Tomoji Kawai

We present electrostatic force microscopy images of double-stranded DNA and transcription complex on an insulating mica substrate obtained with molecular resolution using a frequency-mode noncontact atomic force microscope. The electrostatic potential images show that both DNA and transcription complexes are polarized with an upward dipole moment. Potential differences of these molecules from the mica substrate enabled us to estimate dipole moments of isolated DNA and transcription complex in zero external field to be 0.027 D/base and 0.16 D/molecule, respectively. Scanning capacitance microscopy demonstrates characteristic contrast inversion between DNA and transcription complex images, indicating the difference in electric polarizability of these molecules. These findings indicate that the electrostatic properties of individual biological molecules can be imaged on an insulator substrate while retaining complex formation.

Ribosomes of Escherichia coli were visualized in buffer solution by atomic force microscopy (AFM). A series of time-dependent AFM images showed that ribosomes spontaneously adsorb on mica. Although ribosomes observed in air are forced to flatten on the surface, the height of ribosomal particles obtained under a physiological buffer solution is 21.8+/-0.5 nm, which is consistent with the ideal diameter. We succeeded in observing single ribosomes in a near-native condition.

A Porphyrin/DNA complex stabilized by both ionic bonds and stacking of π conjugates is reported herein. Morphology observation on the single molecular level revealed that the complex exhibits rigid behavior and inhomogeneity with phase separation. These characteristics are the indication of the presence of stacking interaction between porphyrins along the DNA scaffold.

A novel porphyrin-fused porphyrin is formed by an oligomerization reaction of a (porphyrinato)nickel complex with TeCl₄; the isolated compound, [2]porphyracene, was characterized by spectroscopic methods and direct observation using scanning tunnelling microscopy; the excitation energy value of 13460 cm^–1 (743 nm) is the lowest value reported for porphyrin dimers.