Towards Multi-generation Assemblies with Tetraphenylmethane Subunits

The synthesis of tetra(4-hydroxymethylphenyl)methane is reported. Possessing four benzyl alcohol groups, this molecule is anticipated to undergo self-assembly processes analogous to previously studied benzyl alcohol derived, deep-cavity cavitands (Gibb, C. L. D.; Stevens, E. D.; Gibb, B. C. Chem. Commun. 2000, 363–364). Towards such assembly processes, a bis-protected derivative was synthesized and its ability to undergo a macrocyclization reaction determined. Both the protection strategy employed and the macrocyclization approach are important models for more complex, repetitive self-assembly processes that can be envisaged with these types of molecules.     

Straight-chain alkanes template the assembly of water-soluble nano-capsules

Cavitand is sufficiently predisposed to form nano-scale capsules in the presence of templating straight-chain hydrocarbons; quaternary complexes are formed when two copies of smaller guests are encapsulated, whilst larger guests form ternary entities.     

Anion Complexation and The Hofmeister Effect

The ¹H NMR spectroscopic analysis of the binding of the ClO₄^? anion to the hydrophobic, concave binding site of a deep‐cavity cavitand is presented. The strength of association between the host and the ClO₄^? anion is controlled by both the nature and concentration of co‐salts in a manner that follows the Hofmeister series. A model that partitions this trend into the competitive binding of the co‐salt anion to the hydrophobic pocket of the host and counterion binding to its external carboxylate groups successfully accounts for the observed changes in ClO₄^? affinity.     

Nonmonotonic assembly of a deep-cavity cavitand

The synthesis and assembly properties of a new water-soluble deep-cavity cavitand are discussed. For a homologous series of alkanes, the host can form a range of approximately isoenergetic 1:1, 2:1, and 2:2 complexes. As a result of this 'confluence' of binding and assembly the host displays an unusual, nonmonotonic, assembly profile. Thus, no or limited assembly is observed with methane through butane, pentane triggers assembly, and hexane through octane again does not promote assembly, whereas nonane and a larger guest again induce assembly. This unusual behavior is discussed in the context of the diversity of nodes of chemical systems (networks).     

On the accurate determination of pressure- induced line shifts in the 2ν<Subscript>3</Subscript> band of H<Subscript>2</Subscript>O at 1320 nm

A simple technique is demonstrated for the accurate determination of pressure-induced line shifts of water in air. High- and low-pressure water samples are simultaneously probed on selected overtone transitions at 1.32 μm using a current-modulated distributed-feedback diode laser and harmonic detection. The resultant profiles yield an average line shift of -293±30 MHz/atm for the 3,3,0 (002)2,2,1 (000)transition at 227251 GHz and -134±7 MHz/atm for the 3,2,1 (002)2,1,2 (000) transition at 227027 GHz. Comparisons are made between first- and second-harmonic detection, and wavelength- and frequency-modulation regimes. The effect of modulation broadening on the returned line shifts is quantified. Received: 12 August 2002 / Revised version: 21 October 2002 / Published online: 8 January 2003 RID="*" ID="*"Corresponding author. Fax: +44-01865/275410, E-mail: gus.hancock@chemistry.ox.ac.uk     

Determination of the electric field gradient tensor in ferrous chloride tetrahydrate using a polarized mössbauer source

The orientation of the electric field gradient tensor at the iron nucleus in a single crystal of FeCl₂·4H₂O has been determined using a polarized Mössbauer source of ⁵⁷Co in iron metal. The data analysis embodied an accurate thickness correction for the polarization of the absorption cross-section. The principal axis of the tensor lies close to the FeCl bonds of the trans-octahedral FeCl₂(H₂O)₄ unit, but the minor axes are directed between the FeO bonds. The value of the asymmetry parameter obtained, n = 0.40 ± 0.15, is significantly larger than previous estimates.     

Diode laser based detection and determination of pressure-induced broadening coefficients in the {\mathsf{\nu_{1} + \nu_{3}}} combination band of ammonia

Nitrogen, oxygen, air and self-broadening coefficients have been measured in direct absorption for six transitions in the combination band of ammonia at room temperature using a DFB diode laser operating at 1.51 m. Absorption cross-sections for these strong lines, suitable for detection purposes, have been determined. Using 2f wavelength modulation spectroscopy we demonstrate a minimum detectable concentration of 500 ppb in a 75 cm path in 1 s at atmospheric pressure and present a simple method for measurement of broadening coefficients.Received: 13 August 2003, Published online: 21 October 2003PACS: 33.20.Ea Infrared spectra - 33.20.Vq Vibration-rotation analysis - 33.70.Jg Line and band widths, shapes, and shifts