Nature © Macmillan Publishers Ltd 19988 does not suf®ce. These observations indicate that many-body states due to signi®cant electron±electron correlations beyond exchangetype correlations have to be taken into account to describe the lowenergy transport properties of carbon nanotubes.M

The synthesis and spectroscopic characterization of self-assembled cylindrical capsule 1a x 1a of nanometer dimensions is described. Encapsulation studies of large organic guest molecules were performed by using 1H NMR sprectroscopy in [D12]mesitylene solution. In addition to the computational (MacroModel 5.5, Amber* force field) analysis of the capsule's shape and geometry, an experimental approach towards estimation of the internal cavity dimensions is described. This involves using series of homologous molecular "rulers" (e.g. aromatic amides 5a-i). The available space inside the capsule 1a x 1a can be estimated as 5.7 x 14.7 A (error +/- 0.2 A) with this technique. Dibenzoyl peroxide is readily encapsulated in [D12]mesitylene and was shown to be stable to decomposition for at least three days at 70 degrees C inside the capsule. Moreover, 1a x 1a prevents the encapsulated peroxide from oxidizing Ph3P or diphenyl carbazide present in solution. The normal chemical reactivity of the peroxide is restored by release from the capsule by DMF, a solvent that competes for the hydrogen bonds that hold the capsule together. The protection and release of encapsulated species augurs well for the application of capsules in catalysis and delivery.

A change in geometry is necessary on entry into the capsule: a supramolecular associate approximately 1.8 nm long (see schematic representation), which consists of two halves stabilized by hydrogen bonds, influences the intra- and intermolecular interactions of the guest molecules encapsulated. Thus tertiary amides and anilides such as 1, which exist in solution preferably as E rotamers, are fixed in the Z conformation inside the capsule for steric reasons.

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With the redesign of three chemical steps, the throughput of the valsartan manufacturing process could be significantly increased, and with the substitution of chlorobenzene with cyclohexane in the bromination of 4′-methyl-biphenyl-2-carbonitrile (6) to 4′bromomethyl-biphenyl-2-carbonitrile (5), halogenated solvents are no longer used in the whole valsartan production process. The alkylation of (S)-2-amino-3-methyl-butyric acid benzyl ester (8) with 4′-bromomethyl-biphenyl-2-carbonitrile (5), and the acylation of (S)-2-[(2′-cyano-biphenyl-4-ylmethyl)-amino]-3-methyl-butyric acid benzyl ester (4) to (S)-2-[(2′-cyano-biphenyl-4-ylmethyl)pentanoyl-amino]-3-methyl-butyric acid benzyl ester (3) were thoroughly modified. In the acylation of 4 to 3, N-ethyldiisopropylamine was replaced by aqueous sodium hydroxide by using the conditions of the Schotten-Baumann reaction, leading to a better quality of intermediate 3. In the alkylation of 8 with 5, N-ethyldiisopropylamine was indirectly replaced by aqueous sodium hydroxide. The reaction runs under homogenous conditions with (S)-2-amino-3-methyl-butyric acid benzyl ester (8) acting as acceptor for hydrobromic acid; recycling of 8 is performed by extraction with aqueous sodium hydroxide.