We have identified a strategy to communicate a chemical signal between two independent molecular components. One of them is a photoactive merocyanine that switches to a spiropyran, releasing a proton, when stimulated with visible light. The other is a 4,4'-pyridylpyridinium monocation that captures the released proton, producing an electroactive 4,4'-bipyridinium dication. Under the irradiation conditions employed, the photoinduced transformation requires ca. 15 min to reach a photostationary state. In the dark, the ensemble of communicating molecules reequilibrates to the original state in ca. 5 days. These processes can be monitored following the photoinduced enhancement and thermal decay, respectively, of the current for the monolectronic reduction of the 4,4'-bipyridinium dication. The pronounced difference in time scale for the current enhancement and decay steps can be exploited to implement a memory element with a bit retention time of 11 h. A bit of information can be written optically in the chemical system and it can be read electrically and nondestructively. The memory can be reset, extending its permanence in the dark beyond the bit retention time. A binary logic analysis of the signal transduction operated by the communicating molecules reveals the characteristic behavior of sequential logic operators, which are the basic components of digital memories.

Stilbazulenyl nitrone (STAZN), 8, a nitronyl-substituted hydrocarbon, is a novel second-generation azulenyl nitrone with significantly enhanced potency as a chain-breaking antioxidant vs conventional alpha-phenyl nitrones previously investigated as antioxidant therapeutics. A convenient (1)H NMR-based assay for assessing the potency of chain-breaking antioxidants has shown that STAZN is ca. 300 times more potent in inhibiting the free radical-mediated aerobic peroxidation of cumene than is PBN and the experimental stroke drug NXY-059. Such levels of antioxidant efficacy are unprecedented among archetypal alpha-phenyl nitrone spin traps. Furthermore, STAZN outperforms such classical phenolic antioxidants as BHT and probucol and rivals the antioxidant potency of Vitamin E in a polar medium comprised of 80% cumene and 20% methanol. The Volodarskii electron-transfer mechanism involving the intermediacy of the STAZN radical cation has been implicated in attempts to ascertain the basis for the increased potency of STAZN over the three alpha-phenyl nitrones PBN, S-PBN, and NXY-059.

In search of strategies to design photoswitchable fluorescent probes and operate them in aqueous environments, we have envisioned the possibility of incorporating fluorescent, photochromic, and hydrophilic components within the same macromolecular construct. First, we synthesized a fluorophore-photochrome dyad, pairing a BODIPY fluorophore and a spiropyran photochrome in its molecular skeleton, and investigated the photochemical and photophysical properties of this compound in acetonitrile. Under these conditions, the photoinduced isomerization of the spiropyran causes a 56% decrease in the emission intensity of the BODIPY at the photostationary state. The photogenerated isomer has a lifetime of 2.7 × 10 2 s and reverts thermally to the original form, restoring the initial emission intensity. On the basis of these results, we copolymerized a similar BODIPY-spiropyran conjugate with a monomer bearing a pendant polyethylene glycol chain. The resulting polymer is soluble in aqueous environments, and its fluorescence can be modulated by operating the photochromic components with optical stimulation. Specifically, the emission intensity decreases by 40% at the photostationary state and reverts to the initial value after thermal reisomerization of the photochromic components. However, the lifetime of the photogenerated species in neutral buffer is significantly longer than that of the monomeric BODIPY-spiropyran in acetonitrile. The fluorescence of both monomeric and polymeric fluorophore-photochrome assemblies can be switched repeatedly between high and low values by alternating ultraviolet irradiation and storage in the dark. However, the fatigue resistance properties of both systems are relatively poor. In any case, our investigations demonstrate that our design is viable for the realization of hydrophilic and photoswitchable molecular assemblies. In principle, innovative fluorescent probes for biomedical applications can evolve from these studies, if methods to improve their fatigue resistance properties and optimize their reisomerization kinetics can be identified. † Part of the "Larry Dalton Festschrift".

A Corun ƒ a Dedicated to Professor Friedrich Bickelhaupt on the occasion of his 70th birthday.The covalently templated bis-functionalization of C 70 , employing bis-malonate 5 tethered by an antidisubstituted dibenzo [18]crown-6 (DB18C6) ether, proceeds with complete regiospecificity and provides two diastereoisomeric pairs of enantiomeric C 70 crown ether conjugates, (AE)-7a and (AE)-7b, featuring a five o×clock bis-addition pattern that is disfavored in sequential transformations (Scheme 1). The identity of (AE)-7a was revealed by X-ray crystal-structure analysis (Fig. 6). With bis-malonate 6 containing a syn-disubstituted DB18C6 tether, the regioselectivity of the macrocylization via double Bingel cyclopropanation changed completely, affording two constitutionally isomeric C 70 crown ether conjugates in a ca. 1 : 1 ratio featuring the twelve (16) and two o×clock ((AE)-15) addition patterns, respectively (Scheme 3). The X-ray crystal-structure analysis of the twelve o×clock bis-adduct 16 revealed that a H 2 O molecule was included in the crown ether cavity (Figs. 7 and 8). Two sequential Bingel macrocyclizations, first with anti-DB18C6-tethered (5) and subsequently with syn-DB18C6-tethered (6) bis-malonates, provided access to the first fullerene bis-crown ether conjugates. The two diastereoisomeric pairs of enantiomers (AE)-28a and (AE)-28b were formed in high yield and with complete regioselectivity (Scheme 9). The cation-binding properties of all C 70 crown-ether conjugates were determined with the help of ion-selective electrodes (ISEs). Mono-crown ether conjugates form stable 1 : 1 complexes with alkali-metal ions, whereas the tetrakis-adducts of C 70 , featuring two covalently attached crown ethers, form stable 1 : 1 and 1 : 2 host-guest complexes ( Table 2). Comparative studies showed that the conformation of the DB18C6 ionophore imposed by the macrocyclic bridging to the fullerene is not particularly favorable for strong association. Reference compound (AE)-22 (Scheme 4), in which the DB18C6 moiety is attached to the C 70 sphere by a single bridge only and, therefore, possesses higher conformational flexibility, binds K and Na ions better by factors of 2 and 20, respectively. Electrochemical studies demonstrate that cation complexation at the crown ether site causes significant anodic shifts of the first reduction potential of the appended fullerene (Table 3). In case of the C 70 mono-crown ether conjugates featuring a five o×clock functionalization pattern, addition of 1 equiv. of KPF 6 caused an anodic shift of the first reduction wave in the cyclic voltammogram (CV) by 70 to 80 mV, which is the result of the electrostatic effect of the K ion bound closely to the fullerene core (Fig. 14). Addition of 2 equiv. of K ions to C 70 bis-crown ether conjugates resulted in the observation of only one redox couple, whose potential is anodically shifted by 170 mV with respect to the corresponding wave in the absence of the salt (Fig. 16). The synthesis and characterization of novel tris-and tetrakis-adducts of ...