Photodriven Charge Separation and Transport in Self‐Assembled Zinc Tetrabenzotetraphenylporphyrin and Perylenediimide Charge Conduits

Zinc tetrabenzotetraphenyl porphyrin (ZnTBTPP) covalently attached to four perylenediimide (PDI) acceptors self‐assembles into a π‐stacked, segregated columnar structure, as indicated by small‐ and wide‐angle X‐ray scattering. Photoexcitation of ZnTBTPP rapidly produces a long‐lived electron–hole pair having a 26 Å average separation distance, which is much longer than if the pair is confined within the covalent monomer. This implies that the charges are mobile within their respective segregated ZnTBTPP and PDI charge conduits.     

A third mode of DNA binding: Phosphate clamps by a polynuclear platinum complex

We describe a 1.2 A X-ray structure of a double-stranded B-DNA dodecamer (the Dickerson Dodecamer, DDD, [d(CGCGAATTCGCG)]2) associated with a cytotoxic platinum(II) complex, [{trans-Pt(NH3)2(NH2(CH2)6(NH3+)}2-mu-{trans-Pt(NH3)2(NH2(CH2)6NH2)2}] (TriplatinNC). TriplatinNC is a multifunctional DNA ligand, with three cationic Pt(II) centers, and directional hydrogen bonding functionalities, linked by flexible hydrophobic segments, but without the potential for covalent interaction. TriplatinNC does not intercalate nor does it bind in either groove. Instead, it binds to phosphate oxygen atoms and thus associates with the backbone. The three square-planar tetra-am(m)ine Pt(II) coordination units form bidentate N...O...N complexes with OP atoms, in a motif we call the Phosphate Clamp. The geometry is conserved among the 8 observed phosphate clamps in this structure. The interaction appears to prefer O2P over O1P atoms (frequency of interaction is O2P > O1P, base and sugar oxygens > N). The high repetition and geometric regularity of the motif suggests that this type of Pt(II) center can be developed as a modular nucleic acid binding device with general utility. TriplatinNC extends along the phosphate backbone, in a mode of binding we call "Backbone Tracking" and spans the minor groove in a mode of binding we call "Groove Spanning". Electrostatic forces appear to induce modest DNA bending into the major groove. This bending may be related to the direct coordination of a sodium cation by a DNA base, with unprecedented inner-shell (direct) coordination of penta-hydrated sodium at the O6 atom of a guanine.     

New cuprates featuring ladderlike periodic arrays of [Cu3O8]10- trimeric magnetic nanostructures

A new family of cuprates, Li2Cu3(SiO3)4 (1) and Na2Cu3(GeO3)4 (2), was isolated in molten salt media. The extended lattices contain ladderlike periodic arrays of [Cu3O8]10- magnetic nanostructures. Magnetic properties of the Na2Cu3Ge(4-x)SixO12 series, where x = 0, 0.86, and 1.72, were systematically studied. The geometrically induced magnetic couplings are tunable upon cation substitution.     

Molecular dynamics simulation of nanodroplet spreading enhanced by linear surfactants

We utilize molecular dynamics simulations to probe the surfactant-mediated spreading of a Lennard-Jones liquid droplet on a solid surface. The surfactants are linear hexamers that are insoluble in the liquid and reduce the surface tension of the liquid-vapor interface. We study how the interaction of the surfactant hexamers with the solid substrate influences spreading, as well as the dependence of spreading on surfactant concentration. We find that the spreading speed is strongly influenced by the attraction of the hydrophobic surfactant tail to the solid surface. When this attraction is sufficiently strong, surfactant molecules partition to the liquid-solid interface and facilitate spreading. This partitioning can lead to an inhomogeneous distribution of surfactant over the liquid-vapor interface, which could drive the Marangoni convection. We also observe that the surfactant molecules can assemble into micelles on the solid surface. The repulsion between micelles at the liquid-solid interface can lead to break-off and migration of the micelles from the liquid-solid to the gas-solid interface and spreading is facilitated in this way. Our model system contains features that are believed to underlie superspreading in experimental studies of droplet spreading.     

Optimal surrender strategies for equity-indexed annuity investors

An equity-indexed annuity (EIA) is a hybrid between a variable and a fixed annuity that allows the investor to participate in the stock market, and earn at least a minimum interest rate. The investor sacrifices some of the upside potential for the downside protection of the minimum guarantee. Because EIAs allow investors to participate in equity growth without the downside risk, their popularity has grown rapidly.An optimistic EIA owner might consider surrendering an EIA contract, paying a surrender charge, and investing the proceeds directly in the index to earn the full (versus reduced) index growth, while using a risk-free account for downside protection. Because of the popularity of these products, it is important for individuals and insurers to understand the optimal policyholder behavior.We consider an EIA investor who seeks the surrender strategy and post-surrender asset allocation strategy that maximizes the expected discounted utility of bequest. We formulate a variational inequality and a Hamilton-Jacobi-Bellman equation that govern the optimal surrender strategy and post-surrender asset allocation strategy, respectively. We examine the optimal strategies and how they are affected by the product features, model parameters, and mortality assumptions. We observe that in many cases, the “no-surrender” region is an interval (w_l,w_u); i.e., that there are two free boundaries. In these cases, the investor surrenders the EIA contract if the fund value becomes too high or too low. In other cases, there is only one free boundary; the lower (or upper) surrender threshold vanishes. In these cases, the investor holds the EIA, regardless of how low (or high) the fund value goes. For a special case, we prove a succinct and intuitive condition on the model parameters that dictates whether one or two free boundaries exist.     

Mesoporous Silica Supported Multiple Single‐Site Catalysts and Polyethylene Reactor Blends with Tailor‐Made Trimodal and Ultra‐Broad Molecular Weight Distributions

A ternary blend of the bisiminopyridine chromium (III) (Cr‐ 1 ) with the bisiminopyridine iron (II) (Fe‐ 2 ) post‐metallocenes with the quinolylsilylcyclopentadienyl chromium (III) halfsandwich complex (Cr‐ 3 ) was supported on mesoporous silica to produce novel multiple single‐site catalysts and polyethylene reactor blends with tailor‐made molecular weight distributions (MWDs). The preferred cosupporting sequence of this ternary blend on MAO‐treated silica was Fe‐ 2 followed by Cr‐ 1 and Cr‐ 3 . Cosupporting does not impair the single‐site nature of the blend components producing polyethylene fractions with = 10⁴ g · mol⁻¹ on Cr‐ 1 , = 3 × 10⁵ g · mol⁻¹ on Fe‐ 2 , and = 3 × 10⁶ g · mol⁻¹ on Cr‐ 3 . As a function of the Fe‐ 2 /Cr‐ 1 /Cr‐ 2 mixing ratio it is possible to control the weight ratio of these three polyethylenes without affecting the individual average molecular weights and narrow polydispersities of the three polyethylene fractions. Tailor‐made polyethylene reactor blends with ultra‐broad MWD and polydispersities varying between 10 and 420 were obtained. When the molar ratio of Fe‐ 2 /Cr‐ 1 was constant, the ultra‐high molecular polyethylene (UHMWPE, > 10⁶ g · mol⁻¹) content was varied between 8 and 16 wt.‐% as a function of the Cr‐ 3 content without impairing the blend ratio of the other two polyethylene fractions and without sacrificing melt processability. When the molar ratio Fe‐ 2 /Cr‐ 3 was constant, it was possible to selectively increase the content of the low molecular weight fraction by additional cosupporting of Cr‐ 1 . Due to the intimate mixing of low and ultra‐high molecular weight polyethylenes (UHMPEs) produced on cosupported single‐site catalysts a wide range of melt processable polyethylene reactor blends was obtained.

     

Near‐Infrared‐Light‐Triggered Antimicrobial Indium Phosphide Quantum Dots

The emergence of multidrug‐resistant (MDR) pathogens represents one of the most urgent global public health crises. Light‐activated quantum dots (QDs) are alternative antimicrobials, with efficient transport, low cost, and therapeutic efficacy, and they can act as antibiotic potentiators, with a mechanism of action orthogonal to small‐molecule drugs. Furthermore, light‐activation enhances control over the spatiotemporal release and dose of the therapeutic superoxide radicals from QDs. However, the limited deep‐tissue penetration of visible light needed for QD activation, and concern over trace heavy metals, have prevented further translation. Herein, we report two indium phosphide (InP) QDs that operate in the near‐infrared and deep‐red light window, enabling deeper tissue penetration. These heavy‐metal‐free QDs eliminate MDR pathogenic bacteria, while remaining non‐toxic to host human cells. This work provides a pathway for advancing QD nanotherapeutics to combat MDR superbugs.     

Electrochemically programmed, spatially selective biofunctionalization of silicon wires

A method for the spatially selective biofunctionalization of silicon micro- and nanostructures is reported, and results are presented for both single-crystal silicon (111) or (100) surfaces. An electroactive monolayer of hydroquinone was formed on the surface of H-terminated silicon working electrodes via an olefin reaction with UV-generated surface radicals. Molecules presenting either cyclopentadiene or a thiol group can be immobilized onto the regions where the hydroquinone has been oxidized. Molecular size and crystal orientation are evaluated as important factors that dictate the electrode stability in aqueous solution under anodic potentials. Monolayers composed of smaller molecules on (111) surfaces exhibit the highest packing density and are more effective in preventing anodic oxidation of the underlying substrate. Voltammetry, X-ray photoelectron spectroscopy, and atomic force and fluorescence microscopy are utilized to interrogate the kinetic rates of biofunctionalization, the extent of surface coverage, monolayer quality, and the spatial selectivity of the process.     

Bis(pyridine)-based bromonium ions. Molecular structures of bis(2,4,6-collidine)bromonium perchlorate and bis(pyridine)bromonium triflate and the mechanism of the reactions of 1,2-bis(2'-pyridylethynyl)benzenebrominum triflate and bis(pyridine)bromonium triflate with acceptor olefins

1,2-Bis(2'-pyridylethynyl)benzenebromonium triflate (4) and bis(pyridine)bromonium triflate (5) have been prepared and the mechanism of their reaction with various acceptors including eight alkenes of various structure, collidine, and Br(-) are reported. The reaction of 4 with neutral acceptors is second-order overall and involves a preequilibrium dissociation of the bidentate-bound Br(+) to form an unstable monodentate open form (4-op), which reacts with all neutral acceptors at or near the diffusion limit. Br(-) reacts with 4 by a different mechanism involving a direct nucleophilic attack on the Br(+). The reaction of 5 with acceptors proceeds by a dissociative mechanism to reversibly form an unstable intermediate (pyr-Br(+)), which reacts with 4-penten-1-ol, 4-pentenoic acid adamantylidineadamantane and cyclohexene with nearly the same selectivity. The crystal and molecular structures of bis(2,4,6-collidine)bromonium perchlorate (2-ClO(4)) and 5 were determined by X-ray crystallography.