Phase separation of Lal3 inside single-walled carbon nanotubes.

Simple binary solids can be found to adopt unprecedented structures when confined into nanometre-sized cavities, such as the inner cylindrical bore of single-walled carbon nanotubes (SWNT). In the case of the discussed Lal(x)@SWNT encapsulation composite, the Lal2 "crystal" fragment adopts the structure of bulk Lal3, with one third of the iodine positions unoccupied. A complete characterisation of the encapsulation composite was achieved using an enhanced digital restoration approach of high-resolution transmission electron microscopy (HRTEM) images. The resulting complex exit surface wave provides information about the precise structural data of both filling material and host SWNT, establishing the SWNT's chirality and thus enabling a prediction of the composite's overall electron-transport properties.     

Two-photon induced fluorescence and resonance-enhanced ionization of sulfur atoms

Two-photon induced fluorescence and resonance-enhanced photoionization have been observed in atomic sulfur originating from both the ³P_2,1,0 and the ¹D₂ states. Sulfur atoms are generated by the sequential multiphoton dissociation of CS₂ at probing wavelengths. The two-photon absorption process involves the 3 ³P_2,1,0 → 4 ³P_2,0,1 or the 3 ¹D₂ → 4 ¹F₃ transitions with resolution of the individual J″ → J′ transitions in most cases. Intensities of the 3³P_J″ → 4 ³P_J′ transitions have been compared with Hartree-Fock calculated transition probabilities from the analogous transitions in atomic oxygen. Photoionization is observed in a three-photon (two to resonance) ionization originating from the ³P_2,1,0 and the ¹D₂ states. Induced fluorescence is observed at 167 and 180 nm which is dipole-allowed radiation from the intermediate ³S⁰₁ and ¹D⁰₂ states, respectively.     

Phase-transfer catalysis-3: Acetylation of 2-acylcycloalkanones

With the exception of 2-formylcyclohexanone, which yields the E-exo-enol acetate, the phase-transfer catalysed acetylation of 2-acylcyclohexanones produces the 1-acetoxycyclohexene derivatives as the major products. The 1-acetoxy derivative is also obtained in good yield from the acetylation of 2-methoxycarbonylcyclopentanone but, generally, acetylation of 2-acylcyclopentanones yields the E-exo-enol acetates. 2-Acetylcyclopentanone, however, produces not only the E- and Z-exo-enol acetates, but also the endo-enol acetate, in a ratio of ca 2:2:1. The exo and endo-enol acetates were distinguished by ¹³CNMR spectroscopy and use of LIS reagents confirmed the configurational assignments of the exo-isomers     

EXCITED STATES OF DNA AND ITS COMPONENTS AT ROOM TEMPERATURE—III. SPECTRA, POLARISATION AND QUANTUM YIELDS OF EMISSIONS FROM ApA AND poly rA*

Abstract— Corrected normalised emission spectra from 300 to 480 nm and their polarisation are reported for neutral and poly rA at room temperature. Yields are 4 times (ApA) and 6 times (poly rA) greater than the monomer. Comparison of emission spectra and polarisation spectra demonstrates heterogeneity of emission and, following attempts at spectral synthesis, comparison with experimental reference spectra allows the observed total emission spectra to be resolved into four components assigned as I monomer-like emission, II excimer fluorescence, HI monomer phosphorescence, IV excimer phosphorescence; the polarisation of the excimer fluorescences of ApA and poly rA are deduced. The observations can be understood quantitatively using a simple stacking model with excimer emissions originating in the stacked components. Quantitative differences between ApA and poly rA are due to their different hypochromism and extent of stacking. Differences of polarisation are attributed to different stacking geometries, and the directional properties of the transition moment suggest that the excimer fluorescence is largely charge-resonance in nature.     

Chemistry of 6 -pyrido[4,3- ]carbazoles part II: synthetic approaches to 6 -9-methoxy-5, 11-dimethylpyrido[4,3- ] fluorenes

Synthetic approaches to 6 -9-methoxy-5, 11-dimethylpyrido[4,3- ] fluorene are described, thus 2-[1-(4-pyridyl)ethyl]6-methoxyindanone has been reacted with vinylmagnesium bromide to yield 2-[1-(4-pyridyl)ethyl]-6 methoxy-1-vinyl-1-indanol. However, on dehydration this compound rearranges to 2-[1-(4-pyridyl)ethyl]-3-ethylidene-5-methoxyindene rather than the required isomer 3-ethylidine-2-[1-(4-pyridyl)ethyl]-5-methoxyindane needed fro pericyclic ring-closure to the pyrido[4,3- ]fluorene system. Reaction of -2-[1-methyl-1-(4-pyridyl)methylene]-6-methoxyindanone with ethylene triphenylphosphorane similarly gives 6-methoxy-spiro-2-[1-(2,3-dimethyl-3-(4-pyridyl)-cyclopropyl) indanone rather than the desired indane.     

CCR5 antagonists: 3-(pyrrolidin-1-yl)propionic acid analogues with potent anti-HIV activity

[reaction: see text] A novel approach to alpha,alpha-disubstituted-beta-amino acids (beta(2,2)-amino acids) was employed in the synthesis of a series of 3-(pyrrolidin-1-yl)propionic acids possessing high affinity for the CCR5 receptor and potent anti-HIV activity. The rat pharmacokinetics for these new analogues featured higher bioavailabilities and lower rates of clearance as compared to cyclopentane 1.     

Theory of long-lived nuclear spin states in solution nuclear magnetic resonance. I. Singlet states in low magnetic field

We have recently demonstrated the existence of exceptionally long-lived nuclear spin states in solution-state nuclear magnetic resonance. The lifetime of nuclear spin singlet states in systems containing coupled pairs of spins-12 may exceed the conventional relaxation time constant T1 by more than an order of magnitude. These long lifetimes may be observed if the long-lived singlet states are prevented from mixing with rapidly relaxing triplet states. In this paper we provide the detailed theory of an experiment which uses magnetic field cycling to observe slow singlet relaxation. An approximate expression is given for the magnetic field dependence of the singlet relaxation rate constant, using a model of intramolecular dipole-dipole couplings and fluctuating external random fields.     

Magnetic switch of permeability for polyelectrolyte microcapsules embedded with Co@Au nanoparticles

We explored using a magnetic field to modulate the permeability of polyelectrolyte microcapsules prepared by layer-by-layer self-assembly. Ferromagnetic gold-coated cobalt (Co@Au) nanoparticles (3 nm diameter) were embedded inside the capsule walls. The final 5 mum diameter microcapsules had wall structures consisting of 4 bilayers of poly(sodium styrene sulfonate)/poly(allylamine hydrochloride) (PSS/PAH), 1 layer of Co@Au, and 5 bilayers of PSS/PAH. External alternating magnetic fields of 100-300 Hz and 1200 Oe were applied to rotate the embedded Co@Au nanoparticles, which subsequently disturbed and distorted the capsule wall and drastically increased its permeability to macromolecules like FITC-labeled dextran. The capsule permeability change was estimated by taking the capsule interior and exterior fluorescent intensity ratio using confocal laser scanning microscopy. Capsules with 1 layer of Co@Au nanoparticles and 10 polyelectrolyte bilayers are optimal for magnetically controlling permeability. A theoretical explanation was proposed for the permeability control mechanisms. "Switching on" of these microcapsules using a magnetic field makes this method a good candidate for controlled drug delivery in biomedical applications.     

Absolute Configuration of 3-Substituted 1-Azabicyclo[2.2.1]heptanes

The l-azabicyclo[2.2.1]heptan-3-exo-ol ( 2 ) was resolved by fractional crystallisation of its hydrogen tartrate salts. The enantiomers (+)- and (?)- 2 were oxidised to the ketones (?)- 4 and (+)- 4 , respectively (Scheme). CD spectroscopy suggested that (?)- 4 possesses the (1R,4S)-configuration. This absolute configuration was confirmed by single-crystal X-ray diffraction of the derivative (+)-(1R,4R)-3-(1,3-dithian-2-ylidene)-1-azabicyclo [2.2.1]-heptane ((+)- 5 ).     

THE MICROVASCULAR EFFECTS OF PHOTODYNAMIC THERAPY: EVIDENCE FOR A POSSIBLE ROLE OF CYCLOOXYGENASE PRODUCTS

Photodynamic therapy (PDT) of malignant tumours may involve the interruption of tumor and peritumor microcirculation. We have studied the effect of light activation of the photosensitizing drug dihematoporphyrin ether (DHE) on rat subcutaneous arterioles and the modulation of these effects by cyclooxygenase inhibitors indomethacin and acetyl salicylic acid (ASA). Animals received DHE 48 h prior to light activation and additionally either indomethacin, ASA or saline 3 h prior to treatment. Light activation (630 nm, 60 J/cm2) resulted in a significant reduction to 62 +/- 2% SEM of initial blood flow. This effect was inhibited by ASA (98 +/- 8% SEM) and indomethacin (87 +/- 8% SEM). Results from the administration of various doses of both compounds indicate that this inhibition is dose related. The data presented here show that PDT causes a significant reduction in blood flow in normal arterioles and that this effect was inhibited by ASA and indomethacin indicating that prostaglandins or thromboxane A2 may play an important role in the microvascular response to PDT.