Experimental studies of the myosin-actin motor

The mechanical processes generated by the molecular motors, myosin and actin, were measured using single molecule imaging, manipulation, and nanometry techniques. It was shown that the mechanical events of myosin are not tightly coupled with the ATP hydrolysis reaction and that myosin molecules move stochastically. These results indicate that the movement of myosin is driven by thermal motion rather than structural changes occurring in the myosin molecules. Thermal Brownian motion must be biased using the energy released from the hydrolysis of ATP. Thus, the molecular motors can harness thermal energy to perform mechanical work efficiently. Received: 20 November 2001 / Accepted: 11 February 2002 / Published online: 22 April 2002     

A new mechanism for negative differential conductivity in superlattices

Electrons in a superlattice at high fields are suitably described in terms of localized states related to the potential wells. Conduction is dominated by transitions between adjacent wells if the potential drop over a superlattice period exceeds the width of the lowest miniband. It is shown that the probability of these transitions, and consequently the current as well, decrease with increasing field. This effect originates from decreasing overlap between electron states of neighbouring wells, and it is found for the interaction with acoustic phonons and with impurities as well.     

Efficient C-H/C-D exchange reaction on the alkyl side chain of aromatic compounds using heterogeneous Pd/C in D2O

[reaction: see text] An efficient and extensive deuterium incorporation using heterogeneous Pd/C-D(2)O-H(2) system into many different types of unactivated C-H bond positions was developed. The present method provides a deuterium gas-free, totally catalytic, and post-synthetic deuterium labeling method in D(2)O media.     

Systematic solution-phase parallel synthesis of active vitamin D3 analogs with elongated side chains and their cell differentiation activities

Side-chain elongation of active vitamin D3 is acknowledged as a structural modification to enhance its cell differentiation activity; however, the comprehensive structure-activity relationship (SAR) as a result of this modification has not been reported. To clarify the SAR, we synthesized six analogs systematically elongated at the 24-position, 26,27-position, or both by methylene (normal A-ring series 1a-f) in a facile parallel solution-phase synthesis. Using parallel synthesis, we expanded the side chain-elongation study into two 19-exomethylene analog series: 19-nor-A-ring (4a-f) and 2-methylene-19-nor-A-ring (5a-f). In the 19-nor-A-ring analog series, the SAR induced by side-chain elongation was similar to the normal A-ring analog series, but in the 2-methylene-19-nor-A-ring series, the SAR was unique.     

Efficient asymmetric synthesis of novel gastrin receptor antagonist AG-041R via highly stereoselective alkylation of oxindole enolates

An efficient method for asymmetric synthesis of the potent Gastrin/CCK-B receptor antagonist AG-041R was developed. Core oxindole stereochemistry was established by asymmetric alkylation of oxindole enolates with bromoacetic acid esters, using l-menthol as a chiral auxiliary. The key alkylation reaction of the oxindole enolates generated tetrasubstituted chiral intermediates with high diastereoselectivity. The stereoselective alkylation reactions are described in detail.     

Far infrared impurity absorption in a quantum well

We have calculated the energy and lineshape of the 1s → 2p_x,y transition for a hydrogenic impurity located in a quantum well. Due to the dependence of the transition energy on the impurity location, the absorption lineshape is very sensitive to the doping profile. The spectrum, in general, exhibits two peaks, arising from impurities located near the center and the edges of the well.     

Investigations of the band line-up in semimetallic InAs---GaSb superlattices under hydrostatic pressure

Using magneto-optical methods, we have measured the energy separation between the subbands in a semimettalic InAs---GaSb superlattice associated with the InAs conduction band (CB) and the GaSb valence band (VB) as a function of hydrostatic pressure up to 11kBar. The CB-VB energy overlap (Δ) at the InAs---GaSb interface is found to depend less on pressure than predicted on grounds of usual assumptions concerning band energy shifts induced by pressure.Also inter-subband coupling has been observed between the bands in different adjacent materials. This coupling is found to lead to anti-crossing in the subband dispersion relation.