Long chiral metal-organic nanofibers can be grown using conventional coordination chemistry and biologically derived components in a diffusion controlled growth procedure.

Porphyrin-based molecular wires are promising candidates for nanoelectronic and photovoltaic devices due to the porphyrin chemical stability and unique optoelectronic properties. An important aim toward exploiting single porphyrin molecules in nanoscale devices is to possess the ability to control the electrical pathways across them. Herein, we demonstrate a method to build single-molecule wires with metalloporphyrins via their central metal ion by chemically modifying both an STM tip and surface electrodes with pyridin-4-yl-methanethiol, a molecule that has strong affinity for coordination with the metal ion of the porphyrin. The new flat configuration resulted in single-molecule junctions of exceedingly high lifetime and of conductance 3 orders of magnitude larger than that obtained previously for similar porphyrin molecules but wired from either end of the porphyrin ring. This work presents a new concept of building highly efficient single-molecule electrical contacts by exploiting metal coordination chemistry.

By search of a library of closely related structures, two conglomerate imines of the amide of 2-fluorophenylglycine have been discovered and unambiguously characterized. One conglomerate is formed on reaction with benzaldehyde and the other on reaction with 4-Br-benzaldehyde. The crystal structures of both have been determined. Both deracemise on grinding of the crystals under conditions whereby racemisation in solution can occur. Deracemisation of the former compound is hampered both by hydrate formation and formation of a polymorph. In contrast the latter deracemises efficiently. Hydrolysis of the enantiomerically pure (R)-imine to enantiomerically pure (R)-2-fluorophenylglycine proceeds smoothly. Either the (R)- or the (S)-enantiomer of the imine can be produced at will by seeding.

Dedicated to Professor Sir J. Fraser Stoddart on the occasion of his 70th birthdayThe separation of enantiomers, which is an important step in the production of optically active chemicals for use in a variety of applications, is frequently performed using classical diastereomeric resolution, or Pasteurian resolution. [1][2][3][4] This crystallization process relies on the different solubility and crystallization propensity of the diastereomers formed by the enantiomers of a target racemate with a complementary chiral compound (the resolving agent), which forms a complex or a salt with it. The identification of the resolving agents that work for a given racemic mixture in this process relies on an empirical screening, [5] although some rationalization based on phase behavior or arguments based on supramolecular chemistry and molecular recognition can be invoked largely with hindsight. [6] The study of Pasteurian resolution involving surfaces is interesting for a number of reasons, many of which arise from the reduced symmetry possibilities in this low-dimensional environment. [7] Unlike the situation in bulk crystals, spontaneous resolution is observed very frequently on crystalline surfaces wherein domains of opposite handedness arise. [8] Enantiomers often adsorb in mirror-image domains, though their separation and collection is a tremendous task. A demonstration of Pasteurs triage at the nanoscale was shown for mirror-image clusters using the tip of a scanning tunneling microscope (STM) as a nanoscale probe. [9] Diastereomeric interactions on surfaces could be more powerful for practical separations. For instance, transfer of chirality from chemisorbed monolayers to bulk crystals has been used for the selective growth of crystals of one enantiomer in a racemic mixture in solution, which presumably involves diastereomeric interactions between the surface and the crystal nucleus, [11] while for similar cases conglomerates are formed. [12] Visualization of diastereomeric interactions on surfaces is rare. While the observation of diastereomeric interactions for the complex formed between phenylglycine and adenine was seen under ultrahigh vacuum conditions on a metal surface, [10] this process originates from the formation of chiral strips of the prochiral base followed by adhesion of the amino acid to it. It is therefore akin to a spontaneous resolution. There is no information regarding the formation of two-dimensional (2D) crystals of diastereomers in a dynamic system in solution. This observation could be very relevant to separation procedures involving the interaction of chiral molecules with surfaces.Herein we demonstrate diastereoselective adsorption on an achiral surface by surface-mediated complex formation and the in situ visualization at the molecular level by employing STM at the liquid-solid interface (Scheme 1). As part of the process, a 2D crystal is formed, and as such it is a crystallization process, albeit more dynamic than the case of bulk crystals. Although only a small fraction of the molecules...

Water was found to be a suitable solvent for the l-prolinethioamide catalysed aldol reaction of various cyclic ketones with aromatic aldehydes. Treatment of 4-nitrobenzaldehyde with as little as 1.2 equiv. of cyclohexanone in the presence of the protonated catalyst 1-TFA, afforded aldol products in high yields (up to 97%) with high diastereo- and enantioselectivity (up to >5 : 95 dr and 98% ee). The use of a high excess of ketone was avoided by conducting the aldol addition in the presence of water. Furthermore, different 'salting-out' and 'salting-in' salts were investigated and it was proven that the rate of acceleration and the stereochemical outcome of the reaction are affected by hydrophobic aggregation. Scope and limitation studies revealed that electron deficient aldehydes afforded aldol products with high stereoselectivity in the presence of 1-Cl(2)CHCO(2)H. It was shown that various cyclic ketones, under the conditions found, gave aldol products with fair yields, even if they are used in substoichiometric amounts (1.2 to 2.0 equiv.).

Three different routes to rotor-type systems on a gold surface provide sparse and dense layers of rotors with best control exerted using mixed ordered monolayers that guide the creation of the potential molecular machine components from solution.

The aggregation of a tetraaryl-porphyrin with chiral amide-containing side groups depends critically on the central metal ion in the tetrapyrrolic core, an effect shown dramatically in solution as well as in the gel formation by the compounds. In solution, the circular dichroism (CD) spectra of the metalloporphyrins show that they all aggregate to some degree, and in most cases the aggregates of the metal-containing species is more favored than the parent free-base porphyrin. The compound which shows the greatest optical activity is the zinc(II) porphyrin which forms a J-aggregate with large Cotton effects in the CD spectrum. Infrared spectroscopy revealed that this aggregate is favored by interaction of the amide oxygen atom with the zinc(II) ion at the core of the porphyrin. The other metalloporphyrins, containing divalent copper, cobalt, and palladium or manganese(III) acetate all show CD activity, and all but the cobalt compound form gels in hexane or cyclohexane. The morphology of the xerogels formed after evaporation of the solvent from these gels depend greatly on the metal ion, with only the copper porphyrin — which shows a clear H-aggregate in solution — having a fibrous morphology

This article describes a study of the outcome of racemate condensation in different types of monolayers. The study was performed on a resorcinol surfactant bearing an octadecyl chain and a lactate group which formed a monolayer at the interface of graphite and 1-phenyloctane as well as a Langmuir film at the air-water interface. Control experiments with the enantiopure materials provided the characteristics of the chiral organizations. The results obtained on the racemate show that on graphite the molecule forms chiral domains, indicating that spontaneous resolution takes place at the surface, a phenomenon that has been rationalized using molecular modeling. The X-ray crystal structure of the DMSO solvate of one of the enantiomers shows a similar type of packing to this monolayer. On the other hand, in the Langmuir layer it appears that the formation of a racemic compound is favoured, as it is in the solid state in three dimensions. The work shows how the symmetry restrictions in different environments can have a critical influence on the outcome of racemate organization, and underline the tendency of graphite to favour symmetry breaking in monolayers formed at its surface.