Synthesis of leucine-enkephalin analogs containing α-amino squaric acid

Novel Leu-enkephalin analogs 10a-c in which the Tyr¹, Gly², or Gly³ residue of Leu-enkephalin 9 was replaced with α-amino squaric acid analog Sq-Tyr 8b or Sq-Gly 8a were synthesized starting from 14 or 18. Conformational analysis of 10a-c together with its model compound 26 and their opioid receptor binding activity were evaluated.     

Acid-catalyzed isomerization and decomposition of ketone-2,4-dinitrophenylhydrazones

The quantitative analysis of ketones using DNPH is usually conducted in the presence of an acid catalyst. However, this method may cause an analytical error because 2,4-dinitrophenylhydrazones have both E- and Z-stereoisomers. Purified ketone-2,4-dinitrophenylhydrazone comprised only the E-isomer. However, under the addition of acid, both E- and Z-isomers were seen. In the case of 2-butanone-, 2-pentanone- and 2-hexanone-2,4-dinitrophenylhydrazone, the equilibrium Z/E isomer ratios were 0.20, 0.21 and 0.22, respectively. In addition, when trace water was added to the hydrazone derivatives in acetonitrile solution, the concentration of ketone derivatives were seen to decrease and the concentration of free DNPH was seen to increase. The decomposition rate of 2-butanone-2,4-dinitrophenylhydrazone was dependent on the concentration of acid-catalysis and reached an equilibrium state - carbonyl, DNPH, hydrazone-derivative and H₂O - within 10 h at 0.1 mol L⁻¹ phosphoric acid solution. The equilibrium constants of ketone-2,4-dinitrophenylhydrazones, [carbonyl] [DNPH]/[hydrazone] [H₂O], were relatively large and ranged from 0.74 × 10⁻⁴ to 5.9 × 10⁻⁴. Hydrazone derivatives formed from 2-ketones such as 2-pentanone, 2-hexanone and 4-methyl-2-pentanone showed lower equilibrium constants than corresponding 3-ketones. Consequently, only a minimum concentration of catalytic acid must be added. The best method for the determination of ketone-2,4-dinitrophenylhydrazones by HPLC or GC is to add phosphoric acid to both the standard reference solution and samples, forming a 0.001 mol L⁻¹ acid solution, and analyze after 27 h.     

Sol-gel reaction in acrylic polymer emulsions: the effect of particle surface charge

Acrylic polymer-silica hybrid emulsions were synthesized from both anionic and cationic polymer emulsions by simple post-addition of tetraethoxysilane as a silica precursor. Solvent resistance of the films from the hybrid emulsions and the zeta-potential of the hybrid emulsions suggested the different forms of silica components in each hybrid emulsion. Thermal gravimetric analysis, 29Si NMR measurements, and transmission electron microscope observations revealed that the hybrid emulsion from the anionic polymer emulsion was a mixture of anionic polymer particles and homogeneously dissolved silicate oligomer-polymer. On the contrary, the hybrid emulsion from cationic polymer emulsion consisted of polymer core-silica shell particles. The electrostatic interaction between the cationic polymer particle surface and the silicate would be responsible for the accumulation of the silicate onto the particle surface, leading to the silica shell layer formation. The sol-gel condensation reaction of silicate in the acidic emulsion phase was revealed to be controllable by the surface charge of the coexisting particles.     

Distribution of the cationic state over the chlorophyll pair of the photosystem II reaction center

The reaction center chlorophylls a (Chla) of photosystem II (PSII) are composed of six Chla molecules including the special pair Chla P(D1)/P(D2) harbored by the D1/D2 heterodimer. They serve as the ultimate electron abstractors for water oxidation in the oxygen-evolving Mn(4)CaO(5) cluster. Using the PSII crystal structure analyzed at 1.9 ? resolution, the redox potentials of P(D1)/P(D2) for one-electron oxidation (E(m)) were calculated by considering all PSII subunits and the protonation pattern of all titratable residues. The E(m)(Chla) values were calculated to be 1015-1132 mV for P(D1) and 1141-1201 mV for P(D2), depending on the protonation state of the Mn(4)CaO(5) cluster. The results showed that E(m)(P(D1)) was lower than E(m)(P(D2)), favoring localization of the charge of the cationic state more on P(D1). The P(D1)(?+)/P(D2)(?+) charge ratio determined by the large-scale QM/MM calculations with the explicit PSII protein environment yielded a P(D1)(?+)/P(D2)(?+) ratio of ~80/~20, which was found to be due to the asymmetry in electrostatic characters of several conserved D1/D2 residue pairs that cause the E(m)(P(D1))/E(m)(P(D2)) difference, e.g., D1-Asn181/D2-Arg180, D1-Asn298/D2-Arg294, D1-Asp61/D2-His61, D1-Glu189/D2-Phe188, and D1-Asp170/D2-Phe169. The larger P(D1)(?+) population than P(D2)(?+) appears to be an inevitable fate of the intact PSII that possesses water oxidation activity.     

Auger recombination dynamics in hybrid silica-coated CdTe nanocrystals

CdTe quantum dots coated with a silica layer containing CdS-like clusters exhibit intense photoluminescence and a spectral red-shift. Biexciton Auger recombination of these particles is examined by transient absorption spectroscopy. A lengthening of the Auger recombination lifetime by a factor of ～3.5 in the presence of the CdS-like clusters is observed and may contribute to the good PL properties of these nanostructures.     

Total syntheses of (-)- and (+)-goniomitine

The Stille coupling reaction of 3-(benzyloxymethyl)-1-(tert-butyldiphenylsiloxy)ethyl-1-(tributylstannyl)allene with N-(tert-butoxycarbonyl)-2-iodoaniline directly produced the corresponding 2-vinylindole derivative, which was independently transformed into natural (-)-goniomitine and unnatural (+)-goniomitine via the cross-metathesis with chiral oxazolopiperidone lactams. The antiproliferative activity of the synthesized natural (-)-goniomitine in Mock and MDCK/MDR1 cells showed them to be more potent to retard cell growth than unnatural (+)-goniomitine.     

Synthesis and redox properties of π-conjugated 4,5-diazafluorene derivatives incorporating 9-cyanomethylene moiety as an electron acceptor

We have synthesized π-conjugated acceptor-type molecules 3a-d containing a cyanomethylene unit as the electron acceptor site and a 4,5-diazafluorene ligand for metal complexation. In the crystal, the planar 3a molecules stack along the b axis in the head-to-tail fashion. Compound 3a shows distinctive electrochromism and its three differently colored redox states (dianion (3²⁻), anion radical (3⁻), neutral (3)) exhibit remarkable stability.     

Structure of the catalytic, inorganic core of oxygen-evolving photosystem II at 1.9 Å resolution

The catalytic center for photosynthetic water-splitting consists of 4 Mn atoms and 1 Ca atom and is located near the lumenal surface of photosystem II. So far the structure of the Mn(4)Ca-cluster has been studied by a variety of techniques including X-ray spectroscopy and diffraction, and various structural models have been proposed. However, its exact structure is still unknown due to the limited resolution of crystal structures of PSII achieved so far, as well as possible radiation damages that might have occurred. Very recently, we have succeeded in solving the structure of photosystem II at 1.9 ?, which yielded a detailed picture of the Mn(4)CaO(5)-cluster for the first time. In the high resolution structure, the Mn(4)CaO(5)-cluster is arranged in a distorted chair form, with a cubane-like structure formed by 3 Mn and 1 Ca, 4 oxygen atoms as the distorted base of the chair, and 1 Mn and 1 oxygen atom outside of the cubane as the back of the chair. In addition, four water molecules were associated with the cluster, among which, two are associated with the terminal Mn atom and two are associated with the Ca atom. Some of these water molecules may therefore serve as the substrates for water-splitting. The high resolution structure of the catalytic center provided a solid basis for elucidation of the mechanism of photosynthetic water splitting. We review here the structural features of the Mn(4)CaO(5)-cluster analyzed at 1.9 ? resolution, and compare them with the structures reported previously.     

Short and stereoselective synthesis of manzacidins A and C, and their enantiomers

A short and stereoselective synthesis of manzacidins A and C, and their enantiomers was achieved via stereoselective hydrogenation reactions of dehydroamino acid esters 5-8 using a chiral Rh catalyst.     

Inheritance and alteration of genome methylation in F1 hybrid rice

We analyzed the inheritance of DNA methylation in the first filial generation(F1) hybrid of Oryza sativa L. ("Nipponbare"x"Kasalath") by restriction landmark genome scanning (RLGS). Most parental RLGS spots were found in the F1, but eight spots (4%) showed abnormal inheritance: seven of the eight spots were missing in the F1, and one was newly detected in the F1. Here we show demethylation at restriction enzyme sites in the F1. We also found a candidate site of stable heterozygous methylation in the genome. These results show the applicability of the RLGS method for analysis of the inheritance and alteration of methylation in F1 hybrid plants.