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Masahide Tominaga

Publications and source records attributed to Masahide Tominaga.

14 recordsLinked to original sources
PubMed2006

Spontaneous resolution of aromatic sulfonamides: effective screening method and discrimination of absolute structure.

An effective screening method combining parallel synthesis and solid-state CD measurements was established to identify achiral aromatic sulfonamides that show spontaneous resolution with rapidity. We found that 4 of the 12 achiral sulfonamides crystallized as chiral crystals through this method. The chirality of each sulfonamide was discriminated by solid-state CD spectra and Flack parameter in an X-ray analysis. Correspondence between the observed Cotton effect and the absolute configuration could be confirmed by time-dependent DFT calculations. [structure: see text]

Chemistry, Organic↗
PubMed2006

Peptide recognition: encapsulation and alpha-helical folding of a nine-residue peptide within a hydrophobic dimeric capsule of a bowl-shaped host.

A dimeric capsule of coordination bowl 1 encapsulated a nine-residue peptide (Trp-Ala-Glu-Ala-Ala-Ala-Glu-Ala-Trp; 2) within the large hydrophobic cavity in water, and stabilized the alpha-helical conformation of bound 2. An NMR titration experiment revealed that monomeric bowl 1 recognized two Trp residues at the both terminals of 2 through 1/2 = 1:1 to 2:1 complexation. The 1:1 and 2:1 species exist in equilibrium even in the presence of excess 1. It was found that the formation of the 2:1 complex, in which two bowls of 1 wrapped the whole of 2, became dominant by the addition of NaNO3 due to the fact that the enhanced ion strength increased the hydrophobic interaction between Trp residues and the cavity of 1. The alpha-helical conformation of 2 within the dimeric capsule of 1 was elucidated from detailed NOESY analysis.

Dimerization↗
PubMed2005

24-fold endohedral functionalization of a self-assembled M12L24 coordination nanoball.

A ca. 5 nm-sized, roughly spherical hollow complex was assembled from 12 Pd2+ ions and 24 bis(4-pyridylethenyl)-substituted bent ligands. By putting a functional group at the curvature of the ligand, the 24 functional groups were precisely arrayed inward within the spherical complex. When oligo(ethylene oxide) was anchored, the void of the hollow complex was tightly filled with a pseudo poly(ethylene oxide) nanoparticle, which showed metal ion (La3+) absorption property.

Journal Article↗
PubMed2005

Triple helicate constructed by covalent bondings: crystal structure and effective synthesis based on propeller-like substructures.

A triple helicate, having a macrocyclic aromatic amide structure, was synthesized in high yield because of a preorganized component of the tertiary benzenetrianilide moieties in a propeller-like syn conformation at both ends. The helicity was derived from tilted T-shaped aromatic-aromatic (CH-pi) interactions between each of the N-phenyl rings. [structure: see text]

Journal Article↗
PubMed2005

Sequence-selective recognition of peptides within the single binding pocket of a self-assembled coordination cage.

The single binding pocket of a self-assembled Pd6L4 coordination cage recognizes oligopeptides in a highly sequence-selective fashion. In particular, the Trp-Trp-Ala sequence is strongly bound by the cavity (Ka >/=106 M-1). Tripeptides possessing the same residues but in different sequences (i.e., Trp-Ala-Trp and Ala-Trp-Trp) show much poorer affinity. Even singly mutated tripeptides with aromatic-aromatic-aliphatic sequences of the residues (e.g., Trp-Trp-Gly and Trp-Tyr-Ala) are not recognized efficiently. X-ray analysis and NMR reveal that all residues of the Trp-Trp-Ala sequence cooperatively interact with the cage via CH-pi and pi-pi interactions.

Alanine↗
PubMed2005

Coordination assemblies from a Pd(II)-cornered square complex.

The [enPd(II)]2+ (en = ethylenediamine) unit has emerged as a versatile building block in molecular self-assembly. In particular, the 90 degrees coordination angle of the metal has been judiciously used in the design of new discrete two- and three-dimensional structures. Our last 15 years of work with the Pd(II)-cornered unit is summarized in this Account, from the spontaneous formation of a Pd4 square metal complex to a family of architectures such as cages, bowls, boxes, tubes, catenanes, and spheres.

Journal Article↗
PubMed2004

A 3.5-nm coordination nanotube.

A 3.5-nm coordination nanotube was self-assembled from 12 Pd(II) ions and four tape-shaped ligands with the aid of a 3.0-nm template. This tubular structure was unambiguously determined by the single-crystal X-ray analysis. Being cooperatively sustained by 24 Pd(II)-pyridine interactions, the framework was kinetically stable even when the template was removed. The empty tube was, of course, capable of binding other molecules in the cavity.

Crystallography, X-Ray↗
PubMed2002

[Radiation exposure in CT].

The use of CT has increased rapidly in the past two decades, in part because of the development of helical CT and multidetector row CT. The benefits obtained by CT are not, however, without risks. This paper emphasizes the importance of keeping radiation doses during CT procedures as low as reasonably possible, especially for pediatric and small adult patients. In order to evaluate the risk of exposure, precise dosimetry is important. This paper introduces a new film dosimetry system that can be used easily in any institution and with any CT apparatus.

Adult↗