Biomedical subjects

Hiroshi Uji-i

Publications and source records attributed to Hiroshi Uji-i.

4 recordsLinked to original sources

PubMed2006

Two-dimensional porous molecular networks of dehydrobenzo[12]annulene derivatives via alkyl chain interdigitation.

The self-assembly of a series of hexadehydrotribenzo[12]annulene (DBA) derivatives has been scrutinized by scanning tunneling microscopy (STM) at the liquid-solid interface. First, the influence of core symmetry on the network structure was investigated by comparing the two-dimensional (2D) ordering of rhombic bisDBA 1a and triangular DBA 2a (Figure 1). BisDBA 1a forms a Kagomé network upon physisorption from 1,2,4-trichlorobenzene (TCB) onto highly oriented pyrolytic graphite (HOPG). Under similar experimental conditions, DBA 2a shows the formation of a honeycomb network. The core symmetry and location of alkyl substituents determine the network structure. The most remarkable feature of the DBA networks is the interdigitation of the nonpolar alkyl chains: they connect the pi-conjugated cores and direct their orientation. As a result, 2D open networks with voids are formed. Second, the effect of alkyl chain length on the structure of DBA patterns was investigated. Upon increasing the length of the alkyl chains (DBAs 3c-e) a transition from honeycomb networks to linear networks was observed in TCB, an observation attributed to stronger molecule-substrate interactions. Third, the effect of solvent on the structure of the nonpolar DBA networks was investigated in four different solvents: TCB as a polar aromatic solvent, 1-phenyloctane as a solvent having both aromatic and aliphatic moieties, n-tetradecane as an aliphatic solvent, and octanoic acid as a polar alkylated solvent. The solvent dramatically changes the structure of the DBA networks. The solvent effects are discussed in terms of factors that influence the mobility of molecules at the liquid-solid interface such as solvation.

Alkylation↗

PubMed2006

Molecular geometry directed Kagomé and honeycomb networks: toward two-dimensional crystal engineering.

We present here the formation of a molecular Kagomé network within a two-dimensional (2D) crystal on a surface. This system provides a clear example of how, by design, molecular geometry can be expressed at the level of the 2D crystal lattice, leading to the formation of open networks. Key elements to control molecular network formation are core symmetry, location and orientation of interacting and connecting substituents, as well as symmetry matching between the networks and the surface.

Journal Article↗

PubMed2006

[Ru(TAP)3]2+-photosensitized DNA cleavage studied by atomic force microscopy and gel electrophoresis: a comparative study.

Topological modifications of plasmid DNA adsorbed on a variety of surfaces were investigated by using atomic force microscopy (AFM). On mica modified with 3-aminopropyltriethoxysilane (APS) or poly-L-lysine, the interaction between the plasmid DNA and the surface "freezes" the plasmid DNA conformation deposited from solution, and the AFM images resemble the projection of the three-dimensional conformation of the plasmid DNA in solution. Modified mica with low concentrations of Mg(2+) leads to a decrease in the interaction strength between plasmid DNA and the substrate, and the AFM images reflect the relaxed or equilibrium conformation of the adsorbed plasmid DNA. Under these optimized deposition conditions, topological modifications of plasmid DNA were produced under irradiation in the presence of [Ru(TAP)(3)](2+) (TAP = 1,4,5,8-tetraazaphenanthrene), which is a non-intercalating complex, and were followed as a function of illumination time. The observed structural changes correlate well with the conversion of the supercoiled covalently closed circular form (ccc form) into the open circular form (oc form), induced by a single-strand photocleavage. The AFM results obtained after fine-tuning of the plasmid DNA-substrate interaction compare well with those observed from gel electrophoresis, indicating that under the appropriate deposition conditions, AFM is a reliable technique to investigate irradiation-induced topological changes in plasmid DNA.

DNA, Superhelical↗

PubMed2006

Solvent controlled self-assembly at the liquid-solid interface revealed by STM.

The effect of solvent on the two-dimensional (2D) supramolecular ordering of monodendron 1 at the liquid-solid interface has been systematically investigated by means of scanning tunneling microscopy (STM). Solvents range from those with hydrophilic solvating properties, such as alkylated alcohols and acids, to hydrophobic solvents such as alkylated aromatics and alkanes. Dramatic differences in the 2D ordering are observed depending on the nature of the solvent. Of particular interest is the fact that in hydrophobic solvating solvents, such as aliphatic and aromatic hydrocarbons, solvent molecules are coadsorbed in the 2D molecular network while this is not the case for alkylated alcohols or acids. Furthermore, in the case of the coadsorbing solvents, a striking influence of the alkyl chain length has been observed on the 2D pattern formed. The solvent and alkyl chain length dependences are discussed in terms of molecule-molecule interactions (homo and hetero) and molecule-substrate interactions.

Journal Article↗