We describe the preparation of a compound whose molecules consist of two metal sandwich stands carrying tentacles with affinity to metal surfaces and holding an axle that carries a dipolar or a nonpolar rotator. The dipolar rotor exists as three pairs of enantiomers, rapidly interconverting at room temperature. When mounted on a gold surface, each molecule represents a chiral altitudinal rotor, with the rotator axle parallel to the surface. The surface-mounted rotor molecules are characterized by several spectroscopic and imaging techniques. At any one time, in about one-third of the dipolar rotors the rotator is free to turn and the direction of its dipole can be flipped by the electric field applied by an STM tip, as revealed by differential barrier height imaging. Molecular dynamics calculations suggest that electric field normal to the surface causes members of one pair of enantiomers to rotate unidirectionally.

Gold surfaces carrying altitudinal molecular rotors firmly attached through sulfur and/or mercury atoms have been examined by IR spectroscopy. The presence of an intact rotator has been confirmed and its average orientation with respect to the gold surface determined by single reflection thin-layer attenuated total reflection (ATR) spectroscopy, using metal surface selection rules. The requisite IR polarization directions were obtained from IR linear dichroism of a model rotator oriented in stretched polyethylene. The results are compatible with those of prior differential barrier height imaging measurements and molecular mechanics calculations.

Littoral habitats in large rivers are influenced to varying degrees by changes in discharge. Irrigation abstractions can increase the amount of habitat that would naturally be dewatered during low flow periods and therefore it is important to have some knowledge of the potential impact this may have on riverine macroinvertebrates. The macroinvertebrate assemblages of common littoral habitats in riffles, pools and runs in two reaches each of the Macquarie and Mersey Rivers, northern Tasmania, Australia were compared from samples collected during the low flow and irrigation season, between December 1991 and April 1992. The area under water of these habitats, riffle substrata, macrophyte beds and coarse woody debris, responded differently to changes in discharge. Within a reach, the same taxonomic groups often dominated the total number of macroinvertebrates for all habitats, but there were differences in the proportions contributed by these taxa to the different habitats. In general, taxa characteristic of slow‐flowing or lentic habitats, such as ostracods and amphipods, were dominant in macrophyte beds in pools and runs, whereas taxa such as larval elmid beetles and hydropsychid caddisflies were dominant in riffles. A substantial component of the fauna from each habitat within a reach was unique to that habitat, but there was always a similar number of taxa common to all habitats. Classification and ordination grouped samples from both rivers firstly by habitat and secondly by month and reach. Total density and family richness of invertebrates differed by reach, habitat and month in both rivers, except for richness in the Mersey River where habitat was not significant. Differences in densities and numbers of invertebrate families among habitats were not consistent between reaches for each river. This study has highlighted the differences in macroinvertebrate assemblages of several littoral habitats in two lowland rivers in Tasmania. Differences in taxonomic composition, density and richness among habitats within reaches strongly imply the uniqueness of these habitats in terms of the invertebrate faunas that occupy them. We suggest that if maintenance of biotic diversity is an aim of instream flow management, water allocations that address low flows should place a high priority on the maintenance of a diversity of habitats.

Gold surface attachment of altitudinal molecular rotors provided with ten -HgSCH 2 CH 2 SCH 3 "tentacles" has been monitored with ellipsometry, scanning tunneling microscopy, and X-ray photoelectron spectroscopy (XPS). The rotors appear to adsorb on the gold surface in the intended orientation, with rotor axle parallel to the surface, without any inclination for multilayer growth. According to XPS data, the sulfur-containing tentacles start to be detectably oxidized within hours of exposure to air and can be ultimately removed by washing. The rotor molecules nevertheless remain firmly attached in the desired orientation, apparently due to a direct interaction of their Hg atoms with the gold surface. When the tentacles are simplified to -HgOCOCF 3 substituents, the molecules adhere to the surface as well, but not always in the desired orientation.