Reversible Clustering of Gold Nanoparticles under Confinement

A limiting factor of solvent‐induced nanoparticle self‐assembly is the need for constant sample dilution in assembly/disassembly cycles. Changes in the nanoparticle concentration alter the kinetics of the subsequent assembly process, limiting optical signal recovery. Herein, we show that upon confining hydrophobic nanoparticles in permeable silica nanocapsules, the number of nanoparticles participating in cyclic aggregation remains constant despite bulk changes in solution, leading to highly reproducible plasmon band shifts at different solvent compositions.     

Crystal structures of [WI2(CO)3{Ph2P(CH2) n PPh2}] (n = 2 or 3)

[WI₂(CO)₃{Ph₂P(CH₂)₂PPh₂}] (1) crystallizes out in the monoclinic space group P2₁/n, with a = 13.852(7) Å, b = 14.789(19) Å, c = 14.915(19) Å, = 102.86(1)°, Z = 4. [WI₂(CO)₃{Ph₂P(CH₂)₃PPh₂}] (2) crystallizes out in the monoclinic space group P2₁/n, with a = 10.499(15) Å, b = 14.58(2) Å, c = 20.75(3) Å, = 103.59(1)°, Z = 4. Both structures show the metal in a seven-coordinate environment with a carbonyl in the unique capping position, two further carbonyls and a phosphorus in the capped face, and two iodides and the second phosphorus in the uncapped face.     

First synthesis of N-[(aziridin-2-yl)methyl]benzimidazolequinone and analysis of toxicity towards normal and Fanconi anemia cells

A diazole is N-substituted with 1-trityl-2-methylaziridine and demethylated and oxidised with NBS under acidic conditions to give a benzimidazolequinone; this novel anti-tumour agent is marginally more cytotoxic than mitomycin C (MMC) towards the normal human fibroblast cell line GM00637, while the MMC-hypersensitive human Fanconi anaemia (FA) cell line, PD20i, lacking the FANCD2 protein, is also hypersensitive to the benzimidazolequinone, with expression of FANCD2 protein decreasing sensitivity to both MMC and the benzimidazolequinone.     

Long-term influence of manure and mineral nitrogen applications on plant and soil 15N and 13C values from the Broadbalk Wheat Experiment

The Broadbalk Wheat Experiment at Rothamsted Research in the UK provides a unique opportunity to investigate the long-term impacts of environmental change and agronomic practices on plants and soils. We examined the influence of manure and mineral fertiliser applications on temporal trends in the stable N ((15)N) and C ((13)C) isotopes of wheat collected during 1968-1979 and 1996-2005, and of soil collected in 1966 and 2000. The soil delta(15)N values in 1966 and 2000 were higher in manure than the mineral N supplied soil; the latter had similar or higher delta(15)N values than non-fertilised soil. The straw delta(15)N values significantly decreased in all N treatments during 1968 to 1979, but not for 1996-2005. The straw delta(15)N values decreased under the highest mineral N supply (192 kg N ha(-1) year(-1)) by 3 per thousand from 1968 to 1979. Mineral N supply significantly increased to straw delta(13)C values in dry years, but not in wet years. Significant correlations existed between wheat straw delta(13)C values with cumulative rainfall (March to June). The cultivar Hereward (grown 1996-2005) was less affected by changes in environmental conditions (i.e. water stress and fertiliser regime) than Cappelle Desprez (1968-1979). We conclude that, in addition to fertiliser type and application rates, water stress and, importantly, plant variety influenced plant delta(13)C and delta(15)N values. Hence, water stress and differential variety response should be considered in plant studies using plant delta(13)C and delta(15)N trends to delineate past or recent environmental or agronomic changes.     

β‐Alkyloxazolochlorins: Revisiting the Ozonation of Octaalkylporphyrins,and Beyond

The reaction of β‐octaalkylporphyrins (octaethylporphyrin and etioporphyrin I) with ozone generated the corresponding heptaalkyloxazolochlorinhemiacetals in which a pyrrolic subunit of the porphyrins was replaced by an oxazoline moiety. Thus, a pyrrolic β‐carbon with its alkyl substituent was excised and replaced by an oxygen atom, and the neighboring β‐carbon was hydroxylated. This work clarifies the nature of the products first described by Fischer and De?eli?, in 1933, and verifies the work by Shulg′a and coworkers, from 1977. Furthermore, the chemistry of the oxazolochlorin hemiacetals was studied: They could be dehydroxylated or converted to alkyl acetals and gem‐dialkyl derivatives, all possessing chlorin‐type optical spectra. Their oxidative conversions generated a unique tetrahydrofuran‐linked oxazolochlorin dimer and a hexaethylporpholactone. The work expands on the knowledge of converting porphyrins to porphyrinoids of potential utility containing nonpyrrolic building heterocycles.     

Bacterial preparation of enantiopure unactivated aziridine-2-carboxamides and their transformation into enantiopure nonnatural amino acids and vic-diamines

[reaction: see text] Enantiopure (1R,2S)-1-benzyl- and 1-arylaziridine-2-carboxamides were obtained by kinetic resolution of their racemates by Rhodococcus rhodochrous IFO 15564 catalyzed hydrolysis. Several regio- and enantioselective nucleophilic ring openings of (1R,2S)-1-benzylaziridine-2-carboxamide or its LAH-reduced product led to a series of enantiopure products, such as O-methyl-l-serine and some vicinal diamines.     

Hydrogen-atom abstraction from the adenine-uracil base pair

The hydrogen-abstracted radicals from the adenine-uracil (AU) base pair have been studied at the B3LYP/DZP++ level of theory. The A(N9)-U and A-U(N1) radicals, which correspond to hydrogen-atom abstraction at the adenine N9 and uracil N1 atoms, respectively, were predicted to be the two lowest-lying among the nine (AU-H) radicals studied in this study. The removal of the amino hydrogen of the adenine moiety that forms a hydrogen bond with the uracil O4 atom in the AU pair resulted in radical A(N6a)-U, which has the smallest base-pair dissociation energy, 5.9 kcal mol(-1). This radical is more likely to dissociate into the two isolated bases than to recover the hydrogen bond with the O4 atom through N6-H bond rotation along the C6-N6 bond. In general, the radicals generated by C-H bond breaking were higher in energy than those arising from N-H bond cleavage, because the unpaired electrons in the carbon-centered radicals were mainly localized on the carbon atom from which the hydrogen atom was removed. However, the highest-lying radical was found to arise from removal of the N3 hydrogen of uracil. The most remarkable structural feature of this radical is a very short C-H...O distance of 2.094 A, consistent with a substantial hydrogen bond. Although this radical lost the N1...H-N3 hydrogen bond between the two bases, its dissociation energy was predicted to be 12.9 kcal mol(-1), similar to that of the intact AU base pair. This is due to the transfer of electron density from the adenine N1 atom to the uracil N3 atom.     

Positive Solutions of Singular and Nonsingular Fredholm Integral Equations

The existence of positive solutions of the Fredholm nonlinear equation y(t) = h(t) + ∫^T₀k(t, s)[f(y(s)) + g(y(s))] ds is discussed. It is assumed that f is a continuous, nondecreasing function and g is continuous, nonincreasing, and possibly singular.