Indole-based perenosins as highly potent HCl transporters and potential anti-cancer agents.

Prodigiosin is one of the most potent anion transporters in lipid bilayer membranes reported to date. Inspired by the structure of this natural product, we have recently designed and synthesised a new class of H+/Cl- cotransporters named 'perenosins'. Here we report a new library of indole-based perenosins and their anion transport properties. The new transporters demonstrated superior transmembrane transport efficiency when compared to other indole-based transporters, due to favourable encapsulating effects from the substituents on the perenosin backbone. Anion transport assays were used to determine the mechanism of chloride transport revealing that the compounds function as 'strict' HCl cotransporters. Cell viability studies showed that some compounds specifically trigger late-onset cell death after 72 h with a unique correlation to the position of alkyl chains on the perenosins. Further investigations of cell death mechanism showed a mixture of cell cycle arrest and apoptosis was responsible for the observed decrease in cell viability.

Perenosins: a new class of anion transporter with anti-cancer activity.

A new class of anion transporter named 'perenosins' consisting of a pyrrole linked through an imine to either an indole, benzimidazole or indazole is reported. The indole containing members of the perenosin family function as effective transmembrane Cl(-)/NO3(-) antiporters and HCl cotransporters in a manner similar to the prodigiosenes. The compounds reduce the viability of MDA-MB-231 and MCF-7.

Current-Driven Supramolecular Motor with In Situ Surface Chiral Directionality Switching.

Surface-supported molecular motors are nanomechanical devices of particular interest in terms of future nanoscale applications. However, the molecular motors realized so far consist of covalently bonded groups that cannot be reconfigured without undergoing a chemical reaction. Here we demonstrate that a platinum-porphyrin-based supramolecularly assembled dimer supported on a Au(111) surface can be rotated with high directionality using the tunneling current of a scanning tunneling microscope (STM). Rotational direction of this molecular motor is determined solely by the surface chirality of the dimer, and most importantly, the chirality can be inverted in situ through a process involving an intradimer rearrangement. Our result opens the way for the construction of complex molecular machines on a surface to mimic at a smaller scale versatile biological supramolecular motors.

Synthetic ion transporters can induce apoptosis by facilitating chloride anion transport into cells.

Anion transporters based on small molecules have received attention as therapeutic agents because of their potential to disrupt cellular ion homeostasis. However, a direct correlation between a change in cellular chloride anion concentration and cytotoxicity has not been established for synthetic ion carriers. Here we show that two pyridine diamide-strapped calix[4]pyrroles induce coupled chloride anion and sodium cation transport in both liposomal models and cells, and promote cell death by increasing intracellular chloride and sodium ion concentrations. Removing either ion from the extracellular media or blocking natural sodium channels with amiloride prevents this effect. Cell experiments show that the ion transporters induce the sodium chloride influx, which leads to an increased concentration of reactive oxygen species, release of cytochrome c from the mitochondria and apoptosis via caspase activation. However, they do not activate the caspase-independent apoptotic pathway associated with the apoptosis-inducing factor. Ion transporters, therefore, represent an attractive approach for regulating cellular processes that are normally controlled tightly by homeostasis.

Arylpyrrole oligomers as tunable anion receptors.

A novel type of arylpyrrole oligomer possessing an appropriate electropositive cavity has been designed, prepared and analysed for use as readily accessible receptors for negatively charged guests. Affinities of the receptors for various anions were determined by UV/Vis titration experiments and in depth insights into the host-guest interactions were gained by performing (1)H NMR titration experiments and X-ray crystallographic structure analyses. Experimentally determined association constants were correlated with the calculated maximum electrostatic potentials of the electropositive cavities of the receptors, allowing estimation of the strengths of host-guest associations in similar compounds. The joint contribution of aryl C-H and pyrrole N-H hydrogens was shown to be key to a strong guest association, resulting in the arylpyrrole oligomers being efficient anion receptors.

Porphyrin-based sensor nanoarchitectonics in diverse physical detection modes.

Porphyrins and related families of molecules are important organic modules as has been reflected in the award of the Nobel Prizes in Chemistry in 1915, 1930, 1961, 1962, 1965, and 1988 for work on porphyrin-related biological functionalities. The porphyrin core can be synthetically modified by introduction of various functional groups and other elements, allowing creation of numerous types of porphyrin derivatives. This feature makes porphyrins extremely useful molecules especially in combination with their other interesting photonic, electronic and magnetic properties, which in turn is reflected in their diverse signal input-output functionalities based on interactions with other molecules and external stimuli. Therefore, porphyrins and related macrocycles play a preeminent role in sensing applications involving chromophores. In this review, we discuss recent developments in porphyrin-based sensing applications in conjunction with the new advanced concept of nanoarchitectonics, which creates functional nanostructures based on a profound understanding of mutual interactions between the individual nanostructures and their arbitrary arrangements. Following a brief explanation of the basics of porphyrin chemistry and physics, recent examples in the corresponding fields are discussed according to a classification based on physical modes of detection including optical detection (absorption/photoluminescence spectroscopy and energy and electron transfer processes), other spectral modes (circular dichroism, plasmon and nuclear magnetic resonance), electronic and electrochemical modes, and other sensing modes.

Bioactive flake-shell capsules: soft silica nanoparticles for efficient enzyme immobilization.

Amorphous silica particles are used extensively in industrial processes as well as in scientific and biomedical research. Flake-shell silica nanoparticles, prepared by self-templating hydrothermal synthesis, exhibit large surface areas and pore volumes, hollow spherical morphology, as well as hydrophilic surfaces, affording great potential for their application in enzyme immobilization. In this work we show that the shell, which is composed of a network of silica flakes, promotes uptake of enzymes of different sizes, i.e., lysozyme, lipase, and chymotrypsin. Moreover, the capsules provide a favorable porous structure for diffusion of small substrate molecules while permitting enzymes to retain their activity. The silica composition of the capsules provides structural stability, biocompatibility and allows easy functionalization. Amine and dextran functionalities were introduced to modify the shell morphology and to control enzyme loading and activity. The efficient protein immobilization on these inorganic capsules should lead to their application in biocatalysis, biosensing and drug delivery.

Synthetic and structural exploration of [2(4)]tetrathiacalix[2]arene[2]pyrimidines.

A novel class of two atom bridged metacyclophanes-[2(4)]thiacalix[2]arene[2]pyrimidines-has been synthesized via a straightforward S(N)Ar reaction. The conformational properties and intra-annular dimensions of the [2(4)]thiacalix[2]arene[2]pyrimidines were evaluated by X-ray structure analysis and compared with known homothia- and thiacalixarenes. Post-macrocyclization oxidation of the bridging sulfur moieties resulted in a [2(4)]sulfonylcalix[2]arene[2]pyrimidine, which gave access to an unexplored cavity size among sulfonylcalixarenes.

(Thio)ureido anion receptors based on a 1,3-alternate oxacalix[2]arene[2]pyrimidine scaffold.

In pursuit of highly preorganized macrocyclic host molecules for the complexation of anions, a series of oxacalix[2]arene[2]pyrimidine-based bis(thio)ureido receptors were synthesized and fully characterized. The pincer-like 1,3-alternate conformation of the oxacalix[4]arene scaffold, essential for an efficient host-guest interaction, was visualized by single-crystal X-ray analysis and supported by variable-temperature NMR studies. The anion binding properties of the receptors were evaluated via (1)H NMR titration experiments, showing intermolecular interactions with H(2)PO(4)(-), AcO(-), BzO(-), and Cl(-) ions. The host molecule bearing 4-nitrophenyl substituents on the bisurea binding pocket showed association constants in the range of 200-400 M(-1) in the strongly competitive solvent mixture of DMSO/0.5% H(2)O.

Selenacalix[3]triazines: synthesis and host-guest chemistry.

The heteracalixarene series (N/O/S) has been expanded with Se-bridged cyclotrimeric macrocycles. Selenacalix[3]triazines were synthesized by convenient one-pot nucleophilic aromatic substitution reactions and they showed peculiar supramolecular features. The N tridentate binding pocket was capable of coordinating both copper ions and anions.

Morpholinecarbonyl-Rhodamine 110 based substrates for the determination of protease activity with accurate kinetic parameters.

Commonly used fluorogenic substrate analogues for the detection of protease activity contain two enzyme-cleavable bonds conjugated to the fluorophore. Enzymatic cleavage follows a two-step reaction with a monoamide intermediate. This intermediate shows fluorescence at the same wavelength as the final product complicating the kinetic analysis of fluorescence-based assays. Fluorogenic substrate analogues for α-chymotrypsin with one cleavable peptide bond have been prepared from morpholinecarbonyl-Rhodamine 110 (MC-Rh110). A comparison of their kinetic properties with the corresponding (peptide)(2)-Rh110 derivatives revealed that these frequently used double-substituted substrate analogues yield only apparent K(m) and k(cat) values that are quite different from the kinetic parameters obtained from the monosubstituted MC-Rh110 based substrate analogues. Although both the monoamide intermediate and MC-Rh110 are monosubstituted Rhodamine 110 derivatives, they show different spectroscopic properties. The data from the spectroscopic analysis clearly show that these properties are directly related to the electron structure of the fluorophore and not to the previously proposed equilibrium between the lactone form and the open ionic form of the fluorophore. This knowledge about the determinants of the spectroscopic properties of monosubstituted Rhodamine 110 introduces a way for a more systematic development of new fluorogenic protease substrate analogues.

Homothiacalix[4]arenes: synthetic exploration and solid-state structures.

Homothiacalix[n]arenes have been largely underexposed compared with related (homo)heteracalixarenes, although their inherent structural features are particularly attractive for supramolecular host-guest chemistry. In this contribution, the synthetic macrocyclization protocols that afford homothiacalix[n]arenes have been reinvestigated and optimized, providing straightforward access to the parent homothiacalix[4]arene skeleton. Moreover, inner-rim (bis and tetrakis) ester functionalization and dimethylenethia bridge oxidation were successfully performed as well. Solution-phase (variable-temperature) NMR spectroscopy studies and solid-state X-ray structures provided complementary information on the conformational features of the novel macrocycles.

Odd-numbered oxacalix[n]arenes (n = 5, 7): synthesis and solid-state structures.

The critical synthetic access to odd-numbered calix[n]arenes has evidently resulted in less attention for these macrocycles, although specific molecular recognition phenomena have been observed for some of them. A straightforward fragment coupling approach has been designed, applying kinetically controlled nucleophilic aromatic substitution reaction conditions, affording odd-numbered oxacalix[n]arenes (n = 5, 7) selectively in high yields. The solid-state conformational behavior and the oxacalix[n]arene cavity size were explored by single-crystal X-ray diffraction studies.

Efficient fragment coupling approaches toward large oxacalix[n]arenes (n = 6, 8).

The first rational, stepwise synthesis of enlarged oxacalix[n]arenes (n > 4) is described. Variously substituted oxacalix[3]arene[3]pyrimidines were prepared rather selectively by a straightforward [3 + 3] fragment coupling approach after a thorough search for the optimum nucleophilic aromatic substitution conditions. Similar procedures also allowed facile synthesis of unsymmetrical oxacalix[4]- and oxacalix[8]arenes.

Reductive demetallation of Cu-corroles--a new protective strategy towards functional free-base corroles.

A novel procedure for the reductive demetallation of Cu-meso-triarylcorroles has been disclosed. The reversible sequence copper metallation/demetallation was proven to be an effective protection/deprotection strategy towards sophisticated functionalized free-base corroles.

Efficient post-macrocyclization functionalizations of oxacalix[2]arene[2]pyrimidines.

Diversely functionalized oxacalix[2]arene[2]pyrimidines have been synthesized starting from a bis(methylsulfanyl)-substituted oxacalix[4]arene by two efficient post-macrocyclization pathways. Functionalized aryl groups were introduced on the pyrimidine building block via Liebeskind-Srogl cross-coupling reactions, while a variety of O-, S-, N-, and C-nucleophiles were inserted on the calixarene skeleton by nucleophilic aromatic substitution reactions on the bis(methylsulfonyl)oxacalix[4]arene analogue.

Selective synthesis of functionalized thia- and oxacalix[2]arene[2]pyrimidines.

Functionalized oxacalix[m]arene[n]pyrimidines have been synthesized by S(N)Ar on 4,6-dihalopyrimidine building blocks. Depending on the S(N)Ar conditions, either a mixture of oxacalix[n]arenes, ranging from oxacalix[4]- up to oxacalix[12]arene, could be prepared or the oxacalix[4]arene could be synthesized selectively in a high yield. The electrophilic (pyrimidine) and the nucleophilic components could both be varied, allowing the preparation of functionalized oxacalix[4]arenes. Moreover, the procedure also gives access to the analogous thiacalix[4]arenes.