Direct synthesis of 2-substituted 5-oxazolecarbaldehydes was performed by intramolecular reaction of propargylamides through treatment with a catalytic amount of Pd(II) salts in the presence of a stoichiometric amount of reoxidant agent. The heterocyclization process was well-tolerated by a wide range of aryl, heteroaryl, and alkyl propargylamides. This protocol constitutes a valuable synthetic pathway to 5-oxazolecarbaldehydes, alternative to the formylation on oxazole rings, often unsatisfactory in term of regioselectivity and yields.

Flexible solar cells

Thin-film flexible photovoltaics are paving the way to low-cost electricity. Organic, inorganic and organic-inorganic solar cells are deposited over flexible substrates by high-throughput (often roll-to-roll printing) technologies to afford lightweight, economic solar modules that can be integrated into, not installed on, various surfaces. Current conversion efficiencies under standard conditions are in the 3-15 % range, but in real applications the overall productivity is high. These new photovoltaic technologies are ready to provide cheap, clean electricity to the 2 billion people who lack access to the grid as well as to energy-eager companies and families in the developed world facing the increasing costs of electricity generated using fossil fuel resources. This Review focuses on recent achievements in the area of flexible solar cells, highlights the principles behind the main technologies, and discusses future challenges in this area.

A degradation product of halobetasol propionate: characterization and structure

Degradation of halobetasol propionate was observed in the presence of bases. A single cyclization product was isolated and fully characterized by MS, NMR and X-ray crystallography.

Novel functionalized pyridine-containing DTPA-like ligand. Synthesis, computational studies and characterization of the corresponding GdIII complex

A novel pyridine-containing DTPA-like ligand, carrying additional hydroxymethyl groups on the pyridine side-arms, was synthesized in 5 steps. The corresponding Gd(III) complex, potentially useful as an MRI contrast agent, was prepared and characterized in detail by relaxometric methods and its structure modeled by computational methods.

Photocatalysis: a promising route for 21st century organic chemistry

One of the main goals of 21st century chemistry is to replace environmentally hazardous processes with energy efficient routes allowing to totally avoid the use and production of harmful chemicals and to maximise the quantity of raw material that ends up in the final product. Selective photocatalytic conversions will play a major role in this evolution and this account shows how photocatalysis is offering an alternative green route for the production of organics.