Synthesis and evaluation of thermal, photophysical and magnetic properties of novel starlike fullerene–organosilane macromolecules

Thermal, photophysical and magnetic properties of some novel fullerenol–silane adducts are described. Excellent improvement of thermal stability and high char yield due to the presence of silicon is the key feature of these adducts. Highest luminescence quenching due to maximum π–π electronic interactions between phenyl ring and fullerene are observed in the aromatic-silane adducts and the quenching ability of the aromatic ring reduces with further delocalization of the π-electrons as in naphthyl silane. The alkyl vinyl silane, on the other hand, records better fluorescence intensity owing to increase population of the electron density (+I effect) and non-effective charge transfer complex formation between isolated vinylic double bond and fullerene. Emission peak positions of these adducts are comparable to fullerenol because of control derivatization of fullerene ring causing less perturbation of the symmetric π-electronic system. These adducts are paramagnetic in nature with peaks around 3515 G and higher g-values (2.005–2.009) compared to fullerenol (1.985). The fullerenol–silane adducts are synthesized using fullerenol as substrate and different chloro and alkoxy silanes as silylating agents adopting simple nucleophilic displacement and transesterification reactions. All the fullerenol–silane adducts are characterized spectroscopically.     

A mild and regioselective method for alpha-bromination of beta-keto esters and 1,3-diketones using bromodimethylsulfonium bromide (BDMS)

Bromodimethylsulfonium bromide has been found to be an effective and regioselective reagent for alpha-monobromination of beta-keto esters and 1,3-diketones. A wide variety of beta-keto esters and 1,3-diketones undergo chemoselective alpha-monobromination with excellent yields at 0-5 degrees C or room temperature. The notable advantages of this protocol are no need of chromatographic separation, use of less hazardous reagent than molecular bromine, and no added base, Lewis acid, or other catalyst.     

Imaging of atomic layer deposited (ALD) tungsten monolayers on alpha-TiO2(110) by X-ray standing wave Fourier inversion

A single atomic layer of tungsten grown by atomic layer deposition (ALD) on a single-crystal rutile TiO2(110) support is studied by the X-ray standing wave (XSW) technique. The surface structural and chemical properties were also examined using atomic force microscopy, X-ray photoelectron spectroscopy, and low-energy electron diffraction. The XSW measured set of hkl Fourier components for the W atomic distribution function are summed together to produce a model-independent 3D map of the W atoms relative to the rutile lattice. The 3D atomic image shows surface tungsten atoms equally occupying the two nonequivalent Ti sites with a slight outward displacement. This corresponds to the atop and bridge sites with respect to the underlying lattice oxygen atoms. These XSW measurements clearly show that ALD conformal layers can be highly coherent with respect to the substrate lattice.     

Erratum to: Solution behavior of aqueous mixtures of low and high molecular weight hydrophobic amphiphiles

Mixtures of a hydrophobic triblock copolymer (L121, PEO₅PPO₆₈PEO₅) and a hydrophobic anionic surfactant (AOT, Sodium bis(2-ethylhexyl)sulfosuccinate), each alone forming turbid vesicular solutions in water, aggregate to produce a thermodynamically stable, transparent and isotropic solution. Mixed AOT/L121 aggregates could be confirmed by fluorescence, surface tension, differential scanning calorimetry (DSC) and isothermal titration calorimetry (ITC). In an isotropic region, where mixed aggregates are formed, there is a synergistic interaction between monomers of AOT and L121 in the mixture. In addition, Small Angle Neutron Scattering (SANS) experiments provided evidence that mixed aggregates have the shape of either spheres (with a certain polydispersity) or very short ellipsoids (axial ratio below 2), confirming a transition from giant multilamellar vesicles to small aggregates upon mixing the two hydrophobic amphiphiles. Upon dilution, the morphology changes to disk-like. From an examination of the results of all the methods the peculiar behavior of the mixed AOT/L121 system is explained.     

Microwave spectroscopic and theoretical studies on the phenylacetylene···H2O complex: C-H···O and O-H···π hydrogen bonds as equal partners

Rotational spectra of five isotopologues of the title complex, C(6)H(5)CCH···H(2)O, C(6)H(5)CCH···HOD, C(6)H(5)CCH···D(2)O, C(6)H(5)CCH···H(2)(18)O and C(6)H(5)CCD···H(2)O, were measured and analyzed. The parent isotopologue is an asymmetric top with κ = -0.73. The complex is effectively planar (ab inertial plane) and both 'a' and 'b' dipole transitions have been observed but no c dipole transition could be seen. All the transitions of the parent complex are split into two resulting from an internal motion interchanging the two H atoms in H(2)O. This is confirmed by the absence of such doubling for the C(6)H(5)CCH···HOD complex and a significant reduction in the splitting for the D(2)O analog. The rotational spectra, unambiguously, reveal a structure in which H(2)O has both O-H···π (π cloud of acetylene moiety) and C-H···O (ortho C-H group of phenylacetylene) interactions. This is in agreement with the structure deduced by IR-UV double resonance studies (Singh et al., J. Phys. Chem. A, 2008, 112, 3360) and also with the global minimum predicted by advanced electronic structure theory calculations (Sedlack et al., J. Phys. Chem. A, 2009, 113, 6620). Atoms in Molecule (AIM) theoretical analysis of the complex reveals the presence of both O-H···π and C-H···O hydrogen bonds. More interestingly, based on the electron densities at the bond critical points, this analysis suggests that both these interactions are equally strong. Moreover, the presence of both these interactions leads to significant deviation from linearity of both hydrogen bonds.     

Synthesis, spectroscopic, and in vitro photosensitizing efficacy of ketobacteriochlorins derived from ring-B and ring-D reduced chlorins via pinacol-pinacolone rearrangement

In this report, we present a regioselective oxidation of a series bacteriochlorins, which on reacting with either ferric chloride (FeCl(3)) or 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) yielded the corresponding ring-B or ring-D reduced chlorins. The effect of the number of electron-withdrawing groups present at the peripheral position, with or without a fused isocyclic ring (ring-E), did not make any significant difference in regioselective oxidation of the pyrrole rings. However, depending on the nature of substituents, the intermediate bis-dihydroxy bacteriochlorins on subjecting to pinacol-pinacolone reaction conditions gave various ketochlorins. The introduction of the keto-group at a particular position in the molecule possibly depends on the stability of the intermediate carbocation species. The newly synthesized bacteriochlorins show strong long-wavelength absorption and produced significant in vitro (Colon26 cells) photosensitizing ability. Among the compounds tested, the bacteriochlorins containing a keto-group at position 7 of ring-B with cleaved five-member isocyclic ring showed the best efficacy.     

Reactivity of tris(acetylacetonato) iron(III) with tridentate [ONO] donor Schiff base as an access to newer mixed-ligand iron(III) complexes

Two new mixed-ligand iron(III) complexes, [Fe(L(n))(acac)(C(2)H(5)OH)] incorporating coordinated ethanol from the reaction solvent were accessed from the reaction of [Fe(acac)(3)] with [ONO] donor dibasic tridentate unsymmetrical Schiff base ligands derived from condensation of 2-hydroxy-1-napthaldehyde with 2-aminophenol (H(2)L(1)) or 2-aminobenzoic acid (H(2)L(2)). The thermal study (TGA-DTA) provided evidence for weakly bound ethanol which is readily substituted by neutral N-donor molecule imidazole, benzimidazole or pyridine to produce an array of newer complexes, [Fe(L(n))(acac)X] (n=1, 2; X=Im, Bim, Py). The compounds were characterized by elemental analyses, FT-IR, UV-vis, solution electrical conductivity, FAB mass, (1)H and (13)C NMR spectroscopy. Room temperature magnetic susceptibility measurements (μ(eff)～5.8 B.M.) are consistent with spin-free octahedral iron(III) complexes. Cyclic voltammetry of ethanol complexes revealed a quasi-reversible one electron redox response (ΔE(p)>100 mV) for the Fe(III)/Fe(II) couple. Low half wave redox potential (E(1/2)) values suggested easy redox susceptibility. The ground state geometries of the ethanol and imidazole complexes have been ascertained to be distorted octahedral by density functional theory using DMol3 program at BLYP/DNP level.     

Improving Physical Properties via C?H Oxidation: Chemical and Enzymatic Approaches

Physicochemical properties constitute a key factor for the success of a drug candidate. Whereas many strategies to improve the physicochemical properties of small heterocycle‐type leads exist, complex hydrocarbon skeletons are more challenging to derivatize because of the absence of functional groups. A variety of C H oxidation methods have been explored on the betulin skeleton to improve the solubility of this very bioactive, yet poorly water‐soluble, natural product. Capitalizing on the innate reactivity of the molecule, as well as the few molecular handles present on the core, allowed oxidations at different positions across the pentacyclic structure. Enzymatic oxidations afforded several orthogonal oxidations to chemical methods. Solubility measurements showed an enhancement for many of the synthesized compounds.     

Structure property correlations in alcohols through two-photon absorption cross-section measurements

Two-photon absorption (TPA) cross-sections of neat alcohols are shown to be a femtosecond laser measurable property with useful structure property correlations that are directly correlated to the self-phase modulation of the alcohol in question. The amount of self-phase modulation is shown to be a molecular structure dependent property. The real and the imaginary components of the second-order hyperpolarizability are thus shown to be interrelated. Such TPA measurements prove that it is not possible to predict two-photon absorption properties by simple doubling the wavelengths of one-photon absorption spectra.     

Mononuclear to polynuclear transition induced by ligand coordination: synthesis, X-ray structure, and properties of mono-, di-, and polynuclear copper(II) complexes of pyridyl-containing azo ligands

Reactions of two hydrated cupric salts (CuCl(2).2H(2)O and Cu(ClO(4))(2).6H(2)O) with three azopyridyl ligands, viz. 2-[(arylamino)phenylazo]pyridine [aryl = phenyl (HL(1a)), p-tolyl (HL(1b)), and 2-thiomethyl phenyl (HL(1c))], 2-[2-(pyridylamino)phenylazo]pyridine (HL(2)), and 2-[3-(pyridylamino)phenylazo]pyridine (HL(3)), afford the mononuclear [CuClL(1)] (1), dinuclear [Cu(2)X(2)L(2)(2)](n)()(+) (X = Cl, H(2)O, ClO(4); n = 0, 1; 2, 3), and polynuclear [CuClL(3)](n)() (4) complexes, respectively, in high yields. Representative X-ray structures of these complexes 1-4 are reported. X-ray structure analysis of 4 reveals an infinite 1D zigzag chain that adopts a saw-tooth-like structure. Variable-temperature cryomagnetic measurements (2-300 K) on the complexes 2-4 have revealed weak magnetic interactions between the copper centers with J values -1.04, 9.88, and -1.31 cm(-1), respectively. Positive ion ESI mass spectra of the soluble complexes 1-3 are studied which provide the evidence for the integrity of the complexes also in solution. Visible range spectra of the complexes 1-3 in solution consist of intense and broad transitions in the range 700-600 nm. The solid-state spectrum of the insoluble copper complex 4, on the other hand, shows a structured band near 700 nm. The intensities of the transitions of the dinuclear complexes are much higher than those of the corresponding mononuclear copper complexes. Redox properties of the present copper complexes are reported. Notably, the dinuclear complex, 3, displays two successive redox processes: Cu(II)Cu(II) right harpoon over left harpoon Cu(II)Cu(I) right harpoon over left harpoon Cu(I)Cu(I). It catalyzes aerial oxidation of L-ascorbic acid. The catalytic cycle is most effective up to H(2)A/3 (H(2)A = L-ascorbic acid) molar ratio of 20:1.