The estimation of the driving force for photoinduced charge-transfer processes, using the Rehm-Weller equation, requires the employment of redox and spectroscopic quantities describing the participating electron donor and acceptor. Although the spectroscopic data are usually obtained from diluted solutions, the redox potentials are most frequently obtained from electrochemical measurements conducted in concentrated electrolyte solutions. To correct for the differences in the media, in which the various types of measurements are conducted, a term, based on the Born equation for solvation energy of ions, is introduced in the Rehm-Weller equation. The Born correction term, however, requires a prior knowledge of the dielectric constants of the electrolyte solutions used for the redox measurements. Because of limited information for such dielectrics, the values for the dielectric constants of electrolyte solutions are approximated to the values of the dielectric constants of the corresponding neat solvents. We examined the validity of this approximation. Using cyclic voltammetry, we recorded the first one-electron oxidation potential of ferrocene for three different solvents in the presence of 1-500 mM supporting electrolyte. The dielectric constants for some of the electrolyte solutions were extracted from fluorescence measurements of a dimethylaminonaphthalimide chromophore that exhibits pronounced solvatochromism. The dielectric constants of the concentrated electrolyte solutions correlated well with the corresponding oxidation potentials. The dependence of the oxidation potential of ferrocene on the electrolyte concentration for different solvents revealed that the abovementioned approximation in the Born correction term indeed introduces a significant error in the estimation of the charge-transfer driving force from redox data collected using relatively nonpolar solvents.

A series of potent and selective inducible nitric-oxide synthase (iNOS) inhibitors was shown to prevent iNOS dimerization in cells and inhibit iNOS in vivo. These inhibitors are now shown to block dimerization of purified human iNOS monomers. A 3 H-labeled inhibitor bound to full-length human iNOS monomer with apparent K d ϳ1.8 nM and had a slow off rate, 1.2 ؋ 10 ؊4 s ؊1 . Inhibitors also bound with high affinity to both murine full-length and murine oxygenase domain iNOS monomers. Spectroscopy and competition binding with imidazole confirmed an inhibitor-heme interaction. Inhibitor affinity in the binding assay (apparent K d values from 330 pM to 27 nM) correlated with potency in a cellbased iNOS assay (IC 50 values from 290 pM to 270 nM). Inhibitor potency in cells was not prevented by medium supplementation with L-arginine or sepiapterin, but inhibition decreased with time of addition after cytokine stimulation. The results are consistent with a mechanism whereby inhibitors bind to a heme-containing iNOS monomer species to form an inactive iNOS monomer-heme-inhibitor complex in a pterin-and L-arginineindependent manner. The selectivity for inhibiting dimerization of iNOS versus endothelial and neuronal NOS suggests that the energetics and kinetics of monomer-dimer equilibria are substantially different for the mammalian NOS isoforms. These inhibitors provide new research tools to explore these processes.The mammalian nitric-oxide synthase (NOS) 1 family consists of three isoforms as follows: cytokine-inducible (iNOS), neuronal (nNOS), and endothelial NOS (eNOS). NOS isoforms are homodimers that catalyze NADPH-dependent oxidation of L-arginine to nitric oxide (NO) and L-citrulline (1-3). Each monomer subunit of the dimer consists of a C-terminal reductase domain that contains binding sites for NADPH, FAD, FMN, and calmodulin, and an N-terminal oxygenase domain that contains binding sites for heme, tetrahydrobiopterin (H 4 B), and L-arginine (3-7). As in cytochrome P-450, the NOS heme iron coordinates to the protein through a cysteine thiolate (6 -8), binds O 2 as a sixth ligand (9), and participates directly in catalysis (9 -13). The heme ligands CO, Ϫ CN, imidazole, N-phenylimidazoles, and other imidazole-containing compounds all inhibit NO synthesis (10, 14 -17).The NOS isoforms are only active as homodimers (18 -20). For iNOS (5) and nNOS (21-23), only the oxygenase domains of two monomers interact to form the dimer (24). Dimerization of iNOS is required for fully coupled enzyme activity because the flow of electrons during catalysis occurs in trans from the reductase domain of one monomer to the oxygenase domain of the other monomer (25). Dimerization of NOS monomers is initiated by heme insertion, which results in rapid conformational changes (18,19,26). The heme-containing iNOS monomer is an intermediate in dimerization and, in the presence of H 4 B and L-arginine, forms a stable active dimer (18,24,(27)(28)(29).Highly potent and selective pyrimidineimidazole-based iNOS dimerization inhibitors were disc...

The swelling-shrinking transition of hydrogels is crucial for their wide applications such as actuators and drug delivery. We hereby fabricated a smart hydrogel with ferrocene groups on pendant of polymer networks. While it was immersed in the water-soluble pillar[6]arene (WP6) aqueous solution, the hydrogel was dramatically swollen, which was an approximately 11-fold promotion in weight compared with that in pure water, due to the formation of the inclusion complexes between WP6 and ferrocene groups in the hydrogel. In particular, the well-swollen hydrogel exhibited good responsiveness to multistimuli including temperature, pH, redox, and competitive guests by tuning the dissociation/formation of WP6-ferrocene inclusion complexes or the strength of their charges. Meanwhile, potential application of such a smart hydrogel in pH-responsive drug release was demonstrated as well.

A dual-responsive supramolecular network based on pillar[6]arene−ferrocenium redox-controllable recognition motifs in polymeric backbones is constructed with a ferrocenium-functionalized copolymer and a pillar[6]arene copolymer, in which the first example of pillar[6]arene-functionalized copolymer was synthesized through the reversible addition/ fragmentation chain-transfer copolymerization of an acrylate-functionalized pillar[6]arene and methyl acrylate. The resulting supramolecular network exhibits dramatically increased viscosity than the non-cross-linked mixtures and demonstrates a gel-like behavior on macroscale with a transient-network behavior revealed by rheology study. Furthermore, the viscoelastic properties of such supramolecular network can be easily controlled by different external stimuli including redox stimulus and competing host/ guest reagents.

A novel and highly stable inclusion complex was formed between per-butylated pillar[6]arene and a ferrocenium cation, while the reduced form ferrocene only showed extremely weak binding affinity with per-butylated pillar[6]arene in organic solvents.