Nanostructured assemblies of liquid-crystalline supermolecules: from display to medicine

ABSTRACT

Liquid crystal oligomers have a supermolecular structure in which two or more mesogenic units are interconnected through flexible spacers. They can form various molecular packing structures in their liquid-crystalline phases. We present flexible LC oligomers stabilising optically isotropic phases, i.e. blue phases (BPs) and chiral conglomerate phases. Hysteresis free switching, high contrast and wide viewing angle are obtainable in the amorphous BPIII without surface treatment. Spontaneous mirror symmetry breaking in layered phases of achiral flexible linear trimers produces periodic nanostructured surfaces. Then we demonstrate the effects of liquid-crystallinity on anticancer activities. Biological systems have links with liquid crystallinity. We found a molecular assembly of mesogenic molecules possessing an active site as a novel therapeutic approach against solid cancer cells.     

Piperidines: a new class of urease inhibitors

A variety of piperidines (2-12, 14-26) with variable substituents at N-atoms have been synthesized and evaluated as urease inhibitors. The synthesized compounds showed varying degree of urease inhibitory activity ranging from 31.97 to 254 microM. The size and electron-donating or -withdrawing effects of substituents influence the activity, which lead to the formation of urease inhibitors.     

Nitrocyclohexadienones : a new class of nitrating agents

Various nitrocyclohexadienones are proposed as new nitrating agents. These compounds are easy to prepare from corresponding phenols, easy to handle and stable. Nitrocyclohexadienones act as nitronium carriers using rearomatization as the driving force and permit nitration of highly activated substrates under mild conditions and with good yields.     

Oligoindenopyrenes: a new class of polycyclic aromatics

A new class of polycyclic aromatic hydrocarbons--oligoindenopyrenes--has been synthesized featuring a Pd-catalyzed Suzuki-Heck coupling cascade. The oligoindenopyrenes are robust, highly colored substructures of C(70) and have properties that might prove useful in new organic materials or devices. After excitation, the tetraindenopyrene derivative 3d undergoes efficient deactivation (99%) by internal conversion to the ground state. The small fluorescence quantum yield (0.004) is in accordance with the short (0.6 ns) fluorescence decay time.     

Tetraazaperopyrenes: a new class of multifunctional chromophores

Tetraazaperopyrene and a range of derivatives have been synthesised and their photophysical and redox-chemical properties studied. The parent compound, 1,3,8,10-tetraazaperopyrene (1), was prepared by treating 4,9-diamino-3,10-perylenequinone diimine with triethyl orthoformate, whereas the 2,9-disubstituted derivatives of 1 were obtained after treatment with the corresponding carboxylic acid chloride or anhydride (2 mol equiv). The 1,3,8,10-tetraazaperopyrene core structure was established by X-ray diffraction of 2,9-bis(2-bromophenyl)-1,3,8,10-tetraazaperopyrene (6). The UV-visible absorption spectra of the compounds have a characteristic visible pi(*)<--pi absorption band at 440 nm (log epsilon(max)=4.80) with a strong vibrational progression (Delta nu approximately 1450 cm(-1)). Diprotonation of the nitrogen atoms induces a bathochromic shift of this band from 430-440 to 470-480 nm and all four nitrogen atoms are protonated when pure H(2)SO(4) is used as the solvent. The first and second as well as the third and fourth protonations occur concomitantly, which implies that they have very similar pK(a) values and, consequently, similar proton affinities. A theoretical study of the proton affinities in the gas phase and in solution attributes this behaviour to the effects of polar solvents, which dampen the charge of a protonated site at the other end of the molecule and thus effectively decouple the two opposite pyrimidine units in the polycondensed aromatic compound. The photophysical data were modelled in a time-dependent DFT study of 1, 1H(2)(2+) and 1H(4)(4+) in both the gas phase and in a polar solvent. All the dyes show weak fluorescence in organic solvents, however, their protonated conjugate acids show dramatically increased fluorescence intensity. All of the dyes undergo two electrochemically reversible one-electron reductions with cyclovoltammetric half-wave potentials at E(red1) approximately -0.9 V and E(red2) approximately -1.3 V (vs. SCE), which are associated with characteristic spectral changes.     

Myrotoxins: a new class of macrocyclic trichothecenes

An isolate of $\text{Myrothecium roridum}$ which is a pathogen on tomatoes in Texas produces a new class of C27 macrocyclic trichothecenes which contains a nonconjugated diene system that includes a vinyl ether group.     

Bridged triarylamines: a new class of heterohelicenes

A series of bridged triarylamines, which constitute a new class of heterohelicenes, have been synthesized using a simple three-step procedure. These compounds are shown to be highly luminescent chromophores and are capable of being oxidized. The solid-state structures of these helicenes show a tendency for pi-stacking interactions into an overall zigzag motif.     

Supramolecular Chirality: Chiral hydrogen-bonded supermolecules from achiral molecular components

Chiral supermolecules may be obtained from suitable achiral molecular constituents associated through a dissymmetrizing interaction mode. This is the case for the supermolecules I–IV formed by hydrogen-bonding association between the achiral complementary components 1a , b and 2a , b , c . The crystal structures of the supermolecular pairs I–III and of the homochiral aggregate of two ternary supermolecules IV have been determined. The structural data are discussed.     

Geminal imidazolium salts: a new class of gelators

The gelling behavior of some geminal diimidazolium salts was investigated in solvents differing in polarity and hydrogen bond donor ability. The used salts, namely the 3,3'-di-n-decyl-1,1'(1,4-phenylenedimethylene)diimidazolium dibromide [p-Xyl-(decim)(2)][Br](2) (1), the 3,3'-di-n-dodecyl-1,1'(1,4-phenylenedimethylene)diimidazolium dibromide [p-Xyl-(dodecim)(2)][Br](2) (2), and the 3,3'-di-n-dodecyl-1,1'(1,4-phenylenedimethylene)diimidazolium ditetrafluoroborate [p-Xyl-(dodecim)(2)][BF(4)](2) (3), differ in the alkyl chain length and in the anion properties, such as size, shape, and coordination ability. In all cases in which gelation process was observed, the obtained gels were characterized by gel melting temperature determination, resonance light scattering, and UV-vis measurements. On the whole, the investigation allowed to get information about both the thermodynamic stability and the features of the aggregates characterizing the soft materials at the equilibrium. Data collected by us point out that the used organic salts are able to behave as both hydro- and organogelators. In particular, bromide salts formed hydrogels in the presence of α-cyclodextrin allowing to hypothesize that the gelation process is favored by the formation of supramolecular assemblies. To verify this hypothesis, 1D and 2D (1)H NMR measurements were carried out. Both the alkyl chain length and the anion ability to reticulate the three-dimensional network proved to be determinant factors in affecting the gelation process as well as the features of the gel phases. Finally, with the future aim to use the obtained gels as reaction media, the effect of a guest molecule such as the UV-vis active probe Nile Red was studied.     

The quettamines: a new class of isoquinoline alkaloids

Three quettamine type alkaloids, which incorporate either a benzofuran or a dihydrobenzofuran moiety within the molecular framework, have been obtained from $\text{Berberis}$$\text{baluchistanica}$. These are dihydrosecoquettamine ($\text{1}$), secoquettamine ($\text{2}$), and quettamine chloride ($\text{3}$). Alkaloids $\text{1}$ and $\text{3}$ are racemates. Hofmann degradation of quettamine ($\text{3}$) provides secoquettamine ($\text{2}$) and the styrene $\text{4}$ which has a trans relationship between the hydrogens at C-1 and C-α, thus indicating the identical stereochemistry in quettamine. Emde reduction of quettamine leads to dihydrosecoquettamine ($\text{1}$) and the stilbene $\text{5}$. Two other polar alkaloids in the plant are (+)-armepavine methochloride ($\text{6}$) and oblongine chloride ($\text{7}$). An oblongine type alkaloid must be the biogenetic precursor for the quettamines. Arguments are presented favoring direct oxidative coupling in the biogenesis of the cularine alkaloids.     

Multi-vicinal fluoroalkanes: a new class of organofluorine compounds

"Multi-vicinal fluoroalkanes" are straight-chain alkanes in which each adjacent carbon atom is bonded to one fluorine atom. Such molecules may be regarded as intermediate in structure between alkanes and perfluoroalkanes. The alternate fluoromethylene groups also generate stereogenic centres, which need to be controlled during synthesis. This review will describe our recent progress in the preparation of such single isomer motifs and the study of the conformational behaviour of this new class of organofluorine compounds.     

Flip-flop sensors: a new class of silicon sensors

Integrated sensors based on flip-flops have been succesfully fabricated for the measurement of several physical parameters and subsequently tested. The sensors consist of flip-flops in which one circuit element is sensitive to the desired physical parameter. The sensing action consists of alternately bringing the flip-flop into an unstable and a stable state and counting the resulting ones or zeros. This number is a measure for the asymmetry of the flip-flop and thus for the physical parameter. To illustrate the principle, a force sensor based on a flip-flop containing piezoresistors is presented.     

Oxygenic polyoxometalates: a new class of molecular propellers

The oxygen evolving catalyst [Ru(4)(μ-OH)(2)(μ-O)(4)(H(2)O)(4)(γ-SiW(10)O(36))(2)](10-) effects H(2)O(2) dismutation at rates (k = 36.8 ± 1.4 M(-1) s(-1)), one/two order of magnitude higher compared to related tetra-substituted Cu, Fe, Mn, Ni and even Co polyoxometalates, thus providing localised oxygen gas bursts to power nano-propulsion of composite materials.     

Medium-bridged lactams: a new class of non-planar amides

Medium-bridged twisted lactams, in which a non-planar amide bond is achieved by incorporating the nitrogen atom at the bridgehead position in a medium-sized heterocycle, offer an attractive setting in which to study the properties of distorted amide linkages. This Emerging Area article will describe progress in the preparation and study of these compounds. This work shows that compounds containing an even moderately distorted amide bond display useful and unusual chemical properties while retaining a measure of stability that enables their study.     

Imprinted nanomaterials: a new class of synthetic receptors

The molecular imprinting approach provides a unique opportunity for the creation of three-dimensional cavities with tailored recognition properties. Over the last decade this field has expanded considerably, across a variety of disciplines, leading to novel approaches and many potential applications. Progress in the field of materials science has led to significant breakthroughs and the application of the imprinting approach to novel polymeric formats offers new insights and attractive methods for the preparation of synthetic receptors. In particular, nanomaterials have received considerable attention in the developing field of nanotechnology. With a large number of recent developments in the field of molecular imprinting available, this article is focused on a selection of new systems, in particular the different formats of nanomaterials, such as nanogels, nanofibres, nanowires and nanotubes.     

Molecules to supermolecules and self assembly: a study of some cocrystals of cyanuric acid

The preparation and structure elucidation of cocrystals 1a, 1b, 2a-4a, formed from cyanuric acid (CA) and the aza-donor compounds 4,7-phenanthroline, 1,7-phenanthroline, phenazine and 1,3-bis(4-pyridyl)propane, respectively, have been reported. While CA forms different types of self-assembling modes—monomers (1a), dimers (1b and 4a) and infinite tapes (2a and 3a)—the recognition of the constituents, however, is through a triple hydrogen-bonding pattern, consisting of an N-H?N and two C-H?O hydrogen bonds, except in 4a.     

Composition of fullerene-containing styrene-diallyl isophthalate copolymers

The effect of fullerene C₆₀ on the composition of macromolecules in the free-radical copolymerization of styrene with diallyl isophthalate is estimated. It is shown that the maximum amount of C₆₀ is contained in the high-molecular-mass fraction of the products. Constants in the Kuhn-Mark-Houwink equation are determined for the fullerene-containing copolymer synthesized from an equimolar mixture of monomers.     

Enolphosphato-phosphines: a new class of P,O ligands

The new bifunctional ligands Ph(2)PCH[double bond]CPh[OP(O)(OR)(2)] (1) (1a, R = Et; 1b, R = Ph) represent the first examples of P,O derivatives resulting from the association of a phosphine moiety and an enolphosphate group. The Z stereochemistry about the double bond provides a favorable situation for these ligands to act as P,O-chelates. Neutral and cationic Pd(II) complexes have been synthesized and characterized, in which 1a or 1b acts either as a P-monodentate ligand or a P,O-chelate, via coordination of the oxygen atom of the P[double bond]O group. In the latter case, it has been observed that phosphines 1a and 1b can display a hemilabile behavior, owing to successive dissociation and recoordination of the O atom. Competition experiments revealed that phosphine 1a presents a higher chelating ability than 1b, a feature ascribed to the more electrodonating properties of the ethoxy groups in 1a compared to the phenoxy groups in 1b. P,O-Chelation affords seven-membered metallocycles, which is unusual for P,O-chelates. Complexes trans-[PdCl(2)[Ph(2)PCH[double bond]C(Ph)OP(O)(OPh)(2)](2)] (2b), [PdCl[Ph(2)PCHdouble bond]C(Ph)OP(O)(OEt)(2)](mu-Cl)](2) (3a), [complex--see text] (8a'), and [complex--see text] (10a) have been structurally characterized. Interestingly, the seven-membered rings in 8a' and 10a adopt a sofa conformation with the double bond lying almost perpendicular to the plane containing the Pd, the two P, and the two O atoms.