High-extinction ruthenium compounds for sunlight harvesting and hole transport

The compounds Ru(bpy) 2(BTL)(PF 6) 2 and Ru(deeb) 2(BTL)(PF 6) 2, where bpy is 2,2'-bipyridine, deeb is 4,4'-(C 2H 5CO 2) 2-bpy, and BTL is 9'-[4,5-bis(cyanoethylthio)]-1,3-dithiol-2-ylidene]-4',5'-diazafluorene, were found to have very high extinction coefficients in the visible region. In an acetonitrile solution, the extinction of Ru(deeb) 2(BTL)(PF 6) 2 was = 44 000 +/- 1000 M (-1) cm (-1) at lambda = 470 nm. Two quasi-reversible oxidation waves, E 1/2 = +0.88 and +1.16 V, and an irreversible reduction, E pr = -1.6 V, were observed versus ferrocene (Fc (+/0)). At -40 degrees C, a state was observed with spectroscopic properties characteristic of a metal-to-ligand charge-transfer excited state, tau = 25 ns. This same compound was found to photoinject electrons into TiO 2 with a quantum yield Phi = 0.3 +/- 0.2 for 532.5 or 417 nm light excitation in a 0.1 M LiClO 4/acetonitrile electrolyte. In regenerative solar cells, a sustained photocurrent was observed with a maximum incident photon-to-current efficiency of 0.4. The photocurrent action and absorptance spectra were in good agreement, consistent with injection from a single excited state.     

From Glucose to Polymers: A Continuous Chemoenzymatic Process

Efforts to synthesize degradable polymers from renewable resources are deterred by technical and economic challenges; especially, the conversion of natural building blocks into polymerizable monomers is inefficient, requiring multistep synthesis and chromatographic purification. Herein we report a chemoenzymatic process to address these challenges. An enzymatic reaction system was designed that allows for regioselective functional group transformation, efficiently converting glucose into a polymerizable monomer in quantitative yield, thus removing the need for chromatographic purification. With this key success, we further designed a continuous, three-step process, which enabled the synthesis of a sugar polymer, sugar poly(orthoester), directly from glucose in high yield (73 % from glucose). This work may provide a proof-of-concept in developing technically and economically viable approaches to address the many issues associated with current petroleum-based polymers.     

Surface Design for Immobilization of an Antimicrobial Peptide Mimic for Efficient Anti-Biofouling

Microbial surface attachment negatively impacts a wide range of devices from water purification membranes to biomedical implants. Mimics of antimicrobial peptides (AMPs) constituted from poly(N-substituted glycine) „peptoids“ are of great interest as they resist proteolysis and can inhibit a wide spectrum of microbes. We investigate how terminal modification of a peptoid AMP-mimic and its surface immobilization affect antimicrobial activity. We also demonstrate a convenient surface modification strategy for enabling alkyne–azide „click“ coupling on amino-functionalized surfaces. Our results verified that the N- and C-terminal peptoid structures are not required for antimicrobial activity. Moreover, our peptoid immobilization density and choice of PEG tether resulted in a „volumetric“ spatial separation between AMPs that, compared to past studies, enabled the highest AMP surface activity relative to bacterial attachment. Our analysis suggests the importance of spatial flexibility for membrane activity and that AMP separation may be a controlling parameter for optimizing surface anti-biofouling.     

Structural Consequences of S → Se Substitution in some Symmetrical [M(S2CNR2)3] Complexes

The consequences of replacement of the symmetrically chelate ligands in [M(E₂CNR₂)₃] (E = S, Se) complexes of potential 32 symmetry by analogous mixed S,Se unsymmetrical chelates are explored for both small (M = Co) and large (M = In) metal atoms, and R = primary (Et) and secondary (ⁱPr) alkyl substituents by way of low‐temperature single crystal X‐ray studies of [(Co(SSeCNEt₂)₃] ([Co(Se₂CNEt₂)₃] also determined as datum), and [In(SSeCNR₂)₃], R = Et, ⁱPr. The structure of [(ⁱPr₂N·CS·Se)₂] is also recorded.     

A Dual Threat: Redox-Activity and Electronic Structures of Well-Defined Donor–Acceptor Fulleretic Covalent-Organic Materials

The effect of donor (D)–acceptor (A) alignment on the materials electronic structure was probed for the first time using novel purely organic porous crystalline materials with covalently bound two- and three-dimensional acceptors. The first studies towards estimation of charge transfer rates as a function of acceptor stacking are in line with the experimentally observed drastic, eight-fold conductivity enhancement. The first evaluation of redox behavior of buckyball- or tetracyanoquinodimethane-integrated crystalline was conducted. In parallel with tailoring the D-A alignment responsible for “static” changes in materials properties, an external stimulus was applied for “dynamic” control of the electronic profiles. Overall, the presented D–A strategic design, with stimuli-controlled electronic behavior, redox activity, and modularity could be used as a blueprint for the development of electroactive and conductive multidimensional and multifunctional crystalline porous materials.     

B-MWW Zeolite: The Case Against Single-Site Catalysis

Boron-containing materials have recently been identified as highly selective catalysts for the oxidative dehydrogenation (ODH) of alkanes to olefins. It has previously been demonstrated by several spectroscopic characterization techniques that the surface of these boron-containing ODH catalysts oxidize and hydrolyze under reaction conditions, forming an amorphous B₂(OH)_xO_(3−x/2) (x=0–6) layer. Yet, the precise nature of the active site(s) remains elusive. In this Communication, we provide a detailed characterization of zeolite MCM-22 isomorphously substituted with boron (B-MWW). Using ¹¹B solid-state NMR spectroscopy, we show that the majority of boron species in B-MWW exist as isolated BO₃ units, fully incorporated into the zeolite framework. However, this material shows no catalytic activity for ODH of propane to propene. The catalytic inactivity of B-MWW for ODH of propane falsifies the hypothesis that site-isolated BO₃ units are the active site in boron-based catalysts. This observation is at odds with other traditionally studied catalysts like vanadium-based catalysts and provides an important piece of the mechanistic puzzle.     

Analysis of hexabromocyclododecane diastereomers and enantiomers by liquid chromatography/tandem mass spectrometry: chromatographic selectivity and ionization matrix effects

Hexabromocyclododecane (HBCD) is a flame retardant that is undergoing environmental risk assessment. The liquid chromatographic retention and electrospray ionization matrix effects were investigated for HBCD methods of analysis for environmental matrices. Column selectivity towards HBCD diastereomers was evaluated for C30 and C18 stationary phases under different mobile phase conditions and column temperatures. The HBCD elution order was dependent on the shape selectivity of the stationary phase and the mobile phase composition. Greater resolution, on columns with reduced shape selectivity, of beta-HBCD and gamma-HBCD was achieved with the use of an acetonitrile/water (compared with a methanol/water) mobile phase composition. A liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) method for the analysis of HBCD in biological tissues was evaluated for potential matrix effects. The influence of extracted matrix components on HBCD diastereomer and enantiomer analysis was investigated using a postextraction addition approach. Although the analysis of HBCD diastereomers was relatively unaffected by the sample matrix, the responses of the HBCD enantiomers in tissue samples were significantly influenced by matrix effects and other changes to the ionization conditions. The use of racemic 13C-labeled HBCD diastereomers as internal standards for enantiomer fraction measurements corrected for the changes in the mass spectrometer response.     

A FRET-based approach to ratiometric fluorescence detection of hydrogen peroxide

We report the synthesis, properties, and biological applications of Ratio-Peroxyfluor-1 (RPF1), a new ratiometric fluorescent reporter for hydrogen peroxide. RPF1 is comprised of a two-fluorophore cassette, where the spectral overlap between coumarin donor and fluoran/fluorescein acceptor partners can be controlled by the chemoselective peroxide-mediated deprotection of boronic ester pendants on the acceptor dye. RPF1 features good selectivity for hydrogen peroxide over a variety of reactive oxygen species, including superoxide and nitric oxide, a ca. 8-fold increase in fluorescence intensity ratio (lambda517/lambda464) upon H2O2 reaction, and excitation and emission profiles in the visible region. Experiments with viable yeast mitochondria show that RPF1 can monitor and quantify endogenous production of H2O2, establishing the potential utility of this approach for probing peroxide biology in living systems.