Direct UHV-TEM observation of palladium clusters on a silicon surface.

About 1 monolayer of palladium was deposited onto a silicon (111) 7 x 7 surface at a temperature of about 550 K inside an ultrahigh vacuum transmission electron microscope, resulting in formation of Pd2Si nanoislands and a 1 x 1 surface layer. Pd clusters created from an excess of Pd atoms on the 1 x 1 surface layer were directly observed by in situ plan view high-resolution transmission electron microscopy. When an objective aperture was introduced so that electron diffractions less than 0.20 nm were filtered out, the lattice structure of the 1 x 1 surface with 0.33 nm spacing and the Pd clusters with a trimer shape were visualized. It was found that image contrast of the 1 x 1 lattice on the specific height terraces disappeared, and thereby an atomic structure of the Pd clusters was clearly observed. The appearance and disappearance of the 1 x 1 lattice was explained by the effect of the kinematical diffraction. It was identified that a Pd cluster was composed of three Pd atoms without a centered Si atom, which is consistent with the model proposed previously. The feature of the Pd clusters stuck at the surface step was also described.     

Base-labile tert-butoxycarbonyl (Boc) group on phenols

Phenols are deprotected with weak bases from their tert-butoxycarbonyl (Boc) derivatives. Boc deprotection with bases can avoid side reactions during the deprotection with acids. We note the lability of the Boc to bases and are able to utilize it as a new cleavage condition for synthetic studies.     

A facile synthesis of aliphatic polybenzoxazoles from a bis(o-aminophenol) or its hydrochloride and aliphatic dinitriles

A facile one-step method for the synthesis of aliphatic polybenzoxazoles has been developed. Thus, a series of aliphatic polybenzoxazoles having inherent viscosities of 0.2–0.7 dL/g in concentrated sulfuric acid were successfully synthesized by the melt polycondensation of alipatic dinitriles with 4,4′-diamino-3,3′-dihydroxybiphenyl (AHB) or its hydrochloride (AHB–HCl) with the elimination of ammonia or ammonium chloride, respectively. Monomer AHB–HCl was more reactive than the parent AHB, thereby affording higher molecular weight polybenzoxazoles in a shorter reaction time. The aliphatic polybenzoxazoles having 6–10 methylene units were highly crystalline with melting temperatures in the range of 187–308°C, which were stable up to 400°C in a melt state in nitrogen. © 1994 John Wiley & Sons, Inc.     

Wechselwirkung zwischen entgegengesetzt geladenen Polypeptiden

Ohne Zusammenfassung     

TUMOR-LOCALIZING FLUORESCENT DIAGNOSTIC AGENTS WITHOUT PHOTOTOXICITY

In order to develop tumor-localizing fluorescent diagnostic agents without phototoxicity, various heterodimers linked by some spacers between a chlorine derivative and its Mn or Cu complex were synthesized. The representative agent of them was named HAT-D01 and has a molecular formula of m -phthalyl-{[13,17-bispropanoic acid-3-ethenyl-8-formylethylidene-7-hydroxy-2,7,12,18-tetramethyl-porphyrinate]-manganese (III)}-[3'-ethenyl-8'-formylethylidene-7'-hydroxy-2',7', 12', 18'-tetramethyl-porphine-13', 17'-bispropanoyl aspartic acid]-bishydrazone.     

SPECTROSCOPY AND FLUORESCENCE QUENCHING OF TYROSINE IN LIMA BEAN TRYPSIN/CHYMOTRYPSIN INHIBITOR AND MODEL PEPTIDES

The effects of citrate ion concentration and pH on the optical spectra and fluorescence decay have been measured for several tyrosine model compounds and lima bean trypsin/chymotrypsin inhibitor, a protein containing one tyrosine at position 69 and seven disulfides but no tryptophan, in order to determine the location and environment of Tyr 69. Tyrosine in the protein is protected from citrate collisional quenching, as indicated by the dynamic quenching constant 9 to 15 times smaller than those for the model peptides. Static quenching remains, with a Stern-Volmer constant of about 1.0 M-1, somewhat smaller than those of L-tyrosine, tyrosine-glutamate, and leucine-tyrosine-leucine. The elevated pKa of Tyr 69, greater than or equal to 11.6, also indicates protein protection from solvent ions. Though Coulomb repulsion of the Glu 70/citrate pair may play a role in the shielding of Tyr 69 from citrate, our measurements indicate that steric effects of the protein structure are more important. Tyrosinate emission in the protein at neutral pH is minimal.     

Determination of cadmium in river water by sequential metal vapor elution analysis

Determination of cadmium in river water by sequential metal vapour elution analysis (column temperature; > 1500 K) with argon and hydrogen carrier gas and with atomic absorption spectrometric detection is described. The column is made of a molybdenum capillary tube (i.d. 1.22 mm) and the temperature is 1760 K. The cadmium vapor was separated from those of calcium, iron and sodium. The calibration graph was linear up to 15 μ/ml. Relative standard deviations of 0.8–4.3% were obtained in the range 1 to 15 μ/ml. Cadmium in spiked samples (river water) was determined. The results were in good agreement with the amount spiked.     

Stereoselective synthesis of procyanidin B3-3-O-gallate and 3,3″-di-O-gallate, and their abilities as antioxidant and DNA polymerase inhibitor

A simple method for the synthesis of procyanidin B3 substituted with a galloyl group at the 3 and 3″ position is described. Condensation of a benzylated catechin-3-O-gallate electrophile with a nucleophile, catechin and catechin-3-O-gallate, proceeded smoothly and stereoselectively to afford the corresponding dimer gallates, procyanidin B3-3-O-gallate and procyanidin B3-3,3″-di-O-gallate, in good yields. Further, their antioxidant activities on UV-induced lipid peroxide formation, DPPH radical scavenging activity and inhibitory activity of DNA polymerase were also investigated. Among three procyanidin B3 congeners (procyanidin B3, 3-O-gallate and 3,3″-di-O-gallate), the 3,3″-di-O-gallate derivative showed the strongest antioxidant and radical scavenging activity. Interestingly, the 3-O-gallate derivative was the strongest inhibitor of mammalian DNA polymerase with IC₅₀ value of 0.26 μM, although it showed the weakest antioxidant and radical scavenging activity. It became apparent that the presence of a galloyl group at the C-3 position in the proanthocyanidin oligomer was very important for biological activity, however, the antioxidant activity of these compounds was not parallel to the DNA polymerase inhibitory activity.