Molecular assembly of artificial photosynthetic antenna core complex on an amino-terminated ITO electrode

Bacterial photosynthetic membrane proteins, light-harvesting antenna complex (LH1), reaction center (RC), and their combined ‘core’ complex (LH1–RC) are functional elements in the primary photosynthetic events, i.e., capturing and transferring light energy and subsequent charge separation. These photosynthetic units (PSUs) isolated from Rhodospirillum rubrum (Rs. rubrum) were assembled onto an ITO electrode modified with 3-aminopropyltriethoxysilane (APS–ITO). The near IR absorption spectra of PSUs on the assembled electrodes were identical to those of solutions, indicating that the LH1 and LH1–RC core complexes were native on the electrode. Photocurrent response of PSUs on the electrode was examined upon illumination of the LH1 complex at 880 nm. The LH1–RC and a mixed assembly of LH1 and RC exhibited photocurrent response, but not LH1 only, consistent with the function of these PSUs, capturing light energy and transferring electron. This result provides useful methodology for building an artificial fabrication of PSUs on the electrode.     

Conformation-dependent racemization of aspartyl residues in peptides

Biologically uncommon D-aspartyl (D-Asp) residues have been detected in proteins of various tissues of elderly humans. The presence of D-Asp has been explained as a result of the racemization of L-Asp (denoted as Asp) in the protein of inert tissues. We have previously suggested that the racemization of Asp may depend on the conformation of the peptide chain. However, the nature of the peptide conformation that affects the D-Asp formation has not yet been examined. Here we report the kinetics of Asp racemization in two model peptides, (Asp-Leu)(15) and (Leu-Asp-Asp-Leu)(8)-Asp, which form beta-sheet structures and alpha-helical structures, respectively. For the beta-sheet structures, the activation energy of racemization of Asp residues was 27.3 kcal mol(-1), the racemization rate constant at 37 degrees C was 2.14x10(-2) per year and the time required to reach a D/L ratio of 0.99 at 37 degrees C was 122.6 years as estimated from the Arrhenius equation. For the alpha-helical structures, the activation energy of racemization was 18.4 kcal mol(-1), the racemization rate constant 20.02x10(-2) per year and the time 13.1 year. These results suggest that Asp residues inserted in alpha-helical peptides are more sensitive to racemization than Asp residues inserted in peptides adopting beta-sheet structures. The results clearly indicate that the racemization rate of Asp residues in peptides depends on the secondary structure of the host peptide.     

Versatile synthesis of head group functionalized phospholipids via oxime bond formation

A method for introduction of various head groups on phospholipid frameworks via oxime bond formation has been developed for the synthesis of cyclen-Cu(II), pyrene, naphthalene, and other headgroup functionalized phospholipids that can cleave the membrane protein, hemagglutinin.     

PET (positron emission tomography) imaging of biomolecules using metal-DOTA complexes: a new collaborative challenge by chemists, biologists, and physicians for future diagnostics and exploration of in vivo dynamics

Recently, PET has been paid a great deal of attention as a non-invasive imaging method. In this review, the recent advances of PET using biomolecules, such as peptides, monoclonal antibodies, proteins, oligonucleotides, and glycoproteins will be described. So far, PET of biomolecules has been mainly used for diagnosis of cancers. The biomolecules have been conjugated with the DOTA ligand, labeled with radiometals as the beta+ emitter, and targeted to specific tumors, where they have enabled visualization of even small metastatic lesions, due to the high sensitivity of the PET scanners. Some of the biomolecules have been used not only for PET diagnosis, but also for radiotherapeutic treatments by simply changing the radiometals to beta(-) emitters. Collaborative work between chemists, biologists, and physicians will be important for the future of biomolecule-based targeting and diagnosis.     

Acid-catalyzed rearrangement of aryl-substituted homobenzoquinone epoxides

The BF3-catalyzed reactions of diphenyl-substituted and endo-monophenyl-substituted homobenzoquinone epoxides proceeded through a regioselective oxirane ring opening followed by participation of a pi-aryl transannular cyclization to give the tricyclic diketo alcohols. The conformationally semirigid ethano-bridged diphenyl-substituted homologues also provided similar diketo alcohols and the subsequent ring-expanded cycloheptenedione (via a subsequent 1,2-acyl migration associated with cyclopropane ring opening), depending on the methyl-substitution pattern of the quinone frame. However, the exo-monophenyl-substituted and the rigid biphenyl-2,2'-diyl-substituted homobenzoquinone epoxides essentially remained unchanged.     

Contribution of intramolecular C=O...H-N hydrogen bonding to the solvent-induced reentrant phase separation of poly(N-isopropylacrylamide)

Changes in the local environment around amide groups of poly(N-isopropylacrylamide) (PNiPA) during a solvent-induced reentrant phase separation have been investigated by infrared spectroscopy combined with quantum chemical calculations. The addition of methanol or tetrahydrofuran as a cosolvent to an aqueous solution of PNiPA causes spectral changes in the amide I regions. By preparing a dimer model compound for PNiPA, we can establish the assignment of the amide I bands for the polymer in solutions. Hydrogen-deuterium exchange experiments of the amide protons of PNiPA and its dimer models have revealed that the amide groups of PNiPA form an intramolecular C=O...H-N hydrogen bond even in a good solvent. The result has suggested that the change in the amide I envelope of PNiPA observed during the solvent-induced phase transition reflects the modification of the intramolecular C=O...H-N hydrogen bond of PNiPA as well as the variation in solvation state of the amide groups. On the basis of the assignment, we have discussed contributions of the intramolecular C=O...H-N hydrogen bond to the phase behavior of PNiPA.     

Auxiliary-directed oxidation of ursolic acid by ‘Ru’-porphyrins: chemical modulation of cytotoxicity against tumor cell lines

Derivatization of ursolic acid, one of the natural ursene-type pentacyclic triterpenes, was investigated by the oxidation with dioxoruthenium(VI) tetraphenylporphyrins. Oxidation selectivity on the terpene structure was modulated by the auxiliaries introduced on the tetraphenylporphyrin. Chemical oxidation of the ursolic acid affected the cytotoxic activity against tumor cell lines.