Noelia M. Sanchez-Ballester

Activated interiors of clay nanotubes for agglomeration-tolerant automotive exhaust remediation†

Naturally occurring clay nanotubes, halloysite (Al2Si2O5(OH)4·2H2O), with exterior and interior surfaces, respectively, composed of SiOx and AlOx layers, act as an agglomeration-tolerant exhaust catalyst when copper–nickel alloy nanoparticles (Cu–Ni NPs, 2–3 nm) are immobilized at the AlOx interior. Co-reduction of Cu2+ and Ni2+ (respectively derived from CuCl2 and NiCl2) in the presence of sodium citrate (Na3C6H5O7·2H2O) and halloysite yielded the required nanocomposite, Cu–Ni@halloysite. Cu–Ni@halloysite efficiently catalyzes the purification of simulated motor vehicle exhaust comprising nitrogen monoxide (NO) and carbon monoxide (CO) near the activation temperature of Pt-based exhaust catalysts, ≤400 °C, showing its potential as an alternative to Pt-based catalysts. In contrast, a different halloysite nanocomposite with the SiOx exterior decorated with Cu–Ni NPs, Cu–Ni/halloysite, is poorly active even at >400 °C because of particle agglomeration. The enhanced exhaust-purification activity of Cu–Ni@halloysite can ultimately be attributed to the topology of the material, where the alloy NPs are immobilized at the tubular AlOx interior and protected from particle agglomeration by the tubular form and SiOx exterior.

Alcohol-induced decomposition of Olmstead's crystalline Ag(I)–fullerene heteronanostructure yields ‘bucky cubes’

Olmsteads crystalline C60-fullerene–Ag(I) organometallic heteronanostructure [C60{AgNO3}5] undergoes an apparently irreversible structural rearrangement upon exposure to low molecular weight aliphatic alcohols leading to a uniquely structured formation of well-oriented fullerene nano/microcrystals (‘bucky cubes’). The mechanism of rearrangement represents a supramolecular analogue of topotactic processes more commonly associated with some purely inorganic materials, such as maghemite, where chemical changes can occur with addition or loss of materials. Hence C60{AgNO3}5, whose rearrangement occurs at the nano/molecular level (i.e. not atomic scale), undergoes a transformation from a crystalline organometallic complex to well ordered cube-shaped arrays of needle-like fullerene microcrystals which reflect the original cubic crystal morphology and internal structure. Processing of bucky cubes by reduction with hydrazine results in a Ag nanoparticle–C60 crystal nanocomposite with potential for SERS analyses.

Supramolecular Approaches for Drug Development

Various supramolecular systems can be used as drug carriers to alter physicochemical and pharmacokinetic characteristics of drugs. Representative supramolecular systems that can be used for this purpose include surfactant/polymer micelles, (micro)emulsions, liposomes, layer-by-layer assemblies, and various molecular conjugates. Notably, liposomes are established supramolecular drug carriers, which have already been marketed in formulations including AmBisome(®) (for treatment of fungal infection), Doxil(®) (for Kaposis sarcoma), and Visudyne(®) (for age-related macular degeneration and choroidal neovascularization). Microemulsions have been used oral drug delivery of poorly soluble drugs due to improvements in bioavailability and predictable of absorption behavior. Neoral(®), an immunosuppressant used after transplant operations, is one of the most famous microemulsion-based drugs. Polymer micelles are being increasingly investigated as novel drug carriers and some formulations have already been tested in clinical trials. Supramolecular systems can be functionalized by designing the constituent molecules to achieve efficient delivery of drugs to desired sites in the body. In this review, representative supramolecular drug delivery systems, that may improve usability of candidate drugs or add value to existing drugs, are introduced.

Chelate stabilized metal oxides for visible light photocatalyzed water oxidations

Visible light driven photocatalytic water oxidations were undertaken that compared lactate stabilized molecular and nanoparticle cobalt complexes and calcium manganese oxides as simple mimics of the PSII CaMn4O5 catalyst. Analysis showed chelated cobalt oxides formed as <5 nm particles whilst Ca–Mn and Mn oxides were composed of nanoparticles organized into ∼150 nm spherules. O2 yield, turnover frequency and quantum yields were determined for the chelated materials and compared to sintered CaMn3O6 and Co3O4 counterparts. Results show two distinct stages of O2 generation took place with the chelated calcium manganese oxides, a Ca : Mn molar ratio of 1 : 3 gave highest O2 yield in the initial stage. Significantly, O2 generation at extended reaction time re-occurred without addition of fresh reagents and was determined to be promoted by in situ coating of the lactate metal oxide particles with cobalt captured from the decomposed pentaminecobalt(III)chloride electron acceptor. Time course TEM, XPS and EDX analysis indicated the secondary catalyst accumulated cobalt mainly as Co3O4. These nano-micro particles are readily reused and produced a superior O2 output of 85% maximum theoretical yield. Chelated cobalt catalysts resulted in TOF and O2 yield superior to a laser ablated counterpart, whereas calcium manganese oxide lactates promoted generation of effective recyclable water oxidation catalysts which also minimized toxicity and waste for the photocatalytic system.

Visible light promoted photocatalytic water oxidation: effect of metal oxide catalyst composition and light intensity

A range of low-cost nanoparticulate mixed transition metal oxides were prepared using a simple methodology and used as catalysts in visible light promoted water oxidations. The effect of catalyst and daylight equivalent light intensities on reaction efficiency in terms of O2 yields, TOF and proton production was determined.

Visible light promoted photocatalytic water oxidation: proton and electron collection via a reversible redox dye mediator

Visible light promoted photocatalytic water oxidations were conducted using a homogenous cobalt complex as a catalyst that was absorbed onto a silica gel substrate. The porous SiO2 contained Ru(bpy)32+ as a light harvester and the redox quinone analogue DCPIP as a reversible electron mediator as a step towards utilization of protons and electrons liberated in water oxidations for solar fuels.

Unexpected but convenient synthesis of soluble meso-tetrakis(3,4-benzoquinone)-substituted porphyrins

A new route to 3,4-benzoquinone-substituted porphyrins is reported. In attempted nitration reactions on the copper(II) or nickel(II) complexes of 5,10,15,20-tetrakis(3,5-di-t-butyl-4-hydroxyphenyl)porphyrin using lithium nitrate in acetic anhydride-acetic acid/chloroform no nitration products could be detected with the main products being the corresponding complexes of 5,10,15,20-tetrakis(3,4-dioxo-5-t-butylcyclohexa-1,5-dienyl)porphyrin. These o-quinone-substituted porphyrins are available in reasonable yield (> 50%), their synthesis is simple and they are of good solubility. The electrochemical and spectroelectrochemical properties of representative o-quinone-substituted Cu(II) and Ni(II) porphyrin derivatives are also reported.

Self-Assembly of a Mononuclear [FeIII(L)(EtOH)2] Complex Bearing an n-Dodecyl Chain on Solid Highly Oriented Pyrolytic Graphite Surfaces

The synthesis and structures of the N-[(2-hydroxy-3-methyl-5-dodecylphenyl)methyl]-N-(carboxymethyl)glycine disodium salt (HL) ligand and its neutral mononuclear complex [Fe(III) (L)(EtOH)(2)] (1) are reported. Structural and electronic properties of 1 were investigated by using scanning tunneling microscopy (STM) and current imaging tunneling spectroscopy (CITS) techniques. These studies reveal that molecules of 1 form well-ordered self-assemblies when deposited on a highly oriented pyrolytic graphite (HOPG) surface. At low concentrations, single or double chains (i.e., nanowires) of the complex were observed, whereas at high concentration the complex forms crystals and densely packed one-dimensional structures. In STM topographies, the dimensions of assemblies of 1 found on the surface are consistent with dimensions obtained from X-ray crystallography, which indicates the strong similarities between the crystal form and surface assembled states. Double chains are attributed to hydrogen-bonding interactions and the molecules align preferentially along graphite defects. In the CITS image of complex 1 a strong tunneling current contrast at the positions of the metal ions was observed. These data were interpreted and reveal that the bonds coordinating the metal ions are weaker than those of the surrounding ligands; therefore the energy levels next to the Fermi energy of the molecule should be dominated by metal-ion orbitals.

Redetermination of picolinic acid hydrochloride at 150 K

The structure of the title compound, C6H6NO2+·Cl−, was previously determined at ambient temperature [Laurent (1965). Acta Cryst. 18, 799–806]. This redetermination at 150 K is to a far higher precision. On cooling to 150 K, the unit cell contracts most in the π–π stacking direction, b, and rather less so in the directions involving the strongly hydrogen-bonded chains, a and c. The π–π stacking distance is b/2 (3.263 A)All of the atoms lie on a mirror plane. There are two strong hydrogen bonds, O—H⋯Cl and N—H⋯Cl. Cations and anions form hydrogen-bonded, zigzag chains parallel to the a axis.

CCDC 906345: Experimental Crystal Structure Determination

Related Article: N.M.Sanchez-Ballester, L.K.Shrestha, M.R.J.Elsegood, W.Schmitt, K.Ariga, C.E.Anson, J.P.Hill, A.K.Powell|2013|Dalton Trans.|42|2779|doi:10.1039/c2dt32547k