A quasi-passive leg exoskeleton is presented for load-carrying augmentation during walking. The exoskeleton has no actuators, only ankle and hip springs and a knee variable-damper. Without a payload, the exoskeleton weighs 11.7 kg and requires only 2 Watts of electrical power during loaded walking. For a 36 kg payload, we demonstrate that the quasi-passive exoskeleton transfers on average 80% of the load to the ground during the single support phase of walking. By measuring the rate of oxygen consumption on a study participant walking at a self-selected speed, we find that the exoskeleton slightly increases the walking metabolic cost of transport (COT) as compared to a standard loaded backpack (10% increase). However, a similar exoskeleton without joint springs or damping control (zero-impedance exoskeleton) is found to increase COT by 23% compared to the loaded backpack, highlighting the benefits of passive and quasi-passive joint mechanisms in the design of efficient, low-mass leg exoskeletons.

An achiral anthracene−pyrimidine derivative (5-(9-anthracenyl)pyrimidine, 1) forms adduct 1·Cd(NO3)2·H2O·EtOH (2) in chiral space group P21. The metal ion is hexacoordinated with two pyrimidine ligands (equatorial cis), water and ethanol (equatorial cis), and two nitrate ions (axial trans). The chirality arises from a pyrimidine−Cd2+ helical array and is preserved not only in each crystal via homochiral interstrand water−nitrate hydrogen bonding but also in all the crystals in the same chirality as a result of single-colony homochiral crystal growth. Compound 1 also forms achiral (Pbca) trihydrate adduct 1·Cd(NO3)2·3H2O (3) having nonhelical pyrimidine−Cd2+ zigzag chains. Achiral zigzag polymer 3 and chiral helical polymer 2 are interconvertible with each other in the solid states upon exchange of volatile ligands (ethanol and water). The helix winding associated with the conversion of adduct 3 to 2 can be made homochiral by seeding.

When recrystallized from an appropriate solvent, orthogonal bis(resorcino1)-anthracene compound l a as host forms molecular sheets involving an extensive hydrogen-bonded network. This generates supramolecular cavities which incorporate two molecules of recrystallization solvent such as ketones and esters as guests via host-guest hydrogen-bonding, The guest incorporation under competitive recrystallization conditions is highly selective; even a difference by one methylene group in the guests can be discriminated. The supramolecular cavities with included guest molecules are connected with each other, giving more or less continuous channels. Heating host-guest adducts in vacuo affords polycrystalline guest-free apohost. The apohost binds ketone and ester guests not only as liquids but also as gases and solids. The host:guest stoichiometry is 1:2 in most cases. Solid-state complexation using a 1:3 or 1:4 (host to guest) mixture affords 1:2 host-guest cocrystals and 1 or 2 equiv of unreacted guest simply remains as such. The adducts lw2(guest) thus obtained under solid-liquid, solid-gas, or solid-solid conditions exhibit essentially the same powder X-ray diffraction patterns as their authentic single crystals. Apohost la also binds hydrocarbons and haloalkanes such as benzene, p-xylene, and chloroform again in a 1:2 (host to guest) molar ratio. These results demonstrate that guest molecules can diffuse in the crystal lattices of apohost la. As compared with the conesponding recrystallization processes, guest-binding to preformed apohost is apparently far less selective with respect to the guests. This is due to a kinetic preference for smaller guests, even without a hydrogen-bonding site as in hydrocarbons, which are capable of more facile lattice diffusion. The sorption-desorption of liquid and gaseous guests can be repeated many times. The guest-binding properties of apohost l a is discussed from a viewpoint of a functional organic counterpart of porous inorganic crystal zeolites.

Anthracenebisresorcinol derivative 1 as an organic network material shows a novel catalysis in the solid state for the acrolein-cyclohexadiene Diels-Alder reaction. The suggested mechanism involves a catalytic cycle composed of sorption of the reactants in the cavities of polycrystalline host 1, preorganized intracavity reaction, and desorption of the product. The host also promotes stereoselective intracavity reactions for alkyl acrylates and cyclohexadiene but, in this case, not in a catalytic manner. Relevance of the present system as a functional organic analog of zeolites is discussed in light of the kinetics of respective elementary processes and the effects of pulverization of the catalyst thereupon as well as X-ray crystal structures.