Dispersion of the third-order nonlinear optical properties of an organometallic dendrimer(1)

The dispersion of cubic nonlinearity in the organometallic dendrimer 1,3,5-(3,5-{trans-[(dppe)2(4-O2NC6H4CC)RuCC]}2C6H3CCC6H4-4-CC)3C6H3 can be understood in terms of an interplay of two-photon absorption and absorption saturation. Simple dispersion relations reproduce the behavior of both the real and imaginary components of the hyperpolarizability.     

Comparative <Emphasis Type="Italic">in vitro</Emphasis> cytotoxicity assessment of some manufacturednanoparticulate materials characterized by transmissionelectron microscopy

A range of manufactured nanoparticulate materials, including Ag, TiO₂, Fe₂O₃, Al₂O₃, ZrO₂, Si₃N₄, and a range of carbonaceous nanoparticulate materials: single-wall and multi-wall carbon nanotube aggregates and aggregated nanoparticles of black carbon, as well as commercial (mineral grade) chrysotile asbestos nanotube aggregates, have been rigorously characterized by transmission electron microscopy. These nanoparticulate materials ranged in primary particle sizes from roughly 3 to 150 nm (except for the nanotube materials with lengths in excess of 15 μm). Aggregate sizes ranged from 25 nm to 20 μm. Comparative cytotoxicological assessment of these nanomaterials was performed utilizing a murine (lung) macrophage cell line. Considering the chrysotile asbestos to be a positive control, and assigning it a relative cytotoxicity index of unity (1.0), relative cytotoxicity indexes were observed as follows at concentrations of 5 μg/ml: 1.6 and ∼ 0.4 for Ag and TiO₂, respectively; 0.7–0.9 for the Fe₂O₃, Al₂O₃ and ZrO₂, 0.4 for the Si₃N₄, 0.8 for the black carbon, and 0.9 to 1.1 for the carbon nanotube aggregate samples. Observations of a cytotoxic response, nearly identical to that for chrysotile asbestos, for multi-wall carbon nanotube aggregates which very closely resemble anthropogenic multi-wall carbon nanotubes in the environment, raise some concern for potential health effects, especially for long-term exposure.This revised version was published online in August 2005 with a corrected issue number.     

Internal energy deposition in chemical ionization/tandem mass spectrometry

The efficiency of the collision-induced dissociation (CID) process as a function of the internal energy deposited into the ion during the ionization event was evaluated. (M + H)+ ions of pyrrole, pyrrolidine, pyridine and piperidine (five and six-membered ring heterocyclics) were generated by chemical ionization (CI). The internal energy of the ions was varied by using different reagent gases. Both high-energy (keV) and low-energy (eV) CID were performed on these ions. The experiments showed that the (M + H)+ ions of the five-membered ring compounds, pyrrole and pyrrolidine, have higher fragmentation efficiencies than the six-membered ring compounds, pyridine and piperidine. Fragmentation efficiencies in high-energy CID clearly correlate with the internal energy deposited by the ionization technique. Experiments showed that the low-energy CID process is more sensitive than high-energy CID to changes in internal energy.     

A ditopic azacryptate proton cage

A tosylated azacryptand readily protonates at the bridgehead amines, becoming a potential ditopic anion receptor. The in-in conformation of the amines facilitates encapsulation of two bromide guests and represents the first structural evidence that a proton cage cryptate can bind two anions internally.     

First isocyanoazulene and its homoleptic complexes

An efficient synthesis of remarkably stable 6-isocyanoazulene (CN6Az), the first nonbenzenoid organic isocyanide, is described. Its superb pi-accepting potential as a ligand was demonstrated through cyclic voltammetry studies on the binary complexes [Cr(CN6Az)6]0/+. The paramagnetic shift patterns for [Cr(CN6Az)6]+, the only azulenic pi-system studied by paramagnetic NMR, suggest that Cr(dpi) --> CN6Az(ppi*) electron delocalization involves both rings of the azulenyl substituents in [Cr(CN6Az)6]+. This conclusion is supported by density functional theory calculations on the complex [Cr(CN6Az)6][BF4].     

Coupling modulation in photorefractive materials by applying AC electric fields

In general, the application of an electric field to a photorefractive material with optical activity results in a change in the effective electro-optic coefficient, r_eff, which, in turn, alters the coupling between the two beams in a two-wave mixing experiment. When an alternating field is applied, this results in a modulation of both the phase and the coupling of the beams. Equations that have been developed to describe the change in the electro-optic coefficient as function of an applied dc field across an optically active crystal, have been used to demonstrate coupling modulation effects in BSO whilst applying large sinusoidal fields. Methods of overcoming these modulation effects are included.     

Primitive densities of certain sets of primes

While it has already been demonstrated that the set of twin primes (primes that differ by 2) is scarce in the $\text{Σ}\text{1}\text{p}$ (all twin primes) converges whereas $\text{Σ}\text{1}\text{p}$ (all primes) diverges, this paper proves in Theorems 1 and 2 the scarcity of twin primes (and, in general, of primes p which differ by any even integer as well as primes p for which yp + z is prime, y positive, z nonzero, (y, z) = 1) in a novel and natural way — by showing that the natural density of such primes compared to the set of all primes is 0, that is, $\text{lim}{}_{\mathrm{n\to \infty }}\text{(}\text{π′(n)}\text{π(n)}\text{) = 0}$, where π′(n) is the number of, say, twin primes between 1 and n for any n, and π(n) is the number of all primes between 1 and n. Theorem 3 then establishes that if a set of primes is scarce in the sense that the sum of the reciprocals of such primes converges, they are also scarce in the natural density sense outlined above.     

Carbon-13 nuclear magnetic resonance spectroscopy of cephalotaxus alkaloids

Carbon-13 chemical shift assignments have been obtained for the naturally occurring Cephalotaxus alkaloids, cephalotaxine, acetylcephalotaxine, harringtonine, isoharringtonine, drupacine and cephalotaxinone.     

Lineshapes of Cd Auger MNV transitions in the metal and in CdO

The MNV Auger lineshapes are presented for Cd and for CdO and are discussed in terms of the band-like vs atomic-like picture: the Auger line-shape for CdO is compared with photoemission results. It is shown that the Auger MNV transitions are band-like in the metal, while the hole—hole interaction in the final state has a considerable importance in the oxide.