A high-performance liquid chromatography method for determination 2-(n-(N,N,N-trimethyl)-n-alkyl)-5-alkylfuryl halides in dipalmitoylphosphatidilcholine liposome solutions

A high-performance liquid chromatography (HPLC) method for the determination of 2-(4-(N,N,N-trimethyl)-butyl)-5-dodecylfuryl bromide (DFTA) in dipalmitoylphophatidil-choline (DPPC) liposome solutions has been developed. Lipid-soluble furan derivatives, 2,5-disubstituted with different n-alkyl chains and a terminal trimethylammonium group are useful probes for studying singlet oxygen dynamics and equilibria in microcompartmentalized systems. The actual HPLC method uses a gradient elution and DAD detection. The chromatographic separation of these components is achieved using a C18 analytical column with a 10mM solution of 1-heptanesulfonic acid (PIC-7)-methanol (10:90, v/v) as initial mobile phase. Both DFTA peaks are well resolved and free of interference from matrix components and reaction products. The method has been found to be linear (r > 0.999) over a wide concentration range and reliable to perform kinetic experiments in which the time dependent consumption of a tetraalkylammonium surfactant in a microorganized systems composed by lipidic surfactants is followed.     

Giant vesicles of a single-tailed chiral cationic surfactant, (1R,2S)-(-)-N-dodecyl-N-methylephedrinium bromide, in water

Self-assembly properties of a single-tailed chiral cationic surfactant, (1R,2S)-(-)-N-dodecyl-N-methylephedrinium bromide (DMEB), have been studied in water. The molecular self-assemblies of the amphiphile have been characterized by surface tension, fluorescence probes, light scattering, and microscopic techniques. The results have been compared with those of dodecyltrimethylammonium bromide (DTAB) surfactant. The critical aggregation concentration of DMEB was found to be much less than that of DTAB. Surface tension and fluorescence probe studies have suggested formation of micellar structures at low temperature (<28 degrees C) and spontaneous formation of giant vesicles in water above 28 degrees C. The mean size of the aggregates has been measured by a dynamic light scattering method. The micropolarity and microviscosity of the self-assemblies were determined by fluorescence probe technique. The (1)H NMR and FTIR spectra were recorded to elucidate the role of the hydrophobic head group towards the formation of bilayer structures. The phase transition temperatures of the vesicular aggregates were determined by measurement of fluorescence anisotropy at various temperatures.     

Formation of transient intermediates in low-temperature photosensitized oxidation of an 8-(13)C-guanosine derivative

An 8-(13)C-labeled guanosine derivative, 2',3',5'-O-tert-butyldimethylsilyl-N-tert-butyldimethylsilyl-8-(13)C-guanosine, was synthesized and its photosensitized oxidation with singlet oxygen carried out below -100 degrees C. Two transient intermediates that decompose directly to the final major product 5 and CO(2) were detected by (13)C NMR between -100 and -43 degrees C. The two intermediates are carbamic acids based on (13)C NMR and 2D NMR (HMQC, HMBC) spectra and the formation of final product 5 and of 8-CO(2). No endoperoxide intermediate could be detected by low-temperature NMR spectroscopy even at -100 degrees C. A reaction mechanism is proposed involving initial [4 + 2] cycloaddition of singlet oxygen to the imidazole ring to form an unstable endoperoxide, subsequent rearrangement of the endoperoxide to a dioxirane, and decomposition of the dioxirane to the two observed intermediates. Both oxygen atoms of CO(2) are derived from a single oxygen molecule, which strongly supports a dioxirane structure for the precursor of the two observed intermediates. The distribution of products estimated by (13)C NMR accounts for all the (13)C-containing products in the reaction mixture.     

Vesicle-micelle transition in mixtures of dioctadecyldimethylammonium chloride and bromide with nonionic and zwitterionic surfactants

We have investigated the effect of mixing spontaneously formed dispersions of the cationic vesicle-forming dioctadecyldimethylammonium chloride and bromide (DODAX, with X being anions Cl- (C) or Br- (B)) with solutions of the micelle-forming nonionic ethylene oxide surfactants penta-, hepta-, and octaethyleneglycol mono-n-dodecyl ether, C12E(n) (n = 5, 7, and 8), and the zwitterionic 3-(N-hexadecyl-N,N-dimethylammonio)propane sulfonate (HPS). We used for this purpose differential scanning calorimetry (DSC), turbidity, and steady-state fluorescence spectroscopy to investigate the vesicle-micelle (V-M) transition yielded by adding C12E(n) and HPS to 1.0 mM vesicle dispersions of DODAC and DODAB. The addition of these surfactants lowers the gel-to-liquid crystalline phase transition temperature (T(m)) of DODAC and DODAB, and the transition becomes less cooperative, that is, the thermogram transition peak shifts to lower temperature and broadens to disappear when the V-M transition is complete, the vesicle bilayer becomes less organized, and the T(m) decreases, in agreement with measurements of the fluorescence quantum yield of trans-diphenylpolyene (t-DPO) fluorescence molecules incorporated in the vesicle bilayer. Turbidity data indicate that the V-M transition comes about in three stages: first surfactants are solubilized into the vesicle bilayer; after saturation, the vesicles are ruptured, and, finally, the vesicles are completely solubilized and only mixed micelles are formed. The critical points of bilayer saturation and vesicle solubilization were obtained from the turbidity and fluorescence curves, and are reported in this communication. The solubility of DODAX is stronger for C12E(n) than it is for HPS, meaning that C12E(n) solubilizes DODAX more efficiently than does HPS. The surfactant solubilization depends slightly on the counterion, and varies according to the sequence C12E5 > C12E7 > C12E8 > HPS.     

Multifunctional Ligands. Phosphinimine-Substituted Cyanofluoroaromatics Including X-ray Molecular Structures of Three Representative Ligands 4,6-(CN)(2)C(6)F(2)-1,3-(N=PPh(3))(2), 4,6-(CN)(2)C(6)F(2)-1,3-(N=PPh(2)Me)(2) and 4,6-(CN)(2)C(6)F(2)-1-(N=PPh(3))-3-(N=PPh(2)Me). Formation of Rhodium(I) Complexes

Reaction of 1,3-dicyanotetrafluorobenzene with 2 equiv of (trimethylsilyl)iminophosphoranes gave the disubstituted derivatives 4,6-(CN)(2)C(6)F(2)-1,3-AB: 1, A = B = (N=PPh(3)); 2, A = B = (N=PPh(2)Me); and 3, A = (N=PPh(3)), B = (N=PPh(2)Me). Monosubstituted compounds of the type 2,4-(CN)(2)C(6)F(3)-1-A; notably 4, A = (N=PPh(3)), and 5, A = (N=PPh(2)Me), were readily obtained by reaction of 1 molar equiv of the silylated iminophosphorane with the cyanofluoro aromatic. Substitution of the fluorine para to the CN group(s) occurs in all cases. Reactions of 1,2- and 1,4-dicyanotetrafluorobenzene with (trimethylsilyl)iminophosphoranes gave only monosubstituted derivatives 3,4-(CN)(2)C(6)F(3)-1-A (6, A = (N=PPh(3)), and 7, A = (N=PPh(2)Me)) and 2,5-(CN)(2)C(6)F(3)-1-A (8, A = (N=PPh(3)), and 9, A = (N=PPh(2)Me)), respectively, as the result of electronic deactivation of the second substitutional point. 1, 4,6-(CN)(2)C(6)F(2)-1,3-(N=PPh(3)), 2, 4,6-(CN)(2)C(6)F(2)-1,3-(N=PPh(2)Me)(2), and 3, 4,6-(CN)(2)C(6)F(2)-1-(N=PPh(3))-3-(N=PPh(2)Me) have been structurally characterized. For 1 (at 21 degrees C), monoclinic, C2/(c) (No. 15), a = 15.289(2) ?, b = 10.196(1) ?, c = 23.491(6) ?, beta = 91.63(2) degrees, V = 3660(2) ?(3), and Z = 4. The P=N bond length is 1.579(2) ? and the P(V)-N-C(phenyl) angle is 134.0(2) degrees. For 2, (at 21 degrees C) monoclinic, C2/(c) (No. 15), a = 18.694(2) ?, b = 8.576(1) ?, c = 40.084(4) ?, beta = 94.00(1) degrees, V = 6411(2) ?(3), and Z = 8. The P(1)=N(1) bond length is 1.570(4) ?, the P(2)=N(2) bond length is 1.589(3) ?, the P(1)-N(1)-C(14) angle is 131.6(3) degrees, and the P(2)-N(2)-C(16) angle is 131.3(3) degrees. For 3, (at -80 degrees C) monoclinic, P2(1)/c (No. 14), a = 9.210(1) ?, b = 18.113(2) ?, c = 20.015(2) ?, beta = 100.07(1) degrees, V = 3287(2) ?(3), and Z = 4. The P(1)=N(1) bond length (PPh(3) group) is 1.567(4) ?, the P(2)=N(2) bond length (PPh(2)Me group) is 1.581(5) ?, the P(1)-N(1)-C(1) angle is 140.4(4) degrees, and the P(2)-N(2)-C(3) angle is 129.4(4) degrees. These new multifunctional chelating ligands readily react with [Rh(cod)Cl](2) and AgClO(4) to give cationic Rh(I) complexes in which the imine and/or the nitrile groups are coordinated to the Rh center.     

Temperature-induced structural and permeability changes in dioctadecyldimethylammonium bromide (DODAB) vesicles: a fluorescence investigation using 2-[(p-methylamino)phenyl]-3,3-dimethyl-5-carboethoxy-3H-indole as a probe

An investigation of the temperature dependence of the fluorescence spectral characteristics of 2-[(p-methyl-amino)phenyl]-3,3-dimethyl-5-carboethoxy-3H indole (I) in aqueous micelles(sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB)) and surfactant vesicles (dioctadecyldimethylammonium bromide (DODAB)) is presented. The gel-to-liquid crystalline phase transition temperature T_c, determined to be approximately 309 K (36°C) for DODAB vesicles, is in close agreement with the value reported previously. A pretransition at 294 K (21°C) has also been obtained. The blue shift in the fluorescence maximum and the increase in bandwidth are accounted for by the displacement of molecule I towards the interior of the bilayer as a function of temperature. Arrhenius plots for the non-radiative decay processes competing with fluorescence as a function of temperature show relatively high values for the activation energy above the phase transition temperature, indicating the displacement of molecule I to a new, more viscous, less polar site compared with its initial location in DODAB. The highest value of the activation energy in water indicates that the decay dynamics of this molecule are different in water than in the organized media studied here.     

Photooxidation of olefins sensitized by bisazafullerene (C(59)N)(2) and hydroazafullerene C(59)HN: product analysis, emission of singlet oxygen, and transient absorption spectroscopy.

The photooxidation reactions of olefins sensitized by the excited triplet states of bisazafullerene (C(59)N)(2) and hydroazafullerene C(59)HN have been studied. Oxidation yields were compared with those of pristine C(60). The singlet oxygen yields are also determined directly from the emission intensities, which are in good agreement with the oxidation yields. The triplet states of (C(59)N)(2) and C(59)HN have been identified by the time-resolved spectroscopic method by observing the triplet-triplet absorption spectra, which decay in the presence of oxygen. It has been proven that (C(59)N)(2) and C(59)HN have the ability to sensitize the reactions via singlet oxygen in about half of the efficiency of that of pristine C(60). For both azafullerenes, the triplet lifetimes are shorter than that of pristine C(60), which may be related to the nitrogen atom embedded in the C(60) moiety.     

Carbon chains of type C2n+1N(-) (n=2-6): A theoretical study of potential interstellar anions

Linear anions of type C(2n+1)N(-) (n=2-6), which are expected to be good candidates for experimental investigation by microwave spectroscopy and radio astronomy, were studied by means of the coupled cluster variant CCSD(T). Making use of corrections taken over from HC(3)NC(3)N(-) and HC(5)N, accurate equilibrium structures ( approximately 0.0005 A accuracy in bond lengths) have been established for all five anions. The electric dipole moments increase strongly with increasing chain length. For C(13)N(-), a very large equilibrium dipole moment of 16.53 D (with respect to center-of-mass coordinate system, negative end of dipole at terminal carbon site) is predicted. The lowest vertical detachment energies, leading to (2)Sigma states of the radicals for C(3)N(-) and C(5)N(-) and to (2)Pi states in the case of the larger anions, are calculated to lie in the range of 4.40-4.63 eV. The ground-state rotational and quartic centrifugal distortion constants of C(5)N(-) are predicted to be 1389.4 MHz and 33.8 Hz, respectively. All anions studied appear to be fairly normal semirigid linear molecules. Throughout, good agreement with available matrix isolation IR spectroscopic data is obtained and many predictions of spectroscopic properties are made.     

Synthesis and characterization of the SO(2)N(3)(-), (SO(2))(2)N(3)(-), and SO(3)N(3)(-) anions

SO(2) solutions of azide anions are bright yellow, and their Raman spectra indicate the presence of covalently bound azide. Removal of the solvent at -64 degrees C from CsN(3) or N(CH(3))(4)N(3) solutions produces yellow (SO(2))(2)N(3)(-) salts. Above -64 degrees C, these salts lose 1 mol of SO(2), resulting in white SO(2)N(3)(-) salts that are marginally stable at room temperature and thermally decompose to the corresponding azides and SO(2). These anions were characterized by vibrational and (14)N NMR spectroscopy and theoretical calculations. Slow loss of the solvent by diffusion through the walls of a sealed Teflon tube containing a sample of CsSO(2)N(3) in SO(2) resulted in white and yellowish single crystals that were identified by X-ray diffraction as CsSO(2)N(3).CsSO(3)N(3) with a = 9.542(2) A, b = 6.2189(14) A, c = 10.342(2) A, and beta = 114.958(4) degrees in the monoclinic space group P2(1)/m, Z = 2, and Cs(2)S(2)O(5).Cs(2)S(2)O(7).SO(2), respectively. Pure CsSO(3)N(3) was also prepared and characterized by vibrational spectroscopy. The S-N bond in SO(2)N(3)(-) is much weaker than that in SO(3)N(3)(-), resulting in decreased thermal stability, an increase in the S-N bond distance by 0.23 A, and an increased tendency to undergo rotational disorder. This marked difference is due to SO(3) being a much stronger Lewis acid (pF(-) value of 7.83) than SO(2) (pF(-) value of 3.99), thus forming a stronger S-N bond with the Lewis base N(3)(-). The geometry of the free gaseous SO(2)N(3)(-) anion was calculated at the RHF, MP2, B3LYP, and CCSD(T) levels. The results show that only the correlated methods correctly reproduce the experimentally observed orientation of the SO(2) group.     

Polydentate N(2)S(2)O and N(2)S(2)O(2) Ligands as Alcoholic Derivatives of (N,N'-Bis(2-mercaptoethyl)-1,5-diazacyclooctane)nickel(II) and (N,N'-Bis(2-mercapto-2-methylpropane)-1,5-diazacyclooctane)nickel(II)

The synthesis, structural characterization, spectroscopic, and electrochemical properties of N(2)S(2)-ligated Ni(II) complexes, (N,N'-bis(2-mercaptoethyl)-1,5-diazacyclooctane)nickel(II), (bme-daco)Ni(II), and (N,N'-bis(2-mercapto-2-methylpropane)1,5-diazacyclooctane)nickel(II), (bme-daco)Ni(II), derivatized at S with alcohol-containing alkyl functionalities, are described. Reaction of (bme-daco)Ni(II) with 2-iodoethanol afforded isomers, (N,N'-bis(5-hydroxy-3-thiapentyl)-1,5-diazacyclooctane-O,N,N',S,S')halonickel(II) iodide (halo = chloro or iodo), 1, and (N,N'-bis(5-hydroxy-3-thiapentyl)-1,5-diazacyclooctane-N,N',S,S')nickel(II) iodide, 2, which differ in the utilization of binding sites in a potentially hexadentate N(2)S(2)O(2) ligand. Blue complex 1 contains nickel in an octahedral environment of N(2)S(2)OX donors; X is best modeled as Cl. It crystallizes in the monoclinic space group P2(1)/n with a = 12.580(6) ?, b = 12.291(6) ?, c = 13.090(7) ?, beta = 97.36(4) degrees, and Z = 4. In contrast, red complex 2 binds only the N(2)S(2) donor set forming a square planar nickel complex, leaving both -CH(2)CH(2)OH arms dangling; the iodide ions serve strictly as counterions. 2 crystallizes in the orthorhombic space group Pca2(1) with a = 15.822(2) ?, b = 13.171(2) ?, c = 10.0390(10) ?, and Z = 4. Reaction of (bme-daco)Ni(II) with 1,3-dibromo-2-propanol affords another octahedral Ni species with a N(2)S(2)OBr donor set, ((5-hydroxy-3,7-dithianonadiyl)-1,5-diazacyclooctane-O,N,N',S,S')bromonickel(II) bromide, 3. Complex 3 crystallizes in the orthorhombic space group Pca2(1) with a = 15.202(5) ?, b = 7.735(2) ?, c = 15.443(4) ?, and Z = 4. Complex 4.2CH(3)CN was synthesized from the reaction of (bme-daco)Ni(II) with 1,3-dibromo-2-propanol. It crystallizes in the monoclinic space group P2/c with a = 20.348(5) ?, b = 6.5120(1) ?, c = 20.548(5) ?, and Z = 4.     

Synthesis, Characterization, and Thermolysis of C(15)N(12)

Synthesis of 1-methyl-2-fluoro-4,5-dicyanoimidazole was done by halogen exchange between 1-methyl-2-bromo-4,5-dicyanoimidazole and potassium fluoride. Halogen exchange between 1-methyl-2-bromo-4,5-dicyanoimidazole and lithium chloride in N-methylpyrrolidinone at 150 degrees C yielded 1-methyl-2-chloro-4,5-dicyanoimidazole, and additional heating to 210 degrees C resulted in the demethylation to yield 2-chloro-4,5-dicyanoimidazole. Thermolyses of the 2-halo-4,5-dicyanoimidazole derivatives (F, Cl) and 1-iodo-2-halo-4,5-dicyanoimidazole derivatives (Cl, Br, I) between 100 and 290 degrees C were found to yield Tris(imidazo)[1,2-a:1,2-c:1,2-e]-1,3,5-triazine-2,3,5,6,8,9-hexacarbonitrile, or HTT, with (C(5)N(4))(3) composition. HTT has been characterized and purified and the crystal structure obtained. Thermolysis of HTT at 490-500 degrees C gives a material with C/N = 1.020. The thermal properties of HTT and its decomposition products show thermal stability to 350 degrees C.     

Trimerization of alkali dicyanamides M[N(CN)2] and formation of tricyanomelaminates M3[C6N9] (M = K, Rb) in the melt: crystal structure determination of three polymorphs of K[N(CN)2], two of Rb[N(CN)2], and one of K3[C6N9] and Rb3[C6N9] from X-ray powder diffractometry

The alkali dicyanamides M[N(CN)2] (M=K, Rb) were synthesized through ion exchange, and the corresponding tricyanomelaminates M3[C6N9] were obtained by heating the respective dicyanamides. The thermal behavior of the dicyanamides and their reaction to form the tricyanomelaminates were investigated by temperature-dependent X-ray powder diffractometry and thermoanalytical measurements. Potassium dicyanamide K[N(CN)2] was found to undergo four phase transitions: At 136 degrees C the low-temperature modification alpha-K[N(CN)2] transforms to beta-K[N(CN)2], and at 187degrees C the latter transforms to the high-temperature modification gamma-K[N(CN)2], which melts at 232 degrees C. Above 310 degrees C the dicyanamide ions [N(CN)2]- trimerize and the resulting tricyanomelaminate K3[C6N9] solidifies. Two modifications of rubidium dicyanamide have been identified: Even at -25 degrees C, the a form slowly transforms to beta-Rb[N(CN)2] within weeks. Rb[N(CN)2] has a melting point of 190 degrees C. Above 260 degrees C the dicyanamide ions [N(CN)2]- of the rubidium salt trimerize in the melt and the tricyanomelaminate Rb3[C6N9] solidifies. The crystal structures of all phases were determined by powder diffraction methods and were refined by the Rietveld method. alpha-K[N(CN)2] (Pbcm, a = 836.52(1), b = 46.90(1), c =7 21.27(1) pm, Z = 4), gamma-K[N(CN)2] (Pnma, a = 855.40(3), b = 387.80(1), 1252.73(4) pm, Z = 4), and Rb[N(CN)2] (C2/c, a = 1381.56(2), b = 1000.02(1), c = 1443.28(2) pm, 116.8963(6) degrees, Z = 16) represent new structure types. The crystal structure of beta-K[N(CN)2] (P2(1/n), a = -726.92(1), b 1596.34(2), c = 387.037(5) pm, 111.8782(6) degrees, Z = 4) is similar but not isotypic to the structure of alpha Na[N(CN)2]. alpha-Rb[N(CN)2] (Pbcm, a = 856.09(1), b = 661.711(7), c = 765.067(9) pm, Z = 4) is isotypic with alpha-K[N(CN)2]. The alkali dicyanamides contain the bent planar anion [N(CN)2]- of approximate symmetry C2, (average bond lengths: C-N(bridge) 133, C-N(term) 113 pm; average angles N-C-N 170 degrees, C-N-C 120 degrees). K3[C6N9] (P2(1/c), a = 373.82(1), b = 1192.48(5), c = 2500.4(1) pm, beta = 101.406(3) degrees, Z = 4) and Rb,[C6N9] (P2(1/c), a = 389.93(2), b = 1226.06(6), c = 2547.5(1) pm, 98.741(5) degrees, Z=4) are isotypic and they contain the planar cyclic anion [C6N9]3-. Although structurally related, Na3[C6N9] is not isotypic with the tricyanomelaminates M3[C6N9] (M = K, Rb).     

Stability of N4(2-)-based sandwich-like energetic complexes [N4TiN4]2-: effect of spins and counterions

Design and assembly of new aromatic units has received growing attention due to its fundamental and application interests. Recently, a series of singlet sandwich-like complexes [N(4)MN(4)](q) (M = Ti, V, Cr, Fe, Co, Ni) based on the energetic all-nitrogen 6pi-aromatic species N(4)(2-) have been devised. However, how the electronic spins and counterions influence the kinetic stability of sandwich-like complexes has been very little understood, though it is very important to assess their potential use. In this article, we report our DFT study on the stability of the charged [N(4)TiN(4)](2-) and [N(4)TiN(4)TiN(4)](2-) systems as well as the neutral [N(4)TiN(4)]Li(2) system in both singlet and triplet electronic states. We found that the ground state structures of di-deckered [N(4)TiN(4)](2-) and [N(4)TiN(4)]Li(2) as well as the tri-deckered [N(4)TiN(4)TiN(4)](2-) are all in triplet state, rather than the previously reported singlet ones. Therefore, the N(4)(2-) and Ti(2+)-based sandwich-like complexes should be in high spins and may have potential use for new paramagnetic materials. Moreover, our calculations indicate that although the counterions can induce the electronic stabilization, they on the other hand can lead to the considerable kinetic destabilization of the N(4)(2-)-based sandwich-like complexes because the counterions can structurally destroy the perfectness of aromatic N(4)(2-). Thus, in study of the sandwich-like complexes, the effect of counterions cannot be neglected for assessment of the kinetic stability.     

Synthesis of N,N,N-Triethyl-2-[4-(2-phenylethenyl) phenoxy] ethanammonium iodide

The synthesis of N,N,N-triethyl-2-[4-(2-phenylethenyl) phenoxy] ethanammonium iodide, antispasmodic disubstituted olefin, was achieved via palladium-catalyzed cross-coupling of phenylacetylide with aryl bromide followed by hydroalumination.     

Microemulsion-based synthesis of CeO(2) powders with high surface area and high-temperature stabilities

Pure ceria powders, CeO(2), were synthesized in heptane-microemulsified aqueous solutions of CeCl(3) or Ce(NO(3))(3) stabilized by AOT (sodium bis(2-ethylhexyl) sulfosuccinate), DDAB (di-n-didodecyldimethylammonium bromide), or DDAB + Brij 35 surfactant mixtures. Micellar DTAB (n-dodecyltrimethylammonium bromide) and vesicular DDAB systems were also used as media for generating CeO(2). Characterization of the powders by X-ray powder diffractometry, laser-Raman spectroscopy, and Fourier transform infrared spectroscopy revealed that in the presence of surfactants almost-agglomerate-free nanosized crystallites (6-13 nm) of anionic vacancy-free cubic CeO(2) were produced. In the absence of surfactants 21-nm-sized crystallites were formed, comparing with the 85-nm-sized crystallites when cubic CeO(2) was created via thermal decomposition of cerium oxalate. Surface characterization, by X-ray photoelectron spectroscopy, N(2) sorptiometry, and high-resolution electron microscopy showed AOT- or (DDAB + Brij 35)-stabilized microemulsions to assist in formation of crystallites exposing surfaces of large specific areas (up to ca. 250 m(2)/g) but of low stability to high-temperature calcination (28-13 m(2)/g at 800 degrees C). In contrast, the double-chained DDAB was found to generate cubic CeO(2) crystallites of lower initial surface areas (144 (microemulsion) to 125 (vesicles) m(2)/g)) but of higher thermal stability (55-45 m(2)/g at 800 degrees C). Hence, the latter cerias could be considered as appropriate components for total oxidation (combustion) catalysts.     

Monocyclometalated (C N) Gold(III) Metallacycles: Tunable Emission and Singlet Oxygen (1O2) Generation Properties

The synthesis, characterization and photoluminescent properties of four cyclometalated (C N)-type gold(III) complexes bearing a bidentate diacetylide ligand, tolan-2,2’-diacetylide (tda), are reported. The complexes exhibit highly tunable excited state properties and show photoluminescence (PL) across the entire visible spectrum from sky-blue (λ_PL=493 nm) to red (λ_PL=675 nm) with absolute PL quantum yields (PLQY) of up to 75 % in solution, the highest PLQY found for any monocyclometalated Au(III) complex in solution. As a consequence of the use of the strongly rigidifying diacetylide bidentate ligand, a significant increase in the excited state lifetimes (τ₀=16–258 μs) was found in solution and in thin films. The complexes showed remarkable singlet oxygen generation in aerated solution with absolute singlet oxygen quantum yield (ϕ^1Δ) values reaching up to 7.5×10⁻⁵ and singlet oxygen lifetimes (τ₀^1Δ) in the range of 66–95 μs. Furthermore, the radiative and non-radiative rates of singlet oxygen were determined using the ϕ^1Δ and τ₀^1Δ values and correlations are drawn between the formation of singlet oxygen and its interaction with cyclometalated (C N) gold(III) complexes.     

Cyclometalated iridium and platinum complexes as singlet oxygen photosensitizers: quantum yields, quenching rates and correlation with electronic structures

Photophysical properties are reported for a series of cyclometalated platinum and iridium complexes that can serve as photosensitizers for singlet oxygen. The complexes have the formula (C;N)(2)Ir(O;O) or (C;N)Pt(O;O) where C;N is a monoanionic cyclometalating ligand such as 2-(phenyl)pyridyl and 2-(phenyl)quinolyl, and O;O is the ancillary ligand acetylacetonate (acac) or dipivaloylmethane (dpm). Also examined were a series of (N;N)PtMe(2) complexes where N;N is a diimine such as 2,2'-bipyridyl. In general, the cyclometalated complexes are excellent photosensitizers for the production of singlet oxygen, while the (N;N)PtMe(2) complexes were ineffective at this reaction. Quantum yields of singlet oxygen production range from 0.9-1.0 for the cyclometalated Pt complexes and 0.5-0.9 for Ir complexes. Luminescence quenching and singlet oxygen formation of the Ir complexes occurs from a combination of electron and energy transfer processes, whereas the Pt complexes only react by energy transfer. For Ir complexes with low emission energy, physical deactivation of the triplet excited state becomes competitive with energy transfer to ground state dioxygen. The rates of singlet oxygen quenching for the complexes presented here are in the range 6 x 10(6)-2 x 10(7) M(-1) s(-1) for Pt complexes and 2 x 10(5)-2 x 10(7) M(-1) s(-1) for Ir complexes, respectively. Differences in the efficiency of both forming and quenching singlet oxygen between the Ir and Pt cyclometalates are believed to come about from the more exposed coordination geometry in the latter species.     

The structure dependent electrochemical-response of novel 1-(4-mercaptobutyl)-4-(2-ferrocenylvinyl)pyridinium bromide SAMs on an au electrode

The 1-(4-mercaptobutyl)-4-(2-ferrocenylvinyl)pyridinium bromide (1-HS(CH2)(4)-4-[(E)-FcCH=CH]C5H4N)+Br- and its hydrogenated product [1-HS(CH2)(4)-4-(-FcCH2CH2)C5H4N]+Br- were synthesized and assembled on an Au electrode to form self-assembled monolayers which showed a structure-dependent electrochemical-response in phosphate buffer aqueous solutions (pH = 7).     

Adsorption Behavior of N(2), Water, C(6) Hydrocarbons, and Bulkier Benzene Derivative (TMB) on Na-X Zeolite and Its K(+)-, Rb(+)-, and Cs(+)-Exchanged Analogues

The hydrothermal crystallization of X-type zeolite with a Si/Al ratio of 1.15 was achieved from the Na(2)O-Al(2)O(3)-SiO(2)-H(2)O system at 368 K under static conditions. The post-synthesis modification was carried out by a conventional ion-exchange technique to obtain K(+)-, Rb(+)-, and Cs(+)-exchanged samples with different degrees of exchange. All the samples were characterized using chemical analysis, IR, SEM, powder XRD, low-temperature nitrogen adsorption, and equilibrium sorption uptakes of different probe molecules. The relative intensities of the XRD peaks of cation-exchanged zeolite were found to be affected to different extents, depending on the nature and the concentration of nonframework cationic size, without any shift in the positions of reflection. The sorptive properties of the K-, Rb-, and Cs-exchanged samples were studied using nitrogen, water, and different C(6) hydrocarbons including bulkier benzene derivative 1,3,5-trimethylbenzene (TMB) as probe molecules. The trend observed in chemical potential estimated as a function of nitrogen coverage indicates different sorption selectivity because of differences in the cationic size and population. Sorption uptake kinetics for probe molecules such as water, n-hexane, cyclohexane, benzene, and TMB were also studied. The samples with higher degrees of exchange and/or cationic size have shown a decrease in hydrophilic character due to the formation of irregular networks of water molecules connected with preadsorbed water molecules, framework oxygen ions, and nonframework cations. Among C(6) hydrocarbons including TMB, the benzene molecule is found to be the most promising probe for the estimation of openness of structure and surface heterogeneity as well. Copyright 2001 Academic Press.