A break junction method using a scanning tunneling microscope has been applied to electrical conductance measurement of newly designed oligothiophene molecules terminated with a thiocyanate group. The tunneling conduction was evident from an exponential decay of the conductance as a function of the molecular length up to ca. 6 nm. The tunneling decay constant was estimated to be 0.1 A (-1). The pre-exponential factor was 1.3 x 10 (-6) S, which was smaller than that observed for alkanedithiols.

The electrical resistance of single oligothiophene molecular wires with lengths ranging from 2.2 nm (5-mer) to 9 nm (23-mer) was measured by the break junction method. A linear relationship between the molecular length and resistance was found for molecules longer than 11mer, whereas an exponential increase in the resistance was observed for molecules shorter than 11-mer. These results indicate that the carrier transport mechanism changes from tunneling to hopping at around 11-14-mer (5.6 nm).

The Ephedra herb, which has been used in Kampo medicines, originates from terrestrial stems of Ephedra species. It is important to establish cultivation methods and cultivars to secure a stable supply of the Ephedra herb that would meet the quality standards for the ephedrine alkaloids content. In this study, we first grew Ephedra sinica plants derived from seeds in the field for 5 years. Then, for selective breeding of cultivars that could meet the quality standards for the ephedrine alkaloids content, we measured the content of total alkaloids (TAs), ephedrine (Eph), and pseudoephedrine (PEph) in individual plants derived from seedlings and grown for 4 years in the field. The range of the TA content in each individual plant was narrower than that among individual plants grown in the field. Therefore, individual plants were selected according to their TA content, Eph/PEph ratio, and stolon-formation capability. The selected individuals were propagated using stolons, and their TA content was studied for 2 years. In the second year, the TA content in terrestrial stems derived from stolons of the selected individuals was as high as that of their parents. Therefore, it was confirmed that the selected individuals that were propagated using stolons could produce TA reproducibly. This study suggested that selective breeding using stolon propagation is effective for stabilizing Ephedra herb TA content. Key words Ephedra sinica; ephedrine alkaloid content; selective breeding; stolon propagationThe Ephedra herb has been used in traditional Japanese medicines and Kampo medicines. The Japanese Pharmacopeia describes the Ephedra herb as terrestrial stems of Ephedra sinica STAPF, E. intermedia SCHRENK et C. A. MEYER, or E. equisetina BUNGE (Ephedraceae). When stems are dried, they must contain ≥0.7% of total alkaloids (TAs), ephedrine (Eph), and pseudoephedrine (PEph).1) In Japan, the Ephedra herb has been frequently included in Kampo prescriptions, such as Kakkonto, Maoto, and Makyokansekito. However, for obtaining the Ephedra herb, Japan relies on China, which has had export restrictions for the prevention of desertification since 1999.2) Thus, it is necessary to sustainably cultivate Ephedra plants in Japan.Recent studies on ephedrine alkaloids in Ephedraceae have shown that the range of the TA content is wide in each species.3) The Eph content is higher than that of PEph in E. sinica, 4) and the ephedrine alkaloid composition ratio of the Ephedra herb depends on genetic factors. 5) However, other studies have shown that the content of ephedrine alkaloids is affected by environmental factors. 6,7) Even though numerous studies have been conducted on Ephedra plants, there remain questions about ephedrine alkaloids in cultivated Ephedra plants and about cultivation methods for their stabilization. For example, it is not clear how the content of ephedrine alkaloids varies from year to year in individual plants growing in the field, how long cultivated plants maintain their ephedrine alkaloid content in the field, which method...