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Suitably designed molecular and supramolecular species are capable of combining light and chemical inputs to perform functions that mimic those of macroscopic devices. This paper describes the working principles of molecular‐level photochemionic devices for i) chemical switching of photonic input/output signals, ii) chemical tuning of photonic input/output signals, and iii) the transformation of chemical and/or optical signals for logic operation.

With the fabrication of molecular electronic devices (MEDs) and the construction of nanoelectromechanical systems (NEMSs) as incentives, two constitutionally isomeric, redox-controllable [2]rotaxanes have been synthesized and characterized in solution. Therein, they both behave as near-perfect molecular switches, that is, to all intents and purposes, these two rotaxanes can be switched precisely by applying appropriate redox stimuli between two distinct chemomechanical states. Their dumbbell-shaped components are composed of polyether chains interrupted along their lengths by i) two π-electron rich recognition sites—a tetrathiafulvalene (TTF) unit and a 1,5-dioxynaphthalene (DNP) moiety—with ii) a rigid terphenylene spacer placed between the two recognition sites, and then terminated by iii) a hydrophobic tetraarylmethane stopper at one end and a hydrophilic dendritic stopper at the other end of the dumbbells, thus conferring amphiphilicity upon these molecules. A template-directed protocol produces a means to introduce the tetracationic cyclophane, cyclobis(paraquat-p-phenylene) (CBPQT⁴⁺), which contains two π-electron accepting bipyridinium units, mechanically interlocked around the dumbbell-shaped components. Both the TTF unit and the DNP moiety are potential stations for CBPQT⁴⁺, since they can establish charge-transfer and hydrogen bonding interactions with the bipyridinium units of the cyclophane, thereby introducing bistability into the [2]rotaxanes. In both constitutional isomers, ¹H NMR and absorption spectroscopies, together with electrochemical investigations, reveal that the CBPQT⁴⁺ ring is predominantly located on the TTF unit, leading to the existence of a single translational isomer (co-conformation) in both cases. In addition, a model [2]rotaxane, incorporating hydrophobic tetraarylmethane stoppers at both ends of its dumbbell-shaped component, has also been synthesized as a point of reference. Molecular synthetic approaches were used to construct convergently the dumbbell-shaped compounds by assembling progressively smaller building blocks in the shape of the rigid spacer, the TTF unit and the DNP moiety, and the hydrophobic and hydrophilic stoppers. The two amphiphilic bistable [2]rotaxanes are constitutional isomers in the sense that, in one constitution, the TTF unit is adjacent to the hydrophobic stopper, whereas in the other, it is next to the hydrophilic stopper. All three bistable [2]rotaxanes have been isolated as green solids. Electrospray and fast atom bombardment mass spectra support the gross structural assignments given to all three of these mechanically interlocked compounds. Their photophysical and electrochemical properties have been investigated in acetonitrile. The results obtained from these investigations confirm that, in all three [2]rotaxanes, i) the CBPQT⁴⁺ cyclophane encircles the TTF unit, ii) the CBPQT⁴⁺ cyclophane shuttles between the TTF and DNP stations upon electrochemical or chemical oxidation/reduction of the TTF unit, and iii) folded conformations are present in which the CBPQT⁴⁺ cyclophane, while encircling the TTF unit, interacts through its π-accepting bipyridinium exteriors with other π-donating components of the dumbbells, especially those located within the stoppers.

With the fabrication of molecular electronic devices (MEDs) and the construction of nanoelectromechanical systems (NEMSs) as incentives, two constitutionally isomeric, redox‐controllable [2]rotaxanes have been synthesized and characterized in solution. Therein, they both behave as near‐perfect molecular switches, that is, to all intents and purposes, these two rotaxanes can be switched precisely by applying appropriate redox stimuli between two distinct chemomechanical states. Their dumbbell‐shaped components are composed of polyether chains interrupted along their lengths by i) two π‐electron rich recognition sites—a tetrathiafulvalene (TTF) unit and a 1,5‐dioxynaphthalene (DNP) moiety—with ii) a rigid terphenylene spacer placed between the two recognition sites, and then terminated by iii) a hydrophobic tetraarylmethane stopper at one end and a hydrophilic dendritic stopper at the other end of the dumbbells, thus conferring amphiphilicity upon these molecules. A template‐directed protocol produces a means to introduce the tetracationic cyclophane, cyclobis(paraquat‐p‐phenylene) (CBPQT4+), which contains two π‐electron accepting bipyridinium units, mechanically interlocked around the dumbbell‐shaped components. Both the TTF unit and the DNP moiety are potential stations for CBPQT4+, since they can establish charge‐transfer and hydrogen bonding interactions with the bipyridinium units of the cyclophane, thereby introducing bistability into the [2]rotaxanes. In both constitutional isomers, 1H NMR and absorption spectroscopies, together with electrochemical investigations, reveal that the CBPQT4+ring is predominantly located on the TTF unit, leading to the existence of a single translational isomer (co‐conformation) in both cases. In addition, a model [2]rotaxane, incorporating hydrophobic tetraarylmethane stoppers at both ends of its dumbbell‐shaped component, has also been synthesized as a point of reference. Molecular synthetic approaches were used to construct convergently the dumbbell‐shaped compounds by assembling progressively smaller building blocks in the shape of the rigid spacer, the TTF unit and the DNP moiety, and the hydrophobic and hydrophilic stoppers. The two amphiphilic bistable [2]rotaxanes are constitutional isomers in the sense that, in one constitution, the TTF unit is adjacent to the hydrophobic stopper, whereas in the other, it is next to the hydrophilic stopper. All three bistable [2]rotaxanes have been isolated as green solids. Electrospray and fast atom bombardment mass spectra support the gross structural assignments given to all three of these mechanically interlocked compounds. Their photophysical and electrochemical properties have been investigated in acetonitrile. The results obtained from these investigations confirm that, in all three [2]rotaxanes, i) the CBPQT4+cyclophane encircles the TTF unit, ii) the CBPQT4+cyclophane shuttles between the TTF and DNP stations upon electrochemical or chemical oxidation/reduction of the TTF unit, and iii) folded conformations are present in which the CBPQT4+cyclophane, while encircling the TTF unit, interacts through its π‐accepting bipyridinium exteriors with other π‐donating components of the dumbbells, especially those located within the stoppers.

Two molecular shuttles/switches—a slow one and a fast one—in the shape of amphiphilic, bistable [2]rotaxanes have been synthesized and characterized. Both [2]rotaxanes contain a hydrophobic, tetraarylmethane and a hydrophilic, dendritic stopper. They are comprised of two π‐electron‐rich stations—a monopyrrolotetrathiafulvalene unit and a 1,5‐dioxynaphthalene moiety—which can act as recognition sites for the tetracationic cyclophane, cyclobis(paraquat‐p‐phenylene), to reside around. In addition, a model [2]rotaxane, incorporating only a monopyrrolotetrathiafulvalene unit in the rod section of the amphiphilic dumbbell component and cyclobis(paraquat‐p‐phenylene) as the ring component, has been investigated. The dumbbell‐shaped components were constructed using conventional synthetic methodologies to assemble 1) the hydrophobic, tetraarylmethane stopper and 2) the hydrophilic, dendritic stopper. Next, 3) the hydrophobic stopper was fused to the 1,5‐dioxynaphthalene moiety and/or the monopyrrolotetrathiafulvalene unit by appropriate alkylations, followed by 4) attachment of the hydrophilic stopper, once again by alkylation to give the dumbbell‐shaped compounds. Finally, 5) the [2]rotaxanes were self‐assembled by using the dumbbells as templates for the formation of the encircling cyclobis(paraquat‐p‐phenylene) tetracations. The two [2]rotaxanes differ in their arrangement of the π‐electron‐rich units, one in which the SMe group of the monopyrrolotetrathiafulvalene unit points toward the 1,5‐dioxynaphthalene moiety (2⋅4 PF6) and another in which it points away from the 1,5‐dioxynaphthalene moiety (3⋅4 PF6). This seemingly small difference in the orientation of the monopyrrolotetrathiafulvalene unit leads to profound changes in the physical properties of these rotaxanes. The bistable [2]rotaxanes were both isolated as brown solids. 1H NMR and UV‐visible spectroscopy, and electrochemical investigations, reveal the presence of both possible translational isomers at ambient temperature. As a consequence of the existence of both possible translational isomers in these bistable [2]rotaxanes, they exhibit a complex electrochemical behavior, which is further complicated by the presence of folded conformations wherein the monopyrrolotetrathiafulvalene unit is involved in an “alongside” interaction with the tetracationic cyclophane. In the molecular shuttle/switch 2⋅4 PF6a “knob”, in the shape of the SMe group, is situated between the monopyrrolotetrathiafulvalene and the 1,5‐dioxynaphthalene recognition sites, making it possible to isolate both translational isomers (2⋅4 PF6⋅GREEN and 2⋅4 PF6⋅RED) and to investigate the kinetics of the shuttling of the cyclobis(paraquat‐p‐phenylene) tetracation between the two recognition sites. The shuttling processes, which are accompanied by clearly detectable color changes, can be followed by 1H NMR and UV‐visible spectroscopy, allowing the rate constants and energies of activation for the translation of the cyclobis(paraquat‐p‐phenylene) tetracations between the two recognition sites to be determined. In the molecular shuttle/switch 3⋅4 PF6, there is no “knob” situated between the 1,5‐dioxynaphthalene and the monopyrrolotetrathiafulvalene recognition sites, resulting in a considerably faster shuttling of the cyclobis(paraquat‐p‐phenylene) tetracation between these two sites, making the separation of the two possible translational isomers of 3⋅4 PF6impractical. However, the shuttling of the cyclobis(paraquat‐p‐phenylene) tetracation can be followed by dynamic 1H NMR spectroscopy. At low temperatures, the major translational isomer is 3⋅4 PF6⋅RED, while 3⋅4 PF6⋅GREEN is the major isomer at higher temperature. In the bistable [2]rotaxanes shuttling of the cyclobis(paraquat‐p‐phenylene) tetracations can be driven by electrochemical oxidation of the monopyrrolotetrathiafulvalene unit. In complexes in which one of the two dumbbell stoppers is missing, electrochemical oxidation causes dethreading.

Two molecular shuttles/switches—a slow one and a fast one—in the shape of amphiphilic, bistable [2]rotaxanes have been synthesized and characterized. Both [2]rotaxanes contain a hydrophobic, tetraarylmethane and a hydrophilic, dendritic stopper. They are comprised of two π-electron-rich stations—a monopyrrolotetrathiafulvalene unit and a 1,5-dioxynaphthalene moiety—which can act as recognition sites for the tetracationic cyclophane, cyclobis(paraquat-p-phenylene), to reside around. In addition, a model [2]rotaxane, incorporating only a monopyrrolotetrathiafulvalene unit in the rod section of the amphiphilic dumbbell component and cyclobis(paraquat-p-phenylene) as the ring component, has been investigated. The dumbbell-shaped components were constructed using conventional synthetic methodologies to assemble 1) the hydrophobic, tetraarylmethane stopper and 2) the hydrophilic, dendritic stopper. Next, 3) the hydrophobic stopper was fused to the 1,5-dioxynaphthalene moiety and/or the monopyrrolotetrathiafulvalene unit by appropriate alkylations, followed by 4) attachment of the hydrophilic stopper, once again by alkylation to give the dumbbell-shaped compounds. Finally, 5) the [2]rotaxanes were self-assembled by using the dumbbells as templates for the formation of the encircling cyclobis(paraquat-p-phenylene) tetracations. The two [2]rotaxanes differ in their arrangement of the π-electron-rich units, one in which the SMe group of the monopyrrolotetrathiafulvalene unit points toward the 1,5-dioxynaphthalene moiety (2·4 PF6) and another in which it points away from the 1,5-dioxynaphthalene moiety (3·4 PF6). This seemingly small difference in the orientation of the monopyrrolotetrathiafulvalene unit leads to profound changes in the physical properties of these rotaxanes. The bistable [2]rotaxanes were both isolated as brown solids. ¹H NMR and UV-visible spectroscopy, and electrochemical investigations, reveal the presence of both possible translational isomers at ambient temperature. As a consequence of the existence of both possible translational isomers in these bistable [2]rotaxanes, they exhibit a complex electrochemical behavior, which is further complicated by the presence of folded conformations wherein the monopyrrolotetrathiafulvalene unit is involved in an “alongside” interaction with the tetracationic cyclophane. In the molecular shuttle/switch 2·4 PF6 a “knob”, in the shape of the SMe group, is situated between the monopyrrolotetrathiafulvalene and the 1,5-dioxynaphthalene recognition sites, making it possible to isolate both translational isomers (2·4 PF6·GREEN and 2·4 PF6·RED) and to investigate the kinetics of the shuttling of the cyclobis(paraquat-p-phenylene) tetracation between the two recognition sites. The shuttling processes, which are accompanied by clearly detectable color changes, can be followed by ¹H NMR and UV-visible spectroscopy, allowing the rate constants and energies of activation for the translation of the cyclobis(paraquat-p-phenylene) tetracations between the two recognition sites to be determined. In the molecular shuttle/switch 3·4 PF6, there is no “knob” situated between the 1,5-dioxynaphthalene and the monopyrrolotetrathiafulvalene recognition sites, resulting in a considerably faster shuttling of the cyclobis(paraquat-p-phenylene) tetracation between these two sites, making the separation of the two possible translational isomers of 3·4 PF6 impractical. However, the shuttling of the cyclobis(paraquat-p-phenylene) tetracation can be followed by dynamic ¹H NMR spectroscopy. At low temperatures, the major translational isomer is 3·4 PF6·RED, while 3·4 PF6·GREEN is the major isomer at higher temperature. In the bistable [2]rotaxanes shuttling of the cyclobis(paraquat-p-phenylene) tetracations can be driven by electrochemical oxidation of the monopyrrolotetrathiafulvalene unit. In complexes in which one of the two dumbbell stoppers is missing, electrochemical oxidation causes dethreading.

Two dendrimers, incorporating tetrasubstituted porphyrin units as their cores and, in one case, four perbenzoylated and, in the other case, twelve peracetylated β-D-glucopyranosyl residues at their peripheries, have been synthesized in yields of 39 and 16%, respectively. The deprotection of these dendrimers was achieved quantitatively under Zemplén conditions. The protected and deprotected dendrimers were characterized by liquid secondary-ion or matrix-assisted laser desorption ionization time-of-flight mass spectrometry and by a combination of one- and two-dimensional ¹H and ¹³C NMR spectroscopy. All the glycodendrimers were also characterized by absorption and emission spectroscopy, and lifetime measurements. The most relevant result is that both protected and deprotected dendrimers show two fluorescence lifetime values that are different from the porphyrin model compounds. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The concept of machine can be extended to the molecular level by designing and synthesizing (supra)molecular species capable of performing mechanical movements. The energy needed to make a machine work can be supplied as chemical energy, electrical energy, or light. When a chemical “fuel” is used, waste products are formed, whereas this is not the case when suitable photochemical or electrochemical energy inputs are employed. A number of elementary functions performed by molecular-level machines are illustrated, and more complex ones are foreseen.

Research was carried out on the use of ceramics as supports to host mammalian cells. The research was part of a programme whose priority was to study the possibility of using ceramics in the non-traditional sector of the biomedical field. The aim of the study was also to verify the suitability of particular types of ceramics dealt with in the literature for these applications. Among the different samples tested the cordieritic one proved to be very interesting, at least in relation to the cellular cultures considered. The chemical composition of the material is not, however, the only important aspect, since other parameters concur to make the hosting of cells highly acceptable. Of particular importance is the rugosity and porosity of the surface and its flaking, not only externally, but also in the pores.

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A modified bis-p-phenylene-34-crown-10 ring in which one of the 1,4-dioxybenzene units has been replaced by a 9,10-dioxyanthracene unit has been employed as a template for the formation of cyclobis(paraquat-p-phenylene). The [2]catenane which results has been shown by ¹H NMR spectroscopy to exist in solution exclusively in the translationally isomeric form in which (a) only the 1,4-dioxybenzene ring occupies the central cavity of the tetracationic cyclophane and (b) the crown ether ring is prevented from circumrotating through the cyclophane by the large 9,10-dioxyanthracene unit. The absorption spectrum and luminescence properties of this new [2]catenane and of its crown ether component in its free state have been investigated and compared with those of 1,4-dimethoxybenzene and a model anthracene derivative, carrying methylated triethylene glycol chains on the 9 and 10 positions of the anthracene ring. While the absorption spectrum of the crown ether is the sum of the spectra of the two component chromophoric moieties, its emission spectrum shows only the fluorescence band of the 9,10-dioxyanthracene-type unit. The excitation spectrum shows that the disappearance of the 1,4-dioxybenzene type emission in the crown ether is due to a very efficient (kq ≥ 4 × 10¹⁰ s⁻¹) energy-transfer process from the 1,4-dioxybenzene to the 9,10-dioxyanthracene type unit. The absorption spectrum of the [2]catenane is noticeably different from the sum of the spectra of its two cyclic components, particularly as far as the presence of a very broad charge-transfer (CT) band in the visible spectral region (λmax = 545 nm, εmax = 615 M⁻¹ cm⁻¹) is concerned.Comparison with the CT band of a model compound shows that the very broad CT band of the [2]catenane is in fact the result of two component bands originating from the interaction of the two different electron-donor units (1,4-dioxybenzene and 9,10-dioxyanthracene type) present in the crown ether with the electron-acceptor bipyridinium-type units of the cyclobis(paraquat-p-phenylene). The emission spectrum of the [2]catenane does not show any band because of the quenching action (rate constant kq ≥ 5 × 10¹⁰ s⁻¹) of the low-energy non-luminescent charge-transfer levels on the higher energy, potentially luminescent levels of the crown ether.

Bone quality is the result of a complex relationship between bone mass, bone structure, and mechanical characteristics of these individual components. The mass of bone tissue is affected by nutritional factors and other causes, such as bone growth factors like bone morphogenetic proteins (BMPs). Since chitosans promote ordered regeneration of soft tissue and osteoinduction, an osteoporotic model was studied to evaluate the pattern of bone regeneration in the presence of BMP linked to chitosan. BMP was released from the chitosan matrix as a consequence of chitosan biodegradation. Our data show that the association of BMP with chitosan seemed to improve the bone tissue regeneration in a surgical bone defect. This result provides validity to biochemical approaches for therapeutical correction of afflictions in the elderly, such as osteoporosis.

Hydroxyapatite nails, prepared according to a novel method and endowed with better mechanical resistance, were coated with chitosan to impart enhanced biocompatibility and were introduced in the femurs of rabbits. Chitosan was found to be a favorable interface between bone and hydroxyapatite because it promoted an osteoconductive reaction.

The application of bioactive ceramic coatings to prostheses confers strength to a material (ceramic or biological glass) that exerts beneficial effects on bone-tissue growth but that itself lacks the toughness and stability required of an implant device. The rate of bioactivity is related to the chemical reactivity of the material and causes interface dissolution, precipitation and ion-exchange reactions. Ceramics may differ in sintering temperature and thus exhibit differences in their in vitro dissolution features and in vivo performance. To test these effects, in vitro and in vivo studies were carried out on two biocompatible biological glasses and a ceramic of proven bioactivity in view of their potential utilization as covering materials. In addition, a modified chitosan was adsorbed on the surface of a series of hydroxyapatite (HA) samples. Human fibroblasts and/or osteoblasts were used for the in vitro tests, and normal (INT) and osteoporotic (OVX) rats, normal rabbits and sheep for the in vivo studies. Similar chemical changes were observed in both glasses, suggesting that these materials underwent modifications directly dependent on their biological environment. The in vivo tests point to the possibility of improving the bioactivity of ceramic substrates with chitosan. However, the different behaviour of the materials in vitro and in vivo suggests that these tests should be conducted in parallel.

Multicomponent pseudorotaxane superarchitecturesare generated when a tetracationic filament, bearing dialkyl ammonium (NH2+) and 4,4′‐bipyridinium (bpym2+) recognition sites, self‐assembles selectively with various crown ethers, such as dicyclohexyl[24]crown‐8 (Dcy24C8) and 2,3‐ dinaptho[30]crown‐10 (2/3DN30C10) [see figure]. The selective self‐processes were utilized for the development of pH‐controlled supramolecular switches.

The behaviour of lymphoid and epithelial tissues of the tonsil has been studied in rabbits treated with three substances supposed to have antiblastic activity: the 6-aminonicotamide, the dimethyl-dimetansulfonyloxybutane and the enanthic aldehyde. A marked action on the lymphoid tissue was exerted by the first substance, which nearly failed to act on the epithelium; no changes at the level of both tissues were induced by the second, and a cytolytic activity on the epithelium by the third one.

New Ru(II) complexes are presented as potential luminescent sensors, fluorescent labels and DNA photoprobes.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

In the last few years there has been a great interest in developing electronics at a molecular level (molecular electronics), e.g. to construct miniaturized electric circuits that would be much smaller than the corresponding micron-scale digital logic circuits fabricated on conventional solid-state semiconductor chips. An alternative possibility to the use of electron fluxes as a means for information processing (electronics) is that of using optical beams (photonics), but up until now scarce attention has been devoted to the possibility of developing photonics at the molecular level. In this paper we review some recent achievements in the design and construction of molecular-level systems that are capable of transferring, switching, collecting, storing, and elaborating light signals. The combination of molecular photonics with chemionics can lead to a wealth of molecular-level devices capable of information processing.

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The quenching of the luminescence emission intensity and lifetime of (I) and (II) by the heteropolytungstate anions (Mn(OH)PW11O39)6‐and (Co(H2O)SiW11O39)6‐has been studied in aqueous solutions.

The absorption spectra, emission spectra, luminescence lifetimes and photochemical behavior of the host‐guest species originating from the title Pt complex (bpy: bipyridine) and the crown ethers (I)‐(IV) are examined in a systematic way.