Organic & Biomolecular Chemistry A neutral redox-switchable [2]rotaxane Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, USA A limited range of redox-active, rotaxane-based, molecular switches exist, despite numerous potential applications for them as components of nanoscale devices. We have designed and synthesised a neutral, redox-active [2]rotaxane, which incorporates an electron-deficient pyromellitic diimide (PmI)-containing ring encircling two electron-rich recognition sites in the form of dioxynaphthalene (DNP) and tetrathiafulvalene (TTF) units positioned along the rod section of its dumbbell component. Molecular modeling using MacroModel guided the design of the mechanically interlocked molecular switch. The binding affinities in CH2Cl2 at 298 K between the free ring and two electron-rich guests—one (Ka = 5.8 × 102 M−1) containing a DNP unit and the other (Ka = 6.3 × 103 M−1) containing a TTF unit—are strong: the one order of magnitude difference in their affinities favouring the TTF unit suggested to us the feasibility of integrating these three building blocks into a bistable [2]rotaxane switch.

The [2]rotaxane was obtained in 34% yield by relying on neutral donor–acceptor templation and a double copper-catalysed azide–alkyne cycloaddition (CuAAC). Cyclic voltammetry (CV) and spectroelectrochemistry (SEC) were employed to stimulate and observe switching by this neutral bistable rotaxane in solution at 298 K, while 1H NMR spectroscopy was enlisted to investigate switching upon chemical oxidation. The neutral [2]rotaxane is a chemically robust and functional switch with potential for applications in device settings. Submit to this JournalThe search for robust experimental proof of supersolidity has encountered many complicating factors, such as temperature-dependent changes in the mechanical properties of solid He4 which mimic the signature of superfluid flow. As a result, the physical existence and true nature of this unique state of matter are still under debate. Here we consider He4 stabilized by a one-dimensional periodic potential whose lattice spacing is similar to the length scale of the He4−4He interaction.

We use the Bogoliubov transformation to calculate the excitation spectrum, finding that when interactions between nearest or next-nearest neighbors are strongly attractive, there is a finite positive gap in energy between the delocalized ground state and the lowest energy excitations, which is significantly larger than the both the lambda temperature and the melting temperature. Not only does this make the system stable against phase separation of particles and vacancies, but it also means that it should be possible to observe a supersolid at a high-enough temperature that superfluidity in bulk liquid He4 or changes in the mechanical properties of bulk solid He4 do not obscure it. Hotels With Hot Tubs In Room In VancouverThe properties of experimentally achievable materials which could support this type of supersolid are also discussed.Iphone 5 Leather Back Sticker

/10.1103/PhysRevA.91.033602©2015 American Physical Society If venting concerns are keeping you from installing tankless water heaters on your projects, these tips might help you find a simpler, less expensive solution.For many of your customers and projects, selecting a gas tankless water heater is a smart decision. Propane tankless water heaters are one of the most efficient water heating options available, allowing homeowners to reduce energy costs by up to 50Homes For Sale Westover Drive Se Washington Dc percent and reduce greenhouse gas emissions by up to 61 percent compared with standard electric water heaters. But in some cases, misconceptions about the venting needs of gas tankless units might keep construction professionals fromBefore you decide against a tankless water heater for your next project, consider these eight facts about venting.1.

tankless water heaters don't have to use indoor air forTankless water heaters can be vented in two ways:Power-vent units use indoor air for combustion and simply vent the exhaust to the outside. Direct-vent units pull in air from outside the house, so they have two vents for intake and exhaust. power-vent units require only an exhaust vent, they create additional placement concerns: They must be placed in a large-enough room or a room with vents or louvers so that they have adequate make-up air for the gas combustion. direct-vent units use outdoor air, they can be placed in smaller spaces, such as an attic, closet, or small mechanical room.2. don't always need two ventilation pipes, even for direct-vent units. Direct-vent water heaters can use two separate pipes for intake and exhaust, but some manufacturers offer concentric venting, a single pipe that contains an inner exhaust vent and an outer intake vent. Concentric vents provide a couple

of advantages, Trey Hoffman, global product manager for Rinnai,First, with only one pipe, installers only need to make one penetration in the wall or ceiling. Second, unlike exhaust vent pipes, which are hot to the touch and thus require clearance to avoid contact with the wall, concentric vents are cool to the touch because they keep the warm exhaust air on theSo while concentric vents are larger-typically 5 inches in diameter, versus 3 inches for a single pipe-they don't require additional clearanceConcentric vents also offer a safety benefit, Hoffman says. If the inner exhaust vent develops a leak, the exhaust air will stay contained within the intake pipe and can't enter the home.3. have to go through the roof.  Traditional (tank) gas water heaters vent through the roof using galvanized steel B-vents because they work through natural draft, allowing the hot exhaust air to rise up and out of the house. contrast, tankless water heaters' vents can terminate on a side wall because

their combustion fan blows exhaust from the units horizontally. particularly helpful to remodelers or professionals replacing electric tanks (which don't require venting) with propane tankless units, Hoffman says. you had to go through the roof every time, it would make the venting part of your installation much more expensive and difficult," he says. you can go out a side wall means that you have a lot more flexibility in where you put the unit. Now all you have to do is move the plumbing around a bit to accommodate the new position of the water heater." outdoor unit, you don't need to vent at all.  In warmer climates, it's easy to install a tankless water heater outdoors, with no additional ventingTankless units are designed to withstand below-freezing temperatures through self-warming capabilities that prevent freezing and cracking. the heating elements run on an electrical supply, however, tanks can freeze in very cold climates where electrical outages occur, making indoor installations

a better option for those locations.) Replacing a tank water heater with an outdoor tankless unit can even free up indoor floor space, Tommy Olsen, Rheem's market manager for tankless and specialty products, says. "You pick up 9 square feet on the floor, but you also pick up that floor-to-ceiling cube," he says. of the guys I work with replaced the tank in his closet with a tankless unit outside, and now he's got additional pantry space." condensing tankless water heater, you don't need metal venting. Non-condensing tankless water heaters typically transfer to the water only about 80 percent of the heat they generate. The remaining heat creates a hot exhaust gas that requires metal venting, typically stainless steel or thick aluminum. Condensing units, on the other hand, are typically about 95 percent efficient, so the temperature of the exhaust gas is lower - around 110 to 120 degrees. That means they can be vented with a less expensive plastic, generally PVC or

In fact, the price difference in the venting can even offset the cost of the higher-efficiency unit, Olsen says. "The overall installed cost of a high-efficiency unit is typically equal to or lower than that of a mid-efficiency product, so it's an easy up-sell at that point."6. You don't have to have a box stuck to your wall.  new-construction applications, some manufacturers offer recess boxes to keep the tankless water heater inside the wall. At 14 inches wide, non-condensing units can fit between conventional studs; 18-inch-wide condensing units may require more creative framing. "Now your water heater is flush with the outside of the house," Hoffman says. "It makes for a very neat and tidy solution."7. You don't always need separate vents for multiple waterWhile commercial and large residential applications may use multiple tankless units, they don't necessarily require two vent penetrationsRinnai is developing a common-venting system that uses a manifold to