Discotic liquid crystals: a new generation of organic semiconductors

Discotic (disc-like) molecules typically comprising a rigid aromatic core and flexible peripheral chains have been attracting growing interest because of their fundamental importance as model systems for the study of charge and energy transport and due to the possibilities of their application in organic electronic devices. This critical review covers various aspects of recent research on discotic liquid crystals, in particular, molecular design concepts, supramolecular structure, processing into ordered thin films and fabrication of electronic devices. The chemical structure of the conjugated core of discotic molecules governs, to a large extent, their intramolecular electronic properties. Variation of the peripheral flexible chains and of the aromatic core is decisive for the tuning of self-assembly in solution and in bulk. Supramolecular organization of discotic molecules can be effectively controlled by the choice of the processing methods. In particular, approaches to obtain suitable macroscopic orientations of columnar superstructures on surfaces, that is, planar uniaxial or homeotropic alignment, are discussed together with appropriate processing techniques. Finally, an overview of charge transport in discotic materials and their application in optoelectronic devices is given.

Synthesis oftrans-1,trans-2,trans-3, andtrans-4 Bisadducts of C60by Regio- and Stereoselective Tether-Directed Remote Functionalization

The double Bingel reaction of fullerene C60 with bismalonates attached to a Tröger base derived tether afforded trans-1, trans-2, trans-3, and trans-4 bisadducts with excellent regioselectivity. In particular, enantiomerically pure bisadducts with inherently chiral trans-2 or trans-3 addition patterns were prepared starting from enantiomerically pure bismalonates. The absolute configuration of the trans-2 and trans-3 bisadducts was established from their CD spectra. The excellent diastereoselectivity in the double additions to give the trans-2 bisadducts is particularly remarkable given the large distance between the two reacting bonds in opposite hemispheres of the fullerene that is spanned by the tether. Now, all inherently chiral double addition patterns are readily available by tether-directed functionalization using appropriate chiral, nonracemic spacers.

Synthesis of mesogenic phthalocyanine-C60 donor-acceptor dyads designed for molecular heterojunction photovoltaic devices

A series of phthalocyanine-C₆₀ dyads 2a–d was synthesized. Key steps in their synthesis are preparation of the low symmetry phthalocyanine intermediate by the statistical condensation of two phthalonitriles, and the final esterification of the fullerene derivative bearing a free COOH group. Structural characterization of the molecules in solution was performed by NMR spectroscopy, UV–vis spectroscopy and cyclic voltammetry. Preliminary studies suggest formation of liquid crystalline (LC) mesophases for some of the prepared dyads. To the best of our knowledge, this is the first example of LC phthalocyanine-C₆₀ dyads.

Macrocyclic polyamines deplete cellular ATP levels and inhibit cell growth in human prostate cancer cells

In solid tumors, when O(2) partial pressure drops below 10 mmHg, ATP levels rapidly decrease due to the Warburg effect. It is known that certain macrocyclic polyamines catalyze the chemical hydrolysis of ATP with release of inorganic phosphate. Since tumor cells have diminished ATP levels as compared to normal cells, we attempted to deplete cellular ATP with macrocyclic polyamines in an effort to inhibit tumor cell proliferation. Five macrocyclic polyamines, related to the budmunchamine family of alkaloids, were prepared by total synthesis. They were the [17]-N(4) macrocycle 1, the [16]-N(4) macrocycle 20, the [18]-N(4) macrocycle 13, the [20]-N(5) macrocycle 8, and the [13]-N(3) macrocycle 17. Each one of them hydrolyzed ATP in vitro with release of P(i); the largest ring macrocycle 8 was the most efficient catalyst, while the smallest ring macrocycle 17 was the least efficient (P(i) released in these runs was on the order of 40-100 microM). The linear polyamine spermine had no hydrolytic effect on ATP. The macrocycles were found to be cytotoxic when assessed by means of a MTT assay against two human prostate cell lines, DuPro and PC-3, with resultant ID(50) values ranging between 0.5 and 1.8 microM. Colony forming efficiency (CFE) assays performed on DuPro cells, where the macrocycles were used in a concentration range of 1-8 microM, confirmed the cytotoxic effect of each macrocycle. Each killed 3-4 log of DuPro cells. The smallest ring 17 was the least cytotoxic after 24 h of incubation, although after 144 h of incubation it showed significant cytotoxicity at 8 microM. The macrocycles were equally efficient in depleting the intracellular ATP pools; after a 24 h incubation with each macrocycle other than 17 at 1-8 microM concentrations, cellular ATP concentrations were decreased by 3 orders of magnitude. The decrease in ATP levels was more pronounced after a 72 h incubation, when even 17 reduced ATP by 2 orders of magnitude. A linear pentamine of established cytotoxicity was without effect on the ATP pools. The macrocycles depleted almost entirely the intracellular pools of polyamines and were efficiently taken up by cells. A rough correlation could be established between the cytotoxic effect of the macrocyclic polyamines and their ATP-ase like activity in the DuPro cell line. As ATP is a scarce metabolite in cancer cells, where it can only be replenished through the very ATP-inefficient glycolytic pathway; macrocyclic polyamines appear to be promising new anticancer agents.

Semipreparative enantioseparation of Tröger base derivatives by HPLC

We describe the enantioseparation of functionalized derivatives of the Tröger base by HPLC on commercially available chiral stationary phases. Cellulose-derived Chiralcel OJ and brush-type Whelk O1 are demonstrated to be complementary to each other in their scope. On the basis of the results obtained, the separation of selected compounds was successfully transferred onto semipreparative columns. We believe that the availability of enantiopure functionalized derivatives of the Tröger base will stimulate the further use of this interesting molecular scaffold in molecular recognition, asymmetric catalysis, and related areas of research and technology.