Homochiral Structures Research Articles

One-Dimensional Double Helical Structure and 4-Fold Type [2 + 2] Interpenetration of Diamondoid Networks with Helical Fashion

We have prepared unique homochiral structures by the self-assembly of a modified amino acid derivative (terephthaloylmonoalanine, L-TMA) with metal ions such as Zn(II) and Cd(II). An L-TMA ligand and Zn(II) ions formed a left-handed, homochiral, double helical chain. However, while L-TMA and Cd(II) ions topologically formed a diamondoid Cd-L-TMA network with 4-fold type [2 + 2] interpenetration, Cd-L-TMA can be morphologically considered as a three-dimensional network of left-handed, double helices. The double helical structure of Zn-L-TMA originated from the self-assembly of individual helical chains by hydrogen bonds and π−π interactions, whereas the double helical structures of Cd-L-TMA were observed in an interpenetrating diamondoid net.

Comparative Study of Homochiral and Racemic Chiral Metal-Organic Frameworks Built from Camphoric Acid

The study of the crystallization of homochiral or racemic chiral framework materials from enantiopure or racemic ligands is an important step for the rational design of crystalline homochiral materials. The self-assembly of extended frameworks in the presence of enantiopure or racemic ligands is regulated by the differing symmetry requirements of the ligand. By employing both enantiopure and racemic ligands as cross-linking ligands, we have prepared three homochiral and three racemic chiral compounds and their synthesis and structural and topological properties are presented here. It is shown that depending on the chemical compositions and framework topologies, the effect of the ligand handedness on the resulting crystal structure can vary greatly. The ligand handedness can have negligible effect on the crystallization, which leads to an interesting example of two pairs of isostructural achiral and homochiral structures with two types of six-connected nets. In another example reported here, the racemic ch...

Homochiral metal–organic coordination networks from l-typtophan

Three homochiral metal–organic coordination networks [Co 2( l-Trp) 2(Py) 6] · Py · (ClO 4) 2 ( 1), [Ni( l-Trp)(Py) 3] · H 2O · ClO 4 ( 2) and [Co 2( l-Trp)(INT) 2(H 2O) 2(ClO 4)] ( 3), all containing natural amino acid l-HTrp ( l-typtophan), were hydrothermally synthesized and structurally characterized. The compounds 1 and 2 crystallize in the orthorhombic space group C222 1, with a = 10.731(2) Å, b = 19.709(4) Å, c = 27.365(6) Å and Z = 4 for 1 and a = 10.710(10) Å, b = 20.088(18) Å, c = 27.63(3) Å and Z = 8 for 2, respectively. The compound 3 has the monoclinic space group P2 1, with a = 8.1934(14) Å, b = 13.209(2) Å, c = 12.464(2) Å, β = 104.107(3)° and Z = 2. Both 1 and 2 consist of 1D helical chains. Compound 3 is composed of 2D networks, which further assemble into a 3D supramolecular structure via weak interlayer interactions. The optically pure amino acid l-HTrp plays an important role leading to homochiral structures reported here.

Homo- and heterochiral coordination polymers of silver with diaminocyclohexane as bridging ligand: The effect of chirality on argentophilic interactions

Five new coordination polymers have been obtained from silver salts of weakly or non-coordinating anions. In their crystal structures trans-1,2-diaminocyclohexane acts as a bridging ligand and links di- or tri-coordinated Ag(I) to polycationic chains. Relevant structural features such as silver–silver contacts do not only depend on the choice of the counteranion but also reflect the influence of the chirality of the bridging ligand. In racemic crystals, heterochiral strands prevail, and argentophilic interactions may occur between adjacent polymer chains. In one of the homochiral structures, the diaminocyclohexane ligand adopts a new conformation which allows for short intermetal distances within the chain.

On the interpretation of the racemic states of the B 2 phase of banana-shaped mesogens

We show that the racemic states of the B 2 phase of liquid crystals composed of banana-shaped molecules do not satisfy the Curie principle. Thus it is argued that these states cannot exist in bulk samples and the homochiral states constitute the only stable microscopic structures. A reinterpretation of the racemic states with the same macroscopic optical behaviour is proposed in terms of mixtures of the homochiral structures.

Supramolecular chirality: a reporter of structural memory.

Supramolecular chirality: a reporter of structural memory.

Homochiral structures derived from 1-[1-(2-thienyl)cyclohexyl]piperidine (TCP) are potent non-competitive antagonists of glutamate at NMDA receptor sites

The racemates of cis (pip/Me) 1-[1-(2-thienyl)-2-methylcyclohexyl]piperidine and cis (pip/Me) 1-[1-(2-furanyl)-2-methylcyclohexyl]piperidine, 2 derivatives of the noncompetitive N-methyl- d-aspartate (NMDA) antagonist 1-[1-(2-thienyl)cyclohexyl]piperidine (TCP) have been synthesized. The corresponding isomers were resolved by a crystallization procedure, via the diastereoisomeric salts formed with (+)- and (-)-di- O,O′-4-toluoyltartaric acid. The absolute configuration was determined by single-crystal X-ray analysis and by comparison with previously published data in related series. The 4 homochiral structures obtained were tested for their affinity for the PCP receptor sites labelled with [ 3H]TCP. Their neuroprotective potency was assessed in primary cultured neuronal cells against neurotoxicity induced by glutamate. The 2 (-)-1 S, 2 R-isomers displayed the highest affinity for the PCP receptor sites and the highest efficacy for neuronal protection in comparison with the (+)-1 R, 2 S-isomers.

Homochirality and stereospecific activity: evolutionary aspects

The problem discussed in this paper is the connection between the unique property of biopolymers (proteins, DNA and RNA), i.e. homochirality, and their main functional property, i.e. self-replication. Our approach is based on an analysis of the conditions for the origination of the mechanism of self-replication of chiral polymers. It is demonstrated that self-replication could originate only on the basis of homochiral structures, possessing stereospecific (enzymatic) activity. It is also shown that complete breaking of the mirror symmetry of the organic medium is required both at the stage of polymeric takeover and at the stage of formation of structures possessing stereospecific activity. This requirement is satisfied only in the framework of the mechanism of spontaneous symmetry breaking i.e. the mechanism of non-equilibrium phase transition from the racemic state of the organic medium to the chirally pure one. The results obtained suggest that homchirality is a necessary condition for the origination of biological specificity and plays a fundamental role in the formation of structures capable of self-replication.