Unusual photobehaviour of crystalline 7-methoxy-4-methylcoumarin

7-Methoxy-4-methylcoumarin undergoes a solid-state photo [2 + 2] cycloaddition upon UV irradiation to yield two photodimers. The formation of the minor product appears to be a direct consequence of the formation of the topochemically controlled dimer.

Isomerisation of 4-aryl-4-methylhex-5-en-2-ones to 5-aryl-4-methylhex-5-en-2-ones by an intramolecular ene-retro ene reaction sequence

Acid-catalysed thermal rearrangement of 4-aryl-4-methylhex-5-en-2-ones (products of the Claisen rearrangement of beta-methylcinnamyl alcohols and 2-methoxypropene) to isomeric 5-aryl-4-methylhex-5-en-2-ones via an intramolecular ene reaction of the enol tautomer followed by a retro ene reaction of the resultant acetylcyclopropane is described. Formation of the known diketone 13 via the ozonolysis of the rearrangement product 10, confirmed the structures of the rearranged enones, whereas formation of the enone 15 containing an extra methyl group on the styrene double bond confirmed the proposed mechanism. Finally, the rearrangement has been extended to the formal synthesis of beta-cuparenone 20 via the enones 22 and 23.

Proton NMR spectral studies on N-(4-methylphenyl)-2- and 3-pyridinecarboxamides

The H-1 NMR spectra of N-(4-methylphenyl)-2-pyridinecarboxamide and N-(4-methyl-phenyl)-3-pyridine carboxamide in CDCl3 and (CD3)(2)CO have been analysed with the help of the COSY spectra. Accurate H-1 chemical shifts and coupling constants have been obtained from the simulated spectra. From H-1 NMR and Nuclear Overhauser Enhancement (NOE) measurements the molecular conformations are inferred. The pyridyl ring is apparently coplanar with the amide group while the 3-pyridyl ring is nearly perpendicular to the amide plane so that the amide proton is nearer to the 2-pyridyl proton H2 than to H4. The orientation of the 4-methylphenyl group could not be determined.

Synthesis, Structures, and Magnetic Behavior of a Series of Copper(II) Azide Polymers of Cu-4 Building Clusters and Isolation of a New Hemiaminal Ether as the Metal Complex

Four new neutral copper azido polymers, Cu-4(N-3)(8)(L-1)(2)](n) (1), Cu-4(N-3)(8)(L-2)(2)](n) (2), Cu-4(N-3)(8)(L-3)(2)](n) (3), and Cu-9(N-3)(18)(L-4)(4)](n) (4) L1-4 are formed in situ by reacting pyridine-2-carboxaldehyde with 22-(methylamino)ethyl]pyridine (mapy, L-1), N,N-dimethylethylenediamine (N,N-dmen, L-2), N,N-diethylethylenediamine (N,N-deen, L-3), and N,N,2,2-tetramethylpropanediamine (N,N,2,2-tmpn, L-4)], have been synthesized by using 0.5 mol equiv of the chelating tridentate ligands with Cu-(NO3)(2)center dot 3H(2)O and an excess of NaN3. Single-crystal X-ray structures show that the basic unit of these complexes, especially 1-3, contains very similar Cu-4(II) building blocks. The overall structure of 3 is two-dimensional, while the other three complexes are one-dimensional in nature. Complex 1 represents a unique example containing hemiaminal ether arrested by copper(R). Complexes 1 and 2 have a rare bridging azido pathway: both end-on and end-to-end bridging azides between a pair of Cu-II centers. Cryomagnetic susceptibility measurements over a wide range of temperature exhibit dominant ferromagnetic behavior in all four complexes. Density functional theory calculations (B3LYP functional) have been performed on complexes 1-3 to provide a qualitative theoretical interpretation of their overall ferromagnetic behavior.

New La2CuO4 derivatives La(2-2x)Sr(2x)Cu(1-x)M(x)O(4) (M=Ti, Mn, Fe, or Ru): A study of linear Cu-O-M electronic interaction in two dimensions

Oxides of the general formula La2-2xSr2xCu1-xII,M(x)(IV)O(4) (M = Ti, Mn, Fe, or Ru), crystallizing in the tetragonal K,NIF, structure, have been synthesized. For M=Ti, only the x=0,5 member could be prepared, while for M=Mn and Fe, the composition range is 0 Cu(III)-O-Fe(III) valence degeneracy. Increasing the strontium content at the expense of lanthanum in La2-2xSr2xCu1-xFexO4 for x less than or equal to 0.20 renders the samples metallic but not superconducting. (C) 1997 Academic Press.

Oxidation of aqueous sulphur dioxide catalysed by poly-4-vinylpyridine-Cu(II) complex .2. Combined homogeneous and heterogeneous phase oxidation

Aqueous phase oxidation of sulphur dioxide at low concentrations catalysed by a PVP-Cu complex in the solid phase and dissolved Cu(II) in the liquid phase is studied in a rotating catalyst basket reactor (RCBR). The equilibrium adsorption of Cu(II) and S(VI) on PVP particles is found to be of the Langmuir-type. The diffusional effects of S(IV) species in PVP-Cu resin are found to be insignificant whereas that of product S(VI) are found to be significant. The intraparticle diffusivity of S(VI) is obtained from independent tracer experiments. In the oxidation reaction HSO3- is the reactive species. Both the S(IV) species in the solution, namely SO2(aq) and HSO3- get adsorbed onto the active PVP-Cu sites of the catalyst, but only HSO3- undergoes oxidation. A kinetic mechanism is proposed based on this feature which shows that SO2(aq) has a deactivating effect on the catalyst. A rate model is developed for the three-phase reaction system incorporating these factors along with the effect of concentration of H2SO4 on the solubility of SO2 in the dilute aqueous solutions of Cu(II). Transient oxidation experiments are conducted at different conditions of concentration of SO2 and O-2 in the gas phase and catalyst concentration, and the rate parameters are estimated from the data. The observed and calculated profiles are in very good agreement. This confirms the deactivating effect of nonreactive SO2(aq) on the heterogeneous catalysis.

Synthesis and biological evaluation of novel 2-aralkyl-5-substituted-6-(4 `-fluorophenyl)-imidazo2,1-b]1,3,4]thiadiazole derivatives as potent anticancer agents

Levamisole, the imidazo2,1-b]thiazole derivative has been reported as a potential antitumor agent. In the present study, we synthesized, characterized and evaluated biological activity of its novel analogues with substitution in the aralkyl group and on imidazothiadiazole molecules with same chemical backbone but different side chains namely 2-aralkyl-6-(4'-fluorophenyl)-imidazo2,1-b]1,3,4]thiadiazoles (SCR1), 2-aralkyl-5-bromo-6-(4'-fluorophenyl)-imidazo2,1-b]1,3,4]-thiadiaz oles (SCR2), 2-aralkyl-5-formyl-6-(4'-fluorophenyl)-imidazo2,1-b]1,3,4]-thiadia zoles (SCR3) and 2-aralkyl-5-thiocyanato-6-(4'-fluorophenyl)-imidazo2,1-b]1,3,4]-th iadiazoles (SCR4) on leukemia cells. The cytotoxic studies showed that 3a, 4a, and 4c exhibited strong cytotoxicity while others had moderate cytotoxicity. Among these we chose 4a (IC50, 8 mu M) for understanding its mechanism of cytotoxicity. FACS analysis in conjunction with mitochondrial membrane potential and DNA fragmentation studies indicated that 4a induced apoptosis without cell cycle arrest suggesting that it could be used as a potential chemotherapeutic agent. (C) 2011 Elsevier Masson SAS. All rights reserved.

Bis{2-4-(methylsulfanyl)phenyl]-1H-benzimidazol-3-ium} tetrabromidocuprate(II) dihydrate

The asymmetric unit of the title compound, (C14H13N2S)(2)CuBr4]center dot 2H(2)O, contains two cations, one anion and two solvent water molecules that are connected via O-H center dot center dot center dot Br, N-H center dot center dot center dot Br and N-H center dot center dot center dot O hydrogen bonds into a two-dimensional polymeric structure. The cations are arranged in a head-to-tail fashion and form stacks along 100]. The central Cu-II atom of the anion is in a distorted tetrahedral environment.

Stereospecific solid-state NaBH4-promoted reduction of 1-methylpentacyclo[5.4.0.0(2,6).0(3,10).0(5,9)]undecane-8,11-dione

NaBH4 reduction of a cage dione proceeds in a stereospecific fashion to give the endo,endo-diol. This reactivity is related to the crystal structure.

A[Bi3Ti4O13] and A[Bi3PbTi5O16] (A = K, Cs): New n=4 and n=5 members of the layered perovskite series, A[A ' n-1B nO3n+1], and their hydrates

We describe the synthesis and structural characterization of new layered bismuth titanates, A[Bi3Ti4O13] and A[Bi3PbTi5O16]for A = K, Cs, corresponding to n = 4 and 5 members of the Dion-Jacobson series of layered perovskites of the general formula, A[A'n-1BnO3n+1]. These materials have been prepared by solid state reaction of the constituents containing excess alkali, which is required to suppress the formation of competitive Aurivillius phases. Unlike the isostructural niobates and niobium titanates of the same series, the new phases reported here are spontaneously hydrated-a feature which could make them potentially useful as photocatalysts for water splitting reaction. On hydration of the potassium compounds, the c axis expands by ca. 2 Angstrom and loses its doubling [for example, the tetragonal lattice parameters of K[Bi3Ti4O13] and its dihydrate are respectively a = 3900(1)Angstrom c 37.57(2) Angstrom; a 3.885(1) Angstrom, c = 20.82(4) Angstrom]; surprisingly, the cesium analogues do not show a similar change on hydration.

Local environmental structures of Mo in the superionic conducting glass (AgI)(0.6)(Ag2MoO4)(0.4) by anomalous X-ray scattering

The anomalous X-ray scattering (AXS) method using Mo K absorption edges has been employed for obtaining the local structural information of superionic conducting glass having the composition (AgI)(0.6)(Ag2MoO4)(0.4). The possible atomic arrangements in the near-neighbor region of this glass were estimated by coupling the results with the least-squares variational analysis so as to reproduce the differential intensity profile for Mo as well as the ordinary scattering profile. The coordination number of oxygen around Mo is found to be about 4 at the distance of 0.180 mn. This implies that the most probable structural entity in the glass is the MoO4 tetrahedral unit which has been proposed based on infrared spectroscopy. The value of the coordination number of I- around Ag+ is estimated as 4.4 at 0.287 nm, suggesting an arrangement similar to that of crystalline or molten AgI.

Halogen Bonding in 2,5-Dichloro-1,4-benzoquinone: Insights from Experimental and Theoretical Charge Density Analysis

Experimental charge density distribution in 2, 5-dichloro-1, 4-benzoquinone has been carried out using high resolution X-ray diffraction data at 90 K to quantitatively evaluate the nature of C-Cl center dot center dot center dot O=C halogen bond in molecular crystals. Additionally, the halogen bond is studied from geometrical point of view and the same has been visualized using Hirshfeld surface analysis. The obtained results from experimental charge density analysis are compared with periodic quantum calculations using B3LYP 6-31G(d,p) level of theory. The topological values at bond critical point, three-dimensional static deformation density features and electrostatic potential isosurfaces unequivocally establish the attractive nature of C-Cl center dot center dot center dot O=C halogen bond in crystalline lattice.

Modulation of lifetimes and diastereomeric discrimination in triplet-excited substituted butane-1,4-diones through intramolecular charge-transfer quenching

Triplet lifetimes have been determined for the diastereomers of a broad set of butane-l,4-dione derivatives (1-3). A remarkable dependence of lifetimes on conformational preferences is revealed in that the lifetimes are shorter for the meso diastereomers of 1-3 than those for the racemic ones. The intramolecular beta-phenyl quenching is promoted in the case of meso diastereomers by virtue of the gauche relationship between the excited carbonyl group and the beta-aryl ring, while a distal arrangement in the lowest energy conformation (H-anti) in racemic diastereomers prevents such a deactivation. The involvement of charge transfer in the intramolecular beta-phenyl quenching is suggested by the correlation of the triplet lifetimes of the meso diastereomers of compounds 2 with the nature of the substituent on the beta-phenyl rings. In the case of racemic diastereomers, beta-methoxy substitution on the beta-phenyl ring (2-OCH3, 3-OCH3) also led to a decrease of the triplet lifetimes when compared to those of the nonsubstituted compounds (2-H, 3-H). This shortening is accounted for by the deactivation of a small proportion of the excited molecules through beta-phenyl quenching. In addition to the above factors, the lifetimes in the case of meso diastereomers can further be controlled by increasing the energy spacing between the T-1 and T-2 states, since beta-phenyl quenching occurs from the latter for compounds 2 and 3. Through a rational conformational control, a surprisingly long triplet lifetime (300 ns) has been measured for the first time for a purely n,pi* triplet-excited beta-phenylpropiophenone dimer (1-rac).

Molybdenum tetracarbonyl complexes of (aryloxy) lambda(3)-cyclotriphosphazanes; X-ray crystal structure of [Mo(CO)(4){EtNP(OC6H4Br-4)}(3)]

Treatment of the lambda(3)-cyclotriphosphazanes, cis-{EtNP(OR)}(3) [R = C6H4Br-4 (L-1) or C6H4Br-2 (L-2)] with [Mo(CO)(4)(NBD)] (NBD = norbornadiene) yields the mononuclear complexes [Mo(CO)(4)L-1] (1) and [Mo(CO)(4)L-2] (2). which have been characterised by IR, NMR (P-31 and H-1) and FAB mass spectral data. The structure of 1 has been confirmed by single crystal X-ray analysis. The structural and conformational changes brought about by complexation are discussed in terms of a bonding model based on "negative hyperconjugation". (C) 1998 Elsevier Science Ltd. All rights reserved.