The reductive desorption process of self-assembled monolayers of 1-hexadecanethiol, 1-propanethiol, and 3-mercaptopropionic acid on Au(111) has been studied in 0.5 M KOH solution by in-situ scanning tunneling microscopy (STM) and cyclic voltammetry. In-situ STM images of the monolayers at the potentials between −0.2 V and the reduction potentials of each thiols show the pits that are commonly seen in STM images of thiol self-assembled monolayers. A drastic morphological change takes place in the STM image around the peak potential in a cyclic voltammogram for the reductive desorption of adsorbed thiols. The images indicate that 3-mercaptopropionic acid molecules diffuse away from the surface after the reduction because of its higher solubility, while 1-propanethiol and 1-hexadecanethiol molecules stay in the vicinity of the surface forming aggregates. The partial recovery of the 1-hexadecanethiol monolayer after the anodic scan, suggested by cyclic voltammograms, is confirmed by STM, whereas 1-propanethiol aggregates remain at the surface without being reoxidized. The difference in the reoxidation behavior reflects the different amphiphilic properties of the desorbed molecules and the resultant molecular organizations formed on the surface.

A diarylethene possessing one [4]thiaheterohelicene and one benzothiophene, the latter with a chiral methoxymethoxyethyl group on its C-3 position, was proved to work as a switch of specific optical rotation at a wavelength at which both colored and colorless forms have no absorption in solution. The difference of the specific optical rotation was 1300 degrees between the open form and the photostationary state. The specific optical rotation of one of the isolated optically active major colored forms was -4680 degrees. The conversion to the colored form was 64%, and the diastereomeric excess of photocyclization was 47%.

These results suggest that M (an active metabolite of erdosteine) may exert an antiinflammatory effect by scavenging inflammatory cells-derived reactive oxygen species.

No abstract

Quantitative evaluation of Förster-type fluorescence resonance energy transfer (FRET) was undertaken by statistical investigations on perylene-cored anthracene dendrimers.

-Glutamylcysteine synthetase (GCS, EC 6.3.2.2) catalyzes the formation of -glutamylcysteine from L-glutamic acid (Glu) and L-cysteine (Cys) in an ATPdependent manner. While GCS can use various amino acids as substrate, little is known about whether it can use non-amino acid compounds in place of Cys. We determined that GCS from Escherichia coli has the ability to combine Glu and amines to form -glutamylamides. The reaction rate depended on the length of the methylene chain of the amines in the following order: n-propylamine > butylamine > ethylamine methylamine. The optimal pH for the reaction was narrower and more alkaline than for the reaction with an amino acid. The newly found catalytic ability of GCS was used in the production of theanine (-glutamylethylamine). The resting cells of E. coli expressing GCS, in which ATP was regenerated through glycolysis, synthesized 12.1 mM theanine (18 h) from 429 mM ethylamine.

The secondary metabolite 6-demethylchlortetracycline (6-DCT), which is produced by Streptomyces aureofaciens, is used as a precursor of semisynthetic tetracyclines. Strains that produce 6-DCT also produce a melanin-like pigment (MP). The correlation between MP production and 6-DCT production was investigated by using S. aureofaciens NRRL 3203. Production of both MP and 6-DCT was repressed by phosphate or ammonium ions, suggesting that syntheses of these compounds are controlled by the same regulators. Ten chlortetracycline-producing recombinants were derived from 6-DCT-producing mutant NRRL 3203 by gene replacement. All of the recombinants produced chlortetracycline but not MP, indicating that MP production is the results of a defect in the 6-methylation step and suggesting that the polyketide nonaketideamide is a common intermediate leading to MP as well as 6-DCT. To further examine the possibility that MP might be synthesized via the 6-DCT-biosynthetic pathway, mutants defective in 6-DCT biosynthesis were derived from a 6-DCT producer. Some of these mutants were able to produce MP, while others, including mutants with mutations in the gene encoding anhydrotetracycline oxygenase, an enzyme catalyzing the penultimate step in the pathway, produced neither 6-DCT nor MP. Production of 6-DCT and production of MP were restored simultaneously by integrative transformation with the corresponding 6-DCT-biosynthetic genes, indicating that some of 6-DCTbiosynthetic enzymes are indispensable for MP production. These findings suggest that a defect in the 6-methylation step results in redirection of carbon flux from a certain intermediate in the 6-DCT-biosynthetic pathway to a shunt pathway and results in MP production.

Upon irradiation, p-dicyanobenzene reacted with primary, secondary, and tertiary aliphatic amines to give substitution products in which one of the cyano groups was replaced by the amine at α-CH position or by an alkyl group of the amine. o-Dicyanobenzene reacted similarly, but the meta-isomer did not react under similar conditions. The rates of the fluorescence quenching of p-dicyanobenzene with the amines are close to the diffusioncontrolled rate, but are somewhat dependent on the ionization potentials of the amines. When the substitution product was irradiated, the corresponding alkylation product was obtained. The mechanisms of these reactions have been investigated by the use of such proton donors as MeOH(MeOD); on the basis of those investigations, new photochemical reactions involving charge-transfer, followed by proton-transfer and then addition-elimination, are proposed, as well as a new type of photo-induced Birch reduction.